Red clays indicate sub-aerial exposure of the Rio Grande Rise during the Eocene volcanic episode

Autonomous underwater vehicle (AUV) mapping of the western Rio Grande Rise (RGR), South Atlantic, and subsequent exploration and photography of horizontal lava flows exposed in near vertical, faulted escarpments, showed occurrences of red clays/weathered volcanic tops trapped between successive alkaline lava flows. These red clays indicate a hiatus in successive volcanic eruptions. Here, we report detailed mineralogical, geochemical, and rock magnetic characteristics of one such distinct red clay dredged from ~ 650 m water depth in the western RGR. The mineral constituents of the red clay are kaolinite, magnetite, oxidized magnetite (/maghemite), hematite, and goethite, with biogenic calcite and halite occupying voids or precipitated on the surface of the red clay. The chemical index of alteration (CIA) has a value of 93, showing that red clay is a product of extreme chemical weathering of the lava flows. The alkaline volcanic rocks recovered from nearby show an age of ~ 44 Ma, indicating an Eocene age for the volcanism. We show that the red clays are a product of sub-aerial chemical weathering of these Eocene volcanic rocks, in a warm-wet climate, before the thermal subsidence of the RGR to its modern-day bathymetric depth.

Anomalous widespread arid events in Asia over the past 550,000 years

Records of element ratios obtained from the Maldives Inner Sea sediments provide a detailed view on how the Indian Monsoon System has varied at high-resolution time scales. Here, we present records from International Ocean Discovery Program (IODP) Site U1471 based on a refined chronology through the past 550,000 years. The record's high resolution and a proper approach to set the chronology allowed us to reconstruct changes in the Indian Monsoon System on a scale of anomalies and to verify their relationships with established records from the East Asian Monsoon System. On the basis of Fe/sum and Fe/Si records, it can be demonstrated that the Asia continental aridity tracks sea-level changes, while the intensity of winter monsoon winds responds to changes in Northern Hemisphere summer insolation. Furthermore, the anomalies of continental aridity and intensity of winter monsoon winds at millennial-scale events exhibit power in the precession band, nearly in antiphase with Northern Hemisphere summer insolation. These observations indicate that the insolation drove the anomalies in the Indian Summer Monsoon. The good correspondence between our record and the East Asian monsoon anomaly records suggests the occurrence of anomalous widespread arid events in Asia.

A 140-year record of environmental changes in São Sebastião, Brazil

Over the past two centuries, coastal and estuarine areas have experienced environmental stress due to rapid population growth, leading to higher demand, overexploitation, habitat transformation, and pollution, which have severe consequences on the overall ecosystem and human health. This work aims to understand historical perspectives of such environmental stress in a coastal area of São Sebastião city in the São Paulo State of Brazil, which has witnessed rapid changes in land use over the past 60-70 years. We collected eleven surface sediments and one 64 cm long core from the shallow water depth sector of the São Sebastião Channel (SSC), adjacent to the Araçá Bay region. Sediments were dominantly composed of terrestrial siliciclastic material carrying signatures of both local inputs (i.e., weathered granitic and gneissic rocks of Serra do Mar Mountain ranges) and Plata Plume sediments brought by Brazilian coastal currents. Low sediment accumulation (avg. = 0.10 cm yr^-1) between 1880 and 1947 showed a stable environment followed by an abrupt increase in sedimentation (avg. = 0.84 cm yr^-1) from 1947 to 2017. This approximate eight-fold increase in sedimentation after 1947 marked significant anthropogenic changes in the region, which is coincidental with major changes in land use through the construction of the port of São Sebastião (1930s) and BR-101 Highway (1980s). While recent surface sediments showed no pollution of heavy metals, anthropogenic Zn enrichment was found between 1880 and 2000. Zn enrichment was from the combined sources, e.g., agriculture activities, domestic sewage, and possibly Zn coated ship paints. Our study also indicates that planned future expansion of São Sebastião port may further increase the sedimentation rate in SSC and impact the ecosystem of Araçá Bay and SSC.

