Oceanography Prelim 2

Ecosystem Function

primary production forms the base of marine food webs so understanding the variability of primary production in the ocean allows for a better understanding of all marine organisms

biogeochemistry

understand how life in the ocean affects global elemental cycles

global carbon cuycle

big topic because it is closely related to our global warming system

photosynthesis

consumes carbon dioxide gas to form the particulate carbon of algae

difference b/w photosynthesis and respiration

what sinks to the ocean floor

phyloplankton

vast majority of production in the ocean is carried out by chlorophyll containing single-celled organisms

three main groups of phyloplankton

-diatoms: require silica

-flagellates: motile so they are able to avoid sinking in calm waters

-photosynthetic bacteria: able to grow at very low nutrient concentrations

respiration

collectively the generation of CO2 by reactions needed to construct new complex molecules, and to provide basic metabolic needs, consume oxygen. (opposite of CO2)

net primary production (NPP)

difference between the amount of CO2 consumed by photosynthesis and the amount of CO2 produced by respiration. Equivalently, it is the new gain or net loss of carbon within the cell

compensation depth

the depth at which ambient light intensity is equal to the compensation light intensity

dominant cell diameters of phytoplankton assemblage

1.0- 10.0- 100.0

The 4 Phytoplankton Nutrients of Interest to

Oceanographers

1) Nitrogen, 2) Phosphorous, 3) Silica (for diatoms) and 4) Iron because at any given place or time in the ocean it is one of these

four nutrients that is in short supply and can limit the growth of phytoplankton

The Main Source of Nitrogen, Phosphorous and

Silica to the Surface Ocean

The main source of nitrogen, phosphorous and silica

to the surface layer of the ocean is by vertically mixing

or upwelling of nutrient-rich deep-water to the surface

Main source of iron input

dust blowing off of the continents. Southern Ocean

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 an associated 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

subtropical gyres

exhibit low primary production on a per meter square basis and very little seasonal variation

Equatorial Upwelling of Cold Nutrient-Rich Deep

Water in the Eastern Equatorial 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

Equatorial Pacific

Exhibits very little seasonal variability in primary production.

Atlantic

exhibits modest seasonal variability because of sudden seasonal trade wind bursts in the spring

Tidal Mixes

brings nutrients to the surface year-round

Coastal upwelling

seasonally superimposes additional nutrients

The Critical Depth

1. When cells are below the Compensation Depth, they lose carbon because light is too dim to allow for positive net primary production (NPP)

2. The average light level that phytoplankton experience over the course of a day becomes dimmer as mixing depth increases because

cells spend an increasing proportion of the day below the compensation depth in the dark

3. When cells mix below to the Critical Depth they have spent too much of the day below the

compensation depth losing carbon

net losses of carbon experienced while below the compensation depth exceed the net gains of carbon experienced while above the compensation depth

Spring Shoaling of the Thermocline above the ritical Depth

Brings about Positive Net Primary Production (NPP)

1. Changes in the mixing depth

relative to the critical depth

determines if NPP 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

critical depth (due to cold winter

storms) and NPP is negative

3. In spring, mixing is above the

critical depth (due to shallow

thermocline) and NPP is positive

Westerly Wind Region

• 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 of sunlight

- Nutrients are still plentiful from winter mixing so cells have lots of

nutrients and lots of sunlight 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

Global Distribution of Annual Net Primary

Production (NPP)

Oceanic NPP is about 46% of Global NPP

World Ocean Net Primary Production

While the Open Ocean (Trade Winds, Westerly Wind and Polar regions)

exhibit relatively low intensities 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

Pelagic

the water column environment

Benthic

the seafloor environment

Holoplankton

Planktonic organisms that live their entire life in fluid suspension. IE: Copepods

Meroplankton:

Planktonic organisms that spend only part of their life in fluid suspension

Autotrophs

Group of organisms whose carbon for growth comes from non-organic sources. For example, phytoplankton are autotrophs because they use CO2 for their carbon needs

Heterotrophs

Group of organisms whose carbon for growth comes from previously formed organic carbon material. For example, herbivorous zooplankton are heterotrophs because they consume phytoplankton for their carbon needs. Carnivores would also be heterotrophs

Trophic Level

Nutritional feeding level within a food chain or food web e.g., primary producer (i.e., autotroph), primary consumer (herbivore), secondary consumer (first carnivore), tertiary consumer (second carnivore),

et

Size

Size determines almost everything about an organism's position/role in

the community of pelagic organisms (except for the possibility of containing or not containing chlorophyll) (1/10) Marine food webs are said to be strongly size structured

