Precisely - the aerosol cooling effect takes place on a timescale ~ 1-10
years, the CO2 warming effect over ~ 1-10,000 years.
It is well known that volcanic outpourings can have major effects of
this type, especially when extensive outpourings of the kind that
produced the Deccan Traps and Siberian Traps. The Siberian Traps are
associated with the Permian Triassic boundary and in this case the ~ 3
million km3 of molten lava poured over a huge Permo-Carboniferous coal
basin causing massive methane and CO2 emissions over ~600ky. something
similar happened when a large bolide struck the Yucatan limestone
formation ~ 65My ago - causing the end-Cretaceous extinction event.
--
Oliver Tickell
e: [email protected]
On 11/02/2013 22:03, Rau, Greg wrote:
Interesting – no discussion of cooling effects of aerosol release?
Short-lived relative to CO2? -Greg
Volcano Location: Greenhouse-Icehouse Key? Episodic Purging of
'Carbonate Capacitor' Drives Long-Term Climate Cycle
http://www.sciencedaily.com/releases/2013/02/130207115014.htm
Feb. 6, 2013 — A new Rice University-led study finds the real estate
mantra "location, location, location" may also explain one of Earth's
enduring climate mysteries. The study suggests that Earth's repeated
flip-flopping between greenhouse and icehouse states over the past 500
million years may have been driven by the episodic flare-up of
volcanoes at key locations where enormous amounts of carbon dioxide
are poised for release into the atmosphere.
"We found that Earth's continents serve as enormous 'carbonate
capacitors,'" said Rice's Cin-Ty Lee, the lead author of the study in
this month's /GeoSphere/. "Continents store massive amounts of carbon
dioxide in sedimentary carbonates like limestone and marble, and it
appears that these reservoirs are tapped from time to time by
volcanoes, which release large amounts of carbon dioxide into the
atmosphere."
Lee said as much as 44 percent of carbonates by weight is carbon
dioxide. Under most circumstances that carbon stays locked inside
Earth's rigid continental crust.
"One process that can release carbon dioxide from these carbonates is
interaction with magma," he said. "But that rarely happens on Earth
today because most volcanoes are located on island arcs, tectonic
plate boundaries that don't contain continental crust."
Earth's climate continually cycles between greenhouse and icehouse
states, which each last on timescales of 10 million to 100 million
years. Icehouse states -- like the one Earth has been in for the past
50 million years -- are marked by ice at the poles and periods of
glacial activity. By contrast, the warmer greenhouse states are marked
by increased carbon dioxide in the atmosphere and by an ice-free
surface, even at the poles. The last greenhouse period lasted about 50
million to 70 million years and spanned the late Cretaceous, when
dinosaurs roamed, and the early Paleogene, when mammals began to
diversify.
Lee and colleagues found that the planet's greenhouse-icehouse
oscillations are a natural consequence of plate tectonics. The
research showed that tectonic activity drives an episodic flare-up of
volcanoes along continental arcs, particularly during periods when
oceans are forming and continents are breaking apart. The continental
arc volcanoes that arise during these periods are located on the edges
of continents, and the magma that rises through the volcanoes releases
enormous quantities of carbon dioxide as it passes through layers of
carbonates in the continental crust.
Lee, professor of Earth science at Rice, led the four-year study,
which was co-authored by three Rice faculty members and additional
colleagues at the University of Tokyo, the University of British
Columbia, the California Institute of Technology, Texas A&M University
and Pomona College.
Lee said the study breaks with conventional theories about greenhouse
and icehouse periods.
"The standard view of the greenhouse state is that you draw carbon
dioxide from the deep Earth interior by a combination of more activity
along the mid-ocean ridges -- where tectonic plates spread -- and
massive breakouts of lava called 'large igneous provinces,'" Lee said.
"Though both of these would produce more carbon dioxide, it is not
clear if these processes alone could sustain the atmospheric carbon
dioxide that we find in the fossil record during past greenhouses."
Lee is a petrologist and geochemist whose research interests include
the formation and evolution of continents as well as the connections
between deep Earth and its oceans and atmosphere..
