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An isolated mildly depleted mantle source for the north atlantic craton
No full textGeneration of continental crust during early Earth was a vital step towards stabilizing the cratonic lithosphere. How and when this happened is, however, still poorly understood. Radiogenic isotope data from the oldest crust, and minerals therein, provide a unique insight into the timing and processes that operated during Earth’s earliest evolution. Using combined zircon U-Pb, O and Lu-Hf isotope data from a glacial stream-sediment within the Isukasia (Isua) terrane of southern West Greenland, we argue for an isolated mantle source for the ca. 1.3 Ga of initial stages of crustal growth in the North Atlantic Craton. Zircon Hf isotope data between 3939 and 2950 Ma yield strikingly homogeneous, near chondritic signatures, with the few analyses that deviate slightly being indicative of ancient Pb-loss. Combined with published data from carefully selected and well-characterized ca. 3.9–2.6 Ga magmatic rocks of the NAC, almost no indications of reworking of older crust can be detected, but all strongly sub-chondritic data rather fall on Pb-loss trends tracing back to chondritic sources. This long-lived and near-chondritic signature with negligible influence from a strongly depleted mantle, or from un-radiogenic sources, argues for protracted crust separation from an isolated mantle source. We suggest a scenario whereby primary melting to produce basaltic and komatiitic crust leaves an infertile harzburgitic residue, unlikely to re-melt, that becomes sequestered as mantle lithosphere. Hence, domains of primordial fertile mantle are continuously sourced from an undepleted mantle reservoir. Combined with small wavelength mantle convection, a near-chondritic to mildly depleted regional mantle is retained into at least the Mesoarchean
The risk of inbreeding versus outbreeding depression in managing an endangered and locally adapted population of a sedentary bird
No full textA debate in conservation genomics centers on whether to conserve small, fragmented populations independently or blend them through translocations from larger populations. Translocations of red grouse (Lagopus scotica) from Great Britain to supplement the Irish population have been suggested. We incorporate a variety of genetic datasets to address this. We used genome wide data from 23 contemporary and historic red grouse from Great Britain and Ireland. We also investigate microsatellite data, sequence candidate pigmentation genes, and assess phenotypic color variation. Genomic data indicate higher inbreeding in Irish grouse relative to an English population and significant divergence for genomic (FST = 0.095) and microsatellite (FST = 0.03) markers. Contemporary Ne was seven times smaller in the Irish population compared to the English. We identified divergent regions linked to pigmentation, immune response, and food intake. We show phenotypic differences in plumage color and sequence divergence among coding regions in the melanin pathway including MC1R (FST from genomic data of 0.3). The two populations thus appear locally adapted and this divergence between the source and target population when used for conservation translocations can swamp locally adapted alleles and/or introduce maladapted genotypes, leading to outbreeding depression. While it is important to avoid inbreeding by sustaining larger populations, our research emphasizes the need for practitioners to consider population divergence and local adaptation. We advocate against translocations between Ireland and Britain as a conservation strategy in this particular case and underscore the importance of prioritizing local populations where possible
A new genus and a new species of microcotylids (Polyopisthocotyla, Platyhelminthes), gill parasite of the pink dentex Dentex gibbosus (Teleostei, Sparidae) off Tunisia and notes on Polyopisthocotyla and Monopisthocotyla from Dentex spp.
No full textThe study of the polyopisthocotylan parasites of marine fishes in the western Mediterranean is carried on using an integrative approach combining morphology and DNA barcodes. Ktarius patrickbrueli n. gen. n. sp (Polyopisthocotyla, Microcotylidae), from the gills of the pink dentex Dentex gibbosus (Teleostei, Sparidae) from the western Mediterranean Sea off Tunisia, is described. Anatomical and morphological features of the new genus are described, and the molecular barcodes for nuclear and mitochondrial markers (28S rRNA and cox1) are generated. The new genus is closely related to Microcotyle by sharing a symmetrical haptor, inverted question mark-shaped ovary and unarmed vagina. However, Ktarius n. gen. can be distinguished from Microcotyle and other Microcotylinae taxa by an unarmed male copulatory organ, formed by a long muscular cirrus, a basal layer of concentric muscles, and an elongated thick-walled ejaculatory bulb. A partial 28S rDNA sequence of K. patrickbrueli n. gen. n. sp. was obtained and found to be distinct from all known microcotylid sequences, with a p-distance of 5–13%. A phylogenetic tree constructed from available microcotylid sequences revealed that K. patrickbrueli n. gen. n. sp. clustered in a strongly supported clade of Microcotylinae, containing species of Omanicotyle, Bivagina, and Microcotyle confirming its belonging to the Microcotylinae subfamily. The cox1 sequences of K. patrickbrueli n. gen. n. sp. were highly divergent from the closely related genus Pauciconfibula and confirmed its distinction. This new genus is the third polyopisthocotylan genus to be described from sparids of Dentex
120‐years of ecological monitoring data shows that the risk of overhunting is increased by environmental degradation for an isolated marine mammal population: The Baltic grey seal
No full textReply to: Tuvikene et al. The inadequacies of estimating silver eel escapement by studying yellow eels caught in the coastal sea far away from the river mouth. A comment on Rohtla et al. (2021)
No full textRestocking European eel (Anguilla anguilla) is generally considered as a conservation action, but its true conservation value remains unknown and is currently debated over. Estimation of the biomass of escaping silver eels is one way to partially measure the success of restocking. Tuvikene et al. in a comment to Rohtla et al. criticize the data that were used to reach the conclusion that eel conservation goals in a fully restocked eel management unit in Estonia are not being met. While acknowledging some potential and unavoidable sampling biases in our study that need to be addressed in the future, we stand by our general conclusions
Origin and Affinities of the Malmberget Iron Oxide-Apatite Deposit, Northern Sweden: Insights From Magnetite Chemistry and Fe-O Isotopes
No full textEuropean iron ore production is primarily sourced from magnetite dominated iron oxide-apatite ore deposits in the northern Norrbotten ore province of northernmost Sweden. The Malmberget iron oxide-apatite deposit is at present the largest iron ore resource in Europe and is an amphibolite facies grade analogue of the world-famous Kiirunavaara iron oxide-apatite deposit. The Malmberget rock association is characterised by multiple phases of deformation, metamorphism, and alteration that resulted in a geometrically and petrologically complex deposit that is genetically ambiguous. Primary ore textures and emplacement structures of the Malmberget iron oxide-apatite deposit have largely been recrystallised during metamorphic overprinting and now comprise dominantly medium- to coarse-grained granoblastic magnetite. However, isotopic characteristics are preserved and when combined with trace element chemistry, these can be used to understand magmatic vs. hydrothermal origin of the deposit. To unravel the primary origin of the Malmberget magnetite ore, we combined magnetite trace element chemistry and Fe-O stable isotopes to investigate the massive magnetite in the Fabian-Kapten and ViRi ore bodies of the Malmberget iron oxide-apatite deposit. Trace element correlations indicate a high-temperature magmatic to a transitional high-temperature magmatic-hydrothermal origin of the Malmberget iron oxide-apatite ore deposit, with data plotting into fields of clear magmatic affinity in trace element discrimination diagrams. Fe-O data fall into established magmatic fields regardless of subsequent metamorphic modifications, underlining a dominantly (ortho-)magmatic origin of the investigated deposits. Despite an overall magmatic to magmatic-hydrothermal origin for the two ore bodies studied, Fe-O isotope equilibrium calculations of the magnetite suggest a possible temperature discrepancy between the Fabian-Kapten ore body and the ViRi ore body, the latter showing a more pronounced magmatic character. These variations in trace element contents and Fe-O isotopes can be explained by the proximity of the more magmatic signatures to the centre of the ore forming magmatic system
Circa 1.9 Ga Rae‐Hearne collision from Lu–Hf garnet chronology in eclogites
No full textCanada's northern cratons record a complex poly-metamorphic evolution in response to multiple orogenic events. The Snowbird Tectonic Zone (STZ), the principal suture between the Archean Rae and Hearne cratons, is a highly debated structure; it is argued to have accommodated modern-style accretion in either the Neoarchean (2.6–2.5 Ga) or Palaeoproterozoic (ca. 1.9 Ga). To resolve this controversy, we use Lu–Hf garnet geochronology to date an eclogite collected from the East Athabasca mylonite triangle of the STZ. Garnet shows prograde trace-element zoning, and we obtained an age of 1914.5 ± 3.4 Ma. The age is interpreted to date the timing of collision related to deep burial of crust along the STZ. This strongly supports Palaeoproterozoic terminal collision between the Rae and Hearne cratons, and that to constrain high-pressure metamorphism during supercontinent assembly, dating eclogite itself is key.Research funders and strategic development areas (1 of 1): Natural Resources Canada 10.13039/501100000159</p
Potential Chronological Disturbance of the D’Orbigny Angrite Inferred from Discordant 26Al Ages
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Evidence for saprotrophic digestion of glossopterid pollen from Permian silicified peats of Antarctica
No full textWind-blown pollen (pollen rain) is a major contributor to element cycling in modern forests and aquatic ecosystems, particularly in high-latitude and acidic settings where nutrients are a limiting factor. The rich package of proteins, nitrogen and phosphorus residing within pollen is, nonetheless, inaccessible to most organisms, owing to the indigestible sporopollenin walls. Saprotrophic breakdown by fungi, and some non-fungal microorganisms, can make nutrients bioavailable, and represents a key trophic link in element cycling and the transfer of organic carbon. Little is known about when micro-saprotrophs first adapted to exploit pollen, thus establishing this crucial step in the evolution of modern terrestrial ecosystems. One approach is to examine the rich fossil record of palynomorphs. Here we describe translucent bodies referable either to fungi (Chytridiomycota) or water moulds (Oomycetes) within the pollen of glossopterid gymnosperms and cordaitaleans, and fern spores from silicified Permian (Guadalupian–Lopingian) peats of the Toploje Member, Bainmedart Coal Measures, Prince Charles Mountains, Antarctica. These probable holocarpic thalli or oospores exploited the nutrient-rich microgametophyte tissue of dispersed miospores in high-palaeolatitude wetlands. The exceptional preservation of fossil microorganisms in permineralised peats offers insights into the deep-time evolution of intimate ecological relationships, otherwise known only among extant biotas. Permineralisation has preserved sub-micron details of these delicate and cryptic saprotrophs that likely played key roles in cycling nutrients in the acidic forest mires of the Permian. Our study reveals that the extensive recapture of spore/pollen-derived nutrients via saprotrophic digestion was already at play in the high-latitude ecosystems of the late Palaeozoic.This work was supported by Swedish Foundation for Strategic Research (SSF) individual research grant: [Grant Number O. Shevchuk 2022–2024]; Vetenskapsrådet: [Grant Numbers 2020-03314 and 2022- 03920].</p