Dust in the wind drove iron fertilization during ice age

Nitrogen is a critical building block for marine algae, yet the plankton in the Southern Ocean north of Antarctica leave much of it unused partly because they lack another needed nutrient, iron. The late John Martin hypothesized that dust-borne iron carried to the region by winds during ice ages may have fertilized the marine algae, allowing more of the Southern Ocean nitrogen to be used for growth and thus drawing CO2 into the ocean.  
To confirm Martin's hypothesis, the researchers measured isotopes of nitrogen in a sediment sample collected from a site that lies within the path of the winds that deposit iron-laden dust in the Subantarctic zone of the Southern Ocean (labeled ODP Site 1090). They found that the ratios of the types of nitrogen in the sample coincided with the predictions of Martin's hypothesis. The colors indicate simulated ice-age dust deposition from low to high (blue to red). The black contour lines show the concentrations of nitrate (a form of nitrogen) in modern surface waters. -  Image courtesy of Alfredo Martínez-García of ETH Zurich and Science/American Association for the Advancement of Science
Nitrogen is a critical building block for marine algae, yet the plankton in the Southern Ocean north of Antarctica leave much of it unused partly because they lack another needed nutrient, iron. The late John Martin hypothesized that dust-borne iron carried to the region by winds during ice ages may have fertilized the marine algae, allowing more of the Southern Ocean nitrogen to be used for growth and thus drawing CO2 into the ocean.
To confirm Martin’s hypothesis, the researchers measured isotopes of nitrogen in a sediment sample collected from a site that lies within the path of the winds that deposit iron-laden dust in the Subantarctic zone of the Southern Ocean (labeled ODP Site 1090). They found that the ratios of the types of nitrogen in the sample coincided with the predictions of Martin’s hypothesis. The colors indicate simulated ice-age dust deposition from low to high (blue to red). The black contour lines show the concentrations of nitrate (a form of nitrogen) in modern surface waters. – Image courtesy of Alfredo Martínez-García of ETH Zurich and Science/American Association for the Advancement of Science

Researchers from Princeton University and the Swiss Federal Institute of Technology in Zurich have confirmed that during the last ice age iron fertilization caused plankton to thrive in a region of the Southern Ocean.

The study published in Science confirms a longstanding hypothesis that wind-borne dust carried iron to the region of the globe north of Antarctica, driving plankton growth and eventually leading to the removal of carbon dioxide from the atmosphere.

Plankton remove the greenhouse gas carbon dioxide (CO2) from the atmosphere during growth and transfer it to the deep ocean when their remains sink to the bottom. Iron fertilization has previously been suggested as a possible cause of the lower CO2 levels that occur during ice ages. These decreases in atmospheric CO2 are believed to have “amplified” the ice ages, making them much colder, with some scientists believing that there would have been no ice ages at all without the CO2 depletion.

Iron fertilization has also been suggested as one way to draw down the rising levels of CO2 associated with the burning of fossil fuels. Improved understanding of the drivers of ocean carbon storage could lead to better predictions of how the rise in manmade carbon dioxide will affect climate in the coming years.

The role of iron in storing carbon dioxide during ice ages was first proposed in 1990 by the late John Martin, an oceanographer at Moss Landing Marine Laboratories in California who made the landmark discovery that iron limits plankton growth in large regions of the modern ocean.

Based on evidence that there was more dust in the atmosphere during the ice ages, Martin hypothesized that this increased dust supply to the Southern Ocean allowed plankton to grow more rapidly, sending more of their biomass into the deep ocean and removing CO2 from the atmosphere. Martin focused on the Southern Ocean because its surface waters contain the nutrients nitrogen and phosphorus in abundance, allowing plankton to be fertilized by iron without running low on these necessary nutrients.

The research confirms Martin’s hypothesis, said Daniel Sigman, Princeton’s Dusenbury Professor of Geological and Geophysical Sciences, and a co-leader of the study. “I was an undergraduate when Martin published his ‘ice age iron hypothesis,'” he said. “I remember being captivated by it, as was everyone else at the time. But I also remember thinking that Martin would have to be the luckiest person in the world to pose such a simple, beautiful explanation for the ice age CO2 paradox and then turn out to be right about it.”

