Andrew Glikson: Another link between CO2 and mass extinctions of species

by Andrew Glikson, The Conversation, March 22, 2013

It’s long been known that massive increases in emission of CO₂ from volcanoes, associated with the opening of the Atlantic Ocean in the end-Triassic Period, set off a shift in state of the climate which caused global mass extinction of species, eliminating about 34% of genera. The extinction created ecological niches which allowed the rise of dinosaurs during the Triassic, about 250–200 million years ago.

New research released this morning in Science Express has refined the dating of this wave of volcanism. It shows marine and land species disappear from the fossil record within 20,000 to 30,000 years from the time evidence for the eruption of large magma flows appears, approximately 201 million years ago. These volcanic eruptions increased atmospheric CO₂ and increased ocean acidity.

Mass extinctions due to rapidly escalating levels of CO₂ are recorded since as long as 580 million years ago. As our anthropogenic global emissions of CO₂ are rising, at a rate for which no precedence is known from the geological record with the exception of asteroid impacts, another wave of extinctions is unfolding.

Mass extinctions of species in the history of Earth include:

• the ~580 million years-old (Ma) Acraman impact (South Australia) and Acrytarch (ancient palynomorphs) extinction and radiation
• Late Devonian (~374 Ma) volcanism, peak global temperatures and mass extinctions
• the end-Devonian impact cluster associated with mass extinction, which among others destroyed the Kimberley Fitzroy reefs (~360 Ma)
• the upper Permian (~267 Ma) extinction associated with a warming trend
• the Permian-Triassic boundary volcanic and asteroid impact events (~ 251 Ma) and peak warming
• the End-Triassic (201 Ma) opening of the Atlantic Ocean, and massive volcanism
• an End-Jurassic (~145 Ma) impact cluster and opening of the Indian Ocean
• the Cretaceous–Tertiary boundary (K-T) (~65 Ma) impact cluster, Deccan volcanic activity and mass extinction
• the pre-Eocene–Oligocene boundary (~34 Ma) impact cluster and a cooling trend, followed by opening of the Drake Passage between Antarctica and South America, formation of the Antarctic ice sheet and minor extinction at ~34 Ma.

Throughout the Phanerozoic (from 542 million years ago), major mass extinctions of species closely coincided with abrupt rises of atmospheric carbon dioxide and ocean acidity. These increases took place at rates to which many species could not adapt. These events – triggered by asteroid impacts, massive volcanic activity, eruption of methane, ocean anoxia and extreme rates of glaciation (see Figures 1 and 2) – have direct implications for the effects of the current rise of CO₂.


Click on graphs to enlarge.

Figure 1. Trends in atmospheric CO2 and related glacial and interglacial periods since the Cambrian (542 million years ago), showing peaks in CO2 levels (green diamonds) associated with asteroid impacts and/or massive volcanism. CO2 data from Royer (2004 and 2006).

Figure 2. Relations between CO2 rise rates and mean global temperature rise rates during warming periods, including the Paleocene–Eocene Thermal Maximum, early Oligocene, mid-Miocene, late Pliocene, Eemian (glacial termination), Dansgaard–Oeschger cycles, Medieval Warming Period, 1750–2012 and 1975–2012 periods.

In February 2013, CO₂ levels had risen to near 396.80 ppm at Mauna Loa Atmospheric Observatory, compared to 393.54 ppm in February 2012. This rise (3.26 ppm per year) is at the highest rate yet recorded. Further measurements show CO₂ is at near 400 ppm of the atmosphere over the Arctic. At this rate the upper stability threshold of the Antarctic ice sheet, defined at about 500–600 ppm CO₂ would be reached later this century (although hysteresis of the ice sheets may slow down melting).

Our global carbon reserves (including coal, oil, oil shale, tar sands, gas and coal-seam gas) contain considerably more than 10,000 billion tonnes of carbon (see Figure 5). This amount of carbon, if released into the atmosphere, is capable of raising atmospheric CO₂ levels to higher than 1,000 ppm. Such a rise in atmospheric radiative forcing will be similar to that of the Paleocene–Eocene boundary thermal maximum (PETM), which happened about 55 million years ago (see Figures 1, 2 and 4). But the rate of rise surpasses those of this thermal maximum by about ten times.

Figure 3. Plot of percent mass extinction of genera versus peak atmospheric CO2 levels at several stages of Earth history.

