Science Mission 2

Dissolved and particulate manganese and oxygen in the water column of the upper basins of two hypoxic sea lochs.

Loch Etive and Loch Fyne on the west coast of Scotland consist of a series of basins separated by shallow sills. The outer basins experience estuarine circulation whilst the innermost and deepest basins experience infrequent water renewal leading to hypoxia (low levels of oxygen) in the bottom waters.

The manganese cycle

Hypoxia, in the lochs, allows a build-up of both solid phase (authigenic) manganese (IV) and dissolved (pore-water) manganese (II) in the sediment. The dissolved manganese is able to diffuse into the overlying water column where it can be slowly oxidised, into insoluble manganese (IV). This, in turn, then precipitates to the sediment where it becomes buried and is reduced to soluble manganese(II), thus completing the cycle.

Why use Autosub?

The development of Autosub provided a unique, highly versatile submersible platform with which to determine the concentrations of dissolved and particulate manganese and dissolved oxygen throughout two sea lochs. This utilised the ability of Autosub to follow the terrain or to maintain a pre-set depth.

Related publications

Overnell J., Brand T., Bourgeois W. and Statham P.J., 2002. Manganese dynamics in the water column of the upper basin of Loch Etive, a Scottish fjord. Estuarine, Coastal and Shelf Science, 55(3), 481-492.