Resuspension and particle transport in the benthic nepheloid layer in and near Fram Strait in relation to faunal abundances and 234Th depletion

Abstract

The West Spitsbergen Current, flowing northward through Fram Strait, causes a benthic nepheloid layer (BNL) on the western slope of the Yermak Plateau. This BNL is weaker on the eastern side of the Plateau and absent on the Greenland side of the Fram Strait where the East Greenland Current flows south. In this BNL we find throughout a depletion of 234 Th relative to its parent 238 U, and we use this to study the particle dynamics in the BNL. The export flux from the ice-covered surface ocean and from a young bloom found in the ice-free waters off NE Greenland is shown to be negligible, allowing us to explain the 234 Th depletion by interaction with the sediment alone. The depletion, balanced by a similar excess in the surface layer of the sediment, implies the existence of a settlingresuspension loop with an average particle residence time of 1-2 months.The asymmetry with a stronger resuspension loop on the western (80-120 mg m ) is reflected in the numbers of species and individuals of suspension feeders in box core samples, and in epifauna abundance as has been estimated from video observations. The suspension feeders thus contribute to deposit the particles that are advected from more productive ice-free regions. This explanation is in agreement with the eastwest asymmetry in the input of organic material to the sediments of the Yermak Plateau, which has been concluded by Soltwedel et al. (2000) from the distribution of pigments, bacterial activity and meiofauna abundances, observed in a concurrent study at the same stations. On the West Spitsbergen shelf, a very intensive BNL was monitored over one month with a moored filtration system. A part of the sustained high suspended load may be advected over long distances. This study gives an example how the tracer 234 Th can help to determine to what extent suspended particles are in continuous exchange with the seafloor, and where biological mediation and chemical modification can be expected.

Utility of dissolved barium in distinguishing North American from Eurasian runoff in the Arctic Ocean

“…High biological activity is seen especially in the Barents and Laptev seas during our expedition from high carbon export shown for both regions by Cai et al (2010) using the 234 Th method (2.7 and 2.9 mmol m -2 d -1 , respectively). In the basins where the water was covered by sea ice very low export production was observed in 2007 (0.2 mmol m -2 d -1 ) and former years (Cai et al, 2010;Rutgers van der Loeff et al, 2002). Moreover Arrigo et al (2008) estimate that primary production in 2007 was higher by 12.5-20.8 mol m -2 yr -1 compared to 2006 in ice-free areas of the Siberian and Laptev sectors.…”

Lithogenic and biogenic particle fluxes on the Lomonosov Ridge (central Arctic Ocean) and their relevance for sediment accumulation: Vertical vs. lateral transport

“…The most probable transport is related to the Atlantic and intermediate water layers, which may carry material from the Barents and Kara Seas along the Eurasian continental margins and recirculate northwards to the Amundsen Basin, passing the trap position (Rudels et al, 2000). Additional transport of material to the trap position within a benthic nepheloid layer (BNL), which may extend several hundred meters above the seafloor (Rutgers van der Loeff et al, 2002), and local resuspension cannot be excluded. The BNL is maintained by fine particles (e.g., clay minerals), which can be transported over very long distances (Rutgers van der Loeff et al, 2002).…”

“…Additional transport of material to the trap position within a benthic nepheloid layer (BNL), which may extend several hundred meters above the seafloor (Rutgers van der Loeff et al, 2002), and local resuspension cannot be excluded. The BNL is maintained by fine particles (e.g., clay minerals), which can be transported over very long distances (Rutgers van der Loeff et al, 2002). Unfortunately, no data on ARTICLE IN PRESS K. Fahl, E.-M. Nöthig / Deep-Sea Research I 54 (2007) 1256-1272the existence of a BNL at the trap location are available.…”

“…These tracers have been widely used in marine environments to determine particle removal rates, settling velocity of particles, and export of particulate organic carbon, and they may allow to distinguish between vertical and lateral transport of particulate organic matter in more detail (e.g., Yu et al, 2001;Rutgers van der Loeff et al, 2002;Trimble et al, 2004;Baskaran, 2005). These data, however, are not yet available for the area of sediment trap Lomo2.…”

Aliphatic lipids in recent sediments of the Fram Strait/Yermak Plateau (Arctic Ocean): composition, sources and transport processes

“…1). Besides our study, oceanographic and biological investigations were recently performed on similar stations or adjacent Transects and stations (Andreassen et al, 1996;Owrid et al, 2000;Soltwedel et al, 2000;Rudels et al, 2000;Rutgers van der Loeff et al, 2002;Schewe and (Hebbeln and Berner, 1993;Stein et al, 1994;Notholt, 1998;Kierdorf, 2001; and on www.pangaea.de). Samples used for lipid analysis are indicated by white dots.…”