Transcript Lecture 11: Ocean Primary Production and Biogeochemical Controls

Lecture 11: Ocean Primary Production
and Biogeochemical Controls
Oceanic ecosystem largely depends on
the biochemical process of phytoplankton
Learning Objectives
1. Understand the trophic dynamics in the ocean
2. Know the marine productivity and its global
distribution
3. Biological productivity in the upwelling water
ENERGY
Autotrophs: organisms
capable of self-nourishment
by synthesizing food from
inorganic nutrients
heterotrophs: organisms not
belonging to autotrophs; all
animals are heterotrophs
c.f. Fig.10-1 in text
Difference between Mass
(i.e. chemicals) Transfer
and energy path
Difference between Mass
Transfer and energy path
Difference between Mass
Transfer and energy path
Mass transfer is recycling
(self-contained)
Difference between Mass
Transfer and energy path
Physiologic processes
Energy is replenished all
the time
Trophic levels
and dynamics
Although simple, it
reminds us that all of
the energy that a
species expends relies
on the photosynthesis
of plants
Simple food chain
Trophic dynamics: study the interrelationships among
organisms by means of the nutrition flow in the
ecosystem
The first trophic level is the autotroph, i.e. the plant
producer, providing the matter and energy to the
higher trophic levels, i.e. consumers
Omnivore: both
plant and animal
eater
Food Web: a network of interlaced and
interdependent food chains
grazing food chain
phytoplankton → zooplankton → nekton
detritus → deposit feeder → nekton
detritus food chain
Size increases
biomass increases
Energy amount increases
Higher order trophic levels
depend on the lower order
trophic levels
Energy pyramid
Where does the energy
go?
Energy transfer between trophic levels is not efficient
Typically, a positive correlation
exists between body size of aqua
animals and their trophic level
Exceptions?
simple rule
Five basic consuming types of aqua animals
(Fig.10-3 in text)
•Grazer − herbivores (e.g. sea urchin)
•Predator − carnivores (e.g. shark)
•Scavenger − benthic invertebrates (e.g. crab)
•Filter feeder − animals living in burrows
•Deposit feeder − animals living in sediments
Dynamical time
lag exists
between the food
abundance and
animal population
Trophic levels
and dynamics
Food Web
Energy
Sunlight and
nutrition supplies are
two principal factors
that limit the primary
production in the
ocean.
In addition to forming
carbohydrates (via
photosynthesis),
plants also
manufacture other
organic compounds,
including proteins,
lipids, and nucleic
acids such as DNA
and RNA.
Plankton blooms
Cell division causes
diatom populations to
increase dramatically
and rapidly (within
several days) under
preferable growth
conditions
Red tide
Plankton Blooms
Bands of the dionflagellate Lingulodinium polyedrum moving
onshore over the troughs of a series of internal waves
Nonlinear Internal Waves and Phytoplankton
Isopycnals
Have you
noted
how fast
the time
lapse is !
green tide
Alaska
Large scale Eddies
200 km
Note that where do the
Surface CHL-A
1) Central Gyres
2) Upwelling Regions
Production of Organic Carbon Export
Why do we care about the Carbon Export
Production?
• The total amount of carbon in the ocean is about
50 times greater than the amount in the
atmosphere, and is exchanged with the
atmosphere on a time-scale of several hundred
years.
• At least 50% of the oxygen we breathe comes
from the photosynthesis of marine plants.
• Currently, 48% of the carbon emitted to the
atmosphere by fossil fuel burning is sequestered
into the ocean.
• But the future fate of this important carbon sink is
largely uncertain (therefore anxious) because of
potential climate change impacts on ocean
circulation, biogeochemical cycling, and
ecosystem dynamics
=> Definition of primary productivity in the ocean
Roles of bacterial in the ecosystem
1.Bacterial decompose dead tissue and
release essential inorganic nutrients into
the water for recycling by plants.
*NH3 + 2O2 → H+ + NO3- +H2O (aerobic
bacterial)
*SO42- → 2O2 + S2- (anaerobic bacterial)
2.Plays both the starting point (providing
nutrients for plant photosynthesis) and
the ending point (proceeding the decay of
organic matter) of the food cycle that
provides the linkage between nonliving
and living matter.
3.Also serve as food for some species of
zooplankton
2H+ + S2- → H2S
Cyanobacteria (blue-green algae) are
predominantly photosynthetic prokaryotic
(初核質 ) organisms containing a blue
pigment in addition to chlorophyll. They
use sunlight directly to manufacture food
from dissolved nutrients.
