Studies of eddies and interleaving water masses east ...
torn on the continental slope and rise, with a range of salinities from less than 34.65 to less than 34.70 parts per thousand. This is a good indication that bottom water forms from both low-salinity and high-salinity shelf waters along this coastline. Variability in the formation process is suggested by deep temperatures significantly colder than we had observed ten years earlier in the same region. At stations 190 and 197 (see accompanying figure), located in the intra-shelf trench, we found that salinities exceeded 34.70 parts per thousand and temperatures were below - 1.8° C. This water is sufficiently dense to flow off the continental shelf if not topographically or dynamically constrained, but is less dense than high-salinity shelf water in the western Ross Sea. We found minimum temperatures below - 1.9° C at mid-depth near the Mertz and Ninnis glacier tongues. This appears to show melting of these features, analogous to the production of ice shelf water beneath the Ross Ice Shelf U acobs, Amos, and Bruchhausen, 1970). Fieldwork on USCGC Glacier was carried out by A. F. Amos, J . J . Szelag, P. Woodroffe, S. M. Patla, and D. Woodroffe. On the ice shelf, observations were made by P. M. Bruchhausen and S. M. Patla. We gratefully acknowledge support of the Ross Ice Shelf Project (RIsP)
personnel and of Glacier's marine science technicians and electronics chief Stillman. XBT probes were provided by the Naval Fleet Numerical Weather Central. This work has been funded by grant DPP 77-22209 to Columbia University. References Amos, A. F., P. Woodroffe, and D. Woodroffe. 1979. Surface observations from Glacier during Deep Freeze 79. Antarctic Journal of the United States (this issue). Bruchhausen, P. M., J. A. Raymond, S. S. Jacobs, A. L. DeVries, E. M. Thorndike, and H. H. DeWitt. 1979. Fish, crustaceans, and the sea floor beneath the Ross Ice Shelf. Science, 203: 449-51. Jacobs, S. S., A. F. Amos, and P. M. Bruchhausen. 1970. Ross Sea oceanography and Antarctic bottom water formation. Deep-Sea Research, 17: 935-62. Jacobs, S. S., P. M. Bruchhausen, and J . L. Ardai. 1978. Physical oceanography of the Ross Sea. Antarctic Journal of the United States, 13(4): 83-85. Jacobs, S. S., A. L. Gordon, and A. F. Amos. 1979. The effect of glacial melting on the Antarctic surface water. Nature, 277: 46941. Jacobs, S. S., A. L. Gordon, and J . L. Ardai. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203: 43943.
Studies of eddies and interleaving water masses east and south of New Zealand HARRY L. BRYDEN and TERRENCE M. JOYCE Department of Physical Oceanography Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543
As part of International Southern Ocean Studies (isos) in the region east and south of New Zealand, a cruise aboard Wv Knorr was carried out from 12 November to 9 December 1978 (figure 1) to study the dynamics of eddies and of interleaving water masses and to assess their effects on the circulation and water mass structure in the circumpolar region. Eighteen scientists from seven oceanographic institutions in the United States, the U.S.S.R., New Zealand, and Australia participated. During the first part of the cruise, we recovered six moorings deployed in April 1978 from n/v Tangaroa (Heath, Bryden, and Hayes, 1978), deployed one site mooring (to be recovered early in 1980), and took a grid of conductivity-temperature-depth (cTD) stations about the moorings. A cluster of five moorings near 49°30'S/ 170'W (figure 2) had been designed to study the dynamics of eddies and their effects on the Antarctic Circum-
160' E
170'
180'
170' W
Figure 1. Cruise track of RIv Knorr from 12 November to 9 December 1978. Key: A = site of cluster array of moorings and accompanying grid of CTD stations; B = site of single mooring with thermistor chains; C = site of polar front study.
polar Current downstream of a region where the current is strongly influenced by topography. All five moorings were recovered, although the mooring lines on moorings N and M were cut at a depth of about 1,500 117
2 500 00
N
oo
000
M
500 1000
\4900 - —
2000
W
S
1000
2000
K
4000
4000
4000
1km
S
J
Depth Scale
tO km Horizontal Scale
2000
L4000
Figure 2. Positions of current meter in the cluster array near 49°30'S/1 70°W.
