Collapse of the California Current During Glacial
Maxima Linked to Climate Change on Land

coastal California current and SST map Collapse of the California Current During Glacial
Maxima Linked to Climate Change on Land

Science, July 6 2001: 71-76

T. D. Herbert, 1 J. D. Schuffert,1 D. Andreasen,2
L. Heusser,3 M. Lyle,4 A. Mix,5 A. C. Ravelo,2
L. D. Stott,6 J. C. Herguera7

1 Department of Geological Sciences, Brown University
2 University of California, Santa Cruz
3 Lamont-Doherty Earth Observatory
4 Center for Geophysical Investigation of the Shallow Subsurface, Boise State University
5 Oregon State University
6 University of Southern California
7 Centro de Investigación Científica y de Educación Superior de Ensenada

Time series of alkenone unsaturation indices gathered along the California margin reveal large (4° to 8°C) glacial-interglacial changes in sea surface temperature (SST) over the past 550,000 years. Interglacial times with SSTs equal to or exceeding that of the Holocene contain peak abundances in the pollen of redwood, the distinctive component of the temperate rainforest of the northwest coast of California. In the region now dominated by the California Current, SSTs warmed 10,000 to 15,000 years in advance of deglaciation at each of the past five glacial maxima. SSTs did not rise in advance of deglaciation south of the modern California Current front. Glacial warming along the California margin therefore is a regional signal of the weakening of the California Current during times when large ice sheets reorganized wind systems over the North Pacific. Both the timing and magnitude of the SST estimates suggest that the Devils Hole (Nevada) calcite record represents regional but not global paleotemperatures, and hence does not pose a fundamental challenge to the orbital ("Milankovitch") theory of the Ice Ages.

Download the alkenone and isotope data and SST reconstructions for cores
ODP 1012, ODP 1020, and LaPaz 21P , plus the Data Description
from the WDC Paleo Archive.

Figure 2 Figure 3

Fig. 2. Synthesis of glacial-interglacial variations in alkenone SST, arrayed from north to south along the California margin. The time scales come from tuning benthic d18O variations to the SPECMAP chronology. Vertical lines indicate the stratigraphic positions of glacial maxima; note the early warming of SST relative to ice volume at glacial terminations.

Fig. 3. Detail of the last glacial-interglacial transition, documenting the regional nature of the early warming anomaly. The anomaly is most apparent in the southern California region, is present but of smaller amplitude to the north, and is not present off Baja California. Chronology at sites 1012 and 1020 comes from benthic d18O stratigraphy; chronology at sites EW9504-09 and RGS0487 BC9 comes from isotope stratigraphy and 14C accelerator mass spectrometry dating.

Figure 4

Fig. 4. Correspondence between alkenone SST estimated at ODP site 1020 and the "warm" pollen assemblage determined from factor analysis.

Figure 2

Fig. 5. Comparison of a representative alkenone record (ODP 1012) with the Devils Hole d18O record, on independent time scales. The good match, in particular the rise in temperature and d18O of both records before deglaciation, suggests that regional, not global, temperature changes dominate the isotopic composition of the terrestrial record. The growth rate of the Devils Hole vein inferred from the Devils Hole time scale contains an anomalous interval beginning at 438 ka, suggestive of a dating error.

To read or view the full study, please visit the Science website.
It was published in Science July 6 2001: 71-76.

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30 July 2001