scholarly journals First direct evidence for a contiguous Gondwana shelf to the south of the Rheic Ocean

Geology ◽  
2019 ◽  
Vol 47 (8) ◽  
pp. 767-770 ◽  
Author(s):  
Rolf L. Romer ◽  
Uwe Kroner
Keyword(s):  
Continental Shelf ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Direct Evidence ◽  
Oceanic Lithosphere ◽  
Black Shales ◽  
Early Paleozoic ◽  
Rheic Ocean ◽  
Variscan Orogen

Abstract Sea-level rise after the Hirnantian glaciation resulted in the global inundation of continental shelf areas and the widespread formation of early Silurian black shales. Black shales that were deposited on shelves receiving drainage from earlier glaciated areas have high uranium (U) contents because large-scale glacial erosion brought rocks with leachable U to the surface. In contrast, black shales receiving drainage from non-glaciated areas that had lost leachable U earlier have low U contents. Early Silurian U-rich shales formed only on shelf areas that had not been separated from earlier-glaciated mainland Gondwana by oceanic lithosphere. Therefore, early Silurian U-rich black shales within the Variscan orogen provide direct evidence that these areas had not been separated from mainland Gondwana, but were part of the same, contiguous shelf. This implies that the Rheic Ocean was the only pre-Silurian ocean that opened during the early Paleozoic extension of the peri-Gondwana shelf.

scholarly journals Adapting to sea level rise: Emerging governance issues in the San Francisco Bay Region

2018 ◽  
Author(s):  
Pedro J. Pinto ◽  
G. Mathias Kondolf ◽  
Pun Lok Raymond Wong
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
San Francisco ◽  
Urban Areas ◽  
Path Dependence ◽  
Large Scale ◽  
San Francisco Bay ◽  
Metropolitan Region ◽  
Environmental Benefit ◽  
Formidable Challenge

San Francisco Bay, the largest estuary on the Pacific Coast of North America, is heavily encroached by a metropolitan region with over 7 million inhabitants. Urban development and infrastructure, much of which built over landfill and at the cost of former baylands, were placed at very low elevations. Sea-level rise (SLR) poses a formidable challenge to these highly exposed urban areas and already stressed natural systems. “Green”, or ecosystem-based, adaptation is already on the way around the Bay. Large scale wetland restoration projects have already been concluded, and further action now often requires articulation with the reinforcement of flood defense structures, given the level of urban encroachment. While levee setback, or removal, would provide greater environmental benefit, the need to protect urban areas and infrastructure has led to the trial of ingenious solutions for promoting wetland resilience while upgrading the level of protection granted by levees.We analyzed the Bay’s environmental governance and planning structure, through direct observation, interviews with stakeholders, and study of planning documents and projects. We present two cases where actual implementation of SLR adaptation has led, or may lead to, the need to revise standards & practices or to make uneasy choices between conflicting public interests.Among the region’s stakeholders, there is an increasing awareness of the risks related to SLR, but the institutional arrangements are complex, and communication between the different public agencies/departments is not always as streamlined as it could be. Some agencies and departments need to adapt their procedures in order to remove institutional barriers to adaptation, but path dependence is an obstacle. There is evidence that more frank and regular communication between public actors is needed. It also emphasizes the benefits of a coordination of efforts and strategies, something that was eroded in the transition from government-led policies to a new paradigm of local-based adaptive governance.

scholarly journals Tidal wetland resilience to sea level rise increases their carbon sequestration capacity in United States

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Faming Wang ◽  
Xiaoliang Lu ◽  
Christian J. Sanders ◽  
Jianwu Tang
Keyword(s):  
Climate Change ◽  
United States ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Accumulation Rate ◽  
C Sequestration ◽  
Tidal Wetlands ◽  
Tidal Wetland ◽  
Climate Change Scenarios

AbstractCoastal wetlands are large reservoirs of soil carbon (C). However, the annual C accumulation rates contributing to the C storage in these systems have yet to be spatially estimated on a large scale. We synthesized C accumulation rate (CAR) in tidal wetlands of the conterminous United States (US), upscaled the CAR to national scale, and predicted trends based on climate change scenarios. Here, we show that the mean CAR is 161.8 ± 6 g Cm−2 yr−1, and the conterminous US tidal wetlands sequestrate 4.2–5.0 Tg C yr−1. Relative sea level rise (RSLR) largely regulates the CAR. The tidal wetland CAR is projected to increase in this century and continue their C sequestration capacity in all climate change scenarios, suggesting a strong resilience to sea level rise. These results serve as a baseline assessment of C accumulation in tidal wetlands of US, and indicate a significant C sink throughout this century.

