Modeling interannual dense shelf water export in the region of the Mertz Glacier Tongue (1992-2007)

E. A. Cougnon (1, 2, 3) , B. K. Galton-Fenzi (3, 4) , A. J. S. Meijers (5) , B. Legresy (3, 6)

1 CSIRO-UTAS
2 CSIRO - Commonwealth Scientific and Industrial Research Organisation [Canberra]
3 ACE-CRC - Antarctic Climate and Ecosystems Cooperative Research Centre
4 AAD - Australian Antarctic Division
5 BAS - British Antarctic Survey
6 LEGOS - Laboratoire d'études en Géophysique et océanographie spatiales

Ocean observations around the Australian-Antarctic basin show the importance of coastal latent heat polynyas near the Mertz Glacier Tongue (MGT) to the formation of Dense Shelf Water (DSW) and associated Antarctic Bottom Water (AABW). Here, we use a regional ocean/ice shelf model to investigate the interannual variability of the export of DSW from the Adelie (west of the MGT) and the Mertz (east of the MGT) depressions from 1992 to 2007. The variability in the model is driven by changes in observed surface heat and salt fluxes. The model simulates an annual mean export of DSW through the Adelie sill of about 0.070.06 Sv. From 1992 to 1998, the export of DSW through the Adelie (Mertz) sills peaked at 0.14 Sv (0.29 Sv) during July to November. During periods of mean to strong polynya activity (defined by the surface ocean heat loss), DSW formed in the Adelie depression can spread into the Mertz depression via the cavity under the MGT. An additional simulation, where ocean/ice shelf thermodynamics have been disabled, highlights the fact that models without ocean/ice shelf interaction processes will significantly overestimate rates of DSW export. The melt rates of the MGT are 1.20.4 m yr(-1) during periods of average to strong polynya activity and can increase to 3.81.5 m/yr during periods of sustained weak polynya activity, due to the increased presence of relatively warmer water interacting with the base of the ice shelf. The increased melting of the MGT during a weak polynya state can cause further freshening of the DSW and ultimately limits the production of AABW.

Mots clés: dense shelf water; Mertz glacier tongue; Antarctic bottom water; numerical modeling; LAND BOTTOM WATER; EAST ANTARCTICA; SEA-ICE; ADELIE LAND; MASS-BALANCE; OCEAN; CIRCULATION; POLYNYA; VARIABILITY; EXCHANGE

Domaines: Océan, Atmosphère

E. A. Cougnon, B. K. Galton-Fenzi, A. J. S. Meijers, B. Legresy. Modeling interannual dense shelf water export in the region of the Mertz Glacier Tongue (1992-2007). Journal of Geophysical Research. Oceans, 2013, 118 (10), pp.5858-5872. ⟨10.1002/2013jc008790⟩. ⟨hal-00980470⟩