| 1. |
- Blockley, Simon, et al.
(author)
-
Building and testing age models for radiocarbon dates in Lateglacial and Early Holocene sediments
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 26:15-16, s. 1915-1926
-
Journal article (peer-reviewed)abstract
- The growing importance of understanding past abrupt climate variability at a regional and global scale has led to the realisation that independent chronologies of past environmental change need to be compared between various archives. This has in turn led to attempts at significant improvements in the required precision at which records can be dated. Radiocarbon dating is still the most prominent method for dating organic material from terrestrial and marine archives, and as such many of the recent developments in improving precision have been aimed at this technique. These include: (1) selection of the most suitable datable fractions within a record, (2) the development of better calibration curves, and (3) more precise age modelling techniques. While much attention has been focussed on the first two items, testing the possibilities of the relatively new age modelling approaches has not received much attention. Here, we test the potential for methods designed to significantly improve precision in radiocarbon-based age models, wiggle match dating and various forms of Bayesian analyses. We demonstrate that while all of the methods can perform very well, in some scenarios, caution must be taken when applying them. It appears that an integrated approach is required in real life dating situations where more than one model is applied, with strict error calculation, and with the integration of radiocarbon data with sedimentological analyses of site formation processes.
|
|
| 2. |
- Giesecke, Thomas
(author)
-
Moving front or population expansion : How did Picea abies (L.) Karst. become frequent in central Sweden?
- 2005
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 24:23-24, s. 2495-2509
-
Journal article (peer-reviewed)abstract
- The Holocene increase in Picea abies around four central Swedish lakes was analysed using extended pollen counts over the sections comprising the tail of frequent, but discontinuous, occurrences and the beginning of the continuous curve. Simple landscape scenarios were simulated to test possible mechanisms of the spread and population expansion of P. abies in Scandinavia. Predicted patterns of pollen accumulation rates from the landscape scenarios were compared to patterns observed at the four sites to explore how the observed curves could have come about. Simulations of a moving front scenario indicate that pollen accumulation rates should rise faster than the exponential and logistic increase observed at the four sites. Exponential increase of pollen values at the sites is most likely due to locally increasing populations. However, the geography of expanding populations may influence the shape of the curve. Empirical and model results are discussed to gain new insights into the pattern and processes of the spread of P abies in central Sweden. Propagule pressure and self-fertilisation are considered as possible explanations of why small outpost populations that may have existed before the regional expansion of P. abies did not expand earlier.
|
|
| 3. |
|
|
| 4. |
- Greenwood, Sarah L., et al.
(author)
-
Reconstructing the last Irish Ice Sheet 1 : changing flow geometries and ice flow dynamics deciphered from the glacial landform record
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28, s. 3085-3100
-
Journal article (peer-reviewed)abstract
- The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one ‘flowsets’ comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset crosscutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative ‘age-stack’ of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset – its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, ‘smudged’ landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories. The flowsets and their palaeo-glaciological significance that we derive for Ireland provide a regional framework and context for interpreting results from local scale fieldwork, provide major flow events for testing numerical ice sheet models, and underpin a data-driven reconstruction of the Irish Ice Sheet that we present in an accompanying paper – Part 2.
|
|
| 5. |
- Greenwood, Sarah L., et al.
(author)
-
Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28, s. 3101-3123
-
Journal article (peer-reviewed)abstract
- The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheetproperties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel – Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.
|
|
| 6. |
- Gyllencreutz, Richard, et al.
(author)
-
Late Glacial and Holocene sediment sources and transport patterns in the Skagerrak interpreted from mineral magnetic properties and grain size data
- 2006
-
In: Quaternary Science Reviews. - : Elsevier Ltd. - 0277-3791 .- 1873-457X. ; 25:11-12, s. 1247-1263
-
Journal article (peer-reviewed)abstract
- Lateglacial and Holocene changes in circulation, sedimentation and provenance in north-eastern Skagerrak were studied using high-resolution mineral magnetic and grain size data from the 32-m-long IMAGES core MD99-2286. Ages are given in calibrated thousand years BP (‘cal. kyr’). Between 12 and 11.3 cal. kyr, a calving ice front occupied the Oslo Fjord, and sedimentation was strongly influenced by meltwater carrying re-deposited glacial sediments from southern Norway and western Sweden. Between 11.3 and 10.3 cal. kyr, sedimentation was dominated by re-deposited glacial sediments transported by meltwater outflow across south-central Sweden. After the Otteid-Stenselva outlet was closed at 10.3 cal. kyr, glacial marine sedimentation changed to normal marine sedimentation. At 8.5 cal. kyr, a hydrographic shift, marking the onset of modern circulation in the Skagerrak–Kattegat, occurred as a result of increased Atlantic inflow, transgression of former land areas, and opening of the English Channel and the Danish Straits. After 8.5 cal. kyr, sedimentation was governed by input from the Atlantic Ocean and the North Sea, with varying contributions from the South Jutland Current, Baltic Current, and currents along the coasts of western Sweden and southern Norway. From 0.9 cal. kyr until present, the sedimentation was totally dominated by southern North Sea and Atlantic Ocean sources.
|
|
| 7. |
- Helmens, Karin, et al.
(author)
-
Early MIS 3 glacial lake evolution, ice-marginal retreat pattern and climate at Sokli (northeastern Fennoscandia)
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28:19-20, s. 1880-1894
-
Journal article (peer-reviewed)abstract
- Lake development at Sokli, northern Finland, is traced through the analysis of diatoms and other siliceous micro-fossils in a 2-meter thick minerogenic, laminated clay-silt deposit dated to the early part of Marine Isotope Stage (MIS) 3. Fluctuating water levels and changes in lake extent depicted by the siliceous micro-fossil record, together with lithology, suggest that an important part of the sediment sequence was deposited in a glacial lake. The proxy-based glacial lake evolution is tested using a Digital Elevation Model and geomorphologic evidence including eskers dated to the early MIS 3 Tulppio Interstadial at Sokli. Despite the apparent ice-dammed nature of the lake, the sediment is relatively rich in fossils and there are limited signs of re-deposition of older fossil material. The siliceous micro-fossil record together with data from other proxies previously analysed in the same sediment samples provides a coherent picture of past environmental changes around the Sokli site. This is most probably due to the sheltered position of the coring-site in a lake embayment. Quantitative climate reconstructions based on the diatom record show mean July air temperatures as high as present-day values at Sokli, and the temperature ranges indicated by the diatom record are in agreement with temperature reconstructions based on chironomids. The position of Sokli in the northeastern portion of the central area of the Scandinavian glaciations and the northern retreat pattern implies that an important part of eastern Fennoscandia was deglaciated during the early MIS 3 warming event.
|
|
| 8. |
- Hubbard, Alun, et al.
(author)
-
Dynamic cycles, ice streams and their impact on the extent, chronology and deglaciation of the British–Irish ice sheet
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28:7-8, s. 758-776
-
Journal article (peer-reviewed)abstract
- We present results from a suite of forward transient numerical modelling experiments of the British and Irish Ice Sheet (BIIS), consisting of Scottish, Welsh and Irish accumulation centres, spanning the last Glacial period from 38 to 10 ka BP. The 3D thermomechanical model employed uses higher-order physics to solve longitudinal (membrane) stresses and to reproduce grounding-line dynamics. Surface mass balance is derived using a distributed degree-day calculation based on a reference climatology from mean (1961–1990) precipitation and temperature patterns. The model is perturbed from this reference state by a scaled NGRIP oxygen isotope curve and the SPECMAP sea-level reconstruction. Isostatic response to ice loading is computed using an elastic lithosphere/relaxed asthenosphere scheme. A suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities, to yield a subset of experiments that showed close correspondence to offshore and onshore ice-directional indicators, broad BIIS chronology, and the relative sea-level record. Three of these simulations are described in further detail and indicate that the separate ice centres of the modelled BIIS complex are dynamically interdependent during the build up to maximum conditions, but remain largely independent throughout much of the simulation. The modelled BIIS is extremely dynamic, drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time-scale. A series of binge/purge, advance/retreat, cycles are identified which correspond to alternating periods of relatively cold-based ice, (associated with a high aspect ratio and net growth), and wet-based ice with a lower aspect ratio, characterised by streaming. The timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling, but are modulated and phase-lagged to the oscillations within the NGRIP record of climate forcing. Phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate, resulting in major iceberg/melt discharge events into the North Sea and Atlantic Ocean. The broad chronology of the modelled BIIS indicates a maximum extent at 20 ka, with fast-flowing ice across its western and northern sectors that extended to the continental shelf edge. Fast-flowing streams also dominate the Irish Sea and North Sea Basin sectors and impinge onto SW England and East Anglia. From 19 ka BP deglaciation is achieved in less than 2000 years, discharging the freshwater equivalent of 2 m global sea-level rise. A much reduced ice sheet centred on Scotland undergoes subsequent retrenchment and a series of advance/retreat cycles into the North Sea Basin from 17 ka onwards, culminating in a sustained Younger Dryas event from 13 to 11.5 ka BP. Modelled ice cover is persistent across the Western and Central Highlands until the last remnant glaciers disappear around 10.5 ka BP.
|
|
| 9. |
- Håkansson, Lena, et al.
