Technical Report Series
Number 77-6
HYDROGRAPHIC OBSERVATIONS
IN ONSLOW BAY, NORTH CAROLINA
(JULY - AUGUST 1976/0BIS V):
DATA GRAPHICS
by
J. J. Singer
L. P. Atkinson
W. S. Chandler
and
P. G. O'Matley
Georgia Marine Science Center
University System of Georgia
Skidaway Island, Georgia
HYDROGRAPHIC OBSERVATIONS
IN
ONSLOW BAY, NORTH CAROLINA
(JULY- AUGUST 1976/0BIS V}:
DATA GRAPHICS
J. J. Singer
L. P. Atkinson
W. S. Chandler
P. G. O'Malley
Skidaway Institute of Oceanography
P. 0. Box 13687
Savannah, Georgia
31406
The Technical Report Series of the Georgia Marine Science Center
is issued by the Georgia Sea Grant Program and the Marine Extension
Service of the University of Georgia on Skidaway Island (P. 0. Box 13687,
Savannah, Georgia 31406). It was established to provide dissemination of
technical information and progress reports resulting from marine studies
and investigations mainly by staff and faculty of the University System
of Georgia. In addition, it is intended for the presentation of
techniques and methods, reduced data and general information of interest
to industry, local, regional, and state governments and the public.
Informat ion contained in these reports is in the public domain . If this
prepublication copy is cited, it should be cited as an unpublished manuscript.
ACKNOWLEDGEMENTS
The authors would like to thank all those who participated in this
study, both at sea and ashore. These include the following scientists,
technicians and students.
Larry Atkinson
Carroll Baker
Bill Chandler
Don Deibel
Bill Dunstan
Fran Gonsoulin
Eileen Hofmann
Jean Hosford
Mark Kelly
Greg Mcintyre
Patrick 0 1 Malley (at Skidaway)
Gus Paffenhofer
Carol Porter
Joe Sands
Jim Singer
Kathie White
Of these, special thanks go to Carroll Baker for his invaluable
assistance in keeping the CTD-Rosette system operational, to Eileen
Hofmann for directing nutrient analysis and to Jean Hosford for temporarily
taking over shipboard cooking responsibilities in addition to carrying
out her other duties as a technician. Additional thanks go to Amy Edwards
and Lynn Rubicam for their contributions in computer generated data
graphics and data work up. Captain James Rouse, Lee Knight and mates
Paul Glenn and Jim Walker and Gene Brogdon are sincerely thanked for
their dedication and perserverance in completing this project. Mary Lou
Neuhauser is thanked for filling in as ship 1 s cook during the second half
of this project.
Laboratory and dock space at Beaufort, North Carolina was generously
provided by Duke University Marine Laboratory. Dick Barber and Eric
Nelson are gratefully acknowledged for their assistance during our stay
at DUML . Dan Perlmutter and Dan Mcintosh provided drafting assistance
and Paula Vopelak typed the text.
Funding for this research was provided by the U. S. Energy Research
and Development Administration under Contract E(38-l )-889.
This report is published as a part of the Georgia Marine Science
Center 1 s Technical Report series issued by the Georgia Sea Grant Program
under NOAA Office of Sea Grant #04-7-158-44126.
i
TABLE OF CONTENTS
Page
Acknowledgements.
. i
List of Tables.
.iii
List of Figures
iv
Introduction .
1
Methods . . .
4
Biogrids . .
Hydrogrids . . . . . . . . . . . .
Chemical and Physical Procedures.
CTD Data Acquisition.
CTD Data Processing .
CTD Calibration . . .
CTD Error Analysis . .
4
6
7
8
9
11
16
Meteorological Conditions
19
Results . . . . . . . . .
22
Horizontal Distribution of Temperature.
Horizontal Distribution of Salinity .
Horizontal Distribution of Nutrients. . . . . . . . . . .
Vertical Distribution of Physical and Chemical Properties
(Hydro Grids)
Hydro Grid I . . . .
Hydro Grid I I . . .
Hydro Grid III(A-2)
XBT Grid III
Hydro Grid IV . . .
Grid
Grid
Grid
Grid
38
38
39
39
40
40
Vertical Distribution of Physical and Chemical Properties
(Bio Grids)
Bio
Bio
Bio
Bio
22
23
24
62
I. .
62
II .
III.
IV
63
64
63
T-S Plot . .
85
Nitrate Vs . Phosphate
85
Salinity Vs. Silicate
85
Summary and Conclusions
89
List of References . .
90
Appendix .
92
Summary of Events: (OBIS V).
ii
LIST OF TABLES
Page
Table 1.
OBIS V (Summer 1976).
Table 2.
CTO/Oata Flow:
submission. .
.
1
Shipboard acquisition to NODC
.10
Table 3.
Salinity offset for OBIS V.
.11
Table 4.
Specifications for Plessey Model 9400 CTD
system.
.
. .
.
.
. 16
Table 5.
Effects of depth on salinity for OBIS V data.
. 17
Table 6.
Sources of salinity error due to the reported accuracy
of the sensors and the salinity equation.
. 17
;ii
LIST OF FIGURES
Page
Figure 1.
location of the study area.
2
Figure 2.
Approximate current meter mooring locations during
OBISV.
. .
.
.
.
3
Figure 3.
Standard base grid for Onslow Bay, North Carolina
5
Figure 4.
Salinity offsets for Hydro I and Bio I.
. 12
Figure 5.
Salinity offsets for Hydro/Bio II and aborted
Hydro I I I' s
.
. 13
Figure 6.
Sa 1i ni ty offsets for Bi o I II and Hydro/Bi o IV
. 14
Figure 7.
Sa 1i nity offset for aborted Hydro V
. 15
Figure 8.
Wind data (Cape Hatteras -July 1976)
.20
Figure 9.
Wind data (Cape Hatteras - August 1976)
. 21
Figure 10.
Cruise tracks for Hydro Grids I, II and IV and
XBT Grid III.
.
. 26
Figure 11 .
Cruise tracks for aborted grids
.27
Figure 12.
Surface temperature (Hydro Grids 1, II and IV and
XBT Grid I I I) . . .
.
. 28
Figure 13.
Bottom temperature (Hydro Grids I, II and IV and
XBT Grid III)
.29
Figure 14.
Surface salinity (Hydro Grids I, II and IV)
. 30
Figure 15.
Bottom salinity (Hydro Grids I, II and IV).
.31
Figure 16.
Surface nitrate (Hydro Grids I, II and IV).
.32
Figure 17.
Surface phosphate (Hydro Grids I, II and IV).
.33
Figure 18 .
Surface silicate (Hydro Grid IV).
. 34
Figure 19.
Bottom nitrate (Hydro Grids I, II and IV)
.35
Figure 20.
Bottom phosphate (Hydro Grids I, II and IV)
.36
Figure 21.
Bottom silicate (Hydro Grid IV)
.37
Figure 22.
Vertical distribution of temperature (Hydro Grid I)
.42
Figure 23.
Vertical distribution of salinity (Hydro Grid I).
.43
Figure 24 .
Vertical distribution of sigma-t (Hydro Grid I)
.44
iv
LIST OF FIGURES (continued)
Figure 25.
Vertical distribution of nitrate (Hydro Grid I).
Page
.45
Figure 26.
Vertical distribution of phosphate (Hydro Grid I).
.46
Figure 27.
Vertical distribution of temperature (Hydro Grid II) .47
Figure 28.
Vertical distribution of salinity (Hydro Grid II) .
.48
Figure 29.
Vertical distribution of sigma -t (Hydro Grid II)
.49
Figure 30.
Vertical distribution of nitrate (Hydro Grid II)
.50
Figure 31.
Vertical distribution of phosphate (Hydro Grid II)
.51
Figure 32 .
Vertical distribution of temperature (Hydro Grid
III(A-2)).
.
. 52
Vertical distribution of salinity and sigma-t
(Hydro Grid III(A-2)). .
.
. 53
Vertical distribution of phosphate and silicate
(Hydro Grid III(A-2) ). .
. ..
.54
Figure 33.
Figure 34.
Figure 35 .
Vertical distribution of temperature (XBT Grid III) . . 55
Figure 36.
Vertical distribution of temperature (Hydro Grid IV) .56
Figure 37.
Vertical distribution of salinity (Hydro Grid IV).
. 57
Figure 38.
Vertical distribution of sigma-t (Hydro Grid IV)
. 58
Figure 39.
Vertical distribution of nitrate (Hydro Grid IV)
. 59
Figure 40 .
Vertical distribution of phosphate (Hydro Grid IV)
.60
Figure 41.
Vertical distribution of silicate (Hydro Grid IV).
. 61
Figure 42.
Cruise tracks for Bio Grids I, II, III and IV.
. 65
Figure 43.
Vertical distribution of temperature (Bio Grid I).
. 66
Figure 44.
Vertical distribution of salinity (Bio Grid I)
. 67
Figure 45 .
Vertical distribution of sigma-t (Bio Grid I).
.68
Figure 46.
Vertical distribution of nitrate (Bio Grid I).
. 69
Figure 47 .
Vertical distribution of phosphate (Bio Grid I).
. 70
Figure 48.
Vertical distribution of temperature, sigma-t and
salinity (Bio Grid II)
.
. .
.
. 71
v
LIST OF FIGURES (continued)
Page
Figure 49.
Vertical distribution of nitrate and phosphate (Bio
.
.72
Grid II).
. . .
. . .
Figure 50.
Vertical distribution of temperature (Bio Grid I I I) . 73
Figure 51.
Vertical distribution of salinity (Bio Grid III) .
.74
Figure 52 .
Vertical distribution of sigma-t (Bio Grid III)
.75
Figure 53.
Vertical distribution of nitrate (Bio Grid I I I)
.76
Figure 54 .
Vertical distribution of phosphate (Bio Grid I I I)
.77
Figure 55.
Vertical distribution of silicate (Bio Grid III).
.78
Figure 56.
Vertical distribution of temperature (Bio Grid IV). .79
Figure 57.
Vertical distribution of salinity (Bio Grid IV)
. 80
Figure 58.
Vertical distribution of sigma-t (Bio Grid IV).
. 81
Figure 59.
Vertical distribution of nitrate (Bio Grid IV) .
. 82
Figure 60 .
Vertical distribution of phosphate (Bio Grid IV).
. 83
Figure 61.
Vertical distribution of silicate (Bio Grid IV)
. 84
Figure 62.
T-S plot (OBIS V)
Figure 63.
Plot of nitrate Vs. phosphate
. 87
Figure 64.
Plot of sa 1i nity Vs . silicate
. 88
.
vi
. 86
INTRODUCTION
This data report is the third in a series on work in Onslow Bay,
North Carolina (Atkinson et
~·,
1976a, b) (Figure 1).
It, like the
earlier reports, is intended to document the chemical and physical data
obtained.
The report covers cruises 085-089 of the Onslow Bay project.
These cruises comprise Onslow Bay Intrusion Study No. 5 (OBIS V) and were
made aboard the R/V BLUE FIN during the summer of 1976 (Table 1).
The
hydrographic data sets are available from the National Oceanographic Data
Center (NODC).
Table 1.
OBIS V (Summer 1976)
Project Leg
Date
Cruise Number
HYDRO/BIO I
14-18 July
085
HYDRO/BIO II
21-23 July
OB6
HYDRO III (aborted
three times)
28 July-2 August
OB7
XBT/810 III
4-6 August
087
HYDR0/810 IV
14-16 August
088
HYDRO V (aborted)
18 August
089
OBIS V
The objective of OBIS V like that of OBIS II was to collect temperature,
chemical and biological data which could later be correlated with data
recorded by twelve current meters and two thermographs {deployed by North
Carolina State University) which were concurrently operative at seven locations in the study area (Fig . 2).
No attempt will be made at this time,
however, to correlate our data to these related records nor will any of the
1
84
80
36
'
ONSLOW ,.>
BAY
32
32
ATLANTIC
OCEAN
0
150
KM
28
28
84
Figure 1.
Location of the study area
2
7 8.
7
6
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. -~.
...... . . .
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.,
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..
33°30'- -
..
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••
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®
Thermograph (2)
C8J
I
7 8 °
Figure 2.
.
..
·.
·.··
:~P
·: ....-
~
.· ..
...
0~
'1-o
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.. ..
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• ,.,.-_.
. •... . .
.. ..
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FEAR
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..:..
··- - - 3 4'
'
-
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0
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-
3 3' 30'
KllOMEfERS
10
20
..
I
7 7.
7 7 • 3.0'
7 G• 3
o'
Approximate current meter mooring locations during OBIS V.
3
7 6
biological data be presented in this text.
The current meter and biological
data will appear in separate reportsedited by Dr. L. Pietrafesa (N. C.
State University) and Drs. W. Dunstan and G.-A. Paffenhofer (Skidaway
Institute of Oceanography) respectively.
METHODS
The study area was assigned a standard base grid made up of eight
onshore-offshore transects (Fig. 3).
This was identical to the grid
reported in earlier Onslow Bay work (Atkinson et
~-,
1976a, b) except
that one additional offshore station was on occasion added to the transects.
The same permanent station numbers are used.
Each alternating sampling
grid (hydro or bio) was made up of some combination of the base grid 1 s
onshore/offshore transects, depending on the previously observed temperature structure, and/or the time lapse between cruises through the grid
area.
The selected hydrogrid always represents a trade-off between fineness
of scale and the achievement of synopticity.
With this in mind alternate
onshore/offshore transects were omitted, thereby decreasing the alongshore scale from that of our earlier work.
However, it was felt that
this would not significantly alter our view of the larger scale intrusion
phenomenon we were investigating and that the reduced sampling time for a
circuit of the Bay would generate, in number, more surveys.
This in turn
would permit us to better track a single intrusion from beginning to end
(this advantage, however, was lost by such unscheduled factors as bad
weather, equipment malfunction, and ship breakdown).
Biogrids
As originally conceived, a biological grid would detect changes in
various parameters induced by the movement of intruding fronts and the
variance of light conditions with time.
4
It was composed of five stations
7 8.
7G
.~
~~o....··.
LOOKOUT
.......
·''
3 4•3o'--
.
.
,..,
·~
- - - 3 4 .3 0'
_.,
•
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.
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.
114~
~..,
..,~
. .
.'0
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·"'"".~.,
·"'"'
.,....
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.33.30'--
·"'
·"''.
.. ·;;·. :. .
..
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.,,'0 .
.·
3 4•
- - 3 3• 30'
0
Figure 3.
....
fo..
· stAL[
7 8.
.~
.
0
.
.....
.
.
. ·:. ...o
.r::,
I
1 1• 3
o'
7 7°
Ill
ICILO .. fTEIII
10
20
16 • 3
o'
Standard base grid for Onslow Bay, North Carolina.
