Hydrographic Variability in the Bottom Layer of the Iceland Basin

Abstract

The variability of the lowest 400 dbar in the Deep Iceland Basin has been studied for the years 1988?1991. It appears that hydrographic parameters of the Iceland?Scotland Overflow Water in the lowest 100 dbar mainly vary on longer timescales (interannual). Centered around 140 dbar from the bottom, at a more or less constant density level, salinity, dissolved silica, oxygen, and potential vorticity show a maximum in variability. This is attributed to the isopycnal advection of lenses of water with distinct, coherent hydrographic properties. These lenses are assumed to form a mechanism for lateral isopycnal advection of deep water, enriched with either Lower Deep Water or Subpolar Mode Water. The vertical extent of the lenses is determined by a density window between Labrador Sea Water and Iceland?Scotland Overflow Water, centered around σ2.5 = 39.27 kg m?3. The lateral, isopycnal advection, followed by subsequent diapycnal mixing, is proposed as the mechanism to incorporate Lower Deep Water into the Deep Northern Boundary Current and to explain the reported downstream modification of water mass characteristics of Iceland?Scotland Overflow Water in the Deep Northern Boundary current.