1:11 I
Station 08
1:11
09
10
Il
12
13
14
0 .Y......! I 40
.40
.20
8:
80
Computer Plot by STDSECT Rev. 7931 , RID Processing System Thomas Reid a Department of Oceanography Tao., A&M University
100 120 140 Q) 180 180 200 220 240
U. S A. R.P. : DEEP FREEZE 1982 USCG GLACIER ROSS SEA CRUISE LONGITUDE 175 EAST
7ri
80 100 120 140 160 190
.
..............
0 5 10 15 20 25 30 35 40 45 50 55 80 65 70 75
Distance Along Transect (Km)
90 96 90
Figure 3. Ammonium concentrations (in microgram-atoms per liter) in the upper 250 meters along a 64-kilometer (40-mile) transect seaward from the barrier edge of the Ross Ice Shelf at 175 0 E. Shaded area denotes absence of bottle samples; see figure 1 for station locations.
References Amos, A. F. 1982. Physical oceanography of the southwestern Ross Sea, January 1982. Antarctic Journal of the U.S., 17(5). Bidigare, R. R., and Cox, J . L. 1982. Zooplankton metabolic studies in the Ross Sea. Antarctic Journal of the U.S., 17(5). Biggs, D. C. 1982. Zooplankton excretion and NH 4'cycling in nearsurface waters of the southern ocean. I. Ross Sea, austral summer 1977-1978. Polar Biology, 1, 55-67. El-Sayed, S. Z., Biggs, D. C., Stockwell, D., Warner, R., and Meyer, M. 1978. Biogeography and metabolism of phytoplankton and zooplankton in the Ross Sea, Antarctica. Antarctic Journal of the U.S., 13(4),131-133. Glibert, P. M., Biggs, D. C., and McCarthy, J . J. 1982. Uptake of ammonium and nitrate during austral summer in the Scotia Sea. DeepSea Research, 29(7a), 837-850.
Physical oceanography of the southwestern Ross Sea, January 1982 ANTHONY F. AMOS
University of Texas-Austin Marine Science Institute Port Aransas Marine Laboratory Port Aransas, Texas 78373 146
Horrigan, S. G. 1981. Primary production under the Ross Ice Shelf, Antarctica. Limnology and Oceanography, 26, 378-382. Holm-Hansen, 0., Neon, A., and Koike, I. 1982. Phytoplankton distribution, biomass, and activity in the southwest Ross Sea. Antarctic Journal of the U.S., 17(5). Jacobs, S. S., Amos, A. F., and Bruchhausen, P. M. 1970. Ross Sea oceanography and antarctic bottom water formation. Deep-Sea Research, 17, 935-962. 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., Gordon, A. L., and Ardai, J . L. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203, 439-443. Johnson, M. A., Biggs, D. C., and Amos, A. F. 1982. Oceanographic time-series studies with an STD-submersible pump combination. Antarctic Journal of the U.S., 17(5). Olson, R. J . 1980. Nitrate and ammonium uptake in antarctic waters. Limnology and Oceanography, 25, 1064-1074.
