Nutrient Cycles in Marine Ecosystems

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Nutrient Cycles in Marine Ecosystems

• Inputs and outputs to the reservoir of dissolved
  nutrients
• The biological uses of nutrients
• Nutrient Availability and Productivity

2

• Nutrient chemical that an organisms needs to
  live and grow (or a substance used in an
  organisms metabolism) which must be taken from
  the environment

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Demonstrate an understanding that there is a
reservoir of nutrients dissolved in the surface
layer of the ocean
4

• Algae require light for photosynthesis
• Light intensity decreases with depth so
  photosynthesis is restricted to the surface layer
• Known as the photic zone
• Varies from 30 m to 150 m (much less in turbid
  water)
• Surface layer contains many ions

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Remember These?
Ion Mean concentration in seawater (ppt)
chloride 19.345
sodium 10.752
sulphate 2.701
magnesium 1.295
calcium 0.416
hydrogen carbonate 0.145
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• These ions, together with nitrate and phosphate
  ions, form a reservoir of nutrients for the
  growth of algae and other primary producers
• Nitrate and phosphate ions occur at loc
  concentrations in sea water
• Mean concentration of nitrate is 0.5 ppm
• Mean concentration of phosphate is 0.07 ppm

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The Sea-Surface Microlayer

• incredibly thin (few hundred µm)
• important for the chemistry of the ocean
• covers 71 of surface of the planet therefore
  it is the largest single ecosystem
• not well understood (difficult to sample such a
  tiny vertical section of the water column)
• critical link between ocean and atmosphere
• Receives and transmits
• energy
• gases
• solids
• collects matter transported by winds from above
  and by water below

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The Sea-Surface Microlayer

• The upper meter of seawater is divided in to
  sublayers, each with its own biological and
  chemical features. Within the surface layer, (the
  upper 60 cm), the first 0.05 mm contains an
  especially dense concentration of minerals,
  organic chemicals, protozoans and
  micro-organisms. The upper 70 mm has dense
  concentrations of slightly larger organisms,
  including fish eggs, fish larvae, and
  crustaceans. Larger, floating jellyfish and
  seaweeds are found in the upper 30 cm. There are
  many transient creatures that move up and down in
  tune to the sunlight.

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The Sea-Surface Microlayer

• The plants and animals that live in the water
  excrete many organic compounds, such as amino
  acids, proteins, and fatty acids that serve as
  nutrients for bacterial growth. These rise to the
  surface where they are concentrated the thin
  organic skin of the water. This happens in fresh
  water as well as salt water.
• When aquatic organisms die, the oils in their
  bodies may float to the surface before they
  completely decompose.
• The thin layer of oily material on the surface
  of the sea is an important part of the water
  cycle as it helps control the rate of
  evaporation. It is also a highly nutritious food
  source for many species of microscopic plants and
  animals (ie plankton).
• On calm days we say the sea is "slick calm" or
  "oily calm" because the microscopic layer of oil
  is evenly distributed on the surface.

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The Sea-Surface Microlayer

• Wind pushes the oil into long ribbons of calm
  water known as "wind slicks" or "wind rows."
• You can see these on most days when looking at
  the sea from an overlook or from a boat.
• Samples show the plankton and nutrients are
  thousands of times more concentrated in the
  windrows than in water only a few cm deeper or in
  adjacent areas.
• Unfortunately, the oily surface of the sea is
  also the first to receive pollutants from the
  atmosphere. Scientists believe more than 30 per
  cent of all ocean pollution comes from tiny
  particles of dust and smoke in the air - often
  called fallout.
• This settles on the most sensitive and vulnerable
  part of the ocean - its skin.
• The pollutants contain pesticides, heavy metals,
  and industrial and motor vehicle toxins such as
  sulphuric acid, chlorine, and dioxin.

