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Seasonality of feedback mechanisms involved in Pacific coastal Nino events
No full textThe 2017 Pacific Coastal Ni & ntilde;o Event was the strongest of its type. It caused torrential rainfall and devastating flooding in Peru and Ecuador and thus rapidly caught the attention of the scientific community. From reanalysis data, three similar events, occurring in 2008, 2012 and 2014, are identified which are however all weaker, peaked later during the year and led to very little socioeconomic impact. This study focuses on the role of seasonality for the evolution and impact of Coastal Ni & ntilde;o events. Reanalysis products as well as historical simulations from a coupled climate model and targeted model sensitivity experiments are utilized to assess the seasonal varying contributions of surface heat fluxes, horizontal advection and subsurface processes to the modulation of sea surface temperatures off the Peruvian coast. As the atmospheric conditions underlay a strong seasonal cycle with convection only occurring between December and April, warm events in this season are shown to lead to stronger precipitation anomalies. Pacific coastal Ni & ntilde;o events in general are shown to be primarily forced via oceanic processes, but in individual cases local atmospheric forcing plays an important role. However, there is a very high variability between the individual events, with especially the 2017 event standing out due to its forcing, timing, strength and associated precipitation response
The Pleistocene Witch Ground Ice Stream in the central North Sea
No full textThe North Sea Basin has been covered by ice sheets originating from both the British Isles and Scandinavia at multiple times during the Pleistocene. The Witch Ground Basin (WGB) in the central northern North Sea is a critical location in terms of interpreting Late Pleistocene glacial to glacimarine history of the North Sea since it was the location of the Witch Ground Ice Stream that was active on multiple occasions during the Mid to Late Pleistocene. We map five mega‐scale glacial lineation flowsets corresponding to the changing ice flow direction of the Witch Ground Ice Stream and investigate the sedimentological fingerprint and corresponding subglacial depositional processes of this palaeo‐ice stream. We show that sorted sand layers within a subglacial traction till represent periodic hydraulic jacking and ice–bed decoupling at the base of the Witch Ground Ice Stream. In contrast to previous studies that have described glacitectonites deposited below the most recent grounded ice in the WGB, we present analysis of sediment cores that recovered primarily massive diamictons without any obvious deformation structures. The most recent ice cover in the WGB (~18–16 ka) was thought to have been sourced from a localized ice cap over Orkney and Shetland. The presence of chalk clasts sourced from NW of the WGB described in this study from the stratigraphically youngest till confirms this interpretation. The transition from subglacial to glacimarine deposition, while acoustically well defined (from opaque to laminated acoustic units), appears surprisingly uniform in the recovered sediment cores, but can be differentiated based on a change in colour including mottling and banding, presence of whole intact shells, and the increased number of silt and sand lenses. 14 C dating of glacimarine muds indicate high sedimentation rates of between 80 and 260 cm ka −1 . The transition from glacimarine to marine deposition is represented by a comparative decrease in sedimentation rate and deposition of Holocene age sandy mud. This study demonstrates a highly dynamic Witch Ground Ice Stream in the northern North Sea during the Late Pleistocene with evolving subglacial hydrology and depositional processes at the ice stream bed that left a distinct geomorphological and sedimentological fingerprint within the WGB
10-Years of imagery from a cabled-observatory reveals a decreasing trend in coastal fish biodiversity
No full textMonitoring the effects of climate change and other multi-years processes on coastal ecosystems require long-term datasets that may extend into decades. One tool to achieve this are cabled seafloor observatories that can collect continual streams of environmental and biological data as long as the equipment is maintained. Here, we used 10-years of time-lapse images (every 30 mins) from the OBSEA seafloor cabled observatory located at 20 m depth, four km offshore from Vilanova i la Geltrú (Spain) coast, to characterize temporal trends in fish community dynamics. These temporal trends were compared to in situ and remotely-sensed (MODIS-Aqua) data on temperature, salinity, and chlorophyll-a concentration (Chl-a). We observed a reduction in fish diversity over time and an increase in species turnover. Specifically, there was a decrease in the relative abundance of fish species at the lowest trophic levels alongside an increase in predators, suggesting a top-down effect. Of temperature, salinity, and Chl-a, only salinity exhibited a significant change over time. Nevertheless, the Generalized Additive Models (GAMs) revealed significant correlations between fish biodiversity indices and both temperature and Chl-a. Following models results we concluded that environmental variables affected the local fish community only at seasonal level. Including more environmental variables, such as fishing activity and pollution, in the applied models may help explain the detected decreases in biodiversity
