Monday 26 June 2023

Fireball meteor over southern Brazil.

Witnesses in Bahia, Distrito Federal, Espírito Santo, Goiás, Mato Grosso do Sul, Minas Gerais, Paraná, Rio de Janeiro and São Paulo states have reported observing a bright fireball meteor slightly before 6.40 pm local time (slightly before 9.40 pm GMT) on Monday 19 June 2023 (slightly before 6.00 am on Sunday 7 June, GMT). The fireball is described as having moved from northeast to southwest, entering the atmosphere over Minas Gerais State and disappearing over São Paulo. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry.  

The 19 June 2023 Brazilian fireball seen from Passos in Minas Gerais State. Denilson Silva/American Meteor Society.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However, this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

Heat map showing areas where sightings of the meteor were reported (warmer colours indicate more sightings)and the apparent path of the object (blue arrow). American Meteor Society.

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.

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Sunday 25 June 2023

Seeking the source of arsenic in groundwater in the Grand Canyon region, Arizona.

The Grand Canyon is an internationally renowned tourist attraction, drawing visitors from all over the world. It is also viewed as a sacred place by many Native Americans, many of whom make their home there. The Colorado River has been carving out the canyon for over 3 million years, and provides a major source of water for about 40 million people in the United States and Mexico. However, in the area immediately around the Grand Canyon, the water needs of both residents and visitors is almost entirely met from groundwater. This water supply is threatened by a warming climate, as this is associated with a drying environment locally, lowering the rate at which groundwater reserves are recharged. The Grand Canyon region is also home to some of the richest deposits of uranium in the US. Concerns about the impact of this industry on the local water supply led to a 20-year moratorium on new mining activity being put into place in 2012, since which time the United States Geological Survey has been carrying out extensive monitoring of the relationship between mining and water supplies in the region, with the objective of enabling future policy-makers to make informed decisions about uranium mining around the Grand Canyon.

While it is obvious that uranium entering the water supply would be a bad thing, other metals present in uranium ore deposits are probably a greater threat to Human health. Arsenic in particular, while present to an extent in all soils, rocks, and groundwater supplies, is particularly of concern in the Grand Canyon region, and is known to be present in the minerals of the breccia pipe deposits targeted by uranium miners in the area. Elevated levels of arsenic in drinking water are associated with a range of health problems, including skin lesions and cancer of the lung, bladder, kidney, and liver, and both the United States Environmental Protection Agency and World Health Organization set the maximum safe level of arsenic in water supplies at 10 μm/L, whereas the equivalent level for uranium is 30 μm/L.

In a paper published in the journal PLoS Water on 14 June 2023, Fred Tillman of the Arizona Water Science Center of the United States Geological Survey, Kimberly Beisner of the New Mexico Water Science Center of the United States Geological Survey, and Casey Jones of the South Atlantic Water Science Center of the United States Geological Survey, present an analysis of the arsenic content of groundwater in the Grand Canyon area, and its relationship to potential sources, including the mining of uranium.

Study area within the western United States (upper panel) and detail of study area showing Native American land, uranium mines, withdrawal areas, and breccia pipes (lower panel). Tillman et al. (2023).

The Grand Canyon region is sparsely populated, and therefore has a limited number of water extraction wells, something which makes it difficult to assess the extent of the aquifers these wells target. In the absence of such data, topographic features are assumed to deliminate the extent of these aquifers. Tillman et al. looked at an area containing watersheds flowing into the Colorado River between Lees Ferry to the east and the Grand Wash Cliffs to the west. There are known to be two groundwater systems in this area. The shallower of these is a perched aquifer 300 m below the plateau surface, which runs through the in the Permian-age Kaibab Formation, Toroweap Formation, and Coconino Sandstone, which is thought only to be present in the area immediately around the Grand Canyon. The deeper system is about 1 km beneath the plateau surface, and runs through the Mississippian-age Redwall Limestone, the Devonian-age Temple Butte Formation, and the underlying Cambrian-age Muav Limestone of the Tonto Group, which is thought to be present over a much wider area, except where the water-bearing units have been eroded away by canyon formation.

Uranium in the Grand Canyon has been mined from breccia pipes (cave systems, often of volcanic origin, filled in by rock debris, and usually cemented by mineral deposition). These breccia pipes cut through multiple strata in the region, with uranium accumulations generally being found where the pipes cut through the Permian Coconino Sandstone, Hermit Formation, and Esplanade Sandstone. Large scale uranium mining here began in the 1950s, at the Orphan Mine on the southern rim of the Grand Canyon, and there are currently two active mines, as well as eleven former mines targeting breccia pipes within the region. These mines frequently crossed the upper, perched groundwater aquifer, but stopped hundreds of metres short of reaching the lower aquifer. While these mines targeted uranium, the ore bodies also include trace amounts of antimony, arsenic, barium, cadmium, cobalt, copper, mercury, molybdenum, nickel, lead, silver, strontium, vanadium, and zinc; all of these are also found in other rocks in the area, but at much lower concentrations.

Lithology and mine features at breccia-pipe uranium mining sites in the Grand Canyon region. Tillman et al. (2023).

Arsenic is a fairly common element at the Earth's surface, found in a wide variety of rocks and minerals, although rarely at concentrations high enough to cause problems. In the Grand Canyon are it is found in most of the sedimentary rocks at levels of about 5-10 mg/kg, typically at the lower end of this range in sandstones and at the upper end in clays and shales, where it binds to oxides, sulphides, and organic materials. Carbonate rocks tend to have much lower concentrations. A study which looked at over 700 soil samples from the Coconino Plateau in northern Arizona, found that while the average arsenic concentration was less than 10 mg/kg, the maximum was about 70 mg/kg, and a study of seventeen surface-collected aquifer-related rocks from the Grand Canyon found that only two has arsenic concentrations of less than 20 mg/kg, with the maximum being 28.9 mg/kg in the Muav Limestone. Arsenic concentrations from the breccia pipe structures are also known to be significantly higher than in the surrounding rocks, making these structures a potential source of elevated arsenic levels in groundwater, particularly if they are disturbed. Arsenic is usually found at its highest concentrations in sulphide minerals, such as the ore arsenopyrite (iron arsenic sulphide), which, along with other arsenic sulphide minerals, is found within the breccia pipes. Samples obtained from drill-cores and mine waste derived from the breccia pipes show much higher arsenic levels, as high as 5060 mg/kg in waste rock from the Pigeon Mine, 1980 mg/kg in waste from the Kanab North Mine, 15 300 mg/kg in a drill core from the Hack II Mine, and 105 000 mg/kg in the Pineon Plane Mine deposits.

