From: SCHLOERER@rzmain.rz.uni-ulm.de (Jan Schloerer)
Subject: Re: Missing CO2 sink found?
Organization: University of Ulm, Germany
Date: Wed, 30 Sep 1992 19:12:52 GMT
X-News-Reader: VMS NEWS 1.24

In  <1992Sep26.163652.127819@watson.ibm.com>
    Andrew Taylor   (andrewt@watson.ibm.com)   wrote :

> The latest New Scientist suggests three articles in Nature may allow
> the global carbon budget to be balanced.
>
> Keeling and Shertz at NCAR have been measuring atmospheric oxygen
> content. The decline in oxygen content they have measured matches that
> consumed by burning fossil fuels. This indicates that globally,
> biomass currently makes no net contribution to the carbon flow.
>
> The existence of a ~1mm ocean surface layer up to 0.3C cooler has been
> known for 20 years.  Robertson and Wilson at Plymouth Marine
> Laboratory suggest taking this layer into account will increase
> estimated global ocean uptake of carbon (as CO2) by 0.7 gigatonnes.
>
> Falkowski and Wilson from Brookhaven have examined records of
> phytoplankton activity in the Northern Pacific since 1900. They
> conclude that there are no changes signifcant enough to affect
> atmospheric CO2 levels.
>
> Together these three articles would seem (from the New Scientist
> piece) to account for the missing CO2 sink. Perhaps someone more
> knowledgable could review the actual articles
> (Nature vol 358 p723, p738, p741)


Well, having skimmed these and a few related articles, it appears to me
that the missing CO2 sink has not yet been found.  However, from what I
happened to see, the odds seem that the oceanic CO2 sink will go up
once again to its pre-1990 size, so that the missing sink would shrink.

To begin with, the 1992 estimates of the IPCC  (they already knew some
of the recent work reported below) :
    Global fossil fuel emissions 1990                   6.0 +- 0.5 GtC
    Annual average net flux from land-use changes
      (primarily deforestation) during the 1980s        1.6 +- 1.0 GtC
    Fraction of the CO2 emissions which remains
       in the atmosphere (for the last decade)         46   +- 7   %
    Estimate for the annual oceanic uptake              2.0 +- 0.8 GtC
    Imbalance = missing sink                   roughly  1 - 2  GtC/year
1 GtC (gigatonne of carbon = 10^9 tonnes of carbon) corresponds to about
3.7 Gt CO2.  In the atmosphere, 1 ppmv (part per million by volume) CO2
corresponds to about  2.12 GtC  or  7.8 Gt CO2.

Up to 1990, the oceanic CO2 sink was estimated to be about  2 GtC/yr.
The present mystery story began with an audible bang, when Tans, Fung
and Takahashi presented work indicating that the ocean sink might only
be about  1 GtC/year or smaller (Science 247, 1990, 1431-1438), implying
a missing sink of more than 2 GtC/year.  Recently, however, quite a few
papers argued for the former, larger oceanic CO2 sink:

*  Using the carbon-13 decrease in Pacific surface waters between 1970
   and 1990, Quay, Tilbrook and Wong estimated an average net oceanic
   CO2 uptake of 2.1 GtC/year. Mainly due to limited geographic coverage,
   this estimate is rather uncertain, with a standard deviation of
   about 0.75 GtC/year.
     Quay, P.D., B.Tilbrook, C.S.Wong:  Oceanic uptake of fossil fuel
     CO2: carbon-13 evidence.  Science 256 (3 April 1992), 74-79
     Comment:  Richard A.Kerr, same issue, 35

*  Sarmiento and Sundquist argued for several corrections to the Tans-
   Fung-Takahashi ocean uptake budget :
     -  probable net river carbon flux to the ocean   0.4 - 0.7 GtC/yr
     -  correction for carbon monoxide budget               0.3 GtC/yr
     -  preliminary correction for the ocean skin
        temperature effect                            0.1 - 0.6 GtC/yr
   When added to the Tans et al estimate of 0.3 - 0.8 GtC/year, these
   corrections increase the annual uptake of CO2 by the ocean to about
   1.1 - 2.4 GtC/year.
     Sarmiento, J.L.  &  E.T.Sundquist:  Revised budget for the oceanic
     uptake of anthropogenic carbon dioxide. Nature 356 (16 April 1992),
     589-593.  Comment:  Andrew Watson, same issue, 561

*  As mentioned by the New Scientist, Robertson & Watson provided a more
   detailed correction for the thermal skin effect of about 0.7 GtC/year.
   Inserting this  (instead of 0.1 - 0.6 GtC/year)  into the above
   calculation, the ocean uptake becomes about 1.7 - 2.5 GtC/year.
     Robertson, J.E.  &  A.J.Watson:  Thermal skin effect of the surface
     ocean and its implications for CO2 uptake.  Nature 358 (27 August
     1992), 738-740

*  Broecker and Peng found that the deep water formed in the Northern
   Atlantic (in the descending leg of the Gulf Stream) should take up
   at least 0.6 GtC/year, thereby relaxing a constraint on the northern
   ocean sink imposed by the work of Tans et al.  In his comment, Watson
   cautions that, in spite of all these results,  "the jigsaw  [of the
   ocean sink]  still ... has pieces missing."
     Broecker, W.S.  &  T.-H.Peng:  Interhemispheric transport of carbon
     dioxide by ocean circulation, Nature 356 (16 April 1992), 587-589.
     Comment:  A.Watson, same issue, 561-562

If all this turns out to be about right, it would imply an annual CO2
uptake by the ocean of about 2 GtC/year or possibly a bit more, still
leaving a missing sink of about 1 GtC/year or more.  Here, one should
keep in mind that other items in the global carbon budget are also
somewhat shaky, in particular the net flux from land-use changes.

As you mention, the work of Falkowski and Wilson (Nature 358, 27 August
1992, 741-743) seems to indicate that the phytoplankton productivity in
the Northern Pacific has not changed very much during the past 70 years,
in contrast to earlier work which suggested roughly a doubling of phyto-
plankton biomass in that region.  Presently it escapes me, how this work
could account for part of the missing sink.  Did I overlook something ?

Finally, the new oxygen measurement method developed by  Ralph Keeling
(yes, the son)  and  Stephen Shertz   "could make it possible to unravel
the complexities of the carbon cycle"  (Broecker & Severinghaus).  It
measures the O2/N2-ratio to within 5 parts per million. In the long run,
this technique should enable a quite precise estimate of the oceanic CO2
sink.  But this will take time.  Presently there are very few data:
three seasonal cycles from La Jolla, California,  one year's data from
Cape Grim, Tasmania, and one year from Alert, Ellesmere Island (shudder).
The net oceanic sink of 2.5 +- 1.7 GtC/year estimated from these data
is just an illustration of the method.  It is not a definitive result.
  Ralph F. Keeling  &  Stephen R. Shertz:  Seasonal and interannual
  variations in atmospheric oxygen and implications for the global
  carbon cycle.  Nature 358 (27 August 1992), 723-727.
  Comment:  W.Broecker & J.Severinghaus, same issue, 710-711

btw, who was the author of the New Scientist piece ?  Fred Pearce ?


Jan Schloerer          schloerer@rzmain.rz.uni-ulm.de
Klinische Dokumentation           Uni Ulm
Postfach 3880     DW-7900 Ulm     Germany
Newsgroups: sci.environment