Tag Archives: ocean

Keystone plankton ‘go slow’ as ocean acidity rises Updated for 2026

Leave a reply




As the planet’s oceans become more acidic, the diatoms – a major group of alga – in the Southern Ocean could grow more slowly.

Nobody expected this. And since tiny, single-celled algae are a primary food source for an entire ocean ecosystem, the discovery seems ominous.

Bioscientist Clara Hoppe and colleagues from the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, report in the journal New Phytologist that they tested the growth of the Antarctic diatom Chaetoceros debilis under laboratory conditions.

They used two levels of pH – which is an indicator of acidity – and they exposed their tiny volunteers to constant light and to changing light, providing both standard laboratory conditions and lighting levels that approximated to the real world.

Under variable light in high-CO2 world, plant growth slows

In the unblinking glare of light, the diatoms responded well. Their growth levels were consistent with an assumption that more dissolved carbon dioxide – which makes the waters more acidic – would in effect fertilise plant growth.

Under conditions of changing light, however, it was a different story. The algae grew more slowly, which suggests that the oceans could become less efficient at removing carbon from the atmosphere, and perhaps less valuable as a primary food source for the creatures that teem in the Antarctic waters.

“Diatoms fulfil an important role in the Earth’s climate system”, Dr Hoppe says. “They can absorb large quantities of carbon dioxide, which they bind before ultimately transporting part of it to the depths of the ocean. Once there, the greenhouse gas remains naturally sequestered for centuries.”

Previous research into the steady acidification of the oceans has tended to concentrate on the consequences for coral reefs, fisheries, and tourism, but not on the impact on plant life in the seas.

Since carbon dioxide acts as a fertiliser, higher levels dissolved in the water might stimulate more growth. But growth depends not just on more carbon dioxide, but also on reliable sunlight. In the stormy southern seas, this is not steadily supplied.

Dr Hoppe says: “Several times a day, winds and currents transport diatoms in the Southern Ocean from the uppermost water layer to the layers below, and then back to the surface – which means that, in the course of a day, the diatoms experience alternating phases with more and with less light.”

Her co-author, marine biogeochemist Björn Rost, from the Alfred Wegener Institute, says: “Our findings show for the first time that our old assumptions most likely fall short of the mark. We now know that when the light intensity constantly changes, the effect of ocean acidification reverses.

“All of a sudden, lower pH values don’t increase growth, like studies using constant light show. Instead, they have the opposite effect.”

The implication is that, at certain intensities, the photosynthesis chain breaks down. The point at which light becomes too much light is more quickly reached in waters that are more acidic.

Like all such research, the finding has limitations. It applies to one species of single-celled creature in the waters of one ocean, and the tests were in a laboratory on a small scale, and not in a turbulent ocean rich in life. The Alfred Wegener team will continue their studies.

Fisheries at risk

But in the real world, coastal communities in 15 US states could be at long-term economic risk, as ocean acidification starts to take its toll on the commercial oyster fisheries.

Julia Ekstrom, then of the Natural Resources Defense Council and now director of the Climate Adaptation Programme at the University of California, Davis, and George Waldbusser, assistant professor of ocean ecology and biogeochemistry at Oregon State University report with colleagues, in Nature Climate Change, on an unholy mix in the oceans.

They say that a combination of rising greenhouse gas levels, more acid waters, polluted rivers, and upwelling currents put at risk mollusc fisheries from the Pacific Northwest, New England, the Mid-Atlantic states and the Gulf of Mexico – affecting the shellfish industry that is worth at least $1bn to the US.

Oyster larvae are sensitive to changes in ocean water, and more likely to die as pH levels shift towards the acidic. But acidification is not the only source of stress, as nitrogen-rich nutrients and chemical pollutants cascade from the land into the rivers, and wash through estuaries and fish hatcheries on the coast.

Things can be done. Scientists have been looking at ways in which the industry might be able to adapt to change. But how well the oyster stock can adapt in the long term remains problematic.

“Ocean acidification has already cost the oyster industry in the Pacific Northwest nearly $110 million and has jeopardised about 3,200 jobs”, Dr Ekstrom says.

And Dr Waldbusser adds: “Without curbing carbon emissions, we will eventually run out of tools to address the short term, and we will be stuck with a much longer-term problem.”

 

 

Tim Radford writes for Climate News Network.

 

 




390832

Keystone plankton ‘go slow’ as ocean acidity rises Updated for 2026

Leave a reply




As the planet’s oceans become more acidic, the diatoms – a major group of alga – in the Southern Ocean could grow more slowly.

Nobody expected this. And since tiny, single-celled algae are a primary food source for an entire ocean ecosystem, the discovery seems ominous.

Bioscientist Clara Hoppe and colleagues from the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, report in the journal New Phytologist that they tested the growth of the Antarctic diatom Chaetoceros debilis under laboratory conditions.

They used two levels of pH – which is an indicator of acidity – and they exposed their tiny volunteers to constant light and to changing light, providing both standard laboratory conditions and lighting levels that approximated to the real world.

Under variable light in high-CO2 world, plant growth slows

In the unblinking glare of light, the diatoms responded well. Their growth levels were consistent with an assumption that more dissolved carbon dioxide – which makes the waters more acidic – would in effect fertilise plant growth.

