Spatially Complex Distribution of Dissolved Manganese in a Fjord as Revealed by High-Resolution in Situ Sensing Using the Autonomous Underwater Vehicle Autosub

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• 作者：P. J. Statham ; D. P. Connelly ; C. R. German ; T. Brand ; J. O. Overnell ; E. Bulukin ; N. Millard ; S. McPhail ; M. Pebody ; J. Perrett ; M. Squire ; P. Stevenson ; and A. Webb
• 刊名：Environmental Science & Technology
• 出版年：2005
• 出版时间：December 15, 2005
• 年：2005
• 卷：39
• 期：24
• 页码：9440 - 9445
• 全文大小：250K
• 年卷期：v.39,no.24(December 15, 2005)
• ISSN：1520-5851

文摘

Loch Etive is a fjordic system on the west coast ofScotland. The deep waters of the upper basin areperiodically isolated, and during these periods oxygen islost through benthic respiration and concentrations ofdissolved manganese increase. In April 2000 the autonomousunderwater vehicle (AUV) Autosub was fitted with an insitu dissolved manganese analyzer and was used to studythe spatial variability of this element together withoxygen, salinity, and temperature throughout the basin.Six along-loch transects were completed at either constantheight above the seafloor or at constant depth belowthe surface. The ca. 4000 in situ 10-s-average dissolvedMn (Mn_d) data points obtained provide a new quasi-synopticand highly detailed view of the distribution of manganesein this fjordic environment not possible using conventional(water bottle) sampling. There is substantial variability inconcentrations (<25 to >600 nM) and distributions of Mn_d.Surface waters are characteristically low in Mn_d reflectingmixing of riverine and marine end-member waters, bothof which are low in Mn_d. The deeper waters are enrichedin Mn_d, and as the water column always contains someoxygen, this must reflect primarily benthic inputs of reduceddissolved Mn. However, this enrichment of Mn_d isspatially very variable, presumably as a result of variabilityin release of Mn coupled with mixing of water in theloch and removal processes. This work demonstrates howAUVs coupled with chemical sensors can reveal substantialsmall-scale variability of distributions of chemical speciesin coastal environments that would not be resolved byconventional sampling approaches. Such information isessential if we are to improve our understanding of thenature and significance of the underlying processes leadingto this variability.