Changes in ventilation and anthropogenic carbon in the Nordic Seas and Arctic Ocean

Emil Jeansson1, Balamuralli Rajasakaren1, Toste S Tanhua2, Are Olsen3,4 and William M Smethie Jr5, (1)NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Bergen, Norway, (2)Helmholtz Centre for Ocean Research Kiel, GEOMAR, Kiel, Germany, (3)University of Bergen, Geophysical Institute, Bergen, Norway, (4)Bjerknes Centre for Climate Research, Bergen, Norway, (5)Lamont -Doherty Earth Observatory, Palisades, NY, United States
Abstract:
Changes in ventilation and anthropogenic carbon (Cant) are evaluated in the Nordic Seas and Arctic Ocean. The analysis uses data from the GLODAPv2.2019 data product – from the iconic Hudson cruise in 1982, to 2016 (Nordic Seas) – and including recent GEOTRACERS data in 2015 (Arctic Ocean). Mean ages and Cant were calculated from CFC-12 and SF6 using the transit-time distribution approach, and apparent oxygen utilization (AOU) was used together with mean age to evaluate ventilation changes.

The Greenland Sea has changed from a rather homogeneous and relatively well-ventilated water column in early 1980s, to a two-layer situation in the 2000s. The trend in AOU is here negative (positive) for the upper/intermediate (deep) waters, indicating stronger (reduced) ventilation. The changes in Cant inventory in the main Nordic Seas basins from 1982 to 1990s (mean) are very minor, and clearly below the atmospheric increase in CO2, while the mean inventories in the 2000s are significantly larger than the 1990s and markedly faster than the atmospheric change over the same period.

In the Arctic Ocean there is a significant negative trend in mean age in the waters connected to the Atlantic layer, being clearest closer to the inflow regions, indicating stronger advective ventilation of these layers. This ventilation signal gets progressively weaker along the circulation path of the boundary current. The inventory of Cant increased with 47–64% from 1987 to 2015 (Eurasian Basin), while an increase of 38% was seen in the Makarov Basin, from 1991 to 2015.