Under conditions of changing light, however, it was a different story. The algae grew more slowly, which suggests that the oceans could become less efficient at removing carbon from the atmosphere, and perhaps less valuable as a primary food source for the creatures that teem in the Antarctic waters.

“Diatoms fulfil an important role in the Earth’s climate system”, Dr Hoppe says. “They can absorb large quantities of carbon dioxide, which they bind before ultimately transporting part of it to the depths of the ocean. Once there, the greenhouse gas remains naturally sequestered for centuries.”

Previous research into the steady acidification of the oceans has tended to concentrate on the consequences for coral reefs, fisheries, and tourism, but not on the impact on plant life in the seas.

Since carbon dioxide acts as a fertiliser, higher levels dissolved in the water might stimulate more growth. But growth depends not just on more carbon dioxide, but also on reliable sunlight. In the stormy southern seas, this is not steadily supplied.

Dr Hoppe says: “Several times a day, winds and currents transport diatoms in the Southern Ocean from the uppermost water layer to the layers below, and then back to the surface – which means that, in the course of a day, the diatoms experience alternating phases with more and with less light.”

Her co-author, marine biogeochemist Björn Rost, from the Alfred Wegener Institute, says: “Our findings show for the first time that our old assumptions most likely fall short of the mark. We now know that when the light intensity constantly changes, the effect of ocean acidification reverses.

“All of a sudden, lower pH values don’t increase growth, like studies using constant light show. Instead, they have the opposite effect.”

The implication is that, at certain intensities, the photosynthesis chain breaks down. The point at which light becomes too much light is more quickly reached in waters that are more acidic.

Like all such research, the finding has limitations. It applies to one species of single-celled creature in the waters of one ocean, and the tests were in a laboratory on a small scale, and not in a turbulent ocean rich in life. The Alfred Wegener team will continue their studies.

Fisheries at risk

But in the real world, coastal communities in 15 US states could be at long-term economic risk, as ocean acidification starts to take its toll on the commercial oyster fisheries.

Julia Ekstrom, then of the Natural Resources Defense Council and now director of the Climate Adaptation Programme at the University of California, Davis, and George Waldbusser, assistant professor of ocean ecology and biogeochemistry at Oregon State University report with colleagues, in Nature Climate Change, on an unholy mix in the oceans.

They say that a combination of rising greenhouse gas levels, more acid waters, polluted rivers, and upwelling currents put at risk mollusc fisheries from the Pacific Northwest, New England, the Mid-Atlantic states and the Gulf of Mexico – affecting the shellfish industry that is worth at least $1bn to the US.

Oyster larvae are sensitive to changes in ocean water, and more likely to die as pH levels shift towards the acidic. But acidification is not the only source of stress, as nitrogen-rich nutrients and chemical pollutants cascade from the land into the rivers, and wash through estuaries and fish hatcheries on the coast.

Things can be done. Scientists have been looking at ways in which the industry might be able to adapt to change. But how well the oyster stock can adapt in the long term remains problematic.

“Ocean acidification has already cost the oyster industry in the Pacific Northwest nearly $110 million and has jeopardised about 3,200 jobs”, Dr Ekstrom says.

And Dr Waldbusser adds: “Without curbing carbon emissions, we will eventually run out of tools to address the short term, and we will be stuck with a much longer-term problem.”

 

 

Tim Radford writes for Climate News Network.

 

 




390832

Keystone plankton ‘go slow’ as ocean acidity rises Updated for 2026

Leave a reply




As the planet’s oceans become more acidic, the diatoms – a major group of alga – in the Southern Ocean could grow more slowly.

Nobody expected this. And since tiny, single-celled algae are a primary food source for an entire ocean ecosystem, the discovery seems ominous.

Bioscientist Clara Hoppe and colleagues from the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, report in the journal New Phytologist that they tested the growth of the Antarctic diatom Chaetoceros debilis under laboratory conditions.

They used two levels of pH – which is an indicator of acidity – and they exposed their tiny volunteers to constant light and to changing light, providing both standard laboratory conditions and lighting levels that approximated to the real world.

Under variable light in high-CO2 world, plant growth slows

In the unblinking glare of light, the diatoms responded well. Their growth levels were consistent with an assumption that more dissolved carbon dioxide – which makes the waters more acidic – would in effect fertilise plant growth.

Under conditions of changing light, however, it was a different story. The algae grew more slowly, which suggests that the oceans could become less efficient at removing carbon from the atmosphere, and perhaps less valuable as a primary food source for the creatures that teem in the Antarctic waters.

“Diatoms fulfil an important role in the Earth’s climate system”, Dr Hoppe says. “They can absorb large quantities of carbon dioxide, which they bind before ultimately transporting part of it to the depths of the ocean. Once there, the greenhouse gas remains naturally sequestered for centuries.”

Previous research into the steady acidification of the oceans has tended to concentrate on the consequences for coral reefs, fisheries, and tourism, but not on the impact on plant life in the seas.

