Depositional patterns and records in sediment drifts off the Antarctic Peninsula and West Antarctica

The biggest uncertainty in predictions of sea-level rise is what the contribution will be from the great ice sheets on Antarctica and Greenland as climate warms. The West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet are the cause of greatest concern, as they are showing signs of significant ice loss and there are theoretical reasons for expecting them to be most vulnerable. Important sources of information for helping to predict how these ice sheets will change as climate warms are records of their response to past climate changes contained in sea bed sediments around Antarctica. Such records extend further back in time than ice cores from the ice sheets themselves. They can also show how the margins of the ice sheets interacted with changes in ocean temperature and circulation, which recent studies have identified as having an important influence on ice sheets.

Although sedimentary records in the shallow seas close to Antarctica have been periodically disturbed or removed by past expansions of the ice sheets, there are places in the nearby deep ocean where sediments have accumulated continuously over millions of years. The international Integrated Ocean Drilling Program is considering a proposal to send a drilling ship to collect long sediment cores from some of these places. However, before this is done additional survey data are needed to find the sites that will provide the most continuous, detailed records and to make sure that it will be safe to drill those sites. In this research proposal we are seeking funding to collect this essential survey data.

On the same expedition we also propose to collect short sediment cores for pilot studies to confirm that the analytical methods we intend to apply to the longer drill cores will provide reliable information about sediment ages, past climate and past ice sheet behaviour. One of the major difficulties in studying sediment records from the sea bed around Antarctica has been obtaining reliable ages from the sediments. This is because the types of microfossils that are analysed to determine sediment ages in drill cores from most of the world's oceans are rare or absent in many sediment cores collected near Antarctica. By carrying out detailed survey and studying short cores we hope to identify sites where there are sufficient numbers of these microfossils to apply the standard dating techniques. We also plan to test whether a new method of dating sediments that is based on analysis of their magnetic properties will work in the area of the proposed drill sites. It has recently been shown that in many places analysis of the magnetic properties of sea bed sediments can provide records of past changes in the intensity of the Earth's magnetic field, and comparison of these records to well-dated reference records allows ages to be assigned to sediments throughout a core. By comparing ages obtained using this method with ones obtained from microfossils, where they are present, we will be able to find out how well the magnetic dating method works in the study area. If the magnetic method works well, we will be able to establish detailed age models for drill cores without dependence on microfossils, which will greatly extend the area that can be studied by drilling and allow more detailed records of past changes to be derived from the drill cores.

The high-quality datasets collected through this project will be of interest to a wide range of researchers investigating the long-term history of Antarctica and the Southern Ocean and the processes operating in these regions. Combined with the results of the proposed drilling leg that this project is intended to support, they will also have much wider relevance. The records of climate, ice sheet history, sediment accumulation and palaeoceanographic conditions that will be obtained will provide means of testing and refining ice sheet, ocean and coupled atmosphere-ocean general circulation models. Such models are used to predict the contribution from the Antarctic ice sheets to sea-level rise, and are therefore important to policy makers planning coastal defence strategies and land use (N.B. the fourth Intergovernmental Panel on Climate Change reports identified future contributions from polar ice sheets as the largest uncertainty in prediction of sea-level rise).
The results of the project will have immediate relevance to refining the selection of drill sites and ensuring that they are safe to drill. Subsequently the seismic data will be valuable for extrapolating the drilling results to a wider region. The data will also be useful to researchers worldwide (including some in the oil industry) who study the development of deep-sea sediment drifts and the interactions between sedimentation and bottom currents that are involved in their formation. Another group of researchers who will find the new data useful are scientists studying silica diagenetic processes that produce widespread bottom-simulating reflectors in Southern Ocean seismic data and release water, causing fluid overpressure and slope instability.
A further application of the new seismic data will be in reconstructing Southern Ocean palaeobathymetry, which is a central objective of the Circum-Antarctic Stratigraphy Project (CASP, see http://hdl.handle.net/10013/epic.3301, a component of the Scientific Committee on Antarctic Research Antarctic Climate Evolution Programme). The palaeobathymetric maps that this group is developing will provide an improved boundary condition for models of past Southern Ocean circulation. Similarly the data will allow improved estimates to be made of the volumes of sediment eroded from the nearby sector of Antarctica during different periods, which are required by the ANTscape Project (see http://adsabs.harvard.edu/abs/2009AGUFMPP43A1561B , another component of the Scientific Committee on Antarctic Research Antarctic Climate Evolution Programme) as an input in the derivation of Antarctic palaeotopographic maps. The palaeotopographic maps will provide an improved boundary condition for models of past Antarctic Ice Sheets.
The work proposed here will link to ice sheet models in multiple ways. The records from the drilling results that this project is intended to support will have immediate relevance to calibrating the sensitivity of ice sheets to past climate and oceanographic change. In the longer term the seismic data collected will contribute to improved basal boundary conditions for past ice sheets and the Southern Ocean in the past, which will lead to further refinement of numerical models. Progressive improvement in ground truth constraints, calibration of sensitivity, and boundary conditions will reduce model uncertainties and make their sea-level predictions more useful to policy makers and planners.
The considerable public interest in Antarctica and the potential impact of changes there on the global environment provides opportunities for outreach activities from this work (see Pathways to Impact section).
The research team is in general highly experienced, but Researcher Co-Investigator Graham and the BAS Assistant Marine Geologist will both develop new professional skills. Graham will extend his experience of interpreting processed 2D and 3D data by working with multichannel seismic data at the processing stage.