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The export of neritic material from the top of carbonate platforms is a key process in the construction of their slopes. However, our knowledge of the supply pattern of materials from platforms is dominantly based on platforms lying in the euphotic zone during the present sea‐level highstand. This is a somewhat biased perspective as through geological time not all platforms were euphotic. The Saya de Malha Bank in the Mascarene Plateau is an example of a modern mesophotic carbonate platform, and as such, its flooding and export patterns differ from those of euphotic ones. Using cores collected on the western slope of the Saya de Malha Bank, the export patterns of the platform since the last glacial maximum were explored. Material on the platform edge is winnowed and transported to the slope by multiple possible processes. The material on the platform is a combination of high and low magnesium calcite as well as high and low strontium aragonite, integrating pelagic and neritic sources. The ratio of these constituents varies over time with changes in the platform production capability as it was flooded and drowned during the Holocene transgression. The material from the platform is transported in both confined flows, mainly during lowstands, and unconfined flows, mainly during late transgression and early highstand. In the present state of the highstand, supply may have diminished, leading to erosion of the canyon shoulders. [ABSTRACT FROM AUTHOR]

Repeated carbon isotope excursions and widespread organic-rich shale deposition mark the Middle and Upper Devonian series. Various explanations such as extensive volcanism and land plant evolution have been given for these perturbations and the general sensitivity of the Devonian oceans to the development of anoxia, but their repeated nature suggests that astronomical forcing may have controlled their timing. Here, a cyclostratigraphic study of the Kellwasser Crisis at the Frasnian–Famennian stage boundary (ca. 372 Ma) is carried out. The Kellwasser Crisis was one of the most ecologically impactful of the Devonian perturbations and is ranked among the "Big Five" Phanerozoic mass extinctions. The studied site is the Winsenberg roadcut section in the Rhenish Massif, Germany, which represents a quiet tropical shelf basin setting. Centimetre-scale elemental records, generated by portable X-ray scanning, allow for testing of the hypothesis that a 2.4 Myr eccentricity node preceded the Upper Kellwasser event. The study's results are supportive of this hypothesis. We find enhanced chemical weathering (K 2 O / Al 2 O 3) during the period leading up to the Upper Kellwasser and a peak in distal detrital input (SiO 2 / CaO) and riverine runoff (TiO 2 / Al 2 O 3) just prior to the start of the Upper Kellwasser event. We interpret this pattern as the long-term eccentricity minimum facilitating excessive regolith build-up in the absence of strong seasonal contrasts. The Earth's system coming out of this node would have rapidly intensified the hydrological cycle, causing these nutrient-rich regoliths to be eroded and washed away to the oceans, where they resulted in eutrophication and anoxia. An astronomical control on regional climate is observed beyond this single crisis. Wet–dry cycles were paced by 405 kyr eccentricity, with both the Lower and Upper Kellwasser events taking place during comparatively drier times. A precession-sensitive monsoonal climate system prevailed on shorter timescales. Intensification of this monsoonal system following the node may have caused the widespread regolith erosion. We estimate the total duration of the Kellwasser Crisis at ca. 900 kyr, with the individual events lasting for ca. 250 and 100 kyr, respectively. If astronomical control indeed operated via regolith development in monsoonal climates, then land plants may have played an important role. This would not have been through evolutionary steps directly triggering Kellwasser perturbations but by gradually strengthening the climatic response to orbital forcing via soil development – creating soils thick enough to meaningfully respond to orbital forcing – and intensifying the hydrological cycle. [ABSTRACT FROM AUTHOR]

Methane‐derived authigenic seep carbonates occur globally along continental margins. These carbonates are important archives to identify seep dynamics, the source of the ascending methane‐enriched fluids together with their timing, and are an important carbon sequestration mechanism. Recently, seep carbonates were discovered in the Levant Basin in the south‐eastern Mediterranean Sea. To elucidate past seepage activity and dynamics across the basin, different seep carbonate morphologies (chimneys, crusts and pavements) retrieved from the Levant Basin were mapped based on remotely operating vehicle data and analysed using standard sediment petrographic techniques, X‐ray diffraction and stable carbon and oxygen isotope analyses. Carbonate chimneys consist of micrite (δ13CVPDB of −10‰ to +5‰) with dispersed baryte and dolomite crystals, fan‐shaped aragonite (δ13CVPDB of −52‰ to −30‰) and high‐magnesium calcite cements, with the latter often growing from low‐magnesium calcite spherules. Botryoidal low‐magnesium calcite cements are forming in small cavities. Carbonate crusts consist of micrite with low‐magnesium calcite breccias, high‐magnesium calcite nodules (δ13CVPDB of −35‰ to −20‰) and cements, and partially replaced fan‐shaped aragonite cements. Carbonate pavements consist of low‐magnesium calcite microsparite, micritic dolomite and high‐magnesium calcite. Fan‐shaped aragonite is locally present as pore‐lining cement. Iron oxides are often seen coating the low‐magnesium calcite, high‐magnesium calcite and dolomite cements. Chimneys and crusts, characterised by high amounts of high‐magnesium calcite and aragonite, are interpreted to have formed through advective methane fluxes. Pavements, with high quantities of dolomite, are explained as the product of diffusive methane flux. Sediment petrographic and geochemical analysis of the different carbonate morphologies and cement phases therein witness distinct modes of ascending fluid fluxes and their mixing with marine pore water and/or sea water during precipitation of the individual phases. [ABSTRACT FROM AUTHOR]