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Wind Slicks

• Windslick research link

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The Sea-Surface Microlayer

• A polluted surface microlayer has the potential
  to poison much of the complex marine food web,
  including fish, crustaceans, whales, and
  seabirds.
• Destruction of the microlayer may alter the
  exchange of materials between the atmosphere and
  the ocean, thereby affecting global climate.
• Oil pollution also floats on the surface of the
  sea and quickly contaminates this fragile
  environment with chemical toxins.
• Oil, even a very thin layer, spreading over the
  surface of the water at the same time fish are
  releasing their floating eggs can devastate their
  reproductive success

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The Sea-Surface Microlayer

• Heavy metals, and other toxins, are hundreds of
  times more concentrated in the surface windrows
  of the sea than in deeper water. Pesticides are
  found concentrated millions of times greater than
  in the rest of the water.
• As the ozone layer in the upper atmosphere breaks
  down from air pollution, ultraviolet radiation
  increases. This has been shown to have a severe
  impact on the phytoplankton and the eggs of sea
  creatures when they concentrate at the surface.

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The Sea-Surface Microlayer

• Three processes transport matter to the oceans
  surface from below
• Molecular diffusion
• Slow process due to random motion of all
  molecules
• Convective motion
• Vertical circulation of water from transfer of
  heat
• Rising air bubbles
• Bubbles created by waves and wind rise through
  seawater because of their buoyancy
• absorb inorganic/organic matter which is
  ejected into air when bubble bursts at surface

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The Sea-Surface Microlayer

• Result of this atmospheric and oceanic flux of
  material is the enrichment of both dissolved and
  particulate matter in the surface microlayer
• The concentrated materials represent a surface
  coating that can reduce significantly the
  transfer of gases and water vapor across the
  air-sea interface
• Influences the chemistry of lowermost atmosphere
  and uppermost ocean (and possibly, the climate in
  the long run)

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Explain the process by which the reservoir of
dissolved nutrients is replenished, including
upwelling, runoff from the land, and dissolving
of atmospheric gases

• Upwelling is the movement of water from deep in
  the ocean to the surface layer, where the
  nutrients become available to primary producers
• Upwelling brought about by several processes
• Deflection of deep water currents upwards
• Movement of water away from the coast (due to
  wind)
• Upwelling Animation

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Mechanisms that create ocean upwelling

• Wind
• Coriolis Effect
• Ekman Transport

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Upwelling refers to deep water that is brought to
the surface.
Areas of upwelling are created by surface winds
that pull water away from an area. This deficit
of water on the surface invites water to come up
from deeper regions.
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To understand upwelling, you must be familiar
with how the Coriolis Force affects ocean surface
currents. The Coriolis Effect acts on moving
water, because it is not attached to the rotating
Earth. As water flows over the rotating earth,
it appears to deflect to the right in the
Northern Hemisphere and the left in the Southern.
20

• Coriolis Effect link
• Coriolis Video

21
Due to friction between the layers of water in
the ocean and the Coriolis Effect, the net result
of wind blowing across the surface of the water
is transportation of a layer of water 90 degrees
to the direction of the wind. This is known as
Ekman Transport.
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Seasonal upwelling
Wind
Wind
Onshore winds pile water up on shore, thus
surface water will be forced downward. This is
downwelling.
Offshore winds take water away from shore, thus
water from depth will upwell to the surface.
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Upwelled water also contains nutrients
(nitrate, phosphate, silicate) and dissolved
gases (oxygen and carbon dioxide) that are not
utilized at depth because of a lack of
sunlight.Now on the surface, these nutrients
and gases help to fuel photosynthesis by small
algae called phytoplankton.
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Phytoplankton photosynthesize using specialized
color pigments called chlorophyll. Thus, Ocean
Color maps are another way to identify areas of
upwelling. Where on this ocean color map are
high phytoplankton concentrations?
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Even though upwelling areas account for only 1
of the ocean surface, they support 50 of the
worlds fisheries.
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Productivity (phytoplankton growth) of an area
is determined by the rate and the duration of
upwelling.

• Rate of upwelling determines phytoplankton cell
  size.

• Duration of upwelling determines the total amount
  of phytoplankton.

small vs. large
few vs. many
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Classification of upwelling systems in terms of
rate and duration
After Thurman, H.V. (1994)
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-Moderate rates of upwelling for long duration (8
months or longer) provide the ultimate
combination for a large fishery. -With too low
or too high a rate, phytoplankton are small, so
there is a trophic level between the algae and
the fish.therefore the fish receive less energy.
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Stormwater Runoff

• the most common pollutant of streams, rivers, and
  oceans.

