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Spring-neap modulation of internal tide mixing and vertical nitrate fluxes at a shelf edge in summer

Sharples, J.; Tweddle, J. F.; Mattias Green, J. A.; Palmer, M. R.; Kim, Y-N.; Hickman, A. E.; Holligan, P. M.; Moore, C. M.; Rippeth, T. P.; Simpson, J. H.; Krivtsov, V.. 2007 Spring-neap modulation of internal tide mixing and vertical nitrate fluxes at a shelf edge in summer. Limnology and Oceanography, 52 (5). 1735-1747. 10.4319/lo.2007.52.5.1735

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Abstract/Summary

Measurements of the intra-tidal and spring-neap variation in the vertical flux of nitrate into the base of the sub-surface chlorophyll maximum (SCM) were made at the shelf edge of the Celtic Sea, a region with strong internal mixing driven by an internal tide. The neap tide daily mean nitrate flux was 1.3 (0.9 – 1.8, 95% confidence interval) mmol m-2 d-1. The spring tide flux was initially estimated as 3.5 (2.3 – 5.2, 95% confidence interval) mmol m-2 d-1. The higher spring tide nitrate flux was the result of turbulent dissipation occurring within the base of the SCM, compared to deeper dissipation during neap tides, and was dominated by short events associated with the passage of internal solitons. Taking into account the likely under-sampling of these short mixing events raised the spring tide nitrate flux estimate to about 9 mmol m-2 d-1. The neap tide nitrate flux was sufficient to support substantial new production and a considerable fraction of the observed rates of carbon fixation. Spring tide fluxes were potentially in excess of the phytoplankton community’s capacity to uptake nitrate. This potential excess nitrate flux during spring tides may be utilised to support new production during the lower mixing associated with the transition towards neap tide. The shelf edge is shown to be a region with a significantly different phytoplankton community compared to the adjacent Celtic Sea and NE Atlantic Ocean, highlighting the role of gradients in physical processes leading to gradients in ecosystem structure

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.4319/lo.2007.52.5.1735
Programmes: Oceans 2025 > Shelf and coastal processes
ISSN: 0024-3590
Additional Keywords: NISCOCT07 AJWOCT07 HIJ ISI AR0708 JOURNAL OPM2007 ISI PROCESS EXPERIMENT AT SMALL SCALE SHALLOW COASTAL SEAS - FUNCTION AND IMPACTS OF CHANGE SHELF EDGE NITRATE FLUX PHYTOPLANKTON TURBULENCE INTERNAL TIDE CELTIC SEA PHYTOPLANKTON GROWTH GEORGES BANK BREAK DISSIPATION OCEAN BAY BISCAY WAVES AGGREGATIONS
NORA Subject Terms: Marine Sciences
Date made live: 13 Oct 2008 11:49
URI: http://nora.nerc.ac.uk/id/eprint/2674

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