Two Decades of Ross and Weddell Gyre Variability From Observations

Abstract The Weddell and Ross Gyres influence climate‐relevant processes including poleward heat transport, nutrient upwelling and carbon sequestration. However, long‐term tracking of changes to their circulation is limited by the sparsity of observations characteristic of the region. Here we present observational estimates of gyre strength and area over 2003–2023 using satellite altimetry and gridded hydrographic products. We find that strength and area co‐vary across different timescales. The Weddell Gyre has an annual cycle with an amplitude of 20 Sv and a late‐autumn maximum dominating month‐to‐month changes. This gyre also displays a strengthening trend of 0.9 Sv per year until 2015. The Ross Gyre has an annual cycle peaking in late autumn with an amplitude of 10 Sv, but its variability is dominated by interannual changes (7 Sv). Analysis using an ocean‐sea ice model suggests our estimates likely capture >87% and >66% of the variability of the Weddell and Ross Gyres.