Thursday 29 February 2024

Stygobromus anacostensis: A new species of subterranean Amphipod from Washington D.C.

The genus Stygobromus contains 137 described species of Amphipod Crustaceans found in subterranean environments, predominantly in North America. The diversity of this group is particularly high in groundwater habitats of the Piedmont and Atlantic Coastal Plain of Maryland, Virginia, and the District of Columbia, an area from which thirteen species have been described to date, seven from shallow subterranean habitats in the lower Potomac River Basin and the area around Washington D.C. With over 150 identified seepage springs, Washington D.C. is a particularly suitable environment for the study of these Crustaceans, whose known diversity is thought to hide a significant number of cryptic species (species which physically resemble other species, but which are genetically isolated from them).

In a paper published in the journal Subterranean Biology on 15 February 2024, Matthew Niemiller of the Department of Biological Sciences at the University of Alabama in Huntsville, Andrew Cannizzaro of the Department of Biology at Miami University, Thomas Sawicki of the Department of Biological Sciences at Florida Agricultural and Mechanical University, and David Culver of the Department of Environmental Science at the American University, describe a new species of Stygobromus from a hypotelminorheic seepage spring (seepage spring of shallow subterranean origin) at Anacostia Park in metropolitan Washington D.C.

The new species is named Stygobromus anacostensis, where 'anacostensis' means 'from Anacosta' in reference to the place where it was discovered. The species is described on the basis of five specimens collected from a seepage spring that emerges from a small, 2-m high rockface about 5 m from Malcolm X Avenue SE in September and October 2021.

Stygobromus anacostensis, habitus: (A) Holotype male, 5.9 mm (USNM 1606902) (B) Allotype female, 5.3 mm (USNM 1606903). Scale bar is 1 mm. Niemiller et al. (2024).

Stygobromus anacostensis is notable in its small size, with the largest male specimen found measuring 5.9 mm in length while the largest female was only 5.3 mm long. It can be distinguished from all other members of the genus by having two pairs of antennae, with the second pair being clearly shorter than the first, and by blade-like edges to its gnathopods (mouthparts made from modified limbs). A genetic analysis recovered Stygobromus anacostensis as the sister species to Stygobromus potomacus, a species which has also been found in Anacostia Park, as well as in Caledon State Park in Virginia, roughly 100 km to the south.

Stygobromus anacostensisI is known only from a single location, a seepage spting in an urban area. While the site of this spring is on land controlled by the National Park Service, it is close to a major urban thoroughfare, and vulnerable to road salt, as well as any potential drainage improvement work carried out in the area. For this reason, Niemiller et al. recomend that the species be classified as Critically Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species, and given the status of Critically Imperilled under the NatureServe wildlife conservation scheme.

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Wednesday 28 February 2024

Bronze Age metalworks found in northern Oman.

Archaeologists from the Polish Centre of Mediterranean Archaeology at the University of Warsaw have unearthed evidence of Bronze Age metalworking during exploratory work in the Qumayrah Valley of northern Oman. The team, who have been working in Oman since 2016, spent five weeks in the area in November and December 2024, uncovering about 50 structures associated with the Bronze Age Umm an-Nar and Wadi Suq cultures, as well as a smaller amount of Iron Age and later material, according to a press release issued on 12 February 2024.

The approximate location of the Qumayrah Valley in northern Oman. Google Maps.

The oldest structures found date to the Early Bronze Age Umm an-Nar Culture, which is thought to have lasted from about 2600 BC to about 2000 BC, and include round stone towers at the Ajran 1 and QB 6 localities, and a number of tower tombs at Ajran 4. This period appears to have seen a significant economic boom in the region, leading to a rise in population, and more archaeological remains being left behind than in subsequent periods.

Reconnaissance at site QB 6, where the remains of a round tower building made of white limestone were found. Agnieszka Szymczak/Polish Centre of Mediterranean Archaeology.

This Umm an-Nar economic boom is thought to have been driven by long distance trade with India and Mesopotamia, with the main export from Oman being copper. Because of this, the Polish team have been searching for signs of copper working in the Qumayrah Valley. The discoveries made this season include a complex of sites around Wadi Salh, which include slag fields up to 220 m by 50 m and 25 cm to 50 cm thick, along with dozens of stone tools thought to have been used for crushing ore, and the remains of numerous furnaces. Several buildings thought to have been used as workshops have also been identified.

