HIGH-RESOLUTION CLIMATE “WINDOWS” FROM SANTA BARBARA BASIN: INVESTIGATIONS OF QUATERNARY RAPID CLIMATE CHANGE

A lack of sufficiently high-resolution climate records older than ~100 ka has limited understanding of causes, effects, and temporal development of submillennial Quaternary climate change. Santa Barbara Basin (SBB, 34°15 N, 119°45 W) provides uniquely well-preserved sediments spanning the past ~700 kyr. Five piston cores were taken from SBB in August 2005. Their ages were determined using sequence stratigraphy combined with biostratigraphy, tephrochronology and the paleoclimatic record. Each core spans ~5 kyr, with this study focusing on three intervals: ~285 ka, 460 ka and 730 ka. These cores provide the first high-resolution “windows” extending back to near the onset of the “100 ka world.” The results provide critical data on the amplitude, shape, and timing of submillennial-scale oscillations at various orbital (Milankovitch) configurations. We use stable isotopes of planktonic foraminifera (Globigerina bulloides, Neogloboquadrina pachyderma) and benthic foraminifera (Uvigerina peregrina), planktonic foraminiferal assemblage analyses including N. pachyderma coiling ratios, and sediment lamination data to reconstruct temperature, ocean circulation, and basin floor oxygenation at a resolution of ~50 years. Temperature shifts are seen in isotopic analyses of G. bulloides and N. pachyderma, with δ¹⁸O variations of up to 1.4‰ in as briefly as ~80 years and 2.5‰ over ~1000 years during warming. Water column stratification is interpreted from differences between G. bulloides and N. pachyderma δ¹⁸O – colder intervals with similar values indicate reduced stratification, and vice versa. N. pachyderma coiling ratios often vary in tandem with planktonic δ¹⁸O, but exhibit threshold behavior instead of smooth change. Coiling ratios are generally higher during intervals of more negative planktonic δ¹⁸O and/or moderate water column stratification. U. peregrina δ¹⁸O data, although reflecting more stable benthic conditions, do respond along with major shifts in planktonic δ¹⁸O, and change by as much as 1.3‰ during millennial-scale warming. δ¹³C values broadly correlate with shifts in δ¹⁸O, and reflect changing ocean circulation, carbon cycling, and/or methane release. Future work will include benthic foraminiferal assemblage analyses, which will provide more data on ocean circulation and oxygenation.