scholarly journals The comparative biogeography of Philippine geckos challenges predictions from a paradigm of climate-driven vicariant diversification across an island archipelago

2018 ◽  
Author(s):  
Jamie R. Oaks ◽  
Cameron D. Siler ◽  
Rafe M. Brown
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Landscape Fragmentation ◽  
Alternative Interpretation ◽  
Comparative Genomic ◽  
Sea Level Changes ◽  
Glacial Cycles ◽  
Full Likelihood ◽  
The Times ◽  
Evolutionary Lineages

AbstractA primary goal of biogeography is to understand how large-scale environmental processes, like climate change, affect diversification One often-invoked but seldom tested process is the “species-pump” model, in which repeated bouts of co-speciation are driven by oscillating climate-induced habitat connectivity cycles. For example, over the past three million years, the landscape of the Philippine Islands has repeatedly coalesced and fragmented due to sea-level changes associated with glacial cycles. This repeated climate-driven vicariance has been proposed as a model of speciation across evolutionary lineages codistributed throughout the islands. This model predicts speciation times that are temporally clustered around the times when interglacial rises in sea level fragmented the islands. To test this prediction, we collected comparative genomic data from 16 pairs of insular gecko populations. We analyze these data in a full-likelihood, Bayesian model-choice framework to test for shared divergence times among the pairs. Our results provide support against the species-pump model prediction in favor of an alternative interpretation, namely that each pair of gecko populations diverged independently. These results suggest the repeated bouts of climate-driven landscape fragmentation has not been an important mechanism of speciation for gekkonid lizards on the Philippine Islands.

scholarly journals On the geophysical processes impacting palaeo-sea-level observations

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Yusuke Yokoyama ◽  
Anthony Purcell
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Global Climate ◽  
Sea Level Change ◽  
Sea Level Changes ◽  
Factors Affecting ◽  
Ice Volume ◽  
Level Change ◽  
Recent Developments ◽  
Geophysical Processes

AbstractPast sea-level change represents the large-scale state of global climate, reflecting the waxing and waning of global ice sheets and the corresponding effect on ocean volume. Recent developments in sampling and analytical methods enable us to more precisely reconstruct past sea-level changes using geological indicators dated by radiometric methods. However, ice-volume changes alone cannot wholly account for these observations of local, relative sea-level change because of various geophysical factors including glacio-hydro-isostatic adjustments (GIA). The mechanisms behind GIA cannot be ignored when reconstructing global ice volume, yet they remain poorly understood within the general sea-level community. In this paper, various geophysical factors affecting sea-level observations are discussed and the details and impacts of these processes on estimates of past ice volumes are introduced.

Sea level response to Quartenary erosion and deposition in Scandinavia 

2021 ◽  
Author(s):  
Gustav Pallisgaard-Olesen ◽  
Vivi Kathrine Pedersen ◽  
Natalya Gomez
Keyword(s):  
Sea Level ◽  
Sea Level Changes ◽  
Glacial Cycles ◽  
Glacial Erosion ◽  
Erosion And Deposition ◽  
Late Pliocene ◽  
Glacial Origin ◽  
Sediment Deposits ◽  
Mass Redistribution ◽  
Global Sea Level

<div> <p>The landscape in western Scandinavia has undergone dramatic changes through numerous glaciations during the Quaternary. These changes in topography and in the volumes of offshore sediment deposits, have caused significant isostatic adjustments and local sea level changes, owing to erosional unloading and depositional loading of the lithosphere. Mass redistribution from erosion and deposition also has the potential to cause significant pertubations of the geoid, resulting in additional sea-level changes. The combined sea-level response from these processes, is yet to be investigated in detail for Scandinavia.</p> </div><div> <p>In this study we estimate the total sea level change from late-Pliocene- Quaternary glacial erosion and deposition in the Scandinavian region, using a gravitationally self-consistent global sea level model that includes the full viscoelastic response of the solid Earth to surface loading and unloading. In addition to the total late Pliocene-Quaternary mass redistribution, we <span>also </span>estimate transient sea level changes related specifically to the two latest glacial cycles.</p> </div><div> <p>We utilize existing observations of offshore sediment thicknesses of glacial origin, and combine these with estimates of onshore glacial erosion and estimates of erosion on the inner shelf. Based on these estimates, we can define mass redistribution and construct a preglacial landscape setting.</p> </div><div> <p>Our preliminary results show <span>perturbations of</span> the local sea level up to ∼ 200 m since<span> the</span> late-Pliocene in the Norwegian Sea, suggesting that erosion and deposition ha<span>ve</span> influenced the local paleo sea level history in Scandinavia significantly.</p> </div>

scholarly journals Atmospheric circulation changes and their impact on extreme sea levels around Australia

