STIRRING VEGETABLE SOUPAdrian MartinWarwick 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-mesoscale1km-500km

1d-few months

Rules of thumb:eddy size ~20-150kmrotation period ~1-4dmax.current speed ~1m/slifetime ~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.

How sensitive is the difference toA = upwelling fraction of region? I = ratio of upward nitrate fluxes?m = rate of horizontal mixing?

Is the total production for the areamore or less than if the two regions were being mixed?

Parameter values

A 0.025, 0.05, 0.12, 0.25

I 1-1000s~0.006d-1 backgrounds~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 significantoverestimates of production

•Global Carbon Cycle Models may incur significant errors in ignoring the effect of mesoscale turbulence on biology.

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.”

Don Antonio de Ulloa (1716-1795)

Approach

two-box modelexamine sensitivity to fundamentalparameters of system

Twin-pronged

turbulence modelexplore the effect of mixing in more detailin 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

Use same biological modelRange of spatial distributions for forcing, with A constant

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

Forced barotropic quasigeostrophic turbulence

Dq/Dt=F+D18q+D2-2q

q= 2-/R2+f

R=1/5

Pseudospectral for vorticityFinite difference for tracers

Domain size: 512kmResolution: 2kmTyp.eddy size: 40-80kmTyp.eddy vel.: 0.6m/s

29% increase in total primary productionA