HR: 17:45h
AN: OS54A-08    [Abstracts]
TI: Storms in the Sargasso Sea: Rapid Particle Export and DIC Drawdown
AU: * Lomas, M W
EM: mlomas@bbsr.edu
AF: Bermuda Biological Station for Research, Inc., 17 Biological Lane, St Georges, GE01 Bermuda
AU: Nelson, D M
EM: nelsonda@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331 United States
AU: Lipschultz, F
EM: fred@bbsr.edu
AF: Bermuda Biological Station for Research, Inc., 17 Biological Lane, St Georges, GE01 Bermuda
AU: Bates, N R
EM: nick@bbsr.edu
AF: Bermuda Biological Station for Research, Inc., 17 Biological Lane, St Georges, GE01 Bermuda
AU: Walker, C F
EM: cwalker@bbsr.edu
AF: Bermuda Biological Station for Research, Inc., 17 Biological Lane, St Georges, GE01 Bermuda
AU: Krause, J
EM: jkrause@bbsr.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331 United States
AU: Knap, A H
EM: knap@bbsr.edu
AF: Bermuda Biological Station for Research, Inc., 17 Biological Lane, St Georges, GE01 Bermuda
AB: Increasingly, biogeochemical studies are showing that event-scale phenomena, $\sim$3-10 days in duration, have disproportionately large impacts on phytoplankton biomass and export production in oligotrophic ocean basins. During March 2004, we observed the passage of a storm front that significantly impacted biogeochemical cycling in the Sargasso Sea. The passage of the storm resulted in significant shoaling of the 19$^{o}$C isotherm and the 1.0 $\mu$M nitracline. During the four days after the storm, integrated (0-140 m) primary production ($\sim$1500 mg C m$^{-2}$ d$^{-1}$) was 3-4x greater than the mean water column production previously observed by BATS for this time of year. These high rates of primary production preceded a drawdown in depth-averaged, salinity-normalized DIC of 7-8 $\mu$mol kg$^{-1}$. Estimated rates of CO$_{2}$ exchange would have added 0.05 to 0.2 $\mu$mol kg$^{-1}$ d$^{-1}$ to the mixed layer, counteracting the observed drawdown of DIC. These high rates of primary production and DIC drawdown are congruent with elevated rates of silicate uptake, which averaged ~7.5 mmol Si m$^{-2}$ d$^{-1}$, almost 20x the mean rate reported during non-bloom periods at BATS. There was no significant accumulation of phytoplankton biomass as Synechococcus, picoeukaryotes, and $>$5 $\mu$m eukaryotes densities all remained largely constant and suspended biogenic silica concentrations (indicative of diatoms) increased only marginally, suggesting a significant loss term. Indeed, total biogenic silica sedimentation rates at 200 m (486 to 508 $\mu$mol m$^{-2}$ d$^{-1}$) were as large as any rate previously observed in the Sargasso Sea. Rates of particulate organic carbon and nitrogen export also exceeded prior estimates determined as part of the BATS program. This singular, very short-lived ($\sim$3.5 days) event, following a stratification/destratification event in the upper ocean, represents a significant contribution to annual export production, prior to the traditional spring bloom and is therefore excluded from most estimates of annual new and export production. We hypothesize that the high rates of sedimentation with little accumulation in phytoplankton biomass were due to a very active zooplankton grazing community that rapidly consumed phytoplankton as they grew in response to the storm-induced nutrient injection.
DE: 4805 Biogeochemical cycles (1615)
DE: 4815 Ecosystems, structure and dynamics
DE: 4845 Nutrients and nutrient cycling
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting