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8/9/2019 8 Primary Production(2)
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Ocean Primary Production
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Ocean Primary Production1. Why Study Primary Production
2. Requirements for Growth
3. Spatial Variations in the Level of Primary Production Over theGlobal Ocean Due to Biological/Physical Interactions
4. Temporal Variations in the Level of Primary Production Due toBiological/Physical Interaction
! Spring Phytoplankton Bloom and the Critical Depth Theory
5. Total Global Ocean Primary Production
6. Evolving Concepts
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Why Study Primary Production?
1. Base of the Food Web
2. Essential Element of the Global Carbon Cycle
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Primary production forms the base of marine food webs so understanding the variability of primary production in the ocean allows for a better understandingof the variability of all marine organisms --> Ecosystem Function
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Magnitude of CO2 flux between Land and Ocean Reservoirs
1. The global carbon cycle is a big topic because it is closelyrelated to our global warming problem
2. Photosynthesis consumes carbon dioxide gas to form the particulate carbon of algae
3. Respiration by all organisms produces carbon dioxide gas
4. The difference between photosynthesis and respirationis what sinks to the ocean floor
Another major goal of biological oceanography is to understand how life in the
ocean affects global elemental cycles => Biogeochemistry...
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Outline Part I requirements for growth
1. Some Definitions
Phytoplankton, Photosynthesis and Primary Production
2. Effects of Light Intensity on Primary Production
3. Effects of Nutrient Limitation on Primary Production
4. Distribution of Nutrients in the Ocean
5. Summary
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Some Definitions…
Plankton: Small organisms that drift with the ocean currents
Phytoplankton: Small cells (often single cells, but sometimes chains or
colonies of many cells) that contain chlorophyll and drift with oceancurrents
Photosynthesis refers to the chemical reaction that uses water andcarbon dioxide (gas) and the energy of sun light to form glucose and
oxygen. Glucose then serves as the energy source for all subsequent biochemical reactions. The overall photosynthetic reaction is given by:
6CO2 + 6H2O + Light Energy -> C6H12O6 + 6O2
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Light and Nutrient RequirementsStrictly speaking, photosynthesis onlydepends on the availability of water,carbon dioxide and sunlight. Primary
production, however, involves thesynthesis of complex organic
compounds and therefor requires the uptake of plant nutrients for theconstruction of complex molecules thatare needed to form new cellularcomponents.
Consequently, the magnitude of
primary production depends not only onsunlight, but also on the availability ofessential plant nutrients
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Net Primary ProductionReactions needed to construct new complex molecules, and to provide basalmetabolic needs, consume oxygen and generate CO2 which is exactly the opposite
of what happens during photosynthesis. Collectively the generation of CO2 by
this process is referred to as respiration.
Net Primary Production (NPP) is the difference between the amountof CO2 consumed by photosynthesis
and the amount of CO2 produced by
respiration.
Equivalently, it is the Net Gain orNet Loss of carbon within the cell
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The Big Picture About Primary Production...
1. Primary Production Effectively Consumes Carbon Dioxide Gas
and forms particulate organic carbon that can sink into the deep
ocean
2. Primary Production Makes Oxygen
3. Primary Production Requires Light and Essential Plant Nutrients (e.g.,N, P, Si, Fe and a bunch of others)
4. Net Primary Production is Photosynthesis - Respiration = Net Gain orNet Loss of Carbon in the Cell
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Major Phytoplankton GroupsThe vast majority of primary production in the ocean is carried out bychlorophyll containing single-celled organisms referred to collectively as Phytoplankton. There are three main groups of phytoplankton.
1. Diatoms: Require Silica
2. Flagellates: Motile so they are able to avoid sinking in calm waters
3. Photosynthetic Bacteria: Able to grow at very low nutrient concentrations
Bacteria
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Pattern of Light and Nutrient Uptake byPhytoplankton
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Light-Dependency of Net Primary Production1. At light levels below the compensation light level, phytoplankton cells do not have sufficient light to
photosynthesize fast enough to meet their basal metabolic needs and so cell respiration exceeds photosynthesis and this then leads to negative values of net primary production.
2. At low light levels, phytoplankton are light limited.
3. At optimal light levels, phytoplankton are light saturated
4. At very high light levels, phytoplankton are photoinhibited
5. The depth at which the ambient light intensity is equal to the compensation light intensity is called thecompensation depth
n e t p r i m a r y p r o
d u c t i o n
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Nutrient-Dependency of Primary Production1. The amount of nutrient needed for growth by an individual phytoplankton cell is proportional to the
cell’s mass or, equivalently, to the cell’s volume.