During the Ross Sea ammonium flux experiment (see Biggs, Antarctic Journal, this issue), the regional oceanography of the
southwestern Ross Sea was investigated by making surface-tobottom and time-series salinity/temperature profiles (Johnson, Biggs, and Amos, Antarctic Journal, this issue) with a salinitytemperature-depth (STD) sensor. Twenty-eight vertical stations and two main time-series stations were occupied (see station map in Biggs, Antarctic Journal, this issue). Five additional stations were occupied along the sea ice edge in McMurdo Sound to compare with a similar section I made in 1979 (see Jacobs et al. 1981). The present investigation was done aboard USCGC Glacier during Deep Freeze 82, using a ANTARCTIC JOURNAL
Plessey model 9040 STD system with a 12-bottle (2.5-liters each) rosette sampler. Discrete samples were taken with the rosette at 5, 20, 40, 60, 80, 100, 125, 150, 200, and 250 meters, primarily to provide nutrient and chlorophyll data for the ammonium flux experiment, but also for dissolved oxygen determinations and calibration of the STD salinity sensor. Two other samples, at middepth and just off the bottom, were routinely collected for STD calibration. Bottom depths ranged from 357 to 947 meters, and the STD was lowered to within a few meters of the bottom with the aid of a pinger. Thermometry was used to calibrate the STD temperature sensor. The STD sensor used, a "seasoned" veteran of numerous polar cruises, required little correction to bring it up to "water bottle" accuracy. The oceanography of this part of the Ross Sea has been described by Jacobs, Amos, and Bruchhausen (1970), and its 175 EAST SECTION B-15)
0.5
CDW
0.0 I /
I /
-0.5
27.4. 27.5
I /
271' ••":. . / / / 27.0. 20.0 29.2 21t
-in
I
I
I I
—1.5 / I
I
I
RSSW
-2.01
-U,
(a)
GLACIER 1X-82, Static,, 0 12 SIGMA-I Zn
GLACIER -62, Statia,, 0 15 u SIGMA-I cc
W
TEMP. (C) 151
ISW
to
Ln
'1.' TEMP. ID
SAUNITYç0pt -
151 ill ALINITYt
in
10$
20$
20$
30$ 'II
340$ T
4$'
Gt
50$
60$
an
70$
70$
90$
iF
UIS R SAUNIIY(ppt
rIE*.(C)
{
/s
- rTE*'.(C) .5.
SIGMA-I 6 (b)
SIGMA-I U' (c)
Temperature and salinity characteristics of waters along the 1750E meridian near the Ross Ice Shelf (see Biggs, Antarctic Journal, this Issue, for station locations). (a) Composite temperature/salinity diagram, stations 8-15. COW = Circumpolar Deep Water, RSSW = Ross Sea Shelf Water, isw = Ice Shelf Water; salinity (horizontal axis) in parts per thousand, temperature (vertical axis) in °C; dashed lines Indicate isopycnal surfaces in sigma-T units [sigma-T = (p - 1) X 10, where p = In situ density]. (b) Vertical profiles of temperature, salinity, and sigma-T (as) for station 12 over the Pennell Bank; SR = salinities from rosette samples. (c) As in (b), for station 15 adjacent to the Ross Ice Shelf face.
1982 REVIEW
particular relationship to the Ross Ice Shelf by Jacobs, Gordon, and Ardai (1979). Adjacent to the ice shelf, four types of subsurface water have been identified: deep and shallow Ice Shelf Water, a modified form of Circumpolar Deep Water, and deep Ross Sea Shelf Water. A temperature/salinity diagram of the 175°E section (figure, a) illustrates the various water masses found on this cruise. Modified Circumpolar Deep Water was found almost exclusively over the southern portion of the Pennell Bank on the 175°E section (station 12, figure, b), and only occasionally on the adjacent, 173°E section. It can be identified on the temperature/ salinity diagram (figure, a) by the cluster of points midway between and roughly parallel to the 27.8 and 27.9 isopycnals. Whether the Pennell Bank exercises any topographical control over this water mass is not known, but stations 14 and 15 off the bank (profile, figure, c) have completely different water characteristics in the upper 300 meters. Ice Shelf Water is characterized by the proximity of the water to the in situ freezing point, and it is formed by processes occurring under or adjacent to the Ross Ice Shelf. The deeper Ice Shelf Water has temperatures of less than - 2°C and salinities in the range of 34.5 to 34.717c. It is found at a depth near 400 meters, corresponding to the average base of the ice sheet. This water was found at only one station (station 15) on the easternmost (175°E) transect (figure, c), a few hundred meters away from the barrier. The second, shallower type of Ice Shelf Water, usually found at a depth of 250 meters, was not encountered on this cruise. No temperatures of less than - 1.9°C were found shallower than 250 meters. Only at station 14 did the water reach to within 0.2°C of the in situ freezing point at 250 meters. Ross Sea Shelf Water was found at all stations except those over the Pennell Bank and is illustrated in the figure by the bottom water mass, temperature less than -1.9°C, salinity greater than 34.7%. Preliminary geostrophic calculations show flow parallel to the ice shelf face but very little flow between transects into or away from the ice shelf. Using the bottom as a level of no motion, the net transport is toward the west except on the westernmost transect (169°E), where it is toward the east. The characteristics of stations adjacent to the ice shelf and those no more than 10 kilometers away creates a considerable shear in the computed currents. That such a variability exists in a small geographical area is of considerable interest, and preliminary results reveal the important role that the ice shelf and topographic features exert on the regional oceanography. How this regime is related to the observed nutrient distribution has yet to be studied. Property/property diagrams, vertically and horizontally contoured sections, and other calculations are presently being performed on these data. I thank the officers and crew of the USCGC Glacier for their help and support in carrying out this fieldwork. Particular thanks go to Captain J. W. Coste, LTJG Carla Ridnor, Master Chief Marine Science Technician P. St. Joule, and the other technicians. This work was partially supported by National Science Foundation grant DPP 79-21355 to Texas A&M University.