Hydrothermal vents and Chemosynthetic bacteria
Chemical energy released by the
oxidation of inorganic compounds is
used to produce food.
The base of vent community is
occupied by microbes rather
than by plants, because there is
no light in the deep sea.
Global Carbon Cycle
Marine Biota
Export Production inside the ocean
What are the controllers on Export Production?
(1) Nutrient Sources for Primary Production
and (2) limitations of CO2 fluxes
The fluxed of organic carbon must be
sustained by an adequate flux of
macronutrients (P, N, Si)
If macronutrients are unavailable
then the CO2 flux is reduced!
Macronutrients vs. micronutrients (p339 in text)
What are the controllers on Export Production?
1) Ocean nutrient inventory
2) Utilization of nutrients in HNLC condition
3) Change of Redfield Ratio (A. C. Redfield 1958;1963)
What are the controllers on Export Production?
1) Ocean nutrient inventory
Nitrogen appears to be the most
important controlling factor that limit the
primary productivity of ecosystems.
Why ? (important; p339 in text)
• N is an essential nutrient for all living
organisms (nucleic acids and amino acids)
• N has many oxidation states, which makes
speciation and redox chemistry very
interesting
• NH4+ is the preferred N nutrient
Fixation
N2
Nitrification
Mix Layer
depth
NH4
NO3
Uptake
Phytoplankton
Mineralization
Grazing
Chlorophyll
Zooplankton
Mortality
Water column
Continental
shelf
sediments are
responsible for
up to 67% of
marine N
denitrification
estimates
Susp.
particles
Large
detritus
Nitrification
N2
NH4
NO3
De-nitrification
Sediment
Organic matter
Aerobic mineralization
De-nitrification − the removal of fixed N, mostly NO3-, resulting in
the formation of nonbiologically available N, primarily N2 gas
What are the controllers on Export Production?
2) Utilization of nutrients in HNLC
HNLC − High-Nutrient, Low-Chlorophyll
 It describe areas of the ocean where the
number of phytoplankton are low in spite of
high macronutrient concentrations (nitrate,
phosphate, silica acid).
 HNLC is thought to be caused by the scarcity
of iron (a micronutrient which phytoplankton
require for photosynthesis) and high grazing
rates of micro-zooplankton that feed on the
phytoplankton.
 The HNLC condition has been observed in the
equatorial and sub-arctic Pacific Ocean, the
Southern Ocean, and in strong upwelling
regimes, such as off central and northern
California and off Peru.
Southern Ocean HNLC
Southern Ocean HNLC
• Nitrate and phosphate
concentrations are high
year round but standing
stocks of phytoplankton
are always low (0.2-0.4
µg/L; normal yield is 1 µg
/L)
• Iron concentrations in
these waters are subnanomolar: the same as
those that are known to
limit growth of
phytoplankton,
particularly large species
such as diatoms.
• Addition of low levels of
Fe promotes growth of
large phytoplankton.
-bottle experiments
-in situ fertilization
experiments
One of the
possible solutions
to global warming
is to fertilize HNLC
ocean areas
lacking iron with
iron to increase
CO2 absorption
from
phytoplankton.
Redfield ratio (stoichiometry) − the molecular
ratio of carbon, nitrogen and phosphorus in
phytoplankton.
 Redfield (1963) described the remarkable
congruence between the chemistry of the deep
ocean and the chemistry of living things in the
surface ocean (i.e. phytoplankton). Both have N:P
ratios of about 16.
 When nutrients are not limiting, the molar
element ratio C:N:P in most phytoplankton is
116:16:1.
 Redfield thought it wasn't purely coincidental that
the vast oceans would have a chemistry perfectly
suited to the requirements of living organisms.
 He considered how the cycles of not just N and P
but also C and O could interact to result in this
match.
Modern Time
N2 fixation
De-nitrification
N = 25790
N* = N – 16 P
Biologically Mediated Exchange of CO2
Between the Ocean and Atmosphere
Regions with upwelling represent
the productivity
Equatorial
upwelling
Coastal
upwelling
Water
turbidity
ocean
Open ocean
continental shelves
upwelling regions
shallow estuaries
terrestrial area
deserts
forest; grassland
rain forests
farmlands
Both physical and biological processes in the ocean affect
the carbon cycle. In addition, physical processes
influence the net production of biological oceanography.
HW#7 due on 6 June of class time
HW#7 due on 6 June of class time
d)
e)
Question 3:
HW#7 due on 6
June of class
time