Meeting Documents

Using Data-Constrained Modeling to Examine the Drivers of Central Labrador Sea Oxygen Variability

Abstract

The subpolar region of the North Atlantic Ocean plays an important role in determining the oxygen inventory of the global deep ocean. In the Labrador Sea, strong surface winds and deep vertical mixing combine to rapidly subduct highly oxygenated surface waters to depth. These waters form the lightest components of the North Atlantic Deep Water, ventilating the intermediate and deep ocean as they travel along the Atlantic Meridional Overturning Circulation. Interannual variability in Labrador Sea deep convection––and the consequent oxygen saturation of the newly formed waters––thus poses major implications as global ocean oxygenation continues to decline.

To examine the primary drivers of present-day central Labrador Sea oxygen variability, we create a data-constrained oxygen budget using a coupled physical-biogeochemical ocean model (ASTE-BGC). ASTE-BGC physics are provided by the Arctic and Subpolar gyre sTate Estimate (ASTE), developed by using the adjoint data assimilation techniques of the Estimating the Circulation and Climate of the Ocean (ECCO) consortium to constrain the MIT general circulation model to O(106) physical data. The biogeochemical model coupled to this physical state estimate is the Biogeochemistry with Light, Iron, Nutrients, and Gas (BLING) model, which has been further constrained to O(105) BGC-Argo and ship-based biogeochemical observations using a Green’s functions approach.

As a dynamically consistent solution for the 3-D ocean state, we use ASTE-BGC to examine the time-varying contributions of air-sea gas exchange, biology, advective transport, and diffusive mixing to Labrador Sea oxygen content. The SeaCycler mooring, deployed over 2016-2017 in the central Labrador Sea, provides an independent data constraint on ASTE-BGC air-sea and biological fluxes. Co-locating the model and in-situ oxygen budgets in space and time reveals the dominance of air-sea gas exchange in setting the oxygen inventory of the central Labrador Sea.