WG2 HIGHLIGHTS : From the surface to the water column

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WG2 HIGHLIGHTS From the surface to the
water column
Nicolas Gruber et al.
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Themes

• Thermocline O2 varies everywhere you look
• Thermocline O2 varies more than expected
• Variations appear to be primarily physically
  driven

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SUMMARY OF NORTH PACIFIC AOU CHANGES
Kumamoto
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MERIDIONAL SECTION ALONG 150W
1970
1990
1975
NODC data
ANOMALIES relative to 1955-2000 climatology
1980
1985
H. Garcia
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AOU ANOMALIES
C. Deutsch et al.
Relative to 1960s
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GLOBAL OXYGEN AND HEAT
CONTENT CHANGES
heat content (Levitus et al. 2000)
O2 content 100-1500m 70S - 70N
H. Garcia
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MERIDIONAL SECTION ALONG 152W (1997-1991)
AOU
pCFC-12 age
Physical changes dominate OUR changes minimal
OUR
S. Mecking
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MECHANISMS OF AOU CHANGE
C. Deutsch et al.
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DRIVING MECHANISMS

• Sverdrup circulation
• recirculation region increasing and eastern
  Pacific decreasing in strength.
• Ventilation
• Outcrop area and ventilation has changed for 26.6
  layer.

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Paradigm change

• from trends to variability spectrum
• distinct spatial heterogeneity - anomalies tend
  to be conserved
• temporal variations occur on all time-scales,
  with the interior ocean acting as a low-pass
  filter
• Therefore, differences between any two snapshots
  cannot be interpreted as representing linear
  trends

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Mechanisms

• physical dominance
• Changes appear to be forced primarily by changes
  in ocean circulation and ventilation
• there is little evidence for a substantial
  biological contribution to water column trends

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Challenges

• Synthesis between physical forcing, surface
  ocean expression, and water column changes
  (including link between O2 and carbon)
• Role of biology?
• Detection of climate change