Assessing the Ecological Impact of the Antarctic Ozone Hole Using Multisensor Satellite Data

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Assessing the Ecological Impact of the Antarctic
Ozone HoleUsing Multi-sensor Satellite Data
Dan Lubin, Scripps Institution of
Oceanography Kevin Arrigo, Dept. of Geophysics,
Stanford University Osmund Holm-Hansen, Scripps
Institution of Oceanography
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Enhancement of UV Flux at Antarctic Surface

• Measured since 1988
• NSF UV Monitoring Program
• Palmer Station
• McMurdo Station
• Ushuaia, Argentina
• Barrow, AK
• San Diego, CA
• http//www.biospherical.com

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The Antarctic Marine Food Web
Higher Predators (leopard seals, orcas)
Grazing by Krill (Euphausia superba)
Primary Production
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Field Work on Ecological Effects

• Began in late 1980s, primarily at Palmer Station,
  west of Antarctic Peninsula
• Smith et al. (Science, 1990) ICECOLORS 2-4
  reduction in primary production in marginal ice
  zone (MIZ)
• Holm-Hansen et al. (Photochem. Photobiol., 1993),
  reduction lt 1 integrated over entire Southern
  Ocean

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Need for Satellite-Based Assessment

• Comprehensive field work is expensive, limited in
  time and place.
• Previous estimates of total impact on Southern
  Ocean primary production are rough extrapolations
  from point measurements to larger areas.
• Satellite data now offer complete coverage of the
  Southern Ocean for evaluating key forcing factors.

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Surface UVR Algorithm Developmentco-locating
TOMS, AVHRR, SSM/I in 3 regions

• Sea ice more influential than clouds on TOA UV
  radiance.
• Parameterization of UV sea ice albedo as function
  of sea ice concentration.
• Method developed to use TOMS and SSM/I alone.
• see Lubin and Morrow, JGRd (2001).

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AVHRR cloud ID using near-IR (3.5 mm) channel
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Seasonal variability in sea ice concentration
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Total Column Ozonefrom TOMS
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Sea Ice Concentrationfrom SSM/I
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Cloud Effective Optical Depthfrom TOMS
Reflectivity
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UV-A (315-400 nm) Fluxfrom d-Eddington model
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UV-B (280-315 nm) Fluxfrom d-Eddington model
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Biologically Weighted Flux(photoinhibition in
phytoplankton)
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Comparison with Palmer Station UV Monitor Data
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Geographic Assessment of Enhanced UV Fluxes

• Spectral flux weighted by action spectrum for
  photoinhibition in Antarctic phytoplankton
• Define climatological UVR
• in terms of mean cloud attenuation, sea ice, 1979
  total ozone
• evaluate 20-year standard deviation s
• Enhancement where photoinhibition flux exceeds
  climatological mean by 2s or more
• Geographically significant enhancement where the
  enhanced fluxes intersect biomass as determined
  by SeaWiFS
• Lubin et al., GRL 2004

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UVR Enhancement at Palmer Station, Spring 1992
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Use of SeaWiFS to Locate Phytoplankton Biomass
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UVR Enhancements by Southern Ocean SectorLubin
et al., GRL 2004
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Spectral Flux at the Sea Surface

• Edd and Edi are direct and diffuse components
• surface reflection divided into direct and
  diffuse components, both of which are sum of
  specular reflection and reflectance from sea foam
• sea foam reflectance a function of wind stress
• Fresnels law for specular reflection

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In-Water Optics

• Beers law for spectral flux penetration
• Diffuse attenuation coefficient Kd(z) partitioned
  into components describing attenuation by pure
  water, phytoplankton, detritus, and chromophoric
  dissolved organic matter.

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In-Water Optics - Components

• Pure Water coefficents from Smith Baker (1981)
• Plankton (chlorophyll) from Sathyendranath et al.
  (1989)
• Detritus from work by Arrigo et al. (1998)
• CDOM from work by Mitchell and Holm-Hansen
  (1991) Arrigo et al. (1998)

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Phytoplankton Production

• G is phytoplankton growth rate (d-1) calculated
  from temperature and light availability
• C/Chl a is the phytoplankton CChl a mass ratio
  (50)
• Beff is effective phytoplankton concentration
• G is modeled in terms of a temperature-dependent
  maximum rate and a light limitation term

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Cumulative Exposure to UVR

• Throughout the day, the physiological
  inactivation of algal biomass (effective biomass
  Beff) is expressed by reducing Beff with
  increasing UVR exposure.
• At dawn, Beff(z,t) is set Chl a (z,t)
• Vertical mixing simulated by averaging Beff over
  MLD, then applying this average to each layer
  within MLD

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Comparison with Field Observations decrease in
C-fixation relative to no UVR
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Station A59.19 S, 56.89 E04 October

• Photoinhibition dose Hinh varies with time and
  depth, 30 greater in exp. run than control at
  surface
• Assess individual contributions of UV-B and UV-A
• Substantial UV-A contribution to Hinh and Beff
• Panel B 1979 (control)
• Panel C 1992 (exp.)

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Total Change in Primary Production
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Temporal Variation in Primary Production Loss
over Southern Ocean
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Major Conclusion of Small Impact

• Surface UVR-induced losses of primary production
  can be several percent, with large UV-B component
• When integrated to 0.1 light depth, loss of
  primary production throughout Southern Ocean, due
  to enhanced UV-B, is lt 0.25
• Major reasons strong UV-B attenuation with
  depth, location of most ozone depletion over
  Antarctic continent, temporal mismatch between
  maximum ozone loss and maximum phytoplankton
  abundance
• Several sensitivity analyses did not alter this
  conclusion
• changing MLD and mixing time
• temperature dependence of primary production
• Photoacclimation parameter Ek, specifying
  saturation of photosynthesis
• detrital and CDOM absorption
• phytoplankton absorption
• variability in Action Spectrum
• Instantaneous versus cumulative exposure to UVR

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Necessary Future Work

• Improve parameterizations throughout model
• in-water radiative transfer, processes very near
  sea ice
• Repeat experiments for even deeper and
  longer-lasting ozone holes of late 1990s
• Consider regional ecosystem effects