Mean Sea Level as a Reference for Geodetic Leveling

1974 ◽  
Vol 28 (5) ◽  
pp. 524-530 ◽  
Author(s):  
G. W. Lennon
Keyword(s):  
Sea Level ◽  
World Ocean ◽  
Equipotential Surface ◽  
Scientific Discipline ◽  
Mean Sea Level ◽  
Sea Levels ◽  
Coastal Sea ◽  
Long Time ◽  
Marine System

The use of mean sea level as a surface of reference that might provide an independent control for geodetic leveling has been a long term goal arising from the classical analogy between the geoid as an equipotential surface and the surface assumed by a hypothetical undisturbed world ocean. The problems associated with this aim are now known to be vast, and are associated with the dynamics of the marine system, notably its response to meteorological forces, to variations in density and to the effects of basic circulation patterns. In consequence the mean sea level surface varies rapidly in both time and space. This identifies in fact a distinctive scientific discipline, coastal geodesy, in which contributions are required by both geodesists and oceanographers. It has come to be recognized that the coastal zone is a hazardous environment for all observational techniques concerned. On the one hand, the difficulties of measurement of coastal sea levels have only recently been understood; on the other hand, precise leveling procedures are now known to be influenced by the attraction of marine tides and by crustal deformation of tidal loading. Much of the data available for study are therefore inadequate and, moreover, it should be noted that long-time series are required. It is now possible to lay plans for both geodetic and oceanographic procedures to remedy these deficiencies in the long-term interests of the study.

scholarly journals Analysis on the Extreme Sea Levels Changes along the Coastline of Bohai Sea, China

Atmosphere ◽  
2018 ◽  
Vol 9 (8) ◽  
pp. 324 ◽  
Author(s):  
Jianlong Feng ◽  
Delei Li ◽  
Hui Wang ◽  
Qiulin Liu ◽  
Jianli Zhang ◽  
...  
Keyword(s):  
Sea Level ◽  
Bohai Sea ◽  
High Tide ◽  
Tide Gauges ◽  
Mean Sea Level ◽  
Sea Levels ◽  
The Bohai Sea ◽  
Extreme Sea Levels ◽  
The Mean

Using hourly sea level data from four tide gauges, the changes of the extreme sea level in the Bohai Sea were analyzed in this work. Three components (i.e., mean sea level, tide and surge) as well as the tide–surge interaction were studied to find which component was important in the changes of extreme sea levels. Significant increasing trends exist in the mean sea level at four tide gauges from 1980 to 2016, and the increase rate ranges from 0.2 to 0.5 cm/year. The mean high tide levels show positive trends at four tide gauges, and the increasing rate (0.1 to 0.3 cm/year) is not small compared with the long-term trends of the mean sea levels. However, the mean tidal ranges show negative trends at Longkou, Qinhuangdao and Tanggu, with the rate from about −0.7 to −0.2 cm/year. At Qinhuangdao and Tanggu, the annual surge intensity shows explicit long-term decreasing trend. At all four tide gauges, the storm surge intensity shows distinct inter-annual variability and decadal variability. All four tide gauges show significant tide–surge interaction, the characteristics of the tide–surge interaction differ due to their locations, and no clear long-term change was found. Convincing evidence implies that the extreme sea levels increase during the past decades from 1980 to 2016 at all tide gauges, with the increasing rate differing at different percentile levels. The extreme sea level changes in the Bohai Sea are highly affected by the changes of mean sea level and high tide level, especially the latter. The surge variation contributes to the changes of extreme sea level at locations where the tide–surge interaction is relatively weak.

scholarly journals Flooding Conditions at Aveiro Port (Portugal) within the Framework of Projected Climate Change

2021 ◽  
Vol 9 (6) ◽  
pp. 595
Author(s):  
Américo Soares Ribeiro ◽  
Carina Lurdes Lopes ◽  
Magda Catarina Sousa ◽  
Moncho Gomez-Gesteira ◽  
João Miguel Dias
Keyword(s):  
Climate Change ◽  
Sea Level ◽  
Climate Change Impacts ◽  
Storm Surges ◽  
Historical Period ◽  
Return Periods ◽  
Wave Regime ◽  
Mean Sea Level ◽  
Sea Levels ◽  
Far Future

Ports constitute a significant influence in the economic activity in coastal areas through operations and infrastructures to facilitate land and maritime transport of cargo. Ports are located in a multi-dimensional environment facing ocean and river hazards. Higher warming scenarios indicate Europe’s ports will be exposed to higher risk due to the increase in extreme sea levels (ESL), a combination of the mean sea level, tide, and storm surge. Located on the west Iberia Peninsula, the Aveiro Port is located in a coastal lagoon exposed to ocean and river flows, contributing to higher flood risk. This study aims to assess the flood extent for Aveiro Port for historical (1979–2005), near future (2026–2045), and far future (2081–2099) periods scenarios considering different return periods (10, 25, and 100-year) for the flood drivers, through numerical simulations of the ESL, wave regime, and riverine flows simultaneously. Spatial maps considering the flood extent and calculated area show that most of the port infrastructures' resilience to flooding is found under the historical period, with some marginal floods. Under climate change impacts, the port flood extent gradually increases for higher return periods, where most of the terminals are at high risk of being flooded for the far-future period, whose contribution is primarily due to mean sea-level rise and storm surges.

