• European Marine Science
• 2014-2023close
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In this paper we investigated, for two years and with a bi-monthly frequency, how physical, chemical, and biological processes affect the marine carbonate system in a coastal area characterized by high alkalinity riverine discharge (Gulf of Trieste, northern Adriatic Sea, Mediterranean Sea).

Cold seep ecosystems are highly productive, fragmented ecosystems of the deep-sea floor. They form worldwide where methane reaches the surface seafloor, and are characterized by rich chemosynthetic communities fueled by the microbial utilization of hydrocarbons. Here we investigated with in situ (benthic chamber, microprofiler) and ex situ (pore water constituents, turnover rates of sulfate and methane, prokaryote abundance) techniques reduced sites from three different seep ecosystems in the Eastern Mediterranean deep-sea. At all three cold seep systems, the Amon Mud Volcano, Amsterdam Mud Volcano and the Nile Deep Sea Fan Pockmark area, we observed and sampled patches of highly reduced, methane-seeping sulfidic sediments which were separated by tens to hundreds of (kilo)meters with non-reduced oxygenated seafloor areas. All investigated seep sites were characterized by gassy, sulfidic sediments of blackish color, of which some were overgrown with thiotrophic bacterial mats. Fluxes of methane and oxygen, as well as sulfate reduction rates varied between the different sites.

Planktic foraminifera were collected with 150 µm BONGO nets from the upper 200 m water depth at 20 stations across the Mediterranean Sea between 02 May and 02 June, 2013. The main aim is to characterize the species distribution and test the covariance between foraminiferal area density (rho-A) and seawater carbonate chemistry in a biogeochemical gradient including ultraoligotrophic conditions. Average foraminifera abundances are 1.42 ±1.43 ind 10^-3 (ranging from 0.11 to 5.20 ind 10^-3), including 12 morphospecies. Large differences in species assemblages and total abundances are observed between the different Mediterranean sub-basins, with an overall dominance of spinose, symbiont-bearing species indicating oligotrophic conditions. The highest values in absolute abundance are found in the Strait of Gibraltar and the Alboran Sea. The western basin is dominated by Globorotalia inflata and Globigerina bulloides at slightly lower standing stocks than in the eastern basin. In contrast, the planktic foraminiferal assemblage in the warmer, saltier, and more nutrient-limited eastern basin is dominated by Globigerinoides ruber (white). These new results, when combined with previous findings, suggest that temperature-induced surface water stratification, and food availability are the main factors controlling foraminiferal distribution. In the oligotrophic and highly alkaline and supersaturated with respect to calcite and aragonite Mediterranean surface water, standing stocks and rho-A of G. ruber (white) and G. bulloides are affected by both food availability and seawater carbonate chemistry. Rapid warming increased surface ocean stratification impacting food availability and changes in trophic conditions could be the causes of reduced foraminiferal abundance, diversity, and species-specific changes in planktic foraminiferal calcification.

The first record of Antipathella subpinnata ( Ellis and Solander, 1786) for the Azores archipelago is presented based on bottom longline by-catch analysis and ROV seafloor surveys, extending the species western-most boundary of distribution in the NE Atlantic. The species was determined using classic taxonomy and molecular analysis targeting nuclear DNA. Although maximum spine height on Azorean colonies branchlets is slightly smaller than that reported from Mediterranean colonies (0.12 vs 0.16 mm), the analysis of partial 18S rDNA, complete ITS1, 5.8S, ITS2 and partial 28S rDNA suggests that the Azorean and Mediterranean specimens belong to the same species. Video surveys of an A. subpinnata garden detected near Pico Island are used to provide the first in situ description of the species habitat in the region and the first detailed description of a black coral garden in the NE Atlantic. With A. subpinnata being the only coral found between 150 and 196 m depths, this is the deepest black coral garden recorded in the NE Atlantic and the first one to be monospecific. The species exhibited a maximum density of 2.64 colonies/m**2 and occurred across a surface area estimated at 67,333 m**2, yielding a local population estimate of 50,500 colonies.