Previous efforts to test Martin’s hypothesis established a strong correlation of cold climate, high dust and productivity in the Subantarctic region, a band of ocean encircling the globe between roughly 40 and 50 degrees south latitude that lies in the path of the winds that blow off South America, South Africa and Australia. However, it was not clear whether the productivity was due to iron fertilization or the northward shift of a zone of naturally occurring productivity that today lies to the south of the Subantarctic. This uncertainty was made more acute by the finding that ice age productivity was lower in the Antarctic Ocean, which lies south of the Subantarctic region.

To settle the matter, the research groups of Sigman at Princeton and Gerald Haug and Tim Eglinton at ETH Zurich teamed up to use a new method developed at Princeton. They analyzed fossils found in deep sea sediment -deposited during the last ice age in the Subantarctic region – with the goal of reconstructing past changes in the nitrogen concentration of surface waters and combining the results with side-by-side measurements of dust-borne iron and productivity. If the dust-borne iron fertilization hypothesis was correct, then nitrogen would have been more completely consumed by the plankton, leading to lower residual nitrogen concentrations in the surface waters. In contrast, if the productivity increases were in response to a northward shift in ocean conditions, then nitrogen concentrations would have risen.

The researchers measured the ratio of nitrogen isotopes, which have the same number of protons but differing numbers of neutrons, that were preserved within the carbonate shells of a group of marine microfossils called foraminifera. The investigators found that nitrogen concentrations indeed declined during the cold periods when iron deposition and productivity rose, in a manner consistent with the dust-borne iron fertilization theory. Ocean models as well as the strong correlation of the sediment core changes with the known changes in atmospheric CO2 suggest that this iron fertilization of Southern Ocean plankton can explain roughly half of the CO2 decline during peak ice ages.

Although Martin had proposed that purposeful iron addition to the Southern Ocean could reduce the rise in atmospheric CO2, Sigman noted that the amount of CO2 removed though iron fertilization is likely to be minor compared to the amount of CO2 that humans are now pushing into the atmosphere.

“The dramatic fertilization that we observed during ice ages should have caused a decline in atmospheric CO2 over hundreds of years, which was important for climate changes over ice age cycles,” Sigman said. “But for humans to duplicate it today would require unprecedented engineering of the global environment, and it would still only compensate for less than 20 years of fossil fuel burning.”

Edward Brook, a paleoclimatologist at Oregon State University who was not involved in the research, said, “This group has been doing a lot of important work in this area for quite a while and this an important advance. It will be interesting to see if the patterns they see in this one spot are consistent with variations in other places relevant to global changes in carbon dioxide.”

Dust in the wind drove iron fertilization during ice age

Nitrogen is a critical building block for marine algae, yet the plankton in the Southern Ocean north of Antarctica leave much of it unused partly because they lack another needed nutrient, iron. The late John Martin hypothesized that dust-borne iron carried to the region by winds during ice ages may have fertilized the marine algae, allowing more of the Southern Ocean nitrogen to be used for growth and thus drawing CO2 into the ocean.  
To confirm Martin's hypothesis, the researchers measured isotopes of nitrogen in a sediment sample collected from a site that lies within the path of the winds that deposit iron-laden dust in the Subantarctic zone of the Southern Ocean (labeled ODP Site 1090). They found that the ratios of the types of nitrogen in the sample coincided with the predictions of Martin's hypothesis. The colors indicate simulated ice-age dust deposition from low to high (blue to red). The black contour lines show the concentrations of nitrate (a form of nitrogen) in modern surface waters. -  Image courtesy of Alfredo Martínez-García of ETH Zurich and Science/American Association for the Advancement of Science
Nitrogen is a critical building block for marine algae, yet the plankton in the Southern Ocean north of Antarctica leave much of it unused partly because they lack another needed nutrient, iron. The late John Martin hypothesized that dust-borne iron carried to the region by winds during ice ages may have fertilized the marine algae, allowing more of the Southern Ocean nitrogen to be used for growth and thus drawing CO2 into the ocean.
To confirm Martin’s hypothesis, the researchers measured isotopes of nitrogen in a sediment sample collected from a site that lies within the path of the winds that deposit iron-laden dust in the Subantarctic zone of the Southern Ocean (labeled ODP Site 1090). They found that the ratios of the types of nitrogen in the sample coincided with the predictions of Martin’s hypothesis. The colors indicate simulated ice-age dust deposition from low to high (blue to red). The black contour lines show the concentrations of nitrate (a form of nitrogen) in modern surface waters. – Image courtesy of Alfredo Martínez-García of ETH Zurich and Science/American Association for the Advancement of Science