Since carbon dioxide acts as a fertiliser, higher levels dissolved in the water might stimulate more growth. But growth depends not just on more carbon dioxide, but also on reliable sunlight. In the stormy southern seas, this is not steadily supplied.

Dr Hoppe says: “Several times a day, winds and currents transport diatoms in the Southern Ocean from the uppermost water layer to the layers below, and then back to the surface – which means that, in the course of a day, the diatoms experience alternating phases with more and with less light.”

Her co-author, marine biogeochemist Björn Rost, from the Alfred Wegener Institute, says: “Our findings show for the first time that our old assumptions most likely fall short of the mark. We now know that when the light intensity constantly changes, the effect of ocean acidification reverses.

“All of a sudden, lower pH values don’t increase growth, like studies using constant light show. Instead, they have the opposite effect.”

The implication is that, at certain intensities, the photosynthesis chain breaks down. The point at which light becomes too much light is more quickly reached in waters that are more acidic.

Like all such research, the finding has limitations. It applies to one species of single-celled creature in the waters of one ocean, and the tests were in a laboratory on a small scale, and not in a turbulent ocean rich in life. The Alfred Wegener team will continue their studies.

Fisheries at risk

But in the real world, coastal communities in 15 US states could be at long-term economic risk, as ocean acidification starts to take its toll on the commercial oyster fisheries.

Julia Ekstrom, then of the Natural Resources Defense Council and now director of the Climate Adaptation Programme at the University of California, Davis, and George Waldbusser, assistant professor of ocean ecology and biogeochemistry at Oregon State University report with colleagues, in Nature Climate Change, on an unholy mix in the oceans.

They say that a combination of rising greenhouse gas levels, more acid waters, polluted rivers, and upwelling currents put at risk mollusc fisheries from the Pacific Northwest, New England, the Mid-Atlantic states and the Gulf of Mexico – affecting the shellfish industry that is worth at least $1bn to the US.

Oyster larvae are sensitive to changes in ocean water, and more likely to die as pH levels shift towards the acidic. But acidification is not the only source of stress, as nitrogen-rich nutrients and chemical pollutants cascade from the land into the rivers, and wash through estuaries and fish hatcheries on the coast.

Things can be done. Scientists have been looking at ways in which the industry might be able to adapt to change. But how well the oyster stock can adapt in the long term remains problematic.

“Ocean acidification has already cost the oyster industry in the Pacific Northwest nearly $110 million and has jeopardised about 3,200 jobs”, Dr Ekstrom says.

And Dr Waldbusser adds: “Without curbing carbon emissions, we will eventually run out of tools to address the short term, and we will be stuck with a much longer-term problem.”

 

 

Tim Radford writes for Climate News Network.

 

 




390832

Keystone plankton ‘go slow’ as ocean acidity rises Updated for 2026

Leave a reply




As the planet’s oceans become more acidic, the diatoms – a major group of alga – in the Southern Ocean could grow more slowly.

Nobody expected this. And since tiny, single-celled algae are a primary food source for an entire ocean ecosystem, the discovery seems ominous.

Bioscientist Clara Hoppe and colleagues from the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research in Bremerhaven, Germany, report in the journal New Phytologist that they tested the growth of the Antarctic diatom Chaetoceros debilis under laboratory conditions.

They used two levels of pH – which is an indicator of acidity – and they exposed their tiny volunteers to constant light and to changing light, providing both standard laboratory conditions and lighting levels that approximated to the real world.

Under variable light in high-CO2 world, plant growth slows

In the unblinking glare of light, the diatoms responded well. Their growth levels were consistent with an assumption that more dissolved carbon dioxide – which makes the waters more acidic – would in effect fertilise plant growth.

Under conditions of changing light, however, it was a different story. The algae grew more slowly, which suggests that the oceans could become less efficient at removing carbon from the atmosphere, and perhaps less valuable as a primary food source for the creatures that teem in the Antarctic waters.

“Diatoms fulfil an important role in the Earth’s climate system”, Dr Hoppe says. “They can absorb large quantities of carbon dioxide, which they bind before ultimately transporting part of it to the depths of the ocean. Once there, the greenhouse gas remains naturally sequestered for centuries.”

Previous research into the steady acidification of the oceans has tended to concentrate on the consequences for coral reefs, fisheries, and tourism, but not on the impact on plant life in the seas.

Since carbon dioxide acts as a fertiliser, higher levels dissolved in the water might stimulate more growth. But growth depends not just on more carbon dioxide, but also on reliable sunlight. In the stormy southern seas, this is not steadily supplied.

Dr Hoppe says: “Several times a day, winds and currents transport diatoms in the Southern Ocean from the uppermost water layer to the layers below, and then back to the surface – which means that, in the course of a day, the diatoms experience alternating phases with more and with less light.”

Her co-author, marine biogeochemist Björn Rost, from the Alfred Wegener Institute, says: “Our findings show for the first time that our old assumptions most likely fall short of the mark. We now know that when the light intensity constantly changes, the effect of ocean acidification reverses.

“All of a sudden, lower pH values don’t increase growth, like studies using constant light show. Instead, they have the opposite effect.”

The implication is that, at certain intensities, the photosynthesis chain breaks down. The point at which light becomes too much light is more quickly reached in waters that are more acidic.

