When we see records being broken and unprecedented events such as this, the onus is on those who deny any connection to climate change to prove their case. Global warming has fundamentally altered the background conditions that give rise to all weather. In the strictest sense, all weather is now connected to climate change. Kevin Trenberth
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by Tim Radford, Climate News Network, February 13, 2015
LONDON − Scientists believe they may have cracked the mystery of the end of the last ice age. The temperatures suddenly soared, and the glaciers went into retreat, because the deep southern ocean released huge quantities of carbon dioxide.
And the convincing answers have been delivered by analysis of the composition of calcium carbonate shells of ancient marine organisms.
The link between human burning of fossil fuels and the steady rise in atmospheric carbon dioxide levels was proposed more than a century ago and firmly established in the last 30 years.
But the ups and downs of planetary temperatures before the emergence of human civilisation are harder to explain. Fossil evidence suggests a link with carbon dioxide levels, but not necessarily a cause.
Bygone climates
Now paleoceanographer Miguel Martínez-Botí, from the University of Southampton, UK, and ocean and climate change researcher Gianluca Marino, from the Australian National University, report in Nature that they found their evidence in sediment cores – in effect, annual records of bygone climates – rich in the shells of tiny foraminifera called Globigerina bulloides.
This is a species that flourishes in conditions of high nutrients, acting as a kind of biological pump, gulping carbon from the atmosphere.
They found that high concentrations of carbon dioxide dissolved in surface waters of the southern Atlantic Ocean and the eastern equatorial Pacific coincided with rises in atmospheric CO2 at the end of the last ice age.
The implication is that these regions were the source of the carbon dioxide to the atmosphere.
At their coldest, during the ice ages, carbon dioxide levels fell to 185 parts per million. During the interglacials, when the world warmed and lions and hyenas roamed the plains of Europe, the carbon dioxide levels rose to 280 ppm.
Right now, thanks to human activity, CO2 levels are rising ominously towards 400 ppm.
The oceans are home to about 60 times more carbon than the atmosphere and can, it seems, surrender it rapidly.
“The magnitude and rapidity of the swings in atmospheric CO2 across the ice age cycles suggest that changes in ocean carbon storage are important drivers of natural atmospheric CO2 variations,” Dr Martínez-Botí says.
“Our findings support the theory that a series of processes operating in the southernmost sector of the Atlantic, Pacific and Indian oceans, a region known as the Southern Ocean, changed the amount of carbon in the deep sea.
Into the abyss
“While a reduction in communication between the deep sea and the atmosphere in this region potentially locks carbon away from the atmosphere into the abyss during ice ages, the opposite occurs during warm interglacial periods.”
To arrive at their conclusion, the scientists had to analyse subtle evidence from the isotopic composition of the carbonate shells, and then use mathematical techniques to reconstruct a story of a great, faraway sigh of carbon dioxide from the ocean to the atmosphere.
The finding, based on calculated probabilities, is incomplete as there may have been other forces also at play.
Gavin Foster, associate professor in isotope geochemistry at the University of Southampton, says: “While our results support a primary role for the Southern Ocean processes in these natural cycles, we don’t yet know the full story. Other processes operating in other parts of the ocean, such as the north Pacific, may have an additional role to play.”
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.
Deep-sea drilling for sediment samples.William Crawford, IODP/TAMU, CC BY-NC-SA 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 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.
Microscopic shells like this can reveal oceanic acidity.Mariana T. Horigome, Autonomous University of Barcelona, Author provided 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. This article was originally published on The Conversation.
Read the original article.
Credit: Tiago Fioreze / Wikipedia Land-ice decay at the end of the last five ice-ages caused global sea-levels to rise at rates of up to 5.5 metres per century, according to a new study.
An international team of researchers developed a 500,000-year record of sea-level variability, to provide the first account of how quickly sea-level changed during the last five ice-age cycles.
The results, published in the latest issue of Nature Communications, also found that more than 100 smaller events of sea-level rise took place in between the five major events.
Dr Katharine Grant, from the Australian National University (ANU), Canberra, who led the study, says: "The really fast rates of sea-level rise typically seem to have happened at the end of periods with exceptionally large ice sheets, when there was two or more times more ice on the Earth than today.
"Time periods with less than twice the modern global ice volume show almost no indications of sea-level rise faster than about 2 metres per century. Those with close to the modern amount of ice on Earth, show rates of up to 1 to 1.5 metres per century." [Note, however, that there is no past analogue for the current forcing of the climate.]
Co-author Professor Eelco Rohling, of both the University of Southampton and ANU, explains that the study also sheds light on the timescales of change. He says: "For the first time, we have data from a sufficiently large set of events to systematically study the timescale over which ice-sheet responses developed from initial change to maximum retreat."
"This happened within 400 years for 68% of all 120 cases considered, and within 1,100 years for 95%. In other words, once triggered, ice-sheet reduction (and therefore sea-level rise) kept accelerating relentlessly over periods of many centuries."
Professor Rohling speculates that there may be an important lesson for our future: "Man-made warming spans 150 years already and studies have documented clear increases in mass-loss from the Antarctic and Greenland ice sheets. Once under way, this response may be irreversible for many centuries to come."
The team reconstructed sea-levels using data from sediment cores from the Red Sea, an area that is very sensitive to sea-level changes because its only natural connection with the open (Indian) ocean is through the very shallow (137 metre) Bab-el-Mandab Strait. These sediment samples record wind-blown dust variations, which the team linked to a well-dated climate record from Chinese stalagmites. Due to a common process, both dust and stalagmite records show a pronounced change at the end of each ice age, which allowed the team to date the sea-level record in detail.
The researchers emphasise that their values for sea-level change are 500-year averages, so brief pulses of faster change cannot be excluded.
Morgan Schaller, James Wright, and the core sample that helped them understand what happened -- and how fast it happened -- 55 million years ago. Credit: James Wright, Rutgers University "Rapid" and "instantaneous" are words geologists don't use very often. But Rutgers geologists use these exact terms to describe a climate shift that occurred 55 million years ago.
In a new paper in the Proceedings of the National Academy of Sciences, Morgan Schaller and James Wright contend that following a doubling in carbon dioxide levels, the surface of the ocean turned acidic over a period of weeks or months and global temperatures rose by 5 degrees centigrade – all in the space of about 13 years.
Scientists previously thought this process had occurred over 10,000 years.
Wright, a professor of earth and planetary sciences in the School of Arts and Sciences and Schaller, a research associate, say the finding is significant in considering modern-day climate change.
"We've shown unequivocally what happens when CO2 increases dramatically – as it is now, and as it did 55 million years ago," Wright said. "The oceans become acidic and the world warms up dramatically. Our current carbon release has been going on for about 150 years, and because the rate is relatively slow, about half the CO2 has been absorbed by the oceans and forests, causing some popular confusion about the warming effects of CO2. But 55 million years ago, a much larger amount of carbon was all released nearly instantaneously, so the effects are much clearer."
The window to this important decade in the very distant past opened when Wright helped a colleague, Kenneth Miller, and his graduate students split core samples they extracted from a part of southern New Jersey once covered by the ocean.
The patterns found in the long cylinder of sediment told a story. There were distinct clay bands about 2 centimeters thick occurring rhythmically throughout the cores.
A close-up of the core at the heart of Wright's and Schaller's work. Note the regluar dark bands -- "like a tree ring," Schaller said. Credit: James Wright, Rutgers University
"They called me over and said, 'Look at this!" said Schaller. "What jumped out at me were these rhythmic clay layers, very cyclic. I thought, 'Wow, these have got to mean something."
Wright and Schaller surmised that only climate could account for the rhythmic pattern they saw. "When we see cycles in cores, we see a process," Schaller said. "In this case, it's like a tree ring. It's giving us a yearly account through the sediments."
This discovery provided the necessary data to finally solve the huge conundrum surrounding this event – the significant error in how fast the carbon was released.
Whatever the cause of the carbon release,—some scientists theorize that a comet struck the earth—Wright and Schaller's contention that it happened so rapidly is radically different from conventional thinking, and bound to be a source of controversy, Schaller believes.
"Scientists have been using this event from 55 million years ago to build models about what's going on now," Schaller said. "But they've been assuming it took something like 10,000 years to release that carbon, which we've shown is not the case. We now have a very precise record through the carbon release that can be used to fix those models."
Here is a must-see 2012 presentation by Julie
Brigham-Grette of the University of Massachusetts-Amherst, covering the
research her team has been doing into Lake El’gygytgyn
(pronouned El-Guh-Git-Kin), a water-filled meteor crater in Arctic
Russia that came into being after the impact of a ~1-km-diameter
space rock, 3.6 million years ago.
This is incredibly important work because:
The Lake El’gygytgyn region was not glaciated during any of the ice
ages. As a consequence, the more than 300-meter accumulated sequence of lake
sediments represents a continuous, undisturbed sedimentary record going
all the way back from the present to the aftermath of the impact.
The team succeeded in 2009 in extracting cores spanning this entire 3.6 million year period.
The oldest continuous ice core records to date extend back 123,000 years
in Greenland and 800,000 years in Antarctica: the Lake El’gygytgyn cores
go way back beyond those times and provide an unprecedented view of the
past climate of the Arctic.
Results show that during the Pleistocene (2.588 million to 11.7
thousand years ago), there were a number of super-interglacials – like
the present period but much wetter and several degrees warmer in the
Arctic, during which the Greenland and West Antarctic ice-sheets didn’t
just melt a bit. They disappeared.
Skeptical Science recently covered the new 2013 paper by the same
team, describing the Arctic climate in the Lake
El’gygytgyn region during the Pliocene, when boreal forests extended
well up into the Arctic and summer temperatures were 8 oC warmer than they are at present:
The data coming from Lake El’gygytgyn strongly suggest that the
Arctic climate is highly sensitive to small changes in forcing, warming
much faster than the rest of the world in the phenomenon known as Arctic
Amplification. In recent years, Arctic Amplification has emerged as a
strong modern-day climate signal. To cite but one example, the sea-ice
response has been of far greater magnitude than model-based forecasts
projected. Now, the past is giving a similar narrative, and
understanding the climate of the past gives us our best chance of
understanding the climate of the future.
Money quotes at 17:00: “..Greenland Ice sheet has come and gone much more frequently than
any of us had imagined.” 19:48: “..extreme warmth many times throughout the last few million years” and “..It may be much easier to get rid of sea ice than we thought before.”
We have pushed atmospheric CO2 levels to 400 parts per million (ppm) for the first time in human existence.
At the same time, a truly remarkably set of paleoclimate data shows the climate is much more sensitive to CO2 than we thought. And that means returning as quickly as possible back to 350 ppm is a vastly more rational course of action for a non-suicidal civilization, than, say continuing our unrestrained march toward 600 ppm, then 800, and then 1,000.
NOAA reported Friday that the daily mean concentration of CO2 in the air around Mauna Loa, Hawaii, surpassed 400 parts per million this week:
At the same time, a major new Science study of paleoclimate temperatures — based on “the longest sediment core ever collected on land in the Arctic” – revealedwhat happened the last time we had similar CO2 levels:
“One of our major findings is that the Arctic was very warm in the Pliocene [~5.3 to 2.6 million years ago] when others have suggested atmospheric CO2 was very much like levels we see today. This could tell us where we are going in the near future. In other words, the Earth system response to small changes in carbon dioxide is bigger than suggested by earlier models,” the authors state.
Yes, contrary to one or two (misreported) models suggesting a climate sensitivity on the low side, this study joins the myriad analyses of data that find it is likely to prove to be on the high side. For instance, recent observations of relative humidity in the tropics and subtropics found that “Future warming likely to be on high side of climate projections,” according to a November paper in Science.
How sensitive is the climate to increases in CO2, according to this “absolutely new knowledge” of paleoclimate temperatures?
Another significant finding to emerge from this first continuous, high-resolution record of the Middle Pliocene is documentation of sustained warmth with summer temperatures of about 59–61
°F [15–16 °C], about 8 °C [14 °F] warmer than today.
This period of Arctic warmth “coincides, in part, with a long interval of 1.2 million years when the West Antarctic Ice sheet did not exist.” Indeed, sea levels during the mid-Pliocine were about 25 m [82 feet] higher than today!
It is worth noting that a 2009 analysis in Science found that when CO2 levels were this high 15–20 million years ago, it was 5–10 °F warmer globally and seas were also 75–120 feet higher.
Science (1/11) study — On our current emissions path, CO2 levels in 2100 will hit levels last seen when the Earth was 29 °F (16 °C) hotter: Paleoclimate data suggests CO2 “may have at least twice the effect on global temperatures than currently projected by computer models.”
