Glacial Sea Research Articles

Simulated ocean circulation and sediment transport in the North Atlantic during the Last Glacial Maximum and today

Paleocirculation of the North Atlantic Ocean at the last glacial maximum (LGM) is simulated using a large‐scale ocean general circulation model (OGCM). The model is driven by glacial sea surface thermohaline conditions and wind stress. For comparison of past and present circulation patterns, a separate run provides the Holocene/modern circulation patterns based on the present day sea surface climatology. The output of the OGCM is then used in a sedimentation model and in a model to trace water parcel trajectories. The sedimentation model reveals the differences in sediment deposition in the North Atlantic linked to past and present circulation regimes. The trajectory‐tracing model facilitates a better understanding of the thermocline and deep ocean ventilation, the actual three‐dimensional conveying of water, and the role of convection in maintaining the meridional thermohaline overturning. The results of the trajectory‐tracing technique indicate stronger subtropical thermocline ventilation during the LGM. For the deep ocean currents, we find severe alteration of three‐dimensional water motion in response to weakening of the LGM convection and its retreat to the southwest from its present locations. Ocean circulation models can provide sedimentation studies with information on the circulation regime that proxy data used alone cannot. These is because such models furnish both circulation patterns and the ventilating convection depths.

Quaternary sea level variations in the Pacific-Indian Ocean gateways: Response and impact

Abstract The Indonesian Maritime Island, also called the Maritime Continent, is situated in a unique geographic setting relating to regional and global climate change. Tropical monsoons, between Asia and Australia, exert a strong influence on this area. Pacific and Indian Ocean currents pass through the island corridors and rise to the Sunda-Sahul epicontinental platforms bringing nutrients that support reef development. This system may be disturbed during glacial low sea level. However, the deep passage Indian-Pacific Ocean gateways remained open during glaciations allowing deep ocean currents to continue flowing between the emerged Sunda and Sahul platforms. Thus, the coastal plain of the large lowland area, and the large, shallow and stable Sunda-Sahul platforms are sensitive to eustatic sea level changes. Changes in basin volume, in the long term, may be the primary control on global sea level but in the relatively short term global climate change could be the most significant cause of sea level oscillations. Based on a study of uplifted coral reefs, an Upper Pleistocene sea level curve has been constructed for the Indonesian region. This curve had been corrected by using Oxygen Isotope data from ODP Hole 677.

Study of Okinawa Trough sedimentation rates and paleoenvironment based on uranium series isotope

Spectrometry of238U,234U,230Th and,232Th in three Okinawa Trough cores showed that, based on the230Th/232Th activity ratio, the sedimentation rates were about 2.5cm/ka, 2.8cm/ka and 8.5cm/ka respectively during the Holocene and about 20.1cm/ka, 12.29cm/ka, 8.8cm/ka and 12.6cm/ka respectively during the Wurm glacial. To examine the past global climatic and oceanographic changes, the stable oxygen isotopes δ18O and CaCO3 were measured. The Th content and Th/U ratio showed that variations of terrigenous material input from the continental shelf were associated with glacial and interglacial changes and sea level fluctuations.

The response of tropical Australian estuaries to a sea level rise

Estuaries in tropical Australia have a low sediment yield (about 5–20 tonnes km−2 yr−1). The estuaries formed when rising post-glacial sea level invaded coastal valleys 7 to 9000 years ago. Geomorphological and stratigraphic data show that mangrove swamps developed on the flooded plains and in some cases their substrate kept pace with the rising sea level. The bulk of the sediment originated from the sea. When sea level stabilised, 6000 years ago, the flood plains prograded seaward. The channels now are generally stable and in some cases are inherited from the progradation phase. The response of these estuaries to a sea level rise may be inferred both from their evolution during post glacial sea level rise and from hydrodynamics-sedimentological models calibrated against measurements of tidal processes. This was undertaken for Coral Creek, the South Alligator River and the Norman River in north Australia. Modelling indicates that a future sea level rise will generate changes in the dynamics and channel dimensions which mimic post glacial changes. In the macrotidal South Alligator the floodplain will revert to mangrove, the mouth region will widen and sediment will move upstream and onto the floodplain. In the mesotidal, diurnal Norman the channel will widen throughout and sediment will be transported seawards. In Coral Creek the mangrove will retreat landwards.

