Critical and Compensation Depths Spring bloom and seasonal cycle Geographic variation Atlantic vs. Pacific Latitudinal variation

Light Intensity / Irradiance Diatoms Dinoflagellates Coccolithophores Cyanobacteria High Low Nutrients Low High Light Intensity / Irradiance Narrow Broad Light Spectrum Temperature Deep water / Winter Shallow water / Summer

Competition for nutrients μmax1 = μmax2 Ks1<Ks2 μmax2 > μmax1 Equal Ks Species 1 Species 2 Specific Growth Rate μ Max growth rate (a constant) Half-saturation constant Nutrient Concentration N

Keep in mind the physics & chemistry of the mixed layer Wind Light & Heat Nutrients

Draw the mixed layer here

Photosynthesis requires light, Respiration does not Depth Depth + biomass - biomass (Requires light) (Independent of light)

Compensation Depth P = R Compensation depth R P Depth P>R Biomass increases P = R Compensation depth P<R Biomass decreases Depth

Critical Depth GPP=ΣR Net Primary Production (NPP) = 0 Critical depth R P Gross Primary Production (GPP) Sum of Respiration (ΣR) Depth GPP=ΣR Net Primary Production (NPP) = 0 Critical depth

If critical depth > mixed layer depth, GPP>ΣR, NPP >0 R P Gross Primary Production (GPP) Sum of Respiration (ΣR) Depth Bottom of mixed layer Critical depth

If critical depth < mixed layer depth, GPP<ΣR, NPP<0 R P Gross Primary Production (GPP) Sum of Respiration (ΣR) Depth Critical depth Bottom of mixed layer

Critical depth concept is critical! Respiration Photosynthesis Understand why R is a straight line Understand why P is an exponential curve Know the difference between: critical depth and compensation depth Depth

Can you explain why production peaks where it does? Production is a rate e.g. [g C m-2 y-1] Biomass is a concentration e.g. [g C m-2]

Spring bloom in satellite images NASA/Goddard Space Flight Center, The SeaWiFS Project and GeoEye, Scientific Visualization Studio. NOTE: All SeaWiFS images and data presented on this web site are for research and educational use only. All commercial use of SeaWiFS data must be coordinated with GeoEye (http://www.geoeye.com). Data provided by: Norman Kuring (NASA/GSFC) http://svs.gsfc.nasa.gov//vis/a000000/a003500/a003599/index.html

Need to add zooplankton to understand seasonal cycles Phytoplankton Physical mixing processes Nutrients Irradiance Zooplankton

Definitions Phytoplankton Phyto- (plant) and planktos (drifter) drifting single-celled algae Zooplankton Zoo- (animal) and planktos (drifter) Small drifting animals

Definitions Autotrophs get their carbon and energy from inorganic sources. Phytoplankton are autotrophs because they get their carbon from CO2 and energy from light. Heterotrophs get their carbon and energy from pre-formed organic matter. Zooplankton are heterotrophs because they get carbon and energy by eating phytoplankton (or zooplankton).

Some marine heterotrophs (Zooplankton) Protists - single cells Size range: 1 to 1000 μm Life span: days to ~week Crustaceans Size range: 0.01 to 10 cm Life span: weeks to years Gelatinous animals Size range: mm to m Life span: months to ~year ciliates dinoflagellates Copepods are the most numerous multicellular marine animals! krill copepods Greek roots: “auto” =self “hetero”=other “troph”=nutrition or to feed jellyfish salps

Generation times differ Phytoplankton Reproduce by dividing ~ hours to days Limited by: Nutrients, light, temperature Zooplankton Several life stages ~2-4 weeks Limited by: Food availability, temperature

Seasonal evolution of mixed layer

Annual cycle in N. Atlantic Nutrients Light Temperature Mixing Mixing Relative increase Stratified

Annual cycle in N. Atlantic Nutrients Light Temperature Mixing Mixing Stratified Relative increase Spring bloom Fall mini- Phytoplankton biomass Zooplankton biomass This mechanism of bloom formation is described by Sverdrup’s “Critical Depth” hypothesis.

Draw seasonal cycle of temperate and light profiles with critical depth here

Primary production and its seasonal cycle vary greatly in space Chl a from SeaWIFS satellite Nutrient sources to surface waters are: rivers and land runoff upwelling atmosphere   The most productive regions of the oceans are the coastal regions because this is where upwelling is strongest and where river and land runoff meet the sea. Here nutrients result in high productivity rates, which in turn result large fisheries.

Atlantic Ocean is saltier than Pacific Ocean The surface N. Atlantic is saltier than the surface N. Pacific, making surface water denser in the N. Atlantic at a given temperature. This difference is because on average N. Atlantic is warmer than N because local heating from the Gulf Stream. Warmer water evaporates faster, leaving higher-salinity water.

Mixed layer is deeper in Atlantic than in Pacific Atlantic Ocean Depth (m) South pole Equator North Pole Pacific Ocean The surface N. Atlantic is saltier than the surface N. Pacific, making surface water denser in the N. Atlantic at a given temperature. This difference is because on average N. Atlantic is warmer than N because local heating from the Gulf Stream. Warmer water evaporates faster, leaving higher-salinity water. Depth (m) South pole Equator North Pole Temperature

Nutrient limitation varies among oceans Mixed layer is deeper and more nutrient-limited in Atlantic than in Pacific Remineralized nutrients accumulate in deep water, transported by ocean conveyer belt

Atlantic vs. Pacific mixed layer depths Time (month) Dcr Dm (Atl.) Dm (Pac.) NPP>0 NPP>0

Atlantic vs. Pacific spring bloom Winter: Deep mixed layer, Production shuts down Spring: Phytoplankton bloom Zooplankton - slow to catch up Winter: Shallower mixed layer, Continuous low production Spring: Phytoplankton bloom Zooplankton - right there to eat the bloom! Phytoplankton biomass Zooplankton biomass

Latitudinal variation in seasonal cycles driven by variation in irradiance [Also Irradiance] 90oN = N. Pole 60oN ~Anchorage,AK 30oN ~N. Florida 0oN = Equator

Seasonal cycle varies with latitude Nutrients Light [Nutrient] Latitude Light Winter Spring Summer Autumn Winter Lalli & Parsons

Annual cycles in other regions Phytoplankton biomass Zooplankton biomass Try this on your own: Draw the vertical profiles of temperature and light and the critical depth for each region as we did in class for the North Atlantic.

This time watch the Arctic and equator NASA/Goddard Space Flight Center, The SeaWiFS Project and GeoEye, Scientific Visualization Studio. NOTE: All SeaWiFS images and data presented on this web site are for research and educational use only. All commercial use of SeaWiFS data must be coordinated with GeoEye (http://www.geoeye.com). Data provided by: Norman Kuring (NASA/GSFC) http://svs.gsfc.nasa.gov/vis/a000000/a003500/a003599/index.html