Plankton and Productivity Phytoplankton Diversity Nutrients and light Primary production New production Georgia Institute of Technology Biological Oceanography

Fig. 1. Examples of representative marine eukaryotic phytoplankton P. G. Falkowski et al., Science 305, 354 -360 (2004) Published by AAAS

Tricho&Picos Trichodesmium tufts N2-fixing cyanobacteria (Synechocystis) from Station ALOHA (10 µm scale bar)

Diatom Diversity (4) Top left: Chaetoceros debilis: spiny chain diatom Bottom left: Ditylum brightwelli Top right: Coscinodiscus granii NB: Much of the internal volume of the cell is filled by a vacuole. Strands of cytoplasm can be seen running through the vacuole. Images from the Microscopy-UK Library: http://www.microscopy-uk.net/micropolitan/index.html

Emiliana huxleyi coccoliths From the E. huxleyi site: http://www.soes.soton.ac.uk/staff/tt/eh//coccoliths.html

Emiliana huxleyi World From the E. huxleyi site: http://www.soes.soton.ac.uk/staff/tt/eh/

Dinoflagellate Diversity (1) Dinophysis & Ceratium http://www.whoi.edu/science/B/redtide/rtphotos/rtphotos.html

Dinoflagellate Diversity (3) Citharistes sp. Arrow points to chamber containing cyanobacteria. Ornithocercus magnificus. Arrow points to girdle list, which contains cyanobacteria. Inset shows epifluorescence image with cyanobacteria fluorescing orange-yellow. Images from Carpenter 2002 Proc. Roy. Irish Acad. 120B: 15-18.

Phytoplankton Growth Specific growth rate N(t) = Noeµt N = biomass (cell number, PN, PC, etc.) µ = specific growth rate (t-1) Note that µ really reflects the net growth rate N(t) = Noe(p-r)t p = specific production rate (t-1) R = specific respiration rate (t-1)

Marine N Limitation (Ryther & Dunstan 1971) Krebs, Fig. 25.08

“Biolimiting” Behavior – NO3- Data: eWOCE Line A16. Figure prepared with ODV

North Atlantic Nutrient Ratios Data: eWOCE. Plot prepared with ODV

Redfield Ratio The major nutrients occur in roughly constant ratios in deep water and in plankton. Nutrients are removed from warm surface waters by plankton and released at depth by biological remineralization of organic matter. The average ratio of nutrients is called the Redfield ratio after A.C. Redfield. Biological activity drives the ocean to this state!

Nutrient Limitation: N vs. P The N:P ratio of plankton is the same as the N:P ratio of the deep ocean (Redfield ratio). Since N & P therefore enter the upper ocean in the same proportions as they’re required by phytoplankton, why does N appear to be limiting? Food webs preferentially export N from the upper ocean.

Light in the Water Column The deeper you go, the darker it gets… I(z) = Ioe-kz Mann & Lazier Fig. 3.05b (left), Miller Fig. 3.3 (right)

P/I Relationship Lalli Parsons Fig. 3.5

Stratification and Production Size of circles reflects intensity of mixing. Note inhibition of mixing by the pycnocline (A & C). Light decreases exponentially and determines where phytoplankton become light-limited. Below the euphotic depth, phytoplankton die. Mann&Lazier Fig.3.05

Production vs. Depth • Gulf of Alaska data for May (closed circles) and September (open circles) Miller, Fig. 3.9

Patterns in Primary Production Above: Typical annual cycles of primary production. Solid lines show phytoplankton biomass, blue lines show zooplankton biomass. Left: Schematic of relative abundance of light and nutrients at the sea surface as a function of latitude. Lines show relative seasonal change in primary production at three latitudes. Lalli & Parsons, Figs. 3.9 & 3.17

Riley-Sverdrup Bloom Model Assumptions Biomass uniformly distributed P scales with I R is constant Compensation depth (Dc) P = R for individual phytoplankton. Critical depth (Dcr) Community between surface and Dcr in balance. Blooms occur when Dcr > Dmix. Miller, Fig. 1.3

New vs. Regenerated Production NH4+ New vs. Regenerated Production Biological Pump modified from http://www.up.ethz.ch/research/nitrogen_cycle/index

Measurement of Primary Production ∆Biomass Practical difficulties in separating phytoplankton from other components of the ecosystem. Oxygen light-dark bottle method The dark bottle measures community respiration. The light bottle measures net community photosynthesis. 14C Incorporation The dark bottle provides ambiguous information. The light bottle measures something near net production. Long incubations may lead to recycling and equilibration. Bottle effects may compromise all these approaches!

Distribution of Primary Production Open ocean production dominates the budget despite the low areal rates. Bottle effects may lead to underestimates in all environments, but especially in the open ocean.

Chl Distribution: Atlantic Composites: Sep 97 - Aug 98