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Sea Surface Temperatures and Productivity Along the California Margin During the Early Pliocene Warm Period

Dekens, P.S.; Schwartz, V.E.; Miles, J.; and Reed-Sterrett, C.
[email protected]

The early Pliocene is the most recent time in Earth history when average global temperatures were warmer than they are today. Coastal upwelling regions had a particularly strong response to early Pliocene warmth; sea surface temperature records in eastern boundaries were 4-9ºC warmer compared to today. Warmer SST in upwelling regions could have contributed to Pliocene warmth due to cloud and water vapor feedbacks. We will present alkenone (UK’37) SST estimates for the early Pliocene from a latitudinal transect along the California margin.

In addition to records of SST, we characterize productivity at ODP site 1022 (40ºN, 125ºW, 1950m water depth) using diatom assemblages, grain size analysis, smear slides, and organic biomarkers. The smear slide analysis shows a decrease in diatom abundance and an increase in coccolithophorid abundance from 4.2 to 2.8 Ma. These smear slide data could reflect a change in either productivity or preservation. The percent of diatoms indicative of subarctic waters is unchanged from 4.2 to 3 Ma, suggesting that a change in the strength of the California current cannot explain the cooling SST trend. We also found no trend in the percent of upwelling-indicative diatoms, which is consistent with records of alkenone mass accumulation rate, diatom preservation, biosilica, and total organic carbon, none of which show evidence that the upwelling of nutrient-rich subsurface water increased as SST cooled. The fact that upwelling of nutrient-rich water was occurring even when SST were warmer can be explained by a deeper early Pliocene thermocline.

 

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013