8 Primary Production(2)

8/9/2019 8 Primary Production(2)

1/64

Ocean Primary Production

1


2/64

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

2


3/64

Why Study Primary Production?

1. Base of the Food Web

2. Essential Element of the Global Carbon Cycle

3


4/64

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

4


5/64

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...

5


6/64

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

6


7/64

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

7


8/64

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

8


9/64

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

9


10/64

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

10


11/64

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

11


12/64

Pattern of Light and Nutrient Uptake byPhytoplankton

12


13/64

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

13


14/64

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)

14


15/64

Nutrient-Dependency of Primary Production

15


16/64

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

16


17/64

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

17


18/64

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

18


19/64

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

19


20/64

Iron Limitation...

20


21/64

Surface Nitrate Concentration

21


22/64

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

22


23/64

Ocean Primary Production Part II

23


24/64

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

24


25/64

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

25


26/64

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

26


27/64

Spatial Patterns of PrimaryProduction

27


28/64

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

28


29/64

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

29


30/64

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

30


31/64

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

31


32/64

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

32


33/64

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

33


34/64

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

34


35/64

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

35


36/64

5 Major Upwelling Regions in the World

36


37/64

SeasonalChange in thePrevailing

Wind Direction

37


38/64

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

38


39/64

• 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…)

39


40/64

Primary Production

Temporal Variations

40


41/64

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

41


42/64


43/64

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)

43


44/64

Change in Seasonal Thermocline Depth

44


45/64

Summer and Winter Differences in Mixing Depth Due to Changes in the Depth

of the Seasonal Thermocline in Westerly Wind Region

45


46/64

Light Limitation

46


47/64

Light Limitation

47


48/64

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.

48


49/64

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

49


50/64

Spring Phytoplankton Bloom Progression in

Westerly Winds Region

Red line = Thermocline Depth

50


51/64

Large Seasonal Increase in Primary Production Occurs in the North Atlantic Due To:

1. Deep WinterMixing

2. StrongSpringtimeStratification

51


52/64

• 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

52


53/64

Magnitude of Global Primary Production inDifferent Oceanic Provinces

53


54/64

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

54


55/64

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

55


56/64

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.

56


57/64

Evolving Concepts in OceanPrimary Production

57


58/64


59/64

High Nitrate Low Chlorophyll Regions (1. Southern Ocean , 2.Equatorial Pacific and 3. Subarctic Pacific)

59


60/64

The main source of Iron input to the surface ocean is from dust

blowing off of continents

60


61/64

Phosphate Limitation

61


62/64

Station Aloha in the North Pacific Subtropical Gyre

62


63/64

Time Series of N:P Ratio for Total Dissolved, Suspended Particulates in the

North Pacific Subtropical Gyre (from Karl 1999)

63


64/64

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

Documents

8 Primary Production(2)