Using species-specific paleotemperature equations with foraminifera: a case study in the Southern California Bight

Species-specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal delta(18)O values over the last 25 kyr in the Southern California Bight. The equations yield similar temperatures for the delta(18)O values of Globigerina bulloides and Neogloboquadrina pachyderma. In contrast, applying a single palcotemperature equation to G. bulloides and N. pachyderma delta(18)O yields different temperatures, which has been used to suggest that these species record the surface-to-thermocline temperature gradient. In Santa Barbara Basin, an isotopically distinct morphotype of G. bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today. When a more appropriate paleotemperature equation is used for glacial G. bulloides, we obtain more realistic glacial temperatures. Glacial-interglacial temperature differences (G-I DeltaT) calculated in the present study indicate significant cooling (similar to8-10degreesC) throughout the Southern California Bight during the last glacial maximum (LGM). The magnitude of glacial cooling varies from similar to8degreesC near the middle of the Southern California Bight (Tanner Basin and San Nicolas Basin) to similar to9degreesC in the north (Santa Barbara Basin) and similar to9.5-10degreesC in the south (Velero Basin and No Name Basin). Our temperature calculations agree well with previous estimates based on the modern analog technique. In contrast, studies using N. pachyderma coiling ratios, U-37(k') indices, and transfer functions estimate considerably warmer LGM temperatures and smaller G-I DeltaT. (C) 2002 Elsevier Science B.V. All rights reserved.