Sediments in Bottom-Arrested Gravity Plumes: Numerical Case Studies*

Abstract

In the present paper a hydrostatic ''reduced gravity'' model, generally used to simulate transient bottomarrested gravity plumes, was coupled with a sediment transport model. The coupled model considers the respective contribution of suspended sediment particles on the buoyancy of a plume and allows one to simulate autosuspension and size-differential deposition of sediments based on the local turbulence and settling velocities. Simulations using the coupled model reveal that sediment-enriched plumes are able to inject both entrained and original shelf water masses into intermediate and bottom layers of an adjacent ocean basin in an ageostrophic dynamical balance. Hence the mechanism described here is more rapid than classic, ''seawater'' plumes, which are solely driven by surplus density of the water masses. Results suggest that ''turbidity'' plumes may constitute an important process in the formation and renewal of deep waters in the Arctic Ocean. In case a turbidity plume reaches its level of equilibrium density, deposition of suspended particles causes the density of the interstitial fluid to be lower than the density of the ambient fluid. This initiates upward convection within the water column.The substantial difference between TS-and turbidity plumes is described by model experiments that utilize idealized slope and sediment distributions. A realistic simulation of a turbidity plume cascading down the continental slope of the western Barents Sea is presented. The computed distribution of deposited sediments agrees well with observations in an area of high accumulation of shelf-derived sediments. The frequency of occurrence of sediment-enriched gravity plumes originating from the Barents Sea shelf is estimated from the various geological variables (thickness of sediments at the bottom, grain size composition) measured from bottom sediments samples.

Paleomagnetism and rock magnetism from sediments along a continental shelf-to-slope transect in the NW Barents Sea: Implications for geomagnetic and depositional changes during the past 15 thousand years

“…According to Rebesco et al (2011) these ridges are grounding-zone wedges (GZWs) derived by deposition of unconsolidated, saturated subglacial till during episodic stillstands of the overall ice-stream retreat during last deglaciation. The inner area of the trough contains a complex sediment drift composed by two depocenters (Main and Minor drifts, Rebesco et al, 2016) whose onset was related to the interplay of Atlantic and Arctic waters (West and East Spitzbergen currents respectively), and brine-enriched shelf water (BSW, Aagaard et al, 1985;Fohrmann et al, 1998;Thomsen et al, 2001) produced on the shelf during winter which formation started at around 13 cal ka BP . The Kveithola TMF merges with the neighboring, larger Storfjorden TMF, together forming the Kveithola-Storfjorden TMF system built by glacigenic deposits during full glacial conditions and glacimarine sediments during interglacials (Vorren and Laberg, 1997;Lucchi et al, 2013).…”

“…In contrast, the slope Core 17603-3 was recovered from a depocenter, where sediment accumulated under the synergic effect of slow along slope contour currents generating crude sediment layering, and across-slope dense bottom currents supplying sediments from the shelf area (the Turbid and Saline flows named TS plumes by Fohrmann et al, 1998). In this respect, the slope area of site 17603-3 can be considered as an embryonic sediment drift sharing onset and development characteristics with the Bellsund and Isfjorden sediment drifts studied along the Svalbard western margin Lantzsch et al, 2017).…”

Reconstruction of Atlantic water variability during the Holocene in the western Barents Sea

“…1b), is occupied by Arctic water masses (Loeng, 1991). Transport of cold and sediment-laden shelf bottom waters from Spitsbergenbanken through Kveithola Trough to the continental slope is reported by Fohrmann et al (1998). The boundary between Arctic and Atlantic water is the Arctic front (also called the polar front), which forms sharp climatic gradients in terms of temperature, salinity, and sea-ice distribution (Hopkins, 1991).…”

“…The timing of the deglaciation of the surrounding Spitsbergenbanken is not well constrained, but a minimum deglaciation age of 11 200 yr BP has been inferred for Bear Island (Wohlfarth et al, 1995). Meltwater from the glaciers located at Bear Island during the Younger Dryas would have been partly discharged through Kveithola Trough since its inner basin is connected to channels that drain parts of the Bear Island banks (Fohrmann et al, 1998). While the trough was still influenced by meltwater input and presence of sea ice, BWT TF started to rise (Fig.…”

A review of the role of submarine canyons in deep-ocean exchange with the shelf

“…Temperature cooling drives the formation of dense water in all climate zones, while salinity that either fosters or hampers the cascading is generally secondary (Ivanov et al, 2004). Furthermore suspended sediment can have a significant influence upon the density of the bottom water and intensifies the downslope cascading process, increasing the equilibrium depth and eventually provoking ascendant convection of the dense water plume after deposition of the particulate load (Fohrmann et al, 1998;Kämpf et al, 1999).…”