Heat flow in the Weddell Sea
Heat flow in the Weddell Sea
Sea was measured at 13 stations; 1 measurement was obtained in the Scotia Sea. The measurements were made by rigging five thermistors along the coring pipe and one on the core weightstand. Temperature was recorded with an optical instrument mounted on the weightstand. Conductivity was determined by the needle-probe method of Von Herzen and Maxwell (1959) on samples of sediment recovered by the corer. The conductive heat flux was obtained by multiplying the least squares estimate of the temperature gradient by the harmonic mean conductivity along the core. The area presented many difficulties. The hardness of the bottom sediments was responsible for bending many of the cores; it caused tilt and poor penetration, and it damaged rugged exterior cables and connections. On other stations the rough basement, frequently outcropping, distorted the temperature field and was probably the site of water circulation producing convective heat losses (Lister, 1974; Sclater et al.. 1976). Of 31 stations attempted only 14 were successful. The distributuion of stations is shown in figure 1. All stations with a computed heat flux have at least three consistent
VICTOR ZLOTNICKI, 1 2 IAN 0. NORTON, 3 JOHN G SCLATER, I and RICHARD P. VON HERZEN2
'Department of Earth and Planetary Sciences Massachusetts Institute of Technology Cambridge, Massachusetts 02139 2Department of Geology and Geophysics Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543 3 Bernard Price Institute of Geophysical Research University of the Witwatersrand Johannesburg, South Africa
Between 16January and 12 March 1978, on ARA Is/as Orcadas cruise 15, the heat flux through the floor of the Weddell
ç
"00
-
- sot.
HEAT FLOW ISLAS ORCADAS 15/78 4 0 station .number
2
0.57 heat flow units --- 3000m contour d 0 ----.. 5000m
--, : AN
—
DWOCN
20
/ /o'
' .•
1r,
9 — - — — I 4 —
95 J
620 /
eab
:/
----
I. oO j )
o
0 /
J
455
--- — I .--' -
42
--
5%'
ezI /
c
it
f
700
.............. ..........
Figure 1. Location of stations visited during MA Islas Orcadas cruise 15 to measure heat flow. Underlined are the heat flux values, in calories per square centimeter per second. 120
ANTARCTIC JOURNAL
STA11ON 39
K 2,L3.2.P
Figure 2. Profiles of temperature (1, In degrees C) and conductivity (K, in 1O • cal/°C sec cm2) vs. distance from core weightstand, for three stations on
4
cruise ARA Was Orcadas
15. At station 39 the lowermost two thermistors were • torn off the pipe. 10 I)
temperature measurements down the profile and reliable conductivity. Figure 2 shows three of these profiles. Station 55 is right on top of a basement outcrop, which may explain the high value. On the other hand, stations 4,5,8,11,48 can be expected to have their values lowered due to the presence of nearby outcrops. These results show that heat flow can be measured from aboard ARA Islas Orcadas in the southern oceans. Surprisingly high heat flow values are found in the Weddell Sea. These values are especially high in elevated topography south of the South Sandwich fracture zone. Cooling models for the lithosphere allow one to relate the heat flux and depth to the basement with the age of the crust (e.g., Parsons and Sclater, 1977). Additional heat flow measurements in this area (these have been the first) will provide important constraints on the tectonic history of the southern oceans. We are grateful to John Crowe who advised and aided during all the precruise stages; to Jim Akins, whose recording instrument proved 100 percent reliable; to Captain Horacio Badaroux andJohn LaBrecque for managing to get 55 days at sea with high scientific productivity and negligible human frictions; to Paul Dudley Hart and the Argentine officers and crew of the ship for their complete and friendly cooperation. This research was carried out under National Science Foundation grant DPP 76-19053.
References
Lister, C. R. B. 1974. On the penetration of water into hot rock. Geophysical Journal of the Royal Astronomical Society, 39: 465-509. Parsons, B., and J . G. Sclater. 1977. An analysis of the variation of ocean floor bathymetry and heat flow with age,Journal of Geophysical Research, 82: 803-827. Sclater,J. G.,J. Crowe, and R. Anderson. 1976. On the reliability of oceanic heat flow averages. Journal of Geophysical Research, 81: 2997-3006. Von Herzen, R. P., and A. E. Maxwell. 1959. The measurement of thermal conductivity of deep sea sediments by a needle-probe method.Journal of Geophysical Research, 64: 1557-1565.
