An international research team has published the results of an ocean iron fertilization experiment (EIFEX) carried out in 2004 in the current issue of the scientific journal Nature. Unlike the LOHAFEX experiment carried out in 2009, EIFEX has shown that a substantial proportion of carbon from the induced algal bloom sank to the deep sea floor. These results, which were thoroughly analysed before being published now, provide a valuable contribution to our better understanding of the global carbon cycle.
Photo: Alfred Wegener Institute
An international team on board the research vessel Polarstern fertilized in spring 2004 (i.e. at the end of the summer season in the southern hemisphere) a part of the closed core of a stable marine eddy in the Southern Ocean with dissolved iron, which stimulated the growth of unicellular algae (phytoplankton). The team followed the development of the phytoplankton bloom for five weeks from its start to its decline phase. The maximum biomass attained by the bloom was with a peak chlorophyll stock of 286 Milligram per square metre higher than that of blooms stimulated by the previous 12 iron fertilization experiments.
These results contrast with those of the LOHAFEX experiment carried out in 2009 where diatom growth was limited by different nutrient conditions, especially the absence of dissolved silicon in the chosen eddy. Instead, the plankton bloom consisted of other types of algae which, however, have no protective shell and were eaten more easily by zooplankton. “This shows how differently communities of organisms can react to the addition of iron in the ocean“, says Dr. Christine Klaas.
“Such controlled iron fertilization experiments in the ocean enable us to test hypotheses and quantify processes that cannot be studied in laboratory experiments. The results improve our understanding of processes in the ocean relevant to climate change“, says Smetacek. “The controversy surrounding iron fertilization experiments has led to a thorough evaluation of our results before publication", comments the marine scientist as an explanation for the long delay between the experiment to the current publication in Nature.
Summary of the experiment:
A patch of 150 square kilometres (circle with a diameter of 14 kilometres) within an marine eddy of the Antarctic Circumpolar Current was fertilized with seven tonnes of iron sulphate on 13/14 February 2004. This corresponds to an iron addition of one hundredth of a gramme per square metre. The resultant iron concentration of 2 nanomole per litre is similar to values measured in the wake of melting icebergs; the iron concentrations in coastal regions tend to be much higher.
The input of iron in regions with high nutrient concentrations (nitrate, phosphate, silicate) and low chlorophyll content (the so-called high-nutrient / low-chlorophyll regions) stimulates the growth of plankton algae (phytoplankton). After fertilization, the development of the plankton bloom was investigated using standard oceanographic methods over a period of five weeks. From the surface water down to a depth of over 3,000 metres, chlorophyll, organic carbon, nitrogen, phosphate and other parameters were measured to follow the development, demise and sinking of the bloom and the associated export of carbon.
Interview: “Our knowledge of the role of iron in the global carbon cycle is still far from complete”
Iron fertilisation is a subject, which is hotly debated in society. In the interview Dr. Stefan Hain, environmental policy spokesman for the Alfred Wegener Institute, explains which scientific motives are behind iron fertilisation experiments and which international treaties regulate the work of researchers.
Research vessel POLARSTERN, picture taken in September 2004.
An international team on board the research vessel Polarstern fertilized in spring 2004 (i.e. at the end of the summer season in the southern hemisphere) a part of the closed core of a stable marine eddy in the Southern Ocean with dissolved iron, which stimulated the growth of unicellular algae (phytoplankton). The team followed the development of the phytoplankton bloom for five weeks from its start to its decline phase. The maximum biomass attained by the bloom was with a peak chlorophyll stock of 286 Milligram per square metre higher than that of blooms stimulated by the previous 12 iron fertilization experiments.
According to Prof. Dr. Victor Smetacek and Dr. Christine Klaas from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association, this was all the more remarkable because the EIFEX bloom developed in a 100 metre deep mixed layer which is much deeper than hitherto believed to be the lower limit for bloom development.
The bloom was dominated by diatoms, a group of algae that require dissolved silicon to make their shells and are known to form large, slimy aggregates with high sinking rates at the end of their blooms. “We were able to prove that over 50 per cent of the plankton bloom sank below 1000 metre depth indicating that their carbon content can be stored in the deep ocean and in the underlying seafloor sediments for time scales of well over a century“, says Smetacek.
Bloomed during EIFEX: The diatom Chaeotceros atlanticum comes as a chain of cells with four spines on each.
Photo: Marina Montresor, SZN / Alfred Wegener Institute
The bloom was dominated by diatoms, a group of algae that require dissolved silicon to make their shells and are known to form large, slimy aggregates with high sinking rates at the end of their blooms. “We were able to prove that over 50 per cent of the plankton bloom sank below 1000 metre depth indicating that their carbon content can be stored in the deep ocean and in the underlying seafloor sediments for time scales of well over a century“, says Smetacek.
Bloomed during EIFEX: The diatom Chaeotceros atlanticum comes as a chain of cells with four spines on each.
