RESPONSE OF DIATOM AND SILICOFLAGELLATE ASSEMBLAGES TO CLIMATE CHANGE IN THE SANTA BARBARA BASIN
DURING THE PAST 178 YEARS and THE RISE OF THE TOXIC DIATOM PSEUDO-NITZSCHIA AUSTRALIS
science for a changing world
John A. Barron (1), David Bukry (1), and David B. Field (2)
(1) Volcano Science Center MS 910, U.S. Geological Survey, Menlo Park, CA 94025 (jbarron@usgs.gov, dbukry@usgs.gov);
(2) Department of Natural Sciences, Hawaii Pacific University, Kaneohe, HW 96744 (dfield@hpu.edu)
-2.0
-1.5
-3.0
1840
+6
PC2 - cold
-4
-6
1840
Summer-Fall
Spring
50°N
Winter
CC
30°
CC
SCC
CC
1883
+1.0
0
-1.0
-1.0
-2.0
1860
1880
1900
1920
Year
1940
1960
B.
Location map of the Santa Barbara Basin showing the box core
studied, bathymetry in meters, and general surface circulation.
B - Seasonal circulation of the California Current (CC) modified
from P.T. Strub, written comm., 2007; SBB = Santa Barbara Basin;
WWD = West Wind Drift; SCC = Southern California
Countercurrent; PtC = Pt. Conception; DC = Davidson Current.
10 µm
Identifed by Sibel Bargu, Lousisana State University
Occurrence of Pseudo-nitzschia in SB Sediment Samples
x
80
70
P. australis
60
2000
-3.0
?
Warm water diatoms display a moderately
good correlation with Anomaly SST
(R2 value of 0.42759)
Other warm
Nitzschia interupteseriata
1840
1860
1880
1900
1920
Year
1940
1960
1980
40
1.0
Percent
30
Cold water diatoms and Thalassionema nitzschioides,
which is indicate of a shallow thermocline, decline after
1950, in agreement with the planktonic foraminiferal
interpretations of Field et al. (2006a).
Thalassionema spp.
10
1860
1880
1900
1920
Year
1940
Bloom Diatoms
1960
1980
Pseudo-nitzschia multiseries
Rhizosolenia
40
20
1860
1880
1900
1920
1940
1960
1980
2000
Year
3000
1000
1840
1860
+1.0
0
-1.0
-0.5
-1.0
P. multiseries
20
0.5
10
0
1975
1980
1985
Two yr samples
1990
1995
-1.5
100
1840
1860
1880
1900
1920
Year
1940
1960
2000
2005
0
2010
Core top
Unlike diatoms, silicoflagellate assemblages are not significantly different between the
plankton and those preserved in the sediments. However, they are significantly less
abundant than diatoms in Santa Brabara Basin sediment assemblages.
-2.0
?
1980
2000
-3.0
Warm water silicoflagellates
1880
1900
1920
Year
1940
Dictyocha perlaevis
60
Warm water silicoflagellates display a moderately good correlation with Anomaly SST
(R2 value of 0.44799)
1862
40
20
Dictyocha stapedia
1840
1860
1880
1900
1920
Year
1940
1960
1980
2000
100
80
Shallow vs. Deep Thermocline silicoflagellates
Distephanus speculum s.l.
Dictyocha aculeata
60
40
20
0
References
1840
1860
1880
1900
toxic diatom
60
Prior to 1999, bloom-forming diatoms other
than Chaetoceros spores consist of
Rhizosolenia species (mostly R. hebetata or
R. setigera). These have a moderate warm
water preference. Beginning in 1999
Pseudo-nitzschia multiseries and P.
australis (a neurotoxon-secreting diatom)
increase markedly in the sediments.
Distephanus speculum is indicative of upwelling and/or a shallow thermocline.Dictyocha
aculeata is more characteristic of a deeper thermocline.The changing relative abundances of
these two silicoflagellates suggest a deepening of the thermocline in the Santa Barbara Basin
after about 1940, similar to what is suggested by diatoms and planktonic foraminifers.
