Sea-level Indicators Research Articles

Middle Holocene higher sea-level indicators from the south China coast

In a re-examination of the evidence for higher Holocene sea level in the south China coast, we have concluded that the radiocarbon date reported previously for a fixed biomarker in Hong Kong indicated Middle Holocene sea level was no higher than about 2 m above the present mean sea level. Because of the coastal configuration of the biomarker site, the sea-level elevation should be adjusted downwards by about 10 cm to take into account monsoon forcing. In order to further refine the elevation of the higher Middle Holocene sea level, it is necessary to date further fixed biomarkers from other shores with different orientation in the region.

Foraminifera, testate amoebae and diatoms as sea‐level indicators in UK saltmarshes: a quantitative multiproxy approach. W. Roland Gehrels, Helen M. Roe and Dan J. Charman Journal of Quaternary Science Vol 16 No 3 2001, pages 201–220.

AbstractThe original article to which this Erratum refers was published in Journal of Quaternary Science 16 (3) 2001, 201‐220.

Late Quaternary Sea-Level Change in South Africa

A Late Quaternary sea-level curve for South Africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations. Available evidence suggests that sea level in South Africa broadly follows that described from the Caribbean but that deviations occur during sea-level highstands. During the last interglaciation (oxygen isotope stage 5) and the late Holocene, coastal emergence produced higher sea levels in South Africa than those identified in the Caribbean during the same time intervals. This is tentatively ascribed to predicted lithospheric deformation in continental margin settings.

Spatial and temporal variability in the Holocene sea-level record of the South Australian coastline

Studies of past sea levels based on radiocarbon-dated field samples suffer variously from compilation of information from disparate locations and the imprecise nature of the dated indicators. Geographic segregation and systematic elimination of poor samples from time–depth data sets leads to improved interpretation of Holocene sea-level history. An example is presented from Southern Australia, where this is achieved through selection of higher-resolution palaeoenvironmental indicators, separation of transgressive from regressive populations, and geographic regionalisation of data. In Southern Australia, fossil sea-level indicators preserved in prograding coastal plain settings include seagrass, sandflat, mangrove, samphire and chenier ridge organo–sedimentary remains. These provide sea-level time–depth data points with a variety of elevational and dating errors. Preserved organic remains at the transition from Posidonia seagrass to intertidal sandflat environment, and from sandflat to Avicennia mangrove environment provide the most precise local data for tracing sea-level change. Time–depth plots of 233 dated sea-level indicators from South Australia generate a broad sea-level envelope tracing the Southern Australian transgression from 10,000 to ca. 6000 radiocarbon years BP, followed by a more or less consistent level to the present. Finer details of sea-level behaviour are only apparent after systematic selection, separation and regionalisation of the data. The data indicate a very rapid sea-level rise in the early Holocene, at about 16 mm/year, reaching present levels at 6400 years BP. This was followed by regionally variable regression and emergence of the land of 1–3 m, a process that continues to the present. The systematic increase from 1 to 3 m in the elevation of the 6400-year BP highstand with distance away from the shelf margin is consistent with a hydro-isostatic origin for the emergence as predicted by geophysical models.

On eustatic sea level history: Last Glacial Maximum to Holocene

This paper addresses the question of the magnitude and time dependence of the globally averaged (eustatic) rise of sea level that occurred subsequent to the time of Last Glacial Maximum (LGM) at approximately 21,000 calendar years before present. Through the analysis of relative sea level (RSL) histories predicted by a realistic mass conserving and gravitationally self-consistent theory of postglacial sea level change, it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history. One such location is the Island of Barbados in the Caribbean Sea, a site from which a coral based record exists that extends from mid-Holocene to LGM. Because of the sea level ambiguity that is inherent to coral based records, however, it is important that the global ice-equivalent eustatic sea level curve inferred on the basis of the Barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals. It is shown that, when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the Barbados observations, where the maximum relative sea level (RSL) depression is assumed to be near 120 m, then the theory misfits the record from the Sunda Shelf in the Indonesian Archipelago as well as the record from J. Bonaparte Gulf in northern Australia. Both of these recently published records appear to constrain the LGM low stand of RSL to a value above 120 m. The implications of these results for interpretation of the long coral derived records from the Huon Peninsula of Papua, New Guinea and the island of Tahiti are also discussed.

