SHORT-TERM SEA-LEVEL CHANGES AND COASTAL EROSION

AbstractA review of short-term (<3 myr: c. 100 kyr to 2.4 myr) Cretaceous sea-level fluctuations of several tens of metres indicates recent fundamental progress in understanding the underlying mechanisms for eustasy, both in timing and in correlation. Cretaceous third- and fourth-order hothouse sea-level changes, the sequence-stratigraphic framework, are linked to Milankovitch-type climate cycles, especially the longer-period sequence-building bands of 405 kyr and 1.2 myr. In the absence of continental ice sheets during Cretaceous hothouse phases (e.g. Cenomanian–Turonian), growing evidence indicates groundwater-related sea-level cycles: (1) the existence of Milankovitch-type humid-arid climate oscillations, proven via intense humid weathering records during times of regression and sea-level lowstands; (2) missing or inverse relationships of sea-level and the marine δ18O archives, i.e. the lack of a pronounced positive excursion, cooling signal during sea-level lowstands; and (3) the anti-phase relationship of sea and lake levels, attesting to high groundwater levels and charged continental aquifers during sea-level lowstands. This substantiates the aquifer-eustasy hypothesis. Rates of aquifer-eustatic sea-level change remain hard to decipher; however, reconstructions range from a very conservative minimum estimate of 0.04 mm a−1 (longer time intervals) to 0.7 mm a−1 (shorter, probably asymmetric cycles). Remarkably, aquifer-eustasy is recognized as a significant component for the Anthropocene sea-level budget.

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An introduction to causes and consequences of Cretaceous sea-level changes (IGCP 609)

Geological Society London Special Publications ◽

10.1144/sp498-2019-156 ◽

2019 ◽

Vol 498 (1) ◽

pp. 1-8 ◽

Cited By ~ 2

Author(s):

Michael Wagreich ◽

Benjamin Sames ◽

Malcolm Hart ◽

Ismail O. Yilmaz

Keyword(s):

Sea Level ◽

Sea Level Changes ◽

Short Term ◽

Sea Level Fluctuations ◽

Groundwater Aquifer ◽

Sea Level Oscillations ◽

Short And Long Term ◽

Geological Timescale ◽

Land Water

AbstractThe International Geoscience Programme Project IGCP 609 addressed correlation, causes and consequences of short-term sea-level fluctuations during the Cretaceous. Processes causing several ka to several Ma (third- to fourth-order) sea-level oscillations during the Cretaceous are so far poorly understood. IGCP 609 proved the existence of sea-level cycles during potential ice sheet-free greenhouse to hothouse climate phases. These sea-level fluctuations were most probably controlled by aquifer-eustasy that is altering land-water storage owing to groundwater aquifer charge and discharge. The project investigated Cretaceous sea-level cycles in detail in order to differentiate and quantify both short- and long-term records based on orbital cyclicity. High-resolution sea-level records were correlated to the geological timescale resulting in a hierarchy of sea-level cycles in the longer Milankovitch band, especially in the 100 ka, 405 ka, 1.2 Ma and 2.4 Ma range. The relation of sea-level highs and lows to palaeoclimate events, palaeoenvironments and biota was also investigated using multiproxy studies. For a hothouse Earth such as the mid-Cretaceous, humid–arid climate cycles controlling groundwater-related sea-level change were evidenced by stable isotope data, correlation to continental lake-level records and humid–arid weathering cycles.