5
76
along one onshore/offshore transect which were selected for intensive
sampling because of their proximity to an apparent intrusion core.
Samples would be taken offshore and inshore of the intrusion core and in
the core itself.
The cruise track would go back and forth from end
station, to center station, to opposite end station, generally sampling
at three hour intervals over a 24 hour span.
This would result in four
complete transects of the grid with the center station being sampled four
times.
The two immediately adjacent stations would be less intensively
sampled without regard to a specific time interval as the ship cruised to
a center or end station.
However, for the present work, though we started
with the above format in mind, the biogrids ultimately varied from one
another in the time between s ta ti ons, the tota 1 time a 11 oted, the number
of stations sampled, and the number of repetitions of the selected
cruise tracks.
The variations were influenced by such factors as weather
conditions and ship performance, etc.
Typically, at a bio station a CTD-Rosette cast and a zooplankton net
tow were made.
The sampling depths were determined by analysis of the
temperature profile.
If a thermocline was present, samples were taken at
the surface, just above or below the thermocline, at the bottom and
occasionally at other random depths.
surface and bottom samples were taken.
If no thermocline was present just
Water samples were taken for the
analysis of salinity, nitrate, phosphate, silicate,
oxygen,~
vivo
chlorophyll, particle size, phytoplankton cells, zooplankton, and particu1ate carbon.
Hydrogrids
A hydrographic grid was designed to sample the entire Bay to obtain
an updated look at the distribution of properties both preceding and
following the biological sampling period.
6
Such grids were generally on
the order of 24 to 42 hours in duration.
Along a hydrographic grid
track, either CTD-Rosette casts or XBT firings and Niskin bottle casts
were made at all stations.
Niskin sampling depths were determined after
the temperature structure was obtained either from the CTD or XBT, and
samples were taken near the surface, just above or below the thermocline,
at the bottom and occasionally at other random depths.
Samples were
taken for analysis of salinity, nitrate, phosphate, silicate, oxygen and
~vivo
chlorophyll and occasionally for extracted chlorophyll, particle
size and phytoplankton cell analysis.
Chemical and Physical Procedures
Salinity samples were analyzed conductometrically using a Plessey
portable laboratory salinometer.
The values so obtained were used to
calibrate the Plessey model 9400 CTD system.
Because of laboratory space
problems aboard the research vessel, oxygen analysis was delayed until we
returned to port after each cruise.
The Winkler method was used.
However,
post project experiments have indicated that the samples were highly
susceptible to thermal effects.
presented.
Consequently, no oxygen values are
Temperature was determined by deep sea reversing thermometers,
XBT's and the CTD system.
After collection, the nutrient samples were immediately frozen in
polyethylene bottles and stored in the dark until thawed and analyzed
ashore.
Colorimetric determinations of nutrient concentrations were made
with a Bausch and Lomb Spectronic 88 Spectrophotometer with a sample
sipper.
Silicate concentration was determined by the method of Mullin
and Riley (1955) as modified by Strickland and Parsons (1965), and phosphate concentrations were determined by the method of Murphy and Riley
(1962).
Nitrate was determined by the cadmium column reduction technique
as modified by Gardner et
~-
{1976).
7
CTD (Conductivity/Temperature/Depth) Data Acquisition
The CTD unit consisted of a Plessey model 9400 CTD sensor system
with a model 8400 Digital Data Logger and Kennedy model 1600 incremental
magnetic tape recorder for data acquisition and storage.
A redundant
XYY' plot was made of all casts using a Hewlett-Packard model 7046A X-Y
Recorder which was calibrated with a precision 10VDC source.
The CTD
sensor-unit was mated to a General Oceanics model 1015 Mark 5 Rosette
multi-bottle array for water sampling. The Rosette was equipped with 1.7
and 5.0 liter Niskin bottles.
Digitized data was collected only during descent through the water
column {generally less than 50 m deep) as the CTD was lowered at 15m/min
on single conductor cable.
once each 229 milliseconds:
All three parameters (C, T and D) were sampled
every 6 em at the 15 m/min lowering rate.
For primary calibration of temperature and salinity a Niskin bottle
equipped with a protected deep sea reversing thermometer was tripped
after a three minute equilibration period at the maximum sample depth.
Other water samples were collected during ascent following examination of
the downcast temperature profile.
Typica l station time was less than 15
minutes .
The acquisition of CTD data during the downcast and water samples
during the upcast creates some problems that are difficult to solve.
The
factors that come into play are:
1)
The sensors are located at the bottom of the sub-surface unit
to maximize response during the downward motion.
During upward
motion the CTD sensors lie in the wake of the Rosette.
Thus
CTD data is of higher quality during the downcast.
2)
It is generally felt that water samples must be taken during
the upcast.
If they are taken during the downcast the surface
samples may be subjected to dilution by deeper waters.
8
3)
Differential horizontal advection may alter the coherence of
downcast CTD data vs. upcast water sample data.
However, since
gradients in nutrients are typically quite low the minor advective
motions during the time of a station cause negligible mismatch
of nutrient data.
CTD Data Proc essing
The CTD plots were logged and stored with their respective station
sheets .
Data had to be manually digitized from some of these (HYDR0/810 I
and II) because of magnetic tape recording problems.
The remainder of the
data were recorded on tape and extracted and processed according to the
flow scheme shown in Table 2.
by Scarlet (1975).
The flow scheme is essentially that described
Computations and data manipulations were performed on a
CDC CYBER 70.
MAGREAD converts binary coded data to decimal and CTDUNIT converts
decimal units to engineering units.
LAGFILT treats the data for the tempera-
ture lag of the temperature sensor and coarse filters the data for noise .
Then, SIGSALP calculates uncorrected sigma-t and salinity values . At this
stage , salinity and temperature offset corrections are made from the primary
calibration data . Then flow is resumed by repeating SIGSALP with the added
correction factors. DLATCH deletes lines with decreasing or repeated depths
due to ship roll and CTDAVE presents the data in average one meter increments .
NODCFO converts the data to NODC format and NODMER merges additional
data (i . e. , nutrients, weather, latitude, longitude, etc.) for submission to
NODC.
CEMLIST calculates specific volume anomally, oxygen saturation and
apparent oxygen utilization (from the International Oceanographic Tables,
1973), the distance between successive stations, and reads all other data and
formats all data for presentation in a technical report.
9
This final product
Table 2.
CTD/Data flow;
Shipboard Acquisition to NODC submission.
Data Source/Disposition
Program
Tape from Data Logger
MAGREAD (Converts binary coded data to
decimal)
Data File
BIRANG
CTDUNIT (Converts decimal units to engineering units)
LAG
LAGFILT (Course filter and temperature lag)
CAL
Primary calibration
from bottle casts
SIGSALP (Calculates sigma-t and salinity)
LATCH
DLATCH {Removes decreasing and repeated depths)
CTDATA
CTDAVE {One meter averaged data)
AVE
NODCFO {Converts to NODC format)
NODC + HEAD
NODMER (Merges NODC data with Headers and
chemica 1 data)
NODCFNL
Submission to NODC
CEMLIST (Calculates specific volume anomally,
oxygen utilization, etc.)
TECHNICAL REPORT
10
is stored on magnetic tape in our computer system and all data (i.e., CTD,
XBT, chemical etc.) are available through NODC.
CTD Calibration
The data derived from the CTD sensor system is critical to the correct
interpretation of the oceanographic processes.
To insure the highest quality
data an extensive calibration scheme was performed.
The CTD system was calibrated against deep bottle casts in mixed layers:
this was the only way to be sure the sensors and the bottles were both sampling the same water.
However, since a mixed layer was not always observed,
a comparison could not be made at every station.
Consequently, the resulting
mean offset for the mixed layer salinity data of each leg of the project was
used for each entire data set.
This offset decreased through the five week
study period and is tabularized below (Table 3) and presented graphically in
Figures 4 through 7.
No temperature offset was made since the CTD tempera-
ture sensor agreed with the protected reversing thermometers within the range
of accuracy of the
two(~
'\
.02°C).
Likewise, no depth offset was necessary.
The XBT system was found to agree with reversing thermometers to within +
.05°C when compared during Hydro I .
Table 3.
Salinity offset for OBIS V.
o;oo Offset
Project Leg
HYDRO I (c. s.
(c.s.
BIO I
HYDRO/BIO II
ABORTED HYDRO
BIO III
HYDRO/BID IV
(c.s.
(c.s.
ABORTED HYDRO
1-26)
32-36)
III
1-31)
32-42)
V
+
+
+
+
+
+
Stand. Oev.
+ .030
.138
+ .023
+ .008
.333*
.099
.090
.101
. 073
+ .017
+ .022
+ .026
+ .064
+ .019
+ .068
Data Source
XYY' Plotter
II
II
II
Magnetic Tape
II
+ .021
II
+ .008
+ .009
II
II
*The sharp increase in offset during HYDRO I came after field repairs of
the CTD sys tern.
c.s.
= consecutive
station.
11
HYI:>AC
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13 . 380
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MEAN
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4
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7
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16
C~NSECUTIVE
SID
22
19
28
31
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MEAN
l
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a111 .1119 9
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37
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46
49
CONSECUTIVE CAST NUMBE R
Figure 4.
Salinity offsets for Hydro
-- standard deviation).
12
and Bi o I { - mean offset;
a. r s:a
HYI>AO/B I 0
MEAN
II
STANDARD DEVIRTIDN•111.11117
e. rYe
+
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w
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+
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_______________ t_t _________________________ _
+
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+
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CJ
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y
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13
16
19
<!2
2S
28
CON S ECUTIVE CAST NUMBER
AB ORTED HYDRO
I I I15
IIJ.I~
34
37
MEAN
4121
43
-111.11111
S TANDARD DEVIATIONc111.11122
13. I 411J
13. I 3:21
31
- -
~
- - - - - -
0 . 1 113
111.
11.
13 • 1 I<:ll3
'-'
0
1-
13.~9~
w
_,
....
....
CJ
13.13812l
v
co
-
-
i:.
liL Ja712l
lll.I3611J
IIJ.Ii'!S:0
121.11lY121
li'l.li'l31i'l
li'l.l32fi!l
(!J.011i'l
7
10
CONSECUTIVE CAST NUHBER
Figure 5.
Salinity offsets for Hydro/Bio II and aborted Hydro Ill's
( - mean offset; -- standard deviatio n) .
13
-
li:l . I S:li:l
l!liCJ
Ill
MEAN
.. 121.12173
STHNDARD DEVIRTIDNu12f.l<526
2. I Y121
B. 13B
105 • I 2121
....
~
B. liB
.......
11.
11.
e.'"'"
0
1<5.11l91<5
1-
v
I
li5 . 1<581a
...J
11-
li5 . 1i57ia
w
0
Ill
+
+
.,..
+
+
+
+
+
B . l<5611l
li:l . 121S:Ia
.:...
1<5 . 121Y111
+
+
+
li5.1i53111
li:l . 111:CI<5
li:l.l1111<5
27
33
36
CONSECUTIVE CAST NUMBER
HYL>RD/BlO
ra .r s:ra
IV
MEAN
111. 1412!
STANDARD DEVIATIONcl1l.li:l 21
111. 13B
MEAN
.....
Ia . II 111
a...
0. 111!13
....av
11! . 1119111
I
la . l118111
...J
........0
11!.071il
w
co
+
----------------------------------------++
+
+
0.0611!
11l.B31a
+
+
~ . 1215:0
lil.l11Lfl1l
ala.lill9
STANDARD DEVIATI0Ncl1l.l11 111B
lil. t 2111
....
a..
Y2
---- ------ ------- --~---- ------ ------- ----
+
+
---------------------------------~~------
+
11l.lil211!
" . 11!113
------------------------------------~--~~
-+
7
Figure 6 .
+
I9
22
2S:
13
16
CONSECUTI VE CAST NUMBER
!Ia
28
3 I
34
Sa 1 i nity offsets for Bi o II I and Hydro/Bi o IV (-- standard deviation) .
14
37
4111
mean offset·
Ill . I S:lll
ABORTED HYDR:::J V
HERN
Ill . 1411J
....
Q.
a.
1311l
0.
1~0
Ill. II l1l
11.
" . 111ll1l
0
....v
121.121911l
I
11l.ia811l
w
.......
lil . l1l713
ttl
11l.0611l
...J
-".068
STANDARD DEVIATI0Nai1J.I1ll1l9
Cl
_________ + ____________________________ _
_______________________________________ +
13.0S:I1!
11!.11lYI1l
11l.03r.:l
11l.l1l~0
13.0111l
CONSECUTIVE CAST NUHSER
Figure 7.
Salinity offset for aborted Hydro V (-mean offset;
-- standard deviation).
15
CTD Error Analysis
The Plessey model 9400 CTD system has the fol l owing rated accuracy,
resolution and time constants (Table 4).
Specifications for Plessey model 9400 CTD system.
Table 4.
Conductivity
Temperature
± 0.03 mmho/cm
Accuracy
Depth
+ 1.5 m
+ 0.02°C
Resolution
0.0001 mmho/cm
0.0001°C
0.0012 m
Time Constant
0.1 sec
0.35 sec
0.1 sec
Since salinity was not measured directly i t had to be calculated from
the above parameters.
For this work, sal i nity was determined by the equation
of Knowles (1973) for shallow water (p
~
o) using the coefficients of a third
order polynominal he determined for Reeburgh Norma l wate r (Cl
=
19.369°/oo)
as a means of estimating C(35, t, o):
C(35, t, o) = 29.03862 + 0.86024t + 0.46931
10- 4t 3 and C(s, t, p) ~ C(s, t, o)
X
10- 2t 2 - 0.27022
X
and Rt = C(s, t, o)/C(35, t, o).
Then, from the International Oceanographic Tables (1966):
615
= R15 - Rt or R15 = 615
+ Rt
-5
2
2
where 6 15 = 10 Rt(Rt-1) (t-15) {96.7- 72.0Rt + 37.3Rt -(0.63 + 0.21Rt )
2
(t-15)} and S0/oo = -0.08996 + 28.29720 R + 12.80832 R15 - 10.67869
15
R15 3 + 5.98624 R15 4 - 1.32311 R15 5 .
The absolute accuracy of this method is not known.
However, for the
temperature and salinity range observed during this study (16-29°C, 34.536.50;oo) this expression was found to result in calculated salinities
deviating -.010
± .002°/oo from a table of measured experimental values
reported by Jaeger (1973).
16
Since this equation ignores the influence of pressure on the conductivity
sensor, a table of pressure effects on salinity has been compiled (Table 5).
One hundred fifty-six of the 164 casts were made to depths less than or equal
to 40 meters for which it has been estimated that the pressure effect could
increase the calculated salinity by only +.014°/oo (Bradshaw and Schleicher,
The effect on the deepest cast (55 meters) has been calculated to be
1965).
