Relative Sea-level History Research Articles

Ice‐3G: A new global model of Late Pleistocene deglaciation based upon geophysical predictions of post‐glacial relative sea level change

A new high resolution global model of late Pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice‐ocean‐solid Earth interaction is treated in a gravitationally self‐consistent fashion. For the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem. Only radiocarbon controlled relative sea level histories from sites that were actually ice covered (with one or two additions) are employed to constrain the model, leaving relative sea level (RSL) data from sites that were not ice covered to be employed to confirm its consistency. Results for these confirmatory analyses are reported elsewhere. Here the new deglaciation model, referred to as ICE‐3G, is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories, including geologically controlled retreat isochrones, oxygen‐isotope data from deep‐sea sedimentary cores, and coral terrace elevations. The latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial‐interglacial transition.

Warm to Cold Polar Climate Transitions Over the Last 15,000 Years: A Paleoclimatology Record from the Raised Beaches of Northern Norway

Because of the strength of the cold, dry arctic high pressure vortex, and the absence of multiple air-mass sources, climate records from the polar region tend to display a cleaner signal than those from mid-latitude settings. The high arctic presents unique opportunities for the prediction of the natural background pattern of climate change prior to the disturbances generated by manmade atmospheric pollutants. The Varanger Peninsula of northernmost Norway was extensively depressed by an ice dome during the last glacial stage. Deglaciation was accompanied by isostatic recovery at a steady though exponentially decaying rate. Superimposed on the rising land is a discontinuous staircase of cobble beach ridges, deposited during the postglacial period by storms at the coast. The ridges are constructed during brief episodes of weather- and tide-related elevation of sea level and wave run-up. Storminess periods can only occur in the absence of sea ice associated with several decades of mild, relatively warm temperatures. A history of local relative sea level is constructed from over 70 radiocarbon dates of various water-level indicators. The sea-level history is used to construct a chronology of beach-ridge building that documents the cyclic, a periodic nature of arctic storminess conditions. The authors date a dynamicmore » signal with multiple climate transitions from warm, stormy conditions to cool, calm conditions occurring roughly every 200 years between 15,000 years ago to 10,000 years ago. Throughout the Holocene the climate is more settled with longer periods separating the major warm to cool transitions.« less

Post-glacial relative sea-level history of northwestern Spitsbergen, Svalbard

The late Weichselian and Holocene raised-beach sequences on northwestern Spitsbergen provide a detailed record of sea-level oscillations during the last deglacial hemicycle. Initial emergence commenced at ≥13 ka, coincident with local deglaciation, and until 10.5 ka was characterized by a relative slow rate of emergence (1.5 to 5 m/ka) interrupted by minor stillstands or transgressions associated with possible glacier re-advances. The orientation of paleo-spits and the paucity of whale remains at the late Weichselian marinelimit indicate that the prevailing westerly fetch was dampened by a semi-permanent sea-ice cover, allowing long shore-drift to predominate. A period of accelerated emergence (15 to 30 m/ka) between 10.5 and 9 ka is correlative with rapid deglaciation of fiords. The middle and late Holocene is characterized by two brief transgressions: one between 6.5 and 5.0 ka that did not exceed 7 m asl and a present, probable slow rise in sea level that commenced 2 to 1 ka. The strandline tilts in northwestern Spitsbergen, and the pattern and rate of emergence on Svalbard indicate that the maximum glacier loads during the late Weichselian were centered on Nordaustlandet, and on the central and eastern part of the archipelago. Northwestern and southwestern Spitsbergen were marginal to glacial loading and were deglaciated early (≥13 ka) which is presently incompatible with maximum ice sheet extent and the timing and position of deglacial margins recently reconstructed for the Barents Sea and Svalbard. Mountain ranges and large fiords probably confined major outlet glaciers to the central part of the archipelago, preventing inundation of much of western Spitsbergen by an inferred large ice sheet based in eastern Svalbard and the Barents Sea.

