Magnitude Of Sea-level Change Research Articles

Effects of sea level rise on storm surges in the south Yellow Sea: A case study of Typhoon Muifa (2011)

Changes in sea levels due to climate change are expected to alter storm surge intensities worldwide, disproportionately effecting coastal communities. In this study, we explored the impacts of future sea level rise (SLR) on storm surges within various numerical frameworks. The relative mean sea level rise (RMSLR) scenario for a period of 100-yr was applied using satellite altimetry of sea surface height and subsequently adjusted for the influence of glacial isostatic adjustment (GIA) using the ICE-6G/VM5a model. For comparison purpose, two additional RMSLR distributions under Representative Concentration Pathway (RCP) scenarios were also evaluated from climate system model (CSM) ensembles and GIA. These spatially variable RMSLR scenarios were then incorporated into a high-resolution storm surge model using elevated present-day water depths to solve for coupled tide–surge–wave processes. The performance of the model was validated using in situ measurements of astronomical tides, storm tides and ocean waves. Due to the significant variability in the spatial distribution of future relative mean sea level trends in the Yellow Sea, the simplified, uniform RMSLR scenario was found to alter the responses of storm surges. The amplification or attenuation of surge heights was not solely affected by the magnitude of sea level change itself, but also modulated by changing tidal ranges and waves due to SLR. The amplification effects of tidal ranges and nonlinearities within radial sand ridges in the south Yellow Sea tended to be underestimated under the uniform scenario, suggesting that the impacts of SLR on storm surges in this region may represent underestimates.

Has Earth ever been ice-free? Implications for glacio-eustasy in the Cretaceous greenhouse age using high-resolution sequence stratigraphy

AbstractControls on high-frequency sequences formed during super-greenhouse conditions in the Late Cretaceous Western Interior Seaway remain equivocal because of the active foreland basin tectonic setting and the lack of direct evidence of polar glaciations to support a glacio-eustatic origin. This paper quantifies eustatic sea-level changes based on high-resolution sequence stratigraphic analysis and improved chronometry of shallow marine deposits of the Late Cretaceous Gallup Sandstone in New Mexico, USA. Backstripping techniques remove tectonic and compactional subsidence and enable quantification of the magnitude of eustatic sea-level change, that allow evaluation of the dominant controls on the high-frequency sequences to resolve the role of orbitally controlled, climate-driven eustasy versus tectonics. Sixty-five parasequences, constituting 29 parasequence sets and 12 sequences are identified in the ∼1.2 m.y. duration of the Late Cretaceous Gallup system. New 40Ar/39Ar dating of bentonites constrains the durations of the individual parasequences, parasequence sets, and sequences, and that these match Milankovitch periodicity, indicating an orbital climate control. The magnitudes of sea-level changes between parasequences range between −28 m and +22 m, which are compatible with hypotheses of both aquifer and glacio-eustasy. Aquifer-eustasy predicts a reciprocal relationship between floodplain cycles and shallow marine sequences, such that aquifer drawdown and falling water tables should correlate to rising sea levels (highstands), whereas increased aquifer storage and rising water tables should correlate to falling sea levels (lowstands). Our preliminary observations show synchronous, versus reciprocal, relationships that may be more compatible with a glacio-eustatic origin. The results of this study support the hypothesis that the Cretaceous greenhouse was marked by high-frequency, low-amplitude glaciations driven by orbital climate cycles, but further work is required to evaluate the contribution of aquifer-eustasy.

Petroleum reservoir quality prediction: overview and contrasting approaches from sandstone and carbonate communities

AbstractThe porosity and permeability of sandstone and carbonate reservoirs (known as reservoir quality) are essential inputs for successful oil and gas resource exploration and exploitation. This chapter introduces basic concepts, analytical and modelling techniques and some of the key controversies to be discussed in 20 research papers that were initially presented at a Geological Society conference in 2014 titled ‘Reservoir Quality of Clastic and Carbonate Rocks: Analysis, Modelling and Prediction’. Reservoir quality in both sandstones and carbonates is studied using a wide range of techniques: log analysis and petrophysical core analysis, core description, routine petrographic tools and, ideally, less routine techniques such as stable isotope analysis, fluid inclusion analysis and other geochemical approaches. Sandstone and carbonate reservoirs both benefit from the study of modern analogues to constrain the primary character of sediment before they become a hydrocarbon reservoir. Prediction of sandstone and carbonate reservoir properties also benefits from running constrained experiments to simulate diagenetic processes during burial, compaction and heating. There are many common controls on sandstone and carbonate reservoir quality, including environment of deposition, rate of deposition and rate and magnitude of sea-level change, and many eogenetic processes. Compactional and mesogenetic processes tend to affect sandstone and carbonate somewhat differently but are both influenced by rate of burial, and the thermal and pressure history of a basin. Key differences in sandstone and carbonate reservoir quality include the specific influence of stratigraphic age on seawater composition (calcite v. aragonite oceans), the greater role of compaction in sandstones and the greater reactivity and geochemical openness of carbonate systems. Some of the key controversies in sandstone and carbonate reservoir quality focus on the role of petroleum emplacement on diagenesis and porosity loss, the role of effective stress in chemical compaction (pressure solution) and the degree of geochemical openness of reservoirs during diagenesis and cementation. This collection of papers contains case study-based examples of sandstone and carbonate reservoir quality prediction as well as modern analogue, outcrop analogue, modelling and advanced analytical approaches.