The age of Late Pleistocene shorelines and tectonic activity of Taranto area, Southern Italy

The results of isoleucine epimerization ratios in pelecypods ( Glycymeris sp., Arca sp. and Cerastoderma sp.) and U-series dating of bivalves and Cladocora caespitosa sampled from different Late Pleistocene units in the Chéradi Islands and in the coastal areas of Mar Piccolo and Mar Grande near Taranto (Apulia region, Italy) are presented. U-series measurements on pelecypods and on corals directly associated with mollusc samples provide an independent calibration of amino acid data. The D/ L ratios of isoleucine show a strong correlation with age, and thus may be considered as a predictive dating technique. This correlation also supports the reliability of U-series ages obtained for molluscs. These results, including the stratigraphic position, the lithological lateral continuity, the morphological evidence and the palaeontological characteristics of the various units, made it possible to attribute them to different marine trangressive phases referable to oxygen isotope stages (OIS) 5e–c, 5a and 3. No evidence of land emersion between OIS 5e and 5c has been found in the area. Pinkish/red sands deposits located above present sea level (∼1 m) have been referred to OIS 3. The Late Pleistocene morphological evolution and uplift of a complex area between the Apulian foreland and the Bradanic foredeep have been reconstructed. Due to the lack of incontestable indicators of past sea level stands the facies analysis has been performed on U-series dated 89.8 ka, OIS 5c shoreline north of Mar Piccolo and an uplift rate ranging from 0.21–0.27 mm/yr has been calculated.

Shore-line reconstruction around Australia during the Last Glacial Maximum and Late Glacial Stage

Abstract Being both relatively tectonically stable and far from formerly glaciated regions, continental Australia is particularly well-suited for the study of sea-level evolution since the Last Glacial Maximum (LGM) and the Late Glacial Stage. Sea-level data from such regions are valuable indicators of ice-volume equivalent sea level since the effects of glacio-hydro-isostatic terms is less significant for far-field sites though still not negligible. In this study, we review published sea-level observations and results of recently developed numerical models for several areas of coastal Australia and produce corresponding palaeogeographic maps of the results of our numerical models. The results suggest that the Australian continental shelf was largely exposed during the LGM and provide detailed predictions of the timing of inundation as a function of position. Temporal and spatial variation of sea level provide important constraints that can in turn be used to improve the accuracy of numerical models, and better determine important rheological response parameters for the mantle and environmental conditions during the Late Glacial. The palaeoshoreline data from the modeling performed in this study indicate several key locations for future palaeo-environmental studies of sea-level change.

Foraminifera, testate amoebae and diatoms as sea‐level indicators in UK saltmarshes: a quantitative multiproxy approach

AbstractThe vertical distribution of foraminifera, testate amoebae and diatoms was investigated in saltmarshes in the Taf estuary (south Wales), the Erme estuary (south Devon) and the Brancaster marshes (north Norfolk), to assess the use of multiproxy indicators in sea‐level reconstructions. A total of 116 samples were subjected to regression analyses, using the program calibrate, with duration of tidal flooding as the dependent variable. We found that the relationship between flooding duration and taxa was strongest for diatoms and testate amoebae and weakest for foraminifera. The vertical range of testate amoebae in saltmarshes is small. Their lower tolerance limit in present‐day saltmarshes occurs where tides cover the marsh less than a combined total of 7 days (1.9%) in a year. However, they are important sea‐level indicators because information for sea‐level reconstruction is best derived from sediments that originate in the highest part of the intertidal zone. Diatoms span the entire sampled range in intertidal and supratidal areas, whereas the upper limit of foraminifera is found very close to the highest astronomical tide level. Local training sets provide reconstructions with higher accuracy and precision than combined training sets, but their use is limited if they do not represent adequate modern analogues for fossil assemblages. Although analyses are time consuming, a regional training set of all three groups of micro‐organisms yields highly accurate (r2 = 0.80) and precise (low value of root mean square error) predictions of tidal level. This approach therefore could improve the accuracy and precision of Holocene sea‐level reconstructions. Copyright © 2001 John Wiley & Sons, Ltd.

