Sea Level Changes in the Past 6000 Years: Possible Archeological Significance

Geologically speaking, estuaries are ephemeral features of the coasts. Upon formation, most begin to fill in with sediments and, in the absence of sea level changes, would have life spans of only a few thousand to tens of thousands of years (Emery and Uchupi, 1972; Schubel, 1972; Schubel and Hirschberg, 1978). Estuaries have been part of the geologic record for at least the past 200 million years (My) BP (before present; Williams, 1960; Clauzon, 1973). However, modern estuaries are recent features that only formed over the past 5000 to 6000 years during the stable interglacial period of the middle to late Holocene epoch (0–10,000 y BP), which followed an extensive rise in sea level at the end of the Pleistocene epoch (1.8 My to 10,000 y BP; Nichols and Biggs, 1985). There is general agreement that four major glaciation to interglacial periods occurred during the Pleistocene. It has been suggested that sea level was reduced from a maximum of about 80 m above sea level during the Aftoninan interglacial to 100 m below sea level during the Wisconsin, some 15,000 to 18,000 y BP (figure 2.1; Fairbridge, 1961). This lowest sea level phase is referred to as low stand and is usually determined by uncovering the oldest drowned shorelines along continental margins (Davis, 1985, 1996); conversely, the highest sea level phase is referred to as high stand. It is generally accepted that low-stand depth is between 130 and 150 m below present sea level and that sea level rose at a fairly constant rate until about 6000 to 7000 y BP (Belknap and Kraft, 1977). A sea level rise of approximately 10 mm y−1 during this period resulted in many coastal plains being inundated with water and a displacement of the shoreline. The phenomenon of rising (transgression) and falling (regression) sea level over time is referred to as eustacy (Suess, 1906). When examining a simplified sea level curve, we find that the rate of change during the Holocene is fairly representative of the Gulf of Mexico and much of the U.S. Atlantic coastline (Curray, 1965).

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Middle and Late Holocene Sea-Level Changes in Eastern Maine Reconstructed from Foraminiferal Saltmarsh Stratigraphy and AMS 14C Dates on Basal Peat

Quaternary Research ◽

10.1006/qres.1999.2076 ◽

1999 ◽

Vol 52 (3) ◽

pp. 350-359 ◽

Cited By ~ 113

Author(s):

W.Roland Gehrels

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Tidal Range ◽

Sea Level Changes ◽

The Past ◽

Amplitude Fluctuations ◽

Vertical Distributions ◽

Low Amplitude ◽

Long Term Trend

A relative sea-level history is reconstructed for Machiasport, Maine, spanning the past 6000 calendar year and combining two different methods. The first method establishes the long-term (103 yr) trend of sea-level rise by dating the base of the Holocene saltmarsh peat overlying a Pleistocene substrate. The second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long-term trend. The indicative meaning of the peat (the height at which the peat was deposited relative to mean tide level) is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages. The chronology is determined from AMS 14C dates on saltmarsh plant fragments embedded in the peat. The combination of the two different approaches produces a high-resolution, replicable sea-level record, which takes into account the autocompaction of the peat sequence. Long-term mean rates of sea-level rise, corrected for changes in tidal range, are 0.75 mm/yr between 6000 and 1500 cal yr B.P. and 0.43 mm/yr during the past 1500 year. The foraminiferal stratigraphy reveals several low-amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr B.P., and a sea-level rise of 0.5 m during the past 300 year.

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Holocene Relative Sea Level Changes along the Seattle Fault at Restoration Point, Washington

Quaternary Research ◽

10.1006/qres.2000.2180 ◽

2000 ◽

Vol 54 (3) ◽

pp. 384-393 ◽

Cited By ~ 31

Author(s):

Brian L. Sherrod ◽

Robert C. Bucknam ◽

Estella B. Leopold

Keyword(s):

Sea Level ◽

Environmental Changes ◽

Hanging Wall ◽

Sea Level Changes ◽

Diatom Assemblages ◽

Recent Event ◽

Plant Seed ◽

The Past ◽

The One ◽

Fossil Diatoms

At a marsh on the hanging wall of the Seattle fault, fossil brackish water diatom and plant seed assemblages show that the marsh lay near sea level between ∼7500 and 1000 cal yr B.P. This marsh is uniquely situated for recording environmental changes associated with past earthquakes on the Seattle fault. Since 7500 cal yr B.P., changes in fossil diatoms and seeds record several rapid environmental changes. In the earliest of these, brackish conditions changed to freshwater ∼6900 cal yr B.P., possibly because of coseismic uplift or beach berm accretion. If coseismic uplift produced the freshening ∼6900 cal yr B.P., that uplift probably did not exceed 2 m. During another event about 1700 cal yr B.P., brackish plant and diatom assemblages changed rapidly to a tidal flat assemblage because of either tectonic subsidence or berm erosion. The site then remained a tideflat until the most recent event, when an abrupt shift from tideflat diatoms to freshwater taxa resulted from ∼7 m of uplift during an earthquake on the Seattle fault ∼1000 cal yr B.P. Regardless of the earlier events, no Seattle fault earthquake similar to the one ∼1000 cal yr B.P. occurred at any other time in the past 7500 years.

