Alfred Wegener Institute for Polar and Marine Research
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The Expedition PS141 of the Research Vessel POLARSTERN to the Davis Sea and Mawson Sea in 2024
Get PDFAdvances in Permafrost Representation: Biophysical Processes in Earth System Models and the Role of Offline Models
Get PDFABSTRACTPermafrost is undergoing rapid changes due to climate warming, potentially exposing a vast reservoir of carbon to be released to the atmosphere, causing a positive feedback cycle. Despite the importance of this feedback, its specifics remain poorly constrained, because representing permafrost dynamics still poses a significant challenge for Earth System Models (ESMs). This review assesses the current state of permafrost representation in land surface models (LSMs) used in ESMs and offline permafrost models, highlighting both the progress made and the remaining gaps.We identify several key physical processes crucial for permafrost dynamics, including soil thermal regimes, freeze–thaw cycles, and soil hydrology, which are underrepresented in many models. While some LSMs have advanced significantly in incorporating these processes, others lack fundamental elements such as latent heat of freeze–thaw, deep soil columns, and Arctic vegetation dynamics. Offline permafrost models provide valuable insights, offering detailed process testing and aiding the prioritization of improvements in coupled LSMs.Our analysis reveals that while significant progress has been made in incorporating permafrost‐related processes into coupled LSMs, many small‐scale processes crucial for permafrost dynamics remain underrepresented. This is particularly important for capturing the complex interactions between physical and biogeochemical processes required to model permafrost carbon dynamics. We recommend leveraging advancements from offline permafrost models and progressively integrating them into LSMs, while recognizing the computational and technical challenges that may arise in coupled simulations. We highlight the importance of enhancing the representation of physical processes, including through improvements in model resolution and complexity, as this is a fundamental precursor to accurately incorporate biogeochemical processes and capture the permafrost carbon feedback.</jats:p
Theatre of enforcement at sea: The global fight against ‘illegal fishing’ and the criminalisation of fisher peoples and exploitation of fish workers
Get PDFIllegal, unreported, and unregulated (IUU) fishing has been internationally branded as a major threat to oceans. Frequently depicted as having profound societal impacts and operational synergies with other forms of criminal activities, which justify the need for a so-called global fight against IUU fishing to protect the marine commons and secure marine spaces. Whereas industrial fishing is the prime culprit, policy reforms are being promoted to regulate and formalise small-scale/artisanal fishing practices. This raises questions on how enforcement and formalisation processes are translated into practice and shaped by economic interests within and beyond the ocean. In this intervention, we focus on the governance of IUU fishing in Colombia and anchor our critique into two acts — the act of criminalisation and the act of impunity — to uncover a theatre of enforcement at sea. We argue that the punitive approach to IUU fishing criminalises fisher peoples, while domestic, foreign, and transnational capitalist actors continue to operate, depleting oceans and exploiting fish workers’ labour with very limited control. We conclude by asserting that the fight against IUU fishing is in part a fight against precarious fish workers and fisher peoples, rather than against ‘ocean grabbers’, reflecting biased criminalisation processes with differentiated impacts at the intersections of class, gender, and race
Falkland/Malvinas Trough: Indications for Cenozoic tectonic and oceanographic evolution in the southwestern South Atlantic
No full textThe Falkland/Malvinas Trough (F/MT) bounds the southern extremity of the Falkland/Malvinas Plateau. This
Cenozoic bathymetric depression developed as the orogenic foreland basin of the North Scotia Ridge. The
sedimentary infill of the F/MT carries a history of development in a transpressional setting along the South
American-Scotian Plate boundary, in association with the evolution of the Drake Passage-Scotia Sea zone. Since
the F/MT is located on the pathway of the Antarctic Circumpolar Current, the current-controlled depositional
and erosional features within its sedimentary infill provide valuable information on the palaeoceanographic
modifications in the southwestern South Atlantic. Via a set of 2D high-resolution seismic reflection data, the
structural and morphological features of these strata are investigated and discussed with respect to the tectonic
evolution of the Drake Passage-Scotia Sea zone. Evidence of fold structures and normal faulting during Oligocene
to mid-Miocene times in the study area argue for a transpressional regime linked with the development of the
Drake Passage-Scotia Sea zone. The current-related depositional and erosional processes in the F/MT started
between Oligocene to early Miocene times. With the full opening of the Drake Passage, the evolution of the Scotia
Sea and the demise of the Ancestral South Sandwich Arc by the mid-Miocene, an oceanographic setting analogous
to the present would have established. Evidences suggests that since then, with the enhancement of the
abyssal circulation subsequent to the perennial Antarctic glaciation, a precursor of the Weddell Sea Deep Water
has been circulating the F/MT, shaping a confined sediment drift deposit
A Review of Abrupt Permafrost Thaw: Definitions, Usage, and a Proposed Conceptual Framework
Get PDFPurpose of Review: We review how ‘abrupt thaw’ has been used in published studies, compare these definitions to abrupt processes in other Earth science disciplines, and provide a definitive framework for how abrupt thaw should be used in the context of permafrost science
Recent Findings: We address several aspects of permafrost systems necessary for abrupt thaw to occur and propose a framework for classifying permafrost processes as abrupt thaw in the future. Based on a literature review and our collective expertise, we propose that abrupt thaw refers to thaw processes that lead to a substantial persistent environmental change within a few decades. Abrupt thaw typically occurs in ice-rich permafrost but may be initiated in ice-poor permafrost by external factors such as hydrologic change (i.e., increased streamflow, soil moisture fluctuations, altered groundwater recharge) or wildfire.
