Physical oceanography of the Ross Sea
water with temperatures below the freezing point at one atmosphere pressure was found just above the bottom. Since these stations were probably on the oceanic side of the sill separating the Filchner Depression from the main Weddell Sea basin, the extremely cold water may flow downslope and contribute to the bottom water. The water mass probably originates beneath the Filchner Ice Shelf, where the pressure effect allows the water to be cooled below the freezing point at one atmosphere pressure. Another interesting observation was that the intrusion of warm water from the open ocean onto the continental shelf was much more irregular than previously indicated by the single section made during IWSOE in 1973 in the same area. Perhaps this is an indication that the intrusion is an intermittent event or that it occurs with an eddy- or wave-like structure. We hope a detailed analysis of the CTD data and the current meter data will resolve this question. We were assisted by Einar Svendsen and Tor Torresen from the University of Bergen, Norway; Gwyn Griffiths from the Institute of Oceanographic Sciences, England; David Muus and Dwight Wahlberg from Scripps Institution of Oceanography; and Bradford Fowler and James Mitchell from the University of California, Santa Cruz. The Glacier's Marine Science Division assisted in the scientific program,
Physical oceanography of the Ross Sea S.JACOBS, P. BRUCHHAUSEN,andJ. ARDAI
Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964 We made oceanographic measurements through the J-9 access hole on the Ross Ice Shelf (82°22'S. 168°40'W.) and from the usccc Burton Island during December 1977-February 1978. The observations provided information on circulation beneath the ice shelf and on interactions between glacial ice and the adjacent oceans. At J-9 temperatures were measured with reversing thermometers. Water samples were taken from seawater pumped up the hole and with modified "Niskin" bottles, closed from the surface electrically or by messenger. Nearly all the equipment was contaminated by diesel fuel byproducts remaining from the "drilling" operation and by a slushy ice that formed in the hole. Salinity was determined onsite with a laboratory salinometer. Geochemical samples were sent to the United States for analysis. A Geodyne savonius rotor current meter was suspended beneath the ice for periods up to several hours and a modified Thorndike deep-sea camera photographed the sea floor, the ice hole, and biological activity. From Burton Island 80 salinity/temperature/depth (STD) casts were completed (figure 1). Aanderaa current meters and a thermistor chain were bottom-moored at the locations indicated. Fifty XBT (expendable bathythermograph) casts were October 1978
and all the officers and crew gave superb cooperation. This work was supported by National Science Foundation grant DPP 75-14936. 73°30S
- * ! —: A
7530S
42°W
32°W
Figure 2. Positions of hydrographic stations (crosses) and currant motor moorings sit out during iwsoa in 1978 (triangles), and positions of current motor moorings sit out by the Norwegians during uwsot In 1977 (squarss).
made at 5-kilometer intervals over portions of the ship's track. A submarine depression deeper than 1,100 meters was encountered southwest of Terra Nova Bay, near station 168. It is the deepest region on the Ross Sea continental shelf (see Hayes and Davey, 1974), comparable in depth to Discovery Deep beneath the Ross Ice Shelf (Robertson et al., 1977). Seawater beneath the Ross Ice Shelf atJ-9 is above the in situ freezing point below the ice/seawater interface (figure 2). Relatively well-mixed layers exist below the ice and above the bottom, with a transitional region between. Repeated observations showed variations of about 0.05°C. Salinity increased from 34.39 parts per mill near the ice shelf base to 34.83 near bottom, counterbalancing the temperature inversion to produce a predominantly stable water column. The near-bottom layer atJ-9 has about the same characteristics as the high salinity shelf water in the western Ross Sea (figure 2, station 11) and appears to derive from that water mass. Some modifications are probable from freezing in cracks beneath the ice shelf and from geothermal heating. The Northwind section (see Jacobs, 1977) along the ice shelf in the Ross Sea (figure 3) is representative of Burton Island and Eltanin observations. The warm subsurface core centered at station 25 can be traced to the circumpolar deep water north of the continental shelf. There are two regions where water is within 0.2°C of the in situ freezing point. One is near 450 meters and centered at station 22; the other extends the length of the shelf at depths near 200 meters. We hypothesized earlier that this very cold "ice shelf water" has a sub-ice shelf origin (Gordon, 1974; Jacobs et al., 1970). The J-9 observations indicate that it results primarily from melting at the ice shelf base, with the heat supplied from the warmer layers advected southward beneath the Ross Ice Shelf. Current measurements extending through a full tidal cycle were not possible at J-9, but interesting results were obtained nonetheless (figure 4). In the bottom layer current 83
Figure 1. Oceanographic (salinity/temperature/depth) stations occupied from uscoc Burton Island during January-February 1978. (Current meters were set for recovery the following year. Bathymetry after Hayes and Davey, 1974.)
