Alfred Wegener Institute for Polar and Marine Research
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Methane flux from Beringian coastal wetlands for the past 20,000 years
Get PDFAtmospheric methane (CH4) concentrations have gone through rapid changes since the last deglaciation; however, the reasons for abrupt increases around 14,700 and 11,600 years before present (yrs BP) are not fully understood. Concurrent with deglaciation, sea-level rise gradually inundated vast areas of the low-lying Beringian shelf. This transformation of what was once a terrestrial-permafrost tundra-steppe landscape, into coastal, and subsequently, marine environments led to new sources of CH4 from the region to the atmosphere. Here, we estimate, based on an extended geospatial analysis, the area of Beringian coastal wetlands in 1000-year intervals and their potential contribution to northern CH4 flux (based on present day CH4 fluxes from coastal wetland) during the past 20,000 years. At its maximum (∼14,000 yrs BP) we estimated CH4 fluxes from Beringia coastal wetlands to be 3.5 (+4.0/-1.9) Tg CH4 yr−1. This shifts the onset of CH4 fluxes from northern regions earlier, towards the Bølling-Allerød, preceding peak emissions from the formation of northern high latitude thermokarst lakes and wetlands. Emissions associated with the inundation of Beringian coastal wetlands better align with polar ice core reconstructions of northern hemisphere sources of atmospheric CH4 during the last deglaciation, suggesting a connection between rising sea level, coastal wetland expansion, and enhanced CH4 emissions
Recognizing our Reviewers and Authors, and a Few Insights into Tektonika’s Review Process
Get PDFTo mark the publication of this first issue of Tektonika’s second volume, we were inspired to write a short editorial focusing on our reviewers and our review process, providing thoughts and tips on what makes a great review and author rebuttal.</jats:p
Antibiotic‐Induced Gut Microbiota Dysbiosis Modulates Host Transcriptome and m6A Epitranscriptome via Bile Acid Metabolism
Get PDFAbstractGut microbiota can influence host gene expression and physiology through metabolites. Besides, the presence or absence of gut microbiome can reprogram host transcriptome and epitranscriptome as represented by N6‐methyladenosine (m6A), the most abundant mammalian mRNA modification. However, which and how gut microbiota‐derived metabolites reprogram host transcriptome and m6A epitranscriptome remain poorly understood. Here, investigation is conducted into how gut microbiota‐derived metabolites impact host transcriptome and m6A epitranscriptome using multiple mouse models and multi‐omics approaches. Various antibiotics‐induced dysbiotic mice are established, followed by fecal microbiota transplantation (FMT) into germ‐free mice, and the results show that bile acid metabolism is significantly altered along with the abundance change in bile acid‐producing microbiota. Unbalanced gut microbiota and bile acids drastically change the host transcriptome and the m6A epitranscriptome in multiple tissues. Mechanistically, the expression of m6A writer proteins is regulated in animals treated with antibiotics and in cultured cells treated with bile acids, indicating a direct link between bile acid metabolism and m6A biology. Collectively, these results demonstrate that antibiotic‐induced gut dysbiosis regulates the landscape of host transcriptome and m6A epitranscriptome via bile acid metabolism pathway. This work provides novel insights into the interplay between microbial metabolites and host gene expression.</jats:p
Wolbachia populations across organs of individual Culex pipiens: highly conserved intra-individual core pangenome with inter-individual polymorphisms
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Wolbachia is a maternally inherited intracellular bacterium that infects a wide range of arthropods including mosquitoes. The endosymbiont is widely used in biocontrol strategies due to its capacity to modulate arthropod reproduction and limit pathogen transmission. Wolbachia infections in Culex spp. are generally assumed to be monoclonal but the potential presence of genetically distinct Wolbachia subpopulations within and between individual organs has not been investigated using whole genome sequencing. Here we reconstructed Wolbachia genomes from ovary and midgut metagenomes of single naturally infected Culex pipiens mosquitoes from Southern France to investigate patterns of intra- and inter-individual differences across mosquito organs. Our analyses revealed a remarkable degree of intra-individual conservancy among Wolbachia genomes from distinct organs of the same mosquito both at the level of gene presence–absence signal and single-nucleotide polymorphisms (SNPs). Yet, we identified several synonymous and non-synonymous substitutions between individuals, demonstrating the presence of some level of genomic heterogeneity among Wolbachia that infect the same C. pipiens field population. Overall, the absence of genetic heterogeneity within Wolbachia populations in a single individual confirms the presence of a dominant Wolbachia that is maintained under strong purifying forces of evolution.</jats:p
