Elderfield and Rickaby (2000) note that the typically low atmospheric CO2 concentrations of glacial periods have generally been attributed to an increased oceanic uptake of CO2, "particularly in the southern oceans."  However, the assumption that intensified phytoplanktonic photosynthesis may have stimulated CO2 uptake rates during glacial periods has always seemed at odds with the observational fact that rates of photosynthesis are generally much reduced in environments of significantly lower-than-current atmospheric CO2 concentrations, such as typically prevail during glacial periods.

The two scientists provide a new interpretation of Cd/Ca systematics in sea water that helps to resolve this dichotomy, as it allows them to more accurately estimate surface water phosphate conditions during glacial times and thereby determine the implications for concomitant atmospheric CO2 concentrations.  What they find, in their words, is that "results from the Last Glacial Maximum [LGM] show similar phosphate utilization in the subantarctic to that of today, but much smaller utilization in the polar Southern Ocean," which implies, according to Delaney (2000), that Antarctic productivity was lower at that time than it is now, but that subantarctic productivity was about the same as it has been in modern times, due perhaps to greater concentrations of bio-available iron compensating for the lower atmospheric CO2 concentrations of the LGM.

So what caused the much smaller utilization of phosphate in the polar Southern Ocean during the LGM?  Noting that the area of sea-ice cover in the Southern Ocean during glacial periods may have been as much as double that of modern times, Elderfield and Rickaby suggest that "by restricting communication between the ocean and atmosphere, sea ice expansion also provides a mechanism for reduced CO2 release by the Southern Ocean and lower glacial atmospheric CO2."  Hence, it is possible that phytoplanktonic productivity in the glacial Southern Ocean may well have been no higher than it is at the present time, notwithstanding the greater supply of bio-available iron typical of glacial epochs.

In the case of the interglacial period in which we currently live, Dupouy et al. (2000) say it has long been believed that N2 fixation in the world's oceans is unduly low, in consequence of the present low supply of wind-blown iron compared to that of glacial periods, and that this state of affairs leads to low phytoplanktonic productivity, even in the presence of higher atmospheric CO2 concentrations.  The evidence they have acquired to date, however, suggests that marine N2 fixation may be much greater than what has generally been thought to be the case.  In particular, they say that several Trichodesmium species of N2-fixing cyanobacteria have "a nearly ubiquitous distribution in the euphotic zone of tropical and subtropical seas and could play a major role in bringing new N to these oligotrophic systems."  And this feat, in their words, "could play a significant role in enhancing new production."

The importance of these findings is perhaps best appreciated in light of the findings of Pahlow and Riebesell (2000), who in studying data obtained from 1173 stations in the Atlantic and Pacific Oceans, covering the years 1947 to 1994, detected changes in Northern Hemispheric deep-ocean Redfield ratios that are indicative of increasing nitrogen availability there, which increase was concomitant with an increase in export production that has resulted in ever-increasing oceanic carbon sequestration.  These investigators further suggest that the growing supply of nitrogen has its origin in anthropogenic activities that release nitrous oxides to the air.  In addition, the increased carbon export may be partly a consequence of the historical increase in the air's CO2 concentration, which has been demonstrated to have the ability to enhance phytoplanktonic productivity (see Phytoplankton (Growth Response to CO2) in our Subject Index), analogous to the way in which elevated concentrations of atmospheric CO2 enhance the productivity of terrestrial plants, including their ability to fix nitrogen (see Nitrogen Fixation in our Subject Index).

Further elucidating the productivity-enhancing power of the ongoing rise in the air's CO2 content is the study of Pasquer et al. (2005), who employed a complex model of growth regulation of diatoms, pico/nano phytoplankton, coccolithophorids and Phaeocystis spp. by light, temperature and nutrients (based on a comprehensive analysis of literature reviews focusing on these taxonomic groups) to calculate changes in the ocean uptake of carbon in response to a sustained increase in atmospheric CO2 concentration of 1.2 ppm per year for three marine ecosystems where biogeochemical time-series of the data required for model initialization and comparison of results were readily available.  These systems were (1) the ice-free Southern Ocean Time Series station KERFIX (50°40'S, 68°E) for the period 1993-1994 (diatom-dominated), (2) the sea-ice associated Ross Sea domain (76°S, 180°W) of the Antarctic Environment and Southern Ocean Process Study AESOPS in 1996-1997 (Phaeocystis-dominated), and (3) the North Atlantic Bloom Experiment NABE (60°N, 20°W) in 1991 (coccolithophorids).  Their results, in their words, "show that at all tested latitudes the prescribed increase of atmospheric CO2 enhances the carbon uptake by the ocean."  Indeed, we calculate from their graphical presentations that (1) at the NABE site a sustained atmospheric CO2 increase of 1.2 ppm per year over a period of eleven years increases the air-sea CO2 flux in the last year of that period by approximately 17%, (2) at the AESOPS site the same protocol applied over a period of six years increases the air-sea CO2 flux by about 45%, and (3) at the KERFIX site it increases the air-sea CO2 flux after nine years by about 78%.  Although the results of this interesting study based on the complex SWAMCO model of Lancelot et al. (2000), as modified by Hannon et al. (2001), seem overly large, they highlight the likelihood that the ongoing rise in the air's CO2 content may be having a significant positive impact on ocean productivity and the magnitude of the ocean carbon sink.

