Methods

Fieldwork

The methods employed by the team include mapping of glaciology and landforms from satellite image and aerial photographs, over a range of dates from 1988 until present. This allows recent glacial change to be characterised. The construction of digital elevation models from stereoscopic satellite images allows glacial thinning on the Antarctic Peninsula after ice shelf collapse to be monitored and constrained.

In the field, we will use standard geological and glaciological techniques to map landforms and sediment-landform associations, which will allow us to characterise the style of deglaciation (rapid, slow and steady, or stagnating ice), as well as the thermal regime of glaciers at the Glossary (cold-based glaciers, polythermal glaciers, and warm-based glaciers with water at the ice-bed interface). By identifying rock samples from outcrops of glacial sediments, we will reconstruct ice-flow pathways at the LGM and into the Holocene. For example, finding rocks from the Antarctic Peninsula ('erratics') on James Ross Island tells us that glaciers from the APIS overrode James Ross Island at some point in the past.

Finally, we will use cosmogenic nuclide dating on moraines and erratics to date the recession and retreat of glaciers at the start of the Holocene, during Mid-Holocene readvances and the most recent readvance towards the end of the Holocene (last 200 years).

Glossary

APIS	Antarctic Peninsula Ice Sheet
Cosmogenic Nuclide Dating	This is a technique that provides a measure of the exposure age of a boulder. The exposure age is the length of time since the boulder became exposed at the Earth’s surface, for example, after being deposited by a glacier. Cosmogenic nuclide dating works by analysing minerals within the boulder (such as quartz) for nuclides that are formed when certain particles are bombarded by cosmic rays that originate from supernova explosions throughout the galaxy. The most useful nuclides are radioactive, and Beryllium-10 and Aluminium-26 are used most frequently in dating the exposure age of granitic, quartz-rich erratics.
Diamictite	Fully lithified rock containing unsorted grains of all sizes (clay to boulders), originating in this case from glaciers during the Neogene.
Erratic	Glacially-transported boulder that is of a different lithology to the immediate bedrock.
Holocene	The last period of Earth’s history after global deglaciation. The last 10,000 years.
Hyaloclastite	Rock composed of tuff and basalt fragments, formed during subglacial volcanic eruptions.
Ice-cored moraine	Moraine that has a core of glacier ice. These moraines are formed when englacial and subglacial debris is thrust up towards the surface at the glacier snout, which typically is associated with polythermal glaciers. The debris accumulates on the glacier surface at the snout. Once this debris reaches a certain thickness, it may protect the glacier ice from further ablation. If the glacier retreats, the debris-covered portion of the snout is left behind as an ice-cored moraine.
Ice Shelf	Thick, permanent, floating sheet of ice that is derived from terrestrial tributary glaciers. The back pressure from an ice shelf stabilises its tributary glaciers, which may be prone to acceleration, recession and retreat if the ice shelf melts away.
Ice shelf collapse	Ice shelves on the Antarctic Peninsula have been observed to sequentially collapse during the 20^th and 21^st Centuries. This has been linked to climate warming; the limit of viability of ice shelves is thought to be an average annual temperature of -9°C. As this isotherm moves southwards, ice shelves north of this point have rapidly disintegrated. Processes of ice-shelf disintegration include long-term thinning from surface and bottom melting, but rapid disintegration occurs along structural lines. Meltwater ponds on the ice shelf surface also encourage disintegration, as they melt through the ice shelf to the bottom, forming lines of weakness along which ice bergs may calve off.
Last Glacial Maximum (LGM)	The last time when the ice sheet reached its maximum extent, to the shelf break. In the Antarctic Peninsula, this occurred before 18,000 years ago.
Mesa	Flat topped mountain. On James Ross Island, the mesas are formed from flood basalts relating to subglacial volcanic eruptions.
Moraine	Landform generated at the margins of a glacier by the movement of material to the glacier margin. Material may also be derived from debris transported on the glacier’s surface as well as from beneath the glacier.
Polythermal glacier	A glacier that is wet-based in its centre but cold-based at its margins. This may result in thrusting at the ice margin, as the wet-based ice moves downslope under gravity and encounters the cold-based ice, which is frozen to its bed.
Thermal regime	The temperature of the ice at the base of a glacier controls the subglacial environment. If it is warm enough, the ice will melt under the pressure of the ice above. This is the pressure melting point. Ice with water at the bed is warm-based. This ice lubricates the glacier sole and encourages deformation of subglacial sediments, sliding of the glaciers, and formation of tills and glacial landforms. If it is too cold, the ice will not melt, and the glacier will therefore be cold-based. These glaciers are frozen to the bed, exhibit little forward movement and generate few glacial sediments or landforms. Many small glaciers in particular may be polythermal, with warm-based ice in the thicker, upland parts of the glacier but cold-based ice at the thinner margins.
Tidewater glacier	A glacier that originates on land but that flows out over the ocean, where it begins to float.
Till	Sediment that is deposited at the glacier sole. Typically comprises fine-grained detritus, sand and gravel that was eroded, modified and transported by the glacier.
Tillite	Glacial till that has been fully lithified (made hard like rock). In this case, the tillite originates from Neogene glaciation.
Tributary glacier	A glacier that originates on land but flows out into the sea, where it begins to float. If the floating portion of the glacier combines with that of several other glaciers it forms a floating ice shelf.
Quaternary	The last epoch of the Earth’s history; the last two-million years. During this epoch, glaciers and ice sheets came to dominate the Earth’s climate, when large global ‘glacials’ were interspersed with warmer ‘interglacials’.