6 June 2011 ACE workshop 1

Ocean Productivity:Concepts and Measurements

John MarraBrooklyn College, CUNY

6 June 2011 ACE workshop 2

The Major Goal of Biological Oceanography:

“…determination of time-varying plankton productivity in the world

ocean…”

-Barber and Hilting (2002)

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• Productivity• Autotrophs, heterotrophs• New production• Export Production

Concepts

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Rate of photosynthesis Gross primary production, GPP

GPP - autotrophic respiration Net primary production, NPP

NPP - heterotrophic respiration Net community production, NCP

Export Production, EP, the amount of NCP exported (sinking, mixing, ZP vertical migration) to depth

Productivity Defined

Process Ecological Term

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-

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New Production, NP, the fraction of NPP supported by ‘new’ nutrients, and available for export

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Photosynthesis

Carbon dioxide

Water Sugars Oxygen+ +

The Photosynthetic Quotient, or PQ is the amount of oxygen evolved relative to the carbon fixed into organic matter

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Synthesis of Energy from Light

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Productivity Measurements

• Two choices: – Fluxes from in situ dynamics– Fluxes occurring in bottles

• Each has advantages and disadvantages

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The kind of ‘container’

Very physically dynamic in situ volume Very non-dynamic volume

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OxygenCO2 + H2O -> CH2O + O2

The change in oxygen content in a defined quantity of water is the most straightforward measure of Net Community Production.

The problems: 1. All too frequently, the change is negative

(NCP <0) over 12 or 24 h;2. Requires an accurate air-sea exchange

6 June 2011 ACE workshop 10

18Oxygen

CO2 + H218O -> CH2O + 18O2

A good estimate of Gross Primary Production, but may be influenced by the Mehler reaction, or other oxygen consuming reactions within the phytoplankton cell.

6 June 2011 ACE workshop 11

CarbonCO2 + H2O -> CH2O + O2

• It’s carbon! (no worries about value of the the photosynthetic quotient), but…

• Precision is too low for most open ocean work

6 June 2011 ACE workshop 12

14Carbon

• Basis of virtually all satellite algorithms for productivity• Incubation from dawn-dusk very close to Net Primary

Production• Characteristics invite methodological abuse and carelessness

– Easy– Extremely Sensitive– Always gives a ‘positive’ answer

14CO2 + H2O -> 14CH2O + O2

6 June 2011 ACE workshop 13

“…the results of the 14C method fall somewhere between the net phytoplankton production and total

photosynthesis, but exact evaluation of the meaning of the experiments will require an extensive experimental

programme”

G. A. Riley (ca. 1954)

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Productivity has known limits1. Growth rate as a function of temperature (Eppley,1972) 2. The

maximum rate of photo-synthesis normalized to chlorophyll-a, Pb

max, will be ≤ 25(Falkowski, 1981)

3. The quantum yield. 8 quanta of light are required to evolve 1 mol O2, thus, the quantum yield will be < 0.1 (in practice)(e.g., Bannister and Weidemann, 1983)

6 June 2011 ACE workshop 15

Biomass: Changes in POC

• Good for estimating particle production

• Doesn’t measure DOC production

• There are many more optically-based measurements of production in development

6 June 2011 ACE workshop 16

Comparing Fluxes: In Situ and in Containers

6 June 2011 ACE workshop 17

The JGOFS North Atlantic Bloom Experiment, Spring 1989

Over 13 days (mixed layer):• Production = 970

mmols C m-2

• Total increase in POC = 520 mmols C m-2

• Trap flux = 507 mmols C m-2

• (234Th estimates are about half the trap flux.)

m

6 June 2011 ACE workshop 18

N interacts with C in the concept of New Production

NO3

N2

• The amount of production fueled by NO3 or N2 and called the f-ratio

• Best for temperate, and high-latitude areas subject to seasonal mixing, and supply of NO3 from depth

• A good way to evaluate the quantity of production exported to depth

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6 June 2011 ACE workshop 20

Export Production in Time

‘bottom up’ regulation

‘top down’ regulation

grazing

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Export Flux to Depth

6 June 2011 ACE workshop 22

The role of Iron

Boyd et al., 2007

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Next steps: What we don’t know

• Production and dynamics of dissolved organic matter (DOM)

• Respiration and its components• The depth of the Euphotic Zone• Production in large, permeable, diffusive

containers in terms of small, impermeable ones, and vice versa

6 June 2011 ACE workshop 24

DOM

Mixing/advection

hydrolysis/ diagenesis

Riverine inputs

solubilization, grazing,exudation, lysis,

Net PrimaryProduction

EXCHANGE

OPEN OCEANCOASTAL OCEAN

DOM

solubilization, grazing,exudation, lysis,

adapted from Moore 1999

CO2

DIC

SEDIMENTS

Dissolved Organic Matter

DOMlong term C reservoir

Mixing/Advection DIC

Surface

Deep

Net PrimaryProduction

CDOMCDOM

CDOM

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Phytoplankton Primary Production

DOM

CO2

Bacterial remineralization

extracellular release, grazing, lysis, solubilization

inorganic compounds

CO2

Bacterial remineralization

Advection

Lateral transport

bioavailability

• Estimated that 50% of primary production routed through dissolved fraction

• Not typically measured in measurements of productivity

– O2 evolution/CO2 consumption will include it,

– 14C uptake may not– Won’t be measured in particle production methods

• Ultimately comes from photosynthesis (like everything else)• Utilization of labile DOC will be as rapid as photosynthetic production

Export to deeper waters & sediments through aggregate and particulate sinking

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AUTOTROPH BACTERIAL

RESPIRATION

DISSOLVED ORGANIC MATTER

EUPHOTIC DEPTH

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Global Ocean Productivity Through the ‘Ages’

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6 June 2011 ACE workshop 29

Cast of Characters

6 June 2011 ACE workshop 30