Alfred Wegener Institute for Polar and Marine Research
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An intercomparison of models predicting growth of Antarctic krill (Euphausia superba): The importance of recognizing model specificity
Get PDFEuphausia superba is a key species of the Southern Ocean, impacted by climate change and human exploitation. Understanding how these changes affect the distribution and abundance of krill is crucial for generating projections of change for Southern Ocean ecosystems. Krill growth is an important indicator of habitat suitability and a series of models have been developed and used to examine krill growth potential at different spatial and temporal scales. The available models have been developed using a range of empirical and mechanistic approaches, providing alternative perspectives and comparative analyses of the key processes influencing krill growth. Here we undertake an intercomparison of a suite of the available models to understand their sensitivities to major driving variables. This illustrates that the results are strongly determined by the model structure and technical characteristics, and the data on which they were developed and validated. Our results emphasize the importance of assessing the constraints and requirements of individual krill growth models to ensure their appropriate application. The study also demonstrates the value of the development of alternative modelling approaches to identify key processes affecting the dynamics of krill. Of critical importance for modelling the growth of krill is appropriately assessing and accounting for differences in estimates of food availability resulting from alternative methods of observation. We suggest that an intercomparison approach is particularly valuable in the development and application of models for the assessment of krill growth potential at circumpolar scales and for future projections. As another result of the intercomparison, the implementations of the models used in this study are now publicly available for future use and analyses
Metagenome-assembled genomes reveal greatly expanded taxonomic and functional diversification of the abundant marine Roseobacter RCA cluster
Get PDFBackground
The RCA (Roseobacter clade affiliated) cluster belongs to the family Roseobacteracea and represents a major Roseobacter lineage in temperate to polar oceans. Despite its prevalence and abundance, only a few genomes and one described species, Planktomarina temperata, exist. To gain more insights into our limited understanding of this cluster and its taxonomic and functional diversity and biogeography, we screened metagenomic datasets from the global oceans and reconstructed metagenome-assembled genomes (MAG) affiliated to this cluster.
Results
The total of 82 MAGs, plus five genomes of isolates, reveal an unexpected diversity and novel insights into the genomic features, the functional diversity, and greatly refined biogeographic patterns of the RCA cluster. This cluster is subdivided into three genera: Planktomarina, Pseudoplanktomarina, and the most deeply branching Candidatus Paraplanktomarina. Six of the eight Planktomarina species have larger genome sizes (2.44–3.12 Mbp) and higher G + C contents (46.36–53.70%) than the four Pseudoplanktomarina species (2.26–2.72 Mbp, 42.22–43.72 G + C%). Cand. Paraplanktomarina is represented only by one species with a genome size of 2.40 Mbp and a G + C content of 45.85%. Three novel species of the genera Planktomarina and Pseudoplanktomarina are validly described according to the SeqCode nomenclature for prokaryotic genomes. Aerobic anoxygenic photosynthesis (AAP) is encoded in three Planktomarina species. Unexpectedly, proteorhodopsin (PR) is encoded in the other Planktomarina and all Pseudoplanktomarina species, suggesting that this light-driven proton pump is the most important mode of acquiring complementary energy of the RCA cluster. The Pseudoplanktomarina species exhibit differences in functional traits compared to Planktomarina species and adaptations to more resource-limited conditions. An assessment of the global biogeography of the different species greatly expands the range of occurrence and shows that the different species exhibit distinct biogeographic patterns. They partially reflect the genomic features of the species.
Conclusions
Our detailed MAG-based analyses shed new light on the diversification, environmental adaptation, and global biogeography of a major lineage of pelagic bacteria. The taxonomic delineation and validation by the SeqCode nomenclature of prominent genera and species of the RCA cluster may be a promising way for a refined taxonomic identification of major prokaryotic lineages and sublineages in marine and other prokaryotic communities assessed by metagenomics approaches
A tribute to Winfried Lampert: how he injected an integrative vision of evolutionary ecology into the aquatic sciences
Get PDFCore-Log -Seismic Integration for the Cretaceous to Oligocene sequence in the African-Southern Ocean gateway: First results from the Agulhas Plateau (IODP Sites U1579 and U1580)
Get PDFClimate models have identified significant geography-related Cenozoic cooling arising from the opening of Southern Ocean gateways (e.g., Sauermilch et al., 2021). For example, a gradual strengthening of the Antarctic Circumpolar Current (ACC) has been proposed as the primary cause of cooler deep ocean temperatures associated with the transition from the Cretaceous "Supergreenhouse" to the Oligocene icehouse (e.g., Sijp et al., 2014).
IODP Expedition 392 'Agulhas Plateau Cretaceous Climate' drilled four sites in the African-Southern Ocean gateway in 2022 to significantly advance understanding of how temperatures, ocean circulation, and sedimentation patterns evolved as CO2 levels rose and fell and Gondwana broke up (Uenzelmann-Neben et al., 2022).
