Circumpolar water masses
previously acknowledged, A. Amos, P. Woodroffe, and D. Woodroffe contributed long hours to the success of the field programs. References Ainley, D. G., and Jacobs, S. S. In preparation. Seabirds, pack ice and the antarctic slope front in the Ross Sea, Antarctica. Anderson, J. and co-workers. Personal communication. 1980. Edmond, J . M., Jacobs, S. S., Gordon, A. L. , Weiss, R. F., and Mantyla, A. W. 1979. Water column anomalies in dissolved silica over opaline pelagic sediments and the origin of the deep silica maximum. Journal of Geophysical Research, 84, 7809-7826.
Circumpolar water masses ARNOLD L. GORDON
Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964
While the basic water mass components of the southern ocean are well known, there are subtle variations within each of these components. The saline North Atlantic deep water is diluted by low-salinity waters, mostly from the antarctic continental margins. Antarctic bottom water varies from low to high salinity and is derived from select sites along the continental margins of Antarctica as well as within the open ocean. Antarctic intermediate water also has a range of temperature-salinity values, with distinct Atlantic and Pacific varieties. The waters of the Weddell gyre offer some of the more extreme water mass examples, notably a minimum of the 400 300 20
0°
Huppert, H. E., and Turner, J . S. 1980. Iceblocks melting into a salinity gradient. Jacobs, S. S., Huppert, H. E., Holdsworth, G., and Drewry, D., In preparation. Thermohaline steps induced by melting of the Erebus Glacier Tongue. Jacobs, S. S., Szelag, J . J . , Patla, S. M., and Bruchhausen, P. M. 1979. Oceanographic observations near the antarctic continental margin and Ross Ice Shelf. Antarctic Journal of the U.S., 14(5), 116-117. Jacobs, S.S., Gordon, A.L., and Amos, A.F. 1979. Effect of glacial ice melting on the Antarctic surface water. Nature, 277, 469-471. Jacobs, S.S., George, D.T., and Patla, S.M. 1980. CONRAD 17, Hydrographic stations, Nephelometer profiles in the southwest Indian-Antarctic oceans, January-April 1974, CU-1-80-TRI, 217 pp.
relatively warm-saline deep water mass component. Using the historical and 1976-78 Islas Orcadas data sets, the water mass structure of the Weddell (subpolar) gyre is being studied. A schematic of South Atlantic circulation which would produce the observed water mass distribution is shown in the figure. The warm-saline signal, although weak throughout the Weddell gyre, is most evident in a zonal band running from Maud Rise (67°S 0°) eastward to 30°E. The deep water within this band is nearly identical (though somewhat reduced in salinity) to the Pacific near-bottom waters observed in the northern Drake Passage. The route followed by these bottom waters carries the water mass characteristics through the South Georgia-South Sandwich Island Passage, eastward along the midocean ridge, and then to the south near 30°E, marking the most probable eastern extent of the Weddell gyre. The source water mass from the Pacific is elevated from about 4,000 meters to 400 meters below sea level along the 8,000-kilometer path to Maud Rise. A characteristic lateral velocity of 1 centimeter/ second requires a mean upwelling rate of 4.5 X 104 centimeters/ second which would balance the net sinking associated --
40°
50' 50°
60•
70°
bU
1980 REvIEw
10°
Schematic representation ° of proposed Weddell gyre circulation.
89
with antarctic bottom water formation considered to be active in the western perimeter of the Weddell gyre and near the gyre center just to the west of Maud Rise. The warm-saline deep water is advected to the west of Maud Rise along the antarctic continental slope, which requires a sudden poleward offset of this water mass at Maud Rise. Of interest is the role that Maud Rise might play in the initiation of this offset and the consequences in regard to bottom water formation. Another fascinating relation is that the Pacific bottom water source of the Weddell warmdeep water is enriched in salt (relative to water of similar
temperatures elsewhere in the circumpolar belt), by the Ross Sea saline bottom water. This raises the question: Is the convective process believed common in the Weddell Sea preconditioned by the Ross Sea? Another topic being studied is the open ocean convection of the Weddell gyre. Convective processes may be responsible for the rapid early spring melting of sea ice cover, and in its more extreme mode may induce the Weddell Polynya (open water) feature in the winter period. This research is supported by National Science Foundation grant DPP 78-24832.
Physical oceanography data from ARA Islas Orcadas cruise 17-78
The austral winter cruise of ARA Islas Orcadas cruise 17-78 took place from 2 September to 14 October 1978, mainly to obtain biological data related to primary productivity along the pack ice during the late austral winter. In order to determine physical oceanographic conditions, 19 salinitytemperature-depth (STD) stations with rosette samplers were occupied and 117 expendable bathythermographs (xsi"s) were launched during the cruise (figure 1). The std data were processed by correcting temperature and salinity with formulas obtained by comparing with values
TAKASHI ICHIYE
and
MASAMICHI INOUE
Department of Oceanography Texas A&M University College Station, Texas 77843
750
500
550
650
350
45'
25'
395
38• \ XII FALKLAND ISLANDS
'61 117
500
35..
w
55'
SOUTH GEORGIA
550
...4 CAPE HORN 06
\
,28 XB1 . 29
-
zo
.
600
34.