+.020 0 /00.
Table 5.
Effects of depth on salinity for OBIS V data.
Temp. (°C)*
0/oo
Depth ( m)
0/oo Effect
25.00
25.00
23.50
22.00
19.50
19.00
35.50
36.00
36.00
36.00
36.00
36.00
10
20
30
40
50
55
+.003
+.006
+.010
+.014
+.018
+.020
*Averaged over data set or maximum temperature listed by Bradshaw and
Schleicher, 1965.
Other sources of error are attributable to the reported accuracy of the
conductivity and temperature sensors and are summarized below (Table 6).
Table 6.
Sources of salinity error due to the reported accuracy of the
sensors and the salinity equation.
Maximum Error
Parameter
+ .023°/oo
Conductivity
Temperature
Depth
Equation*
+ .0160/oo
+ .014°/oo (95% of casts)
Total
+ .055 to -.041°/oo
+ .002°/oo
*The negative component of the equation error is not included because it
is compensated for by an offset factor added to the data set.
17
The total error reported above is applicable to all data recorded on
magnetic tape and does not consider the digitizing errors which may have
occurred for HYDRO/BIO•s I and II.
We estimate that temperature was
digitized to an accuracy of~ .005°C and conductivity to ~.01 mmho/cm. Such
accuracy could result in additional salinity errors of ~.005 °/oo and ~.009 °/oo,
respectively.
Actually, the largest standard deviation of all the mixed layer samples
taken for salinity calibration purposes implies an accuracy, after offset, of
~.030
0
joo.
This value is probably a more realistic measure of the quality of
the data set except in strong thermoclines (>1°C change/m) than the composite
maximum error reported above for the sensor package.
18
METEROLOGICAL CONDITIONS
Wind data from Cape Hatteras, North Carolina1 are presented in
Figures 8 and 9.
These data are derived from the monthly summaries for
July and August 1976 (U. S. Department of Commerce, July and August 1976)
and are plotted in GMT at six hour intervals.
The data show that the winds were generally southwesterly during
July 1976 with three brief (2-3 days or less) periods of northeasterly
winds.
The average wind velocity for July was 4.4 meters/second.
In
August, periods of both northeasterly and southwesterly winds were observed.
These were separated by a period of variable winds which included the
highest observed velocities (10.7 meters/second).
This variable direc-
tion and highest velocity period coincided with the passage of Hurricane
Belle 87 kilometers southeast of Cape Hatteras (141 kilometers east of
Cape Lookout) at 1300 GMT on 9 August.
The closest approach of the eye
of the hurricane to the study area came at 1000 GMT on 9 August when it
was 91 km east of the shelf break (200 m isobath) in the northeastern
sector of the Bay along the 34°00.0 north lattitude line.
11
The average
wind velocity for August was 3.9 meters/second.
The average high and low air temperatures for the entire study
period were 28.9°C and 21.7°C respectively.
Meteorological data were
also collected by the ship's crew at each station.
These additional data
are available through NODC.
1cape Hatteras lies 116 kilometers northeast of Cape Lookout.
19
36~
33~
3~~
'27~
z
'2'-1~
f-
'21~
a
v
w
n::
c
l
EI~
IS:~
1'2~
!3~
6~
3~
t
15
20
t
t
HYDRO
HYDRO I
t
25
30
25
30
II
16
1'-1
c
z
a
1'2
v
w
lJ1
'
lJ1
Cl:
w
1w
~
I~
El
6
'-1
'2
20
15
\..JULY
Figure 8.
Wind data (Cape Hatteras - July 1976).
20
1976
:::3:3121
:::3 121121
:z
0
I-
21121
V
w
0::
1 8121
c
1 2121
9121
6121
t
5
t
+'5
10
t
20
HYDRO IV
XBT II I
lEi
Hurricane Belle
1'-4
c
:z
0
v
12
lfl
1121
w
'
lfl
0::
w
B
1-
w
:L
2
20
AUGUST
Figure 9.
Wind data (Cape Hatteras - August 1976).
21
1976
RESULTS
Horizontal Distribution of Temperature
The cruise tracks for Hydro Grids I, II and IV and XBT Grid III are
shown in Figure 10.
All subsequent surface and bottom horizontal plots
are derived from data collected along these cruise tracks.
Several
cruises were aborted {Figure 11) and no horizontal plots are presented.
Figures 12 and 13 show the surface and bottom temperature distribution
throughout the Bay during each grid.
CTD and XBT data sets.
These plots are derived from both
Surface temperatures are generally taken from
depths of 1 to 2 meters below the surface and bottom temperature either
from depths 2 to 3 meters above the bottom as indicated by the shipboard
fathometer system for CTD data or at the bottom for XBT data.
Surface temperatures ranged from a low of 25.50C to a high of 29.ooc
over the course of the study period.
The lowest temperatures were observed
off Cape Fear and the highest temperatures were found offshore and parallel
to the shelf break.
Some surface structure is apparent in the temperature
plots for regions off Cape Fear and in Figure 12{d) one can see the
thermal wall of the Gulf Stream.
Figure 13 shows the bottom temperature structure observed during the
study period.
The movement of colder water onto the shelf and/or the
appearance of cold cores is evident in all plots.
The early stage of an
intrusion event is shown in Figure 13(a) with waters as low as 21.5°C
having moved onto the shelf in the southernmost offshore corner.
This is
the same region in which intrusions were observed to move onto the shelf
in our earlier work (Atkinson et
~-,
1976).
In Figure 13(b) there is
evidence of an intrusion moving onto the shelf in this same region.
There is also evidence of another intrusion which has moved shoreward and
22
has been isolated.
It is defined by the 23.0°C isotherm.
Conceivably,
this older and warmer core could be a stranded portion of the intrusion
first observed in Figure 13(a) (the time lapse between the two plots is
roughly seven days).
Current meter data collected by Dr. L. Pietrafesa
will help in ascertaining whether or not this is in fact the case.
In Figure 13(c) another intrusion is stranded on the shelf.
different intrusion than that shown stranded in Figure 13(b).
It is a
This
conclusion is based on the lower temperatures exhibited (21.5 vs. 23.0°C).
Also, it is unlikely that this core is related to the one shown just
moving onto the shelf in Figure 13(b) since still another intrusion was
observed moving onto the shelf during an aborted hydro grid made between
these two (Figure 32, page 52).
In Figure 13(d) there is an old intrusion isolated on the shelf as
indicated by the 23.0°C core.
This could be the same core as depicted in
Figure 13(c) although it is unlikely.
from the current meter data.
Actual confirmation should come
Also in this figure, there is clear evidence
of the movement of deeper Gulf Stream waters onto the shelf.
Horizontal Distribution of Salinity
Horizontal salinity plots are given for Hydro Grids I, II and IV.
Since no hydrography was done during XBT Grid I I I no salinities are
available for that grid .
Surface samples were taken within 1 to 2 meters
of the surface and bottom samples were taken generally within 2 to 3
meters of the bottom as indicated by the fathometer.
The data presented
are a composite of that which was collected with the CTD system as calibrated against bottom mixed layer water samples, and near surface and
bottom bottle samples taken when the CTD system was inoperable.
The surface salinity in Onslow Bay ranged from a low of 34.40°/oo to
a high of 36.100/oo .
In Figure 14(a) and 14(b) low salinity waters
23
appear to be moving into the Bay from the southwest (possibly emanating
from the vicinity of Cape Fear and the mouth of the Cape Fear River).
Both observations were in part during or following periods of southwesterly winds (Figure 8).
Also, in Figure 14(a) other low salinity
waters appear to be advecting from the northeast (Cape Lookout).
These
combined observations suggest a complex surface circulation in the Bay.
In addition, there are various mixing processes apparent along the outer
third of the shelf.
Figure 14(d) clearly depicts the edge of the Gulf
Stream with its associated high sa l inities.
The bottom horizontal salinity s tructure is by comparison much
simpler.
Salinities here generally range from a low of 35.80°/oo near-
shore to a high of 36.40°/oo offshore.
The higher salinities (36.30 to
0
36.40 /oo) are coincident with intruded Gulf Stream waters.
In Figures
15(b) and 15(d) mid-bay salinity cores of >36.30°/oo and >36.20°/oo
respectively are representative of the two cores depicted in the temperature structure of Figures 13(b) and 13(d).
In addition, the Cape Lookout
area appears to be a source of low salinity waters (Figure 15[a]).
This
same trend was seen in surface waters for this region.
Horizontal Distribution of Nutrients
Data sets for nutrients are available only for Hydro Grids I, II and
IV.
In addition, silicate data is available only for Hydro Grid IV.
Surface samples were taken within 1 to 2 meters of the surface and bottom
samples were taken generally within 2 to 3 meters of the bottom.
Surface nitrate concentrations were generally less than 0.5
for the three hydro grids (Figure 16).
~mole/liter
The only exception occurred in
Hydro Grid I (Figure 16[a]) where highs of 2.7 and 0.8
~mole/liter
were
observed in the northern nearshore region of the Bay.
An explanation is
not obvious and no corresponding highs in phosphate concentrations were
observed (Figure 17[a]).
Offshore of this same region there is an area
24
of higher nitrate (>0.5
~mole/liter)
which corresponds to a region of
higher phosphate (>0.05
~mole/liter)
(Figure 17[a]).
Figures 12(a) and
14(a) also reveal this to be an isolated region of lower temperature
(<26.0°C) and higher salinity (>35.50°/oo) than the surrounding waters.
Surface phosphate concentrations were low (generally <0.05
~mole/
liter) for Hydro Grid II (Figure 17[b]), but during Hydro Grid IV (Figure
17[d]), possible upwelling effects were exhibited near the shelf break
where deeper Gulf Stream waters had moved onto the shelf.
concentrations as high as 0.10
~mole/liter
are noted.
Phosphate
Likewise, the
movement of Gulf Stream waters onto the shelf can be seen in the surface
silicate plot of Figure 18(d) where silicate concentrations range from
1.0 to 2.0
~mole/liter
along the outer third of the shelf.
Elevated bottom nutrient concentrations (Figures 19, 20 and 21}
appear to be associated with newly intruding waters.
This, in fact, is
essentially the sole source of detected nitrate (Figure 19).
phate plots, however,
su~gest
The phos-
nearshore influences which are probably
associated with runoff (Figure 20[a] and [b]).
In addition, plots 20(b)
and (d) show traces of older intrusion cores stranded on the shelf.
This
latter observation suggests that nitrate is depleted more rapidly than
phosphate, that phosphate is in excess, or that phosphate is regenerated.
Finally, the silicate plot (Figure 2l[d]) along with depicting newly
intruded waters on the shelf, also suggests a source of high silicate
waters in the vicinity of Cape Lookout.
From this observation it is
apparent that silicate is a good indicator of both intruding Gulf Stream
waters and some specific low salinity nearshore waters.
25
...
...
"
.._oa•avr
••·so·-
.·.
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•
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14 · 16rnii/7S
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..! ...
..
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tO
.
(d)
(c)
Figure 10.
Grid 1I I.
. . --.-
Cruise tracks for Hydro Grids I, II and IV and XBT
26
_,,.,~
10
..I ...
"
,.
...
- - 1 4 ' JO'
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I.OO•Oiolf
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HYO't() . GAIO [D I A· 21
l O· l lt ml / 6 _ , ,.
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(a)
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Cruise tracks for aborted grids.
27
HYDRO GRIO 1l lA)
18/1ZIIl / 76
0
,.I
(d)
(c)
Figure 11.
. -~
..
.-1'
\)')0' - -
II'JO'
.. l,..
f '• JO'
.
-~~ · ·
·' WYORO·G.A..O m (&· l l
-
·'
..:.
•'
:Z / '5liJI/76
--J4'SO"
.•.
·''
;
Q
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••
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l#"lfi'-
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,.;1
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10
• WYORO GIIIO D
s.,.,,oc:.
r .m,.rat ur•
21 - Z3 / .m / 7S
'' t s o'
••
I
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- J S•l.O
!
• •t.. • • l f t • t
==10
10
10
I
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i'
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ICA t.. l
0
,, ·.
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,,..
I
I
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PP!O"
(a)
"
(b)
~4-lff' -
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.... .
r-·
f/
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'l
. HYOIIO Gll10 Ill
Swfoc.e Tti!IP\pefot w e
~~~
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(c)
Figure 12.
Grid III).
. . ..... ...,,.. -JJ•.to l
o==r.-.
Fir'To
. ,.
•c
i4-i6tl!ml71
J J•lo'-
I
"l,
,,.].,.
(d)
Surface temperature (Hydro Grids I, II and IV and XBT
28
o·
..
-
0
10
10
.,.
' •• 1 0
(a)
..l
I
I
,,. • cr'
, • • )0"
(b)
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.,.
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.. l...
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(c)
Figure 13 .
Grid I I I).
~
10
"l...
(d)
Bottom temperature (Hydro Grids I, II and IV and XBT
29
...
i
,,, •so·-~
...
I
I
..J
' • ' J O'
I
,,.,..•
,.
"l, ..
"
(b)
(a)
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4 - 5/liiD/76
J)'lO'- -
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,,.,I
(c)
Figure 14.
I
,.l, . .
.
(d)
Surface salinity (Hydro Grids I, II and IV).
30
,..
I 'F'
) 0'
I
~-~~Coo - ·· ····
· / l380
l • "IO'-
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.
~6.40)640 .
'y
20
. . . ·??.
-
36
t3'l 0'
,.! ,•.
• , . )0
H'JO--
,,.
, 1'
3630 ..........
/
~'/;..·HYORO GRID II
10- / / •• •
BOTT OM SALI NITY ._
' (l6 4 0·
ZI - :Z3 1 iiiJ76 _ , 1.
I
I
(b)
"
lOOM: OUT
- - s • "JD'
,,.
_ _ , ,.. l o'
1 4.' )0 ' -
___ ,..
•£ • 11
p>'
,,.,o--
U • 41
I
t •
•
·~· •I
l i' H f
r' • I
,,l,o.
Jo"
~·
3620
..
))')0--
/~;I '/
BOTTO .. SALI NITY Yo.
1<4 · 16 / mlt/7 6 l
.l
J ••
' ' 'Jdf
Bottom salinity (Hydro Grids I, II and IV) .
31
f. ~YOAO GIUO Ill
; l630
( d)
(c)
••
. )6 30
• :16 10
XBT GRIO ID
· - ~f"2ll!f 76
--- ···
r-;::v. l
;-:::;_
,.t'
Figure 15.
"
1. 001£0Uf
.
. NO DATA
I r'
50
,,
,
~0
(a)
,t~ ~
~~·
3.6.~
20 .
· ~YORO
l ) · l ~/:2ll / 76
/·
p~:_
>l6 40
GRID r
•
80TTOJoli SAUNITY ":f..