But what about increasing temperatures? Sarmiento et al. (2004) conducted a massive computational study that employed six coupled climate model simulations to determine the biological response of the global ocean to the climate warming they simulated from the beginning of the Industrial Revolution to the year 2050.  Based on vertical velocity, maximum winter mixed-layer depth and sea-ice cover, they defined six biomes and calculated how their surface geographies would change in response to their calculated changes in global climate.  Next, they used satellite ocean color and climatological observations to develop an empirical model for predicting surface chlorophyll concentrations from the final physical properties of the world's oceans as derived from their global warming simulations, after which they used three primary production algorithms to estimate the response of oceanic primary production to climate warming based on their calculated chlorophyll concentrations. When all was said and done, the thirteen scientists from Australia, France, Germany, Russia, the United Kingdom and the United States arrived at a global warming-induced increase in global ocean primary production that ranged from 0.7 to 8.1%, which is a far, far cry from the disastrous consequences routinely predicted by climate alarmists.

So what do real-world measurements of oceanic productivity reveal?  Goes et al. (2005) analyzed seven years (1997-2004) of satellite-derived ocean color data pertaining to the Arabian Sea, as well as associated sea surface temperatures (SSTs) and winds.  They report that for the region located between 52 to 57°E and 5 to 10°N, "the most conspicuous observation was the consistent year-by-year increase in phytoplankton biomass over the 7-year period."  This phenomenon was so dramatic that by the summer of 2003, in their words, "chlorophyll a concentrations were >350% higher than those observed in the summer of 1997."  They also report that the increase in chlorophyll a was "accompanied by an intensification of sea surface winds, in particular of the zonal (east-to-west) component," noting that these "summer monsoon winds are a coupled atmosphere-land-ocean phenomenon, whose strength is significantly correlated with tropical SSTs and Eurasian snow cover anomalies on a year-to-year basis."  More specifically, they say that "reduced snow cover over Eurasia strengthens the spring and summer land-sea thermal contrast and is considered to be responsible for the stronger southwest monsoon winds."  In addition, they state that "the influence of southwest monsoon winds on phytoplankton in the Arabian Sea is not through their impact on coastal upwelling alone but also via the ability of zonal winds to laterally advect newly upwelled nutrient-rich waters to regions away from the upwelling zone."  Their final conclusion about the matter is that "escalation in the intensity of summer monsoon winds, accompanied by enhanced upwelling and an increase of more than 350% in average summertime phytoplankton biomass along the coast and over 300% offshore, raises the possibility that the current warming trend of the Eurasian landmass is making the Arabian Sea more productive."

To the north and west on the other side of Eurasia, Marasovic et al. (2005) analyzed monthly observations of basic hydrographic, chemical and biological parameters, including primary production, that had been made since the 1960s at two oceanographic stations, one near the coast (Kastela Bay) and one in the open sea.  They found that mean annual primary production in Kastela Bay averaged about 430 mg C m^-2 d^-1 over the period 1962-72, exceeded 600 mg C m^-2 d^-1 over the period 1972-82, and rose to over 700 mg C m^-2 d^-1 over the period 1982-96, accompanied by a similar upward trend in percent oxygen saturation of the surface water.  The initial value of primary production in the open sea was much less (approximately 150 mg C m^-2 d^-1), but it began to follow the upward trend of the Kastela Bay data after about one decade.  Marasovic et al. thus conclude that "even though all the relevant data indicate that the changes in Kastela Bay are closely related to an increase of anthropogenic nutrient loading, similar changes in the open sea suggest that primary production in the Bay might, at least partly, be due to global climatic changes," which, in their words, are "occurring in the Mediterranean and Adriatic Sea open waters" and may be directly related to "global warming of air and ocean," since "higher temperature positively affects photosynthetic processes."

Raitsos et al. (2005) investigated the relationship between Sea-viewing Wide Field-of-view Sensor chlorophyll-a measurements in the Central Northeast Atlantic and North Sea (1997-2002) and simultaneous measurements of the Phytoplankton Color Index (PCI) collected by the Continuous Plankton Recorder survey, which is an upper-layer plankton monitoring program that has operated in the North Sea and North Atlantic Ocean since 1931.  By developing a relationship between the two data bases over their five years of overlap, they were able to produce a Chl-a history for the Central Northeast Atlantic and North Sea for the period 1948-2002.  Of this record they say that "an increasing trend is apparent in mean Chl-a for the area of study over the period 1948-2002."  They also say "there is clear evidence for a stepwise increase after the mid-1980s, with a minimum of 1.3mg m^-3 in 1950 and a peak annual mean of 2.1 mg m^-3 in 1989 (62% increase)."  Alternatively, it is possible that the data represent a more steady long-term upward trend upon which is superimposed a decadal-scale oscillation.  In a final comment on their findings, they note that "changes through time in the PCI are significantly correlated with both sea surface temperature and Northern Hemisphere temperature," citing Beaugrand and Reid (2003).

