Pre-Bølling warming in Santa Barbara Basin, California: surface and intermediate water records of early deglacial warmth

A new piston core from Santa Barbara Basin, California provides evidence of the timing, magnitude, and character of deglaciation, including evidence of warming prior to Termination IA. IMAGES Site MD02-2503 (570 m water depth) consists of intermittently laminated hemipelagic sediments extending to Interstadial (D/O) event 6 (∼34 ka), that accumulated at ∼135 cm/ka. During the deglacial episode (16.75-10 ka), δ18O values decreased by 3.2‰ in the planktonic species Globigerina bulloides, indicating a total warming of 8-9 °C recorded by surface-dwelling foraminifera (inferred by removing the 1‰ influence of ice volume change). Similarly, benthic species (Bolivina argentea and Uvigerina peregrina) record a 1.65‰ δ18O decrease across the deglacial, interpreted as a 2-3 °C warming at upper intermediate depths. δ18O values of both planktonic and benthics indicate that surface and intermediate waters began to warm ∼2 ka prior to Termination IA, beginning at ∼16.5 ka. Intermediate water warming exhibits similar structure and synchronous timing with surface waters. These findings are consistent with a growing number of records from around the globe that exhibit pre-Bølling warming prior to Termination IA, and extends the record of such processes to the northern Pacific.