Spatially complex distribution of dissolved manganese in a fjord as revealed by high-resolution in situ sensing using the autonomous underwater vehicle autosub

Peter Statham, Drew Connolly, CR German, Tim Brand, Julian Overnell,

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)

Abstract

Loch Etive is a fjordic system on the west coast of Scotland. The deep waters of the upper basin are periodically isolated, and during these periods oxygen is lost through benthic respiration and concentrations of dissolved manganese increase. In April 2000 the autonomous underwater vehicle (AUV) Autosub was fitted with an in situ dissolved manganese analyzer and was used to study the spatial variability of this element together with oxygen, salinity, and temperature throughout the basin. Six along-loch transects were completed at either constant height above the seafloor or at constant depth below the surface. The ca. 4000 in situ 10-s-average dissolved Mn (Mn-d) data points obtained provide a new quasi-synoptic and highly detailed view of the distribution of manganese in this fjordic environment not possible using conventional (water bottle) sampling. There is substantial variability in concentrations (600 nM) and distributions of Mn-d. Surface waters are characteristically low in Mn-d reflecting mixing of riverine and marine end-member waters, both of which are low in Mn-d. The deeper waters are enriched in Mn-d, and as the water column always contains some oxygen, this must reflect primarily benthic inputs of reduced dissolved Mn. However, this enrichment of Mn-d is spatially very variable, presumably as a result of variability in release of Mn coupled with mixing of water in the loch and removal processes. This work demonstrates how AUVs coupled with chemical sensors can reveal substantial small-scale variability of distributions of chemical species in coastal environments that would not be resolved by conventional sampling approaches. Such information is essential if we are to improve our understanding of the nature and significance of the underlying processes leading to this variability.
Original languageEnglish
Pages (from-to)9440-9445
Number of pages6
JournalENVIRON SCI TECHNOL
Volume39
Issue number24
DOIs
Publication statusPublished - 2005

Keywords

  • Environmental Sciences
  • CARBON
  • WATER COLUMN
  • SCOTTISH SEA LOCH
  • Engineering, Environmental
  • PLUMES
  • SEDIMENTS
  • IRON
  • BASIN

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