Simulation-based inference as a paradigm for scientific machine learning in the cryosphere and beyond
Get PDFMechanistic or dynamical models based on governing equations are ubiquitous throughout science and engineering. Such models, also referred to as &#8220;simulators&#8221;, are typically characterized by a forward mapping from some set of inputs or parameters to one or more output quantities of interest. In many cases, the inputs required for the forward model are either unknown or represent approximations of unresolved processes. Bayesian inference provides a natural framework for constraining this model uncertainty using observed data. Such a framework is especially valuable in cryospheric application domains such as permafrost research, where direct observations of many quantities of interest, e.g. subsurface temperature and soil moisture, are only sparsely available. Mechanistic models based on known physics therefore play an indispensable role in filling these gaps. However, virtually all methods for Bayesian inference require repeated evaluation of the forward model which is often computationally challenging, especially for dynamical systems. As a result, computational requirements of statistical inference very quickly become intractable even for systems of only moderate complexity. The burgeoning field of &#8220;simulation-based inference&#8221; (SBI) aims to leverage modern computational methods from machine learning (ML) and data assimilation (DA) to overcome these challenges and facilitate large scale uncertainty quantification in complex scientific models. In this work, we show how SBI can be seen as a unifying theoretical framework that bridges the gap between existing DA methods (e.g. variants of the ensemble Kalman filter) and full-fledged Bayesian inference with the goal of facilitating hybrid statistical-physical modeling of complex systems. We present a novel set of software tools for making SBI more accessible to researchers along with benchmarks of several methods drawn from both the ML and DA literature. Two of these benchmarks are based on use cases from Arctic land surface modeling: degree day approximation of snowmelt and geothermal inversion of historical climate change from boreholes in Arctic permafrost. We highlight the contributions that SBI can make to solving such inverse problems and discuss further potential applications in the cryosphere and beyond.</jats:p
Trade-offs in a reef-building coral after six years of thermal acclimation
Get PDFThere is growing evidence that reef-building corals can acclimate to novel and challenging thermal conditions. However, potential trade-offs that accompany acclimation remain largely unexplored. We investigated physiological trade-offs in colonies of a globally abundant coral species (Pocillopora acuta) that were acclimated ex situ to an elevated temperature of 31 °C (i.e., 1 °C above their bleaching threshold) for six years. By comparing them to conspecifics maintained at a cooler temperature, we found that the energy storage of corals was prioritized over skeletal growth at the elevated temperature. This was associated with the formation of higher density skeletons, lower calcification rates and consequently lower skeletal extension rates, which entails ramifications for future reef-building processes, structural complexity and reef community composition. Furthermore, symbionts were physiologically compromised at 31 °C and had overall lower energy reserves, likely due to increased exploitation by their host, resulting in an overall lower stress resilience of the holobiont. Our study shows how biological trade-offs of thermal acclimation unfold, helping to refine our picture of future coral reef trajectories. Importantly, our observations in this six-year study do not align with observations of short-term studies, where elevated temperatures were often associated with the depletion of energy reserves, highlighting the importance of studying acclimation of organisms at relevant biological scales
Thermal priming of Saccharina latissima, a promising strategy to improve seaweed production and restoration in future climates