Figure 2. Temperature and salinity vs. depth for J-9 observations and four Northwind stations along the Ross ice Shelf. (See figure 3 for relative station positions. The vertical positions of the current meter (CM) recordings, figure 4, are shown by triangles.)
IMP'FI'AI(/fl' (-cl
84
SAL INITY(%.) ANTARCTIC JOURNAL
SHIRASE
IROSS ISLAND
AACT
Figure 3. Temperature (°C) above in situ freezing point along the Ross Ice Shelf (uscGc Northwind salinity/temperature/ depth stations). (Most stations are within 1 kilometer of the barrier. Note warm subsurface core centered at station 25 and deeper cold core at station 22.)
I
North
(W/LLAMS.J9P6)
Is 14 20
20.3
12
CM
20
DEC 77
22 East 8 0 2
cm/aft
17
4
is
19 20
CM `2 21 DEC 77
'P
'6
q— ID
CM 4 2021
23
DEC '
27 DEC 77
CM 5
CM '5
Figure 4. Current velocity and direction at hourly intervals for five observation periods at J-9, and (inset) the predicted spring tide (Williams, 1976). (The vertical position of each set of current observations is shown in figure 2.) meter (CM 2-4) velocities reached a maximum of 17 centimeters per second and suggest a clockwise tidal current ellipse aimed with the axis of a depression in the submarine topography (Robertson et al., 1977). In the top layer (CM 5) a counterclockwise tidal current may occur. The spring tidal flow predicted forJ-9 by Williams (1976) is shown for comparison. A photograph of a fish near bottom appears in figure 5. This and other photographs provide the first evidence that vertebrates exist this far from the open sea (475 kilometers) and add to the other evidence that there is active circulation between the open oceans and the sub-ice shelf regions (Jacobs et al., in preparation). This work was supported by National Science Foundation grant DPP 76-11872 to Columbia University. Assistance was provided by the University of Nebraska/Cold Regions Research and Engineering Laboratory/Browning drillers, by Burton Island personnel, and by Arnold Gordon. Edward Thorndike designed and built the camera and nephelometer, Peter Suckling modified the water sampling bottles; and Arthur DeVries and Hugh DeWitt identified the fish. October 1978
Figure 5. An 18-centimeter-long fish, Trematomus Ioennbergii, near bottom under the shelf at J-9. (The round object is a weight attached to the camera. A piece of bait (knockwurst) is attached to the weight.) References Gordon, A. L. 1974. RISP Science Plan (1st ed., prepared by Ross Ice Shelf Project Steering Group). Ross Ice Shelf Project Management Office, 135 Bancroft Hall. University of Nebraska, Lincoln, Nebraska 68508. Hayes, D. E., and F. J. Davey. 1974. Bathymetrics of the Ross Sea. In: Initial Reports of the Deep Sea Drilling Project, Vol. 28 Part 5, National Science Foundation, Washington, D.C. pp. 885-907. Jacobs, S. S. 1977. Ross Ice Shelf Project: Physical oceand'graphy. Antarctic Journal of the US. 12(4): 43-46. Jacobs, S. S., A. F. Amos, and P. M. Bruchhausen. 1970. Ross Sea oceanography and antarctic bottom water formation. Deep-Sea Research. 17: 935-962. .Jacobs, S. S., A. L. Gordon, J. L. Ardai,Jr., and P. M. Bruchhausen. In preparation. Circulation and melting beneath the Ross Ice Shelf.
