Benthic fluxes of trace metals in the Chukchi Sea and their transport into the Arctic Ocean

Highlights • Frequent sediment resuspension may have buffered D-Fe released from shelf sediments. • 228Ra was used to estimate trace element fluxes from the Chukchi shelf sediments. • The estimated sediment 228Ra flux ranks among the highest reported globally. • About 10–25% of the Chukchi shelf sediment Fe flux is exported to the Arctic Ocean. The Chukchi Sea is a primary site for shelf-ocean exchange in the Arctic region and modifies Pacific-sourced water masses as they transit via the Bering Strait into the Arctic Ocean. The aim of this study was to use radium and trace metal distributions to improve our understanding of biogeochemical cycles in the Bering and Chukchi Seas, and evaluate their potential response to future changes in the Arctic. We investigated the distributions of dissolved and total dissolvable trace metals (Cd, Fe, Ni, Cu, Zn, Mn, Co, and Pb) in the Bering and Chukchi Seas during spring. In addition, the long-lived radium isotopes (226Ra and 228Ra) were measured as tracers of benthic trace metal inputs. Trace metal concentrations, especially Fe and Mn, were highly elevated in Chukchi shelf waters compared with the open Arctic Ocean and Bering Strait. Trace metal, nutrient, and Ra patterns suggested that Fe, Mn, and Co concentrations were predominantly controlled by reductive benthic inputs, whereas the other trace metals were influenced by biological uptake and release processes. We propose that Fe, Mn, and Co in the Chukchi Sea are supplied from shelf sediments during winter overturning, and we combine the 228Ra fluxes with the distributions of Fe, Mn, and Co to provide a first estimate of their benthic fluxes in the region. The average benthic flux of 228Ra was 1.49 × 108 atoms m−2 d−1, which is among the highest rates reported globally. Estimated dissolved Fe (D-Fe) flux from the sediments was 2.5 μmol m−2 d−1, whereas D-Mn and D-Co fluxes were 8.0 μmol m−2 d−1 and 0.2 μmol m−2 d−1, respectively. The off-shelf transport of D-Fe to the Arctic Ocean is estimated to be about 10–25% of the benthic Fe flux, with the remainder retained on the shelf due to scavenging and/or phytoplankton uptake. Our results highlight the importance of the Chukchi Sea as a major source of the micro-nutrients to the Arctic Ocean, thereby supporting primary production. Long-term changes in factors that affect cross-shelf mixing, such as the observed reduction in ice cover, may therefore enhance shelf nutrient inputs and primary productivity in the Arctic

Strike-slip faults mediate the rise of crustal-derived fluids and mud volcanism in the deep sea

We report on newly discovered mud volcanoes located at ∼4500 m water depth ∼90 km west of the deformation front of the accretionary wedge of the Gulf of Cadiz, and thus outside of their typical geotectonic environment. Seismic data suggest that fluid flow is mediated by a >400-km-long strike-slip fault marking the transcurrent plate boundary between Africa and Eurasia. Geochemical data (Cl, B, Sr, 87Sr/86Sr, δ18O, δD) reveal that fluids originate in oceanic crust older than 140 Ma. On their rise to the surface, these fluids receive strong geochemical signals from recrystallization of Upper Jurassic carbonates and clay-mineral dehydration in younger terrigeneous units. At present, reports of mud volcanoes in similar deep-sea settings are rare, but given that the large area of transform-type plate boundaries has been barely investigated, such pathways of fluid discharge may provide an important, yet unappreciated link between the deeply buried oceanic crust and the deep ocean

Sex differences in treatment strategy for coronary artery aneurysms: Insights from the international Coronary Artery Aneurysm Registry

