Ocean acidification and the end-Cretaceous mass extinction

Heterohelix globulosa foraminifera isolated from the K-Pg boundary clay at Geulhemmerberg in the Netherlands. Image credit: Michael J. Henehan/PNAS

The Cretaceous–Paleogene extinction that followed the Chicxulub impact was one of the five great Phanerozoic mass extinctions. Three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, pterosaurs, marine reptiles, ammonites, and planktonic foraminifera. The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed. The impacto also caused sudden ocean acidification, impacting marine ecosystems and the carbon cycle. Around the time of the impact, 23,000 to 230,000 cubic miles of magma erupted out of the mid-ocean ridges, all over the globe. One of the largest eruptive events in Earth’s history. This pulse of global marine volcanism played an important role in the environmental crisis at the end of the Cretaceous. Marine volcanism also provides a potential source of oceanic acidification, but a new study by Yale University indicates that the sudden ocean acidification was caused by the Chicxulub bolide impact (and not by the volcanic activity) that vaporised rocks containing sulphates and carbonates, causing sulphuric acid and carbonic acid to rain down. The evidence came from the shells of planktic and benthic foraminifera.

Foraminifera are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. Ocean acidification in the geological record is often inferred from a decrease in the accumulation and preservation of CaCO3 in marine sediments, potentially indicated by an increased degree of fragmentation of foraminiferal shells. In the early 1990’s it was recognised that the boron isotopic composition of marine carbonates was determined largely by ocean pH. Usingy the boron isotope-pH proxy to planktic and benthic foraminifera, the new study determinated the ocean pH drop following the Chicxulub impact.

The Cretaceous/Palaeogene extinction boundary clay at Geulhemmerberg Cave. Image credit: Michael J. Henehan

The boron isotope composition of carbonate samples obtained from a shallow-marine sample site (Geulhemmerberg Cave, The Netherlands) preserved sediments from the first 100 to 1000 years after the asteroid’s impact. The data from the Geulhemmerberg Cave indicate a marked ∼0.25 pH unit surface ocean acidification event within a thousand years. This change in pH corresponds to a rise in atmospheric partial pressure of CO2 (pCO2) from ∼900 ppm in the latest Maastrichtian to ∼1,600 ppm in the immediate aftermath of bolide impact.

Ocean acidification was the trigger for mass extinction in the marine realm. Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, echinoderms, corals, and coralline algae. Additionaly, ocean acidification can intensify the effects of global warming, in a dangerous feedback loop.

Anthropogenic climate change and ocean acidification resulting from the emission of vast quantities of CO2 and other greenhouse gases pose a considerable threat to ecosystems and modern society. Since the Industrial Revolution the pH within the ocean surface has decreased ~0.1 pH and is predicted to decrease an additional 0.2 – 0.3 units by the end of the century. This underlines the urgency for immediate action on global carbon emission reductions.

 

 

References:

Michael J. Henehan el al., “Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact,” PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1905989116

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94–107, https://doi.org/10.5670/oceanog.2009.100.

 

Aftermath: The first day of the Cenozoic

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

In the late ’70, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth, making the feature one of the largest confirmed impact structures on Earth. The Cretaceous–Paleogene extinction that followed the Chicxulub impact was one of the five great Phanerozoic mass extinctions. The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed.

The Chicxulub impact site is the only known impact structure on Earth with an unequivocal peak ring but it is buried and only accessible through drilling. In April to May 2016, a team by International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) drilled the Chicxulub peak ring offshore. The core recovered during the expedition provides a window into the immediate aftermath of the impact.

Timeline of events recorded inside the impact crater.

The recovered core was divided into 4 Units. The Unit 1 is 111.63-m-thick postimpact sedimentary rock. The Unit 2 is 104.28-m thick and dominantly suevite. The Unit 3 is 25.41-m-thick impact melt rock, with some clasts present. The Unit 4 consists of shocked granitic target rocks, preimpact sheet intrusions, and intercalations of suevite and impact melt rock. There are high abundances of charcoal in Unit 1. The charcoal likely originated from impact-related combustion of forested landscapes surrounding the Gulf of Mexico. Data indicate that Chicxulub impact released sufficient thermal radiation to ignite flora up to 1,000 to 1,500 km from the impact site. The upper few centimeters of the unit 2 contain abundant reworked Maastrichtian planktic foraminifera that indicate redeposition of sediments that were unconsolidated at the time of the impact.

The lack of evaporites in the recovered sedimentary section, supports the impact generated sulfate aerosol production and extinction mechanisms, including global cooling and limitations on photosynthesis. Core samples also revealed that a high-temperature hydrothermal system was established within the crater but the appearance of burrowing organisms within years of the impact indicates that the hydrothermal system did not adversely affect seafloor life. These impact-generated hydrothermal systems are hypothesized to be potential habitats for early life on Earth and other planets.

 

References:

Sean P. S. Gulick, Timothy J. Bralower, Jens Ormö, Brendon Hall, Kliti Grice, Bettina Schaefer, Shelby Lyons, Katherine H. Freeman, Joanna V. Morgan, Natalia Artemieva, Pim Kaskes, Sietze J. de Graaff, Michael T. Whalen, Gareth S. Collins, Sonia M. Tikoo, Christina Verhagen, Gail L. Christeson, Philippe Claeys, Marco J. L. Coolen, Steven Goderis, Kazuhisa Goto, Richard A. F. Grieve, Naoma McCall, Gordon R. Osinski, Auriol S. P. Rae, Ulrich Riller, Jan Smit, Vivi Vajda, Axel Wittmann, and the Expedition 364 Scientists. The first day of the Cenozoic. PNAS, 2019 DOI: 10.1073/pnas.1909479116

Morgan, J. V., Gulick, S. P. S., Bralower, T., Chenot, E., Christeson, G., Claeys, P., … Zylberman, W. (2016). The formation of peak rings in large impact craters. Science, 354(6314), 878–882. doi:10.1126/science.aah6561

Christopher M. Lowery et al. Rapid recovery of life at ground zero of the end-Cretaceous mass extinction, Nature (2018). DOI: 10.1038/s41586-018-0163-6

Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval.

The Jurassic/Cretaceous Boundary

Map of the Jurassic/Cretaceous Boundary by C. Scotese.

The Jurassic/Cretaceous (J/K) boundary, 145 Myr ago, remains as the less understood of major Mesozoic stratigraphic boundaries. Sedimentological, palynological and geochemical studies, indicate a climatic shift from predominantly arid to semi arid conditions in the latest Jurassic to more amicable humid conditions in the earliest Cretaceous. The continued fragmentation of Pangaea across the Late Jurassic and Early Cretaceous led to large-scale tectonic processes, on both regional and global scale, accompanied by some of the largest volcanic episodes in the history of the Earth; eustatic oscillations of the sea level; potentially heightened levels of anoxia, oceanic stagnation, and sulphur toxicity; along with two purported oceanic anoxic events in the Valanginian and Hauterivian. There’s also evidence of three large bolide impacts in the latest Jurassic, one of which might have been bigger than the end-Cretaceous Chicxulub impact.

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

The J/K interval represents a period of elevated extinction, and involves the persistent loss of diverse lineages, and the origins of many major groups that survived until the present day (e.g. birds). The magnitude of this drop in diversity ranges from around 33% for ornithischians to 75–80% loss for theropods and pterosaurs. Mammals suffered an overall loss of  diversity of 69%. Crocodyliforms suffered a major  decline across the Jurassic/Cretaceous boundary in both the marine and terrestrial realms; while non-marine turtles declined by 33% of diversity through the J/K boundary. In contrast, lepidosauromorphs greatly increased in diversity (48%) across the J/K boundary, reflecting the diversification of major extant squamate clades, including Lacertoidea, Scincoidea and Iguania.

