Borealization of the Arctic Ocean in Response to Anomalous Advection From Sub-Arctic Seas

Abstract

Borealization of the Arctic Ocean future suggests that Arctic borealization will continue under scenarios of global warming. Results from this synthesis further our understanding of the Arctic Ocean's complex and sometimes non-intuitive Arctic response to climate forcing by identifying new feedbacks in the atmosphere-ice-ocean system in which borealization plays a key role.

Understanding Regional and Seasonal Variability Is Key to Gaining a Pan-Arctic Perspective on Arctic Ocean Freshening

“…Implicit in these works is often the presumption of homogeneity in the lateral, vertical and temporal distributions of photosynthesizing species, and more-or-less uniform conditions of nutrient availability. The second involves the northward invasion of subarctic species or borealization (e.g., Polyakov et al, 2020). Implicit in these works is the presumption that new species entering local food webs take on the ecological function of the species they replace, with minimal cascading effects, and that regionality plays no constraining role.…”

“…Freshening has been shown to have contributed to ML shoaling over the last three decades, with a larger impact observed in winter than in summer, and in the AB (20-40 m) compared to the EB (10 m; Peralta-Ferriz and Woodgate, 2015;Wang et al, 2019). And these extreme differences in stratification between the AB and EB may continue to diverge into the future (Polyakov et al, 2020). As FW is removed from the ML by sea ice formation over winter, the insulating effects of the sea ice cover progressively limit heat loss to the atmosphere (Rudels et al, 1996) and reduce winddriven mixing, whereas penetrative convection by brine rejection helps to mix and homogenize the upper water column (Figure 3).…”

“…Arrigo and van Dijken, 2015) at least until surface nutrient supplies are depleted (e.g., Vancoppenolle et al, 2013;Slagstad et al, 2015). Atlantic waters are anticipated to continue to warm and the redistribution of boreal species along this warming gradient will contribute to the "borealizetion" of the Arctic along the Atlantic water flow path (Polyakov et al, 2020). Sea ice retreat from the shelves will increase wind-driven shelf-basin exchange, thus contributing to increased nutrient fluxes and increased currents.…”

“…Much of the future freshening of the AO will be observable in the central basins (Canada, Makarov, and Amundsen;Shu et al, 2018), and as such, the deep Arctic basins will continue to diverge, with the AB further stratifying and the EB becoming less so (Polyakov et al, 2020). Further stratification in the AB may push primary producers further from the surface away from light toward exploitable nutrients (cf.…”

“…For example, an intensified hydrological cycle is anticipated to follow in a warming climate, and with sea ice decline, a greater fraction of the internal FW burden now cycles seasonally between the solid (ice) and liquid (halocline) lids, the latter of which has both a seasonal and perennial structure, as emphasized here. Further, it is now established that responses to climate change are decidedly regional, and that effects will be felt disproportionally among seasons (Polyakov et al, 2017(Polyakov et al, , 2018(Polyakov et al, , 2020. We focus here on these two "lids" as a central location for FW exchanges and cycling on seasonal and regional time and space scales, with particular emphasis on the upper ocean.…”