Revising key parameters for long-term carbon cycle models

2021 ◽  
Author(s):  
Chloé M. Marcilly ◽  
Trond H. Torsvik ◽  
Mathew Domeier ◽  
Dana L. Royer
Keyword(s):  
Sea Level ◽  
Age Distribution ◽  
Silicate Weathering ◽  
Geological Time ◽  
Sea Levels ◽  
Climate Fluctuations ◽  
Climate Gradients ◽  
Sea Level Fluctuations ◽  
Temperature And Precipitation

<p>CO<sub>2</sub> is the most important greenhouse gas in the Earth’s atmosphere and has fluctuated considerably over geological time. However, proxies for past CO<sub>2 </sub>concentrations have large uncertainties and are mostly limited to Devonian and younger times. Consequently, CO<sub>2</sub> modelling plays a key role in reconstructing past climate fluctuations. Facing the limitations with the current CO<sub>2</sub> models, we aim to refine two important forcings for CO<sub>2</sub> levels over the Phanerozoic, namely carbon degassing and silicate weathering.</p><p>Silicate weathering and carbonate deposition is widely recognized as a primary sink of carbon on geological timescales and is largely influenced by changes in climate, which in turn is linked to changes in paleogeography. The role of paleogeography on silicate weathering fluxes has been the focus of several studies in recent years. Their aims were mostly to constrain climatic parameters such as temperature and precipitation affecting weathering rates through time. However, constraining the availability of exposed land is crucial in assessing the theoretical amount of weathering on geological time scales. Associated with changes in climatic zones, the fluctuation of sea-level is critical for defining the amount of land exposed to weathering. The current reconstructions used in<sub></sub>models tend to overestimate the amount of exposed land to weathering at periods with high sea levels. Through the construction of continental flooding maps, we constrain the effective land area undergoing silicate weathering for the past 520 million years. Our maps not only reflect sea-level fluctuations but also contain climate-sensitive indicators such as coal (since the Early Devonian) and evaporites to evaluate climate gradients and potential weatherablity through time. This is particularly important after the Pangea supercontinent formed but also for some time after its break-up.</p><p>Whilst silicate weathering is an important CO<sub>2</sub> sink, volcanic carbon degassing is a major source but one of the least constrained climate forcing parameters. There is no clear consensus on the history of degassing through geological time as there are no direct proxies for reconstructing carbon degassing, but various proxy methods have been postulated. We propose new estimates of plate tectonic degassing for the Phanerozoic using both subduction flux from full-plate models and zircon age distribution from arcs (arc-activity) as proxies.</p><p>The effect of revised modelling parameters for weathering and degassing was tested in the well-known long-term models GEOCARBSULF and COPSE. They revealed the high influence of degassing on CO<sub>2</sub> levels using those models, highlighting the need for enhanced research in this direction. The use of arc-activity as a proxy for carbon degassing leads to interesting responses in the Mesozoic and brings model estimates closer to CO<sub>2 </sub> proxy values. However, from simulations using simultaneously the revised input parameters (i.e weathering and degassing) large model-proxy discrepancies remain and notably for the Triassic and Jurassic.</p><p> </p>

scholarly journals On the Long-Term Behaviour of Glacial Ice under Moving Traffic Load: A Case Study

1985 ◽  
Vol 31 (109) ◽  
pp. 369-371
Author(s):  
S. G. Vombatkere
Keyword(s):  
Sea Level ◽  
Traffic Load ◽  
Motor Vehicles ◽  
Glacial Ice ◽  
Mean Sea Level

AbstractA Bailey bridge built on a permanent ice body at an altitude of 5580 m above mean sea-level has been carrying regular traffic of 7 tonne motor vehicles for over 2 years. The problems posed by the ice body, its behaviour under the load of the bridge and traffic, its summer and winter behaviour, and the problems posed in the construction and maintenance of the bridge are studied and discussed.

High Stands of Holocene Sea Levels in the Northwest Pacific

1978 ◽  
Vol 10 (1) ◽  
pp. 1-29 ◽  
Author(s):  
Paolo A. Pirazzoli
Keyword(s):  
Sea Level ◽  
Outer Zone ◽  
Local Scale ◽  
Northwest Pacific ◽  
The Sea Of Japan ◽  
Sea Levels ◽  
Level Change ◽  
Recent Emergence ◽  
The Japanese Archipelago

