Prof. Heidi Fuchs

hfuchs@marine.rutgers.edu

Suggestions for getting an A• How to deal with equations?

– Don’t panic!– If you understand an equation, you can

understand the process it describes

• Why so many graphs?– Teach you how to read (and draw) different

kinds of graphs– Illustrate principals and processes

• When in doubt, think about what’s happening with the physics.

Suggestions for getting an A• How to deal with equations?

– Don’t panic!– If you understand an equation, you can

understand the process it describes

• Why so many graphs?– Illustrate principals and processes– Teach you how to read (and draw) different

kinds of graphs

• When in doubt, think about what’s happening with the physics.

Suggestions for getting an A• How to deal with equations?

– Don’t panic– If you understand an equation, you can

understand the process it describes

• Why so many graphs?– Illustrate principals and processes– Teach you how to read (and draw) different

kinds of graphs

• When in doubt, think about what’s happening with the physics. Ask questions!

An informal survey…

Biology of mixed layer

• Primary production

by Phytoplankton - small drifting organisms

that photosynthesize

• Competition and limits on production

• Critical and compensation depths

Photosynthesis (P)

Carbon dioxide (C,O)

+ Water (H,O)

+ Nutrients (N,P)

+ Light energy

Oxygen (O)

+ Organic matter (C,H,O,N,P)

proteinsfats carbohydrates nucleic acids

Requires chloroplasts

Plants, algae

Respiration (R)

Carbon dioxide (C,O)

+ Water (H,O)

+ Nutrients (N,P)

Oxygen (O)

+ Organic matter (C,H,O,N,P)

proteinsfats carbohydrates nucleic acids

Every living thing respires

Primary Production - Definitions

Gross Primary Production (GPP) = rate of carbon fixation by photosynthesis units = [Mass / Area / Time], e.g. [g C m-2 y-1]

Respiration (R) =

rate of carbon (CO2) loss through metabolism

Net Primary Production (NPP) = GPP - ΣR

Need GPP>ΣR for net growth!

Production ≠ Biomass

• Production is

a rate

e.g. [g C m-2 y-1]

• Biomass is a

concentration

e.g. [g C m-2]

“Paradox of the Plankton” There are many species of phytoplankton,

despite few limiting resources and lots of mixing.

Phytoplankton (single-celled primary producers) have various competitive strategies that enable coexistence.

• Large (5-2000 μm)

• Have unique life cycle & blooms

• Small (2-25 μm)

• Have CaCO3 tests

• Large (2-200 μm)

• Have silica frustules

• Small (<1 μm) or Large (0.5-4 mm)

• Nitrogen fixers

Four major playersCyanobacteria Diatoms

Coccolithophores Dinoflagellates

What limits production?

• Nutrients

• Light– Intensity– Spectrum

• Temperature

• Grazing by zooplankton

The environment varies in space and time. Different phytoplankton grow well under different conditions.

High LowNutrients

Low High Light Intensity

Narrow BroadLight Spectrum

Low HighTemperature

Dee

p w

ater

/ W

inte

r

Sha

llow

wat

er /

Sum

mer

Nutrients

• N, P, Si, Fe• Nitrogen is most often limiting in ocean• Bioavailable forms of inorganic N:

–Nitrate (NO3-)

–Ammonium (NH4+)

–Nitrite (NO2-)

At low nutrient concentrations, smaller phytoplankton tend to grow faster

Assume cell is a sphere.

Surface area:

Volume:

Surface area to volume ratio:

Smaller cells have relatively more surface areafor taking up nutrients.

r

r

N = [Nutrient]

μ = Specific growth rate (d-1)

Growth rate varies with [nutrient]

Curve “saturates”

Ks

μmax/2

μmax

N = [Nutrient]

μ = Specific growth rate (d-1)

Growth rate varies with [nutrient]

Michaelis-Menten Kinetics

“half-saturation constant”

Diatoms

•High μmax

•High Ks

Coccolithophores

•Low μmax •Low Ks

High or variable nutrientsHigh mixing, upwellingLow average irradianceHigh turbulence

Chronically low nutrientsStratified conditionsHigh average irradiance Low turbulence

Different strategies of nutrient use

Larger plankton (diatoms and dinoflagellates) most adapted to high-nutrient conditions.

