Southern Hemisphere Signature in Glacial-Deglacial Sequence of SST and Denitrification Along the Peru Margin

We present results of a multi-proxy investigation of the sea surface temperature (SST), paleoproductivity, and dentrification history of the Peru margin over the last 55 ka. A high resolution(sedimentation rates 10-25 cm/kyr)composite record from the latest Holocene to about 19 ka was obtained by combining AMS 14C alkenone ages and δ 15N stratigraphy. An off-margin core offers lower deposition rates, but contains carbonate microfossils for oxygen isotope stratigraphy, and extends the records to early MIS 3. We find that denitrication largely dissapeared at the Last Glacial Maximum, and remained weak through the remainder of the Glacial sequence. SSTs were tightly coupled to δ 15N, even on a millenial scale, with colder temperatures corresponding to less enriched nitrogen isotope values and less intense denitrification. Both δ 15N and alkenone-derived SSTs led sea level changes by about 5 kyr at the last deglaciation, in a pattern reminiscent of high latitude southern hemisphere temperature changes. The high productivity of the present Peru margin lagged both these changes, indicating that the SST and denitrification "switches" were remotely forced, in all probability by changes in the temperature and nutrient properties of Antarctic mode waters. Within the Holocene, the coupling of SST and denitrification persisted, but less tightly than observed for the glacial-interglacial time scale