Subsurface currents in the southeast Ross Sea
Ross Sea Buoy Program 1987
Ross Sea Buoy Program 1988
Figure 2. Ross Sea buoy program, 1987.
Figure 3. Ross Sea buoy program, 1988.
tablish a longer lasting barometric station in the Ross Sea, data buoy 3883 was configured for a 3-year design life, and was parachuted onto the surface of B-9. D. Barnett of the Joint Ice Center has compared position reports from 3883 with satellite images of B-9, and estimates that the buoy lies within 10 kilometers of the geometric center of the iceberg.
This research was supported by National Science Foundation grants DPP 87-05181 and DPP 88-08172. I wish to thank the personnel of the United States Air Force Military Airlift Command, Naval Support Force Antarctica, and Antarctic Services for their excellent assistance in carrying out this project.
Subsurface currents in the southeast Ross Sea S. JACOBS Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964
Crary (1961) reported the results of ocean current observations made through the sea ice on Kainan Bay (approximately 78°10'S 162°30'W) in April and June 1957, and in July 1958. Difficulties were noted with accumulations of "plate or scale ice," seals taking a breather through the oceanographic hole, and Ekman Current-Meter anomalies that may have been caused by ice formation in the instrument. Nonetheless, a few dozen good measurements were obtained over 15-120-minute intervals at depths of 250-300 meters, mostly below the level of shelf ice near Kainan Bay. The maximum recorded velocity 80
was 35.7 centimeters per second, the average of 12.2 centimeters per second, and the average direction near 330°. Crary indicated that the currents were to some extent tidal and that a predominance of directional currents toward the northwest may have been due to the limited observation period. He also discussed the likelihood of a wind-driven current near the ice shelf front, and the probable effects of basal melting and freezing of the ice shelf on the density field and resulting ocean currents. In February 1985, Oregon State University recovered Aanderaa current meters from a mooring site at 77°40.8'S 160°24.2'W, about 10 kilometers north of the Ross Ice Shelf and 75 kilometers northeast of Kainan Bay. Both meters on that mooring, at 255- and 540-meter depths, showed prevailing currents between 310° and 350°. At 255 meters, a mean drift toward approximately 320° for most of 1984 (figure 1) agreed remarkably well with the earlier Crary results. Departures from the persistent north-northwestern flow, occurred primarily during the winter and early spring months (mid-May through mid-October). This may have resulted from a reorganization of the shelf water/deep ocean exchanges in response to sea ice forANTARCTIC JOURNAL
M.
5 Km
Figure 1. A progressive vector diagram of the 255-meter depth ocean current at mooring "I," 77 0 40.8'S 160°24.2'W, for 371 days beginning 28 January 1984. The record is low-pass filtered (tides removed), with open squares at the first day of each month. This "Eulerian" current measurement has the recording instrument fixed in space so the figure scales approximate the distance a water parcel would travel if ocean motion throughout the region were coherent with that at the mooring.
9 (Navy/NOAA 1983-1988) suggests differential motion between the sea ice and deeper water on the shelf. Temperature measurements have indicated net southward flow in the deeper layers between approximately 1700 and 175°W, perhaps sufficient to deflect B-9 from its northwesterly course. In addition, the change in direction was consistent with the seasonal reversal in the 1984 current observations (figure 1). Another current-meter mooring near the ice shelf at 170°W revealed a complex flow pattern during 1984, but with mean drift to the southwest (figure 15b in Jacobs 1989). East of 160°W, subsurface flow could be toward or away from the sub-ice shelf cavity. A shallow surface current may follow the coastline into the eastern Ross Sea, but the deep slope current probably tracks westward near the shelf break, like a 35 x 20 kilometer iceberg (B-2) that crossed that sector in late 1983. In the southeast Ross Sea, the net transport of sea ice is generally toward the northwest, driven by prevailing southerly winds off the ice shelf. A data buoy deployed on the sea ice at 77°45'S 165°17'W on 13 June 1987 had moved approximately 190 kilometers to the northwest by 20 July 1987 (Moritz 1987). Both the surface and subsurface flows in the southeast Ross Sea thus appear contrary in direction to those inferred by Klepikov and Grigoryev (1966). Assuming the basic circulation has not changed significantly over the past three decades, this illustrates the difficulty of estimating currents from sparse hydrographic data and relatively weak dynamic topography. Our studies of the Ross Sea ocean circulation and its interactions with sea ice and glacial ice have been supported by National Science Foundation grant DPP 85-12540. Current-meter data were processed by Oregon State University.
