Alfred Wegener Institute for Polar and Marine Research
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Investigation on Autoencoder-Clustering for a Semi-Supervised Classification Task in Benthic Habitat Mapping
Get PDFIn this thesis, we investigate a semi-supervised clustering approach for the use of benthic habitat mapping. Specifically, we introduce a model that extends existing deep clustering methods by utilizing labeled as well as unlabeled data. Our model builds upon deep-learning-based dimensionality reduction and integrates a clustering loss, so that feature extraction and class seperation can jointly be optimized. By utilizing the full range of available backscatter data alongside a limited number of labeled grab samples, our method ultimately aims to reduce the dependency on extensive ground-truthing, making habitat mapping more efficient. We evaluate our model by using benchmark datasets as well as real-world backscatter data from two study sites in the Sylt Outer Reef
Development of a flexible data assimilation system for a 3D unstructured-grid ocean model under Earth System Modeling Framework
No full textWe develop a new data assimilative (DA) system by combining two parallel frameworks: the Parallel DA Framework (PDAF) and the Earth System Modeling Framework (ESMF). The new DA system is built on ESMF at the top level driving PDAF and any combination of Earth system model (ESM) components, thereby allowing maximum flexibility and ease of implementation of DA in fully coupled ESM applications, with minimal intrusive code changes to the original model components. We demonstrate the new DA system using the 3D unstructured-grid ocean model SCHISM as the ESM component. The new system is validated using both simple benchmarks and a realistic simulation of the Kuroshio current system around Taiwan. The new system improves the model skill for temperature and surface elevation before, during and after typhoon events. The flexibility and ease of implementation make the new system widely applicable for other coupled ESMs, thus paving the way for a new generation of data assimilative cross-scale ESMs
Characterization of the daily and circadian valve behavior of the European flat oyster Ostrea edulis
Get PDFMarine organisms exhibit a multitude of biological rhythms synchronized with the interactions of the sun-, earth-, and moon cycles. However, the biological rhythms in bivalves remain poorly studied. This study focuses on the native European flat oyster (Ostrea edulis), an endangered species of coastal ecosystems and a key organism in restoring of biogenic reef habitats. We aim to determine whether a molecular endogenous circadian rhythm exists in O. edulis and to characterize its daily expression. To address these questions, the oysters’ valve behavior, as an output of the circadian clock expression, was recorded under different light conditions and free-running regimes using non-invasive valvometry. This work demonstrates the existence of a circadian clock mechanism that generates a labile behavioral circadian oscillation under free-running conditions. In light: dark conditions, a diel rhythm appears nocturnal, synchronizable to a shift of light phase, and remains unmodified whether the oysters are fed or not. This rhythm anticipates light: dark changes, indicating its endogenous origin. Finally, when exposed to artificial light at night the daily behavior is disrupted. This study characterizes the circadian behavioral rhythm of O. edulis’s as plastic and labile. This plasticity would be advantageous in terms of ecological adaptability but increases sensitivity to anthropogenic pressures such as light pollution
Shifting influences of Indian Ocean Dipole and western Pacific subtropical high on annual precipitation δ18O in southern East Asia
Get PDFClarifying relationships between stable oxygen isotope ratios in precipitation (δ18Op) and atmospheric circulations including the Indian Ocean Dipole (IOD) and western Pacificc subtropical high (WPSH) forms the basis of paleocirculation reconstructions. However, whether the IOD and WPSH modulate interannual variations of δ18Op remains unclear. Here, we reveal the links between the IOD/WPSH and the annual δ18Op in southern East Asia. We found that the IOD strongly in uenced annual δ18Op before 1999 by changes in moisture supply from different transport pathways and convection. However, the link became decoupled after 1999, resulting from the transition of the IOD from a symmetric to an asymmetric pattern. In contrast, significantly enhanced WPSH emerges as an important influence on annual δ18Op after 1999. Therefore, the IOD and WPSH alternately influence interannual variation of δ18Op around 1999. Our findings imply that signals of IOD and WPSH should be considered in different
periods to better interpret paleoclimate records
Blue Carbon Potential in Germany: Status and Future Development