Researchers from Princeton University and the Swiss Federal Institute of Technology in Zurich have confirmed that during the last ice age iron fertilization caused plankton to thrive in a region of the Southern Ocean.

The study published in Science confirms a longstanding hypothesis that wind-borne dust carried iron to the region of the globe north of Antarctica, driving plankton growth and eventually leading to the removal of carbon dioxide from the atmosphere.

Plankton remove the greenhouse gas carbon dioxide (CO2) from the atmosphere during growth and transfer it to the deep ocean when their remains sink to the bottom. Iron fertilization has previously been suggested as a possible cause of the lower CO2 levels that occur during ice ages. These decreases in atmospheric CO2 are believed to have “amplified” the ice ages, making them much colder, with some scientists believing that there would have been no ice ages at all without the CO2 depletion.

Iron fertilization has also been suggested as one way to draw down the rising levels of CO2 associated with the burning of fossil fuels. Improved understanding of the drivers of ocean carbon storage could lead to better predictions of how the rise in manmade carbon dioxide will affect climate in the coming years.

The role of iron in storing carbon dioxide during ice ages was first proposed in 1990 by the late John Martin, an oceanographer at Moss Landing Marine Laboratories in California who made the landmark discovery that iron limits plankton growth in large regions of the modern ocean.

Based on evidence that there was more dust in the atmosphere during the ice ages, Martin hypothesized that this increased dust supply to the Southern Ocean allowed plankton to grow more rapidly, sending more of their biomass into the deep ocean and removing CO2 from the atmosphere. Martin focused on the Southern Ocean because its surface waters contain the nutrients nitrogen and phosphorus in abundance, allowing plankton to be fertilized by iron without running low on these necessary nutrients.

The research confirms Martin’s hypothesis, said Daniel Sigman, Princeton’s Dusenbury Professor of Geological and Geophysical Sciences, and a co-leader of the study. “I was an undergraduate when Martin published his ‘ice age iron hypothesis,'” he said. “I remember being captivated by it, as was everyone else at the time. But I also remember thinking that Martin would have to be the luckiest person in the world to pose such a simple, beautiful explanation for the ice age CO2 paradox and then turn out to be right about it.”

Previous efforts to test Martin’s hypothesis established a strong correlation of cold climate, high dust and productivity in the Subantarctic region, a band of ocean encircling the globe between roughly 40 and 50 degrees south latitude that lies in the path of the winds that blow off South America, South Africa and Australia. However, it was not clear whether the productivity was due to iron fertilization or the northward shift of a zone of naturally occurring productivity that today lies to the south of the Subantarctic. This uncertainty was made more acute by the finding that ice age productivity was lower in the Antarctic Ocean, which lies south of the Subantarctic region.

To settle the matter, the research groups of Sigman at Princeton and Gerald Haug and Tim Eglinton at ETH Zurich teamed up to use a new method developed at Princeton. They analyzed fossils found in deep sea sediment -deposited during the last ice age in the Subantarctic region – with the goal of reconstructing past changes in the nitrogen concentration of surface waters and combining the results with side-by-side measurements of dust-borne iron and productivity. If the dust-borne iron fertilization hypothesis was correct, then nitrogen would have been more completely consumed by the plankton, leading to lower residual nitrogen concentrations in the surface waters. In contrast, if the productivity increases were in response to a northward shift in ocean conditions, then nitrogen concentrations would have risen.

The researchers measured the ratio of nitrogen isotopes, which have the same number of protons but differing numbers of neutrons, that were preserved within the carbonate shells of a group of marine microfossils called foraminifera. The investigators found that nitrogen concentrations indeed declined during the cold periods when iron deposition and productivity rose, in a manner consistent with the dust-borne iron fertilization theory. Ocean models as well as the strong correlation of the sediment core changes with the known changes in atmospheric CO2 suggest that this iron fertilization of Southern Ocean plankton can explain roughly half of the CO2 decline during peak ice ages.

