Late Holocene fluctuations in the front of the Muller Ice
Late Holocene fluctuations in the front of the Muller Ice Shelf, Antarctic Peninsula EUGENE W. D0MAcK, Department of Geology, Hamilton College, Clinton, New York 13323 ANDREW B. STEIN, Delta Environmental Consultants, Inc., New Berlin, Wisconsin 53151
ce shelves are important environmental indicators along the I Antarctic Peninsula. In fact, the recent warming trend over the last half of this century is believed to be responsible for the destruction of the Wordie Ice Shelf located at approximately 69° south (Doake and Vaughan 1991). To investigate the fluctuation of the Muller Ice Shelf (figure 1), we collected surface sediment samples, piston cores, and kasten cores close to the present calving line. We conducted detailed grain size and compositional analyses on the sediment cores and surface samples to discern the past extent and status of the Muller Ice Shelf. The sand content of surface and downcore samples was most revealing. A modern sand-rich fades is associated with the calving terminus of the Muller Ice Shelf. The sand is well sorted and is rich in heavy minerals (Frederick 1991; Stein 1992). The sand is being brought into the marine environment by processes acting at the calving terminus of the Muller Ice Shelf. Such processes are related to eolian transport of sand across the surface of the Muller Ice Shelf and concentration, perhaps by meltwater, into transverse crevasses that form just behind the calving front of the ice shelf. The sand rich facies is limited to within 4 kilometers of the ice front. Downcore, the sand facies is not persistent; it can be found in cores taken close to the ice front but only down to a depth of 60 to 75 centimeters (figure 2). This suggests that the source of sand input
PC7I1071
0072 561 G60 tC73 559 557 KC 75
Ice Shelf •..• Factes no recovery
50 Trr
100
Open Fjord Fades
sy 150
:
Mud,
pebbles, grey
Pebbly Mud, greeruh
::::::• sot,
o"o Jo grey
EPM
I
no pebbles, grey 300 n
Depth (cm)
4 (Carbon-14 age. years B.P.)
Laliemand Fjord: Loubet Coast, Antarctic Peninsula Figure 2. Core lithology and correlation between cores collected in Lailemand Fjord in 1991 off the RN Polar Duke. Core and surface grab sites are located in figure 1. PC denotes piston core; IC denotes trigger core; KC denotes kasten core; G denotes Smith McIntyre grab sample.
into Lallemand Fjord is only a recent one. To determine when the sand was first brought into the system, sedimentation rates were calculated for core 72 using lead-210 ( 210 Pb) accumulation curves (figure 3). The rate of 2.1 millimeters per year was determined using the 210 Pb accumulation curves in figure 3. This means that the sand input into Lallemand Fjord began approximately 243 years ago. If sand input is directly related to the ice-front environment of the Muller Ice Shelf, then it can be inferred that the Muller Ice Shelf is a relatively recent feature of Lallemand Fjord. If ice shelves accurately reflect the climate of the region, then it must be assumed that there has been a recent cooling trend over the past 240 years. The most recent historical record, however, shows that the Muller Ice Shelf is disintegrating (figure 1). This work was supported by National Science Foundation grant OPP 89-15977. We would like to thank Geoff Pierson of the State University of New York at Stony Brook for the 210 Pb analyses.
Figure 1. The area of the Loubet Coast with Lailemand Fjord. The inset shows the Muller ice Shelf. Note the dates of various ice-front positions from 1974 to 1990 based upon photographs and ship observations.
ANTARCTIC JOURNAL - REVIEW 1993 96
References
Activity (dpm) 0.0 5.0
Doake, C.S., and Vaughan, D.G., 1991. Rapid disintegration of the Wordie Ice Shelf in response to atmospheric warming. Nature. 350(63 16), 328-330. Frederick, B. 1991. The interpretive utility of magnetic susceptibility measurements in modern antarctic glacial-marine sediment. (B.A. honors report, Colgate University, Hamilton, New York.) Stein, A.B. 1992. Growth of the Muller Ice Shelf during the latter half of the Little Ice Age as documented by glacial marine sediments and radiogeochemistry. (B.A. thesis, Hamilton College, Clinton, New York.)
