The mystery of a massive 9Gt of CO2 that came and went — could it be phytoplankton?

There is a mystery peak in global CO2 levels in 1990. For some reason from 1989 suddenly global carbon levels jumped higher than they normal would and by 9,000 million tonnes (that’s equivalent to 2,500 mT of carbon)*. It’s only a little blip in an upward line, but as a deviation from the long steady norm, it’s a dramatic change (see the second graph below). Within a few years the excess disappeared and the reasonably straight line increase in CO2 resumed. The sudden jump is equivalent to nearly half of our total annual human fossil fuel emissions. Nothing about this peak fits with the timing of human induced fossil fuel emissions. These were not big years in our output (indeed it coincides with the collapse of the soviet block when inefficient Russian industry was shut down) .

The mystery of the massive CO2 bubble exposes how little we know about why CO2 levels rise and fall, and whether human emissions make much difference. The world is spending $4 billion dollars a day trying to change this global CO2 level of 0.04% (400ppm) but apparently other large forces are at work pushing up CO2, and then absorbing it, and we don’t even know what they are.

Tom Quirk has been dedicated in isolating this quixotic spike, and hunting for the cause.  He wondered if the ocean was responsible. By looking at isotopes of carbon he finds that it was not produced out of the dissolved CO2 from the ocean. Instead the CO2 was released from  a biological source, and mostly one in the Northern Hemisphere. With some great sleuthing he finds a remarkable paper from 15 years ago that documents a sudden drop in fish stocks at the same time. He puts forward a suggestion that there was a regime shift in the ocean then, and the currents stopped stirring up as many nutrients. This meant phytoplankton activity was lost, fish starved, and the lack of activity by marine biology meant CO2 accumulated in the air. Within the next few years the phytoplankton recovered and drew out that extra CO2.

It’s as if there was an extra three China’s on Earth for a year — pouring out extra CO2. We see how fast biology absorbs that extra load, and wonder (yet again) what the fuss is all about. Tax the krill instead eh?

–Jo

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Some inconvenient measurements

Guest Post by Tom Quirk

There is an unexplained atmospheric CO2 “bubble” centred around 1990. The apparent smooth and continuous rise in atmospheric CO2 concentrations is broken by an anomaly that can be seen in the figure below.

 

 

Average yearly CO2 concentrations at the South Pole and Point Barrow from Scripps measurements. The straight line is a best fit to the South Pole data with an annual increase of 1.5 ppm per year.

Plotting the residual differences of measurements from the straight line fit shows that as the world cooled in the 1960s excess CO2 accumulated at low annual rates. During the 1970s and 1980s CO2 was accruing at about 1.5 ppm per year, the average rate of the last 55 years. Then suddenly in 1989 – 1991 large amounts of CO2 were added to and withdrawn from the atmosphere. A further turning point occurred in 1995 when the annual rate of increase reached its highest level.

 

Residual differences from straight line fit to average yearly CO2 concentrations at the South Pole *see above). Also similar residuals for Mauna Loa and Point Barrow. Note the break in the trends in 1977 and 1995 at the times of phase changes in the  PDO and ADO^[1]

The anomaly does not vary significantly from summer to winter.

The figure above shows the residual differences in the annual value of the CO2 anomaly by latitude for SIO and NOAA measurement stations at the peak years of 1988 to 1991. Notice also that there is no reduction in the anomaly in the Southern Hemisphere where the oceans are said to be the main sink of CO2.

This anomaly extends from the north to the south latitudes and is the equivalent of 2.5 +/- 0.4 GtC of CO2 entering and leaving the atmosphere.

Where did the CO2 come from?

The isotopic composition of the CO2 tells us whether it comes from the ocean, or from something biological. Carbon has two stable isotopes and is 99% carbon-12 and 1% carbon-13. Let us track the changes in carbon-13 from measurements at SIO sites at the South Pole, Mauna Loa and Point Barrow. The measure δ¹³C is the difference in tenths of a percent of total carbon from a carbon standard where the ocean is δ¹³C ~ 0. Plants (alive or dead – fossil fuels) are δ¹³C ~ -26. This is the result of photosynthesis depleting the fixing of carbon-13 as the lighter carbon-12 CO2 is favoured by having a higher reaction rate.

 

 

There is a step like decrease in δ¹³C with step changes particularly in 1983, 1987 and 1997 at the time of El Nino’s. The trends from 1989 to 1994 show an increase in δ¹³C.

Now a simple analysis is to consider the ocean and plants as the two original sources of CO2. We know the isotopic composition of the CO2 so the components in the atmosphere can then be found. These contributions are shown below. There is no peaking in the ocean source CO2 in 1988-91 but a peak in the plant source.

The residual contribution for the peak can be obtained using the same analysis that was applied to the total CO2 concentration measurements. So the ocean residual differences in the CO2 anomaly show no contribution by latitude for SIO and NOAA measurement stations at the peak years from 1989 to 1991. Thus the original source of the anomaly is a plant contribution. But notice again that there is a constant component in the Southern Hemisphere with no detectable evidence of an ocean interaction.

 

 

The cause of the anomaly might be variations in sea surface temperatures and winds or biological activity.

In 2000, Hare and Mantua published a detailed study^[2] of 100 time series for biological and physical measurements that showed “regime shifts” in 1977 and 1989 in the Northern Pacific Ocean and the Bering Sea. The shifts included significant falls in fish growth and size of catches.

So the explanation may be that the fall off in biological activity is due to a fall off in phytoplankton growth as phytoplankton are at the base of the food chain  Wind changes will drive ocean current changes with consequent  changes in the level of nutrients in the water and these may limit the growth of phytoplankton. This is found in El Nino years on the west coast of South America.^[3]

The loss of phytoplankton results in less CO2 being removed from the ocean and hence less removed from the atmosphere. So in 1988 the atmosphere becomes enriched in carbon-12 CO2 with a dramatic fall in δ¹³C.

This 2.5 +/- 0.4 GtC bubble is natural variability on a significant scale. For comparison total fossil fuel emissions were 6.1 GtC in 1990 and only some 50% of these emissions would be absorbed by the oceans according to the present accepted explanation.

This analysis raises the question whether the sources and sinks of CO2 are fully understood.

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REFERENCES

[1^] Tom Quirk: Did the Global Temperature Trend Change at the End of the 1990s? (2012) Asia-Pacific J. Atmos. Sci., 48(4), 339-344, DOI:10.1007/s13143-012-0032-4 PDF

[2^] S.R. Hare, N.J. Mantua (2000): Empirical evidence for North Pacific regime shifts in 1977 and 1989. Progress in Oceanography 47, 103–145

[3^] Michael J. Behrenfeld, Robert T. O’Malley, David A. Siegel, Charles R. McClain, Jorge L. Sarmiento, Gene C. Feldman, Allen J. Milligan, Paul G. Falkowski, Ricardo M. Letelier & Emmanuel S. Boss (2006) Climate-driven trends in contemporary ocean productivity: Nature Vol. 444| doi:10.1038/nature05317

* UPDATED to clarify. The bubble is bigger than first thought. The post originally said “2.5Gt of CO2” but actually it is much more than that. It’s 2.5Gt of carbon, but that is equivalent to a monster sized 9.2Gt of carbon dioxide. (1Gt = 1,000 Mt. 44 tons of CO2 contains 12 tons of carbon.) One extra China on Earth for a year was also changed to “three extra China’s”. h/t to Richard in comments for spotting the incongruent numbers.