The Breistroffer Event (OAE1d) was an

oceanic anoxic event An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved Oxygen, oxygen (O2), creating toxic, Euxinia, euxinic (anoxic waters, anoxic and wikt:sulfidic, sulfidic) waters. Although anoxic events have no ...

(OAE) that occurred during the middle

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

period, specifically in the latest

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

, around 101 million years ago (Ma).

Causes

A rise in

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 ...

and consequent negative carbon isotope excursion (CIE) ensued at the start of OAE1d, causing global temperatures to rise by 2 °C. During the Breistroffer Thermal Maximum, as this climatic interval has been referred to, Earth's mean surface air temperature was 23.3 °C. Average

sea surface temperatures Sea surface temperature (or ocean surface temperature) is the ocean temperature, temperature of ocean water close to the surface. The exact meaning of ''surface'' varies in the literature and in practice. It is usually between and below the sea ...

(SSTs) were 3 to 5 °C higher than today. Mercury anomalies from the time of the event implicate

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive ( sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The format ...

volcanism Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...

from the

Kerguelen Plateau The Kerguelen Plateau (, ), also known as the Kerguelen–Heard Plateau, is an oceanic plateau and large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about to the southwest of Australia and is near ...

as the cause of the rise in global temperatures. An alternative hypothesis implicating enhanced monsoons forced by

Milankovitch cycles Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term was coined and named after the Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he pr ...

rather than volcanism has also been proposed, based on the lack of unradiogenic osmium isotope ratio fluctuations observed during OAE1d. Total organic carbon values and

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

isotope records from the La Grita Member of the Capacho Formation of Venezuela show a cyclic variation supporting the enhanced monsoonal hypothesis. One possible cause of OAE1d relates to a possible 5-6 Myr cycle in the rate of

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

weathering throughout the middle of the Cretaceous period, at one of the peaks of which OAE1d ensued. This cycle would have been sustained and enhanced by fast-acting positive feedbacks of increased biological productivity and deoxygenation in response to elevated oceanic phosphate concentrations, but eventually mitigated and reversed by longer term negative feedbacks of increasing

atmospheric oxygen Atmospheric chemistry is a branch of atmospheric science that studies the chemistry of the Earth's atmosphere and that of other planets. This multidisciplinary approach of research draws on environmental chemistry, physics, meteorology, compute ...

content, which would have increased

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

activity and caused a decline in

vegetation Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...

, slowing down

chemical weathering Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs ''in situ'' (on-site, with little or no movem ...

and returned the

phosphorus cycle The phosphorus cycle is the biogeochemical cycle that involves the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the moveme ...

back to its starting state.

Effects

Anoxia developed because of the reduction of seawater

solubility In chemistry, solubility is the ability of a chemical substance, substance, the solute, to form a solution (chemistry), solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form su ...

caused by global temperature rise. Increased terrigeneous flux of nutrients into the ocean is known to have occurred in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

and

Venezuela Venezuela, officially the Bolivarian Republic of Venezuela, is a country on the northern coast of South America, consisting of a continental landmass and many Federal Dependencies of Venezuela, islands and islets in the Caribbean Sea. It com ...

during OAE1d and may have been an additional factor helping to deoxygenate seawater. The OAE that occurred resulted in a positive CIE, reflecting an enhancement in burial of organic carbon. The positive CIE's presence in nearshore settings, indicating that deep water anoxia expanded into shallow water. On land, a brief warm-wet climatic spike and a surge in

angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...

biodiversity occurred coevally with the deposition of black shales during OAE1d. Angiosperm mangal and conifer-dominated

swamps A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

thrived during this warm-wet spike in what is now central

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. In

Bulgaria Bulgaria, officially the Republic of Bulgaria, is a country in Southeast Europe. It is situated on the eastern portion of the Balkans directly south of the Danube river and west of the Black Sea. Bulgaria is bordered by Greece and Turkey t ...

, where angiosperms were still a minor component of the

flora Flora (: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. The corresponding term for animals is ''fauna'', and for f ...

that was dominated by

gymnosperms The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...

and

pteridophyte A pteridophyte is a vascular plant (with xylem and phloem) that reproduces by means of spores. Because pteridophytes produce neither flowers nor seeds, they are sometimes referred to as " cryptogams", meaning that their means of reproduction is ...

spores, plant communities remained stable across OAE1d.

References

Albian Stage {{improve categories, date=May 2023

Causes

Effects

See also

References