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Demonstrate an understanding that the reservoir
of dissolved nutrients is depleted by uptake into
organisms in food chains
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Explain how productivity may be limited by the
availability of dissolved nutrients
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Primary production is the total amount of carbon
(C) in grams converted into organic material per
square meter of sea surface per year (gm C/m2/yr).
General Marine Productivity

• Factors that limit plant growth and reduce
  primary production include solar radiation and
  nutrients as major factors and upwelling,
  turbulence, grazing intensity and turbidity as
  secondary factors.
• Only 0.1 to 0.2 of the solar radiation is
  employed for photosynthesis and its energy stored
  in organic compounds.

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• Macronutrients and micronutrients are chemicals
  needed for survival, growth and reproduction in
  large and small quantities, respectively.
• Upwelling and turbulence return nutrients to the
  surface.
• Overgrazing of autotrophs depletes the population
  and leads to a decline in productivity.
• Turbidity reduces the depth of light penetration
  and restricts productivity even if nutrients are
  abundant.

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Productivity varies greatly in different parts of
the ocean in response to the availability of
nutrients and sunlight.

• In the tropics and subtropics sunlight is
  abundant, but it generates a strong thermocline
  that restricts upwelling of nutrients and results
  in lower productivity.
• High productivity locally occurs in areas of
  coastal upwelling, in the tropical waters between
  the gyres, and in coral reefs.

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• In temperate regions productivity is distinctly
  seasonal.
• Polar waters are nutrient-rich all year but
  productivity is only high in the summer when
  light is abundant.

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Variations in Primary Productivity
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Mixing plays an important role in the limitation
of primary production by nutrients.

• Mixing plays an important role in the limitation
  of primary production by nutrients.
• Inorganic nutrients, such as nitrate, phosphate,
  and silicate acid are necessary for phytoplankton
  to synthesize their cells and cellular machinery.
  
• Because of gravitational sinking of particulate
  material (such as plankton, dead or fecal
  material), nutrients are constantly lost from the
  photic zone, and are only replenished by mixing
  or upwelling of deeper water.
• Summer increased solar heating, reduced winds
  leads to vertical stratification (thermocline)
  which makes it more difficult for upwellings

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Mixing plays an important role in the limitation
of primary production by nutrients.

• Between mixing events, primary production (and
  the resulting processes that leads to sinking
  particulate material) constantly acts to consume
  nutrients in the mixed layer
• In many regions, this leads to nutrient
  exhaustion and decreased mixed layer production
  in the summer
• Even in the presence of abundant light not
  always a limiting factor!
• As long as the photic zone is deep enough,
  primary production may continue below the mixed
  layer where light-limited growth rates mean that
  nutrients are often more abundant

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Primary productivity varies from 25 to 1250 gm
C/m2/yr in the marine environment and is highest
in estuaries and lowest in the open ocean.

• In the open ocean primary productivity
  distribution resembles a bulls eye pattern
  with lowest productivity in the center and
  highest at the edge of the basin.
• Water in the center of the ocean is a clear blue
  because it is an area of downwelling, above a
  strong thermocline and is almost devoid of
  biological activity.

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• Continental shelves display moderate productivity
  between 50 and 200 gm C/m2/yr because nutrients
  wash in from the land, and tide- and wave-
  generated turbulence recycle nutrients from the
  bottom water.
• Polar areas have high productivity because there
  is no pycnocline to inhibit mixing.
• Equatorial waters have high productivity because
  of upwelling.
• Centers of circulation gyres, which occupy most
  of the open ocean, are biological deserts.

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The Sargasso Sea and Vertical Profiles
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Remember.

• Although rate of productivity is very low for the
  open ocean compared to areas of upwelling, the
  open ocean has the greatest biomass productivity
  because of its enormous size.

