Introduction to Primary Production, Introduction to Primary Production, Respiration and Nutrient CyclingRespiration and Nutrient Cycling –Cont. –Cont.

1) REVIEW

1) Why we care?A) Coupling of atmosphere and ocean

2) Ocean carbonate system & importance to chemistryin the of sea water

3) Processes in controlling distribution of oxygen & dioxide in the ocean.

4) Ocean circulation and oxygen, carbon dioxide and nutrients

Oscar Schofield (oscar@ahab.rutgers.edu)

THYLAKOID THYLAKOID MEMBRANEMEMBRANE

STROMASTROMA

CYTOSOLCYTOSOL

LHCLHC LHCLHC

1/2 O2 + 2H+H2O

4Mn Yze-

2H+

PQ

PQPQ

PQPQ

Qb

Qb

Cyt

och

rom

e b 6-

f-F

e nn

2H+

2H+2H+

PC/cyt c6

Ph

otos

yste

m I

CHLOROPLASTCHLOROPLAST

P700

A0

Fx

Fa/ Fb

Fd

AT

P s

ynth

ase

com

plex

CF0

CF1

3/2ADP + 3/2Pi 3/2ATP + 3/2Pi

NADPHH+ + NADP+6H+

1/2CH2O + 3/2ADP + 3/2PiH+ + 1/2CO2

THYLAKOID LUMENTHYLAKOID LUMEN

EP680

Pheo

e-

e-

Ph

otos

yste

m I

ID2D1

E

Qa

Qb

2 x e-

PH

Min

ute

s to

Hou

rs

NUCLEUSNUCLEUS

PLHC geneLHC gene

Repressor proteins

Day

s to

Wee

ks

fluorescence

light intensitylight intensity

oxyg

en

evolu

tion

oxyg

en

evolu

tion

0

0.5

1.5

2.5

3.5

0 50 100 150 200 250 3000

0.02

0.04

0.06

0.08

qu

an

tum

yie

ld o

f oxyg

en

evolu

tion

qu

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Pmax

Ik = Pmax/

OKAY:

Ocean Photosynthesis occurs

Why do you care?

t Processes/Platforms:Time and Space Scales

Dickey, 2001a

OCEANOGRAPHY IS FRIGGIN’ HARDOCEANOGRAPHY IS FRIGGIN’ HARD

Stewart et al., 1998

Monthly mean sea level at San Francisco

(1855-1990)

Annual averages of sea level

at Venice and Trieste(1875-1980)

(from N.Gruber)

Respiration

Photosynthesis

CO2

O2

CO2

O2

Abundance of Gases in Air and Seawater Abundance of Gases in Air and Seawater and Gas Exchangeand Gas Exchange

In addition to dissolved salts, organic molecules and suspended solids, sea In addition to dissolved salts, organic molecules and suspended solids, sea water contains water contains dissolved gasesdissolved gases. Most of these gases enter the sea from the . Most of these gases enter the sea from the atmosphere, but others are produced within the ocean by marine organisms or atmosphere, but others are produced within the ocean by marine organisms or are derived from the Earth’s interior (e.g. helium).are derived from the Earth’s interior (e.g. helium).

CO2

CO2

O2

O2

CH3He

Diffusion or gas exchange

There will be a net uptake (or loss) of a gas by sea water from the There will be a net uptake (or loss) of a gas by sea water from the atmosphere until the sea water reaches atmosphere until the sea water reaches saturationsaturation. At saturation, the . At saturation, the gas exchange process is said to be in equilibrium, i.e. the rates of gas exchange process is said to be in equilibrium, i.e. the rates of exchange in and out are equal.exchange in and out are equal.

Bud Bud

time

Bud

Saturation values are gas concentrations when a solution (here we are concerned with sea water but the term applies to any solution) has reached equilibrium with its overlying gas mixture (here the atmosphere). That is, saturation values are the most chemically favorable conditions. Since some gases are more soluble than others, the proportion of gases dissolved in saturated sea water is different from the proportion in the atmosphere.