A slag field in Wadi Salh; flags mark stone tools for crushing ore. Agnieszka Szymczak/Polish Centre of Mediterranean Archaeology.

Iron Age remains are much less common in the region, but the team did find a site, QA 20, where what appears to have been an Iron Age observation tower and accompanying settlement was located at the intersection of two valleys. The settlement, thought to have dated to between 1100 BC and 600 BC, comprised a dense arrangement of adjoining houses on either side of a narrow street. Thirty three rooms have been excavated so far at this site, covering an area of about 1400 m².

Representatives of the local community, teachers and students from schools in the village of Qumayrah with members of the Omani-Polish expedition at the QA 20 site. Olga Puszkarewicz/Polish Centre of Mediterranean Archaeology.

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Sunday 25 February 2024

Looking for the Chinguetti Meteorite.

In 1916 a young French army officer called Captain Gaston Ripert reported being taken to see a giant meteorite in the Mauritanian desert, south of Chinguetti. The story is a strange one, with Ripert claiming he was taken blindfolded, at night, on a ten hour Camel ride into the desert, where he observed a huge iron structure 100 m long and 40 m wide, recovering a smaller, 4.5 kg meteorite from its surface. Shortly after returning to Chinguetti, where he was commander of the local Camel corps, Ripert reported that his guide, a local chief, was poisoned, leaving him unable to relocate the site.

The eccentric nature of this story led many people to dismiss it out of hand. It was not unusual for western travellers of the time to make up tales of wild adventure; some even paid ghostwriters to create particularly entertaining tales. However, officers in colonial armies were supposed to refrain from such nonsense, and some aspects of Ripert's story were hard to rectify with the story being complete fiction. 

During the past century a number of expeditions have sought to locate Ripert's meteorite, with the first in 1924, although by this time Ripert was stationed in Cameroon, and could only be communicated with by letters. This meant that the early searches concentrated on the area to the southwest of Chinguetti, although Ripert later clarified that the area he was taken to was probably to the southeast. The French naturalist and explorer Théodore Monod mounted a number of expeditions to find the meteorite, starting in 1934, but was unable to locate it. In the 1950s an expedition by the French army used a declinometer  (instrument for measuring magnetic declination) in a search for the meteorite, without success, and in the 1990s a team from the British TV station Channel 4 used a magnetometer during a search for the meteorite, but took only a few measurements.

Despite all this, there are a number of elements of the story suggest that it was not complete fiction, not the least of this being Ripert's willingness to talk to experts about his journey for the rest of his life. The smaller rock which Ripert recovered did prove to be a meteorite, albeit one which, when subjected to radionuclide analysis in 2001 was shown not to have been part of a larger body (radionuclides form near the surface of asteroids due to a constant bombardment by cosmic rays, but these can only penetrate a little way, so the radionuclides they form are absent from the interior of large bodies). Finally, Ripert reported observing metallic needles protruding from the large meteorite, which he tried unsuccessfully to break off, finding that they were too ductile (able to be deformed without losing toughness) for the tools he had at hand). In 2003, the American geologist and meteorite specialist William Cassidy reported similar ductile metal needles protruding from nickel-rich zones of iron meteorites, but this was clearly unknown to science in 1916.

A fragment of the smaller meteorite brought back by Gaston Ripert in the collection of the Smithsonian National Museum of Natural History. Wikimedia Commons.

In a paper published on the arXiv database at Cornell University on 21 February 2024, Robert Warren  of Salisbury in England, Stephen Warren of the Astrophysics Group at Imperial College London, and Ekaterini Protopapa of the Department of Physics at the University of Oxford, describe the results of a more recent search for the Chinguetti Meteorite, and the prospects for either discovering its existence or proving its non-existence in the future.

Warren et al. began by collating remote-sensing data covering the region from multiple sources; they are reasonably confident that other researchers will have searched Google Earth for signs of the meteorite,  but they also accessed data from other sources, including the Shuttle Radar Topography Mission, the Advanced Land Observing Satellite (ALOS), and Landsat.

