Tracking the British–Irish Ice Sheet’s Retreat and Readvance via Isotope Geochemistry: New Evidence from NW Scotland and the Adjacent Continental Shelf

Abstract

Understanding the deglaciation of the British-Irish Ice Sheet (BIIS) provides critical insight into the behaviour of modern marine-terminating ice sheets and informs models of how future climate change may affect modern regions experiencing ice loss. This thesis applies the osmium-isotope (187Os/188Os) system alongside a suite of traditionally applied proxies to three key settings to advance the understanding of the nature of BIIS retreat and readvance and its impact on relative sea level. Osmium, carbon, sulphur and nitrogen isotopic analysis combined with X-ray fluorescence (XRF), alkenone biomarkers and benthic foraminifera were applied to a fjord, Loch Sunart, on the northwest coast of Scotland. This palaeoenvironmental study displays how water column stratification can develop in a fjord setting following large-scale deglaciation and significant meltwater release and how such changes can be resolved in the 187Os/188Os record. To further understand the interactions between ice sheet dynamics and sea-level change this multiproxy approach was applied to an isolation basin, Loch Bad na h-Achlaise. The 187Os/188Os record at this site not only yields a detailed record of relative sea-level fall in response to deglaciation but also when combined with a robust age model provides an estimate of the rate of sea-level fall and the timing of the marine limit. Finally, to examine the style and pattern of the advance and retreat of the BIIS offshore, the 187Os/188Os system was applied to a series of sediment cores from an offshore marine transect within the Minch. The 187Os/188Os records of these cores prove the utility of this isotope system in reconstructing not just broad scale retreat of the ice margin across the transect but also the oscillation of the ice margin during periods of readvance indicating the sensitivity of the osmium isotope proxy to more nuanced changes in ice sheet behaviour. The settings of this study were chosen to gain greater insight into the regional nature of BIIS retreat on coastal, inland and offshore sites. This thesis reveals new insights into the dynamics and temporal behaviour of the BIIS following the Last Glacial Maximum that were not fully known. Moreover, through the application of the osmium-isotope system to diverse sites the utility of 187Os/188Os is demonstrated, especially when applied as part of a multiproxy toolkit, as a powerful technique for reconstructing glacially influenced palaeoenvironmental records.