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Glacial-interglacial variation in organic carbon burial on the slope of the N.W. European Continental Margin (48-50 degrees N)

Hall, Ian Robert and McCave, I. N. 1998. Glacial-interglacial variation in organic carbon burial on the slope of the N.W. European Continental Margin (48-50 degrees N). Progress in Oceanography 42 (1-4) , pp. 37-60. 10.1016/S0079-6611(98)00027-5

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Abstract

The sources and fate of organic carbon (Corg) were examined at two sites on the Goban Spur and a single site within the Porcupine Sea-Bight on the N.W. European slope between 48°N and 50°N. Here we present data on the sedimentary Corg concentration, its 13C/12C composition (δ13Corg) and Corg/N of 224 total and 119 fine fraction (<63 μm) samples as a time series running from the instantaneous marker horizon Heinrich Layer 2 (25.5 ka BP) through the last glacial isotope stage 2 and interglacial isotope stage 1 to the present. The significance of the N.W. European slope as a depositional sink for Corg has declined in the past twenty thousand years, with flux values decreasing two to three-fold from the late glacial (60–70 mg C cm−2 ka−1) to low late Holocene values. Significant shifts are seen in the δ13Corg signature of both the total and fine fractions between the present interglacial and last glacial. The open slope of the Goban Spur is characterised by relatively low values over the last glacial, with minimum values for the total sediment of around −24.5‰ occurring at ca. 18 ka BP, and generally increasing values during the Holocene with the most recent samples having values of ca. −19.2 to −20.2‰. In the Porcupine Sea-Bight a different relationship is evident with samples from the Last Glacial Maximum being generally higher, while values from the Holocene are lower with a minimum of −23.3‰ occurring just below the mixed layer. Similar trends are observed in the fine fraction albeit with a different dynamic range. Paired analysis of δ13Corg and Corg/N are consistent with the organic matter being a climatically forced mixture from C3-photosynthetic terrigenous and marine organic matter sources. An increased influence of terrestrial Corg is suggested on the glacial Goban Spur and Holocene Porcupine Sea-Bight, and vice versa. We suggest that this may be explained by modern wind-driven flushing of terrigenous carbon across the Armorican and Celtic shelves to the N.W. and thence into Porcupine Sea-Bight. During the last glacial increased strength of westerly winds created a residual current regime driving material to the S.W., where it was transported in vigorous tidal off-shelf flushing to the upper slope, followed by slope current transfer to the Goban Spur. Much of this material was presumably delivered by the `Great Channel River' to the outer shelf, thus leading to enhanced flux of terrestrial Corg on the Goban Spur. The influence of a freshwater plume from meltwater discharge of the European ice sheet in this region is supported by foramininiferal δ18O data from which a palaeo-salinity reconstruction shows a greatest negative anomaly of −2.55 (that is S-35) at the time of maximum terrestrial Corg content in the sedimentary material. In addition to showing that surface waters over Goban Spur were relatively fresh throughout the glacial, our results also reveal variability in surface salinity on shorter timescales.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: G Geography. Anthropology. Recreation > GC Oceanography
Publisher: Elsevier
ISSN: 0079-6611
Last Modified: 04 Jun 2017 04:00
URI: http://orca.cf.ac.uk/id/eprint/30539

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