Facies Stratigraphy and Relative Sea-Level History--Upper Cretaceous Eutaw Formation, Central and Eastern Alabama: ABSTRACT

ABSTRACT The Eutaw Formation (130 to 400 ft thick) rests disconformably on incised valleys (a type 1 unconformity) occuring at the top of the underlying non-marine Tuscaloosa Formation (Cenomanian-early Turonian). The Eutaw is topped by an erosional discontinuity which has slight relief and a discontinuous conglomeratic lag. In the outcrop and shallow subsurface, the Eutaw Formation has four main paralic and nearshore facies which are arranged in two discontinuity-bounded genetic packages of facies (or parasequences) both of which developed in a single eustatic cycle. The Eutaw facies are: carbonaceous and ostried-rich clayey silts (back barrier); planar, trough, and low-angle cross-bedded medium-fine sands (barrier island); fossiliferous bioturbated fine sands (lower shoreface); and calcareous clays, silts, and sands (inner shelf). The intraformational facies discontinuity is likely a parasequence boundary developed at maximum eustatic high stand in latest Santonian.

Isolating the Effects of Thrust Belt Tectonism from Relative Sea Level History: An Example from the Cretaceous Western Interior: ABSTRACT

Isolating the Effects of Thrust Belt Tectonism from Relative Sea Level History: An Example from the Cretaceous Western Interior: ABSTRACT

The last glaciation and relative sea level history of Northwest Ellesmere Island, Canadian high arctic

AbstractPhilips Inlet and Wootton Peninsula are located at 82°N and 85°W on the northwest coast of Ellesmere Island and are composed of three bedrock controlled zones: (1) 900 m undulating plateau dissected by fiords; (2) a deeply fretted cirque terrain >1200m; (3) a 300m plateau bounded by coastal cliffs. Each zone contains different glacier morphologies and these control glacigenic sediment and landform assemblages. The extent of the last glaciation is mapped using the distribution of moraines, kames, meltwater channels and glacimarine sediments. Glaciers advanced on average <10 km from their present margins and many piedmont lobes coalesced and floated in the sea. Morainal banks were deposited at the grounding lines of floating glaciers, and where debris‐charged basal ice occurred, subaqueous fans were deposited upon deglaciation. Marine shells dating 20.2 ka BP (<2km from present ice margin) and 14.9ka BP (from a morainal bank) document full glacial marine fauna. Thirty‐three radiocarbon dates document glacier retreat patterns and are used to reconstruct the postglacial sea level history (glacioisostatic rebound pattern). An equidistant shoreline diagram is constructed using the 8.5ka BP shoreline as a guide. Tilts from 0.73‐0.85m/km are calculated for this shoreline. Using two firm control points and tilts from elsewhere on northern Ellesmere Island, the 10.1 ka BP (full glacial) marine limit descends from 117m as at the fiord heads to 63 m asl at the north coast. Deglaciation started with a pronounced calving phase throughout the field area between 10.1 and 7.8ka BP. This chronology is similar to that from northeast Ellesmere Island and attests to an early Holocene warming trend recorded in high arctic ice cores. A maximum lag of 2.1 ka exists between the field area and locations to the south of the Grant Land Mountains suggesting differences in glacioclimatic regimes on either side of the mountain range. Persistent reconstructions of all‐pervasive ice sheets for the last glaciation of the area are obsolete and should be abandoned.

Holocene Sea Level History and Neotectonics of the United States Mid-Atlantic Region: Applications and Corrections

Published local relative Holocene sea level histories, derived from various dated materials at positions along the United States east coast, fail to agree on the timing and magnitude of sea level change. Published eustatic curves suffer the same disagreement and have lead to recent declarations in the literature that a true eustatic history is unattainable. This has been generally accepted by workers in light of the myriad of complicating factors which have been identified as influencing the position of sea level through time. In this study, a single local relative sea level curve (Kraft 1976) has been analyzed for elevation and temporal errors resulting from fine sediment compaction, paleotidal-range, and neotectonic phenomena. Additionally, the cross-latitude history of vertical crustal velocity along the United States east coast is suggested as providing a means of correlating adjacent curves which have been corrected in such a manner. This enhances the applicability of a local relative curve for purposes of understanding the regional sedimentology and stratigraphy associated with Holocene sea level rise. It is suggested that the pursuit of eustasy may best be conducted through the use of corrected, globally distributed, local relative sea level histories which together define regional trends and non-eustatic factors. In this way the histories of eustatic and non-eustatic phenomena may be separated.

