Location and time
SOIREE, the first Southern Ocean in situ iron fertilisation experiment, was performed in February 1999 from the MV Tangaroa. The experiment took place in the Australasian–Pacific sector of the Southern Ocean approximately 2000 km southwest of Tasmania (61º S 140º E) from 9 to 22 February 1999.687
The experiment
Around 3800 kg of acidified ferrous sulphate (FeSO4) with 165 g of sulphur hexafluoride (SF6) used as a tracer, was added to the 65 metres deep surface
mixed layer over about 50 square kilometres.688 SF
6 is used as a tracer as itallows
the scientists to find the fertilised waters even if the iron is used up, and can be
686 LOHA is Hindi for iron, FEX stands for Fertilization Experiment. 687 Boyd, above n 96,2428.
analysed at extremely low levels. This allows the scientists to re-fertilise if needed, providing a separate verification of being ‘in the patch’.689 Due to a
decrease in ambient levels of dissolved iron within days, subsequent additions of 1550–1750 kg of FeSO4 were made on days three, five and seven of the
experiment.690 It should be noted that according to the IPCC,691 SF
6 is the most
potent greenhouse gas that it has evaluated, with a global warming potential of 22 800 times that of CO2 when compared over a 100 year period. However, SF6
is insoluble in water and denser than air at sea level. Its use as a tracer is consistent with current procedures at the time. The very small amount used in the experiment would be inconsequential as a GHG and poses little or no threat to the environment.
Throughout the 13 day experiment there were ‘iron mediated increases in phytoplankton growth rates with a marked increase in chlorophyll’.692 During the
experiment the centre of the patch was marked with a buoy and fitted with a GPS693 and ARGOS.694 After about two days, the iron-enriched area had
increased to over 100 square kilometres and by day 13 it had covered an area of over 200 square kilometres. The SOIREE bloom persisted for more than 40 days following the departure of the scientific team from the site and was observed via the NASA SeaWiFS695 satellite.696 It is interesting to note that the
SOIREE bloom persisted for so long after departure from the site.697 This was
much longer than originally anticipated and over this time the fertilised patch was observed to change from a small, circular region into an extended ribbon of
689 Prof. Tom Trull, email correspondence on file with author 12 July 2010. 690 Boyd, above n 96, 2425.
691 P Forster, V Ramaswamy, P Artaxo, T Berntsen, R Betts, D W Fahey, J. Haywood, J Lean, D C Lowe, G
Myhre, J Nganga, R. Prinn, G. Raga, M. Schulz, R Van Dorland, ‘2007: Changes in Atmospheric Constituents and in Radiative Forcing’ in S Solomon, D Qin, M Manning, Z Chen, M Marquis, K B Averyt, M Tignor, H L Miller (eds) Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change,(2007) 212.
692 Boyd, above n 96, 2438. 693 Global Positioning System.
694 Global ocean observing program <www.argo.net> at 1 December 2009.
695 Sea-viewing Wide Field-of-view Sensor <http://oceancolor.gfs.nasa.gov/SeaWiFS> at 1 December
2009.
696 Boyd, above n 96, 2425–38. 697 Boyd, above n 96,2425.
181 chlorophyll. The ribbon then began to curl on itself, into a horseshoe shape,
which was easily visible on the SeaWiFS satellite. Both the size and the length of the bloom can be seen as the bright semi-circular arc in the high-resolution SeaWiFS image in Figures 6 and 7. The size and shape illustrates the fluid nature of the bloom.
Findings
During the experiment diatoms were observed to be the dominant bloom with the dominant diatom observed later in the study as Fragilariopsis kerguelensis. This is important as one of the early criticisms of ocean fertilisation was that certain species will dominate over others, which with a large scale, long term bloom may influence the ecosystem in the immediate area of the fertilisation site and bloom. Another concern is that large phytoplankton blooms may be difficult to control and contain. The fact that the SOIREE bloom not only persisted for longer than originally expected, but also was unable to be contained within the experiment patch, demonstrates that at the time of this experiment scientists were still trying to understand the process and unpredictability of blooms created by artificial ocean fertilisation.
