Oceanic Islands Research Articles

Accreted seamounts/oceanic plateaus in the Fuyun accretionary complex in the southern Altaids

ABSTRACT The Late Palaeozoic tectonic evolution of the Chinese Altai-East Junggar orogenic belt, particularly regarding the subduction of the Ob-Zaisan Ocean, remains a topic of ongoing debate. In this study, we present geochronological, geochemical, and Sr-Nd isotopic data of alkaline basic blocks recently discovered in the Fuyun accretionary complex along the Erqis tectonic belt, which represents a relic of the Ob-Zaisan Ocean in the southwest of Fuyun County. Apatite U-Pb dating of three gabbro and one basalt samples reveals that they were formed in the Early Carboniferous (334 ± 8 Ma, 344 ± 19 Ma, 347 ± 28 Ma, and 350 ± 13 Ma, respectively). The gabbro samples display similar geochemical characteristics, with strong enrichment in light rare-earth elements and depletion in heavy rare-earth elements, which are comparable to typical ocean island basalts (OIB). In addition, the OIB-type basic samples (three gabbros and one basalt) exhibit depleted isotopic compositions with low initial 87Sr/86Sr ratios of 0.7041 to 0.7051 and positive εNd(t) values of + 5.24 to + 7.11. Thus, we suggest that the OIB-type gabbro and basalt blocks within the tectonic mélange were derived from a plume-related mantle source. Integrating these results with previous studies, we propose that these OIB-like basic blocks in the tectonic mélange might represent the relics of mantle plume-derived seamounts/oceanic plateaus. These blocks were likely accreted into the Fuyun accretionary complex due to its convex topography, associated with the southward subduction of the Ob-Zaisan Ocean during the latest Early Carboniferous.

Mafic Intrusions in the Cuona Area, Eastern Tethyan Himalaya: Early Kerguelen Mantle Plume Activity and East Gondwana Rifting

The widespread occurrence of Mesozoic ocean island basalt (OIB)-like igneous rocks in the Southern Tibetan Himalayan Belt provides important constraints on the rifting of East Gondwana. This study undertook a petrological, geochronological, and geochemical investigation of mafic intrusive rocks in the Cuona area of the eastern Tethyan Himalayan Belt. The mafic intrusions have OIB-type geochemical signatures, including diabase porphyrite, gabbro, and diabase. Zircon U–Pb dating indicates that the diabase porphyrite formed at 135.0 ± 1.6 Ma. The diabase porphyrite and gabbro are enriched in high-field-strength elements (Nb and Ti) and large-ion lithophile elements (Sr and Pb) and experienced negligible lithospheric mantle or crustal contamination. The diabase is enriched in large-ion lithophile elements (LILEs, e.g., La and Ce) and depleted in high-field-strength elements (HFSEs, e.g., Ru, Zr and Ti). In general, the mafic intrusions exhibit significant light REE enrichment and heavy REE depletion and have no Eu anomalies. Whole-rock neodymium (εNd(t) = 1.55) and zircon Hf (εHf(t) = 0.60–3.73) isotopic compositions indicate derivation of the magma from enriched type I mantle. We propose that the diabase porphyrite and diabase formed in a continental margin rift setting, influenced by the Kerguelen mantle plume, and represent magmatism related to the breakup of East Gondwana. However, the gabbro formed in a relatively stable continental intraplate environment, likely derived from deep magmatic processes associated with the Kerguelen mantle plume. Our results provide new constraints on the early activity of the Kerguelen mantle plume and offer insights into the breakup and tectonic evolution of East Gondwana.

Population differentiation in the white-fronted chat (Epthianura albifrons) at a continental scale: implications for dispersal, biogeography and conservation

The capacity for dispersal is an important determinant of a species’ resilience to decline from the serial extinction of local populations. Dispersal of animals can be difficult to measure directly but population genetics provides a powerful tool for identifying dispersal limits. This study used microsatellite markers to investigate population structuring of the white-fronted chat (Epthianura albifrons) across its geographic range. Because the species is threatened in the north-eastern part of its range, the primary aim was to identify barriers limiting dispersal. Isolation by distance was not apparent across the 3000 km mainland range but populations on three oceanic islands, and two mainland sites surrounded by urbanisation, were genetically distinct from each other and the other mainland sites. The small populations that were surrounded by urbanised land had significantly lower genetic diversity (allelic diversity and heterozygosity) than the other mainland populations, with the oceanic island populations showing intermediate levels of diversity. These results suggest that although being a partially nomadic species, which facilitates its dispersal over continuous habitat, the species does not have the flight capacity of some other small passerines and is sensitive to habitat discontinuity. Populations inhabiting small areas of coastal saltmarsh in areas with large human populations are likely to face increasing threat levels.

Geochronology and geochemistry of late Cenozoic volcanics on Naozhou Island, South China: insights into the interaction between the paleo-subduction slab and the Hainan mantle plume

The mechanisms and processes of interaction between paleo-subducted slabs and mantle plumes are not well understood, primarily due to the challenges associated with direct observation. The Leiqiong Area (LQA), located in the northwestern South China Sea (SCS), may provide an ideal site to study the interaction between mantle plumes and paleo-subducted slabs. Extensive Late Cenozoic volcanic activities are present in the LQA, encompassing the Leizhou Peninsula (LP) and northern Hainan Island. This study conducted K-Ar dating, major and trace element analysis, and Sr-Nd-Pb-Hf isotopic analysis on volcanic rock samples from Naozhou Island, the largest volcanic island in the northeastern part of the LQA. The dating results show two periods of magmatic activities on Naozhou Island (3.6 Ma and 1 Ma). The geochemical results indicate that the columnar jointed basalts from Naozhou Island mainly show characters of oceanic island basalt (OIB). The isotopic data suggest origins of depleted MORB mantle (DMM) and Enriched Mantle Ⅱ (EMⅡ), with EMⅡ potentially originating from the Hainan mantle plume. In view of these findings, the study further integrates data (Geochronology, trace elements and isotopic composition) from other volcanic rocks in the LQA to explore the deep mechanisms of extensive volcanic activity and plume-slab interactions along the northwestern SCS margin. We discovered that the volcanic rocks from southern LP and northern Hainan Island are characterized by OIB, IAB and OIB-IAB transition like, however, the volcanic rocks from Naozhou Island (northern LP) and Weizhou Island (western LP) are characterized by OIB like merely. This can be explained by a branched Hainan mantle plume model and may indicate the interaction between Hainan mantle plume and paleo-subdected slab mainly focuse on the center location of the plume rather than distal margin. This conjecture is also in accord with the subduction direction of the Late Mesozoic subduction zone along the northern margin of the SCS.

Local human pressures modulate turf sediment loads in a warm-temperate oceanic island.

Local human pressures modulate turf sediment loads in a warm-temperate oceanic island.

Transcrustal magmatic system in lamprophyre dike constructed by multiple magma reservoirs

Abstract The mineral assemblages, chemistry, and textures of igneous rocks can record crucial information on magmatic processes in transcrustal magmatic systems. To effectively identify such processes, we present systematic petrological, mineralogical, and geochronological data for a suite of lamprophyre dikes that intruded early flood basalts in the Tuoyun basin of Western Tianshan. The lamprophyre dikes show ocean island, basalt-like trace element patterns and depleted Sr-Nd isotope compositions, suggesting that they were derived from a depleted mantle source. Apatite U-Pb dating reveals that the lamprophyre dikes were emplaced at 66 Ma. These lamprophyre dikes consist of three groups of mineral assemblages: (1) Type-I Clinopyroxene (Cpx); (2) Amphibole (Amp) core and Apatite (Ap); and (3) Amp rim, Type-II Cpx, K-feldspar (Kfs), and Plagioclase (Pl). These mineral assemblages are in chemical disequilibrium and correspond to three magma reservoirs within the transcrustal magmatic system. Textural and geochemical features demonstrate that Type-I Cpx represents antecrysts captured from lower crustal crystal mushes. The Amp cores have the same rare earth element patterns as their enclosed Type-I Cpx inclusions, demonstrating that the cores were produced through peritectic reactions consuming Cpx. The third assemblages occur as microlites formed by shallow crystallization of evolved melts. Thermobarometric calculations suggest a lower crust magma reservoir at 20–30 km depth, a middle crust magma reservoir at ∼15 km depth, and a shallow upper crust magma reservoir at <5 km depth, making up a magma plumbing system of the lamprophyre dikes. The transcrustal magmatic system involves multiple stages of open-system processes, including the recycling of early-formed crystals, multiple magma replenishment, peritectic reactions, and crystal fractionation, resulting in the formation of lamprophyre dikes.

Persistence of davemaoite at lower-mantle conditions

Abstract The lower mantle occupies over half of Earth’s volume, and accordingly, its mineralogy is crucial in determining the structure and dynamics of Earth. Davemaoite, the calcium silicate perovskite, was believed to coexist with bridgmanite in the lower mantle and is considered essential for understanding the chemical evolution and dynamics of Earth’s lower mantle. However, the presence of davemaoite is challenged due to the potential for high calcium silicate solubility in bridgmanite. Here we use an ultrahigh-pressure multi-anvil technique to show experimentally that the calcium solubility in bridgmanite is insufficient to eliminate davemaoite under mantle conditions, including typical mantle pressure, temperature and chemical compositions. We conclude that davemaoite has been stable in Earth’s lower mantle since its formation. Due to the limited calcium solubility in bridgmanite, davemaoite-enriched domains are expected at the core–mantle boundary. These domains could serve as the principal reservoir for incompatible elements in the lower mantle and may be the source for some ocean island basalts. Furthermore, our study offers an explanation for the observed large low-shear-wave-velocity provinces at the bottom of the lower mantle. These provinces may consist of davemaoite-enriched materials crystallized from basal magma ocean in early Earth history.

Traditional systems and contemporary transitions on an oceanic island: Insights for participatory fisheries management from Minicoy Island, India

Traditional systems and contemporary transitions on an oceanic island: Insights for participatory fisheries management from Minicoy Island, India

The role of marine debris as a vector, dispersal agent, and substrate for non-indigenous species on Oceanic Islands (Northeast Atlantic).

Marine debris (MD) can be a transport vector for diverse marine communities, including non-indigenous species (NIS). This study assessed MD potential role as a substrate for colonization and dispersal vector for NIS in the Madeira Archipelago (NE Atlantic) by examining three MD categories: floating (FMD), seafloor (SMD), and beached (BMD). Opportunistic sampling, conducted in collaboration with local maritime stakeholders, documented MD sightings with photographs and GPS coordinates. A total of 92 MD items were inspected, revealing 108 fouling species across 11 phyla, with 13% identified as NIS. SMD exhibited the highest proportion of NIS (9.6%), followed by BMD (4.4%) and FMD (3.9%). Notably, the study provides evidence that FMD functions as both a substrate and a dispersal vector for NIS in Madeira waters. Combining biogeographic analyses, oceanographic modelling, and MD identification marks, this study highlighted the North Atlantic Subtropical Gyre's currents as key pathways, transporting MD items from the Wider Caribbean, the North American east coast, and the Iberian Peninsula to Madeira within 2-3years. These findings emphasize Madeira's dual role as both a recipient and exporter of MD, with implications for NIS introductions and secondary spread. This study underscores the urgent need for standardized monitoring, stakeholder engagement, and proactive MD management strategies to mitigate NIS introductions and protect sensitive marine ecosystems like Macaronesia from the ecological risks of biological invasions.

Metal(loid) contamination in tiger sharks (Galeocerdo cuvier) from a remote oceanic island in the Equatorial Atlantic Ocean and potential impacts on physiological parameters.