••·•o - ·
> :16 20
l"
.JO'
"
1.. oo• o u r
- - J .!1 " ) 0'
" 00 . 0~ t
- - • • • J O'
---···
H'\"OfiO GIUO I
SURFACE. NITR AT E »ti'IOie / l
14 ·1 $1'rn1'71!1i
-
J
• H:YD"O GRID II
SUAFAC( N'ITJit.A T( 6Uft01 e / l
'' '10--
' " 10'
:Z:I-23/'Dl/76
- J J " lO
c==--
0
J...
' ,.I,•.
.,.
.I..
"
I
1 , . Uf
(a)
fO
10
..l ..
,.
(b)
L 00 ~ 0lJT
_ _ , ... . , 0
1 •"1 0 -
___ ,..
. NO DA:rA
,
[
..
• HYDIIO. G~ID Ill:
SUAf"AC[ NIT RATE Uf'ft061/l
X8T GltiD aJ
,,.10'--
4 • 5/l!Dll76
U"JO' - -
- J J"Jd
:
14-16/'iDJ./76
1
,,.
I
, , . Jd
I
,,.
oCI
1)
••
"1 .•.
..
...I
I
'I" lCf"'
,.
(d)
(c)
Figure 16 .
-
, ,. Jd
==-
c:=-
Surface nitrate (Hydro Grids I, II and IV).
32
10
10
"1 ...
"
"oo • our
_ _ , ,.•s o
1..
) 4'1 0 -
OO• 011 r
- - J • • s:
___ ,..
< 0~
--- ···
' l··· 0~
• HYDRO GRID t
SURFACE PHOSPHAT[
· HYDRO GRID U
SURFACE PHOSPHATE
t.~moM/L
.t l • ,o· - -
H"lO--
10
f ' •
=ro -.to
0
10
'
I
I
ra • t o
'O'
,..mo~e / L
~1 - Zli1W/76
"
...
I
I
r , . ,.
, •• J 0
(b)
(a)
..
.,
f.. 00 .. 0UI
10'
. NO DA.TA
, • • Jo' -
- - ) 4 ')0
--- ···
/
)~/ - · ··
,, ...
/~.
SIT CiltiO
· HYOIIO GR>O llr
SuR•&CE PIOOSPH4TE 14 ·16/YlU /7 6
_
m
4· St!llll t15
JJ • J.o' - -
=-
0
, J'
I
ur
,,
,.
(c)
Figure 17.
....I
10
,.I, ..
(d)
Surface phosphate (Hydro Grids I, II and IV).
33
10
IL
J
l'
JO'
J • " t O' -
,..
. NO DATA
c ~ ~
l
. NO DATA
, l' ,
..HYOAO GRID 1
'' ' )0--
1 4 - l ~f'D / 76
HYDRO GfUO II
-
1 l ' Hf
..l ...
I
, , . td'
21-2 3 / E l 76
li•" JO' - -
,,.
II'
I
"[
S- CI"
(a)
j
,,
,.
--s •·~ o·
3.-·s o·-
..
'
...
r' ' '
v•.·;
. ;;.;7
.
;
,
.
,
_,
.
. ..
·. .
·/1: ~>1.~ ~0 ~·
,(1..11
XIT GRlO
m
·~ f lllll/16
-
-
11'10"
u·scr- -
=-
...
J• JO
I. OO ICO UT
- - U "JO
.. ~~~ ..~·~
___ ,..
NO DA.TA
)1"10' -
,
(b)
L.O oa ouor
j l •·so -
-
..I...
I
' ' "ld'
..... ............
14 - US i mli / 71
·\~
0
••
,..
(c}
Figure 18.
,) (!.
• HYO~O GRID Ill:
SURFACE SILICATE u -lo fl
I
' ''l ..
,..
(d)
Surface silicate (Hydro Grid IV).
34
10
-
JJ' H1'
JO
,.! ...
"
__ ,. .,cr
__ ,, .,g
I. 00 & OUT
I,.O OC OUf
---···
--- ···
' HYDRO GRID li
• HY OAO GAIO 1
BOTTO,. ~ IT RA TE 14 ·1 5 / ml/76
... ...
\
" '- ••• ,,
~
0
I
10
..
-
~
/l
Jl "J O
-
Jl " JO
~
0
10
10
10
.. l...
I.
I
,,.,
, , • 10
l l "lo'
BO TTOW N IT RATE J.~ ,.O i e /L
;~/ 2 0:- ...~:-~.):~.~ ~~···
S)"lO'- -
(a)
( b)
...
r., O O IIC OUf
lo.OO • OUI
- - J t "JO'
\ • "10 -
- - ) <11 "1 0'
l • "JO--
. ..,, ,
~
.·
~·
. NO DA.TA
--- ···
.'-
urGR1Dm
u · Jo· - -
} )'1 0"- -
.==.• ..
...
I
, ,. id
..
,..
<O 5
, ,..
.....
• - 51'ill1 1 ra
.
zo:-
I..
/
4!1
Bottom nitrate (Hydro Grids I, II and IV).
14 - 16 / 'illi./ 71
- J . )"J O'
==0
10 a:o
..l ...
,,.,
(d)
35
.~;;
---···
' HYDRO GRID Ill:
80 TTOM NIT ,.AT£ JiiMO it ll
.'
(c)
Figure 19.
.
"
~
"
I
~OOIIiOUt
L 00 a 01.1 T
_ _ , ,.. , o·
-- t.o~~•Jo"
••• JQ '- -
___ ,..
.< 05
HYDRO GRID I
BOTTON PHOSPHATE
14 ·1 )/m./76
\1 ' 1 0 - -
U& \.1
••
• /
~ ~~
-
' HYDRO GRIOli
05
~ 10-.
,,. 1o·- -
1 J' , o·
...
.J..
I
lO
ll - 23/:llll/76
H • ~l
• • ~o. ••• t ,al
....,_
0
!IOTTOIO PHOSJ>tiAT( _.,.o iL
10
"l, .
••
.
..
_
, ., ••
l l i , . IOJ 11 11
..l,..
,,.
(a)
(b)
,,
__ ,.., .,a
t.. CJOIIOU T
~
..
~ , o·--
.NO DATA
1'{ 1"
!.. OO • OU' l
, . . ,o -
_ _ , 4 '1 0'
--- ···
~···
XBT GIOIO M
~ -5 l lllll l 7 6
I
, , . tef
,.
..l
U'lO' - -
...
lO'
I
11').1(
(d)
(c)
Figure 20.
...
Bottom phosphate (Hydro Grids I, II and IV).
36
..
...
'.
~
I
I. 00.
o u'
·NO DATA
00
1..
- - J4 'l o •
. NO DA.TA
___ ,..
,r,.
II:
out
--J ~" JO '
) 4 "10'- -
--- ···
1"(.611
HYOf>O GRIO I
1 4 -I ~ I'E:I 116
U"\0 - -
s• to
HYDRO GRIO Q
Zl-2:3/ .El l 76
U'JD--
-
J
1· 10
=
••
to
0
.,.
"
...
I ' '
I
I
7 1 . }.0'
)0"
(a)
(b)
I. OD IC OU T
- - ) A' tD'
. NO DA.TA
---···
l( a •
UT GRID m
4 • 5 / lll!l/76
-
Sl"lO'
0
..l ,.. ..
I
, , . )d'
Bottom silicate (Hydro Grid IV).
37
10
"l
,,.}-.,..
)0"
(d)
(c)
Figure 21.
I
10
..
Vertical Distribution of Physical and Chemical Properties (Hydro Grids)
In the following figures the arrows indicate the cruise direction.
The transects have been arranged to give the cusp shape nature of the Bay
and the proper relationship of stations along one onshore/offshore transect to those of the next.
is obtained.
In this way a three dimension view of the Bay
The bottom bathymetry is an averaged value from the various
cruises along the given transects.
Temperature plots are derived from
CTD and XBT data; salinity plots from CTD and/or bottle samples; sigma-t
from available data as reported above; and nutrients (N0 3 , P0 4 and Si0 3)
from water samples collected at selected depths as indicated on the
respective plots.
Hydro Grid I.
The vertical temperature structure during Hydro Grid
I (Figure 22) demonstrates the temperature gradient which is characteristic
of intrusions and shows that intrusions are not restricted to the shelf
break.
Note the apparent movement of colder waters far onto the shelf
along the bottom in transect (d) and the presence of a warmer core (24.5°C)
isolated along transect (a).
The corresponding salinity and sigma-t
plots (Figures 23 and 24) also show strong vertical gradients with increasing salinity and sigma-t values with depth.
Such trends confirm the off
shelf origin of these waters.
The movement of colder bottom waters onto the shelf serves as a
mechanism for the transport of nutrients onto the shelf.
trations as high as 2.0
~mole/liter
Nitrate concen-
are observed along transect (d)
(Figure 25) which had the coldest (21.5°C) penetration of off shelf
waters (Figure 22[d]).
Concentrations as high as 1.5
~mole/liter
noted for station 27 where the coldest waters were only 24.5°C.
are
Further-
more, at station 47 where 23.ooc water were observed, no significant
nitrate concentrations are detected.
38
Further onshore along transect (c)
there is a core of high nitrate water with values as high as 2.8
~mole/liter
in slightly warmer water than that found closer to the shelf break.
A
satisfactory explanation for this last observation is not provided beyond
the possibility of a bad sample.
Phosphate concentrations (Figure 26)
directly attributable to an intrusion are shown only for transect (d).
No silicate data are available.
Hydro Grid II.
In Figure 27 the vertical temperature structure in
the Bay during Hydro Grid II is presented.
counterpart of Figure 13(b).
This figure is the vertical
Once again there is an intrusion apparently
moving onto the shelf along the two southern transects.
Also, there is
evidence of another older intrusion core (23.0 - 24.QOC) centered at
stations 25, 43 and 62.
Salinity of 36.25°/oo and sigma-t•s of 24.5 and
25.0 correspond to both the older and new intrusions (Figures 28 and 29).
Both the nitrate and phosphate plots (Figure 30 and 31) show high concentrations at station 66 coincident with the new intrusion and its coldest
tongue.
However, only the phosphate plot shows any evidence of the older
intrusion, but only along the transects which pass through the two coldest
cores.
High phosphates reported at station 39 are probably due to runoff.
No silicate data are available.
Hydro Grid Ili(A-2).
Figure 32 shows the vertical temperature
structure along two northern transects made during the second aborted
attempt at Hydro Grid III.
There is no corresponding horizontal plot,
and salinity, sigma-t, phosphate and silicate data are available only for
transect (a).
Figure 32 exhibits an isolated intrusion core and a newer
intrusion apparently moving onto the shelf.
outlined by the 24.ooc isotherms.
Both of these features are
In Figure 33, salinity and sigma-t
values of 36.25°/oo and 24.5 respectively represent these intrusion cores
on the shelf and, in Figure 34, near bottom silicate values of 2.0
liter roughly approximate these cores as well.
39
~mole/
The phosphate plot in
this latter figure is less conclusive though it does exhibit two regions
of higher concentrations.
XBT Grid III.
during XBT Grid III.
Figure 13(c).
No nitrate· data are available.
Figure 35 shows the vertical temperature structure
This figure corresponds to the horizontal plot of
It clearly shows a cold core (21.5°C to 22.5°C) along the
length of the Bay and suggests the possibility of another core having
moved further nearshore in transect (a) (station 21).
Such an observa-
tion is not inconsistent with our findings in September 1975 (Atkinson et
~-,
1976).
No salinity, sigma-t or nutrient data are available in
conjunction with this grid.
However, a bio grid was run across stations
53-57 and will be presented later (page 63).
Hydro Grid IV.
In Figure 36, the vertical temperature structure
during Hydro Grid IV is shown.
It reveals a stranded intrusion with a
core of 23.0 to 24.0°C along much of the length of the Bay.
It also
shows evidence of other waters moving onto the shelf behind it.
This is
not surprising in view of the horizontal plot of Figure 13(d) which shows
a rather massive movement of bottom waters onto the shelf along its
entire length.
In Figures 37 and 38 high salinity and sigma-t values
(36.25°/oo and 24.5 respectively) correlate only to station 33, the
coldest region on the mid-shelf.
Similarly high, and higher values are
noted for the outer edge of the shelf.
It is also noted here that the
coldest penetration of this particular intrusion occurs along the
northern transects of the Bay.
This is the first documentation we have
of intruding waters moving into the northern offshore section of the Bay
in advance of the southern sector.
This observation and the overall
movement of Gulf Stream waters onto the shelf at this time may have been
influenced by the passage of Hurricane Belle on 9 August.
40
The nitrate, phosphate and silicate plots of Figures 39-41 support
the obvious conclusion that the intrusion centered around station 33 is
the older of the two.
That is, all three nutrient species are found to
be either negligible or very low, thereby suggesting that they have been
used up.
Of course, there is the possibility that there were no nutrients
to begin with .
In contrast, looking at the waters moving onto the shelf
one can see considerable quantities of nutrients along three of the transects.
0.50
a~d
Nitrate, phosphate and silicate concentrations as high as 8.4,
6.1
~mole/liter
respectively are observed.
high nutrient waters is seen along transect (c).
No sign of these
This is due generally
to a lack of onshore penetration of the colder waters exhibited along the
other three transects.
High silicate values (2.5 umole/liter) at station
13 are unrelated to the intrusion phenomenon.
They appear to be due to
the movement of waters south from the Cape lookout area (see Figure
21[d]).
41
TEMPERA T UR E ·c
GRID
HYDRO
14-1
I
/ ::sz::.r::r/76
STATI ON
2
1121
I:
2121
r
3121
1-
ll.
w
Q
;,
..
···.-:
.-:11_;-~~~..-~
2 121
2 1
3
'-1
NUME3ER
6
!i
11219
8
7
cO
(a)
4121
5"121
6121
18
19
22
24
2
25"
128
27
26
1121
(b)
2121
3 121
'-1121
5"121
.
6121
~
Jl'"e~
38
39
'-1121
'-11
42
'-13
'-1'-i
Y!i
'-i6
'-17
1'-18
2:6)..
'
1121
2121
(c)
3121
·=\·
'-1121
5"121
6121
5"8
1121
·::~'
2121
3121
'-i121
S.9
6121
61
62
ZH
63
',
64
6S
2' S
2$. S
M .O
66
167
'26~
,-----~
·~· Z>O-~
Zl S
----..
:-~ ~ ~·ri"J·.~~t.~·~.'f.; ·. '_,:
'- l40
~
· !
S121
6121
Figure 22 .
Vertical distribution of temperature (Hydro Grid I).
42
(d)
5 R L I
~l
I T y
HYDF-10
'X .
