the ocean habitat - soest · 2011. 2. 28. · the ocean habitat life at the microscale friday,...

The Ocean HabitatLife at the microscale

Friday, February 25, 2011

Marine Planktonic Food Web

Prokaryotes


Most Life in the Sea is Microscopic


• Fish

• Copepods

• Diatoms

• Dinoflagellates

• Nanoflagellates

• Cyanobacteria

• Prokaryotes

• Viruses

What’s in a liter of water?NONE

10

1,000

10,000

1,000,000

100,000,000

1,000,000,000

10,000,000,000


http://www.youtube.com/watch?v=zOZi9v9p1lU




Reynolds Number

Re =

u = velocity (m/s)L= length (m)v = kinematic viscosity m2/s (10-6 for water)

Dimensionless number useful for determining relative importance of inertial versus viscous forces

uLv


Laminar vs Turbulent Flow

http://video.google.com/videoplay?docid=-4535320633959087386#docid=1827702182265329855Friday, February 25, 2011

Reynolds NumberRe =

u = 1 m/sL= 2 mv = 10-6 m2/s

uLv

Re = 1 x 210-6

= 2,000,000

Human Swimming

u = 0.000150 m/sL= 0.0000002 mv =10-6 m2/s

Re = 0.000150 x 0.000000210-6

=0.00003

Bacterium Swimming


• Large whale 10m/s

• Tuna 10 m/s

• Copepod 20 cm/s

• Invert Larva 1 mm/s

• Protozoan 35 µm/s

• Bacterium 150 µm/s

Reynolds Numbers

300,000,000

30,000,000

300

0.3

0.0003

0.00003


Viscosity

http://video.google.com/videoplay?docid=-4535320633959087386#docid=-4556431258553465670




Length Scales of Variability

L = 2π(v / e)1/43Kolmogoroff Length Scale

v = kinematic viscosity of water = 10 m s e = turbulent energy dissipation = 10 to 10 W kg

(winds 5 - 15 m s )

-1-6

-8 -6 -1

-1

2

3-6 mm20-30 mmFriday, February 25, 2011

Diffusion dominates transport at the microscale

F = D dC/dz

Values for Diffusivity (m2/s)

Heat = 1.5 x 10-7

Nutrient = 1.5 x 10-9

D = L2/t so t = L2/Dif L = 1 mm

7 sec11 min



L = 2π(v / e)1/43

L = 2π(vD / e)1/42

Kolmogoroff Length Scale

Batchelor Scale

v = kinematic viscosity of water = 10 m s e = turbulent energy dissipation = 10 to 10 W kg

(winds 5 - 15 m s ) D = molecular diffusivity = X m s

-1-6

-8 -6 -1

-1-12

2



• turbulence = 6 - 20 mm

• heat = 2 - 14 mm

• salt/nutrient = 0.2 - 1 mm


Eddy Diffusivity

• Typical eddy diffusivity for horizontal diffusion (deep ocean) is 500 m2 s-1

• 6 x 10-5 m2 s-1 vertical (deep ocean)

• Compare to molecular diffusivities of 10-7 10-11

Eddy diffusivities for deep sea from Gargett (1984) J. Mar. Res. 42: 359-395


Nutrient Diffusion

• Horizontal eddy diffusion (500 m^2/s):

• Vertical eddy diffusion (6 x 10-5 m^2/s):

• Molecular diffusion (1.5 x 10-9 m^2/s):

t = L2/D

Time for nutrients to diffuse 10 meters

20 seconds

19 days

2000 years

assuming empirical estimates on the km scale


The Problem for Small Cells

• no turbulence at the micro-scale

• diffusion is very slow

• Swimming or sinking by large cells can increase the nutrient flux to the cell to some degree.

• Boundary layers make swimming less effective for smallest cells


F = D dC/dz


Marine Snow


F. Azam & R. A. Long 2001

Photo D.C. Smith

Microscale Hot Spots Exist

colonized marine snow particle


F. Azam 1998

Microscale Patchiness and Hotspots

Creates niche space contributing to microbial diversity


Bacterial Motility

• Old models based on E. coli

• about 25 µm per sec

• run and tumble

• New observations show high speed bursts (45 to 300 µm per sec), stops and, direct reversals

• Swimming does not increase flux directly, but can move the cell to a place where nutrient concentrations are higher


Paradox of the plankton (Hutchinson)

Utilization of the same resource by two species in a homogenous environment will lead to elimination of the less competitive species

G. E. Hutchinson posed the question: Why is there so much diversity among phytoplankton? Because according to ecological theory, namely the competitive exclusion principle of Gause:

The simple explanation (recognized by Hutchinson) is that the pelagic marine environment is far from

homogeneous


the ocean habitat - soest · 2011. 2. 28. · the ocean habitat life at the microscale friday,...

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