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