HR: 14:10h
AN: PP33D-03    [Abstracts]
TI: ⁴He in Modern Cape Verde Corals: A High-Resolution Proxy Record of N. African Climate
AU: * Mukhopadhyay, S
EM: sujoy@eps.harvard.edu
AF: Harvard University, Dept. of Earth & Planetary Sciences, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Kreycik, P
PP33D-03 AF: Harvard University, Dept. of Earth & Planetary Sciences, 20 Oxford Street, Cambridge, MA 02138 United States
AU: Schrag, D P
PP33D-03 AF: Harvard University, Dept. of Earth & Planetary Sciences, 20 Oxford Street, Cambridge, MA 02138 United States
AB: Mineral dust from arid and semi arid regions is an important component of climatic processes. The amount of dust emitted off continents is intimately linked with precipitation, which may itself be linked to atmospheric circulation driven by oceanic sea surface temperatures. Hence, reconstructing dust fluxes off continents with sub-decadal resolution can provide us with fundamental insights into feedbacks in the climate system. Unfortunately, such high-resolution dust flux records prior to the establishment of the Barbados dust sampling station are largely lacking. Here we show that ⁴He concentrations in annual bands in corals provides a high-resolution, reliable, and robust proxy record of dust flux from continents. Some traces phases in dust, such as zircons, are rich in U and Th and thus have extremely high concentrations of ⁴He. As some fraction of the dust settles out of the atmosphere and through the water column, corals incorporate the dust in their skeletons through filter feeding. Since the alpha stopping distance is greater than the particle size of wind blown dust, the mineral grains will not accumulate radiogenic helium after the dust is incorporated into the corals. We have measured the ⁴He concentration in annual bands dating back to 1960's in a modern coral that was collected in 1996 off the island of Sal, part of the Cape Verde archipelago. The coral is therefore, situated close to, and directly west of the dust source in the Sudano-Sahel region of the African continent. The ⁴He record from the coral shows remarkable similarity with the record from the Barbados dust sampling station. There is a continuous increase in ⁴He baseline values by a factor of two from the mid 1960's to the early 1990's as well as two pronounced peaks in the early 1970's and mid 1980's associated with severe drought in the Sudano-Sahel region. Our proxy record from the Cape Verde Island demonstrates that ⁴He concentrations in corals can be used reliably to reconstruct dust fluxes from continental land masses at sub-decadal resolution. Our results also imply that ⁴He concentration in deep-sea sediments can be utilized to provide quantitative information about dust flux off continents and atmospheric circulation patterns.
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4914 Continental climate records
DE: 4916 Corals (4220)
DE: 4924 Geochemical tracers
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005