Lee said the conclusions in the study developed over several years,
but the initial idea of the research dates to an informal
chalkboard-only seminar at Rice in 2008. The talk was given by Rice
oceanographer and study co-author Jerry Dickens, a paleoclimate
expert; Lee and Rice geodynamicist Adrian Lenardic, another co-author,
were in the audience.
"Jerry was talking about seawater in the Cretaceous, and he mentioned
that 93.5 million years ago there was a mass extinction of deepwater
organisms that coincided with a global marine anoxic event -- that is,
the deep oceans became starved of oxygen," Lee said. "Jerry was
talking about the impact of anoxic conditions on the biogeochemical
cycles of trace metals in the ocean, but I don't remember much else
that he said that day because it had dawned on me that 93 million
years ago was a very interesting time for North America. There was a
huge flare-up of volcanism along the western margin of North America,
and the peak of all this activity was 93 million years ago.
"I thought, 'Wow!'" Lee recalled. "I know coincidence doesn't mean
causality, but it certainly got me thinking. I decided to look at
whether the flare-up in volcanic activity that helped create the
Sierra Nevada Mountains may also have affected Earth's climate."
Over the next two years, Lee developed the idea that continental-arc
volcanoes could pump carbon dioxide into the atmosphere. One indicator
was evidence from Mount Etna in Sicily, one of the few active
continental-arc volcanoes in the world today. Etna produces large
amounts of carbon dioxide, Lee said, so much that it is often
considered an outlier in global averages of modern volcanic carbon
dioxide production.
Tectonic and petrological evidence indicated that many Etna-like
volcanoes existed during the Cretaceous greenhouse, Lee said. He and
colleagues traced the likely areas of occurrence by looking for
tungsten-rich minerals like scheelite, which are formed on the margins
of volcanic magma chambers when magma reacts with carbonates. It
wasn't easy; Lee spent an entire year pouring through World War II
mining surveys from the western U.S. and Canada, for example.
"There is evidence to support our idea, both in the geological record
and in geophysical models, the latter of which show plausibility," he
said. For example, in a companion paper published last year in
G-Cubed, Lenardic used numerical models that showed the opening and
breakup of continents could change the nature of subduction zones,
generating oscillations between continental- and island-arc dominated
states.
Though the idea in the GeoSpheres study is still a theory, Lee said,
it has some advantages over more established theories because it can
explain how the same basic set of geophysical conditions could produce
and sustain a greenhouse or an icehouse for many millions of years.
"The length of subduction zones and the number of arc volcanoes
globally don't have to change," Lee said. "But the nature of the arcs
themselves, whether they are continental or oceanic, does change. It
is in the continental-arc stage that CO_2 is released from an
ever-growing reservoir of carbonates within the continents."
Rice co-authors include Dickens and Lenardic, both professors of Earth
science; Rajdeep Dasgupta, assistant professor of Earth science; Bing
Shen, postdoctoral research associate; Benjamin Slotnick, graduate
student; and Kelley Liao, a graduate student who began work on the
project as undergraduate. Additional co-authors include Yusuke
Yokoyama of the University of Tokyo, Mark Jellinek of the University
of British Columbia, Jade Star Lackey of Pomona College, Tapio
Schneider of Caltech and Michael Tice of Texas A&M. The research was
supported by the Packard Foundation, the Atmosphere and Ocean Research
Institute at the University of Tokyo, the National Science Foundation
and the Miller Institute at the University of California, Berkeley.
------------------------------------------------------------------------
*Journal Reference*:
1.C.-T. A. Lee, B. Shen, B. S. Slotnick, K. Liao, G. R. Dickens, Y.
Yokoyama, A. Lenardic, R. Dasgupta, M. Jellinek, J. S. Lackey, T.
Schneider, M. M. Tice. *Continental arc-island arc fluctuations,
growth of crustal carbonates, and long-term climate change*.
/Geosphere/, 2012; 9 (1): 21 DOI: 10.1130/GES00822.1
<http://dx.doi.org/10.1130/GES00822.1>
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