Bottom-current variability during the last glacial-deglacial transition, Northern Rockall Trough and Faroe Bank Channel, NE Atlantic

Abstract

Synopsis Two sediment gravity cores and a multicore collected from contourite sediment drifts north and south of the Wyville Thomson Ridge provide a detailed textural record of bottom-current variability since the last glaciation. Four radiocarbon dates indicate that collectively the cores span the last c . 40 ka including the last stadial-interstadial cycle. The Northern Rockall Trough drift cores contain contouritic sediments of Last Glacial Maximum to Holocene age ( c . 18 ka to present). The core from the Faroe Bank Channel contains glaciomarine contouritic sediments of mid-Devensian to Holocene age ( c . 40 ka to present). Both gravity cores were analysed for magnetic susceptibility, wet bulk density, fractional porosity and P-wave velocity further to detailed (1 cm interval) grain-size analyses. The mean sortable silt fraction (10 to 63 μm) of the grain-size data is used to reconstruct the ancestral flow of two different water masses: Norwegian Sea Deep Water in the Faroe Bank Channel and North Atlantic Deep Water in the Northern Rockall Trough. During glaciation, the flow of both water masses was suppressed, although still active, with mean sortable silt values of between 25 and 30 μm during the Last Glacial Maximum. Ice-rafted debris dated at 37 935 14 C years in the Faroe Bank Channel may correspond to Heinrich Event H4. The bottom-current response to the climate amelioration of the early Holocene is one of a steady increase in flow. This response is noted at both sites suggesting a deep-water connectivity between the Northern Rockall Trough and Faroe Bank Channel. Present day flow of North Atlantic Deep Water in the Northern Rockall Trough has been measured at up to 11 cm s −1 corresponding to mean sortable silt values of 36 to 40 μm, compared to glacial and stadial values of <30 μm, suggesting weaker North Atlantic and Norwegian Sea Deep Water flows of <10 cm s −1 during this time.