Arsenic from rock can easily become dissolved in groundwater under the right concentrations, however, it is difficult to make direct predictions about the persistence and movement of arsenic in groundwater, as it is sensitive to changes in pH, oxidation-reduction potential, and the presence of iron oxides, with the effect that the amount of dissolved arsenic within an aquifer can vary considerably over quite short distances. Troublingly, unlike most heavy metals, arsenic can become mobilised in water at pH levels between 6.5 and 8.5, under both oxidising and reducing conditions. Arsenic can form different aqueous ions at different pH levels; between pH 3 and pH 7 it will form monovalent arsenate anions, at pH7-11 it forms divalent arsenic, while under mildly reducing conditions it forms uncharged arsenite ions. Arsenite is the most mobile of these forms, while arsenate is the most easily resorbed onto rocks, but all will precipitate out or redissolve in response to pH or radox potential of the water. Studies in other areas of the US have suggested that arsenic is most prone to dissolving in groundwater when conditions are oxic and the pH is higher than 7.

High arsenic levels in groundwater are generally associated with aquifers with favourable geochemical conditions, geothermal springs, or mining activities. Arsenic can be a significant portion of magma (and volcanic ash), and thus is often concentrated in geothermal water flowing through volcanic systems. Thus, many hot springs in the Yellowstone National Park have been shown to have arsenic concentrations as high as 10 mg/L. Clearly, arsenic-rich rocks are a particularly good source of arsenic ions, but under the right conditions, aquifer waters can become enriched in arsenic even when the rocks they are flowing through are not particularly enriched in arsenic. In the Bengal Basin of Bangladesh disolved arsenic in aquifers can reach as high as 3.2 mg/L, despite the sediments through which these waters flow having arsenic levels of less than 2-20 mg/L. High residency time of water within an aquifer (i.e. 'old water') also appears to help arsenic build up within the water, particularly if the water has either a high pH or a neutral pH under reducing conditions. Arsenic levels in water can also rise when the water is exposed to mine ores or waste rock, particularly where sulphide-rocks are becoming oxidised following disturbance due to Human activities.

Data on the concentration of arsenic in water samples from springs and wells in the e Grand Canyon region were obtained from the USGS National Water Information System database, with additional data provided by a USGS–National Park Service sampling partnership which ran from 2016 through 2017, and involved Grand Canyon National Park staff collecting samples from spring locations in the park, which were then processed at USGS laboratories.

Eighty seven replicate pairs of samples were available (replicate pairs are environmental samples collected as close together in time and space as is possible, to ensure their reliability; in this instance all replicate sample pairs produced a variation in arsenic concentration of less than 1.2 μm/L). Of these, seven pairs produced arsenic levels in excess of the recommended 10 μm/L. Analyses of these pairs for uranium, sulphide levels, and total dissolved solids, produced similar levels of matching, suggesting that the analyses being used for these was reliable, but testing for iron produced quite high variations between samples when the iron concentration was below about 100 μm/L.

Test results for arsenic in groundwater were available for 652 samples collected from 230 sites in the Grand Canyon region between June 1977 and September 2022. Forty eight of these samples came from wells, and 182 from springs, with most of the springs emerging from the Grand Canyon walls and floor, and drawing their water from a variety of sources above, within, and below the Permian strata that host uranium ore in breccia pipes. Wells are typically located on the plateau above the canyon, and reach depths of between 24 m and 1100 m. 

Fifty two of the 230 sample sites had arsenic concentrations of below 1 μm/L, and 202 (88%) had levels below 10 μm/L, considered to be the maximum safe level of exposure. Of the remaining 28 sites, 25 had arsenic levels below 40 μm/L. The highest arsenic concentration was found at Pumpkin Spring, at 875 μm/L. Twenty two of the sites with arsenic concentrations above 10 μm/L are springs discharging into the Colorado River or its tributaries, all but two of these (Saddle Canyon Spring and Fence Fault Left Spring) discharge from the South Rim of the Grand Canyon. The highest arsenic concentrations in springwater are found in the southwest of the study area, in or around the Hualapai Indian Reservation.

Map of the maximum arsenic concentration observed at 230 groundwater sites in the Grand Canyon study area. Tillman et al. (2023). 

At 173 of the sites in the study, data on both water pH and arsenic concentration was available, with the values ranging from pH 3.8 to pH 8.8, with a median of pH 7.7, though only a week correlation between pH and arsenic concentration could be detected. Disolved oxygen concentrations were available for 152 of the study sites; dissolved oxygen concentration ranged from less than 1 mg/L to 11.5 mg/L, with no correlation between dissolved oxygen concentration and dissolved arsenic concentration. Data on the concentration of sulphate (oxidised sulphur) was available for 185 of the sites in the study, ranging from 1.5 mg/L to 3450 mg/L, with a median of 730 mg/L, with no correlation between dissolved sulphates and dissolved arsenic. Dissolved iron concentrations were available for 187 of the study sites, with values ranging from less than 0.2 μg/L to 10 300 μg/L with a median of 4 μg/L, though no correlation could be found between dissolved iron concentration and dissolved arsenic concentrations. Information on total dissolved solids was available for 183 of the study sites, with concentrations ranging from 69 mg/L to 9630 mg/L, with a median of 459 mg/L; no correlation was found between total dissolved solids and dissolved arsenic levels. Data for the age of water (i.e. how long it has spent within the aquifer) is available for 138 of the study sites (based upon the presence of tritium generated by nuclear test explosions), with no correlation found between water age and arsenic concentration.

