Effects of climate change on methane emissions from seafloor sediments in the Arctic Ocean: A review

Rachael H James,Jacek Piskozub,Ira Leifer,Rolf Kipfer,Lisa Vielstädte,Ingeborg Bussmann,Philippe Bousquet,Jens Greinert,Helge Niemann,Tina Treude,Gregor Rehder,Matthias Haeckel,Ilia Ostrovsky

doi:10.1002/lno.10307

Abstract

AbstractLarge quantities of methane are stored in hydrates and permafrost within shallow marine sediments in the Arctic Ocean. These reservoirs are highly sensitive to climate warming, but the fate of methane released from sediments is uncertain. Here, we review the principal physical and biogeochemical processes that regulate methane fluxes across the seabed, the fate of this methane in the water column, and potential for its release to the atmosphere. We find that, at present, fluxes of dissolved methane are significantly moderated by anaerobic and aerobic oxidation of methane. If methane fluxes increase then a greater proportion of methane will be transported by advection or in the gas phase, which reduces the efficiency of the methanotrophic sink. Higher freshwater discharge to Arctic shelf seas may increase stratification and inhibit transfer of methane gas to surface waters, although there is some evidence that increased stratification may lead to warming of sub‐pycnocline waters, increasing the potential for hydrate dissociation. Loss of sea‐ice is likely to increase wind speeds and sea‐air exchange of methane will consequently increase. Studies of the distribution and cycling of methane beneath and within sea ice are limited, but it seems likely that the sea‐air methane flux is higher during melting in seasonally ice‐covered regions. Our review reveals that increased observations around especially the anaerobic and aerobic oxidation of methane, bubble transport, and the effects of ice cover, are required to fully understand the linkages and feedback pathways between climate warming and release of methane from marine sediments.

Highlights

Arctic and sub-Arctic marine sediments are thought to host vast reservoirs of methane stored in methane hydrate ( 100–9000 Gt C: Kvenvolden 1988; Biastoch et al 2011; Hunter et al 2013; Kretschmer et al 2015) and trapped beneath submerged permafrost either as hydrate, or as free gas ( 2–1400 Gt C: McGuire et al 2009; Shakhova et al 2010) (Table 1)
As high latitudes of the northern hemisphere are expected to experience a larger temperature increase than other regions due to climate change (IPCC 2013), there is a need to better understand the linkages between environmental variables and the processes that regulate methane emissions from Arctic marine sediments into the atmosphere (e.g., Biastoch et al 2011; Ferre et al 2012; Steinle et al 2015)
The Arctic Ocean and shelf seas are generally welloxidized so methane that escapes the sub-seafloor anaerobic oxidation of methane (AOM) filter and enters the water column is liable to be oxidized by methane oxidation (MOx) (Eq 2)

Summary

Introduction

Arctic and sub-Arctic marine sediments are thought to host vast reservoirs of methane stored in methane hydrate ( 100–9000 Gt C: Kvenvolden 1988; Biastoch et al 2011; Hunter et al 2013; Kretschmer et al 2015) and trapped beneath submerged permafrost either as hydrate, or as free gas ( 2–1400 Gt C: McGuire et al 2009; Shakhova et al 2010) (Table 1). Models of hydrate behaviour based on predictions of ocean warming offshore western Svalbard indicate that the seafloor methane flux from the continental slope and shelf region is likely to increase in future years (MarınMoreno et al 2013; Kretschmer et al 2015).

Results

Conclusion