Eocene Thermal Maximum 2 (ETM-2), also called H-1 or the Elmo (Eocene Layer of Mysterious Origin) event, was a transient period of
global warming
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
that occurred around either 54.09
Ma or 53.69 Ma.
It appears to be the second major
hyperthermal that punctuated the long-term warming trend from the Late
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), E ...
through the early
Eocene
The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
(58 to 50 Ma).
The hyperthermals were geologically brief time intervals (<200,000 years) of global warming and massive input of isotopically light carbon into the atmosphere.
The most extreme and best-studied event, the
Paleocene-Eocene Thermal Maximum (PETM or ETM-1), occurred about 1.8 million years before ETM-2, at approximately 55.5 Ma. Other hyperthermals likely followed ETM-2 at nominally 53.6 Ma (H-2), 53.3 (I-1), 53.2 (I-2) and 52.8 Ma (informally called K, X or ETM-3). The number, nomenclature, absolute ages and relative global impact of the Eocene hyperthermals are the source of much current research.
In any case, the hyperthermals appear to have ushered in the Early Eocene Climatic Optimum, the warmest sustained interval of the
Cenozoic Era
The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configu ...
.
They also definitely precede the
Azolla event
The Azolla event is a scenario hypothesized to have occurred in the middle Eocene epoch, around , when blooms of the freshwater fern ''Azolla'' are thought to have happened in the Arctic Ocean. As they sank to the stagnant sea floor, over a per ...
at about 49 Ma.
ETM-2 is clearly recognized in sediment sequences by analyzing the stable carbon isotope composition of carbon-bearing material.
[ The 13C/ 12C ratio of calcium carbonate or organic matter drops significantly across the event. This is similar to what happens when one examines sediment across the PETM, although the magnitude of the negative carbon isotope excursion is not as large. The timing of Earth system perturbations during ETM-2 and the PETM also appear different.][ Specifically, the onset of ETM-2 may have been longer (perhaps 30,000 years) while the recovery seems to have been shorter (perhaps <50,000 years).][ (Note, however, that the timing of short-term ]carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
perturbations during both events remains difficult to constrain).
A thin clay-rich horizon marks ETM-2 in marine sediment
Marine sediment, or ocean sediment, or seafloor sediment, are deposits of insoluble particles that have accumulated on the seafloor. These particles have their origins in soil and rocks and have been transported from the land to the sea, mainly ...
from widely separated locations. In sections recovered from the deep-sea (for example those recovered by Ocean Drilling Program
The Ocean Drilling Program (ODP) was a multinational effort to explore and study the composition and structure of the Earth's oceanic basins. ODP, which began in 1985, was the successor to the Deep Sea Drilling Project initiated in 1968 by th ...
Leg 208 on Walvis Ridge
The Walvis Ridge (''walvis'' means whale in Dutch and Afrikaans) is an aseismic ocean ridge in the southern Atlantic Ocean. More than in length, it extends from the Mid-Atlantic Ridge, near Tristan da Cunha and the Gough Islands, to the African ...
), this layer is caused by dissolution of calcium carbonate.[ However, in sections deposited along continental margins (for example those now exposed along the ]Waiau Toa / Clarence River
The Clarence River (; officially Waiau Toa / Clarence River) is a major river which flows through the Kaikōura Ranges in the northeast of New Zealand's South Island. At roughly long, it is the longest river in Canterbury and the eighth longest ...
, New Zealand), the clay-rich horizon represents dilution by excess accumulation of terrestrial material entering into the ocean.[ Similar changes in sediment accumulation are found across the PETM.][ In sediment from ]Lomonosov Ridge
The Lomonosov Ridge (russian: Хребет Ломоносова, da, Lomonosovryggen) is an unusual underwater ridge of continental crust in the Arctic Ocean. It spans between the New Siberian Islands over the central part of the ocean to Elle ...
in the Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
, intervals across both ETM-2 and the PETM shows signs of higher temperature, lower salinity and lower dissolved oxygen.[
The PETM and ETM-2 are thought to have a similar generic origin,][ although this idea is at the edge of current research. During both events, a tremendous amount of 13C-depleted carbon rapidly entered the ocean and atmosphere. This decreased the 13C/12C ratio of carbon-bearing sedimentary components, and dissolved carbonate in the deep ocean. Somehow the carbon input was coupled to an increase in Earth surface temperature and a greater seasonality in precipitation, which explains the excess terrestrial sediment discharge along continental margins. Possible explanations for changes during ETM-2 are the same as those for the PETM, and are discussed under the latter entry.
The H-2 event appears to be a "minor" hyperthermal that follows ETM-2 (H-1) by about 100,000 years. This has led to speculation that the two events are somehow coupled and paced by changes in ]orbital eccentricity
In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...
.[
As in the case of the PETM, reversible dwarfing of mammals has been noted during the ETM-2.]
See also
* Paleocene–Eocene Thermal Maximum
The Paleocene–Eocene thermal maximum (PETM), alternatively (ETM1), and formerly known as the "Initial Eocene" or "", was a time period with a more than 5–8 °C global average temperature rise across the event. This climate event o ...
References
External links
*
* {{Cite web, url=http://www.agu.org/pubs/crossref/2009/2008PA001655.shtml, title=Patterns and magnitude of deep sea carbonate dissolution during Eocene Thermal Maximum 2 and H2, Walvis Ridge, southeastern Atlantic Ocean, author1=Lucy Stap , author2=Appy Sluijs , author3=Ellen Thomas , author4=Lucas Lourens
History of climate variability and change
Eocene