INTRODUCTION: Sex disparities exist in coronary artery disease (CAD) in terms of risk profile, clinical management and outcome. It is unclear if differences are also present in coronary aneurysms, a rare variant of CAD. METHODS: Patients were selected from the international Coronary Artery Aneurysm Registry (CAAR; ClinicalTrials.gov: NCT02563626), and differences between groups were analysed according to sex. The CAAR database is a prospective multicentre registry of 1565 patients with coronary aneurysms (336 females). Kaplan-Meier method was used for event-free survival analysis for death, major adverse cardiac events (MACE: composite endpoint of death, heart failure and acute coronary syndrome) and bleeding. RESULTS: Female patients were older, were more often hypertensive and less frequently smoker. They were treated conservatively more often compared to male patients and received significantly less frequently aspirin (92% vs 88%, p = 0.002) or dual antiplatelet therapy (DAPT) (67% vs 58%, p = 0.001) at discharge. Median DAPT duration was also shorter (3 vs 9 months, p = 0.001). Kaplan-Meier analysis revealed no sex differences in death, MACE or bleeding during a median follow-up duration of 37 months, although male patients did experience acute coronary syndrome (ACS) more often during follow-up (15% vs 10%, p = 0.015). CONCLUSIONS: These CAAR findings showed a comparable high-risk cardiovascular risk profile for both sexes. Female patients were treated conservatively more often and received DAPT less often at discharge, with a shorter DAPT duration. ACS was more prevalent among male patients; however, overall clinical outcome was not different between male and female patients during follow-up

Rifting under steam – how rift magmatism triggers methane venting from sedimentary basins

During opening of a new ocean magma intrudes into the surrounding sedimentary basins. Heat provided by the intrusions matures the host rock creating metamorphic aureoles potentially releasing large amounts of hydrocarbons. These hydrocarbons may migrate to the seafloor in hydrothermal vent complexes in sufficient volumes to trigger global warming, e.g. during the Paleocene Eocene Thermal Maximum (PETM). Mound structures at the top of buried hydrothermal vent complexes observed in seismic data off Norway were previously interpreted as mud volcanoes and the amount of released hydrocarbon was estimated based on this interpretation. Here, we present new geophysical and geochemical data from the Gulf of California suggesting that such mound structures could in fact be edifices constructed by the growth of black-smoker type chimneys rather than mud volcanoes. We have evidence for two buried and one active hydrothermal vent system outside the rift axis. The vent releases several hundred degrees Celsius hot fluids containing abundant methane, mid-ocean-ridge-basalt (MORB)-type helium, and precipitating solids up to 300 m high into the water column. Our observations challenge the idea that methane is emitted slowly from rift-related vents. The association of large amounts of methane with hydrothermal fluids that enter the water column at high pressure and temperature provides an efficient mechanism to transport hydrocarbons into the water column and atmosphere, lending support to the hypothesis that rapid climate change such as during the PETM can be triggered by magmatic intrusions into organic-rich sedimentary basins

Cold-water corals in the Bay of Biscay - occurrences and distribution in space and time (TransBiscay) - Cruise No. M84/5, May 31 - June 21, 2011, Vigo (Spain) - Brest (France)

The scientific objectives of METEOR cruise M84/5 focused on the measurement and analysis of the environmental controls of modern and fossil cold-water coral growth along a transect in the Bay of Biscay. In four working areas we successfully deployed lander systems and CTD/Ro’s to document the physical and hydrochemical characteristics of bottom water masses and the water column in general. These are used to shed light on potential linkages to modern cold-water coral growth and distribution. These investigations were flanked by plankton tows in surface waters. The base for all investigations was a thorough hydroacoustic survey to characterize potential cold-water coral bearing areas with living colonies. Based on these maps we deployed all video-guided gear such as the OFOS-video sled, the TV grab, and the lander systems. Benthic assemblages and sedimentary structures have been documented and sampled with the OFOS and a box corer. Simultaneously, genetic samples of the living coral material were taken for additional studies. Furthermore, we have taken gravity cores to investigate the paleoceanographic conditions as well as the timing of cold-water coral colonization in the Bay of Biscay. Along with the coring efforts, a detailed sampling and study of porewater properties was performed. An additional aim of this cruise was to investigate the influence of boundary exchange processes on the Neodymium isotopy in bottom waters along the pathway of the Mediterranean Outflow water (MOW) by taking multiple samples with the CTD/Ro. The new data and samples of this METEOR cruise will provide the framework to investigate the timing of cold-water coral colonization in the Bay of Biscay, as well as its interplay with the ambient hydrography and geochemistry. This successful cruise has provided the basis to investigate the scientific aims of this expedition in great detail