Evidence of Holocene sea levels higher than the present level have often been reported from the Northwest Pacific. Eustatic interpretations have been propounded, but age and level of the maximum transgression vary with each new analysis. In this investigation, after an inventory of approximately 250 items of data, some of which are new, a tentative synthesis transcending local scale is advanced. The highest levels are reported from Taiwan, where they often reach several tens of meters in altitude. In the Ryûkyûs and in the main islands of the Japanese Archipelago, evidence of recent emergence is found along most of the coasts. Elevation increases towards the oceanic trenches, but former sea levels at above 6 m and even higher may also be recognized along the coasts of the Sea of Japan. In a few areas, such as in the Niigata Plain, marks of Holocene sea levels higher than at present are lacking. On the other hand, in other basins regarded as subsiding, such as those in the Nôbi and the Kantô plains, evidence of recent emergence is quite frequent. In many places, marks of several sea levels indicate that a step-by-step uplift has occurred. All the investigated insular arcs, therefore, seem to be situated in epeirogenic areas formed by several more or less large blocks affected by relative movements. The blocks are larger in the Outer Zone of Southwestern Japan; in the Inner Zone, an intricate network of fault lines marks the boundaries of many smaller independent blocks. During great earthquakes, relative movements of uplift, subsidence, tilting, or undulation occur in one or several blocks, depending on the position of the epicentres. Subsidence, however, must often be simply of a temporary nature, because a long-term uplift trend seems to prevail in most regions, even if it occurs at different rates. This interpretation may explain the cause of the great variety of ages and elevations of the former sea levels (with the oldest ages corresponding to the highest elevations) and the great number of indicators of step-by-step sea-level change. The inference, drawn by several authors, that the Holocene sea level in the Northwest Pacific was higher than at present, is, therefore, reasonable on a local scale, but does not define an eustatic sea level.

scholarly journals Global sea level reconstruction for 1900–2015 reveals regional variability in ocean dynamics and an unprecedented long weakening in the Gulf Stream flow since the 1990s

Ocean Science ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 997-1016
Author(s):  
Tal Ezer ◽  
Sönke Dangendorf
Keyword(s):  
Sea Level ◽  
Gulf Stream ◽  
Tide Gauge ◽  
Meridional Overturning Circulation ◽  
Ocean Dynamics ◽  
South Atlantic Bight ◽  
Regional Variability ◽  
Coastal Sea ◽  
Global Sea Level

Abstract. A new monthly global sea level reconstruction for 1900–2015 was analyzed and compared with various observations to examine regional variability and trends in the ocean dynamics of the western North Atlantic Ocean and the US East Coast. Proxies of the Gulf Stream (GS) strength in the Mid-Atlantic Bight (GS-MAB) and in the South Atlantic Bight (GS-SAB) were derived from sea level differences across the GS. While decadal oscillations dominate the 116-year record, the analysis showed an unprecedented long period of weakening in the GS flow since the late 1990s. The only other period of long weakening in the record was during the 1960s–1970s, and red noise experiments showed that is very unlikely that those just occurred by chance. Ensemble empirical mode decomposition (EEMD) was used to separate oscillations at different timescales, showing that the low-frequency variability of the GS is connected to the Atlantic Multi-decadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC). The recent weakening of the reconstructed GS-MAB was mostly influenced by weakening of the upper mid-ocean transport component of AMOC as observed by the RAPID measurements for 2005–2015. Comparison between the reconstructed sea level near the coast and tide gauge data for 1927–2015 showed that the reconstruction underestimated observed coastal sea level variability for timescales less than ∼5 years, but lower-frequency variability of coastal sea level was captured very well in both amplitude and phase by the reconstruction. Comparison between the GS-SAB proxy and the observed Florida Current transport for 1982–2015 also showed significant correlations for oscillations with periods longer than ∼5 years. The study demonstrated that despite the coarse horizontal resolution of the global reconstruction (1∘ × 1∘), long-term variations in regional dynamics can be captured quite well, thus making the data useful for studies of long-term variability in other regions as well.

scholarly journals ANALYSIS OF MAXIMUM SEA LEVELS IN SOUTHERN ENGLAND

1978 ◽  
Vol 1 (16) ◽  
pp. 53
Author(s):  
J. Graff ◽  
D.L. Blackman
Keyword(s):  
Sample Size ◽  
Sea Level ◽  
Linear Trend ◽  
South Coast ◽  
Annual Maximum ◽  
Return Periods ◽  
The South ◽  
Mean Sea Level ◽  
Sea Levels ◽  
Southern England

Along the south coast of England, series of observed annual maximum sea levels, ranging from 16 years to 125 years have been analysed for each of 10 ports. The Jenkinson method of analysis was used to compute the frequency of recurrence of extreme levels. For a number of these ports the series of annual maxima are shown to have significant trends of the same order as those for mean sea level. The Jenkinson method can be simply adjusted to cope with maxima having a component linear trend, making it possible to allow for such trends in computing the frequency of recurrence of extreme levels. If a trend in the annual maxima varies throughout the sample of observations it is shown that difficulties arise in using the Jenkinson method to compute acceptable statistics. It is also shown that for certain ports having long series of observed annual maxima it may be necessary to restrict the sample size of observations in order to compute estimates of the recurrence of extreme levels within reasonable return periods.

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.

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