How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic


Carbon Sequestration (General) - Summary
As the CO2 content of the air continues to rise, nearly all of earth's plants will respond by increasing their photosynthetic rates and producing more biomass.  Such increases in productivity will likely lead to greater amounts of carbon sequestration in both above- and below-ground plant parts, as well as in soils.  But how powerful are the carbon sequestering abilities of earth's vegetation?  Can they be negatively impacted by an increase in air temperature?  In this summary, we review the results of various studies that have addressed these and other important questions pertaining to biospheric carbon sequestration.

In Southern Europe, Allen et al. (1999) analyzed sediment cores from a lake in Italy and the Mediterranean Sea, determining that over the past 102,000 years, the warm period of the Holocene produced the greatest organic carbon content in vegetation, which was more than double that observed for any other period in this historic record.  Similarly, in Northern Eurasia, Velichko et al. (1999) reconstructed carbon storage in vegetation and determined that plant life in Northern Eurasia was much more productive and efficient in sequestering carbon at higher, rather than lower, air temperatures.  In fact, vegetative carbon storage during the Holocene Optimum, which occurred about 6,000 years ago, was calculated to be 120% greater than present day carbon sequestration in this region.  Thus, warmer was definitely better than colder in terms of vegetative productivity for these areas.

On a smaller time-scale covering parts of the last two decades, Schimel et al. (2000) used three ecosystem models to simulate changes in soil and vegetative carbon fluxes in the United States for the period 1980 to 1993.  On average, the models calculated a terrestrial carbon sink of 0.08 Pg carbon per year (1 Pg = 1015 g) for this region, with the bulk of the sink resulting from the aerial fertilization effect of the rising CO2 content of the atmosphere.  Also, as noted in our Editorial of 20 September 2000, research of Oechel et al. (1993, 1995, 2000) suggests that although the Alaskan Arctic tundra may well have been a net source of CO2 for the atmosphere during the mid-1980s and early 1990s, it has since that time become a carbon sink, which is in harmony with the implications of the recent experimental work of Johnson et al. (2000).

In addition to stimulating terrestrial carbon storage, even during times of warming - indeed, especially during times of warming - the rising atmospheric CO2 concentration should also enhance oceanic carbon sequestration.  Wolf-Gladrow et al. (1999), for example, reviewed the direct effects of atmospheric CO2 enrichment on marine biota and oceanic "carbon pumps," concluding that an increase in the air's CO2 content should increase the capacity of earth's oceans to take up and store more atmospheric CO2.

On another research front, Joos and Bruno (1998) utilized ice cores and direct observations of atmospheric CO2 and 13C to reconstruct the histories of terrestrial and oceanic uptake of anthropogenic carbon over the past two centuries.  They determined that during the initial portion of this period, and persisting into the first decades of the past century, the biosphere as a whole supplied carbon to the atmosphere.  Thereafter, however, the biosphere became a carbon sink.  In further scrutinizing their data, the authors noted that the current global carbon sink has been growing in magnitude for at least the last hundred years.

In reviewing the progress of research dealing with the global carbon cycle, Tans and White (1998) concluded that "early estimates of huge losses of carbon from plants and soils due to biomass burning and deforestation have recently given way to the idea of a terrestrial biosphere nearly balanced (globally) with respect to carbon."  Indeed, after analyzing O2/N2 measurements of background air collected at Cape Grim, Tasmania from 1978 to 1997, Langenfelds et al. (1999) determined that the surface fluxes of carbon over this 19-year period were "essentially in balance."  In other words, essentially all of the carbon released to the air as a consequence of the activities of man was removed from the atmosphere by the biological activities of predominantly terrestrial vegetation.

In assessing the ability of earth's vegetation to sequester carbon in the future, it is important to consider the findings of Luz et al. (1999), who estimate that the biospheric productivity of the planet as a whole is currently at its highest point in the past 82,000 years, as is the atmospheric CO2 concentration.  Further, it is well established that plant productivity rises with increasing levels of atmospheric CO2.  Thus, one might expect future productivity to rise in tandem with the CO2 content of the air.

