Extending the High-Resolution Global Climate Record in Santa Barbara Basin: Preliminary Results and Implications

A major legacy of Michael Sarnthein is his ample demonstration of the necessity for high-resolution paleoceanography and chronology to understand processes of late Quaternary climate change. Consistent with this legacy we have begun to extend the remarkable, high resolution climate record of the Santa Barbara Basin beyond 160 ka found at the base of ODP Site 893. Safety issues prevented drilling of older basinal sediments. However, active folding, uplift and erosion have exposed a sequence of dipping sediments of upper bathyal paleodepths (500-1000 m) now at shallow (160 m) ocean floor depths on the Mid-Channel Trend. Integrative studies of high-resolution seismic and sediment stratigraphy of 33 piston cores have provided an excellent marine climatic sequence that may represent each of the oxygen isotopic stages (OIS) of the last 500 ka (possibly as old as OIS16). Precise core locations on the ocean floor have provided both individual time windows and composite, overlapping sediment records likely to reveal paleoclimatic behavior prior to 150 ka at high stratigraphic resolution not available in ice cores. The lithostratigraphy of the sequence suggests late Quaternary basinal environmental behavior similar to Site 893 and involving major changes in oxygenation state and inferred climatic oscillations over the last 500 kys. Pristinely laminated intervals inferred to represent interglacials and interstadials alternate with massive, bioturbated, sandier intervals representing glacials and stadials. Intermediate oxygenation states are suggested by diffuse or discontinuous laminations. Certain earlier cool episodes record potentially millennial-scale climate oscillations in oxygen minimum zone strength, as during OIS3, in response to changing ventilation and/or surface-ocean productivity. The episodic dysoxic intervals reflect a semi-isolated basin for at least the last 500 ka. Several glacial terminations are well recorded. For example, a composite record of four overlapping cores may have captured the important deglacial episode from OIS12 to 11. This work confirms the presence of an accessible, high-resolution Quaternary climatic sequence for future drilling and piston coring. The success of this expedition suggests that active margin settings should be sought rather than avoided for high-resolution global climate studies.