10.0 15.0 20.0 25.0
5 10 15 20 25 Depth 30 (cm) 35 40 45 50 55 60 65 70 75
Figure 3. Downcore 210Pb activity for cores 72 (solid dots) and 75 (open dots).
Modern sedimentation within Andvord Bay, Antarctic Penisula EUGENE W. DOMACK, Department of Geology, Hamilton College, Clinton, New York 13323 KERRY A. MAMMONE, Department of Geosciences, Oregon State University, Corvallis, Oregon 97331-5506
o assess the modern sedimentation regime within AndT vord Bay, we deployed sediment traps for a 5-month period (from mid-October to mid-March). The trap mooring is illustrated in the figure. A moored system of three funnelshaped sediment traps, each with a collection area of 0.8018 square meters (m 2), was deployed for 159 days in Andvord Bay, a fjord just off the northern Antarctic Peninsula region at 64049.15'S 62 039.3'W. The mooring was deployed on 15 October 1991 by Eugene Domack and retrieved 26 March 1992 during cruise 92-2 of the R/V Polar Duke. Sediment traps were deployed at depths of 230, 397, and 441 meters (m) over a bottom depth of 450 m (figure). Traps were not deployed at any depths shallower than 230 m so as not to be disturbed by icebergs. Trap material was analyzed for sand and gravel content, total organic carbon, and biogenic silica. The total sediment
• .
philtizolanktm
marker float wfthfl3g
I
175 M
230 float (ICC-CUC 1
3q7
b urtu)
(3)
ttttl
I I 2'12m (2)
(I) swivel - ..
la to grolllatIlxe ( rapt of reutral uganctj)
smail anhar small anchor (
s mall anclrar 20m
loom-
Diagram of sediment-trap mooring as deployed in Andvord Bay during the 1991-1992 austral summer season.
ANTARCTIC JOURNAL - REVIEW 1993 97
ce shelves are important environmental indicators along the I Antarctic Peninsula. In fact, the recent warming trend over the last half of this century is believed to be responsible for the destruction of the Wordie Ice Shelf located at approximately 69° south (Doake and Vaughan 1991). To investigate the fluctuation of the Muller Ice Shelf (figure 1), we collected surface sediment samples, piston cores, and kasten cores close to the present calving line. We conducted detailed grain size and compositional analyses on the sediment cores and surface samples to discern the past extent and status of the Muller Ice Shelf. The sand content of surface and downcore samples was most revealing. A modern sand-rich fades is associated with the calving terminus of the Muller Ice Shelf. The sand is well sorted and is rich in heavy minerals (Frederick 1991; Stein 1992). The sand is being brought into the marine environment by processes acting at the calving terminus of the Muller Ice Shelf. Such processes are related to eolian transport of sand across the surface of the Muller Ice Shelf and concentration, perhaps by meltwater, into transverse crevasses that form just behind the calving front of the ice shelf. The sand rich facies is limited to within 4 kilometers of the ice front. Downcore, the sand facies is not persistent; it can be found in cores taken close to the ice front but only down to a depth of 60 to 75 centimeters (figure 2). This suggests that the source of sand input
PC7I1071
0072 561 G60 tC73 559 557 KC 75
Ice Shelf •..• Factes no recovery
50 Trr
100
Open Fjord Fades
sy 150
:
Mud,
pebbles, grey
Pebbly Mud, greeruh
::::::• sot,
o"o Jo grey
EPM
I
no pebbles, grey 300 n
Depth (cm)
4 (Carbon-14 age. years B.P.)
