Borehole temperatures reveal a changed energy budget at Mill Island, East Antarctica, over recent decades

Abstract

Abstract.A borehole temperature record from the Mill Island (East Antarctica) icecap reveals a large surface warming signal manifested as a 0.75 K temperature difference over the approximate 100 m depth in the zone of zero annual amplitude below the seasonally varying zone. The temperature profile shows a break in gradient around 49 m depth, which we model with inverse numerical simulations, indicating that surface warming started around the austral summer of 1980/81 AD ±5 yr. This warming of approximately 0.37 K per decade is consistent with trends seen in both instrumental and other reconstructions for Antarctica and, therefore, suggests that regional-rather than local-scale processes are largely responsible. 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 also potentially plays a role at this location due to the proximity of the Shackleton Ice Shelf and sea-ice zone.

A glaciochemical study of the 120 m ice core from Mill Island, East Antarctica

“…As a result, the diffusion length reached 6.7 cm at a depth of 43 m in the firn. With the high snow accumulation rate in the Mill Island ice core (1.430 mIE yr −1 Roberts et al, 2013), this is small enough to ignore.…”

“…The stratigraphy of the MI0910 ice core shows ∼ 1 to 5 mm thickness of higher density layers distributed occasionally throughout the entire ice core (Roberts et al, 2013). These layers may be due to melt, but the cause of each layer is difficult to explicitly investigate by close inspection alone (Kinnard et al, 2008).…”

“…Mill Island experiences a polar maritime climate and high precipitation, particularly on its eastern flank, due to moist and warm air masses from the Southern Ocean brought onshore by low pressure systems. The site also experiences dry and cold air masses associated with strong katabatic winds from the continent and low-level cloud, fog, and rime formation over the summit caused by localised summer sea breezes associated with nearby seaice breakout (Roberts et al, 2013). Mill Island record is mainly influenced by local conditions rather than wider-scale atmospheric conditions.…”

“…The thickness of annual layers was corrected using the density profile and vertical strain rate, assuming that ice thinning is only caused by vertical strain. According to the method and density profile in (Roberts et al, 2013), the vertical strain rate was estimated by least squares fitting from the density-corrected thickness of each annual layer. The flow correction is broadly consistent with the estimated ice thickness and a uniform vertical strain rate.…”

“…Mill Island is the most northerly Antarctic ice core site outside of the Antarctic Peninsula, and therefore the Mill Island ice core comprises the most northerly climate record for East Antarctica (Roberts et al, 2013). Mill Island experiences a polar maritime climate and high precipitation, particularly on its eastern flank, due to moist and warm air masses from the Southern Ocean brought onshore by low pressure systems.…”