Changing sea ice conditions have led to increases in net primary production (NPP) in the northern Chukchi Sea, driven in part by massive under‐ice phytoplankton blooms. These blooms increase particle export to the sediments and could affect the rate of sedimentary denitrification. We use a 1‐D coupled ecosystem model forced with satellite‐derived sea ice conditions to quantify changes in particle export, nitrification, and denitrification on the northern Chukchi shelf. Between 1988 and 2018, increases in annual NPP drove secular increases in particle export to the benthos (1.8 ± 0.8 mmol m−2 yr−1), water‐column and sedimentary nitrification (1.2 ± 0.4 and 1.1 ± 0.4 mmol m−2 yr−1, respectively), and sedimentary denitrification rates (1.3 ± 0.5 mmol m−2 yr−1). Increased annual export to the benthos and denitrification were driven by higher rates early in the year (from January to June) and are highest in years where under‐ice blooms (UIBs) dominate. Greater denitrification rates in the northern Chukchi Sea would likely reduce NPP in downstream regions such as the Greenland Sea and promote greater N2 fixation in the North Atlantic. Furthermore, sea ice loss and a change in advection of nitrogen (N)‐replete waters through the Bering Strait will likely increase winter N concentrations in the northern Chukchi Sea. Through N sensitivity experiments, we found that 30% of all added N was lost through denitrification, diminishing the N supply available downstream of the Chukchi Sea. Thus, increased particle export associated with UIBs has the potential to markedly alter the N cycle both in the northern Chukchi Sea and in adjacent waters.

As Arctic sea ice has thinned and begun to retreat earlier in the year, there have been substantial changes in the timing and magnitude of regional net primary production (NPP). Most notably, field, remote sensing, and model‐based studies have demonstrated that massive under‐ice phytoplankton blooms (UIBs) contribute substantially to annual NPP and can even drive increases in sedimentary nitrogen recycling and loss through coupled partial nitrification‐denitrification. In this study, we used a 1‐D biogeochemical model (CAOS‐GO) to compare the magnitude of NPP associated with UIBs in the northern and southern Chukchi Sea between 1988 and 2018. While UIBs were critical in driving interannual variation and secular increases in annual NPP and sedimentary nitrification and denitrification in the northern Chukchi Sea, UIBs were far less important at our southern site. As the length of the under‐ice (UI) period diminished between 1988 and 2018 in the southern Chukchi Sea, there was a decrease in the amount of NPP produced during the UI period. Despite higher rates of both annual NPP and denitrification at the southern site, there were no secular trends in these rates over time. Our results indicate that, as sea ice continues to retreat earlier, the impact of UIBs on the biogeochemistry of the Chukchi Sea is likely to diminish.