Presenter: Lauren Moseley (Lamont-Doherty Earth Observatory of Columbia University)

Description:
The subpolar North Atlantic (SPNA) is one of the most intense regions of air-sea gas exchange in the global ocean. In the SPNA, deep convection produces highly-oxygenated water masses which form the densest components of the Atlantic Meridional Overturning Circulation. The circulation of these waters ventilates the intermediate and deep waters of the North Atlantic and regulates the oxygen inventory of the global ocean. However, we still lack critical knowledge about how SPNA oxygen has varied over the past few decades and how this relates to changes in water mass properties and circulation. While many ocean models predict substantial oxygen loss as global warming intensifies, the strength of these predictions often varies widely from model to model. To better quantify the current trajectory of ocean oxygen and more rigorously evaluate climate models, we must develop a mechanistic understanding of how space-time variability in SPNA convection impacts oxygen saturation in intermediate and deep waters. We address this need by using the regional Arctic Subpolar gyre sTate Estimate (ASTE), which is based on the MIT General Circulation Model (MITgcm) and assimilates physical in-situ and satellite data using tools developed by the Estimating the Circulation and Climate of the Ocean (ECCO) consortium. We couple ASTE to a biogeochemical model (BLING) to simulate the response of ocean ecology and carbon chemistry to the physical state. In this study, we use a Green’s functions approach to optimize model initial conditions and biogeochemical parameters; this optimization is constrained by BGC-Argo dissolved oxygen, nitrate, and chlorophyll-a profiles for the 2002-2017 model period. We then construct a three-dimensional oxygen budget that provides crucial insight into the importance of air-sea exchange as the primary driver of the seasonality and variability of the SPNA oxygen cycle.