Abrupt Climate Change and Millenial-Scale Oscillations in Marine Sedimentary Geochemistry at 300 and 700ka, Santa Barbara Basin, California

S. Afshar¹, R. J. Behl², J. P. Kennett³, and the R/V Melville SBCore Team
¹California State University, Long Beach, CA, [email protected]
²California State University, Long Beach, CA, [email protected]
³University of California, Santa Barbara, CA, [email protected]

Millennial to decadal oscillations in stable isotopes, Total Organic Carbon (TOC) and CaCO₃ have been discovered in two ~300 ka and ~700 ka cores from Santa Barbara Basin (SBB). These cores provide short, stratigraphic “windows” that permit study of abrupt paleoceanographic and paleoclimatic change further back in time than previously investigated at ultra-high resolution. The cores, acquired in 2005, were analyzed at 1-2 cm resolution (~10-20 yr). Both cores record climate oscillations represented by sea-surface temperature changes of similar magnitude and abruptness to the Dansgaard-Oeschger events of Marine Isotopic Stage 3 (MIS 3). Like MIS 3, interstadials are laminated, whereas stadials are bioturbated. Onset and termination of interstadials occurred in <100 yrs or slightly longer. TOC variations correlate strongly and positively with temperature and inversely with sediment density. The relation between TOC and laminated sediment differs from MIS 3 in that persistent laminations occur only when average TOC exceeds 1.5%, suggesting the necessity of a quantifiable threshold in organic matter flux and oxygen utilization for preservation of varved sediments. Unlike TOC, %CaCO₃ correlates poorly with climate or sedimentary fabric.

A termination-scale, cold-to-warm transition at ~300 ka shown by oxygen isotopes consists of a series of sawtooth-like steps in which temperature and TOC increase while carbonate decreases. In the ~700 ka core, changes in TOC correlate with periodic ~1200-yr climate oscillations of consistent isotopic magnitude, in contrast to the “Bond Cycle” structure of decreasingly strong interstadials in MIS 3. Both TOC and sea surface temperature exhibit sawtooth patterns.

In general, variations in TOC (0.5-2.8%) are much less than carbonate (0-15%). Although CaCO₃ exhibits some covariation with TOC, sedimentary fabric, or oxygen isotopes, it’s inconsistent behavior questions it’s value as a productivity proxy in SBB, and instead highlights the need for other productivity proxies such as biogenic opal or trace element geochemistry.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009