HR: 1330h
AN: PP12A-0234    [PDF]
TI: Variations in Solar Activity: Can it Induce Apparent Variations in the Extraterrestrial $^{3}$He Flux to the Oceans?
AU: * Mukhopadhyay, S
EM: sujoy@eps.harvard.edu
AF: Harvard University, Dept. Earth & Planet. Sci., Cambridge, MA 02138 United States
AB: Helium-3 in sediments can be used to trace the flux of interplanetary dust particles (IDPs). If the accretion rate of IDPs is constant, measurements of $^{3}$He in sediments can be used as a constant flux proxy to invert sediment depth records to time records. Recent research indicates that solar activity may have varied with the 100 ka glacial-interglacial cycles, with higher solar activity during the interglacials. Varying solar activity changes the upper atmospheric density profile, which will likely change the peak temperature, and consequently the He loss, experienced by IDPs during atmospheric entry heating. As a result, a 100 ka solar cycle could potentially change the $^{3}$He flux reaching the Earth's surface even if the IDP accretion rate from space remains constant. Hence, it is important to explore the consequences of varying atmospheric density on the use of $^{3}$He as a constant flux proxy in paleoclimatological applications. I also investigate whether atmospheric density changes driven by the 100 ka solar cycle may explain the discrepancy between the theoretical calculations of the IDP accretion rate and that derived from measurements of $^{3}$He in sediments. The theoretical calculations indicate that IDP accretion rate has varied by a factor of two over the past million years, with higher fluxes during the glacial periods. However, He measurements indicate that the IDP flux is probably constant, or possibly higher in the interglacial periods. As a starting point for modeling the effect of varying atmospheric density, I have investigated the expected variability in the $^{3}$He flux over a solar cycle, when the difference in atmospheric densities above 150 km can be greater than a factor of two between periods of low and high solar activity. At altitudes below 100 km the variability in density is less than 20%. The atmospheric density profiles for high and low solar activity were obtained from the MSIS-E-90 model atmosphere. The continuous distributions of the IDP size, velocity, and entry angles were discretized into bins. A total of 12240 entry heating simulations, representing all possible permutations of the size, velocity, and entry angle bins, were run for the two atmospheric density profiles. Initial results indicate that the expected variability in $^{3}$He flux is likely to be ~10% over a solar cycle. The detailed results from the above simulations will be presented.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1050 Marine geochemistry (4835, 4850)
DE: 4825 Geochemistry
DE: 6015 Dust
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting