Climate Change and the legacy of the Challenger expedition

SEM images of selected planktonic foraminifera specimens; (i) T. trilobus (Tara), (j) G. ruber (Tara), (k) G. ruber (Challenger), (l) G. bulloides (Challenger), (m,n) G. ruber test cracked to reveal wall texture (Tara), (o,p) G. ruber test cracked to reveal wall texture (Challenger). From Fox et al., 2020.

It all began in 1868, with British naturalist William B. Carpenter and Sir Charles Wyville Thomson, Professor of Natural History at Edinburgh University. They persuaded the Royal Society of London to sponsor a prolonged voyage of exploration across the oceans of the globe. But it was not until 1872 that Royal Society of London obtained the use of the HSM Challenger from the Royal Navy. The ship was modified for scientific work with separate laboratories for natural history and chemistry. The cost of expedition was £200,000 – about £10 million in today’s money. The expedition was led by Captain George Nares and the scientific work was conducted by Wyville Thomson assisted by Sir John Murray, John Young Buchanan, Henry Nottidge Moseley, and the German naturalist Rudolf von Willemoes-Suhm. From 1872 to 1876, Murray developed a pioneering device which could register the temperature of the ocean at great depths, and assisted in the collection of marine samples. After the dead of Thomson in 1882, John Murray became director and edited the Challenger Expedition Reports. 

The science and ship crew of the HMS Challenger in 1874.

 

The planktonic foraminifera collected during the HMS Challenger expedition are part of the historical collection of the Natural History Museum, London. Their importance as tool for paleoclimate reconstruction was recognized early in the history of oceanography. The samples collected almost 150 years ago provide an extraordinary opportunity to understand the effects of one of the most urgent questions of our time with regards to anthropogenic environmental change: ocean acidification. 

 

Planktonic foraminifera are a group of marine zooplankton with a shell composed of secrete calcite or aragonite, with no internal structures and different patterns of chamber disposition (trochospiral, involute trochospiral and planispiral growth); with perforations and a variety of surface ornamentations like cones, short ridges or spines. Their shells 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. By comparing the sediment samples from the HMS Challenger Expedition (1872–1876) with the recent Tara Oceans expedition material (2009–2016), the researchers found that the composition of the planktonic foraminifera has changed significantly since the pre-industrial period, and revealed that all modern specimens had up to 76% thinner shells than their historic counterparts.

 

 

 

Nano-CT representative reconstructions and measurements for Neogloboquadrina dutertrei from Tara (a–c), and Challenger (d–f). From Fox et al., 2020.

Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus 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. 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. 

After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration. In the coming decades, the ocean’s biogeochemical cycles and ecosystems will become increasingly stressed by ocean warming, acidification and deoxygenation. This scenario underlines the urgency for immediate action on global carbon emission reductions.

 

References:

Fox, L., Stukins, S., Hill, T. et al. Quantifying the Effect of Anthropogenic Climate Change on Calcifying Plankton. Sci Rep 10, 1620 (2020). https://doi.org/10.1038/s41598-020-58501-w

Jonkers, L., Hillebrand, H., & Kucera, M. (2019). Global change drives modern plankton communities away from the pre-industrial state. Nature. doi:10.1038/s41586-019-1230-3

Wyville Thompson, C. The Voyage of the “Challenger”. The Atlantic. 2 volumes (1878).

Dohrn, Anton. (1895). The Voyage of HMS “Challenger” A Summary of the Scientific Results. http://doi.org/10.1038/052121a0

 

 

From Mantell to de Ricqlès: A brief history of Paleohistology

Bone microstructure of M. intrepidus (NCSM 33392). From Zanno et al., 2019.

The aim of Paleohistology is the study of the microstructure of fossilized skeletal tissues. Despite that the organic components of mineralised tissues decay after death, the inorganic components of bone preserve the spatial orientation of organic components such as osteocyte lacunae, vascular canals, and collagen fibres.

The techniques for the microscopic study of biological tissues began in 1828, when two British scientists, Henry Witham and William Nicol, experimented by grinding sheets of petrified tree trunk into traslucents sheets so that they could viewed under the microscope. Few years later the new technique was applied to fossil vertebrates by Agassiz. In 1849, John Thomas Quekett published his most important paper on the histological structure of bone in mammals, birds, reptiles, and fish. He described vascular canals, lacunae and canaliculi, and trabecular endosteal bone.

Dorsal dermal spine of the Hylaerosaurus (From Mantell, 1850a. Plate XXVII)

The next important advance was the first clear description of dinosaur bone microstructure: Hylaerosaurus made by British paleontologist Gideon Mantell in 1850. In his work, Mantell provides a drawing of a thin section from a “dorsal dermal spine” of Hylaerosaurus. The same year, Mantell described a transverse thin section from a humerus of Pelorosaurus, and notes that the bone exhibits an “intimate structure beautifully preserved; the bone cells, and Haversian canals, are as distinct as in recent bones.” In 1871, John Phillips described the structure of pterosaur bones from the Stonesfield ‘Slate’ (Bathonian, Middle Jurassic, England) and noted that pterosaur bones contained longitudinal “Haversian canals” and figured “lacunae… with many short excurrent somewhat branched tubules”.

Detail of the humerus of Vegavis iaai (MACN-PV 19.748) in polarised light. Scale = 1 mm. (From G, Marsà et al., 2017)

A century later, the introduction of hard plastic resins, the development of tungsten carbide microtome blades, the use of very thin diamond-edged saw blades, and the examination of bone tissue with surgically implanted orthopedic devices fostered new methods for studying the histology of fully mineralized bone.

Armand de Ricqlès, in the 1960s and 1970s, observed that paleohistological features could be correlated with growth rates and thus could indirectly shed light on the thermal physiology of extinct organisms. He based his conclusions on the neontological observations of Rodolfo Amprino. Quantitative studies confirmed that avascular bone is deposited more slowly than vascular bone, and radial bone is deposited faster than laminar bone. De Ricqlès early histological examinations of dinosaur bones suggested that they did not grow in a manner similar to extant cold-blooded reptiles (which deposit poorly vascularized cortical bone, interrupted by many lines of arrested growth). On the contrary, the evidence indicated that dinosaurs had a physiology that more closely approximated that of extant, fast-growing, endothermic birds. He included pterosaurs in a discussion on reptile bone histology and emphasised the structural similarities with bird bones such as the large diaphyseal medullary cavities enclosed by a dense cortex, with spongiosa in the epiphyseal region. The studies conducted by de Ricqlès opened a new path for paleohistology and his work continues to influence the field today.

References:
Bailleul AM, O’Connor J, Schweitzer MH. 2019. Dinosaur paleohistology: review, trends and new avenues of investigation. PeerJ 7:e7764 https://doi.org/10.7717/peerj.7764

Quekett J. (1849) On the intimate structure of bone, as composing the skeleton, in the four great classes of animals, viz., mammals, birds, reptiles, and fishes, with some remarks on the great value of the knowledge of such structure in determining the affinities of minute fragments of organic remains. Transactions of the Microscopical Society of London. 1849;2(1):46–58. doi: 10.1111/j.1365-2818.1849.tb05102.x.
Mantell Gideon Algernon (1850) XVII. On a dorsal dermal spine of the Hylæosaurus, recently discovered in the strata of Tilgate Forest140 Phil. Trans. R. Soc. http://doi.org/10.1098/rstl.1850.0018

Mantell Gideon Algernon (1850b) XVI. On the pelorosaurus; an undescribed gigantic terrestrial reptile whose remains are associated with those of the iguanodon and other saurians in the strata of Tilgate Forest, in Sussex140Phil. Trans. R. Soc. http://doi.org/10.1098/rstl.1850.0017

De Ricqlès (1969) De Ricqlès A. L’histologie osseuse envisagée comme indicateur de la physiologie thermique chez les tétrapodes fossiles. Comptes Rendus Hebdomadaires des Séances de l’Academie des Sciences, Serie D: Sciences Naturelles. 1969;268:782–785