High resolution windows into early Holocene climate: [formula omitted] coral records from the Huon Peninsula

High-precision measurements of Sr Ca ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have UTh mass spectrometric ages of 8920 ± 60 yr and 7370 ± 50 yr, and δ 234U(t) values of 145 ± 2, similar to modern seawater. The Sr Ca coral records provide 5–6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of ± 1°C, with occasional excursions of ± 2°C, which may indicate the more frequent recurrence of very strong ENSO (El Niño-Southern Oscillation) events. Mean annual Sr Ca temperatures of 24.2 ± 1.1°C and 22.9 ± 0.8°C have been obtained, which are ∼ 2–3°C cooler than that exhibited by a modern Porites. These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (∼ 6°C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at ∼ 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at ∼ 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.

Comparing simulated glacial climate and paleodata: A reexamination

Glacial sea surface temperatures (SSTs) simulated by an atmosphere‐mixed layer ocean model are compared with those reconstructed by the Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) Project using planktonic microfossils. Two methods of comparison are employed. The first is global and uses the subjectively analyzed (i.e., hand contoured, then digitized) data set published by CLIMAP. The second is restricted to only those discrete locations where the CLIMAP sediment cores were taken. Both methods indicate that many aspects of the reconstructed glacial SST changes are simulated reasonably well by the model, although there are areas of disagreement. The extent of the disagreement appears smaller when the SSTs are sampled at discrete locations, because the largest discrepancies occur in the subtropical Pacific where data are sparse. When examined separately for each ocean, the magnitude of the disagreement in low latitudes roughly corresponds to the magnitude of the uncertainties in SST estimation using planktonic microfossils, being largest in the Pacific and smallest in the Atlantic. Because the largest discrepancies occur where uncertainties in estimation are large, no clear determination of whether the climate model exaggerates or underestimates low‐latitude climate sensitivity appears possible. Nonetheless, sampling at discrete locations may be the best procedure for evaluating climate model performance, because errors associated with extending analyses to data‐void areas can be avoided and uncertainties associated with inadequate spatial sampling made more evident.

Late glacial sea level and ocean margin environmental changes interpreted from biostratigraphic and lithostratigraphic studies of isolation basins in northwest Scotland

Abstract Detailed biostratigraphic and lithostratigraphic analyses from isolation basins at Ardtoe, Rumach, Loch nan Eala and Fearnbeg, northwest Scotland, allow an interpretation of sea level movements and environmental changes within the Lateglacial Interstadial and Younger Dryas (13-10 ka BP ). Microfossil analyses illustrate the gradual transition of the isolation basins from marine basins to freshwater lakes within an area of isostatic uplift. These data provide evidence for a fall in relative sea level in northwest Scotland from the mid-Lateglacial Interstadial to the early Holocene. Pollen, diatom and dinoflagellate cyst (dinocyst) analyses link the oceanic record of major climate and oceanic circulation changes with the terrestrial biostratigraphic record. Movement of the oceanic Polar Front west and north during a period of relative climatic amelioration within the Lateglacial Interstadial and a corresponding change in the position of the North Atlantic Current may be inferred from the dinocyst record. This is followed by a relative cooling.

Post glacial sea levels on the Western Canadian continental shelf: evidence for rapid change, extensive subaerial exposure, and early human habitation

Grounded piedmont type glaciers inundated and isostatically loaded the deep troughs which indent the Western Canadian continental shelf, as far west as the shelf edge. Glaciers do not appear to have covered the offshore banks east of the Queen Charlotte Islands (Haida Gwaii). Ice retreated from the shelf at approximately 13,500 14C yr B.P. Rapid emergence of the crust followed the ice retreat and resulted in a relative fall of sea level. At 10,400 14C yr B.P. relative sea level on the continental shelf was more than 100 m below that of today and large areas of the Queen Charlotte Basin were subaerially exposed. Eustatic sea-level rise, coupled with subsidence of a glacioisostatic forebulge, allowed sea levels to rise very rapidly, and reach the present shoreline on the Queen Charlotte Islands (Haida Gwaii) by about 9100 14C yr B.P. Dated shoreline deposits (shells), submerged wood remnants, and barnacles on stone tools at elevations between −110 m and +14 m suggest a sea-level rise of 6.3 cm per year between 12,200 and 11,000 calender years. Our reconstructions of the paleogeography and paleoenvironments suggest a hospitable environment for human habitation existed in areas that are now submerged. Stone tools excavated from intertidal deposits support this interpretation. Significant local variations in the depth of synchronous shorelines are described and attributed to localized differences in isostatic load. The documented rates of crustal adjustment are much greater than those used in conventional geophysical (forebulge) models. Regional high-resolution seismic reflection data (3400 line km) shows little evidence for post-glacial faulting and suggest that most crustal adjustments appear to have been isostatically rather than tectonically driven. Subaerial exposure and subsequent sea-level transgression were the dominant post-glacial processes that determined the morphology, texture and paleoenvironment of the Western Canadian continental shelf.

