Past Sea-level Changes Research Articles

Location of the ancient Tindari harbour from geoarchaeological investigations (NE Sicily)

In the Greek and Roman periods, the fortified town of Tindari's military and trading importance combined with its strategic location in north-east Sicily allowed it to control traffic on the Tyrrhenian Sea for many centuries. Historical sources (Polybius, Cicero, Livy and Appian) testify to the flourishing maritime activity of the ancient town, but do not supply any information on the location, size or configuration of its harbour. Because a town as important as Tindari must have had a landing place for ships, we examined new sources of information with the aim of identifying its location. Historiographical and archaeological surveys produced evidence of a well-organised harbour. Geomorphological investigations, performed along the Tindari Promontory, identified Holocene uplifted and submerged notches indicating past sea level changes. Furthermore, it was found that in the last four centuries the combined actions of marine and fluvial dynamics had produced a progressive filling of the Oliveri lowland and a progradation of the shoreline, which was responsible for the burial of ancient buildings. The palaeotopographic reconstruction of the Tindari Cape Promontory and Oliveri coastal plain in the 4th century BC shows a safe landing place south-east of the Tindari Cape that was suitably protected from prevailing winds.

Foraminifera and tidal notches: Dating neotectonic events at Korphos, Greece

Fossil assemblages of foraminifera and thecamoebians from three salt-marsh cores recovered at Korphos, Greece, provided evidence for five transgression events since the mid Holocene. Marsh accretion rates based on radiocarbon-dated peat and geomorphic evidence from a series of discrete, v-shaped, submerged tidal notches indicated that these transgression events were rapid and episodic. Correlation of the tidal notches with the transgression horizons in the salt-marsh stratigraphy revealed a stepwise pattern of relative sea-level change at Korphos, which is best explained by coseismic subsidence related to fault displacement (earthquakes) associated with the Hellenic subduction zone. A comparison between the Korphos data and a model of Holocene sea-level change for the Peloponnesus reinforces this interpretation as sea-level rose in a series of jumps by amounts greater than accounted for by eustatic and glacio-hydro-isostatic factors (up to ~ 2.0 m). This study illustrates that by combining microfossil, sedimentary and geomorphic records of past sea-level change, problems frequently encountered with each record individually (e.g. dating submerged notches and autocompaction of marsh sediments) may be overcome.

Earthquake‐induced turbidites triggered by sea level oscillations in the Upper Cretaceous and Paleocene of Italy

AbstractEarthquakes are widely recognized as triggers for turbidites, submarine debris flows and slumps. In tectonically active areas, surprisingly small changes in stress can trigger seismic events, implying that past sea level changes may be important in controlling the timing of seismicity and the occurrence of turbidites. We apply this idea in an analysis of turbidites from the upper Cretaceous–Paleocene Scaglia Rossa Formation of the Umbria‐Marches region of Italy. These turbidites are composed of resedimented foraminiferal tests derived from fluidizing deep‐water (∼1500 m), pelagic sediments; seismic triggering is the most likely triggering mechanism given this setting and composition. The timing of these turbidites (and associated synsedimentary slumps), constrained by biostratigraphy and magnetostratigraphy, reveals an unusual, non‐random temporal pattern that appears to correlate well with proposed eustatic fluctuations. This correlation between turbidites and eustatic fluctuations leads us to suggest that stress and pore fluid pressure changes associated with changing sea level may trigger periods of increased seismicity in the geological past.

Phenotypic plasticity of Vermetidae suspension feeding: a potential bias in their use as Biological Sea‐Level Indicators

AbstractSome organisms represent useful Biological Sea‐Level Indicators (Bio SLI) thanks to their constant position relative to sea level and allow the reconstruction of past sea level changes. The sessile gastropods Vermetidae are among the most used indicators, since their shells often resist time averaging and can be easily dated with 14C. However, all these vermetids have a level of precision (± 0.5–1 m), obtained from data on the Mediterranean Dendropoma petraeum (Monterosato, 1884). We found a certain degree of plasticity in this species; it can also live subtidally, not in correspondence with the main sea level, where it feeds adopting a mixed feeding strategy. Considering this variability and the almost complete lack of knowledge for other Bio SLI vermetids, it appears clear that a common value of precision cannot be maintained and the precision of other vermetid species remains to be tested.

