Glacial-interglacial modulation of eastern tropical North Pacific denitrification over the last 1.8-Myr

Abstract

A 1.8 Myr-long δ15N record from the California margin provides the first continuous record of denitrification in the Eastern Tropical North Pacific (ETNP) over the entire Pleistocene epoch. Comparison of the nitrogen isotopic time series with proxies for ice volume, sea surface temperature (SST), and biological productivity place variations in the intensity of the denitrification zone in the context of global and regional climatic changes. Throughout the Pleistocene, ETNP denitrification remained linked to glacial-interglacial climate cycles. The pacing of denitrification cycles switched from 41-kyr in the mid- to early Pleistocene to 100-kyr in the late Pleistocene, in tandem with the well-known frequency shift identified from ice volume records. It therefore appears that denitrification remained an integral component of the marine feedbacks to orbital forcing, and through its effect on the nitrate inventory of the ocean might have played a role in driving atmospheric CO2 cycles throughout the Pleistocene. Copyright 2005 by the American Geophysical Union.