Laliemand Fjord: Loubet Coast, Antarctic Peninsula Figure 2. Core lithology and correlation between cores collected in Lailemand Fjord in 1991 off the RN Polar Duke. Core and surface grab sites are located in figure 1. PC denotes piston core; IC denotes trigger core; KC denotes kasten core; G denotes Smith McIntyre grab sample.
into Lallemand Fjord is only a recent one. To determine when the sand was first brought into the system, sedimentation rates were calculated for core 72 using lead-210 ( 210 Pb) accumulation curves (figure 3). The rate of 2.1 millimeters per year was determined using the 210 Pb accumulation curves in figure 3. This means that the sand input into Lallemand Fjord began approximately 243 years ago. If sand input is directly related to the ice-front environment of the Muller Ice Shelf, then it can be inferred that the Muller Ice Shelf is a relatively recent feature of Lallemand Fjord. If ice shelves accurately reflect the climate of the region, then it must be assumed that there has been a recent cooling trend over the past 240 years. The most recent historical record, however, shows that the Muller Ice Shelf is disintegrating (figure 1). This work was supported by National Science Foundation grant OPP 89-15977. We would like to thank Geoff Pierson of the State University of New York at Stony Brook for the 210 Pb analyses.
Figure 1. The area of the Loubet Coast with Lailemand Fjord. The inset shows the Muller ice Shelf. Note the dates of various ice-front positions from 1974 to 1990 based upon photographs and ship observations.
ANTARCTIC JOURNAL - REVIEW 1993 96
References
Activity (dpm) 0.0 5.0
Doake, C.S., and Vaughan, D.G., 1991. Rapid disintegration of the Wordie Ice Shelf in response to atmospheric warming. Nature. 350(63 16), 328-330. Frederick, B. 1991. The interpretive utility of magnetic susceptibility measurements in modern antarctic glacial-marine sediment. (B.A. honors report, Colgate University, Hamilton, New York.) Stein, A.B. 1992. Growth of the Muller Ice Shelf during the latter half of the Little Ice Age as documented by glacial marine sediments and radiogeochemistry. (B.A. thesis, Hamilton College, Clinton, New York.)
10.0 15.0 20.0 25.0
5 10 15 20 25 Depth 30 (cm) 35 40 45 50 55 60 65 70 75
Figure 3. Downcore 210Pb activity for cores 72 (solid dots) and 75 (open dots).
Modern sedimentation within Andvord Bay, Antarctic Penisula EUGENE W. DOMACK, Department of Geology, Hamilton College, Clinton, New York 13323 KERRY A. MAMMONE, Department of Geosciences, Oregon State University, Corvallis, Oregon 97331-5506
o assess the modern sedimentation regime within AndT vord Bay, we deployed sediment traps for a 5-month period (from mid-October to mid-March). The trap mooring is illustrated in the figure. A moored system of three funnelshaped sediment traps, each with a collection area of 0.8018 square meters (m 2), was deployed for 159 days in Andvord Bay, a fjord just off the northern Antarctic Peninsula region at 64049.15'S 62 039.3'W. The mooring was deployed on 15 October 1991 by Eugene Domack and retrieved 26 March 1992 during cruise 92-2 of the R/V Polar Duke. Sediment traps were deployed at depths of 230, 397, and 441 meters (m) over a bottom depth of 450 m (figure). Traps were not deployed at any depths shallower than 230 m so as not to be disturbed by icebergs. Trap material was analyzed for sand and gravel content, total organic carbon, and biogenic silica. The total sediment
• .
philtizolanktm
marker float wfthfl3g
I
175 M
230 float (ICC-CUC 1
3q7
b urtu)
(3)
ttttl
I I 2'12m (2)
(I) swivel - ..
la to grolllatIlxe ( rapt of reutral uganctj)
smail anhar small anchor (
s mall anclrar 20m
loom-
Diagram of sediment-trap mooring as deployed in Andvord Bay during the 1991-1992 austral summer season.
ANTARCTIC JOURNAL - REVIEW 1993 97
