Impact of increasing inflow of warm Atlantic water on the sea‐air exchange of carbon dioxide and methane in the Laptev Sea

Abstract

The Laptev Sea is generally a sink for atmospheric carbon dioxide and a source of methane to the atmosphere. We investigate how sensitive the net sea-air exchange of carbon dioxide and methane in the Laptev Sea are to observed changes in the inflow of Atlantic water into the Arctic Ocean and in atmospheric conditions occurring after 1990. Using a time-dependent coupled physical-biogeochemical column model, both the physical and biogeochemical effects are investigated in a series of sensitivity experiments. The forcing functions are kept constant at 40 year climatological values except successively selected drivers that vary in time. Their effects are examined by comparing two periods, 1971-1989 and 1991-2009. We find that the flux of carbon dioxide is more sensitive to the increased Atlantic water inflow than the methane exchange. The increased volume transport of water in the Atlantic layer increases the ocean net uptake of carbon dioxide more than the warming of the incoming bottom water as the vertical advection is enhanced in the first case. The methane cycling is mainly affected by the increase in temperature, irrespective of whether the warming originates from the atmosphere or the incoming bottom water, causing increased outgassing to the atmosphere. In summary, our results suggest that the observed changes in the atmosphere and ocean potentially had a substantial impact on carbon dioxide uptake on the Siberian Shelf. However, the results suggest that the impact on the outgassing of methane might have been relatively modest compared to the interannual variability of sea-air fluxes of methane.

Methane cycling within sea ice: results from drifting ice during late spring, north of Svalbard

“…In general, methane excess in seawater could also originate from sediments. In our case, a potential source could have been the area west of Svalbard (Sahling et al, 2014;Smith et al, 2014;Westbrook et al, 2009). However, methane released from sediments are laterally transported in the deep ocean and do not reach the surface waters (Damm et al, 2005;Graves et al, 2015;Silyakova et al, 2020).…”

“…In particular, sea ice retreat may quickly induce enhanced methane (CH 4 ) emissions from the surface ocean into the atmosphere due to the loss of its barrier function for seaair gas exchange (Wåhlström and Meier, 2014). Moreover, the resulting decreased temporal flux retention of methane under the ice reduces oxidation intensity to the less potent CO 2 (Wåhlström et al, 2016). There is evidence that sea ice is crucial for Arctic methane cycling, e.g., as a vector for stored methane, transporting it to remote areas far away from its sources (Damm et al, 2018).…”

Seasonal methane dynamics in three different Siberian water bodies

“…In the Arctic, mean atmospheric methane mixing ratio increased by 6 ppb per year from 2001 to 2017 (Platt et al, 2018). Especially the Laptev Sea, in eastern Siberia, is generally a source of methane to the atmosphere, with a great interannual variability of sea-air fluxes of methane (Wåhlström et al, 2016). Also, Saunois 55 and co-authors estimated increased methane emission for freshwater systems and wetlands, but a better quantification of the emissions of different contributor (streams, rivers, lakes and ponds) is needed (Saunois et al, 2016).…”