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AbstractIn the Western Tropical South Pacific, a hotspot of dinitrogen‐fixing organisms has been identified. The survival of these species depends on the availability of dissolved iron (DFe); however, the source of this DFe is still unclear. DFe was measured along a transect from 175°E to 166°W near 19–21°S. The distribution of DFe showed high spatial variability: low concentrations (∼0.2 nmol kg−1) in the South Pacific gyre and high concentrations (up to 50 nmol kg−1) in the west of the Tonga arc, indicating that this arc is a clear boundary between iron‐poor and iron‐rich waters. An optimal multiparameter analysis was used to distinguish the relative importance of physical transport relative to non‐conservative processes on the observed distribution. This analysis demonstrated that the shallow hydrothermal sources present along the Tonga‐Kermadec arc are responsible for the high concentrations observed in the photic layer. Nevertheless, in contrast to what has been observed for deep hydrothermal plumes, our results highlighted the rapid decrease in DFe concentrations near shallow hydrothermal sources. This is likely due to a shorter residence time of surface water masses combined with several biogeochemical processes at play (precipitation, scavenging, biological uptake, and photoreduction). This study clearly highlights the role of shallow hydrothermal sources on the DFe cycle within the Tonga‐Kermadec arc where a strong link to biological activity in surface waters can be assessed, despite the small but significant fraction of DFe ultimately stabilized. It also emphasizes the need to consider the impact of these sources for a better understanding of the global iron cycle.

Manipulation is usually required for biomass calculation and food estimation for optimal fish growth in production facilities. However, the advances in computer-based systems have opened a new range of applied possibilities. In this study we used image analysis and a neural network algorithm that allowed us to successfully provide highly accurate biomass data. This developed system allowed us to compare the effects of reduced levels of human-animal interaction on the culture of adult Senegalese sole (Solea senegalensis) in terms of body weight gain. For this purpose, 30 adult fish were split into two homogeneous groups formed by three replicates (n = 5) each: a control group (CTRL), which was standard manipulated and an experimental group (EXP), which was maintained under a lower human-animal interaction culture using our system for biomass calculation. Visible implant elastomer was, for the first time, applied as tagging technology for tracking soles during the experiment (four months). The experimental group achieved a statistically significant weight gain (p < 0.0100) while CTRL animals did not report a statistical before-after weight increase. Individual body weight increment was lower (p < 0.0100) in standard-handled animals. In conclusion, our experimental approach provides evidence that our developed system for biomass calculation, which implies lower human-animal interaction, improves biomass gain in Senegalese sole individuals in a short period of time.

Permafrost is widespread in the High Arctic, including the Norwegian archipelago of Svalbard. The uppermost permafrost intervals have been well studied, but the processes at its base and the impacts of the underlying geology have been largely overlooked. More than a century of coal, hydrocarbon, and scientific drilling through the permafrost in Svalbard shows that accumulations of natural gas trapped at the base of permafrost are common. These accumulations exist in several stratigraphic intervals throughout Svalbard and show both thermogenic and biogenic origins. The gas, combined with the relatively young permafrost age, is evidence of ongoing gas migration throughout Svalbard. The accumulation sizes are uncertain, but one case demonstrably produced several million cubic metres of gas over 8 years. Heavier gas encountered in two boreholes on Hopen may be situated in the gas hydrate stability zone. While permafrost is demonstrably ice-saturated and acting as seal to gas in lowland areas, in the highlands permafrost is more complex and often dry and permeable. Svalbard shares a similar geological and glacial history with much of the Circum-Arctic, suggesting that sub-permafrost gas accumulations are regionally common. With permafrost thawing in the Arctic, there is a risk that the impacts of releasing of methane trapped beneath permafrost will lead to positive climatic feedback effects.

Abstract. Given the role of the ocean in mitigating climate change through CO2 absorption, it is important to improve our ability to quantify the historical ocean CO2 uptake, including its natural variability, for carbon budgeting purposes. In this study we present an exhaustive intercomparison between two ocean modelling practices that can be used to reconstruct the historical ocean CO2 uptake. By comparing the simulations to a wide array of ocean physical and biogeochemical observational datasets, we show how constraining the ocean physics towards observed temperature and salinity results in a better representation of global biogeochemistry. We identify the main driver of this improvement to be a more realistic representation of large scale meridional overturning circulation together with improvements in mixed layer depth and sea surface temperature. Nevertheless, surface chlorophyll was rather insensitive to these changes, and, in some regions, its representation worsened. We identified the causes of this response to be a combination of a lack of robust parameter optimization and limited changes in environmental conditions for phytoplankton. We conclude that although the direct validation of CO2 fluxes is challenging, the pervasive improvement observed in most aspects of biogeochemistry when applying data assimilation of observed temperature and salinity is encouraging; therefore, data assimilation should be included in multi-method international efforts aimed at reconstructing the ocean CO2 uptake.

Current shifts in ecosystem composition and function emphasize the need for an understanding of the links between environmental factors and organism fitness and tolerance. The examples discussed here illustrate how recent progress in the field of comparative physiology may provide a better mechanistic understanding of the ecological concepts of the fundamental and realized niches and thus provide insights into the impacts of anthropogenic disturbance. Here we argue that, as a link between physiological and ecological indicators of organismal performance, the mechanisms shaping aerobic scope and passive tolerance set the dimensions of an animal's niche, here defined as its capacity to survive, grow, behave, and interact with other species. We demonstrate how comparative studies of cod or killifish populations in a latitudinal cline have unraveled mitochondrial mechanisms involved in establishing a species' niche, performance, and energy budget. Riverine fish exemplify how the performance windows of various developmental stages follow the dynamic regimes of both seasonal temperatures and river hydrodynamics, as synergistic challenges. Finally, studies of species in extreme environments, such as the tilapia of Lake Magadi, illustrate how on evolutionary timescales functional and morphological shifts can occur, associated with new specializations. We conclude that research on the processes and time course of adaptations suitable to overcome current niche limits is urgently needed to assess the resilience of species and ecosystems to human impact, including the challenges of global climate change.

Abstract Currently, in tropical regions such as the southern Gulf of Mexico (sGM), there are no legal guidelines for assessing the quality of the seafloor. We aim to determine whether the seafloor sustainability of the sGM is evenly distributed, based on pressures that human activities produce upon the marine coastal environment, represented by the water quality, sediment quality, and benthic fauna. We analysed physicochemical characteristics and benthic fauna at 183 sites, sampled during five annual surveys (rainy and dry seasons) in the sublittoral and bathyal zones. Socioeconomic indicators were obtained from official national censuses. We calculated a pressure index (PI) based on water quality, sediment quality, and socioeconomic indicators. PI values ranged from 1 to 2.67, with the highest values being observed at coastal sites. Our approach determined that the benthic quality in the study area was related to depth and oil industry influence and that the sGM's seafloor sustainability was unevenly distributed. For sustainability, we determined specific situations for each site or group of sites: (1) sensitive - sites with high benthic quality and low PI; (2) naturally variable - sites for which the poor benthic quality was not related to the PI; (3) degraded - sites with poor benthic quality and high PI; and (4) resilient - sites with good benthic quality and high PI. This differentiation in sustainability situations might be used as a reference for linking socioeconomic activities in the coasts with the ecological status of marine environments from shallow to deep.