In the marine realm, sauropterygians and ichthyosaurs show evidence for a notable decline in diversity across the J/K boundary, which continued into the Hauterivian for both groups.

Stratigraphic ranges of major Jurassic–Cretaceous theropod (A), sauropod (B), and ornithischian (C) dinosaur clades through the Middle Jurassic to Early Cretaceous (From Tennant et al,. 2016)

Stratigraphic ranges of major Jurassic–Cretaceous theropod (A), sauropod (B), and ornithischian (C) dinosaur clades through the Middle Jurassic to Early Cretaceous (From Tennant et al,. 2016)

Eustatic sea level is the principal mechanism controlling the Jurassic–Cretaceous diversity of tetrapods. Rising sea levels leads to greater division of landmasses through creation of marine barriers, modifying the spatial distribution of near-shore habitats and affecting the species–area relationship, which can lead to elevated extinctions. This fragmentation can also be a potential driver of biological and reproductive isolation and allopatric speciation, the combination of which we would expect to see manifest in the diversity signal. Additionally, the diversity of fully marine taxa was more probably affected by the opening and closure of marine dispersal corridors, whereas that of terrestrial and coastal taxa was more probably dependent on the availability of habitable ecosystems, including the extent of continental shelf area (Tennant, et al., 2016).

References:

Tennant J,P., Mannion P. D., Upchurch P., Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval, Nature Communications, ISSN: 2041-1723 DOI: 10.1038/ncomms12737

Tennant, J. P., Mannion, P. D., Upchurch, P., Sutton, M. D. and Price, G. D. (2016), Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover. Biol Rev. doi:10.1111/brv.12255 

Butler, R. J., Benson, R. B. J., Carrano, M. T., Mannion, P. D. & Upchurch, P. Sea level, dinosaur diversity and sampling biases: investigating the ‘common cause’ hypothesis in the terrestrial realm. Proc. R. Soc. B 278, 1165–1170 (2011).

A palaeobotanical perspective on the Permian extinction.

 

Leaf bank of Glossopteris leaves (Adapted from Mcloughlin, 2012)

Leaf bank of Glossopteris leaves (Adapted from Mcloughlin, 2012)

The fossil record indicates that more than 95% of all species that ever lived are now extinct. Occasionally, extinction events reach a global scale with many species of all ecological types dying out in a near geological instant. These are mass extinctions. They were originally identified in the marine fossil record and have been interpreted as a result of catastrophic events or major environmental changes that occurred too rapidly for organisms to adapt. Mass extinctions are probably due to a set of different possible causes like basaltic super-eruptions, impacts of asteroids, global climate changes, or continental drift. A central question in the understanding of mass extinctions is whether the extinction was a sudden or gradual event. This question may be addressed by examining the pattern of last occurrences of fossil species in a stratigraphic section.

Jack Sepkoski and David M. Raup identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. The most recently identified mass extinction occurred during the Middle Permian, about  262 million years ago, and it was first recognised in the marine realm as a turnover among foraminifera, with fusulinaceans among the principal casualties.

Sin título

Total diversity patterns of continental diversity (solid line) and marine diversity (dotted line) at the family level. Arrows indicate the mass extinction events. (From Cascales-Miñana and Cleal 2015)

Extinction dynamics in the marine and terrestrial biotas followed different trajectories, and only the Permo-Triassic event coincided with a clear and abrupt diminution of both realms. Moreover, analysis of the paleobotanical record has suggested that plants may have suffered an additional extinction event, that is not reflected significantly in the marine realm, at the Carboniferous–Permian boundary. Evidence also suggests that  terrestrial environments suffered a single global pulse of extinction in the latest Permian, affecting both the fauna and flora (Cascales-Miñana and Cleal 2015).

During the end-Permian Event, the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. A key factor for plant resilience is the time-scale: if the duration of the ecological disruption did not exceed that of the viability of seeds and spores, those plant taxa have the potential to recover (Traverse, 1988).

