Abstract. Drought poses increasing challenges to global food production. Knowledge about the influence of drought on crop development and the role of soil properties for crop drought severity is important in drought risk analysis and for mitigating drought impacts at the landscape level. Here, we tested if satellite images from Sentinel-2 could be used to assess the impacts of drought on crop development and the influence of soil properties on crop drought responses at the landscape scale and what the responses were. As a case study, we assessed winter wheat growth on 13 fields belonging to commercial farmers in southern Sweden in a dry year (2018) and in a year with normal weather conditions (2021). To track crop growth, the green leaf area index (GLAI) was estimated from satellite imagery using a radiative transfer model. Proxies for winter wheat growth rate, peak GLAI, and the timing of peak GLAI were derived from the GLAI development at the single-field level. We then compared the crop growth proxies between the 2 years and related the year-to-year differences between fields to measured soil properties. We found lower estimated growth rates, lower peak GLAI, and earlier peak GLAI in the dry year compared to the year with normal weather conditions. A higher peak GLAI in the dry year was related to a higher growth rate, and this was not shown in the year with normal precipitation. Differences in crop development between years were large for some fields but small for other fields, suggesting that soil properties play a role in crop response to drought. We found that fields with a higher plant available water capacity had a higher growth rate in the dry year and smaller relative differences in growth rate between the 2 years. This shows the importance of soils in mitigating drought conditions, which will likely become more relevant in an increasingly drier climate. Our case study demonstrates that satellite-derived crop growth proxies can identify crop responses to drought events and that satellite imagery can be used to discover impacts of soil properties on crop development at scales relevant to commercial farming.

Abstract. Hydrocarbon seepage at the deep seafloor fuels flourishing chemosynthetic communities. These seeps impact the functionality of the benthic ecosystem beyond hotspots of gas emission, altering the abundance, diversity, and activity of microbiota and fauna and affecting geochemical processes. However, these chemosynthetic ecotones (chemotones) are far less explored than the foci of seepage. To better understand the functionality of chemotones, we (i) mapped seabed morphology at the periphery of gas seeps in the deep eastern Mediterranean Sea, using video analyses and synthetic aperture sonar; (ii) sampled chemotone sediments and described burrowing using computerized tomography; (iii) explored nutrient concentrations; (iv) quantified microbial abundance, activity, and N2 fixation rates in selected samples; and (v) extracted DNA and explored microbial diversity and function using amplicon sequencing and metagenomics. Our results show that gas seepage creates burrowing intensity gradients at seep ecotones, with the ghost shrimp Calliax lobata primarily responsible for burrowing, which influences nitrogen and sulfur cycling through microbial activity. Burrow walls form a unique habitat, where macromolecules are degraded by Bacteroidota, and their fermentation products fuel sulfate reduction by Desulfobacterota and Nitrospirota. These, in turn, support chemosynthetic Campylobacterota and giant sulfur bacteria Thiomargarita, which can aid C. lobata nutrition. These interactions may support enhanced productivity at seep ecotones.

Abstract. Rotation forestry based on clear-cut harvesting, site preparation, planting and intermediate thinnings is currently the dominant management approach in Fennoscandia. However, understanding of the greenhouse gas (GHG) emissions following clear-cutting remains limited, particularly in drained peatland forests. In this study, we report eddy-covariance-based (EC-based) net emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from a fertile drained boreal peatland forest 1 year after wood harvest. Our results show that, at an annual scale, the site was a net CO2 source. The CO2 emissions dominate the total annual GHG balance (23.3 t CO2 eq. ha−1 yr−1, 22.4–24.1 t CO2 eq. ha−1 yr−1, depending on the EC gap-filling method; 82.0 % of the total), while the role of N2O emissions (5.0 t CO2 eq. ha−1 yr−1, 4.9–5.1 t CO2 eq. ha−1 yr−1; 17.6 %) was also significant. The site was a weak CH4 source (0.1 t CO2 eq. ha−1 yr−1, 0.1–0.1 t CO2 eq. ha−1 yr−1; 0.4 %). A statistical model was developed to estimate surface-type-specific CH4 and N2O emissions. The model was based on the air temperature, soil moisture and contribution of specific surface types within the EC flux footprint. The surface types were classified using unoccupied aerial vehicle (UAV) spectral imaging and machine learning. Based on the statistical models, the highest surface-type-specific CH4 emissions occurred from plant-covered ditches and exposed peat, while the surfaces dominated by living trees, dead wood, litter and exposed peat were the main contributors to N2O emissions. Our study provides new insights into how CH4 and N2O fluxes are affected by surface-type variation across clear-cutting areas in forested boreal peatlands. Our findings highlight the need to integrate surface-type-specific flux modelling, EC-based data and chamber-based flux measurements to comprehend the GHG emissions following clear-cutting and regeneration. The results also strengthen the accumulated evidence that recently clear-cut peatland forests are significant GHG sources.