Summary: Permafrost thaw alters greenhouse gas emissions, soil and vegetation properties, and hydrologic flow, threatening infrastructure and the cultures and livelihoods of northern communities. The term ‘abrupt thaw’ has emerged in scientific discourse over the past two decades to differentiate processes that rapidly impact large depths of permafrost, such as thermokarst, from more gradual, top-down thaw processes that impact centimeters of near-surface permafrost over years to decades. However, there has been no formal definition for abrupt thaw and its use in the scientific literature has varied considerably. Our standardized definition of abrupt thaw offers a path forward to better understand drivers and patterns of abrupt thaw and its consequences for global greenhouse gas budgets, impacts to infrastructure and land-use, and Arctic policy- and decision-making
Phase and gain stability for adaptive dynamical networks
Get PDFIn adaptive dynamical networks, the dynamics of the nodes and the edges influence each other. We show that we can treat such systems as a closed feedback loop between edge and node dynamics. Using recent advances on the stability of feedback systems from control theory, we derive local, sufficient conditions for steady states of such systems to be linearly stable. These conditions are local in the sense that they are written entirely in terms of the (linearized) behavior of the edges and nodes. We apply these conditions to the Kuramoto model with inertia written in an adaptive form and the adaptive Kuramoto model. For the former, we recover a classic result, and for the latter, we show that our sufficient conditions match necessary conditions where the latter are available, thus completely settling the question of linear stability in this setting. The method we introduce can be readily applied to a vast class of systems. It enables straightforward evaluation of stability in highly heterogeneous systems
Investigating the influence of tourism on the Wadden Sea using a multi-layer social-ecological network
Get PDFCoastal zones are the epicentre of significant social, cultural, and economic development worldwide. A human activity with increasing importance for coastal ecosystems is the expanding tourism sector, a core economic activity, one of the fastest-growing sectors worldwide and included in the list of cultural ecosystem services. The World Heritage Site of the Wadden Sea, located in the south-eastern North Sea, belongs to the coastal ecosystems of outstanding value and is a highly attractive area for tourism. Given the complexity of potential ecological, social, and socio-economic relationships involved in tourism, single-discipline studies fall short in capturing the full range of interactions between tourism's economic value and its ecological influences. To bridge the gap between these social and ecological aspects, a comprehensive approach utilising Social-Ecological Systems (SES) has been suggested by different authors and employed to study human-nature linkages. Social-ecological networks (SENs) provide a suitable tool to study SES, utilising language, methods, and models common in both natural and social sciences. Hence, we used a SEN approach to study tourism's ecological, and socio-economic relations in the Wadden Sea with the aim to provide a holistic picture of the relationships between tourism and ecological nodes, socio-economic nodes, other ecosystem services, and threats that might influence the area's natural value. We constructed a multi-layer social-ecological network with 30 nodes and 147 edges representing to our knowledge the first SEN approach in the Wadden Sea. With a total degree of 37, tourism was the most connected node in the SEN, with numerous direct and indirect relationships to nodes from the same and other layers indicating a huge potential for cascade effects. Furthermore, we identified 12 loops in the network related to tourism that could result in positive or negative feedbacks. Furthermore, critical data and knowledge gaps were revealed to fully capture the complexity of tourism interaction in the Wadden Sea. By highlighting the interconnectedness of tourism, ecosystem services, and anthropogenic threats, this study provides guidance for sustainable management practices that can preserve the Wadden Sea for future generations
Characterizing organisms from three domains of life with universal primers from throughout the global ocean
Get PDFWe introduce the Global rRNA Universal Metabarcoding Plankton database (GRUMP), which consists of 1194 samples that were collected from 2003–2020 and cover extensive latitudinal and longitudinal transects, as well as depth profiles in all major ocean basins. DNA from unfractionated (>0.2 µm) seawater samples was amplified using the 515Y/926 R universal three-domain rRNA gene primers, simultaneously quantifying the relative abundance of amplicon sequencing variants (ASVs) from bacteria, archaea, eukaryotic nuclear 18S, and eukaryotic plastid 16S. Thus, the ratio between taxa in one sample is directly comparable to the ratio in any other GRUMP sample, regardless of gene copy number differences. This obviates a problem in prior global studies that used size-fractionation and different rRNA gene primers for bacteria, archaea, and eukaryotes, precluding comparisons across size fractions or domains. On average, bacteria contributed 71%, eukaryotes 19%, and archaea 8% to rRNA gene abundance, though eukaryotes contributed 32% at latitudes >40°. GRUMP is publicly available on the Simons Collaborative Marine Atlas Project (CMAP), promoting the global comparison of marine microbial dynamics
