nutrients, upwelling and geochemical tracers

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nutrients, upwelling and geochemical tracers

• Nitrogen cycling when the going gets tough
• Silica is THE upwelling nutrient
• Tracers talking more about theory than
  application.
• Geochemical tracers trace
• Circulation
• Climate
• Geochemical tracers are
• Signals in sediments
• Isotopes (composition of the sediments)
• Microfossils

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Biolimiting constituents (a.k.a. nutrients)
Nitrate (NO3-) Does not limit growth of
bluegreen algae
(cyanobacteria) they fix nitrogen.
Silicate (H2SiO4) Limits the growth of diatoms
Phosphate (HPO4) the ultimate limiting nutrient
for plant growth
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Vertical distribution of nutrients
nitrate 10-6 mol/liter
Phosphate 10-6 mol/liter
silicate 10-6 mol/liter
Libes, 1992
nutrients become fully depleted during
stratification
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Hydrocast gear
Niskin bottle rosette with 36 bottles for
collecting sub-surface water
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Annual Stratification sequence
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The simple Nitrogen cycle
0
-III
III
V
-III
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Different oxidation states of nitrogen
Libes, 1992
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The Nitrogen cycle- reality
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Annual Stratification sequence
Recycling of nutrients at its peak and
nutrients at a minimum productivity slows down,
respiration picks up.
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The Nitrogen cycle when nutrients are low the
saviors come along
0
Energy intensive
-III
III
V
-III
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New versus regenerated production
Lalli and Parsons
Note the biggest arrow is upwelled NO3
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The Nitrogen cycle when things get tough
You see the other half of the cycle
The saviors
The spoilers
Energy intensive
Anaerobic
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Low oxygen and the spoilers
?CO2
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The Nitrogen cycle the spoilers
Lost to the system
0
Anaerobic respiration
-III
III
V
-III
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The Nitrogen cycle the whole story
Lost to the system
Input to the system
0
Anaerobic respiration
Energy intensive
-III
Input to the system
III
V
-III
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Vertical distribution of nutrients
nitrate 10-6 mol/liter
Phosphate 10-6 mol/liter
silicate 10-6 mol/liter
Libes, 1992
In upwelling zones/during upwelling phosphorous
and nitrate are generally not fully depleted
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Silica the upwelling nutrient
Silicate (H2SiO4) Limits the growth of
diatoms SiO2 (Silica) is an important nutrient
only for diatoms Upwelling zones are areas with
high diatom productivity because silica is
plentiful This is because silica from deep water
is upwelled there.
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The silica cycle
Silica is undersaturated and dissolves it only
forms deposits under major productivity areas
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Silica cycling in an upwelling zone
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Coastal Upwelling zones in the world ocean
Mann and Lazire
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Open ocean zones of upwelling .
Mann and Lazire
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Distribution of siliceous sediments
Distribution of siliceous sediments largely
aligns with upwelling zones
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How do we trace the movement of components in the
ocean?

• We start off with nutrients because they are
  trace-ablethey control productivity.

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The biological pump.
How do we know it changed in the past? How do we
trace carbon movement through the system?
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How do we trace the movement of components in the
ocean?

• We start off with nutrients because they are
  trace-ablethey control productivity.
• With major components like carbon, how can we
  track the cycling of that?
• How can we trace things in the past?

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Geochemical tracers
Two isotopes of concern Oxygen isotopes
?18O Carbon isotopes ?13C
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Geochemical tracers
Oxygen is 16O99.759 17O0.037 18O0.204
? notation is simply the ratio of 1618 in the
sample relative to a standard ..
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del notation
?A (RA -1) x1000 RSt which is the
same as (18/16O)CaCO3 sample 1) x1000
(18/16O)CaCO3 std The
result is we use per mil as our units and we
always speak about the data in reference
to the isotope of interest
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Fractionation of oxygen isotopes
snow
Ice -35
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The record of ? 18O in the sediment record
The distillation is controlled by temperature
salinity and ice volume. The record is
primarily a a function of temperature and ice
volume
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Geochemical tracer carbon isotopes
Carbon isotopes 12C98.89 13C1.11 14Csmal
l and variable
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Fractionation of carbon is primarily
biologically mediated
Plants discriminate against 13C during
photosynthesis. The the ultimate ?13C amount
varies with plant type and substrate.
Libes chapt. 29
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Fractionation of carbon is primarily
biologically mediated
Plants discriminate against 13C during
photosynthesis. The the ultimate ?13C amount
varies with plant type and substrate.
Libes chapt. 29
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The biological pump moves organic carbon
The biological pump moves organic matter with
its depleted isotopic signal from the surface
ocean to the deep water masses..
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The conveyor belt circulation
And thermohaline circulation moves CO2 through
the system
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Controls on the fractionation of 13C
Water downwells DIC enriched Low nutrients High
O2
13C
13C
13C
12C
13C
13C
12C
12C
12C
13C
13C
DIC (in Water) more depleted with increasing age
13C
12C
12C
12C
12C
12C
Porewaters very sensitive to remineralization can
be very depleted in 13C
12C
12C
12C
12C
12C
12C
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The vertical profile of ?13C reflects the global
thermohaline circulation
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Silica cycling in an upwelling zone