Competition for nutrients Major phytoplankton groups Light Review Competition for nutrients Major phytoplankton groups Light Critical and Compensation Depths Spring bloom and seasonal cycle Geographic variation Atlantic vs. Pacific Latitudinal variation

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

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

Light attenuates exponentially with depth. Longer wavelengths have greater absorption by particles and attenuate more with depth. Too much light damages cells and reduces photosynthesis (photoinhibition). depth Irradiance

Compensation & Critical Depth

Video of mixed layer with wind mixing (go to 8:21)

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 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

Need Dcr>Dm for NPP>0 Early spring diatoms, dinos Late spring coccoliths Plankton 0-100 m (# per L) 2-3 week delay in bloom of copepods These are the data underlying Sverdrup’s “critical depth” hypothesis. Depth (m)

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.

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

Atlantic Ocean is saltier than Pacific Ocean

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

Draw Atlantic vs. Pacific mixed layer depths

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

Spring bloom mechanism Critical depth hypothesis – Sverdrup 1953 (this is the one we’ve been talking about) Recent alternative hypotheses: -Dilution recoupling hypothesis – Behrenfeld 2010 -Stratification onset hypothesis – Chiswell 2011 -Shutdown of turbulent convection hypothesis – Taylor and Ferrari 2011

Phytoplankton Irradiance Physical mixing processes Nutrients Irradiance Zooplankton Higher Trophic Levels Sinking & Senescence Particle Dynamics Particle Flux (Carbon flux)