Coral Reefs and Shoreline Sedimentation: Bathtub Rings around the Sea

Deep sea and ice cores show that sea level and thus global temperature fluctuated often during the past 1.8 million years. Fossil coral reefs, tidal flats, and beaches are precise indicators of former sea level. Although large fluctuations are indicated by the geologic record, this paper focuses on the younger well-documented fluctuations recorded by coral reefs and shoreline deposits that accumulated during the past 140,000 years. During this relatively short period, fossil coral species and depositional processes have remained unchanged and diagenetic alteration of fossils and sediments was minimal. Coral reefs and shoreline accumulations were selected as sea-level indicators for two reasons: (1) they serve as bathtub rings and/or dipsticks for determining former sea levels, and (2) human activity had no influence on the sea in which they grew or accumulated. Emergent coral reefs worldwide suggest that global sea level was at least 6 m above present during isotope stage 5e ∼120 ka. Drowned coral reefs and oolitic beaches indicate sea level was ∼100 m below present during stage 2 as little as 12 ka. As many as eight sea-level fluctuations occurred between stages 2 and 5e, each of which was greater than those projected to result from burning fossil fuels. Ice core data suggest even more fluctuations between stages 5a and 5e. Because the record is written in stone, geologists, especially sedimentologists, should be well qualified to make future predictions. Geologists have for the most part been excluded from official decision making. Direct measurements of air:sea CO2 gas fluxes and carbonate sediment production rates were measured in whitings located on the Great Bahama Bank and in laboratory cultures of calcifying cyanobacteria and unicellular green algae. In situ gas flux measurements showed a reduction in atmospheric CO2 relative to adjacent waters outside of whitings. Similar results were also observed in laboratory cultures. Calcification rates in whitings and laboratory cultures ranged from ∼0.06 to 34.5 g CaCO3m−3hr−1. These results suggest that production of microbial carbonates may serve as a sink for inorganic carbon. Laboratory cultures of calcifying microbes were subjected to biological buffers to examine the role of photosynthetic uptake of inorganic carbon species in calcification. Results from these experiments indicate that microbial calcification mechanisms depend upon the species of inorganic carbon available to cells for photosynthesis and, thus, atmospheric CO2 concentrations. These results suggest fluctuations in Phanerozoic dominance trends for calcareous cyanobacteria and algae may be linked to fluctuations in atmospheric CO2.

Late Holocene higher sea-level indicators from the South China coast

Dating of a relict shell horizon (Saccostrea cucullata) on Hong Kong Island located approximately 1.7 m above present day high tide level constrains the timing of a late Holocene higher sea-level. At 5140 ± 50 yr BP sea-level in the South China area was 4-5 m higher with respect to the Principal Datum (2.7 m below high tide mark) than at present.

Microatolls as sea-level indicators on a mid-ocean atoll

Microatolls are discoid corals with flat upper surfaces that develop when upward coral growth is constrained by exposure at low tide. They have been widely viewed as important and relatively precise indicators of modern and paleo sea-level positions because of their sensitivity to the water/air interface, though this has rarely been directly established by survey to a precise datum. This study involved an accurate survey of 282 microatolls growing in a range of intertidal environments (open reef flats, interisland passages, lagoons) across the Cocos (Keeling) Islands, a mid-ocean atoll in the Indian Ocean. The upper surface elevation of modern microatolls was found to vary through more than 40 cm across the environments in which these corals occur on Cocos, representing more than 30% of the spring tide range. Much of the variation reflects subtle ponding at low water levels across extensive low-gradient reef surfaces associated with interisland passages. Microatolls in open reef flat habitats are typically constrained within the narrowest and most consistent elevation range around the atoll. The environment in which individual fossil microatolls occurred when they were alive is significant in reconstructing former sea levels.

Holocene and Late Pleistocene relative sea level fluctuations along the east coast of India

Abstract Hermatypic coral colonies and intertidal fossil bearing grainstone, packstone and sandstone beds of Holocene and of a Late Pleistocene highstand are exposed above the present High Tide Level (HTL) at a number of locations along the east coast of India from Cape Comorin to Rameswaram. Being a passive margin boundary, free from indications of Late Quaternary seismogenic movements, this sector provides a benchmark for defining minor relative sea level perturbations during the Late Pleistocene and Holocene highstands along a tropical coast lying between latitudes 5°N and 10°N. A series of marine terraces, carved on and locally blanketted by Late Pleistocene biotic and terrigenous accumulations, occur at different elevations (up to 4.4 m) above LTL at Manappad Point, possibly signifying discrete stillstand episodes followed by abrupt intervals of rising/falling sea level. Sea level indicators of the Holocene highstand occur in this sector, as well as along the fringes of the Godavari delta further north. The Holocene highstand reached nearly 3 m above LTL at 7.3 ka, remained stable for approximately 1.7 kyr and was followed by a relative sea level fall. Between 5.2 and 4.2 ka, there was a second pulse of relative sea level rise of a few metres leading to a fresh spurt in coral growth along the northern coast of Mandapam and Rameswaram. This was nearly contemporaneous with fresh melting of ice sheets of Antarctica. The Little Ice Age (LIA) witnessed a minor (>1 m) relative sea level fall along this coast, resulting in rapid diagenetic hardening and infiltration of goethite into the emerged foreshore sand at Karikovil and its neighbourhood. This was followed by a rise of the sea level during the last few centuries.