 

References:

Borja Cascales-Miñana, José B. Diez, Philippe Gerrienne & Christopher J.Cleal (2015): A palaeobotanical perspective on the great end-Permian biotic crisis, HistoricalBiology, DOI: 10.1080/08912963.2015.1103237

Aberhan M. 2014. Mass extinctions: ecological diversity maintained. NatGeosci. 7:171–172.

Cascales-Miñana B, Cleal CJ. 2014. The plant fossil record reflects just two great extinction events. Terra Nova. 26(3):195–200.

A brief introduction to the stratigraphy of mass extinctions.

gallery_image_11433

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen).

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup used a simple form of time series analysis at the rank of family to distinguish between background extinction levels and mass extinctions in marine faunas, and identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five. The most recently identified mass extinction occurred during the Middle Permian, about  262 million years ago, and it was first recognised in the marine realm as a turnover among foraminifera, with fusulinaceans among the principal casualties.

A central question in the understanding of mass extinctions is whether the extinction was a sudden or gradual event. This question may be addressed by examining the pattern of last occurrences of fossil species in a stratigraphic section.  Also, the geochemical history recorded in marine sediments preserves a valuable record of environmental change during mass extinctions. However, stratigraphical processes of sediment accumulation could affect the chronology of environmental change. And of course, the Signor–Lipps effect complicates the timing of extinction.

The trilobite Kainops invius, in lateral and ventral view. From Wikimedia Commons

The trilobite Kainops invius, in lateral and ventral view. From Wikimedia Commons

The last occurrences of fossil species generally predate the times of extinction. Based on principles of sequence stratigraphy, marine ecology, and evolution, numerical models of fossil occurrences in stratigraphic sections suggest that the last occurrences of fossil species are controlled by stratigraphic architecture. In some cases, stratigraphical architecture can give the illusion of a double pulse or even a triple pulse of extinction (Holland, 2015).

The Cambrian and Lower Ordovician record involve the abrupt termination of many shallow-water trilobite lineages, a reduction in the number of biofacies across the shelf, and the immigration and origination of new lineages; and in many locations, the extinction is closely associated with an unconformity. With the notable exception of the end-Cretaceous extinction, mass extinction events have similar stratigraphical expressions. In depositional dip settings, they are recorded as a single cluster of last occurrences that is closely associated with a major flooding surface, which in some cases is combined with a sequence-bounding subaerial unconformity. Where depositionally downdip sections are available, such as for the Late Ordovician and the Late Devonian, two clusters of last occurrences are present. They may suggest discrete pulses of extinction, although they are equally consistent with a more prolonged extinction. In the Late Devonian, the faunal changes occur in three separate episodes, with the Taghanic event at the end of the Givetian, the Kellwasser event at the end of Frasnian and the Hangenberg event at the end of the Famennian. Of these, the Kellwasser event is the largest. One of the characteristics of the Kellwasser event is that the extinction was more severe in shallow-water faunas, and the stratigraphical pattern of last occurrences is consistent not only with a pulse of extinction timed with the flooding surface, but also with a more protracted interval of extinction. (Holland et Patzkowsky, 2015)

References:

Holland, S. M., Patzkowsky, M. E. (2015), The stratigraphy of mass extinction. Palaeontology. doi: 10.1111/pala.12188

Bambach, R.K., Knoll, A.H. and Wang, S.C., 2004. Origination, extinction, and mass depletions of marine diversity. Paleobiology, 30, 522–542.

Steve C. Wang, Aaron E. Zimmerman, Brendan S. McVeigh, Philip J. Everson, and Heidi Wong, (2012), Confidence intervals for the duration of a mass extinction, Paleobiology, 38(2), pp. 265–277.

Seth D. Burgess, Samuel Bowring, and Shu-zhong Shen, High-precision timeline for Earth’s most severe extinction, PNAS 2014, doi:10.1073/pnas.1317692111

Wignall, P. B. 2001. Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay (Devon, SW England). Proceedings of the Geologists’ Association, 112, 349–360