Figure 4. The Paleocene–Eocene Thermal Maximum (PETM) represented by sediments in the Southern Ocean, central Pacific and South Atlantic oceans. The data indicate: (a) deposition of an organic matter-rich layer consequent on extinction of marine organisms, (b) lowering of δ18O values representing an increase in temperature, and (c) a sharp decline in carbonate contents of sediments representing a decrease in pH and increase in acidity (Zachos et al. 2008).

The Paleocene–Eocene boundary thermal maximum event about 55 million years ago saw the release of approximately 2,000–3,000 billion tons of carbon to the atmosphere in the form of methane (CH₄). It led to the extinction of about 35–50% of benthic foraminifera (see Figures 3 and 4), representing a major decline in the state of the marine ecosystem. The temperature rise and ocean acidity during this event are shown in Figures 4 and 6.

Based on the amount of carbon already emitted and which could continue to be released to the atmosphere (see Figure 5), current climate trends could be tracking toward conditions like those of the Paleocene–Eocene event. Many species may be unable to adapt to the extreme rate of current rise in greenhouse gases and temperatures. The rapid opening of the Arctic Sea ice, melting of Greenland and west Antarctic ice sheets, and rising spate of floods, heat waves, fires and other extreme weather events may signify a shift in the state of the climate, crossing tipping points.

Figure 5. CO2 emissions from fossil fuels (2.12 GtC ~ 1 ppm CO2). Estimated reserves and potentially recoverable resources.

By analogy to medical science analysing blood count as diagnosis for cancer, climate science uses the greenhouse gas levels of the atmosphere, pH levels of the ocean, variations in solar insolation, aerosol concentrations, clouding states at different levels of the atmosphere, state of the continental ice sheets and sea ice, position of high pressure ridges and climate zones and many other parameters to determine trends in the climate. The results of these tests, conducted by thousands of peer-reviewed scientists world-wide, have to date been ignored, at the greatest peril to humanity and nature.

Continuing emissions contravene international laws regarding crimes against humanity and related International and Australian covenants. In the absence of an effective global mitigation effort, governments world-wide are now presiding over the demise of future generations and of nature, tracking toward one of the greatest mass extinction events nature has seen. It is time we learned from the history of planet Earth.

Figure 6. The Paleocene–Eocene boundary thermal maximum. http://www.uta.edu/faculty/awinguth/petm_research/petm_home.html

Andrew Glikson does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.


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

Doug O'Harra: What role does the Bering Strait play in moderating global temperatures?

What role does the Bering Strait play in moderating global temperatures?

by Doug O'Harra, Alaska Dispatch, April 18, 2012

Alaska’s Bering Strait may play a critical role in the regulation of the global climate — including a knack for maintaining the Atlantic Ocean “conveyor belt”that bathes northern Europe in eon-long kisses of sultry currents and warm wet weather.

But squeeze shut the 53-mile-wide narrows between the Pacific and Arctic oceans off the western tip of Alaska — something that occurred during the last ice age when continental ice sheets locked up much of the world’s fresh water — and the oceanic engine that stabilizes the home planet's climate becomes much more likely to go on the fritz and stay that way for a long time.

These resulting shutdowns have previously stalled the Gulf Stream and triggered abrupt swings between warmer and frigid climates, what scientists call Dansgaard-Oeschger and Heinrich events. These jarring shifts struck the North Atlantic as many as 25 times between 80,000 and about 11,000 years ago, all during moments when the Bering Land Bridge blocked all flow between Pacific and Arctic oceans.

The possibility that a modern version of this process might cause an overnight return to ice age conditions was dramatized (and exaggerated to a fantastic and preposterous degree) by Hollywood in the 2004 climate-disaster flick "The Day After Tomorrow."

But a new study using highly sophisticated computer models predicts there will be no real-life sequel any time soon — not as long as the Pacific and Arctic keep swapping spit through the gap dividing Alaska from Siberia. 

“A diverse group of climate researchers has found after running computer simulations that the strait that separates North America and Russia might be serving as a global temperature stabilizer,” explained this Physics.org story about the findings. “When the strait is blocked, melting glacial freshwater in the Arctic Ocean can’t make its way to the Pacific, causing it to back up and eventually flow into the Atlantic.”