Like all such research, the finding has limitations. It applies to one species of single-celled creature in the waters of one ocean, and the tests were in a laboratory on a small scale, and not in a turbulent ocean rich in life. The Alfred Wegener team will continue their studies.

Fisheries at risk

But in the real world, coastal communities in 15 US states could be at long-term economic risk, as ocean acidification starts to take its toll on the commercial oyster fisheries.

Julia Ekstrom, then of the Natural Resources Defense Council and now director of the Climate Adaptation Programme at the University of California, Davis, and George Waldbusser, assistant professor of ocean ecology and biogeochemistry at Oregon State University report with colleagues, in Nature Climate Change, on an unholy mix in the oceans.

They say that a combination of rising greenhouse gas levels, more acid waters, polluted rivers, and upwelling currents put at risk mollusc fisheries from the Pacific Northwest, New England, the Mid-Atlantic states and the Gulf of Mexico – affecting the shellfish industry that is worth at least $1bn to the US.

Oyster larvae are sensitive to changes in ocean water, and more likely to die as pH levels shift towards the acidic. But acidification is not the only source of stress, as nitrogen-rich nutrients and chemical pollutants cascade from the land into the rivers, and wash through estuaries and fish hatcheries on the coast.

Things can be done. Scientists have been looking at ways in which the industry might be able to adapt to change. But how well the oyster stock can adapt in the long term remains problematic.

“Ocean acidification has already cost the oyster industry in the Pacific Northwest nearly $110 million and has jeopardised about 3,200 jobs”, Dr Ekstrom says.

And Dr Waldbusser adds: “Without curbing carbon emissions, we will eventually run out of tools to address the short term, and we will be stuck with a much longer-term problem.”

 

 

Tim Radford writes for Climate News Network.

 

 




390832

How does multiple climate variables and consumer diversity loss together “filter” natural communities? Updated for 2026

Leave a reply

eklc3b6f2

As the oceans gradually become warmer and more acidified, an increasing number of studies test the effects of climate change on marine organisms. As most climate change experiments have studied effects of single climate variables on single species, more and more researchers ask themselves how this lack of realism affects our ability to accurately assess and predict effects of climate change (Wernberg et al. 2012). Interestingly, theory and a growing body of studies suggests that different climate variables can strongly interact (Kroeker et al. 2013), that climate effects can change with presence/absence of strong consumers (Alsterberg et al. 2013), and that effects on communities are more informative than those on single species, as they allow experimenters to assess what traits that makes organisms sensitive or resistant (Berg et al. 2010). In our new paper “Community-level effects of rapid experimental warming and consumer loss outweigh effects of rapid ocean acidification” we found that warming and simulated consumer loss in seagrass mesocosms both increased macrofauna diversity, largely by favoring epifaunal organisms with fast population growth and poor defenses against predators.

Eklöf1

These results corroborate theory, and exemplify how trait- and life-history based approaches can be used to in more detail understand – and potentially predict – effects of climate change. Meanwhile, simulated ocean acidification (pH 7.75 vs. 8.10) had no detectable short-term effects on any of the investigated variables, including organisms with calcium-carbonate shell. While this lack of effect may be partly explained by the short duration of our experiment and/or the relatively crude endpoints, seagrass-associated macrofauna routinely experience diurnal pH variability that exceed predicted changes in mean pH over the coming century (Saderne et al. 2013). Consequently, by living in a variable pH these organisms could be relatively resilient to ocean acidification (see e.g. Frieder et al. 2014). In summary, it seems that at least in the short term, rapid warming and changes in consumer populations are likely to have considerably stronger effects than ocean acidification on macrofauna communities in shallow vegetated ecosystems.

References cited above:

Alsterberg, C., Eklöf, J. S., Gamfeldt, L., Havenhand, J. and Sundbäck, K. 2013. Consumers mediate the effects of experimental ocean acidification and warming on primary producers. – PNAS 110: 8603-8608.

Berg, M. P., Kiers, E. T., Driessen, G., van der Heijden, M., Kooi, B. W., Kuenen, F., Liefting, M., Verhoef, H. A. and Ellers, J. 2010. Adapt or disperse: understanding species persistence in a changing world. – Global Change Biol 16: 587-598.

Frieder, C. A., Gonzalez, J. P., Bockmon, E. E., Navarro, M. O. and Levin, L. A. 2014. Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae? – 20: 754-764.

Kroeker, K. J., Kordas, R. L., Crim, R., Hendriks, I. E., Ramajo, L., Singh, G. S., Duarte, C. M. and Gattuso, J.-P. 2013. Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming. – Glob. Change Biol. 19: 1884-1896.

Saderne, V., Fietzek, P. and Herman, P. M. J. 2013. Extreme Variations of pCO2 and pH in a Macrophyte Meadow of the Baltic Sea in Summer: Evidence of the Effect of Photosynthesis and Local Upwelling. – PloS ONE 8: e62689.

Wernberg, T., Smale, D. A. and Thomsen, M. S. 2012. A decade of climate change experiments on marine organisms: procedures, patterns and problems. – Glob. Change Biol. 18: 1491-1498.