GRID
[
I S: / V::: [ / 7 6
I Y-
STA T I ON
N U M <'if-..:: R
2
7
6
J52~
1121
;[
,_
:!.
'_J
Q
,- 35_50 __ _ -- )600 - - --
J 5 25
8
112!9
J~ 50
-~:..:----,.;~~0= --·;-= o:.:-- ·----J625
2121
I
(a)
> 36 2 ~
3121
'-i121
S:121
6121
18
19
212!
21
112!
23
22
3~2)
3515
~;:·
0
2S:
26
...:~-7~,
35_~
27
128
--=-~.:-::.:-:.~._:-;_0:;~:::::::-.-=---·=-=:~?:"_r_='c_='c:='="=-='~~=~- ~6 Oo - _' .., ._
----- -~
212!
(b)
3121
'-i121
S121
612!
1'-iB
1 12!
(c)
2121
3121
Yl2!
S:121
612!
S:B
S9
6121
61
62
63
6'-i
6S:
66
167
1121
2121
(d)
312l
'-il2!
S:121
6121
Figure 23.
Vertical distribution of salinity (Hydro Grid I).
43
SI GM A - T
HYDRO
GRID
I
I '-t - I S" / YLT /7 6
5 TR T I ON
N U M EH : R
3
r-~--~----- ~--_J----~--~~
Z,j-0
> 230
__
7
8
1 1219
_ L_ _ _ _L __ __ L _ _ _ _ _
I:
I
1:!..
w
Q
- --
(a)
3
'-t121
S121
6121
18
19
21
22
23
2S
26
27
128
> Zl.O
1121
2121
(b)
3121
'-t121
S121
6121
38
39
'-t121
'-tl
'-t2
'-t'-t
'-tS
'-t6
'-17
l'-t8
1121
2121
(c)
3121
'-1121
5121
6121
112l
(d)
212l
3121
'-i121
S121
6121
Figure 24 .
Vertical distribution of sigma-t (Hydro Grid I).
44
NITRATE
HYDRO
I Y -1
<UMO LE/L )
r
GRID
~/YCI/76
STAT IO N
1 11!
r:
I
1-
Q
w
... .. ,
y
3
2
N UM BER
6
~
7
-
~~-
111!9
~
<0-'
;_
:211!
8
·o
..._.
(a)
31a
Yla
S:la
0
61<l
18
19
:2 1a
21
23
22
2Y
2S:
..
27
I Ia
<0-~
212l
-.'
3 !2l
26
·.
·o ~
27
1 28
¢=I
----
0 .5
(b)
.'"1:
Y!2l
S:0
6!2l
38
39
Y((l
Y l
111!
yy
Y3
Y2
YS:
• • -•••
31<!
2 8 10
..
Yl1!
.:.·~/'
Y7
I YS
~
<0.5
--c-:---::,-...
.
. /
21a
Y6
(c)
I
'· •
:{-
.
...... ~--:
'.";f. :
S:l<!
61a
s:s
I Ia
S:9
611!
6 1
6:2
--r::==~~~~~;~ __ ,~~":
63
6Y
65:
66
167
<0.5
o_, . . ---iD:--
21a
,
3121
----~---~~---•
, ~-
· - - 2 .0_
Y 121
S:l1!
6121
Figure 25.
¢=I
Vertical distribution of nitrate (Hydro Grid 1).
45
(d)
PHOSPHATE
HYDRO
GRID
(l.JMOLE/L)
I
1"-1 - I S : / m / 7 6
STATION
3
2
- - ~- -
I Ia
I:
I
f-
D..
w
0
21a
s:
"-1
...
......
r.;.•
3 t<l
•4,"l
.
-.~-,
...
5
7
lla9
8
< .0!1
I
- -;
NUMBER
·.,.,. --..;_;
~
(a)
).
"-1111
-..,..
-~.
.....
t•
'
S:la
51a
18
19
21a
21
22
23
2"-1
2S:
26
27
128
I !a
(b)
21a
31a
Yl<!
......
S:t<l
-,
61<!
-~
··38
39
Yt<l
"-11
Y3
"-12
Y"-1
""1S:
Y6
Y7
IYB
< 05
112J
21a
(c)
312J
..;
·'.~
Yla
s:ca
·.:f..,
51a
S:8
S: 9
51
62
63
6Y
6S:
66
1 67
I !a
21<!
(d)
31a
""11a
S:121
51a
Figure 26.
Vertical distribution of phosphate (Hydro Grid 1).
46
·c
TEMPERFI T lJRE
HYDRO
GRID
II
21-23/::lZ:II /7 6
STAT IO N
2
I
1-
Ei
7
8
1 1219
- =-==·---2_1ip
1 121
I:
s:
3
NUME3ER
(a)
2121
3121
Y121
0..
w
S:121
0
6121
18
19
2121
21
22
23
2S:
26
27
1 28
1 121
2121
(b)
3121
Y121
S:121
6121
IY B
1121
2121
(c)
3121
Y121
S:0
6121
10
2 1tl
(d)
30
Y0
S:121
6121
Figure 27.
Vertical distribution of temperature (Hydro Grid II).
47
SA LI NITY
HYDRO
x.
GRID
I:I
2 I -23 /V I I /76
STA TION
....
3
s;
v
I
.....
a.
w
6
··.
1 121
I:
NUM~ER
7
8
'
1~151
--- l...lfOO- - - - .. "
- )l.Z~ S3. ~
l~
11219
~
z'
'
\
.
'
~~
"' ..
2121
(a)
:::.·· ](1 .~
3121
'-!121
S:121
0
6121
18
19
2121
21
2:2
23
:2'-i
2S:
27
:26
1 :?.8
---....
<:=
\
1121
'2121
)~.2;
-
(b)
3121
Y121
S:121
6 1<J
38
39
Yl<l
'-il
'-1:2
'-13
'-i Y
Y6
'-iS:
'-17
I YB
~
,
I !a
(c)
:2121
31<!
Y121
S:I<J
5121
S:B
S:3
6121
6 1
6'2
63
6'-i
6S:
66
167
<:=
1121
(d)
'2121
3121
..
~
Yl<l
S:121
5121
Figure 28 .
Vert i ca 1 distribution of salinity (Hydro Grid I I).
48
SIGMR-T
HYDRO
GRID
II
2 1 -23 /::sz::::r::I / 76
STATION
2
1 121
I:
21il
"
31il
I
~
0..
w
-
...
NUMBER
3
.-2'·'--------.,
.
~;·.,.
(a)
..,lil
S:121
0
6 121
18
1'3
2r21
23
21
2S:
26
27
128
1121
(b)
2121
3 121
..,121
S:121
6121
1 121
(c)
2121
3121
..,121
S:121
5121
S:B
S:9
6121
62
61
63
6..,
ES:
66
167
llil
(d)
21il
31il
S:l2l
6121
Figure 29.
Vertical distribution of sigma-t (Hydro Grid II).
49
NITRATE
HYDRO
<UMOLE/L)
GRID
!:I
21-23/::sz::::r::::r:/76
STATION
2
3
s:
4
NUMBER
7
6
112!
I:
:r
(a)
~-~~· -~: -~·. :\;!t. ~
312!
Yl2!
w
S:l2!
0
109
<OS
212!
~
a..
8
. ".··
.
27
128
612!
18
19
20
21
22
23
2'-i
1121
2S:
26
<o.,
(b)
2121
312!
'-112!
S:l2!
6121
38
39
4 0
Yl
'-!2
Y3
112!
'-t'-t
'-IS:
Y6
'-17
IY8
<o.s
(c)
20
3121
~.-,..!¥.";:.. ..:~~t·~( t·~;:>...~
'-112!
S:121
612l
5:8
5:9
612l
61
62
1121
63
6'-i
6S:
66
167
<O.'
2121
{d)
3121
'-1121
.. , -;.•. ...:f-.. r•• -
..,
S:l<l
60
Figure 30 .
Vertical distribution of nitrate (Hydro Grid II).
50
PHO SP HATE
H YDR O
< U MOLE/L>
GRID
II
21- 23 /JZ::CI: / 76
ST A TI ON
I
2
3
~
S
NU MB E R
6
7
8
1 09
110!1
I:
I
~
(a)
210!1
3Ci!l
~toil
(l
w
0
Sl<l
610!1
18
19
2121
21
22
23
2S
2 ~
2 6
27
12 8
1 10!1
(b)
210!1
30
'-110!1
Sl<l
612!
38
39
'-1 121
'-15
'-13
'-i l
1 ~8
I
( .05
(c)
,'' ,~,
...
.
SB
S9
6121
6 1
52
-·~
6S
63
56
167
.05
<..os
1121
, , - - - - - - .0$_- -
2121
3121
I
-~
•
> .05
I
I
_,05
......
'-1121
S121
6121
Figure 31.
Vertical distribution of phosphate (Hydro Grid II).
51
(d)
·c
TEMPERA T URE
HYDRO
GR I D
3111 - 3 1 /
III
<A-2>
/ 76
S T AT ION
1 121
9
I I
12
13
14
NUMBER
IS:
16
17
I I 8
1 121
(a)
2121
I
~
a.
w
0
3 121
Y121
5:121
6121
28
29
3121
31
32
33
34
36
3S:
37
13 8
1 111
-- 21.o --- - ZJ.s ... ---- --- ------::::::: z•.o
2121
ZS.O
,----~
3121
23, s '
2l.0 ~ 2.S
...
4121
5:111
6111
Figure 32.
Vertical di~tribution of temperature (Hydro Grid III
(A-2)).
52
(b)
SALINITY
HYDR O
:<:.
GRID
30 - 31/
~
<R-2)
/76
S TA T ION
9
10
I I
13
12
I
....
c..
w
0
IS:
1"-i
10
I:
N U MBER
---::.
'
16
17
I 18
'
'
___ _____
____ _-4' ~,
,'
2121
(a)
30
Y121
S:121
6121
SIGMA - T
HYDR O
GR I D
III
<A - 2>
3 121 - 31/lZ:CI/76
ST A T
9
1121
I I
12
13
I
ON
Nl ~MBE R
IY
IS:
16
17
I 18
1121
I:
2121
I
;-
Y121
w
S:0
c..
0
(b)
3121
6121
Figure 33 .
Vertical distribution of salinity and sigma-t (Hydro
Grid III(A-2)).
53
PHO SPHAT E
HYDR O
C~ M OLE/L)
GRID
III
C A-2)
31i'J - 3 1 / :ll:I:I:/76
STATION
g
10
I I
13
12
I~
NUM13ER
I S:
16
17
I 18
=>
I I<!
l:
I
(a}
2t21
31<1
I-
ll.
w
0
6 0
SILICHTE
HYDRO
C ~M OLE/L)
G RID
III
<A-2>
3 t2l -31/ :'ilii /7 6
STATION
9
l t2l
I I
12
13
I~
NUM6ER
IS:
16
17
I 18
1121
I:
"
I
1-
D..
w
0
2121
(b)
3121
~(21
S:IO!l
6121
Figure 34. Vertical distribution of phosphate and silicate (Hydro
Grid II I ( A-2) ) .
54
TEMPECRR TU RE
XBT
GR I D
"C
m
Y - s:/ r m / 7 6
STAT ION
18
2(21
19
2 1
23
22
N UM6E R
2Y
2S:
26
27
128
/ (21
E
I
f-
!l.
w
(a)
2(21
3(21
Y(21
s; (21
C>
6(21
38
39
Y l
Y2
Y3
Y6
Y7
I YB
<=
1(21
2(21
(b)
3(21
'-1(21
5;(21
6(21
S:8
s;g
60
61
62
63
6Y
65:
66
167
1(21
2(21
(c)
30
y(21
S:(21
6121
Figure 35.
Vertical distribution of temperature (XBT Grid III).
55
TEMPERATURE
HYDRO
GRID
·c
-oL
IY-16/YI:IT/76
ST
1121
9
I I
12
13
TION
IY
NUM13ER
I S:
16
1121
I:
I
I-
!L
w
0
(a)
2121
31<!
'-ill!
.,
S:l<!
612l
29
28
3 12l
31
32
33
3S:
36
37
138
=::>
1 12l
(b)
212l
312l
Yla
S:la
612l
Y9
Y8
S:la
S:l
S:2
S:3
S:Y
s:s:
S:6
S:7
IS: B
<?
112l
(c)
21<!
312l
'-ill!
S:121
6121
67
68
59
7121
71
72
73
7'-i
17S:
=::>
1121
(d)
212l
312l
Yla
S:121
6121
Figure 36.
Vertical distribution of temperature (Hydro Grid IV) .
56
SAL I NITY
HYDRO
;< ,
GR I D
t:::'Z:
I Y -1 6 / r m / 7 6
•:;Tr~
1121
9
I I
1'2
13
T I ON
I ·~
NIJMBE:R
15
16
18
II
<=
1121
I:
'2121
I
f-
Y0
w
S121
n..
0
(a)
3121
., ..;~
6121
'28
29
3121
31
3'2
33
3Y
35
36
138
31
=::>
l6.00
>J600~-·
1 121
2121
3121
(b)
36.Z~
Y121
p
:.-
S:121
6121
Y8
Y9
S:121
S:l
S:2
S:3
S:Y
s:s
S:/
S:6
IS:8
<::=
36.00
~
1121
'2121
.'
3121
Y121
- ""
S:121
(c)
'
6121
67
68
69
7121
71
7'2
73
7Y
17S:
~
~600
1 121
'-....
(d)
'2121
3121
Jsz~
Y0
S:121
6121
Figure 37.
Vertical distribution of salinity (Hydro Grid IV).
57
SIGMR - T
H Y DRO
GRID
LV:.
/76
SlH FI !J N
1 121
9
I I
12
13
1'-t
NUMtH : H
16
IS:
17
I 18
¢::J
1121
l:
I
r
:_
w
0
2121
(a)
3 121
'-1121
S:121
6121
28
29
3121
31
32
33
3'-t
3S:
36
37
13!:3
c;.>
1121
2121
(b)
3121
'-1121
S:121
6121
'-19
'-18
S:121
S: l
S:<!
90
1121
S:3
S:Y
s:s:
S:6
S:7
IS:8
>D.O
DO
<!Ill
'-~- · -·- -·
31<1
.
> 2Z.5
;,_,~
(c)
_23.-'----
21 0-
'-1121
S:121
6121
67
68
69
7121
71
72
73
----
23.0
1 121
2121
3121
7'-t
17S:
DD
'--(d)
24.0 z4 ~
,
'-1121
25.0
S:121
6121
Figure 38.
Vertical distribution of sigma-t (Hydro Grid IV).
58
N I
TR~Il
HYDF-1 0
CWMrll.E"/L)
F.
GR I D
Dl:
1 '-l-16 /:ll:CCI/76
'. ~TI~T
g
10
!:
20
r:
30
1-
'-l f2l
'..!
