213
atmospheric circulation on the ocean; while this certainly does not rule
out either feedbacks from anomalous ice and SST conditions on the atmosphere, or autonomous oscillations of the ocean's overturning circulation,
it does tend to minimise them.
2 Variability of deep convection in the Greenland
Sea, and its controls
2.1 General description
The deep water of the Greenland Sea [GSDW] is renewed from two sources,
either by horizontal exchange with the deep waters of the Arctic Ocean
through Fram Strait [sill depth 2600 m], or by vertical exchange as a result
of local, deep-reaching, open-ocean convection.
Inputs from these two sources have very different effects on the hydrographic character of the GSDW (Aagaard, 1981; Swift, Takahashi and
Livingston, 1983). Arctic Ocean Deep Water is largely formed by "slope
convection", in which dense water from the broad Arctic shelves (the result of brine rejection during seasonal ice-formation; Nansen, 1906, Midttun, 1985) spills over the shelf-edge and descends the Slope, encountering and entraining a warm intermediate layer of Atlantic water as it does
so. The product then penetrates to a depth determined by its initial salinity and by the subsequent alteration of its () - S characteristics during
descent. As Rudels and Quadfasel point out [1991]' the large volumes of
the Eurasian and Canadian Basins effectively buffer the Arctic Ocean Deep
Water against change so that its () - S properties are thought to be relatively stable in time, despite obvious interannual changes in the production
of sea-ice, and presumably of brine.
However, in the context of the present discussion, the key point is that,
as pointed out by Meincke, Jonsson and Swift, [1992]' the downslope penetration of high salinity shelf water at freezing temperatures and the net
entrainment of warm Atlantic waters produce a net downward flux of heat
and salt for the Arctic Basins, in stark contrast to the situation in the
Greenland Sea where, in the stepwise convective process, the entrainment
of freshwater in haline plumes at freezing temperatures, and the penetrative character of the plumes in the intermediate warm layer results in an
upward flux of heat and salt [Figure 1, from Meincke, Jonsson and Swift,
op cit]. As a direct result, the AODW is the warmest and most saline
atmospheric circulation on the ocean; while this certainly does not rule
out either feedbacks from anomalous ice and SST conditions on the atmosphere, or autonomous oscillations of the ocean's overturning circulation,
it does tend to minimise them.
2 Variability of deep convection in the Greenland
Sea, and its controls
2.1 General description
The deep water of the Greenland Sea [GSDW] is renewed from two sources,
either by horizontal exchange with the deep waters of the Arctic Ocean
through Fram Strait [sill depth 2600 m], or by vertical exchange as a result
of local, deep-reaching, open-ocean convection.
Inputs from these two sources have very different effects on the hydrographic character of the GSDW (Aagaard, 1981; Swift, Takahashi and
Livingston, 1983). Arctic Ocean Deep Water is largely formed by "slope
convection", in which dense water from the broad Arctic shelves (the result of brine rejection during seasonal ice-formation; Nansen, 1906, Midttun, 1985) spills over the shelf-edge and descends the Slope, encountering and entraining a warm intermediate layer of Atlantic water as it does
so. The product then penetrates to a depth determined by its initial salinity and by the subsequent alteration of its () - S characteristics during
descent. As Rudels and Quadfasel point out [1991]' the large volumes of
the Eurasian and Canadian Basins effectively buffer the Arctic Ocean Deep
Water against change so that its () - S properties are thought to be relatively stable in time, despite obvious interannual changes in the production
of sea-ice, and presumably of brine.
However, in the context of the present discussion, the key point is that,
as pointed out by Meincke, Jonsson and Swift, [1992]' the downslope penetration of high salinity shelf water at freezing temperatures and the net
entrainment of warm Atlantic waters produce a net downward flux of heat
and salt for the Arctic Basins, in stark contrast to the situation in the
Greenland Sea where, in the stepwise convective process, the entrainment
of freshwater in haline plumes at freezing temperatures, and the penetrative character of the plumes in the intermediate warm layer results in an
upward flux of heat and salt [Figure 1, from Meincke, Jonsson and Swift,
op cit]. As a direct result, the AODW is the warmest and most saline