Altimetry in Drake Passage : variations of the baroclinic, barotropic and total Antarctic Circumpolar Current volume transports

Christine Provost (CNRS UPMC LOCEAN, France)


Zoe Koenig (UPMC, LOCEAN, France); Ramiro Ferrari (CONICET, CIMA, Argentine); Young-Hyang Park (MNHN, LOCEAN, France); Nathalie Sennéchael (MNHN, LOCEAN, France)

Event: 2016 Ocean Surface Topography Science Team Meeting

Session: Others (poster only)

Presentation type: Type Poster

The complex bathymetry of the Drake Passage and the meridional extent of the Shackleton Fracture Zone, in particular, force the Subantarctic Front (SAF) and the Polar Front (PF) to veer to the north, and the flow of the Antarctic Circumpolar Current concentrates in the Yaghan Basin, northern Drake Passage. Altimetry products were carefully assessed in the Drake Passage using in situ data from Argo floats and from the CNES-supported Drake project (ship hydrography with LADCP and 3 years of current meter moorings) (Barré et al., 2008, Barré et al., 2011; Provost et al., 2011, Renault et al., 2011, Ferrari et al., 2012, Ferrari et al., 2013; Ferrari et al., 2014).

A 20 year long volume transport time series of the Antarctic Circumpolar Current across the Drake Passage was estimated from the combination of information from in situ current meter data (2006–2009) and satellite altimetry data (1992–2013) (Koenig et al., 2014). A new method for transport estimates accounting for the dependence of the vertical velocity structure on surface velocity and latitude was designed. The internal consistency and the robustness of the method were carefully assessed. Comparisons with independent data demonstrated the accuracy of the method. The full-depth volume transport has a mean of 141 Sv (standard error of the mean 2.7 Sv), a standard deviation (std) of 13 Sv, and a range of 110 Sv. Yearly means vary from 133.6 Sv in 2011 to 150 Sv in 1993 and standard deviations from 8.8 Sv in 2009 to 17.9 Sv in 1995. The canonical ISOS values (mean 133.8 Sv, std 11.2 Sv) obtained from a-year-long record in 1979 are very similar to those found here for year 2011 (133.6 Sv and 12 Sv). Full-depth transports and transports over 3000 m barely differ as in that particular region of Drake Passage the deep recirculations in two semiclosed basins (Yaghan and Ona Basin) have a close to zero net transport.

The 20-year long volume transport time series of the ACC through Drake Passage (DP) were analyzed to better understand the ACC transport variability and its potential causes (Koenig et al., 2016). The time series of three transport components (total (TT), barotropic (BT), and baroclinic (BC)) present energetic intraseasonal fluctuations, with a salient spectral peak at 50 and 36 days, with the largest (least) variance being associated with the BT (BC) component.
Low-frequency variations are much less energetic with a significant variance limited to the annual and biannual timescales and show a non-stationary intermittent link with the Southern Annular Mode and the Nino 3.4 index for interannual timescales.
The region around 57°S in the Yaghan Basin appears to be a strategic point for a practical monitoring of the ACC transport, as the whole-track TT is significantly correlated with the local TT (r = 0.53) and BT (r  = 0.69) around 57°S. These local BT (and TT) variations are associated with a well-defined tripole pattern in altimetric sea level anomaly (SLA). There is evidence that the tripole pattern associated with BT is locally generated when the BC-associated mesoscale SLAs, which have propagated eastward from an upstream area of DP, cross the Shackleton Fracture Zone to penetrate into the Yaghan Basin. Barotropic basin modes excited within the Yaghan Basin are discussed as a plausible mechanism for the observed energy-containing intraseasonal spectral peaks found in the transport variability.

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Poster show times:

RoomStart DateEnd Date
Grande Halle Thu, Nov 03 2016,11:00 Thu, Nov 03 2016,18:00
Christine Provost