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AGU Ocean Sciences Meeting (Feb. 2002) COAST abstracts:


New Insights from High Resolution and Long-Term Chemical Measurements
with the MBARI In Situ Ultraviolet Spectrophotometer (ISUS):
Optical Nitrate and Bisulfide Determinations

Luke J. Coletti, Kenneth S. Johnson, Carole M. Sakamoto, Zanna
Chase, Francisco P. Chavez, John A. Barth, Peter G. Strutton,
Steve E. Fitzwater, Nicole Tervalon, Peter M. Walz

Recent advances in the development of In Situ Ultraviolet
Spectrophotometers (ISUS) now make it possible to rapidly
collect UV spectra with wavelength resolution better than 1 nm for
extended periods of time.  Many dissolved compounds of interest to
oceanographers and limnologists, e.g., nitrate, nitrite, bisulfide,
bromide, iodide, thiosulfate, and organic material, absorb UV light.
Each of these compounds has a unique absorption spectrum, which
allows individual components in complex mixtures to be quantified
using numerical methods to deconvolve the spectra.

The MBARI ISUS has been successfully deployed in a variety of
diverse environments and operational modes.  Profiling data will
be shown from deployments on an Autonomous Underwater Vehicle (AUV)
within Monterey Bay and in the Arctic, towed undulating vehicles off
Monterey Bay (Sea Sciences Acrobat) and off the Oregon coast Chelsea
(SeaSoar), and vertical casts on a CTD/Rosette system.  Data from
long-term (6 month) mooring deployments in the equatorial Pacific
and Monterey Bay, as well as real-time seafloor observations above
a cold seep in the Monterey Bay using a Remotely Operated Vehicle
(ROV), illustrate the dynamic capabilities of ISUS to characterize
a broad range of important environments.

Characterization of spatial and temporal variability of dissolved
chemicals is greatly enhanced by the ability to measure concentations
directly with no chemical manipulation and with a temporal resolution
of approximately 1 second.  In this poster, we will focus on the
new scientific insights that are derived from these data sets.