This new paper is just the latest to suggest the Arctic will warm much faster than the models have suggested. For instance, back in 2006, scientists analyzed deep marine sediments to understand the Paleocene Eocene thermal maximum, a brief period some 55 million years ago of “widespread, extreme climatic warming that was associated with massive atmospheric greenhouse gas input.” That Nature study (subs. req’d) found Arctic temperatures almost beyond imagination – above 23 °C (74 °F) – temperatures more than 18 °F warmer than climate models had predicted when applied to this period. The three dozen authors conclude that existing climate models are missing crucial feedbacks that can significantly amplify polar warming.
Clearly our climate models don’t do a good job of explaining what’s happening in the Arctic right now:
Arctic sea ice is melting much, much faster than even the best climate models had projected (actual observations in red). The reason is most likely unmodeled amplifying feedbacks. The image (from Climate Crocks via Arctic Sea Ice Blog) comes from a 2007 GRL research paper by Stroeve et al.
And this underestimation of polar amplification in turn leads the authors of the new study — and many other scientists — to conclude that the climate’s overall sensitivity is on the high side. As the UK Guardianreports:
Prof Robert Spicer, at the Open University and not part of the new study, agreed: “This is another piece of evidence showing that climate models have a systematic problem with polar amplification,” i.e., the fact that global warming has its greatest effects at the poles. “This has enormous implications and suggests model are likely to underestimate the degree of future change.”
Given that the Arctic is already losing ice several decades faster than any major climate model had projected, we should expect that the permafrost — which contains twice as much carbon as the atmosphere currently does — will also go faster than the models suggest.
We find that simulated western Arctic land warming trends during rapid sea ice loss are 3.5 times greater than secular 21st century climate-change trends. The accelerated warming signal penetrates up to ,km inland….
Anyone betting on a low sensitivity of the climate to carbon is literally betting against history.
Finally, this new analysis of Arctic sediments is a very impressive piece of work whose conclusions are hard to dismiss:
“It shows a huge warming – unprecedented in human history,” said Prof Scott Elias, at Royal Holloway University of London, and not involved in the work. “It is a frightening experiment we are conducting with our climate.”
The sediments have been slowly settling in Lake El’gygytgyn since it was formed 3.6 million years ago, when a kilometre-wide meteorite blasted a crater 100 km north of the Arctic circle. Unlike most places so far north, the region was never eroded by glaciers, so a continuous record of the climate has lain undisturbed ever since. “It’s a phenomenal record,” said Prof Peter Sammonds, at University College London. “It is also an incredible achievement [the study's work], given the remoteness of the lake.” Sixteen shipping containers of equipment had to be hauled 90 km over snow by bulldozers from the nearest ice road, used by gold miners.
Previous research on land had revealed glimpses of the Arctic climate and ocean sediments had recorded the marine climate, but the disparate data are not consistent with one another. “Lake El’gygytgyn may be the only place in the world that has this incredible unbroken record of sediments going back millions of years,” said Elias. “When you have a very long record it is very different to argue with.”
If you want to learn more about this research, you can read the news release, the study itself (subs. req’d) or watch this video from the lead author, where you will also learn how to pronounce “El’gygytgyn”:
Quarternary Science Reviews, 29 (2010) 1757–1778; doi:10.1016/j.quascirev.2010.02.010 History of sea ice in the Arctic
Leonid Polyak*, Richard B. Alley, John T. Andrews, Julie Brigham-Grette, Thomas M. Cronin, Dennis A. Darby, Arthur S. Dyke, Joan J. Fitzpatrick, Svend Funder, Marika Holland, Anne E. Jennings, Gifford H. Miller, Matt O’Regan, James Savelle, Mark Serreze, Kristen St. John, James W. C. White and Eric Wolff Abstract
Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past. This information can be provided by proxy records from the Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO2 after the Paleocene–Eocene Thermal Optimum, and consistently covered at least part of the Arctic Ocean for no less than the last 13–14 million years. Ice was apparently most wide-spread during the last 2–3 million years, in accordance with Earth’s overall cooler climate. Nevertheless, episodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorter-term (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.
Readers, for a discussion of the proxy records and the limitations of the various sediment cores from the Arctic Ocean and its margins, go to the link below and page 4.