(author)
-
Be-10 ages from central east Greenland constrain the extent of the Greenland ice sheet during the Last Glacial Maximum
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 26:19-21, s. 2316-2321
-
Journal article (peer-reviewed)abstract
- Traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the East Greenland continental margin during the Last Glacial Maximum (LGM): ice to the shelf break south of Scoresby Sund and ice extending no further than to the inner shelf at and north of Scoresby Sund. We report new Be-10 ages from erratic boulders perched at 250 m a.s.l. on the Kap Brewster peninsula at the mouth of Scoresby Sund. The average Be-10 ages, calculated with an assumed maximum erosion rate of 1 cm/ka and no erosion (respectively, 17.3 +/- 2.3 ka and 15.1 +/- 1.7 ka) overlap with a period of increased sediment input to the Scoresby Sund fan (19-15 ka). The results presented here suggest that ice reached at least 250 m a.s.l. at the mouth of Scoresby Sund during the LGM and add to a growing body of evidence indicating that LGM ice extended onto the outer shelf in northeast Greenland. (C) 2007 Elsevier Ltd. All rights reserved.
|
|
| 10. |
- Kullman, Leif
(author)
-
Early postglacial appearance of tree species in northern Scandinavia : review and perspective
- 2008
-
In: Quaternary Science Reviews. - Oxford : Pergamon Press. - 0277-3791 .- 1873-457X. ; 27:27-28, s. 2467-2472
-
Journal article (peer-reviewed)abstract
- This paper reviews megafossil evidence for the first postglacial records of different tree species in northern Scandinavia. Betula pubescens coll. appeared at the Arctic coast of northern Norway by 16. 900 yr BR In addition, Betula Pubescens (14, 000 yr BP), Pinus sylvestris (11, 700 yr BP) and Picea abies (11, 000 yr BP) existed on early ice- free mountain peaks (nunataks) at different locations in the Scandes during the Lateglacial. Larix sibirica, currently not native to Fennoscandia, and several thermophilous broadleaved tree species were recorded in the earliest part of the Holocene. The conventional interpretation of pollen and macrofossil records from peat and sediment stratigraphies do not consider the Occurrence of the species mentioned above that early at these northern and high altitude sites. This very rapid arrival after the local deglaciation implies that the traditional model of far distant glacial refugial areas for tree species has to be challenged. The Current results are more compatible with a situation involving scattered "cryptic" refugia quite close to margin of the ice sheet at its full-glacial extension. This fits a more general pattern currently emerging on different continents. In general, "cryptic" refugia should be considered in connection with modelling extinction risks related to modern and possible future "climatic crises".
|
|
| 11. |
- Large, DJ, et al.
(author)
-
The influence of climate, hydrology and permafrost on Holocene peat accumulation at 3500 m on the eastern Qinghai-Tibetan plateau
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28:27-28, s. 3303-3314
-
Journal article (peer-reviewed)abstract
- Peatland of the eastern Qinghai–Tibetan Plateau lies at the convergence of the East Asian and Indian monsoon systems in eastern Asia. To understand the evolution of this peatland and its potential to provide new insights into the Holocene evolution of the East Asian monsoon a 6 m peat core was collected from the undisturbed central part of a peat deposit near Hongyuan. The age-depth profile was determined using 16 14C-AMS age dates, the peat analysed for a range of environmental variables including carbon, nitrogen and hydrogen concentration, bulk density, δ13C and the associated spring water analysed for hydrogen and oxygen isotopes. The age-depth profile of the recovered peat sequence covers the period from 9.6 to 0.3 kyr BP and is linear indicating that the conditions governing productivity and decay varied little over the Holocene. Using changes in carbon density, organic carbon content and its δ13C, cold dry periods of permafrost characterised by low density and impeded surface drainage were identified. The low δ18O and δD values of the spring water emanating around the peat deposit, down to −13.8 and −102‰ (VSMOW), respectively, with an inverse relationship between electrical conductivity and isotopic composition indicate precipitation under colder and drier conditions relative to the present day. In view of the current annual mean air temperature of 1 °C this suggests conditions in the past have been conducive to permafrost. Inferred periods of permafrost correspond to independently recognised cold periods in other Holocene records from across China at 8.6, 8.2–7.8, 5.6–4.2, 3.1 and 1.8–1.5 kyr BP. The transition to a cold dry climate appears to be more rapid than the subsequent recovery and cold dry periods at Hongyuan are of longer duration than equivalent cold dry periods over central and eastern China. Light–dark banding peat on a scale of 15–30 years from 9.6 to 5.5 kyr BP may indicate a strong influence of decadal oscillations possibly the Pacific Decadal Oscillation and a potential link between near simultaneous climatic changes in the northwest Pacific, ENSO, movement of the Intertropical Convergence Zone and the East Asian Monsoon.
|
|
| 12. |
- Unkel, Ingmar, et al.