Constraints on the Greenland Ice Sheet since the Last Glacial Maximum from sea-level observations and glacial-rebound models

Geomorphological descriptions of changes in the extent of the Greenland Ice Sheet (GIS) have been combined with glacial-isostatic-adjustment models to reproduce the sea-level history of Greenland since the Last Glacial Maximum (LGM). The contribution to past sea-level change around Greenland due to ice-load changes outside of that region has been considerable (± 10's of meters), while still contributing a rise of several mm yr −1 today. The isostatic contribution to relative sea level around Greenland from changes in the GIS is found by iteratively perturbing preliminary ice models with different LGM extents and deglaciation starting times. The resulting first-order model that provides the best agreement between observed and predicted sea level contributes 3.1 and 1.9 m water-equivalent of additional ice relative to present-day ice volumes at the LGM and Younger Dryas, respectively. The GIS in most areas does not appear to have extended far onto the continental shelf, the exceptions being southern-most Southwest Greenland and northern East Greenland, as well as at the coalescence of the Northwest Greenland and Innuitian Ice Sheets. Changes in ice thickness since the LGM were >500 m along the present-day outer coast and >1500 m along some parts of the present-day ice margin. The observed mid- to late-Holocene fall in sea level to below the present-day level and the subsequent transgression seen in some areas implies that the GIS retreated behind the present-day margin by distances of the order of 40 km before readvancing.

Surface distributions of salt-marsh foraminifera from Connecticut, USA: modern analogues for high-resolution sea level studies

Salt-marsh foraminifera are routinely used as sea-level indicators since their vertical distribution is closely linked with elevation relative to the tidal frame. The precise nature of these relationships is variable in time and space, and the accuracy of sea-level reconstructions depends upon the selection of appropriate modern analogues that reliably reflect past fauna–environment associations. The marshes of Connecticut, USA, are sites of ongoing research seeking to produce high-resolution records of sea-level change, yet, little published data regarding their modern foraminiferal distributions exist. This paper presents new surface foraminiferal data from three Connecticut salt-marshes and evaluates their suitability as modern analogues for past sea-level changes. The results indicate that significant intra- and inter-site variability between these marshes and those of neighbouring states exists. As a consequence of this, the extrapolation of fauna–environment relationships developed from marshes with different hydrographic, physiographic, vegetative or climatic characteristics may produce erroneous reconstructions, even when adjusted for variations in tidal range. These errors are potentially greatest if single ‘indicator’ species are used since the relative abundance of individual taxa does not vary consistently with elevation, even in high marsh environments from the same site. Whilst cluster analysis demonstrates that foraminiferal assemblages from Connecticut are vertically zoned with respect to mean high water (MHW), the composition, elevation and height range of these zones is variable between sites. This spatial heterogeneity results in reconstructions of relatively low and variable precision that restricts their utility in high-resolution sea-level research. New studies seeking to distil decimetre-scale changes in relative sea level will need to employ quantitative methods capable of combining multi-site information to develop fauna–environment relationships that capture this spatial variability. Reconstructions will be most precise when employing local foraminiferal distributions, but may require the collection of additional modern analogue samples from other regions when the extant foraminiferal population of a site differs in composition from its sub-fossil counterpart.