 

About these ads

Mercury – thanks to our pollution, tuna will soon be unsafe for human consumption Updated for 2026

Leave a reply




Whether man-made sources of mercury are contributing to the mercury levels in open-ocean fish has been the subject of hot debate for many years.

My colleagues Carl Lamborg, Marty Horgan and I analyzed data from over the past 50 years and found that mercury levels in Pacific yellowfin tuna, often marketed as ahi tuna, is increasing at 3.8% per year. The results were reported earlier this month in the journal Environmental Toxicology and Chemistry.

This finding, when considered with other recent studies, suggests that mercury levels in open-ocean fish are keeping pace with current increases in human-related, or anthropogenic, inputs of mercury to the ocean.

These levels of mercury – a neurotoxin – are now approaching what the EPA considers unsafe for human consumption, underscoring the importance of accurate data. With this article, I’ll explain the evolution of the science to this point and our findings. I expect our analysis will either quiet the debate or add more fuel to the fire.

Busting the dilution myth

Motivated by the seminal environmental book Silent Spring, environmental chemists have long found widespread mercury pollution in wastewater from industrial activities.

Surprisingly, mercury also appeared far from point sources – in ‘pristine’ lakes of Scandinavia and northeastern North America. It took many years and careers to understand why mercury wound up in these ‘pristine’ lakes.

Once emitted from natural or man-made sources, such as coal-burning power plants, mercury can travel as a gas many times around the globe before falling with rain, snow, or dust. Once out of the air and in the water, it can then be taken up by fish.

There has been a false perception, however, that the open ocean – far removed from point sources of pollution – is too voluminous to be polluted with mercury from atmospheric fallout.

The shorthand for saying oceans can’t be significant sinks for air-borne pollutants is ‘dilution is the solution to pollution.’ The argument is that lakes are concentrated environments because they are in direct contact with their watersheds that collect rain and snow, but the deep open ocean is an extremely dilute environment.

Two manuscripts published in Science in the early 1970s supported this argument. The first stated that mercury pollution could only result in a negligible increase in mercury levels in open ocean water.

But my colleagues and I found these conclusions were based on faulty data. Before the advent of clean sampling techniques that prevent contamination before, during, or after collection, it was accepted that natural mercury levels of open ocean waters ranged in the low parts per billion.

But we now know that a typical mercury level is about 200 parts per quadrillion. That means the natural mercury level of open ocean water is about 5,000 times lower than previously thought – and that it takes a lot less mercury from other sources to pollute the open ocean.

The second manuscript reported no difference in mercury levels in tuna between museum specimens dating from 1878-1909 and samples caught during 1970-1971. This finding may be true, but also has a critical error in that mercury levels in the museum specimens were not ‘corrected’ for lipid (fat) loss.

Mercury is primarily in fish muscle and preservation with ethanol causes significant loss of fats. The net effect is that this preservation technique ‘inflates’ the mercury concentration in the tissue that remains.

As a result, we question how valid these findings are. In other words, this second study doesn’t conclusively demonstrate whether mercury levels in fish have gone up, down, or stayed steady.

But where’s the mercury coming from?

More recently, the focus of debate has been on the source of mercury in open-ocean fish. The mercury absorbed by fish is a compound called methylmercury, a form readily taken up by plant and animal cells but not easily eliminated.

Because of this, mercury is concentrated with each step of the food chain. As a result, methylmercury levels in predatory fish are about a million times greater than in the water in which they swim.

In lakes, there is overwhelming evidence that methylmercury is formed in sediments and bottom waters that are devoid of oxygen. But where is methylmercury in oceans formed?

In 2003, Princeton scientists published a hypothesis to answer the question of where methylmercury comes from in open ocean fish. The hypothesis was based on the observation, mentioned above, that there was no increase in mercury levels in yellowfin tuna near Hawaii between 1971 and 1998.

With no increase in mercury levels in tuna during a period of greatly increasing anthropogenic mercury emissions, the scientists presented the idea that methylmercury in the open ocean forms from mercury naturally present in deep waters, sediments, or hydrothermal vents.

Subsequently, however, independent studies have shown that there is not enough methylmercury in deep waters of the ocean to account for mercury in open ocean fish.

One of these studies also found that methylmercury is formed on sinking particles in the water that provide a micro-environment devoid of oxygen. That research showed that the methylmercury is formed from mercury coming from above – that is, the atmosphere – which we know is polluted from human activities.

Finally and most importantly, we know mercury levels in ocean water are increasing globally.

What the numbers say

Given the ongoing debate, our study set out to test a simple question: have mercury levels in fish stayed the same over time?

We assembled data from published sources for mercury in yellowfin tuna from Hawaii to compare three different time periods: 1971, 1998, and 2008. The comparison had to factor in the size of each tuna for each time period, because mercury level increases with size.

The statistical comparison indicated mercury levels were higher in 2008 than in either 1971 or 1998. As a result, we concluded that mercury levels are increasing in yellowfin tuna near Hawaii. The rate of increase between 1998 and 2008 of 3.8% per year is equivalent to a modeled increase in mercury in ocean waters in the same location.