Extensive Oxygen Consumption in the Intertidal Infiltration Zone of Beach Aquifers—The Impact of Seasonal Input Filtration Efficiency and Morphodynamics
Get PDFAbstract Seawater infiltration into the permeable sands of beach aquifers creates a high input of biogeochemical reactants driven by tides and waves. The upper sand layer acts as a filter, retaining particulate organic matter (POM), which is degraded by bacteria under predominantly oxic conditions. The seasonal variation of seawater POM and oxygen (O 2 ) entering the infiltration zone, combined with the POM filtration efficiency of the highly morphodynamic upper layer, determines the organic matter turnover and subsequent redox gradients along porewater flowpaths. We investigated these effects by quantifying the seasonal O 2 consumption rates directly from the incubations of sediments taken along a transect in the seawater infiltration zone at Spiekeroog Beach, Germany. We carried out a two‐monthly year‐long sampling campaign with high spatial resolution measurements down to 1 m depth. In summer, O 2 consumption rates of up to 106 μM hr −1 were found in the first decimeters with a significant decline over depth, indicating efficient retention of reactive POM in the surface layer. Seasonal variation in organic carbon of the sand's suspendable particulates indicates rapid turnover and little storage. In winter, rates decreased significantly to below 11 μM hr −1 . Integrated over the investigated oxic layer, the estimated carbon mineralization varies between 15 (winter) and 143 (summer) mmol C m −2 d −1 with a yearly average of 73 mmol C m −2 d −1 . The yearly CO 2 production of 35 kg per meter shoreline characterizes the beach as a high‐throughout system with rapid OM remineralization in the retention layer, especially in summer, but with little OM storage.
Plain Language Summary On the coast, sandy beaches act as a filter for seawater. Seawater seeps into the sand, and organic particles such as algae remains are trapped between the sand grains. Bacteria live on the surface of the sand grains and use the oxygen dissolved in seawater to break down the organic material. We investigated how seasonal changes from spring to winter, and the particle filtration affects the oxygen consumption by bacteria. Our study found that oxygen consumption follows the availability of fresh algal material during the year and is greatest in summer, when temperatures are high and algal blooms are intense. This cycle determines when and where in the sediment bacteria are active and controls the breakdown of the organic algae material to carbon dioxide (CO 2 ). We found that overall bacteria in the beach sands degrade a high amount of organic matter compared to other sandy seabeds. Our findings therefore give valuable information on bacterial activity present in beach sands, which impacts the breakdown of organic material and determines the quality of the beach groundwater that ultimately flows back into the ocean. These processes impact the health of coastal ecosystems and have consequences for human activities, such as fisheries or recreation.
Key Points Seasonal variations in organic matter inputs and temperature regulate oxygen consumption in intertidal beach aquifers Retention of fresh particulate organic matter in the sand body in summer leads to a highly reactive top layer in the beach infiltration zone Seasonal variations of organic carbon content in the fine fraction of the sediments indicate rapid organic matter turnover and low storag
Sentinel-3 Altimetry Thematic Products for Hydrology, Sea Ice and Land Ice
Get PDFThis paper presents the Copernicus Sentinel-3 level-2 altimetry Hydro-Cryo “Thematic Products”, operationally generated by ESA since September 2023. In comparison to previous product versions, the level-2 processing is now performed through three independent chains, generating three families of “Thematic Products”, for measurements acquired over hydrological, sea ice and land ice areas, respectively. Prior to the operational deployment, a full mission reprocessing was achieved with the thematic processors, providing a complete and harmonised dataset to the users. In this paper, the new architecture of the ground segment processing is presented, along with the major algorithmic developments. The main data content of the Thematic Products is also described, to indicate the key product variables for the end users. The Thematic Products have been evaluated by the Sentinel-3 Mission Performance Cluster (MPC) experts. The major results and outcomes are presented, showing the significant performance improvement achieved in comparison to previous processing versions