Oceanography - Nutrient Cycling - Chapter 6

What is a biogeochemical cycle?

The transfer of compounds or nutrients between living and nonliving components of an ecosystem

What is one major purpose of biogeochemical cycling?

To transform elements into biologically usable forms

What is an example of converting nitrogen into a biologically usable form?

N2 can be converted into NO3-

What is an example of converting carbon into a biologically usable form?

CO2 can be converted into organic carbon

What are important nutrients in marine biogeochemical cycles?

C P N Si S Fe and others

What are major nutrient sources in the ocean?

The atmosphere land organisms and upwelling of deep nutrient-rich water

What nutrients can come from the atmosphere?

N2 and CO2

What nutrients commonly come from land?

P Si and Fe

What nutrients can organisms provide?

Organic N and organic C

How does upwelling act as a nutrient source?

It brings deep nutrient-rich water toward the surface

What are major nutrient sinks in the ocean?

Organisms export to the deep ocean and sedimentation

Why are organisms considered a temporary nutrient sink?

They temporarily store nutrients in biomass before those nutrients are recycled or exported

What are macronutrients?

Nutrients required in relatively large amounts

What are examples of macronutrients?

N P and Si

What are micronutrients?

Nutrients required in smaller amounts

What are examples of micronutrients?

Fe Mg and other trace metals

What are constituent elements?

Elements required for life that are already abundant

What are examples of constituent elements?

C H and O

What is an inorganic compound in this presentation?

A compound lacking both C and H

What are examples of inorganic compounds?

N2 and CO2

What is an organic compound in this presentation?

A compound containing C and H

What are examples of organic compounds?

Urea and organic matter

What are dissolved compounds?

Small compounds that pass through filtration

What are examples of dissolved pools?

DOC DIC DON DIN and CDOM

What types of material can contribute to dissolved compounds?

Soil particles soluble plant material and cellular debris

What are particulate compounds?

Larger compounds and cells that are collected by filtration

What are examples of particulate pools?

POC and PON

What are examples of particulate material?

Cells fecal pellets detritus and sediments

What does DOC stand for?

Dissolved organic carbon

What does DIC stand for?

Dissolved inorganic carbon

What does DON stand for?

Dissolved organic nitrogen

What does DIN stand for?

Dissolved inorganic nitrogen

What does POC stand for?

Particulate organic carbon

What does PON stand for?

Particulate organic nitrogen

Approximately what percentage of phytoplankton tissue is oxygen?

About 60 percent

Approximately what percentage of phytoplankton tissue is carbon?

About 20 percent

Approximately what percentage of phytoplankton tissue is hydrogen?

About 10 percent

Approximately what percentage of phytoplankton tissue is made of macronutrients?

About 1 to 5 percent

Approximately what percentage of phytoplankton tissue is made of micronutrients?

Less than 0.05 percent

What kinds of changes occur in biogeochemical pathways?

Phase changes inorganic to organic transformations and reduction oxidation reactions

What does reduction mean?

Gain of electrons and often loss of oxygen

What does oxidation mean?

Loss of electrons and often gain of oxygen

What is an example of oxidation in the nitrogen cycle?

NH3 to NO2- to NO3-

What elements are important in carbohydrates?

C

What elements are important in lipids?

C N P and S

What elements are important in proteins?

C N P and S

What elements are important in nucleic acids?

C N and P

What elements are important in cell membranes?

C N and P

What nutrients can serve as enzyme cofactors?

Fe Zn Cu and vitamins

What elements can act as photosystem ligands?

Fe S and Mn

What elements are important in pigments?

C N and Mg

What elements are important in biological energy molecules?

C N and P

Who was Alfred C. Redfield?

An American oceanographer known as the grandfather of ocean biogeochemical cycles

What is the Redfield ratio?

The molar ratio of elements in average phytoplankton biomass

What is the Redfield C:N:P:Fe ratio?

106:16:1:0.0075

What is the Redfield N:P ratio?

16:1

What is important about the Redfield ratio in ocean water?

Average ocean nutrient ratios are similar to average phytoplankton biomass ratios

What can deviations from the Redfield ratio suggest?

Nutrient limitation

What is eutrophication?

The accumulation of excess nutrients in an ecosystem

What does eutrophication do to nutrient limitation?

It releases the ecosystem from nutrient limitation

What can eutrophication cause?

Algal blooms including potentially harmful algal blooms

What does HAB stand for?

Harmful algal bloom

How can eutrophication lead to low oxygen?

Decomposition of excess organic matter consumes O2

How does decomposition during eutrophication affect CO2?

It produces CO2

How does eutrophication affect oxygen conditions?

It can create hypoxic or anoxic conditions

How can eutrophication affect pH?

Increased CO2 from decomposition can decrease pH

What is one major ecological consequence of eutrophication?

Fish kills

What is eutrophication the opposite of?

Oligotrophic conditions

What is nutrient limitation?

A condition where insufficient nutrient concentrations restrict biological production

How does nutrient limitation affect primary production?

It sets an upper limit on primary production

How can nutrient limitation affect community composition?

Different phytoplankton have different nutrient requirements so the limiting nutrient can favor some groups over others

What special nutrient ability do some cyanobacteria have?

They can fix N2

Why do diatoms have a special nutrient requirement?

They require relatively large amounts of silica

What association involving Phaeocystis is mentioned in the presentation?

Phaeocystis can depend on bacteria and vitamin B12

What does N:P greater than 16 suggest?

Phosphorus limitation

What does N:P less than 16 suggest?

Nitrogen limitation

What is the largest carbon reservoir?

The ocean

How much more carbon does the ocean contain than the atmosphere?

About 60 times more

About what fraction of DIC is associated with ocean atmosphere exchange in the presentation?

About 90 percent

What can oceanic CO2 become?

DIC through carbonate chemistry or organic carbon through photosynthesis

What process converts organic carbon back into DIC at depth?

Remineralization

What are the two major carbon pumps discussed?

The solubility pump and the biological pump

What is the solubility pump?

The physical transport of dissolved CO2 into the ocean interior through gas exchange and circulation

What factors affect CO2 solubility in seawater?

Temperature pCO2 and wind

Where does more CO2 dissolve in the ocean?

At high latitudes

Why does more CO2 dissolve at high latitudes?

Cold water can hold more dissolved CO2

What is the net CO2 flux at high latitudes?

From the atmosphere into the ocean

How does thermohaline circulation help move carbon?

Cold CO2-rich water sinks and transports carbon into the deep ocean

Where can deep water later upwell?

In warmer tropical regions

Why can tropical upwelling release CO2?

Warm water holds less CO2

What is the net CO2 flux in warm upwelling regions?

From the ocean to the atmosphere

What is the timescale of the solubility pump?

Hundreds to thousands of years

How do the solubility pump and biological pump interact?

They work together to transport carbon from the surface ocean into deeper waters

What is the biological pump?

The biological transfer of carbon from surface waters to deeper waters through photosynthesis sinking organic matter and remineralization

What happens to CO2 during photosynthesis?

It is fixed into organic carbon

How does photosynthesis affect surface ocean pCO2?

It lowers surface ocean pCO2

What happens to much of the organic matter produced at the surface?

It sinks and is decomposed or consumed

What can decomposed organic matter become?

DOC and DIC

Approximately what percentage of surface carbon is remineralized according to the presentation?

About 65 percent

Approximately what percentage of carbon reaches the seafloor?

About 0.1 percent