Deeper thermocline
1920
Year
1940
1960
1980
2000
Distephanus speculum minutus
40
20
Octactis
Distephanus octangulatus
0
1840
1860
1880
1900
1920
Year
1940
1960
1980
2000
Distephanus speculum minutus, the cooler-water form, dominates the total D. speculum s.l. but virtually
disappears between 1940 and 1999. Octactis, a tropical upwelling form, fluctuates at low percentages.
Distephanus octangulatus, a subarctic form, is restricted to the early 1860’s and early 1920’s.
Chaetoceros spores
2000
0
+2.0
0
2000
Pseudo-nitzschia australis
60
1840
+3.0
x
2000
Deeper thermocline
Cold water taxa
1840
PDO (January)
SST record from the updated Kaplan reconstruction
for the 5°X 5°- grid centered at 122.5°W, 32.5°N
+0.5
Fragilariopsis doliola
20
0
+1.0
0
30
1862 flood?
+1.5
1.5
50
Year
Silicoflagellates
2.0
80
Warm water diatoms
20
80
Macoma layer 1841
1980
30
0
Percent of Diatom
Assemblage*
110°W
+2.0
The diatom assemblage represents a composite of
two years’ depostion. The great majority of diatom
taxa that dominate in the surface plankton are not
preserved in the sediments. This is especially true
of Chaetoceros, a bloom-forming diatom,
associated with spring upwelling events.
Chaetoceros is mostly only represented by
resting spores in the sediment. Thus, diatom
relative abundances are tablulated as percent of
the Chaetoceros spore-free assemblage*.
10
# per 0.80 mL
120°
+3.0
-0.5
1872
130°
PDO (January)
50
1896 (grey layer)
1892
2000
0
1919
DC
1980
+0.5
0
20°
1960
Anomaly SST (°C)
+1.0
Percent of Diatom
Assemblage*
PtC
1940
SST record from the updated Kaplan reconstruction
for the 5°X 5°- grid centered at 122.5°W, 32.5°N
40
SBB
1920
Year
Anomaly SST (°C)
+1.5
WWD
CC
1900
Diatoms
WWD
40° WWD
1880
Percent of Silicoflagellate
Assemblage
A.
1937
1860
Pseudo-nitzschia multiseries
Samples represent single years between AD 2007 and 1994, two years composite between 1993 and 1839. Data plotted at age of older year.
(This study expands on that of Barron et al., 2010, which covered the years 1940-2001 in nearby box core SBBC2902)
40
1945
Deeper thermocline
Field et al., (2006a) state, “The association of G. bulloides with PC1 apparently reflects a preference for enhanced near-surface stratification during conditions
of shoaling of isotherms (perhaps because prey would be more concentrated under these conditions than with a strictly isothermal water column). Accordingly,
we interpret PC1 as the foraminiferal response to anomalous near-surface temperatures that modify stratification across the annual cycle of shoaling and
deepening of isotherms”.
Percent of Diatom
Assemblage*
400
0
2000
-2
1967
60
1980
0
1976
400
1960
Planktonic foraminiferal factor PC1 displays a
good correlation with Anomaly SST
(R2 value of 0.55965)
1840
1963
1957
1940
+2
-1.5
200
1920
Year
PC1 -warm
+4
200
400
1900
Percent of Silicoflagellate
Assemblage
r
ive
SBBC0806
1880
Percent of Silicoflagellate
Assemblage
R
ra
1997
0
60
1860
Pseudo-nitzschia australis
Ratio Pseudo-nitzschia / Chaetoceros spores
-1.0
G. scitula
-1.0
N. pachderma (sin)
-0.5
G. ruber
Other subtropical
T. quinqueloba
N. pachderma (dex.)
0
0
Anomaly SSTs after Kaplan et al,, 1998.
(http://www.esrl.noaa.gov/psd/data/gridded/
data.kaplan_sst.html)
PDO Index of Mantua et al., 1997.
