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Physics of small organisms in fluids. Chemical plumes. What happens to detritus ?. Fecal pellets Marine snow. Sinking through water column. Remineralization. Marine snow aggregates. How fast Where To what extent. Recycling of nutrients. Sequestering of carbon. …. 5 mm.

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Presentation Transcript
slide1
Physics of small organisms

in fluids

Chemical plumes

slide2
What happens to detritus ?

Fecal pellets

Marine snow

Sinking through water column

Remineralization

Marine snow aggregates

How fast

Where

To what extent

Recycling of nutrients

Sequestering of carbon

5 mm

Photo: Alice Alldredge

slide3
Organisms associated with detritus

Rich resource

Bacteria

Ciliates

Dinoflagellates

Copepods

Larval fish

colonizers

visitors

gulp

What mechanisms bring about contact?

Plume of released solutes

Photo: Alice Alldredge

slide4
Following a chemical trail

First demonstration:

The shrimp Segestes acetes following an amino acid trail generated by a sinking

wad of cotton that was soaked in a solution of fluorocein and

dissolved amino acids.

Hamner & Hamner 1977

slide6
Physics of small organisms in a fluid: advection - diffusion

advection

diffusion

Pe < 1: diffusion dominates

Heuristic

says nothing about flux

Pe > 1: advection dominates

slide7
Plume associated with marine snow

Re = 1 to 10

Pe≈ 1000

slide9
Centropages typicus: pheromone trail

17 cm long: 30 sec old

Espen Bagoien

slide10
Sinking rate (w, cm/s)

Leakage rate (L, mol/s)

The particle:

Detection ability – threshold (C* mol/cm3)

Swimming speed (v, cm/s)

The organism:

Turbulence (e cm2/s3, + ….)

Diffusion (D, cm2/s)

*****

The medium:

w

Physical parameters for plume encounter

What are relevant plume charcteristics ?

Approach: analytic and numerical modelling.

slide11
Particle size dependent properties

Sinking rate:

Stokes' law

Empirical observations

Marine snow:

a = 0.13, b = 0.26

Fecal pellets:

a = 2656, b = 2

Leakage rate:

Empirical observations

(particle specific leakage rate & size dependent organic matter content)

c = 10-12, d = 1.5

slide12
Detection threshold

Species and compound specific

Typical free amino acid concentration: 3 10-11 mol cm-3

specific amino acid concentrations < than this

Copepod behavioural response (e.g. swarming): 10-11 mol cm-3

Copepod neural response: 10-12 mol cm-3

C* from2 10-12 to 5 10-11 mol cm-3

slide13
Zero turbulence

Length of the plume

Time for which plume element remains detectable

For marine snow r = 0.5 cm and detection threshold C* = 310-11 mol/cm3

Z0* = 100 cm

T0* = 900 sec

V0* = 2.5 cm3 (5particle)

s0* = 16 cm2 (20 particle)

w

Jackson & Kiørboe 2004

slide14
Effect of turbulence on plume

Straining and Stretching:

Elongates plume lenght

1

Increases concentration gradients – molecular diffusion faster

2

Turbulent

shear event

Nonuniform: gaps along plume length

3

w + v

w

Visser & Jackson 2004

slide15
Direct numerical simulations: solve the Navier Stokes equations

Very accurate

Hugely expensive

Large eddy simulations: solve the Navier Stokes equations for a limited number of scales

Relatively accurate

Hugely expensive

Modelling turbulence

Kinematic simulations: analytic expressions that generate turbulence like chaotic stirring

Easily done

slide16
Remember: Kolmogorov spectra theory

energy density spectrum, E(k) (L3/T2)

Governed by 2 parameters

viscosity n

dissipation rate e

wave number, k (2p/ℓ)

slide18
Synthetic turbulence simulations

Wave number, k, ranges from kmin to kmax

Assumed energy spectrum:

frequency:

Amplitude of Fourier

coefficients:

Random unit vector in 3 D:

Random 3 D vectors of magnitude an and bn respectively

Fung, 1996. J Geophys Res

slide19
Path of sinking particle

Plume

Path of a neutrally plume tracer

Particle tracking by Runge-Kutta integration

Simulation

Particle

slide20
Plume

Plume concentration

Gaussian distribution of solute

C

f

r

C*

r*

l

r

slide21
stretching

diffusing

Plume construct: stretching and diffusing

slide22
Mesopelagic (10-8 cm2/s3)

Marine snow: r = 0.1 cm

w = 0.07 cm/s (60 m/day)

slide23
Themocline (10-6 cm2/s3)

Marine snow: r = 0.1 cm

w = 0.07 cm/s (60 m/day)

slide24
Surface (weak) (10-4 cm2/s3)

Marine snow: r = 0.1 cm

w = 0.07 cm/s (60 m/day)

slide25
Surface (strong) (10-2 cm2/s3)

Marine snow: r = 0.1 cm

w = 0.07 cm/s (60 m/day)

slide26
Model runs

10 levels of turbulence

3 particle sizes each for marine snow and fecal pellets

4 replicates for each turbulence – size pairing

3 detection threshold

Metrics of interest

Length; cross-sectional area; degree of fragmentation

Natural time scales:

turbulence: g = (n / e)1/2 or 1 / mean rate of strain

plume: T0* time scale for plume element to drop below threshold of detection.

Metric scale:

nonturbulent values

slide27
Total Volume

Symbols: different detection threshold

Colour: different particle size

Rate of turbulent straining

Rate of diffusion

Fit:

p < 0.0001

Visser & Jackson 2004

slide28
Total Cross section

Fit:

p < 0.0001

Visser & Jackson 2004

slide31
Copepod encounter with appendicularian houses

Appendicularia

Copepods

Oncaea

(cyclopoida)

Microsetella

(harpacticoida)

0.7 mm

Fritillaria

borealis

Oncaea borealis

Microsetella norvegica

Oikopleura

dioica

5 mm

Oncaea similis

slide33
b

s

u

slide34
C* = 3 10-8 µM

L = 9 10-14 mol s-1

Maar, Visser, Nielsen, Stips & Saito. accepted

slide35
v = 0.1 cm s-1

b = 100 µ

w = 10 m day-1

Maar, Visser, Nielsen, Stips & Saito. accepted

slide36
Copepod encounter with appendicularian houses
  • surface
  • (above 20 m depth)
  • =10-2 cm2/s3

g = 1 s-1

0.6 per day per copepod

2.5 per day per appedicularian house

10% per day

10 m day-1

Chouse = 244 m-3 below 30 m

5x

Ccopepod = 1000 m-3

  • below thermocline
  • (below 30m depth)
  • =10-7 cm2/s3

g = 10-3 s-1

4.4 per day per copepod

18 per day per appedicularian house

50% per day

slide38
Summary remarks

Despite complexity there seem to be global functions relating plume metrics in turbulent and non-turbulent flows.

About 50% of the detectable signal becomes disassociated from the particle in high turbulence.

Significant advantages can be had for chemosensitive organisms searching for detrital material in low turbulent zones (below the thermocline).

Aspects turbulence and its effects on mate finding still to be explored

slide39
Relative motion

Sensing ability

Turbulence

1

Encounter rate is everything to plankton

Find food

Find mates

Avoid predators

How to

slide40
2

Encounter processes

Random walks link microscopic (individual) behaviour with macroscopic (population) phenomena

Random walk - diffusion

Ballistic - Diffusive

Scale of interactions

slide41
Ingestion rate

turbulence

3

Encounter rate and turbulence: Dome - shape

slide42
4

Patchiness

Simple population models + chaotic stirring → complex spatial patterns

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