S:0
Q
I
I I
12
13
F=::.
I ON
1'-i
IJM~~: R
IS:
16
17
I IB
<=
< 0~
(a)
50
29
28
3121
3 1
32
33
3'-l
3S:
36
37
138
=>
112l
<0
( b)
212l
3 0
Y0
S:C21
60
'-19
'-18
S:t2l
S:l
S:2
S:3
S:Y
s:s:
10
S: 6
S:7
I S:B
<=
<O ~
20
(c)
312!
Y QI
S:121
612!
67
68
69
7 121
71
72
73
7'-i
17S:
=:>
1(21
(d)
2121
3C2l
"'112!
S:121
6!2l
Figure 39 .
Vertical distribution of nitrate (Hydro Grid IV).
59
PHOSPHATE
HYDRO
<~MDLE/L)
GRID
:J3L
I Y - I 6 /V I I I /76
STAT ION
I ill
9
-
10
l:
"
I
12
I I
13
NUM13ER
IS:
IY
17
16
............ . . -------
I 18
'
<_()!!
<::=
JO
• 03
''
20
(a)
311!
fa_
'-10
'Q
S:C2l
611!
28
29
311!
3 1
33
32
3Y
3S:
I
/> .0~
10
I
211!
I
'
''
I
,,
138
I
'
'
=>
I
<03
I
'
:----,
3C2l
37
36
I
{b)
YC2l
S::0
60
YB
Y9
S::121
S:l
S::2
s:s:
S:Y
5.3
S:6
~
1121
< 0~
- - - - _()!!
. ,,
'
.05
I
L ..... --- ----- _.. '
20
,,'
'
I
'
S:7
IS:B
,
<::=
<05
{c)
....
,,-o~
31<'l
'-40
, : . ::.:·
~<>~-\.~~(~·:.·
-·
S:fll
6f2l
67
68
7f2l
69
71
17S::
7 '-4
73
•.-
,:-;::,:~:~.:.~;~~{. .~.. ~:~ ·"f~ -~1: ....
-----*
-~..- ... ;...J'?·.-', .. -· ·::
. _ ..;•.:.·
3f2l
.; .~·
',
·\ r'\
'
Y C2l
(d)
',
10
~
'. l'
S: fll
~ .17
612l
Figure 40.
S>
< .03
lfll
2 f2l
72
Vertical distribution of phosphate (Hydro Grid IV) .
60
SILICATE
HYCR O
<UMOLE/L>
GRID
I::sz::
1 4-16/:"Tl:I:L/76
STATION
1121
9
,...
10
I:
20
12
13
1-
a.
w
Q
14
IS:
16
17
I 18
~~ ..
10
, -------2_0-----....... ''; -----
/
/
I
N UMBER
/
(a)
• 2!j
30
40
S:0
60
29
28
3121
3 1
33
/ \
1121
3S:
3'-1
I
> OS
/
37
36
138
\
~
\
10
0.!1
> 1. !!'
1.5
.~l·.: ~:,}r~-:~,.:,·: :\:. ·:J,'d:'i·:.· .:,·i~ 3·~.:;.•1~· -,:~;".·r.~:.-~;;-;/~-="'"--\
. . :.~-,._' ~,'~·. :,:·,.
20
3121
·i.':•.
"''
4121
(b)
:)''. :~~..
.....
S:121
60
48
49
S:0
S:l
S:2
I
<O!j
10
I
,
3 121
,·'!,;,
S:7
<:=
> 1.5
I
.j'o.t~i/;v.
I S:8
'
to
0.5
I
S:6
I
I
2121
s:s:
S:4
S:3
0.5
(c)
40
S:121
60
67
68
69
70
71
72
73
74
17 S:
:
112l
'I
\
20
....... _
-
30
.r~!,p
•\ ___ 1..3 -~ ·
··:
.....,;.,
' z.o ·
40
'
S: 0
.1.5
612l
Figure 41.
Vertical di s t r i but i on of silicate (Hydro Grid IV).
61
(d)
Vertical Distribution of Physical and Chemical Properties (Bio Grids)
The tracks for the four bio grids made during th is study period are
shown in Figure 42.
These correspond to regions of particular interest as
ascertained from the hydro grids discussed in the preceding section.
Only
tracks (a) and (c) (Bio Grids I and III) were completed as originally
conceived:
four complete transects of the selected set of stations in a
24 hour period.
Bio Grid II consistcdof one passage along the indicated
transect over a 12 hour span and Bio Grid IV
the indicated stations over a 9 hour span.
con~sted
of two samplings of
For repeated transects, data
collected at the end or turning station of one plot were used for the same
station in the next plot.
Bio Grid I.
Sampling was identical to that reported earlier.
Bio Grid I suggests the recent separation of a cold core
from an intruding tongue (Figure 43).
This is probably related to the
intrusion first observed moving onto the shelf 2 1/2 days earlier during
Hydro Grid I (Figure 22).
0
At that time a bottom temperature of 21.5 C was
observed at station 65 and still colder waters appeared to be moving onto
the shelf.
During the Bio Grid, temperatures at this same station were
observed to increase.
with time in Figure 43.
In particular, note the change in the 22.0°C isotherm
It flattens and disappears.
This change is possibly
due to horizontal and vertical diffusion or to advection laterally along
the shelf or to a combination of the two.
Figures 44 and 45 characterize
this region of intruded waters with typically high salinity and sigma-t
values.
Figure 46 indicates that by the end of the second leg of the Bio Grid
detectable nitrate concentrations at station 65 (the 22.0°C core) had
fallen below 0.5
~mole/liter .
During the earlier Hydro Grid (Figure 25,
page 45) concentrations as high as 2.0 umole/liter had been observed .
This
suggests that even in a relatively young and cold intrusion core most of
o2
the nitrate may be used up before the core has moved very far onto the
shelf .
In contrast, phosphate exhibited its greatest concentrations in
the Bio Grid at station 65.
This is shown in Figure 47(a) and (d).
The
lack of similar cores in plots (b) and (c) is thought to be due to the
sampling method.
The core of high phosphate water was apparently quite
small vertically and was not sampled every time .
No silicate data are
available.
Bio Grid II .
shelf.
Bio Grid II consists of one transect the width of the
The temperature, sigma-t and salinity plots (Figure 48) show an
intrusion along the outer shelf with temperatures as low as 20.5°C at
station 158.
of 23 . 0°C.
Also there is an older intrusion at mid-shelf with a core
Both of these features were observed during Hydro Grid II
along transects both north and south of this one, the most recent of
which passed over the 23.0°C core 10 hours earlier (Figure 27, page 47).
As was the case for the hydro grid, no trace of the older core is seen in
the nitrate data.
In addition, what trace there was of the older core in
the phosphate record of Hydro Grid II is lost in Bio Grid II.
The newer
intrusion, however, is well defined by both nitrates and phosphates
(Figure 49).
No silicate data are available.
Bio Grid III .
Bio Grid III is represented in the temperature,
salinity and sigma-t plots of Figures 50-52.
Note the well defined
22 . 0°C core on the shelf with its characteristic salinity and sigma-t
profiles .
The position of the 22.5°C isotherm suggests negligible
onshore movement but perhaps some slight offshore movement over the 24
hour span of the bio grid.
may have occurred .
In addition, lateral movement along the shelf
The apparent fluctuation in the size of the 22.0°C
core is at least in part due to the scaling field for the parameter being
contoured.
Nitrate, phosphate and silicate concentrations as high as
G3
7. 3, 0.18 and 3.5
~mole/liter
respectively were observed {Figures 53-55)
They al so suggest an offshore movement.
It is interesting to note that this intrusion core is isolated on
the shelf with significant nitrate and phosphate concentrations whereas
earlier in Bio Grid I an intrusion with a similar 22.0°C core exhibited
negligible nitrate but similar phosphate concentrations.
A possible
explanation may lie in the relative age of the two .
Bio Grid IV.
Bio Grid IV consists of two passages along one transect.
It was made nearly 24 hours l ater than the previous passage over this
same transect during Hydro Grid IV (Figure 36).
The 23.0°C core is still
well defined as are the high salinity and sigma-t features (Figures 5658).
No significant onshore/offshore movement is apparent with respect
to the earlier grid.
Nitrate concentration is negligible but phosphate
data still show some traces as defined by the 0.05
(Figures 59 and 60).
~ mole/liter
contours
The silicate data (Figure 61) are difficult to
interpret.
64
,..
J<t•to·-
.
_,.
..
.·'
.•.
.•'
I
".
•'
·'o
•'
.. ..
.. ..
·"
.•'
·' ..
.•'
·'' .~ ,
.. ,.
:1'
.•'
,.
"' ·
,.l, ..
I
,.
~a'
10
.•
_,.
I
-~ .
..
,
·'
, , . )jf'
.
__ ,..
~ -6 / lZIII /76
u.u.l u
'/
.·'
.•'
.• ..
•t,:· .
'
_,,~_,rt
))'10'- -
· ~ ~ ·•• ••• •
10
.
· .~,
...
I
....
·'
JJ ' ) . .
(d)
Cruise tracks for Bio Grids I, II, III and IV.
65
..
·'
..
;' ;
IO ~ Git i O
~ ·
·'
. . . .. .
10
..l,.,
.•'
. _,,.
,.
~
0
·'
,,
(c)
Figure 42.
-ll'JtT
1.0
·'
810-atiOm
·'•'
·'-~--···
..L..
,.
,,.,ct'
.
,,
u · so--
I
·'
I
lO
,.
.·.•. ·'' .•. ·'' _,~ '
·''
.•'
·''
23/mi / 76
.
:>
.•.
.•'
·''
.·•.•'
0
.•
·'
(b)
-~
•'
.•
.
. _,,....
(a)
.•'
_,.
.•.
,
:..'; ... ...... . ...
_,.,.,~
tO
·'' ....
..•
.•'
t7.utr m J rG
0
.•'
.•'
.. •• ..
.•.. .
·''
·'' ,.
. ,.
·'
......
•'
••o
IIIC) . c;ltl()l
·'
I
.
·"
.•..•. .•
.•·.•. .·•
.,.
r r.
:>'
..·..
·'' ,
.......
[2.
16tnii/76
-
o
10
-
ss•JO'
to
..l,.,
..
TEMPERATURE
13 10
GRID
18/
·c
I
/76
STATION
6121
SB
61
62
N U MB E R
63
6'-i
6S
56
167
1121
I:
I
1-
(a)
2121
3121
'-i 121
[L
W
S 121
0
6121
sa
S9
6121
61
62
63
6'-i
6S
66
167
1121
(b)
2121
3121
'-1121
S:121
6121
sa
S9
6121
61
62
63
65:
21
~
66
l70
167
l1. ~ ..
~~-m- ­
1 121
~
-----~~2J.o-::.·
... _. __
2121
3 121
(c)
~.- ~
'-1121
S 121
6 121
S:B
S:9
6 121
63
61
6'-i
6S:
66
167
1 121
2 121
(d )
3121
'-1121
S 121
6121
Figure 43.
Vertical distr i bution of temperature (Bio Grid I) .
66
S A LI NITY
1310
~.
GR I D
I 8/:'Q' I J: /76
ST ATI O N
s:s
6 1
S:9
62
N U M13 ER
63
6Y
6S:
66
167
1 121
:E
I
(a)
2121
3121
1-
:1
w
0
S:121
6121
S:B
S:9
6121
61
62
63
6Y
66
6S:
•• ___ __ _ 3~
16 7
~0 ----.'::~~,·------~~~~
1121
-~,7~ --- - -~ - --
2121
--
..
~-00
~
--- - • . 36l~ --- -- - - - -- - --------- -- ·
3121
(b)
Y121
S:121
. ;:.
~
6121
6121
S:B
61
62
63
6Y
6S:
66
167
1121
2121
(c)
3121
Y121
S:121
6121
S:B
S:9
6121
61
62
63
6Y
3~~
66
6S:
3~ 2 ~
3:!tl0
167
•• ••
~~~~~
1121
2121
3121
Y121
S:121
6121
Figure 44 .
Vertical distribution of salinity (Bio Grid I).
67
(d)
SIGMA-T
!310
GRID
I 8/VTl/76
" THTION
s:e
S:9
512!
51
62
NUM13~_: R
6 '-i
63
6S:
16 7
66
=::>
Ill!
r:
::
'-
..._
Cl
(a)
2 121
3 121
Y121
S:121
6 121
S:B
S:9
6121
5 1
62
63
6 '-i
5S:
6 6
__ __ •• 23 ~ .
1 121
167
<=
23.0
---
~240~
2121
> 2 ~. 0
----
;;;; • • 24.!1 .
3121
(b)
--~
~
Y121
S:121
':~
6121
S: B
S:9
6 12!
6 1
62
6 '-i
63
6S:
6 6
1 67
=::>
1 121
(c)
2 121
..
3 121
Y121
S:121
612!
s: e
S:9
6121
61
62
6'-i
63
__
1121
23
6S:
~-
66
1 67
<=
> 22 ~
ZlO
~------
2121
-~,0~
3 121
,.. '! 1'
~.
-
.
.
>2~0
Y121
S: 121
..
6 121
Figure 45 .
Vertical distribution of sigma-t (Bio Grid I).
68
(d)
N l
TRRTE
S ID
<UMDLE/L)
GRID
I
1 8/::ll:II/76
STATION
S:B
S:9
60
61
52
NUMBER
63
5'-i
5S:
56
157
~
10
I:
I
30
1-
'-1 0
w
a
S::0
a.
(a)
20
60
S:B
S:9
60
6 1
62
63
10
6'-i
6S:
66
1 67
<=
<O-~
20
(b)
..
30
'-10
·=···
... ' -
·~..-;
-
S:121
>.
6121
S:B
S::9
60
6 1
62
63
6'-i
6S:
1121
66
167
~
<~
20
(c)
30
-/f'i:~·'::~·.:~.,·~ ··~-<~~~~·. . ::~~::...::
'-i121
S::0
6121
S:B
10
2121
S:9
6121
6 1
62
·;~;f::t:
- ...f,:L ~.
6:3
6'-i
6S:
66
16 7
<=
<05
"~.\~~ ~~-~~~" ••.. ~
(d)
3121
<·;'(··.::,·,:. ·~ ••
'-1121
S:0
60
Figure 46.
Vertical distribution of nitrate (Bio Grid I).
69
<UMOLE/L>
PHOSPHATE
1310
GRID
I
18/::!Ll:I/76
NUMB E R
STATION
s:a
S:9
6111
6 1
62
6'-i
63
6S:
16 7
66
II
>~
1 111
I:
:r
....
ll.
w
0
(a)
2111
3111
·•:'·
, .•• o "·"'~·
Lila
·'
s:r:a
5111
s:a
S:9
6111
61
63
62
6'-1
6S:
1111
.)0
2111
~10
-• .15
,,.
