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 ...

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 that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pala ...

through the early

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

(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 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 atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major compon ...

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, mai ...

from widely separated locations. In sections recovered from the deep-sea (for example those recovered by Ocean Drilling Program 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 Africa ...

), 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 Ell ...

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 bet ...

. As in the case of the PETM, reversible dwarfing of mammals has been noted during the ETM-2.

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

See also

References

External links