(author)
-
Deglacial environmental changes on Isla de los Estados (54.4°S), southeastern Tierra del Fuego
- 2008
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 27:15-16, s. 1541-1554
-
Journal article (peer-reviewed)abstract
- The island of Isla de los Estados is situated at 54.5 degrees S, 64 degrees W, east of Argentinian Tierra del Fuego, and is located in a sensitive geographic position in relation to the zonal circulation between Antarctica and South America. Its terrestrial records of the last deglaciation, recording atmospheric conditions but within an oceanic setting, can help to clarify changes of regional circulation patterns, both atmospheric and marine. Here, we present geochemical analyses from 16-10 ka cal BP of a peat core from Lago Galvarne Bog at the northern coast of the island, and a lake sediment core from Laguna Cascada 3 kin further south. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning on both cores as well as age-depth modeling based on AMS-C-14 dating. Deglaciation and onset of peat formation in the coastal areas began before 16 ka cal BP followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland. Data Suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14.5 ka cal BP. The warming trend slows down until ca 13.5 ka cal BP, followed by arid conditions culminating around 12.8 ka cal BP. Our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10.6 ka cal BP, contemporaneous with the onset of the Antarctic thermal optimum. This indicates large-scale shifts in the placement of zonal flow and the Westerlies at the beginning of the Holocene. (C) 2008 Elsevier Ltd. All rights reserved.
|
|
| 13. |
- Vandergoes, MJ, et al.
(author)
-
Cooling and changing seasonality in the Southern Alps, New Zealand during the Antarctic Cold Reversal
- 2008
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 27:5-6, s. 589-601
-
Journal article (peer-reviewed)abstract
- A comprehensively 14C AMS dated pollen and chironomid record from Boundary Stream Tarn provides the first chironomid-derived temperature reconstruction to quantify temperature change during Lateglacial times (17,500–10,000 cal yr BP) in the Southern Alps, New Zealand. The records indicate a ca 1000-year disruption to the Lateglacial warming trend and an overall cooling consistent with the Antarctic Cold Reversal (ACR). The main interval of chironomid-inferred summer temperature depression (2–3 °C) lasted about 700 years during the ACR. Following this cooling event, both proxies indicate a warming step to temperatures slightly cooler than present during the Younger Dryas chronozone (12,900–11,500 cal yr BP). These results highlight a direct linkage between Antarctica and mid-latitude terrestrial climate systems and the largely asynchronous nature of the interhemispheric climate system during the last glacial transition. The greater magnitude of temperature changes shown by the chironomid record is attributed to the response of the proxies to differences in seasonal climate with chironomids reflecting summer temperature and vegetation more strongly controlled by duration of winter or by minimum temperatures. These differences imply stronger seasonality at times during the Lateglacial, which may explain some of the variability between other paleoclimate records from New Zealand and have wider implications for understanding differences between proxy records for abrupt climate change.
|
|
| 14. |
- Väliranta, Minna, et al.
(author)
-
Early Weichselian interstadial (MIS 5c) summer temperatures were higher than today in northern Fennoscandia
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 28:9-10, s. 777-782
-
Journal article (peer-reviewed)abstract
- Only fragmentary biostratigraphical interstaidial data exist from northern European high latitudes. The palaeoenvironmental interpretations for the early part of the Last Glaciation in northern Fennoscandia are mainly based on palynological evidence that suggests open birch woodland and a sub-arctic climate. Plant macrofossils from the Sokli sediment sequence in Finnish Lapland provide different evidence of interstadial climate conditions. The assemblage includes several species that currently have considerably more southern distribution ranges. This indicates that ca 100,000 years ago summer temperatures were warmer than today. The mean minimum July temperature may have been as high as 16 degrees C and the effective temperature sum may have been 1000 in day-degree units (d.d.), the modern values being 13 degrees C and 650 d.d., respectively. The contemporary astronomical forcing mechanisms may have resulted in a weaker north-south temperature gradient and a longer growing period, creating more favourable climate conditions compared with today.
|
|
| 15. |
- Ampel, Linda, et al.
