Ocean acidification trends and carbonate system dynamics across the North Atlantic subpolar gyre water masses during 2009-2019

Abstract

The CO2-carbonate system dynamics in the North Atlantic subpolar gyre (NASPG) were evaluated between 2009 and 2019. Data were collected aboard eight summer cruises through the Climate and Ocean: Variability, Predictability and Change (CLIVAR) 59.5 degrees N section. The ocean acidification (OA) patterns and the reduction in the saturation state of calcite (Omega(Ca)) and aragonite (Omega(Arag)) in response to the increasing anthropogenic CO2 (C-ant) were assessed within the Irminger, Iceland, and Rockall basins during a poorly assessed decade in which the physical patterns reversed in comparison with previous well-known periods. The observed cooling, freshening, and enhanced ventilation increased the interannual rate of accumulation of C-ant in the interior ocean by 50 %-86 % and the OA rates by close to 10 %. The OA trends were 0.0013-0.0032 units yr(-1) in the Irminger and Iceland basins and 0.0006-0.0024 units yr(-1) in the Rockall Trough, causing a decline in Omega(Ca) and Omega(Arag) of 0.004-0.021 and 0.003-0.0013 units yr(-1), respectively. The C-ant-driven rise in total inorganic carbon (C-T) was the main driver of the OA (contributed by 53 %-68 % in upper layers and > 82 % toward the interior ocean) and the reduction in Omega(Ca) and Omega(Arag) (> 64 %). The transient decrease in temperature, salinity, and A(T) collectively counteracts the C-T-driven acidification by 45 %-85 % in the upper layers and in the shallow Rockall Trough and by < 10 % in the interior ocean. The present investigation reports the acceleration of the OA within the NASPG and expands knowledge about the future state of the ocean.