Using the reasoning that the only way a 40 m high meteorite could have disappeared in the deserts of Mauritania is for it to have been covered by a sand dune, Warren et al. began by searching for a region of high dunes which could be reached from Chinguetti by Camel in under 10 hours. There are two bands of dunes close to Chinguetti; the Les Boucles field, most of which is within 20 km of the city, and the Batraz field, which is between 40 and 60 km to the southeast. Much of the intervening area is also covered by sand dunes, but these are not large enough to describe an object as that described by Ripert.

Map showing the high sand dunes, greater than 30 m height, to the south of Chinguetti. Warren et al. (2024).

Warren et al. made two trips into the desert from Chinguetta, in the company of experienced local chameliers, one lasting eleven days and one lasting six. They found that Camels typically travel at speeds of between 2.0 and 3.6 km per hour, assuming good terrain, with the maximum speed achieved by unburdened Camels being about 5.0 km per hour. 

However, even assuming that Ripert and his guide were riding Camels unburdened by anything other than themselves, it is unlikely that this maximum speed would have been achieved for 10 hours, because the primary concern of the chameliers is for the welfare of their Camels, which are not only the most important assets they own, but also their only way of getting back to safety should a problem arise. This meant that if Warren et al.'s chameliers expected a journey to take four hours, they would travel for two hours, then give the Camels a three hour break to rest and feed, before completing the journey, something they were quite inflexible about. Neither would they travel in a straight line on anything other than the flattest terrain, but instead would zig-zag to avoid taking the Camels over steps and ledges, and would never take their Camels over the tops of dunes.

Ripert himself mentioned taking several detours during his journey, which makes a journey 50 km in a straight line from Chinguetta even less plausible. However, for the sake of convenience, Warren et al. take the area within 50 km of the city as a search area. This includes the more distant Batraz Dune Field, which Warren et al. consider unlikely, although they do concede that there is a route along a dry river bey which could bring a determined Camel rider this far in 10 hours if breaks were neglected. They also rule out the area of the Les Boucles Dune Field which lies within 10 km of the city, reasoning that Ripert, who was in charge of the local Camel Corps, would have recognised a location in this area. 

A sand dune in the Les Boucles Dune Field to the south of Chinguetta. Bruno Locatelli/Google Maps.

Having defined their search area, Warren et al. then searched their dataset for dunes large enough to have covered the meteorite described by Ripert. According to Ripert's description, the northeastern side of the meteorite was already covered by a dune at the time when he visited. The area is noted for its strong, prevailing winds, which blow northeast to southwest more-or-less constantly all year round, causing sand dunes to migrate in the same direction, and Ripert stated in 1932 that he thought it possible that the meteorite would already have been covered by the dune. Taking Ripert's estimate that the meteorite was 40 m high, it would require a dune more than 40 m high to cover it.

Sand dunes in a desert do not typically stack up against one-another; instead, they are usually discrete structures, with flat spaces between them. Warren et al. identified dunes higher than 30 m high in their remote sensing dataset, in order to give an error of margin, creating a map showing dunes which meet this criterion within the two dune fields. Since dunes are unlikely to have moved more than 100  m since 1916, the meteorite, if buried, must be within 100 m of the western edge of the dune covering it. 

Since a height of 30-40 m is reached within 300-400 m of the western flank of the dunes, it would in theory be possibly for a walk along the western flank of the dunes with a magnetometer (a passive instrument that measures changes in the Earth's magnetic field), and be confident of passing within 500 m of the meteorite, a distance at which it ought to be highly detectable.

Warren et al. also not that a magnetic survey of the area has been carried out by aircraft on behalf of the Mauritanian Ministry of Petroleum Energy and Mines by the Fugro geological surveying company, using funds provided by the World Bank, and this data has subsequently been made available to teams of scientists working on other projects. With this in mind, Warren et al. wrote to the Ministry requesting access to the data, but have yet to receive an answer.

