Weathering fluxes and sediment provenance on the SW Scottish shelf during the last deglaciation

Arosio, R., Crocket, K. C., Nowell, G. M., Callard, S. L., Howe, J. A., Benetti, S., Fabel, D. , Moreton, S. and Clark, C. D. (2018) Weathering fluxes and sediment provenance on the SW Scottish shelf during the last deglaciation. Marine Geology, 402, pp. 81-98. (doi:10.1016/j.margeo.2017.08.017)

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Abstract

The reconstruction of past ice sheet dynamics can shed a light on long-term ice stream activity, and in turn provide constraints on the response of modern ice sheets to climate change. The Hebrides Ice Stream (HIS) flowed across part of the western Scottish shelf to the shelf-break during the last glacial cycle and drained a large portion of the northern sector of the British Irish-Ice Sheet. To investigate the deglacial dynamics of the HIS following the Last Glacial Maximum, lead (Pb) isotope records were extracted from the FeMn oxyhydroxide and detrital fractions of recovered laminated glacimarine mud sequences to monitor the changing activity of HIS during its retreat. These provide timing and some source information of glacially weathered inputs to the marine environment. The FeMn oxyhydroxide fraction in the samples is dominated by allochthonous particles (pre-formed) and shows a marked decrease from radiogenic (≤ 20.05 206Pb/204Pb) at ~ 21 cal ka BP to less radiogenic Pb isotope compositions (~ 19.48) towards the Windermere Interstadial (15.4–13 ka). This decrease represents a reduction in the flux of subglacially-derived radiogenic Pb to the continental shelf is interpreted as being associated with the break-up of the ice-stream in western Scotland around that time. The Pb, Sr and Nd isotopic signatures of the detrital fraction indicate a preponderance of Moine-sourced fine sediments (originated from the NW Highlands) in the core locations from ~ 21 to 15 cal ka BP (Dimlington Stadial - Windermere Interstadial), most likely dictated by the orientation of ice flow, tidal and oceanic current directions and sediment delivery. In contrast, ice rafted debris in a ~ 21 cal ka BP old basal diamicton contains volcanic-derived material, suggesting different provenance for different grain sizes. The FeMn oxyhydroxide 208Pb/204Pb ratio shows an unusual inversion relative to the other Pb isotope ratios, and is attributed to the introduction of secondary weathering phases from a source with contrasting 208Pb/204Pb but similar 206Pb/204Pb and 207Pb/204Pb. In the detrital fraction, the inversions are constrained to periodic spikes, which may indicate an increased contribution from a high Th/U source, potentially the neighbouring Archaean amphibolitic Lewisian basement in the Outer Hebrides. This study demonstrates how geochemical investigation on continental shelves can be used to constrain the timing, activity and flow sources of palaeo-ice streams.

Item Type:Articles
Additional Information:The work was supported by the NERC Radiocarbon Facility (allocation number 1878.1014). Thanks are due to the staff at the SUERC AMS Laboratory, East Kilbride for carbon isotope measurements. This manuscript benefited from discussions with Friedhelm von Blanckenburg, Tina van de Flierdt and Derek Vance. Riccardo Arosio has received funding for this research from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme Glaciated North Atlantic Margins (GLANAM) FP7/2007-2013 under RAE grant agreement no. 317217. This work was also supported by the Natural Environment Research Council consortium grant; BRITICE-CHRONO NE/J009768/1.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Moreton, Dr Steven and Fabel, Dr Derek
Authors: Arosio, R., Crocket, K. C., Nowell, G. M., Callard, S. L., Howe, J. A., Benetti, S., Fabel, D., Moreton, S., and Clark, C. D.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Marine Geology
Publisher:Elsevier
ISSN:0025-3227
ISSN (Online):1872-6151
Published Online:31 August 2017
Copyright Holders:Copyright © 2018 Elsevier
First Published:First published in Marine Geology 402:81-98
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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