2. The amount of nutrient that can be transported into a cell is proportional to the cell’s surface area .
3. Small cells have a larger surface area to volume ratio than do larger cells so smaller cells can grow better at lower nutrient concentrations
(smaller cells can more efficiently supply their needs)
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Nutrient-Dependency of Primary Production
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Phytoplankton cells need a wide range of different chemical elements(nutrients) for growth (e.g., Cu, Zn, etc...), but there are four nutrients
that are of most interest to oceanographers -
Nitrogen
Phosphorous
Silica ( for diatoms)
Iron
The interest is due to the fact that any given place or time in the oceanit is one of these four nutrients that is in short supply and can limit thegrowth of phytoplankton
The 4 Phytoplankton Nutrients of Interest to Oceanographers
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1. The main source of nitrogen, phosphorous and silica to thesurface layer of the ocean is
by vertically mixing orupwelling of nutrient-richdeep-water to the surface
2. The example data given at the right is for nitrate, but
the same general patternholds for phosphate andsilicate.
The Main Source of Nitrogen, Phosphorous and Silica to theSurface Ocean
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uestionGiven... 1. Most nutrients (except for iron as you soon will see) sit in the deeper part of
the ocean and are occasionally brought to the surface ocean to “feed the phytoplankton”
2. The the main mechanism for getting deep nutrients into the surface (sunlit) layer of the ocean is mixing across the thermocline/pcynocline
Then-- What do you expect might happen to ocean primary production undera global warming scenario that enhances only temperature of the surface layerof the ocean and leaves the deep layer cold - i.e., strengthens the thermocline/
pcynocline
a) Increase
b) Decrease
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1.The thermocline acts to hold phytoplankton near the sunlitsurface ocean
2.The thermocline also acts as asignificant barrier to upwardmixing of nutrient rich deep water.The stronger the thermalstratification the strong the
inhibition of nutrient mixing
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Iron Limitation...
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Surface Nitrate Concentration
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The main source of Iron input to the surface ocean is fromdust blowing off of continents
1. Southern Ocean
2. Subpolar NorthPacific
3. Eastern Equatorial
Pacific
Iron Limited Regions
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Ocean Primary Production Part II
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Summary of Light and Nutrient Control of Primary Production
1. In the surface ocean, light is often plentiful but nutrients are often limiting
2. In the deep ocean, nutrients (except iron) are
often plentiful but light is limiting
3. The surface and deep waters are usuallyseparated by a thermocline
4. Primary production is enhanced whenever the physical oceanography allows for the best of
both worlds (high light and high nutrients) tocome together in the same place at the same time
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The main source of Iron input to the surface ocean is fromdust blowing off of continents
1. Southern Ocean
2. Subpolar NorthPacific
3. Eastern Equatorial
Pacific
Iron Limited Regions
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Outline Part II - Spatial Patterns Due to Physical BiologicalInteractions
Subtropical Gyre Regions
Equatorial Pacific and Atlantic Regions
Coastal Regions
Outline Part III - Temporal Patterns and also Overall Global Ocean Production
Westerly Wind Belt Region and the Critical Depth Concept
Magnitude of Global Primary Production
Current/Future Trends in Primary Production Research
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Spatial Patterns of PrimaryProduction
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Surface convergence of the Ekman Layer in the subtropics (forced by the Trade and Westerly Winds) forms a mound/lens of warm (low-nutrient) water (and associated gyre rotation) and anassociated downward surface layer velocity into the deeper ocean.