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Sea Level Fluctuation During the Past 6000 yr at the Coast of Mauritania

Quaternary Research ◽

10.1016/0033-5894(74)90017-9 ◽

1974 ◽

Vol 4 (3) ◽

pp. 282-289 ◽

Cited By ~ 29

Author(s):

G. Einsele ◽

D. Herm ◽

H.U. Schwarz

Keyword(s):

Sea Level ◽

High Accuracy ◽

Level Fluctuation ◽

Sea Level Changes ◽

Tidal Zone ◽

The Past ◽

Marine Terraces ◽

Open Sea ◽

Sea Level Fluctuation ◽

Ecological Methods

In an area regarded to be very favorable for the study of Holocene sea level changes one or several eustatic (?) oscillations of sea have been found using sedimentological and ecological methods. After a maximum of +3 m during the Nouakchottian stage (= Middle Flandrian or Late Atlantic) about 5500 YBP a drop of sea to −3.5 ± 0.5 m about 4100 YBP is testified by stromatolitic algae indicating the former sea level within the tidal zone with high accuracy. This evidence is supported by the observation of post-Nouakchottian regressive and transgressive geologic sequences, by buried beach deposits and flooded hardgrounds, post-Nouakchottian marine terraces of different height and age, the cutting off of one large and several small bays from the open sea, etc. Possibly one or two smaller oscillations followed between 4000 and 1500 YBP (derived sea level curve Fig. 3).

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A System to Improve Port Navigation Safety and Its Use in Italian Harbours

Applied Sciences ◽

10.3390/app112110265 ◽

2021 ◽

Vol 11 (21) ◽

pp. 10265

Author(s):

Maurizio Soldani ◽

Osvaldo Faggioni

Keyword(s):

Sea Level ◽

Atmospheric Pressure ◽

Environmental Parameters ◽

Sea Surface ◽

Economic Losses ◽

Sea Level Changes ◽

Traffic Lights ◽

The Past ◽

Sea Level Variations ◽

The Mediterranean Basin

This article describes research aimed at developing a system able to support local authorities and port communities in optimizing port navigation, avoiding or managing critical situations induced by sea-level variations in harbours and minimizing environmental damages and economic losses. In the Mediterranean basin, sea-level changes are mostly due to astronomical tides, related to the gravitational attraction between Earth, Moon and Sun. Nevertheless, sea-level variations are also influenced by meteorological tides, which are geodetic adjustments of sea surface due to atmospheric pressure variations above a water basin. So, starting from monitoring or forecasting environmental parameters in harbours, the system updates port bathymetric maps based on sea-level variations (acquired in the past, measured in real-time, or expected in the future) and detects hazardous areas for a certain ship moving inside a port at a given moment, by means of the implementation of “virtual traffic lights”. The system was tested on some real situations, including the analysis of maritime accidents (stranding of ships), providing satisfactory results by correctly signalling potentially dangerous areas variable over time. The architecture of the system and results achieved using it in the ports of Livorno and Bari, in Italy, are herewith described.

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Sea-level rise in Venice: historic and future trends (review article)

Natural Hazards and Earth System Science ◽

10.5194/nhess-21-2643-2021 ◽

2021 ◽

Vol 21 (8) ◽

pp. 2643-2678 ◽

Cited By ~ 4

Author(s):

Davide Zanchettin ◽

Sara Bruni ◽

Fabio Raicich ◽

Piero Lionello ◽

Fanny Adloff ◽

...

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Tide Gauge ◽

Average Rate ◽

Sea Level Changes ◽

Relative Sea Level ◽

The Past ◽

Gauge Data ◽

Relative Sea Level Rise ◽

Sea Level Variations

Abstract. The city of Venice and the surrounding lagoonal ecosystem are highly vulnerable to variations in relative sea level. In the past ∼150 years, this was characterized by an average rate of relative sea-level rise of about 2.5 mm/year resulting from the combined contributions of vertical land movement and sea-level rise. This literature review reassesses and synthesizes the progress achieved in quantification, understanding and prediction of the individual contributions to local relative sea level, with a focus on the most recent studies. Subsidence contributed to about half of the historical relative sea-level rise in Venice. The current best estimate of the average rate of sea-level rise during the observational period from 1872 to 2019 based on tide-gauge data after removal of subsidence effects is 1.23 ± 0.13 mm/year. A higher – but more uncertain – rate of sea-level rise is observed for more recent years. Between 1993 and 2019, an average change of about +2.76 ± 1.75 mm/year is estimated from tide-gauge data after removal of subsidence. Unfortunately, satellite altimetry does not provide reliable sea-level data within the Venice Lagoon. Local sea-level changes in Venice closely depend on sea-level variations in the Adriatic Sea, which in turn are linked to sea-level variations in the Mediterranean Sea. Water mass exchange through the Strait of Gibraltar and its drivers currently constitute a source of substantial uncertainty for estimating future deviations of the Mediterranean mean sea-level trend from the global-mean value. Regional atmospheric and oceanic processes will likely contribute significant interannual and interdecadal future variability in Venetian sea level with a magnitude comparable to that observed in the past. On the basis of regional projections of sea-level rise and an understanding of the local and regional processes affecting relative sea-level trends in Venice, the likely range of atmospherically corrected relative sea-level rise in Venice by 2100 ranges between 32 and 62 cm for the RCP2.6 scenario and between 58 and 110 cm for the RCP8.5 scenario, respectively. A plausible but unlikely high-end scenario linked to strong ice-sheet melting yields about 180 cm of relative sea-level rise in Venice by 2100. Projections of human-induced vertical land motions are currently not available, but historical evidence demonstrates that they have the potential to produce a significant contribution to the relative sea-level rise in Venice, exacerbating the hazard posed by climatically induced sea-level changes.

