BIODEEP (EVK3-2000-00042) Second year Scientific Report
(April 1st 2002 – March 31st 2003)
Annex to WP2
Contribution from partner 10 - University of Utrecht
Introduction
During the Urania 2002 cruise (BiodeepIII), a mooring of 3 sediment traps from the Bannock basin
was successfully recovered (Tab. 1). Also from the Urania basin the sediment trap mooring was
recovered, but it appeared that none of the traps had functioned properly, all for different reasons.
This is the first time in the long history of this type of traps that non-functioning is observed.
Sediment trap samples from the lowest trap at 3500 m (within anoxic brine) and from the middle
trap at 2500 m (in oxic seawater) were analysed for elemental composition. Additionally, C and N
contents were measured for the anoxic samples of the the Bannock basin. From these data, average
yearly fluxes of different elements could be calculated for each the oxic and the anoxic trap.
Tab. 1: Depths of sediment traps deployed in Bannock
September 1999- May 2000.
Bannock basin
Urania basin
Station BD03
Depth (m) Station PS 027
ST1
1500
ST1
ST2
2500
ST2
ST3
3500
ST3
ST4
Basin during May 2001-June 2002 and in Urania basin during
Depth (m)
460
1500
2800
3500
In order to compare the data from Bannock basin with Urania basin, an earlier sample set (from a
sediment trap mooring 1999-2000) from Urania basin was investigated for elemental analysis as
well. Again, samples from the lowest trap (3500 m, within anoxic brine) and one upper trap (2800
m) were analysed for elemental composition.
Also, suspended matter samples from the 4 different basins (L´Atalante, Urania, Bannock and
Discovery basins) were investigated. However, the analysis proved to be very difficult because of a)
the very little amount of material on the filters and b) the high salt content on the filters. For this
reasons, it is agreed with the partners that the sampling of suspended matter will be done again
during the June/July Biodeep cruise. It is essential that the filters are washed after filtration on
board ship to remove the salt load in order to have reliable results during later analysis.
However, a salt correction was applied for the data available on suspended matter from unwashed
filters (see below).
Methodology:
For total elemental analysis the sediment trap and suspended matter cellulose acetate filters
including the sample were dried at 40C and weighed. Subsequently, the filters were sealed in a
Teflon bomb with 2.5 ml HF and 2.5 ml HClO4/HNO3 and dissolved by oven heating at 90C for 5
hours. The solutions were evaporated to dryness and redissolved in 7.5 ml 1 M HNO 3, and analysed
with an inductively coupled plasma atomic emission spectrometer (ICP/AES; Perkin Elmer Optima
3000). Filter blanks as well as a calibration series of an in-house standard sediment (MM91) were
simultaneously processed and used to calculate separate calibration lines for each element. Before
evaporation of HF during total dissolution of the sample, a subsample was taken out and was
analysed photospectrometically for Si according to the method described in Rutten et al. (2000).
C/N analysis was done with an Elemental Analyser (Fisons NA 1500).
BIODEEP (EVK3-2000-00042) Second year Scientific Report
(April 1st 2002 – March 31st 2003)
Results and Discussion
Sediment traps
One important result is the striking difference of total mass accumulation in the different traps, both
in the different basins and in the oxic vs. anoxic traps at the same site. The average fluxes for the
analysed elements from September to May for the respective sampling years are plotted in Fig. 1.
In the Bannock basin, the anoxic trap accumulated about 30x more material than the oxic one (4
mg*m-2*d-1), in the Urania basin, the value is about 100x higher in the anoxic trap than the oxic trap
(15 mg*m-2*d-1).
-2
mg*m *d
-1
2000
1000
0
BB oxic
BB anoxic
UB oxic
UB anoxic
Fig. 1: Average (sept.-may) total mass fluxes to the different sediment traps.
