Porewater nutrient concentrations and benthic nutrient fluxes across the Pakistan margin OMZ

Clare Woulds, Matthew Schwartz, Tim Brand, G Cowie, Gareth Law, S R Mowbray

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Abstract

Porewater concentrations and benthic fluxes of phosphate, silicate, ammonia, nitrate and nitrite were measured at five sites spanning the Pakistan margin oxygen minimum zone (OMZ), in order to characterise the biogeochemical processes occurring, and to assess whether oxygen concentration and a seasonal pulse of organic matter are controlling factors. Typical concentrations of 1-70 mu M, 50-250 mu M, 0-270 mu M, 30 cm) in the sediment. These processes are all redox-sensitive, and their intensities varied across the margin, suggesting that oxygen concentration exerts a strong influence over nutrient concentrations and cycling. Variation in nutrient concentrations and fluxes before and after the summer monsoon was limited to an oxygen-driven change to the PO43- profile at one site, indicating that either nutrient profiles do not generally alter on seasonal timescales, or that any impact of the monsoon had subsided before the post-monsoon sampling period. Porewater profile modelling tended to underestimate the magnitude of fluxes, but was in general agreement with the directions of measured fluxes, and in situ and shipboard flux measurements also generally agreed. Phosphate and H4SiO4 concentrations and benthic fluxes on the Pakistan margin were similar to those reported at abyssal sites from around the world, while NH4+ and NOT concentrations and fluxes were comparable to shallower, more productive and/or hypoxic marine settings. (C) 2008 Elsevier Ltd. All rights reserved.
Original languageEnglish
Pages (from-to)333-346
Number of pages14
JournalDEEP-SEA RES PT II
Volume56
Issue number6-7
DOIs
Publication statusPublished - 2009

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Keywords

  • NORTH PACIFIC
  • OXYGEN-DEFICIENT ZONE
  • ARABIAN SEA
  • SOUTH ATLANTIC
  • PORE-WATER
  • ORGANIC-MATTER
  • OMAN MARGIN
  • Oceanography
  • CONTINENTAL-MARGIN
  • DEEP-SEA SEDIMENTS
  • SHELF

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