“Polarstern” in the southwest Atlantic from 7th January to 17th March 2009. The interdisciplinary team of 48 scientists on board “Polarstern” will closely collaborate in monitoring the algal bloom expected to grow in the fertilized patch of the ocean and studying its effects on the chemistry and biology for at least 45 days.
The results of LOHAFEX will be of great interest to both ocean ecologists and geochemists because the minute, unicellular algae suspended in the sunlit surface layer known as phytoplankton not only provide the food sustaining all oceanic life but also play a key role in regulating concentrations of the greenhouse gas CO2 in the atmosphere.
Background
The Southern Ocean encircling Antarctica is rich in the nutrients nitrate, phosphate and silicon but phytoplankton growth is limited by the supply of iron which is a crucial ingredient of all organisms. Iron is highly insoluble in sea water, so, unlike the other nutrients, is quickly lost in sinking particles. Addition of trace amounts of iron to these waters, whether from natural sources (contact with land masses and via settling dust blown of the continents) or by artificial iron fertilization (from a ship releasing dissolved iron sulfate to the surface layer), results in rapid algal growth leading to development of phytoplankton blooms.
Phytoplankton grow by taking up CO2 dissolved in sea water and converting the carbon into biomass (organic matter). Because the CO2 sdissolved in the ocean’s surface layer is in equilibrium with the atmosphere, blooms cause a deficit which is compensated by uptake from the atmosphere. The fate of the bloom biomass determines how long this CO2 is retained in the ocean. If the organic matter is recycled by bacteria and zooplankton - unicellular protozoa and a variety of small animals that graze on phytoplankton - within the surface layer, and the iron selectively lost, then the CO2 taken up is returned to the atmosphere within months. However, the organic particles in the form of phytoplankton cells and zooplankton faecal material that settle out of the surface layer sequester CO2 for longer time scales depending on how deep they sink. Carbon transported in particles that sink below 3,000 m is sequestered for centuries and the portion buried in the sediments for much longer.
Five iron fertilization experiments in the Southern Ocean have created phytoplankton blooms but only in the previous experiment EIFEX carried out from Polarstern was it possible to actually follow the rain of particles sinking through the underlying deep water column because the experiment was carried out in the closed core of a stationary, rotating eddy. LOHAFEX will also be conducted in a pre-selected eddy but the size of the patch will be twice as large – 300 km2 fertilized with 20 tonnes of iron sulfate. EIFEX had to be terminated after 35 days while the bloom was still growing and sinking but LOHAFEX will last 10 days longer and quantify the amount sinking to depth more accurately.
Another goal of LOHAFEX is to study the effects of iron fertilization on the zooplankton, in particular the shrimp-like krill, which is the main food of Antarctic penguins, seals and whales. Stocks of krill have declined by over 80% during the past decades and their response to the iron-fertilized bloom will indicate whether the decline is due to declining productivity of the region for which there is evidence. Thus, large-scale iron fertilization of the krill habitat could well help in boosting their stocks to their former high densities and facilitate long-term recovery of the decimated great whale populations. TheTamshee says: this research program is fascinating, you have got too take your hats off to the scientists who think up these worthy concepts - I certainly hope it is a great success - time will tell.
The results of LOHAFEX will be of great interest to both ocean ecologists and geochemists because the minute, unicellular algae suspended in the sunlit surface layer known as phytoplankton not only provide the food sustaining all oceanic life but also play a key role in regulating concentrations of the greenhouse gas CO2 in the atmosphere.
Background
The Southern Ocean encircling Antarctica is rich in the nutrients nitrate, phosphate and silicon but phytoplankton growth is limited by the supply of iron which is a crucial ingredient of all organisms. Iron is highly insoluble in sea water, so, unlike the other nutrients, is quickly lost in sinking particles. Addition of trace amounts of iron to these waters, whether from natural sources (contact with land masses and via settling dust blown of the continents) or by artificial iron fertilization (from a ship releasing dissolved iron sulfate to the surface layer), results in rapid algal growth leading to development of phytoplankton blooms.
Phytoplankton grow by taking up CO2 dissolved in sea water and converting the carbon into biomass (organic matter). Because the CO2 sdissolved in the ocean’s surface layer is in equilibrium with the atmosphere, blooms cause a deficit which is compensated by uptake from the atmosphere. The fate of the bloom biomass determines how long this CO2 is retained in the ocean. If the organic matter is recycled by bacteria and zooplankton - unicellular protozoa and a variety of small animals that graze on phytoplankton - within the surface layer, and the iron selectively lost, then the CO2 taken up is returned to the atmosphere within months. However, the organic particles in the form of phytoplankton cells and zooplankton faecal material that settle out of the surface layer sequester CO2 for longer time scales depending on how deep they sink. Carbon transported in particles that sink below 3,000 m is sequestered for centuries and the portion buried in the sediments for much longer.
Five iron fertilization experiments in the Southern Ocean have created phytoplankton blooms but only in the previous experiment EIFEX carried out from Polarstern was it possible to actually follow the rain of particles sinking through the underlying deep water column because the experiment was carried out in the closed core of a stationary, rotating eddy. LOHAFEX will also be conducted in a pre-selected eddy but the size of the patch will be twice as large – 300 km2 fertilized with 20 tonnes of iron sulfate. EIFEX had to be terminated after 35 days while the bloom was still growing and sinking but LOHAFEX will last 10 days longer and quantify the amount sinking to depth more accurately.
Another goal of LOHAFEX is to study the effects of iron fertilization on the zooplankton, in particular the shrimp-like krill, which is the main food of Antarctic penguins, seals and whales. Stocks of krill have declined by over 80% during the past decades and their response to the iron-fertilized bloom will indicate whether the decline is due to declining productivity of the region for which there is evidence. Thus, large-scale iron fertilization of the krill habitat could well help in boosting their stocks to their former high densities and facilitate long-term recovery of the decimated great whale populations. TheTamshee says: this research program is fascinating, you have got too take your hats off to the scientists who think up these worthy concepts - I certainly hope it is a great success - time will tell.
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