Alternating seismic uplift and subsidence in the late Holocene at Madang, Papua New Guinea: Evidence from raised reefs

Well‐preserved mid‐late Holocene coral reefs are exposed in low coastal cliffs in the vicinity of the Madang lagoon on the north coast of Papua New Guinea. Results from U/Th and 14C dating of corals, surveying, and field mapping indicate several major changes in relative sea level over this period. Specifically, there is evidence for a relative sea level fall of ≥4.5 m about 3000 calendar years B.P., followed by relative sea level rises of ∼1.5 m about 2400 calendar years B.P. and ≥0.5 m about 1200 calendar years B.P. and a subsequent relative sea level fall of ≥3 m some time in the past 1000 years. Since regional eustatic sea levels are believed to have been dropping gradually over this time frame, these observed changes in relative sea level are interpreted as reflecting alternating tectonic uplift and subsidence. Furthermore, the detailed structure and age relationships of the coral deposits indicate that both uplift and subsidence occurred rapidly, most probably as coseismic events with vertical displacements of 0.5 to 4.5 m. These events may be related to rupture on NW‐SE trending reverse faults which have been mapped in the nearby Adelbert Range and possibly on NE trending cross faults which have been inferred from seismicity. This interpretation implies a much greater degree of tectonic instability and potential seismic hazard in the region than previously recognized, although the inferred coseismic vertical displacements are shown to be consistent with present‐day local seismicity. In a broader context, the study illustrates how detailed analysis of vertical changes in coral reef structure and assemblages may be used as a sensitive indicator of changing relative sea level, capable of resolving century timescale events and reversals.

A new evidence of a higher Quaternary sea-level in Langkawi Islands

Shell deposits were observed at a wave-cut notch on the Setul Limestone in Pulau Tanjung Dendang, Langkawi. The elevation of shell deposits is approximately 23 m above the present sea-level. The most reliable sea-level marker is Saccostrea cuccullata which is found encrusted on the Setul Limestone. Radiocarbon ages of the two samples Saccostrea cuccullta are 6,970 ± 120 and 7,090 ± 100 yr. B.P. This indicates that the maximum Holocene sea-level reached 23 m above the present sea-level during 7,000 yr. B.P. This is the highest sea-level indicator reported in this region. This discovery provides a new information about the sea-level curve prior to 6,000 yr. B.P.

Dendropoma lower intertidal reef formations and their palaeoclimatological significance, NW Sicily

Most carbonate rocky shores of NW Sicily are marked by a coalescence of shells of the gastropod Dendropoma in a construction that is variably developed as a response to wave impact. Here, we review all the available information on these constructions and find that the fossil reefs are reliable sea-level indicators. The thickness of the reef samples never exceeds 30–40 cm below sea-level, whereas all 14 C dates fall within a range of few centuries. Some small fragments ejected by violent sea storms date back to 2500 years cal BP. No samples older than 6200 years cal BP have been detected so far. The present distribution of Mediterranean vermetid platforms should result from a northward migration related to the long term effect of the Holocene sea surface temperature (SST) warming. Some consideration on the morphology of the reefs and the comparison with the available data point out that Dendropoma reefs are excellent biological indicators of sea-level fluctuations especially when detected and sampled in tectonically stable areas as those in NW Sicily.

The use of Jadammina macrescens (Brady) and Balticammina pseudomacrescens Brönnimann, Lutze and Whittaker (Protozoa: Foraminiferida) as sea-level indicators

In studies of foraminiferal distributions in saltmarshes in New England and Atlantic Canada, Balticammina pseudomacrescens and Jadammina macrescens have formerly been grouped as Trochammina macrescens. This study recognises them as distinct species and shows that they have significantly different distributions on the surface of saltmarshes in Maine. Here, relative abundances of J. macrescens correlate with tidal elevation ( r 2=0.55, p=0.00), whereas those of B. pseudomacrescens do not ( r 2=0.03, p=0.34). Therefore, J. macrescens is a better sea-level indicator in Maine marshes than B. pseudomacrescens. In Menunketesuck River marsh, Connecticut, a clear vertical zonation of saltmarsh foraminifera is absent, which hinders interpretation of fossil data. This study shows that, in Maine, separating B. pseudomacrescens and J. macrescens in counts of fossil data facilitates the detection of transgressional and regressional events in the biostratigraphical record and, hence, the reconstruction of local sea-level histories. Regional variability between northern and southern New England saltmarshes necessitates the establishment of local reference sets of modern analogue data to aid palaeoecological interpretations.

Abstract: Foraminifera and Arcellacea Zonation as Sea Level Indicators in Brazilian Mangroves and Freshwater Marsh 

Abstract: Foraminifera and Arcellacea Zonation as Sea Level Indicators in Brazilian Mangroves and Freshwater Marsh 

New data on historical relative sea level movements in Pozzuoli, phlaegrean fields, Southern Italy

During the past 2000 years, vertical movements (bradysism) of several meters amplitude have occurred in the active volcanic caldera of the phlaegrean Fields and notably in the bay of Pozzuoli, near Naples (Southern Italy). Biological sea level indicators (boring Lithophaga shells) were documented up to 7 meters above present sea level on the three marble columns of the Roman marketplace. Fossil specimens of the coral Astroides calycularis were also found 7 m above present sea level, in a former marine cave.1 km east of the Roman marketplace (Rione Terra cliff). Radiocarbon dating of this biological material and the sedimentary filling of an excavated roman structure in Rione Terra suggest that two different crises of submersion of more or less the same amplitude have occurred since Roman times: an Early Middle Age submersion ending between the 5th and the 7th century AD and a Late Middle Age submersion during the 13th–14th century AD, preceding the volcanic eruption of Monte Nuovo in 1538.

Holocene coastal tectonics in NE Brazil

Abstract We have identified two beachrock facies in NE Brazil which can be used as reliable sea-level indicators. Facies (a) represents the lower foreshore and the upper shoreface, being mainly characterized by coarse unsorted sandstones with trough cross-stratification, whereas facies (b) corresponds to sediments deposited on the middle to lower foreshore and is usually characterized by medium to coarse, better sorted sandstones which form seaward-dipping, swash cross beds. The age of the beachrock bodies ranges from c. 7000 to 1150 cal. a bp . Although the relative sea-level record is complicated by oscillations which are probably due to minor climatic changes, it was possible to identify a general rise at c. 7000 cal. a bp which reached its maximum of +2 m c. 5000 cal. a bp and then started to fall to its present level some 300 years later. Our sea-level data are consistent with glacio-hydroisostatic models for the region but dates of 4080 cal. a bp on shells in growth position at +5 m above sea level and 2780 cal. a bp on a beachrock at sea level east of the Carnaubais fault point to rapid, possibly coseismic, late Holocene emergence.

The use of testate amoebae in studies of sea-level change: a case study from the Taf Estuary, south Wales, UK

Micropalaeontological techniques play an important role in high-resolution studies of sea-level change. Salt-marsh foraminifera are among the most valuable groups of sea-level indicators as their distribution shows a narrow vertical zonation which can be accurately related to former sea level. This paper focuses on testate amoebae (‘thecamoebians’), a closely related group of protozoans which have also been widely reported in salt marshes, but only in low numbers and diversities and only in the size fraction used in foraminiferal analyses (<63 μm). A new preparation technique is described which is based on the analysis of the <63,um fraction using high power light microscopy. This technique is applied to surface sediment samples from a salt marsh in the Taf estuary in south Wales. The results show that small testate amoebae (<63 μm) are much more abundant and diverse in salt-marsh sediments than the larger testate amoebae (>63 μm). Species diversity increases from 2 (>63 prm) to 36 (<63 μm) and the maximum abundance is 65 600 individuals per cm3. The assemblages display a distinct spatial zonation across the marsh surface which appears to be closely related to elevation and to tidal parameters. The surface distribution of the testate amoebae is compared with the distribution of foraminifera and diatoms at the same site. The implications of using <63-μm testate amoebae as a tool for sea-level reconstruction are discussed.