Trophic Transfer Efficiency

depends on 1. Exploitation Efficiency and 2. Gross Production Efficiency

Exploitation Efficiency

1. strategies for detecting prey

2. strategies for capturing prey once detected

3. counter strategies to avoid detection in the first place

4. counter strategies to frustrate capture if detected

Diel Vertical Migration (Avoid Detection)

Much of the zooplankton community migrates up to the surface layer of the ocean at night to feed in the dark while also avoiding visual predators like small fish. During the day they migrate down to the safety of the darkness found at depth

Exploitation Efficiencies in Spring Blooms in the temperate north atlantic regions

During long winter periods grazers (copepods mainly) sink into the deep ocean and enter a diapause (i.e.,

hibernation) stage and thereby become decoupled from any variations in primary production above.

2. In spring, phytoplankton standing stock can initially grow to very high density because it is not held in check by strong grazing pressure (phytoplankton growth is decoupled from grazing) until the large grazers have a chance to come out of diapause, grow and reproduce to

the high numbers needed to control increases in phytoplankton abundance.

3. This allows for exceptional phytoplankton blooms during

the decoupled period

**Exploitation efficiency is very low in this case- much of the phyloplankton is not found by the grazers and instead sinks into the deep ocean as dead phytoplankton cells

Exploitation Efficiencies in Tropical Environments

1. Grazers remain active throughout

the year and consume

phytoplankton as fast as it is made.

2. Any increase in production is

quickly met by an increase in

consumption.

3. This leaves standing stock of

phytoplankton nearly constant

throughout the year

**Exploitation efficiency is very high in this case- almost all phyloplankton is found and consumed by grazers

Gross Growth (Production) Efficiency

Amount of CONSUMER

BIOMASS produced divided by amount of PREY INGESTED. This

efficiency ranges between 20% and 60%

Trophic Transfer Efficiency is a function of

Exploitation Efficiency (10% to 90% )

Gross Production Efficiency (20% to 60%)

The combined effect of both exploitation and gross production efficiencies yields an overall

trophic transfer efficiency of about 10% to 20%

The number of trophic levels between phytoplankton and

harvestable fish

smaller in high nutrient regions such as coastal upwelling regions

Highest production of harvestable fish is in the

coastal ocean region

1. The open-ocean region comprises most of the global ocean primary production, but phytoplankton in this region are small and so there are a lot of trophic steps (7 steps) to get to harvestable fish and each trophic step reduces carbon biomass

production by 1/10 so for 7 steps there is a 1/107 reduction altogether.

2. The coastal region has less overall primary production, but it benefits greatly by having just 2 trophic steps to harvestable fish which makes for very efficient transfer of carbon from primary producer to harvestable fish in this region and so it is this region that is the most productive for fish.

Use of Epifluorescent Microscopy and Fluorescent DNA Stains Became Widespread Between 1975 and 1985

• Dramatically increased estimates of bacterial concentrations in the ocean

• Also allowed easy distinction between autotrophic and

heterotrophic flagellate cells (i.e., chlorophyll containing or chlorophyll

lacking)

Bacteria-Sized Autotroph

-Came to be Known as Prochlorococcus

-The Discovery was Made using a New Technique called Analytical Flow Cytometry

-High Abundance, especially in Oligotrophic Regions

oligotrophic (low nutrient) open-ocean environments

the growth advantage goes to the smallest phytoplankton cells which are now recognized to be represented mainly by

Prochlorococcus.

Prochlorococcus

the main contributor to primary

production in open-ocean

environments.

-autotrophic bacterium

-responsible for more than a quarter of the global ocean primary production

Heterotrophic Bacteria

highly abundant in all ocean environments

Oligotrophic:

Pelagic environment (water column) that has naturally very low plant nutrient concentrations

--the vast subtropical gyres are oligotrophic

Eutrophic

Pelagic environment (water column) that has naturally high plant nutrient concentrations

--coastal upwelling zones are eutrophic

Global Carbon Cycle

The pathway that carbon takes from CO2(gas) to particulate organic

carbon (through photosynthesis), and on into particulate organic carbon of

higher trophic levels, varies when nutrient concentration varies

efficient biological carbon pump

when the dominant phytoplankton cells are large, the dominant grazers are large and their large fecal material easily sinks to the deep ocean taking organic carbon down with it