The study — The role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability — is part of a broader research effort into how ocean circulation impacts the Earth’s climate. Climate scientist Aixue Hu at the National Center for Atmospheric Research and many of 11 co-authors on the new study have previously found that the Bering Strait may be a key factor in global climate dynamics.

"The global climate is sensitive to impacts that may seem minor," Hu explained in this 2010 story. "Even small processes, if they are in the right location, can amplify changes in climate around the world."

In the newest study, Hu and her team ran two sets of computer simulations — one where plunging sea levels had closed the Bering Strait again, and one where the Bering Strait remained open and allowed salty Pacific water into the Arctic and fresh Arctic water to escape into the Pacific.

In each scenario, the researchers gradually added more and more fresh water to the North Atlantic in latitudes spanning from Cuba to England. The goal was to trigger the shutdown of the Atlantic circulation and cause one of those abrupt cooling events inside the computer simulation.

They succeeded. But first, how does all this colossal mixing cause such jarring climate shocks in the real world?

The flow of the Gulf Stream and other elements of the global ocean circulation system deliver warm salty water to the North Atlantic, where it cools, grows denser, and sinks. At depth, this dense salty water starts flowing south. It then keeps rolling, eventually crawling into other hemispheres along a network of deep ocean currents that meander the globe over hundreds of years while equalizing the climate.

But introduce massive amounts of less dense fresh water into the mix, and the North Atlantic sinking starts to sputter, slowing the deep currents to the point where they temporarily die. (Here’s a discussion of a sudden cooling event about 8,000 years ago possibly caused by the draining of massive glacier lakes in North America.)

"One thing that can slow this circulation down, is, if you add freshwater to that area of the North Atlantic, it lowers the density," explained Woods Hole researcher Bruce Peterson, in this 2002 National Geographic story about the process. "It counteracts the process that is increasing density. … If you stop the process, you stop the conveyor that brings warm water north.”

The paradoxical result, Peterson added, can be a chilldown of northern Europe and perhaps the entire northern hemisphere.

Thus, smooth functioning of the Atlantic ocean “conveyor” becomes a “critical link” in keeping the world’s climate from making these wild swings. 

“If waters of the far North Atlantic don't sink,” Hu told Science Now here,  “much of the large-scale ocean circulation worldwide temporarily collapses. One result: the Gulf Stream, which brings climate-warming waters from the equator to the North Atlantic, comes to a halt.”

If this sounds familiar, you might be remembering the iron-jawed turn by Dennis Quaid in the 2004 climate disaster movie, when he skied to the rescue through an instantaneous ice age caused by shutdown of the Atlantic’s internal circulation. At the time, scientists called the plot of the movie absurd, but acknowledged there was a kernel of scientific truth in the premise.

Back to the computer modeling study. Hu and her team found that the Bering Strait’s status appears to play a key and curious role in the timing of the whole process.

“In both sets of simulations, surface waters became so fresh that they never got denser than the underlying salty water, and therefore never sank, shutting down ocean circulation and plunging areas around the North Atlantic, including Greenland, into a cold spell,” wrote Sid Perkins in this Science Now story about the study.

“However, the researchers noted a critical difference between the sets of simulations: When the Bering Strait was closed, it took as many as 1,400 years for ocean circulation to recover; when the strait was open, the circulation rarely took more than 400 years to recuperate.”

Here’s how hydro-geologist Scott Johnson explains the new findings in this story on the technology news blog Ars Technica:

“The Bering Strait exerts its influence by controlling flow between the Arctic and the North Pacific. Normally, fresher water flows into the Arctic, but when freshwater is being added to the North Atlantic some of it leaks into the Arctic and out to the Pacific. That helps keep the overturning circulation in the North Atlantic from clogging up so easily. In contrast, when the Bering Strait is closed, the freshwater in the North Atlantic piles up and lingers.”

The bottom line?

“Even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as (long as) the Bering Strait remains open,” Hu and her team wrote in the paper.

“And that’s just one more reason why the day after tomorrow probably won’t resemble The Day After Tomorrow," Johnson added here.

http://www.alaskadispatch.com/article/what-role-does-bering-strait-play-moderating-global-temperatures

Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability, PNAS, Aixue Hu et al.