Three high resolution multicore records have been collected at three sites in the western Mediterranean with a MC400-Multicorer system during the MedSeA cruise (Mediterranean Sea Acidification in a changing climate) on 2 May to 2 June 2013 onboard the R/V Angeles Álvarino. Core MedSeA-S3-c1 was retrieved in the Alboran basin (Lat. 36.0746° N, Long. 04.11040° W) at a water depth of 1137 m, with a core length of 33 cm. Core MedSeA-S23-c1 was recovered at a water depth of 1156 m in the Balearic basin offshore Barcelona (Lat. 41.1121° N, Long. 2.38200° E) with a core length of 43 cm. MedSeA-S7-c2 was collected at the Strait of Sicily (Lat. 37.7080° N, Long. 12.40553° E) at a water depth of 263 m, with a core length of 46.5 cm. All three cores have been analyzed for changes in size normalized weight (SNW) and stable carbon isotopes (δ13C), measured in planktic foraminiferal clacite shells of the two species Globigerina bulloides and Globigerinoides elongatus. Boron (δ11B) isotopes have been measured in tests of Globigerinoides elongatus at the Alboran site, and in Globigerinoides ruber albus at the Strait of Sicily. Complementary data for the Strait of Sicily record has been obtained, including a 210Pb based age depth model, sea surface temperatures (SST), alkenone concentrations and planktic foraminiferal assemblage changes. The Strait of Sicily record (MedSeA-S7-c2) covers around the last 200 a, describing environmental changes throughout the Industrial Era (IE) at high temporal resolution. The Alboran (MedSeA-S3-c1) and Balearic Sea (MedSeA-S23-c1) records spanning the last about 1 ka at lower temporal resolution, displaying oceanographic changes throughout the transition from the pre-industrial era to present, as discussed in (Pallacks et al., 2021; doi:10.1016/j.gloplacha.2021.103549). Data has been collected to investigate the response of marine calcifiers to the combined effects of climate change stressors on decadal to centennial timescales, caused by anthropogenic CO2 emissions.

This study investigated the bacterial diversity associated with microbial mats of polar deep-sea cold seeps. The mats were associated with high upward fluxes of sulfide produced by anaerobic oxidation of methane, and grew at temperatures close to the freezing point of seawater. They ranged from small patches of 0.2–5 m in diameter (gray mats) to extensive fields covering up to 850 m2 of seafloor (white mats) and were formed by diverse sulfide-oxidizing bacteria differing in color and size. Overall, both the dominant mat-forming thiotrophs as well as the associated bacterial communities inhabiting the mats differed in composition for each mat type as determined by microscopy, 16S rRNA gene sequencing and automated ribosomal intergenic spacer analysis. While the smaller gray mats were associated with a highly diverse composition of sulfide oxidizers, the larger white mats were composed of only 1–2 types of gliding Beggiatoa filaments. Molecular analyses showed that most of the dominant mat-forming sulfide oxidizers were phylogenetically different from, but still closely related to, thiotrophs known from warmer ocean realms. The psychrophilic nature of the polar mat-forming thiotrophs was tested by visual observation of active mats at in situ temperature compared to their warming to >4 °C. The temperature range of mat habitats and the variation of sulfide and oxygen fluxes appear to be the main factors supporting the diversity of mat-forming thiotrophs in cold seeps at continental margins.

Three high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins) have been analyzed for sea surface temperature (SST), coccolithophore and planktic foraminiferal abundance changes. Age-depth models at both sites were developed by a combination of 210Pb and 14C dating techniques, describing high sedimentation rates at both study sites, covering the time interval from the Medieval climate anomaly to present. Alkenone derived SST of core MedSeA-S3-c1 and MedSeA-S23-c3 are in good agreement with other results, tracing temperature changes through the Common Era (CE) and show a clear warming emergence at about 1850 CE. Analysis of relative abundance of calcareous nannoplankton assemblages (coccolithophores) was done on core MedSeA-S3-c1 (150 µm. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides). The relative abundance changes of Globorotalia truncatulinoides plus Globorotalia inflata describe the intensity of deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. Our data suggests that planktic foraminiferal abundance and species changes in the western Mediterranean Sea is already affected by accelerated anthropogenic warming, overprinting natural cycles in this region.

