HR: 0800h
AN: C51B-0390    [Abstracts]
TI: 210-Pb Study of Fjord Sedimentation Rates in the South Shetland Islands and Antarctic Peninsula
AU: * Kimball, B L
EM: brittk4@u.washington.edu
AF: School of Oceanography and Department of Earth and Space Sciences, Box 357940, Seattle, WA 98195, United States
AU: Nittrouer, C A
EM: nittroue@ocean.washington.edu
AF: School of Oceanography and Department of Earth and Space Sciences, Box 357940, Seattle, WA 98195, United States
AU: Landowski, C M
EM: clandows@email.arizona.edu
AU: Koppes, M
EM: koppes@geog.ubc.ca
AU: Hallet, B
EM: hallet@u.washington.edu
AF: School of Oceanography and Department of Earth and Space Sciences, Box 357940, Seattle, WA 98195, United States
AB: As part of a study concerning the factors controlling rates of glacial erosion and sedimentation across climatic regimes, sixteen kasten cores were collected from ten fjords in the South Shetland Islands and Antarctic Peninsula in April and May, 2007 from the R/VIB Nathaniel B. Palmer. They were sampled for ²¹⁰Pb measurements of accumulation rates and associated sedimentological observations (x-radiography, sedimentology). The cores were collected from basins within a few kilometers of the calving front at the respective glacier, where sediment accumulation was observed in 3.5 kHz sub-bottom profiles. Core lengths ranged from 34-289 cm; in 7 of the 16 core locations, multiple deployments were required to retrieve even a short sediment core due to the hardness of the bed. For most of the cores (10 of 16) sandy mud has accumulated steadily at rates ranging from 1 to 10 mm/y over the past century, as tightly defined by clear linear trends of 10 to 15 log ²¹⁰Pb values versus depth, with r² ranging from 0.75-0.98. The rates of accumulation appear to be independent of distance from the calving front, and most likely reflect variability in glacial-marine sediment delivery to, and basin morphology of, individual fjords. Several cores show evidence of variable sedimentation with pulses of sand emplacement. Three cores contained a surficial layer >50 cm thick of uniform ²¹⁰Pb activity, indicating recent, rapid deposition of a large turbidity current or mass flow. The consistency of many of the ²¹⁰Pb profiles implies that, over the past century, the glacial-marine processes that supplied, transported and deposited sediment in these sub-polar and polar fjords have not varied markedly. This contrasts with other glacial-marine systems in warmer regions such SE Alaska, where sedimentation in the fjords from calving temperate glaciers tends to vary significantly, and where the accumulation tends to slow as the calving front recedes rapidly from the core location. The rates of sedimentation reported here for the last 10 to 100 years off the Antarctic Peninsula will be compared to those on a millennial time scale derived from ¹⁴C data, and will be interpreted in the context of corresponding bathymetric and glaciological data as they become available.
DE: 0720 Glaciers
DE: 1115 Radioisotope geochronology
DE: 3022 Marine sediments: processes and transport
DE: 4901 Abrupt/rapid climate change (1605)
DE: 5754 Polar regions
SC: Cryosphere [C]
MN: 2007 Fall Meeting