Andrews Abstract:: 43rd International Arctic Workshp

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Was sediment exported from Baffin Bay across Davis Strait to the Labrador Sea during the last glacial cycle?

Andrews, John T ¹ ; Gibb, Olivia T ² ; Jennings, Anne E ³ ; Simon, Quentin ⁴

¹ INSTAAR and Department of Geological Sciences, Box 450, University of Colorado, CO 80309, USA
² GEOTOP, Université du Québec à Montréal, C.P. 8888 Succ. Centre-Ville, Montréal, QC H3C 3P8, Canada
³ INSTAAR and Department of Geological Sciences, Box 450, University of Colorado, CO 80309, USA
⁴ GEOTOP, Université du Québec à Montréal, C.P. 8888 Succ. Centre-Ville, Montréal, QC H3C 3P8, Canada

Quaternary glacial marine sediments in both Baffin Bay and the Labrador Sea contain units that are dominated by detrital carbonates, eroded from mainly Paleozoic outcrops that floor many of the large grabens (e.g. Hudson Strait, Lancaster Sound), which were the product of early Tertiary rifting. In the Labrador Sea, these detrital carbonate-rich sediments (DC sediments or events), define the widely studied North Atlantic Heinrich (H-)-events. On the slope and floor of the Labrador Sea the DC sediments in the < 2 mm fraction are dominated by calcite versus dolomite in ratios ~6:1 and as a result magnetic susceptibilities within H-events are troughs. The DC-rich sediments thin along the transport path toward W/NW Europe where the carbonate in H-events is mainly dolomitic and where H-events are peaks in magnetic susceptibility. In contrast to Labrador Sea, DC sediments in Baffin Bay are marked by high weight %s of dolomite and low calcite, often with iron substituting into the crystal structure, which gives the sediment a buff, brownish color. As a consequence, the question that has been raised is whether Baffin Bay DC events (BBDC) and H-events are coeval, and if not, whether there are demonstrable leads and/or lags in the two areas? A corollary question is whether the DC events are associated with the importation of “warm” Atlantic Waters (Hiscott et al., 1989)? And yet another important question is whether, as has been suggested, an ice shelf ever existed in Baffin Bay and the Labrador Sea during the LGM interval, and is indeed a necessary condition for ice stream collapses?

To attempt an answer to these questions we undertook a study of a site cored during the HU2008029 cruise (Andrews et al., in press) and which recovered a box core (0006BC), and trigger and piston cores (0008TC, 0008PC) from a site in ~ 840 m of water and just to the south of the 600 m deep Davis Strait sill (Fig. 1). The main proxy for sediment export and provenance is the quantitative mineralogy of the < 2 mm sediment fraction, obtained from X-ray diffraction analysis using the methods developed by Eberl and used in Baffin Bay by Andrews and Eberl (2011). We compare the records from this site to a detailed record constructed by Simon et al (2012) from HU2008029-016PC from the deep central basin of Baffin Bay, and a series of cores from the slope and sea floor of the Labrador Sea, including HU2008029-0004TC and PC. A radiocarbon-based chronology for the 0008 site, based on 12 dates on planktonic foraminifera, had to be rejected, and an alternative depth/age model was developed based on correlation of DC events in Baffin Bay (016PC) and on the Labrador Sea slope (HU97049-007PC). Site 0008TC/PC shows a series of 5 dolomite-rich DC (Fig. 2) events derived from outcrops north of Baffin Bay and one (basal) calcite-rich event (probably originated from Hudson Strait). However, the bulk of the sediment is associated with two large West Greenland ice streams that reached the shelf break (Jennings et al., subm.; O'Cofaigh et al., in press). It appears that there is no evidence for collapse of the northern ice streams coeval with H-1 (~16 cal ka BP) nor H-2 (~24 cal ka BP).

Andrews, J.T., Eberl, D.D., 2011. Surface (sea floor) and near-surface (box core) sediment mineralogy in Baffin Bay as a key to sediment provenance and ice sheet variations. Canadian Journal of Earth Science 48, 1307-1328.

Andrews, J.T., Gibb, O.T., Jennings, A.E., Simon, Q., in press. Variations in the provenance of sediment from ice sheets surrounding Baffin Bay during MIS 2 and 3 and export to the Labrador Sea: Site HU2008029-0008 Davis Strait. Journal of Quaternary Science.

Jennings, A.E., Walton, M.E., O Cofaigh, C., Killfeather, A.A., J.T., A., Ortiz, J.D., de Vernal, A., Dowdeswell, J.A., subm. Paleoenviroments during Younger Dryas-early Holocene Greenland ice retreat from outer Disko Trough, central West Greenland. Journal of Quaternary Science.

O'Cofaigh, C., Dowdeswell, J.A., Jennings, A.E., Hogan, K.A., Killfeather, A.A., Hiemstra, J.H., Noormets, R., Evans, J., McCarthy, D.J., Andrews, J.T., Lloyd, J.M., Moros, M., in press. An extensive and dynamic ice sheet on the West Greenland shelf durting the last glacial cycle. Geology.

Simon, Q., St-Onge, G., Hillaire-Marcel, C., 2012. Late Quaternary chronostratigraphic framework of deep Baffin Bay glaciomarine sedimentts from high-resolution paleomagnetic data. Geochemistry, Geophysics, Geosystems, 13, Q0AO03, doi:10.1029/2012GC004272 .

Fig 1.

Figure 1: Map of the Davis Strait area and location of relevant core sites.

Fig 2.

Figure 2: Graph of the down-core variations in dolomite (black line) and calcite weight % (grey line with filled circles) in HU2008029-0008PC on a chronology tied to HU97049-007PC (See Fig. 1)