Geomorphic Development of the Ota River Lowland, Southern Part of the Fukuroi City, Shizuoka Prefecture, Japan

The Ota River Lowland is located in the middle part of the Tokai region, Central Japan, extending about 20km from north to south and 12km from east to west. The Lowland is mainly composed of muddy deposits which are carried by the Ota River.The purpose of this paper is to clarify the formative process of the Ota River Lowland. This study is based on the analysis of data from boring, the results of radiocarbon dating, the distribution of archaeological remains, the distribution of the Jori grid-system, and old maps.The sediments of the Ota River Lowland are divided into six units: the basal gravel layer (BG), the lower silt and clay layer (LC), the middle sand layer (MS), the middle silt and clay layer (MC), the upper sand layer (US), and the upper silt and clay layer (UC). The basal gravel layer is considered to represent the river bed gravel in the Last Glacial Age. The lower silt and clay layer was deposited under a low salinity environment and is divided into silt and clay. The silt layer contains a small quantity of shell and the clay layer contains a little humus. The middle sand layer is contrasted to the Holocene Basal Gravel Bed (HBG). The HBG was named by Endo et al. (1982), and indicates the basal gravel layer of the Holocene deposits. The middle silt and clay layer contains a large quantity of shell which shows that the depositional environment was affected greatly by marine water. The upper sand layer is the marine deposits, containing a little biotite, pyrite and magnetite, and is supposed to represent the deposit which is carried by the Tenryu River. The upper silt and clay layer is composed of humic silt and clay, and is considered to have been deposited in a sedimentary environment of backmarsh.In conclusion, the geomorphic development of the Ota River Lowland during the latest Pleistocene to the present is summarized as follows.1) In the latest Pleistocene, the Ota River Lowland was developed in the former fluvial valley formed by the lowest sea level of the Last Glacial Age. Afterward, the former fluvial valley was drowned by transgression, and was filled with silt and clay (about 20, 000-10, 000 years ago).2) About 10, 000 years ago, the sea level dropped because of the cold climate episode and the fluvial sand accumulated in the drowned valley again.3) In the early Holocene, the sea level rose rapidly. As a result, the Ota River Lowland became a bay. After the culmination of the post glacial sea level rise, the sea level remained stable. At this time, the sediments of the Tenryu River drifted into the bay of the Ota River Lowland, and closed the bay mouth (about 10, 000-6, 000 years ago).4) The closed bay became a brackish, swampy lagoon (about 6, 000-1, 900 years ago).5) In the late Yayoi period, the sea level rose again and the sea water flowed into the middle part of the Ota River Lowland (about 1, 900-1, 700 years ago).6) By the seventh century, the Jori grid-system was enforced and the sea level dropped again. However, the water area was left in the southern part of the Ota River Lowland as before (about 1, 700-1, 300 years ago).7) The water area disappeared owing to the Hoei earthquake in 1707 (about 300 years ago).

Modeling the Late Quaternary Indian Ocean Circulation

An ocean general circulation model (OGCM) of the Indian Ocean is forced by paleoclimate simulations for five time slices over the last 126,000 years. Using an annual period sinusoidal fit to the perpetual January and July paleoclimatic model forcing, the OGCM produces seasonal cycles in velocity fields, both vertical and horizontal, and temperature/salinity fields at these five times. The simulations indicate that the southern hemisphere upper ocean circulation of the Indian Ocean is essentially/invariant to climatic fluctuation on this time scale. They also suggest that the low‐insolation (18,000 years B.P.) northern hemisphere upper ocean summer circulation was very much weaker compared to high‐insolation periods (such as 9000 years B.P. and 126,000 years B.P.), by perhaps an order of magnitude. By contrast, the simulated low‐insolation winter northern hemisphere upper ocean circulation was substantially stronger than during high insolation periods. Equatorial upwelling, as simulated, is shown to be a mainly boreal summer event, reduced by an order of magnitude during low‐insolation conditions. A similar reduction in upwelling is seen along the Arabian coast, but a less severe decrease along the Somalian coast. The model simulation of February and August sea surface temperature at 18,000 years B.P., the height of the last glaciation, is generally within 1°–2°C of paleoclimate reconstructions. The effect of lower glacial sea level on the circulation is shown to be only local.

