Krissy Reeve

• The Weddell Gyre (WG) supplies heat towards the Antarctic ice shelves and regulates the density of water masses that feed the deepest limb of the global overturning circulation. Our understanding of WG hydrography is limited due to sparse data availability. Long-term trends are masked by significant variability, and previous estimates show a large range in the strength of the WG’s circulation. In this thesis, Argo float profile and trajectory data spanning the WG from 2002-2016 are utilised to determine the horizontal circulation and heat distribution within Warm Deep Water (WDW): the primary heat source to the WG. Objective mapping is applied, providing maps of temperature and salinity for 50-2000 dbar. The stream function is obtained, from which horizontal circulation is described. Volume transports are calculated and placed into context of historical estimates. The heat budget for a 1000 m thick layer encompassing the core of WDW is presented, to investigate mechanisms of heat distribution throughout the WG. The circulation describes an elongated, cyclonic, double-cell gyre. The weaker western cell is barotropic and the stronger eastern cell is influenced by baroclinic shear. There is an inflow of 83 ± 22 Sv into the WG (28 ± 7 Sv WDW). Significant recirculation in the gyre interior is observed (71 ± 28 Sv, 15 ± 8 Sv is WDW). The large variation in previous estimates of the WG strength is likely due to zonal variation in the gyre structure. There is a balance between mean horizontal advection and horizontal turbulent diffusion (representative of eddy processes). Heat is turbulently diffused northward from the southern limb into the interior cell (6.5 ± 3 TW), and coastward towards the ice shelves (inferred as 12.5 ± 10 TW). One outstanding question concerns the response of the double-cell circulation to long-term changes in the wind field, and how this might alter the mechanisms by which heat is injected into and subsequently redistributed throughout the WG.