It appears to explain long-term changes in the frequency of fire over many centuries, and it may explain what's been happening in the West in recent years."Climate ultimately drives fire," said Mitchell Power, assistant professor of geography at the University of Utah and curator of the Garrett Herbarium at the Natural History Museum of Utah.
Power is lead author of the new study which explored lake-bottom sediments in hundreds of locations around the world.
The 20 scientists involved in the project concluded that there were fewer fires following the onset of a global cooling trend hundreds of years ago. Conversely, there were more fires after the trend reversed into a period of global warming.
"Our climate is the primary controller of fire, and so we have seen this in the last decade," Power said. "Temperatures have warmed. We're seeing more fires. We're seeing a longer fire season."
Power's involvement in the studies stems from his curiosity after the Milford Flat Fire devastated more than 300,000 acres in western Utah in 2007. He wondered how often big fires like that happen.
He now has collected a library of clues, core samples of sediments extracted from lake bottoms in North America and South America. He collected many samples from Spring Lake in Millard County near Milford Flat. He also obtained data samples extracted by other scientists in 600 lakes throughout the world.
"Lakes are like nature's museum," Power explained.
The evidence in the core samples is microscopic bits of charcoal that wash or blow into lakes. Power studied charcoal in sediments deposited over 2,000 years. The study found a strong correlation between the frequency of wildfires and long-term climate trends, particularly during and after the so-called Little Ice Age, named for a period of cooling several hundred years ago.
"When the atmosphere warms up and we have a century or more of warming, we get more fire," Power said. "When things cool down, we get less fire."
That may seem obvious, but it undercuts a rival theory.
Scientists already knew fires declined in the Americas after the Little Ice Age set in. But a previous theory blamed the decline in fire on a devastating population collapse that took place after Columbus arrived in 1492. The Europeans who followed Columbus brought diseases that drastically reduced Native American populations. Previous scholars have suggested the population collapse led to a sharp decline in agricultural burning. That would have lowered the amount of charcoal in corresponding sediment layers in lake bottoms.
Power's study refutes that theory. It found that the decline in fires was not confined to the Americas. "The rest of the world also shows evidence of decreased fire and cooling," Power said.
The decline in fires also was earlier than could be explained by the population collapse. "Before Columbus came, before any of the Spaniards arrived, before diseases spread, this began as early as about 1350 A.D.," Power said. "There's a really strong coupling of temperature and fire, and this was under way well before this demographic collapse."
He believes the upsurge of wildfires in recent years is linked to a globally documented increase in temperatures. Warming trends play a role in drying out fuels and making them more explosive. Another factor appears to be increased air convection; a warmer climate has more thunderstorms and that can mean more lightning-caused fires.
by Liz Kalaugher, editor,environmentalresearchweb, March 26, 2012
For many years scientists have known that iron is often associated with organic carbon in sediment but did not know why. Now researchers from Canada have found that just over 20% of the organic carbon in sediments is directly bound to reactive iron phases.
They estimate that worldwide 19–45 Gigatonnes of organic carbon are locked up in surface marine sediments in this way. Because reactive iron phases are metastable over long time periods, the sediments could be an efficient "rusty sink" for organic carbon.
"Burial in sediments is the only long-term sink of organic carbon on the planet, on geological timescales," Yves Gélinas of Concordia University told environmentalresearchweb. "Yet only a tiny fraction of organic carbon – about 0.3% – produced in the surface waters through photosynthesis eventually reaches the seafloor and is preserved in sediments. The rest is degraded in the water column and at the surface of the sediment."
The most widely accepted explanation for the tiny proportion of organic carbon preserved, says Gélinas, is that it's protected by sorption on clay mineral surfaces in the water column and in sediments.
"Our work shows that iron oxides are also very important, which is totally new," he added. "Why does it matter? Simply because iron oxides are not stable in anoxic [no-oxygen] environments (they form only in oxic settings), while clay minerals are stable whatever the redox conditions of the system."
The expansion of oceanic "dead zones" – regions where oxygen levels are too low to sustain life – could eventually affect this iron complexation mechanism for preserving organic carbon. According to Gélinas, this will "create a positive feedback mechanism fuelling greater oxygen consumption" as more organic matter will be degraded in the water column or at the surface of the sediments, using additional oxygen and so contributing to the expansion of dead zones.
