Thursday, 20 January 2022

Tonga devastated by tsunami following eruption on the Hunga Ha'apai volcano

Three people, including a British citizen, have been confirmed dead and many more are missing following a tsunani that swept across the island nation of Tonga on Saturday 15 January 2022, following an eruption on the Hunga Ha'apai volcano. The volcano, which is usually underwater and is about 65 km to the north of the nation's capital, Nukuʻalofa, began erupting on 20 December 2021, producing a small island by the first week of January. However, on 15 January the centre of this island sank abruptly beneath the sea about two hours before the eruption. Vulcanologists have hypothesised that the eruption was caused by the collapse of a magma chamber, allowing seawater to come into contact with the hot magma, and triggering a phreatic explosion (rapid expansion of gas as a large volume of water turns to vapour more-or-less instantly).

Devastation on Tonga caused by the 15 January 2022 tsunami. Consulate of the Kingdom of Tonga.

Following the explosion a huge wave swept across the islands of Tonga, then out across the Pacific Ocean, reaching Australia and New Zealand in four hours, Japan in eight hours, California in ten hours and Alaska in eleven. Ths islands of Tonga suffered extensive damage, which destroyed much of the nation's communications infrastructure, with the extent of the destruction only becoming clear as ships from the New Zealand Navy reached the area several days later. As well as the obvious problems caused by the devastation of the nation's infrastructure, much of the area has been covered by sulphur-rich volcanic dust, which can be harmful if breathed in, and can react with fresh water to form sulphuric acid, threatening drinking water supplies. 

How a submarine phraetic explosion can cause a tsunami. BBC.

Hunga Ha’apai lies on the Tonga/Kermadec Ridge, and is fed by the subduction of the Pacific Plate beneath the Australian Plate along the Kermadec/Tonga Trench. As the Pacific Plate sinks into the Earth, it is warmed by the heat from the planets interior. This leads to partial melting of the Pacific Plate, with some of the melted material rising through the overlying Australian Plate as magma, fuelling the volcanos of the Kermadec/Tonga Ridge.

Diagram showing subduction along the Tonga Trench, and how this feeds the volcanoes of the Tonga Volcanic Arc. York University.

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Magnitude 5.3 Earthquake off the Athos Peninsula, Greece.

The United States Geological Survey recorded a Magnitude 5.3 Earthquake at a depth of 9.3 km, beneath the Aegean Sea, off the south coast of the Athos Peninsula in northeast Greece, slightly before 1.50 pm local time (slightly before 11.50 am GMT) on Sunday 16 January 2022. No damage or injuries have been reported following this event, but people have reported feeling the event from much of Chalkidiki and Thessaloniki. 

The approximate location of the 16 January 2022 Greek Earthquake. USGS.

The Aegean Sea is underlain by the Aegean Sea Plate, a small tectonic plate caught between the African Plate to the south, the Anatolian Plate to the east and the Eurasian Plate to the northwest. The Anatolian Plate is being pushed to the west by the northward movement of the Arabian Plate to the east, pushing the Aegean Plate south and west into collision with the northward moving African Plate. Part of the African Plate is being subducted beneath the Aegean Plate along the Hellenic Trench, which runs to the south of the Greek Islands from Cyprus to Crete then northwest under the Ionian sea parallel to the Peloponnesian Coast. This is not a smooth process, as the plates frequently stick together then break apart once the pressure has built up sufficiently, leading to (fairly frequent) Earthquakes.
Simplified map of the plate movements of the eastern Mediterranean. Univeriteit Utrecht.

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Wednesday, 19 January 2022

Analysing silver from Phoenician hoards.

From about 4000 BC onwards the use of silver became widespread in the ancient world. This was obtained by smelting lead-ores in a furnace, and then cupellatiting (oxidising) the resultant metal to separate silver and gold. Lead ores, generally galena (lead sulphate) and cerussite (lead carbonate), were typically mined by a deep pit method, digging vertically down to a seem then following it horizontally. Silver  was important to many ancient peoples, among whom were the Phoenicians, who built city states such as Tyre, Sidon and Byblos, ‘Akko and Dor in Lebanon and on the northern shores of the southern Levant during the Iron Age, roughly from the eleventh century BC onwards, and who travelled widely on trading expeditions, bringing innovations such as the alphabet, murex-based purple dyeing and masterful craftsmanship to the western Mediterranean, where they established colonies in North Africa, Sardinia and Iberia. In the ninth century BC the Phoenicians began to exploit jarosite (potassium-iron sulphate) ores in Iberia, from which silver was also extracted as a biproduct.

Cupellation remained the most common way to obtain silver throughout the classical period, producing silver that still contains small amounts of lead. This is useful to modern archaeologists, who can use lead-isotope analysis to determine the source of silver. Other elements tend to be largely purged from the silver by this method, although gold and bismuth isotopes have sometimes been used to determine the origin of silver. 

Silverware was widely used as a trade commodity in the Near East before the adoption of coinage, with more than 40 silver hoards dating to between 2000 and 600 BC having been unearthed in the southern Levant.

In a paper published in the journal Applied Sciences on 12 January 2022, Tzilla Eshel of the Zinman Institute of Archaeology and School of Archaeology and Maritime Cultures at the University of Haifa, Ofir Tirosh of the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem, Naama Yahalom-Mack of the Institute of Archaeology at the Hebrew University of Jerusalem, Ayelet Gilboa, also of the Zinman Institute of Archaeology and School of Archaeology and Maritime Cultures at the University of Haifa, and Yigal Erel, also of the Fredy and Nadine Herrmann Institute of Earth Sciences at the Hebrew University of Jerusalem, present the results of a study which used lead and silver isotopes in silver artefacts to show changes in the source of silver reaching the southern Levant over a period of almost 1500 years, spanning the Bronze and Iron ages.

Map of the Southern Levant showing sites with Bronze and Iron Age silver hoards. Svetlana Matskevich in Eschel et al. (2022).

Examination of the lead isotope content of 250 silver items from 22 hoards suggests that Middle Bronze Age items (dating from between 2000 and 1550 BC), were made using silver from Anatolia and the Aegean. In the Late Bronze Age (from about 1550 to about 1250 BC), a time when gold probably replaced silver as the main trading currency, silver from the mines of Laurion (about 50 km south of Athens) begins to appear. During the Early Iron Age (roughly 1200 to 950 BC), following the end-Bronze Age collapse, silver appears to have been rare in the region, and was frequently adulterated with high lead content copper, making it hard to identify the origin of the artefacts. From about 950 BC onwards, Phoenicians revived the trade in silver, importing the metal from the Taurus mountains in Anatolia, and from Iglesiente in south-west Sardinia and later from the Pyrite Belt in Iberia, then from 630 BC onwards Greek traders slowly supplanted the Phoenicians, bringing in silver and copper from Laurion and Siphnos in the Aegean. 

This fits well with the previous understanding of the trade in sliver in the ancient Mediterranean Basin, but only gives a broad view of the geographic areas from which silver was being imported to the region; it does not shed any light on development of silver production practices and the exploitation of new ores. For this purpose, Eschel et al. turned to silver isotopes, which have a number of advantages in the tracing of the origin of ores. Silver will fractionate isotopically during supergene weathering; that is to say weathering caused by oxidation of minerals as water percolates through the rock in near surface environments, as well as during the formation of salts and sulphosalts. The upshot of this is that the proportion of different silver isotopes can vary even within different parts of the same mine, potentially giving a very high resolution way of determining the origin of the metal, and at very least, it is usually possible to tell the difference between silver minerals that formed in deep or shallow environments, with those that formed hydrothermally in shallow environments typically having a higher proportion of the heavier isotope silver¹⁰⁹ than those from deeper environments. 

This method has been applied previously to Hellenistic, Roman, and Medieval coins with some success, but not to pre-coinage silver hoards. As well as studying the origin of silver in Bronze and Iron Age hoards, Eschel et al. were able to study how the way in which the silver was preserved altered the isotopic ratio of the metal. It has previously been shown that the patterna on silver coins is isotopically lighter than the coins themselves, as the lighter isotope silver¹⁰⁷ is preferentially consumed in the making of silver sulphates. The silver from the Levantine hoards was stored in different ways, with some hoards stored in ceramic vessels, some in cloth bundles, and some in both, offering different levels of protection against intrusions by ground-water, which will tend to re-mineralise silver, altering its isotopic composition.

Silver hoards analysed in the study: (a) silver from the Shiloh hoard (without pendant), courtesy of the Israel Museum, Jerusalem. (b) Silver from hoard Tell el-‘Ajjul 1312, courtesy of the Israel Antiquities Authority. (c) The Dor silver hoard, the Israel Museum and the Tel Dor Expedition. (d) The ‘Akko silver hoard. (e) The ‘Ein Hofez silver hoard image courtesy of the Israel Antiquities Authority. (f) The ‘Arad silver hoard, courtesy of the Institute of Archaeology at Tel Aviv University. (g) Selected items from ‘Ein Gedi hoard, the Israel Museum, Jerusalem. Eschel et al. (2022).

Eschel et al. chose 45 silver artefacts for silver isotope analysis, all of known chemical and lead isotopic compositions and generally not suspected to be alloyed or mixed with metals from different sources. 

The oldest of these items came from the Middle/Late Bronze Age transitional period (roughly 1650-1500 BC) sites at Shiloh on the West Bank and Tell el-‘Ajjul in the Gaza Strip. The precise origin of these hoards is unclear, but both have jewelery with Anatolian motifs and lead isotopic analysis has suggested that the silver came from Anatolia or the Aegean. Both hoards were found wrapped in cloth bundles.

Silver from the Iron Age (roughly 950-700 BC) hoards at Dor, south of Haifa on Israel's Mediterranean coast, and ‘Akko in the coastal plain region of the Northern District of Israel, have been shown to come from Iglesiente, on southwest Sardinia, and have been associated with Phoenician trading in Anatolia and Sardinia in the Iron Age. The Dor hoard was found wrapped in a bundle, then placed within a ceramic vessel which was covered by a bowl, the 'Akko hoard was simply placed within a ceramic pot.

Silver items from the Iron Age (roughly 950-700 BC) hoards at ‘Ein Hofez inthe Carmel Mountains of northern Israel and 'Arad in the Southern District of Israel, on the border of the Negev and the Judean deserts have been shown to contain lead from Rio Tinto in Iberia, although this is only provides an approximate location for its origin, since jarosite ores from several parts of Iberia are known to have been brought to Rio Tinto for processing with lead. Other items from the ‘Ein Hofez hoard contain lead from Linares and other parts of Iberia, with one item coming from Anatolia. 

The Late Iron Age (roughly 630-586 BC) hoard from ‘Ein Gedi, in Israel west of the Dead Sea, near Masada and the Qumran Cave, contains silver placed unbundled within a cooking pot, covered by a ceramic lamp under the floor of a room. The lead in this silver indicates that it comes from Laurion in Greece, suggesting that it was brought to the area by a Greek trader.

Combining the silver and lead isotope analyses strongly suggests that the Phonicean hoards of Dor, ‘Akko, ‘Ein Hofez and Arad contain silver from Sardinia, Iberia and Anatolia, while the Late Iron Age hoard from ‘Ein Gedi contains Aegean silver, and the earlier, Bronze Age hoards of Shiloh and Tell el-‘Ajjul contain a mixture of Anatolian and Aegean silver. The isotopic ratios of the silver items from Phoenician hoards showed predominantly ratios consistent with having come from hypogene ores, that is to say ores that formed deep within the Earth, which had not undergone significant weathering related isotopic fractionation, whereas the isotopic ratios seen in the earlier Bronze Age and later Greek hoards showed more fractionation, probably indicating that they came from shallower ores which had undergone some surface weathering. 

While all the samples used were taken by drilling into the items to extract silver free from corrosion, some of the items still showed signs of sliver chloride formation at the level from which the sample was taken. This is symptomatic of corrosion through exposure to chlorine ions in groundwater, indicating that these samples were less protected from the environment than other samples. This was found in items from the hoards from Tell el-‘Ajjul, ‘Akko, and ‘Ein Hofez. The silver from Shiloh, Dor, ‘Arad and ‘Ein Gedi were apparently better protected. 

Based upon these findings, Eschel et al. were able to make the following observations. 

Hoards sealed in ceramic vessels were predicted to be best protected against contact with the soil and groundwater within it. The hoards from Dor (which was sealed in a vessel and bundled in cloth, and Ein ‘Gedi, which was sealed in a vessel but not bundled, showed no signs of corrosion, and therefore were apparently protected as expected.

Hoards wrapped tightly within cloth bundles were predicted to be less well protected against groundwater, though it was likely that the silver in the middle of the bundle would be protected somewhat by the silver around it. This would include the hoards at ‘Arad, which was tightly bundled and placed within a ceramic vessel, and which showed no signs of corrosion, and Shiloh, which was bundled but not placed within a vessel, where again no signs of corrosion were found.

Hoards placed within unsealed ceramic vessels were thought likely to be less well protected against groundwater. This included the hoards from ‘Ein Hofez and ‘Akko, both of which showed signs of corrosion.

Finally, silver which was neither bundled nor placed in a vessel was thought to be at the greatest risk of corrosion due to contact with the soil and groundwater. This was the case only with the hoard from Tell el-’Ajjul, which again showed signs of silver chloride formation.

The hoards from Tell el-‘Ajjul, ‘Akko, and ‘Ein Hofez all showed greater isotopic fractioning, which was taken as a sign of the silver in them having come from shallow ore sources, where this could occur prior to the silver being mined. Eschell et al. also note that the silver from these hoards also appeared to be less pure, and suggest that these combined may be a sign that they have been altered after deposition by their original owners, rather than evidence of a different mining origin or smelting technique to the other material.

Eschell et al.'s findings suggest that native silver (silver found in a pure state, which typically comes from deep, hypogene sources) was quite rare in the ancient world, and that most of the silver used came from shallow, supergene sources,

The Phoenicians are known to have brought silver to the Levan from the mid-10th century BC onwards, and from Iberia during the ninth and eighth centuries BC. It is unclear whether the Phoenicians themselves were the drivers of the improving metallurgical techniques being used in the areas where they traded, or whether they were just skilled traders able to aquire this silver and ship it across the Mediterranean. Anatolia is known to have been major centres of silver production from about the third millennium onwards, but the amount of silver being exported appears to have rapidly grown during the Phoenician era. Silver confidently assigned to a Sardinian origin is often found in Phoenician hoards, but no ancient mineworking have been discovered in Sardinia, so it is unclear when mining started there. Silver extracted in Iberia, in contrast, appears to have been exclusively developed by the Pheonicians, who targeted deep, low-lead ore bodies in the Iberian Pyritic Belt from about 800 BC onwards. The Romans began exporting silver from Iberia around 200 BC, but only targeted shallow ores with silver isotope fractionation, not the deep ores the Phoenicians were able to access.

The low levels of isotope fractionation seen in Phoenician sliver objects from Anatolia and Sardinia suggest that the Phoenicians were using the same deep-mining methods there in the tenth century BC, indicating that these people were more than talented sailors, but skilled workers in other fields, capable of transfering skills from one end of the Mediterranean to the other.

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Sunday, 16 January 2022

Pristimantis gretathunbergae: A new species of Rain Frog from Panama, named in honour of Swedish climate activist Greta Thunberg.

Tropical forests are noted for their high biodiversity and species richness, with a wide range of ecological variables which favour the emergence of numerous species with limited distributions among some groups of Animals and Plants. One such group are the Anurans (Frogs), of which very high species numbers are found in many tropical regions. One particularly notable group of Frogs are the Rain Frogs, Pristimantis spp., of the Caribbean and Central and South America. The genus Pristimantis currently contains at least 574 species (possibly the highest number of species in any Vertebrate genus), distributed primarily in Tropical Andes of Colombia, Ecuador, and Peru, yet is considered to be understudied, with many more species likely to exist (124 species have been described within the past decade), and many of the currently described species having uncertain relationships to other members of the group. The species richness within this genus is driven by its ability to breed away from water, enabling them to colonise environments closed to other Frogs, while the taxonomic uncertainty is caused by the high variability of many species, with members of different species often resembling one-another than they do members of their own species. This is slowly being unravelled with modern genetic methods, although this is showing an even greater diversity within the genus than previously supposed, apparently caused by a recent radiation event, resulting in the genus now comprising 7.4% of all known Anuran species, and 6.7% of all Lisamphibians.

In a paper published in he journal ZooKeys on 10 January 2022, a team of scientists led by Konrad Mebert of the Programa de Pós-graduação em Zoologia at the Universidade Estadual de Santa Cruz, Global Biology, and Los Naturalistas, describe a new species of Rain Frog from Panama.

The new species is named Pristimantis gretathunbergae, in honour of Swedish climate activist Greta Thunberg, for her 'authentic voice that exposes the motivations behind the diplomatic curtain of politicians and business stakeholders'. The species is described upon the basis of a series of specimens collected on the top of Cerro Chucantí in the Maje Mountains of Darién Province, Panama, though the species was later shown to be found across a wider area.

Colouration in life of specimens of Pristimantis gretathunbergae sp. nov. and Pristimantis cruentus from eastern Panama. (A) Holotype male (MHCH 3082), Cerro Chucantí. (B) Paratype female (SMF97520), Cerro Chucantí. (C) :eft, paratype female (MHCH 3081), right Pristimantis cruentus female (MHCH3034). (D) Female from Cerro Chucantí, not collected. (E) Female (MHCH3115) La Javillosa. (F) Female, Cerro La Javillosa, Ambroya, Maje Mountain Range (SMF97517). (G) Female (MHCH3079), Rio Tuquesa. Coloured lines point to some diagnostic characters as follow: red: blackish iris; yellow: single spine-like tubercle; turquoise: light-coloured upper lip; pink: cream, yellow to red groin. Mebert et al. (2022).

Pristimantis gretathunbergae has a slightly blotchy brown colouration, more notable on the darker upper surface than the paler lower side, this is accentuated by a scattering of tubercles on the dorsal surface. The tympanum (ear) is invisible, or at least hard to distinguish, the snout is short and slightly rounded, and the upper eyelid has a spine-like tubercle. Each vomer (bone in the roof of the mouth, behind the jaw, bears 5-10 teeth. The groin and inner thighs are white, yellow or orange-red, some with flecks matching the dorsal ground colour or red. The iris is black, though some individuals have a very dark red iris, or a black iris with red-golden speckling.

Habitat, mating, and parental care in females of Pristimantis gretathunbergae from Cerro Chucantí. (A) Habitat on Cerro Chucantí at about 1300 m above sealevel. (B) Understory Bromeliad with a Pristimantis gretathunbergae in situ (blue line) and zoomed in on inset (MHCH 3115). (C) Amplectant pair on axillary part of Bromeliad leaf (not collected). (D) Same female after amplexus guarding eggs. (E) Female of Pristimantis gretathunbergae taking care of its eggs with a male Pristimantis cruentus holding on the female in reverse position (not collected). (F) Female with eggs about to hatch, note the transparency of the egg membrane (not collected). Mebert et al. (2022).

Wider sampling, combined with genetic profiling of collected specimens, found that Pristimantis gretathunbergae is present across much of eastern Panama, and could potentially be present in adjacent areas of Colombia. The species was found in the Darien Mountains within Embera Comarca and the Maje Mountains within Darien and Panama Provinces, including the type locality at Cerro Chucantí. The species was also found to be present in parts of western Panama, including the Piedras-Pacora Mountains in Panama Province, and Cerro Bruja in Colon Province, both within the Chagres National Park. Beyond the Panama Canal Pristimantis gretathunbergae is present in the Altos del Maria region of the Gaita Hills in Panama Oeste Province, and in the region of El Cope within the Omar Torrijos National Park in Coclé Province.

Pristimantis gretathunbergae has been recorded at altitudes of between 718 and 1439 above sealevel, predominantly within montane forest (cloud forest consisting predominantly of trees covered with Moss and a large variety of understory and midstory Bromeliads). During the nights the Frogs were found from 50 cm to 3 m above the ground on tree bark and in the Bromeliad foliage; in the day they hid between Bromeliad leaves. In the rainy season the males make a sporadic 'chack' call. Females have been observed guarding clusters of eggs in Bromeliads and on Moss-covered tree branches. The species has not been observed eating, but other members of the genus Pristimantis feed primarily on small Arthropods, such as Ants, Orthopterans, and Spiders.

Despite its widespread distribution, Mebert et al, believe that Pristimantis gretathunbergae is likely to face decline of many populations due to habitat destruction caused by anthropogenic pressure. Only a few areas where the species is found are within National Parks or other protected areas, and the species is known only from patches of primary forest and slightly disturbed areas, many of which are surrounded by agriculture and pastures. The species is also found close to areas where Amphibian populations have been decimated by the Chytrid Fungus, Batrachochytrium dendrobatidis, which the species must also be presumed to be threatened by. For this reason, Mebert et al. recommend that Pristimantis gretathunbergae be classified as Vulnerable under the terms of the International Union for the Conservation of Nature’s Red List of Threatened Species

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Saturday, 15 January 2022

Neopagetopsis ionah: Vast nesting colony of Jonah's Icefish found in the Weddell Sea, AntLilian Boehringerarctica.

Crocodile Icefish, Channichtyidae, are highly specialised Perciform Fish found in the waters around Antarctica. They are sometimes known as White-blooded Icefish, as they lack haemoglobin; the cold waters around Antarctica being so saturated in oxygen that these Fish no not need a specialised means to transport it to their tissues (water is able to retain more free oxygen at lower temperatures). These Fish are known to nest in colonies, with a few tens of Fish typically building their nests together in a favoured spot.

In a paper published in the journal Current Biology on 13 January 2022, Autun Purser and Laura Hehemann of the Alfred Wegener Institute at the Helmholtz Centre for Polar and Marine Research, Lilian Boehringer, also of the Alfred Wegener Institute, and of Universität Bremen, Sandra Tippenhauer again of the Alfred Wegener Institute, Mia Wege of the Alfred Wegener Institute and the Mammal Research Institute at the University of Pretoria, Horst Bornemann, Santiago Pineda-Metz, Clara Flintrop, Florian Koch, and Hartmut Hellmer, again of the Alfred Wegener Institute, Patricia Burkhardt-Holm of the Programme Man-Society-Environment at the University of Basel, Markus Janout, again of the Alfred Wegener Institute, Ellen Werner of the HafenCity University Hamburg, Barbara Glemser of Universität Bremen and the Max Planck Institute for Marine Microbiology, Jenna Balaguer, also of the Alfred Wegener Institute, Andreas Rogge of the Alfred Wegener Institute and the Institute for Ecosystem Research at Kiel University, Moritz Holtappels, once again of the Alfred Wegener Institute, and Frank Wenzhoefer of the Alfred Wegener Institute, the Max Planck Institute for Marine Microbiology, and the Department of Biology at the University of Southern Denmark, describe a vast colony of Channichtyida Icefish numbering tens of thousands of nests, discovered on the eastern flank of the Filchner Trough within the Weddell Sea.

The colony is of Jonah's Icefish, Neopagetopsis ionah, a benthopelagic species (species that lives just above thes seafloor) known from the Weddell Sea, Kapp Norvegica, Halley Bay, Vahsel Bay, the Antarctic Peninsula, and the Ross Sea, with a pelagic juvenile stage (juvenile stage that lives in the water column), which has been reported from the Weddell Sea, South Shetland Islands, and McMurdo Sound. Purser et al. report a colony of about 16 160 Icefish covering an area of about 45 600 m², which was discovered by the Ocean Floor Observation and Bathymetry System, towed camera platform deployed by the RV Polarstern.

Seafloor images of the most expansive Icefish breeding colony discovered to date (A) Left: Neopagetopsis ionah in an active Fish nest on the eastern flank of the Filchner Trough, 497-m depth. Each 15-cm-deep nest has been shaped by removing the fine sediment and exposing numerous small stones, upon which the light blue eggs are laid. Right: dense array of active Fish nests. (B) Two Fish nests, spaced 15 cm from each other, imaged from the active nesting area of the Filchner Trough eastern flank. The left nest is in active use, whereas the right nest contains the remains of dead Fish only. [A] Surrounding seafloor with thin layer of phytodetritus visible. [B] Faint rim of very fine black rocky material marks the extreme extent of the active Fish nest. [C] A ring of uniform grey upper sediments cut through by the nest structure forms the upper sides of each active nest. [D] A ring of slightly coarser black rock fragments makes up the lower flanks of the active Fish nest. [E] The base of the active Fish nest is made up of numerous rock fragments from a range of lithologies, presumably carried to the area by ice rafting from a range of Antarctic source lithologies. [F] Neopagetopsis ionah eggs cover much of the rocky nest base layer. [G[ Adult Fish commonly observed centrally placed within the nest. [H[ Nest containing dead Fish in various states of decay. [I] Recently deceased Fish being fed on by a Starfish. [J] At least three additional adult Fish carcasses covered with Bacterial mat(s). [K] Numerous Ophiuroids in highest abundance within and surrounding nests containing dead Fish. [L] Small Fish, potentially a scavenger. [M] Pycnogonid of 20-cm diameter, commonly observed in the vicinity of active nests. In this image, several Neopagetopsis ionah eggs seem to be visible below the Pycnogonid. (C) Unused nest arrays on the Filchner Sill and elsewhere in the Filchner Trough. [1] Station 26_7; various sessile suspension feeders occupy the center of nests. [2] Station 30_7; small sessile fauna use small rocks within the unoccupied nest as a substrate on which to settle. [3] Station 54_1; some infilling of the center of the unused nest with sediment and hydrodynamically trapped detritus. [4] Station 72_8; softer sediments render the edges of the unused nests less distinct, though the central nest floor is abundant with larger stone fragments. Purser et al. (2022).

The deepest parts of the colony were at a depth of 535 m, the shallowest 420 m. Nests were of a fairly uniform size, about 75 cm wide and 15 cm deep, and were a minimum of 25 cm from their neighbours, even in the most densely populated parts of the colony. Of the total 16 160 nests directly imaged by camera, 12 020 (79%) were currently occupied (defined by the presence of either a Fish and eggs or just eggs). Another 15% of the nests were empty, 9% contained at least one dead Fish, and 2% contained Fish but not eggs.

The nests were bowl shaped and comprised a ring of stones, with a base of fine-grained material. The Icefish kept these areas free of any debris, as well as guarding the eggs against predators and fanning them to ensure a good supply of oxygen. The outer ring of stones may serve to prevent the eggs being blown away by this fanning action. 

In addition to the occupied area, further, more widely spaced nests could be observed in the area around the colony, all empty and all less than 100 m deeper than the deepest colony nests or less than 100 m shallower than the shallowest colony nests, though the edge of the colony is quite abrupt in both directions, suggesting that the edge of the environmentally suitable zone was also abrupt, but had moved in the past, presumably in response to climate variability.

Throughout the period of the study the seafloor temperature remained between -1.0°C and 0°C. This is typical of the modified Warm Deep Water current, which flows upward onto the Weddell Shelf, through the Filchner Trough and other similar troughs. These waters have an oxygen saturation of 65-75%, which is lower than the surrounding waters, which have an average oxygen saturation of 80%, and a temperature of -2.0°C to -1.5°C, supporting the idea that the eggs need very specific environmental conditions to survive.

Chlorophyll a levels and primary production appeared to be higher above the colony area, and areas with unoccupied nests, than the surrounding waters, with the highest concentrations of particles around the modified Warm Deep Water current-High-Salinity Shelf Water interface. The majority of these particles were below 300 μm in equivalent spherical diameter, with the density of particles increasing at night, which is probably indicative of zooplankton migrating into the photic zone to feed at night. This would suggest a potential food source, both for the nesting Icefish and for their larvae, known to migrate into overlying waters following hatching.

The benthic invertebrate community around the colony was both low density and low diversity; dominated by Brittle Stars and Star Fish, and with some conspicuously large Pycnogonids ('Sea Spiders'), which were often in excess of 15 cm in diameter, and were often seen near eggs or egg husks outside of Fish nests, potentially washed out by currents or Fish movements. This is a distinctive fauna, and suggests that the Icefish are modifying the environment sufficiently to shape the local invertebrate community.

The carcasses of the Icefish appeared to provide an important food source for invertebrates. As many as four dead Fish were seen in a single nest, which since no more than two live Fish were ever seen in association with a single nest, suggest that the dead Fish, which are close to neutrally bouyant, can accumulate within nests. Brittle Stars, Starfish, Octopus, and various Fish species opportunistically feeding were observed around dead Icefish. It is likely that the breeding season takes a high toll on Icefish, as several months of tending eggs is apparently exhausting.

The area around the colony is also known to be home to a group of Weddell Seals, Leptonychotes weddelli, some of which have been tracked by satellite for long periods of time. These Seals are known to dive deeply looking for food, and to take Jonah's Icefish, suggesting that the colony may be serving as a regular food source for them. Other Seal species, such as Elephant Seals, Mirounga leonina, have also been seen in the area.

Abandoned nests outside the colony also appeared to play a significant ecological role, being colonised by sessile organisms, such as tube dwelling Polychaetes, colonial bryozoans, and Sponges. These sites also appeared to be hydrodynamically trapping phytodetritus, which would make them an excellent site for sessile organisms.

Because these observations were based upon a single observing season, a number of important questions about the breeding behaviour of the Jonah's Icefish remain unanswered. It is unclear how often the Fish build new nests; do they reuse them each year, or construct new ones? Do the Fish remain with the eggs from when they are laid till when they hatch, or do they leave to forage? How do the predators of both the Fish and their eggs behave around the colony? How do the hatchling Fish behave when they emerge? How do the Fish behave during the mating and spawning seasons? To what extent is the colony a food source for Weddell Seals, and how do they exploit it? In order to address these problems two LED light-and-camera systems were positioned 3 m above the seafloor and left collecting data, with the plan being to return and collect them in 2023 or 2024.

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Tsunami warning issued across the Kingdom of Tonga following an eruption on the Hunga Ha'apai underwater volcano.

A tsunami warning was issued to people living in coastal areas on all the islands of the Kingdom of Tonga on Thursday 13 January 2022, following an eruption on the Hunga Ha'apai underwater volcano, which produced a column of gas and ash about 20 km high. In the event, the largest wave observed was only about 30 cm high, which reached Nuku'alofa on the north coast of the island of Tongatapu at about 12.30 pm local time. The volcano began its current eruptive cycle on 20 December 2021, prior to which it had been inactive since 2015.

GOES-17 satellite imigary of the 13 January 2022 Hunga Ha'apai underwater volcano eruption. University of Wisconsin Madison/Space Science and Engineering Center/CIMMS Satelite Blog.

Hunga Ha’apai lies on the Tonga/Kermadec Ridge, and is fed by the subduction of the Pacific Plate beneath the Australian Plate along the Kermadec/Tonga Trench. As the Pacific Plate sinks into the Earth, it is warmed by the heat from the planets interior. This leads to partial melting of the Pacific Plate, with some of the melted material rising through the overlying Australian Plate as magma, fuelling the volcanos of the Kermadec/Tonga Ridge.

Diagram showing subduction along the Tonga Trench, and how this feeds the volcanoes of the Tonga Volcanic Arc. York University.

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Friday, 14 January 2022

Asteroid 2022 AY5 passes the Earth.

Asteroid 2022 AY5 passed by the Earth at a distance of about 101 700 km (0.27 times the average distance between the Earth and the Moon, or 0.07% of the distance between the Earth and the Sun), at about 10.35 am GMT on Monday 10 January 2022. There was no danger of the asteroid hitting us, though were it to do so it would not have presented a significant threat. 2022 AY5 has an estimated equivalent diameter of 3-9 m (i.e. it is estimated that a spherical object with the same volume would be 3-9 m in diameter), and an object of this size would be expected to explode in an airburst (an explosion caused by superheating from friction with the Earth's atmosphere, which is greater than that caused by simply falling, due to the orbital momentum of the asteroid) more than 33 km above the ground, with only fragmentary material reaching the Earth's surface.

The relative positions of 2022 AY5 and the Earth on at midnight GMT on 23 December 2021. JPL Small Body Database.

2022 AY5 was discovered on 11 January 2022 (the day after its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2022 AY5 implies that it was the 149th asteroid (object Y5 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 25, with a number added to the end each time the alphabet is ended so that A = 1, A1 = 26, A2 = 51, etc., which means that Y5 implies the 149th asteroid (G5 = (25 x 5) + 24 = 149) discovered in the first half of December 2022 (period 2022 A - the year being split into 24 half-months represented by the letters A-Y, with I being excluded).

The orbit and current position of 2022 AY5. The Sky Live 3D Solar System Simulator.

2022 AY5 has a 721 day (1.97 year) orbital period, with an elliptical orbit tilted at an angle of 0.83° to the plain of the Solar System which takes in to 0.90 AU from the Sun (90% of the distance at which the Earth orbits the Sun) and out to 2.25 AU (225% of the distance at which the Earth orbits the Sun, and more than the distance at which the planet Mars orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that Asteroid 2022 AY5 has occasional close encounters with the Earth, with the most recent having happened in September 2021, and the next predicted for November 2023. The asteroid also has occasional close encounters with the planet Mars, with the last thought to have happened in July 2003, and the next predicted in June 2037.

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