Abstract. Aquifers harbor unique and highly adapted species, contributing to critical ecological processes and services. Understanding the key factors driving invertebrate assemblages in aquifers is a challenging task that, traditionally, has primarily been achieved in karst. This study aimed to uncover the factors influencing the composition and functionality of groundwater crustaceans (dimensional range from 0.036 to 1 mm) in a volcanic aquifer in central Italy. The aquifer consisted of three adjacent aquifer units (AUs) showing different geochemistry (i.e., sulfate-depleted, K-rich and, alkaline earth). We adopted a multidisciplinary approach, integrating hydrogeology, geology, microbiology, and ecology to determine whether the environmental differences that we highlighted in the three AUs were reflected in the biological assemblages. We unveiled significant differences in both the taxonomic and functional composition of groundwater crustaceans across the three AUs, and these patterns remained consistent throughout the survey period. Notably, the sulfate-depleted AU lacked groundwater-obligate species, burrowers, and stenothermal and moderately stenothermal species. The K-rich and alkaline-earth AUs had different species; however, these species exhibited similar functions related to locomotion, diet, and feeding habit. Stenothermal and moderately stenothermal crustacean species were only found in the K-rich AU, which lacked epigean species. Our findings suggest that major ions (SO42-, Ca2+, NO3-, and K+), trace elements (B, Al, V, Se, and Ba), microbial factors, and carbohydrate catabolic profiles might be the main descriptors of groundwater-obligate species abundances in the volcanic aquifer. Our findings revealed a correlation between the abundances of groundwater-obligate crustaceans and low-nucleic-acid (LNA) cells, suggesting a potential selective feeding behavior of groundwater invertebrate species on the aquatic microbial community. Our research emphasizes the need to consider diverse hydrogeological contexts within individual aquifers. Potential avenues for future research should further consider food web dynamics in groundwater communities and their impact on carbon and nutrient cycling.

Abstract. Caves are well-known archives that preserve valuable information about the past, relevant for reconstructing past climates and environments. We sampled sediments from a 480 cm deep profile, and 16S ribosomal ribonucleic acid (rRNA) gene-based metabarcoding analyses were undertaken that complemented lithological logging, sedimentology, and optically stimulated luminescence (OSL) dating. These analyses revealed different sedimentation conditions along the profile with various water inputs. The OSL age of the sediments places the profile between 74.7 ± 12.3 to 56 ± 8 ka (base to top). However, the more recent Last Glacial Maximum (LGM) paleofloods might have occurred in the upper and lower passages of the cave. Bacterial compositions changed with depth, from soil bacteria (present in the upper part of the sediment profile) to thermophilic/sulfurous bacteria (abundant in the deeper samples of the profile). Considering the thermophilic bacteria, we could only assume their origin from a surface of hot sulfurous springs, old thermal springs, or sapropel sediments.

Abstract. Coastal waters are impacted by a range of natural and anthropogenic factors, which superimpose on effects of increasing atmospheric CO2, resulting in dynamically changing seawater carbonate chemistry. Research on the influences of dynamic pH/pCO2 on marine ecosystems is still in its infancy, although effects of ocean acidification have been extensively studied. In the present study, we manipulated the culturing pH to investigate physiological performance and fatty acid (FA) composition of two coastal diatoms, Skeletonema costatum and Thalassiosira weissflogii, in both steady and fluctuating pH regimes. Generally, seawater acidification and pH variability showed neutral or positive effects on the specific growth rate, chlorophyll a, and biogenic silica contents of the two species. Decreased pH inhibited the net photosynthetic rate by 27 % and enhanced the mitochondrial respiration rate of S. costatum by 36 % in the steady pH regime, while these rates were unaltered by decreased pH in the fluctuating regime. Acidification conditions led to lower saturated FA and higher polyunsaturated FA proportions in both species, regardless of steady or fluctuating regimes. Our results indicate that coastal acidification could affect primary production in a different way from ocean acidification. Together with the altered nutritional quality of prey for higher trophic levels, coastal acidification might have far-reaching consequences for marine ecosystem functioning.

