The large meander of the Kuroshio western boundary current is well known to influence the local climate, fisheries, and aquaculture by greatly modulating regional heat transport, but its impacts on biogeochemical processes remain unclear. Using high-resolution numerical ocean modelling and long-term observational datasets, we show that the path of the Kuroshio determines the extent of the shallow nutricline region, where winter convective mixing replenishes nutrient availability for subsequent blooms of phytoplankton during spring. During the large meander phase, this mechanism triggers offshore phytoplankton blooms that are otherwise absent during the non-large meander phase. The large meander also modulates the spatial distributions of primary production, air-sea carbon flux, and export production. These biogeochemical impacts of the Kuroshio large meander exert bottom-up control on regional marine ecosystems that is disproportionate to the thermal effect, and therefore need to be assessed to understand the large meander's overall impacts on fisheries and aquaculture.

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.