Magnetic susceptibility of antarctic glacial marine sediments
References Domack, E. W., L. A. Burkley, and C. it Williams. 1989. Character of modern glacial marine sediments: Antarctic Peninsula and South
Shetland Islands. Antarctic Journal of the U.S., 24(5)133-115. Harden, S. L., D. J. DeMaster, and C. A. Nittrouer. 1992. Developir4g sediment chronologies for high-latitude continental shelf deposits: 1 radiochemical approach. Marine Geology, 103:69-97.
Magnetic susceptibility of antarctic glacial marine sediments 0
EUGENE W. DOMACK
Geology Department Hamilton College Clinton, New York 13323
Scorr
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
100
ISHMAN
U.S. Geological Survey Reston, Virginia 22092
We measured the magnetic susceptibility of three piston cores from the Gerlache Strait area of western Antarctic Peninsula in order to develop the method as a means of correlation between cores and as an aid to the sedimentological interpretation of individual cores. We measured susceptibility using a Bartington MS-2 core scanning sensor on unsampled halves of split cores. The results are reported as CGS x 10 units. We collected core PD88 151 from the northern reaches of the Gerlache Strait (64'13.108' S 61714.713'W) during cruise Ill of the R/V Polar Duke in early 1988. Figure 1 illustrates the relationship of total carbon to magnetic susceptibility within this core. From the data it is apparent that there is significant variation in the magnetic susceptibility despite the visual observation of homogeneity within the core. It is also apparent that the carbon content, which is a reflection of the biogenic component within the core, varies inversely with the susceptibility. Hence, we can subdivide the core into three distinct intervals based upon the carbon and susceptibility measurements. The uppermost portion (0 to 150 centimeters) is characterized by relatively high susceptibility, 50 to 75 x 10 CGS, and relatively low total carbon contents, generally less than 1 percent. A middle section of the core contains relatively low but variable susceptibility and very high to moderate carbon contents. The lower third of the core (from 375 to 560 centimeters) is characterized by very low susceptibilities, less than 10 x 10 CGS, and high total carbon contents. Clearly the magnetic susceptibility is reflecting compositional changes within the core that are somehow related to the variation in the contribution of biogenic material in the core. When the biogenic content is high, with high total carbon values, there would be less terrigenous material and more biogenic silica and calcium carbonate.
64
Total Carbon %
200 (D C,
400 500 600
0 20 40 60 80 Magnetic Susceptibility (CGS x 10-6) ==
Figure 1. Downcore trends In total organic carbon and magnetic susceptibility for core PD88 151. Note inverse relationship between carbon content and susceptibility. In fact, the two peaks in the total carbon content correspond to foraminifera-rich samples that indicate elevated levels of calcium carbonate in the core. These two intervals correspond to moderate lows in the susceptibility curve. Therefore it seems that the
ANTARCTIC JOURNAL
Magnetic Susceptibility (x 106 CGS) PD88 22
DF85 63 0
0 20 40 60 80 100
0 20 40 60 80 100
o1 .1
PD88 151 0 20 40 60 80 100 1 04
100
100
100
200
200
200
300
300
300
400
400
400
500
500
500
C.) 800
600
600
700
700
800
800
900
Onn
1000
1100
1200-'
Igure 2. Downcore trends In magnetic susceptibility for cores DF85 63, P088 22, and P088151. Note similarity in trend of susceptibility for II three cores. 4agnetic susceptibility is a quick and easy method for evaluating variable susceptibility interval that overlies a low and constant relative composition, be it biogenic or terrigenous, within a susceptibility interval. The depth at which the transition takes ore. If the compositional changes within core 151 represent place varies from core to core, which suggests that there is a basin-wide changes in the nature of sedimentation, then suscep- difference in the sedimentation rate of the three cores. If this is tbility records of other cores should reflect a similar pattern, indeed the case, then it implies a basin-wide change in deposiA comparison of the magnetic susceptibility of three cores is tional conditions. i lustrated in figure 2. Core DF85 63 was collected during Deep These preliminary results indicate that magnetic susceptibilreeze 1985 from a deep basin just south of the southern entrance ity is a useful tool in the interpretation of antarctic glacial marine t ) the Bismarck Strait while core PD88 22 was collected by us from sediments. Its wider application should allow for the resolution e central basin of Andvord Bay, about midway within the of several problems pertinent to the paleoenvironmentally hiserlache Strait. All three cores are siliceous muds that are visu- tory of the Antarctic Peninsula. ily homogeneous. There is a similar pattern to the susceptibility This work was supported by National Science Foundation ecords of all three cores in that there is a relatively high but grants DPP 86-13565 and DPP 89-15977.