Sedimentology of 40 000 year Milankovitch‐controlled cyclothems from central Hawke's Bay, New Zealand

ABSTRACTCyclothemic sedimentary rocks of the Plio‐Pleistocene Petane Group outcrop extensively in the Tangoio block of central Hawke's Bay, New Zealand. They are products of inner to mid‐shelf sedimentation and were deposited during glacio‐eustatic sea level fluctuations along the western margin of a shallow, pericontinental seaway located in a forearc setting. The succession consists of five laterally continuous cyclothems, each containing a fine grained interval of silt and a coarse grained interval of siliciclastic sand ± gravel or limestone. Five sedimentary facies assemblages comprising 20 separate facies have been recognized. Coarse grained intervals of cyclothems were deposited mostly during relative sea level lowstands and contain up to four facies assemblages: (1) a non‐marine assemblage (with three component facies, representing braided river and overbank environments); (2) an estuarine assemblage (with three component facies, representing tidal flat and mud‐dominated estuarine environments); (3) a siliciclastic shoreline assemblage (with six component facies, representing greywacke pebble beach, shoreface and inner shelf environments); and (4) a carbonate shelf assemblage (with four component facies, representing tide‐dominated, inshore and shallow marine environments). Fine grained intervals of cyclothems were deposited during sea level highstands when the Tangoio area was generally experiencing mid‐shelf sedimentation. This produced an offshore assemblage consisting of four component facies. The distribution of facies assemblages during relative sea level lowstands was dependent upon proximity to the shoreline, the type and rate of sediment supply to the basin, and shelf hydrodynamics. Carbonate shelf facies dominate coarse grained intervals in Cyclothems 3–5, but siliciclastic shoreline and non‐marine facies dominate in Cyclothems 1 and 2. The abrupt change from siliciclastic to carbonate sedimentation during relative sea level lowstand deposition is thought to have been induced by rapidly falling interglacial to glacial sea level accentuated by regional tectonic shoaling. This caused most of the terrigenous sediment supply to bypass the Tangoio area. Consequently, carbonate sediment accumulated in inshore and shallow marine settings. Facies assemblages rarely show lateral interdigitation, but are vertically stratified over the entire Tangoio block. Facies successions in each cyclothem preserve a record of relative sea level change during deposition of the Petane Group and are consistent with a Plio‐Pleistocene sea level change in eastern New Zealand of c. 75–150 m, i.e. approximately the magnitude suggested for Late Quaternary glacio‐eustatic sea level changes.

Glacial Isostasy, sea Level and Mantle Rheology (Proceedings of the NATO Advanced Workshop, Erice, Italy, 1990)

Glacial Isostasy, sea Level and Mantle Rheology (Proceedings of the NATO Advanced Workshop, Erice, Italy, 1990)

Quaternary sequence stratigraphy of the Brisbane River delta, Moreton Bay, Australia

The Quaternary geological history of the Brisbane River delta front and prodelta was interpreted using seismic stratigraphic and sequence stratigraphic principles. During the last major glacial sea level episode, the floor of the bay was exposed and eroded by stream channels. In the subsequent postglacial marine transgression, the palaeochannels of the Brisbane and Pine Rivers were backfilled with mud. Sea level continued rising until about 6500 years ago and a highstand has persisted since then. During the Quarternary, sediment deposition in Moreton Bay was controlled by sea-level fluctuations, channel migration, and palaeotopography. There were at least four depositional episodes prior to the last glacial period, plus the presenet postglacial episode. Periods of low sea level occurred between highstands and the sea bed exposed and eroded. Eight major seismic reflectors were recognised and six seismic sequences defined. The seismic sequences represent five highstand systems tracts and one transgressive systems tract. The relationships between eustacy and system tract type were applied to glacio-eustatic sea-level curves to determine relative ages of sequences in Moreton Bay. The application of sequence stratigraphy to high frequency sea-level fluctuations was demonstrated. The stratigraphic system established within the context of sequence stratigraphy will provide a reference for future work within the region.

