Oligotrophic Trend following surface freshening in the western Arctic Ocean basin

Observations between 1994 and 2018 show that nitrate-depleted waters thickened and expanded northward in the western Arctic Ocean during this time, following a freshening trend in surface waters. Abrupt deepening of nitrate-depleted waters occurred in the Beaufort Gyre during 2005–2009 and throughout the western Arctic Ocean during 2008–2010. Owing to freshwater convergence associated with the anticyclonic Beaufort Gyre, the expansion of nitrate-depleted water is estimated to have occurred earlier in the Beaufort Gyre than in the western Arctic Ocean. The oligotrophic trend would have had a profound influence on observed ecosystem trends and related biogeochemical processes. This means that the Beaufort Gyre can be referred to as the “precursor” for the biogeochemical events response to freshening in the western Arctic Ocean.