(author)
-
Paleolimnological response to millennial and centennial scale climate variability during MIS 3 and 2 as suggested by the diatom record in Les Echets, France
- 2008
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 27:15-16, s. 1493-1504
-
Journal article (peer-reviewed)abstract
- A 27 m long sediment sequence retrieved from the central part of the Les Echets basin in France has been analysed in sub-centennial resolution for biogenic silica and fossil diatom remains. The sequence corresponds to the later part of Marine Isotope Stage (MIS) 3 and to most of MIS 2. Distinct changes in diatom productivity, diversity and taxonomic composition between 36.2 and 31.7 kyr BP appear to relate to Dansgaard–Oeschger (DO) climate variability. Intervals characterized by low diversity, productivity and small-sized benthic diatom taxa are most likely a response to colder conditions in relation to DO stadials. In contrast, higher diversity, productivity and a high abundance of planktonic taxa indicate a response to warmer temperatures during DO interstadials. The time interval between 30.3 and 15.7 kyr BP is characterized by continuous low diatom productivity and a benthic dominated community with intermediate species richness, suggesting a transition to more stable conditions. Three time intervals with extremely low concentrations of diatom valves (46.1–36.2, 31.7–30.3 and 26.3–23.6 kyr BP) overlap with ages reported for Heinrich (H) events 4, 3, and 2. We speculate that the lake at Les Echets suffered from severe ecological stress as a response to H events. This is the first detailed study exemplifying the response of a lake, based on diatoms, to climate variability during late part of MIS 3 and most of MIS 2 in Europe.
|
|
| 16. |
- Andresen, Camilla Snowman, et al.
(author)
-
Early Holocene terrestrial climatic variability along a North Atlantic Island transect: palaeoceanographic implications
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:15-16, s. 1989-1998
-
Journal article (peer-reviewed)abstract
- A synthesis of the early Holocene climatic development in the North Atlantic region is presented, based on three previously published lake records from southern Greenland (Lake N14), Iceland (Lake Torfadalsvatn) and the Faroe Islands (Lake Lykkjuvotn). The interval 11500-8500 cal BP has been divided into five phases with respect to the inferred strength of the North Atlantic Current (NAC) and Irminger Currents (IC). Phase 1 (11 500-10 750 cal BP) was characterised by the first establishment of the NAC and IC in the vicinity of the studied sites, interrupted by the Preboreal Oscillation around 11 200cal BP. Phase 2 (10 750-10 100 cal BP) was marked by a further warming step in southern Greenland rather concordant with a change into colder and more variable winters on the Faroe Islands. It is proposed that this could partly be related to a series of melt water outbursts disturbing the thermohaline circulation in the eastern Atlantic Ocean, resulting in a warming trend in the western region. During Phase 3 (10 100-9400cal BP) the strength of the IC reaching northwestern Iceland intensified. A more stable regime in surface circulation was established at the onset of Phase 4 (9400-8900 cal BP) in southern Greenland and was followed by a change towards further warm conditions on Iceland at the onset of Phase 5 (8900-8500 cal BP). (C) 2007 Elsevier Ltd. All rights reserved.
|
|
| 17. |
|
|
| 18. |
- Benediktsson, Ivar, et al.
(author)
-
Instantaneous end moraine and sediment wedge formation during the 1890 glacier surge of Brúarjökull, Iceland
- 2008
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 27:3-4, s. 209-234
-
Journal article (peer-reviewed)abstract
- Contemporary understanding of the behaviour of surging glaciers and ice streams is hampered by the lack of data on landsystem evolution and sedimentary environments. This study concerns the ice-marginal environment of the surge-type Brúarjökull in Iceland. The sediment distribution in the glacier forefield as well as the morphology, sedimentology and tectonic architecture of the 1890 end moraine is investigated for highlighting the interaction between very dynamic ice and sediment/landform associations. As a result of substrate/bedrock decoupling during the 1890 surge, subglacial sediment was dislocated across the bedrock surface and deformed compressively, leading to gradual substrate thickening and the formation of a sediment wedge in the marginal zone. A drop in subglacial porewater pressure at the very end of the surge led to substrate/bedrock coupling and a stress transfer up into the sediment sequence causing brittle deformation of the substrate. Simultaneously, the glacier toe ploughed into the topmost part of the marginal sediment wedge initiating the moraine-ridge construction. Fine-grained and incompetent sediment deformed in ductile manner, resulting in a narrow moraine dominated by rooted folds, while coarse-grained and competent sediment deformed in brittle fashion, resulting in a wider moraine dominated by thrust blocks. A new sequential model of subglacial and ice-marginal processes operating during a glacier surge is proposed, illustrating the stepwise formation of a marginal sediment wedge and an end moraine—a twofold, inseparable marginal end-product that formed during the last days of the 1890 surge.
|
|
| 19. |
- Björck, Svante, et al.
