12
S.S. Jacobs, C.F. Giulivi
is comprised of a mixed layer of variable thickness, with or without an underlying “winter water” layer. As AASW cools, thickens, and becomes saltier in winter,
much of it is transformed back into shelf waters.
5 General Circulation
The large-scale océan circulation on the Ross Sea continental shelf consists of
AASW, LSSW and MCDW inflows from the north and east (Figs. 4 and 5) that are
seasonally cooled and warmed, salinized by sea ice formation and freshened by
meltwater. Surface circulation on the open shelf generally moves ice and water to
the west and north, and is bounded by a strong, narrow Coastal current along the
Ross Ice Shelf and another westward flow near the continental shelf break [26].
Intense winter sea ice formation and its removal from the coastlines produces the
nearly isothermal LSSW and HSSW. Coastal upwelling in these same régions is
consistent with the large-scale density field [2] and with prédominant offshore
winds.
Shelf waters contribute directly to bottom water formation near the continental shelf break [1, 6]. In addition, some portion of the HSSW and LSSW drains
into the deeper cavity beneath the Ross Ice Shelf, where glacial ice is melted,
probably most strongly near the deep grounding lines. This occurs because seawater freezing température decreases with increasing pressure, and results in a
deep ISW plume that emerges in the central Ross Sea (Fig. 4). Both this outflow
and shallower filaments near the ice front may contain ice crystals, produced as
the rising water reacts to supercooling [7, 31]. Circulation, melting and subséquent freezing beneath the shelf ice hâve been inferred from measurements near,
on and beneath the ice, and from models of the sub-ice circulation (e.g., [3,6,3238]). The strength of the sub-ice circulation and its exchanges with the open Ross
Sea are likely to vary considerably over interannual and longer periods in
response to changes in HSSW salinity and volume [15].
The Ross Sea continental shelf is covered by sea ice for most of the year, with
decay and growth both starting near the ice shelf front, typically in late October
and late February. Northward transport of sea ice is strongest in the western sector, where barrier and katabatic winds maintain the large Ross Sea Polynya adjacent to the ice shelf front [39] and a small, persistent polynya near 75°S on the
Victoria Land coast [40], The volume and salinity of HSSW will dépend in part
on the volume of sea ice produced on the continental shelf and exported from it
each year. Detailed records of ice transport are not yet available, however, and sea
ice thickness data are scarce [41]. The length of the sea ice season on the shelf
varied by about a month from 1979 to 1987, with little apparent interannual
change in winter ice concentration [9]. A longer Comiso sea ice record from the
entire Ross Sea displays strong interannual changes in the sea ice extent [15] at a
period comparable to that of the “Antarctic circumpolar wave” [42].
MCDW intrudes year-round at intermediate depths onto the continental shelf
[10, 18], and overrides the HSSW at some locations in the western sector. Since
the HSSW shoals rapidly westward, the “warm” MCDW that pénétrâtes this sector will lie directly beneath the AASW, from which it cannot easily be discrimi-
S.S. Jacobs, C.F. Giulivi
is comprised of a mixed layer of variable thickness, with or without an underlying “winter water” layer. As AASW cools, thickens, and becomes saltier in winter,
much of it is transformed back into shelf waters.
5 General Circulation
The large-scale océan circulation on the Ross Sea continental shelf consists of
AASW, LSSW and MCDW inflows from the north and east (Figs. 4 and 5) that are
seasonally cooled and warmed, salinized by sea ice formation and freshened by
meltwater. Surface circulation on the open shelf generally moves ice and water to
the west and north, and is bounded by a strong, narrow Coastal current along the
Ross Ice Shelf and another westward flow near the continental shelf break [26].
Intense winter sea ice formation and its removal from the coastlines produces the
nearly isothermal LSSW and HSSW. Coastal upwelling in these same régions is
consistent with the large-scale density field [2] and with prédominant offshore
winds.
Shelf waters contribute directly to bottom water formation near the continental shelf break [1, 6]. In addition, some portion of the HSSW and LSSW drains
into the deeper cavity beneath the Ross Ice Shelf, where glacial ice is melted,
probably most strongly near the deep grounding lines. This occurs because seawater freezing température decreases with increasing pressure, and results in a
deep ISW plume that emerges in the central Ross Sea (Fig. 4). Both this outflow
and shallower filaments near the ice front may contain ice crystals, produced as
the rising water reacts to supercooling [7, 31]. Circulation, melting and subséquent freezing beneath the shelf ice hâve been inferred from measurements near,
on and beneath the ice, and from models of the sub-ice circulation (e.g., [3,6,3238]). The strength of the sub-ice circulation and its exchanges with the open Ross
Sea are likely to vary considerably over interannual and longer periods in
response to changes in HSSW salinity and volume [15].
The Ross Sea continental shelf is covered by sea ice for most of the year, with
decay and growth both starting near the ice shelf front, typically in late October
and late February. Northward transport of sea ice is strongest in the western sector, where barrier and katabatic winds maintain the large Ross Sea Polynya adjacent to the ice shelf front [39] and a small, persistent polynya near 75°S on the
Victoria Land coast [40], The volume and salinity of HSSW will dépend in part
on the volume of sea ice produced on the continental shelf and exported from it
each year. Detailed records of ice transport are not yet available, however, and sea
ice thickness data are scarce [41]. The length of the sea ice season on the shelf
varied by about a month from 1979 to 1987, with little apparent interannual
change in winter ice concentration [9]. A longer Comiso sea ice record from the
entire Ross Sea displays strong interannual changes in the sea ice extent [15] at a
period comparable to that of the “Antarctic circumpolar wave” [42].
MCDW intrudes year-round at intermediate depths onto the continental shelf
[10, 18], and overrides the HSSW at some locations in the western sector. Since
the HSSW shoals rapidly westward, the “warm” MCDW that pénétrâtes this sector will lie directly beneath the AASW, from which it cannot easily be discrimi-