Late Weichselian and Holocene Relative Sea-level History of Bröggerhalvöya, Spitsbergen

AbstractRadiocarbon-dated whalebones from raised beaches record a relative sea-level history for Bröggerhalvöya, western Spitsbergen that suggest a two-step deglaciation on Svalbard at the end of the late Weichselian glaciation. The late Weichselian marine limit was reached at about 13,000 yr B.P. and was followed by relatively slow emergence until about 10,000 yr B.P. either in response to ice unloading in the Barents Sea, initial retreat of local fjord glaciers, or some combination of the two. Rare whale skeletons dating between 13,000 and 10,000 yr B.P. indicate that the Norwegian Sea was at least seasonally ice free during that interval. Deglaciation of Spitsbergen is recorded by the rapid emergence of Bröggerhalvöya after 10,000 yr B.P. This was followed by a transgression during the mid-Holocene, here named the Talavera Transgression, and another in modern times. Raised beach morphologies suggest striking differences in nearshore depositional processes before and after 10,000 yr B.P. that are probably related to changes in the rate of uplift and in sea-ice conditions.

Deglaciation‐induced vertical motion of the North American continent and transient lower mantle rheology

The last deglaciation event of the current ice age, which began approximately 18,000 years ago and ended about 7000 years ago, continues to exert a profound influence on the vertical motion of the solid earth in and surrounding the regions which were once ice covered. Observations of such vertical motions may be employed to constrain the radial viscoelastic structure of the planet and therefore to contribute in an important way to the understanding of geodynamic processes in general. In this paper both present‐day rates of vertical motion as recorded on tide gauges and long time scale records of vertical motion as recorded in 14C‐controlled relative sea level histories are employed to refine previously constructed models of the radial viscoelastic structure. An interesting sidelight to this analysis is the demonstration that the lower mantle viscosity inferred from the vertical motion data could represent a transient rather than the steady state value, a fact which would help considerably to reconcile the small viscosity stratification required by the glacial rebound data with the large stratification which seems to be required by some recent analyses of the geoid height anomalies associated with internal density heterogeneity of the mantle which has been revealed by application of seismic tomographic techniques. A further product of these new analyses is obtained by the application of the glacial isostatic adjustment model to filter this signal from the secular trends of relative sea level observed on tide gauges from both the east and west coasts of the North American continent. These results may be important in the context of recently proposed scenarios of climatic change.

The effects of transient rheology on the interpretation of lower mantle viscosity

We have reexamined the role played by transient rheology in the interpretation of mantle viscosity. This investigation has been carried out by comparing the amplitude responses with the data of secular variation of, the relative sea‐level histories at sites well within the ice margins and at the ice margin like the city of Boston. A linear Burgers’ body rheology has been assumed in the lower mantle. The data near the edge of the ice load proves most sensitive to the transient viscosity structure. The non‐monotonic behavior of sea‐level data near Boston can be explained both by a steady‐state lower mantle viscosity of 1022P with a thick lithosphere and also by a transient lower mantle rheology but with a thin lithosphere. The long‐term viscosity of the lower mantle in this second model has a steady‐state value of around 5×1023P.

The thickness of the continental lithosphere

Two independent sets of geophysical data are shown to be particularly sensitive to the thickness of the continental lithosphere. Both are connected with the response of the planet to the last deglaciation event of the current ice age. The first set of data consists of relative sea level histories in the age range 0–10 kyr B.P. from sites along the eastern seaboard of North America. Such data appear to require a continental lithospheric thickness in excess of 200 km. The second set of data consists of the ILS record of the motion of the rotation pole over the time range 0–75 years B.P., which reveals a secular drift at the rate of 0.95 (±0.15) deg/106 years toward Hudson Bay. When the viscosity profile of the mantle is fixed to that required to explain free air gravity and relative sea level data from within the ice margin and the observed nontidal acceleration of planetary rotation, then these observations also suggest a continental lithospheric thickness of the same order.