Robertson,J. D., C. R. Bentley,J. W. Clough, and L. L. Greischar. 1977. Sea Bottom Topography and Crustal Structure Below the Ross Ice Shelf Antarctica (Contribution 345). University of Wisconsin,
Geophysical and Polar Research Center, Madison, Wisconsin.
Williams II, R T. 1976. The Ocean Tide Beneath the Ross Ice Shelf. Un-
published master's thesis, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
85
Physical oceanography of the Ross Sea S.JACOBS, P. BRUCHHAUSEN,andJ. ARDAI
Lamont-Doherty Geological Observatory Columbia University Palisades, New York 10964 We made oceanographic measurements through the J-9 access hole on the Ross Ice Shelf (82°22'S. 168°40'W.) and from the usccc Burton Island during December 1977-February 1978. The observations provided information on circulation beneath the ice shelf and on interactions between glacial ice and the adjacent oceans. At J-9 temperatures were measured with reversing thermometers. Water samples were taken from seawater pumped up the hole and with modified "Niskin" bottles, closed from the surface electrically or by messenger. Nearly all the equipment was contaminated by diesel fuel byproducts remaining from the "drilling" operation and by a slushy ice that formed in the hole. Salinity was determined onsite with a laboratory salinometer. Geochemical samples were sent to the United States for analysis. A Geodyne savonius rotor current meter was suspended beneath the ice for periods up to several hours and a modified Thorndike deep-sea camera photographed the sea floor, the ice hole, and biological activity. From Burton Island 80 salinity/temperature/depth (STD) casts were completed (figure 1). Aanderaa current meters and a thermistor chain were bottom-moored at the locations indicated. Fifty XBT (expendable bathythermograph) casts were October 1978
and all the officers and crew gave superb cooperation. This work was supported by National Science Foundation grant DPP 75-14936. 73°30S
- * ! —: A
7530S
42°W
32°W
Figure 2. Positions of hydrographic stations (crosses) and currant motor moorings sit out during iwsoa in 1978 (triangles), and positions of current motor moorings sit out by the Norwegians during uwsot In 1977 (squarss).
made at 5-kilometer intervals over portions of the ship's track. A submarine depression deeper than 1,100 meters was encountered southwest of Terra Nova Bay, near station 168. It is the deepest region on the Ross Sea continental shelf (see Hayes and Davey, 1974), comparable in depth to Discovery Deep beneath the Ross Ice Shelf (Robertson et al., 1977). Seawater beneath the Ross Ice Shelf atJ-9 is above the in situ freezing point below the ice/seawater interface (figure 2). Relatively well-mixed layers exist below the ice and above the bottom, with a transitional region between. Repeated observations showed variations of about 0.05°C. Salinity increased from 34.39 parts per mill near the ice shelf base to 34.83 near bottom, counterbalancing the temperature inversion to produce a predominantly stable water column. The near-bottom layer atJ-9 has about the same characteristics as the high salinity shelf water in the western Ross Sea (figure 2, station 11) and appears to derive from that water mass. Some modifications are probable from freezing in cracks beneath the ice shelf and from geothermal heating. The Northwind section (see Jacobs, 1977) along the ice shelf in the Ross Sea (figure 3) is representative of Burton Island and Eltanin observations. The warm subsurface core centered at station 25 can be traced to the circumpolar deep water north of the continental shelf. There are two regions where water is within 0.2°C of the in situ freezing point. One is near 450 meters and centered at station 22; the other extends the length of the shelf at depths near 200 meters. We hypothesized earlier that this very cold "ice shelf water" has a sub-ice shelf origin (Gordon, 1974; Jacobs et al., 1970). The J-9 observations indicate that it results primarily from melting at the ice shelf base, with the heat supplied from the warmer layers advected southward beneath the Ross Ice Shelf. Current measurements extending through a full tidal cycle were not possible at J-9, but interesting results were obtained nonetheless (figure 4). In the bottom layer current 83
Figure 1. Oceanographic (salinity/temperature/depth) stations occupied from uscoc Burton Island during January-February 1978. (Current meters were set for recovery the following year. Bathymetry after Hayes and Davey, 1974.)
Figure 2. Temperature and salinity vs. depth for J-9 observations and four Northwind stations along the Ross ice Shelf. (See figure 3 for relative station positions. The vertical positions of the current meter (CM) recordings, figure 4, are shown by triangles.)
IMP'FI'AI(/fl' (-cl
84
SAL INITY(%.) ANTARCTIC JOURNAL
SHIRASE
IROSS ISLAND
AACT
Figure 3. Temperature (°C) above in situ freezing point along the Ross Ice Shelf (uscGc Northwind salinity/temperature/ depth stations). (Most stations are within 1 kilometer of the barrier. Note warm subsurface core centered at station 25 and deeper cold core at station 22.)
I
North
(W/LLAMS.J9P6)
Is 14 20
20.3
12
CM
20
DEC 77
22 East 8 0 2
cm/aft
17
4
is
19 20
CM `2 21 DEC 77
'P
'6
q— ID
CM 4 2021
23
DEC '
27 DEC 77
CM 5
CM '5
Figure 4. Current velocity and direction at hourly intervals for five observation periods at J-9, and (inset) the predicted spring tide (Williams, 1976). (The vertical position of each set of current observations is shown in figure 2.) meter (CM 2-4) velocities reached a maximum of 17 centimeters per second and suggest a clockwise tidal current ellipse aimed with the axis of a depression in the submarine topography (Robertson et al., 1977). In the top layer (CM 5) a counterclockwise tidal current may occur. The spring tidal flow predicted forJ-9 by Williams (1976) is shown for comparison. A photograph of a fish near bottom appears in figure 5. This and other photographs provide the first evidence that vertebrates exist this far from the open sea (475 kilometers) and add to the other evidence that there is active circulation between the open oceans and the sub-ice shelf regions (Jacobs et al., in preparation). This work was supported by National Science Foundation grant DPP 76-11872 to Columbia University. Assistance was provided by the University of Nebraska/Cold Regions Research and Engineering Laboratory/Browning drillers, by Burton Island personnel, and by Arnold Gordon. Edward Thorndike designed and built the camera and nephelometer, Peter Suckling modified the water sampling bottles; and Arthur DeVries and Hugh DeWitt identified the fish. October 1978
Figure 5. An 18-centimeter-long fish, Trematomus Ioennbergii, near bottom under the shelf at J-9. (The round object is a weight attached to the camera. A piece of bait (knockwurst) is attached to the weight.) References Gordon, A. L. 1974. RISP Science Plan (1st ed., prepared by Ross Ice Shelf Project Steering Group). Ross Ice Shelf Project Management Office, 135 Bancroft Hall. University of Nebraska, Lincoln, Nebraska 68508. Hayes, D. E., and F. J. Davey. 1974. Bathymetrics of the Ross Sea. In: Initial Reports of the Deep Sea Drilling Project, Vol. 28 Part 5, National Science Foundation, Washington, D.C. pp. 885-907. Jacobs, S. S. 1977. Ross Ice Shelf Project: Physical oceand'graphy. Antarctic Journal of the US. 12(4): 43-46. Jacobs, S. S., A. F. Amos, and P. M. Bruchhausen. 1970. Ross Sea oceanography and antarctic bottom water formation. Deep-Sea Research. 17: 935-962. .Jacobs, S. S., A. L. Gordon, J. L. Ardai,Jr., and P. M. Bruchhausen. In preparation. Circulation and melting beneath the Ross Ice Shelf.
Robertson,J. D., C. R. Bentley,J. W. Clough, and L. L. Greischar. 1977. Sea Bottom Topography and Crustal Structure Below the Ross Ice Shelf Antarctica (Contribution 345). University of Wisconsin,
Geophysical and Polar Research Center, Madison, Wisconsin.
Williams II, R T. 1976. The Ocean Tide Beneath the Ross Ice Shelf. Un-
published master's thesis, Virginia Polytechnic Institute and State University, Blacksburg, Virginia.
85