Spatial patterns of microbial diversity in Fe-Mn deposits and associated sediments in the Atlantic and Pacific oceans

Mining of deep-sea Fe-Mn deposits will remove crusts and nodules from the seafloor. The growth of these minerals takes millions of years, yet little is known about their microbiome. Besides being key elements of the biogeochemical cycles and essential links of food and energy to deep-sea, microbes have been identified to affect manganese oxide formation. In this study, we determined the composition and diversity of Bacteria and Archaea in deep-sea Fe-Mn crusts, nodules, and associated sediments from two areas in the Atlantic Ocean, the Tropic Seamount and the Rio Grande Rise. Samples were collected using ROV and dredge in 2016 and 2018 oceanographic campaigns, and the 16S rRNA gene was sequenced using Illumina platform. Additionally, we compared our results with microbiome data of Fe-Mn crusts, nodules, and sediments from Clarion-Clipperton Zone and Takuyo-Daigo Seamount in the Pacific Ocean. We found that Atlantic seamounts harbor an unusual and unknown Fe-Mn deposit microbiome with lower diversity and richness compared to Pacific areas. Crusts and nodules from Atlantic seamounts have unique taxa (Alteromonadales, Nitrospira, and Magnetospiraceae) and a higher abundance of potential metal-cycling bacteria, such as Betaproteobacteriales and Pseudomonadales. The microbial beta-diversity from Atlantic seamounts was clearly grouped into microhabitats according to sediments, crusts, nodules, and geochemistry. Despite the time scale of million years for these deposits to grow, a combination of environmental settings played a significant role in shaping the microbiome of crusts and nodules. Our results suggest that microbes of Fe-Mn deposits are key in biogeochemical reactions in deep-sea ecosystems. These findings demonstrate the importance of microbial community analysis in environmental baseline studies for areas within the potential of deep-sea mining.

Presence of biogenic magnetite in ferromanganese nodules

Transmission electron microscopy (TEM) and rock magnetic study of ferromanganese nodule sample JC120-104B collected from Clarion-Clipperton zone (CCZ) in the eastern Pacific Ocean indicate the presence of biogenic magnetite (magnetofossils). First-order reversal curves (FORCs) and decomposition of isothermal remanent magnetization (IRM) curves were used as the main tool for the characterization of magnetic properties of the bulk magnetic minerals present in the sample. TEM was performed for the direct identification of biogenic magnetic minerals (magnetofossils). The nodule sample has distinctive alternating Mn and Fe-rich layers per micro-X-ray fluorescence data. While diagenetic precipitation of Mn is known for the less oxygenated environment, the presence of biogenic magnetite is also common in the environments where the supply of oxygen is limited. Moreover, the increase in magnetic properties is consistent with the increase in Mn-content, which is related to favourable conditions for Mn precipitation as well as magnetite biomineralization in oxic-suboxic transition zone. Investigations on magnetofossil fingerprints lead to a better understanding of paleoenvironmental conditions involved in the formation and growth of deep-sea ferromanganese nodules.

Abyssal oceanic circulation and acidification during the Middle Eocene Climatic Optimum (MECO)

The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at around 40 Ma and lasted about 500 kyr. We study this event in an abyssal setting of the Tasman Sea, using the IODP Core U1511B-16R, collected during the expedition 371. We analyse magnetic, mineralogical, and chemical parameters to investigate the evolution of the sea bottom conditions at this site during the middle Eocene. We observe significant changes indicating the response to the MECO perturbation. Mn oxides, in which Mn occurs under an oxidation state around +4, indicate a high Eh water environment. A prominent Mn anomaly, occurring just above the MECO interval, indicates a shift toward higher pH conditions shortly after the end of this event. Our results suggest more acid bottom water over the Tasman abyssal plain during the MECO, and an abrupt end of these conditions. This work provides the first evidence of MECO at abyssal depths and shows that acidification affected the entire oceanic water column during this event.

Dataset of characteristic remanent magnetization and magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform)

This data article describes data of magnetic stratigraphy and anisotropy of isothermal remanent magnetization (AIRM) from "Magnetic properties of early Pliocene sediments from IODP Site U1467 (Maldives platform) reveal changes in the monsoon system" [1]. Acquisition of isothermal magnetization on pilot samples and anisotropy of isothermal remanent magnetization are reported as raw data; magnetostratigraphic data are reported as characteristic magnetization (ChRM).