"Iron has become a very popular research topic in chemical oceanography since the discovery that it is a limiting nutrient for primary productivity in large areas of the ocean," said Gélinas. "We show for the first time that iron also plays an important role in organic carbon preservation. We are definitely in the Iron Age of oceanography."
Gélinas and colleagues from Concordia University and McGill University tested sediments from around the world sampled from freshwaters, estuaries, river deltas, continental margins and the deep sea, using an iron reduction method previously used in soils.
"We now better understand the controls on organic matter preservation in sediments through its stabilization by iron complexation," said Gélinas. "[This] means that we can do a better job building models representing carbon preservation and cycling in marine environments. It also means better prediction of the evolution of the organic carbon preservation function in these models as bottom-water dissolved oxygen concentrations keep decreasing."
Now Gélinas says the team plans to get a clearer idea of the types of chemical bonds that link iron and organic matter, and how changes in local redox conditions affect their relative proportions in sinking particulates and sediments.
"We have recently obtained Synchrotron X-Ray beam time at the Brookhaven National Light Source Laboratory (NLSL) in Long Island, US, and acquired a very promising first set of data showing that our working hypothesis – that iron complexation to organic carbon plays a much greater than anticipated role in preserving a large fraction of organic carbon in sediments – is correct," he said. "We have applied for more beam time at the NSLS and at the Canadian Light Source Synchrotron in Saskatchewan to pursue this work."
The team would also like to estimate the importance of the mechanism in the stabilization of soil organic carbon.
Gas Hydrate Stability Zone Dynamics and Global Climate Change
V. E. Romanovsky and T. E. Osterkamp, Department of Geology & Geophysics, Geophysical Institute
The results of investigations of ice cores from Greenland and Antarctica, deep-sea sediment cores, as well as other paleoclimate investigations, show that, during the Pleistocene-Holocene time, significant changes in global temperature and greenhouse gas content in the atmosphere occurred. In general, such changes were associated with ice age rhythms. Preliminary analysis of these data shows that the changes in greenhouse gas contents did not always lead the corresponding global temperature changes. Moreover, the global temperature changes preceded the greenhouse gas concentration variations. Certain connections exist between global sea level changes and greenhouse gas concentrations in the atmosphere. Although the data about sea level changes are more reliable only for the last 20-25 thousand years, it can be noted that in most cases the sea level changes lead the greenhouse gas concentration changes.
The key to understanding the relationship between sea level variations and the change in concentration of greenhouse gases may be the gas hydrate stability zone and subsea permafrost dynamics within the arctic shelves. During the ice ages of the Pleistocene, these shelves were emergent and subjected to deep freezing several times. Tremendous amounts of gas, particularly methane, were trapped by the permafrost layer within the shelves. The thermodynamic conditions in this case were proper for thick layers (up to 600-1,000 m) of gas hydrates. The intensity of gas hydrate created within the subsea sediments varies between sites. This depends on the organic substance content in the sediments and on thermodynamic conditions. According to the most common estimations, the total volume of carbon in the form of gas hydrates in the ocean sediments is 10,000 to 11,000 Gt.
Figure 1. (below) 15,000 years ago. The shelf at Barrow was exposed and frozen. The hydrate stability zone was largest.
Figure 2. (below) 4,000 years ago. Subsea permafrost and hydrate stability zone continued to degrade. The free gas at 65-80 km offshore could have been released to the atmosphere.
Figure 3. (above) Present time. Subsea permafrost at Barrow exists 8-10 km offshore. The contribution of greenhouse gases to the atmosphere from hydrate destabilization during the last 3,000 years was much less than 3,000-4,000 years ago, assuming rapid transport of the gases to the seabed.
There are three main areas of gas hydrate occurrences: the region of continuous onshore permafrost, the region of subsea permafrost within the arctic shelves, and the oceanic region of the outer continental margin. The first and the third regions are currently characterized by fairly stable conditions. Due to gas hydrate stability zone dynamics, changes in the concentration of greenhouse gases can be initiated only in the region of continental shelves with gas hydrates.