4.93 49I0S+ N
AN 4.95 4.17 LW 4.51 4.70 ?505 '00 jAM 4.89
meters and so the top two current meters on each mooring were lost. All other current meters appear to have functioned normally. The CTD survey about the cluster (figure 3) indicated that an eddy, albeit a weak one, was present. The CTD stations in this survey show both subtropical and subantarctic waters in vertical profile. This suggests that the region is one of active mixing of water masses. A sixth mooring, near 51°S1175°E, had been designed to study the seasonal evolution of surface mixed layers on Campbell Plateau, identified by McCartney (1977) as being associated with the production of subantarctic mode water. This mooring was recovered intact, although the uppermost thermistor chain recorder was flooded (possibly because of a leak in the pressure sensor) and the middle thermistor chain had developed an oil leak. The remaining three thermistor chains and two current meters appear to have functioned normally. It is interesting that the CTD station near this mooring showed the water column to be well mixed in temperature but stratified in salinity. After taking an expendable bathythermograph (xBT) section while steaming toward 60°S/160°E, we began a study of the dynamics of interleaving water masses in the polar front zone and their effects on water mass structure. First, we located the polar front, determined its orientation from four crossings, and took a CTD section principally across the axis of the front. Then, in order to follow a water parcel for several days, we deployed two neutrally buoyant floats (vcM's) at depths of 215 and 630 meters on the warmer side of the front. (A third float was lost during a recovery attempt as a result of difficulty in maneuvering the ship near the float in rough seas.) As the floats were tracked, CTD work consisted of stations over the floats, tow-yo profiles around the shallower float (VCM 5), and stations poleward and equatorward of the float track to bracket the water masses in the front (figure 4). We found that the water mass structure of the area is typified by a minimum temperature region near a depth of 200 meters and by interleaving structures that are more prominent on the front's warmer side (figure 5). During a four-day period, VCM 5, which was within the minimum temperature layer, moved southward and then eastward at a speed of 50 to 70 centimeters per
I65
166E
58t
447k AK
AS
56,30
4.66
4.21 495OS + 17030W
+ t7OW
Figure 3. Temperature at 1,000 decibars from grid of CTD stations around the cluster array. Heavy triangles denote moorings. Temperature values are given at each CTD station position (located by decimal point in value). Temperature is contoured every 0.25°C. 118
59*
* I63L
I64
€5
66
Figure 4. CTD stations and float tracks during polar front study. Each CTD station is denoted by a dot. A dot with dashed line denotes a tow-yo station. Float tracks are shown by solid lines.
02 (MI/1) 4 6
0 8r
(CC)
Sta. 58.. S ..
Sta. 158
Sta. 157 Sta. l57
33.8 34,0 34.2 34.4 34.6 34.8 SALINITY %
Figure 5. Water mass structure typical of the polar front zone at CTD stations 157 and 158. Shown are diagrams of potential temperature versus oxygen and salinity for each station. Note the interleaving structures near the minimum temperature layer, which are more prominent on the warmer side of the front.
