Transport of fine-grained sediment in oceanic currents: Holocene supply to sediment drifts around Flemish Cap by the Labrador Current

Abstract Hemipelagic sediment on the upper continental slope is commonly transported from the adjacent continental shelf, but along-slope transport of sediment by thermohaline currents may be an important source of sediment. One such case is Flemish Cap, a promontory of the eastern Canadian continental shelf protected from direct continental sediment supply by the deep-water Flemish Pass. Pleistocene sediment drifts around Flemish Cap accumulated glacially derived sediment from the north, transported by the Labrador Current. This study determines the changing sources and controls on the accumulation of bioturbated hemipelagic sediment through the Holocene. From a set of >150 box cores in water depths of 600–1200 m, some 30 push cores, up to 55 cm long, were studied in detail for stratigraphic variation in grain size, bulk geochemistry (XRF) and detrital petrology (granule petrology and qXRD). Criteria were developed to identify trawling disturbance. Two Holocene stratigraphic units, A) almost lacking ice-rafted detritus and B) with some coarse IRD and higher detrital carbonate, correlate with similar units farther north on the Labrador Shelf and Slope. Sedimentation rates based on 26 radiocarbon dates were ~ 0.02–0.03 m/ka over much of the region below the 800 m isobath, locally reaching 0.1 m/ka in some sediment drifts, but as low as 0.01 m/ka on southeastern Flemish Cap. Where sedimentation rate was >0.03 m/ka, the record of flow vigor from the sortable silt proxy since 6 ka shows three different zones of Labrador Current flow with different timing of changes in flow vigor. The mid to early Holocene record shows that the meltwater-driven inner Labrador Current extended across the entire study area. Where sedimentation rates are lower, periods of sediment bypassing are inferred and the sortable silt record varies little. Correlation with external drivers is hampered by century-scale core resolution and sparse dating control. The distinctive abundance of dolomite rock flour in hemipelagic sediments around Flemish Cap indicates important supply from Baffin Bay icebergs during the entire Holocene, diluted prior to 6 ka by sediment from Hudson Strait and some Labrador ice streams. Baffin Bay icebergs melt preferentially in the southern Labrador Sea, dropping their load, with the fine grained component transported to the south by the Labrador Current. Similar partitioning of coarse- from fine-grained components of IRD may take place on other high-latitude outer continental margins.