A hyperthermal event corresponds to a sudden warming of the planet on a
geologic time scale
The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochro ...
.
The consequences of this type of event are the subject of numerous studies because they can constitute an analogue of current
global warming
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
.
Hyperthermal events
The first event of this type was described in 1991 from a
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
core extracted from a drilling of the
Ocean Drilling Program
The Ocean Drilling Program (ODP) was part of an international project to explore and study the composition and structure of Earth's oceanic basins. This collaborative effort spanned multiple decades and produced comprehensive data that improved un ...
(ODP) carried out in
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...
in the
Weddell Sea
The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha C ...
.
This event occurs at the boundary of the
Paleocene
The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...
and
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided b ...
s approximately 56 million years ago. It is now called the
Paleocene-Eocene Thermal Maximum (PETM). During this event, the temperature of the oceans increased by more than 5 °C in less than 10,000 years.
Since this discovery, several other hyperthermal events have been identified in this lower part of the
Paleogene
The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...
geological period
The geologic time scale or geological time scale (GTS) is a representation of time based on the geologic record, rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating stratum, strata ...
:
* the Dan-C2 event at the beginning of the
Danian
The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretac ...
stage
Stage, stages, or staging may refer to:
Arts and media Acting
* Stage (theatre), a space for the performance of theatrical productions
* Theatre, a branch of the performing arts, often referred to as "the stage"
* ''The Stage'', a weekly Brit ...
of the Paleocene, about 65.2 million years ago, quite the basis of the
Cenozoic era
The Cenozoic Era ( ; ) is Earth's current geological Era (geology), era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, Insect, insects, birds and flowering plant, angiosperms (floweri ...
;
* the Danian-Selandian event at the transition between the Danian and
Selandian
The Selandian is a stage in the Paleocene. It spans the time between . It is preceded by the Danian and followed by the Thanetian. Sometimes the Paleocene is subdivided in subepochs, in which the Selandian forms the "middle Paleocene".
Stratig ...
stages of the Paleocene, about 61 million years ago;
* the two events following the PETM during the
Eocene climatic optimum
The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', 'Dawn') and ...
:
** the
Eocene Thermal Maximum 2 (ETM2) about 53.2 million years ago,
** and the Eocene Thermal Maximum 3 (ETM3) about 52.5 million years ago.
But the PETM event remains the most studied of the hyperthermic events.
Other hyperthermic events occurred at the end of most
Quaternary glaciation
The Quaternary glaciation, also known as the Pleistocene glaciation, is an alternating series of glacial period, glacial and interglacial, interglacial periods during the Quaternary period that began 2.58 Year#SI prefix multipliers, Ma (million ...
s. Probably the most notable of these is the abrupt warming marking the end of the
Younger Dryas
The Younger Dryas (YD, Greenland Stadial GS-1) was a period in Earth's geologic history that occurred circa 12,900 to 11,700 years Before Present (BP). It is primarily known for the sudden or "abrupt" cooling in the Northern Hemisphere, when the ...
, which saw an average annual temperature rise of several degrees in less than a century.
Causes
While the consequences of these hyperthermic events are now well studied and known, their causes are still debated.
Two main tracks, possibly complementary, are mentioned for the initiation of these sudden warmings:
* orbital forcing with long and/or short Earth cycle eccentricity maxima that accentuate significant seasonal contrasts and lead to global warming;
* remarkable volcanic activity, especially in the North Atlantic province.
Consequences
Marine warming due to PETM is estimated, for all latitudes of the globe, between 4 and 5 °C for deep ocean waters and between 5 and 9 °C for surface waters.
Carbon trapped in clathrates buried in high latitude sediments is released to the ocean as
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
() which will quickly oxidize to
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
().
Ocean acidification and carbonate dissolution
As a result of the increase in dissolved in seawater, the oceans are acidifying. This results in a dissolution of the carbonates; global sedimentation becomes essentially clayey. This process takes place in less than 10,000 years while it will take about 100,000 years for the carbonate sedimentation to return to its pre-PETM level mainly by capture through greater silicate weathering on the continents.
Disruption of ocean circulations
The δ13C ratios of the carbon isotope contents of the
carbonate
A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...
s constituting the shells of the
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
foraminifera
Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
have shown an upheaval in the oceanic circulations during the PETM under the effect of global warming.
This change took place over a few thousand years. The return to the previous situation, again by
negative feedback
Negative feedback (or balancing feedback) occurs when some function (Mathematics), function of the output of a system, process, or mechanism is feedback, fed back in a manner that tends to reduce the fluctuations in the output, whether caused ...
thanks to the " pump" of silicate weathering, took about 200,000 years.
Impacts on marine fauna
While the
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
foraminifera
Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
had gone through the
Cretaceous-Tertiary extinction that occurred around 66 million years ago without difficulty, the hyperthermic event of the PETM, 10 million years later, decimated them with the disappearance of 30 to 50% of existing
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
.
The warming of surface waters also leads to
eutrophication
Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...
of the marine environment which leads to a rapid increase by
positive feedback
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop where the outcome of a process reinforces the inciting process to build momentum. As such, these forces can exacerbate the effects ...
of emissions.
Impacts on terrestrial fauna
Mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
s that experienced a great development after the
extinction of the end of the Cretaceous will be strongly affected by the climatic warming of the Paleogene. Temperature increases and induced climate changes modify the flora and the quantities of fodder available for herbivores. This is how a large number of groups of mammals appear at the beginning of the
Eocene
The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...
, about 56 million years ago:
*
Artiodactyls
Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other thre ...
;
*
Perissodactyls;
*
Primate
Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...
s;
*
Hyaenodontidae
Hyaenodontidae ("hyena teeth") is a family of placental mammals in the extinct superfamily Hyaenodonta, Hyaenodontoidea. Hyaenodontids arose during the early Eocene and persisted well into the early Miocene. Fossils of this group have been found ...
...
Analogies with current global warming
Even if the hyperthermal events of the Paleogene appear extremely brutal on the
geologic time scale
The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochro ...
(in a range of a few thousand years for an increase of the order of 5 °C), they remain significantly longer than the durations envisaged in the current models of
global warming
Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes ...
of anthropogenic origin.
The various studies of hyperthermal events insist on the phenomena of
positive feedback
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop where the outcome of a process reinforces the inciting process to build momentum. As such, these forces can exacerbate the effects ...
s which, after the onset of a warming, accelerate it considerably.
References
See also
*
Paleocene–Eocene Thermal Maximum
The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized by a ...
*
Eocene climatic optimum
The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', 'Dawn') and ...
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