Following this line of reasoning, Xiao et al. (1998) used a process-based ecosystem model to compute global net ecosystem production from 1990 to 2100 based on three scenarios of atmospheric CO2 and temperature change.  In all cases where these two parameters increased together, they reported positive increases in global net ecosystem productivity, which is indicative of parallel increases in carbon sequestration.  Thus, it is likely that global carbon sequestration will become ever more robust in the coming decades, as we discuss in more detail in our Editorial of 1 December 1999.

References
Allen, J.R.M., Brandt, U., Brauer, A., Hubberten, H.-W., Huntley, B., Keller, J., Kraml, M., Mackensen, A., Mingram, J., Negendank, J.F.W., Nowaczyk, N.R., Oberhansli, H., Watts, W.A., Wulf, S. and Zolitschka, B.  1999.  Rapid environmental changes in southern Europe during the last glacial period.  Nature 400: 740-743.

Johnson, L.C., Shaver, G.R., Cades, D.H., Rastetter, E., Nadelhoffer, K., Giblin, A., Laundre, J. and Stanley, A.  2000.  Plant carbon-nutrient interactions control CO2 exchange in Alaskan wet sedge tundra ecosystems.  Ecology 81: 453-469.

Joos, F. and Bruno, M.  1998.  Long-term variability of the terrestrial and oceanic carbon sinks and the budgets of the carbon isotopes 13C and 14C.  Global Biogeochemical Cycles 12: 277-295.

Langenfelds, R.L. Francey, R.J. and Steele, L.P.  1999.  Partitioning of the global fossil CO2 sink using a 19-year trend in atmospheric O2Geophysical Research Letters 26: 1897-1900.

Luz, B., Barkan, E., Bender, M.L., Thiemens, M.H. and Boering, K.A.  1999.  Triple-isotope composition of atmospheric oxygen as a tracer of biospheric productivity.  Nature 400: 547-550.

Oechel, W.C., Hastings, S.J., Vourlitis, G., Jenkins, M., Riechers, G. and Grulke, N.  1993.  Recent change of Arctic tundra ecosystems from a net carbon dioxide sink to a source.  Nature 361: 520-523.

Oechel, W.C., Vourlitis, G.L., Hastings, S.J. and Bochkarev, S.A.  1995.  Change in Arctic CO2 flux over two decades: Effects of climate change at Barrow, Alaska.  Ecological Applications 5: 846-855.

Oechel, W.C., Vourlitis, G.L., Hastings, S.J., Zulueta, R.C., Hinzman, L. and Kane, D.  2000.  Acclimation of ecosystem CO2 exchange in the Alaskan Arctic in response to decadal climate warming.  Nature 406: 978-981.

Schimel, D., Melillo, J., Tian, H., McGuire, A.D., Kicklighter, D., Kittel, T., Rosenbloom, N., Running, S., Thorton, P., Ojima, D., Parton, W., Kelly, R., Sykes, M., Neilson, R. and Rizzo, B.  2000.  Contribution of increasing CO2 and climate to carbon storage by ecosystems in the United States.  Science 287: 2004-2006.

Tans, P.P. and White, J.W.C.  1998.  The global carbon cycle: In balance, with a little help from the plants.  Science 281: 183-184.

Velichko, A.A., Zelikson, E.M. and Borisova, O.K.  1999.  Vegetation, phytomass and carbon storage in Northern Eurasia during the last glacial-interglacial cycle and the Holocene.  Chemical Geology 159: 191-204.

Wolf-Gladrow, D.A., Riebesell, U., Burkhardt, S. and Bijma, J.  1999.  Direct effects of CO2 concentration on growth and isotopic composition of marine plankton.  Tellus 51B: 461-476.

Xiao, X., Melillo, J.M., Kicklighter, D.W., McGuire, A.D., Prinn, R.G., Wang, C., Stone, P.H. and Sokolov, A.  1998.  Transient climate change and net ecosystem production of the terrestrial biosphere.  Global Biogeochemical Cycles 12: 345-360.