What’s the source of the mercury? The overwhelming scientific evidence points to anthropogenic sources of mercury polluting open ocean waters and methylmercury being produced in the water column and then accumulating in fish. The average mercury level in a Pacific yellowfin tuna is approaching a level the US EPA considers unsafe for human consumption (0.3 parts-per-million).

Fish are an important source of food for billions of people worldwide and a solution to the problem is not to eat less fish, but to choose fish lower in mercury, as the EPA and FDA jointly recommend.

The ultimate solution to the problem is to control mercury emissions to the atmosphere at their source, which is the aim of the new United Nations Environment Programme’s Minamata Convention on Mercury.

 

 

Paul Drevnick is Assistant Research Scientist at the University of Michigan.

This article was originally published on The Conversation. Read the original article.

The Conversation

 




390393

Carbon stored deep in Antarctic waters ended the last ice age Updated for 2026

Leave a reply




It’s well known that carbon in the atmosphere is causing global warming. What is less well known, outside of scientific circles at least, is the role oceans have to play in this.

Our seas contain 60 times more carbon than the atmosphere, and they can release it at sufficiently rapid rates to cause dramatic changes in the climate. In fact, as we describe in research published in Nature, CO2 released by the oceans brought about the end of the last ice age.

More than 50 million cubic kilometres of ice once covered North America and Scandinavia. It melted away between approximately 19,000 and 10,000 years ago, releasing enough water to raise the sea level by about 130 metres.

This came after CO2 concentrations increased by approximately 50%, from 180 to 280 parts per million between the last ice age and the current interglacial period. To explain such a pronounced increase, we have to look at the ocean.

Scientists have thought for a long time that the southern sectors of the Atlantic, Indian and Pacific Oceans, a region known as the Southern Ocean, may be key to explaining the increase in atmospheric CO2.

Large volumes of deep water loaded with carbon come to the surface in this area. However, the low concentration of certain nutrients (for example iron) in surface waters limits the metabolism of planktonic organisms, which cannot fully consume all the carbon brought to the surface ocean, resulting in CO2 being ‘outgassed’ to the atmosphere.

We wanted to assess if the ocean contributed to the atmospheric CO2 increase during the last deglaciation, so it made sense to look at areas that are important today for the ocean-atmosphere exchange of carbon: the Atlantic Sector of the Southern Ocean and the Eastern Equatorial Pacific, another area where deep, cold water rises to the surface.

But how can we then go back in time and check if these areas were a source of CO2 in the atmosphere? The answer is buried a few thousand meters below the surface of the oceans.

The well-kept secrets secrets of long dead plankton

Research vessels such as the Joides Resolution are capable of drilling the sea floor to recover long sequences of sediments in which the history of the oceans is recorded. The sediments contain, among other things, fossils of tiny organisms that once lived in the upper ocean, called foraminifera. These creatures build chalky shells, and the waters they live in influence their chemical composition.

After death, the shells sink to the bottom of the oceans, where they accumulate. We analysed the sediment cores and looked for the isotopic composition of the element boron present in shells that lived during particular times of interest.

Boron tells us pH levels of the waters, which in turn tells us about carbon levels: a high concentration of CO2 in the waters will make them more acidic (lower pH), and vice versa.

We found a link. When the glaciers of the last ice age were melting, and the atmospheric CO2 was increasing, the surface waters of the Southern Ocean and the Eastern Equatorial Pacific were also more acidic. This signalled an increased concentration of CO2 – much higher than those in the atmosphere.

This is the key finding of our research: the deep ocean was a source of CO2 to the atmosphere during key intervals of the last deglaciation, which explains the large increase in CO2 concentrations.

Where did this carbon come from?

It’s the next obvious question. Previous research has found that the last ice age saw much less carbon exchanged between ocean and atmosphere than we see today, mostly because the Southern Ocean was intensely stratified at the time and deep waters rarely made it to the surface.

Nutrients and CO2 were accumulating in the deep Southern Ocean, due to the decay of the organic matter that was being produced in the surface ocean and transported to the abyss.

During the deglaciation, the effective communication between deep and upper ocean was re-established, and this carbon ‘reservoir’ was leaked to the atmosphere.

Since the beginning of the industrial revolution the oceans have absorbed an estimated 155 billion tonnes of carbon, about 30% of the total human emissions.

The present atmospheric CO2 concentrations, approximately 400 parts per million, have not been seen on Earth since the Pliocene, around 3 million years ago, and the rate of increase is unprecedented in the period of on-off glaciers we have had since.

Humanity is performing a large scale experiment with the Earth, and the consequences are already being seen in the form of increased atmospheric and oceanic temperatures, raising sea levels and ocean acidification, to name a few.

How the oceanic uptake of CO2 is going to operate in the future remains unknown, but studies like ours advance our understanding of how the ocean works to store and release carbon on timescales of millennia and that therefore are way beyond the reach of the instrumental record.

 

 

The paper: ‘Boron isotope evidence for oceanic carbon dioxide leakage during the last deglaciation‘ by M. A. Martínez-Botí et al is published in Nature.

Miguel Martinez-Boti is Visiting Researcher, National Oceanography Centre at the University of Southampton.

Gianluca Marino is Researcher in Oceans & Climate Change at the Australian National University.