scholarly journals Coastal Flooding in the Maldives Induced by Mean Sea-Level Rise and Wind-Waves: From Global to Local Coastal Modelling

2021 ◽  
Vol 8 ◽  
Author(s):  
Angel Amores ◽  
Marta Marcos ◽  
Rodrigo Pedreros ◽  
Gonéri Le Cozannet ◽  
Sophie Lecacheux ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Land Reclamation ◽  
Flood Hazard ◽  
Wind Waves ◽  
Coastal Flooding ◽  
Major Drawback ◽  
Mean Sea Level

The Maldives, with one of the lowest average land elevations above present-day mean sea level, is among the world regions that will be the most impacted by mean sea-level rise and marine extreme events induced by climate change. Yet, the lack of regional and local information on marine drivers is a major drawback that coastal decision-makers face to anticipate the impacts of climate change along the Maldivian coastlines. In this study we focus on wind-waves, the main driver of extremes causing coastal flooding in the region. We dynamically downscale large-scale fields from global wave models, providing a valuable source of climate information along the coastlines with spatial resolution down to 500 m. This dataset serves to characterise the wave climate around the Maldives, with applications in regional development and land reclamation, and is also an essential input for local flood hazard modelling. We illustrate this with a case study of HA Hoarafushi, an atoll island where local topo-bathymetry is available. This island is exposed to the highest incoming waves in the archipelago and recently saw development of an airport island on its reef via land reclamation. Regional waves are propagated toward the shoreline using a phase-resolving model and coastal inundation is simulated under different mean sea-level rise conditions of up to 1 m above present-day mean sea level. The results are represented as risk maps with different hazard levels gathering inundation depth and speed, providing a clear evidence of the impacts of the sea level rise combined with extreme wave events.

scholarly journals Copernicus Sea Level Space Observations: A Basis for Assessing Mitigation and Developing Adaptation Strategies to Sea Level Rise

2021 ◽  
Vol 8 ◽  
Author(s):  
Jean-François Legeais ◽  
Benoît Meyssignac ◽  
Yannice Faugère ◽  
Adrien Guerou ◽  
Michaël Ablain ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Adaptation Strategies ◽  
Sea Level Changes ◽  
Global Mean Sea Level ◽  
The Stability ◽  
Scientific Questions ◽  
Processing Steps

It is essential to monitor accurately current sea level changes to better understand and project future sea level rise (SLR). This is the basis to support the design of adaptation strategies to climate change. Altimeter sea level products are operationally produced and distributed by the E.U. Copernicus services dedicated to the marine environment (CMEMS) and climate change (C3S). The present article is a review paper that intends to explain why and to which extent the sea level monitoring indicators derived from these products are appropriate to develop adaptation strategies to SLR. We first present the main key scientific questions and challenges related to SLR monitoring. The different processing steps of the altimeter production system are presented including those ensuring the quality and the stability of the sea level record (starting in 1993). Due to the numerous altimeter algorithms required for the production, it is complex to ensure both the retrieval of high-resolution mesoscale signals and the stability of the large-scale wavelengths. This has led to the operational production of two different sea level datasets whose specificities are characterized. We present the corresponding indicators: the global mean sea level (GMSL) evolution and the regional map of sea level trends, with their respective uncertainties. We discuss how these products and associated indicators support adaptation to SLR, and we illustrate with an example of downstream application. The remaining gaps are analyzed and recommendations for the future are provided.

scholarly journals Future sea-level rise drives rocky intertidal habitat loss and benthic community change

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9186 ◽  
Author(s):  
Nikolas J. Kaplanis ◽  
Clinton B. Edwards ◽  
Yoan Eynaud ◽  
Jennifer E. Smith
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Environmental Changes ◽  
Community Change ◽  
Rocky Intertidal ◽  
Areal Extent ◽  
Intertidal Habitat ◽  
Large Area ◽  
Habitat Area

