PHANTOM : On the ACC between 160°W and 40°W

Camila Artana (Mercator Océan, France)


Camila Artana (Mercator Océan, France); Christine Provost (LOCEAN, Sorbonne Université, CNRS, France); Young-Hyang Park (LOCEN, Sorbonne Université,MNHN, France); Nathalie Sennéchael (LOCEAN, Sorbonne Université, MNHN, France); Lea Poli (LOCEAN, Sorbonne Université, France); Isabelle Durand (LOCEAN, Sorbonne Université, MNHN, France); Clement Bricaud (Mercator Océan, France); Jean-Michel Lellouche (Mercator Océan, France); Giles Garric (Mercator Ocean, France); Marie Helene Rio (ESA, France); Isabelle Pujol (CLS, France); Maxime Ballarotta (CLS, France); Ramiro Ferrari (CIMA UMI IFAECI, France); Jae-Hak Lee (KIOST, Korea); Taewook Park (Kopri, Korea); Tae-Wan Kim (kopri, Korea); SH Lee (Kopri, Korea); CS Hong (Kopri, Korea)

Event: 2020 Ocean Surface Topography Science Team Meeting (virtual)

Session: Salient results from the 2017-2020 OSTST PIs

Presentation type: Type Forum

Phantom activities concentrated on the Antarctic Circumpolar Current (ACC) pathways and strength between 160°W and 40°W, with a focus on the Udintsev Fracture Zone (144°W) in the South Pacific Ocean, Drake Passage (DP, 80°W-40°W), and the Malvinas Current (MC) region marking the northernmost extent of the ACC (60°W-40°W). We combined satellite altimetry and in situ data, model outputs in collaboration with Mercator-Ocean and CLS. International cooperations were carried out with Korea (KOPRI and KORDI) and Argentina (UMI IFAECI).
An up‐to‐date map of the ACC fronts (Park et al., 2019) was constructed from the CNES-CLS MDT18 (Rio et al., 2020). The ACC is narrowest in the Udintsev Fracture Zone (UFZ), with a concentration of the three major ACC fronts within a distance as short as 170 km, about 40% narrower than that at Drake Passage. In situ observations from two recent cruises on board Korean icebreaker Araon at 144°W confirmed the satellite altimetry‐derived frontal circulation in the UFZ region and yielded a baroclinic transport relative to the bottom of 113 Sv, as in DP.
The volume transport of ACC through the DP is an important climatic parameter. However, the mean and variations of the ACC transport are still under debate in spite of recent observational efforts (French DRAKE experiment, US cDrake experiment). GLORYS12 velocities compared well with the current-meter data from the DRAKE (in the water column) and cDrake (50 m above seafloor) in terms of means and standard deviations; most correlations between the reanalysis and measured velocity time series were significant. The 25 years of the ACC total volume transport has a mean of 155 ± 3 Sv and a std of 6.7 Sv and no significant trend (Artana et al., 2019).
We also used GLORYS12, to estimate the ACC transport through the Udintsev and Eltanin Fracture Zones. GLORYS12 reproduces well the vertical structure of the ACC (significant velocity correlations with observations). The mean ACC transport is 155 +-3 SV with a std of 7 Sv, same as in DP (Park et al., in prep). Monthly transport streamfunction was calculated in the central South Pacific region (40°-65°S, 160°-250°E) for 1993-2019; its first EOF is anticorrelated with ENSO while EOF2 is correlated with the SAM. The negative ENSO is associated with a strengthening of (altimetry-derived) surface currents along the northern boundary of the ACC, while the SAM mode strengthens the central branches of ACC. The combination of these two EOFs reproduces well (r = 0.5) the low frequency (> 3 months) variability of the ACC in the South Pacific sector upstream DP (Park et al., in prep).
We revisited the Malvinas Current (MC) from DP to the Brazil-Malvinas Confluence (BMC), one of the most energetic regions of the world ocean. In contrast to the BMC and DP, the MC exhibits a moderate eddy kinetic energy (EKE), as EKE from the DP leaks through deep passages and dissipates over the Malvinas Plateau, a hotspot for dissipation (Artana et al., 2016). We discovered the occurrence of recurrent blocking and feeding events of the MC at the exit of the Malvinas Plateau. Variations in water characteristics in the recirculation region are consistent with changes in the occurrence of blocking and feeding events (Artana et al., 2018c). The MC transport was computed across 5 sections. GLORYS12 provides a MC transport mean of 27±0.3 Sv with a std that increases close to the BMC (Artana et al., in prep). GLORYS12 transport at 41°S compares well with MC transport computed from mooring and altimetric data (Artana et al., 2018). The impact of trapped waves propagating along the Patagonian slope (Poli et al., 2020) in the MC transport and in the BMC position are under investigation. We examined the BMC, confluence of the subtropical front (STF) and SAF, from the synoptic scale to 25-years trend (Artana et al., 2019). The MC transport exceeds the mean BC transport by at least 12 Sv, forcing the BC to separate from the coast at 15° north of the zero wind-stress curl. The SAF and STF positions vary over a wide range of spatial (about 800 km) and temporal scales. Synoptic variations in the front positions are large; seasonal migrations are small, while variations at the interannual scale are important (300 and 200 km for the STF and SAF, respectively).
Artana et al., (2019). Advances in Space Research, doi:10.1016/j.asr.2019.11.033, Artana et al., (2019). Journal of Geophysical Research: Oceans, doi:10.1029/2019JC015289, Artana et al., (2018). JGR :O, doi:10.1029/2018JC014528, Artana et al., (2018). JGR :O, doi: 10.1029/2018JC013887,Artana et al., (2018) . JGR :O, doi:10.1002/2017JC013600, Artana, et al., (2016). JGR:O, doi :1002/2016JC011889, Park et al., (2019. JGR:O, doi:10.1029/2019JC015024, Park et al. (in prep.) Low-frequency variability of ACC transport in the Pacific sector and concurrent atmospheric forcing, Poli et al., (2020).JGR:O, doi:10.1029/2020JC016549 (revised), Rio et al., (2020) The new CNES-CLS18 MDT. (in prep.)
Camila Artana
Mercator Océan