The Amon mud volcano (MV), located at 1250 m water depth on the Nile Deep Sea Fan, is known for its active emission of methane and non-methane hydrocarbons into the hydrosphere. Previous investigations showed a low efficiency of hydrocarbon-degrading anaerobic microbial communities inhabiting the Amon MV center in the presence of sulphate and hydrocarbons in the seeping subsurface fluids. By comparing spatial and temporal patterns of in situ biogeochemical fluxes, temperature gradients, pore water composition and microbial activities over three years, we investigated why the activity of anaerobic hydrocarbon degraders can be low despite high energy supplies. We found that the central dome of the Amon MV, as well as a lateral mud flow at its base, showed signs of recent exposure of hot subsurface muds lacking active hydrocarbon degrading communities. In these highly disturbed areas, anaerobic degradation of methane was less than 2% of the methane flux. Rather high oxygen consumption rates compared to low sulphide production suggest a faster development of more rapidly growing aerobic hydrocarbon degraders in highly disturbed areas. In contrast, the more stabilized muds surrounding the central gas and fluid conduits hosted active anaerobic hydrocarbon-degrading microbial communities. Furthermore, within three years, cell numbers and hydrocarbon degrading activity increased at the gas-seeping sites. The low microbial activity in the hydrocarbon-vented areas of Amon mud volcano is thus a consequence of kinetic limitations by heat and mud expulsion, whereas most of the outer mud volcano area is limited by hydrocarbon transport.

In this study the importance of spatial scales on nematode species distribution and patterns of biodiversity and turnover in cold seeps was investigated. Therefore it was identified how nematode assemblages differ in densities and composition at different spatial scales within and between three geographically separated cold seeps, the Central pockmark area, the Amon and the Amsterdam, all located in the Eastern Mediterranean area. The replicated sampling of several reduced habitats at each seep allowed to elucidate the most important scale of turnover. The spatial scales included here range within habitat (centimeters, micro-scale), within a cold seep (10s to 100's of meters, meso-scale) and between different seeps (10 to 100s of kilometers, macro-scale). The results show that a typical cold seep fauna was found in all reduced samples. Compared to the reference samples, nematode densities were generally higher, with a low genus diversity, and a high dominance of only a few species, some of them being present in all three seep areas. When determining the scale of turnover using relative genera proportions, it appeared that the highest turnover rate was present between seeps (macro-scale). However, calculating the turnover based on presence/absence transformed nematode genera data showed the highest turnover rate between replicate samples (micro-scale) and habitats of the same seep (meso-scale). This shows that nematode assemblages are patchily distributed, even in a single habitat, and implicates that the sampling effort during sampling campaigns should be focused on replicate sampling and multiple habitats of the same seep. This way a more complete image of the present nematode community will be obtained.

Biogeochemical measurements in sediment cores collected with a TV-MUC in the Black Sea during MSM15/1, Northwest Crimea (HYPOX Project), at water depths between 105-207 m. Sampling was performed along gradient of oxygen bottom water concentrations between oxic (150 µmol L-1), variable hypoxic (3-60 µmol L-1 O2) and anoxic, sulfidic conditions. concentrations of organic carbon (Corg) and nitrogen (N) were measured on finely powdered, freeze-dried subsamples of sediment using a using a Fisons NA-1500 elemental analyzer. For organic carbon determination samples were pre-treated with 12.5% HCl to remove carbonates. Chlorophyll a (chl a), phaeopigments (PHAEO) and chloroplastic pigment equivalents (CPE) was measured according to Schubert et al., (2005) and total hydrolyzable amino acids (THAA) and single amino acid: ASP, GLU, SER, HIS, GLY, THR, ARG, ALA, TYR, MET, VAL, PHE, ILE, LEU, LYS following Dauwe et al., 1998.