CDRmare Insights: New guidelines on the uniform and knowledge-based assessment of marine CO2 removal methods
No full textIn the CDRmare research consortium ASMASYS, experts from the natural sciences, social sciences and humanities have developed an extensive assessment framework for ocean-based carbon dioxide (CO2) removal methods and projects. By applying this framework, responsible actors can systematically gather and compile all necessary information to make an evidence-based decision on the potential implementation of marine CO2 removal methods
Numerical modelling of erosional landforms driven by offshore groundwater flow on siliciclastic continental margins: a conceptual approach
No full textOffshore freshened groundwater (OFG) has long been hypothesised to be a key factor shaping continental margins worldwide. Field observations from siliciclastic margins suggest strong causal links between sub-seafloor OFG flow and seafloor depressions, canyons and landslide scars. These links have been hard to validate due to a paucity of appropriate field data and difficulty in simulating the subsurface flow and geomorphic processes in the laboratory. Here we present a numerical study that simulates the geomorphic action of sub-seafloor OFG seepage in an idealised 3D continental margin. Analysis of the coupling conditions highlights the multiplicative nature of the primary driving mechanisms (seepage-induced erosion and slope instability), suggesting a continuous transition between flow- and stress-controlled landforms. We find that OFG can create landforms in siliciclastic margins when buried flow pathways exist. Shelf-break depth determines landform type and timing. Shelf-breaks deeper than the sea-level lowstand lead to shallow circular depressions in the mid-shelf region, while those shallower than the lowstand yield V-shaped and theatre-headed valleys in the outer shelf to upper slope. Landforms emerge during falling sea-levels, starting as pockmark trains along the edges of the buried channels. Sensitivity studies show that: (1) channel width and depth affect only landform size, not type, and (2) OFG-related landforms are mainly erosion-driven and can evolve into slope failures in coarse-grained sediments with low cohesive strength. Our model aligns with field observations of pockmarks, canyons, and landslides in various continental margin settings
Impact of non-normal flow rule on linear kinematic features in pan-Arctic ice-ocean simulations
No full textThe standard sea ice viscous-plastic (VP) rheology is based on an elliptical yield curve and a normal flow rule. This formulation implies that the post-failure deformations are always normal to the yield curve. A drawback of this is that modifications to the yield curve also lead to notable changes to the deformations. We implemented the plastic potential approach of Ringeisen et al. (2021) in the CICE sea ice model. With this formulation, deformations are normal to an elliptical plastic potential which is defined independently from the yield curve. This an interesting capability as it allows to independently optimize deformations while parameters defining the yield curve could serve to adjust landfast ice and to a lesser extent sea ice drift. We investigated the impact of a non-normal flow rule in pan-Arctic simulations. Compared to the standard VP rheology, the non-normal flow rule leads to a more active sea ice cover with narrower linear kinematic features (LKFs) and a higher LKF density. The higher divergence with the non-normal flow rule causes an enhanced ice growth and larger Arctic sea ice volume. In idealized experiments, Ringeisen et al. (2021) showed that the non-normal flow rule can correct the unrealistic (too large) intersection angles between LKFs. However, in our pan-Arctic simulations, the non-normal flow rule does not correct the unrealistic intersection angles which are often around 90°. Results suggest that these frequent 90° angles are partly caused by the alignment of LKFs with the computational grid
Large Foundation Model Empowered Discriminative Underwater Image Enhancement