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Short-Term Sea Level Changes of the Upper Cretaceous Carbonates: Calibration between Palynomorphs Composition, Inorganic Geochemistry, and Stable Isotopes

Minerals ◽

10.3390/min10121099 ◽

2020 ◽

Vol 10 (12) ◽

pp. 1099

Author(s):

Ahmed Mansour ◽

Thomas Gentzis ◽

Michael Wagreich ◽

Sameh S. Tahoun ◽

Ashraf M.T. Elewa

Keyword(s):

Sea Level ◽

Late Cretaceous ◽

Upper Cretaceous ◽

Freshwater Algae ◽

Sea Level Changes ◽

Short Term ◽

Sea Level Oscillations ◽

Rising Sea Level ◽

Southern Tethys

Widespread deposition of pelagic-hemipelagic sediments provide an archive for the Late Cretaceous greenhouse that triggered sea level oscillations. Global distribution of dinoflagellate cysts (dinocysts) exhibited a comparable pattern to the eustatic sea level, and thus, considered reliable indicators for sea level and sequence stratigraphic reconstructions. Highly diverse assemblage of marine palynomorphs along with elemental proxies that relate to carbonates and siliciclastics and bulk carbonate δ13C and δ18O from the Upper Cretaceous Abu Roash A Member were used to reconstruct short-term sea level oscillations in the Abu Gharadig Basin, southern Tethys. Additionally, we investigated the relationship between various palynological, elemental, and isotope geochemistry parameters and their response to sea level changes and examined the link between these sea level changes and Late Cretaceous climate. This multiproxy approach revealed that a long-term sea-level rise, interrupted by minor short-term fall, was prevalent during the Coniacian-earliest Campanian in the southern Tethys, which allowed to divide the studied succession into four complete and two incomplete 3rd order transgressive-regressive sequences. Carbon and oxygen isotopes of bulk hemipelagic carbonates were calibrated with gonyaulacoids and freshwater algae (FWA)-pteridophyte spores and results showed that positive δ13Ccarb trends were consistent, in part, with excess gonyaulacoid dinocysts and reduced FWA-spores, reinforcing a rising sea level and vice versa. A reverse pattern was shown between the δ18Ocarb and gonyaulacoid dinocysts, where negative δ18Ocarb trends were slightly consistent with enhanced gonyaulacoid content, indicating a rising sea level and vice versa. However, stable isotope trends were not in agreement with palynological calibrations at some intervals. Therefore, the isotope records can be used as reliable indicators for reconstructing changes in long-term sea level rather than short-term oscillations.

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Review: Short-term sea-level changes in a greenhouse world — A view from the Cretaceous

Palaeogeography Palaeoclimatology Palaeoecology ◽

10.1016/j.palaeo.2015.10.045 ◽

2016 ◽

Vol 441 ◽

pp. 393-411 ◽

Cited By ~ 66

Author(s):

B. Sames ◽

M. Wagreich ◽

J.E. Wendler ◽

B.U. Haq ◽

C.P. Conrad ◽

...

Keyword(s):

Sea Level ◽

Sea Level Changes ◽

Short Term

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A Probabilistic Model of Coastal Bluff-Top Erosion in High Latitudes Due to Thermoabrasion: A Case Study from Baydaratskaya Bay in the Kara Sea

Journal of Marine Science and Engineering ◽

10.3390/jmse8030169 ◽

2020 ◽

Vol 8 (3) ◽

pp. 169

Author(s):

Mohammad Akhsanul Islam ◽

Raed Lubbad ◽

Mohammad Saud Afzal

Keyword(s):

Sea Level ◽

Probabilistic Model ◽

Coastal Erosion ◽

Global Climate ◽

High Sensitivity ◽

Kara Sea ◽

The Arctic ◽

Field Observations ◽

Sea Level Changes ◽

Erosion Mechanisms

Arctic coastal erosion demands more attention as the global climate continues to change. Unlike those along low-latitude and mid-latitude, sediments along Arctic coastlines are often frozen, even during summer. Thermal and mechanical factors must be considered together when analysing Arctic coastal erosion. Two major erosion mechanisms in the Arctic have been identified: thermodenudation and thermoabrasion. Field observations of Arctic coastal erosion are available in Baydaratskaya Bay in the Kara Sea. The objective of this study is to develop a probabilistic model of thermoabrasion to simulate the measured coastal erosion at two sites where observations suggest thermoabrasion is dominant. The model simulates two time periods: (a) the summer of 2013 (2012–2013) and (b) the summer of 2017 (2016–2017). A probabilistic analysis is performed to quantify the uncertainties in the model results. The input parameters are assumed to follow normal and lognormal distributions with a 10% coefficient of variation. Monte Carlo simulation is applied to determine the erosion rates for the two different cases. The simulation results agree reasonably well with the field observations. In addition, a sensitivity analysis is performed, revealing a very high sensitivity of the model to sea-level changes. The model indicates that the relation between sea-level rise and thermoabrasional erosion is exponential.

