Statistical relationships among proxies of climate, productivity and the carbon cycle across climatic regimes, Santa Barbara Basin, California

American Geophysical Union, San Francisco, December 2008

Carlye D. Peterson¹; Richard J. Behl¹; Christine M. Rodrigue²; Cathleen M. Zeleski³; and Tessa M. Hill⁴

¹ Department of Geological Sciences, California State University, Long Beach
² Department of Geography, California State Univesity, Long Beach
³ Department of Earth and Ocean Science, Saddleback College
⁴ Department of Geology and Bodega Marine Laboratory, University of California, Davis

The ultra-high-resolution record from Santa Barbara Basin (SBB) provides an opportunity to study the relationships among climate, productivity and the carbon cycle across climatic regimes. We conducted a statistical analysis of multi-proxy data derived chiefly from splits of identical samples from Core MD02-2503, recovered from the central SBB near ODP Site 893. The record spans 33.5 to 4.5 ka (Cal. Yr bp) and includes Glacial, Pre B&řslash;lling Warming, Deglaciation, and Interglacial climatic intervals. Data sets of % CaCO₃, % total organic carbon (TOC), C/N ratios, d¹⁸O G. bulloides, % silt, and porosity (gamma ray attenuation) were examined by principal components analysis (PCA) to group the best-correlated variables into two components in order to better understand the sensitivity of the proxies to external forcing. Component one includes d¹⁸O G. bulloides (negative loading) and TOC (positive loading), whereas component two includes CaCO₃ (negative loading) and C/N (positive loading). PCA not only indicates which variables are related in their behavior, but also the relative sensitivity to forcing under different climatic conditions, thus suggesting the existence of threshold changes in response to forcing functions. Examined over time, PCA suggests during the glacial interval d¹⁸O and C/N ratios are more sensitively responsive to forcing, whereas during the Holocene interglacial, variation in sensitivity of TOC and CaCO₃ is emphasized. PCA also highlights distinctive behavior during shorter events within the glacial and Holocene, where one or both components deviated from the general trends. For example, during the Younger Dryas, neither component departs from zero and, during Dansgaard-Oeschger events, both components deviate in the same direction. Further investigation is needed, but linear regressions over the entire record show the highest overall negative correlation between d¹⁸O and TOC, with warmer surface water correlating with higher TOC. The next best correlation is a negative one between C/N and CaCO₃, reflecting the influence of marine productivity vs. terrestrial organic carbon contribution. This study lays the groundwork for statistical analysis and characterization of proxy behavior during earlier climatic cycles that will be studied from new cores from the SBB, hopefully ranging back to 1.2 Ma.