Taken together, this makes it difficult for nutrients to move upward to the the surface ocean and so primary production of exceptionally low year-round in the subtropical gyres
low surface layer nutrients present
through all seasons
convergence of the Ekman Layer insubtropical gyres
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Subtropical Gyres Exhibit Low Primary Production (on a per meter square basis) and
Very Little Seasonal Variation
Winter
FallSummer
Spring
0 75 150
Seasonal Net Primary Production (g C m-2 season-1)
12510025 50
90 N
60 N
30 N
0
30 S
60 S
90 S
90 N
60 N
30 N
0
30 S
60 S
90 S
90 N
60 N
30 N
0
30 S
60 S
90 S
90 N
60 N
30 N
0
30 S
60 S
90 S
60 W60 E 120 E 180 W 120 W 0 60 W60 E 120 E 180 W 120 W 0
60 W60 E 120 E 180 W 1 20 W 0 60 W60 E 120 E 180 W 120 W 0
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Equatorial Upwelling of Cold Nutrient-Rich Deep Water in the EasternEquatorial Pacific and Atlantic
1. Easterly Trade Winds Cause Surface Waters to Pile Up in the West
2. Themocline is Deep in the West and Shallow in the East
3. Proximity of Thermocline Near the Surface in the East Enhances Upwelling of Cold and Nutrient-Rich Deep-Water to the Lighted Region of the Surface Ocean and Thus Enhances Biological
Productivity in this Area
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The Equatorial Pacific Exhibits Very Little Seasonal Variability in Primary
Production. Atlantic Exhibits Modest Seasonal Variability Because of SuddenSeasonal Trade Wind Bursts in Spring
Winter
FallSummer
Spring
0 75 150
Seasonal Net Primary Production (g C m-2 season-1)
12510025 50
90 N
60 N
30 N
0
30 S
60 S
90 S
90 N
60 N
30 N
0
30 S
60 S
90 S
90 N
60 N
30 N
0
30 S
60 S
90 S
90 N
60 N
30 N
0
30 S
60 S
90 S
60 W60 E 120 E 180 W 120 W 0 60 W60 E 120 E 180 W 120 W 0
60 W60 E 120 E 180 W 120 W 0 60 W60 E 120 E 180 W 120 W 0
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Coastal Re ions
1. Tidal Mixing occurs in shallow continental shelf regions
Seasonally Steady
Mixes the water column from bottom to top and brings bottom water rich in nutrients to the ocean surface
2. Coastal Upwelling results from Wind/Ekman Offshore Transport
Seasonally Variable
Greatly enhances upward movement of deep water that is rich innutrients
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1. Tidal mixing occurs as the tide wave motion accelerates horizontally when it is squeezed onto the shallow continental shelf.
2. The high speed tidal currents break into vigorous turbulence that causesmixing from top to bottom of the continental shelf water column
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Vertical Distribution of Chlorophyll and Temperature Over the Continental
Shelf (vertically uniform green region)
Shelf Region
Tidal MixingFront
Offshore Deep Ocean
Notice the abrupt change in chlorophyll distribution into fully mixed from top to bottom(left side of figure) on the shelf side of the tidal mixing front
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Coastal Upwelling Along the Washington Oregon Coast
1. Wind blowing out of the northdrives the Ekman layer to theright (northern hemisphere) which is offshore
2. The offshore transport of theEkman surface layer is replaced by upwelling of deeper coldnutrient-rich water along thecoast
3. Wind blowing out of the south drives the Ekman Layer again to the right (becausenorthern hemisphere) which is onshore
4. The onshore transport of the Ekman surface layer is driven downward - a processcalled downwelling
upwelling downwelling
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5 Major Upwelling Regions in the World
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SeasonalChange in thePrevailing
Wind Direction
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Seasonal Changes in Coastal Primary Production
Chlorophyll Concentration (mg/m3)
.01 1.0 10.0 30.0
UpwellingNon
Upwelling
Tidal Mixing brings nutrients to the surface year-round.Coastal Upwelling seasonally superimposes additional nutrients
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• Dramatic increases in primary production occur wherever and whenever deep - nutrient rich - water is brought up to the oceansurface
• Subtropical Gyre Primary Production:
• low primary production year-round because of persistent lens of warm water
• Equatorial Primary Production: • Modest seasonality in the Atlantic • Strong interannual variation in the Pacific because of El Nino
(more on this in later lectures)
• Coastal Primary Production
• high year round • exceptionally high during upwelling periods in certain regions
California, Chile, Portugal, Northwest Africa, South Africa and Arabian Peninsula
Conclusions (So Far…)
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Primary Production
Temporal Variations
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Outline Part II - Spatial Patterns Due to Physical BiologicalInteractions
Subtropical Gyre Regions
Equatorial Pacific and Atlantic Regions
Coastal Regions
Outline Part III - Temporal Patterns and also Overall GlobalOcean Production
Westerly Wind Belt Region and the Critical Depth Concept
Magnitude of Global Primary Production
Current/Future Trends in Primary Production Research
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Westerly Wind Belt Region (c.a. 30-60 degree latitude)
1. Strong Seasonal Variation in Sea-Surface Temperature in Both the Pacific and Atlantic
2. Strong Seasonal Change in the Depth of the Seasonal Thermocline in the Atlantic - but not the Pacific (the Pacific is not salty enough)
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Change in Seasonal Thermocline Depth
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Summer and Winter Differences in Mixing Depth Due to Changes in the Depth
of the Seasonal Thermocline in Westerly Wind Region
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Light Limitation
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Light Limitation
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The Critical Depth1. When cells are below the Compensation Depth,
they lose carbon because light is too dim to allowfor positive net primary production (NPP)
2. The average light level that phytoplanktonexperience over the course of a day becomes
dimmer as mixing depth increases because cellsspend an increasing proportion of the day belowthe compensation depth in the dark
3. When cells mix below to the Critical Depth theyhave spent too much of the day below thecompensation depth losing carbon
net losses of carbon experienced while belowthe compensation depth exceed the net gainsof carbon experienced while above thecompensation depth.