 

0.016 0.009 Ar

0.014 0.0003 CO2

0.343 0.209 O2

0.626 0.780 N2

Proportion in

saturated sea

Proportion in

AirGas

at 15 C and 35‰

 The gas solubilities of CO2 > Ar > O2 >N2

A saturation value depends on:-temperature (boiling water)-salinity (boiling water)

 Generally, cold water can hold more dissolved gases than warm water of the same salinity, and fresh water can hold more dissolved gases than salt water of the same temperature. 

 

Conditions Saturation Conc. for O2 (mol/kg)

Freshwater (25oC) 258

Seawater (25oC) 206

Freshwater (5oC) 398

Seawater (5oC) 308

Carbonate System

Although COAlthough CO22 is a soluble gas in sea water, it also is a soluble gas in sea water, it also

reacts chemically with waterreacts chemically with water and is present in sea water and is present in sea water as a one of two dissolved anions, as a one of two dissolved anions, bicarbonatebicarbonate and and carbonatecarbonate, and as , and as carbonic acid.carbonic acid.

FORMS of CARBON DIOXIDE IN SEA WATERcarbon dioxide CO2 (dissolved)

carbonic acid H2CO3

bicarbonate HCO3-

carbonate ion CO32-

Reactions 2 and 3 (below) are acid-base reactions. Bicarbonate ion which is one of the major ions in sea water can act as both an acid and a base.

 1). CO2 + H2O H2CO3

 2). H2 CO3 + H2O H3O

+ + HCO3-

acid base acid base 

3). HCO3- + H2O H3O

+ + CO32-

acid base acid base 

pH is a short hand scale for representing the acidity or alkalinity of a solution which depends on the concentration of hydrogen ions (H+) (or

hydronium ions, H3O+ ) in the solution. pH = - log (H+)

The carbonate system is largely responsible for maintaining seawater pH close to a value of 8. i.e., slightly alkaline. This is largely because in the ocean, sea water is also in contact with sediments that contain carbonate minerals the most important of which is calcite (CaCO3).

 If excess acid is added to the deep ocean (say for example via hydrothermal vent emissions) the acid is neutralized by reacting with carbonate ions in solution, and these are replaced by dissolution of carbonates in the sediments. If excess base is added more carbonate minerals precipitate and and are removed to the sediments.

Respiration

Photosynthesis

CO2

O2

CO2

O2

phytoplankton need: 

lightCO2

nutrientswater

 In the ocean, light and nutrient availability may limit the rate of photosynthesis.

THE MAJOR FORESTS IN THE SEA ARE PHYTOPLANKTONTHE MAJOR FORESTS IN THE SEA ARE PHYTOPLANKTON

In the text, photosynthesis is represented very simply . It can be represented more completely, if we think of it as a process that generates the organic matter in phytoplankton cells. Phytoplankton organic matter is made up of a large number of organic compounds (e.g. proteins, lipids, carbohydrates), but on average it has atomic ratios of C to N to P of 106 to 16 to 1. Thus, the process of photosynthesis can be represented as: hv

106CO2 + 122H2O + 16HNO3 + H3PO4 (CH2O)106(NH3)16H3PO4 + 138O2

 

This reaction illustrates the need for the nutrients: nitrate and phosphate. It also shows that for every 106 CO2 molecules taken up, approximately

138 O2 molecules are liberated.

 

Irradiance Intensity

Z (meters)

Ik

Photosynthesis

BiomassNutrients

In the photic zone, photosynthesis leads to high oxygen concentrations and low total-CO2. When photosynthesis

rates are high, oxygen concentrations can rise above saturation. This is a state called supersaturation.

Marine bacteria, fungi, protozoans and animals that can not get energy from photosynthesis, decompose organic matter. This process is called respiration. It can be represented as the reverse of photosynthesis. (CH2O)106(NH3)16H3PO4 + 138O2 106CO2 + 122H2O + 16HNO3 + H3PO4

Respiration puts CO2 and nutrients back into the water. Respiration depletes

O2 , making deep waters undersaturated with respect to the oxygen in the

atmosphere. Respiration occurs throughout the entire water column and in sediments, but its effect on the distributions of oxygen and total-CO2 are usually not seen until

depths below the euphotic zone.

