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MMM SEMINAR NCAR
DMS Fluxes and Scales of Variability in and around the
California Current Upwelling System
Ian Faloona
Dept. of Land, Air, and Water Resources
University of California, Davis
Dimethylsulfide
(DMS) is an insoluble, reduced form of the highly mobile element sulfur. It is
the principal agent carrying sulfur from the world’s oceans, where it is
relatively abundant, to the continents where it is often a limiting nutrient.
Rapid oxidation in the atmosphere results in hygroscopic aerosols that can
influence marine cloud properties and consequently DMS has been strongly
implicated in a climate feedback between the biosphere and atmosphere. Some of
the first direct eddy covariance measurements of its flux were made off the
coast of Baja California onboard the NCAR C-130 during the second
Dynamics and Chemistry of Marine Stratocumulus Experiment (DYCOMS-II). These
unique measurements compare well with prior estimates of DMS fluxes, but allude
to much larger fluxes upwind in the vicinity of the highly productive waters of
the California
Current system. Horizontal gradients, scalar variance, and ideas of an
equilibrium marine boundary layer (MBL) are examined to extract as much
information about the nature of DMS sources as possible. Particularly
noteworthy is the large variance exhibited by this compound, well above what is
expected from top-down and bottom-up scalar diffusion. Several suggestions of
the origin of this “excess” variance will be discussed, including source
heterogeneity, entrainment variability, and other sources internal to the MBL
turbulence.
Shoreline
data collected four years later at Bodega Bay, California exhibited considerable
variability, with concentrations ranging from 30-1,300 pptv
over the course of several days during onshore flow. These slower response data
reveal a surprisingly direct relationship to the local oceanic upwelling
strength, the square root of the wind speed, and the reciprocal of boundary
layer height. From scalar budget considerations it will be shown that this type
of functional dependence can be explained by an advective
steady state. The nature of the dependence on upwelling strength further
implies that the oceanic DMS has its origins in the organic-rich sediments of
the continental shelf, much different from the conditions found over the open
ocean during DYCOMS-II. We conclude that the coastal DMS represents a
heretofore unexplored biogeochemical connection between the microbial
communities that reside in these shallow, anaerobic marine sediments and the
atmosphere.
Thursday,
23 March 2006, 3:30 PM
Refreshments 3:15
PM
NCAR-Foothills
Laboratory
3450
Mitchell Lane
Bldg 2 Auditorium (Rm.1022)