PLIOCENE-PLEISTOCENE BENTHIC FORAMINIFERAL ASSEMBLAGES AT IODP SITE 1014 (TANNER BASIN): A POTENTIAL ANALOGUE FOR NEAR-FUTURE BENTHIC BIODIVERSITY CHANGES ON THE SOUTHERN CALIFORNIA MARGIN?

The early to middle Pliocene was characterized by atmospheric CO₂ concentrations and sea surface temperatures similar to those projected to occur as early as the next decade on the current warming trajectory. There have been comparatively few extinction and origination events since the Pliocene, and hence Pliocene marine faunas are generally similar to the modern and studies of their ecological responses to climate changes can serve as a possible analogue for predicting coming biodiversity changes. We examined benthic foraminifera assemblages from IODP site 1014A, a hemipelagic site in the Tanner Basin on the southern California margin. Benthic temperatures at this site are not yet well constrained, but surface temperatures reconstructed from the alkenone unsaturation index (U^K₃₇) cooled by ~10℃ from the Zanclean to the Calabrian. Preliminary analyses suggest that this cooling was associated with a collapse in benthic foraminiferal diversity, as the mean sample-standardized species richness of Pliocene samples is twice that of Pleistocene samples. Early Pliocene (~4 Ma) samples are numerically dominated by species of Gyroidina, Buccella, and Bulimina while Late Pliocene and Pleistocene samples are dominated by species of Melonis, Bolivina, and Uvigerina. The abundance of the latter is consistent with other evidence that cooling was accompanied by enhanced upwelling and increased benthic hypoxia. Our preliminary results are also consistent with numerous other neontological and paleoecological studies showing that the diversity of benthic foraminiferal assemblages tracks climate and temperature variations in space and time. Ongoing work will refine the timing and nature of benthic biodiversity changes at this site and add to the growing database of paleoecological analogs for modeling future biodiversity changes on a rapidly warming planet.