Unlike all of the previous criteria, no correlation between dissolved uranium and dissolved arsenic in groundwater has previously been reported, however, since concerns have been raised about the possibility of arsenic entering the water supply due to the activities of uranium mines, Tillman et al. also examined this relationship. Information on both uranium and arsenic concentrations were available from 205 sites, with uranium concentrations ranging from m 0.114 μg/L to 231 μg/L, with a median of 3.7 μg/L. No correlation was found between uranium concentration and arsenic concentration. 

Travertine is a type of limestone formed around hot mineral springs. In the Grand Canyon area, travertine springs are often associated with faults, and appear to be correlated with high arsenic concentrations. Travertine springs in the area include Pumpkin Spring (which produced the highest dissolved arsenic concentration in the study at 875 μg/L), Travertine Falls Spring (243 μg/L), and Travertine Canyon (100 μg/L), all of which are on the Hualapai Indian Reservation in the western part of the Grand Canyon region. Pumpkin Spring is known to be fault controlled, and considered to discharge waters from the Tapeats Sandstone, although its water is warm, which implies that at least some of it is derived from a deeper source. Fence Spring (arsenic concentration 16.4 μg/L) is another travertine spring located on the Fence Fault Zone, in the eastern part of the Grand Canyon region, and other travertine springs with high arsenic concentrations are known throughout the southwestern United States, , including Mammoth Hot Springs in Yellowstone National Park, and Montezuma Well located in the Verde Valley of Arizona, suggesting a possible mantle-source for arsenic, and groundwater mixing with deep-earth hydrothermal fluids as a mechanism for arsenic to reach surface environments.

Pumpkin Spring on the Colorado River in the Grand Canyon, a mineral pool with an arsnic concentration of 875 μg/L. Atlas Obscura.

The origin of arsenic in water at other springs is less clear. Near Travertine Falls Spring (arsenic concentration 38 μg/L) and Travertine Canyon Spring (35 μg/L) are located close to breccia pipes with elevated levels of uranium, but no fault system appears connected with these pipes. Wooley Spring (arsenic concentration 35.8 μg/L) ) is located north of the Grand Canyon on the Kaibab Indian Reservation and discharges from the Kayenta Formation of the Glen Canyon Group of Jurassic age, which is present in limited northern parts of the study area. The Havasu Spring (arsenic concentration 17 μg/L) is another travertine well, which acts as the primary source of water for the Havasupai Tribe in Supai Village, while Supai Well No. 3 (arsnic consentration 4-12 μg/L) is a 46 m deep alluvium well located two kilometres downstream of Havasu Spring.

Groundwater in Arizona, and the southwestern US in general, is known to be elevated in arsenic compared to the rest of the US. Arsenic levels in well water in the southwest have been shown to exceed the maximum safe level twice as often as water from wells in other parts of the country. This arsenic is thought to be primarily derived from geothermal springs and water passing through volcanic rocks. Groundwater sites in Arizona outside the Grand Canyon region have arsenic levels which range from less than 1 μg/L to 1400 μg/L, with the median being 4 μg/L, with 25% of these sites exceeding the maximum safe level. The highest arsenic concentration in water in Arizona is found at Verde Hot Springs, near the town of Camp Verde in Yavapai County, with an arsenic level of 1400 μg/L, which is again thought to be geothermally influenced, with Pumpkin Spring having the second highest arsenic levels. The highest arsenic level recorded at a well in Arizona came from a 150 m deep well identified as C-19-01 28ADC, near the border with Mexico, and was taken in 1978. Thus, although the Grand Canyon region has high levels of arsenic in its groundwater compared to most of the US, it is actually low compared to the rest of Arizona.

Verde Hot Springs, near the town of Camp Verde in Yavapai County, with an arsenic level of 1400 μg/L. Greg Walters/Wikimedia Commons.

Limited information is available on the groundwater around the uranium mines in the Grand Canyon region, due to a low number of wells in this area. The Pinenut Mine Well is located on the Pinenut Mine site to the north of the Grand Canyon, and sources water from the Mississippian Redwall Limestone. The Pinenut Mine initially opened in 1986, and then closed in 1989, was re-opened in 2009, and closed again as part of the 20-year moratorium on mining imposed in 2013. Arsenic levels in the Pinenut Mine Well were recorded at 6.2 μg/L, in 2009 (prior to the mine re-opening), 13.5 μg/L in 2012 (while the mine was operating), 4.2 μg/L in 2014 (after the mine had closed again), and at 11 μg/L in 2018. The closest well outside the Pinenut Well site, Willow 1 Spring, 7 km to the north of the mine, has been monitored continuously since 2009, due concerns about uranium contamination. This well has recorded arsenic levels between 0.6 μg/L to 3.1 μg/L over that time.

A groundwater mine at the Pinyon Plain Mine (formerly the Canyon Mine) south of the Grand Canyon near the town of Tusayan, which extracts water from the Redwall–Muav aquifer, has been sampled regularly by the USGS since 2003, producing arsenic concentrations ranging from 0.16 μg/L to 0.5 μg/L. An additional well was installed at the same site in 2017 for monitoring purposed, targeting the perched groundwater of the Coconino Sandstone. It was hypothesized that any increase in arsenic in the water caused by mining activity would be detected in this perched groundwater first, but in fact the arsenic levels have fallen steadily since monitoring started, from 4.6 μg/L in 2017 to 0.51 μg/L in 2022.

The Pigeon Mine, to the north of the Grand Canyon, no longer has a well on site, though a monitoring well was installed 4.5 km to the northeast of the site in 2022. This well reaches the Coconino Sandstone aquifer, with a recorded arsenic level of 0.9 μg/L. There are also three natural springs located close to the mine; the Pigeon Spring, 2 km to the east of the mine, Willow Spring 2, about 1.5 km to the southwest of the mine, and Wildband Spring, about 2.2 km southeast of the mine. Pigeon Spring has been monitored continuously since 2016, due to high uranium levels. Arsenic levels at Pigeon Spring have been recorded at between 0.3 μg/L and 2.2 μg/L, while the highest recorded level at Willow Spring 2 was 0.73 μg/L and the highest at Wildbrand Spring was 1 μg/L.

The Orphan Lode Mine (often referred to simply as the Orphan Mine) is an abandoned uranium mine on the South Rim of the Grand Canyon. Groundwater associated with this mine emerges at the Upper Horn Bedrock Spring e at the base of bedrock cliffs near the Redwall-Muav Limestone contact about 500 m down gradient of the Orphan Mine, then is re-absorbed into the rock, emerging at two lower springs further downslope. Uranium levels at the Upper Spring have been recorded as high as s 293 μg/L, but the highest arsenic level recorded was 24.2 μg/L, with the level usually below 10 μg/L. Uranium levels at the lower springs have been recorded in the range 7.2 to 39.3 μg/L, while the range for arsenic is less than 2.5 to 7.7 μg/L. 

The abandoned Grandview Mine (also referred to as Last Chance Mine) is a former breccia pipe copper mine on the South Rim of Grand Canyon. The ore targeted here was mostly within the Redwall Limestone, and was known to contain high levels of arsenic. Miners Spring, about 0.6 km southeast of the mine discharges from the Redwall-Muav aquifer. This spring was sampled six times between n 2000 and 2016, producing arsenic levels in the range 17 μg/L to 19.3 μg/L. Another nearby spring, Miners Spring at Trail in Hance Canyon, was sampled once in 1981, producing an arsenic level of 20 μg/L. Two further springs are located further to the southeast; JT Spring being 3.5 km from the mine and Red Canyon Spring about 5 km; JT Spring has produced arsenic levels of 14.4 μg/L, and Red Canyon Spring of 17 μg/L. Two unnamed springs are found about 1.5 km to the west of the Grandview Mine, and have produced arsenic concentrations of 4.8 μg/ L and 1.6 μg/L, respectively.

Many sites within the Grand Canyon region have arsenic levels above what is considered safe in drinking water, although there is no apparent connection to uranium mining, with only a few samples associated with the Pinenut and Grandview mine exceeding safe values, and these not being among the highest levels recorded in the region. However, groundwater in the area is known to move slowly, so there is still the possibility that arsenic contamination of groundwater is happening at these mines, but has yet to be detected. 

During mine operations, mine waste is typically piled up within the fenced off mining compound. This is known to be a source of a wide range of pollutants, as rainwater leaches through the spoil, so runoff from such tips is generally contained within a drainage system leading to a lined retention pond. Wind-blown dust can still be a problem, carrying metals and other chemicals to nearby sites, and sometimes entering water systems, although this is unlikely to be a problem for aquifers in the Grand Canyon region, the shallowest of which is 300 m below the surface, and no evidence of recharge from recent groundwater. 

Water from aquifers can enter mines and become enriched in metals. This is likely to be a problem for the upper, perched aquifer in the Grand Canyon region; this is typically managed by actively pumping water from the mine into a surface containment pond. The sump pool at the Hermit Mine has produced arsenic levels of 1090 μg/L, while waters within the shaft at Pinyon Plain Mine (which has yet to begin mining uranium) were found to contain 299 μg/L arsenic. As long as water continues to be pumped out of a mine, and the lining containment pool is not breached, this system should prevent metal contaminants from a mine flowing back into aquifers.

The end-of-life process for mines has changed over the time in which mining has occurred in the Grand Canyon region, with the Orphan Lode Mine simply being abandoned at the end of its life, followed by subsequent tightening of regulations over the decades, so that the most recent mine to close, the Pinyon Plain Mine, requires 30 years of groundwater monitoring subsequent to the mine closure. Modern mine closure requires that any water-bearing strata be sealed off, that the mine be sealed off at the surface, and that surface conditions be returned to a clean state. Mine operators typically do this by returning mine spoil to the mine before sealing at the surface. 

The contents of breccia pipes tends to be variable, and unevenly distributed, with a mixture of ore and non-ore rocks. However, rocks deemed to be to low in uranium to be worth processing, may still contain high levels of other metals, such as arsenic. These metals may leach out when rainwater passes through mine dumps; stream sediments below the Hack Canyon Mine Complex are known to contain significantly higher levels of arsenic than those above the complex, although these elevated levels do not (at the moment) reach far downstream. 

Any similar contamination from a mine on the Coconino Plateau would need to pass through hundreds of metres of rock before reaching the upper, perched aquifer, something highly unlikely given the low rainfall levels in the area, although potentially water could pool within an improperly sealed mine, react with sulphate minerals there to form an acid solution, and allow the freeing and downward movement of metal ions. 

After a mine has been closed and sealed, water entering the mine shaft is not usually pumped to the surface. Modern mines are required to seal off aquifers entering mines before abandonment, but there is no actual evidence on how reliable this process is. Furthermore, many mines in the Grand Canyon region were closed down before this requirement was introduced. Any water entering a mine shaft infilled with mine debris would encounter an environment enriched in non-targeted metals, such as arsenic, which might then be carried back into the aquifer. Experimental results suggest that this ought to result in an elevated arsenic content in the water within the aquifer, although not forever, as the supply of metal within the shaft would be finite. This elevated arsenic level would be highest closest to the mine, falling as the water moves further away and is mixed with water that has not passed through the mine.

There is currently no evidence that elevated levels of arsenic originating at breccia pipe mines are moving through aquifers in the Grand Canyon region. However, the low rate at which water moves in the region could mean that any such movement would not be detected for decades after it began, meaning that even the 30 years of groundwater monitoring required at closing mines may not be sufficient to detect any problems.

The Grand Canyon region is home to some of the world's most productive uranium mines, but concern about the environmental impact of this industry led to a 20 year moratorium on new mining activities being imposed in 2012. Since this time, the United States Geological Survey has carried out extensive environmental monitoring in the region, aimed at enabling future legislators to make informed decisions about mining activity in the region. Current data suggests that high levels of arsenic are found at many sites in this area, but that this does not appear to be related to mining activity. However, the data at the current time is not sufficient to enable the possibility of mining causing elevated arsenic levels within aquifers, requiring  the monitoring program to be continued.

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Saturday 24 June 2023

Shri devi: The (previously unknown) skull of a Dromaeosaurid Dinosaur from the Late Cretaceous Baruungoyot strata of Mongolia.

The Dromaeosaurs were a group of small-to-medium sized Theropod Dinosaurs, closely related to the earliest Birds. They are noted for the presence of an enlarged and highly curved claw on their second toe, a long, straight tail formed from tightly interlocked caudal vertebrae, and the presence of feathers. The group were widespread, with numerous fossils from the Cretaceous of Asia, North and South America, and Europe, although their Bird-like, often delicate skeletons did not usually preserve well, so most species are known only from fragmentary remains. One area where more complete Dromaeosaur skeletons are more frequently found is the Djadokhta strata of the Gobi Desert, Mongolia, an area which has produced several fairly complete skeletons of the Late Cretaceous Dromaeosaur, Velociraptor mongoliensis

These Upper Cretaceous deposits of the Gobi desert have produced a range of other Velociraptorine Dromaeosaurs, including Adasaurus mongoliensisTsaagan mangas, 'VelociraptorosmolskaeLinheraptor exquisitusShri devi, and Kuru kulla, although most of these are known only from a single specimen.

In a paper published in the journal Acta Paleontologica Polonica on 21 June 2023, Łukasz Czepiński of the  Institute of Palaeobiology of the Polish Academy of Sciences, describes a new Dromaeosaur specimen from the Late Cretaceous Baruungoyot strata  of the Gobi Desert, which he assigns to the species Shri devi.

The new specimen, ZPAL MgD-I/97, was collected in 1970 by a Polish-Mongolian Palaeontological Expedition, and initially described and illustrated as Velociraptor sp., then later redescribed as a specimen of Velociraptor mongoliensis. However, upon re-examination of the specimen, Czepiński disagrees with this diagnosis, noting that the skull is much less elongated than in that species.

(A) Map of Mongolia and Inner Mongolia of China with the Upper Cretaceous sites yielding remains of dromaeosaurid dinosaurs. (B) Photograph of Khulsan locality, from where the specimen described in this paper was collected, photographed in the 1970 during the Polish-Mongolian Paleontological Expeditions (from the Collections of the Institute of Palaeobiology of the Polish Academy of Sciences). Czepiński (2023).

Specimen ZPAL MgD-I/97 comprises a partial skull, including the left jugal, left lacrimal, left maxilla, fragment of the right maxilla, palatine elements, both dentaries lacking the anteriormost portions, both splenials, surangulars, and angulars, in close association with a distal portion of the left hindlimb, containing the distal parts of the left fibula and tibia, astragalus and complete pes, with four metatarsals and all phalanges. The holotype specimen of Shri devi, MPC-D 100/980, is a partial articulated skeleton including cervical, dorsal, and proximal caudal vertebrae, the right femur, the right and left tibiotarsa, and the right pes but lacking a skull, There is almost no overlap in the bones of the two specimens, with ZPAL MgD-I/97 being about 20% smaller than MPC-D 100/980, but both specimens preserve a single hind foot (left in ZPAL MgD-I/97 and right in MPC-D 100/980), and Czepiński is confident that these are similar enough to assign the two specimens to the same species.

Reconstruction of the Dromaeosaurid Dinosaur Shri devi, based on ZPAL MgD-I/97 and MPC-D 100/980. (A) Skull; missing elements reconstructed on the base of Velociraptor mongoliensis (MPC-D 100/25 and MPC-D 100/54). (B) Whole body silhouette with known remains of the holotype and referred material. Czepiński (2023).

The skull of Shri devi is apparently much shorter than in other Mongolian Dromaeosaurids, based upon the shape of the antorbital fenestra (opening in the skull in front of the eye), which is almost round in Shri devi, but elongated in most Mongolian Dromaeosaurids, despite Shri devi otherwise being very similar, and presumably closely related to, Velociraptor mongoliensis. A similar short-snouted condition is seen in many North American Dromaeosaurids, though these are not thought to be closely related to Shri devi, suggesting that this is an ecological adaptation, rather than an indicator of relatedness.

Dromaeosaurid Dinosaur Shri devi (ZPAL MgD-I/97) from the Upper Cretaceous, Khulsan, Ömnögovi, Gobi Desert, Mongolia. Photographs (A₁), (A₂), (A₄), and (A₅) and 3D model (A₃), (A₆), and (A₇) obtained from the CT scan of the left side of the skull in dorsal (A₁), medial (A₂, A₃), anterior (A₆), and lateral (A₇) views. Elements of the left palate in dorsal (A₄) and ventral (A₅) views. Right maxilla in the lateral (A₈, A₉) and anterior (A₁₀) views, with the margin of the antorbital fenestra indicated by dashed lines, and the close up of the fifth (A₁₁) and the second (A₁₂) preserved tooth in labial views showing very weakly developed denticles on the mesial carina. Right mandible in the lateral (A₁₃) and (A₁₄) and medial (A₁₅) and (A₁₆) views. (B) Explanatory drawings of the skull in left (B₁) and right (B₂) lateral views with the preserved bones (in grey). Czepiński (2023).

Most of the Dromaeosaurid Dinosaurs from Mongolia, particularly those with very long snouts, are found in palaeodesert environments, covered by aeolian sands. Both specimens of Shri devi, on the other hand, comes from a more mixed environment, with a mixture of aeolian and fluvial deposits, suggesting a wetter (though still fairly arid) environment. The available prey to a small predatory Dinosaur would appear to have been similar in both environments, including Lizards, Mammals, Protoceratopsids, Oviraptorosaurs, and Birds (larger Ankylosaurids were also present, but unlikely to have been hunted by small Dromaeosaurs), suggesting that the variation in snout length is unlikely to be related to feeding. Instead, Czepiński suggests that an elongated snout may have been related to an elongated sinus, something which would have improved thermoregulation in Dromaeosaurs living in exposed, arid environments.

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Thursday 22 June 2023

Extreme marine heatwave in Baltic and around British and Irish coasts.

One of the most extreme marine heatwaves ever recorded is currently affecting the waters of the Baltic Sea and around the coasts of Britain and Ireland, according to a press release issued by the European Space Agency on 20 June 2023. The Baltic Sea is currently 8°C above the annual average for June, based upon data from the years 1981-2016, while the North Sea is currently 5°C above average, with the northwest coast of the UK between Durham and Aberdeen particularly affected.

Sea surface temperatures on 18 June 2023, relative to average June temperatures for the period 1981-2016. European Space Agency.

Marine heatwaves tend to be closely linked to other extreme weather events, typically causing these to be longer and more intense, with the two systems potentially creating a feedback loop in which each system intensifies the other. They are also often associated with mass deaths of Fish and other marine organisms, as warmer water is capable of retaining less dissolved oxygen than cool water.

This event is part of a trend of rising ocean and atmospheric temperatures, with the global average sea surface temperature in both April and May being the highest ever recorded in those months, according to the UK's Met Office, which has temperature records going back to 1850.

These high sea temperatures are linked to other extreme weather events which have been affecting the planet this year, including the fires sweeping across the forests of Canada, the heatwaves being experienced in many parts of the world, and a sharp reduction in the levels of sea ice around Antarctica.

June 2023 looks likely to be another record-breaking month, with the Copernicus Climate Change Service reporting that the first 11 days of the month each saw the hottest global average temperatures recorded for that date, and average global temperatures exceeding pre-industrial temperatures by 1.5°C, the first time this has ever happened in June. 

While the high temperatures in the North and Baltic seas are expected to be a temporary event, further high temperature events are expected in the coming months, driven by an emerging El Niño system in the South Pacific, with predictions currently indicating that 2024 will be the hottest year ever recorded.

El Niño is the warm phase of a long-term climatic oscillation affecting the southern Pacific, which can influence the climate around the world. The onset of El Niño conditions is marked by a sharp rise in temperature and pressure over the southern Indian Ocean, which then moves eastward over the southern Pacific. This pulls rainfall with it, leading to higher rainfall over the Pacific and lower rainfall over South Asia. This reduced rainfall during the already hot and dry summer leads to soaring temperatures in southern Asia, followed by a rise in rainfall that often causes flooding in the Americas and sometimes Africa. Worryingly climatic predictions for the next century suggest that global warming could lead to more frequent and severe El Niño conditions, extreme weather conditions a common occurrence.

Movements of air masses and changes in precipitation in an El Niño weather system. Fiona Martin/NOAA.

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Wednesday 21 June 2023

Evidence from Tam Pà Ling in northern Laos suggests Modern Humans reached Southeast Asia by 86 000-68 000 years ago.

Both genetic and fossil evidence suggests that Modern Humans emerged in Africa about 300 000 years ago. The timing of subsequent dispersals into Eurasia, however, is much less well defined, with numerous models having emerged, which nevertheless can be split into two broad groups; an early dispersal during Marine Isotope Stage 5 (roughly 130 000-80 000 years ago), and a late dispersal, after Marine Isotope Stage 5. Most genetic evidence supports the ancestors of all modern non-African populations having left the continent between 50 000 and 60 000 years ago, and subsequently diverged from one-another, with some groups moving east into Asia and others west into Europe. There is, however, some genetic evidence supporting the idea that modern Australasians are at least partly descendent from a Modern Human population which left Africa earlier, although the DNA of this group makes up less than 1% of that of modern Austrolasian populations.

A number of sites in the Middle East and around the eastern Mediterranean Basin have yielded fossils considered to be Modern Humans, dating to between 210 000 and 90 000 years ago, supporting the idea of an early dispersal at least a small way out of Africa. There are also a number of fossils from China, which have been considered to Modern Humans between 127 000 and 70 000 years old, although recent re-examination of these has shown that all suffer with problems with their dating and/or their assignment to Modern Humans. Further south, material attributed to Modern Humans at Lida Ajur in Sumatra has been dated to 73 000-63 000 years before the present, and at Tam Pà Ling in northern Laos has been dated to 70 000-46 000 years before the present, while Madjedbebe, the oldest archaeological site in Australia (which only Modern Humans are thought to have reached), has been dated to 65 000 years before the present. It these findings are correct, then they apparently represent an older Human excursion into Southeast Asia and beyond, possibly by a group with no living ancestors.

In a paper published in the journal Nature Communications on 13 June 2023, a team of archaeologists led by Sarah Freidline of the Department of Anthropology at the University of Central Florida, and the Department of Human Origins at the Max Planck Institute for Evolutionary Anthropology, describe new fossil  material from Tam Pà Ling site, and provide an updated chronology for the site. 

The Tam Pà Ling site was discovered in 2009, when a partial cranium (TPL 1) was unearthed in a cave on the Pà Hang karstic tower, on the southeasterd flank of P’ou Loi Mountain, in Houaphanh Province, northeastern Laos. Further excavations yielded two mandibles (TPL 2 & TPL 3), a rib (TPL 4), a phalanx (TPL 5), and most recently a partial frontal bone (TPL 6) and tibia (TPL 7), which Freidline et al. describe for the first time. 

Photograph of the TPL 6 frontal bone. (a) Anterior view of the left superciliary arch and supraorbital margin, and portions of the frontal squama and temporal line; (b) endocranial surface including some of the left orbital plate and frontal crest; (c) left lateral view. Freidline et al. (2023).

A combination of radiocarbon and uranium series dating has been used to date the previous finds from Tam Pà Ling, establishing a chronological sequence in which the first discovered skull (TPL 1) and mandible (TPL 2), both from the upper 25 cm of sediment, are about 46 000-years-old. Two soil samples collected from depths of 4.0 m and 5.0 m yielded dates of 48 000 years before the present. This short time interval/large increase in depth combination has caused questions to be asked about the accuracy of the dating methods used.

Sedimentation in the Tam Pà Ling cave is thought to have been linked to the annual monsoon cycle, with contiguous fine-grained layers across the site and no sign of secondary disturbance. The cave is thought to have opened gradually, during a period of drier conditions during which slabs of limestone fell from the cave roof, and the fine sediments being deposited onto these. The South Asian Monsoon is believed to have been continuous since Marine Isotope Stage 5, giving a minimum age for this dry period. Freidline et al. used a combination of dating techniques to obtain new dates for strata below 5.0 m within Tam Pà Ling cave, extending the age range to 7.0 m and an age of 86 000 years.

Stratigraphic sections of the main excavation (trench 3) at Tam Pà Ling. Profile 1 on the right is located at the base of the slope directly facing the entrance of the cave, and Profile 2, which is about 5 m adjacent to the east wall. Freidline et al. (2023).

Next, Freidline et al. carried out a morphometric analysis, comparing the Tam Pà Ling fossils to similar bones from a selection of other Humans and Hominins. 

TPL 6 is a partial left frontal bone that is broken at one-third of its total length and shows a fracture on its upper right side. A principal component analysis of its shape placed it firmly among Modern Human specimens from the Holocene and Late Pleistocene, including the Minatogawa individuals from Okinawa, Japan, which are dated to between 22 000 and 20 000 years ago, the Zhoukoudian Upper Cave individuals, from Beijing, China, dated to between 20 000 and 10 000 years ago, and the Wadjak (37 000-28 000-years-old), and Lake Mungo individuals (about 40 000 years old) of Australia, the  Salkhit individual (34 950-33 900-years-old) from Mongolia, and Holocene Individuals from Southeast Asia.

The previously described skull, TPL 1, is larger and more robust that TPL 6, but also plots with Late Pleistocene and Holocene Modern Humans. This more complete skull has a maxilla (upper jaw), a highly distinctive feature for separating Neanderthals, early Modern Humans, and later Modern Humans, with this feature clearly grouping with later Modern Humans such as Liujiang Man, from Guangxi in China, dated to between 159 000 and 60 000 years before the present (although these dates have been questioned), the Zhoukoudian Upper Cave individuals, and Laetoli Hominin 18, about 120 000-years-old from Kenya. The subnasal region of this skull is sloping and its palate broad, also Modern Human traits, with the shape of these features placing TPL 1 close to the Qafzeh 6 individual, about 100 000-years old, from Israel, Liujiang Man, and a number of Late Pleistocene and Holocene specimens. Other features of this skull fall within the overlap of early and later Modern Human morphologies.

The first of the two isolated mandibles found at Tam Pà Ling cave, TPL 2, was found to  map with Late Pleistocene and Holocene Modern Humans, being closest to the Tianyuandong individual, from Zhoukoudian and dated to between 42 000 and 39 000 years before the present. and the Tam Hang South individuals, from northern Laos and dated to about 15 700 years before the present.

The second isolated mandible, TPL 3 has a pronounced chin (a feature unique to Modern Humans), and is morphologically most similar to Late Pleistocene Humans, such as the Zhoukoudian Upper Cave individuals, and the Minatogawa individuals.

Freidline et al.'s new data extends the known Human presence at Tam Pà Ling cave 10 000 years further into the past, increasing the known period of residence to about 56 000 years. The new specimens, frontal TPL 6 and tibia TPL7, indicate that Modern Humans have been present in Southeast Asia for at least 68 000 years. These skeletons are of a gracile (slender) type, inconsistent with more archaic Human types, though it is unclear if their ancestors were recent arrivals from Africa or the Middle East, or were part of an unknown local population. The earliest known Modern Humans in Asia are found at Misliya Cave in Israel, and are dated to between 194 000 and 179 000 years before the present, with a number of slightly younger sites known from elsewhere in the Middle East, but the main Modern Human expansion into Asia seems not to have happened till about 65 000-45 000 years ago, when almost all non-African populations rapidly distributed across the Eurasian landmass. The oldest known Human genomes all date to between 45 000 and 35 000 years before the present. Available genetic data from Southeast Asia is much more recent, but shows that a hunter-gatherer population was largely replaced by an incoming farming population about 4000 years ago, although both of these populations seem to have been part of the rapid expansion from Africa 45 000-35 000 years ago. The later fossils from Tam Pà Ling cave fall within the range of this rapid expansion phase, but the new material, TPL 6 and TPL 7, are much older, dated to between 73 000 and 67 000 years before the present. This raises two possibilities; either the Tam Pà Ling fossils represent an older, Human dispersal into Southeast Asia, which has not contributed to the DNA of living Humans, or they represent part of an older successful Human migration into Asia, which has contributed to the DNA of living Humans, but which has not previously been identified. Unfortunately, attempts to recover DNA from the molars of TPL 1 and TPL 3 were unsuccessful, leaving the question unanswered at this time.

Morphometric analysis of the specimens, identifies them firmly as Modern Humans, being close in form to a number of Late Pleistocene individuals from East Asia, notably Zhoukoudian Upper Cave 101, from Beijing (China), Minatogawa 2, from Okinawa (Japan), Liujiang Man, from Gunagxi (China), Tabon Man, from Palawan (Philippins), and Tianyuandong 1, also from Beijing. The Tam Pà Ling individuals show quite a lot of variation, something previously recorded in the Zhoukoudian Upper Cave and Minatogawa populations, and supporting the hypothesis that these Late Pleistocene populations were quite heterogeneous. The frontal bone TPL 6 and mandible TPL 2 are notably slender, more so than any other specimens in the database, with the exception of the (much smaller) Homo floriensis fossils. The partial cranium, TPL 1, and second mandible, TPL 3, are more robust, falling within the general range of Late Pleistocene populations. Curiously, the later fossils appear more robust than the gracile early frontal TPL 6, against a general tendency for more modern Homo sapiens to be more gracile, while more archaic forms are more robust. If their is a line of decent through these fossils, then this suggests that the more robust traits were acquired locally through genetic drift or as an adaptation to local conditions, challenging the assumption made in other parts of the Eurasia that the appearance of more robust features is a sign of interbreeding with more archaic populations.