Proceedings of the National Academy of Sciences (April 9, 2012); doi:10.1073/pnas.1116014109

Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability

1. Aixue Hu*, 
2. Gerald A. Meehl, 
3. Weiqing Han, 
4. Axel Timmermann, 
5. Bette Otto-Bliesner, 
6. Zhengyu Liu, 
7. Warren M. Washington, 
8. William Large, 
9. Ayako Abe-Ouchi, 
10. Masahide Kimoto, 
11. Kurt Lambeck and 
12. Bingyi Wu

1. ^aClimate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80305;
2. ^bDepartment of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO 80301;
3. ^cDepartment of Oceanography, University of Hawaii, HI 96822;
4. ^dCenter for Climate Research, Nelson Institute for Environmental Studies, University of Wisconsin, Madison, Wisconsin 53706;
5. ^eAtmosphere and Ocean Research Institute, University of Tokyo, Chiba 277-8568, Japan;
6. ^fResearch School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia; and
7. ^gChinese Academy of Meteorological Sciences, Beijing, China 100081

1. Edited by Isaac M. Held, Geophysical Fluid Dynamics Laboratory/NOAA, Princeton, NJ, and approved March 8, 2012 (received for review September 28, 2011)

Abstract

Abrupt climate transitions, known as Dansgaard-Oeschger and Heinrich events, occurred frequently during the last glacial period, specifically from 80–11 thousand years before present, but were nearly absent during interglacial periods and the early stages of glacial periods, when major ice-sheets were still forming. Here we show, with a fully coupled state-of-the-art climate model, that closing the Bering Strait and preventing its throughflow between the Pacific and Arctic Oceans during the glacial period can lead to the emergence of stronger hysteresis behavior of the ocean conveyor belt circulation to create conditions that are conducive to triggering abrupt climate transitions. Hence, it is argued that even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as the Bering Strait remains open.

http://www.pnas.org/content/early/2012/04/02/1116014109.abstract

Mea S. Cook et al., PaleoRepeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea

Paleoceanography, 26 (2011) PA2210; doi: 10.1029/2010PA001993

Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea

Key Points

• There are multiple episodes of intense vertical methane flux in MIS3 sediments
• The episodes have similar timing and duration as D-O events
• These sites are too cold and deep for the Clathrate Gun Hypothesis

Mea S. Cook (Geosciences Department, Williams College, Williamstown, MA, USA), Lloyd D. Keigwin (Geology and Geophysics Department, Woods Hole Oceanographic Institution, Woods Hole, MA, USA), and Daniel Birgel and Kai-Uwe Hinrichs (MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany)

Abstract

There is controversy over the role of marine methane hydrates in atmospheric methane concentrations and climate change during the last glacial period. In this study of two sediment cores from the southeast Bering Sea (700 m and 1467 m water depth), we identify multiple episodes during the last glacial period of intense methane flux reaching the seafloor. Within the uncertainty of the radiocarbon age model, the episodes are contemporaneous in the two cores and have similar timing and duration as Dansgaard-Oeschger events. The episodes are marked by horizons of sediment containing ¹³C-depleted authigenic carbonate minerals; ¹³C-depleted archaeal and bacterial lipids, which resemble those found in ANME-1 type anaerobic methane oxidizing microbial consortia; and changes in the abundance and species distribution of benthic foraminifera. The similar timing and isotopic composition of the authigenic carbonates in the two cores is consistent with a region-wide increase in the upward flux of methane-bearing fluids. This study is the first observation outside Santa Barbara Basin of pervasive, repeated methane flux in glacial sediments. However, contrary to the “Clathrate Gun Hypothesis” (Kennett et al., 2003), these coring sites are too deep for methane hydrate destabilization to be the cause, implying that a much larger part of the ocean's sedimentary methane may participate in climate or carbon cycle feedback at millennial timescales. We speculate that pulses of methane in these opal-rich sediments could be caused by the sudden release of overpressure in pore fluids that builds up gradually with silica diagenesis. The release could be triggered by seismic shaking on the Aleutian subduction zone caused by hydrostatic pressure increase associated with sea level rise at the start of interstadials.

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Received 19 May 2010; accepted 25 January 2011; published 11 May 2011.

Citation: Cook, M. S., L. D. Keigwin, D. Birgel, and K.-U. Hinrichs (2011), Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea, Paleoceanography, 26, PA2210, doi:10.1029/2010PA001993.

http://www.agu.org/pubs/crossref/2011/2010PA001993.shtml