The benthic nepheloid layer (BNL) north of the Keweenaw Peninsula in Lake Superior: Composition, dynamics, and role in sediment transport

Document Type

Conference Proceeding

Publication Date

1-1-2004

Abstract

As part of the Keweenaw Interdisciplinary Transport Experiment in Superior (KITES) project, measurements were made of the extent and the composition of the BNL in Lake Superior off the northwest coast of the Keweenaw Peninsula. Between 1998 and 2000, transmissometer profiles were obtained frequently along three transects oriented perpendicularly to the coast. Large-volume water samples were filtered, and the BNL particles were analyzed for major elements (C, N, P) and 210Pb. In 1998 and 1999, an ROV was deployed to facilitate sampling of this layer. These measurements together with ancillary data from the KITES project show that the BNL develops each summer when the lake is stably stratified and disappears in early fall as the thermocline erodes. Particles within the BNL are enriched in biogenic elements and 210Pb relative to material in surface sediments and relative to material collected in sediment traps, but are enriched in phosphorus relative to epilimnetic seston. There is a large inventory of solids suspended within the BNL (approximately 100,000 metric tons in a 20-km band along the Keweenaw Peninsula); this inventory appears quickly (1-2 weeks) in summer and disappears equally quickly via settling in fall. The large inventory of organic carbon indicates that particles are concentrated from a large area of surface waters into a considerably smaller region where the BNL exists.

Publication Title

Journal of Great Lakes Research

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