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Multiple Submerged Tidal Notches: A Witness of Sequences of Coseismic Subsidence in the Aegean Sea, Greece

Journal of Marine Science and Engineering ◽

10.3390/jmse9040426 ◽

2021 ◽

Vol 9 (4) ◽

pp. 426

Author(s):

Anna Karkani ◽

Niki Evelpidou

Keyword(s):

Sea Level ◽

Late Holocene ◽

Aegean Sea ◽

Sea Level Changes ◽

Short Term ◽

Aegean Region ◽

Return Times ◽

Average Return ◽

Coseismic Subsidence

In some islands of the Aegean, there is evidence of the occurrence of repeated rapid subsidences during the Late Holocene. In this paper, the shape of tidal notches that may be well-preserved underwater is recalled in order to reconstruct sequences of coseismic subsidences and other relative sea-level changes, which occurred during, at least, the last few millennia. A reanalysis of the published measurements of submerged tidal notches in several islands reveals that subsidence trends in many areas of the Aegean are not continuous with gradual movement but, also, are the result of repeated coseismic vertical subsidences of some decimetres at each time. The estimated average return times are of the order of approximately some centuries to one millennium. Although the results cannot be used for short-term predictions of earthquakes, they may provide useful indications on the long-term tectonic trends that are active in the Aegean region.

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Glacial-driven sea-level changes in the Late Triassic

10.5194/egusphere-egu21-6117 ◽

2021 ◽

Author(s):

Meng Wang ◽

Mingsong Li ◽

David B. Kemp ◽

Slah Boulila

Keyword(s):

Sea Level ◽

Lake Level ◽

Principal Component ◽

Late Triassic ◽

Sea Level Changes ◽

Short Term ◽

Noise Modeling ◽

Austrian Alps ◽

Groundwater Aquifer ◽

Newark Basin

<p>Projecting future anthropogenic sea-level rise requires a comprehensive understanding of the mechanistic links between climate and short-term sea-level changes under a warming climate. Two different hypotheses, glacioeustasy and groundwater aquifer eustasy, have been proposed to explain short-term, high amplitude sea-level oscillations during past greenhouse intervals. However, the aquifer eustasy hypothesis &#8211; supported by subjective evidence of sequence stratigraphy in the Late Triassic greenhouse, has never been rigorously tested. Here we test these competing hypotheses using a recently proposed, objective approach of sedimentary noise modeling for both sea- and lake-level reconstructions for the first time. Sedimentation rate estimates and astronomical calibration of multiple paleoclimate proxies from the lacustrine Newark Basin and the marine Austrian Alps enable the construction of a highly resolved astronomical time scale for the Late Triassic. Using this timescale, sedimentary noise modeling for both lacustrine and marine successions is carried out through the Late Triassic. Lake level fluctuations reconstructed by sedimentary noise modeling and principal component analysis revealed that million-year scale lake-level variations were linked to astronomical forcing with periods of ~3.3 Myr, ~1.8 Myr, and ~1.2 Myr. Our objective water-depth reconstructions demonstrate that lake-level variations in the Newark Basin correlate with sea-level changes in the Austrian Alps, rejecting the aquifer eustasy hypothesis and supporting glacioeustasy as the sea-level driver for the Late Triassic. This study thus emphasizes the importance of high-resolution, objective reconstruction of sea- and lake-levels and supports the hypothesis that fluctuations in continental ice mass drove sea-level changes during the Late Triassic greenhouse.</p>

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