Talk by Laura Herraiz-Borreguero

Detecting freshwater sources and fate near the Mertz Glacier Tongue, East Antarctica, using noble gases

Abstract
Antarctic Bottom Water (AABW) plays a key role in the global exchange of heat, freshwater, nutrients, oxygen and carbon between the surface and the deep ocean. However the sensitivity of AABW formation to fresh water contributions from sea ice and continental ice/ocean interaction are poorly understood. Helium and neon noble gas measurements provide a means to trace sea ice and glacial meltwater influences via their unique dissolved gas saturation pattern (Schlosser, 1986; Schlosser et al., 1990). Here we present helium and neon noble gases and oxygen stable isotope measurements from near the Mertz Glacier Tongue (MGT), East Antarctica, to study the impact of the MGT calving on AABW formation and local ocean circulation. We will show that the source of the observed helium in Ice Shelf Water is associated with subglacial freshwater that had entered the ocean through the MGT grounding line. This is the first time that freshwater flux from beneath the grounding line of an Antarctic ice shelf has been detected. Preliminary results from the helium and oxygen isotopes indicate that the source water masses involved in the formation of AABW in Adélie Land are Circumpolar Deep Water and, Antarctic Shelf waters (Ice Shelf Water and Dense Shelf Water), in an almost 50:50 contribution. Results from this analysis will help further our understanding of the physical processes driving the freshening of AABW observed in the Indian sector of the Southern Ocean.