No full textThe underwater color disparity is an important cue for enhancing an underwater image. Applying the underwater color disparity indiscriminately to the entire underwater image tends to give rise to foreground-background crosstalk with either excessive foreground or insufficient background enhancement. To address the discriminativeness between underwater color disparities in foreground and background regions, we develop a discriminative underwater image enhancement method empowered by large foundation model technology. We first utilize the segment anything model (SAM) to generate segmentation masks, dividing the underwater image into foreground and background regions. This enables accurate foreground-background separation. Then, we conduct adaptive color compensation and fusion to improve the color histogram similarity for foreground and background regions separately. This corrects color deviations and improves contrasts in a discriminative manner that avoids the foreground-background crosstalk. Finally, we propose high-frequency edge fusion to extract high-frequency components from both the original underwater image and the fused image, and then fuse these components to obtain the final enhanced image. This eliminates blurred details arising from the discriminative processing of foreground and background regions. Our method represents the pioneering application of large foundation model technology to empower underwater image enhancement. Experimental results indicate that our method outperforms nine state-of-the-art underwater image enhancement methods in visual quality, achieves superior results across five underwater image quality evaluation metrics on three underwater image datasets, and is beneficial for practical applications such as underwater feature matching. We release our code at https://gitee.com/wanghaoupc/UIE_SAM
Parallels and discrepancies between non‐native species introductions and human migration
No full textBiological invasions and human migrations have increased globally due to socio-economic drivers and environmental factors that have enhanced cultural, economic, and geographic connectivity. Both processes involve the movement, establishment, and spread of species, yet unfold within fundamentally different philosophical, social and biological contexts. Hence, studying biological invasions (invasion science) and human migration (migration studies) presents complex parallels that are potentially fruitful to explore. Here, we examined nuanced parallels and differences between these two phenomena, integrating historical, socio-political, and ethical perspectives. Our review underscores the need for context-specific approaches in policymaking and governance to address effectively the challenges and opportunities of human migration and harm from biological invasions. We suggest that approaches to studying the drivers of biological invasions and human migration provide an excellent opportunity for transdisciplinary research; one that acknowledges the complexities and potential insights from both fields of study. Ultimately, integrating natural and social sciences offers a promising avenue for enriching the understanding of invasion biology and migration dynamics while pursuing just, equitable, and sustainable solutions. However, while human migration is a clear driver of biological invasions, drawing on principles from biological invasions to understand past and current human migration risks oversimplification and the potential for harmful generalisations that disregard the intrinsic rights and cultural dynamics of human migrations. By doing so, we provide insights and frameworks to support the development of context-specific policies that respect human dignity, foster cultural diversity, and address migration challenges in ways that promote global cooperation and justice. This interdisciplinary approach highlights the potential for transdisciplinary research that acknowledges complexities in both fields, ultimately enriching our understanding of invasion biology and migration dynamics while pursuing equitable and sustainable solutions
Trace metal biogeochemistry in the ocean: From chemical principles to biological complexity
No full textIn many oceanic regions, low concentrations of micronutrient trace metals exert strong control on phytoplankton growth, ecosystem structure, and carbon cycling. However, the task of linking trace metal concentrations with primary productivity is complicated by the interplay among physical, chemical, and biological processes. Paying tribute to the Morel et al. (2003) chapter from this series, we explore trace-metal phytoplankton interactions, with an emphasis on ocean-derived measurements and experiments. Specifically, we synthesize our current understanding on bioavailability of dissolved iron, trace metal accumulation in phytoplankton, and global (micro)nutrient limitation patterns, which are each underpinned by fundamental chemical and biological processes. We then showcase two microbial interactions that impact Fe biogeochemistry: (a) the two-way interactions between marine viruses and Fe that toggle Fe fate between regeneration for reuse by marine microbes and export to the deep ocean, and (b) the mineral-microbe interactions within colonies of the cyanobacteria Trichodesmium spp. that likely add “new” Fe from dust. We end with some directions and challenges in line with the multidisciplinary trajectory of trace metal biogeochemistry research