The impacts of sea-level rise (SLR) are likely to be the greatest for ecosystems that exist at the land-sea interface, where small changes in sea-level could result in drastic changes in habitat availability. Rocky intertidal ecosystems possess a number of characteristics which make them highly vulnerable to changes in sea-level, yet our understanding of potential community-scale responses to future SLR scenarios is limited. Combining remote-sensing with in-situ large-area imaging, we quantified habitat extent and characterized the biological community at two rocky intertidal study locations in California, USA. We then used a model-based approach to estimate how a range of SLR scenarios would affect total habitat area, areal extent of dominant benthic space occupiers, and numerical abundance of invertebrates. Our results suggest that SLR will reduce total available rocky intertidal habitat area at our study locations, leading to an overall decrease in areal extent of dominant benthic space occupiers, and a reduction in invertebrate abundances. As large-scale environmental changes, such as SLR, accelerate in the next century, more extensive spatially explicit monitoring at ecologically relevant scales will be needed to visualize and quantify their impacts to biological systems.

Deriving a Physically-Based Calving Rate Law for Marine Ice-Cliff Instability

2020 ◽  
Author(s):  
Anna Crawford ◽  
Joe Todd ◽  
Doug Benn ◽  
Jan Åström ◽  
Thomas Zwinger
Keyword(s):  
Viscous Flow ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Ice Sheet ◽  
Rate Law ◽  
Grounding Line ◽  
Physically Based ◽  
Calving Rate ◽  
Global Sea Level

<p><span>Rapid grounding line retreat at marine-terminating glaciers could expose ice cliffs with heights greater than those on observational record. However, the finite strength of ice places a limit on the height of subareal cliffs. It is proposed that marine ice-cliff instability (MICI) will begin once a stable height threshold is exceeded. If a glacier is situated over a retrograde slope, as is the case for Thwaites Glacier and much of the West Antarctic Ice Sheet, MICI can be expected to accelerate </span><span>as retreat progresses</span><span> and increasingly tall and unstable ice cliffs are </span><span>formed. This is consequential for global sea level rise, yet large uncertainties remain in the prediction of MICI retreat rates. </span></p><p><span>We investigate MICI by pairing the full Stokes continuum model Elmer/Ice and the Helsinki Discrete Element Model (HiDEM)</span><span>. Viscous flow, simulated in Elmer/Ice, is found to be a necessary pre-condition for MICI collapse. Forward advance and bulging lead to ice-front instability and pervasive crevassing in HiDEM. This culminates in full-thickness calving events. We do not observe calving at ice faces prior to viscous deformation. </span><span>HiDEM simulations that implement viscous flow (HiDEM-ve) also show forward advance and waterline bulging, similar to the Elmer/Ice simulations. However, the importance of granular shear is highlighted by pronounced shear bands and patterns of surface lowering in HiDEM-ve output. These results emphasize the importance and complexity of viscous and brittle process interaction during MICI.</span></p><p><span>A simulation matrix of grounded termini shows that calving frequency and magnitude increase with the thickness of the calving front. The time required for viscous flow to recreate unstable conditions is influenced by thickness as well as ice temperature and basal friction. Simulations of buoyant termini are seen to calve through basal-crevassing and block-rotation, as opposed to incising surface-crevasses. Lastly, we observe that b</span><span>uttressing </span><span>mélange can</span><span> suppress retreat rate</span><span> if a sufficient resistive force is delivered to the calving front. A </span><span>physically-based law for MICI retreat rate is derived from our simulation matrix; this calving rate law can be incorporated into large-scale ice sheet models to constrain projections of Antarctic retreat and associated global sea level rise. Our results will also be used to investigate the future retreat of Thwaites Glacier, which is vulnerable to MICI due to a retreating grounding line, fragile floating ice shelf, and precarious positioning above an overdeepening basin</span><span>. </span></p>

Relocate People to Safer Ground

2019 ◽  
pp. 169-188
Author(s):  
Hill and
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Political Stability ◽  
Sudden Onset ◽  
Economic Opportunity ◽  
The World ◽  
The Face ◽  
Slow Onset

Whether the world is prepared for it or not, climate change will drive large-scale migration. The impacts of climate change—both slow-onset changes, such as sea-level rise and drought, and sudden-onset events, such as extreme storms and wildfires—push people from their homes. Managed well, migration can yield enormous benefits, offering greater opportunities for those who relocate and injecting new talent and energy into receiver communities. But climate change threatens to unleash “disruptive migration,” that is, sudden migration that could strain social, economic, and political stability. The task ahead in the face of climate change is to encourage managed, gradual migration that minimizes disruption, moves people out of harm’s way, and turns displacement into economic opportunity. This chapter outlines the strategies and tools that exist to make this possible.

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