Dropping down to the Southern Ocean, Hirawake et al. (2005) analyzed chlorophyll a data obtained from Japanese Antarctic Research Expedition cruises made by the Fuji and Shirase ice-breakers between Tokyo and Antarctica from 15 November to 28 December of nearly every year between 1965 and 2002 in a study of interannual variations of phytoplankton biomass, calculating results for the equatorial region between 10°N and 10°S, the Subtropical Front (STF) region between 35°S and 45°S, and the Polar Front (PF) region between 45°S and 55°S.  They report that an increase in chl a was "recognized in the waters around the STF and the PF, especially after 1980 around the PF in particular," and that "in the period between 1994 and 1998, the chl a in the three regions exhibited rapid gain simultaneously."  They also say "there were significant correlations between chl a and year through all of the period of observation around the STF and PF, and the rates of increase are 0.005 and 0.012 mg chl a m^-3 y^-1, respectively."  In addition, they report that the satellite data of Gregg and Conkright (2002) "almost coincide with our results."  In commenting on these findings, the Japanese scientists say that "simply considering the significant increase in the chl a in the Southern Ocean, a rise in the primary production as a result of the phytoplankton increase in this area is also expected."

In light of these several real-world observations, we not only find no indications of any widespread decline in oceanic productivity over the 20th century in response to climate-alarmist-feared increases in air temperature and CO2 concentration, we see evidence that just the opposite is occurring, thanks to these very same environmental changes, which are actually proving to be beneficial.

References
Beaugrand, G. and Reid, P.C.  2003.  Long-term changes in phytoplankton, zooplankton and salmon related to climate.  Global Change Biology 9: 801-817.

Delaney, P.  2000.  Nutrients in the glacial balance.  Nature 405: 288-291.

Dupouy, C., Neveux, J., Subramaniam, A., Mulholland, M.R., Montoya, J.P., Campbell, L., Carpenter, E.J. and Capone, D.G.  2000.  Satellite captures Trichodesmium blooms in the southwestern tropical Pacific.  EOS, Transactions, American Geophysical Union 81: 13, 15-16.

Elderfield, H. and Rickaby, R.E.M.  2000.  Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean.  Nature 405: 305-310.

Goes, J.I., Thoppil, P.G., Gomes, H. do R. and Fasullo, J.T.  2005.  Warming of the Eurasian landmass is making the Arabian Sea more productive.  Science 308: 545-547.

Gregg, W.W. and Conkright, M.E.  2002.  Decadal changes in global ocean chlorophyll.  Geophysical Research Letters 29: 10.1029/2002GL014689.

Hannon, E., Boyd, P.W., Silvoso, M. and Lancelot, C.  2001.  Modelling the bloom evolution and carbon flows during SOIREE: implications for future in situ iron-experiments in the Southern Ocean.  Deep-Sea Research II 48: 2745-2773.

Hirawake, T., Odate, T. and Fukuchi, M.  2005.  Long-term variation of surface phytoplankton chlorophyll a in the Southern Ocean during 1965-2002.  Geophysical Research Letters 32: 10.1029/2004GL021394.

Lancelot, C., Hannon, E., Becquevort, S., Veth, C. and De Baar, H.J.W.  2000.  Modelling phytoplankton blooms and carbon export in the Southern Ocean: dominant controls by light and iron in the Atlantic sector in austral spring 1992.  Deep Sea Research I 47: 1621-1662.

Marasovic, I., Nincevic, Z., Kuspilic, G., Marinovic, S. and Marinov, S.  2005.  Long-term changes of basic biological and chemical parameters at two stations in the middle Adriatic.  Journal of Sea Research 54: 3-14.

Pahlow, M. and Riebesell, U.  2000.  Temporal trends in deep ocean Redfield ratios.  Science 287: 831-833.

Pasquer, B., Laruelle, G., Becquevort, S., Schoemann, V., Goosse, H. and Lancelot, C.  2005.  Linking ocean biogeochemical cycles and ecosystem structure and function: results of the complex SWAMCO-4 model.  Journal of Sea Research 53: 93-108.

Raitsos, D., Reid, P.C., Lavender, S.J., Edwards, M. and Richardson, A.J.  2005.  Extending the SeaWiFS chlorophyll data set back 50 years in the northeast Atlantic.  Geophysical Research Letters 32: 10.1029/2005GL022484.

Sarmiento, J.L., Slater, R., Barber, R., Bopp, L., Doney, S.C., Hirst, A.C., Kleypas, J., Matear, R., Mikolajewicz, U., Monfray, P., Soldatov, V., Spall, S.A. and Stouffer, R.  2004.  Response of ocean ecosystems to climate warming.  Global Biogeochemical Cycles 18: 10.1029/2003GB002134.