2019 ◽  
Vol 19 (5) ◽  
pp. 1067-1086 ◽  
Author(s):  
Frank Colberg ◽  
Kathleen L. McInnes ◽  
Julian O'Grady ◽  
Ron Hoeke
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Climate Models ◽  
Tide Gauge ◽  
Austral Summer ◽  
Sea Level Changes ◽  
Sea Level Variability ◽  
Sea Levels ◽  
Extreme Sea Levels ◽  
Coastal Sea

Abstract. Projections of sea level rise (SLR) will lead to increasing coastal impacts during extreme sea level events globally; however, there is significant uncertainty around short-term coastal sea level variability and the attendant frequency and severity of extreme sea level events. In this study, we investigate drivers of coastal sea level variability (including extremes) around Australia by means of historical conditions as well as future changes under a high greenhouse gas emissions scenario (RCP 8.5). To do this, a multi-decade hindcast simulation is validated against tide gauge data. The role of tide–surge interaction is assessed and found to have negligible effects on storm surge characteristic heights over most of the coastline. For future projections, 20-year-long simulations are carried out over the time periods 1981–1999 and 2081–2099 using atmospheric forcing from four CMIP5 climate models. Changes in extreme sea levels are apparent, but there are large inter-model differences. On the southern mainland coast all models simulated a southward movement of the subtropical ridge which led to a small reduction in sea level extremes in the hydrodynamic simulations. Sea level changes over the Gulf of Carpentaria in the north are largest and positive during austral summer in two out of the four models. In these models, changes to the northwest monsoon appear to be the cause of the sea level response. These simulations highlight a sensitivity of this semi-enclosed gulf to changes in large-scale dynamics in this region and indicate that further assessment of the potential changes to the northwest monsoon in a larger multi-model ensemble should be investigated, together with the northwest monsoon's effect on extreme sea levels.

PISM paleo simulations of the Antarctic Ice Sheet over the last two glacial cycles

2020 ◽  
Author(s):  
Torsten Albrecht ◽  
Ricarda Winkelmann ◽  
Anders Levermann
Keyword(s):  
Boundary Conditions ◽  
Sea Level ◽  
Ice Sheet ◽  
Sea Level Changes ◽  
Glacial Cycles ◽  
Antarctic Ice Sheet ◽  
History Of ◽  
Global Sea Level ◽  
Glacial Time ◽  
The Antarctic

<p>Simulations of the glacial-interglacial history of the Antarctic Ice Sheet provide insights into dynamic threshold behavior and estimates of the ice sheet's contributions to global sea-level changes, for the past, present and future. However, boundary conditions are weakly constrained, in particular at the interface of the ice-sheet and the bedrock. We use the Parallel Ice Sheet Model (PISM) to investigate the dynamic effects of different choices of input data and of various parameterizations on the sea-level relevant ice volume. We evaluate the model's transient sensitivity to corresponding parameter choices and to different boundary conditions over the last two glacial cycles and provide estimates of involved uncertainties. We also present isolated and combined effects of climate and sea-level forcing on glacial time scales. </p>

Dynamics and evolution of continental margin clinoform systems

2020 ◽  
Author(s):  
Gerben de Jager ◽  
Dicky Harishidayat ◽  
Benjamin Emmel ◽  
Ståle Emil Johansen
Keyword(s):  
Sea Level ◽  
Continental Margin ◽  
Water Depth ◽  
Large Scale ◽  
Barents Sea ◽  
Source Rocks ◽  
Sea Level Changes ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Geological Processes