Prior to Exp 392, seismostratigraphic models developed for the African-Southern Ocean gateway relied solely on age data from remote drilling sites and information from piston cores, gravity cores, and dredge samples. As a result, a high level of uncertainty had to be assumed for reflector age information, particularly for the sparsely sampled pre-Miocene sedimentary column.
We here present preliminary findings from a revised seismostratigraphy based on core-log-seismic integration at Sites U1579 (central Agulhas Plateau) and U1580 (southern Agulhas Plateau), both of which are located at the heart of the African-Southern Ocean gateway. Core density and velocity data were edited, corrected to in-situ conditions, and combined with downhole logging data. Synthetic seismograms provide an accurate traveltime to depth conversion and show an excellent correlation of drilling results with the site survey seismic field records.
A first correlation of the seismic reflection data with the preliminary shipboard bio- and magnetostratigraphy reveals that the published seismostratigraphic models are erroneous and need revisions, for example, a reflector interpreted to represent a lower Eocene sea level highstand on the Agulhas Plateau has now been identified as the Cretaceous/Paleogene (K/Pg) boundary. Further prominent reflectors can be associated with the Eocene-Oligocene transition (EOT), the top and bottom of zeolitic siliciclastic sandstones (Santonian) and intra-basalt reflections, interpreted as sills.
The core-seismic correlation allows tying major changes in other physical properties (e.g., colour reflectance, natural gamma radiation), chemical composition (e.g., major element ratios from XRF core scanning) and sedimentological parameters (e.g., grain size) to the seismic grids, which will aid reconstructions of oceanic circulation changes and magmatism variations in relation to the development of the Agulhas Plateau
Age of emplacement and paleolatitude of the Agulhas Plateau – IODP Expedition 392, Site U1582
Get PDFThe Agulhas Plateau (AP), along with Maud Rise (MR) and Northeast Georgia Rise (NEGR), is part of the greater Southeast African Large Igneous Province (LIP) that is hypothesized to have been emplaced above the Bouvet hotspot during breakup of Africa and East Antarctica. Since their emplacement in the Late Cretaceous, these prominent submarine plateaus have been rifted along a triple junction and have controlled connectivity between the South Atlantic, Southern Ocean, and southern Indian Ocean basins. Igneous rocks recovered on a basement high at Site U1582 (located at ~37°S) on the northern Agulhas Plateau hold clues to the age, paleolatitude, nature of LIP basement, and its relation to the mid-ocean ridges that separated the AP from MR and NEGR. At Site U1582, a pillow basalt sequence with intercalated sediments was recovered. Based on initial shipboard biostratigraphy, a Santonian age (~85 Ma) was assigned to this unit. The moderately altered, mildly porphyritic mafic igneous basement rocks recovered at Site U1582 contain abundant veins and carbonate-filled voids. We report in situ U-Pb ages of carbonate vein and void fills (n=20) along with paleomagnetic directions (n=25) from the basaltic basement. The oldest carbonate formed at ~95 Ma (Cenomanian), which we interpret as early diagenetic ages that immediately postdate LIP emplacement during cooling and associated fracturing. Younger vein generations reflect basement carbonation due to seawater circulation, which prevailed until long after LIP emplacement. Basaltic basement rocks at Site U1582 record magnetic field directions reliably. Paleomagnetic analysis yields a negative inclination (normal polarity), which we correlate with Chron C34n (Cretaceous Normal Superchron). We calculate a ~45-50°S preliminary mean paleolatitude that allows us to refine plate kinematic reconstructions and to test the genetic relationship between the AP, MR and NEGR. Our combined age-paleolatitude dataset has implications for Cretaceous paleogeography, ocean circulation, and oceanic crust carbonation timescales
Natural thermal stress-hardening of corals through cold temperature pulses in the Thai Andaman Sea
Get PDFInvestigating the Radar Response of Englacial Debris Entrained Basal Ice Units in East Antarctica Using Electromagnetic Forward Modeling
Get PDFRadio-echo sounding (RES) reveals patches of high backscatter in basal ice units, which represent distinct englacial features in the bottom parts of glaciers and ice sheets. Their material composition and physical properties are largely unknown due to their direct inaccessibility but could provide significant information on the physical state as well as on present and past processes at the ice-sheet base. Here, we investigate the material properties of basal ice units by comparing measured airborne radar data with synthetic radar responses generated using electromagnetic (EM) forward modeling. The observations were acquired at the onset of the Jutulstraumen Ice Stream in western Dronning Maud Land (DML) (East Antarctica) and show strong continuous near-basal reflections of up to 200-m thickness in the normally echo-free zone (EFZ). Based on our modeling, we suggest that these high-backscatter units are most likely composed of point reflectors with low dielectric properties, suggesting thick packages of englacial entrained debris. We further investigate the effects of entrained particle size, and concentration in combination with different dielectric properties, which provide useful information to constrain the material composition of radar-detected units of high backscatter. The capability and application of radar wave modeling in complex englacial environments is therefore a valuable tool to further constrain the composition of basal ice and the physical conditions at the ice base
A web-based portal for serving geospatial information on permafrost disturbances to permafrost communities
Get PDFPermafrost is warming at a global scale, yet land surface change associated with abrupt permafrost thaw strongly affects permafrost communities and Arctic research stations at the local scale. In the ERC PETA-CARB, ESA CCI Permafrost, and NSF Permafrost Discovery Gateway projects, remote sensing time series were used to detect and map permafrost disturbances at high spatial resolution across large regions to quantify landscape change, hydrological dynamics, and permafrost vulnerability. The multitude of geospatial datasets that were produced in these projects provide useful information also for local scales. Hence, the question arises how such large and complex science datasets can be made available for permafrost communities and Arctic research stations to deal with the issues and challenges they experience with land surface disturbances and permafrost thaw at the local scale. The geospatial datasets are published according to the FAIR principles and are available to the research community via well-established channels such as the GTN-P database, the PANGAEA world data centre, and the geodata portal Arctic Permafrost Geospatial Centre (APGC).
