An experiment to artificially stimulate plankton growth in a 50 km² test area of ocean. This led to a better understanding of the emission and absorption of gases from the ocean, and the effect this has on the climate.

The interaction between the atmosphere and ocean plays a key role in our climate and weather. For example, the world’s oceans absorb approximately 30–40% of the carbon dioxide produced by human activity. Without this buffer climate change would be much more rapid and severe. This is particularly important in the vast expanses of the Southern Ocean where gas exchange is efficient because the ocean surface is roughened by the strong winds and large waves, and temperatures are low.

The Problem

Trying to predict future climate change when the feedback processes driven by the ocean are not understood is very difficult. The movement of gases in and out of the ocean is understood in theory, but there have been few experiments which directly measure gas fluxes in a controlled environment. The aim of the SOLAS Air–sea Gas Exchange (SAGE) experiment was to study the exchange of climate reactive gases in a semi-controlled situation, by stimulating the growth of plankton by fertilizing the ocean with iron sulphate over 50 km² of ocean.

The Solution

To get the full picture, we also need to consider biology and simple plankton in the ocean that drive the biological pumping of CO₂ through photosynthesis. And it is not just carbon dioxide that needs to be considered. The plankton in the ocean could also play a role in climate change by emitting the gas dimethyl sulphide (DMS). This leads to the creation of aerosols that effect the extent and reflectivity of marine cloud cover. Even modest changes of DMS emission could have significant effects on global temperature.

Only by understanding the physical, biological and chemical processes governing the interchange of gases, can we confidently predict timing and magnitude of future changes in climate. To mount this multidisciplinary SOLAS study we brought together researchers from around 20 organisations to work in the logistically challenging environment of the Southern Ocean.

The New Zealand component of this work is sponsored by the Foundation for Research, Science and Technology. For further information contact solas@niwa.co.nz

The Result

The experimental stage was completed in 2004. You can find out more about this, and other, iron fertilisation experiments in this article by Cliff Law.

One of the first results from SAGE was the publication of a windspeed-gas exchange parameterisation that includes measurements at the highest windspeeds of any dataset to date (Ho et al, 2006).

Ho, D. T., C. S. Law, M. J. Smith, P. Schlosser, M. Harvey, and P. Hill. 2006. Measurements of air-sea gas exchange at high wind speeds in the Southern Ocean: Implications for global parameterizations, Geophys. Res. Lett., 33, L16611, doi:10.1029/2006GL026817.

Other SAGE results were published in a Special Issue of Deep-Sea Research II.
http://www.sciencedirect.com/science/journal/09670645/58/6