Abstract. The biological carbon pump (BCP) comprises a wide variety of processes involved in transferring organic carbon from the surface to the deep ocean. This results in long-term carbon sequestration. Without the BCP, atmospheric CO2 concentrations would be around 200 ppm higher. This study reveals that ocean dynamics at the mesoscale and submesoscale could have a major impact on particulate organic matter (POM) vertical distribution. Our results indicate that intense submesoscale frontal regions, such as those between mesoscale eddies, could lead to an important accumulation and transport of POM from the mixed-layer depth (MLD) down to the mesopelagic zone. To reach these conclusions, a multifaceted approach was applied. It included in situ measurements and marine snow images from a BGC-Argo float equipped with an Underwater Vision Profiler (UVP6), satellite altimetry data, and Lagrangian diagnostics. We focused our study on three intense features in marine snow distribution, observed during the 17-month-long float mission in the Cape Basin in the southwest of Africa. These features were located in the frontal region between mesoscale eddies. Our study suggests that a particle injection pump induced by a frontogenesis-driven mechanism has the potential to enhance the effectiveness of the biological pump by increasing the depth at which carbon is injected into the water column. This work also emphasizes the importance of establishing repeated sampling campaigns targeting the interface zones between eddies. This could improve our understanding of the mechanisms involved in the deep accumulation of marine snow observed at eddy interfaces.

Abstract. Numerical coupled ocean circulation biogeochemical modules are routinely employed in Earth system models that provide projections into our warming future to the Intergovernmental Panel on Climate Change (IPCC). Previous studies have shown that a major source of uncertainties in the biogeochemical ocean component is vertical, or rather diapycnal, ocean mixing. The representation of diapycnal mixing in models is affected by several factors, including the (poorly constrained) parameter choices of the background diffusivity, the choice of the underlying advection numerics and the spatial discretization. This study adds to the discussion by exploring these effects in a suite of regional coupled ocean circulation biogeochemical model configurations. The configurations comprise the Atlantic Ocean off Mauritania – a region renowned for its complex ocean circulation driven by seasonal wind patterns, coastal upwelling and peculiar mode water eddies featuring toxically low levels of dissolved oxygen. Based on simulated argon saturation as a proxy for effective mixing, we conclude that the resolution effect beyond mesoscale on diapycnal mixing is comparable to other infamous spurious effects, such as the choice of advection numerics or a change in the background diffusivity of less than 60 %.

Abstract. Recent studies have highlighted the important role of vegetated coastal ecosystems in atmospheric carbon sequestration. Saltmarshes constitute 30 % of these ecosystems globally and are the primary intertidal coastal wetland habitat outside the tropics. Eddy covariance (EC) is the main method for measuring biosphere–atmosphere fluxes, but its use in coastal environments is rare. At an Australian temperate saltmarsh site on French Island, Victoria, we measured CO2 and water gas concentration gradients, temperature, wind speed, and radiation. The marsh was dominated by a dense cover of Sarcocornia quinqueflora. Fluxes were seasonal, with minima in winter when vegetation is dormant. Net ecosystem productivity (NEP) during the growing season averaged 10.54 g CO2 m−2 d−1, decreasing to 1.64 g CO2 m−2 d−1 in the dormant period, yet the marsh remained a CO2 sink due to some sempervirent species. Ecosystem respiration rates were lower during the dormant period compared with the growing season (1.00 vs. 1.77 µmolCO2m-2s-1), with a slight positive relationship with temperature. During the growing season, fluxes were significantly influenced by light levels, ambient temperatures, and humidity, with cool temperatures and cloud cover limiting NEP. The ecosystem water use efficiency of 0.86 g C kg−1 H2O was similar to other C3 intertidal marshes, and evapotranspiration averaged 2.48 mm d−1 during the growing season.

Abstract. Changing snow regimes and warmer growing seasons are some climate factors influencing the productivity and growth of high-elevation forests and alpine treelines. In low-latitude mountain regions with seasonal snow and drought regimes such as the Pyrenees, these climate factors could negatively impact forest productivity. To address this issue, we assessed the relationships between climate, snow, and inter- and intra-annual radial growth and stem increment data in an alpine Pinus uncinata treeline ecotone located in the central Spanish Pyrenees. First, we developed tree-ring-width chronologies of the study site to quantify climate–growth relationships. Second, radial growth, tree water deficit, and shrinking–swelling cycles were quantified and identified at monthly to daily scales using fine-resolution dendrometer data. These variables were extracted for three climatically different years, including one of the hottest summers on record in Spain (2022), and they were related to soil water content, soil and air temperature, and the dates of snow duration across the treeline ecotone. Warmer February and May temperatures enhanced tree radial growth, probably because of an earlier snow meltout, the start of the growing season, and the higher growth rates in spring, respectively. The characteristic circadian cycle of stem increment, defined by night swelling and day shrinking, was detected in summer and fall. However, this pattern was inverted during the snow season from November through April, suggesting a transition phase characterized by wet soils and swollen stems preceding the spring onset of growth. Air temperature, soil temperature and moisture, and the presence of snow are strong indicators of how much and for how long mountain trees can grow. Shifts in daily stem increment patterns reveal changes in early growth phenology linked to snow melting.