SANTA BARBARA BASIN DIATOM RECORD
SUGGESTS COINCIDENCE OF COOLER SST WITH
WIDESPREAD OCCURENCE OF DROUGHT IN THE
WEST DURING THE PAST 2,200 YEARS
John Barron, U.S. Geological Survey, Menlo Park, CA
Acknowledgements:
David Field, MBARI
Arndt Schimmelmann, Indiana Univ.
Drought associated with La Niña
The Dust Bowl
The 1950s
This pattern also
typical of the extended
20thC droughts …
-Widespread drought in
northern and southern
mid-latitudes coincides
w/ cold equatorial
Pacific - La Niña
The most
recent
Slide from R. Seager
Epic droughts
in the West -Tree Ring Studies
LONG-TERM CHANGES IN DROUGHT AREA IN THE 'WEST'
% DROUGHT AREA
100
THE CENTRAL DATES OF THE
SIGNIFICANT (p<0.05) EPOCHS
ARE INDICATED WITH ARROWS
1150 1253
936 1034
80
60
Cook et al.,
Science
(2004)
40
DRIER
20
0
WETTER
800
1321
1613
1829
1915
900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
YEAR
The recent drought pales next to the epic AD
900 - 1300 drought (Medieval Warm Period).
•Why did such an unusually long drought occur?
•Extended La Niña-like conditons?
Cobb et al., 2003 NATURE
La Niña
El Niño
Corals -equatorial Pacific
MWP droughts
Tree ring index -So. California vs. Alberta
Alkenones & the diatom F. doliolus show similar trends
Alkenone SST (oC)
14
late Holocene
13
early Holocene YD Bø.-Al.
middle Holocene
12
modern
11
10
9
8
7
Percent Diatom
30
Fragilariopsis doliolus -gyre
20
10
0
N. seminae -subarctic
0
1
2
3
4
5
6
7
8
9
Calendar ka
10 11 12 13 14 15 16
Core Top Diatom Transect at 41-42°N
60
18
October SST
50
16
T. nitzschioides
(offshore productive)
40
15
30
14
20
13
12
133
132
Open ocean
Fragilariopsis doliolus
(gyre)
131
130
129
128
Longitude
10
127
126
125
0
124
Shore
Percent
SST (°C)
17
High Resolution study of Santa Barbara Basin
• Cooperative study with David Field (MBARI) planktonic forams, oxygen isotopes, box cores
Study of ODP 893A at 5 cm intervals (2,200 yr B.P. to
~1880 A.D.)
--- Varve chronology from Arndt Schimmelmann
--- Diatoms (Barron), silicoflagellates (D. Bukry)
High diatom
flux Mar.- May
El Niño
-reduced
diatom flux
-increased lith.
flux, warm
diatoms, non
planktonic
diatoms
Increased density (lithogenic content) does not seem
to coincide with reduced drought until post 1600 A.D.
Increased non-planktonic diatoms (El Niño?) shows
some correspondence with low drought prior to 1600 A.D.
Warm water diatoms?
Offshore productive
Warm,
gyre
Planktonic foraminifer G. bulloides
Low Fd/Tn ratios coincide w/ cooler proxy SSTs
from planktonic foraminifer isotopes
Low ice cap accumulation in Peru (La Niña)
coincides with low Fd/Tn ratios
Comparison with Recent Record from 2001 Box
Core 2901 - David Field, MBARI
•
•
•
•
Slab samples representing 2 varve years
1940 to 2001
Preliminary diatom counts 1950-2000
Compare with instrumental SST record
El Niño
La Niña
Problems to Resolve
•
•
•
•
•
Terrigenous dilution, preservation bias
Different age resolution (2 yr in box core vs. 3-8 yr., spaced
every 12-43 yr in ODP 893A)
Representation of blooms in box core (fecal pellets with
Rhizosolenia spp.)
Thalassionema spp. (offshore productivity) ~20% in box core,
~30% in ODP 893A)
Fragilariopsis doliolus (gyre) ~15% in box core, ~6% in ODP
893A) -Secular warming?
Surprise