Changes in sea-level are linked to glacial-interglacial variability and have been claimed as the main factor controlling the production of carbonate platform factories. The Maldives archipelago (Indian Ocean), composed of two rows of atolls that enclose an inner sea, is a very sensitive region to sea-level changes. The sediments of the Inner Sea, offer an excellent study site to explore the impact of sea-level changes on carbonate platforms. Elemental geochemical composition records, obtained by X-ray fluorescence (XRF) core-scanning, from the Maldives Inner Sea (IODP Site U1467), have been used in this work to evaluate the influence of orbitally-driven sea-level fluctuations on the carbonate production and export from the neritic environment into the Maldives Inner Sea over the last 1.3 million years. High Sr aragonite-rich carbonates (HSAC) from neritic settings are deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the values of the Sr/Ca ratio. In contrast, during sea-level lowstand periods large areas of the atolls were exposed or unable to grow and the demise in the carbonate production and sediment export is reflected as low Sr/Ca values in the Inner Sea. However, we propose that sea level is not the only factor controlling the production of HSAC during sea-level highstands since several interglacial periods before and after the Mid-Brunhes event (MBE, ~430 ka) indicate high carbonate production (high Sr/Ca). The intensity of the summer monsoon and the Indian Ocean Dipole probably modulated the production at the atolls. Marine Isotope Stage 11 stands out as a period with high sea-level and rather high carbonate production in the Maldives platform. This extraordinary carbonate production in the Maldives atolls (and in other low latitude carbonate platforms) probably contributed to the Mid-Brunhes dissolution event through a strong shelf-to-basin fractionation of carbonate deposition. [ABSTRACT FROM AUTHOR]

The oceans play a major role in the earth's climate by regulating atmospheric CO2. While oceanic primary productivity and organic carbon burial sequesters CO2 from the atmosphere, precipitation of CaCO3 in the sea returns CO2 to the atmosphere. Abiotic CaCO3 precipitation in the form of aragonite is potentially an important feedback mechanism for the global carbon cycle, but this process has not been fully quantified. In a sediment-trap study conducted in the southeastern Mediterranean Sea, one of the fastest warming and most oligotrophic regions in the ocean, we quantify for the first time the flux of inorganic aragonite in the water column. We show that this process is kinetically induced by the warming of surface water and prolonged stratification resulting in a high aragonite saturation state (ΩAr ≥ 4). Based on these relations, we estimate that abiotic aragonite calcification may account for 15 ± 3% of the previously reported CO2 efflux from the sea surface to the atmosphere in the southeastern Mediterranean. Modelled predictions of sea surface temperature and ΩAr suggest that this process may weaken in the future ocean, resulting in increased alkalinity and buffering capacity of atmospheric CO2. [ABSTRACT FROM AUTHOR]

Marginal seas and shelf environments exhibit a variable behavior with respect to air-sea CO2 fluxes in response to large variations in temperature, primary productivity, freshwater balance etc. The Southeastern Mediterranean Sea (SEMS) represents an extreme example of a marine system radically altered due to anthropogenic forcing such as the damming of the Nile, which reduced fresh water and nutrient input to the basin, and significant warming over the last few decades. Here we present a long-term record of seawater pH in the SEMS, which is a combination of a reconstructed record together with more recent in situ measurements that demonstrate the SEMS response to these pressures. The reconstructed record is derived from high resolution measurements of δ13C of vermetid reefs together with a long time series of hydrographic data following the damming of the Nile. The record indicates that the SEMS has experienced a significant acidification of ΔpH/Δt = –0.022 ± 0.002 decade–1. This rate exceeds those of the open-ocean time series, but is lower compared to rates measured in the Western Mediterranean Sea. The continued increase of salinity/alkalinity in the SEMS since the damming of the Nile appears to have strengthened the carbon buffer with respect to acidification, which lowered the acidification rate of this region by an estimated 27%. However, this is masked by the effect of relatively rapid warming trends (~+1 °C/decade) in the region which resulted in nearly year-round super-saturation of pCO2 in the surface layer of the SEMS. Ongoing measurements of the carbonate system since 2009 in the SEMS indicates that the system is thermodynamically governed, with a minimal biological feedback. The SEMS has become a net source of atmospheric CO2 annually on the order of 0.44 Tg C y-1, a figure that is expected to grow with continued warming in the future. [ABSTRACT FROM AUTHOR]