0$
23
018 019
600
SOUTH ORKNEY ISLANDS SOUTH SHETLAND ISLANDS, SID O XBT
0
0
75'
o
65'
550
Figure 1. Location of sic stations (in open circles) and of cruise 17-78.
90
XBT
450
350
250
stations (in closed circles) occupied during ARA Islas Orcadas
ANTARCr!C JOURNAL
Circumpolar water masses ARNOLD L. GORDON
Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964
While the basic water mass components of the southern ocean are well known, there are subtle variations within each of these components. The saline North Atlantic deep water is diluted by low-salinity waters, mostly from the antarctic continental margins. Antarctic bottom water varies from low to high salinity and is derived from select sites along the continental margins of Antarctica as well as within the open ocean. Antarctic intermediate water also has a range of temperature-salinity values, with distinct Atlantic and Pacific varieties. The waters of the Weddell gyre offer some of the more extreme water mass examples, notably a minimum of the 400 300 20
0°
Huppert, H. E., and Turner, J . S. 1980. Iceblocks melting into a salinity gradient. Jacobs, S. S., Huppert, H. E., Holdsworth, G., and Drewry, D., In preparation. Thermohaline steps induced by melting of the Erebus Glacier Tongue. Jacobs, S. S., Szelag, J . J . , Patla, S. M., and Bruchhausen, P. M. 1979. Oceanographic observations near the antarctic continental margin and Ross Ice Shelf. Antarctic Journal of the U.S., 14(5), 116-117. Jacobs, S.S., Gordon, A.L., and Amos, A.F. 1979. Effect of glacial ice melting on the Antarctic surface water. Nature, 277, 469-471. Jacobs, S.S., George, D.T., and Patla, S.M. 1980. CONRAD 17, Hydrographic stations, Nephelometer profiles in the southwest Indian-Antarctic oceans, January-April 1974, CU-1-80-TRI, 217 pp.
relatively warm-saline deep water mass component. Using the historical and 1976-78 Islas Orcadas data sets, the water mass structure of the Weddell (subpolar) gyre is being studied. A schematic of South Atlantic circulation which would produce the observed water mass distribution is shown in the figure. The warm-saline signal, although weak throughout the Weddell gyre, is most evident in a zonal band running from Maud Rise (67°S 0°) eastward to 30°E. The deep water within this band is nearly identical (though somewhat reduced in salinity) to the Pacific near-bottom waters observed in the northern Drake Passage. The route followed by these bottom waters carries the water mass characteristics through the South Georgia-South Sandwich Island Passage, eastward along the midocean ridge, and then to the south near 30°E, marking the most probable eastern extent of the Weddell gyre. The source water mass from the Pacific is elevated from about 4,000 meters to 400 meters below sea level along the 8,000-kilometer path to Maud Rise. A characteristic lateral velocity of 1 centimeter/ second requires a mean upwelling rate of 4.5 X 104 centimeters/ second which would balance the net sinking associated --
40°
50' 50°
60•
70°
bU
1980 REvIEw
10°
Schematic representation ° of proposed Weddell gyre circulation.
89
with antarctic bottom water formation considered to be active in the western perimeter of the Weddell gyre and near the gyre center just to the west of Maud Rise. The warm-saline deep water is advected to the west of Maud Rise along the antarctic continental slope, which requires a sudden poleward offset of this water mass at Maud Rise. Of interest is the role that Maud Rise might play in the initiation of this offset and the consequences in regard to bottom water formation. Another fascinating relation is that the Pacific bottom water source of the Weddell warmdeep water is enriched in salt (relative to water of similar
temperatures elsewhere in the circumpolar belt), by the Ross Sea saline bottom water. This raises the question: Is the convective process believed common in the Weddell Sea preconditioned by the Ross Sea? Another topic being studied is the open ocean convection of the Weddell gyre. Convective processes may be responsible for the rapid early spring melting of sea ice cover, and in its more extreme mode may induce the Weddell Polynya (open water) feature in the winter period. This research is supported by National Science Foundation grant DPP 78-24832.
Physical oceanography data from ARA Islas Orcadas cruise 17-78
The austral winter cruise of ARA Islas Orcadas cruise 17-78 took place from 2 September to 14 October 1978, mainly to obtain biological data related to primary productivity along the pack ice during the late austral winter. In order to determine physical oceanographic conditions, 19 salinitytemperature-depth (STD) stations with rosette samplers were occupied and 117 expendable bathythermographs (xsi"s) were launched during the cruise (figure 1). The std data were processed by correcting temperature and salinity with formulas obtained by comparing with values
TAKASHI ICHIYE
and
MASAMICHI INOUE
Department of Oceanography Texas A&M University College Station, Texas 77843
750
500
550
650
350
45'
25'
395
38• \ XII FALKLAND ISLANDS
'61 117
500
35..
w
55'
SOUTH GEORGIA
550
...4 CAPE HORN 06
\
,28 XB1 . 29
-
zo
.
600
34.
0$
23
018 019
600
SOUTH ORKNEY ISLANDS SOUTH SHETLAND ISLANDS, SID O XBT
0
0
75'
o
65'
550
Figure 1. Location of sic stations (in open circles) and of cruise 17-78.
90
XBT
450
350
250
stations (in closed circles) occupied during ARA Islas Orcadas
ANTARCr!C JOURNAL