The extensive Russian arctic shelves play an especially important role because of their large area and usual shallow sea depth. Sea level changes and history of climatic variations during the Late Pleistocene through Holocene determine the subsea permafrost existence and dynamics. During the ice ages, low sea levels exposed much of the vast Siberian shelf to cold air temperatures which allowed permafrost to aggrade in these shelves. Temperature and pressure values associated with these conditions are favorable for the formation of gas hydrates. These shelves have now been submerged and the cold surface boundary condition has been replaced by a warm one. Consequently, the permafrost in these shelves is now degrading and warmer temperatures have made the gas hydrates unstable. When the permafrost disappears, the gas from the decomposed hydrates can pass through the sediments and water to the atmosphere creating a significant positive feedback loop to enhance climatic warming.
Estimates of the potential gas fluxes to the atmosphere and the timing of these gas fluxes require detailed information on the dynamics of thawing subsea permafrost and gas hydrate decomposition. A numerical model was used to investigate the potential stability fields of the gas hydrates associated with subsea permafrost.
To estimate the dynamics of possible methane release to the atmosphere, curves for the volume of destabilized sediments in time were constructed for Cape Thompson and Barrow. These curves showed extremely sharp peaks, which means that most of the gas could have been released into the atmosphere during a short period of time (less than one millennium). The timing of these events was different for Cape Thompson (1 ka ago) and Barrow (3 ka ago).
These calculations can, with proper environmental and paleogeographical conditions, be used to estimate permafrost and gas hydrate equilibrium zone dynamics within the continental shelves of Siberia and North America.
Slow release of fossil carbon during the Palaeocene–Eocene Thermal Maximum
Ying Cui¹*, Lee R. Kump¹, Andy J. Ridgwell², Adam J. Charles³, Christopher K. Junium¹, Aaron F. Diefendorf¹, Katherine H. Freeman¹, Nathan M. Urban¹ and Ian C. Harding³
Abstract
The transient global warming event known as the Palaeocene–Eocene Thermal Maximum occurred about 55.9 Myr ago. The warming was accompanied by a rapid shift in the isotopic signature of sedimentary carbonates, suggesting that the event was triggered by a massive release of carbon to the ocean–atmosphere system. However, the source, rate of emission and total amount of carbon involved remain poorly constrained. Here we use an expanded marine sedimentary section from Spitsbergen to reconstruct the carbon isotope excursion as recorded in marine organic matter. We find that the total magnitude of the carbon isotope excursion in the ocean–atmosphere system was about 4°/oo. We then force an Earth system model of intermediate complexity to conform to our isotope record, allowing us to generate a continuous estimate of the rate of carbon emissions to the atmosphere. Our simulations show that the peak rate of carbon addition was probably in the range of 0.3–1.7 Pg C/yr, much slower than the present rate of carbon emissions.
The Conclusion's money paragraph:
"The quantities of carbon added during the PETM span the estimates of current fossil-fuel resources, suggesting that the PETM could serve as a good analogue for future warming. However, the peak rates of PETM carbon addition in these simulations (also see refs 9, 15 and 25), and in complementary simulations based on other published isotope records, are a small fraction of the present rate of fossil-fuel burning. Thus, although the current overall capacity for society to perturb the carbon cycle is comparable to that of the PETM, the rate at which we are imposing the current perturbation on the Earth system may be unprecedented."
The transient global warming event known as the Palaeocene–Eocene Thermal Maximum occurred about 55.9Myr ago. The warming was accompanied by a rapid shift in the isotopic signature of sedimentary carbonates, suggesting that the event was triggered by a massive release of carbon to the ocean–atmosphere system. However, the source, rate of emission and total amount of carbon involved remain poorly constrained. Here we use an expanded marine sedimentary section from Spitsbergen to reconstruct the carbon isotope excursion as recorded in marine organic matter. We find that the total magnitude of the carbon isotope excursion in the ocean–atmosphere system was about 4‰. We then force an Earth system model of intermediate complexity to conform to our isotope record, allowing us to generate a continuous estimate of the rate of carbon emissions to the atmosphere. Our simulations show that the peak rate of carbon addition was probably in the range of 0.3–1.7PgCyr−1, much slower than the present rate of carbon emissions.
Explore further: Antarctica could raise sea level faster than previously thought
Explore further: Late Cretaceous Period was likely ice-free
At the same time, a major new Science study of paleoclimate temperatures — based on “the longest sediment core ever collected on land in the Arctic” – revealed what happened the last time we had similar CO2 levels:
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