A diatom model for inferring sea level change in the coastal waters of Hong Kong

Diatoms were identified and enumerated from surface sediments of 25 sites in Double Haven, Hong Kong. The relationship between diatom species distribution and 14 environmental variables was examined using Detrended Correspondence Analysis (DCA) and Canonical Correspondence Analysis (CCA). Water depth was identified as the most important environmental variable influencing the distribution of diatoms in Double Haven. Subsequently a Weighted Average (WA) calibration model was developed to infer water depth. The reliability of the model was evaluated by the error of prediction (RMSEboot= 3.479) and the correlation (r2= 0.7342) between observed and diatom-inferred values. This predictive calibration model has the potential to infer past sea level change in Hong Kong and the adjacent coastal areas.

Analysis of δ 13C, δ 15N, and δ 34S in organic matter from the biominerals of modern and fossil Mercenaria spp.

The response of primary producers to changes in environmental and sea-level conditions is an important topic in the study of estuarine ecosystems. Currently, sea levels are rising, and North American estuaries are in declining ecological health (USEPA, 2002 National Coastal Condition Report. USEPA, Washington, DC). This investigation examines the base of the estuarine food web by evaluating the diets of modern and fossil Mercenaria spp. These clams are infaunal, primary consumers that feed on suspended organic matter. Proteinaceous materials secreted within the biominerals of shell-building organisms are derived from the same diet sources as soft tissue and, therefore, are also capable of recording diet information. We have developed an empirical relationship between the isotopic composition of shell organic matter and soft tissue, which allows food web analyses in fossils to proceed in the same manner as modern food web studies. The Δ tissue-shell for δ 13C, δ 15N, and δ 34S is 0.1, 0.7, and 1.8‰. Isotopic analyses of modern Mercenaria spp. shells from coastal Virginia (δ 13C: −12.8 to −15.9‰, δ 15N: 11.3 to 13.7‰), and the Gulf of Mexico coast of Florida (δ 13C: −19.4 to −21.0‰, δ 15N: 7.2–9.9‰) demonstrate that diets are derived from phytoplankton and local salt marsh plants. Shell organic-matter δ 13C varies from −13.1 to −27.5‰ and δ 15N varies from 2.4 to 9.8‰ in Quaternary Mercenaria spp. from coastal Virginia, North and South Carolina, and Georgia. These data demonstrate that past diet sources have changed in space and time. The fact that past sea-level changes have been accompanied by shifts in local primary production is evidence that significant changes might also occur in association with presently rising sea levels.

Spatial genetic subdivision between northern Australian and southeast Asian populations of Pristipomoides multidens: a tropical marine reef fish species

Nucleotide sequence polymorphism in the left domain of the control region of the mitochondrial genome of over 700 goldband snapper ( Pristipomoides multidens) was surveyed using both direct sequencing and innovative restriction enzyme cleavage analysis techniques. Southeast Asian populations were sampled adjacent to western Irian Jaya, northern Papua New Guinea and western Timor. Six Australian populations were sampled from adjacent to Exmouth in western Australia to Weipa in the northern Gulf of Carpentaria. The results show that significant genetic structure occurs among Indonesian and Australian waters along national boundaries; 14% of the total molecular variance among restriction site haplotypes was due to genetic distinction between Indonesian and Australian samples. Several lines of evidence suggest that gene flow does not occur freely along the northern and western Australian coastline, particularly on the northwestern Kimberley coast. Australian fisheries managers need to be alerted to the possibility of at least one genetically distinct population of this important commercial species which should be protected from over-harvesting that may otherwise lead to localised extinction and the erosion of genetic diversity. There is no convincing biological argument for the observed genetic disjunction in the Kimberley area. It may be due to the combined effect of past sea-level changes, sampling error or patterns of exploitation.

