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STIRRING VEGETABLE SOUP
Adrian Martin
Warwick Turbulence Symposium: Workshop March 2006
"Environmental Turbulence from Clouds through the Ocean"
Coccolithopore
Emiliania huxleyi
100 Gt C y-1
60% land, 40% water
Scales of Interest
Mesoscale and sub-mesoscale
1km-500km
1d-few months
Rules of thumb:
eddy size ~20-150km
rotation period ~1-4d
max.current speed ~1m/s
lifetime ~weeks-months
phytoplankton doubling time ~1d
Horizontal velocity
Vertical velocity
Data from PRIME cruise, June 1996
Data
from
Dundee
Satellite
Receiving
Station
Processed
by
Steve
Groom,
RSDAS,
PML
Given that phytoplankton and physical forcing of phytoplankton are `patchy’…
What effect do stirring and mixing have on production?
Suppose that upwelling and ambient
regions are isolated.
Is the total production for the area
more or less than if the two regions
were being mixed?
How sensitive is the difference to
A = upwelling fraction of region?
I = ratio of upward nitrate fluxes?
m = rate of horizontal mixing?
Parameter values
A
0.025, 0.05, 0.12, 0.25
I
1-1000
s~0.006d-1 background
s~1.6d-1 upwelling
m
0-10d-1
139% increase in total primary production
Martin et al., Global Biogeochemical Cycles, 2002
208% increase in total primary production
Martin et al., Global Biogeochemical Cycles, 2002
C. Pasquero, Geophysical Research Letters, 32, L17603, 2005
C. Pasquero, Geophysical Research Letters, 32, L17603, 2005
Conclusions
•Turbulence strongly affects plankton ecology and plays a major
role in controlling regional primary production at the mesoscale.
•Lateral turbulent stirring and mixing is just as important as the
vertical supply of nutrients.
•Correlations between coherent structures and upwelling
regions can exert a very strong influence on production.
•Use of standard effective diffusivities may result in significant
overestimates of production
•Global Carbon Cycle Models may incur significant errors
in ignoring the effect of mesoscale turbulence on biology.
Don Antonio de Ulloa (1716-1795)
May 1735 - “[Encountered coloured water]
extending about two miles from North to South and
about six to eight hundred fathoms from West to
East. The colour of the water was yellow.”
Approach
Twin-pronged
two-box model
examine sensitivity to fundamental
parameters of system
turbulence model
explore the effect of mixing in more
detail
in particular the influence of coherent
structures
Same biological model in each case.
Ecosystem Model
Oschlies and Garcon, 1999
Two Box Model
Base value (I=1,m=0): 0.076mMol N /m3/d
Two-box model:
Advantage:
Clearest demonstration of sensitivity to m, I and A
Disadvantage:
Very crude representation of mixing
Motivation for turbulence model:
Explicit modelling of mixing due to mesoscale turbulence
Sensitivity to distribution of upwelling
Role of coherent structures
Use same biological model
Range of spatial distributions for forcing, with A constant
Forced barotropic
quasigeostrophic turbulence
Dq/Dt=F+D18q+D2-2q
q= 2-/R2+f
R=1/5
Pseudospectral for vorticity
Finite difference for tracers
Domain size: 512km
Resolution:
2km
Typ.eddy size: 40-80km
Typ.eddy vel.: 0.6m/s
A
29% increase in total primary production