<p>Clinoforms are aquatic sedimentary features commonly associated with strata prograding from a shallower water depth into a deeper water depth. They are very sensitive to changes in water depth, rapidly moving along the shelf in response to sea level changes.  By reconstructing the initial clinoform geometry of buried clinoforms, an estimate of the paleo water depth (PWD) can be made. When this is done for several subsequent clinoform sets the amounts and rates of bathymetric changes can be calculated.</p><p>Here we present a novel approach to estimate clinoform parameters and depositional depths for continental margin clinoforms using seismic reflections, wellbore and biostratigraphy data. Seismic interpretation of three relatively east-west regional full-stack seismic reflection data from the continental margin of the western Barents Sea revealed twelve Late Cenozoic horizons. The clinoform shapes have been restored by removing the effects of compaction and flexural isostasy (backstripping). This includes the effects of glacial/interglacial scenarios on horizons with strong glaciomarine seismic indications.</p><p>Based on the reconstructed clinoform geometries we use empirical relationships from literature between clinoform geometry and depositional depth to estimate PWD values. In these analyses it is possible to estimate the PWD of the upper rollover point and the toe point by measuring the bottomset height, foreset height and topset height. A sensitivity analysis study has also been done on several different scenarios, varying elastic thickness, decompaction and net to gross ratio. Comparison with biostratigraphic water depth estimates indicate that PWD estimates revealed from clinoform parameters give reliable results.</p><p>Any mismatch between the backstripped PWD values and the PWD values derived from the clinoform geometry can then be attributed to geological processes not included in the backstripping process. Among others, these could be explained by rifting, thermal effects in the lithosphere, faulting or eustatic sea level changes. This allows the quantification of the magnitude of these large-scale crustal processes through time.</p><p>We will demonstrate that this method can further constrain the PWD on the continental margin clinoform system and thus can help to improve the understanding of the interplay between sedimentary processes and large-scale crustal processes. Furthermore, the PWD estimates will be a reliable input for further analysis of source-to-sink and stratigraphic forward modeling studies as well as reservoir and source rocks prediction on the petroleum development and exploration.</p><p> </p>

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 Late Triassic – Jurassic development of the Danish Basin and the Fennoscandian Border Zone, southern Scandinavia

2003 ◽  
Vol 1 ◽  
pp. 459-526 ◽  
Author(s):  
Lars H. Nielsen
Keyword(s):  
Sea Level ◽  
Large Scale ◽  
Upper Triassic ◽  
Border Zone ◽  
Late Triassic ◽  
Sea Level Changes ◽  
Sequence Stratigraphic ◽  
The North ◽  
Layer Cake ◽  
Thermal Cooling

The continental to marine Upper Triassic – Jurassic succession of the Danish Basin and the Fennoscandian Border Zone is interpreted within a sequence stratigraphic framework, and the evolution of the depositional basin is discussed. The intracratonic Permian–Cenozoic Danish Basin was formed by Late Carboniferous – Early Permian crustal extension followed by subsidence governed primarily by thermal cooling and local faulting. The basin is separated from the stable Precambrian Baltic Shield by the Fennoscandian Border Zone, and is bounded by basement blocks of the Ringkøbing–Fyn High towards the south. In Late Triassic – Jurassic times, the basin was part of the epeiric shallow sea that covered most of northern Europe. The Upper Triassic – Jurassic basin-fill is subdivided into two tectono-stratigraphic units by a basinwide intra-Aalenian unconformity. The Norian – Lower Aalenian succession was formed under relative tectonic tranquillity and shows an overall layer-cake geometry, except for areas with local faults and salt movements. Deposition was initiated by a Norian transgression that led to shallow marine deposition and was accompanied by a gradual climatic change to more humid conditions. Extensive sheets of shoreface sand and associated paralic sediments were deposited during short-lived forced regressions in Rhaetian time. A stepwise deepening and development of fully marine conditions followed in the Hettangian – Early Sinemurian. Thick uniform basinwide mud blankets were deposited on an open storm-influenced shelf, while sand was trapped at the basin margins. This depositional pattern continued until Late Toarcian – Early Aalenian times when the basin became restricted due to renewed uplift of the Ringkøbing–Fyn High. In Middle Aalenian – Bathonian times, the former basin area was subjected to deep erosion, and deposition became restricted to the fault-bounded Sorgenfrei–Tornquist Zone. Eventually the fault margins were overstepped, and paralic–marine deposition gradually resumed in most of the basin in Late Jurassic time. Thus, the facies architecture of the Norian – Lower Aalenian succession reflects eustatic or large-scale regional sea-level changes, whereas the Middle Aalenian – Volgian succession reflects a strong tectonic control that gradually gave way to more widespread and sea-level controlled sedimentation. The uplift of the Ringkøbing–Fyn High and most of the Danish Basin occurred concurrently with the uplift of the North Sea and a wide irregular uplifted area was formed, which differs significantly from the postulated domal pattern.

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