[1] We investigate basal melting of all Antarctic ice shelves by a circumpolar ice shelf-sea ice-ocean coupled model and estimate the total basal melting of 770-944 Gt/yr under present-day climate conditions. We present a comparison of the basal melting with previous observational and modeling estimates for each ice shelf. Heat sources for basal melting are largely different among the ice shelves. Sensitivities of the basal melting to surface air warming and to enhanced westerly winds over the Antarctic Circumpolar Current are investigated from a series of numerical experiments. In this model the total basal melting strongly depends on the surface air warming but is hardly affected by the change of westerly winds. The magnitude of the basal melting response to the warming varies widely from one ice shelf to another. The largest response is found at ice shelves in the Bellingshausen Sea, followed by those in the Eastern Weddell Sea and the Indian sector. These increases of basal melting are caused by increases of Circumpolar Deep Water and/or Antarctic Surface Water into ice shelf cavities. By contrast, basal melting of ice shelves in the Ross and Weddell Seas is insensitive to the surface air warming, because even in the warming experiments there is high sea ice production at the front of the ice shelves that keeps the water temperature to the surface freezing point. Weakening of the thermohaline circulation driven by Antarctic dense water formation under warming climate conditions is enhanced by basal melting of ice shelves.Citation: Kusahara, K., and H. Hasumi (2013), Modeling Antarctic ice shelf responses to future climate changes and impacts on the ocean,

The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (−560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km. Runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western Ross Sea. This early episode of ice-shelf collapse is not observed in the eastern Ross Sea, where more episodic grounding line retreat took place. More widespread (∼280,000 km2) retreat of the ancestral Ross Ice Shelf occurred during the late Holocene. This event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open-marine sediment as well as an increase in radiogenic beryllium (10Be) concentrations. The timing of ice-shelf breakup is constrained by compound specific radiocarbon ages, the first application of this technique systematically applied to Antarctic marine sediments. Breakup initiated around 5 ka, with the ice shelf reaching its current configuration ∼1.5 ka. In the eastern Ross Sea, the ice shelf retreated up to 100 km in about a thousand years. Three-dimensional thermodynamic ice-shelf/ocean modeling results and comparison with ice-core records indicate that ice-shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf.

[1] Using an ice-ocean coupled model with fine horizontal resolution around East Antarctica, sea ice production and dense shelf water (DSW) formation in coastal polynyas are investigated. The model reproduces well the locations of coastal polynyas and the high sea ice production there. DSW is formed over the continental shelves under a number of coastal polynyas. A threshold density, beyond which net production of DSW takes place, is largely different among coastal polynyas. The densest and most vigorous DSW formation occurs in the Cape Darnley and Mertz-Ninnis Glacier polynyas followed by somewhat less but still significant DSW formation in the Prydz-Barrier and Vincennes polynyas. Assuming mixing of the DSW outflowing across the shelf break with typical Modified Circumpolar Deep Water over the continental slope, the maximum possible formation rate of Antarctic Bottom Water (AABW) is estimated to be 7.58 Sv around East Antarctica between 60°E and 150°E, with the Cape Darnley and Mertz-Ninnis Glacier polynyas exhibiting the most active formation rates of 2.13 and 1.97 Sv, respectively. From a series of numerical experiments, it is found that the treatment of coastline and grounded icebergs has a large impact on both sea ice production and formation of DSW and AABW.Citation: Kusahara, K., H. Hasumi, and T. Tamura (2010), Modeling sea ice production and dense shelf water formation in coastal polynyas around East Antarctica,

Antarctic Bottom Water (AABW) is a critical component of the global climate system, occupying the abyssal layer of the World Ocean and driving the lower limb of the global meridional overturning circulation. Around East Antarctica, the dense shelf water (DSW) precursor to AABW is predominantly formed by enhanced sea ice formation in coastal polynyas. The dominant source region of AABW supply to the Australian-Antarctic Basin is the Adélie and George V Land coast, in particular, polynyas formed in the western lee of the Mertz Glacier Tongue (MGT) and the grounded iceberg B9b over the Adélie and the Mertz Depressions, respectively. The calving of the MGT, which occurred on 12-13 February 2010, dramatically changed the environment for producing DSW. Here, we assess its impact using a state-of-the-art ice-ocean model. The model shows that oceanic circulation and sea ice production in the region changes immediately after the calving event, and that the DSW export is reduced by up to 23%.