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

The sources and fate of organic carbon (C-org) were examined at two sites o n the Goban Spur and a single site within the Porcupine Sea-Eight on the N. W. European slope between 48 degrees N and 50 degrees N. Here we present da ta on the sedimentary C-org concentration, its C-13/C-12 composition (delta (13)C(org)) and C-org/N of 224 total and 119 fine fraction ( < 63 mu m) sam ples as a time series running from the instantaneous marker horizon Heinric h Layer 2 (25.5 ka BP) through the last glacial isotope stage 2 and intergl acial isotope stage 1 to the present. The significance of the N.W. European slope as a depositional sink for C-org has declined in the past twenty tho usand years, with Aux values decreasing two to three-fold from the late gla cial (60-70 mg C cm(-2) ka(-1)) to low late Holocene values. Significant sh ifts are seen in the delta(13)C(org) signature of both the total and fine f ractions between the present interglacial and last glacial. The open slope of the Goban Spur is characterised by relatively low values over the last g lacial, with minimum values for the total sediment of around -24.5 parts pe r thousand occurring at ca. 18 ka EP, and generally increasing values durin g the Holocene with the most recent samples having values of ca. -19.2 to - 20.2 parts per thousand. In the Porcupine Sea-Eight a different relationshi p is evident with samples from the Last Glacial Maximum being generally hig her, while values from the Holocene are lower with a minimum of -23.3 parts per thousand occurring just below the mixed layer. Similar trends are obse rved in the fine fraction albeit with a different dynamic range. Paired ana lysis of delta(13)C(org) and C-org/N are consistent with the organic matter being a climatically forced mixture from C-3-photosynthetic terrigenous an d marine organic matter sources. An increased influence of terrestrial C-or g is suggested on the glacial Goban Spur and Holocene Porcupine Sea-Eight, 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-Eight. During the last glacial incre ased strength of westerly winds created a residual current regime driving m aterial to the S.W., where it was transported in vigorous tidal off-shelf f lushing 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 nux of terrestrial C-o rg on the Goban Spur. The influence of a freshwater plume from meltwater di scharge of the European ice sheet in this region is supported by foraminini feral delta(18)O data from which a palaeo-salinity reconstruction shows a g reatest negative anomaly of -2.55 (that is S-35) at the time-of maximum ter restrial C-org content in the sedimentary material. In addition to showing that surface waters over Goban Spur were relatively fresh throughout the gl acial, our results also reveal variability in surface salinity on shorter t imescales. (C) 1998 Elsevier Science Ltd. All rights reserved.