Currently, the scientific data is not readily designed and presented to be interpreted by non-scientists and non-experts. We are designing a tailored web-based portal specifically targeting non-scientific user communities, stakeholders, and rightsholders. We will develop interactive maps and adequate cartographic visualizations for near real-time information on land surface changes, hot spots of disturbances, and potential areas of active permafrost thaw. While focusing on the local scale, the data will be explorable up to the panarctic scale and may open new avenues for understanding permafrost change for the general public. Through planned consultations with local permafrost communities and stakeholders we aim to ensure that their actual information needs are met
Global sensitivity analysis of a one-dimensional ocean biogeochemical model
Get PDFOcean biogeochemical (BGC) models are a powerful tool for investigating ocean biogeochemistry and the global carbon cycle. The potential benefits emanating from BGC simulations and predictions are broad, with significant societal impacts from fisheries management to carbon dioxide removal and policy-making. These models contain numerous parameters, each coupled with large uncertainties, leading to significant uncertainty in the model outputs. This study performs a global sensitivity analysis (GSA) of an ocean BGC model to identify the uncertain parameters that impact the variability of model outputs most. The BGC model Regulated Ecosystem Model 2 is used in a one-dimensional configuration at two ocean sites in the North Atlantic (BATS) and the Mediterranean Sea (DYFAMED). Variance-based Sobol' indices are computed to identify the most influential parameters for each site for the quantities of interest (QoIs) commonly considered for the calibration and validation of BGC models. The most sensitive parameters are the chlorophyll to nitrogen ratio, chlorophyll degradation rate, zooplankton grazing and excretion parameters, photosynthesis parameters, and nitrogen and carbon remineralization rate. Overall, the sensitivities of most QoIs were similar across the two sites; however, some differences emerged because of different mixed layer depths. The results suggest that implementing multiple zooplankton function types in BGC models can improve BGC predictions. Further, explicitly implementing heterotrophic bacteria in the model can better simulate the carbon export production and CO2 fluxes. The study offers a comprehensive list of the most important BGC parameters that need to be quantified for future modeling applications and insights for BGC model developments
Quantification of metabolic niche occupancy dynamics in a Baltic Sea bacterial community
Get PDFProgress in molecular methods has enabled the monitoring of bacterial populations in time. Nevertheless, understanding community dynamics and its links with ecosystem functioning remains challenging due to the tremendous diversity of microorganisms. Conceptual frameworks that make sense of time series of taxonomically rich bacterial communities, regarding their potential ecological function, are needed. A key concept for organizing ecological functions is the niche, the set of strategies that enable a population to persist and define its impacts on the surroundings. Here we present a framework based on manifold learning to organize genomic information into potentially occupied bacterial metabolic niches over time. Manifold learning tries to uncover low-dimensional data structures in high-dimensional data sets that can be used to describe the data in reduced dimensions. We apply the method to re-construct the dynamics of putatively occupied metabolic niches using a long-term bacterial time series from the Baltic Sea, the Linnaeus Microbial Observatory (LMO). The results reveal a relatively low-dimensional space of occupied metabolic niches comprising groups of taxa with similar functional capabilities. Time patterns of occupied niches were strongly driven by seasonality. Some metabolic niches were dominated by one bacterial taxon, whereas others were occupied by multiple taxa, depending on the season. These results illustrate the power of manifold learning approaches to advance our understanding of the links between community composition and functioning in microbial systems