From this data it is apparent that the fluxes in the anoxic basins are highly exaggerated due to
resuspension of material within the basins due to slumping of material from the flanks of the basins
and, additionally in the Urania basin, resuspension due to gas expulsions. The oxic traps which are
deployed above the brine basin interface instead show reliable data on what is reaching the anoxic
basins from above. Total mass fluxes differ by a factor of about 4 between Urania and Bannock
basin. This difference is not caused completely by a different amount of biogenic (opal, carbonate)
or by enhanced dust deposition in the basins, because extra-Si and carbonate fluxes (calculated from
Ca fluxes) vary by a factor of 1.25 and 3 between the basins (Tab. 2). The enhanced input of
material is thus caused additionally by higher terrigenous input into the Urania basin area.
Looking at the concentrations of extra Si (Extra Si is the excess silicon above the silicon
concentration of the clay (terrigenous) matrix in the sample) it appears that it is much higher in the
high-flux samples than in the other samples. This additional input of Si may originate from two
sources: biogenic Si due to a plankton bloom or quartz input due to storms from the Sahara.
Enhanced Si-input is observed in summer and that is the time of severe wind-driven Saharan dust
input in the whole Mediterranean Sea (Güllü et al., 1996). This indicates that the dust input, which
also drags down biogenic and other particles through the water column, is the dominating factor for
mass flux varibilities in the oxic traps.
BIODEEP (EVK3-2000-00042) Second year Scientific Report
(April 1st 2002 – March 31st 2003)
Tab. 2: Average (sept.-may) elemental fluxes to different sediment traps. Extra Si is the excess silicon above the silicon
of the clay (terrigenous) matrix in the sample and represents mainly eolian input of quartz from the saharan dust. nd: no
data. Units: Ca, Fe, S, Si and extra Si: mg*m-2*d-1, all other: µg*m-2*d-1.
Ba
Bannock basin
oxic
anoxic
Urania basin
oxic
anoxic
Ca
Fe
Mn
S
Si
extra Si
2.8
51.5
1.0
18.9
0.3
3.2
3.8
73.0
nd
1.0
0.8
24.7
0.4
nd
9.0
84.4
3.1
134.8
0.5
36.6
23.9
1000.9
nd
353.7
1.2
154.4
0.5
nd
Cd
Bannock basin
oxic
anoxic
Urania basin
oxic
anoxic
Co
Cu
Ni
Pb
Zn
0.01
nd
0.2
2.0
0.5
9.2
0.3
4.6
0.26
nd
1.7
nd
0.02
nd
0.8
29.4
2.5
62.5
1.0
228.2
1.39
nd
3.0
nd
Data on carbonate concentrations in the Bannock basin anoxic trap (BD003 ST3) are reported in
Tab. 3. These data are calculated from the difference of total C and organic C measurements and
give more accurate values of carbonate than recalculation from Ca data because the usual
assumption that the Ca in carbonate-rich sediments almost entirely is related to CaCO3 is not valid
in the anoxic basins due to the formation of gypsum. The average C/N ratio of the material is 19.3
and is considerably higher than the Redfield ratio of about 6.6.
Tab. 3. Total concentrations and fluxes (averages from May 01-June 02) of Bannock basin anoxic trap (BD003 ST3).
average
CaCO3
(wt%)
CaCO3
(mg*m-2*d-1)
C org
(wt%)
C org
(mg*m-2*d-1)
N
(wt%)
N flux
(mg*m-2*d-1)
33.03
84.81
2.21
4.86
0.11
0.3
The determination of biogenic (CaCO3, Corg) components and extra Si (mainly dust with possible
contribution of opal) of the sediment from the anoxic Bannock basin trap allows to describe the
total composition of the material as 56.1% terrigenous, 33% Carbonate, 8.7% extra Si and 2.2%
Corg (Fig. 2). From the carbonate determination the amount of excess Ca may be estimated which
is not incorporated into carbonate, but may be present mainly as Gypsum. This amounts to about
10% which is included in the terrigenous fraction.
56.1
33
2.2
CaCO3
extra Si
Corg
Terr.
8.7
Fig. 2: Average total composition of anoxic Bannock basin sediment trap material.
BIODEEP (EVK3-2000-00042) Second year Scientific Report
(April 1st 2002 – March 31st 2003)
In order to get further insights into variations of elemental fluxes into the Bannock basin which
might be related to seasonal changes, flux data are plotted according to the four seasons. From these
plots it becomes obvious that the major part of about 50% of elements and carbonate is transported
in the summer to the anoxic Bannock basin trap. The remaining fraction is transported preferentially
in spring, followed by less input during autumn and minimum input in winter times. The high
average fluxes in summer are due to an exceptional high flux in the July-August sample. This high
flux might be caused by a major resuspension event within the basin, because such high flux is not
recorded in the oxic trap above the basin.
CaCO3 flux
Si flux
spring
20%
summer
49%
winter
13%
autumn
18%
spring
22%
winter
11%
autumn
14%
S flux
Mn flux
spring
20%
winter
12%
autumn
16%
summer
53%
summer
52%
spring
17%
winter
14%
summer
50%
autumn
19%
Fig. 3: Average fluxes for carbonate, total Si, S and Mn for Bannock basin anoxic trap recalculated on a seasonal basis.
Suspended matter
Suspended matter analysis is important in order to know how much material is suspension and also
of what composition this material is. However, during the analysis of the filters containing the
suspended matter, severe problems were encountered. Apart from the very little amount of sample
on the filter is was a major problem that the filters were not washed after filtration in order to
remove the remaining brine. So the data produced are highly influenced by salt contents which
results in high errors in the analysis. A salt correction was applied to the data assuming all Na in
Bannock, Urania and L´Atalante basins samples is present as NaCl and all Mg in Discovery basin
samples is present as MgCl2. The results show that the highest amount of suspended matter is
encountered in the Discovery basin, whereas Bannock and L´Atalante basin brines show similar
suspended matter loads. Urania brine has the least amount of suspended matter (Fig. 4).
Although the chemical analysis shows high errors due to the salt influence, the overall trends for the
different brines are considered to be meaningful. The concentrations of e.g. K show similar values
for all the brines except for Discovery basin brine. The same trend is observed for S. Contrasting
this, Ca concentrations are high in Urania basin brine, followed by approx half the concentration in
Bannock brine. L´Atalante and Discovery brines are much more depleted in Ca than the others.
These data indicate that there are major differences in the brine suspended matter compositions.
These differences may have an important impact on microbiological activity and therefore should
be analysed more precisely with carefully washed samples.
BIODEEP (EVK3-2000-00042) Second year Scientific Report
(April 1st 2002 – March 31st 2003)
30
total mass (mg/l)
25
20
15
10
5
0
AB
UB
DB
BB
50000
12000
40000
10000
Ca (ppm)
K (ppm)
Fig.4: Suspended matter average total mass concentrations.
30000
20000
8000
6000
4000
10000
2000
bdl
0
0
AB
UB
DB
BB
AB
UB
DB
BB
Fig.4: K and Ca average concentrations of suspended matter from the different brines. bdl: below detection limit.
References:
Rutten, G. J. de Lange, P. Ziveri, J. Thomson, P. J. M. van Santvoort, S. Colley and C. Corselli
(2000): Recent terrestrial and carbonate fluxes in the pelagic eastern Mediterranean; a comparison
between sediment trap and surface sediment. Palaeogeography, Palaeoclimatology, Palaeoecology,
158, 197-213
Güllü G.H., Ölmez I. & Tuncel G. (1996) Chemical concentrations and elements size distributions
of aerosols in the eastern Mediterranean during strong dust storms. In: Guerzoni S. & Chester R.
(eds.) The impact of desert dust across the Mediterranean. Environm. Sci. Technol. Libr. 11, 339347. Kluwer Academic Publishers, Dordrecht.