These results contrast with those of the LOHAFEX experiment carried out in 2009 where diatom growth was limited by different nutrient conditions, especially the absence of dissolved silicon in the chosen eddy. Instead, the plankton bloom consisted of other types of algae which, however, have no protective shell and were eaten more easily by zooplankton. “This shows how differently communities of organisms can react to the addition of iron in the ocean“, says Dr. Christine Klaas.
“We expect similarly detailed insights on the transportation of carbon between atmosphere, ocean and sea bottom from the further scientific analysis of the LOHAFEX data”, adds Prof. Dr. Wolf-Gladrow, Head of Biosciences at the Alfred Wegener Institute, who is also involved in the Nature study.
Iron plays an important role in the climate system. It is involved in many biochemical processes such as photosynthesis and is hence an essential element for biological production in the oceans and, therefore, for CO2 absorption from the atmosphere. During past ice ages the air was cooler and drier than it is today and more iron-containing dust was transported from the continents to the ocean by the wind. The iron supply to marine phytoplankton was hence higher during the ice ages. This natural process is simulated in iron fertilisation experiments under controlled conditions.
Photo: Marina Montresor, SZN / Alfred Wegener Institute
Iron plays an important role in the climate system. It is involved in many biochemical processes such as photosynthesis and is hence an essential element for biological production in the oceans and, therefore, for CO2 absorption from the atmosphere. During past ice ages the air was cooler and drier than it is today and more iron-containing dust was transported from the continents to the ocean by the wind. The iron supply to marine phytoplankton was hence higher during the ice ages. This natural process is simulated in iron fertilisation experiments under controlled conditions.
Diatom Chaetoceros atlanticus
“Such controlled iron fertilization experiments in the ocean enable us to test hypotheses and quantify processes that cannot be studied in laboratory experiments. The results improve our understanding of processes in the ocean relevant to climate change“, says Smetacek. “The controversy surrounding iron fertilization experiments has led to a thorough evaluation of our results before publication", comments the marine scientist as an explanation for the long delay between the experiment to the current publication in Nature.
Summary of the experiment:
A patch of 150 square kilometres (circle with a diameter of 14 kilometres) within an marine eddy of the Antarctic Circumpolar Current was fertilized with seven tonnes of iron sulphate on 13/14 February 2004. This corresponds to an iron addition of one hundredth of a gramme per square metre. The resultant iron concentration of 2 nanomole per litre is similar to values measured in the wake of melting icebergs; the iron concentrations in coastal regions tend to be much higher.
The input of iron in regions with high nutrient concentrations (nitrate, phosphate, silicate) and low chlorophyll content (the so-called high-nutrient / low-chlorophyll regions) stimulates the growth of plankton algae (phytoplankton). After fertilization, the development of the plankton bloom was investigated using standard oceanographic methods over a period of five weeks. From the surface water down to a depth of over 3,000 metres, chlorophyll, organic carbon, nitrogen, phosphate and other parameters were measured to follow the development, demise and sinking of the bloom and the associated export of carbon.
In addition, the phytoplankton and zooplankton species and bacterial numbers and abundance were determined. The chlorophyll content rose over a period of 24 days after fertilization. Thereafter, phytoplankton aggregates formed and sank within a few days to depths of 3,700 metres. Long spines of these diatoms and mucous substances led to aggregate formation and export of the fixed carbon from the surface to the sea floor. This process was monitored for five weeks after the start of fertilization.
Are iron fertilisation experiments in the ocean necessary from a scientific perspective?
Stefan Hain: Yes, because there are still several gaps in our scientific knowledge on the past, present and future role of this essential element on organisms, the entire food web and the carbon cycle. Hypotheses and assertions of a more or less scientific nature exist. However these can only be checked in the laboratory or using models to a limited extent, because the natural processes and interactions in the sea are far too complex for this. It is only possible to test individual organisms in the laboratory, but not the interaction of several factors. The way relationships of organisms alter with respect to each other in the food web and the material flow, in other words how the system changes, also goes unrecorded.
Stefan Hain: Yes, because there are still several gaps in our scientific knowledge on the past, present and future role of this essential element on organisms, the entire food web and the carbon cycle. Hypotheses and assertions of a more or less scientific nature exist. However these can only be checked in the laboratory or using models to a limited extent, because the natural processes and interactions in the sea are far too complex for this. It is only possible to test individual organisms in the laboratory, but not the interaction of several factors. The way relationships of organisms alter with respect to each other in the food web and the material flow, in other words how the system changes, also goes unrecorded.
The extremely different results of previous experiments in the field have shown how little we know about the marine system. In addition ocean fertilisation is being considered as a possible way of extracting carbon dioxide from the atmosphere, thereby combating climate change. The efficacy of the method and the associated risks are being hotly debated, however. Targeted and controlled experiments are needed to create a scientifically sound basis on which decisions can be made.
