HR: 11:20h
AN: T12A-05    [Abstracts]
TI: Seamount Moats in the Central Equatorial Pacific Ocean: Origins and Implications
AU: * Pockalny, R
EM: robp@gso.uri.edu
AF: Graduate School of Oceanography / University of Rhode Island, Narragansett Bay Campus South Ferry Rd, Narragansett, RI 02882, United States
AU: Murphy, E
EM: elmurphy@vassar.edu
AF: Vassar College, 124 Raymond Ave., Poughkeepsie, NY 12604, United States
AU: Spivack, A
EM: spivack@gso.uri.edu
AF: Graduate School of Oceanography / University of Rhode Island, Narragansett Bay Campus South Ferry Rd, Narragansett, RI 02882, United States
AB: Numerous seamounts in the central equatorial Pacific Ocean are surrounded by shallow, circular depressions, which we term seamount moats. These moats are typically 50-150 m deep, 1-2 km wide, and surround relatively small seamounts (e.g., relief less than 500 m). The majority of the seamount moats are located on crust of Cretaceous age (70-130 Ma) at depths greater than 4500 m. Perhaps the most interesting aspect of the moat distribution is the predominance of these features within 5 degrees of the equator. Any moats found beyond this equatorial zone occur on seafloor shallower than 3500 m and are typically associated with more recent volcanic events. Several possible origins for these features have been explored (e.g., lithosphere flexure, sediment scour, tectonic collapse); however, we prefer a sediment dissolution model similar to that proposed by Bekins et al. (2007). In this model, carbonate-rich seawater enters the fractured, permeable ocean crust and begins to warm. The retrograde solubility of carbonate results in the distributed precipitation of carbonate minerals within the crustal aquifer. The remaining water then exits the crust through the seamounts and cools again to ambient seawater temperatures. At these cooler temperatures, the water is under-saturated with respect to carbonate and begins to dissolve the carbonates within the overlying or adjacent sediments. There are several interesting implications for this carbonate dissolution scenario to explain the origin of the seamount moats. First, significant hydrothermal circulation occurs in crust much older than previously assumed (e.g., 70-130 Ma). Second, discharge rates calculated for the missing sediment volume are comparable or slightly less than previous estimates for younger crust (e.g., 1 m/yr). Finally, the distributed precipitation of carbonates suggests the ocean crust may be a significant reservoir for the global carbon budget.
DE: 3015 Heat flow (benthic)
DE: 3021 Marine hydrogeology
DE: 3037 Oceanic hotspots and intraplate volcanism
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4825 Geochemistry
SC: Tectonophysics [T]
MN: 2007 Fall Meeting