October 1978
Miocene glaciomarine sediments from site J-9, Ross Ice Shelf, Antarctica THOMAS E. RONAN,JR.' Department of Earth and Space Sciences University of California, Los Angeles Los Angeles, California 90024 PETER N. WEBB Department of Geology Northern Illinois University DeKalb, Illinois 60115 JERE H. LIPPs and TED E. DELACA Department of Geology University of California, Davis Davis, California 95616
Bottom sediments were collected from beneath the Ross Ice Shelf at RISP (Ross Ice Shelf Project) site J-9. (82°22'S.168°38'W.) during the 1977-78 austral summer. The access hole was made through the ice shelf with a Browning flame-jet and the sampling gear was lowered 657 meters to the seafloor by winch. Two bottom-sampling devices were used. A cylindrical sphincter corer with an internal diameter of 22.5 centimeters was used to obtain about 1/3 square meter of sample cored to a depth of 14 centimeters. Ten such samples were obtained. Deeper bottom penetration was achieved with a conventional gravity corer 4-centimeter internal diameter. Eleven gravity cores were collected; the longest was 102 centimeters. The sedimentary succession obtained may be subdivided into two distinct lithologic units as shown in figure 1. Igneous, metamorphic, and sedimentary pebble and granule * Deceased. 121
Sea was measured at 13 stations; 1 measurement was obtained in the Scotia Sea. The measurements were made by rigging five thermistors along the coring pipe and one on the core weightstand. Temperature was recorded with an optical instrument mounted on the weightstand. Conductivity was determined by the needle-probe method of Von Herzen and Maxwell (1959) on samples of sediment recovered by the corer. The conductive heat flux was obtained by multiplying the least squares estimate of the temperature gradient by the harmonic mean conductivity along the core. The area presented many difficulties. The hardness of the bottom sediments was responsible for bending many of the cores; it caused tilt and poor penetration, and it damaged rugged exterior cables and connections. On other stations the rough basement, frequently outcropping, distorted the temperature field and was probably the site of water circulation producing convective heat losses (Lister, 1974; Sclater et al.. 1976). Of 31 stations attempted only 14 were successful. The distributuion of stations is shown in figure 1. All stations with a computed heat flux have at least three consistent
VICTOR ZLOTNICKI, 1 2 IAN 0. NORTON, 3 JOHN G SCLATER, I and RICHARD P. VON HERZEN2
'Department of Earth and Planetary Sciences Massachusetts Institute of Technology Cambridge, Massachusetts 02139 2Department of Geology and Geophysics Woods Hole Oceanographic Institution Woods Hole, Massachusetts 02543 3 Bernard Price Institute of Geophysical Research University of the Witwatersrand Johannesburg, South Africa
Between 16January and 12 March 1978, on ARA Is/as Orcadas cruise 15, the heat flux through the floor of the Weddell
ç
"00
-
- sot.
HEAT FLOW ISLAS ORCADAS 15/78 4 0 station .number
2
0.57 heat flow units --- 3000m contour d 0 ----.. 5000m
--, : AN
—
DWOCN
20
/ /o'
' .•
1r,
9 — - — — I 4 —
95 J
620 /
eab
:/
----
I. oO j )
o
0 /
J
455
--- — I .--' -
42
--
5%'
ezI /
c
it
f
700
.............. ..........
Figure 1. Location of stations visited during MA Islas Orcadas cruise 15 to measure heat flow. Underlined are the heat flux values, in calories per square centimeter per second. 120
ANTARCTIC JOURNAL
STA11ON 39
K 2,L3.2.P
Figure 2. Profiles of temperature (1, In degrees C) and conductivity (K, in 1O • cal/°C sec cm2) vs. distance from core weightstand, for three stations on
4
cruise ARA Was Orcadas
15. At station 39 the lowermost two thermistors were • torn off the pipe. 10 I)
temperature measurements down the profile and reliable conductivity. Figure 2 shows three of these profiles. Station 55 is right on top of a basement outcrop, which may explain the high value. On the other hand, stations 4,5,8,11,48 can be expected to have their values lowered due to the presence of nearby outcrops. These results show that heat flow can be measured from aboard ARA Islas Orcadas in the southern oceans. Surprisingly high heat flow values are found in the Weddell Sea. These values are especially high in elevated topography south of the South Sandwich fracture zone. Cooling models for the lithosphere allow one to relate the heat flux and depth to the basement with the age of the crust (e.g., Parsons and Sclater, 1977). Additional heat flow measurements in this area (these have been the first) will provide important constraints on the tectonic history of the southern oceans. We are grateful to John Crowe who advised and aided during all the precruise stages; to Jim Akins, whose recording instrument proved 100 percent reliable; to Captain Horacio Badaroux andJohn LaBrecque for managing to get 55 days at sea with high scientific productivity and negligible human frictions; to Paul Dudley Hart and the Argentine officers and crew of the ship for their complete and friendly cooperation. This research was carried out under National Science Foundation grant DPP 76-19053.
References
Lister, C. R. B. 1974. On the penetration of water into hot rock. Geophysical Journal of the Royal Astronomical Society, 39: 465-509. Parsons, B., and J . G. Sclater. 1977. An analysis of the variation of ocean floor bathymetry and heat flow with age,Journal of Geophysical Research, 82: 803-827. Sclater,J. G.,J. Crowe, and R. Anderson. 1976. On the reliability of oceanic heat flow averages. Journal of Geophysical Research, 81: 2997-3006. Von Herzen, R. P., and A. E. Maxwell. 1959. The measurement of thermal conductivity of deep sea sediments by a needle-probe method.Journal of Geophysical Research, 64: 1557-1565.
October 1978
Miocene glaciomarine sediments from site J-9, Ross Ice Shelf, Antarctica THOMAS E. RONAN,JR.' Department of Earth and Space Sciences University of California, Los Angeles Los Angeles, California 90024 PETER N. WEBB Department of Geology Northern Illinois University DeKalb, Illinois 60115 JERE H. LIPPs and TED E. DELACA Department of Geology University of California, Davis Davis, California 95616
Bottom sediments were collected from beneath the Ross Ice Shelf at RISP (Ross Ice Shelf Project) site J-9. (82°22'S.168°38'W.) during the 1977-78 austral summer. The access hole was made through the ice shelf with a Browning flame-jet and the sampling gear was lowered 657 meters to the seafloor by winch. Two bottom-sampling devices were used. A cylindrical sphincter corer with an internal diameter of 22.5 centimeters was used to obtain about 1/3 square meter of sample cored to a depth of 14 centimeters. Ten such samples were obtained. Deeper bottom penetration was achieved with a conventional gravity corer 4-centimeter internal diameter. Eleven gravity cores were collected; the longest was 102 centimeters. The sedimentary succession obtained may be subdivided into two distinct lithologic units as shown in figure 1. Igneous, metamorphic, and sedimentary pebble and granule * Deceased. 121
