Pb isotopes from Fram Strait sediments since the LGM

Pb isotopes and geochemical monitoring of Arctic sedimentary supplies and water mass export through Fram Strait since the Last Glacial Maximum

Maccali, J. ; Hillaire-Marcel, C. ; Carignan, J. ; Reisberg, L.

Paleoceanography, 2012, 27, PA1201

Abstract :

Elemental and Pb isotope measurements were performed on leachates and residues from surface sediments and two <50 cm cores (MC04 and MC16) collected along a NE-SW transect through Fram Strait. Geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the Strait : 1) the easternmost edge of the Strait ; 2) the eastern part of the Strait off the Svalbard margins ; and 3) the western part of the Strait, influenced by supplies from Svalbard, the Nordic seas with possible contributions from northwestern Siberian margins, and sea ice and water outflow from the Arctic, respectively. Core MC16, in the third domain beneath the outflowing Arctic waters, spans the Last Glacial Maximum present interval. Sediments from this core were leached to obtain detrital (residues) and exchangeable (leachates) fractions. Detrital supplies to core MC16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in Arctic sedimentary sources. Detrital 206Pb/204Pb and 208Pb/206Pb ratios illustrate two mixing trends, Trends A and B, corresponding to the pre- and post-Younger Dryas (YD) intervals, respectively. These trends represent binary mixtures with a common end-member (Canadian margins) and either a Siberian (Trend A) or Greenland (Trend B) margin end-member. The YD is marked by an isotopic excursion toward the Canadian end-member, suggesting a very active Beaufort Gyre possibly triggered by massive drainage of the Laurentide ice sheet. Pb isotope compositions of leachates, thought to represent the signature of the overlying water masses, define a unique linear trend coincident with Trend A. This suggests that water masses acquired their signature through exchange with particulate fluxes along the Canadian and Siberian continental margins.

Figure. 208Pb/206Pb versus 206Pb/204Pb diagram illustrating the detrital trends along with data from the literature for marine sediments and potential source regions. (a) GIN Seas and European sources along with residues from cores MC04 and MC16 and surface sediments. (b) Arctic sources and sediments along with residues from core MC16.