How does the Labrador Sea take inputs from the Atlantic and a melting Arctic, modify them via atmospheric exchange and local physical and biogeochemical processes to thereby influence the export products that influence the global ocean and climate?
In most of the oceans, the biological pump is the principal process connecting the surface and the deep ocean. However the Labrador Sea is a rare exception, with a solubility pump bringing surface carbon directly and rapidly to the deep ocean, and its high-density waters, through convective mixing. This Labrador Sea water, which contains high anthropogenic CO2 and oxygen then spreads over the rest of the North Atlantic, partially via a fast track in Deep Western Boundary Current and partly through interior pathways. Deep convection may also be highly relevant to the exchange of other biogenic/thermogenic trace gases, such as N2O.
Using novel time-series measurements of multiple gases with differing exchange characteristics and responses to biological activity, as well as numerical modelling, we will consider a large range of temporal scales from minutes to decades, and thus we will estimate the rates of gas exchange, differentiate the roles of physical, chemical and biological processes on gases fluxes and redistribution, and determine the impacts of stratification, re-stratification and lateral exchange on the "breathing" process. These results will also provide key information concerning the potential responses of photosynthesis, organic carbon export, and microbial respiration to warming, increased acidity, and changing regional nutrient sources.
How does lateral boundary/interior exchange, especially of freshwater, control and potentially limit the 'breathing'? Freshwater influences stratification, mixing (via instability processes, eddy exchanges, thermohaline intrusions) and thus biology, air-sea gas exchange at the sea surface, and biogeochemistry of the central Labrador Sea. Entry points for freshwater from the Labrador shelf will be investigated, as well as the horizontal transport directly influencing the central Labrador Sea, with a focus on understanding the processes controlling their evolution. We will then represent these processes in high resolution eddy-permitting models.
How can we improve the ability of high-resolution numerical models to represent this "breathing" through its controlling processes, and its sensitivity to climatic change? Eddy-resolving numerical models need a better representation of high-frequency (daily to seasonal) and small-scale (sub-mesoscale to mesocale) processes to resolve regional water and gas exchanges. We will test models against long-term data from the DFO monitoring program, and against the high-frequency data revealed by the central mooring coupled with gliders. We will couple the physical models with biophysical and biogeochemical ones and explore the spatial and process dynamics of the system. We will work to get consistent rates of CO 2 and oxygen uptake between eddy-resolving numerical models and those using resolutions typical of climate models and thus improve short-term (sub-decadal), as well as longer-term, climate predictability.