Variability of the intermediate-depth Deep Western Boundary Current at the Carolina Slope since the Last Glacial Maximum from mean sortable silt size

The Deep Western Boundary Current (DWBC) transports freshly ventilated waters from the subpolar North Atlantic southwards in the lower limb of the Atlantic Meridional Overturning Circulation (AMOC). As AMOC transports large amounts of heat polewards, variations in its strength can have major implications for regional and global climate. We have reconstructed variations in the DWBC at intermediate depths since the Last Glacial Maximum using the dynamical proxy of mean sortable silt size (mean SS) on core KN140-2-51GGC at 1790 m water depth on the Carolina Slope. Samples were treated to remove organic material, carbonates, and biogenic opal, and grain sizes were measured with a Retsch Camsizer optical instrument. The record shows several changes in mean SS through the transition from LGM to Holocene. Coarser mean SS, typically interpreted as reflecting faster current speeds and winnowing of finer sediments, occurs at the LGM and may record vigorous Glacial North Atlantic Intermediate Water flow, although downslope transport of sediment due to lower sea level also may contribute to the coarse mean SS. Finer mean SS at the time of Heinrich Event 1 may reflect a slower DWBC at this depth, consistent with other studies suggesting reduced AMOC activity at intermediate to deep levels at this time. A dramatic rise in mean SS between 14 and 13 ka, the most notable feature of the record, suggests acceleration of the DWBC in the later part of the Bolling-Allerod, followed by an abrupt drop in mean silt size at the start of the Younger Dryas. Mean SS remains low into the early Holocene, with short-lived (decadal-scale) drops at 8.2 ka and 0.2 ka, and increasing millennial-scale variability into the later Holocene. Our record likely reflects both general Holocene climate and oceanographic stability compared to the deglacial, and contributions to the DWBC of Labrador Sea Water in the later Holocene after its inception.