The benthic-pelagic coupling affects the surface water carbonate system above groundwater-charged coastal sediments

Submarine groundwater discharge (SGD) can be a significant source of dissolved nutrients, inorganic and organic carbon, and trace metals in the ocean and therefore can be a driver for the benthic-pelagic coupling. However, the influence of hypoxic or anoxic SGD on the carbonate system of coastal seawater is still poorly understood. In the present study, the production of dissolved inorganic carbon (DIC) and alkalinity (AT) in coastal sediments has been investigated under the impact of oxygen-deficient SGD and was estimated based on the offset between the measured data and the conservative mixing of the end members. Production of AT and DIC was primarily caused by denitrification and sulphate reduction. The AT and DIC concentrations in SGD decreased by approximately 32% and 37% mainly due to mixing with seawater counterbalanced by reoxidation and CO2 release into the atmosphere. Total SGD-AT and SGD-DIC fluxes ranged from 0.1 to 0.2mol m-2 d-1 and from 0.2 to 0.3mol m-2 d-1, respectively. These fluxes are probably the reason why the seawater in the Bay of Puck is enriched in AT and DIC compared to the open waters of the Baltic Sea. Additionally, SGD had low pH and was undersaturated with respect to the forms of the aragonite and calcite minerals of CaCO3. The seawater of the Bay of Puck also turned out to be undersaturated in summer (Inner Bay) and fall (Outer Bay). We hypoth​e​size that SGD can potentially contribute to ocean acidification and affect the functioning of the calcifying invertebrates

The role of anaerobic methane oxidation on the carbonate authigenesis in sediments of the subtropical Beibu Gulf, South China Sea: A reactive–transport modelling approach

The formation and burial of authigenic carbonate in marine sediment significantly affect the sedimentary carbon cycle and its isotopic mass balance in geological history. Anaerobic oxidation of methane (AOM) is the primary driver of authigenic carbonate precipitation within the sulfate-methane transition zone (SMTZ). Quantitative estimations of the role of AOM on the authigenic carbonate precipitation and its carbon isotope under non-steady-state processes (e.g., changes in methane fluxes at the bottom sediment, sedimentation rates or organic fluxes in the surface sediment), however, are still limited. In this study, we use geochemical data from porewater (e.g., the concentration of sulfate, calcium, magnesium, strontium, dissolved inorganic carbon, total alkalinity) and solid sediment (e.g., organic matter content, and carbonate content) in different depositional environments of the subtropical Beibu Gulf, South China Sea, combined with a diagenetic reactive-transport modelling approach, to estimate the mineralogy of authigenic carbonate, the relationship between AOM and authigenic carbonate precipitation, and the impact of AOM rate on carbon isotope of sediment carbonate (δ13CCar). The results show that high-Mg carbonates (high-Mg calcite and dolomite) are the main type of authigenic carbonate (∼80%) formed in the methane-bearing sediments, leading to higher porewater Sr2+/Ca2+ (>0.02) and Mg2+/Ca2+ (>20) within the SMTZ. Our modelling analysis highlights that the non-steady-state induced by increased methane flux from the underlying sediments can significantly accelerate the authigenic carbonates formation within the SMTZ. Using parametric sensitivity analysis, we observed that even a 1% increase in the authigenic carbonate fraction of sediment carbonates results in significant changes in δ13CCar within the SMTZ (from −1‰ to −2‰), mainly due to lighter carbon isotopes produced by more intensive AOM processes. Noteworthily, the terrestrial-to-marine transition was identified by the sediment and porewater geochemical profiles at site SO-8. Although lower authigenic carbonate precipitation occurs in terrestrial sedimentary environments, the proportion of authigenic carbonate in terrestrial environments (11%) is much higher than that in marine environments (1%), resulting in carbon isotopes of carbonate in terrestrial sediments becoming more negative (−5‰)

The impact of intertidal areas on the carbonate system of the southern North Sea

The coastal ocean is strongly affected by ocean acidification because of its shallow water depths, low volume, and the closeness to terrestrial dynamics. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea, a northwest European shelf sea, revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent back-barrier tidal areas (Wadden Sea) in summertime is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea tidal basins and the North Sea and the consequences for the carbonate system in the German Bight are estimated using a 3D ecosystem model. The aim of this study is to differentiate the various sources contributing to observed high summer TA in the southern North Sea. Measured TA and DIC in the Wadden Sea are considered as model boundary conditions. This procedure acknowledges the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. According to the modelling results, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is less than a previous estimate but within a comparable range. The interannual variabilities in TA and DIC, mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Dynamics in the carbonate system are found to be related to specific weather conditions. The results suggest that the Wadden Sea is an important driver for the carbonate system in the southern North Sea. On average 41 % of TA inventory changes in the German Bight were caused by riverine input, 37 % by net transport from adjacent North Sea sectors, 16 % by Wadden Sea export, and 6 % were caused by internal net production of TA. The dominant role of river input for the TA inventory disappears when focusing on TA concentration changes due to the corresponding freshwater fluxes diluting the marine TA concentrations. The ratio of exported TA versus DIC reflects the dominant underlying biogeochemical processes in the Wadden Sea. Whereas aerobic degradation of organic matter played a key role in the North Frisian Wadden Sea during all seasons of the year, anaerobic degradation of organic matter dominated in the East Frisian Wadden Sea. Despite the scarcity of high-resolution field data, it is shown that anaerobic degradation in the Wadden Sea is one of the main contributors of elevated summer TA values in the southern North Sea