Biogenic Gas in Deltaic Sediments, Moreton Bay, Queensland

High resolution seismic profiling records of the Brisbane River delta show a seismic character that is opaque in places. This seismic character is thought to be caused by the presence of interstitial gas. The gas presence is classified into two zones according to position of the upper gas interface in the seismic record and the opacity of the section. The distribution of gas has been mapped and appears to align with palaeochannels of the Brisbane River formed during the last Glacial sea level low about 18 000 yr BP. The seismic character of the gas-charged sediments is similar to Postglacial gas-charged sediments investigated elsewhere in Australia and overseas. It is considered that the Brisbane River delta gas results from biogenic decomposition of organic matter accumulated in palaeotopographic lows during the Postglacial marine transgression. More research is necessary to determine the exact nature of the gas.

A Simple Two‐Layered Model for Shoaling of the Eastern Mediterranean Pycnocline Due to Glacio‐Eustatic Sea Level Lowering

A simple two‐layered model is developed to assess the depth of the permanent pycnocline in the eastern Mediterranean during glacial times. Shoaling of this pycnocline, from its present depth below the euphotic layer to a depth within that layer at glacial times, has been inferred from the planktonic foraminiferal record (Rohling and Gieskes, 1989). In this paper, a two‐layered model is applied to study the origin of the glacial shoaling of the permanent pycnocline. The model suggests that shoaling is due to glacial sea level lowering. Using literature‐based glacial salinity and inflow reduction values, the model yields an estimated depth of about 80 m for the glacial pycnocline. This estimate represents an upper depth limit, since the model discards possible differences in the basin's heat loss between glacial and interglacial times.

Late Quaternary paleoceanography of the South China Sea: Glacial‐interglacial contrasts in an enclosed basin

The sea surface paleotemperature of the South China Sea (SCS) is estimated quantitatively, based on the quantitative analysis of planktonic foraminiferal faunas recovered from piston cores V36‐06‐3, V36‐06‐5, and SO49‐KL8 on the northern continental slope. The results lead to a reconstruction of the history of paleocirculation patterns during the last 200,000 years. The postglacial and interglacial transbasinal circulation pattern was replaced by a semienclosed basin flow pattern during glacial episodes. Lowered sea level transformed the SCS into a semienclosed basin with the only passageway to the open ocean in its northeastern corner. The East Asian Monsoon, which governs circulation patterns in the SCS both today and during the late Quaternary, created both clockwise (summer) and counterclockwise (winter) surface gyres during glacials. The inflow of tropical surface water‐masses from both the Pacific and Indian oceans decreased or was completely cut off from this marginal sea, causing a greater decrease in glacial sea surface temperature than in the open ocean of the same latitude. Inferred increased influence of Pacific Temperate Waters and decreased influence of Tropical‐Subtropical Waters are confirmed by changes in the planktonic foraminiferal assemblages. Glacial‐interglacial fluctuation in sea surface temperature (SST) (6.8–9.3°C for winter and 2–3°C for summer), as well as the seasonality (4–6°C for postglacial and interglacials and 9–10°C for glacials), are much greater than the adjacent open western Pacific, reflecting the amplification of the climatic signal in the marginal sea.

The late Quaternary history of Greely Fiord and its tributaries, west-central Ellesmere Island

Moraines and meltwater channels mark the limit of the last glaciation that interfingered with the sea around the perimeter of Greely Fiord and its tributaries. The extent of this ice advance was dictated predominantly by its proximity to the sea. Consequently, the large tidewater glaciers at the fiord heads today were so constrained by calving that they advanced only 5–10 km. Similarly, grounding-line deposits from widespread plateau ice caps also terminate just below marine limit. The most extensive outlet glaciers, which advanced 20–35 km beyond present margins, are simply those that had access to the most extensive terrain above marine limit, i.e., the northwest margin of the Agassiz Ice Cap.Forty-one new 14C dates are presented. The onset of the last ice advance must predate marine shells collected from sediments overlying a former grounding line when sea level was 122 m higher than present. At this site, the lowermost shells collected from glaciomarine silts dated 38 070 ± 410 BP, whereas a surface sample 13 m above them dated 22 900 ± 190 BP. Although both dates may be minimum estimates, they are nonetheless associated with an ice margin that retreated only a few kilometres by 7850 BP, suggesting the maintenance of the glacioisostatic loading (and relative sea level) during the interim. Nearby, shells in growth position overlying bedrock confirm that relative sea level was > 83 m asl by 38 010 ± 410 BP (minimum age). These marine deposits lie outside the last ice limit and are not overlain by glacigenic sediments.Distal to the last ice limit, Greely Fiord was occupied by the full glacial sea, whose limit is marked by discontinuous beaches and wave-cut benches. The full glacial sea rises from 116 m north of Greely Fiord to a maximum elevation of 148 m bordering its south shore from which it descends to 112 m asl near the head of Cañon Fiord. Numerous 14C dates on shells collected within 8 m of marine limit show that the full glacial sea remained stable from at least 8400 to 7400 BP. Several other shell samples collected ~20 m below marine limit are much older (> 22 000 BP). The position of relative sea level between ca. 8000 and > 22 000 BP is uncertain; however, stratigraphic evidence for an intervening regression has not been found.The modest extent of the last ice limit encircling Greely Fiord, together with its occupancy by the full glacial sea, is fully compatible with the paleogeography previously reported from northeast Ellesmere Island and northwest Greenland. Furthermore, this data base provides a reinterpretation of a 500 km transect previously reported along west-central Ellesmere Island to the south and affirms that the Innuitian Ice Sheet, defined sensu stricto for the last glaciation, is supplanted by the full glacial Innuitian Sea, which penetrated the Queen Elizabeth Islands, constraining the last ice limit.