References Biggs, D. C. 1982. Ross Sea ammonium flux experiment. Antarctic Journal of the U.S., 17(5).
Jacobs, S. S., Amos, A. F., Bruchhausen, P. M. 1970. Ross Sea oceanogra147
phy and antarctic bottom water formation. Deep-Sea Research, 17, 935-962.
Jacobs, S. S., Gordon, A. L., and Ardai, J. L., Jr. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203, 439-443. Jacobs, S. S., Huppert, H. E., Holdsworth, G., and Drewry, D. J . 1981.
Oceanographic time-series studies with an sm-submersible pump combination
Thermohaline steps induced by melting of the Erebus Glacier Tongue. Journal of Geophysical Research, 86(C7), 6547-6555. Johnson, M., Biggs, D. C., and Amos, A. F. 1982. Oceanographic timeseries studies with an STD-submersible pump combination. Antarctic Journal of the U.S., 17(5).
STD time-series data for station 17 in the east and station 33 in the west (figure 2; see figure 1 in Biggs, Antarctic Journal, this issue, for locations) show evidence of internal wave activity, particularly in the temperature signal. The STD recorder was held in the thermocline at depths of 68 meters (station 17) and 65 meters (station 33). The vertical temperature structure near
MARK A. JOHNSON and DOUGLAS C. BIGGs Department of Oceanography Texas A&M University College Station, Texas 77843
ANTHONY F. AMOS University of Texas-Austin Marine Science Institute Port Aransas Marine Laboratory Port Aransas, Texas 78373
As part of the Ross Sea ammonium flux experiment, we investigated the temperature, salinity, and nutrient signature of the ice shelf water that flows northward from beneath the Ross Ice Shelf into the Ross Sea. Working with the hypothesis that ice shelf water is a principal source of subsurface ammonium (see Biggs, Antarctic Journal, this issue), we identified the mesoscale variability of water column ammonium along four meridional lines of Niskin-bottle cast salinity-temperature-depth (STD) and stations and contrasted this with fine-scale variability determined from hydrocasts with an STD recorder-submersible pump combination. Following the drift path of a surface buoy drogued at 100 meters within the subsurface ammonium maximum, we pumpsampled the upper 120 meters of the water column using a Berkeley model AL-28 centripetal pump mounted to the frame of a Plessey 9040 STD recorder (see figure 1). Two vertical casts and a 2-3-hour horizontal cast were completed at each of two drogue stations. The pump pushed water to analytical equipment aboard the ship for continuous measurement of ammonium, nitrate, nitrite, silicate, dissolved oxygen, and in vivo fluorescence. Details of this sampling and analytical system have been given by Johnson (1981). The horizontal drift hydrocasts, during which the pump was suspended for several hours within the thermocline, generated concurrent time-series data on nutrients, chlorophyll, temperature, and salinity. Ship drift complicates the interpretation of the time-series data. During the horizontal pump cast at station 17, the ship was pushed by surface currents and the wind at a speed of about 1 knot, whereas ship drift was only about 1/3 knot at station 33. 148
Figure 1. Submersible pump mounted to the frame of a Plessey 9040 salinity-temperature-depth recorder, showing Niskin bottles for discrete sampling and pump-hose combination for continuous sampling.
ANTARCTIC JOURNAL
1:11
09
10
Il
12
13
14
0 .Y......! I 40
.40
.20
8:
80
Computer Plot by STDSECT Rev. 7931 , RID Processing System Thomas Reid a Department of Oceanography Tao., A&M University
100 120 140 Q) 180 180 200 220 240
U. S A. R.P. : DEEP FREEZE 1982 USCG GLACIER ROSS SEA CRUISE LONGITUDE 175 EAST
7ri
80 100 120 140 160 190
.
..............
0 5 10 15 20 25 30 35 40 45 50 55 80 65 70 75
Distance Along Transect (Km)
90 96 90
Figure 3. Ammonium concentrations (in microgram-atoms per liter) in the upper 250 meters along a 64-kilometer (40-mile) transect seaward from the barrier edge of the Ross Ice Shelf at 175 0 E. Shaded area denotes absence of bottle samples; see figure 1 for station locations.
References Amos, A. F. 1982. Physical oceanography of the southwestern Ross Sea, January 1982. Antarctic Journal of the U.S., 17(5). Bidigare, R. R., and Cox, J . L. 1982. Zooplankton metabolic studies in the Ross Sea. Antarctic Journal of the U.S., 17(5). Biggs, D. C. 1982. Zooplankton excretion and NH 4'cycling in nearsurface waters of the southern ocean. I. Ross Sea, austral summer 1977-1978. Polar Biology, 1, 55-67. El-Sayed, S. Z., Biggs, D. C., Stockwell, D., Warner, R., and Meyer, M. 1978. Biogeography and metabolism of phytoplankton and zooplankton in the Ross Sea, Antarctica. Antarctic Journal of the U.S., 13(4),131-133. Glibert, P. M., Biggs, D. C., and McCarthy, J . J. 1982. Uptake of ammonium and nitrate during austral summer in the Scotia Sea. DeepSea Research, 29(7a), 837-850.
Physical oceanography of the southwestern Ross Sea, January 1982 ANTHONY F. AMOS
University of Texas-Austin Marine Science Institute Port Aransas Marine Laboratory Port Aransas, Texas 78373 146
Horrigan, S. G. 1981. Primary production under the Ross Ice Shelf, Antarctica. Limnology and Oceanography, 26, 378-382. Holm-Hansen, 0., Neon, A., and Koike, I. 1982. Phytoplankton distribution, biomass, and activity in the southwest Ross Sea. Antarctic Journal of the U.S., 17(5). Jacobs, S. S., Amos, A. F., and Bruchhausen, P. M. 1970. Ross Sea oceanography and antarctic bottom water formation. Deep-Sea Research, 17, 935-962. 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., Gordon, A. L., and Ardai, J . L. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203, 439-443. Johnson, M. A., Biggs, D. C., and Amos, A. F. 1982. Oceanographic time-series studies with an STD-submersible pump combination. Antarctic Journal of the U.S., 17(5). Olson, R. J . 1980. Nitrate and ammonium uptake in antarctic waters. Limnology and Oceanography, 25, 1064-1074.