(author)
-
A Holocene lacustrine record in the central North Atlantic: proxies for volcanic activity, short-term NAO mode variability, and long-term precipitation changes
- 2006
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 25:1-2, s. 9-32
-
Journal article (peer-reviewed)abstract
- Lake and peat corings on three Azores islands in the central North Atlantic, resulted in the discovery of a 6000 year long lacustrine sequence in a small crater lake, Lake Caveiro, on the island of Pico. This island is dominated by Pico mountain (2351 m), Portugal's highest mountain, and the lake site is situated at 903 in asl. Two sediment profiles, one central and one littoral, were sampled. Due to large facial shifts and disconformities in the littoral cores the analyses were concentrated on the central core; only the earliest 1000 years of the littoral core were studied to complement the central profile. We used sedimentology, geochemistry, diatom analyses, magnetic properties, and multivariate statistics, together with C-14 and Pb-210 dating techniques, to analyse the environmental history of the lake. Volcanic activity seems to have had a dominating impact on sediment changes and partly also on the diatom assemblages; a large number of tephras are found and seem to be connected with large (diatom) inferred pH variations. However, by a combination of methods, including multivariate techniques, we infer that precipitation changes can be detected through the volcanic noise. In the youngest part of the record (AD 1600-2000), with its decadal resolution, these humidity variations seem partly related to shifts in dominating NAO mode. The more long-term precipitation changes further back in time (350-5100 cal yr BP) roughly correspond to the well-known North Atlantic drift-ice variations as well as other North Atlantic records; low precipitation during drift-ice periods. We think these alterations were driven by changes in the thermolialine circulation as large-scale equivalences to the Great Salt Anomaly; low sea surface A temperatures and changes in circulation patterns of the central North Atlantic decreased the regional precipitation. Cooler/drier periods occurred 400-800, 1300-1800, 2600-3000, 3300-3400 and possibly also 4400-4600 cal yr BP,. while 300-400, 900-1000, 2000-2400, 3100-3200, 3800-4000 and 4700-5000 cal yr BP seem to have been more humid phases on the Azores. (c) 2005 Elsevier Ltd. All rights reserved.
|
|
| 20. |
- De Angelis, Hernán, et al.
(author)
-
Palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:9-10, s. 1313-1331
-
Journal article (peer-reviewed)abstract
- In this paper, we describe mapping of palaeo-ice streams in the Foxe/Baffin sector of the Laurentide Ice Sheet by means of geomorphological interpretation of high-resolution satellite images. Our interpretations were guided by a glaciological inversion scheme, aided by digital elevation models, publicly available sonar surveys and field studies. As a result, we produced a map depicting the location, geometry and relative temporal changes of palaeo-ice streams and analysed their palaeoglaciological implications for the Foxe/Baffin sector. We conclude that in the period between the Last Glacial Maximum and approximately 7.0 kyr BP, the Foxe/Baffin sector was largely drained by topographically controlled outlet glaciers and ice streams, which were organized in a relatively stable pattern. During this time, large areas of Melville Peninsula and central Baffin Island were subject to cold-based conditions. Between 7.0 and 6.0 kyr BP, the Foxe/Baffin sector collapsed catastrophically in the Foxe Basin, after which its remnant portion became confined to Baffin Island. During this collapse, rapid successions of small transient ice streams occurred along wide, loosely defined topographical corridors in two sectors of Baffin Island. The presently available landform archive on emerged land is not sufficient to conclusively support the existence of fully scaled ice streams along the whole length of Hudson Strait. As an alternative solution, we propose that topographically controlled ice streams might have occurred along the deepest parts of Hudson Strait, with attendant cold-based ice zones on marginal areas and islands at the head of the strait.
|
|
| 21. |
- de Jong, Rixt, et al.
