Temporal variability of Delta C-14, delta C-13, and C/N in sinking particulate organic matter at a deep time series station in the northeast Pacific Ocean

A Pourmand
F Marcantonio
TS Bianchi
EA Canuel
EJ Waterson

Abstract

We present new excess Pa-231/Th-230 activity ratios and lipid biomarker results from northeastern Arabian Sea sediments (core 93KL) spanning the past 50 ka in an effort to constrain further the relationship between climate at low and high latitudes. Pa-231/Th-230 activity ratios are maintained at values significantly higher than the water-column production ratio of 0.093. Average Pa-231/Th-230 activity ratios are lower during the last glacial period than during the Holocene. The lowest Pa-231/Th-230 activity ratios coincide with the timing of Heinrich Events 1-5. Profiles of lipid biomarker fluxes and Pa-231/Th-230 activity ratios from 32 to 12 ka show similar patterns, suggesting that Pa-231 is more efficiently scavenged relative to Th-230 at times when diatoms make up a proportionally larger part of the primary biomass signal. In the Holocene, high Pa-231/Th-230 activity ratios may indicate enhanced Pa-231 export from the southern to the northern Indian Ocean via intensified thermohaline circulation.