The Palaeocene Era was a period of significant global warming,
culminating in the Palaeocene-Eocene Thermal Maximum, when around 2000 gigatons
of isotopicly light carbon are thought to have been released into the
atmosphere over a relatively short time interval (less than 60 000 years), due
to melting of deep-sea methane hydrates and permafrost in high latitude and
altitude soils. This resulted in a brief period of extreme global warming
driven by the sudden input of more-or-less all available greenhouse gasses into
the atmosphere, then followed by a period of cooling in the early Eocene as
these gasses were lost from the atmosphere.
It should be noted that predictions of the results of human-induced
global warming in the near future often predict more severe warming than
occurred at the end of the Palaeocene; this is because these scenarios include
not just the melting of permafrost and methane hydrates due to warming, but
also the pumping of large amounts of carbon dioxide from the burning of fossil
fuels (which did not occur during the Palaeocene), and therefore resulting in a
much more severe warming, albeit from a cooler starting point.
Though we know that the temperature rose sharply around the globe at
the end of Palaeocene, exactly how far it rose in many areas is unclear. One
such area is the tropical oceans, which are important for the understanding of
global climate patterns. The best way of determining sea temperatures in the
past is generally accepted to be oxygen isotope analysis of minerals from the
preserved shells of pelagic or planktonic organisms. Such organisms, if they
lived close to the surface in open water can give a good measure of the
temperature of the water as warmer water contains a higher proportion of
isotopicly heavy oxygen. Inshore waters are prone to more extreme temperature
fluctuations, as water trapped in enclosed bays can be heated more extremely,
but this does not reflect the temperature over wider areas and is therefore not
considered useful for understanding global climate patterns.
However this is difficult to study for tropical waters around the
Palaeocene-Eocene Thermal Maximum, as the rise in atmospheric carbon dioxide
led to oceanic acidification (carbon dioxide dissolves in water to form
carbonic acid), leading to a rise in the carbonate compensation depth
(the depth beneath which calcium carbonate will dissolve in water – calcium
carbonate dissolves more readily at greater pressure, resulting in a pressure
boundary rises as the ocean becomes more acidic and falls as the acidity does).
Thus many end-Palaeocene deep water sediments, from which microfossil shells
are usually extracted to perform oxygen isotope analysis, lack any such shells.
In a paper published in the journal Geology on 25 July 2014, a team of
scientists led by Tracy Aze of the School of Earth and Ocean Sciences at CardiffUniversity describe the results of a study of planktonic Foraminifera shells
from a location in Tanzania interpreted as having been an outer shelf
environment 19˚ from the equator, that was remote from any land but had a depth
of only about 300 m (i.e. above the carbonate compensation depth).
Azeet al. analysed
specimens of the Foraminifera Acarinina,
Morozovella, and Subbotina from across the late Palaeocene and early Eocene. This
resulted in a maximum temperature estimate close to the Thermal Maximum of
~36-43˚C, however the sediments around the Thermal Maximum are extremely
depleted in Foraminifera, suggesting that temperatures may have been even
higher, resulting either in seawater too acidic to preserve calcium carbonate
shells or too warm to have been inhabited by Foraminifera.
A Foraminifera of the genus Morozovella. Clay Kelly et al. (2001).
Studies in other areas have suggested that Foraminifera from
equatorial and tropical regions migrated towards the poles around the Thermal
Maximum, while experiments on modern members of the group suggest that these
are unable to tolerate temperatures much above ~33˚C, so that even if
Palaeocene Foraminifera were more tolerant of high temperatures, it is
difficult to see them surviving in water much above ~43˚C.
See also…
Preserved wood from an Early Eocene kimberlite pipe in northwestern Canada’s Slave Province. Kimberlite pipes are produced by rapid volcanic intrusions carrying...
Fossil Thrips from the Early Eocene of France. Thrips (the term is both singular and plural) are tiny (usually less
than 1 mm) Insects related to Lice and True Bugs. They have wings, but
are poor flyers, and feed by sucking fluids from plant or animal hosts.
Thrips do not undergo metamorphosis, the young are essentially smaller,
non-reproducing versions of the adults. Due to their small size and
ubiquitous nature, it is...
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