Abstract

Sulfate aerosols (of both biogenic and anthropogenic origin) play a key role in the Earth’s radiation balance both directly through scattering and absorption of solar and terrestrial radiation, and indirectly by modifying cloud microphysical properties. However, the uncertainties associated with radiative forcing of climate due to aerosols substantially exceed those associated with the greenhouse gases. The major source of sulfate aerosols in the remote marine atmosphere is the biogenic compound dimethylsulfide (DMS), which is ubiquitous in the world’s oceans and is synthesized by plankton. Climate models point to significant future changes in sea-ice cover in the Arctic Ocean due to warming. This will have consequences for primary production and the sea-to-air flux of a number of biogenic compounds, including DMS. In this paper we discuss the impact of warming on the future production of DMS in the Arctic Ocean. A DMS production model has been calibrated to current climate conditions with satellite ocean colour data (SeaWiFS) using a genetic algorithm, an efficient non-derivative based optimization technique. We use the CSIRO Mk 2 climate model to force the DMS model under enhanced greenhouse climate conditions. We discuss the simulated change in DMS flux and its consequences for future aerosol production and the radiative budget of the Arctic. Significant decreases in sea-ice cover (by 18.5% annually and 61% in summer—autumn), increases in mean annual sea surface temperature of 1°C, and a decrease of mixed layer depth by 13% annually are predicted to result in annual DMS flux increases of over 80% by the time of equivalent CO<sub>2</sub> tripling (2080). Estimates of the impact of this increase in DMS emissions suggest significant changes to summer aerosol concentrations and the radiative balance in the Arctic region.

Highlights

  • IntroductionOne of the strongest high-latitude feedbacks is thought to be the ice–albedo feedback mechanism, in which a positive temperature perturbation will melt sea ice, lowering the surface albedo, increasing the absorbed solar radiation and causing a further temperature increase

  • Global climate is intimately connected to variability in the polar oceans

  • In our previous studies in the Antarctic Southern Ocean, the seasonal shallowing of mixed layer depth (MLD) was found to be critical to phytoplankton growth and the DMS production rate (Gabric et al, 2003); the mean MLD in the Barents Sea is shallow all year round, ranging from about 40 m during winter to less than 5 m in July–August (Fig. 2a)

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Summary

Introduction

One of the strongest high-latitude feedbacks is thought to be the ice–albedo feedback mechanism, in which a positive temperature perturbation will melt sea ice, lowering the surface albedo, increasing the absorbed solar radiation and causing a further temperature increase. This positive feedback on warming leads global climate models to find enhanced warming in the Northern Hemisphere polar regions in transient simulations with increasing atmospheric greenhouse gases (Houghton et al, 1996, 2001).

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