Inefficient biological pump

when the dominant phytoplankton is small and grazers are small and fecal matter is so small that it cannot easily sink and the particulate carbon is instead respired back to CO2

fixed chemical stoichiometry

all living things have a roughly fixed ratio of major elements in their cells

-because of this the pattern of cycling and export to the deep ocean for all of major elements will look quite similar

Nitrogen Cycling

the concept of new and recycled primary production

Total primary production

recycled + new primary production

New Primary production

uses Nitrate (NO3) from the deep ocean for its nitrogen source

Recycled Primary Production

uses Ammonia (NH4) generate by animal excretion in the upper ocean for its nitrogen source

Eutrophic (high nutrients)

conditions are dominated by large cell and most of the primary production is new production

oligotrophic (low nutrients)

conditions are dominated by small cells and most of the primary production is recycled production

As nutrient concentration is reduced

...competitive growth advantage shifts to small phytoplankton cells

Molecular Structure of Water

Water is a highly polar molecule

Hydrogen Bond

electrostatic attraction between partial + and - charges on separate polar molecules

Low Temperature Limit of Water

-Energy of the hydrogen bond is greater than the energy of the thermal bond

-maximum # of H bonds

-maximum order, low thermal motion

-regular lattice structure of ice

-solid

Intermediate Case of Water

-E h-bond is equivalent of E thermal

-clusters of H- bonded water (structural water)

-interspersed non-H bonded water (free water)

-liquid water

High temp limit of water

E h-bond < E thermal

-minimum number of H bonds

-minimum order, rapid thermal motion

-independant, non interacting gas molecules

-water vapor (gas)

Specific Heat Capacity

Amount of heat required to raise 1 gram of liquid water by 1 degree Celsius. This is among the highest of any substance on earth

Latent Heat Vaporization

Amount of heat required to convert 1 gram of liquid water to water vapor

-540 calories per gram

Waters high heat capacity

-means that it takes an exceptionally large amount of heat energy to change ocean temperatures

-all thing being equal- if you have more heat energy coming into the earth than leaving the earth you should observe a steady rise in global temperature

Condensation

latent heat released into the atmosphere by condensation of water vapor to form clouds and rain

Evaporation

Latent heat removed from the ocean and stored in the atmosphere in the form of water vapor

Molecular Properties of Water

-strong polar nature makes it a very good solvent for ionic constituents

-hydrogen bonds are weak, but below 100C they are strong enough to allow individual water molecules to bond temporarily with other water molecules to form liquid water

-high specific heat capacity

-high latent heat of vaporization- allows large amounts of heat to be removed from the ocean, stored at latent heat in the form of water vapor and then transported by winds to other parts of planet where it can then be released to the atmosphere as sensible hear upon precipitation

salinity

a measure of the salt concentration in a sea water example

-often expressed as the number of gramps of salt contained in a thousand grams of seawater

salt in the ocean

the magnitude of input and output rates have been roughly equal for millions of years

Surface ocean salt concentration

the total amount of salt in the ocean does not vary, but the unequal addition/removal of freshwater over the global ocean's surface creates large regional differences in surface ocean salinity

Salinities in the ocean

set at the air-sea interface

-overall, salinity is a direct function of evaporation minus precipitation

Atlantic Ocean Salinity

Once removed from the surface the salinity remains constant unless it mixes with other water masses

Salinity Variation

-while salinity may vary considerably in different regions, the relative proportion of one ion to another does not vary

Geochemical Cycles

keeping track of elemental inputs, chemical transformations and outputs

Conservation Constituents of seawater

those that are only varied by physical exchange processes at the sea surface.

Once the water leaves the surface, salinity, temperature and inert gas concentration are conserved

Non-conservative Constituents

those that are varied by processes (other than mixing) that occur anywhere in the water column

Plant Nutrients

Nonconservative constituents

1- Low in surface layer because of rapid uptake by phytoplankton in the presence of sunlight

2- High at depth because of respiration/ remineralization and no uptake by phytoplankton in the dark

global warming

expected to increase the strength of the thermocline and thereby reduced vertical mixing and diffusion across this boundary and make the oxygen minimum zone even lower

Photosynthesis Consumes

CO2 in the surface ocean to form particulate organic carbon

Respiration Produces

CO2 in the deep ocean