Table 3 ESAS CH4 sea-air flux results and comparisons with earlier studies.

Annual EC fluxes assume that 100% of CH4 trapped in or under ice for part of the year eventually reaches the atmosphere. The whole-ESAS CH4 emission estimate from EC fluxes is lower than estimates given in three earlier measurement-based studies (2, 4, 24), shown at the bottom of this table. Part of this difference is due to the inclusion of the Chukchi Sea in the present study, which accounts for 29.4% of the ESAS area and had markedly lower sea-air fluxes than the Laptev or East Siberian seas, the two seas that the earlier three studies based their results solely on. Inclusion of low flux observations from the Chukchi Sea in the earlier measurement-based studies could have reduced pan-ESAS areal flux estimates in all of them. The flux values in (24) were reported in Tg- C- CH4 year1 and have been converted to Tg CH4 year1 here in Table 3. Extrapolating the whole-ESAS fluxes from only our observed Laptev Sea and East Siberian Sea regional fluxes, as in previous studies (2, 4, 24), we obtain the slightly higher annual CH4 flux estimate of 2.43 mg m−2 day−1 or 2.07 Tg year1. This is still the lowest whole-ESAS value yet reported based on in situ measurements but is closest to the recent bulk flux measurement from the same cruise (Table 3) and is within the range of the only inverse modeling study for the ESAS region (3). The highest value, 4.65 Tg year−1, is obtained by combining the data of (2, 24) for depths <35 m with (4) for deeper waters and accounting for bubble losses using the model of (9). Estimating small fluxes possibly missed by the EC system due to the EC noise levels, we add 1.53 Tg year1 to our total (see text for explanation). This is our best estimate for pan-ESAS CH4 fluxes based on SWERUS-C3 data alone and is close to the 2.9 Tg year−1 of (4).

Shelf Sea*Sea area (×103 km2)Calculated
bulk flux
(mg m−2 day−1)
(EC) CH4 flux
(mg m−2 day−1)
Annual (EC)
CH4 flux
(Tg year−1)
Laptev4983.904.580.83
East Siberian9873.7 (13.8)1.740.62
Chukchi620No data0.140.03
ESAS21051.941.49
ESAS (extrapolation without
Chukchi data as in previous
studies)
14853.8 (12.3)2.432.07
ESAS [EC + estimated flux in
EC noise (present study)]
21053.02
ESAS [0- to 35-m depth range
based on (24) and (2) +
depth-based bubble
dissolution model; >35-m
depths based on (4)].
21054.65
Previous studies (method used)
Areal fluxAnnual flux
ESAS (3) (inverse model)0–5.90–4.5
ESAS (2) (ebullition only; bubble counting with sonar)22.19§
ESAS (24) (various measurements, primarily surface water concentrations)13.910.6
ESAS (4) (surface water and atmospheric concentrations; Laptev and East Siberian seas only)3.82.9

*Sea areas defined as in (7).

†Calculated bulk fluxes are from data presented in (4).

‡Calculated bulk flux values in parentheses include ice-covered areas, where calculated fluxes are hypothetical, and may represent temporary ice-out fluxes.

§Total ESAS annual CH4 flux including diffusive emissions was reported as 17 Tg year−1 in (2).