Water chemistry reveals a significant decline in coral calcification rates in the southern Red Sea

Experimental and field evidence support the assumption that global warming and ocean acidification is decreasing rates of calcification in the oceans. Local measurements of coral growth rates in reefs from various locations have suggested a decline of ~6–10% per decade since the late 1990's. Here, by measuring open water strontium-to-alkalinity ratios along the Red Sea, we show that the net contribution of hermatypic corals to the CaCO3 budget of the southern and central Red Sea declined by ~100% between 1998 and 2015 and remained low between 2015 and 2018. Measured differences in total alkalinity of the Red Sea surface water indicate a 26 ± 16% decline in total CaCO3 deposition rates along the basin. These findings suggest that coral reefs of the southern Red Sea are under severe stress and demonstrate the strength of geochemical measurements as cost-effective indicators for calcification trends on regional scales

Basin-scale estimates of pelagic and coral reef calcification in the Red Sea and Western Indian Ocean.

Basin-scale calcification rates are highly important in assessments of the global oceanic carbon cycle. Traditionally, such estimates were based on rates of sedimentation measured with sediment traps or in deep sea cores. Here we estimated CaCO3 precipitation rates in the surface water of the Red Sea from total alkalinity depletion along their axial flow using the water flux in the straits of Bab el Mandeb. The relative contribution of coral reefs and open sea plankton were calculated by fitting a Rayleigh distillation model to the increase in the strontium to calcium ratio. We estimate the net amount of CaCO3 precipitated in the Red Sea to be 7.3 ± 0.4·10(10) kg·y(-1) of which 80 ± 5% is by pelagic calcareous plankton and 20 ± 5% is by the flourishing coastal coral reefs. This estimate for pelagic calcification rate is up to 40% higher than published sedimentary CaCO3 accumulation rates for the region. The calcification rate of the Gulf of Aden was estimated by the Rayleigh model to be ∼1/2 of the Red Sea, and in the northwestern Indian Ocean, it was smaller than our detection limit. The results of this study suggest that variations of major ions on a basin scale may potentially help in assessing long-term effects of ocean acidification on carbonate deposition by marine organisms

Recognition and treatment of law enforcement violence against detainees and prisoners: A survey among Israeli physicians and medical students

Introduction: Physicians regularly encounter victims of violence. Although some at-risk groups are increasingly recognized as such, the risks faced by prisoners and detainees are often overlooked. The scope of violence against them is unknown and their treatment is often hampered by unique social and institutional impediments. This article reviews the need for improved recognition and protection of such patients and the associated obstacles, while presenting information on the experience, knowledge and attitudes of physicians in Israel regarding the maltreatment of prisoners and detainees. Methods: We sent a questionnaire to physicians and medical students in Israel to enquire about their knowledge concerning examination and treatment of persons under police custody who appear to be victims of violence as well as their attitude concerning torture. Results: We received answers from443 physicians and 114 medical students. Most physicians would correctly examine and document the injuries, but only 59% would report their suspicions of violence to the Ministry of Health. Though 60% of physicians objected in principle to the use of torture, a majority endorsed the use of physical and psychological pressure during interrogation. Moreover, 29% of physicians thought it is permissible for physicians to examine detainees and verify their health so that torture can begin or continue. Discussion: Our study shows that there is a need for development and implementation of treatment and reporting protocols as well as educational programs concerning the ethical and legal requirements of physicians towards detainees and prisoners in Israel. Limitations of our study are discussed

Carbonates dissolution and precipitation in hemipelagic sediments overlaid by supersaturated bottom-waters - Gulf of Aqaba, Red Sea

Whether CaCO₃ dissolves within the top centimeters of marine sediments overlaid by deep, supersaturated bottom waters remains an area of debate in geochemistry. This uncertainty stems from the fact that different methods used to assess CaCO₃ dissolution rates often provide what appear to be profoundly different results. Here we combine microelectrode and porewater chemistry profiles, core incubation experiments, mineral characterizations and observations of the state of preservation of coccolithophorid exoskeletons for a holistic view of carbonate reactions within the top 30 centimeters of hemipelagic sediments from the Gulf of Aqaba, Red Sea. Calculations based on pH and O₂ microelectrode data suggest that rapid metabolic dissolution of carbonate minerals occurs in these sediments within the top two millimeters. Porewater chemistry supports these calculations. The porewater-based observations are further supported by sedimentological characteristics such as aragonite content, and dissolution pitting and fragmentation of coccoliths in sediment layers deposited over the last 200 y. Dissolution appears to be occurring today within surface sediments despite the bulk porewater solution being supersaturated with respect to aragonite and Mg-calcite. In spite of intense dissolution within the sediments, there is no evidence for significant alkalinity and/or calcium fluxes (transport) into bottom waters. It appears that the supersaturated bottom water promotes the removal of all excess alkalinity and calcium produced within the sediment, by CaCO₃ precipitation at or above the sediment/bottom water interface. The precipitation mechanism may be by either benthic organisms (biogenic precipitation) or inorganically (direct precipitation on settling CaCO₃ grains). We suggest that authigenic precipitation of (Ca,Mn)CO₃ as it becomes supersaturated below 3 cm in the sediments can reconcile the evidence for carbonate dissolution in what appears to be supersaturated conditions. This means that MnCO₃ replaces CaCO₃ within the nanofossils below similar to ~3 cm, and that part of the manganese rich CaCO₃ is bioturbated upwards into undersaturated conditions, facilitating dissolution of these fossils. Diminished calcite and aragonite concentrations in sediments deposited in recent decades are proposed to be a result of increased manganese cycling rates and greater rates of coupled dissolution within the interfacial sediments, possibly combined with diminished calcareous plankton productivity, in response to increased surface water primary productivity