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Irons Influence

• Micronutrient iron (used as cofactor in enzymes
  and important processes like nitrogen fixation)
  has been discovered to have a significant role in
  oceanic primary productivity
• Major source of irons to oceans is the dust from
  the Earths deserts (carried through wind)
• In regions far removed from deserts or that are
  not reached by dust carrying winds (eg North
  Pacific ocean), lack of iron can severely limit
  the amount of primary productivity
• Known as HNLC (High-Nutrient, Low-Chlorophyll)
  regions, because the scarcity of iron both limits
  phytoplankton growth and leaves a surplus of
  other nutrients
• Some scientists have suggested introducing iron
  to these areas as a means of increasing primary
  productivity and sequestering carbon dioxide from
  the atmosphere.

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Demonstrate an understanding that the nutrients
taken up by organisms in food chains may sink to
the sea floor in faeces or after death, may be
incorporated into coral reefs, or may be removed
by harvesting
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MARINE ENERGY FLOW AND NUTRIENT CYCLES
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DETRIVORES AND DETRITUS

• Some heterotrophs (e.g., earthworms, flies,
  beetles, crabs, sea cucumbers, ants, vultures,
  hyenas, etc.) depend on detritus (dead organic
  material/biomass), rather than live organic
  material.
• Note animals can be both a herbivore and a
  detrivore, or a carnivore or omnivore and a
  detrivore, i.e., they eat both living and dead
  organisms.

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DETRIVORES AND DETRITUS

• In some ecosystems more energy for the support of
  higher trophic levels in the ecosystem comes from
  detritus than from living plants and animals
  (note this can be true in terrestrial,
  freshwater and marine ecosystems), with detritus
  serving as an energy source for an interacting
  system of herbivores, carnivores and decomposers.
  E.G., APHOTIC ZONE

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Marine Snow
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Marine Snow
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DECOMPOSERS

• Decomposers play a very important role in
  mineralisation by breaking down organic
  substances into inorganic compounds that are
  again available for reuse by producers.

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Show that each of the nutrient cycles listed
below can be summarized as shown in Fig 4.1 and
state the biological use of each nutrient

• nitrogen which is used to make proteins
• carbon which is used to make all organic
  materials
• magnesium which is used to make chlorophyll
• calcium which is used to make bones, corals, and
  shells
• phosphorous which is used to make DNA and bone

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Ecology
Biological Processes Geological Processes
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The Carbon Cycle

• Key role in Earths thermostat
• Absorbed by ocean, utilized by plants in
  photosynthesis, humans in digestion
• Sinks (storage) in lithosphere (largest reservoir
  limestone and other sedimentary rock),
  hydrosphere (ocean), atmosphere (CO2) and in the
  biosphere (dead animals, wood, plants)
• Released by fires, decomposition, volcanoes, and
  human respiration

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The Oxygen Cycle

• Essential for animals
• Taken in during respiration
• Released by plants in photosynthesis
• Disrupted by the same factors that disrupt the
  carbon cycle
• Clear cutting of trees
• Increased burning of fossil fuels
• Pollution to phytoplankton containing water

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The Nitrogen Cycle

• 78 of troposphere is N2, 0 utilized in
  respiration
• Present in proteins, moves through food chain
• Most complex cycle
• Disrupted by
• Burning fuel (releases nitric oxides)
• Increased use of fertilizer
• Removal from topsoil
• Addition to aquatic ecosystems

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Conversion of Atmospheric Nitrogen to usage
nitrogen
N2
Soil
Acid soil
bacteria
NH4
NH3
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Nitrogen Cycle

• N2 gas is modified by nitrogen fixing bacteria
  into ammonia (NH3) (nitrogen fixation)
• Bacteria turn nitrogenous waste and detritus into
  ammonia (ammonification)
• NH3 is converted into nitrite (N02) which is used
  to produce nitrate (N03) (nitrification)
• Other bacteria convert nitrite into gas which
  enters the air (denitrification)

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The Phosphorous Cycle

• Very slow process
• Found only in sedimentary rocks and water (not in
  atmosphere)
• Released as rocks erode
• Travels through food chain
• Released by decomposition

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The Sulfur Cycle

• Most stored underground
• Released by volcanoes and swamps
• Plants assimilate the sulfur
• Bacteria break it down
• 99 of all that reaches atmosphere is by humans
  (industries, burning fuel, refining petroleum)

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