Contrasting fluvial styles across the mid-Pleistocene climate transition in the northern shelf of the South China Sea: Evidence from 3D seismic data

Multiple successions of buried fluvial channel systems were identified in the Quaternary section of the mid-shelf region of the northern South China Sea, providing a new case study for understanding the interplay between sea level variations and climate change. Using three commercial 3D seismic surveys, accompanied by several 2D lines and a few shallow boreholes, the sequence stratigraphy, seismic geomorphology and stratal architecture of these fluvial channels were carefully investigated. Based on their origin, dimensions, planform geometries and infill architectures, six classes of channel systems, from Class 1 to Class 6, were recognized within five sequences of Quaternary section (SQ1 to SQ5). Three types of fluvial systems among them are incised in their nature, including the trunk incised valleys (Class 1), medium incised valleys (Class 2) and incised tributaries (Class 3). The other three types are unincised, which comprise the trunk channels (Class 4), lateral migrating channels (Class 5) and the stable channels (Class 6). The trunk channels and/or the major valleys that contain braided channels at their base are hypothesized to be a product of deposition from the “big rivers” that have puzzled the sedimentologists for the last decade, providing evidence for the existence of such rivers in the ancient record.Absolute age dates from a few shallow boreholes indicate that the landscapes that were associated with these fluvial systems changed significantly near the completion of the mid-Pleistocene climate transition (MPT), which approximately corresponds to horizon SB2 with an age of ∼0.6 Ma BP. Below SB2, the Early Pleistocene sequence (SQ1) is dominated by a range of different types of unincised fluvial systems. Evidence of incised valleys is absent in SQ1. In contrast, extensive fluvial incision occurred in the successions above horizon SB2 (within SQ2–SQ5). Although recent studies call for increased incision being a product of climate-controlled increase in river discharge, the down-dip location of our study area suggests that relative sea level change was the most important control of the evolution of fluvial systems. However, it is acknowledged that climate change was also important through its role in regulating glacio-eustasy. We speculate that the small amplitude and periodicity of sea level cycles before and during the MPT were not sufficient to fully expose the shelf and cause extensive fluvial incisions. Completion of the MPT as well as the onset of 100 ky climate cycles at ∼0.6 Ma, during which the duration of cycles and magnitude of sea level change both increased, are considered to be triggering event for extensive development of incised fluvial systems. In addition to the eustatically driven causes of enhanced incision, the intensification of the East Asia monsoon at 0.9 Ma and 0.6 Ma driven by the episodic uplift of the Tibetan Plateau may have also significantly enhanced the amplitude of sea level falls and thus the fluvial incisions of the northern shelf of the South China Sea.

Analysis of the regional pattern of sea level change due to ocean dynamics and density change for 1993–2099 in observations and CMIP5 AOGCMs

Predictions of twenty-first century sea level change show strong regional variation. Regional sea level change observed by satellite altimetry since 1993 is also not spatially homogenous. By comparison with historical and pre-industrial control simulations using the atmosphere–ocean general circulation models (AOGCMs) of the CMIP5 project, we conclude that the observed pattern is generally dominated by unforced (internal generated) variability, although some regions, especially in the Southern Ocean, may already show an externally forced response. Simulated unforced variability cannot explain the observed trends in the tropical Pacific, but we suggest that this is due to inadequate simulation of variability by CMIP5 AOGCMs, rather than evidence of anthropogenic change. We apply the method of pattern scaling to projections of sea level change and show that it gives accurate estimates of future local sea level change in response to anthropogenic forcing as simulated by the AOGCMs under RCP scenarios, implying that the pattern will remain stable in future decades. We note, however, that use of a single integration to evaluate the performance of the pattern-scaling method tends to exaggerate its accuracy. We find that ocean volume mean temperature is generally a better predictor than global mean surface temperature of the magnitude of sea level change, and that the pattern is very similar under the different RCPs for a given model. We determine that the forced signal will be detectable above the noise of unforced internal variability within the next decade globally and may already be detectable in the tropical Atlantic.

