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Concept test. We, human beings, along with all animals are causing a net increase of atmospheric CO 2 because our breath contains CO 2 when we exhale. (1) True (2) False (3) Debatable. oxygen cycle. Observations Processes Climate change impacts Future projections.

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concept test
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
oxygen cycle

oxygen cycle



Climate change impacts

Future projections


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
observed variability of oceanic o 2
Observed variability of oceanic O2

Gruber et al. (2007)

  • Global ocean deoxygenation?


Stramma et al 2008


Oxygen and marine ecosystem

Image from an ROV off the Oregon coast after a low oxygen event

Figure 1. Keeling et al., (2010)

Low O2 can reduce the respiratory capacity of marine heterotrophs, leading to reduced physiological performance or death.

glacial interglacial changes
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 Geenet al. [2003]

global oxygen cycle processes
Global oxygen cycle: processes

Vertical profile of observed O2

controls on atmospheric oxygen
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


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 5mmolO2/kg

Distribution of oxygen-depleted waters

  • Indo-Pacific is more depleted in oxygen relative to the Atlantic
  • Oxygen gets depleted in some coastal regions

Oxygen utilization

Apparent Oxygen Utilization


Heat content of the ocean

Integrated effect of respiration

Biological productivity

Aging of water masses


Declining oxygen in warming climate

Warming and circulation change

Temperature increase

Slower vertical exchange of waters


Future projection

  • Model simulations for the 21st century future climate
  • What are the uncertainties?

Expanding OMZ?!

California Current Region

Tropical Pacific Region

Deutsch et al. (2011)

Stramma et al. (2008)

Decadal-scale fluctuations or climate trend?


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

Initial cond(time=t)

T, S, nutrient, carbon, alkalinity

Boundary cond:

Heating, wind,

dust, atmos pCO2, dust…



time = t+1

T, S, nutrient, carbon, alkalinity, biological productivity, …

a h indcast simulation
A hindcast simulation

O2 on sq= 26.8


  • Expansion of OMZ during late 20th century
  • Minimum extent of OMZ around mid 1970s

Eastern tropical Pacific O2

Model climatology

enso cycle and o 2 compensations
ENSO cycle and O2 Compensations

+O2 inventory

OMZ contraction



-O2 inventory

OMZ expansion


Major El-Nino events

the mechanism upwelling and aou
The Mechanism: Upwelling and AOU

Deutsch et al. (2011)



  • Warmer and decreased O2sat
  • Weaker lateral O2supply
  • Decreased biological O2 consumption
  •  OMZ contraction
  • Colder and increased O2sat
  • Stronger lateral O2 supply
  • Increased biological O2 consumption
  •  OMZ expansion
land vs ocean co 2 uptake1
Land vs ocean CO2 uptake


Slope = a

Decline of oceanic O2

Slope = b

Accounting for ocean O2outgassing implies that CO2 uptake by land must have been smaller, and ocean CO2 uptake larger than previously thought.

+ Ocean outgassing

oxygen ocean biogeochemistry and climate
Oxygen, ocean biogeochemistry and climate

O2 changes indicate:

Changes in ocean circulation and biological productivity

Greenhouse effect

Changes in the carbon cycle and ocean CO2 uptake.

Transport + mixing

Photosynthesis + respiration

Oceanic carbon, O2 cycle

Atmospheric Climate

Light, SST, dust

Heat, water, momentum exchange

Ocean circulation

Biological Productivity

Nutrient Supply