Although Martin had proposed that purposeful iron addition to the Southern Ocean could reduce the rise in atmospheric CO2, Sigman noted that the amount of CO2 removed though iron fertilization is likely to be minor compared to the amount of CO2 that humans are now pushing into the atmosphere.

“The dramatic fertilization that we observed during ice ages should have caused a decline in atmospheric CO2 over hundreds of years, which was important for climate changes over ice age cycles,” Sigman said. “But for humans to duplicate it today would require unprecedented engineering of the global environment, and it would still only compensate for less than 20 years of fossil fuel burning.”

Edward Brook, a paleoclimatologist at Oregon State University who was not involved in the research, said, “This group has been doing a lot of important work in this area for quite a while and this an important advance. It will be interesting to see if the patterns they see in this one spot are consistent with variations in other places relevant to global changes in carbon dioxide.”

Fossil CSI: Prehistoric clues to oil, environment revealed

More than 200 delegates from around the world will assemble at the University of Houston (UH) next week to share research and discoveries about oil and the environment at an international conference on the economic and environmental use of fossils.

Specifically examining microfossils, which are invisible to the naked eye, the scientists who participate in this quadrennial gathering represent leaders in various branches of stratigraphy, the branch of geology that studies rock layers in the Earth’s crust. Notable presenters will include the authors of the last decade of geologic time scales, which are a system of chronological measurements that relate stratigraphy to time. These time scales are used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history.

The conference, Geologic Problem Solving with Microfossils III, will be held at UH March 10-13. Kicking off the activities will be poster sessions at the Hilton UH Sunday and Monday evening, with oral presentations taking place Monday through noon Wednesday in room 100 of the Science and Engineering Classroom building.

“We will have some of the world leaders in research on global time scales presenting at this conference. They are the keepers of the keys to time for the fossil record over the course of the last 550 million years in sedimentary rocks,” said Don Van Nieuwenhuise, director of Professional Geoscience Programs at UH in the Department of Earth and Atmospheric Sciences. “They also are keeping track of available age data back into the Precambrian age, extending as far back in time as 4.5 billion years ago. The work of hundreds of scientists from all over the world entails integrating data generated from the Earth, Moon, Mars and Venus.”

The various presentations lined up will show how microfossils are used to understand environmental conditions, such as global warming and cooling, from prehistoric times to the present. Talks also will cover how microfossils are used to age-date rocks, as well as provide clues to finding oil and gas resources not only in conventional sand and limestone, but also unconventional shale plays.

In addition to discussions of practical applications in oil and gas exploration and production, Van Nieuwenhuise says basic science about stratigraphy and environmental monitoring will be showcased. Since microfossils are found in abundance in oil and gas well samples, scientists can then link the environmental signals of similar living microscopic organisms, flora and fauna in a region, also called microbiota, to understand the fossil and rock record.

“This has led to the use of these organisms as environmental monitors for various forms of pollution,” he said. “Once researchers determine the baseline abundances and distributions of microbiota in a given habitat, we can then determine if pollutants have disrupted their habitat and populations. Some microbiota develop deformities related to pollutant influences and other environmental stresses.”

Intended to reflect today’s broadening application of micropaleontology, presentations will include talks on the microfossil record of major oceanic events, microfossils and unconventional resources, reconstructing past environments using microfossils, paleoclimatology and paleoceanography related to sea-level change, and new technologies and techniques in microfossil studies.

Sponsored by the North American Micropaleontology Section of the Society for Sedimentary Geology, this conference broadly focuses on the use of microfossils for solving geological problems. Initiated in 2005 and held every four years, this event has been well received and growing in attendance. Attendees of past meetings have said the open problem-solving theme of the conference and the broad participation of specialists from varied disciplines creates a rich environment for collaboration and sharing of ideas and knowledge.

Fossil CSI: Prehistoric clues to oil, environment revealed

More than 200 delegates from around the world will assemble at the University of Houston (UH) next week to share research and discoveries about oil and the environment at an international conference on the economic and environmental use of fossils.

