Circulation and water mass transports on the East Antarctic shelf in the Mertz Glacier region

Abstract

The East Antarctic shelf off Adélie-George V Land is known to be an important region for Dense Shelf Water (DSW) formation as a result of intense sea ice production in the Mertz Glacier Polynya during the winter season. It is also a region where the warm modified Circumpolar Deep Water (mCDW) penetrates onto the shelf during the summer. Using hydrographic observations from a summer survey in 2008 we implement a box inverse model to propose a comprehensive view of the steady state circulation on this shelf in summer. Additional information from mooring observations collected on the depression slope is used to provide context to the retrieved circulation scheme. Over the depression slope, the summer baroclinic structure of the currents is found to contrast with the almost barotropic structure in winter.The summer circulation is strongly constrained by the DSW distribution and forms a clockwise circulation primarily transporting the fresh surface waters and the warm mCDW around the dome of DSW. Over the upper flank of the Mertz Bank, the inflow branch transports the mCDW towards the Mertz Glacier, while, over the lower part of the slope, the outflow branch returns to the sill a diluted mode of the same water mass. A total of 0.19 Sv of mCDW inflows at the sill and two-third reach the Mertz Glacier and recirculate in front of it, allowing the mCDW to penetrate into the deeper part of the depression. Possible scenarios of interaction between the mCDW and the DSW with the glacier are examined. It is shown that, despite the water mass pathways and transports suggest possible ice-ocean interaction, both lateral and basal melting were likely small in summer 2008. Finally, our results suggest that, in addition to bathymetric features, the distribution of the residual DSW which is left from the preceding winter sets up regional pressure gradients which provide a seasonal control on the shelf circulation. In particular, the spring collapse of the convective patch would contribute to setting up a deep pycnocline which strongly impacts the shelf circulation in the following summer, with possible feedback of the mCDW transports on the polynya activity and water mass formation.

Bathymetry‐Constrained Navigation of Argo Floats Under Sea Ice on the Antarctic Continental Shelf

“…The depth‐constrained path (yellow) agrees with the bottom depths measured by the float, as expected. The derived float trajectory is also consistent with float drift between known positions and with the cyclonic circulation in the Adélie Depression inferred from oceanographic surveys (Lacarra et al, 2011; Martin et al, 2017; Williams et al, 2010) and numerical simulations (Cougnon et al, 2017; Kusahara et al, 2017).…”

Influence of ocean tides and ice shelves on ocean–ice interactions and dense shelf water formation in the D’Urville Sea, Antarctica

“…This warm bias might be induced by the mean circulation simulated by our model: the westward current crossing the Mertz Sill and Adélie Depression carries large amount of relatively warm mCDW. Such intrusions of mCDW have been suggested by Snow et al (2016) and Martin et al (2017) before the calving, but the amount of mCDW entering the Adélie Depression through the Mertz Sill are unknown in the current state. Summer observations, however, indicate intrusions of CDW east of the Mertz Sill (Aoki et al, 2017), without entering the Adélie Depression.…”

“…This current forms east of the Mertz Sill, from the confluence of a cold and fresh coastal current from the south and the inflow of CDW from the north. This confluence leads to the sporadic inflow of mCDW into the Adélie Depression (intrusions of mCDW from the east were suggested by Snow et al, 2016 andMartin et al, 2017).…”

Regional Changes in Icescape Impact Shelf Circulation and Basal Melting

“…The Adélie and George V Land coast (AGVL; 136-148 ∘ E) is one of the most monitored regions in East Antarctica with many studies covering the MGT (e.g., Giles, 2017;Legrésy et al, 2004;Lescarmontier et al, 2015;Massom et al, 2015;Mayet et al, 2013), the polynya distribution (e.g., Dragon et al, 2014;Fogwill et al, 2016;Massom et al, 2001;Tamura et al, 2012), the local bathymetry (e.g., Beaman et al, 2011), and the ocean circulation (e.g., Lacarra et al, 2014;Martin et al, 2017;Shadwick et al, 2013;Snow et al, 2016;Williams et al, 2008Williams et al, , 2010. Prior to the MGT calving, the AGVL region had the second highest sea ice production along the East Antarctic coast (Tamura et al, 2016), partly due to the presence of the MGT and other icebergs in the area (e.g., B9B iceberg) which formed barriers to westward moving sea ice within the Antarctic coastal current (Barber & Massom, 2007).…”