This article was originally published on The Conversation. Read the original article.

The Conversation

 




390221

How does climate variables and diversity loss “filter” natural communities? Updated for 2026

Leave a reply

As the oceans gradually become warmer and more acidified, an increasing number of studies test the effects of climate change on marine organisms. As most climate change experiments have studied effects of single climate variables on single species, more and more researchers ask themselves how this lack of realism affects our ability to accurately assess and predict effects of climate change (Wernberg et al. 2012). Interestingly, theory and a growing body of studies suggests that different climate variables can strongly interact (Kroeker et al. 2013), that climate effects can change with presence/absence of strong consumers (Alsterberg et al. 2013), and that effects on communities are more informative than those on single species, as they allow experimenters to assess what traits that makes organisms sensitive or resistant (Berg et al. 2010). In our new paper “Community-level effects of rapid experimental warming and consumer loss outweigh effects of rapid ocean acidification“ we found that warming and simulated consumer loss in seagrass mesocosms both increased macrofauna diversity, largely by favoring epifaunal organisms with fast population growth and poor defenses against predators.

Eklöf1

These results corroborate theory, and exemplify how trait- and life-history based approaches can be used to in more detail understand – and potentially predict – effects of climate change. Meanwhile, simulated ocean acidification (pH 7.75 vs. 8.10) had no detectable short-term effects on any of the investigated variables, including organisms with calcium-carbonate shell. While this lack of effect may be partly explained by the short duration of our experiment and/or the relatively crude endpoints, seagrass-associated macrofauna routinely experience diurnal pH variability that exceed predicted changes in mean pH over the coming century (Saderne et al. 2013). Consequently, by living in a variable pH these organisms could be relatively resilient to ocean acidification (see e.g. Frieder et al. 2014). In summary, it seems that at least in the short term, rapid warming and changes in consumer populations are likely to have considerably stronger effects than ocean acidification on macrofauna communities in shallow vegetated ecosystems.

eklc3b6f2

 

References cited above:

Alsterberg, C., Eklöf, J. S., Gamfeldt, L., Havenhand, J. and Sundbäck, K. 2013. Consumers mediate the effects of experimental ocean acidification and warming on primary producers. – PNAS 110: 8603-8608.

Berg, M. P., Kiers, E. T., Driessen, G., van der Heijden, M., Kooi, B. W., Kuenen, F., Liefting, M., Verhoef, H. A. and Ellers, J. 2010. Adapt or disperse: understanding species persistence in a changing world. – Global Change Biol 16: 587-598.

Frieder, C. A., Gonzalez, J. P., Bockmon, E. E., Navarro, M. O. and Levin, L. A. 2014. Can variable pH and low oxygen moderate ocean acidification outcomes for mussel larvae? – 20: 754-764.

Kroeker, K. J., Kordas, R. L., Crim, R., Hendriks, I. E., Ramajo, L., Singh, G. S., Duarte, C. M. and Gattuso, J.-P. 2013. Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming. – Glob. Change Biol. 19: 1884-1896.

Saderne, V., Fietzek, P. and Herman, P. M. J. 2013. Extreme Variations of pCO2 and pH in a Macrophyte Meadow of the Baltic Sea in Summer: Evidence of the Effect of Photosynthesis and Local Upwelling. – PloS ONE 8: e62689.

Wernberg, T., Smale, D. A. and Thomsen, M. S. 2012. A decade of climate change experiments on marine organisms: procedures, patterns and problems. – Glob. Change Biol. 18: 1491-1498.

 

About these ads

UN talks begin on a new law to save our oceans Updated for 2026

Leave a reply




The United Nations has resolved to modernise international law on the sustainable use of the high seas and their wildlife.

The move could lead to new laws to address many of the oceans most severe problems, including measures to combat over-fishing and illegal fishing, the regulation of ‘by catch’ by fishing vessels, and the conservation of endangered species.

Other issues on the agenda include the protection of the seabed from deep sea mining, ocean acidification from rising levels of carbon dioxide in the atmosphere, marine biodiversity prospecting, regulation of offshore oil and gas prospecting, and the clean up of vast floating islands of plastic waste.

Following the decision by the United Nations Informal Working Group on Biodiversity Beyond National Jurisdiction (BBNJ), negotiations will now begin for a new international agreement for the sustainable use and conservation of marine biodiversity in the high seas.

Encouraging and historic

The decision was welcomed by David Miliband, Co-chair of the Global Ocean Commission (GOC), who had himself addressed delegates at the BBNJ meeting. It was “encouraging to see the UN agreeing to take action”, he said.

“This was one of the main demands identified by the Global Ocean Commission. I’m glad the message is getting across. The consensus reached last week will be remembered as a milestone in the modernisation of ocean governance.”

GOC Commissioner Robert Hill, who was the first Chairperson of the BBNJ when it was formed in 2006, called last week’s decision “historic”, adding:

“As always with UN processes, the work is far from over. First, we have to ensure the consensus recommendation is not undermined when it goes before the General Assembly in a few months and, second, it will be important to monitor closely the treaty negotiation – including the Preparatory Committee process and ultimately the international conference.”

