concept test we, human beings, along with all animals are causing a net increase of atmospheric co 2...
TRANSCRIPT
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Concept test• We, human beings, along with all animals are causing a
net increase of atmospheric CO2 because our breath contains CO2 when we exhale.
• (1) True• (2) False• (3) Debatable
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OXYGEN CYCLEObservations
Processes
Climate change impacts
Future projections
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Measuring oxygen in the seawater
• Oxygen is the third most frequently measured
ocean tracer following T and S
• Winkler titration method (1888)
- Wet chemistry, performed on site
- Most accurate
• Electronic and optical sensors
- Calibration is crucial
- Possible to deploy on floats, gliders, etc
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Observed oxygen distribution
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Observed variability of oceanic O2
• Global ocean deoxygenation?Gruber et al. (2007)
NPIW
Stramma et al 2008
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Image from an ROV off the Oregon coast after a low oxygen event
Low O2 can reduce the respiratory capacity of marine heterotrophs, leading to reduced physiological performance or death.
Oxygen and marine ecosystem
Figure 1. Keeling et al., (2010)
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Glacial-interglacial changes?
• The intensity of the North Pacific Oxygen Minimum Zone has varied over the past 100ky.
• This has implications for the ocean’s redox chemistry and the overall fertility of the ocean.
• Reasons for the O2 changes are unclear.
Van Geen et al. [2003]
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Global oxygen cycle: processes
Vertical profile of observed O2
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Controls on atmospheric oxygen• More than 90% of oxygen molecule is in the atmosphere
• 20% of atmospheric gas
• Opposite tendency relative to CO2
• Source: photosynthesis• Sink: respiration
• Geologic timescale• Burial of organic matter leads
to atmospheric O2 increase
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Observations of oceanic oxygen
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Oceanic oxygen
• Near saturation at the surface- O2 is within a few percent of saturation with
atmosphere (high concentrations)
- O2 ≈ O2sat(T,S)
• Consumed by respiration
• Depleted at depth
- Hypoxic: below 60 mmolO2/kg
- Suboxic: below 5 mmolO2/kg
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Oxygen Minimum ZoneFigure 3a
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HH L
Ocean vertical motions
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Distribution of oxygen-depleted waters
• Indo-Pacific is more depleted in oxygen relative to
the Atlantic
• Oxygen gets depleted in some coastal regions
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Downwelling supplies O2 to the ocean
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Upwelling and biological productivity
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Oxygen utilization
Apparent Oxygen Utilization
TemperatureHeat content of the ocean
Integrated effect of respirationBiological productivityAging of water masses
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Declining oxygen in warming climate
Warming and circulation change
Temperature increase
Slower vertical exchange of waters
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Future projection
• Model simulations for the 21st century future climate
• What are the uncertainties?
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Expanding OMZ?!
Deutsch et al. (2011)
California Current Region
Stramma et al. (2008)
Tropical Pacific Region
Decadal-scale fluctuations or climate trend?
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Ocean biogeochemistry model
• Divide up the oceans into grid cells• Input: solar heating, rain rate, surface wind, …• Given the state at time=t, predicts for t+1
Computercode
Initial cond (time=t) T, S, nutrient, carbon, alkalinity
Boundary cond:Heating, wind, dust, atmos pCO2, dust…
time = t+1T, S, nutrient, carbon, alkalinity, biological productivity, …
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A hindcast simulation
Climatology
Model climatology
O2 on s q = 26.8• Expansion of OMZ during late 20th
century
• Minimum extent of OMZ around mid
1970s Eastern tropical Pacific O2
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ENSO cycle and O2 Compensations
+O2 inventoryOMZ
contraction
-O2
inventoryOMZ
expansionMajor El-Nino events
O2- AOU
O2sat
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The Mechanism: Upwelling and AOU
La-Nina El-Nino
Deutsch et al. (2011)
• Colder and increased O2sat
• Stronger lateral O2 supply
• Increased biological O2
consumption
OMZ expansion
• Warmer and decreased O2sat
• Weaker lateral O2 supply
• Decreased biological O2
consumption
OMZ contraction
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Land vs ocean CO2 uptake
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Land vs ocean CO2 uptake
+ Ocean outgassing
Decline of oceanic O2
O2 outgassing
Slope = a
Slope = b
Accounting for ocean O2 outgassing implies that CO2 uptake by land must have been smaller, and ocean CO2 uptake larger than previously thought.
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Ocean circulation
Oxygen, ocean biogeochemistry and climate
Heat, water, momentum exchange
Light, SST, dust
Greenhouse effect
Changes in the carbon cycle and ocean CO2 uptake.
Biological Productivity
Atmospheric Climate
Nutrient Supply
Changes in ocean circulation and biological productivity
Oceanic carbon, O2
cycle
Transport + mixing
Photosynthesis + respiration
O2 changes indicate: