Identifying the dynamics of the British ice-sheet during the last 60 ka via environmental magnetic analysis of IRD composition

Climate change is one of the most pressing and complex environmental issues currently facing human societies. The ability to accurately predict future climate change is becoming critical in influencing governmental policies but, at the heart of such predictions, is the essential pre-requisite of understanding how our climate system operates. Studies of marine sediments are a vital resource in this regard as they provide continuous, long-term records (often extending back over 120,000 years) containing evidence of climatic change. While periods of long-term climate change have long been identified from climate records (i.e. from cold (glacial) to warm (interglacial) conditions), recent research has also provided evidence for very rapid and abrupt changes at rates considerably greater than that predicted as a consequence of human impacts upon climate over the next 50 years. However, our understanding of the triggers or thresholds underpinning such rapid and abrupt climate change is far from complete. In marine sediment records throughout the Atlantic, some periods of abrupt climate change are associated with layers of ice-rafted debris (IRD). Such layers, which occur during the last glacial climate phase (between approximately 11,000 and 60,000 years before present) are termed Heinrich (H) layers. IRD represents sediment transported via icebergs and deposited upon melting. Evidence suggests they are a product of massive and abrupt ice-discharges and their co-incidence with periods of abrupt climate change suggests some sort of a causal link. Whatever the forcing mechanism causing such massive iceberg discharges (external climate change or internal feedback mechanisms within the ice/sheet), such discharges into the Atlantic could provide a stimulus for more general climate change as the influx of large volumes of cold, fresh, water may trigger a change in ocean circulation patterns. Current evidence indicates the Laurentide ice-sheet (LIS) as the dominant source of IRD in H layers. Recent mineralogical and isotopic evidence has also demonstrated IRD contributions from European ice masses and possible differences in timing and cyclicity of IRD deposition from European and LIS sources. These differences have significant consequences for the climatic interpretation of H layers. Synchroneity in the behaviour of the European and North American ice-sheets implies a common external forcing mechanism. In contrast, timing differences in iceberg production suggests either internal, ice-sheet specific controls or regional climatic stimuli. Resolution of this debate is critical to our understanding of the palaeoclimatic significance of H layers. The ability to identify which ice-sheet is contributing IRD to the sediment record at a core site is central in unravelling these uncertainties. Traditional forms of chemical or mineralogical analysis are often time consuming and expensive, limiting the temporal resolution that can be achieved. However, environmental magnetic analysis provides an extremely sensitive and rapid method of identifying the iron mineral types and concentrations within a sediment which, in turn, are strongly influenced by the geological sources that contributed materials to the sediment. This research aims to establish the role of British ice-sheet (BIS) in delivering IRD to NE Atlantic marine sediments based on detailed environmental magnetic analysis. We will examine the timing of BIS IRD contributions relative to IRD derived from the LIS by analysing high-temporal resolution sediment cores. In association with other proxy climate records from the same cores (made available through our collaborators), we will examine the hypothesis that environmental magnetic data can provide detailed insights into the growth, behaviour and climatic response of the British ice-sheet through the last major glacial climatic phase and add considerably to our understanding of natural climate change through that period.