Dimethyl sulfide dynamics in first-year sea ice melt ponds in the Canadian Arctic Archipelago

Margaux Gourdal,Maurice Levasseur,Michel Gosselin,Guillaume Massé,Michael Scarratt,Joannie Charette,Martine Lizotte,Michel Poulin

doi:10.5194/bg-15-3169-2018

Abstract

Abstract. Melt pond formation is a seasonal pan-Arctic process. During the thawing season, melt ponds may cover up to 90 % of the Arctic first-year sea ice (FYI) and 15 to 25 % of the multi-year sea ice (MYI). These pools of water lying at the surface of the sea ice cover are habitats for microorganisms and represent a potential source of the biogenic gas dimethyl sulfide (DMS) for the atmosphere. Here we report on the concentrations and dynamics of DMS in nine melt ponds sampled in July 2014 in the Canadian Arctic Archipelago. DMS concentrations were under the detection limit (< 0.01 nmol L−1) in freshwater melt ponds and increased linearly with salinity (rs = 0.84, p ≤ 0.05) from ∼ 3 up to ∼ 6 nmol L−1 (avg. 3.7 ± 1.6 nmol L−1) in brackish melt ponds. This relationship suggests that the intrusion of seawater in melt ponds is a key physical mechanism responsible for the presence of DMS. Experiments were conducted with water from three melt ponds incubated for 24 h with and without the addition of two stable isotope-labelled precursors of DMS (dimethylsulfoniopropionate), (D6-DMSP) and dimethylsulfoxide (13C-DMSO). Results show that de novo biological production of DMS can take place within brackish melt ponds through bacterial DMSP uptake and cleavage. Our data suggest that FYI melt ponds could represent a reservoir of DMS available for potential flux to the atmosphere. The importance of this ice-related source of DMS for the Arctic atmosphere is expected to increase as a response to the thinning of sea ice and the areal and temporal expansion of melt ponds on Arctic FYI.

Highlights

Melt ponds represent an important but understudied component of the Arctic sea ice system
Rösel et al (2012) reported a 15 % increase of the relative melt pond fraction for the month of June during the last decade (2001–2011) in the Arctic, most likely attributable to global climate change. This partly reflects the progressive replacement of multi-year sea ice (MYI) by first-year sea ice (FYI) observed since the 1980s (National Snow and Ice Data Center, NSIDC, http://nsidc.org, last access: June 2017), favouring the formation of shallow melt ponds that spread over increasingly large areas (Agarwal et al, 2011; Ehn et al, 2011)
Results from the Ice3-MP1 experiments are not presented since DMSPd and dimethyl sulfide (DMS) concentrations showed no variation during the 24 h incubation period in the controls and in the amended treatments

Summary

Introduction

Melt ponds represent an important but understudied component of the Arctic sea ice system. Rösel et al (2012) reported a 15 % increase of the relative melt pond fraction for the month of June during the last decade (2001–2011) in the Arctic, most likely attributable to global climate change. This partly reflects the progressive replacement of multi-year sea ice (MYI) by FYI observed since the 1980s (National Snow and Ice Data Center, NSIDC, http://nsidc.org, last access: June 2017), favouring the formation of shallow melt ponds that spread over increasingly large areas (Agarwal et al, 2011; Ehn et al, 2011). The importance of melt ponds in the Arctic, as a water–air interface involved in heat and gas exchanges, is expected to increase in the future

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Discussion

Conclusion