Understanding the responses of air‐sea carbon dioxide (CO₂) flux to rapid environmental changes in the highly productive Chukchi Sea is of great significance for the climate prediction in the Arctic Ocean. Through analyzing the 1998–2015 hindcast simulation of a coupled ocean–sea ice–biogeochemical model, this study identifies that the key factors influencing oceanic carbon uptake in the Chukchi Sea vary seasonally. The effects of these seasonal carbon uptakes on the total annual carbon sink vary at different timescales. The model solution suggests that the Chukchi Sea acts as a perennial carbon sink of atmospheric CO₂ with the annual mean influx of −3.73 ± 3.90 mmol m⁻² d⁻¹. Quantitative analyses reveal that the sea ice concentration predominates the annual cycle of air‐sea CO₂ flux, while primary production and wind speed strengthen the capacity for carbon uptake during June–July (melt season) and October–December (freeze season), respectively. The total annual carbon sink shows an increasing trend during 1998–2015 with a multi‐year average of 9.22 ± 1.93 Tg C y⁻¹. The carbon uptakes during June–July and August–September (open water season), which are respectively regulated by primary production and open water area at interannual scale, present significant long‐term increases and jointly determine the secular increase trend of the total annual carbon sink. Interannual CO₂ absorption during the freeze season is sensitive to the sea ice concentration and wind conditions, presenting the greatest year‐to‐year variation but insignificant long‐term trend, and modulates the interannual amplitude of the total annual carbon sink.

This study reveals that the yearday of open‐water onset (t_open) in Bering Strait can be predicted with a lead time of about 4 months using a regression equation t_open = 37.45C_CN + 125.2 (in Julian days), with an averaged absolute error of 5 days and the maximum error of 12 days, where C_CN is the ice concentration averaged from 16th January to 15th February near Cape Navarin. This “predictor” is revealed through analyzing the solution of a regional ocean and sea‐ice model. A key factor contribution to the prediction is that the prior winter ice concentration is controlled by the sea surface temperature, and persists into the start of the melting phase near the marginal ice zone in the Cape Navarin area. As ice melts near Cape Navarin, successive melting due to solar heat absorption and lateral heat transport occurs rapidly downstream along Anadyr Current.

The expansion of dissolved inorganic carbon (DIC)-rich water carried by the Pacific inflow creates a DIC maximum layer and exerts important influences on ocean acidification in the subsurface Arctic Ocean. This study analyzed shifts in the DIC distribution of the subsurface Arctic Ocean during 1998–2015 through hindcast simulation using a three-dimensional ocean-sea ice-biogeochemical model. For this purpose, the study was divided into two time periods (1998–2007 and 2008–2015). The results showed that the lower boundary layer of the Pacific Winter Water, defined as an isopycnal of 27 kg m⁻³, became deeper by ∼50 m in the central Canada Basin and expanded northward during 2008–2015 relative to 1998–2007. Accordingly, the subsurface DIC maximum layer deepened and expanded northwards into the Makarov Basin at high latitudes around 85° N. During 2008–2015, DIC concentrations, averaged over a 50–250 m water column, increased significantly in the Chukchi-East Siberian Shelfbreak and Makarov Basin. The DIC increase over the shelfbreak is mainly attributable to increased local biological degradation and the transportation of DIC-rich water from the Chukchi Shelf through Barrow Canyon. Estimates of the DIC budget indicated that advection controlled the increase in DIC content in the Makarov Basin during 2008–2015. This is attributed to the shift of the ocean circulation pattern, in which the ocean current along the Chukchi-East Siberian Slope to the Makarov Basin became stronger during 2008–2015, promoting the transport of DIC-rich Pacific Water into the Makarov Basin.