A 300 000-yr coral reef record of sea level changes, Mururoa atoll (Tuamotu archipelago, French Polynesia)

The accurate dating of fossil coral reefs is of prime importance in determining the timing of deglaciation events and thus understanding the mechanisms driving glacial–interglacial cycles. So far, the most useful coral reef records of past sea level changes are those related to the last deglaciation and the Last Interglacial period. U/Th ages for older isotopic stages are more limited, due to the scarcity of datable material, reflecting diagenetic alteration. Most data are from emergent parts of reefs and reef terraces in active subduction zones where relative sea level records may be biased by variations in rates of tectonic uplift. New constraints on sea level changes over the past 300 000 yr are based on high-precision U-series age measurements of successive reef units on Mururoa. These have been cored in four continuous 300-m-long drill holes with seaward inclinations of 30 to 45° on the northeastern rim of the atoll. Past sea level positions have been calculated from the radiometric ages of corals by correcting the present depth of subsurface horizons both for thermal subsidence and for depositional palaeodepth. The location of this atoll at a considerable distance from former ice sheets (‘far field’) minimises the influence of glacio–isostatic rebound. Prominent units formed during four periods of relative sea level highstands, including the Holocene and stages 5 (∼125 ka), 7 (∼212 ka) and 9 (∼332 ka). These are primarily composed of coralgal frameworks that grew in very shallow water. Three periods of relative low stand correspond to stages 2 (∼17–23 ka), 4 (∼60 ka) and 8 (∼270 ka) during which small reefs developed in association with large bioclastic accumulations. Good agreement with the timing of sea level changes based on oxygen isotope measurements in deep-sea cores is noted for most of the dated reef units. We report here the first accurate coral record of the Last Glacial Maximum in the Pacific, 135–143 m below the present sea surface, suggesting that sea level may have been lower than expected during this period.

Sea level rise: History and consequences

The world's coastal zones are regions of major and increasing population density and the location of a number of the world's larger cities. The combination of continuing development of these coastal regions and possible sea level rise during the 21st century is creating the potential for economic and social crises in many nations. As a result, it is imperative that we better understand past and present sea level change.

Significance of pteropods in deciphering the late Quaternary sea-level history along the southwestern Indian shelf

The paper evaluates the usefulness of pteropods in palaeobathymetric synthesis along the southwestern continental shelf of India. Core samples collected from the shelf off north Kerala (SW coast of India) were studied for faunal assemblages (pteropods and foraminifers), calcium carbonate contents and lithological characteristics. A fundamental precept for considering any organism as a bathometer is that it should be highly sensitive to changing water depths. To ascertain this, the bathymetric distribution patterns of modern pteropods as well as planktonic and benthic foraminifers were recorded in core-top samples. The results reveal that certain pteropod species (Limacina inflata, Creseis acicula, Creseis virgula, and Creseis chierchiae) are highly depth sensitive. The response of these species to depth changes was assessed in terms of the L. inflata and Creseis spp. abundance ratio. A model for the relationship between water depths and the L. inflata/Creseis spp. ratio is proposed for the southwestern shelf of India. Variations of benthic/planktonic foraminifers (BF/PF) and pteropods/planktonic foraminifers (Pt/PF) in the modern sediments were also found to be depth controlled. Two sediment cores, representing the last 36,000 and 23,000 years, were collected to investigate past sea-level changes. These cores comprised two distinct lithological units, the upper unit corresponding to the Holocene, and the lower unit to the last glacial period. The L. inflata/Creseis spp. model was successfully applied to the fossil record for reconstructing the palaeobathymetry of the shelf study locations. Down-core variations in the BF/PF and Pt/PF ratios support these inferred sea-level changes. Major periods of sea-level oscillations were also found to have a strong influence on the calcium carbonate distribution. For both core sites, the palaeobathymetric curves reflect consistency in terms of changing sea level. The results suggest that the sea level stood around 100 m below the present mean sea level during the last glacial maximum. A rapid rise in sea level was documented between 15 and 10 ka B.P. The sea-level rise has been slower since 7 ka B.P.

Microsatellite analysis of genetic structure in the mangrove species Avicennia marina (Forsk.) Vierh. (Avicenniaceae).