Assessing Sedimentary Boundary Layer Calcium Carbonate Precipitation and Dissolution Using the Calcium Isotopic Composition of Pore Fluids

We present pore fluid geochemistry, including major ion and trace metal concentrations and the isotopic composition of pore fluid calcium and sulfate, from the uppermost meter of sediments from the Gulf of Aqaba (Northeast Red Sea) and the Iberian Margin (North Atlantic Ocean). In both the locations, we observe strong correlations among calcium, magnesium, strontium, and sulfate concentrations as well as the sulfur isotopic composition of sulfate and alkalinity, suggestive of active changes in the redox state and pH that should lead to carbonate mineral precipitation and dissolution. The calcium isotope composition of pore fluid calcium (δ44Ca) is, however, relatively invariant in our measured profiles, suggesting that carbonate mineral precipitation is not occurring within the boundary layer at these sites. We explore several reasons why the pore fluid δ44Ca might not be changing in the studied profiles, despite changes in other major ions and their isotopic composition, including mixing between the surface and deep precipitation of carbonate minerals below the boundary layer, the possibility that active iron and manganese cycling inhibits carbonate mineral precipitation, and that mineral precipitation may be slow enough to preclude calcium isotope fractionation during carbonate mineral precipitation. Our results suggest that active carbonate dissolution and precipitation, particularly in the diffusive boundary layer, may elicit a more complex response in the pore fluid δ44Ca than previously thought

The role of microbial sulfate reduction in calcium carbonate polymorph selection

Microbial sulfate reduction is a dominant metabolism in many marine sedimentary environments. The influence of this metabolism on the kinetics of CaCO3 growth, as well as the dominant polymorphs precipitated, is poorly understood. To investigate the role of microbial metabolism on CaCO3 precipitation and polymorph selection, we conducted growth experiments with the sulfate reducing bacteria (D. bizertensis) in media with varying Mg/Ca and different seeding materials (calcite and kaolinite). Our results suggest that sulfate reducing bacteria both induce carbonate mineral precipitation through an increase in alkalinity and serve as a nucleation sites for the growing carbonate mineral; the majority of the carbonate minerals produced were on cell material rather than mineral seeds. We also find the Mg/Ca and presence of phosphate in the media play a key role in controlling the rates of carbonate mineral precipitation and calcium carbonate polymorph selection. In media where the Mg/Ca is greater than 2, crystalline monohydrocalcite (MHC) is the primary carbonate mineral produced. Although phosphate concentrations have a lesser effect on which polymorph initially precipitates, a series of transformation experiments suggests that the presence of phosphate stabilizes MHC crystals and prevents its transformation to more stable calcium carbonate polymorphs. Collectively, these results suggest that the polymorph of microbially-mediated calcium carbonate cements is determined by the solution chemistry upon nucleation.Ministry of Education Malaysia, SLAI (Skim Latihan Akademik IPTA) scholarship to CY

On calcium-to-alkalinity anomalies in the North Pacific, Red Sea, Indian Ocean and Southern Ocean

An important factor for predicting the effect of increased CO2 on future acidification of the ocean is a proper understanding of the interactions controlling production and dissolution of calcium carbonate minerals (CaCO3). The production and dissolution of CaCO3 in the ocean can be assessed over large spatial scales by measuring seawater calcium concentrations and total alkalinity (AT), yet past studies suggest that there could be large discrepancies between calcium and AT-based balances of the CaCO3 cycle in the North Pacific and Indian Oceans. Here, we analyse water column samples collected along transects in the North Pacific, Southern Ocean, tropical Indian Ocean and Red Sea for their concentrations of calcium, nutrients, and AT. We find that there is an excess calcium over AT anomaly in the top 1000 m of the tropical Indian Ocean water-column. The source of this anomaly is the dissolution of subsurface gypsum deposits in the Red Sea. We find no evidence for calcium-over-AT anomalies in the North Pacific, in contrast to previous studies. Our results show that, in most cases, calcium and AT data agree well and can be used to reconstruct the marine CaCO3 cycle

Rainbow non-boyant hydrothermal plumee GEOTRACES study, Cruise No. M176/2, 01.09.2021-06.10.2021, Emden (Germany) – Emden (Germany), Rainbow Plume

On cruise M176/2 we conducted detailed water column surveys in close vicinity to the Rainbow hydrothermal vent field and up to a distance of 60 km along the hydrothermal plume flow. Our aim was to determine the fate of hydrothermally derived trace elements and isotopes (TEIs) with increasing distance from the source, including an assessment of changes in physical and chemical speciation. We assessed to what extent TEIs are controlled by vent supply, particle removal processes and advection. Sampling of Th, Ra and He isotopes was conducted to facilitate quantification of hydrothermal fluxes and removal of TEI and fingerprint sources to elucidate TEI distributions. Atmospheric and deep water (micro)nutrient supply to the surface ocean was assessed to investigate controls on microbial ecosystem functioning, including productivity and diazotrophy. In addition, the role of dissolved organic nitrogen (DON) as a N source to phytoplankton was assessed. The work used GEOTRACES trace metal clean sampling and analysis approaches and the cruise forms a GEOTRACES Process Cruise