second. Four tow-yo profiles of approximately four hours duration were made near the float. In this operation, the CTD was lowered and raised successively between depths of 50 and 500 meters as the ship steamed at 2 knots. These stations were designed to examine differences in variability of interleaving water masses in along-front and cross-front directions. After two days, the deeper float was substantially behind the shallower float, so we recovered it and redeployed it near the shallower float at a depth of 430 meters to provide an estimate of velocity shear. This study indicated that interleaving layers can be followed over horizontal scales of 5 kilometers. It is planned to quantify the differences between the scales of along-frontal and cross-frontal in-
DRAKE 79 operations aboard AGS
Yelcho
STEVEN WORLEY Department of Oceanography Texas A&M University College Station, Texas 77843
R. E. STILL School of Oceanography Oregon State University Corvallis, Oregon 97331
terleaving layers and compare these figures with results in Drake Passage described by Joyce, Zenk, and Toole (1978). After the polar front study, a CTD section was taken from 60°S/160°E onto the Campbell Plateau, across the plateau and Snares Gap, and onto the continental shelf just south of the southern coast of New Zealand. This section should provide a description of the nature of water that flows onto Campbell Plateau from the west and that must evolve into subantarctic mode water on the plateau. This section should complement McCartney's survey of waters on the plateau performed during the two months prior to this cruise. In all, 79 CTD stations and numerous XBT profiles were taken. Water sample analysis for salinity using a Guideline salinometer and for dissolved oxygen using Winkler titrations will enable at-sea calibrations for the CTD data of 0.003 parts per thousand and 0.1 milliliter per liter to be improved ashore. This work has been supported by the Office for the International Decade of Ocean Exploration of the National Science Foundation under grants OCE 77-22887 and OCE 77-28355 to Woods Hole Oceanographic In stitution. Our accomplishments would have been much fewer without the cooperation and enthusiasm of the officers and crew of iJv Knorr. In particular, Bosun Cotter constructed a winch that greatly aided mooring recovery operations and CTD winch opetators Brennan, Brodrick, Daly, O'Neil, Tibbetts, and Wessling did consistently good work in cold and windy weather. References Heath, R. A., H. L. Bryden, and S. P. Hayes. 1978. Interaction of the Antarctic Circumpolar Current with topography south of New Zealand. Antarctic Journal of the United States, 13(4): 76-78. Joyce, T. M., W. Zenk, and J . M. Toole. 1978. The anatomy of the Antarctic Polar Front in the Drake Passage. Journal of Geophysical Research, 83: 6093-6113. McCartney, M. S. 1977. Subantarctic mode water. In A Voyage of Discovery, ed. M. Angel. Deep-Sea Research, supplement to volume 24, pp. 103-19.
HELLMUTH A. SIEVERS Chilean Naval Hydrographic Institute Valparaiso, Chile
The second phase of the Dynamic Response and Kinematics Experiment, 1979 (DRAKE 79) was carried out aboard the Chilean naval vessel AGS Yelcho. This phase had two objectives. The first was to define the thermal and density fields during the austral fall surrounding an array of current meters, temperature/pressure recorders, thermistor chains, and bottom pressure recorders moored in the Drake Passage. The second objective was to add through-passage pressure-measuring capability to the array by deploying a shallow-water pressure gauge to the west of existing recorders at Isla Diego Ramirez. 119
personnel and of Glacier's marine science technicians and electronics chief Stillman. XBT probes were provided by the Naval Fleet Numerical Weather Central. This work has been funded by grant DPP 77-22209 to Columbia University. References Amos, A. F., P. Woodroffe, and D. Woodroffe. 1979. Surface observations from Glacier during Deep Freeze 79. Antarctic Journal of the United States (this issue). Bruchhausen, P. M., J. A. Raymond, S. S. Jacobs, A. L. DeVries, E. M. Thorndike, and H. H. DeWitt. 1979. Fish, crustaceans, and the sea floor beneath the Ross Ice Shelf. Science, 203: 449-51. Jacobs, S. S., A. F. Amos, and P. M. Bruchhausen. 1970. Ross Sea oceanography and Antarctic bottom water formation. Deep-Sea Research, 17: 935-62. Jacobs, S. S., P. M. Bruchhausen, and J . L. Ardai. 1978. Physical oceanography of the Ross Sea. Antarctic Journal of the United States, 13(4): 83-85. Jacobs, S. S., A. L. Gordon, and A. F. Amos. 1979. The effect of glacial melting on the Antarctic surface water. Nature, 277: 46941. Jacobs, S. S., A. L. Gordon, and J . L. Ardai. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203: 43943.
