Late Quaternary sediment flux on sedimentary drifts in the Northeast Atlantic

Abstract

Comparison between the last glacial and Holocene periods of the terrigenous and carbonate sediment flux distributions in the whole Northeastern Atlantic basin points out the role of deep circulation relative to other processes. During the Holocene, the global terrigenous flux is similar to that during the glacial period (4 compared with 4.7 g cm −2 ky −1), despite a general decrease of terrigenous supplies. The flux distribution, however, is different: high values are located in areas of bottom-current sedimentation (contourite drifts) instead of along continental margins where downslope processes are dominant and areas with major ice-rafting. The global carbonate flux is higher during the Holocene (3 compared with 1.5 g cm −2 ky −1), but the carbonate flux distribution matches that of the terrigenous flux. Both flux patterns are strongly controlled by reworking and redeposition of sediments by bottom currents. Flux variation in three cores collected on the Feni, Gardar and Faro drifts, compared to areas of little or no bottom-current activity, highlights the deep-water circulation fluctuations since the last glacial maximum. In areas dominated by downslope processes (Bay of Biscay) or by ice-rafted sediment deposition (Mid-Atlantic Ridge around 45°N) the sediment fluxes are maximum during the deglacial warming and minimum during the Holocene period. Areas dominated by bottom-current sedimentation are all characterized by highest sedimentation during the Holocene, but the flux variations reveal that the Norwegian Sea Water Overflow (NSWO) and the Mediterranean Outflow (MO) fluctuated differently according to the regional climatic context and the latitudinal transgression of climatic warming. On the Feni and Gardar drifts, higher Holocene fluxes coincide with the re-initiation of NSWO at about 10,000 yrs BP. The highest flux on the Gardar Drift results from a stronger outflow across the Iceland—Faeroe Ridge than across the Faeroe—Scotland Ridge. This flow is responsible for high sediment fluxes all along the eastern side of the Mid-Atlantic Ridge as far south as 45°N. On the Faro Drift, the reactivation of the Mediterranean Outflow (MO) took place earlier, as three episodes of greater bottom-current activity occurred since about 15,000 yrs BP. Fluxes are maximum during the deglacial warming, and remain high during the Holocene.