3111
•_:i-: ...
'-i111
.
>o~
· -~
(b)
~
'
s:r:a
6111
S:B
S::9
6111
61
62
6'-1
63
6S:
.JO
1111
66
167
>.o~
(c)
2111
> .1 0
3111
..
'-ita
.~.::r.i·:;:
·. -~:·...
'•
.
,.
S::121
-:
~
6121
S:B
S:9
6111
62
6 1
6'-1
63
6S:
167
66
~
> .05
1121
2121
•
:-
3121
.~
'-i121
-·· .\..'
-
.10~15
'
<.15
...
s:r:a
(d)
---- ·-·---.--- - -- -·~'-I ~
•
·"
-., . .:
,t..'
6121
Figure 47.
Vertical distribution of phosphate (Bio Grid I).
70
6 10
GRID
II
23/3ZII:/76
STATION
TEMPERAT U R E
NUMBE R
'C
YB
1 111
I:
2111
.,.
'·
(a)
3111
I
t-
Yl1l
w
S:111
0
6111
S I G MA-T
YB
S:121
'-i9
S: l
S:6
IS:B
(b)
S:l1l
611!
SALINITY
"A.
1 121
(c)
2121
3121
S:121
6121
Figure 48. Vertical distribution of temperature, sigma-t and
salinity (Bio Grid II).
71
N IT RATE
E!IIO
CUMOLE/L)
GRID
I:!
23/3Z:J:I/76
S TAT· I ON
'-18
~~
~ I
'-19
NUME!IER
S:6
S:7
I S:S
1 121
I:
2!21
:r
a.
3!21
....
'-1!21
w
S:121
0
(a}
6121
PHOSPHA TE
E510
GRID
CUMOLE/L)
II
:.23/3Z:J:I/7E>
ST A TION
'-19
N U MBER
s:s:
S: l
S: 6
S:7
IS:8
(b)
I
....
'-1 0
w
~121
a.
0
Figure 49. Vertical distribution of nitrate and phosphate
(Bio Grid I I).
72
TEMPERATURE 'I:
1'5 1 0
m
GR ID
S:-6/Yrr:::I /76
STATION
YB
Y9
5:11!
S:l
S:2
NUMBER
S:3
s:s:
S:Y
S:6
2JO
I
fQ.
w
Cl
IS:B
~
- - uo_ ,,-- ~- --- •• :~:2i'.c
\,
1 121
I:
S:7
I
-
211!
3121
•..
1
·~.~
•
' •'
¥
••
Yl<l
·::·
~· .. ~~l
\-!;:..~•_,t
· - · ...._:1
~'
'•'
,'----~ - - ~
lZD .... .... _...
22
'
~
(a)
2l0 ..... ' ... 24
il.~'
\
'
5:11!
.t;'
6111
YB
y g
S:121
S:l
S:2
S:3
s:s:
S:Y
S:6
S:7
IS:B
c:::::;>
1 11!
(b)
211!
3121
Yl2!
~
;·:.. . .-~;...
. .:., ,
·::·'~·
S:l1l
611l
YB
yg
S:l1l
S: l
S:2
S:3
S:Y
s:s:
S:6
S:7
I S:B
<=
111l
(c)
211l
311!
:_
-~
Yl1l
5:11!
611l
YB
Y9
5:11!
S:l
S:2
S:3
S:Y
s:s:
S:Ei
S:7
IS:B
c:::::;>
1 11!
(d)
211!
311!
Y0
5:11!
611l
Figure 50.
Vertical distribution of temperature (Bio Grid Ill') .
73
SALINITY
'A.
510
m
GRID
S - 6/::IZIII/76
S TRTION
Y8
Y9
N U MSER
ss:
S3
Sl
IS:B
'
l~
-
-
1121
I:
S:7
S6
.)~2:!.
~-= =~ _:-_-.-:-~-~-=3&-25:-~- -3~..~-0Q
2121
(a)
3121
Y8
Y9
S:l
S:2
S:3
s:s:
S:Y
S7
S:6
}~.2'
IS:B
I
' .. ~~0
,,
rra
- --::.;;.~"=- ::::=-;;:-···-·
20
- - ),7$-
(b)
lltl~
31<1
'-tla
_,,.
Y8
Y9
S:l
S:2
S:3
1121
s:s:
S:Y
S:6
S:7
IS:B
'
~;~~~
21<1
> ·"
3121
Yla
-
(c)
2:~
..- '1..' _ .-
s:ra
61<1
'-tB
Y9
S:l
S:2
S:3
S:Y
s:s:
S:6
S:7
IS:B
1 121
2121
!.
(d)
3121
Yra
S:121
6121
Figure 51.
Vertical distribution of salinity (Bio Grid III).
74
S I GHA-T
6 10
m
GR I D
S:-6 /3Z:I:TI /7 6
T AT ION
'-iB
'-i9
S: l2l
S: l
S: 2
S:3
NU MB ER
S: '-i
s:s:
>2.2
1111
I:
I
'-i111
w
S:l2l
0
S:7
I S:B
<=
:!1
" "--::::
-- -==-- ----------:=·:~
~no
3111
1-
a.
~~ ~-
2111
S: 6
(a)
-~
612l
'-iB
'-i9
5:111
S: l
S:2
S: 3
S:'-i
s: s:
S:6
S:7
IS:B
~
~:~~~
-=:::::::::::..~•• o- -
112l
212l
-
312l
;;.: t-. ~
> l,.O
(b)
l: ' D ......... ... .:-:-
'-il2l
S:l2l
6111
'-iB
'-i9
S: l
S:l2l
S:3
S:2
S:'-i
s: s:
S:6
S: 7
I S:B
<=
> U ~
112l
212l
3111
;1-.'(·"'
, ...
.
uo
'
'-i111
.:.:
.
(c)
-,
'-i'-~ -:~~ --.
-
S:111
·~;;
.::.;; ·c;•:.o;
6li!l
'-iB
'-i9
S: l
S:li!l
S::2
S:3
S:'-i
s:s:
S:6
S: 7
IS:B
~
lli!l
(d)
2li!l
3li!l
.\.-..
-.
', .
'-ili!l
S:li!l
6li!l
Figure 52.
Vertical distribution of sigma-t (Bio Grid I I I).
75
().J MOLE/L)
N ITRATE
S ID
m
GR ID
S:-6/YIIJ:/76
STATION
YB
I"'
I:
I
2121
Y0
!..J
0
S:121
a.
S:IZI
S:l
S:2
S:3
s:s:
S:Y
S:7
S:6
IS:B
<:=
<0~
"
'~?,_ . ~
.: ~J-;C~;:;~:~r
30
;-
Y9
NUMBER
-~ : •••: .. , •
i':,.'t\. •.·•.. ·-.• . .-.'!:
••
• ':!'.···
(a)
.
.·t.o· -· · o~--
.. ·/~~13· \
-
-»'"..-'t
.. ·
. ;'- •. ··- !,.:._~t·
6121
YB
Y9
S:lil
S:l
S:2
S:3
s:s:
S:Y
S:5
S:7
IS:B
c::::O>
<0.5
I "'
•
2121
3(3
-.
Y(a
~\
=':
_,os __ ____ :
(b)
. ~ /~~-~-. .............. ,
.·r.
,••7 ·_,... -:-.;.;..
...
.:
\'.
s:"'
6(3
YB
S:W!I
Y9
S:l
S:2
S:3
s:s:
S:Y
• t.4
1121
S:6
S:7
IS:B
<:=
<0.5
2121
(c)
310!!
Y121
S:121
60
YB
yg
S:lil
S:l
S:2
S:3
s:s:
S:Y
S:6
S:7
IS:B
c::::O>
<O~
10
?5·· 1.0::.:.::....
20
( \
30
l
Y121
•
·'
•
,--•e~
.z..o .....
'
.
..
...~--~ . . . ::.f.--,:~. -J '
·.
~
. . . . tl·l ... ~-
S:ICI
6121
Figure 53 .
Vertical distribution of nitrate (Bio Grid III).
76
(d)
PHOSPHATE
13 I 0
<UHOLE/L)
GR I D I I I
S-6/3ZIII/76
STAT
'"iB
s
Sill
'"i9
I
S2
I
ON
5:3
NUMBER
ss
S:'"i
I:
I
f-
0..
w
0
2111
~
. __, ,
----·;:o;·--------
.
.
.
3111
ISS
'~
<D!I
I 111
5:7
S:6
~ ---
(a)
~.10·---- -..~
I
'"ill!
Sill
6111
'"iB
s: I
Sill
'-19
S:2
S:3
s:s:
S:'"i
------ -:-- -.~----
211l
3111
I
S7
ISB
~
···~JO/
.......
.. ..
J()-
< .0~
I Ill
S:6
· ---o~
G ·"
--- - - - __ : -- .0~- ---~
(b)
.1 ~0
' ...,:'
"· ....
:..,.,
Ylll
Sill
611l
'"i8
'-19
s:
S:lll
I
S:2
S3
s:s:
S'"i
:
>.O~
_, .()!!'
I l1l
2111
? .., :
••
+;,..;
I sa
S:7
.10;.
10
3111
S:6
~
··---- ...
8
~<_QI
~
I
(c)
:
"~· ~-~ 'i,cik\t ~~: ::;:: ,,,;~~~~~"'""'r
·
Ylll
S:l1l
611l
'-18
'-19
S:lll
S:l
S:2
S:3
S:'-t
s:s:
1 11l
20
311l
S:6
S:7
I S:B
~
<O~
:--;--:--~-:---.:.·.-.. _-·----:-----r-.._--- o~i--- ---~'
.~.... ; .. ":t~~; . ~;·;~.~
~
'
'-tl1l
S:l1l
60
Figure 54 .
Vertical distribution of phosphate (Bio Grid III).
77
(d)
<1-!MDLE/L)
SILICATE
1310
m
GR I D
s: - 6 / r m / 7 6
ST ATI O N
YB
Y9
S:l<l
S:l
S:2
N U MBE R
S:Y
S:3
1.0/
--
Ita
I:
< •~
2t11
.,,,..
I
1-
0..
w
0
3t11
s:s:
- •.o
--
S7
S6
..,- ---
I S:B
<=
>I~
----~~~
.
..... ,
(a)
~ , :-
·'
/ /}z.
'•
Ytil
._.,.· . .·:
S:l<l
6t11
YB
Y9
S:ta
S:l
S:3
S:2
11<1
S:Y
S:7
IS:B
c::::>
~ZD~
<I,
31<1
S:6
> '·'
..... 1.0
21<1
s:s:
(b)
.
! • ··~.
Yl<l
~· !···; ~-~
S:ta
6t11
YB
11<1
Y9
S:Ja
S:l
S:3
S:2
S:Y
s:s:
S:6
S:7
IS:B
<=
_.,-~.~ --~,~·;
~--
2t11
,,
31<1
•
(c)
\-- --2...5
•
•
\'
•
•
\
, • 3.0 ,
I
2..0
~ :3~i;j~£r j.· ~~ .:. :~:-·~-
Yl2!
S:ta
......... ,
6t11
YB
Y9
S:l<!
S:l
S:2
S:3
S:Y
1.0/
/
'"
21a
<I~
s:s:
-..,.--
S:6
S:7
IS:B
c::::>
>1.5
(d)
312!
Yla
S:l2!
61a
Figure 55 .
Vertical distribution of silicate (Bio Grid I I I).
78
TEMPERATUR E
13 I 0
t::
:0Z:
GR I 0
16/::sz::::cr:r: / 7 6
STAT ION
29
<: 9
31<1
3 1
33
NUMBER
3 6
37
1 38
I til
I:
I
)--
tl
w
c
(a)
2(.3
31<1
Yl<l
~ til
6til
I til
(b)
5 1<!
Figure 56.
Vertical distribution of temperature (Bio Grid IV).
79
SALINITY
610
X.
GRID
I 6/V:
:QL
/76
STATION
28
29
3 121
31
32
33
NUMBER
3Y
3S:
36
37
13 8
1 121
(a)
2121
I
f-
0..
w
0
3121
Y121
S:121
6121
28
29
3121
3 1
32
33
3Y
3S:
36
3 7
1 38
1 121
(b)
2121
3 121
S:121
6121
Figure 57.
Vertical distribution of salinity (Bio Grid IV).
80
SIGMA-T
1310
IY.:
G R ID
16/::sz:::I:II/76
STI"'T I O N
:28
29
31i!!
31
3:2
>22 .~
I Ii!!
~
Yli:'l
!ili:'l
0
3!i
36
37
138
u.o
_,/
~--.
31i:'l
w
3'-t
·---- 2~. ~....
> 2~.5
--
:21i!!
I
33
NUMBER
(a)
61i:'l
28
29
3 1i!!
31
32
33
3'-t
3!i
36
37
138
lli:'l
(b)
21i!!
31i:'l
Yli:'l
!i121
61i:'l
Figure 58.
Vertical distribution of sigma-t (Bio Grid IV).
81
NITRATE
E5 10
CUH DLE / L )
GR I D
I3z::
16/::llm/76
5
2B
29
3 121
31
RTION
3:2
33
NUM B ER
34
36
37
138
1121
1:
I
:2121
(a)
3121
1-
o._
w
0
1 121
:2121
(b)
3121
'-l121
S:121
6121
Figure 59.
Vertical distribution of nitrate (Bio Grid IV).
82
PHOSPHATE
13 I D
CUMOLE/L)
I3Z:
GFI I 0
IEi/:'ll:III/76
S T ATION
28
31
29
33
NUMBER
3S:
36
37
138
1121
I:
I
1-
0..
w
0
(a)
2121
311l
411l
S:l1l
611l
28
29
311l
33
31
3S:
36
37
138
1 121
(b)
211l
3121
Figure 60.
Vertical distribution of phosphate (Bio Grid IV).
83
SILICATE
(~MOLE/L)
6 10
:CSZ::
GRID
I 6 /:lZ:IIT / 7 6
'-TRTIO N
28
29
3121
31
3 2
33
NUMBER
3'-1
3S
36
37
13 8
1121
(a)
2121
I
1--
0...
w
0
3121
'-II<!
S 121
6121
28
29
::3 121
31
33
3'-1
3S
36
::37
13 8
(b) -
Figure 61.
Vertical distribution of silicate (Bio Grid IV).
84
T-S Plot
A T-S plot of all temperature and salinity data is presented (Figure
62).
The shelf waters are characterized by the low salinity-high temperature
region of the plot.
Gulf Stream waters are apparent in the highest tempera-
ture region and generally along the right hand edge of the plot.
Slope
waters are less easily defined but they occur between the shelf and Gulf
Stream values (Stefansson, Atkinson and Bumpus, 1971).