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Spring Shoaling of the Thermocline above the Critical Depth Brings about Positive NetPrimary Production (NPP)
1. Changes in the mixing depth relative to the critical depth determines ifNPP is positive or negative and
thereby determines if phytoplankton blooms will occur (i.e., if/when there is positive NPP) .
2. In winter, mixing is below the criticaldepth (due to cold winter storms) andNPP is negative
3. In spring, mixing is above the criticaldepth (due to shallow thermocline) andNPP is positive
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Spring Phytoplankton Bloom Progression in
Westerly Winds Region
Red line = Thermocline Depth
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Large Seasonal Increase in Primary Production Occurs in the North Atlantic Due To:
1. Deep WinterMixing
2. StrongSpringtimeStratification
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• Deep vertical mixing in winter
– brings high levels of nutrients to the surface
– causes phytoplankton to mix below the critical depth and so even though nutrients are plentiful, cells spend too much time in the dark and NPP is light limited.
• Formation of shallow thermocline in spring
– depth of mixing confined above the shallow thermocline and above the critical depth so phytoplankton spend much of the day high in the water column where there is lots ofsunlight
– Nutrients are still plentiful from winter mixing so cells have lots of nutrients and lots ofsunlight and spring bloom forms
• Continued stratification in summer
– Mixing remains shallow, and above the critical depth, but nutrients are depleted and NPP is nutrient limited.
Westerly Wind Region
Polar Ocean Regions same as temperate ocean, but melting of ice shelf enhances stratification
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Magnitude of Global Primary Production inDifferent Oceanic Provinces
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Field, C. B., M. J. Behrenfeld et al. (1998) Sci. 281:237-240
NPP (g C m-2 yr-1)
Global Distribution of Annual Net Primary Production (NPP)
1. Global NPP is about104 Gt C yr-1
2.Terrestrial NPP is about54% of Global NPP
3.Oceanic NPP is about 46% of Global NPP
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World Ocean Net Primary Production
Total Global Ocean = 50 Gt Carbon per Year
Note: Gt = Gigaton = 109 metric tones = 1015 grams
Longhurst et al. (1995), Journal of Plankton Research, 17 (6): 1245-1271
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World Ocean Net Primary Production
While the Open Ocean (Trade Winds, Westerly Wind and Polar regions) exhibit relatively lowintensities of primary production (NPP per square meter) relative to coastal regions, they contribute
most (71%) as a whole to the global ocean total NPP because of the vast areas comprising these regions.
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Evolving Concepts in OceanPrimary Production
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High Nitrate Low Chlorophyll Regions (1. Southern Ocean , 2.Equatorial Pacific and 3. Subarctic Pacific)
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The main source of Iron input to the surface ocean is from dust
blowing off of continents
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Phosphate Limitation
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Station Aloha in the North Pacific Subtropical Gyre
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Time Series of N:P Ratio for Total Dissolved, Suspended Particulates in the
North Pacific Subtropical Gyre (from Karl 1999)
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1. Nitrogen most often limits the growth of phytoplankton in theocean, but iron and phosphate may limit growth in certainimportant oceanic regions.
2. Global ocean primary production is of the same order ofmagnitude as the global terrestrial system.
3. The rate of primary production per square meter in the open
ocean is low, but because this region is so vast, the open ocean asa whole dominates total global ocean primary production.
Conclusions