Studies of eddies and interleaving water masses east and south of New Zealand HARRY L. BRYDEN and TERRENCE M. JOYCE Department of Physical Oceanography Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543
As part of International Southern Ocean Studies (isos) in the region east and south of New Zealand, a cruise aboard Wv Knorr was carried out from 12 November to 9 December 1978 (figure 1) to study the dynamics of eddies and of interleaving water masses and to assess their effects on the circulation and water mass structure in the circumpolar region. Eighteen scientists from seven oceanographic institutions in the United States, the U.S.S.R., New Zealand, and Australia participated. During the first part of the cruise, we recovered six moorings deployed in April 1978 from n/v Tangaroa (Heath, Bryden, and Hayes, 1978), deployed one site mooring (to be recovered early in 1980), and took a grid of conductivity-temperature-depth (cTD) stations about the moorings. A cluster of five moorings near 49°30'S/ 170'W (figure 2) had been designed to study the dynamics of eddies and their effects on the Antarctic Circum-
160' E
170'
180'
170' W
Figure 1. Cruise track of RIv Knorr from 12 November to 9 December 1978. Key: A = site of cluster array of moorings and accompanying grid of CTD stations; B = site of single mooring with thermistor chains; C = site of polar front study.
polar Current downstream of a region where the current is strongly influenced by topography. All five moorings were recovered, although the mooring lines on moorings N and M were cut at a depth of about 1,500 117
2 500 00
N
oo
000
M
500 1000
\4900 - —
2000
W
S
1000
2000
K
4000
4000
4000
1km
S
J
Depth Scale
tO km Horizontal Scale
2000
L4000
Figure 2. Positions of current meter in the cluster array near 49°30'S/1 70°W.
4.93 49I0S+ N
AN 4.95 4.17 LW 4.51 4.70 ?505 '00 jAM 4.89
meters and so the top two current meters on each mooring were lost. All other current meters appear to have functioned normally. The CTD survey about the cluster (figure 3) indicated that an eddy, albeit a weak one, was present. The CTD stations in this survey show both subtropical and subantarctic waters in vertical profile. This suggests that the region is one of active mixing of water masses. A sixth mooring, near 51°S1175°E, had been designed to study the seasonal evolution of surface mixed layers on Campbell Plateau, identified by McCartney (1977) as being associated with the production of subantarctic mode water. This mooring was recovered intact, although the uppermost thermistor chain recorder was flooded (possibly because of a leak in the pressure sensor) and the middle thermistor chain had developed an oil leak. The remaining three thermistor chains and two current meters appear to have functioned normally. It is interesting that the CTD station near this mooring showed the water column to be well mixed in temperature but stratified in salinity. After taking an expendable bathythermograph (xBT) section while steaming toward 60°S/160°E, we began a study of the dynamics of interleaving water masses in the polar front zone and their effects on water mass structure. First, we located the polar front, determined its orientation from four crossings, and took a CTD section principally across the axis of the front. Then, in order to follow a water parcel for several days, we deployed two neutrally buoyant floats (vcM's) at depths of 215 and 630 meters on the warmer side of the front. (A third float was lost during a recovery attempt as a result of difficulty in maneuvering the ship near the float in rough seas.) As the floats were tracked, CTD work consisted of stations over the floats, tow-yo profiles around the shallower float (VCM 5), and stations poleward and equatorward of the float track to bracket the water masses in the front (figure 4). We found that the water mass structure of the area is typified by a minimum temperature region near a depth of 200 meters and by interleaving structures that are more prominent on the front's warmer side (figure 5). During a four-day period, VCM 5, which was within the minimum temperature layer, moved southward and then eastward at a speed of 50 to 70 centimeters per
I65
166E
58t
447k AK
AS
56,30
4.66
4.21 495OS + 17030W
+ t7OW
Figure 3. Temperature at 1,000 decibars from grid of CTD stations around the cluster array. Heavy triangles denote moorings. Temperature values are given at each CTD station position (located by decimal point in value). Temperature is contoured every 0.25°C. 118
59*
* I63L
I64
€5
66
Figure 4. CTD stations and float tracks during polar front study. Each CTD station is denoted by a dot. A dot with dashed line denotes a tow-yo station. Float tracks are shown by solid lines.
02 (MI/1) 4 6
0 8r
(CC)
Sta. 58.. S ..
Sta. 158
Sta. 157 Sta. l57
33.8 34,0 34.2 34.4 34.6 34.8 SALINITY %
Figure 5. Water mass structure typical of the polar front zone at CTD stations 157 and 158. Shown are diagrams of potential temperature versus oxygen and salinity for each station. Note the interleaving structures near the minimum temperature layer, which are more prominent on the warmer side of the front.
second. Four tow-yo profiles of approximately four hours duration were made near the float. In this operation, the CTD was lowered and raised successively between depths of 50 and 500 meters as the ship steamed at 2 knots. These stations were designed to examine differences in variability of interleaving water masses in along-front and cross-front directions. After two days, the deeper float was substantially behind the shallower float, so we recovered it and redeployed it near the shallower float at a depth of 430 meters to provide an estimate of velocity shear. This study indicated that interleaving layers can be followed over horizontal scales of 5 kilometers. It is planned to quantify the differences between the scales of along-frontal and cross-frontal in-
DRAKE 79 operations aboard AGS
Yelcho
STEVEN WORLEY Department of Oceanography Texas A&M University College Station, Texas 77843
R. E. STILL School of Oceanography Oregon State University Corvallis, Oregon 97331
terleaving layers and compare these figures with results in Drake Passage described by Joyce, Zenk, and Toole (1978). After the polar front study, a CTD section was taken from 60°S/160°E onto the Campbell Plateau, across the plateau and Snares Gap, and onto the continental shelf just south of the southern coast of New Zealand. This section should provide a description of the nature of water that flows onto Campbell Plateau from the west and that must evolve into subantarctic mode water on the plateau. This section should complement McCartney's survey of waters on the plateau performed during the two months prior to this cruise. In all, 79 CTD stations and numerous XBT profiles were taken. Water sample analysis for salinity using a Guideline salinometer and for dissolved oxygen using Winkler titrations will enable at-sea calibrations for the CTD data of 0.003 parts per thousand and 0.1 milliliter per liter to be improved ashore. This work has been supported by the Office for the International Decade of Ocean Exploration of the National Science Foundation under grants OCE 77-22887 and OCE 77-28355 to Woods Hole Oceanographic In stitution. Our accomplishments would have been much fewer without the cooperation and enthusiasm of the officers and crew of iJv Knorr. In particular, Bosun Cotter constructed a winch that greatly aided mooring recovery operations and CTD winch opetators Brennan, Brodrick, Daly, O'Neil, Tibbetts, and Wessling did consistently good work in cold and windy weather. References Heath, R. A., H. L. Bryden, and S. P. Hayes. 1978. Interaction of the Antarctic Circumpolar Current with topography south of New Zealand. Antarctic Journal of the United States, 13(4): 76-78. Joyce, T. M., W. Zenk, and J . M. Toole. 1978. The anatomy of the Antarctic Polar Front in the Drake Passage. Journal of Geophysical Research, 83: 6093-6113. McCartney, M. S. 1977. Subantarctic mode water. In A Voyage of Discovery, ed. M. Angel. Deep-Sea Research, supplement to volume 24, pp. 103-19.
HELLMUTH A. SIEVERS Chilean Naval Hydrographic Institute Valparaiso, Chile
The second phase of the Dynamic Response and Kinematics Experiment, 1979 (DRAKE 79) was carried out aboard the Chilean naval vessel AGS Yelcho. This phase had two objectives. The first was to define the thermal and density fields during the austral fall surrounding an array of current meters, temperature/pressure recorders, thermistor chains, and bottom pressure recorders moored in the Drake Passage. The second objective was to add through-passage pressure-measuring capability to the array by deploying a shallow-water pressure gauge to the west of existing recorders at Isla Diego Ramirez. 119
