ALBERT

Description: Predicting the implications of ongoing ocean climate warming demands a better understanding of how short-term thermal variability impacts marine ectotherms, particularly at beyond-optimal average conditions during summer heatwaves. Using a globally important model species, the blue mussel Mytilus, in a 5-week-long experiment, we (a) assessed growth performance traits under 12 scenarios, consisting of four thermal averages (18.5, 21, 23.5 and 26℃) imposed as constant or daily fluctuating regimes with amplitudes of 2 or 4℃. Additionally, we conducted a short-term assay using different mussel individuals to (b) test for the species capacity for suppression and recovery of metabolic performance traits (feeding and aerobic respiration) when exposed to a 1-day thermal fluctuation regime (16.8–30.5℃). Using this high-resolution data, we (c) generated short-term thermal metabolic performance curves to predict and explain growth responses observed in the long-term experiment. We found that daily high-amplitude thermal cycles (4℃) improved mussel growth when fluctuations were imposed around an extreme average temperature of 26℃, representing end-of-century heatwaves. In contrast, thermal cycles negatively affected mussel growth at a less extreme average temperature of 23.5℃, resembling current peak summer temperature scenarios. These results suggest that fluctuations ameliorate heat stress impacts only at critically high average temperatures. The short-term assay demonstrated that during the warming phase, animals stopped feeding between 24 and 30℃ while gradually suppressing respiration. In the subsequent cooling phase, feeding and respiration partially and fully recovered to pre-heating rates respectively. Furthermore, nonlinear averaging of short-term feeding responses (upscaling) well-predicted longer term growth responses to fluctuations. Our findings suggest that fluctuations can be beneficial to or detrimental for the long-term performance of ectothermic animals, depending on the fluctuations' average and amplitude. Furthermore, the observed effects can be linked to fluctuation-mediated metabolic suppression and recovery. In a general framework, we propose various hypothetical scenarios of fluctuation impacts on ectotherm performance considering inter- or intra-species variability in heat sensitivity. Our research highlights the need for studying metabolic performance in relation to cyclic abiotic fluctuations to advance the understanding of climate change impacts on aquatic systems. A free Plain Language Summary can be found within the Supporting Information of this article

Description: It is generally assumed that seismic activity at volcanoes is closely connected to degassing processes. Intuitively, one would therefore expect a good correlation between degassing rates and seismic amplitude. However, both examples and counterexamples of such a correlation exist. In this study on Villarrica volcano (Chile), we pursued a different approach to relate gas flux and volcanic seismicity using 3 months of SO$_2$ flux rate measurements and 12 days of seismic recordings from early 2012.〈br /> We analyzed the statistical distributions of interevent times between transient seismic waveforms commonly associated with explosions and between peaks in the degassing time series.〈br /> Both event types showed a periodic recurrence with a mode of 20-25 s and around 1 h for transients and degassing, respectively. The normalized interevent times were fitted by almost identical log-normal distributions. Given the actually very different time scales, this similarity potentially indicates a scale-invariant phenomenon. We could reproduce these empirical findings by modelling the occurrence of transients as a renewal process from which the degassing events were derived recursively with increasing probability since the previous degassing event. In this model, the seismic transients could be either produced by degassing processes within the conduit or by gas release at the lava lake surface while the longer intervals of the degassing events may be explained by accumulation of gas either in the magma column or in the juvenile gas plume.〈br /> Additionally, we analyzed volcano-tectonic events, which behaved very differently from the transients. They showed the clustered occurrence of tectonic earthquakes.

Description: Proteobacteria Alphaproteobacteria Rhizobiales Hyphomicrobiaceae Blas.to.chlo'ris. Gr. masc. n. blastos bud shoot; Gr. masc. adj. chloros green; N.L. fem. n. Blastochloris green bud shoot. Proteobacteria / Alphaproteobacteria / Rhizobiales / Hyphomicrobiaceae / Blastochloris Blastochloris species are anoxygenic phototrophic Alphaproteobacteria that have bacteriochlorophyll b in their photosynthetic reaction centers. Crystals of the photosynthetic reaction centers of Blastochloris viridis were the first that have been studied in high‐resolution structure analysis at 3 Å resolution. Internal photosynthetic membranes are present as lamellae underlying and parallel to the cytoplasmic membrane. Cells are rod shaped to ovoid and exhibit polar growth, budding, and asymmetric cell division and form rosette‐like cell aggregates. They are motile by means of subpolar flagella and stain Gram‐negative. Straight‐chain monounsaturated C18:1 is the predominant component of cellular fatty acids. Ubiquinones and menaquinones are present, and the lipopolysaccharides are characterized by a 2,3‐diamino‐2,3‐deoxy‐d‐glucose (DAG)‐containing, phosphate‐free lipid A with amide‐bound C14:0 3OH. DNA G + C content (mol%): 63.8–68.3. Type species: Blastochloris viridis (Drews and Giesbrecht 1966) Hiraishi 1997 (Rhodopseudomonas viridis Drews and Giesbrecht 1966).