The SOIREE experiment confirmed that iron limitation in the spring and summer polar waters did affect the growth rates of phytoplankton at the site.698
The phytoplankton biomass and rates of photosynthesis were elevated after the addition of iron in these HNLC waters in the Southern Ocean. This increase in primary production did cause a large draw down of CO2 and macronutrients, with a subsequent increase in the dimethylsulfide (DMS) levels. The increases in DMS levels during the trials are trends that under climate change conditions may represent negative feedbacks with respect to global warming. It was also found that the changes in the levels of climate related gases appear to be mediated by different algal groups, with diatoms for pCO2 and haptophytes 699 for
dimethylsulfoniopropionate (DMSPp), a metabolite found in marine
phytoplankton.
698 Boyd, above n 96, 2425–38.
Figure 6: SOIREE bloom 1999
Image shows the SOIREE bloom on 8 March 1999 with outline of Australia shown clearly in the upper centre of the image. The SOIREE bloom is seen as a horseshoe curled shape in the lower centre of picture and identified with red arrow and shows the scale of the bloom. This bloom is shown in greater detail in the image below. The red, yellow and blue horseshoe shaped area is the phytoplankton bloom in response to the iron. Graph shows chlorophyll concentration (mg/m3). (Source: Courtesy of NASA SeaWiFS700. )
Figure 7: SOIREE experiment 1999
183
Results
The draw down was due mainly to proliferation of diatom stocks. The experiment showed that plankton growth and community composition can be controlled by iron in the summer months in the polar waters of the Southern Ocean. The fate of the phytoplanktonic carbon remained unknown, however.701
The longevity of the SOIREE bloom appears to be due to the persistently elevated levels of iron after day 11 and 12. The entrainment of the surrounding waters rich with silicic acid may have also contributed towards the longevity of the bloom.702 The SeaWiFS satellite image showed no significant downward
particulate export of the accumulated phytoplankton and it is thought that the onset of a mass sedimentation event may have been prevented by the ‘horizontal dispersion of high chlorophyll waters from within the patch into the surrounding HNLC waters’.703 SOIREE found that although there was an increase in diatom
production following the addition to iron in the patch, there was no increase to carbon export.704 This is a significant finding in relation to the verification
required if ocean fertilisation is to be used as a carbon trading mechanism.
Prior to fertilisation, the phytoplankton community was dominated by picoplankton and nanoplankton, with a low abundance of diatoms. After the iron fertilisation, however, there was a shift in the community structure. The picoplankton increased but was grazed down to their original levels by the micro-zooplankton. Of the nanoplankton, haptophytes (<20 µm) increased in abundance, as did different species of diatoms in the larger phytoplankton. Carbon export was monitored by the deficit of total thorium in the upper 100
701 P W Boyd, et al ‘A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron
fertilization’ (2000) 407 Nature 695–701.
702 Boyd, above n 96, 2425–38. 703 Boyd, above n 96, 2435.
704 Philip W Boyd, Andrew J Watson, Cliff S Law, Edward R Abraham, Thomas Trull, Rob Murdoch,
Dorothee C E Bakker, Andrew R Bowie, K O Buesseler, Hoe Chang, Matthew Charette, Peter Croot, Ken Downing, Russell Frew, Mark Gall, Mark Hadfield, Julie Hall, Mike Harvey, Greg Jameson, Julie LaRoche, Malcolm Liddicoat, Roger Ling, Maria T Maldonado, R. Michael McKay, Scott Nodder, Stu Pickmere, Rick Pridmore, Steve Rintoul, Karl Safi, Philip Sutton, Robert Strzepek, Kim Tanneberger, Suzanne Turner, Anya Waite, John Zeldis, ‘A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization’ (2000) 407 Nature 695–702.
metres of water and measurement of particulate organic carbon in sediment traps. The thorium technique showed no increase in carbon export. There was some increase in the export of particulate organic carbon from the sediment traps. However, when this data was considered against the controls the results were found to be ambiguous.705