Borehole temperatures reveal a changed energy budget at Mill Island, East Antarctica over recent decades
1Department of Sustainability, Environment, Water, Population and Communities, Australian Antarctic Division, Hobart, Tasmania, Australia
2Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Private Bag 80, Hobart, Tasmania 7001, Australia
3CSIRO Marine and Atmospheric Research, Castray Esplanade, Hobart, Tasmania 7000, Australia
4Marine Climate Risk Group, Department of Environment and Geography, Macquarie University, Eastern Road, Macquarie University, New South Wales 2109, Australia
5Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia
Abstract. A borehole temperature record from the Mill Island (East Antarctic) icecap reveals a large surface warming signal manifested as a 0.75 K temperature difference over the approximate 100 m depth below the seasonally varying zone. The temperature profile shows a break in gradient between 49 and 69 m depth, which we model with inverse numerical simulations, indicating that surface warming started around the austral summer of 1980/1981 AD ± 5 yr. This warming of approximately 0.37 K per decade is large by Antarctic standards and is only exceeded in regions of the Antarctic Peninsula. While this warming may reflect regional scale air temperature increases, the lack of comparable trends for other East Antarctic sites suggests local influences are largely responsible for the observed trend. Alteration of the surface energy budget arising from changes in radiation balances due to local cloud, the amount of liquid deposition and local air temperatures associated with altered air/sea exchanges potentially play a key role at this location due to the proximity of the Shackleton Ice Shelf and sea-ice zone.