HR: 10:35h
AN: OS32A-02    [Abstracts]
TI: Oceanic volcanic 3He: where is it going?
AU: * Jenkins, W J
EM: wjenkins@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Raod, Woods Hole, MA 02543, United States
AU: Naveira, A
EM: acng@noc.ac.uk
AF: National Oceanography Centre, European Way, Southampton, SO14 3ZH, United Kingdom
AU: Schlosser, P
EM: schlosser@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9W, Pallisades, NY 10964, United States
AU: Lott, D E
EM: dlott@whoi.edu
AF: Woods Hole Oceanographic Institution, 360 Woods Hole Raod, Woods Hole, MA 02543, United States
AU: Newton, R
EM: rnewton@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9W, Pallisades, NY 10964, United States
AB: Various estimates that have been made of the flux of volcanic ³He from the solid earth suggest that of order 1000 moles per year are introduced into the abyssal ocean, and that a significant fraction of this occurs within the Pacific. Away from the points of injection, this ³He serves as a valuable conservative tracer of deep water flow, especially as part of the global planetary scale overturning circulation. In the southeastern South Pacific in particular, the deep ³He distribution highlights the return of Pacific Deep Water to the Antarctic Circumpolar Current (ACC) region. Using data acquired during the World Ocean Circulation Experiment and other cruises, we calculate the flux of deep ³He in the Antarctic Circumpolar Current at three critical points: south of Africa, south of Australia, and in the Drake Passage. The average zonal flux of ³He in the ACC is about 1300 mol y^-1, roughly comparable in magnitude to the estimated global volcanic flux. This average transport must represent a balance between the entrainment of ³He -tagged deep waters and losses due to other mechanisms. The truly remarkable result is that the flux divergence between Australia and the Drake Passage is barely significantly greater than zero, and can at most be ~ 100 mol y^-1. The implication of this small number is either that the (1) volcanic flux is in fact much smaller than previously estimated, (2) the returning Pacific Deep Water is upwelled and in large part returned northward at intermediate depths in the Pacific without significant entrainment in the ACC, or (3) upwelling and degassing of 3He in the ACC is sufficiently strong to closely compensate for the 3He entrained during its passage through the Pacific sector. We address these basic questions by consideration of the data available, along with presenting calculations of the observed flux of ³He from the surface ocean to the atmosphere during the WOCE surveys. The patterns and quantities thus observed have interesting implications for both the topology of the global conveyor and the nature of upwelling and outgassing in the southern hemispheric oceans. Moreover, the correlation between abyssal ³He and nutrients allows us to constrain the contribution of this upwelling to new production in the southern ocean.
DE: 4532 General circulation (1218, 1222)
DE: 4805 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4912)
DE: 4820 Gases
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4860 Radioactivity and radioisotopes
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting