Deglacial intermediate water reorganization: new evidence from the Indian Ocean

S Romahn,J Groeneveld,A Mackensen,J Pätzold

doi:10.5194/cp-10-293-2014

Abstract

Abstract. The importance of intermediate water masses in climate change and ocean circulation has been emphasized recently. In particular, Southern Ocean Intermediate Waters (SOIW), such as Antarctic Intermediate Water and Subantarctic Mode Water, are thought to have acted as active interhemispheric transmitter of climate anomalies. Here we reconstruct changes in SOIW signature and spatial and temporal evolution based on a 40 kyr time series of oxygen and carbon isotopes as well as planktic Mg/Ca based thermometry from Site GeoB12615-4 in the western Indian Ocean. Our data suggest that SOIW transmitted Antarctic temperature trends to the equatorial Indian Ocean via the "oceanic tunnel" mechanism. Moreover, our results reveal that deglacial SOIW carried a signature of aged Southern Ocean deep water. We find no evidence of increased formation of intermediate waters during the deglaciation.

Highlights

Despite growing evidence that intermediate water masses originating from the Southern Hemisphere are an important component of the global thermohaline circulation, there is disagreement about the variability of chemical properties and the spatial dimension of these water masses through time
The deglacial decline of δ18Op starts at 18.2 kyr and shows a clear setback to higher values at 13 kyr, which appears to resemble the Greenland ice cores and Northern Hemisphere climate variability
The record exhibits a deglacial decline starting at 19.5 kyr, and a slackening of δ18Ob decrease during the Antarctic Cold Reversal (ACR)

Summary

Introduction

Despite growing evidence that intermediate water masses originating from the Southern Hemisphere are an important component of the global thermohaline circulation, there is disagreement about the variability of chemical properties and the spatial dimension of these water masses through time. AAIW is thought to transmit climate anomalies from the Southern Ocean to the tropics, via the so-called “oceanic tunnel” (Liu and Yang, 2003; Pena et al, 2013). This term describes the flow of southern-sourced waters via an intermediate water level pathway to the low latitude thermocline, where entrainment of this extratropical water has a cooling effect on tropical sea surface temperature (SST). The growing number of high-resolution SST records from shallow depths of tropical oceans, showing an Antarctic-type SST pattern for the last deglaciation (Kiefer et al, 2006; Naidu and Govil, 2010; Mohtadi et al, 2010; Visser et al, 2003; Weldeab et al, 2006), supports this idea and indicates that AAIW is essential for interhemispheric forcing of climate variability

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