HR: 11:50h
AN: OS22A-07    [Abstracts]
TI: Time Series Fluid Compositions from the TAG Hydrothermal Mound, MAR: 1986-2004
AU: Parker, C M
EM: cheryl.parker@unh.edu
AF: Complex Systems Research Center, EOS, University of new Hampshire, 370 Morse Hall, Durham, NH 03824-3525 United States
AU: * Von Damm, K L
EM: kvd@eos.sr.unh.edu
AF: Complex Systems Research Center, EOS, University of new Hampshire, 370 Morse Hall, Durham, NH 03824-3525 United States
AU: Beers, K A
EM: kbeers@cisunix.unh.edu
AF: Complex Systems Research Center, EOS, University of new Hampshire, 370 Morse Hall, Durham, NH 03824-3525 United States
AU: Green, D R
EM: drhg@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, European Way, Southampton, SO14 3ZH United Kingdom
AU: Alker, B J
EM: bja199@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, European Way, Southampton, SO14 3ZH United Kingdom
AU: German, C R
EM: cgerman@whoi.edu
AF: Woods Hole Oceanographic Institution, Woods Hole Rd, Woods Hole, MA 02543 United States
AB: High temperature hydrothermal fluids have been collected from the TAG Mound, Mid-Atlantic Ridge in 1986, 1990, 1993, 1994, 1995, 2003, and 2004. This 18-year time series brackets the ODP drilling at this site in 1994. Because of the changing distribution of high temperature venting, sampling was limited to only those parts of the mound that were safely accessible to an HOV/ROV, and therefore a single "vent" neither existed nor was sampled over this time period. The maximum measured temperature of the fluids at the time of water sample collection was 370°C in 2003, with values ≥364°C also reported for 1990, 1993, 1995 and 2004. For the entire time series the Cl content of the venting fluids has remained greater than the seawater value, and constant within error at 640±10 mmol/kg. This constancy is also observed for both Na and Sr. Other elements, however, vary significantly. In some cases, such as for Fe, this can be attributed to poor sample quality, which led to artificially low values in 1986. Mn is typically not affected by substantial mixing of vent fluids with seawater in the sampling bottles, which can lead to significant loss of sulfide-forming metals such as Fe. The Mn endmember values are generally lower post-drilling (aver: 678 vs. 779 umol/kg). In contrast, Ca concentrations post-drilling are always >30 mmol/kg, while reported pre-drilling values are as low as 26 mmol/kg. K varies from 17-20 mmol/kg (~15%), well outside analytical error, but without a simple trend. In 1986, Li values >400 umol/kg were reported, and not until 2003 are values this high observed once again. Finally, reported Si values ranged from 18.4-22.0 mmol/kg (~8%), a larger variation than expected from analytical error alone. The variation in Si does not display a simple temporal trend, nor does it correlate with the measured exit temperature of the fluids. It therefore appears that real variations have occurred in the chemical compositions of the vent fluids sampled at TAG, but they display neither a simple temporal trend, nor the same trend from element-to-element. Possible explanations for the causes of these variations will be examined.
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3035 Midocean ridge processes
DE: 3075 Submarine tectonics and volcanism
DE: 4832 Hydrothermal systems (0450, 1034, 3017, 3616, 8135, 8424)
DE: 4835 Marine inorganic chemistry (1050)
SC: Ocean Sciences [OS]
MN: Fall Meeting 2005