Do scientific iron fertilisation experiments damage the environment?
Stefan Hain: No serious researcher will intentionally cause damage to the environment. Therefore all experiments that the Alfred Wegener Institute has conducted were preceded by many years of planning and painstaking considerations. In the case of EIFEX and LOHAFEX we intentionally fertilised small ocean eddies. Their water masses have only little exchange with the surrounding sea. All previously conducted iron fertilisation experiments were also on a small scale and no negative effects were determined. Whether any damage to the marine environment could occur in the case of repeated, widespread fertilisation remains a matter of speculation – it has not been possible until now to investigate this.
Do scientific iron fertilisation experiments damage the environment?
Stefan Hain: No serious researcher will intentionally cause damage to the environment. Therefore all experiments that the Alfred Wegener Institute has conducted were preceded by many years of planning and painstaking considerations. In the case of EIFEX and LOHAFEX we intentionally fertilised small ocean eddies. Their water masses have only little exchange with the surrounding sea. All previously conducted iron fertilisation experiments were also on a small scale and no negative effects were determined. Whether any damage to the marine environment could occur in the case of repeated, widespread fertilisation remains a matter of speculation – it has not been possible until now to investigate this.
Dr. Stefan Hain, environmental policy spokesman of the Alfred Wegener Institute
Photo: AW
Do legally binding national or international regulations currently exist on iron fertilisation experiments and how do you classify these as environmental policy spokesman of the Alfred Wegener Institute?
Stefan Hain: Several international organisations such as the Convention on Biological Diversity have delivered opinions and recommendations on the subject of ocean fertilisation. The London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (1972 and 1996 Protocol Thereto) banned commercial ocean fertilisation experiments in the year 2008. At the same time all countries were agreed that controlled, legal scientific basic research on the subject should be permitted and is needed to improve our knowledge on the carbon cycle and relevant processes in the sea.
Do legally binding national or international regulations currently exist on iron fertilisation experiments and how do you classify these as environmental policy spokesman of the Alfred Wegener Institute?
Stefan Hain: Several international organisations such as the Convention on Biological Diversity have delivered opinions and recommendations on the subject of ocean fertilisation. The London Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (1972 and 1996 Protocol Thereto) banned commercial ocean fertilisation experiments in the year 2008. At the same time all countries were agreed that controlled, legal scientific basic research on the subject should be permitted and is needed to improve our knowledge on the carbon cycle and relevant processes in the sea.
Two years later a framework was passed under this Convention that is drawn on for the assessment and approval of proposals for scientific research experiments on ocean fertilisation. It also applies to Germany. However owing to its extensive requirements and conditions, it is hardly possible for even an institute with the size and capacity of the Alfred Wegener Institute to comply with the requirements of this assessment guide. It would no longer be possible today to carry out experiments such as EIFEX and LOHAFEX.
Does the continuation of ocean fertilisation experiments still have any useful purpose at all, and does the Alfred Wegener Institute plan any more experiments of this kind?
Stefan Hain: If we really want to understand how material flows in the ocean function under different climate conditions, if we want to check hypotheses, laboratory tests and forecasting models, then we need in situ experiments of this kind. All previous scientific results, including those currently published by EIFEX, suggest that only a small part of the annual carbon dioxide emissions would be extracted from the cycle even with widespread iron fertilisation. Therefore our principal objective must still be to reduce these carbon dioxide emissions.
Does the continuation of ocean fertilisation experiments still have any useful purpose at all, and does the Alfred Wegener Institute plan any more experiments of this kind?
Stefan Hain: If we really want to understand how material flows in the ocean function under different climate conditions, if we want to check hypotheses, laboratory tests and forecasting models, then we need in situ experiments of this kind. All previous scientific results, including those currently published by EIFEX, suggest that only a small part of the annual carbon dioxide emissions would be extracted from the cycle even with widespread iron fertilisation. Therefore our principal objective must still be to reduce these carbon dioxide emissions.
However if governments feel compelled to use iron fertilisation of the ocean as an additional measure to reduce the carbon dioxide cycle in the atmosphere, we must be able to make a sound scientific assessment of the possible impact and risks of ocean fertilisation. Previous experiments, such as those conducted by the Alfred Wegener Institute, have contributed greatly to this. Currently we are in the process of completely evaluating the data from past iron fertilisation experiments. If new questions arise from their findings, it will be necessary to consider whether and how these can be answered – for example using an experimental research approach.Original publication:
Contacts and sources:
Contacts and sources:
Alfred Wegener Institute
Citation: Victor Smetacek, Christine Klaas et al. (2012): Deep carbon export from a Southern Ocean iron-fertilized diatom bloom. Naturedoi:10.1038/nature11229
Citation: Victor Smetacek, Christine Klaas et al. (2012): Deep carbon export from a Southern Ocean iron-fertilized diatom bloom. Naturedoi:10.1038/nature11229
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