Abstract
Abstract. Summer sea ice cover in the Arctic Ocean has declined sharply during the last decades, leading to changes in ice structures. The shift from thicker multi-year ice to thinner first-year ice changes the methane storage transported by sea ice into remote areas far away from its origin. As significant amounts of methane are stored in sea ice, minimal changes in the ice structure may have a strong impact on the fate of methane when ice melts. Hence, sea ice type is an important indicator of modifications to methane pathways. Based on measurements of methane concentration and its isotopic composition on a drifting ice floe, we report on different storage capacities of methane within first-year ice and ridged/rafted ice, as well as methane supersaturation in the seawater. During this early melt season, we show that ice type and/or structure determines the fate of methane and that methane released into seawater is a predominant pathway. We suggest that sea ice loaded with methane acts as a source of methane for polar surface waters during late spring.
Highlights
Sea ice is an important component of the Arctic system that plays a significant role for gas exchange between ocean and atmosphere (Parmentier et al, 2013)
Ridged and rafted ice types can be especially relevant for the methane cycling due to the fact that they remain more consolidated even in the melt season and allow us to investigate methane-related processes in certain layers of these ice structures
The type and structure of Arctic sea ice affect the capacity for methane storage (Fig. 9)
Summary
Sea ice is an important component of the Arctic system that plays a significant role for gas exchange between ocean and atmosphere (Parmentier et al, 2013). One major sea ice formation area in the Arctic Ocean is the Siberian shelf (Mysak, 2001), constituting a significant source of methane (Shakhova et al, 2010). The methane reservoir estimate in the East Siberian and Laptev seas ranges from 1.6 and 5.7 Gg CH4 in the seawater, varying by season and depending on the ice cover (Shakhova et al, 2005; McGuire et al, 2009). In these shallow shelf seas, methane released from the sediment may be entrapped in sea ice during ice formation (Damm et al, 2015). After its formation on the Siberian shelves, sea ice loaded with methane is transported by the wind away from the source area and towards Fram Strait by the Transpo-
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