Introducing Wulong bohaiensis, the dancing dragon

Wulong bohaiensis. From Poust et al., 2020

Birds are the most species-rich class of tetrapod vertebrates. They originated from a theropod lineage more than 160 million years ago. The evolutionary history of Birds is at the root of the paravian radiation, when dromaeosaurids, troodontids, and avialans were diverging from one another. Within the clade Paraves we found the morphology and soft tissue changes associated with the origin of modern avian flight. One of this key changes was the difference of nearly four orders of magnitude in body size, a pivotal element in the origin of powered avian flight. In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. Most of these fossils are from the Jehol Biota of northeastern China, dated between approximately 130.7 and 120 million years ago.
The Jehol Biota included two formations: the Yixian Formation, and the Jiufotang Formation, and contain the most diversified avifauna known to date. Among them are the long bony-tailed Jeholornis, only slightly more derived than Archaeopteryx, and many fossils of troodontids like Mei long, Sinovenator changii, Sinusonasus magnodens and Jinfengopteryx elegans. Now, the recently described Wulong bohaiensis, from the Jiufotang Formation, shed new light on the evolution of Birds. This small, feathered dromaeosaurid theropod lived in the Early Cretaceous (Aptian) and was discovered by a farmer more than a decade ago. The holotype (D2933) is a complete articulated skeleton (only some ribs are missing)and exhibits special preservation of keratinous structures.

An X-ray of Wulong showing wrist and vertebra detail on the right. (Poust et al., 2020)

Wulong (meaning “dancing dragon”) is distinguished by the following autapomorphic features: long jugal process of quadratojugal, cranially inclined pneumatic foramina on the cranial half of dorsal centra, transverse processes of proximal caudals significantly longer than width of centrum, presence of 30 caudal vertebrae producing a proportionally long tail, distally located and large posterior process of the ischium, and large size of supracoracoid fenestra (>15% of total area). The holotype has several gross osteological markers of immaturity like the unfused dorsal and sacral vertebrae, but mature feathers are present across the entire body of Wulong.

The feathered dinosaurs from the Jehol Biota are key to understand the origin of birds and dinosaur behavior. In modern birds development of ornamental feathers is generally timed to co-occur with sexual maturity. The presence of such elaborate feathers in the immature Wulong demonstrates that nonavian dinosaurs had a very different strategy of plumage development then their living relatives.

References:

Poust, AW; Gao, C; Varricchio, DJ; Wu, J; Zhang, F (2020). “A new microraptorine theropod from the Jehol Biota and growth in early dromaeosaurids”. The Anatomical Record. American Association for Anatomy. doi:10.1002/ar.24343

“Lucifer’s Hammer killed the dinosaurs”

Lucifer’s Hammer Hardcover (1977)

The end of the Mesozoic era at ca. 66 million years ago (Ma) is marked by one of the most severe biotic crisis in Earth’s history: the Cretaceous-Paleogene (K-Pg) mass extinction. During the event, three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, pterosaurs, marine reptiles, ammonites, and planktonic foraminifera. Two planetary scale disturbances were linked to this mass extinction event: the eruption of the Deccan Traps large igneous province, and the collision of an asteroid of more than 10 km in diameter with the Yucatan Peninsula.

“Lucifer’s Hammer”, written by Larry Niven and Jerry Pournelle, was the first major science fiction novel to try to deal realistically with the planetary emergency of an impact event. It was published in 1977. Almost at the same time, 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.

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

“Lucifer’s Hammer killed the dinosaurs,” said US physicist Luis Alvarez, in a lecture on the geochemical evidence he and his son found of a massive impact at the end of the Cretaceous period. A year later, 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. 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 combination of dust and aerosols precipitated a severe impact winter in the decades after 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.

The Deccan traps

Early work speculated that the Chicxulub impact triggered large-scale mantle melting and initiated the Deccan flood basalt eruption. Precise dating of both, the impact and the flood basalts, show that the earliest eruptions of the Deccan Traps predate the impact. But, the Chicxulub impact, and the enormous Wai Subgroup lava flows of the Deccan Traps continental flood basalts appear to have occurred very close together in time. Marine volcanism also provides a potential source of oceanic acidification, but a recemt 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. More recently, a new study focused on carbon cycle modeling and paleotemperature records shows that the Chicxulub impact was the primary driver of the end-Cretaceous mass extinction.The global temperature compilation reveals that ~50% of Deccan Trap CO2 outgassing occurred well before the impact. Additionalty, the Late Cretaceous warming event attributed to Deccan degassing is of a comparable size to small warming events in the Paleocene and early Eocene.

References:
P.M. Hull et al., “On impact and volcanism across the Cretaceous-Paleogene boundary,” Science (2019). Vol. 367, Issue 6475, pp. 266-272 https://science.sciencemag.org/content/367/6475/266

Alvarez, L., W. Alvarez, F. Asaro, and H.V. Michel. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction: Experimental results and theoretical interpretation. Science 208:1095–1108.

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