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Fall AGU Meeting (Dec. 2002) COAST abstracts:

COAST overview (Barth)

Abstracts should be cited as:

EOS Trans. AGU, 83 (47),
Fall Meet. Suppl.,
Abstract XXXXX-XX, 2002


Investigation of the Wind-Driven Coastal Ocean off Oregon: A COAST

J A Barth 

The Coastal Ocean Advances in Shelf Transport (COAST) project seeks
to understand and quantify cross-shelf transport and transformation
processes in the strongly wind-driven coastal ocean off central
Oregon. Two intensive field efforts were conducted in summer
2001 together with coordinated ocean circulation/ecosystem and
atmospheric modeling. A primary goal is to contrast the coastal
ocean response in a region of relatively simple alongshore bottom
topography versus that associated with a substantial submarine
bank. Heceta Bank (44.3N) rises to over 50% of the surrounding
continental shelf water depth and widens the shelf to 60 km from the
relatively narrow, straight 25-km wide shelves both to the north
and south. High ocean production is associated with Heceta Bank
and cold, chlorophyll-rich upwelled water has been observed well
seaward of the continental shelf break south of the Bank. During
May-June and August 2001, two vessels conducted interdisciplinary
research off central Oregon. One ship conducted rapid, high spatial
resolution surveys of the three-dimensional thermohaline, bio-
optical, zooplankton and velocity fields using SeaSoar, shipboard
ADCP and a towed, multi- frequency acoustics instrument. Surface
maps of nutrients, pCO2 and iron were also made. A second ship
collected high-vertical resolution cross-shelf profiles of water
properties:  temperature, salinity and turbulence parameters from
a loosely tethered microstructure profiler; nutrients, carbonate
species, phytoplankton photosynthesis parameters, and particulate
and dissolved organic material from a pumped profiling system. An
instrumented aircraft measured properties of the lower atmosphere
and upper ocean during and between the month-long intensive field
experiments. A set of moorings measured physical and bio-optical
parameters from May-August and a land-based radio system continuously
measured surface currents hourly over a region encompassing the
Bank. A high-resolution, three-dimensional shelf circulation and
coupled ecosystem ocean model and a mesoscale atmospheric model
are being used to investigate the dynamics of the system. During
summer 2001, upwelled water was present near the coast and a wide
($\geq 75$~km) cold region over the Bank showed elevated surface
chlorophyll with peak values in excess of 15~mg~m$^{-3}$. In the
north, upwelling over simple bottom topography exhibited a classic
response with a mid-shelf baroclinic coastal jet accompanied
by upwelled isopycnals. On the southern edge of the Bank, the
flow is highly three- dimensional including a strong baroclinic,
equatorward jet near or seaward of the shelfbreak, a region of
northward recirculation flow over the Bank and a small area of
weaker upwelling adjacent to the coast. Lastly, although the COAST
program is scheduled to study wintertime downwelling in Jan-Feb 2003,
strong summertime downwelling was experienced during August 2001
when a remnant tropical typhoon transited the area with southerly
winds in excess of 40 knots. The thermohaline, bio-optical and
velocity response to this event are contrasted to those observed
during relaxation, i.e. periods with weak or no wind forcing when
pressure forces can drive inshore northward flow but isopycnals
remain upwelled.