The level of genetic variation throughout the entire worldwide range of the mangrove species Avicennia marina (Forsk.) Vierh. was examined using microsatellite markers. Three microsatellite loci detected high levels of allelic diversity (70 alleles in total), essential for an accurate estimation of population genetic parameters. The informativeness of the microsatellite loci tended to increase with increasing average number of repeats. The levels of heterozygosity detected for each population, over all loci, ranged from 0.0 to 0.8, with an average of 0.407, indicating that some populations had little or no genetic variation, whereas others had a large amount. Populations at the extremes of the distribution range showed reduced levels of heterozygosity, and significant levels of inbreeding. This is not unexpected as these populations may be subject to founder effects and environmental constraints. The presence of genetic structure was tested in A. marina populations using three models: (i) a single panmictic model; (ii) the discrete subpopulation model; and (iii) the isolation by distance model. The discrete subpopulations model was supported by the overall measures of population differentiation based on the infinite alleles model (F-statistics), and the stepwise mutation model (R statistics). In addition, an analysis of molecular variance (AMOVA), using both theoretical models, found that most of the variation was between populations (41-71%), and within individuals in the total population (31-49%). There was little variation among individuals within populations (0-10%). There was no significant isolation by distance. The high levels of genetic differentiation observed among populations of A. marina may be due to environmental and ecological factors, particularly past sea level and climatic changes.

Biogeography and conservation biology of Florida's Geolycosa wolf spiders: threatened spiders in endangered ecosystems

The state of Florida has a complex biogeography which is the product of past sea level changes and associated ocean currents creating numerous inland sand ridge systems which are home to a unique biota adapted to the seasonally dry conditions found on these sandy uplands. Among these xeric-adapted taxa is a suite of wolf spider species in the genus Geolycosa. Geolycosa wolf spiders are habitat specialists and poor dispersers, and many taxa have ranges restricted to specific ridge systems. We found that the six Geolycosa species typical of Florida's scrubs and sandhills (G. escambiensis Wallace, G. ornatipes (Bryant), G. micanopy Wallace, G. patellonigra Wallace, G. hubbelli Wallace and G. xera McCrone) have current distributions that correlate with the historical biogeography of the state. There are species typical of the Lake Wales Ridge and associated ridges (G. xera and G. hubbelli), species found on the more coastal ridges (G. patellonigra and G. micanopy) and species whose ranges are divided by the Apalachicola River drainage (G. escambiensis and G. ornatipes). We also found that Geolycosa wolf spiders tend to occur in species pairs which use different microhabitats: those which burrow in areas covered in leaf litter, and those which use only barren sites. These latter species require habitat management plans that include burns, that maintain the habitat in an open condition.

Evidence of sea-level fall in sequence stratigraphy: Examples from the Jurassic: Comment and Reply

Research Article| January 01, 2000 Evidence of sea-level fall in sequence stratigraphy: Examples from the Jurassic: Comment and Reply: REPLY A. Hallam A. Hallam 1School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Search for other works by this author on: GSW Google Scholar Author and Article Information A. Hallam 1School of Earth Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2000) 28 (1): 96. https://doi.org/10.1130/0091-7613(2000)28<96:EOSFIS>2.0.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation A. Hallam; Evidence of sea-level fall in sequence stratigraphy: Examples from the Jurassic: Comment and Reply: REPLY. Geology 2000;; 28 (1): 96. doi: https://doi.org/10.1130/0091-7613(2000)28<96:EOSFIS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Coe and Hesselbo challenge my interpretations of two key horizons in the Jurassic of Dorset on the basis of their own detailed researches, Coe on the Oxfordian, and Hesselbo on the Lower Jurassic. Let me deal with them in turn. Coe argues that the concretions in question postdate burrows from younger strata and hence cannot reveal evidence of penecontemporary erosion as I claimed. I would like to have this demonstrated to me in the field, and all I can say here is that the evidence needs to be strong and unequivocal to counteract what appears, on the face of it,... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Response of Mangrove Shorelines to Sea-level Change.

