Lecture 13
Primary Production – Chemical Tracers
Topics
Production (primary, new, export, net, gross)
Respiration
What is primary production?
DINutrients ⇒ POM
Primary Producers
Autotrophs
Mostly photosynthesizers (they use light energy) called phytoplankton
phyto = light
plankton = small drifting organisms
Some chemotrophs (don’t need light)
live in unusual environments like
hydrothermal vents, anoxic environments
Units
Many different units are used for primary production.
mmolC m-2 d-1, mgC m-2 d-1 , gC m-2 y-1, and Gt C y-1
(1 Gt = 1 Pg = 109 tons = 1013 kg = 1015g)
Chemical Oceanographers always recommend that moles be the
preferred unit,
mmol C m-2 d-1
Use of moles makes comparison of stoichiometric ratios between
nutrients and carbon easier.
How is primary production measured?
14C
From satellites
O2 mass balance
Light models
δ18O
Measuring Primary Productivity
Classic Approach – 14C
Method:
1) Add known amount of
14C to a bottle
containing plankton.
2) Let photosynthesis
happen.
3) Filter POC-14C
4) Measure how much 14C
has been fixed by
phytoplankton.
Global Net primary Production by 14C (from Berger et al., 1988, 1989)
Global Average Ocean Chlorophyll
Chlorophyll from space (~upper 20m)
Global Ocean Primary Production
-from space using chlorophyll
What are the factors that determine these patteerns?
Global Annual Net Primary Production from remote sensing models
NPP = APAR (400-700nm) x ε (7% APAR absorbed by plankton; 31% by land plants)
(from Field et al., 1998) total = 104.9 Pg y-1
τC
terrestrial = 56.4 (53.8% of total) ⇒ 426 gC m-2 y-1 ⇒ 99.8% of biomass ⇒ 19y
ocean
= 48.5 (46.2% of total) ⇒ 140 gC m-2 y-1 ⇒ 0.2% of biomass ⇒ 2-6 d
gC m-2 y-1
Example: Global Carbon Cycle – What is Net Primary Production?
Variability - CalCOFI Sampling Grid
Is this sufficient to describe variability?
Coastal T and Chl
California Current
(by CZCS satellite)
Chlorophyll – left
SST – right
NASA SeaWiFS data for ocean chlorophyll
and primary production
For Animation of Global Data:
go to http://earthobservatory.nasa.gov/Observatory
Note:
1. High Latitudes – high and variable
Spring Bloom in N. Atlantic (NABE)
2. Coastal Regions – high and patchy
3. Central Gyres - low
4. Equatorial Regions (EqPac) – higher and El Nino
5. Arabian Sea – response to monsoon forcing
6. Southern Ocean – seasonal
7. Seasonality
Production by ocean and land areas (from Pilson)
139 gC m-2 y-1
Historial estimates of total ocean primary production
Koblents-Mishke et al (1968)
Ryther (1969)
Eppley and Peterson (1979)
Romankevich (1984)
Martin et al (1987)
Berger et al (1987)
Field et al (1998)
Value (Gt C y-1)
23
20
19.1
23.7
25
51
26.9
48.5
**Note: 1 Gt = 1Pg = 109 tons = 1012 kg = 1015 gms**
**The best value for ocean
appears to be about
50 Gt C y-1**
Food Web Structure
Different N Sources
New Production
- NO3 - as N source (from diffusion/upwelling from below and
from the atmosphere via nitrogen fixation and nitrification)
Regenerated Production - NH4+ and urea as N source
New/Net/Export Flux
The f-ratio:
f = NO3 uptake / NO3 + NH4 uptake
(defined by Dugdale and Goering, 1969)
If we write P = gross production and R = respiration then we can also approximate f as:
f = P-R
P
also called the ratio of net to gross production
Food Web Cartoon
Follow the N!
Follow the C!
Follow the O2!
Fe plays a role!
DON
Euphotic Zone (~100m)
At steady state:
New NO3 =
O2 flux to atm =
PON (and DON) export
PON
Total Global New Production from NO3 upwelling
(from Chavez and Toggweiler)
estimated upward velocity, NO3 concentration advected up
and then new production
O2 Flux Method
Gas exchange
Write a mass balance
P → O2
R
Mixing
O2 Flux Method
Internal Rotating Sphere (IRS)
Sediment Trap
Hedges and Peterson (UW)
Particle Interceptor Traps
(PITs)
Knauer and Martin
(Moss Landing)
Primary Production by Ocean Provinces from POC Export
(from Martin et al., 1987)