Carbon cycle instability and orbital forcing during the Middle Eocene Climatic Optimum

The Middle Eocene Climatic Optimum (MECO) is a global warming event that occurred at about 40 Ma. In comparison to the most known global warming events of the Paleogene, the MECO has some peculiar features that make its interpretation controversial. The main peculiarities of the MECO are a duration of ~500 kyr and a carbon isotope signature that varies from site to site. Here we present new carbon and oxygen stable isotopes records (δ¹³C and δ¹⁸O) from three foraminiferal genera dwelling at different depths throughout the water column and the sea bottom during the middle Eocene, from eastern Turkey. We document that the MECO is related to major oceanographic and climatic changes in the Neo-Tethys and also in other oceanic basins. The carbon isotope signature of the MECO is difficult to interpret because it is highly variable from site to site. We hypothesize that such δ¹³C signature indicates highly unstable oceanographic and carbon cycle conditions, which may have been forced by the coincidence between a 400 kyr and a 2.4 Myr orbital eccentricity minimum. Such forcing has been also suggested for the Cretaceous Oceanic Anoxic Events, which resemble the MECO event more than the Cenozoic hyperthermals.

Fingerprints of partial oxidation of biogenic magnetite from cultivated and natural marine magnetotactic bacteria using synchrotron radiation

Magnetotactic bacteria are a multi-phyletic group of bacteria that synthesize membrane-bound magnetic minerals. Understanding the preservation of these minerals in various environments (e.g., with varying oxygen concentrations and iron supply) is important for understanding their role as carriers of primary magnetizations in sediments and sedimentary rocks. Here we present X-ray near edge structure (XANES) spectra for Fe in magnetotactic bacteria samples from recent sediments to assess surface oxidation and crystal structure changes in bacterial magnetite during early burial. Our results are compared with a XANES spectrum of cultivated Magnetofaba australis samples, and with magnetic properties, and indicate that oxidation of magnetite to maghemite increases with depth in the sediment due to longer exposure to molecular oxygen. These results are relevant to understanding magnetic signatures carried by magnetofossils in oxic sediments and sedimentary rocks of different ages.

The abrupt onset of the modern South Asian Monsoon winds

The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment’s content of particulate organic matter. A weaker ‘proto-monsoon’ existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system.

Prismatic magnetite magnetosomes from cultivated Magnetovibrio blakemorei strain MV-1: a magnetic fingerprint in marine sediments?

The magnetic properties (first-order reversal curves, ferromagnetic resonance and decomposition of saturation remanent magnetization acquisition) of Magnetovibrio blakemorei, a cultivated marine magnetotactic bacterium, differ from those of other magnetotactic species from sediments deposited in lakes and marine habitats previously studied. This finding suggests that magnetite produced by some magnetotactic bacteria retains magnetic properties in relation to the crystallographic structure of the magnetic phase produced and thus might represent a 'magnetic fingerprint' for a specific magnetotactic bacterium. The use of this fingerprint is a non-destructive, new technology that might allow for the identification and presence of specific species or types of magnetotactic bacteria in certain environments such as sediments.

MHC class II alleles associated with clinical and immunological manifestations of HIV-1 infection among children in Catalonia, Spain

Children with perinatally-acquired HIV-1 infection were studied to determine if major histocompatibility complex (MHC) genes are involved in progression to pediatric AIDS. Molecular genetic techniques were used to genotype loci in the class II region (DRB1, DQA1, DQB1, DPA1, DPB1, LMP2 and LMP7). HIV-infected children were classified by clinical manifestations and degree of immunosuppression using age-specific CD4 T-lymphocyte counts at enrollment. Alleles at the DPB1 and DQB1 loci showed independent and opposite associations; DPB1*0301 showed a trend toward protection while DQB1*0201 appeared to be a risk factor for developing severe immunosuppression and severe clinical outcomes. Presence of DQB1*0201 conferred a greater than 10-fold increased odds of having severe clinical manifestations and a 2.8-fold increased odds of severe immunosuppression. Presence of DPB1*0301 was associated with a greater than 8-fold decreased odds of severe immunosuppression and severe clinical manifestations. These results support host genetic influences on HIV-1 outcomes in children.