Last year the GOC called for a new Implementing Agreement under the UN Convention on the Law of the Sea (UNCLOS) to prioritise ocean health and resilience, restore ocean productivity, guard against irresponsible, inefficient and wasteful exploitation, and allow for the creation of high seas marine protected areas (MPAs).

Such an agreement would extend governance to the 64% of the global ocean – and 45% of the planetary surface – that lies outside national jurisdiction, and provide a mechanism to conserve valuable high seas services such as carbon sequestration, worth between US$74 and US$222 billion annually, currently in jeopardy.

Time to end the high seas ‘failed state’

“The high seas are like a failed state“ , said Miliband. “Poor governance and the absence of policing and management mean valuable resources are unprotected or being squandered. The high seas belong to us all. We know what needs to be done but we can’t do it alone. A joint mission must be our priority.”

The GOC’s call was relayed and supported by more than 285,000 citizens from 111 countries, who signed a petition that was delivered to the UN Secretary General at the opening of the current Session of the UN General Assembly in September last year.

The BBNJ was mandated by the Rio+20 2012 Earth Summit to address the governance and conservation of the high seas – the portion of the ocean beyond a country’s 200-mile Exclusive Economic Zone. These areas beyond national jurisdiction represent 64% of the ocean’s surface, and 45% of our entire planet.

 

 

Join the call: ‘Help secure a living ocean, food and prosperity – propose a new agreement for high seas protection‘.

 

 




389729

Antarctica: warming ocean trebles glacial melt Updated for 2026

Leave a reply




The Antarctic ice shelf is under threat from a silent, invisible agency – and the rate of melting of glaciers has trebled in the last two decades.

The ocean waters of the deep circumpolar current that swirl around the continent have been getting measurably warmer and nearer the ocean surface over the last 40 years, and now they could be accelerating glacier flow by melting the ice from underneath, according to new research.

And a separate study reports that the melting of the West Antarctic glaciers has accelerated threefold in the last 21 years.

West Antarctic ice sheet – a potential 4.8m of sea level rise

If the West Antarctic ice sheet were to melt altogether – something that is not likely to happen this century – the world’s sea levels would rise by 4.8 metres, with calamitous consequences for seaboard cities and communities everywhere.

Researchers from Germany, Britain, Japan and the US report in Science journal that they base their research on long-term studies of seawater temperature and salinity sampled from the Antarctic continental shelf.

This continued intrusion of warmer waters has accelerated the melting of glaciers in West Antarctica, and there is no indication that the trend is likely to reverse.

Other parts of the continent so far are stable – but they could start melting for the first time. “The Antarctic ice sheet is a giant water reservoir”, said Karen Heywood, professor of environmental sciences at the University of East Anglia, UK.

“The ice cap on the southern continent is on average 2,100 metres thick and contains 70% of the world’s fresh water. If this ice mass were to melt completely, it could raise global sea level by 60 metres. That is not going to happen, but it gives you an idea of how much water is stored there.”

Temperatures in the warmest waters in the Bellinghausen Sea in West Antarctica have risen from 0.8°C in the 1970s to about 1.2°C in the last few years.

“This might not sound much, but it is a large amount of extra heat available to melt the ice“, said Sunke Schmidtko, an oceanographer at the Geomar Helmholtz Centre for Ocean Researchin Kiel, Germany, who led the study. “These waters have warmed in West Antarctica over 50 years. And they are significantly shallower than 50 years ago.”

Unpredictable consequences on ice and ecology

The apparent rise of warm water, and the observed melting of the West Antarctic ice shelf, could be linked to long-term changes in wind patterns in the Southern Ocean. Although melting has not yet been observed in other parts of the continent, there could be serious consequences for other ice shelves.

The shelf areas are also important for Antarctic krill – the little shrimp that plays a vital role in the Antarctic ocean food chain – as they serve as protective ‘nurseries’ for the young crustaceans. Warming ice shelves may have unpredictable consequences for spawning cycles, krill abundance, and wider ocean biodiversity.

Meanwhile, according to US scientists writing in Geophysical Research Letters, the glaciers of the Amundsen Sea in West Antarctica are shedding ice faster than any other part of the region.

Tyler Sutterley, a climate researcher at the University of California Irvine, and NASA space agency colleagues used four sets of observations to confirm the threefold acceleration.

They took their data from NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, from a NASA airborne project called Operation IceBridge, from an earlier satellite called ICESat, and from readings by the European Space Agency’s Envisat satellite.

Glaciers losing 16 billion tonnes of ice a year

The observations spanned the period 1992 to 2013 and enabled the researchers to calculate the total loss of ice, and also the rate of change of that loss. In all, during that period the continent lost 83 billion tonnes of ice per year on average.

After 1992, the rate of loss accelerated by 6.1 billion tonnes a year, and between 2003 and 2009 the melt rate increased by 16.3 gigatonnes a year on average. So the increasing rate of loss is now nearly three times the original figure.

“The mass loss of these glaciers is increasing at an amazing rate”, said Isabella Velicogna, Earth system scientist at both UC Irvine and the NASA Jet Propulsion Laboratory.

 

 

Tim Radford writes for Climate News Network.

 

 




388308