During the Ross Sea ammonium flux experiment (see Biggs, Antarctic Journal, this issue), the regional oceanography of the
southwestern Ross Sea was investigated by making surface-tobottom and time-series salinity/temperature profiles (Johnson, Biggs, and Amos, Antarctic Journal, this issue) with a salinitytemperature-depth (STD) sensor. Twenty-eight vertical stations and two main time-series stations were occupied (see station map in Biggs, Antarctic Journal, this issue). Five additional stations were occupied along the sea ice edge in McMurdo Sound to compare with a similar section I made in 1979 (see Jacobs et al. 1981). The present investigation was done aboard USCGC Glacier during Deep Freeze 82, using a ANTARCTIC JOURNAL
Plessey model 9040 STD system with a 12-bottle (2.5-liters each) rosette sampler. Discrete samples were taken with the rosette at 5, 20, 40, 60, 80, 100, 125, 150, 200, and 250 meters, primarily to provide nutrient and chlorophyll data for the ammonium flux experiment, but also for dissolved oxygen determinations and calibration of the STD salinity sensor. Two other samples, at middepth and just off the bottom, were routinely collected for STD calibration. Bottom depths ranged from 357 to 947 meters, and the STD was lowered to within a few meters of the bottom with the aid of a pinger. Thermometry was used to calibrate the STD temperature sensor. The STD sensor used, a "seasoned" veteran of numerous polar cruises, required little correction to bring it up to "water bottle" accuracy. The oceanography of this part of the Ross Sea has been described by Jacobs, Amos, and Bruchhausen (1970), and its 175 EAST SECTION B-15)
0.5
CDW
0.0 I /
I /
-0.5
27.4. 27.5
I /
271' ••":. . / / / 27.0. 20.0 29.2 21t
-in
I
I
I I
—1.5 / I
I
I
RSSW
-2.01
-U,
(a)
GLACIER 1X-82, Static,, 0 12 SIGMA-I Zn
GLACIER -62, Statia,, 0 15 u SIGMA-I cc
W
TEMP. (C) 151
ISW
to
Ln
'1.' TEMP. ID
SAUNITYç0pt -
151 ill ALINITYt
in
10$
20$
20$
30$ 'II
340$ T
4$'
Gt
50$
60$
an
70$
70$
90$
iF
UIS R SAUNIIY(ppt
rIE*.(C)
{
/s
- rTE*'.(C) .5.
SIGMA-I 6 (b)
SIGMA-I U' (c)
Temperature and salinity characteristics of waters along the 1750E meridian near the Ross Ice Shelf (see Biggs, Antarctic Journal, this Issue, for station locations). (a) Composite temperature/salinity diagram, stations 8-15. COW = Circumpolar Deep Water, RSSW = Ross Sea Shelf Water, isw = Ice Shelf Water; salinity (horizontal axis) in parts per thousand, temperature (vertical axis) in °C; dashed lines Indicate isopycnal surfaces in sigma-T units [sigma-T = (p - 1) X 10, where p = In situ density]. (b) Vertical profiles of temperature, salinity, and sigma-T (as) for station 12 over the Pennell Bank; SR = salinities from rosette samples. (c) As in (b), for station 15 adjacent to the Ross Ice Shelf face.
1982 REVIEW
particular relationship to the Ross Ice Shelf by Jacobs, Gordon, and Ardai (1979). Adjacent to the ice shelf, four types of subsurface water have been identified: deep and shallow Ice Shelf Water, a modified form of Circumpolar Deep Water, and deep Ross Sea Shelf Water. A temperature/salinity diagram of the 175°E section (figure, a) illustrates the various water masses found on this cruise. Modified Circumpolar Deep Water was found almost exclusively over the southern portion of the Pennell Bank on the 175°E section (station 12, figure, b), and only occasionally on the adjacent, 173°E section. It can be identified on the temperature/ salinity diagram (figure, a) by the cluster of points midway between and roughly parallel to the 27.8 and 27.9 isopycnals. Whether the Pennell Bank exercises any topographical control over this water mass is not known, but stations 14 and 15 off the bank (profile, figure, c) have completely different water characteristics in the upper 300 meters. Ice Shelf Water is characterized by the proximity of the water to the in situ freezing point, and it is formed by processes occurring under or adjacent to the Ross Ice Shelf. The deeper Ice Shelf Water has temperatures of less than - 2°C and salinities in the range of 34.5 to 34.717c. It is found at a depth near 400 meters, corresponding to the average base of the ice sheet. This water was found at only one station (station 15) on the easternmost (175°E) transect (figure, c), a few hundred meters away from the barrier. The second, shallower type of Ice Shelf Water, usually found at a depth of 250 meters, was not encountered on this cruise. No temperatures of less than - 1.9°C were found shallower than 250 meters. Only at station 14 did the water reach to within 0.2°C of the in situ freezing point at 250 meters. Ross Sea Shelf Water was found at all stations except those over the Pennell Bank and is illustrated in the figure by the bottom water mass, temperature less than -1.9°C, salinity greater than 34.7%. Preliminary geostrophic calculations show flow parallel to the ice shelf face but very little flow between transects into or away from the ice shelf. Using the bottom as a level of no motion, the net transport is toward the west except on the westernmost transect (169°E), where it is toward the east. The characteristics of stations adjacent to the ice shelf and those no more than 10 kilometers away creates a considerable shear in the computed currents. That such a variability exists in a small geographical area is of considerable interest, and preliminary results reveal the important role that the ice shelf and topographic features exert on the regional oceanography. How this regime is related to the observed nutrient distribution has yet to be studied. Property/property diagrams, vertically and horizontally contoured sections, and other calculations are presently being performed on these data. I thank the officers and crew of the USCGC Glacier for their help and support in carrying out this fieldwork. Particular thanks go to Captain J. W. Coste, LTJG Carla Ridnor, Master Chief Marine Science Technician P. St. Joule, and the other technicians. This work was partially supported by National Science Foundation grant DPP 79-21355 to Texas A&M University.
