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From the CoOP Newsletter Issue No. 10, December 1999:


Coastal Ocean Advances in Shelf Transport (COAST)

Project Leaders (Oregon State University): Jack Barth, Patricia Wheeler and
  John Allen

Co-Principal Investigators (all OSU unless indicated otherwise): Mark Abbott,
  John Bane (UNC), Tim Boyd, Doug Caldwell, Tim Cowles, Jianping Gan,
  Burke Hales, Mike Kosro, Ricardo Letelier, Murray Levine, Jim Moum,
  Bill Peterson (also NMFS), Roger Samelson, Yvette Spitz and 
  Alexander van Geen (LDEO)

A collaboration between scientists at Oregon State University, the University
of North Carolina and the Lamont-Doherty Earth Observatory has been funded
by CoOP to address a specific set of scientific hypotheses related to
cross-shelf transport processes in a wind-driven system by conducting field
experiments off the Oregon coast together with coordinated ocean
circulation/ecosystem and atmospheric modeling.  The hypotheses, motivated
below, are:  (H1) the presence of upwelling and downwelling jets and fronts
locally alters cross-shelf circulation in the surface and bottom boundary
layers and in the interior; (H2) alongshore topographic variations dictate the
relative importance of two-dimensional versus three-dimensional cross-shelf
transport processes; (H3) patterns of turbulence on the shelf during upwelling
and downwelling are influenced by fronts and jets, and the levels of turbulence
can reach sufficient intensity to influence the mesoscale circulation; (H4) the
magnitude and distribution of primary production on the shelf and its
subsequent transport offshore is controlled solely by the geometry of upwelling
as described in H1 and H2; (H5) (a hypothesis competing with H4) alongshore
variations in turbulent mixing control the magnitude and distribution of
primary production, e.g. via enhanced nutrient and/or trace chemical supply
from the bottom boundary layer; (H6) the reduced cross-shelf transport implied 
by the presence of a downwelling front allows nutrients, trace metals and seed 
stocks of phytoplankton and zooplankton to accumulate in the mid- to 
inner shelf, thus priming the system for a strong biological response at the 
outset of upwelling.

The Oregon coastal ocean exhibits a strong wind-driven response, both
physically and biologically and in both upwelling favorable (summer) and
downwelling favorable (winter) seasons.  Off northern Oregon, the region of
active upwelling is narrow and the bottom topography is relatively uniform
alongshore.  Here, three-dimensional effects should be minimized and the
presence of a strong baroclinic upwelling jet and front will locally alter
cross-shelf circulation in the surface and bottom boundary layers (BBL) and in
the interior.  Off central Oregon, the continental shelf broadens and
alongshore uniformity is broken by Heceta Bank.  The distribution of cold water
and surface chlorophyll from satellite imagery mimics the width of the
continental shelf, suggesting the control of bottom topography on shelf
circulation and upwelling.  An exception to this general pattern is associated
with Heceta Bank, where cold, chlorophyll-rich upwelled water is found well
seaward of the continental shelf break, representing an important cross-shelf
transport process.  Far less is known about the shelf flow and thermohaline
fields during the downwelling season.  Recent two-dimensional modeling results
predict the formation of a strong downwelling front and jet near the
mid-shelf.  Offshore of the mid-shelf density front there is onshore transport
in a surface Ekman layer, which turns downward at the mid-shelf front, and
returns offshore in a thick BBL.  Inshore of the downwelling front, the water
column is well mixed, the alongshore flow is considerably reduced compared with
that in the mid-shelf jet, and cross- shelf flow is nearly zero.  Thus, the
inner shelf is a region of relatively quiescent flow.

To address the above hypotheses we will make intensive observations in two 
regions off the Oregon coast during the upwelling season: one north of Newport
in a region of relatively simple topography and one south of Newport centered 
on Heceta Bank.  High-resolution sampling will be conducted using two ships
simultaneously.  One ship will conduct rapid, high-resolution surveys of the
three-dimensional thermohaline, bio-optical, zooplankton and velocity fields
using SeaSoar, shipboard ADCP and a towed, multi-frequency acoustics system
(Barth, Cowles, Peterson).  A second ship, operating within the same region, 
will conduct high-vertical resolution profiling of water properties: T, S, 
turbulence (Moum, Caldwell), nutrients and carbonate species (Hales),
phytoplankton photosynthesis parameters via Fast Repetition Rate fluorometry
(Letelier, Abbott), particulate and dissolved organic material (Wheeler,
Cowles) and the important trace metal iron (van Geen).  We will conduct two 
three-week cruises during the upwelling season (June and August) 2001 and
sampling will take place in both the northern and southern regions during each
cruise in order to directly compare results.  A downwelling experiment will be
conducted during Jan-Feb 2003 during one three-week cruise and measurements
will be concentrated in the northern study region where the bottom topography
is simpler.

An instrumented aircraft will be used to make measurements of the lower 
atmosphere (wind, temperature, humidity, pressure) and the upper ocean (SST,
ocean color, subsurface temperature via AXBTs) (Bane).  A set of moorings, 
spanning the continental shelf in each study region and equipped with
instruments to measure velocity, T, C, spectral irradiance, phytoplankton
fluorescence and particulate light scattering, will be deployed during both
upwelling and downwelling experiments (Levine, Boyd, Kosro, Abbott, Cowles,
Letelier) .  Land-based coastal radar will be used to make high-spatial 
resolution surface current maps (Kosro).  A high-resolution, three-dimensional
shelf circulation and coupled ecosystem ocean model will be used in direct 
support of the field experiments by contributing to the dynamical synthesis of
the observations and for relevant process studies (Allen, Gan, Spitz).  A
mesoscale atmospheric modeling effort will provide estimates of surface
forcing, continuous in space and time, for the ocean model and for 
interpretation of the oceanic observations (Samelson).

The COAST project will obtain satellite remote sensing information through
existing projects at OSU: ocean color (Mark Abbott) and SST (Ted Strub).
Other collaborations include the regular sampling being done off Newport
through GLOBEC (Jane Huyer, Bob Smith, et al.) and the nearshore (15-m
isobath) observations being made as part of the PISCO project to study
oceanographic influences on marine communities in the rocky intertidal
(Jane Lubchenko and Bruce Menge, OSU Zoology).