References mation and a more active winter thermohaline circulation (Pillsbury and Jacobs 1985). In October 1987, a large section of the eastern Ross Ice Shelf, extending from the Bay of Whales east to Edward VII Peninsula, broke away to form the 150 x 35 kilometer "B-9" iceberg (Navy/National Oceanic and Atmospheric Administration [NOAA], 1983-1988; Jacobs, 1987). Figure 2 shows the location of that iceberg at the time of calving, in relation to the currentmeter sites discussed above. Because an iceberg's keel vastly exceeds the size of its sail, movement is more dependent upon subsurface currents than surface currents or winds. B-9 drifted slowly in a generally northwest direction (approximately 295°) from mid-October 1987 through mid-April 1988, then northward through the end of May to 76°30'S 169°50'W, still on the continental shelf. Its movement was more to the south and west during early June 1988, probably to the left of the direction of sea-ice drift. A zone of lower sea-ice concentration near B-
1988 REVIEW
Crary, A.P. 1961. Glaciological studies at Little America Station, Antarctica, 1957 and 1958. IG Y glaciological report, 5. New York: American Geographical Society. Jacobs, S. 1987. Antarctic ice: How much smaller? Eos, 68(51), 1793. Jacobs, S. 1989. Marine controls on modern sedimentation on the Antarctic Continental Shelf. Marine Geology, 85, Klepikov, V.V., and Y.A. Grigoryev. 1966. Water circulation in the Ross Sea. (Soviet Antarctic Expedition Information Bulletin 56.) Translated for American Geophysical Union, 1(6), 52-54. Moritz, R.E. 1987. Ross Sea data buoy project. (Report to the National Science Foundation.) Navy/NOAA Joint Ice Center. 1983-1988. Northern ice limit. (Weekly charts.) Suitland, Maryland: Polar Oceanography Center. Pillsbury, R.D., and S. Jacobs. 1985. Preliminary observations from long-term current meter moorings near the Ross Ice Shelf, Antarctica. In S.S. Jacobs (Ed.), Oceanology of the Antarctic Continental Shelf.
(Antarctic Research Series, Vol. 43.) Washington, D.C.: American Geophysical Union.
81
165
29
75
14J
160
iBM
22JUN88
77
477
1 MZ07A
23F
23M 08F 09M 03 17F 24,29 D 21 J 14 J
17 D OD
76 1985 WHALES
-- ___-1962----- -' ...'
1
AINAN BAY
ROSS ICE SHELF 79
L 75'
170
165
60 S
Figure 2. The eastern Ross Ice Shelf front in 1962, 1985, and 1988 (estimated), relative to the Kainan Bay and "I" current-meter observations. The shaded section east of the Bay of Whales calved the 150 x 35 kilometers "B-9" iceberg in October 1987. B-9 drifted generally northwest through May 1988, as shown by the satellite-derived locations of its approximate center, reported by the Navy/NOAA Joint Ice Center (19831988). Some of the apparent short-term motion may result from a combination of satellite position resolution, rotation after calving and the relatively high length/width ratio. Icebergs act as "Lagrangian" current meters, moving with the integrated flow over some cross section of the water column. Both dimensions of this large iceberg may exceed the width of shelf currents and eddies that push it around. (km denotes kilometer.)
A fish story from the Antarctic, II T.B. KELLOGG and D.E. KELLOGG Departnent of Geological Sciences
and Institute for Quaternary Studies University of Maine, Orono, Maine 04469
During the course of geological investigations on the western part of the McMurdo Ice Shelf in 1978, we observed eight live and several dead Weddell seals (Leptonychotes weddelli) near the tide crack along the north shore of Bratina Island (figure), and located their access holes to the sea. Both adults and pups 82
were seen. The water level in these holes was approximately 2 meters below the ice surface, and the seals had considerable difficulty emerging. These animals were living approximately 15 kilometers from the nearest open water, and they may represent an isolated population much like that at White Island (Kooyman et al. 1979). We observed fish remains, both intact and regurgitated, at this location. Rare fresh fish remains were also observed on the McMurdo Ice Shelf near the north end of Black Island adjacent to a crack or rift, but no live seals were seen although a mummified specimen was found. These observations suggest at least one location for future research on isolated seal populations and bear on the origin of organic remains on the McMurdo Ice Shelf surface. Decapitated fish were first reported from the McMurdo Ice Shelf near the Dailey Islands by Scott (1905, vol. 1, p. 155) and later by Swithinbank, Darby, and Wohlschlag (1961). Debenham (1919, p. 67) proposed that sediment and biotic adfreezing ANTARCTIC JOURNAL
Ross Sea Buoy Program 1988
Figure 2. Ross Sea buoy program, 1987.
Figure 3. Ross Sea buoy program, 1988.
tablish a longer lasting barometric station in the Ross Sea, data buoy 3883 was configured for a 3-year design life, and was parachuted onto the surface of B-9. D. Barnett of the Joint Ice Center has compared position reports from 3883 with satellite images of B-9, and estimates that the buoy lies within 10 kilometers of the geometric center of the iceberg.
This research was supported by National Science Foundation grants DPP 87-05181 and DPP 88-08172. I wish to thank the personnel of the United States Air Force Military Airlift Command, Naval Support Force Antarctica, and Antarctic Services for their excellent assistance in carrying out this project.
Subsurface currents in the southeast Ross Sea S. JACOBS Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964
Crary (1961) reported the results of ocean current observations made through the sea ice on Kainan Bay (approximately 78°10'S 162°30'W) in April and June 1957, and in July 1958. Difficulties were noted with accumulations of "plate or scale ice," seals taking a breather through the oceanographic hole, and Ekman Current-Meter anomalies that may have been caused by ice formation in the instrument. Nonetheless, a few dozen good measurements were obtained over 15-120-minute intervals at depths of 250-300 meters, mostly below the level of shelf ice near Kainan Bay. The maximum recorded velocity 80
was 35.7 centimeters per second, the average of 12.2 centimeters per second, and the average direction near 330°. Crary indicated that the currents were to some extent tidal and that a predominance of directional currents toward the northwest may have been due to the limited observation period. He also discussed the likelihood of a wind-driven current near the ice shelf front, and the probable effects of basal melting and freezing of the ice shelf on the density field and resulting ocean currents. In February 1985, Oregon State University recovered Aanderaa current meters from a mooring site at 77°40.8'S 160°24.2'W, about 10 kilometers north of the Ross Ice Shelf and 75 kilometers northeast of Kainan Bay. Both meters on that mooring, at 255- and 540-meter depths, showed prevailing currents between 310° and 350°. At 255 meters, a mean drift toward approximately 320° for most of 1984 (figure 1) agreed remarkably well with the earlier Crary results. Departures from the persistent north-northwestern flow, occurred primarily during the winter and early spring months (mid-May through mid-October). This may have resulted from a reorganization of the shelf water/deep ocean exchanges in response to sea ice forANTARCTIC JOURNAL
M.
5 Km
Figure 1. A progressive vector diagram of the 255-meter depth ocean current at mooring "I," 77 0 40.8'S 160°24.2'W, for 371 days beginning 28 January 1984. The record is low-pass filtered (tides removed), with open squares at the first day of each month. This "Eulerian" current measurement has the recording instrument fixed in space so the figure scales approximate the distance a water parcel would travel if ocean motion throughout the region were coherent with that at the mooring.
9 (Navy/NOAA 1983-1988) suggests differential motion between the sea ice and deeper water on the shelf. Temperature measurements have indicated net southward flow in the deeper layers between approximately 1700 and 175°W, perhaps sufficient to deflect B-9 from its northwesterly course. In addition, the change in direction was consistent with the seasonal reversal in the 1984 current observations (figure 1). Another current-meter mooring near the ice shelf at 170°W revealed a complex flow pattern during 1984, but with mean drift to the southwest (figure 15b in Jacobs 1989). East of 160°W, subsurface flow could be toward or away from the sub-ice shelf cavity. A shallow surface current may follow the coastline into the eastern Ross Sea, but the deep slope current probably tracks westward near the shelf break, like a 35 x 20 kilometer iceberg (B-2) that crossed that sector in late 1983. In the southeast Ross Sea, the net transport of sea ice is generally toward the northwest, driven by prevailing southerly winds off the ice shelf. A data buoy deployed on the sea ice at 77°45'S 165°17'W on 13 June 1987 had moved approximately 190 kilometers to the northwest by 20 July 1987 (Moritz 1987). Both the surface and subsurface flows in the southeast Ross Sea thus appear contrary in direction to those inferred by Klepikov and Grigoryev (1966). Assuming the basic circulation has not changed significantly over the past three decades, this illustrates the difficulty of estimating currents from sparse hydrographic data and relatively weak dynamic topography. Our studies of the Ross Sea ocean circulation and its interactions with sea ice and glacial ice have been supported by National Science Foundation grant DPP 85-12540. Current-meter data were processed by Oregon State University.
References mation and a more active winter thermohaline circulation (Pillsbury and Jacobs 1985). In October 1987, a large section of the eastern Ross Ice Shelf, extending from the Bay of Whales east to Edward VII Peninsula, broke away to form the 150 x 35 kilometer "B-9" iceberg (Navy/National Oceanic and Atmospheric Administration [NOAA], 1983-1988; Jacobs, 1987). Figure 2 shows the location of that iceberg at the time of calving, in relation to the currentmeter sites discussed above. Because an iceberg's keel vastly exceeds the size of its sail, movement is more dependent upon subsurface currents than surface currents or winds. B-9 drifted slowly in a generally northwest direction (approximately 295°) from mid-October 1987 through mid-April 1988, then northward through the end of May to 76°30'S 169°50'W, still on the continental shelf. Its movement was more to the south and west during early June 1988, probably to the left of the direction of sea-ice drift. A zone of lower sea-ice concentration near B-
1988 REVIEW
Crary, A.P. 1961. Glaciological studies at Little America Station, Antarctica, 1957 and 1958. IG Y glaciological report, 5. New York: American Geographical Society. Jacobs, S. 1987. Antarctic ice: How much smaller? Eos, 68(51), 1793. Jacobs, S. 1989. Marine controls on modern sedimentation on the Antarctic Continental Shelf. Marine Geology, 85, Klepikov, V.V., and Y.A. Grigoryev. 1966. Water circulation in the Ross Sea. (Soviet Antarctic Expedition Information Bulletin 56.) Translated for American Geophysical Union, 1(6), 52-54. Moritz, R.E. 1987. Ross Sea data buoy project. (Report to the National Science Foundation.) Navy/NOAA Joint Ice Center. 1983-1988. Northern ice limit. (Weekly charts.) Suitland, Maryland: Polar Oceanography Center. Pillsbury, R.D., and S. Jacobs. 1985. Preliminary observations from long-term current meter moorings near the Ross Ice Shelf, Antarctica. In S.S. Jacobs (Ed.), Oceanology of the Antarctic Continental Shelf.
(Antarctic Research Series, Vol. 43.) Washington, D.C.: American Geophysical Union.
81
165
29
75
14J
160
iBM
22JUN88
77
477
1 MZ07A
23F
23M 08F 09M 03 17F 24,29 D 21 J 14 J
17 D OD
76 1985 WHALES
-- ___-1962----- -' ...'
1
AINAN BAY
ROSS ICE SHELF 79
L 75'
170
165
60 S
Figure 2. The eastern Ross Ice Shelf front in 1962, 1985, and 1988 (estimated), relative to the Kainan Bay and "I" current-meter observations. The shaded section east of the Bay of Whales calved the 150 x 35 kilometers "B-9" iceberg in October 1987. B-9 drifted generally northwest through May 1988, as shown by the satellite-derived locations of its approximate center, reported by the Navy/NOAA Joint Ice Center (19831988). Some of the apparent short-term motion may result from a combination of satellite position resolution, rotation after calving and the relatively high length/width ratio. Icebergs act as "Lagrangian" current meters, moving with the integrated flow over some cross section of the water column. Both dimensions of this large iceberg may exceed the width of shelf currents and eddies that push it around. (km denotes kilometer.)
A fish story from the Antarctic, II T.B. KELLOGG and D.E. KELLOGG Departnent of Geological Sciences
and Institute for Quaternary Studies University of Maine, Orono, Maine 04469
During the course of geological investigations on the western part of the McMurdo Ice Shelf in 1978, we observed eight live and several dead Weddell seals (Leptonychotes weddelli) near the tide crack along the north shore of Bratina Island (figure), and located their access holes to the sea. Both adults and pups 82
were seen. The water level in these holes was approximately 2 meters below the ice surface, and the seals had considerable difficulty emerging. These animals were living approximately 15 kilometers from the nearest open water, and they may represent an isolated population much like that at White Island (Kooyman et al. 1979). We observed fish remains, both intact and regurgitated, at this location. Rare fresh fish remains were also observed on the McMurdo Ice Shelf near the north end of Black Island adjacent to a crack or rift, but no live seals were seen although a mummified specimen was found. These observations suggest at least one location for future research on isolated seal populations and bear on the origin of organic remains on the McMurdo Ice Shelf surface. Decapitated fish were first reported from the McMurdo Ice Shelf near the Dailey Islands by Scott (1905, vol. 1, p. 155) and later by Swithinbank, Darby, and Wohlschlag (1961). Debenham (1919, p. 67) proposed that sediment and biotic adfreezing ANTARCTIC JOURNAL
