HR: 09:20h
AN: OS51D-06    [Abstracts]
TI: Evolution of Iron Along the Conveyor Belt: North Atlantic to North Pacific
AU: * Boyle, E A
EM: eaboyle@mit.edu
AF: Earth,Atm.,Planet. Sci, Mass. Institute of Technology, E34-258 77 Mass. Ave., Cambridge, MA 02139 United States
AU: Bergquist, B A
EM: bardot@mit.edu
AF: Earth,Atm.,Planet. Sci, Mass. Institute of Technology, E34-258 77 Mass. Ave., Cambridge, MA 02139 United States
AB: We have obtained three new full water-column profiles of iron in the ocean from regions where no data was previously available: in the western North Atlantic (10$\deg$N 45$\deg$W and 24.5$\deg$S 37$\deg$W), and in the central North Pacific (26$\deg$N 175$\deg$W). Together with other profiles in the literature, we now can describe the large-scale deepwater ($>$2500 m)distribution of Fe with some confidence. In the North Atlantic, deepwater Fe is $\sim$0.7 nmol/kg; by the time NADW has traveled to 24.5$\deg$S in the western Atlantic, Fe has decreased to $\sim$0.5 nmol/kg. The salinity and micronutrients are the same at the northern and southern sites, so we attribute the Fe decrease to particulate scavenging as the water travels south. Using C14 estimates for the transit time between these sites, we estimate a deepwater scavenging residence time of 270 +/- 140 years. Most of the decrease occurs in the 0.02-0.4 um colloidal fraction. By the time deepwater has reached the north Pacific, Fe has decreased slightly; three stations (two at HOT-ALOHA near Hawaii and the other further to the northeast) show deepwater Fe levels of 0.45 +/- 0.05 nmol/kg; $>$75% of this Fe is in the soluble $<$0.02 um fraction. These deepwater data help put to rest the notion that "dissolved" ($<$0.4 um) deepwater Fe is fixed at $\sim$0.6 nmol/kg, but raises the question of whether deepwater "soluble" ($<$0.02 um) iron is fixed at $\sim$0.4 nmol/kg, with most of the deepwater reactivity confined to the colloidal fraction.
DE: 4809 Colloids
DE: 4875 Trace elements
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting