Modulation of the northward penetration of Antarctica intermediate waters into the eastern equatorial Indian Ocean under glacial and interglacial conditions.

The Indo-Pacific warm pool is the warmest and most dynamic ocean-atmosphere-climate system on Earth and was subject to significant climate changes during the Pleistocene glacial-interglacial transitions. This has been shown to significantly affected the strength of surface waters that redistribute heat from the tropics to the southern part of the Indian Ocean. Here we investigate the response of the oceanic circulation at intermediate depth (1200 m) of the eastern equatorial Indian Ocean (EEIO) with neodymium (Nd) isotopes in the context of the climatic oscillation of the last 500 ka. The most striking feature of our new dataset is the seesaw Nd record that mimics glacial-interglacial cycles. While the interglacial periods are characterized by a higher contribution of the less radiogenic neodymium (~ - 7εNd) Antarctic Intermediate Water (AAIW), the glacial periods are characterized by more radiogenic water mass of Pacific origin (~ - 5εNd). To explain the increase in the εNd signature toward a more radiogenic signature as the Indo-Pacific connection is reduced under the low sea level of the glacial periods, we show that under global cooling, the AAIW advances northward into the tropics, which is a consequence of the general slowdown of the thermohaline circulation. Therefore, oceanic mixing at intermediate depth in the eastern tropical Indian intermediate water is modulated by the production rate of the AAIW in the Southern Ocean. Our study provides new evidence for the role that changes in the deep oceanic conditions play in amplifying externally forced climate changes that ultimately lead to drier/moister atmospheric conditions and weaker/stronger monsoons during glacial/interglacial periods over eastern tropical Indian Ocean.

Increased coral biomineralization due to enhanced symbiotic activity upon volcanic ash exposure.

Coral reefs, which are among the most productive ecosystems on earth, are in global decline due to rapid climate change. Volcanic activity also results in extreme environmental changes at local to global scales, and may have significant impacts on coral reefs compared to other natural disturbances. During explosive eruptions, large amounts of volcanic ash are generated, significantly disrupting ecosystems close to a volcano, and depositing ash over distal areas (10s - 1000s of km depending on i.a. eruption size and wind direction). Once volcanic ash interacts with seawater, the dissolution of metals leads to a rapid change in the geochemical properties of the seawater column. Here, we report the first known effects of volcanic ash on the physiology and elemental cycling of a symbiotic scleractinian coral under laboratory conditions. Nubbins of the branching coral Stylophora pistillata were reared in aquaria under controlled conditions (insolation, temperature, and pH), while environmental parameters, effective quantum yield, and skeletal growth rate were monitored. Half the aquaria were exposed to volcanic ash every other day for 6 weeks (250 mg L-1 week-1), which induced significant changes in the fluorescence-derived photochemical parameters (ΦPSII, Fv/Fm, NPQ, rETR), directly enhanced the efficiency of symbiont photosynthesis (Pg, Pn), and lead to increased biomineralization rates. Enhancement of symbiont photosynthesis is induced by the supply of essential metals (Fe and Mn), derived from volcanic ash leaching in ambient seawater or within the organism following ingestion. The beneficial role of volcanic ash as an important micronutrient source is supported by the fact that neither photophysiological stress nor signs of lipid peroxidation were detected. Subaerial volcanism affects micronutrient cycling in the coral ecosystem, but the implication for coral ecophysiology on a reef scale remains to be tested. Nevertheless, exposure to volcanic ash can improve coral health and thus influence resilience to external stressors.

The first articulated skeletons of enigmatic Late Cretaceous billfish-like actinopterygians.

Only few candidates of Mesozoic fishes with a similar body plan and ecological niche to the modern billfishes are suggested as their analogues. Several specimens were recovered from Cenomanian deposits in Germany and Lebanon and display a billfish-like fusiform body with elongated premaxillae. They are found close to the plethodids and show a unique combination of characters (rostrum pointed and extremely elongated, double articular head of the quadrate, anteroposteriorly elongated abdominal centra indicating a slender body and different types of scales on the body) allowing their inclusion in a new genus. Two 'Protosphyraena' species are also assigned to this new genus. This fish can be considered as an ecological analogue to the extant xiphioids sharing their feeding habits. This fish was abundant and roamed, as an apex predator, the Central Tethys and the Boreal realms during the Cenomanian.

Metal-rich organic matter and hot continental passive margin: drivers for Devonian copper-cobalt-germanium mineralization in dolomitized reef-bearing carbonate platform.

The abundance and types of reef-bearing carbonate platforms reflect the evolution of Devonian climate, with conspicuous microbial-algal reefs in the warm Early and Late Devonian and sponge-coral reefs in the cooler Middle Devonian. A dolomitized Wenlock-Lower Devonian microbial-algal reef-bearing carbonate platform hosts epigenetic copper-cobalt-germanium (Cu-Co-Ge) sulfide mineralization at Ruby Creek-Bornite in the Brooks Range, Alaska. Here, we present rhenium-osmium (Re-Os) radiometric ages and molybdenum and sulfur (δ98/95Mo = +2.04 to +5.48‰ and δ34S = -28.5 to -1.8‰) isotope variations for individual Cu-Co-Fe sulfide phases along the paragenetic sequence carrollite-bornite-pyrite. In the context of a hot, extensional passive margin, greenhouse conditions in the Early Devonian favored restriction of platform-top seawater circulation and episodic reflux of oxidized brines during growth of the carbonaceous carbonate platform. Molybdenum and sulfur isotope data signal the stepwise reduction of hot brines carrying Cu during latent reflux and geothermal circulation for at least ca. 15 million years from the Early Devonian until Cu-Co sulfide mineralization ca. 379-378 million years ago (Ma) in the Frasnian, Late Devonian (weighted mean of Re-Os model ages of carrollite at 379 ± 15 Ma [n = 4]; Re-Os isochron age of bornite at 378 ± 15 Ma [n = 6]). On the basis of petrographic relationships between sulfides and solid bitumen, and the Mo and S isotope data for sulfides, we imply that the endowment in critical metals (e.g., Co, Ge, Re) in the Ruby Creek-Bornite deposit is linked to the activity of primary producers that removed trace metals from the warm Early Devonian seawater and concentrated Co, Ge, and Re in algal-bacterial organic matter in carbonate sediments. Supplementary Information: The online version contains supplementary material available at 10.1007/s00126-022-01123-1.

Provenance, paleoweathering, depositional setting and paleoclimatic constraints of cretaceous and neogene deposits of The Mamfe Basin, southwest Cameroon.

The Cretaceous and Neogene deposits from the Mamfe Basin consisting of sandstone, shale and claystone were studied using petrography, and major, traces and REEs analyses to address sediment source, environment setting, prevailing paleoclimate as well as tectonic regime of the basin. The angular to subangular shape of detrital grains reflects the mineralogical and textural immaturity of sediments and the proximity of the sediment supply source. Sedimentary rocks are composed of a significant number of lithic debris, organic matter, ostracods as well as subrounded heavy minerals referring to notable igneous and metamorphic rocks bordering the Mamfe Basin. The plots of major element ratios including iron oxide/potasium oxide (Fe2O/K2O) against silicium oxide/aluminium oxide (SiO2/Al2O3) combined with that of sodium oxide/potassium oxide (Na2O/K2O) compared to silicium oxide/aluminium oxide (SiO2/Al2O3) are characteristic of greywacke and shale with few arkoses. The pronounced Eu negative anomaly of chondrite normalized REEs along with the plot of La/Th vs Hf and Co/Th vs La/Sc suggest that sediments are in general from felsic and intermediate source rock provenance, only subordinated contribution of mafic source. The negative anomaly of Yb suggests igneous fractionation under highly reducing conditions. The chemical index of alteration values of 47-70 combined with chemical index of weathering values of 0.6-84 suggest low to moderate weathering process of the sediment in the basin. This result is further confirmed by an index of chemical variability values of 0.6-100 and Zr/Sc ratio of 0.06-2.96. The REEs distribution displays a substantial content in LREE, low content in HREE and noticible proportion of (La/Yb)N ratio (mean >9), poor (Gd/Yb)N ratio in the Cross River Formation (mean <2) and slightly moderate (Gd/Yb)N ratio in the other formations (mean >2). This result implies that sediments from the Ngeme, Nfaitok and Baso formations derived from post-Archean rocks. Geochemical paleoenvironmental proxies including Sr/Cu, Sr/Ba, Ga/Rb vs Sr/Cu and SiO2 vs K2O + NaO2+Al2O3 are in favor of arid to semi-arid conditions during the deposition. Trace Elemental ratios such as Sr/Cu, Sr/Ba, V/Ni, U/Th, Ni/Co, V/Sc, and V/Cr values indicate a predominance of oxic conditions during deposition. In contrast, some authigenic pyrite, hematite, siderite and vivianite which are iron-rich minerals suggests episodic reducing conditions in the basin. The study provides a valuable information in evaluating sediments source, depositional environment, tectonic regime as well as the paleoclimatic conditions prevailing in the basin during the depositional period. The geochemistry of rocks of the Ngeme and Baso formations suggest passive continental margin setting and Ngeme, Nfaitok and Cross River formations suggest oceanic island Arc tectonic setting.

Late Pennsylvanian carbonate platform facies and coral reef: new insights from southern China (Guizhou Province).

The Pennsylvanian is characterized by intense paleoenvironmental changes related to glacio-eustatic sea-level fluctuations and major tectonic events, which affected the evolution of biocommunities. Most known Pennsylvanian tropical reefs and mounds are predominantly composed of calcareous algae (e.g. phylloid algae, Archaeolithophyllum), calcareous sponges, fenestrate bryozoans, Tubiphytes, and microbialites. However, in Houchang (southern China), the Late Pennsylvanian carbonate platform records a large coral reef lacking any analogs in age (Gzhelian), size (80-100 m thick) and composition (high biodiversity). The large coral reef developed at the border of the Luodian intraplatform basin. The intraplatform basin is characterized by the deposition of green algal grainstone, coated grain grainstone and bioclastic packstone, grainstone, floatstone and rudstone in shallow-waters. In the deep-water shelf, lithofacies are composed of burrowed bioclastic wackestone, microbioclastic peloidal packstone, grainstone, and fine-grained burrowed wackestone and packstone. In this context, the coral reef developed on a deep-shelf margin, in a moderate to low energy depositional environment, below the FWWB. The scarcity of Pennsylvanian coral reefs suggests global unfavorable conditions, which can be attributed to a complex pattern of several environmental factors, including seawater chemistry (aragonite seas), paleoclimatic cooling related to continental glaciation, and the biological competition with the more opportunistic and adaptive phylloid algal community that occupied similar platform margin paleoenvironments. The existence of the large Bianping coral reef in southern China, as well as a few additional examples of Pennsylvanian coralliferous bioconstructions, provides evidence that coral communities were able to endure the Late Paleozoic fluctuating paleoenvironmental conditions in specific settings. One of such settings appears to have been the deep shelf margin, where low light levels decreased competition with the phylloid algal community.

The driving mechanisms of the carbon cycle perturbations in the late Pliensbachian (Early Jurassic).

The Early Jurassic (late Pliensbachian to early Toarcian) was a period marked by extinctions, climate fluctuations, and oceanic anoxia. Although the causes of the early Toarcian Oceanic Anoxia Event (OAE) have been fairly well studied, the events that lead to the Toarcian OAE, i.e. the events in the late Pliensbachian, have not been well constrained. Scenarios of the driving mechanism of biotic and environmental changes of the late Pliensbachian have ranged from LIP volcanism (the Karoo-Ferrar LIP), ocean stagnation, and changing ocean circulation, to orbital forcing. The temporal relationship between the Karoo LIP and the late Pliensbachian (Kunae-Carlottense ammonite Zones) are investigated in an effort to evaluate a causal relationship. We present the first absolute timescale on the Kunae and Carlottense Zones based on precise high-precision U-Pb geochronology, and additional geochemical proxies, for a range of environmental proxies such as bulk organic carbon isotope compositions, Hg concentration, and Hg/TOC ratios, and Re-Os isotopes to further explore their causal relationship. The data presented here show that causality between the Karoo LIP and the late Pliensbachian events cannot be maintained.

Barium isotope fractionation during the experimental transformation of aragonite to witherite and of gypsum to barite, and the effect of ion (de)solvation.

In this study, we present the experimental results for stable barium (Ba) isotope fractionation (137Ba/134Ba) during the transformation of aragonite (CaCO3) and gypsum (CaSO4·2H2O) in Ba-bearing aqueous solution to witherite (BaCO3) and barite (BaSO4), respectively. The process was studied at three temperatures between 4 and 60 °C. In all cases, the transformation leads to a relative enrichment of the lighter 134Ba isotope in the solid compared to the aqueous solution, with 137/134Ba enrichment factors between -0.11 and -0.17 ‰ for BaCO3, and -0.21 and -0.26 ‰ for BaSO4. The corresponding mass-dependent 138/134Ba enrichment factors are -0.15 to -0.23 ‰ for BaCO3, and -0.28 to -0.35 ‰ for BaSO4. The magnitude of isotope fractionation is within the range of recent reports for witherite and barite formation, as well as trace Ba incorporation into orthorhombic aragonite, and no substantial impact of temperature can be found between 4 and 80 °C. In previous studies, ion (de)solvation has been suggested to impact both the crystallization process of Ba-bearing solids and associated Ba isotope fractionation. Precipitation experiments of BaSO4 and BaCO3 using an methanol-containing aqueous solution indicate only a minor effect of ion and crystal surface (de)solvation on the overall Ba isotope fractionation process.

Barium isotope fractionation during experimental formation of the double carbonate BaMn[CO3](2) at ambient temperature.

In this study, we present the first experimental results for stable barium (Ba) isotope ((137)Ba/(134)Ba) fractionation during low-temperature formation of the anhydrous double carbonate BaMn[CO(3)](2). This investigation is part of an ongoing work on Ba fractionation in the natural barium cycle. Precipitation at a temperature of 21±1°C leads to an enrichment of the lighter Ba isotope described by an enrichment factor of-0.11±0.06‰ in the double carbonate than in an aqueous barium-manganese(II) chloride/sodium bicarbonate solution, which is within the range of previous reports for synthetic pure BaCO (3) (witherite) formation.