Twenty-five years of Mercator ocean reanalysis GLORYS12 at Drake Passage: velocity assesment and volume transport

ARTANA CAMILA; FERRARI RAMIRO; C. BRICAUD; JAE HAK LEE; PARK, YOUNG-HYANG; CHRISTINE PROVOST

Congreso; OSTST virtual meeting; 2020

The volume transport of ACC through the Drake Passage (DP) is an important climatic index. However, the mean and variations of the transport are still under debate in spite of recent observational efforts (French DRAKE experiment, US cDrake experiment). Combining in situ (3 years of DRAKE current meter moorings) and satellite altimetric data a first 20-year long time series of the ACC volume transport at DP (1992?2012) in the upper 3000 m was obtained with a mean of 140 Sv (± 2.2 Sv), a standard deviation of 10 Sv (Koenig et al., 2014; 2016). In contrast, the mean total transport estimated from the near-bottom current meter records and C-PIES from cDrake, reached 173.3 ± 11 Sv over 4 years (Donohue et al., 2016). Velocities in Drake Passage from the 25-year GLORYS12 Mercator Ocean reanalysis were compared with satellite altimetry-derived surface velocities and independent in-situ velocity measurements from the DRAKE (2006?2009) and cDrake (2007?2011) experiments. GLORYS12 assimilates satellite along-track sea level anomalies and, as expected, model velocities are in rather good agreement with gridded altimetry derived velocities (r ~ 0.5, above 99% confidence level). GLORYS12 velocities also compared well with the currentmeter data from the DRAKE (in the water column) and cDrake (50 m above seafloor) experiments in terms of means and standard deviations; most correlations between the reanalysis and directly measured velocity time series were significant (r ~ 0.5 for DRAKE and r ~ 0.4 for cDrake, above 99% confidence level). We used the GLORYS12 reanalysis to examine the Antarctic Circumpolar Current (ACC) total volume transport across three sections in Drake Passage. The 25 years of the ACC total volume transport has a mean of 155 ± 3 Sv and a standard deviation of 6.7 Sv. Annual mean values span over a range of 12 Sv. The spectrum of the GLORYS12 total transport time series shows energy peaks (above 95% confidence level) at the intraseasonal, semi-annual and annual periods and no significant low-frequency variations (beyond 2 years) or trend, in agreement with previous studies. This first assessment of GLORYS12 velocities in Drake Passage is very encouraging for monitoring the regional variability of the ACC. We plan to further investigate the short-term variations and longer term (30 years) evolution of the fronts? intensity/location and ACC transport in Drake Passage using new satellite and model products (BACI proposal).