Learn how plants respond to higher atmospheric CO2 concentrations

How does rising atmospheric CO2 affect marine organisms?

Click to locate material archived on our website by topic


Another Negative Feedback to Curtail Global Warming
Reference
Geibert, W., Assmy, P., Bakker, D.C.E., Hanfland, C., Hoppema, M., Pichevin, L.E., Schroder, M., Schwarz, J.N., Stimac, I., Usbeck, R. and Webb, A. 2010. High productivity in an ice melting hot spot at the eastern boundary of the Weddell Gyre. Global Biogeochemical Cycles 24: 10.1029/2009GB003657.

Background
The authors write that "the Southern Ocean (SO) plays a key role in modulating atmospheric CO2 via physical and biological processes," but that "over much of the SO, biological activity is iron-limited," which restricts the SO's ability to do its job in this regard. However, they note that "new in situ data from the Antarctic zone south of Africa in a region centered at ~20°E-25°E reveal a previously overlooked region of high primary production." Thus, they sought to learn the cause of this anomalous production, which is an integral part of the globe's deep-ocean carbon transferal system, whereby massive quantities of CO2-carbon recently absorbed from the atmosphere are photosynthetically incorporated into photoplanktonic biomass, which either directly or indirectly -- via marine food chains -- is transported to the bottom layers of the sea, where it experiences long-term separation from the atmosphere.

What was done
Based on data obtained from expedition ANT XX/2 to the Weddell Gyre (WG) that took place from 24 November 2002 to 23 January 2003 -- which was carried out on the icebreaker RV "Polarstern" -- Giebert et al. acquired "an in situ biogeochemical data set to complement indirect information from modeling and remote sensing techniques." This data set included multiple water samples for analyses of nutrients, oxygen, phyotoplankton species identification and pigment and chlorophyll-a concentration, as well as for measurements of particulate matter, temperature, salinity and the radionuclides 234Th and 238U.

What was learned
First of all, the eleven researchers -- hailing from Germany, New Zealand, South Africa and the United Kingdom -- determined that "sea ice together with enclosed icebergs is channeled by prevailing winds to the eastern boundary of the WG," where a sharp transition to warmer waters causes melting of ice that contains significant amounts of iron previously deposited upon it by aeolian transport of iron-rich dust. And as the larger icebergs penetrate deeper into the sea, they say that "they are exposed to warmer waters even during winter, when sea ice is present and growing," so that the "continuous melting of icebergs in winter will lead to rising fresher and potentially iron-enriched waters from below, in the immediate vicinity of icebergs," which meltwater "would spread under the sea ice as a thin lens of fresher water, where it can refreeze due to its comparatively low salinity, and it can undergo processes of sorption and biological uptake," which hypothesis, in their words, "is consistent with maxima of iron concentrations in the lowermost parts of sea ice prior to the onset of spring melting (Lannuzel et al., 2008)." Thus, as they conclude, "this melting hot spot causes an enhanced input of iron and salinity-driven stratification of the surface waters," which are the ideal conditions for sustaining the "intense phytoplankton blooms" that characterize the waters they studied.

What it means
Geibert et al. state that their findings "imply that future changes in sea-ice cover and dynamics could have a significant effect on carbon sequestration in the SO." And if those changes were to include enhanced melting of Antarctic sea ice and icebergs, such as climate alarmists continually claim will occur, the planet's deep-ocean carbon transferal system would shift into a higher gear and effectively sequester greater amounts of CO2-carbon from the atmosphere, reducing its rate of rise and thereby reducing the strength of the CO2 greenhouse effect.

Reference
Lannuzel, D., Schoemann, V., de Jong, J., Tison, J.L. and Chou, L. 2007. Distribution and biogeochemical behavior of iron in the East Antarctic sea ice. Marine Chemistry 106: 18-32.

Reviewed 24 November 2010