Depth Distributions of Oxygen and Total-CO2/ Light/

Photosynthesis and Respiration

In the upper ocean, these two profiles appear almost as mirror images. This is because both oxygen and carbon dioxide are involved in the production and destruction of organic matter, i.e. the soft tissues of marine plants and animals. CO2 is also taken up by some plants and

protozoa to make calcium carbonate (CaCO3) hard parts.

Since these shells dissolve at depth in the ocean, total-CO2 profiles may not co-vary as closely with oxygen

profiles at depth.

The greatest changes in oxygen and total-CO2

occur in the uppermost ~80 m of the ocean. This depth range corresponds to euphotic zone, the zone where there is sufficient light for phytoplankton (single celled plants that have chlorophyll) to grow through the process of photosynthesis.

The Biological Pump About 10% of the carbon fixed by photosynthesis in the surface layer each year, escapes this layer by sinking into the deep ocean. This flux is called New Production or Export Production.

Physical mixing processes

Nutrients

IrradianceIrradiance

PhytoplanktonPhytoplankton

SinkageSinkage & & SenescenceSenescence

Particle DynamicsParticle Dynamics

Carbon FluxCarbon Flux

ZooplanktonZooplankton

Higher Trophic LevelsHigher Trophic Levels

Nutrients

Biologically derivednutrients

Newproduction

Regeneratedproduction

Exportproduction

The biological pump is an important mechanism for

removing fossil fuel CO2 from the

atmosphere into the ocean because

 

Sequestration of Atmospheric CarbonSequestration of Atmospheric Carbon

Nearly all of the sinking particulate organic matter is converted back to CO2 through

respiration in the deep ocean. Photosynthesis followed by a) the transport of carbon into the deep ocean and b) the respiration of the majority of this carbon, is called the "biological pump".

 

The biological pump is an important mechanism for removing fossil fuel CO2 from the atmosphere into the ocean because

 1. it lowers surface CO2 concentrations, and

2. it transports particulate carbon into the deep-ocean, where even if it is oxidized back to CO2, it is removed from contact with the

atmosphere for on the order of 500 years. Models show the pump is doubly important at high latitudes because here the waters of the deep ocean are formed. First of all cold waters have higher saturation values for gases than warm. Then if primary production rates are high too, even more CO2 will exchange

from the atmosphere to the cold surface waters of the arctic and antarctic regions. The sinking of this water "captures" the CO2 and

removes it from contact with the atmosphere. 

Ocean circulation eventually brings the respired CO2 back to the surface, but the

net effect is to keep the deeper ocean enriched in dissolved inorganic carbon.

HabWatch Workshop, Villefranche sur Mer, 11-21 June 2003

SH: Coastal upwelling

Open University, 1998

Pacific Ocean

CO2 rich water

CO2 off gas (bud)

Geographic Differences in Nutrient Profiles

(Takahashi et al 1995)

Net CO2 flux

SeaWiFS Team/GSFC/NASA

Surface distribution of chlorophyll a using SeaWiFS data sets:Note physical forcing effects: Coastal, Equator, North Atlantic

Nutrient Limitation

Many elements are necessary for life, but only those in short supply are limiting to photosynthesis. Oceanographers consider nitrate, phosphate, silica, iron and several other trace metals to be the most biolimiting elements. Silicon is important for the growth of diatoms. Iron is required for photosynthetic electron transport and the synthesis of chlorophyll. Nutrient profiles generally increase with depth. Concentrations may be below detection in surface waters, especially in the open ocean. 

Nutrient sources to surface waters are:rivers and land runoffupwellingatmosphere

 The most productive regions of the oceans are the coastal regions because this is where upwelling is strongest and where river and land runoff meet the sea. Here nutrients result in high productivity rates, which in turn result large fisheries. 

40N

74W75W

39N

Temperature oC19 20 21 22 24

July 6, ’98 - AVHRR

FieldStation

LEO

40N

74W75W

39N

FieldStation

Chlor-a (mg/m3)

.1 .3 .5 1 2 4

July 11, ‘98 - SeaWiFS

LEO

Barnegat

Cape May

New Jersey Coastal Upwelling

HistoricalHypoxia/Anoxia

Geographic Differences in Nutrient Profiles