High LowNutrients

Low High Light Intensity / Irradiance

Narrow BroadLight Spectrum

Low HighTemperature

Dee

p w

ater

/ W

inte

r

Sha

llow

wat

er /

Sum

mer

PAR = photosynthetically active radiation (visible light wavelengths)

Irradiance = power of electromagnetic radiation per unit area of ocean’s surface (e.g. W m-2) - or -energy per area per time (e.g. mol photons m-2 s-2).

Light (PAR) attenuates with depth

Iz = irradiance at depth z

Units of [Watts m-2] or[mol photons m-2 s-1]

Light attenuates as it is absorbed and scattered by particles in the water.

Z

IzZ0

Hiscock et al. 2008

Average Primary Production saturates at high PAR (photosynthetically active radiation)

Inside Fe patchOutside Fe patch

Species adapt to different light levels

Irradiance

1

0

Ryther 1956

Photo-inhibition at high light levels

Too much light damages cells and reduces photosynthesis (photo-inhibition)

Diatoms most adapted to low-light conditions

High LowNutrients

Low High Light Intensity / Irradiance

Narrow BroadLight Spectrum

Low HighTemperature

Dee

p w

ater

/ W

inte

r

Sha

llow

wat

er /

Sum

mer

Attenuation varies with wavelength.

More wavelengths are available near the surface.

Plankton use colored pigments to harvest light at different wavelengths.

violet red

Different color pigments absorb different wavelengths of light

Pigments (colored molecules)

Phytoplankton with different pigments

Chlorophyll*

Phytoplankton with multiple pigments capture more wavelengths

• All phytoplankton have chlorophyll• Coccolithophores and diatoms have carotenoids• Cyanobacteria have phycoerythrin, phycocyanin

Coccolithophores and Cyanobacteria most adapted to broad spectrum of light found in shallower mixed layer

High LowNutrients

Low High Light Intensity / Irradiance

Narrow BroadLight Spectrum

Low HighTemperature

Dee

p w

ater

/ W

inte

r

Sha

llow

wat

er /

Sum

mer

Growth-temperature curves vary among species but share upper limit

Temperature oC

Gro

wth

rat

eUpper limit

(Eppley 1972)

Diatoms grow fastest at low temperatures

Temperature oC

Div

isio

ns p

er d

ayDiatoms Flagellates

Diatoms most adapted to colder temperatures

High LowNutrients

Low High Light Intensity / Irradiance

Narrow BroadLight Spectrum

Low HighTemperature

Dee

p w

ater

/ W

inte

r

Sha

llow

wat

er /

Sum

mer

Keep in mind the physics & chemistry of the mixed layer

Nutrients

Light & HeatWind

Primary production varies with depth

Respiration

Dep

th

Photosynthesis

Dep

th

+biomass

-biomass

(Requires light)

(Independent of light)

Compensation Depth

Dep

th

P>R Biomass increases

P = R Compensation depth

P<R Biomass decreases

R P

Critical Depth

0

GPP=ΣRNet Primary Production (NPP) = 0Critical depth

Dep

th

R P

Gross Primary Production(GPP)

Sum of Respiration(ΣR)

Dep

th

R P

Bottom of mixed layer

Critical depth

If critical depth > mixed layer depth, GPP>ΣR, NPP >0

Gross Primary Production(GPP)

Sum of Respiration(ΣR)

Dep

th

R P

Critical depth

Bottom of mixed layer

If critical depth < mixed layer depth, GPP<ΣR, NPP<0

Gross Primary Production(GPP)

Sum of Respiration(ΣR)

Dep

th

Respiration Photosynthesis

Critical depth concept is critical!

• Understand why R is a straight line

• Understand why P is an exponential curve

• Know the difference between:

critical depth

and

compensation depth