The Great Lakes as a test model for profile response to sea level changes /

"December 1984."

Conference on Continental Margin Mass-wasting and Pleistocene Sea-level Changes, August 13-15, 1980 /

Mode of access: Internet.

Sedimentary archives of climate and sea-level changes during the Holocene in the Rhone prodelta (NW Mediterranean Sea)

A 7.38 m-long sediment core was collected from the eastern part of the Rhone prodelta (NW Mediterranean) at 67 m water depth. A multi-proxy study (sedimentary facies, benthic foraminifera and ostracods, clay mineralogy, and major elements from XRF) provides a multi-decadal to century-scale record of climate and sea-level changes during the Holocene. The early Holocene is marked by alternative silt and clay layers interpreted as distal tempestites deposited in a context of rising sea level. This interval contains shallow infra-littoral benthic meiofauna (e.g. Pontocythere elongata, Elphidium spp., Quinqueloculina lata) and formed between ca. 20 and 50 m water depth. The middle Holocene (ca. 8.3 to 4.5 ka cal. BP), is characterized, at the core site, by a period of sediment starvation (accumulation rate of ca. 0.01 cm yr−1) resulting from the maximum landward shift of the shoreline and the Rhone outlet(s). From a sequence stratigraphic point of view, this condensed interval, about 35 cm-thick, is a Maximum Flooding Surface that can be identified on seismic profiles as the transition between delta retrogradation and delta progradation. It is marked by very distinct changes in all proxy records. Following the stabilization of the global sea level, the late Holocene is marked by the establishment of prodeltaic conditions at the core site, as shown by the lithofacies and by the presence of benthic meiofauna typical of the modern Rhone prodelta (e.g. Valvulineria bradyana, Cassidulina carinata, Bulimina marginata). Several periods of increased fluvial discharge are also emphasized by the presence of species commonly found in brackish and shallow water environments (e.g. Leptocythere). Some of these periods correspond to the multi-decadal to centennial late Holocene humid periods recognized in Europe (i.e. the 2.8 ka event and the Little Ice Age). Two other periods of increased runoffs at ca. 1.3 and 1.1 ka cal. BP are recognized, and are likely to reflect periods of regional climate deterioration that are observed in the Rhone watershed.

U.S. west coast relative sea levels from tide gauges [abstract]

EXTRACT (SEE PDF FOR FULL ABSTRACT): Examining secular changes in relative sea level along the U.S. west coast, we have identified strong tectonic signals. Tectonism exists not only on a coherent plate-wide scale (assuming a rigid plate approximation), but also on a sub-plate scale. In fact, differential tectonism between exotic or suspect geological terrain explains much of the spatial patterns of west coast tide-gauge data. Peltier's isostatic model appears not to explain the spatial pattern, implying glacio-isostatic adjustment is not the dominant contribution to the low-frequency signals. Eustatic effects cannot be identified unambiguously. These studies suggest several major questions/observations with regard to relative sea-level studies ...

Isolation basin records of late Quaternary sea-level change, central mainland British Columbia, Canada.

Isolation basin records from the Seymour-Belize Inlet Complex, a remote area of central mainland British Columbia, Canada are used to constrain post-glacial sea-level changes and provide a preliminary basis for testing geophysical model predictions of relative sea-level (RSL) change. Sedimentological and diatom data from three low-lying (<4 m elevation) basins record falling RSLs in late-glacial times and isolation from the sea by ~11,800–11,200 14C BP. A subsequent RSL rise during the early Holocene (~8000 14C BP) breached the 2.13 m sill of the lowest basin (Woods Lake), but the two more elevated basins (sill elevations of ~3.6 m) remained isolated. At ~2400 14C BP, RSL stood at 1.49 ± 0.34 m above present MTL. Falling RSLs in the late Holocene led to the final emergence of the Woods Lake basin by 1604 ± 36 14C BP. Model predictions generated using the ICE-5G model partnered with a small number of different Earth viscosity models generally show poor agreement with the observational data, indicating that the ice model and/or Earth models considered can be improved upon. The best data-model fits were achieved with relatively low values of upper mantle viscosity (5 × 1019 Pa s), which is consistent with previous modelling results from the region. The RSL data align more closely with observational records from the southeast of the region (eastern Vancouver Island, central Strait of Georgia), than the immediate north (Bella Bella–Bella Coola and Prince Rupert-Kitimat) and areas to the north-west (Queen Charlotte Sound, Hecate Strait), underlining the complexity of the regional response to glacio-isostatic recovery.

Benthic foraminifera and sea level analyses from IODP Hole 310-M0005D

The course of sea-level fluctuations during Termination II (TII; the penultimate deglaciation), which is critical for understanding ice-sheet dynamics and suborbital climate variability, has yet to be established. This is partly because most shallow-water sequences encompassing TII were eroded during sea-level lowstands of the last glacial period or were deposited below the present sea level. Here we report a new sequence recording sea-level changes during TII in the Pleistocene sequence at Hole M0005D (water depth: 59.63 m below sea level [mbsl]) off Tahiti, French Polynesia, which was drilled during Integrated Ocean Drilling Program Expedition 310. Lithofacies variations and stratigraphic changes in the taxonomic composition, preservation states, and intraspecific test morphology of large benthic foraminifers indicate a deepening-upward sequence in the interval from Core 310-M0005D-26R (core depth: 134 mbsl) through -16R (core depth: 106 mbsl). Reconstruction of relative sea levels, based on paleodepth estimations using large benthic foraminifers, indicated a rise in sea level of about 90 m during this interval, suggesting its correlation with one of the terminations. Assuming that this rise in sea level corresponds to that during TII, after correcting for subsidence since the time of deposition, a highstand sea-level position would be 2 ± 15 m above present sea level (masl), which is generally consistent with highstand sea-level positions in MIS 5e (4 ± 2 masl). If this rise in sea level corresponds to that during older terminations, the subsidence-corrected highstand sea-level positions (30 ± 15 masl for Termination III and 54 ± 15 masl for Termination IV) are not consistent with reported ranges of interglacial sea-level highstands (-18 to 15 masl). Therefore, the studied interval likely records the rise in sea level and associated environmental changes during TII. In particular, the intervening cored materials between the two episodes of sea-level rise found in the studied interval might record the sea-level reversal event during TII. This conclusion is consistent with U/Th ages of around 133 ka, which were obtained from slightly diagenetically altered (i.e., < 1% calcite) in situ corals in the studied interval (Core 310-M0005D-20R [core depth: 118 mbsl]). This study also suggests that our inverse approach to correlate a stratigraphic interval with an approximate time frame could be useful as an independent check on the accuracy of uranium-series dating, which has been applied extensively to fossil corals in late Quaternary sea-level studies.

Mid-Holocene sea-level and coral reef demise : U-Th dating of subfossil corals in Moreton Bay, Australia

It is increasingly apparent that sea-level data (e.g. microfossil transfer functions, dated coral microatolls and direct observations from satellite and tidal gauges) vary temporally and spatially at regional to local scales, thus limiting our ability to model future sea-level rise for many regions. Understanding sealevel response at ‘far-field’ locations at regional scales is fundamental for formulating more relevant sea-level rise susceptibility models within these regions under future global change projections. Fossil corals and reefs in particular are valuable tools for reconstructing past sea levels and possible environmental phase shifts beyond the temporal constraints of instrumental records. This study used abundant surface geochronological data based on in situ subfossil corals and precise elevation surveys to determine previous sea level in Moreton Bay, eastern Australia, a far-field site. A total of 64 U-Th dates show that relative sea level was at least 1.1 m above modern lowest astronomical tide (LAT) from at least ˜6600 cal. yr BP. Furthermore, a rapid synchronous demise in coral reef growth occurred in Moreton Bay ˜5800 cal. yr BP, coinciding with reported reef hiatus periods in other areas around the Indo-Pacific region. Evaluating past reef growth patterns and phases allows for a better interpretation of anthropogenic forcing versus natural environmental/climatic cycles that effect reef formation and demise at all scales and may allow better prediction of reef response to future global change.

Incised palaeo-channels of the Late Middle Pleistocene Thames: age, origins and implications for fluvial palaeogeography and sea-level reconstruction in the southern North Sea Basin.

Multidisciplinary investigations of the infills of steeply-incised buried channels on the coast of Essex, England, provide important insights into late Middle Pleistocene climate and sea-level change and have a direct bearing on the differentiation of MIS 11 and MIS 9 in terrestrial records. New data are presented from Rochford and Burnham-on-Crouch where remnants of two substantial palaeo-channels filled with interglacial sediment can be directly related to the terrace stratigraphy of the Thames. The sediments in both channels accumulated in an estuarine environment early in an interglacial when mixed oak forest was becoming established. Lithological evidence suggests that the interglacial beds post-date the brackish-water infill of an older palaeo-channel ascribed to the Hoxnian and correlated with part of MIS 11, and pre-date terrace gravels (Barling Gravel) ascribed to MIS 8. An MIS 9 attribution is supported by molluscan biostratigraphy, palaeo-salinity and amino-acid racemization data. The relative sea-level record in this area thus includes evidence for two major marine transgressions during MIS 11 and MIS 9, with local maxima of >10 m O.D. Both are associated with sediments that show ‘Hoxnian’ palynological affinities. The wider significance of these findings, and of an intermediate phase of pronounced fluvial incision during MIS 10, is discussed.