(http://jisao.washington.edu/pdo/PDO.latest)
G. bulloides
N. dutertrei
O. universa
Anomaly SST (°C)
+1.0
Anomaly SST (°C)
a
Cl
X
+2.0
+0.5
Anomaly SST (°C)
a
nt
2008
PDO (January)
SST record from the updated Kaplan reconstruction
for the 5°X 5°- grid centered at 122.5°W, 32.5°N
+1.0
Assignment of years to varves and comparison with chronology suggested by Arndt Schimmelmann’s chronology
(http://mypage.iu.edu/~aschimme/paleocl.html)
Sa
Santa Barbara
According to published studies the first recorded large-scale toxigenic P. australis bloom in the
SBB occurred in June 1998 as part of more widespread blooms and shellfish poisoning along the
central California coast (Trainer et al., 2000). Although high numbers (or blooms) of P. australis
were reported in plankton studies off the Scripps Pier in La Jolla during the 1930’s, 1967, and
1983, blooms of P. australis associated with toxic domoic acid levels were first reported in 1991 in
Monterey Bay (Lange et al., 1994). Biologists have shown that Pseudo-nitzschia blooms
correspond to lowered sea surface temperatures and increased salinity that are typical of coastal
upwelling events, but they have debated whether increased nutrients levels from river runoff have
been a factor in the recent increase of the blooms (Schnetzer et al., 2003). Laboratory studies
have demonstrated that toxin production in some species of Pseudo-nitzschia may increase under
silicic acid or phosphate limitation (Schnetzer et al., 2003; Silver et al., 2011). Mengelt and Prézelin
(2005) and others have suggested Pseudo-nitzschia is less suceptible to growth inhibition by
Ultraviolet A (320 to 400 nm) radiation than other planktic diatoms and therefore can remain in
near surface waters for longer periods of time. Whatever the cause, our 178 year-long diatom
sediment record suggests that the recent increase of Pseudo-nitzschia blooms in the Santa
Barbara Basin has occurred at the expense of Chaetoceros and Rhizosolenia, the natural
bloom-forming diatoms in the Santa Barbara Basin.
+3.0
Anomaly SST (°C)
+1.5
Box Core SBB0806
Pt. Conception
The Pseudo-nitzschia story
Field et al., 2006a -Science
Loading
Diatoms and silicoflagellate assemblages studied in two year-increments of varved samples in Santa Barbara Basin (SBB) box core
0806 spanning AD 1839 to 2007 suggest that unprecedented warming of surface waters began at about AD 1940, which is in agreement with CalCOFI SST data (Field et al., 2006b) and changes in planktonic foraminferal assemblages (Field et al., 2006a). Di
Lorenzo et al. (2005) and these studies argued that increased stratification and deepening of the thermocline occurred during the latter
half of the 20th Century within 50–100 km of the southern California coast in response to anthropogenically-forced global warming.
Diatoms (Thalassionema nitzschioides =TN) and silicoflagellates (Distephanus speculum s.l. =DS) indicative of cooler waters and a
shallow thermocline declined markedly in relative numbers in the SBB beginning at about AD 1940. Prior to that time, TN constituted
on average ~30% of the Chaetoceros-free diatom sediment assemblage and DS on average ~36% of the silicoflagellate assemblage.
Between AD 1940 and 1996 these relative abundances drop to ~20% (TN) and ~8% (DS). Cooling of surface waters coincident with
the onset of negative PDO conditions in the North Pacific in AD 1998 brought about a return to pre-AD 1940 values of these cool water
taxa (TN ~31%, DS ~25%). However, this recent regional cooling appears to have been accompanied by profound changes to surface
water productivity events in the SBB. Pseudo-nitzschia australis, a diatom associated with domoic acid, a neurotoxin that causes
shellfish poisoning and marine mammal deaths, appeared suddenly in the SBB sediment record in AD 1999 and increased
significantly in numbers as a bloom-forming taxon (relatively to Chaetoceros spores) in AD 2003. Prior to AD 2003 diatom blooms represented in the SBB sediment record consisted predominantly of Chaetoceros spores and less commonly of Rhizosolenia spp.
