Global Observations of Physical and Biogeochemical Processes in the Ocean

Abstract

We employ numerous global, or semi-global, datasets to observe the large-scale variability of physical and biogeochemical phenomena. In Chapter 1, we use Argo floats to estimate the vertical displacement of internal gravity waves. Internal wave intensity is found to be positively correlated with bathymetric roughness and proximity to the seafloor. The global variability of internal wave intensity also strongly resembles patterns of diapycnal diffusivity established by prior studies, suggesting breaking internal waves are largely responsible for abyssal mixing. In Chapter 2, we use Argo floats equipped with dissolved oxygen sensors to measure oxygen drawdown beneath the mixed layer, which is representative of respiration and remineralization of organic matter. We observe strong regional variability across the eight locations examined. Depth-integrated respiration is used as a lower-bound for organic carbon exported from the surface ocean. We find that carbon export and export efficiency is low at weakly seasonal locations, and high at strongly seasonal locations. In Chapter 3, we use a variety of datasets to construct composite averages of mesoscale eddy characteristics. By using repeat hydrography, we are able to estimate the nitrate anomaly within the interior of eddies. Additionally, satellite observations allow us to estimate the chlorophyll anomaly at the surface. By combining subsurface and surface observations, we examine how the nitrate anomaly covaries with the chlorophyll anomaly. Although our observations only allow us to explore global variability very coarsely, we find that the influence of mesoscale eddies on nutrients and chlorophyll is significantly different at low-, mid-, and high-latitude.