Nitrate vs. Phosphate
A plot of nitrate vs. phosphate is made of the entire data set (Figure 63).
It reveals that most of the data are characterized by low values of these
parameters.
The lower values correspond to what are thought to be older
intrusions with regenerated or unused phosphate and the higher value with the
newer and cold intrusion events.
A line drawn through zero and the higher
nitrate concentrations would closely approximate the 16:1 ratio so characteristic of deepP.r off shelf waters.
Salinity vs. Silicate
This plot (Figure 64) is a composite of all silicate data collected
during the study.
It shows the high salinity region of the surface Gulf
Stream waters with silicate in the 1.0 to 3.0
~ mole/liter
range.
Also,
deeper Gulf Stream waters are represented by the higher silicate values
in this region. The shelf waters are represented by silicate values less
than 3.0 ~mole/liter in waters less than 36.00°/oo.
No significant near-
shore processes (runoff) appear to be evident from this plot.
However, it
should be noted that silicate data are not available for the first half
of the study period (Hydro Grids I and II) and this may account for such
an absence .
85
Salinity ( 0 /oo)
-·
-. ~
.:·
·- - · ---- --- +- ----- ---+ --- ----- - + -- -------+- ------ -- +----- -- --+- --- - -- - - ·~
+
+++
+++
OBS - 9
14 Ju ly
+
18 August 1976
+++++-+-+++++++++
+++++++++++++++++++ T
++++++++++++++++
+++++++++++++++
+
++++++++++++
+
++++++++++
25
+
+
+++++++++
++++++-+
+
+++++
+++++
+++++++++
+++++
+
+
+++++
+
20
u
0
+
+
+++ +
+ +
+
+ + -+-++
+ ++++
+ +
++++
++ +
+++
+
+
+
++
+
<1)
s..
::::J
+-'
ro
s..
15
<1)
c...
E
<1)
1+
+
10
+
+
5
+
+
+
+---------+-- ------- +------- -- +---- -----+-------~-·---------+----- - ---++
Figure 62.
T-S plot (OBIS V).
86
IS.li:'l
0::
w
I-
+
_J
.........
w
_J
10.0
D
z:
::J...
+
+
+
w
Ia:
0::
I-
z
S.li:'l
••
+ +
+
\
•
• ++
++
+ ++
I
+
+
lJ1
PHOSPHATE
Figure 63.
Plot of nitrate Vs. phosphate.
87
,UMOLE/LITER
37
>-
1-
..
. I ... ·' ,.
• • I ... •
z
.J
II
:
..
I
I
...
!.
...
36
III
I
•
..
•: •
I
1 •
..
:
3S:
.
., ·.·
.....
Ul
N
SlliCATE
Figure 64.
Plot of salinity Vs. silicate.
88
m
lSI
SUMMARY AND CONCLUSIONS
The data collected during OBIS V indicate the occurrence of at least
four different intrusion events over the course of the study period.
It
seems probable that there were more than four such events and if so this
should show up in the current meter data.
Three intrusion cores were
observed isolated on the shelf and three cold tongues were observed
moving onto the shelf during the three hydro grids and the one XBT grid.
In addition, there may be some correlation between some of these intrusion tongues and the isolated cores.
The passing of Hurricane Belle on 9 August may be responsible for
the appearance of the cold water on the shelf on 14-16 August during
Hydro Grid IV.
This may also explain an intrusion event commencing in
the northeastern offshore sector of Onslow Bay in advance of the southern
sector where all previous intrusions had been observed to beg i n.
hurricane
1
S
The
closest passage of the Bay came in this same northeastern
sector.
Low temperature, high salinity and high sigma-t values correlate to
the intrusion phenomenon.
In addition, relatively high nitrate and
phosphate concentrations correspond to what appear to be the youngest
intrusion events.
In the older intrusion cores often times significant
phosphate concentrations persist in spite of negligible nitrate concentrations.
This is probably due to unused or regenerated phosphate.
Silicate appears to be a more conservative tracer.
However, it has the
added complication that higher values are characteristic of both hi gh
salinity intrusion waters and lower salinity nearshore waters.
Analysis
of all of these data relative to the current meter data should provide a
rather complete description of the Onslow Bay system during the observational period.
89
LIST OF REFERENCES
Atkinson, L. P. , J. J. Singer and L. J. Pietrafesa.
intrusion study:
1976a.
Onslow Bay
Hydrographic observations during current meter servicing
cruises in August, October and December 1975 (OBIS I, III and IV).
Georgia Marine Science Center, Technical Report 76-4.
Atkinson, L. P., J. J . Singer, W. M. Dunstan and L. J. Pietrafesa .
Hydrography of Onslow Bay, North Carolina:
1976b.
September 1975 (OBIS II) .
Georgia Marine Science Center, Technical Report 76-2.
Br adshaw , A. and K. E. Schleicher.
1965.
el ectrical conductance of sea water.
The effect of pressure on the
Deep-Sea Res., 12 : 151-162.
Gardner, W. S. , D. S. Wynne and W. M. Dunstan .
1976 .
for the manual analysis of nitrate in sea water.
Jaeger, J. E.
1973.
Simplified procedure
Mar. Chern . , 4: 393- 396 .
The determination of salinity from conductivity,
temperature, and pressure measurements.
Proceedings Second S/T/0
Conference and Workshop, January 24- 26, 1973, 29-43 .
Knowles, C. E.
1973.
tion of salinity .
CTD sensors, specific conductance and the determinaUniversity of North Carolina Sea Grant Program, Sea
Grant Publication UNC-SG-73-16.
Mullin, J. B. and J. P. Riley.
1955.
The colorimetric determination of
s i li cate with special reference to sea and natural wate rs.
Anal . Chim.
Acta 12:162- 176 .
Murphy, J . and J. P. Riley.
1962.
Modified single solution method for the
determination of phosphate in natural waters.
Anal. Chim. Acta 27:31-
36 .
National Institute of Oceanography at Great Britain and UNESCO.
1966.
International Oceanographic Tables, Wormley, Godalming, Surrey, England.
90
National Institute of Oceanography of Great Britain and UNESCO.
1973.
International Oceanographic Tables, Vol. 2, Wormley, Godalming,
Surrey, England.
Stefansson, U., L. P. Atkinson and D. F. Bumpus.
1971.
Hydrographic
properties and circulation of the North Carolina shelf and slope
waters.
Deep-Sea Res., 18, 383-420.
Strickland, J. D. H. and T. R. Parsons.
analysis.
1965.
A manual of sea water
Fisheries Res. Board of Canada, Bull. No . 125 (2nd ed.),
Ottawa.
U. S. Department of Commerce, NOAA, EDS.
1976.
Local climatological
data, monthly summary, Cape Hatteras, North Carolina, July and
August 1976.
National Climatic Center, Asheville, N. C.
91
APPENDIX
SUMMARY OF EVENTS:
OBIS V
92
SUMMARY OF EVENTS: (OBIS V)
Cruise OB5 - OB9 (in EDT)
0923 - 8 July
to
Departed Skidaway Institute, Savannah, GA (Atkinson
Baker).
Arrived at Duke University Marine Lab (DUML),
1445 - 9 July
the land base for OBIS V.
0845 - 9 July
Tested CTD while enroute to DUML (System inoperative repairs made).
1335 - 10 July
to
1737 - 10 July
Departed DUML (Atkinson, Singer, Chandler, Hofmann,
Kelly, Porter, White, Baker, Paffenhofer, Diebel, Sands,
Mcintyre, and Hosford).
The purpose of this day cruise
was to test the repaired CTD and to allow all personnel
to become familiar with planned procedures.
Carroll
Baker still had to work on the electronics.
The Rosette
bottles were not tripping.
We also later discovered that
the magnetic tape had not received the data signals (only
headers and blank data sets were recorded).
It took a
week to discover this because the tapes were sent to the
computer center at UGA, and then from our terminal a
programming sequence was used to extract the data from
the tapes.
Fortunately we had backup XYY' trace for all
data sets.
11 July
At the DUML dock Carroll Baker worked on the CTD.
The
SCR in the Rosette was replaced, but still the bottles
were not tripping.
The problem was found to be cold
solders in the Rosette deck unit.
93
1500 - 12 July
to
1820 - 12 July
Departed DUML (Atkinson, Singer, Kelly, Porter,
White, Baker, Paffenhofer, Sands, Mcintyre, and
Hosford) for HYDRO GRID I.
We were delayed from an early
departure by an out of town trip for spare CTD electronics,
a trip to the hardware store by the crew, and having to
take the cook to the bus station after firing him.
When
we did get off, six foot seas at the sea buoy and severe
storm warnings turned us back.
However, we did make one
CTD cast and it was handled well from the A- frame off the
stern .
1915 - 13 July
to
1940 - 15 July
HYDRO GRID I .
Departed DUML with the same scientific
crew as for 12 July.
At 0200 on 14 July we started
firing XBTs and hanging bottles because of a short in the
CTD cable.
Both the Sandpiper depth finder and the
Raytheon fathometer were inoperable, so the last available
unit (Simrad) gave depths in fathoms with minimal
accuracy.
At 1007, 14 July we resumed CTD casts after
replacing the CTD 9-pin conductor and fixing the short.
At 0300 15 July, the CTD shorted out again.
It appeared
that the cable had been caught in the sheave of the
winch.
We cut off 10 feet of sea cable, re-scotchcasted
it, and had the CTD operational at 0840, 15 July.
meantime, we fired XBTs and hung bottles.
In the
When CTD
operations resumed, the XYY' plotter could not be
calibrated with the 10V source so we had to use the
built-in settings of .25V/cm for depth and .5V/cm for
94
conductivity and temperature .
Finally, as noted
earlier, data was not recorded on magnetic tape during
this cruise because of a problem with the Digital Data
Logger (DOL) so data analysis relied on the XYY' traces.
During the cruise we were unaware of this problem.
0947 - 17 July
to
0335 - 18 July
BIO GRID I .
Departed DUML (Atkinson, Baker, Chandler,
Porter, Paffenhofer, Diebel, Sands, Mcintyre, and
Hosford).
An intrusion seen in the south end of Onslow
Bay during HYDRO GRID I brought us back there for a
biological and hydrographic transect.
an XBT was fired at Station 62.
At 1846, 17 July
The results were
unexciting, so we started the transect at Station 63,
going offshore and including stations 64 through 167.
We made four passes; the CTD operated perfectly!
In
heavy seas we used a lead weight to dampen the swinging
Rosette .
It was also necessary to dampen the slack in
the sea cable as the boat rolled during a cast.
The
same lack of data transfer to the magnetic tape occurred
as in HYDRO GRID I.
0825 - 21 July
to
0145 - 24 July
HYDRO/BIO II.
Departed DUML (Singer, Chandler, White,
Kelly, Paffenhofer, Diebel, Sands, Mcintyre, and Hosford) .
We did a hydrogrid that covered the entire bay.
It
directed us to stations 49 - 157 for the subsequent
biogrid along which a single transect was made.
worked well.
The CTD
Personnel were instructed to zero and
calibrate (full scale) the XYY' plotter more frequently
95
because data had not been going on the magnetic tapes.
The XYY' plotter's autogrip did not hold very well for
most of the cruise .
0810 - 28 July
to
1723 - 28 July
Departed DUML (Singer, Chandler, Hofmann, Porter,
Paffenhofer, Diebel, Sands, Dunstan, and Hosford) for
HYDR0/810 III.
After the first two hydrogrid stations,
we proceeded to a current meter mooring to attach a buoy
for NCSU.
After completing the task, we returned to port
because of poor radio communications.
Carroll Baker had
repaired the DDL so that data was being recorded; however, the headers did not have file gaps in front of
them, and the depth signal was now folding at one quarter
of what should have been full scale .
0800 - 30 July
to
0730 - 31 July
Departed DUML (Chandler, Hofmann, Porter, White, Paffenhofer,
Diebel, Sands, Dunstan, and Hosford).
This time we com-
pleted one track of HYDRO GRID III, but the seas became
too rough (5 to 6 feet) to safely use the CTD.
Conse-
quently, XBTs were used for the next three stations
before we retreated to port . Spiking occurred on the
XYY' traces, possibly due to a loose connector to the
CTD . We also had ship problems.
generators broke down.
One of the two
When this happened, the power
was cut off and then returned to the DDL .
Subsequently,
a new tape had to be loaded . Also radio communications
were poor.
Data went on magnetic tapes in the same way
as the last cruise.
96
1114 - 2 August
to
2345 - 2 August
Departed DUM L {Chandler, Hofmann, Porter, White,
Paffenhofer, Diebel, Sands, Hosford, Kelly and
Waslenchuk).
An XBT grid was planned instead of the
usual hydrogrid in order to make up for lost time.
intrusion could be located by such a grid.
An
After one
transect was completed, the sewage holding tanks backed
up and flooded the "stateroom", so we returned to port.
0811 - 4 August
to
1750 - 6 August
XBT/BIO III .
Departed DUML (Atkinson, Singer, Hofmann,
Kelly, Paffenhofer, Diebel, Sands, Mcintyre, and Hosford).
An XBT grid was run in place of a hydrogrid; then a
biogrid was run at stations 53- 57.
It was observed
that radio communication interferes with the XYY 1 plotter.
Prior to the last station the BLUE FIN
The Coast Guard Cutter POINT
~~RTIN
1
S
v-drive broke.
and later a smaller
CG vessel, towed the BLUE FIN to Southport, North
Carolina.
Data went on the magnetic tapes in the same
way as the last cruise.
August 9
A hurricane warnfng and shaft repairs kept us in port.
0800 - 14 August
HYDRO/BIO IV.
to
1815 - 16 August
Departed Southport (Atkinson, Singer,
Porter, White, Paffenhofer, Diebel, Sands and Hosford).
After completing five hydrogrid stations the analog fold
on the depth scale was off.
of 150 m.
It cycled at 37 . 5 m instead
The 10V calibrating source became inoperable,
so built-in calibrated spans (.25V/cm for depth and .5V
for conductivity and temperature) had to be used.
The
biogrid following the hydrogrid consisted of two transects
over an old intrusion (stations 32- 35).
97
It was noted
that entering a manual file gap before a new header
permitted the recording of data and headers in separated
files as desired.
Consequently the tape quality was
improved for the data set but still exhibited folding
in the depth record.
0816 - 18 August
to
0043 - 19 August
HYDRO/BIO V.
Departed DUML (Singer, Chandler, White,
Kelly, Paffenhofer, Diebel, Sands, Hosford and Gonsoulin).
We planned to use XBTs to locate a possible biogrid area,
but the XBT was inoperable from the start (bad tube) .
Consequently CTD casts were made until rough seas
terminated all work at 1646, 18 August, ending the
OBIS work.
1
76
The magnetic tapes recorded data well, except
for the folds in depth which were later corrected with
software modifications.
98