(R. hebetata and R. setigera). Fecal pellets dominated by valves of P. australis, however, are abundant in both the AD 2003 and 2006
samples, coincident with recorded incidents of domoic acid increase and widespread shellfish poisoning in the SBB.
Planktonic Foraminifers
Percent of Diatoms*
Abstract
1960
1980
2000
*Barron, John A., Bukry, David, and Field, David, 2010. Santa Barbara Basin diatom and silicoflagellate records suggests coincidence of cooler SST with
widespread occurrence of drought in the west during the past 2200 years. In 23rd Pacific Climate Workshop (PACLIM), Starratt, S.W. (ed.), Quaternary
International 215:34-44. doi:10.1016/j.quaint.2008.08.007.
*Di Lorenzo, E., A. J. Miller, N. Schneider and J. C. McWilliams, 2005. The warming of the California Current: Dynamics and ecosystem implications.
Journal of Physical Oceanography, 35, 336-362.
*Field, D.B., Baumgartner, T.R., Charles, C.D., Ferreira-Bartrina, V., and Ohman, M.D., 2006a. Planktonic foraminifera of the California Current reflect
20th-Century warming. Science 311, 63-66.
*Field, D., Cayan, D., and Chavez, F., 2006b. Secular warming in the California Current and North Pacific. California Cooperative Ocean Fisheries
Investigation (CalCOFI) Report 47, 1-17.
*Kaplan, A., M. Cane, Y. Kushnir, A. Clement, M. Blumenthal, and B. Rajagopalan, 1998. Analyses of global sea surface temperature 1856-1991,Journal of
Geophysical Research, 103, 18,567-18,589.
*Lange, C.B., Reid, F.M.H., and Vernet, M., 1994. Temporal distribution of the potentially toxic diatom Pseudo-nitzschia australis at a coastal site in
Southern California. Marine Ecology Progress Series 104, 309-312.
*Lange, C.B., Weinheimer, A.K., Reid, F.M, and Thunell, R.C., 1997. Sedimentation patterns of diatoms, radiolarians, and silicoflagellates in Santa Barbara
Basin, California. California Cooperative Ocean Fisheries Investigation (CalCOFI) Report 38,161-170.
*Mantua, N.J., Hare, S.R., Zhang, Y., Wallace, J.M., and Francis, R.C., 1997. A Pacific decadal climate oscillation with impacts on salmon. Bulletin of the
American Meteorological Society 78, 1069-1079.
*Mengelt, C. and Prézelin B.B., 2005. UVA enhancement of carbon fixation and resilience to UV inhibition in the genus Pseudo-nitzschia may provide a
competitive advantage in high UV surface waters. Marine Ecology Progress Series. 301,81-93.
*Schimmelmann, A., Lange, C.B., Roark, E.B., and Ingram, B.L., 2006. Resources for paleoceanographic and paleoclimatic analysis: a 6,700-year
stratigraphy and regional radiocarbon reservoir-age (DR) record based on varve counting and 14C-AMS dating for the Santa Barbara Basin, offshore
California, U.S.A. Journal of Sedimentary Research 76, 73-79.
*Schnetzer, A., Miller, P.E., Schaffner, R.A., Stauffer, B.A., Jones, B.H., Weisberg, S.B., DiGiacomo, P.M., Berelson, W.M., and Caron, D.A., 2007.
Blooms of Pseudo-nitzschia and domoic acid in the San Pedro Channel and Los Angeles harbor areas of the Southern California Bight, 2003-2004.
Harmful Algae 6, 206-217.
*Silver, M.W. and others. 2011. Toxic diatoms and domoic acid in natural and iron enriched water of the oceanic Pacific. Proc. Nat. Acad. Sci. USA 107,
20762-20767.
*Trainer, V.L., Adams, N.G., Bill, B.D., Stehr, C.M., Wekell, J.C., Moeller, P., Busman, M. and Woodruff, D., 2000. Domoic acid production near California
coastal upwelling zones, June 1998, Limnol. Oceanogr. 45, 1818–1833.