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?