Get PDFSaccharina latissima is a brown algal kelp species of ecological and economic importance. As the rise in sea surface temperature will threaten not only wild populations of S. latissima but also the productivity of kelp farms, crop enhancement techniques will become crucial to mitigate this threat. Priming is a common strategy in crop plants, in which seeds are pre-exposed to a moderate stress to improve the performance and tolerance of plants when exposed to harsher conditions. We investigated the potential of thermal priming to improve growth and tolerance of S. latissima. Kelp gametophytes primed at 20°C for 2, 4 and 6 weeks and then re-transferred to 5°C were compared to a naïve treatment maintained at 5°C. Gametophytes priming increased growth of subsequently formed sporophytes by up to 30% (for 4 weeks priming) compared to the naïve treatment. Female gametophyte growth in the priming environment was positively correlated to offspring sporophyte growth, indicating a maternal effect. Sporophytes were exposed to a heat stress of 20, 22, 23 and 24°C for two weeks. Sporophytes from 4- and 6-weeks primed gametophytes exhibited 11 days longer tolerance at 22°C, 7 days longer tolerance at 23°C and 1°C higher thermal tolerance over 7 days compared to naïve sporophytes and sporophytes from 2 weeks priming. A priming time of 4 weeks was optimal for both sporophyte growth and thermal tolerance. Our results suggest that priming is a promising crop enhancement technique that could improve yield for seaweed farmers and restoration of kelp forests threatened by warming climates
Long-term carbon storage in shelf sea sediments reduced by intensive bottom trawling
Get PDFAbstractBottom trawling represents the most widespread anthropogenic physical disturbance to seafloor sediments on continental shelves. While trawling-induced changes to benthic ecology have been widely recognized, the impacts on long-term organic carbon storage in marine sediments remains uncertain. Here we combined datasets of sediment and bottom trawling for a heavily trawled region, the North Sea, to explore their potential mutual dependency. A pattern emerges when comparing the surface sediment organic carbon-to-mud ratio with the trawling intensity represented by the multi-year averaged swept area ratio. The organic carbon-to-mud ratio exhibits a systematic response to trawling where the swept area ratio is larger than 1 yr−1. Three-dimensional physical–biogeochemical simulation results suggest that the observed pattern is attributed to the correlated dynamics of mud and organic carbon during transport and redeposition in response to trawling. Both gain and loss of sedimentary organic carbon may occur in weakly trawled areas, whereas a net reduction of sedimentary organic carbon is found in intensely trawled grounds. Cessation of trawling allows restoration of sedimentary carbon stock and benthic biomass, but their recovery occurs at different timescales. Our results point out a need for management of intensely trawled grounds to enhance the CO2 sequestration capacity in shelf seas.</jats:p
How is the surface phytoplankton community composition changing in the Arctic Fram Strait in the last two decades?
Get PDFIn the Arctic Ocean, phytoplankton are highly influenced by sea ice conditions and brine release. Phytoplankton dynamics are subject to the timing of nutrient and light-dependent biological production. Fram Strait (located between Svalbard and Greenland) as an important gateway to the Arctic, is a region where the cold ice-covered Arctic water exits from the western side and the warm Atlantic water enters the Arctic Ocean through the eastern side of the Strait. The two contrasting water masses interact in the central Fram Strait leading to complex phytoplankton dynamics especially under a rapidly changing Arctic climate. Within the framework of the Copernicus Marine Service Evolution Program, we have generated global chlorophyll a products of several phytoplankton functional types (PFTs) derived from multi-sensor ocean color data, for a consistent long-term monitoring of the surface ocean PFTs. The two-decade observations enable us to study the inter-annual variation and analyze the trend of the surface phytoplankton community structure on different scales. Focusing on the Fram Strait, we first perform a gap-filling method to reconstruct the satellite PFT products for Arctic waters, then evaluate the reconstructed PFT observations using in situ data from AWI established LTER Observatory HAUSGARTEN area, which includes data sets of bio-optical properties, pigment composition, phytoplankton taxonomic data from expeditions in the past years. We further investigate the current state and the two-decade trends of the major PFTs; present and interpret their phenological patterns, inter-annual changes and the potential connections between the PFT shifts/trends and climate drivers in the Fram Strait