Magnitude of the 8.2\xa0ka event freshwater forcing based on stable isotope modelling and comparison to future Greenland melting

Wilton Aguiar,Katrin J Meissner,Alvaro Montenegro,Anders E Carlson,Mauricio M Mata,Ilana Wainer,Luciana Prado

doi:10.1038/s41598-021-84709-5

Abstract

The northern hemisphere experienced an abrupt cold event ~ 8200 years ago (the 8.2 ka event) that was triggered by the release of meltwater into the Labrador Sea, and resulting in a weakening of the poleward oceanic heat transport. Although this event has been considered a possible analogue for future ocean circulation changes due to the projected Greenland Ice Sheet (GIS) melting, large uncertainties in the amount and rate of freshwater released during the 8.2 ka event make such a comparison difficult. In this study, we compare sea surface temperatures and oxygen isotope ratios from 28 isotope-enabled model simulations with 35 paleoproxy records to constrain the meltwater released during the 8.2 ka event. Our results suggest that a combination of 5.3 m of meltwater in sea level rise equivalent (SLR) released over a thousand years, with a short intensification over ~ 130 years (an additional 2.2 m of equivalent SLR) due to routing of the Canadian river discharge, best reproduces the proxy anomalies. Our estimate is of the same order of magnitude as projected future GIS melting rates under the high emission scenario RCP8.5.

Highlights

The northern hemisphere experienced an abrupt cold event ~ 8200 years ago that was triggered by the release of meltwater into the Labrador Sea, and resulting in a weakening of the poleward oceanic heat transport
The range of estimates of the magnitude of total freshwater release during the 8.2 ka event is large[10,11], ranging from 1.5 to 9 m in equivalent sea-level rise (SLR)[16,22]. Some of these scenarios were previously used to simulate the cold event with numerical climate models in an attempt to estimate the climatic impacts of the freshwater discharge[23,24,25], and simulation skill was evaluated by comparison with sea surface temperature (SST)
Our first set of simulations evaluate how well different freshwater sources to the North Atlantic reproduce ocean anomalies associated with the 8.2 ka event

Summary

Introduction

The northern hemisphere experienced an abrupt cold event ~ 8200 years ago (the 8.2 ka event) that was triggered by the release of meltwater into the Labrador Sea, and resulting in a weakening of the poleward oceanic heat transport This event has been considered a possible analogue for future ocean circulation changes due to the projected Greenland Ice Sheet (GIS) melting, large uncertainties in the amount and rate of freshwater released during the 8.2 ka event make such a comparison difficult. Due to a model-dependent stability of ocean overturning, location of deep convection sites and meridional heat transport, the simulated SST response to freshwater forcing varies significantly between distinct simulations[27,28] This model dependency makes it difficult to test which freshwater source played the dominant role in triggering the 8.2 ka based on the comparison between the simulated SST response and reconstructed SST changes. These uncertainties can be reduced by using a combination of active and non-active tracers, such as oxygen isotopes as well as SSTs

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