Impact of submarine groundwater discharge on biogeochemistry and microbial communities in pockmarks

The impact of submarine groundwater discharge (SGD) on coastal sea biogeochemistry has been demonstrated in many recent studies. However, only a few studies have integrated biogeochemical and microbiological analyses, especially at sites with pockmarks of different degrees of groundwater influence. This study investigated biogeochemical processes and microbial community structure in sediment cores from three pockmarks in Hanko, Finland, in the northern Baltic Sea. Pockmark data were supplemented by groundwater and seawater measurements. Two active pockmarks showed SGD rates of 0.02 cm d-1 and 0.31 cm d-1, respectively, based on porewater Cl- profiles, while a third pockmark had no SGD influence. Reactive transport modelling (RTM) established that the porewater systems of these active pockmarks are dominated by advection, resulting in the focusing of biogeochemical reactions and the microbial community into a thin zone at the sediment surface. The advection further reduces the accumulation of organic matter in the surface sediments, resulting in the absence of a sulfate-methane transition zone (SMTZ) at these pockmarks. Furthermore, the RTM estimated low rates of consumption of SO42-, and low rates of production of CH4, NH4+, DIC at the active pockmarks. Archaeal communities in the active pockmarks were dominated by ammonia-oxidizing archaea of predominantly groundwater origin. In contrast, at the inactive pockmark, the lack of SGD has permitted rapid deposition of organic-rich mud. The porewater system in the inactive pockmark is dominated by diffusion, leading to orders of magnitude higher metabolite concentrations at depth compared to the active pockmarks. The biogeochemical environment in the inactive pockmark resembles typical organic-rich mud seafloor in the area, with sulphate reduction and methanogenesis dominating organic matter remineralization. Accordingly, methanogens dominate the archaeal community, whereas sulfate reducers dominate the bacterial community. RTM results suggest that sulfate-mediated anaerobic oxidation of methane (S-AOM) also occurs at this site. Although depth-integrated fluxes of SO42-, CH4, NH4, DIC at the inactive pockmark are orders of magnitude higher compared to the active pockmarks, processes at the inactive pockmark represent internal recycling in the coastal sea. Fluxes observed at the active pockmarks, although comparatively small in magnitude, are partly influenced by external inputs to the sea through SGD. Hence, effluxes across the sediment-water interface at these sites partly represent direct external fluxes to the marine environment, in addition to diagenetic recycling at the benthic interface. The study highlights that SGD can result in significant spatial heterogeneity of biogeochemical processes and microbial community structure in the coastal zone, and that the overall effects of SGD and associated solute fluxes at an SGD site are a function of the number of pockmarks, the rate of SGD, and the ratio of active to inactive pockmarks.Peer reviewe

New genetic loci link adipose and insulin biology to body fat distribution.

Body fat distribution is a heritable trait and a well-established predictor of adverse metabolic outcomes, independent of overall adiposity. To increase our understanding of the genetic basis of body fat distribution and its molecular links to cardiometabolic traits, here we conduct genome-wide association meta-analyses of traits related to waist and hip circumferences in up to 224,459 individuals. We identify 49 loci (33 new) associated with waist-to-hip ratio adjusted for body mass index (BMI), and an additional 19 loci newly associated with related waist and hip circumference measures (P < 5 × 10(-8)). In total, 20 of the 49 waist-to-hip ratio adjusted for BMI loci show significant sexual dimorphism, 19 of which display a stronger effect in women. The identified loci were enriched for genes expressed in adipose tissue and for putative regulatory elements in adipocytes. Pathway analyses implicated adipogenesis, angiogenesis, transcriptional regulation and insulin resistance as processes affecting fat distribution, providing insight into potential pathophysiological mechanisms

Pore water and peat geochemistry measured close to Rostock (Germany) in 2015

In natural coastal wetlands, high supplies of marine sulfate suppress methanogenesis. Coastal wetlands are, however, often subject to disturbance by dyking and drainage for agricultural use and it has been shown that they can turn to potent methane sources when rewetted for remediation, suggesting that the sulfate-related methane suppressing mechanisms were suspended by the preceding land use measures. Here, we unravel the hydrological relocation and biogeochemical S and C transformation processes that induced high methane emissions in a disturbed and rewetted peatland despite former brackish impact. The underlying processes were investigated along a transect of increasing distance to the coastline using a combination of concentration patterns, stable isotope partitioning and analysis of the microbial community structure. We found that dyking and freshwater rewetting caused a distinct freshening and an efficient depletion of the brackish sulfate reservoir by dissimilatory sulfate reduction (DSR). Despite some legacy effects of brackish impact expressed as high amounts of sedimentary S and elevated electrical conductivities, contemporary metabolic processes operated mainly under sulfate-limited conditions. This opened up favorable conditions for the establishment of a prospering methanogenic community in the top 30-40 cm of peat, the structure and physiology of which resembles those of terrestrial organic-rich environments. Locally, high amounts of sulfate persisted in deeper peat layers through the suppression of DSR, probably by competitive electron acceptors of terrestrial origin, for example Fe(III), but did not interfere with high methane emissions on ecosystem scale. Our results indicate that the climate effect of disturbed and remediated coastal wetlands cannot simply be derived by analogy with their natural counterparts. From a greenhouse gas perspective, the re-exposure of dyked wetlands to natural coastal dynamics would literally open up the floodgates for a replenishment of the marine sulfate pool and constitute an efficient measure to reduce methane emissions