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65
Shetland Islands. Antarctic Journal of the U.S., 24(5)133-115. Harden, S. L., D. J. DeMaster, and C. A. Nittrouer. 1992. Developir4g sediment chronologies for high-latitude continental shelf deposits: 1 radiochemical approach. Marine Geology, 103:69-97.
Magnetic susceptibility of antarctic glacial marine sediments 0
EUGENE W. DOMACK
Geology Department Hamilton College Clinton, New York 13323
Scorr
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
100
ISHMAN
U.S. Geological Survey Reston, Virginia 22092
We measured the magnetic susceptibility of three piston cores from the Gerlache Strait area of western Antarctic Peninsula in order to develop the method as a means of correlation between cores and as an aid to the sedimentological interpretation of individual cores. We measured susceptibility using a Bartington MS-2 core scanning sensor on unsampled halves of split cores. The results are reported as CGS x 10 units. We collected core PD88 151 from the northern reaches of the Gerlache Strait (64'13.108' S 61714.713'W) during cruise Ill of the R/V Polar Duke in early 1988. Figure 1 illustrates the relationship of total carbon to magnetic susceptibility within this core. From the data it is apparent that there is significant variation in the magnetic susceptibility despite the visual observation of homogeneity within the core. It is also apparent that the carbon content, which is a reflection of the biogenic component within the core, varies inversely with the susceptibility. Hence, we can subdivide the core into three distinct intervals based upon the carbon and susceptibility measurements. The uppermost portion (0 to 150 centimeters) is characterized by relatively high susceptibility, 50 to 75 x 10 CGS, and relatively low total carbon contents, generally less than 1 percent. A middle section of the core contains relatively low but variable susceptibility and very high to moderate carbon contents. The lower third of the core (from 375 to 560 centimeters) is characterized by very low susceptibilities, less than 10 x 10 CGS, and high total carbon contents. Clearly the magnetic susceptibility is reflecting compositional changes within the core that are somehow related to the variation in the contribution of biogenic material in the core. When the biogenic content is high, with high total carbon values, there would be less terrigenous material and more biogenic silica and calcium carbonate.
64
Total Carbon %
200 (D C,
400 500 600
0 20 40 60 80 Magnetic Susceptibility (CGS x 10-6) ==
Figure 1. Downcore trends In total organic carbon and magnetic susceptibility for core PD88 151. Note inverse relationship between carbon content and susceptibility. In fact, the two peaks in the total carbon content correspond to foraminifera-rich samples that indicate elevated levels of calcium carbonate in the core. These two intervals correspond to moderate lows in the susceptibility curve. Therefore it seems that the
ANTARCTIC JOURNAL
Magnetic Susceptibility (x 106 CGS) PD88 22
DF85 63 0
0 20 40 60 80 100
0 20 40 60 80 100
o1 .1
PD88 151 0 20 40 60 80 100 1 04
100
100
100
200
200
200
300
300
300
400
400
400
500
500
500
C.) 800
600
600
700
700
800
800
900
Onn
1000
1100
1200-'
Igure 2. Downcore trends In magnetic susceptibility for cores DF85 63, P088 22, and P088151. Note similarity in trend of susceptibility for II three cores. 4agnetic susceptibility is a quick and easy method for evaluating variable susceptibility interval that overlies a low and constant relative composition, be it biogenic or terrigenous, within a susceptibility interval. The depth at which the transition takes ore. If the compositional changes within core 151 represent place varies from core to core, which suggests that there is a basin-wide changes in the nature of sedimentation, then suscep- difference in the sedimentation rate of the three cores. If this is tbility records of other cores should reflect a similar pattern, indeed the case, then it implies a basin-wide change in deposiA comparison of the magnetic susceptibility of three cores is tional conditions. i lustrated in figure 2. Core DF85 63 was collected during Deep These preliminary results indicate that magnetic susceptibilreeze 1985 from a deep basin just south of the southern entrance ity is a useful tool in the interpretation of antarctic glacial marine t ) the Bismarck Strait while core PD88 22 was collected by us from sediments. Its wider application should allow for the resolution e central basin of Andvord Bay, about midway within the of several problems pertinent to the paleoenvironmentally hiserlache Strait. All three cores are siliceous muds that are visu- tory of the Antarctic Peninsula. ily homogeneous. There is a similar pattern to the susceptibility This work was supported by National Science Foundation ecords of all three cores in that there is a relatively high but grants DPP 86-13565 and DPP 89-15977.
992 REVIEW
65