Between 13 and 17 December 2022 Warren et al. carried out a magnetometer survey of the eastern part of the Les Boucles Dune Field on foot, covering the western edges of six large dunes, based upon which they are confident that the presence of a large iron meteorite beneath these dunes can be ruled out. Based upon the time this took, they estimate that a survey of all the potential dunes would require an expedition lasting three weeks. 

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Saturday 24 February 2024

Aethozoon flavum: An in-faunal solitary Bryozoan found in deep sea sediments from Mayotte Island.

Bryozoans are a phylum of suspension feeding Lophotrochozoans found in all aquatic environments from lakes and rivers to the deep oceans. Bryozoans have a simple bodyplan, with a ciliated tentacle crown called a lophophore, which is used to collect food, and a u-shaped digestive tract, all of which is contained within a thick body wall, the cystid, which is often mineralized. The majority of Bryozoans are colonial with linked cystids, often forming elaborate structures, as well as connected digestive tracts, which enable them to share food. 

In a paper published in the journal Marine Biodiversity on 21 February 2024, Thomas Schwaha of the Department of Evolutionary Biology at the University of Vienna, Daniela Zeppilli of Biologie et Écologie des Ecosystèmes marins Profonds at the University of BrestAlberto González‑Casarrubios of the Department of Biodiversity, Ecology and Evolution at the Complutense University of Madrid, and Diego Cepeda of the Department of Biology and Research Centre for Biodiversity and Global Change at the Autonomous University of Madrid, describe a new species of solitary Bryozoan from the sediments around Fani Maoré, a recently discovered submarine volcano off eastern Mayotte, a French overseas department in the Comoros Islands of the southern Indian Ocean.

Visible fauna was not present around Fani Maoré, but sediment samples recovered from the site were found to be rich in meiofauna (small benthic Invertebrates), with an unknown Aethozoid Bryozoan being the most abundant non-Nematode species. 

Aethozoids are a small and poorly understood group of non-mineralized, usually solitary, Bryozoans, with only five previously described species in four genera; Aethozoon pellucidum, from the northeast Atlantic, and recently the deep Kuril-Kamchatka Trench at depths of greater that 7000 m, Aethozooides uraniae from the deep-sea hypersaline anoxic Urania basin of the eastern Mediterranean, Franzenella limicola from the shallow Baltic, and Solella radicans and Solella monniotae from the deep North Atlantic.

The new species is placed in the genus Aethozoon and given the specific name flavum, the Latin word for yellow, in reference to the colour of the examined specimens. These are between 1787 μm and 2996 μm in length (average length 2281 μm), with a wider basal section 295 μm to 392 μm in length which contains the containing gonads, digestive tract, retractor muscles and funicular system. Two types of appendage are present at the base, kenozooidal cystid appendages, which appear tp be used for asexual reproduction; with examined specimens having a budding stages attached, and the related Aethozooides uraniae also produces buds from kenozooidal cystid appendages. Aethozoon flavum is also apparently capable of sexual reproduction, with all examined specimens being similtaneous hermaphrodites. Not all specimens of Aethozoon flavum had kenozooidal cystid appendages, while some had two. The other type of appendages are known as non-kenozooidal cystid appendages, and are less clear in purpose, but may be remnants of former attachment to a parent zooid.

Details of single zooids of Aethozoon flavum. (a) Holotype (MNHNIB-2017-723) showing long, non-kenozooidal cystid appendages; (b) Paratype (MNHN-IB-724) showing shorter cystid appendages including two shorter kenozooidal ones; (c) Paratype (MNHN-IB-725) showing zooid devoid of polypide and kenzooidal cystid appendage with distal bud; (d) Schematic drawing. Abbreviations: alt, anal tube; am, apertural muscles; b, bud; bdb, basal duplicature band; ca, cardia; cae, caecum; db, duplicature band; fg, foregut; fuc, funicular cords; kca, kenozooidal cystid appendage; int, intestine; nca, nonkenozooidal cystid appendage; ply, polypide; py, pylorus; o, orifice; rm, retractor muscles;  v, vestibulum; vw, vestibular wall. Schwaha et al. (2024).

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Friday 23 February 2024

Eruptions on Mount Popocatépetl.

