Helium: A new tracer in Antarctic oceanography

The abyssal characteristics of the world oceans are strongly influenced by the northward propagation of Antarctic Bottom Water (AABW). An important source of AABW is Weddell Sea Bottom Water (WSBW), which is formed, in part, on the continental slope of the southern Weddell Sea^1-3. The formation of WSBW on the continental slope is related to the floating ice shelves of the southern Weddell Sea (Filchner/Ronne Ice Shelves). Western Shelf Water (WSW) is modified under the ice shelves by cooling and admixture of melt water to form Ice Shelf Water (ISW), and a substantial part of the ISW flows over the sill that separates the Filchner Depression from the Weddell Sea and participates in the formation of WSBW^4,5. The data reported here demonstrate that the water/ice interaction leads to a strong ⁴He-supersaturation of the ISW due to dissolution of air entrapped in the ice-shelf melt water. The ⁴He-supersaturation of the ISW can be used as a tracer of this water mass and also influences the ⁴He balance of the WSBW.