Get PDFClimate change and biodiversity loss are global challenges that need to be addressed through a combination of measures. However, political and societal action has not yet kept pace with the urgency of these challenges. Marine carbon sequestering habitats ("Blue Carbon habitats") are globally recognized for their role in climate change mitigation and for their co-benefits and ecosystem functions, e.g., as habitat providers. In Germany, research on the Blue Carbon potential of coastal and marine ecosystems has gained momentum in recent years. However, a synergistic approach with an inclusive decision-making process is crucial to ensure political action. Current challenges are considerable knowledge gaps and the limited accessibility and transferability of existing data. Funding of research projects at different administrative levels impacts coordination, output and visibility. Here, we present a general overview of existing knowledge and identified knowledge gaps in Blue Carbon research and focus on potential Blue Carbon ecosystems (BCEs) of the German coast. Furthermore, we identify windows of opportunity and provide actionable recommendations at the science-policy-society interface by examining the current framework for Blue Carbon in Germany. Based on this, ongoing research can be further prioritized and funded in order to simultaneously strengthen the political decision-making process. The results of this study, supported by the lessons learned from a case study on the German coast, recommend a two-pronged strategy to not only avoid additional release of already stored carbon through ecosystem conservation and sustainable governance and management, but also to increase net carbon storage through (re-)establishing BCEs
Magmatic activity at the slowest spreading rates: insights from a high-resolution earthquake catalog obtained from Gakkel Ridge Deep (Arctic Ocean)
Get PDFAt the eastern end of Gakkel Ridge, Arctic Ocean, spreading rates drop below 5 mm/y near the termination of the active mid-ocean ridge in the Laptev Sea. A small-scale ocean bottom seismometer network deployed for one year at a volcanic center near Gakkel Ridge Deep in sea ice covered waters revealed abundant microseismicity despite the low spreading rate. In order to reveal spreading processes, we analyze a manually picked earthquake catalog refined by low-magnitude events detected by template matching. We attribute seismicity occurring randomly in time and space to tectonic stress release along the ridge. During short time periods of hours to days, seismicity is organized in time and densely clustered in space with signs of migration away from an aseismic area. In analogy to volcanic centers at Knipovich Ridge and in Iceland, we interpret the seismicity as signs of ongoing localized magmatism occurring even at the slowest spreading rates. </jats:p
Turbulence Observations below Drifting Sea Ice: TKE Production and Dissipation in the Meltwater-Influenced Boundary Layer
No full textDuring Arctic summer, meltwater inputs and a fragmented ice cover impede quantifying the role of boundary stress for turbulent mixing in the ice–ocean boundary layer. Here, we show that less than two-thirds of the turbulent kinetic energy (TKE) generated from mean flow shear under drifting sea ice is dissipated, and the remainder can be attributed to balancing stabilizing buoyancy fluxes. We deployed a high-resolution acoustic Doppler current profiler under an ice floe to estimate Reynolds stress, shear production, and dissipation rate of TKE. At 0.75 m below the interface, dissipation rates from 1.5 3 1029 to 4.2 3 1027 m2 s23 and shear production from 6.9 3 10210 to 7.7 3 1027 m2 s23 were measured (5%–95% percentiles), with shear production exceeding dissipation on average. The turbulent stress was largest during an event with ~9.2-h-period oscillations in the upper ocean, consistent with tidally forced lee waves generated near steep topography. An overall estimate of the quadratic skin drag coefficient representative of the ice floe is CD0 5 7:0 3 1024. We further identified three qualitative regimes of atmosphere–ice–ocean coupling in our observations: a high-frequency range [>4 cycles per day (cpd)] in which the ice acts like a rigid lid atop the ocean, an intermediate range, and a low-frequency range (<0.8 cpd), where wind-driven ice drift determines the under-ice current. As the latter only contained half of the variance of the ice-relative flow, we emphasize that resolving subdaily time scales is crucial in observing and modeling atmosphere–ice–ocean coupling
Learning from the oceans’ interconnectedness: matters of writing and publishing in interdisciplinary scholarship
Get PDFAbstract The recurring recognition of the inseparable interconnection between societies and marine environments has led to the desire to move beyond traditional silos of scientific understanding. Integrating discrete disciplines from marine social and natural sciences is increasingly attempted to tackle cross-boundary research challenges. Consequently, much literature focuses on why and how to design and implement interdisciplinary projects. There is surprisingly less attention to the delivery of such projects—how to write and publish their results. Drawing from our writing and publishing experiences within different interdisciplinary projects, we shed light on the challenges we are facing and how to overcome them. We reflect on why good interdisciplinary writing matters and demonstrate the omission of work on writing and publishing in interdisciplinary teams in marine science literature, before we offer guidance towards effective writing relationships. Better understanding diverse writing and publishing traditions is essential in harnessing the full potential of cutting-edge interdisciplinary marine scholarship. Writing from the front lines as a marine social and a marine natural scientist, this paper mixes academic styles: third person narration with first person testimony, to argue that writing challenges need to be openly discussed and to showcase how to work towards successful integration