Abstract
As a contribution to the Regional Carbon Cycle Assessment and Processes
phase 2 (RECCAP2) project, we present synthesized estimates of Arctic
Ocean sea-air CO2 fluxes and their uncertainties from 8 surface ocean
pCO2-observation products, 18 ocean biogeochemical hindcast and data
assimilation models and 6 atmospheric inversions. For the period of
1985−2018, the Arctic Ocean was a net sink of CO2 of 116 ± 4 TgC yr−1 in
the pCO2 products and 92 ± 30 TgC yr−1 in the models. The CO2 uptake
peaks in late summer and early autumn, and is low in winter when sea ice
inhibits sea-air fluxes. The long-term mean CO2 uptake in the Arctic
Ocean is primarily caused by steady-state fluxes of natural carbon (70 ±
15 %), and enhanced by the atmospheric CO2 increase (19 ± 5 %) and
climate change (11 ± 18 %). The annual mean CO2 uptake increased from
1985 to 2018 at a rate of 31 ±13 TgC yr−1dec-1 in the pCO2 products and
10 ± 4 TgC yr−1dec-1 in the models. Moreover, 77 ± 38 % of the trend in
the net CO2 uptake over time is caused by climate change, primarily due
to rapid sea ice loss in recent years. Both, the mean CO2 uptake and the
trend, is substantially weaker in the atmospheric inversions.
Uncertainties across all estimates are large, in the pCO2 products
because of scarcity of observations and in the models because of missing
processes.