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BAS Project Update
In January, the HMS Endurance put Sledge Romeo (a joint team of British Antarctic Survey and University of Leicester scientists and field assistants) into the field at James Ross Island. The scientists were looking at the pattern of climate change locked up in the rocks of the Antarctic Peninsula. The rocks they were studying are from the Neogene period (a period in geologic time) that spans 2 to 24 million years ago. This is the last period of time in which there were CO2 emissions and temperatures comparable to the predicted values for the next couple of hundred years. The information they glean from the rocks will then be fed into forward-looking climate models in order to understand how the planet will be affected by present and future climate changes.
The rocks themselves are located in areas dotted around James Ross Island, sandwiched between Cretaceous marine sediments and Neogene volcanic rocks. The HMS Endurance is critical to this fieldwork, as the Lynx helicopters allow the scientists to access remote inland areas of the island, where field camps are established. The BAS group have three field camps this season and a handful of helicopter day trips throughout a two month period, ending in early March.
BAS Field Camp
Glacigenic sediments, or sediments deposited by glaciers and glacial processes, provide a superb indicator for past climate. By studying the glacigenic sediments on James Ross Island, we can determine the extent of the Antarctic Peninsula Ice Sheet and the local James Ross Island Ice Cap at a number of times in the last six million years. We can also determine whether the glacigenic sediment was deposited by a land-based or marine-terminating glacier and in what position the sediment was deposited (beneath, on top of, or within the glacier).
Tom, BAS Field Assistant, stands next to geologic outcrop of glacial sediment and volcanic rock.
In the past six million years, the ice-covered Mount Haddington volcano has erupted multiple times. The lava that erupted from this volcano covered up the glacial sediment that was beneath the ice, thus preserving the basal sediment in pristine condition. This gives the scientists a unique opportunity to observe a snapshot view of the conditions at the interface between the glacier and the underlying material. The ice—bedrock interface beneath glaciers and ice sheets is an extremely variable environment, where hydrological and thermal conditions vary both spatially and temporally. By studying the sediments, we can answer important questions about glacier dynamics, which is important for determining the stability of modern Antarctic ice, particularly as global climate warms.
The glacigenic sediments are a combination of fossiliferous (sediments containing fossils) and unfossiliferous material. Fossils are recovered from three different sediment types on James Ross Island: in sediments accumulating during the interglacial warm periods in shallow marine seas, in glacigenic sediments interspersed with the volcanic rocks as amalgams of material sometimes scraped off the Cretaceous rock deposits by ice action, and rare marine fossils are also preserved within marine-emplaced volcanic sediment.
The richest fossil assemblages from the interglacial marine sediments are those from the Cockburn Island Formation. There, the most impressive fossil remains are the abundant large ‘Pecten’ molluscs. Locked in their shells are geochemical and morphological signals of the past climate. But these rocks also preserve an impressive array of colonial bryozoans, barnacles, and lots of microfossils of ostracod crustaceans and marine foraminifers – a kind of amoeba with a shell. The glacigenic sediments, ripped-up from beneath the advancing ice sheets, contain similar fossil assemblages to those of the marine interglacial sediments, and are dominated volumetrically by molluscs. But these deposits also include much older material reworked from the Cretaceous. Studying these fossils can tell us much about the marine environment around James Ross Island during periods of relative warmth, the interglacials that may have been similar to climate today, and about much cooler periods when the island was locked in ice.
The rare fossils found in the volcanic tuffs include starfish-like animals that were trapped and buried by rapid sedimentation. These small fossil ‘Pompeii-like’ volcanic events are important because they provide an unusual window on what was living on the seabed beside the volcanoes at the time of eruption. The dominance of starfish-like animals in these deposits also suggests a climatic signature. Marine communities dominated by echinoderms (starfish, sea urchins etc.) signal cooling of the climate earlier in the Cenozoic history of Antarctica. In this cooling environment fast paced animals like teleost (‘boney’) fish and decapod crustaceans (like crabs) that are the dominant predators of shallow marine shelves at lower (warmer) latitudes, were out-competed by slow moving predators like echinoderms. For this reason some Antarctic marine shelf communities look more like Palaeozoic assemblages from the Silurian, than modern marine shelf communities.
Checking out the local geology
In conclusion, the glacial sediments and the fossils within provide the BAS scientists with many clues regarding the past climate. The information that they obtain about past climate regimes will then be fed into forward-looking climate models in order to see how our future environment will be affected by climatic changes.
If you would like to contact the scientists about this work, please email Anna Nelson at aene@bas.ac.uk or Mark Williams at mri@leicester.ac.uk.
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