Marine Ecosystems and Food Webs
Carbon Cycle
Marine Biota
Export Production
Export Production of Organic Carbon
Ocean Ecosystem Structure
Trophic levels
and dynamics
Ocean Ecosystem Structure
Trophic levels
and dynamics
Ocean Ecosystem Structure
Trophic levels
and dynamics
Ocean Ecosystem Structure
Trophic levels
and dynamics
Ocean Ecosystem Structure
Example of a more complex Food Web
Ocean Ecosystem Structure
Energy Transfer between
Trophic Levels is not efficient
Trophic levels
and dynamics
Food Web
Energy
ENERGY
How about Mass Transfer?
How do we measure Biomass?
Mass transfers are more easy to keep track than energy transfers
Alaska
Large scale Eddies
200 km
• Color sensor satellites: MODIS, SeaWiFS, MERIS,
OCTS, and CZCS
http://oceancolor.gsfc.nasa.gov/SeaWiFS
A simplified diagram of an ecosystem
A useful way to keep track of biomass in the
lower trophic levels is to follow the path of
MACRONUTRIENTS
Carbon
C
Phosphorus
Nitrogen
P
N
Redfield Ratio
C:N:P
106 : 16 :
Atlantis in 1934
and today
1
Redfield A.C., On the proportions of organic derivations in seawater
and their relation to the composition of plankton. In James Johnson
Memorial Volume. (ed. R.J. Daniel). University Press of Liverpool, pp.
177-192, 1934. This works stems from his participation as a
physiologist in the voyages of WHOI's first research vessel Atlantis.
C:N:P
source
1) atmosphere
source
1) from N2 atmosphere gas
2) ocean subsurface
3) remineralization of dead organic matter
4) biological (e.g. excretions)
source
1) not biological, not atmospheric
2) fluvial
At large Nitrogen appears to be the limiting factor
in ocean productivity in today’s oceans
What is the explanation for the Redfield ratio?
• Redfield (1958) “biological control of chemical
factors" in the ocean: living organisms in the
ocean evolved to have a N:P ratios of about 16
→ when N is not limiting then N and P but also C
and O interact to produce this relation.
• Very stable in deep ocean
• Not so stable between phytoplankton species.
• Perhaps only general average?
Simple Nitrogen Model
Net Primary Production (NPP)
~45 Pg C/yr
hn
NPP
S(No-N)
N
D D
D

N
P
kn  N
 zZ
pP
g P 2
(1   )
Z
2
g P
z Z 2
N=nitrogen
P=phytoplank.
Z=zooplank.
D=detritus
P
~1 Pg C
(0.2 % of
photosynthetic
biomass)
gP 2
Z
2
g  P
Z
ws D
h
Phytoplankton biomass turns over in about a week!
Description of the oceanic ecosystem
based on Nitrogen exchanges
N2
Nitrification
Mix Layer
depth
Phytoplankton
Grazing
Chlorophyll
Zooplankton
Mortality
Water column
Mineralization
NH4
NO3
Uptake
Fixation
Susp.
particles
Large
detritus
Nitrification
N2
NH4
NO3
Denitrification
Sediment
Organic matter
Aerobic mineralization
Carbon Cycle
Marine Biota 45 GIC/yr
Export Production
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
upwelling, eddy fluxes) modulates the
fluxes of essential nutrients
 Ocean nutrient inventory
 Utilization of nutrients in HNLC (High
Nutrients Low Chlorophyll regions)
 Changes in Redfield Ratio
Export Production of Organic Carbon
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
upwelling, eddy fluxes) modulates the
fluxes of essential nutrients
 Ocean nutrient inventory
 Utilization of nutrients in HNLC (High
Nutrients Low Chlorophyll regions)
 Changes in Redfield Ratio
What are the controls on Primary Production?
Nutrient Sources for Primary Production
The flux of organic carbon must be
sustained by an adequate flux of
macronutrients
If macronutrients are unavailable
then primary production is reduced!
Surface CHL-A
1) Central Gyres
2) Upwelling Regions
Phytoplankton Blooms and Physical Environment
Bands of the dionflagellate Lingulodinium
polyedrum moving onshore over the troughs
of a series of internal waves
Nonlinear Internal Waves and Phytoplankton
Isopycnals
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
upwelling, eddy fluxes) modulates the
fluxes of essential nutrients
 Ocean nutrient inventory
 Utilization of nutrients in HNLC (High
Nutrients Low Chlorophyll regions)
 Changes in Redfield Ratio
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
Nitrogen
appears
be the limiting
factorthe
for
upwelling,
eddy to
fluxes)
modulates
in modern
time.
fluxes ofgrowth
essential
nutrients
 Ocean nutrient inventory
C:N:P
106 : 16 :
1
Modern TIME
N2 fixation
Denitrification
N = 25790
N* = N – 16 P
(Gruber & Sarmiento 1997)
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
upwelling, eddy fluxes) modulates the
fluxes of essential nutrients
 Ocean nutrient inventory
 Utilization of nutrients in HNLC (High
Nutrients Low Chlorophyll regions)
 Changes in Redfield Ratio
Southern Ocean HNLC
Map of annual average nitrate concentrations in
the surface waters of the oceans. Data from
Levitus, World Ocean Atlas, 1994.
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
upwelling, eddy fluxes) modulates the
fluxes of essential nutrients
 Ocean nutrient inventory
 Utilization of nutrients in HNLC (High
Nutrients Low Chlorophyll regions)
 Changes in Redfield Ratio
What are the controls on Primary Production?
 Ocean Circulation (e.g. gyres, coastal
upwelling, eddy fluxes) modulates the
fluxes of essential nutrients
 Ocean nutrient inventory
 Utilization of nutrients in HNLC (High
Nutrients Low Chlorophyll regions)
 Changes in Redfield Ratio