Award: OCE-1129973

The ocean plays a fundamental role in regulating Earth's climate by acting as a vast store of CO2, the principal greenhouse gas in Earth's atmosphere. The amount of carbon-and other climatically important gases-stored in the ocean depends on the intricate interaction between the physical exchange of gas between air and water, ocean circulation and biology. These in turn are all complex and poorly understood processes that act on scales ranging from millimeters to thousands of kilometers and thus extremely difficult to represent in the computer models used to simulate climate and its future evolution. Our study uses a combonation of measurements and computer simulations to better our understanding of these processes and ultimately improve their representation and simulation in climate models. Specifically, we focused on noble gases which, because of their inert nature, are invaluable tracers of the physically driven processes that cycle gases in the ocean. We performed simulations of Ne, Ar, Kr, Xe and Ar36 and compared our model results with observations. One of the challenges of performing global simulations of this kind is that we're ultimately interested only in a seasonally repeating equilibrium distribution of gas concentrations. However, as ocean circulation is relatively slow it takes several thousand years of simulated time to reach this equilibrium making it computationally very expensive to carry out such calculations. To address this we developed and applied a novel computational method (known as matrix-free Newton-Krylov) that allows us to compute such periodic solutions quickly. Since this particular challenge arises in many scientific and engineering problems we believe this technique should be broadly useful in many other fields. Our particular simulations allowed us to isolate the effect of individual processes, including atmospheric pressure effects, the dissolution of gases at the surface and the effect of small bubbles in mediating transfer of gas between the air and seawater. We found that in high-latitude regions (e.g., around Antarctica), which are especially important for climate as they form the principal conduit for absorption of gases such as CO2, our model simulations showed the greatest disagreement with oceanic measurements of noble gases. This was true for a range of ocean circulation models suggesting that important deficiencies remain in how we model ocean physical processes at high latitudes with implications for simulating past and future oceanic uptake and storage of carbon. Last Modified: 11/30/2015 Submitted by: William M Smethie Jr.