How does rising atmospheric CO2 affect marine organisms?

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Ocean Productivity in a Warming World
Volume 9, Number 50: 13 December 2006

The titles of the first press reports we read sounded ominous. Global warming will reduce ocean productivity and marine life. Warmed-up oceans reduce key food link. Global warming will stifle oceans. Climate change is killing the oceans' microscopic 'lungs'. We immediately wondered: What new horror story had the world's climate alarmists invented this time?

Going to the source of the cataclysmic concerns - an article in the 7 Dec 2006 issue of Nature written by Behrenfeld et al. (2006) - we found it was something for which the supporting data looked almost halfway decent ... initially, at least.

Working with NASA's Sea-viewing Wide Field-of-view Sensor (Sea WiFS), the team of ten U.S. scientists calculated monthly changes in net primary production (NPP) from similar changes in upper-ocean chlorophyll concentrations detected from space over the past decade (see figure below). They report that this period was dominated by an initial NPP increase (represented by their initial ascending straight line) of 1,930 teragrams of carbon per year (Tg C yr-1), which they attributed to the significant cooling of "the 1997 to 1999 El Nio to La Nia transition," and they note that this increase was "followed by a prolonged decrease [represented by their subsequent descending straight line] averaging 190 Tg C yr-1," which they attributed to subsequent warming.

Figure Caption: Monthly anomalies of global NPP (green line) plus similar results for the permanently stratified ocean regions of the world (grey circles and black line), adapted from Behrenfeld et al. (2006).

The means by which changing temperatures were claimed by the researchers to have driven the two sequential linear-fit trends in NPP is based on their presumption that a warming climate increases the density contrast between warmer surface waters and cooler underlying nutrient-rich waters, so that the enhanced stratification that occurs with warming "suppresses nutrient exchange through vertical mixing," which decreases NPP by reducing the supply of nutrients to the surface waters where photosynthesizing phytoplankton predominantly live. In contrast, the ten scientists suggest that "surface cooling favors elevated vertical exchange," which increases NPP by enhancing the supply of nutrients to the ocean's surface waters, which are more frequented by phytoplankton than are under-lying waters, due to light requirements for photosynthesis.

This is all well and good; but it is informative to note that from approximately the middle of 2001 to the end of the data series in early 2006 (which interval accounts for more than half of the entire data record), there has been, if anything, a slight increase in global NPP. Does this observation mean there has been little to no net global warming since mid-2001? Or does it mean that the global ocean's mean surface temperature actually cooled a bit over the last five years? Any way you look at it, to paraphrase Simon and Garfunkel, climate alarmists lose, for neither alternative is what one would expect if the earth was truly racing headlong into a CO2-induced climate inferno, as the world's climate alarmists are continually ranting and raving it is doing ... and doing, as they like to suggest, with an unprecedented vengeance.

On the other hand, the relationship between global warming and oceanic productivity may not be nearly as strong as what Behrenfeld et al. have suggested; and they actually leave themselves some significant "wiggle room" in this regard, saying "modeling studies suggest that shifts in ecosystem structure from climate variations may be as [important as] or more [our italics] important than the alterations in bulk integrated properties reported here," noting that some "susceptible ecosystem characteristics" that might be so shifted include "taxonomic composition, physiological status, and light absorption by colored dissolved organic material." Hence, it is possible that given enough time, the types of phenomena Behrenfeld et al. describe as possibly resulting in important "shifts in ecosystem structure" could well compensate, or even over-compensate, for what might initially appear to be negative warming-induced consequences.

Another reason for not concluding too much from the oceanic NPP data set of Behrenfeld et al. is that it may be of too short a duration to reveal what might be occurring on a much longer timescale throughout the world's oceans, or that its position in time may be such that it does not allow the detection of far greater short-term changes of the opposite sign that may have occurred a few years earlier or that might occur in the near future.

Consider, for example, the fact that the central regions of the world's major oceans were long thought to be essentially vast biological deserts (Ryther, 1969), but that several studies of primary photosynthetic production conducted in those regions over the 1980s (Shulenberger and Reid, 1981; Jenkins, 1982; Jenkins and Goldman, 1985; Reid and Shulenberger, 1986; Marra and Heinemann, 1987; Laws et al., 1987; Venrick et al., 1987; Packard et al., 1988) yielded results that suggested marine productivity at that time was twice or more as great as it likely was for a long time prior to 1969, causing many of that day to speculate that "the ocean's deserts are blooming" (Kerr, 1986).

Of even greater interest, perhaps, is the fact that over this particular period of time (1970-1988), the data repository of Jones et al. (1999) indicates the earth experienced a (linear-regression-derived) global warming of 0.333C, while the data base of the Global Historical Climatology Network indicates the planet experienced a similarly-calculated global warming of 0.397C. The mean of these two values (0.365C) is nearly twice as great as the warming that occurred over the post-1999 period studied by Behrenfeld et al.; yet this earlier much larger warming (which according to the ten researchers' way of thinking should have produced a major decline in ocean productivity) was concomitant with a huge increase in ocean productivity. Consequently, it would appear that just the opposite of what Behrenfeld et al. suggest about global warming and ocean productivity is likely to be the more correct of the two opposing cause-and-effect relationships.

Sherwood, Keith and Craig Idso

Behrenfeld, M.J., O'Malley, R.T., Siegel, D.A., McClain, C.R., Sarmiento, J.L., Feldman, G.C., Milligan, A.J., Falkowski, P.G., Letelier, R.M. and Boss, E.S. 2006. Climate-driven trends in contemporary ocean productivity. Nature 444: 752-755.

Jenkins, W.J. 1982. Oxygen utilization rates in North Atlantic subtropical gyre and primary production in oligotrophic systems. Nature 300: 246-248.

Jenkins, W.J. and Goldman, J.C. 1985. Seasonal oxygen cycling and primary production in the Sargasso Sea. Journal of Marine Research 43: 465-491.

Jones, P.D., Parker, D.E., Osborn, T.J. and Briffa, K.R. 1999. Global and hemispheric temperature anomalies -- land and marine instrument records. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, TN, USA.

Kerr, R.A. 1986. The ocean's deserts are blooming. Science 232: 1345.

Laws, E.A., Di Tullio, G.R. and Redalje, D.G. 1987. High phytoplankton growth and production rates in the North Pacific subtropical gyre. Limnology and Oceanography 32: 905-918.

Marra, J. and Heinemann, K.R. 1987. Primary production in the North Pacific central gyre: Some new measurements based on 14C. Deep-Sea Research 34: 1821-1829.

Packard, T.T., Denis, M., Rodier, M. and Garfield, P. 1988. Deep-ocean metabolic CO2 production: Calculations from ETS activity. Deep-Sea Research 35: 371-382.

Reid, J.L. and Shulenberger, E. 1986. Oxygen saturation and carbon uptake near 28N, 155W. Deep-Sea Research 33: 267-271.

Ryther, J.H. 1969. Photosynthesis and fish production in the sea. Science 166: 72-76.

Shulenberger, E. and Reid, L. 1981. The Pacific shallow oxygen maximum, deep chlorophyll maximum, and primary production, reconsidered. Deep-Sea Research 28: 901-919.

Venrick, E.L., McGowan, J.A., Cayan, D.R. and Hayward, T.L. 1987. Climate and chlorophyll a: Long-term trends in the central North Pacific Ocean. Science 238: 70-72.