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Influence of the "Hypsithermal Age" and "Neoglaciation" climatic conditions on the Brazilian coast.

Pesquisas em Geociências ◽

10.22456/1807-9806.20296 ◽

2001 ◽

Vol 28 (2) ◽

pp. 213 ◽

Cited By ~ 2

Author(s):

KENITIRO SUGUIO

Keyword(s):

United States ◽

Gulf Of Mexico ◽

Sea Level ◽

Southeastern United States ◽

Climatic Conditions ◽

Brazilian Coast ◽

Sea Level Changes ◽

Relative Sea Level ◽

Sea Levels ◽

The Past

Meanwhile the highest relative sea-level is the present one in southeastern United States (Gulf of Mexico) or in Netherlands coast, most of the Brazilian coast exhibited Holocene sea-levels higher than the present in the past. The Brazilian curves, representing the relative sea-level changes during last 7.000 years, are outlined using sedimentological, biological and prehistorical past sea-level records. This paper shows that these relative sea-level records, during the Holocene, can be suitably used to demonstrate the influence of the worldwide known paleoclimatic events, like the “Hypsithermal Age” and “Neoglaciation” on the Brazilian coast.

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Sea-level changes in the Bohai Sea, northern China, constrained by coastal loess accumulation over the past 200 ka

Quaternary Science Reviews ◽

10.1016/j.quascirev.2021.107368 ◽

2022 ◽

Vol 277 ◽

pp. 107368

Author(s):

Shuangwen Yi ◽

Lin Zeng ◽

Zhiwei Xu ◽

Yao Wang ◽

Xianyan Wang ◽

...

Keyword(s):

Sea Level ◽

Bohai Sea ◽

Northern China ◽

Sea Level Changes ◽

The Bohai Sea ◽

The Past

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Holocene Sea-Level Changes in Palau, West Caroline Islands

Quaternary Research ◽

10.1016/0033-5894(80)90048-4 ◽

1980 ◽

Vol 14 (2) ◽

pp. 199-209 ◽

Cited By ~ 20

Author(s):

William H. Easton ◽

Teh-Lung Ku

Keyword(s):

Sea Level ◽

Average Rate ◽

Good Evidence ◽

Tectonic Activity ◽

Sea Level Changes ◽

The Past ◽

Fringing Reefs ◽

Tide Level ◽

Caroline Islands ◽

Calcareous Deposits

Abstract14C ages supplemented by 230Th/234U determinations have been obtained for calcareous deposits on Koror, Babelthuap, Auluptagel, and Adorius Islands in the Palau Group, West Caroline Islands. Test borings for a bridge between Koror and Babelthuap reveal shoreface terraces consisting largely of bioclastic sand, but resembling fringing reefs. The base of the shoreface terraces dates to between 7000 and 8000 14C yr B.P. and the upper surfaces are slightly younger than 4000 yr B.P. Spacing of the subsurface isochrons indicates that the rate of sedimentation increased up-section on Koror terrace and decreased up-section on Babelthuap terrace. The average rate of deposition in the terraces was 0.5 cm/yr. Isochrons in the Babelthuap shoreface terrace are 7 m higher than those in the Koror terrace. If deposition was sufficient to keep the surfaces of the terraces at low tide level, then the Babelthuap side was essentially stable and the Koror side was uplifted between about 8000 and 6300 yr ago, and then subsided until 4000 yr ago; since then there has been about 2 m of uplift. “Top hat” microatolls on Koror terrace indicate that relative sea level has dropped about 30 cm in the past 75 yr. In the absence of good evidence for changes of level in water ponded in a moat, it is likely that the microatolls indicate uplift of the terrace. On the other hand, if tectonic activity was minimal, then differences in the two terraces are due to differences in sedimentation with the Koror side of the channel being substantially subtidal between about 7000 and 5000 yr B.P. Taking the composite eustatic sea-level curve of Hawaii and elsewhere as a reference standard, it is deduced that Auluptagel Island has risen 0.8 m in the last 2900 yr, and Adorius Island has risen approximately 8 m in the last 5000–6000 yr.

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