Assessment of sea‐surface temperature at 42°N in the California Current over the last 30,000 years

摘要

Assessment of changes in surface ocean conditions, in particular, sea‐surface temperature (SST), is essential to understand long‐term changes in climate especially in regions where continental climate is strongly influenced by oceanographic processes. To evaluate changes in SST in the northeast Pacific, we have analyzed long‐chain alkenones of prymnesiophyte origin at 38 depths in a piston and associated trigger core collected beneath the contemporary core of the California Current System at 42°N, ∼270 km off the coast of Oregon/California. The samples span 30,000 years of deposition at this location. Unsaturation patterns(U37K′)in the alkenone series display a statistically significant difference (p≪ 0.001) between interglacial (0.44 ± 0.02,n= 11) and glacial (0.29 ± 0.04,n= 20) intervals of the cores. Detailed examination of other compositional features of the C37, C38, C39alkenone series and a related C36alkenoate series measured downcore suggests the publishedU37K′‐ temperature calibration(U37K′=0.034×T+0.039), defined for cultures of a strain ofEmiliania huxleyiisolated from the subarctic Pacific, provides best estimates of winter SST at our study site. This inference is purely statistical and does not imply, however, that the phytoplankton source of these biomarkers is most productive in winter or at the ocean surface. The temperature record forU37K′implies (1) an ∼4°C shift occurred in winter SST from ∼ 7.5 ± 1.1°C at the last glacial maximum to ∼ 11.7 ± 0.7°C in the present interglacial period, and (2) this warming trend was confined to the time frame 14–10 Ka within the glacial to interglacial transition period. These conclusions are corroborated entirely by results from an independent SST transformation of radiolarian species assemblage data o