On the Seasonal Western Boundary Current System of the Weddell Gyre
Authors: Pereira-Vázquez Tania , Aguiar-González Borja , Marrero-Díaz Ángeles , Veny Marta , Rodríguez-Santana Ángel 
Published: May 2024

Abstract. We investigate the seasonal Western Boundary Current System (WBCS) of the Weddell Sea Gyre using two open-access global ocean circulation reanalysis products (NEMO and HYCOM at different resolutions), direct velocity measurements and altimetry data across an extended version of the historical ADELIE transect, hereafter E-ADELIE. The NEMO-based products are GLORYS2V4 and GLORYS12V1, provided daily with 0.25º and 0.08° of horizontal resolution, respectively. The HYCOM-based product is GLBv0.08, provided daily with 0.08º of horizontal resolution between 40° S and 40° N, and 0.04º beyond these latitudes. The ADELIE extension is made to include a novel, persistent current, previously unreported, which we name as the Inner Weddell Current (IWC). With this approach, we aim to assess whether these open-access products capture properly the dynamics, natural mode of variability and spatio-temporal scales of the WBCS so that we can set the groundwork for future interannual variability studies. E-ADELIE is located at a key location of the WBCS, before it splits into different branches that redistribute Weddell Sea waters either leaving the basin towards Bransfield Strait, towards the South Atlantic Ocean, or recirculating within the gyre. The analyses include the characterization of the horizontal and vertical structure of the WBCS and its volume transport. Results show that both reanalysis products agree on key dynamics features only at high model resolutions; NEMO at the lower-resolution version lacks the typical multi-jet structure of the WBCS. The altimetry data is also in agreement in showing this year-round multi-jet structure but in winter, when data gaps prevent us from a comprehensive view. The cross-transect volume transport variability from the reanalysis products is consistent with the seasonality of the basin scale wind forcing in all model cases, with minimum values (25 ± 5 Sv) from September to December and maximum values (33 ± 5 Sv) from March to July. Also, the time-averaged transport aligns at approximately 30 ± 5 Sv in all products. Major discrepancies exist towards the interior of the gyre, where the IWC differs strongly among reanalysis products. The IWC is found about 50 km east of the Weddell Front extending up to 600 Km offshore, standing out as a bottom-reaching, broad current transporting ~14±3 Sv in NEMO and ~39±5 Sv in HYCOM. According to available Shipboard Acoustic Doppler Current Profiler (SADCP) measurements from two different surveys, LG0003a and NBP0106, we find the IWC surface volume transport (0–300 m depth) is about 6.67 Sv and 7.64 Sv, respectively between 400 and 720 km offshore the Antarctic Peninsula. When computing the same estimates from the reanalysis products, we obtain lower volume transports values ranging from 2–4 Sv. Results from this study suggest that the high-resolution version of NEMO (GLORYS12V1) approaches the real ocean in the western Weddell Sea the closest when compared to observations and literature. These results open the avenue for future research investigating the variability of the WBCS of the Weddell Gyre at interannual scales at a key location for water mass exchange between ocean basins.