Specifically examining microfossils, which are invisible to the naked eye, the scientists who participate in this quadrennial gathering represent leaders in various branches of stratigraphy, the branch of geology that studies rock layers in the Earth’s crust. Notable presenters will include the authors of the last decade of geologic time scales, which are a system of chronological measurements that relate stratigraphy to time. These time scales are used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred throughout Earth’s history.

The conference, Geologic Problem Solving with Microfossils III, will be held at UH March 10-13. Kicking off the activities will be poster sessions at the Hilton UH Sunday and Monday evening, with oral presentations taking place Monday through noon Wednesday in room 100 of the Science and Engineering Classroom building.

“We will have some of the world leaders in research on global time scales presenting at this conference. They are the keepers of the keys to time for the fossil record over the course of the last 550 million years in sedimentary rocks,” said Don Van Nieuwenhuise, director of Professional Geoscience Programs at UH in the Department of Earth and Atmospheric Sciences. “They also are keeping track of available age data back into the Precambrian age, extending as far back in time as 4.5 billion years ago. The work of hundreds of scientists from all over the world entails integrating data generated from the Earth, Moon, Mars and Venus.”

The various presentations lined up will show how microfossils are used to understand environmental conditions, such as global warming and cooling, from prehistoric times to the present. Talks also will cover how microfossils are used to age-date rocks, as well as provide clues to finding oil and gas resources not only in conventional sand and limestone, but also unconventional shale plays.

In addition to discussions of practical applications in oil and gas exploration and production, Van Nieuwenhuise says basic science about stratigraphy and environmental monitoring will be showcased. Since microfossils are found in abundance in oil and gas well samples, scientists can then link the environmental signals of similar living microscopic organisms, flora and fauna in a region, also called microbiota, to understand the fossil and rock record.

“This has led to the use of these organisms as environmental monitors for various forms of pollution,” he said. “Once researchers determine the baseline abundances and distributions of microbiota in a given habitat, we can then determine if pollutants have disrupted their habitat and populations. Some microbiota develop deformities related to pollutant influences and other environmental stresses.”

Intended to reflect today’s broadening application of micropaleontology, presentations will include talks on the microfossil record of major oceanic events, microfossils and unconventional resources, reconstructing past environments using microfossils, paleoclimatology and paleoceanography related to sea-level change, and new technologies and techniques in microfossil studies.

Sponsored by the North American Micropaleontology Section of the Society for Sedimentary Geology, this conference broadly focuses on the use of microfossils for solving geological problems. Initiated in 2005 and held every four years, this event has been well received and growing in attendance. Attendees of past meetings have said the open problem-solving theme of the conference and the broad participation of specialists from varied disciplines creates a rich environment for collaboration and sharing of ideas and knowledge.

3-D microscope opens eyes to prehistoric oceans and present-day resources

A University of Alberta research team has turned their newly developed 3-D microscope technology on ancient sea creatures and hopes to expand its use.

U of A engineering professor Dileepan Joseph and two graduate students produced a 3-D imaging system called Virtual Reflected-Light Microscopy. The technology consists of a regular optical microscope, a light source, a platform that moves the objects being photographed and software programs that extract shape and reflectance from images and transform this digital information into a 3-D image. To see the full effect on a computer screen viewers wear simple, paper framed 3-D glasses with red and cyan colored lenses. Viewers also control a virtual light source, which they reposition using their web browser.

The test subjects used in the development of the VRLM were drilling core samples taken from beneath the floor of the Pacific Ocean. Joseph, Ph.D candidate Adam Harrison and master’s student Cindy Wong produced 3-D images of ancient protozoa or microfossils that were mixed in with the sand and rock in the core samples.

Joseph says the VRLM gives geoscientists and computer programs in development much more information than simple images. The goal is to accelerate species identification of the tiny and numerous microfossils. Such identifications are used to date the rock from which the creatures are pulled. The microfossil species digitized by the U of A’s VLRM prototype were found in rock known by geologists to be 60 million years old.

Geoscientists can use that kind of strata dating information in Earth sciences research and in the search for energy resources. The U of A researchers say there are multiple industrial and academic uses for their 3-D microscope technology.