Robust metrics for assessing the performance of different verbal autopsy cause assignment methods in validation studies

<p>Abstract</p> <p>Background</p> <p>Verbal autopsy (VA) is an important method for obtaining cause of death information in settings without vital registration and medical certification of causes of death. An array of methods, including physician review and computer-automated methods, have been proposed and used. Choosing the best method for VA requires the appropriate metrics for assessing performance. Currently used metrics such as sensitivity, specificity, and cause-specific mortality fraction (CSMF) errors do not provide a robust basis for comparison.</p> <p>Methods</p> <p>We use simple simulations of populations with three causes of death to demonstrate that most metrics used in VA validation studies are extremely sensitive to the CSMF composition of the test dataset. Simulations also demonstrate that an inferior method can appear to have better performance than an alternative due strictly to the CSMF composition of the test set.</p> <p>Results</p> <p>VA methods need to be evaluated across a set of test datasets with widely varying CSMF compositions. We propose two metrics for assessing the performance of a proposed VA method. For assessing how well a method does at individual cause of death assignment, we recommend the average chance-corrected concordance across causes. This metric is insensitive to the CSMF composition of the test sets and corrects for the degree to which a method will get the cause correct due strictly to chance. For the evaluation of CSMF estimation, we propose CSMF accuracy. CSMF accuracy is defined as one minus the sum of all absolute CSMF errors across causes divided by the maximum total error. It is scaled from zero to one and can generalize a method's CSMF estimation capability regardless of the number of causes. Performance of a VA method for CSMF estimation by cause can be assessed by examining the relationship across test datasets between the estimated CSMF and the true CSMF.</p> <p>Conclusions</p> <p>With an increasing range of VA methods available, it will be critical to objectively assess their performance in assigning cause of death. Chance-corrected concordance and CSMF accuracy assessed across a large number of test datasets with widely varying CSMF composition provide a robust strategy for this assessment.</p

Origin of high Mg and SO 4 fluids in sediments of the Terceira Rift, Azores – indications for caminite dissolution in a waning hydrothermal system

During R/V Meteor cruise 141/1, pore fluids of near surface sediments were investigated to find indications for hydrothermal activity in the Terceira Rift (TR), a hyper‐slow spreading center in the Central North Atlantic Ocean. To date, submarine hydrothermal fluid venting in the TR has only been reported for the D. João de Castro seamount, which presently seems to be inactive. Pore fluids sampled close to a volcanic cone at 2800 m water depth show an anomalous composition with Mg, SO4, and total alkalinity (TA) concentrations significantly higher than seawater and a nearby reference core. The most straightforward way of interpreting these deviations is the dissolution of the hydrothermally formed mineral caminite (MgSO4 0.25Mg(OH)2 0.2H2O). This interpretation is corroborated by a thorough investigation of fluid isotope systems (δ26Mg, δ30Si, δ34S, δ44/42Ca, and 87Sr/86Sr). Caminite is known from mineral assemblages with anhydrite, and forms in hydrothermal recharge zones only under specific conditions such as high fluid temperatures and in altered oceanic crust, which are conditions generally met at the TR. We hypothesize that caminite was formed during hydrothermal activity and is now dissolving during the waning state of the hydrothermal system, so that caminite mineralization is shifted out of its stability zone. Ongoing fluid circulation through the basement is transporting the geochemical signal via slow advection towards the seafloor