Seismic Depth Conversion Problems Associated with the Mississippi Canyon in the Vicinity of Ewing Bank Block 305 Field, Offshore Louisiana: ABSTRACT

Ewing Bank Block 305 field is located on the outermost edge of the continental shelf, approximately 145 km south of New Orleans, Louisiana. The geology of the field is fairly typical of other fields found offshore of Louisiana, except there is a huge, partly filled, Pleistocene submarine canyon that overlies the field. This canyon, which is commonly referred to as the Mississippi Canyon, causes a large seismic depth conversion problem that makes it virtually impossible to correctly map the structure of the field using normally processed marine seismic data The Mississippi Canyon is a large erosional feature that was formed at the mouth of the ancestral Mississippi River during the last glacial sea level lowstand. In the vicinity of the field, the canyon is about 10 km wide and 1 km deep, which is approximately two-thirds the size of the Grand Canyon of the Colorado River, and is filled mostly with Holocene sediments. Because the sediments that fill the canyon are very young, their interval velocities are much lower than the interval velocities of the sediments that form the canyon walls. This creates abrupt near surface lateral velocity variations that distort the geometry of seismic reflectors such that the timemore » geometries seen on seismic lines are not at all indicative of the structure of the subsurface. Using a model-based processing technique and available well control, the authors have been able to solve this difficult depth conversion problem and have gained a better understanding of the geology of this field.« less

Application of ams dating to the paleogeography of the canadian high arctic

During the last glaciation, the ice limit on northern Ellesmere Island was only 5–40 km beyond present ice margins due to the area's severe aridity. Many glaciers calved into a full glacial sea that transgressed the ice-free fiords and interislands channels to 140 m asl. Chronological evidence for the full glacial sea was first provided by conventional 14C dates on large samples ( > 40 g) that predated the onset of deglaciation and emergence by 1000 to 3000 years. Because some shell samples yielded conventional dates that ranged from 7025 to 10760 BP it was recognized that AMS dating of individual valves was necessary to determine their true range of ages. This paper discusses the application of AMS dating to the improved understanding of the full glacial sea. The full glacial sea is important geophysically and paleoclimatically because it records the complete history of glacial loading and unloading. Furthermore, the full glacial sea contradicts the popular notion that pervasive high latitude ice sheets inundated the Northern Hemisphere around 18000 BP. The new perspectives generated by the full glacial sea and the prospects of AMS dating will test many basic views concerning glacial dynamics and the evolution of the landscape in Arctic Canada.

The late Quaternary history of Hall Land, northwest Greenland: Reply

The last ice limit on Hall Land, northwest Greenland, is marked by the Newman and Petermann moraines, which were deposited 40–60 km beyond the present ice margins in Newman Bay and Petermann Fiord, respectively. These moraines flank the eastern and western coasts of Hall Land but do not extend into its intervening central plain. As a result of glacioisostatic depression at this time, a full glacial sea transgressed the entire central plain via a narrow estuary located between the Newman Moraine and the northern plateau of Hall Land. The limit of this full glacial sea is isostatically tilted from 116 m asl on the adjacent coast of Ellesmere Island to 150 m asl on the southwest extremity of the central plain, where it reaches its apex. Pervasive marine silts cover the central plain and laterally thicken towards the Newman and Petermann moraines. Because of the height of the full glacial sea, these moraines were deposited in a submarine environment and mark the grounded margins of ice shelves floating in Hal...