HR: 0830h
AN: OS41C-38    [PDF]
TI: Nutrient Processes in a Regional Model of the Ross Sea
AU: Smith, W O
EM: wos@vims.edu
AF: Virginia Institute of Marine Science, College of William and Mary, Gloucester Pt, VA 23062 United States
AU: Dinniman, M S
EM: msd@ccpo.odu.edu
AF: Center for Coastal Physical Oceanography, Old Dominion University Crittenton Hall , Norfolk, VA 23529 United States
AU: * Klinck, J M
EM: klinck@ccpo.odu.edu
AF: Center for Coastal Physical Oceanography, Old Dominion University Crittenton Hall , Norfolk, VA 23529 United States
AU: Hofmann, E E
EM: hofmann@ccpo.odu.edu
AF: Center for Coastal Physical Oceanography, Old Dominion University Crittenton Hall , Norfolk, VA 23529 United States
AB: A regional numerical model of the Ross Sea is used to analyze processes by which silicate and nitrate advect and diffuse on the Ross Sea shelf and are removed by phytoplankton. As part of a JGOFS synthesis and modeling project, we consider the path of nutrients from the ocean to the subpycnocline waters of the shelf, as well as the vertical flux to the surface layers. Uptake of nutrients is based on the historical distribution of chlorophyll and appears as a sink. Path, timing and nutrient ratios are used as diagnostics. We use the Rutgers/UCLA Regional Ocean Model System (ROMS) with a grid resolution of 5 km horizontally and 24 levels vertically. A gridded bathymetry is derived from ETOPO5, and initial temperature and salinity are derived from the World Ocean Atlas (WOA98). Both nitrate and silicate are active in the model and initial distributions come from a newly developed, gridded, monthly nutrient and chlorophyll climatology for the Ross Sea that is created from observations from many cruises (mostly from the U.S. Southern Ocean JGOFS program) combined with WOA98 gridded fields. Monthly wind stress is from the ECMWF reanalysis climatology. Ice masked surface heat and salt flux are constructed from the SSM/I and ECMWF reanalysis climatologies using the COARE bulk flux algorithms. Vertical mixing in the interior and surface boundary layer uses the K profile parameter (KPP) scheme. Open boundaries use adaptive nudging (Marchesiello 2000) to monthly climatologies of temperature, salinity, nutrients as well as depth averaged circulation from the OCCAM global circulation model. Effects of the Ross Ice Shelf are imposed through nudging to climatological temperature and salinity in a buffer zone. Nutrients are removed from the near surface at rates that depend on the new gridded chlorophyll concentration as well as model nutrients. The new biogeochemical climatologies show a strong seasonal variability in parts of the western Ross Sea, where data are available. Residual surface nutrients in summer are likely due to iron limitation. The climatologies can be used to compare individual cruises to long-term mean conditions and therefore quantify large-scale variations of biogeochemically relevant variables. Model results show that nutrients enter the shelf along the NW shelf break (near Cape Adair) and along the eastern shelf break (Cape Colbeck). Surface nitrate is reduced from 30 to 6 uM in 20 days where the chlorophyll concentration is high, while silicate is reduced from 80 to 30 uM. Subpycnocline nutrients remain near initial levels of 30 and 75 uM, respectively. Surface nutrients in the model will continually decline to zero unless some process, like iron limitation, halts uptake even with nutrients.
DE: 4845 Nutrients and nutrient cycling
DE: 4207 Arctic and Antarctic oceanography
DE: 4219 Continental shelf processes
DE: 4255 Numerical modeling
SC: OS
MN: 2002 Ocean Sciences Meeting