References Biggs, D. C. 1982. Ross Sea ammonium flux experiment. Antarctic Journal of the U.S., 17(5).
Jacobs, S. S., Amos, A. F., Bruchhausen, P. M. 1970. Ross Sea oceanogra147
phy and antarctic bottom water formation. Deep-Sea Research, 17, 935-962.
Jacobs, S. S., Gordon, A. L., and Ardai, J. L., Jr. 1979. Circulation and melting beneath the Ross Ice Shelf. Science, 203, 439-443. Jacobs, S. S., Huppert, H. E., Holdsworth, G., and Drewry, D. J . 1981.
Oceanographic time-series studies with an sm-submersible pump combination
Thermohaline steps induced by melting of the Erebus Glacier Tongue. Journal of Geophysical Research, 86(C7), 6547-6555. Johnson, M., Biggs, D. C., and Amos, A. F. 1982. Oceanographic timeseries studies with an STD-submersible pump combination. Antarctic Journal of the U.S., 17(5).
STD time-series data for station 17 in the east and station 33 in the west (figure 2; see figure 1 in Biggs, Antarctic Journal, this issue, for locations) show evidence of internal wave activity, particularly in the temperature signal. The STD recorder was held in the thermocline at depths of 68 meters (station 17) and 65 meters (station 33). The vertical temperature structure near
MARK A. JOHNSON and DOUGLAS C. BIGGs Department of Oceanography Texas A&M University College Station, Texas 77843
ANTHONY F. AMOS University of Texas-Austin Marine Science Institute Port Aransas Marine Laboratory Port Aransas, Texas 78373
As part of the Ross Sea ammonium flux experiment, we investigated the temperature, salinity, and nutrient signature of the ice shelf water that flows northward from beneath the Ross Ice Shelf into the Ross Sea. Working with the hypothesis that ice shelf water is a principal source of subsurface ammonium (see Biggs, Antarctic Journal, this issue), we identified the mesoscale variability of water column ammonium along four meridional lines of Niskin-bottle cast salinity-temperature-depth (STD) and stations and contrasted this with fine-scale variability determined from hydrocasts with an STD recorder-submersible pump combination. Following the drift path of a surface buoy drogued at 100 meters within the subsurface ammonium maximum, we pumpsampled the upper 120 meters of the water column using a Berkeley model AL-28 centripetal pump mounted to the frame of a Plessey 9040 STD recorder (see figure 1). Two vertical casts and a 2-3-hour horizontal cast were completed at each of two drogue stations. The pump pushed water to analytical equipment aboard the ship for continuous measurement of ammonium, nitrate, nitrite, silicate, dissolved oxygen, and in vivo fluorescence. Details of this sampling and analytical system have been given by Johnson (1981). The horizontal drift hydrocasts, during which the pump was suspended for several hours within the thermocline, generated concurrent time-series data on nutrients, chlorophyll, temperature, and salinity. Ship drift complicates the interpretation of the time-series data. During the horizontal pump cast at station 17, the ship was pushed by surface currents and the wind at a speed of about 1 knot, whereas ship drift was only about 1/3 knot at station 33. 148
Figure 1. Submersible pump mounted to the frame of a Plessey 9040 salinity-temperature-depth recorder, showing Niskin bottles for discrete sampling and pump-hose combination for continuous sampling.
ANTARCTIC JOURNAL