Geomorphic expression of late Quaternary sea level changes along the southern Saurashtra coast, western India

Geomorphic expression of land-sea interaction is preserved in the form of abandoned cliffs, marine terraces, shore platforms and marine notches along the southern Saurashtra coast. These features have been used to ascertain the magnitude of sea level changes during late Quaternary. Notch morphology and associated biological encrustation have been used to estimate the magnitude and duration of palaeo-sea strands. Marine notches and other erosive features occurring between 12 and 15 m above the present Biological Mean Sea Level (BMSL) are attributed to the last interglacial corresponding to the Marine Isotopic Stage 5 (MIS-5). However, 6 to 9 m upliftment of the coastal fringe is attributed to this sea level. The second major high sea strand was identified during the mid-Holocene when the sea rose 2 m above the present level. Notches corresponding to this high sea level are recorded 4 to 5 m above the present BMSL.

Three-Dimensional Numerical Modeling of Deltaic Depositional Sequences 1: Influence of the Rate and Magnitude of Sea-Level Change

ABSTRACT A three-dimensional numerical model of deltaic deposition is used to investigate the influence of sea-level changes on delta development and sequence variability. Results illustrate the three-dimensional morphology of key stratal surfaces and architecture of stratal units (systems tracts) and highlight the importance of the rate and magnitude of sea-level change in controlling the evolution of deltaic depositional sequences. High rates of sea-level fall lead to the development of a limited number of major incised channels that focus sediment supply to a few elongate, finger-like forced regressive lobes separated by large areas of nondeposition. In contrast, low rates of sea-level fall cause only minor channel incision, which occurs late during sea-level fall. As a result, sediment is supplied more uniformly to the delta front, leading to an attached, laterally continuous forced regressive apron. During lowstand and subsequent sea-level rise, the delta morphology and internal geometry are strongly controlled by the rate of rise. High rates lead to: i) poorly developed lowstand wedges that are drowned early, ii) high-magnitude transgressions, and iii) the late development of maximum flooding surfaces. The stratigraphy developed during sea-level rise is also strongly influenced by the incised-valley system created during the preceding sea-level fall. If deep, major valleys developed that captured most of the sediment supply, the resultant stratigraphy has well developed lowstand wedges that are flooded relatively late during sea-level rise. Even within a single delta, systems tracts and key stratal surfaces show three-dimensional variability and two-dimensional sections often lack significant elements of the stratigraphy. As a result, analysis of two-dimensional sections can often lead to miscorrelation and erroneous interpretations of the controlling processes.

Holocene Sea Level History and Neotectonics of the United States Mid-Atlantic Region: Applications and Corrections

Published local relative Holocene sea level histories, derived from various dated materials at positions along the United States east coast, fail to agree on the timing and magnitude of sea level change. Published eustatic curves suffer the same disagreement and have lead to recent declarations in the literature that a true eustatic history is unattainable. This has been generally accepted by workers in light of the myriad of complicating factors which have been identified as influencing the position of sea level through time. In this study, a single local relative sea level curve (Kraft 1976) has been analyzed for elevation and temporal errors resulting from fine sediment compaction, paleotidal-range, and neotectonic phenomena. Additionally, the cross-latitude history of vertical crustal velocity along the United States east coast is suggested as providing a means of correlating adjacent curves which have been corrected in such a manner. This enhances the applicability of a local relative curve for purposes of understanding the regional sedimentology and stratigraphy associated with Holocene sea level rise. It is suggested that the pursuit of eustasy may best be conducted through the use of corrected, globally distributed, local relative sea level histories which together define regional trends and non-eustatic factors. In this way the histories of eustatic and non-eustatic phenomena may be separated.

Ocean Temperature-Induced Change in Lithospheric Thermal Structure: A Mechanism for Long-Term Eustatic Sea Level Change

Eustatic sea level change can be produced by a change in ocean bottom water temperature through an alteration of the upper thermal boundary condition of oceanic lithosphere. The consequent evolution of lithospheric thermal structure can cause thermal expansion or contraction of the lithosphere. If continental lithosphere remains unaffected by the change in ocean temperatures, "eustatic" sea level will change as measured in the continental frame of reference. A two-dimensional finite difference model has been formulated and shows that if ocean bottom water temperature were to change rapidly by 14°C, as it may have during the Tertiary, sea level would change by 8 m in 8 m.y., and 17 m in 40 m.y. This result is in agreement with the one-dimensional error function solution for a heating or cooling halfspace. However, the changes in lateral heat flow between ocean water and the continental slope, and between oceanic and continental lithosphere, can produce epeirogenic motions of the continental margins (and thus may represent a climatic control on epeirogenic processes). Thus, the affected margins should not be used as a reference frame against which to measure the magnitude of sea level change produced by this mechanism. While this mechanism of water temperature-induced change in lithospheric thermal structure produces effects with magnitudes which are less than those resulting from changes in the average age of ocean floor and operates on timescales longer than those of ice volume changes, the effects of the mechanism are relatively simple to calculate and should be included when consideration is made of eustatic sea level changes in the past.