Rapid rise in Effective Sea-Level in southwest Bangladesh: Its causes and contemporary rates

Evidence is presented from three estuarine tide gauges located in the
Sundarban area of southwest Bangladesh of relative sea level rise
substantially in excess of the generally accepted rates from altimetry, as
well as previous tide-gauge analyses. It is proposed that the difference
arises from the use of relative mean sea level (RMSL) to characterise the
present and future coastal flood hazard, since RMSL can be misleading in
estuaries in which tidal range is changing. Three tide gauges, one located in
the uninhabited mangrove forested area (Sundarban) of southwest
Bangladesh, the others in the densely populated polder zone north of the
present Sundarban, show rates of increase in RMSL ranging from 2.8 mm
a-1 to 8.8 mm a-1. However, these trends in RMSL disguise the fact that high
water levels in the polder zone have been increasing at an average rate of
15.9 mm a-1 and a maximum of 17.2 mm a-1. In an area experiencing tidal
range amplification, RMSL will always underestimate the rise in high water
levels; consequently, as an alternative to RMSL, the use of trends in high
water maxima or ‘Effective Sea Level Rise’ (ESLR) is adopted as a more
strategic parameter to characterise the flooding hazard potential. The rate
of increase in ESLR is shown to be due to a combination of deltaic
subsidence, including sediment compaction, and eustatic sea level rise, but
principally as a result of increased tidal range in estuary channels recently
constricted by embankments. These increases in ESLR have been partially
offset by decreases in fresh water discharge in those estuaries connected
to the Ganges. The recognition of increases of the effective sea level in the
Bangladesh Sundarban, which are substantially greater than increases in
mean sea level, is of the utmost importance to flood management in this
low-lying and densely populated area.

Late Holocene sea-level fall and turn-off of reef flat carbonate production: Rethinking bucket fill and coral reef growth models

Relative sea-level rise has been a major factor driving the evolution of reef systems during the Holocene. Most models of reef evolution suggest that reefs preferentially grow vertically during rising sea level then laterally from windward to leeward, once the reef flat reaches sea level. Continuous lagoonal sedimentation ("bucket fill") and sand apron progradation eventually lead to reef systems with totally filled lagoons. Lagoonal infilling of One Tree Reef (southern Great Barrier Reef) through sand apron accretion was examined in the context of late Holocene relative sea-level change. This analysis was conducted using sedimentological and digital terrain data supported by 50 radiocarbon ages from fossil microatolls, buried patch reefs, foraminifera and shells in sediment cores, and recalibrated previously published radiocarbon ages. This data set challenges the conceptual model of geologically continuous sediment infill during the Holocene through sand apron accretion. Rapid sand apron accretion occurred between 6000 and 3000 calibrated yr before present B.P. (cal. yr B.P.); followed by only small amounts of sedimentation between 3000 cal. yr B.P. and present, with no significant sand apron accretion in the past 2 k.y. This hiatus in sediment infill coincides with a sea-level fall of similar to 1-1.3 m during the late Holocene (ca. 2000 cal. yr B.P.), which would have caused the turn-off of highly productive live coral growth on the reef flats currently dominated by less productive rubble and algal flats, resulting in a reduced sediment input to back-reef environments and the cessation in sand apron accretion. Given that relative sea-level variations of similar to 1 m were common throughout the Holocene, we suggest that this mode of sand apron development and carbonate production is applicable to most reef systems.

Sea Level Variations during the Late Quaternary and Coastal Evolution along the Northern Kerala, South West of India

In the present investigation, an attempt is made to document various episodes of transgression and regression during the late Quaternary period from the study of coastal and shelf sequences extending from the inland across the beach to the shelf domain. Shore parallel beach ridges with alternating swales and occurrence of strand line deposits on the shelf make the northern Kerala coast an ideal natural laboratory for documenting the morpho-dynamic response of the coast to the changing sea level. The objectives of the study are lithographic reconstruction of environments of deposition from the coastal plain and shelf sequences; documentation of episodes of transgression and regression by studying different coastal plain sequences and shelf deposits and evolve a comprehensive picture of late Quaternary coastal evolution and sea level changes along the northern Kerala coast by collating morphological, lithological and geochronological evidences from the coastal plain and shelf sequences. The present study is confined to two shore-normal east-west trending transects, Viz. Punjavi and Onakkunnu, in the northern Kerala coast.

Onset of recent rapid sea-level rise in the western Atlantic Ocean

A high-resolution record of sea-level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2m thick salt-marsh peat sequence at Chezzetcook, Nova Scotia, Canada. Former mean tide level positions are reconstructed with a precision of +/- 0.055 in using a transfer function derived from distributions of modern salt-marsh foraminifera. Our age model for the core section older than 300 years is based on 19 AMS C-14 ages and takes into account the individual probability distributions of calibrated radiocarbon ages. The past 300 years is dated by pollen and the isotopes Pb-206, Pb-207, Pb-210, Cs-137 and Am-241. Between AD 1000 and AD 1800, relative sea level rose at a mean rate of 17cm per century. Apparent pre-industrial rises of sea level dated at AD 1500-1550 and AD 1700-1800 cannot be clearly distinguished when radiocarbon age errors are taken into account. Furthermore, they may be an artefact of fluctuations in atmospheric C-14 production. In the 19th century sea level rose at a mean rate of 1.6mm/yr. Between AD 1900 and AD 1920, sea-level rise accelerated to the modern mean rate of 3.2mm/yr. This acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming. (c) 2005 Elsevier Ltd. All rights reserved.