Paleogene calcareous nannofossil biostratigraphy of the Atlantic coastal plain

Reconnaissance nannofossil sampling of outcrops, well cuttings, and cores from New Jersey to North Carolina reveals strata representative of the entire Paleogene except for NP 3 and NP 24–25. Lowest Paleocene strata (NP 1–2) occur in the subsurface of central New Jersey and equivalents may exist in North Carolina. Mid-to-upper Paleocene beds (NP 5–9) occur in central New Jersey, Virginia, and North Carolina, cropping out as the Vincentown, Aquia, and Beaufort Formations respectively. Lower Eocene assemblages appear to occur only in the subsurface of Virginia where a section representing continuous open marine deposition from NP 4–5 to NP 23 exists. Middle Eocene strata (NP 14–17) occur in New Jersey, Delaware, Maryland, Virginia, and North Carolina, whereas upper Eocene beds are represented only in Virginia and North Carolina. The Virginia section is mainly clastic whereas that of North Carolina seems to represent wave-influenced carbonate banks exhibiting several hardgrounds (Castle Hayne Formation). Nannofossil assemblages of NP 15 and NP 18–20 (but not NP 16–17) suggest that the Castle Haynes Formation might represent two separate marine transgressions separated by a hiatus. Lower Oligocene assemblages (NP 21–22) were found only in the subsurface of Virginia and North Carolina, and mid-Oligocene ones only in Virginia. Samplings of the Atlantic Coast onshore sequence is continuing, and undoubtedly some of the many apparent marine hiatuses we encountered might be filled in. Nonetheless, the lower Paleocene, upper Paleocene, middle Eocene, and lower Oligocene appear to represent marine transgression whereas the middle Paleocene, lower and upper Eocene, and upper Oligocene represent marine regressions. These oscillations correlate well with global relative sea-level history, but differ in detail owing to local tectonic overprinting.

Postglacial rebound and the focal mechanisms of eastern Canadian earthquakes

A detailed numerical model of postglacial rebound for the eastern Canadian Arctic is described with special attention being paid to Baffin Island. This numerical model is able to account for the observed uplift patterns as recorded by the relative sea-level histories of discrete sites distributed throughout the study area. These uplift patterns show regional trends, so the same model can be used to interpolate between data sites and to estimate the uplift history at any arbitrary site within the study area.By treating the lithosphere as a thin elastic plate, spatial variations in the uplift pattern can be translated into estimates of lithospheric stress. The model predicts the variations in uplift as a function of both space and time since deglaciation and can therefore be used to estimate the temporal evolution of lithospheric stress following deglaciation.The stress so calculated is treated as a perturbation to an ambient stress field having its origin in other processes. Postglacial rebound is shown to be capable of triggering earthquakes in prestressed regions but rarely capable of dictating the focal mechanisms of these earthquakes.

Negative evidence for a mid-Holocene high sea level along the coastal plain of the Great Barrier Reef Province

New data are presented from the north Queensland coastal plain which indicate that present Holocene sea level was reached about 6000 years B.P. and has not deviated significantly since then. Together with negative geomorphic evidence for higher sea levels along the coastal plain, this implies that previous reports of evidence for higher stands may have resulted from misinterpretation of field evidence. Close agreement with sealevel data from central Queensland and New South Wales indicates that eastern Australia has followed a common relative sea-level history and has been an area of relative tectonic stability.

Sea level change in the Holocene on the northern Great Barrier Reef

Detailed studies, utilizing a range of both well controlled sea level criteria and dates, are required if Holocene time-sea level curves are to be established with any degree of confidence. This paper is restricted to an interpretation of Expedition results from the northern Great Barrier Reef, excluding those from the drill core. Extensive colonies of emergent fossil corals in growth position indicate that present sea level was first reached about 6000 a b. p. Elevations of cay surfaces, cemented rubble platforms, microatolls, coral shingle ridges, reef flats and mangrove swamps, referenced to present sea level show an array of heights. However, levels of particular features are accordant on many reefs: it is believed that these can be related to particular sea levels. Radiometric dating provides the time framework. Ages of samples from similar deposits on different reefs are surprisingly consistent. Oscillations in sea level since 6000 a b.p ., relative to present sea level, are identified with varying degrees of confidence. This history of relative sea level does not separate eustatic from noneustatic components.

Glacial isostasy and relative sea level: A global finite element model

We review the subject of glacial isostatic adjustment and the structure of global models which have been developed to describe this phenomenon. Models of glacial isostasy have two basic ingredients: 1. (1) an assumed deglaciation history, and 2. (2) an assumed constitutive relation for the rheology of the planetary interior. Although both of these “functionals of the model” are imperfectly known, the parameters which are required to describe them are simultaneously constrained by observations of relative sea level. By comparing the model predictions of relative sea level for times subsequent to a major deglaciation event at a global distribution of sites, with the observed history of relative sea level at these sites, rather stringent bounds may be placed upon the model parameters.