Marine Chemistry, 56, 1-14, 1997
Inter-relationships among these parameters proved to be effective at delineating three water masses: Columbia River Plume Water (CRPW), Sheld Deep Water (SDW), and Shelf Bottom Water (SBW). CRPW had variable amounts of FDOM, dissolved Mn, and Chl a as the plume mixed with coastal water. SBW was characterized by high concentrations of Chl a and low concentrations of dissolved Mn, suggesting a surface or near-surface source. The properties of SDW were intermediate between humic-rich plume water and turbid bottom water.
FDOM displayed a quasi-linear and inverse relationship with salinity inside the estuary and nearshore coastal plume which supports previous work relating this parameter to the humic-rich terrestrial component of dissolved organic matter (DOM). There was, however, considerable evidence of lower FDOM levels within te estuarine turbidity maximum (ETM) and near the seaward boundary of the plume. There weree aldo elevated levels of FDOM near the bottom at some locations on the shelf, suggesting that there may be a significant benthic flux of this material. Thus FDOM appears to be more reactive than previously thought when looked at in detail.
Dissolved Mn also displayed non-conservative behavior in the estuary and across the plume showing significant input into surface waters. The sharpest Mn gradient on the shelf occurred near the seaward edge of the plume in an area of relatively high turbidity and Chl a, and relatively low FDOM. These contributions are consistent with the presence of a chemical front near the plume boundary where Mn-oxides are reduced during the oxidation of humic ligands. This process would release dissolved Mn and promote productivity in the turbid zone associated with the leading edge of the plume jet. This study demonstrates that chemical sensors can provide highly resolved, detailed information on trace substance distribution and variabilty in marine environments.
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