Metal(loid) contamination in tiger sharks (Galeocerdo cuvier) from a remote oceanic island in the Equatorial Atlantic Ocean and potential impacts on physiological parameters.

Refining management strategies in marine protected areas in oceanic islands: a non-indigenous species risk index for strategic prioritization

Non-indigenous Species (NIS) pose significant threats to marine biodiversity globally, especially in ecologically sensitive habitats such as Marine Protected Areas (MPAs). This study uses data collected in the Autonomous Region of Madeira (North Atlantic), Portugal, to create a spatial model aiming to (1) develop a spatially explicit index of NIS dispersal from known hotspots such as ports, harbours, marinas, and anchoring areas; (2) assess the relative vulnerability of Madeira's MPAs to local NIS dispersion and establishment; and (3) provide insights for a scalable NIS monitoring framework and evaluating invasion risks. The spatial model integrates maritime traffic intensity and proximity to NIS hotspots, using a straightforward approach that can be applied in data-limited contexts. While designed to address Madeira's regional challenges, the model is adaptable to other biogeographic contexts and can incorporate additional complexity, such as species-specific traits or ecological layers, to suit different settings. Our findings underscore the role of maritime infrastructure and vessel traffic in NIS spread, revealing the vulnerability of Madeira's MPAs due to insufficient ecological monitoring and the absence of NIS monitoring and early detection programs. This study provides practical recommendations for improving MPA management and mitigating NIS risks, contributing to regional conservation efforts. Additionally, it establishes a baseline risk assessment approach that can be customised and expanded to guide NIS management and biodiversity conservation in other regions, particularly those with similar challenges.

Seasonal dynamics of zooplankton communities in a recent lava delta on an oceanic island in the Central East Atlantic Ocean

Abstract We examined the structure of the zooplankton community in a Special Area of Conservation affected by the recent formation of lava deltas caused by a volcanic eruption on the island of La Palma (Canary Islands) in the Central East Atlantic Ocean. Seasonal variability in biomass, abundance, and composition of the zooplankton community was analyzed, both in total and within different size ranges. The results showed higher biomass values in winter at 30 m and in spring–summer at 10 m depth, possibly related to seasonal changes in food availability and seawater temperature. Significant differences were observed in the biomass of the smaller size range compared to larger sizes. Similarly, organisms in the smaller size range were the most abundant, primarily due to the community being dominated by copepods, which represented 80.43% of the total abundance in winter, decreasing to 47.14% in spring–summer. At the same time, a significant increase was observed in decapod larvae, gastropods, invertebrate eggs, and cladocerans during the warmer season. An increase in gelatinous organisms, especially siphonophores, was also observed in spring–summer for the largest size range, suggesting potential seasonal changes in the zooplankton trophic structure. This study indicates a limited direct impact of volcanic activity on zooplankton biomass but highlights the importance of understanding seasonal variability in community structure for managing marine conservation. Continuous monitoring of zooplankton dynamics is crucial for detecting potential future impacts on the food web and developing targeted conservation management strategies.

Grain boundary diffusion cannot explain the W isotope heterogeneities of the deep mantle

The low 182W/184W and high 3He/4He in some ocean island basalts compared to the bulk mantle values may derive from the Earth’s core through long-term core-mantle interactions. It has been proposed that the grain boundary diffusion of siderophile elements is an efficient mechanism for core-mantle interaction and may effectively modify the W isotopic compositions of the plume-source mantle. In this study, we perform large-scale molecular dynamics simulations driven by machine learning potentials of ab initio quality to investigate the diffusion of W along ferropericlase grain boundaries and in (Mg,Fe)O liquid. Here we show that the diffusion of W is sluggish under core-mantle boundary conditions, and thus is unlikely to have observable impacts on the W isotopic compositions of terrestrial igneous rocks.

Barium Isotope Fingerprint for Recycled Ancient Sediment in the Source of EM1‐Type Continental Basalts

AbstractThe origin of enriched mantle 1 (EM1) endmember, characterized by low 206Pb/204Pb and 143Nd/144Nd ratios in ocean island basalts, has long been debated. This is because melting of surrounding peridotite, together with the EM1 component, can dilute the “EM1 fingerprints” in these rocks. Here, we present barium isotope data for well‐characterized EM1‐type continental basalts from northeast China to constrain their nature and origin. Our results show that these basalts have δ138/134Ba values ranging from −0.1‰ to 0.08‰, which are lower than the depleted MORB mantle. Correlations between δ138/134Ba and K/U, Ba/Th, U/Pb, εNd and 206Pb/204Pb suggest a heterogeneous source involving binary mixing between the lithospheric mantle and an EM1 component. The EM1 component, characterized by light δ138/134Ba and low 206Pb/204Pb ratios, can be attributed to the addition of recycled ancient sediments to the source. This study indicates that Ba isotopes have potential to trace crustal material recycling into Earth's deep mantle.

Molecular analysis confirms Agama picticauda invasion on Western Indian Ocean islands

The Western Indian Ocean biodiversity hotspot hosts a remarkable array of endemic species, but invasive alien species increasingly threaten its unique ecosystems. Lizards of the West African Agama agama species group are successful colonizers, with recent introductions to Grande Comore (Comoros Archipelago) and Reunion Island. Systematic revisions within the native range of the A. agama species group have left many of the introduced populations without clear identity. We used molecular methods to determine the identities of the Agama species introduced to Grande Comore and Reunion Island, define their respective likely origin, and assess body size characteristics for each island population. We identified Agama picticauda as the species present on both islands with likely origins in two distinct Western African regions. Agamas from Reunion Island had longer and wider heads with greater body weight than Grande Comore individuals. Sexual size dimorphism on both islands was driven by weight, with males being heavier than females. We provide foundations for further research on the ecology and impacts of A. picticauda on Western Indian Ocean islands and to aid in the development of targeted management strategies for controlling this invasive reptile.

Global phylogeny of the family Gomphillaceae (Ascomycota, Graphidales) sheds light on the origin, diversification and endemism in foliicolous lineages.

Foliicolous lichens grow on living leaves of vascular plants. They are mostly found in tropical to subtropical or temperate rainforests. Many phenotype-based species are considered as pantropical or even sub-cosmopolitan, either attributed to old ages, having existed prior to continental breakups or long-distance dispersal. We built a much expanded, global phylogeny of Gomphillaceae, the most diverse group of leaf-dwelling lichenised fungi. Our sampling encompassed six major biodiversity hotspots: MIOI (Madagascar and the Indian Ocean Islands), the Caribbean, New Caledonia, the Colombian Chocó, Mesoamerica and the Atlantic coast of Brazil. It was based on multilocus sequence data (mtSSU rDNA, nuLSU rDNA and RPB1), including 2207 sequences of 1256 specimens. Species delimitation methods combined with a phenotype matrix identified 473 putative species. Amongst these, 104 are confirmed as described, 213 are classified as cryptic or near cryptic (hidden diversity), 100 represent new species to science (identified on the basis of phenotype) and 56 remain unidentified. Amongst the 104 species with a valid name, 40.5% are distributed across 2-5 continents (lichenogeographical regions) by applying the phenotype-based species concept. However, using the integrative approach to delineate species, this estimate is reduced to 9%. We estimate the global species richness of Gomphillaceae at 1,861-2,356 species. The timing of species-level divergences suggests that the current distribution of foliicolous lichens is shaped more by long-distance dispersal and rapid diversification than by vicariance. The origin of the family and major clades appears to be in the Neotropics, with subsequent numerous dispersal events. Our results support the separation of three major lineages, corresponding to the former families Asterothyriaceae, Gomphillaceae s.str. and Solorinellaceae, which should be recognised at the subfamily level.

Palaeozoic high-Ti basalt, an indicator for incipient rifting, at the Saxo-Thuringian passive margin, NE-Bavaria (Germany)

We investigated mafic igneous rocks found in the vicinity of the allochthonous Münchberg Massif in the Saxo-Thuringian Zone of the European Variscides, NE Bavaria. The basaltic magmas were injected during the Ordovician, Silurian and Devonian into contemporaneous marine sedimentary rocks of the Saxo-Thuringian Basin. Ordovician sills east and Devonian volcanic to subvolcanic rocks west of the Münchberg Massif show high Fe and Ti contents that place them in the rarely occurring group of high Fe–Ti basalts with FeO content of up to 17.6 wt% and up to 5.7 wt% TiO2. Covariation of Nb, Y and Zr with major elements indicates compositional control by fractionation. Trace element patterns are similar to those of ocean island basalt and continental intraplate magmatic rocks. Nd isotope signatures of the mafic rocks from the Early Palaeozoic until the Devonian resemble those of the regional continental lithospheric mantle of the Saxo-Thuringian and Bohemian zones. Their Sr isotope signatures show the variable influence of post-magmatic mobilisation. The major source of these mafic rocks is likely the subcontinental lithospheric mantle. The Pb isotope compositions of the mafic rocks do not allow distinguishing between mantle and crustal sources but resemble the regional crustal signatures. Crustal contamination in the mafic rocks is minor. The geochemical signatures of the mafic igneous rocks and continuous deposition of their host sediments indicate a long-standing passive margin setting between the northern part of Gondwana and the Saxo-Thuringian. In contrast, the trace element patterns and isotope characteristics of post-Devonian mafic dykes in the allochthonous Münchberg Massif are significantly different: They are related to a late stage of subduction during the Variscan orogeny.Graphical abstract

Phylogenetic origin of dioecious Callicarpa (Lamiaceae) species endemic to the Ogasawara Islands revealed by chloroplast and nuclear whole genome analyses.

Phylogenetic origin of dioecious Callicarpa (Lamiaceae) species endemic to the Ogasawara Islands revealed by chloroplast and nuclear whole genome analyses.

Geographic and Biological Drivers Shape Anthropogenic Extinctions in the Macaronesian Vascular Flora

ABSTRACTWhether species extinctions have accelerated during the Anthropocene and the extent to which certain species are more susceptible to extinction due to their ecological preferences and intrinsic biological traits are among the most pressing questions in conservation biology. Assessing extinction rates is, however, challenging, as best exemplified by the phenomenon of ‘dark extinctions’: the loss of species that disappear before they are even formally described. These issues are particularly problematic in oceanic islands, where species exhibit high rates of endemism and unique biological traits but are also among the most vulnerable to extinction. Here, we document plant species extinctions since Linnaeus' Species Plantarum in Macaronesia, a biogeographic region comprised of five hyperdiverse oceanic archipelagos, and identify the key drivers behind these extinctions. We compiled 168 records covering 126 taxa, identifying 13 global and 155 local extinction events. Significantly higher extinction rates were observed compared to the expected global background rate. We uncovered differentiated extinction patterns along altitudinal gradients, highlighting a recent coastal hotspot linked to socioeconomic changes in Macaronesian archipelagos from the 1960s onwards. Key factors influencing extinction patterns include island age, elevation, introduced herbivorous mammals, and human population size. Trait‐based analyses across the floras of the Azores and Canary Islands revealed that endemicity, pollination by vertebrates, nitrogen‐fixing capacity, woodiness, and zoochory consistently tended to increase extinction risk. Our findings emphasize the critical role of geography and biological traits, alongside anthropogenic impacts, in shaping extinction dynamics on oceanic islands. Enhancing our knowledge of life‐history traits within island floras is crucial for accurately predicting and mitigating future extinction risks, underscoring the urgent need for comprehensive biodiversity assessments in island ecosystems.

Zooplankton abundance and biovolume size-spectra in the western tropical Atlantic - From the shelf towards complex oceanic current systems.

Zooplankton abundance and biovolume size-spectra in the western tropical Atlantic - From the shelf towards complex oceanic current systems.