The response of mangrove shorelines to sea-level change is a function their overall sediment budget. Whereas mangroves have often been viewed as a source of organic productivity which is supplied to adjacent estuarine waters, they are generally considered a sink for sediments. Though often displaying a shore-parallel zonation of mangrove species, this need not indicate succession, or that the shoreline is prograding. Despite pronounced zonation, such as in southwestern Florida where mangroves occur adjacent to freshwater wetlands of the Everglades, interpretations based upon stratigraphy have ranged from a view of mangroves as builders of land, to one of retreat as a result of sea-level rise over the past few thousand years. Fossil mangrove material may be used to determine the pattern of fluctuations of sea level over the late Quaternary, and may also indicate the nature of response of mangrove shorelines to past sea-level changes. Mangrove sediments provide a relatively good record of sea-level rise, particularly where there has been a rapid supply of inorganic sediment to the coast, but are poorer indicators of sea-level fall or periods of stable sea level. The function of mangrove ecosystems differs in different environmental settings, and a framework is proposed within which to view the role of mangroves. Sedimentation beneath mangroves modifies the way in which the shoreline responds to changes in sea level, and the timescale over which sedimentation rateis considered is Iikely to influence the way in which mangroves appear to have responded. Future changes are to be expected on mangrove shorelines, but differentiating between natural changes, human-induced changes, or responses to global environmental change will be difficult, and may differ between locations.

The Rise and Fall of Last Interglacial Sea-Levels

The Rise and Fall of Last Interglacial Sea-Levels

Here today, gone tomorrow

Shorelines are ephemeral boundaries that might serve as a forest floor or a seafloor thousands of years from now. What will happen to present shorelines is determined thousands of miles away, by the behavior of continental ice sheets in Antarctica and Greenland. To investigate the timing and magnitude of past sealevel changes and their relationship to the waxing and waning of ice sheets over the past 25 million years, scientists working for the Ocean Drilling Program are beginning to collect sediment and rock samples below the ocean floor off the coast of New Jersey, near the edge of the continental shelf. Scientists from seven countries will extract more than two miles of cores from an immense pile of sediments that accumulated on the ocean floor over millions of years. By analyzing the sedimentary layers, researchers will document the precise timing and scale of sea level changes, which are hypothesized to result from the advance and retreat of continentsized ice sheets that stored and released water during climate cycles.

Scour in large braided rivers and the recognition of sequence stratigraphic boundaries

Alluvial scour into shallow marine sediments may be caused by the incision of a river adjusting to a new base level1–4 following a fall in sea level. The identification of such erosion surfaces1–3 has therefore been pivotal in the reconstruction of past sea-level changes from ancient sedimentary sequences1–14. Here we report data from a study of the Jamuna river, Bangladesh, one of the world's largest modern braided rivers15, which illustrate that bed scour associated with channel confluences and bends alone can be substantial—as much as five times greater than the mean channel depth. Indeed, the basal erosion surfaces produced by such deep scours have characteristics similar to those of boundaries in some ancient sedimentary sequences that have been assumed to result from sea-level fall1–14, potentially leading to radically different interpretations of past variation in base level and climate. We suggest that, to discount unambiguously the influence of fluvial scour in ancient sediments, the erosive boundary should be greater than five times the mean channel depth and extend for distances greater than the floodplain width. Ideally, it should be traceable between different basins.

Geoidal topography: Origin and time consistency

The geoid topography is a direct measure of the irregular density distribution within the Earth. Hence, the geoid is an important tool in deciphering the internal structures and conditions. Deformations of the geoid — i.e. the mean sea level — with time, therefore, give evidence of density changes within the Earth. Past sea level changes that can be shown not to originate from tectonic processes, changes in the oceans’ water volume, changes in the oceans’ basin volumes or local dynamic sea level effects are found to represent paleo-geoid changes (Morner, 1976, 1981a, 1983a). Such paleogeoid changes have now been identified for time units ranging from a few years to several million years (Morner, op. cit.). This gives evidence of rapid processes within the Earth changing the density distribution; i.e. it gives evidence of a high-dynamic Earth.