Mount Popocatépetl, a 3020 m high stratovolcano (cone-shaped volcano made up of layers of ash and lava) about 70 km from Mexico City in the eastern Trans-Mexican Volcanic Belt, began suffering regular seismic events (small Earthuakes associated with the movement of magma in chambers beneath the volcano) on 14 February 2024, followed by a series of eruptions which produced ash columns up to 6 km high, which drifted to the north, northeast, and south. Ashfalls were reported in the municipalities of Nativitas, Santa Isabel, Tetlatlahuaca, Tlaxcala, Santa Ana Chiautempan, and Zacatelco, and Hermanos Serdán International Airport, was forced to be closed while ash was cleared from its runways. Earthquakes and smaller eruptions persisted for the nest week, with an ashfall again reported in the municipality of Hueyapan on 19 February. A 12 km exclusion zone around the volcano has been declared as a precaution.

An eruption on Mount Popocatépetl seen from Puebla. Daniel Llerandi/BBC.

Popocatépetl has been more or less constantly erupting since the mid 1990s, but most of the time this activity remains at a low level. Major eruptions on Popocatépetl are a cause for concern as the volcano is in a densely populated area, with 30 million people living within the potential hazard zone. The last major eruption, a Plinian (or Vesuvian) event in about 800 AD, triggered a series of pyroclastic flows and lahars that scoured the basins around the volcano.

The volcanoes of the Trans-Mexican Volcanic Belt are fuelled by the subduction of the Cocos Plate beneath the North American Plate along the Middle American Trench to the south of Mexico. As the subducting plate sinks into the Earth it is melted by the heat and pressure, and volatile minerals liquefy and rise through the overlying North American Plate as magma, fuelling Mexico's volcanoes. 

The subduction of the Cocos Plate beneath the North American Plate in Mexico, and how it leads to volcanoes and Earthquakes. King Saud University.

The Cocos Plate is thought to have formed about 23 million years ago, when the Farallon Plate, an ancient tectonic plate underlying the East Pacific, split in two, forming the Cocos Plate to the north and the Nazca Plate to the south. Then, roughly 10 million years ago, the northwesternmost part of the Cocos Plate split of to form the Rivera Plate, south of Beja California.

The position of the Cocos, Nazca and Rivera Plates. MCEER/University at Buffalo.

In a paper published in the Journal of Geophysical Research: Solid Earth, in 2011, a team led by Igor Stubailo of the Department of Earth and Space Sciences at the University of California Los Angeles, published a model of the subduction zone beneath Mexico using data from seismic monitoring stations belonging to the Mesoamerican Seismic Experiment, the Network of Autonomously Recording Seismographs, the USArray, Mapping the Rivera Subduction Zone and the Mexican Servicio Sismologico Nacional.

The seismic monitoring stations were able to monitor not just Earthquakes in Mexico, but also Earthquakes in other parts of the world, monitoring the rate at which compression waves from these quakes moved through the rocks beneath Mexico, and how the structure of the rocks altered the movement of these waves.

Based upon the results from these monitoring stations, Stubailo et al. came to the conclusion that the Cocos Plate was split into two beneath Mexico, and that the two plates are subducting at different angles, one steep and one shallow. Since the rate at which a plate melts reflects its depth within the Earth, the steeper angled plate melts much closer to the subduction zone than the shallower angled plate, splitting the Trans-Mexican Volcanic Belt into sections above the different segments of the Cocos Plate, and causing it to apparently curve away from the subduction zone.

Top the new model of the Cocos Plate beneath Mexico, split into two sections (A & B) subducting at differing angles. (C) Represents the Rivera Plate, subducting at a steeper angle than either section of the Cocos Plate. The Split between the two has been named the Orozco Fracture Zone (OFZ) which is shown extended across the Cocos Plate; in theory this might in future split the Cocos Plate into two segments (though not on any human timescale). Bottom Left, the position of the segments on a map of Mexico. Darker area is the Trans-Mexican Volcanic Belt, orange circles are volcanoes, brown triangles are seismic monitoring stations, yellow stars are major cities. Bottom Right, an alternative model showing the subducting plate twisted but not split. This did not fit the data. Stubailo et al. (2012).

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