Ocean Biogeochemical Processes

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Ocean Biogeochemical Processes

• David M. Glover
• Woods Hole Oceanographic Institution

In collaboration with Nelson Frew, Scott Doney,
Scott McCue, Ivan Lima (WHOI) Montserrat Fuentes
(NCSU), Norm Nelson (UCSB) Robert Evans and
Arthur Mariano (RSMAS)
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Biogeochemical Processes

• Physical processes influence these either
• Passively Turbulent advection and stirring
• Actively Changes in plankton growth rates and by
  trophic interactions via nutrient supply and MLD
  changes
• Quantification important for proper assimilation
  into models
• Altimetry has been instrumental in characterizing
  physical processes.
• More and more investigators are turning to models
  to provide better coverage than either satellite
  or field data or both!

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Global scale
Killworth et al. (2004)
Vertical upwelling of chlorophyll
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Global scale

• SeaWiFS 9km daily GAC to 0.5x1.0 and 9.92d,
  Gaussian 1 2d gap filler, westward-only 2D
  bandpass
• TOPEX along track GDR Gaussian 150km w/ 200km
  search to 1x1 9.92d, then 0.5x1 westward only
  2D bandpass.

Killworth et al. (2004)

• Spectrum has signif. peak at
• 0.152 deg-1 and 2.64 yr-1
• Corresponds to wavelength of
• 6.58 degrees and a period of
• 138 days.
• Not shown peak phase is 0.86
• rads corresponding to a 19 day
• lead of clorophyll over SSHA.
• Consistent with horizontal
• advection

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Gyre scale
Charria et al. (2006)
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Autospectra N. Atlantic Icelandic Basin58.5N
19.4W to 59.2N 20.25W
Mesoscale
CF chlorophyll fluorescence ?C490 beam
attenuation anomaly ? potential temperature S
salinity

• Below kT spectra follows k-2, above spectra
  follows k-3
• k-2 consistent with turbulent physical mixing as
  conservative tracer
• k-3 phytoplankton patches controlled by
  biological sources and sinks

Garcon et al. (2001)
Washburn et al. (1998)
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Mesoscale
Isopycnal ?1 seasonal and ?2 permanent
thermoclines
Sweeney et al. (2003)
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Upwelling eddy timeline
Mesoscale
Sweeney et al. (2003)
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Temperature and New Production in a 0.1 N.
Atlantic Simulation
Mesoscale
McGillicuddy et al. (2003)
Coupled physical-biogeochemical eddy resolving
model, POP GCM with idealized nutrient transport
model to simulate biogeochemical processes
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Mesoscale

• Dominant terms in new production equation
  averaged over euphotic zone.
• All fields smoothed with 24-point, e-folding
  Gaussian filter.
• Contours in (b) show max wintertime MLD
• In subtropics eddy-resolving simulations imply
  vertical eddy advection plays an important role
  in driving new production

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Mesoscale
Spatial length scale
Resolved variability

• A similarity seen in physical and biological
  spatial decorrelation length scales
• Suggests, but does not prove, a causative link
• Does not directly address how physical turbulence
  governs biological spatial scales

Unresolved variability
Doney et al. (2003)
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Submesoscale
Glover et al. (unpub)
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Geostatistical Jargon Translated
Overall Variability ?
? Resolved Variability
? Decorrelation Scale
? Unresolved Variability
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Submesoscale

• Approximately half of the unresolved
• mesoscale variability can be resolved
• as submesoscale variability.
• The remaining unresolved variability is
• local in scale or noise.

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Altimeter Estimation of Mean Square Slope
Geometric Optics (GO) model for quasi-specular
scattering of microwave radiation For a
nadir-looking altimeter (? 0) Difference
of TOPEX/Jason-1 dual-frequency (Ku- (13.6 GHz)
and C-band (5.3 GHz)) slope estimates brackets
wavenumbers 40-100 rad/m Transfer velocity is
derived from altimeter differenced mean square
slope estimates using a quadratic dependence of k
on mean square slope for this wavenumber range
Frew et al., JGR, 2004
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Global scale
Frew et al. (in rev.)
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Surface XKW for ECO_T62gx3v5.22 1993
Global scale

• WHOI/NCAR/Irvine multi-functional group,
  multi-nutrient ecosystem model (Moore et al.,
  2004)
• Coupled to full-depth ocean BGC model (CCSM-POP)
• Surface physics forcing (1957-2004) from NCEP
  reanalysis and satellite products (Yeager and
  Large, 2004)
• Time-varying atmospheric dust/iron deposition
  (NCAR/MATCH simulations)
• Fixed pre-industrial atmospheric CO2 (280 ppm)
  transient anthropogenic CO2 simulations
• Reference run uses NCEP winds and Wanninkhof
  (1992) relationship
• Replace Wanninkhof ks with TOPEX-based ks.

Glover et al. (unpub)
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Global scale
Carbon dioxide flux
Oxygen flux
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Global scale
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Application to Satellite Altimetry
Global scale
-Model derived DIC/SSH slope -Observed
satellite SSH anomalies (AVISO)
Doney et al. (unpub)
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Summary

• Better understanding (modeling) of the influence
  of physical processes on biogeochemical
  processes, and any feedbacks, is possible through
  data-data and model-data analysis.
• Native scales of resolution in space and time of
  biological sensors (ocean color) and physical
  circulation sensors (altimetry) do not match.
• Current altimetry sensors sample the global to
  mesoscales, but reach submesoscales only
  along-track.
• Altimeter with 120km swath, 1km and 8d
  resolution, Ku and Ka nadir s, would be a
  welcomed addition.

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