The TPL 6 frontal is closest in form to Minatogawa 2, another frontal from Okinawa in Japan, dated to about 20 000 years before the present. Of the three sets of remains at Minatogawa, the more complete skeleton, Minatogawa 1, is more robust, and considered to be male, while the two more fragmentary sets of remains, frontal Minatogawa 2 and mandible Minatogawa 3, are more gracile and thought to be female. Collectively, these individuals have been suggested to be closer to southern Australo-Melanesian populations than to more northern, Asian populations, along with other fossils from Liujiang, in Guangxi, South China, Niah Cave, in Sarawak, Malaysian Borneo, and Wadjak, East Java. The differences in size and robustness between TPL 1 and TPL 6 are similar to those between Minatogawa 1 and Minatogawa 2, though while the latter two are thought to be roughly contemporary, TPL 1 and TPL 6 are thought to be separated by about 30 000 years. The differences between the remains could, therefore, represent sexual dimorphism, changes in the stature of the population over time, or interbreeding with members of a more robust Human population. It is also possible that the assessment of TPL 6 as an adult is incorrect, and that this individual was in fact an adolescent member of a population with a slightly different development than living Humans. Nevertheless, Freidline et al. believe that the similarity of TPL 6 to later remains from Tam Pà Ling combined with the absence of any evidence of genetic continuity from Marine Isotope Stage 5 to the current day in Asia, means that the most likely explanation is that the Tam Pà Ling population comprises members of an earlier Human expansion into Southeast Asia, which has left no survivors. The oldest Human remains in Southeast Asia from which DNA has been extracted, the 7800-year-old remains from Pha Faen, also in Laos, produced no genetic evidence of descent from an earlier dispersal.

The second oldest fossil form Tam Pà Ling is the partial mandible, TPL 3, which has been dated to about 70 000 years before the present, and which a previous morphometric analysis placed close to Pleistocene Archaic Humans, including Neanderthals and Middle Pleistocene Hominins, but outside the range of even early Modern Humans. this was due to a wide bi-mental breadth (i.e. the breadth of the front of the jaw), which is in turn associated with a wide ramus (the hinge which connects the lower jaw to the skull), a feature associated with Archaic Humans. However, TPL 3 has a well-developed chin, a feature otherwise exclusively associated with Modern Humans.

The Zhiren 3 mandibular corpus, from Guangxi in South China, which has been dated to about 100 000 years ago (although this date has recently been challenged), also has a combination of a large width and a chin (albeit less well developed than in TPL 3), combined with an apparently modern dentition. This specimen has been suggested to possibly represent a hybridization between early dispersing Modern Humans and a local Archaic Human population. Freidline et al.'s study suggests that there is a considerable overlap in shape between the anterior symphysis of the mandible in Modern Humans and Neanderthals, while other Archaic Humans, including Homo erectus, Homo floriensis, and Denisovans, have more distinct shapes. Zhiren 3 is more archaic in its structure than TPL 3, but both are decidedly more modern than the Denisovan Xiahe mandible, which is very robust, lacks a chin, and has a receding symphysis. Neither Zhiren 3 nor TPL 3 show any affinity to the Xiahe mandible; both are more similar to the mosaic structures of early Modern Humans from Africa. Zhiren 3 appears most similar to specimens from Minatogawa, Zhoukoudian Upper Cave, and Border Cave in South Africa. It is also small, a feature shared with the Minatogawa, Zhoukoudian Upper Cave, Border Cave, and Tam Pà Ling remains, as well as the Klasies River Mouth remains (also South Africa). This suggests that Zhiren 3 could either represent a member of an early, unsuccessful dispersal of Modern Humans into Asia, or one of the earliest members of a late dispersal.

The TPL 2 mandible is younger, smaller, and in some ways morphologically more modern than TPL 3. Despite this it has a notably robust lateral corpus, more so than seen in Homo erectus skulls, although all other features point to it being a Modern Human jaw. Notably, TPL 2 is small, smaller than any other apparently adult mandible in Freidline et al.'s study, with the exception of one assigned to Homo floriensis. Morphologically, TPL 2 is closest to mandibles from the Tam Hang Rockshelter (northern Laos) thought to be from young adult women, and dated to about 15 700 years ago. These individuals are estimated to have been between 140 cm and 153 cm tall, which is short by modern Western standards, but not exceptionally so, and is also comparable to the Minatogawa individuals, and many Holocene populations from East and Southeast Asia. Notably, among living and recent Humans, populations with short statures are often found in tropical forests, and the Late Pleistocene environment at Tam Pà Ling has been reconstructed as a tropical forest, much as it is today. Furthermore, a study of carbon isotopes from two of the teeth of TPL 1 suggested that that individual had forest-associated diet.

TPL 1 was found in the same layer as TPL 2, with both being dated to between 52 000 and 40 000 years ago. TPL 1 resembles other Late Pleistocene Modern Humans from Asia, notably the Zhoukoudian Upper Cave and Palawan individuals. The Zhoukoudian Upper Cave individuals have been suggested to show affinities with Upper Palaeolithic individuals from Europe, and earlier Modern Humans from Africa and the Levant, and appear to have retained some archaic traits rather than acquired them by interbreeding with a more archaic population.

The fossils from Tam Pà Ling give an insight into Human variability during the Late Pleistocene of Southeast Asia. The site shows a Human presence in the region between 86 000 and 42 000 years ago, including the oldest confidently assigned Modern Human cranial remains in Southeast Asia. The TPL 6 frontal bone shows a dispersal into Southeast Asia by a Modern Human population by 70 000 years ago, although it is by no means certain that this population has living descendants. This cranial has a remarkably slender form, making it highly probable that it is a representative of a group migrating into the area for the first time, and highly unlikely that it is descended from or admixed with a local Archaic Human population. These fossils add to our understanding of a region which appears to have had a rich and diverse Human and Hominin population during the Middle and Late Pleistocene, including Homo erectus, Homo floriensis, Homo luzonensis, Denisovans, and Modern Humans.

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