Description: Keypoints This contribution is a reply on a comment submitted by A. Argnani. The alternate interpretation of the wide-angle seismic model is discussed. The Alfeo Fault system is proposed to be the current location of STEP fault. Abstract Andrea Argnani in his comment on Dellong et al., 2020 (Geometry of the deep Calabrian subduction (Central Mediterranean Sea) from wide‐angle seismic data and 3D gravity modeling), proposes an alternate interpretation of the wide-angle seismic velocity models presented by Dellong et al., 2018 and Dellong et al., 2020 and proposes a correction of the literature citations in these paper. In this reply, we discuss in detail all points raised by Andrea Argnani.

Description: Seamounts are ubiquitous on the oceanic plate; those situated near convergent margins will eventually undergo subduction. Using six prestack depth migrated MCS profiles transecting the Aleutian Trench, we investigate deeply buried seamounts offshore Kodiak Island, within 145–155°W and 55–58°N. A distinct sedimentary horizon exists in all six seismic profiles, at or above the average height of seamounts, which appears to be the preferred structural detachment zone. Where drilled, this horizon contains gravel‐sized debris interpreted to be ice rafted and marks the onset of intensification of Northern Hemisphere glaciation at ~2.7 Ma. Beneath this horizon, sediments prior to the Surveyor Fan development were deposited, all or the majority of these sediments will eventually be subducted. Despite the subducted seamounts being deeply buried, these features cause enhanced surface slope of the accretionary prism. Our observations lead us to propose a model for the stages of subduction for deeply buried seamounts. These stages include the following: (1) Prior to subduction, the protothrust zone undergoes enhanced shortening, (2) frontal thrust steepening and enhanced backthrusting occurs during subduction with a potential décollement step down seaward and a steeping outward of the deformation front to the limit of the protothrust zone, and (3) further subduction results in a pattern of uplift farther into the wedge resulting in enhanced out‐of‐sequence thrusting and persistence of the more seaward deformation front position. This pattern is distinct from the dominance of embayments and effective removal of prism material during seamount subduction described along margins with less deeply buried edifices.

Description: A coordinated regional climate model (RCM) evaluation and intercomparison project based on observations from a July–October 2014 trans‐Arctic Ocean field experiment (ACSE‐Arctic Clouds during Summer Experiment) is presented. Six state‐of‐the‐art RCMs were constrained with common reanalysis lateral boundary forcing and upper troposphere nudging techniques to explore how the RCMs represented the evolution of the surface energy budget (SEB) components and their relation to cloud properties. We find that the main reasons for the modeled differences in the SEB components are a direct consequence of the RCM treatment of cloud and cloud‐radiative interactions. The RCMs could be separated into groups by their overestimation or underestimation of cloud liquid. While radiative and turbulent heat flux errors were relatively large, they often invoke compensating errors. In addition, having the surface sea‐ice concentrations constrained by the reanalysis or satellite observations limited how errors in the modeled radiative fluxes could affect the SEB and ultimately the surface evolution and its coupling with lower tropospheric mixing and cloud properties. Many of these results are consistent with RCM biases reported in studies over a decade ago. One of the six models was a fully coupled ocean‐ice‐atmosphere model. Despite the biases in overestimating cloud liquid, and associated SEB errors due to too optically thick clouds, its simulations were useful in understanding how the fully coupled system is forced by, and responds to, the SEB evolution. Moving forward, we suggest that development of RCM studies need to consider the fully coupled climate system.

Description: Green sulfur bacteria, the Chlorobiaceae, have gained much attention because of unique structures of the photosynthetic apparatus and the presence of chlorosomes as very powerful light antenna that can capture minute amounts of light. This has important ecological consequences, because the efficient light‐harvesting determines the ecological niche of these bacteria at the lowermost part of stratified environments where the least of light is available. The oxidation of sulfide as their outmost important photosynthetic electron donor involves the deposition of elemental sulfur globules outside the cells and separates the process of sulfide oxidation to sulfate into two parts. This is the basis for stable syntrophic associations between green sulfur bacteria and sulfur‐ and sulfate‐reducing bacteria in which the sulfur compounds are recycled. The green sulfur bacteria are distantly related to other bacteria and systematically members of the Chlorobiaceae family with Chlorobium, Chlorobaculum, Prosthecochloris and Chloroherpeton as representative genera. Green sulfur bacteria depend on light for life due to their obligate phototrophic metabolism. Green sulfur bacteria are most efficient in photosynthesis due to the presence of light‐harvesting organelles, the chlorosomes, which are filled with bacteriochlorophyll molecules. Green sulfur bacteria are offsprings of one of the most ancient bacterial lineages performing biosynthesis of bacteriochlorophyll and photosynthesis. Green sulfur bacteria inhabit the lowermost light‐receiving part of the chemocline in the stratified environment due to their high sensitivity to oxygen, high tolerance to the toxic sulfide and highly efficient light capture. Green sulfur bacteria are important drivers of oxidation of reduced sulfur compounds in the stratified, sulfide‐containing environment receiving low irradiation.