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Global Interannual Upper Ocean Heat Content Variability
Gregory C. Johnson (NOAA/PMEL), John M. Lyman (UH/JIMA & NOAA/PMEL),Josh K. Willis (NASA/JPL),
Sydney Levitus (NOAA/NODC), Claudia Schmid (NOAA/AOML), & Gustavo Goni (NOAA/AOML)
• Estimate Annual Average Upper Ocean Heat Content– In situ data (XBTs, Argo floats, CTDs, autonomous pinnipeds, etc.)
– Satellite altimetry (Aviso weekly merged delayed-mode maps)• Can combine in situ & altimetry data (e.g. Willis et al., 2004)• Can also use altimetry for in situ error estimates
– Subsample 13 years like a single years in situ distribution– Map subsampled years & compare to fully resolved fields
• Recent Decrease in global average upper ocean heat content– Significant
• Where has the upper ocean heat gone?– Out to space . . . or into the abyss?
2005 Upper Ocean Heat Content
•Combined data set–Follow Willis et al. (2004)–In situ thermal data &–Satellite altimetric data
•2005 relative to 1993-2002 ->
–Warm subpolar N. Atlantic
–Likely NAO–Warm S. Ocean band
–Likely SAM•2005-2004 (Short Time-Scale) ->
–Large-amplitude small-scale variations
–Ocean advection–Equatorial Pacific cooling
–Fading El Niño
Long Time-Scale (13-Year) Linear Trends
•Longer time-period ->
•Smaller amplitude & larger scale
•Big N. Atlantic Change–NAO 1996 shift in winds
•Big. N Pacific Change–PDO Large-scale wind shifts
•Big. S. Ocean Changes–SAM Large-scale wind shifts
•Overall warming trend?–~ 5% of area at 95% CI –Hmm . . .–Look at global integral . . .
Annual Global Upper OHCA Variations
•Decadal increase:–Willis et al. (2004)–Levitus et al. (2005)
•What about the recent decrease?
•An observing systemchange?
–Argo went global in 2004–Remove floats(& more) blue–Don’t remove seasonal cycle red–New error analysis
•The cooling remains
Annual Global Upper OHCA Variations
•Levitus et al.•Has Different:
–Mapping–Quality Control–Data Sets (slightly)–Reference Period
•Similar recent cooling
World Ocean 0 - 700 m
New Refined Error Analysis
•Use SSHA as upper OHCA proxy•Altimetry gives 13 years of SSHA
•For a given year (say 1955)
–Use SSHA from 1993-2005–subsample SSHA like 1955–Map yearly subsampled SSHA–Difference subsampled & full–Time series -> error estimate
•Means of + and - differences •Not exactly the error estimate
–Global anomalies biased low–Because no data -> no anomaly–(conservative choice)
Interannual Error Estimate
•Three different regimes
–Before the XBT–XBT starts in 1960’s
–Number increases
–Argo starts in 2000’s
–Coverage improved
•Note 2002 vs. 2005–Both years ~ 150,000 profiles–Distributions different
•Caveat! 13-years too short
–Few ENSO–NAO, PDO, etc.–Most valid from 1993 on
Same Profile Numbers, Different Errors
•Measure of in situ coverage
–Blue good, red bad•2002 mostly ship tracks & moorings
–Little S. Ocean coverage–Will improve with time
–NODC collects data
–Satellite altimetry (Aviso weekly merged delayed-mode maps)
•2005 mostly float tracks
–Even spatial distribution–Even temporal distribution–Few gaps
–Ice–EEZs–Shallow Seas
Earlier Downturn in 1980’s
•Levitus et al. (2005) OHCA
–Big 1980-1983 cooling–New error estimates–Significant
–(Note caveat)•Early error bars large
–Likely underestimates
•After XBT advent–Interannual significance
Ocean Heat Anomaly Distribution?
•1993 to 2003 change (red)
–Surface intensified–Approaches 0 by 750 m–Some wiggles with depth
•2003 to 2005 change (blue)
–Smaller in amplitude–Surface warming–Mid-depth cooling–Approaching 0 at depth?
•1993 to 2005 change (black)
–More surface intensified–Surface warming–Mid-depth cooling–400-m zero-crossing
Heat in the Deep Ocean
•Levitus et al. (2005)
•Annual 0-700 m (red)•Pentadal 0-3000 m (gray)
•May not be different within uncertainties
•Upper Ocean has most variability
•What about the abyss?
S. Atlantic Antarctic Bottom Water Warms
•2005 CO2/CLIVAR vs.•1989 WOCE A16S & C•1995 WOCE A23•AABW changes
•+0.04 C warming•Bottom 1500 dbar•95% significant•Global budgets?