(author)
-
Late Holocene effective precipitation variations in the maritime regions of south-west Scandinavia
- 2009
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 28:1-2, s. 54-64
-
Journal article (peer-reviewed)abstract
- At present, the climate in south-west Scandinavia is predominantly controlled by westerlies carrying moist Atlantic air, which forms a main source of precipitation in all seasons. Past variations in the ratio between precipitation and evaporation (effective precipitation) from terrestrial sites, however, may indicate changes in the degree of maritime influence. Palaeoclimatic archives in this region are thus ideally situated to study past changes in atmospheric circulation patterns. In this study, multi-proxy comparisons of records from three peat bogs and two lakes are used to reconstruct regional-scale variations of effective precipitation in south-west Sweden during the Late Holocene. The total aeolian sediment influx into two peat bogs is used as a proxy for storm activity. The frequency of storm phases increases strongly after ca 2500 cal yrs BP. Dry conditions occur on a regional scale around 4800-4400, 2000-1700, 1300-1000, 700-500 and 300-100 cal yrs BP. In addition, a comparison to winter precipitation reconstructed from four Norwegian glaciers shows similar variations during the past ca 2000 years. This indicates that the climate in both regions was controlled by large-scale atmospheric circulation dynamics of the North Atlantic region. The strong variability of effective precipitation and storm activity after ca 2500 cal yrs BP indicates a highly variable climate. (C) 2008 Elsevier Ltd. All rights reserved.
|
|
| 22. |
- Glasser, Neil, et al.
(author)
-
The glacial geomorphology and Pleistocene history of South America between 38 degrees S and 56 degrees S
- 2008
-
In: QUATERNARY SCIENCE REVIEWS. - : Elsevier. - 0277-3791. ; 27:3-4, s. 365-390
-
Journal article (peer-reviewed)abstract
- This paper presents new mapping of the glacial geomorphology of southern South America between latitudes 38 degrees S and 56 degrees S, approximately the area covered by the former Patagonian Ice Sheets. Glacial geomorphological features, including glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques, were mapped from remotely sensed images (Landsat 7 ETM +, pan-sharpened Landsat 7 and ASTER). The landform record indicates that the Patagonian Ice Sheets consisted of 66 main outlet glaciers, together with numerous local cirque glaciers and independent ice domes in the surrounding mountains. In the northern part of the mapped area, in the Chilean Lake District (38-42 degrees S), large piedmont glaciers developed on the western side of the Andes and the maximum positions of these outlet glaciers are, in general, marked by arcuate terminal moraines. To the east of the Andes between 38 degrees S and 42 degrees S, outlet glaciers were more restricted in extent and formed "alpine-style" valley glaciers. Along the eastern flank of the Andes south of similar to 45 degrees S a series of large fast-flowing outlet glaciers drained the ice sheet. The location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes. West of the Andes at this latitude, there is geomorphological evidence for an independent ice cap close to sea level on the Taitao Peninsula. The age of this ice cap is unclear but it may represent evidence of glacier growth during the Antarctic Cold Reversal and/or Younger Dryas Chronozone. Maximum glacier positions are difficult to determine along much of the western side of the Andes south of 42 degrees S because of the limited land there, and it is assumed that most of these glaciers had marine termini. In the south-east of the mapped area, in the Fuegan Andes (Cordillera Darwin), the landform record provides evidence of ice-sheet initiation. By adding published dates for glacier advances from the literature we present maps of pre-Last Glacial Maximum (LGM) glacier extent, LGM extent and the positions of other large mapped moraines younger than LGM in age. A number of large moraines occur within the known LGM limits. The age of these moraines is unknown but, since many of them lie well outside the established maximum Neoglacial positions, the possibility that they reflect a return to glacial climates during the Younger Dryas Chronozone or Antarctic Cold Reversal cannot be discounted.
|
|
| 23. |
- Kjær, Kurt H, et al.
(author)
-
Subglacial decoupling at the sediment/bedrock interface: a new mechanism for rapid flowing ice
- 2006
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 25:21-22, s. 2704-2712
-
Journal article (peer-reviewed)abstract
- Abstract in UndeterminedOn millennial or even centennial time scales, the activity of rapid flowing ice can affect climate variability and global sea level through release of meltwater into the ocean and positive feedback loops to the climate system. At the surge-type glacier Bruarjokull, an outlet of the Vatnajokull ice cap, eastern Iceland, extremely rapid ice flow was sustained by overpressurized water causing decoupling beneath a thick sediment sequence that was coupled to the glacier. This newly discovered mechanism has far reaching consequences for our understanding of fast-flowing ice and its integration with sediment discharge and meltwater release. (c) 2006 Elsevier Ltd. All rights reserved.
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
- Ljung, Karl, et al.
(author)
-
Variable Be-10 fluxes in lacustrine sediments from Tristan da Cunha, South Atlantic: a solar record?
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:7-8, s. 829-835
-
Journal article (peer-reviewed)abstract
- A 650-yr-long sediment sequence from a crater lake on Tristan da Cunha, South Atlantic, was analysed for its Be-10 content. Based on C-14 dating, and sedimentary, geochemical, magnetic and palynological records, the period between 900 and 1450 AD appears to have been unusually stable in terms of sedimentation and vegetation and therefore this period was chosen for analysis of the Be-10 content. During this period of highly organic sedimentation and closed vegetation, the pattern of Be-10 flux variations follows the Be-10 fluctuations from the GRIP ice core and estimated C-14 production rates well. However, before and after this stable period, variable sedimentation rates have to be accounted for to obtain results that are comparable to the established Be-10/C-14 records. Our data show not only the possibility of obtaining detailed enough Be-10 flux data from sedimentary sequences to reconstruct past solar forcing but also how sensitive this type of record is to sedimentary and environmental changes. If suitable archives can be found, they have the potential to improve reconstructions of solar activity far back in time. (c) 2007 Elsevier Ltd. All rights reserved.
|
|
| 27. |
|
|
| 28. |
|
|
| 29. |
- Muscheler, Raimund, et al.
(author)
-
Solar activity during the last 1000 yr inferred from radionuclide records
- 2006
-
In: Quaternary Science Reviews. - 0277-3791. ; 26, s. 82-97
-
Journal article (peer-reviewed)abstract
- Identification of the causes of past climate change requires detailed knowledge of one of the most important natural factors—solar forcing. Prior to the period of direct solar observations, radionuclide abundances in natural archives provide the best-known proxies for changes in solar activity. Here we present two independent reconstructions of changes in solar activity during the last 1000 yr, which are inferred from 10Be and 14C records. We analyse the tree-ring 14C data (SHCal, IntCal04 from 1000 to 1510 AD and annual data from 1511 to 1950 AD) and four 10Be records from Greenland ice cores (Camp Century, GRIP, Milcent and Dye3) together with two 10Be records from Antarctic ice cores (Dome Concordia and South Pole). In general, the 10Be and 14C records exhibit good agreement that allows us to obtain reliable estimates of past solar magnetic modulation of the radionuclide production rates. Differences between 10Be records from Antarctica and Greenland indicate that climatic changes have influenced the deposition of 10Be during some periods of the last 1000 yr. The radionuclide-based reconstructions of past changes in solar activity do not always agree with the sunspot record, which indicates that the coupling between those proxies is not as close as has been sometimes assumed. The tree-ring 14C record and 10Be from Antarctica indicate that recent solar activity is high but not exceptional with respect to the last 1000 yr.
|
|
| 30. |
- Muscheler, Raimund, et al.
(author)
-
Solar activity during the last 1000 yr inferred from radionuclide records
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:1-2, s. 82-97
-
Journal article (peer-reviewed)abstract
- Identification of the causes of past climate change requires detailed knowledge of one of the most important natural factors-solar forcing. Prior to the period of direct solar observations, radionuclide abundances in natural archives provide the best-known proxies for changes in solar activity. Here we present two independent reconstructions of changes in solar activity during the last 1000 yr, which are inferred from Be-10 and C-14 records. We analyse the tree-ring C-14 data (SHCal, IntCa104 from 1000 to 1510 AD and annual data from 1511 to 1950 AD) and four Be-10 records from Greenland ice cores (Camp Century, GRIP, Milcent and Dye3) together with two Be-10 records from Antarctic ice cores (Dome Concordia and South Pole). In general, the Be-10 and C-14 records exhibit good agreement that allows us to obtain reliable estimates of past solar magnetic modulation of the radionuclide production rates. Differences between Be-10 records from Antarctica and Greenland indicate that climatic changes have influenced the deposition of Be-10 during some periods of the last 1000 yr. The radionuclide-based reconstructions of past changes in solar activity do not always agree with the sunspot record, which indicates that the coupling between those proxies is not as close as has been sometimes assumed. The tree-ring C-14 record and Be-10 from Antarctica indicate that recent solar activity is high but not exceptional with respect to the last 1000 yr. (c) 2006 Elsevier Ltd. All rights reserved.
|
|
| 31. |
- Möller, Per
(author)
-
Rogen moraine: an example of glacial reshaping of pre-existing landforms
- 2006
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 25:3-4, s. 362-389
-
Journal article (peer-reviewed)abstract
- Rogen moraine is widely distributed in the core areas of the former Scandinavian and Laurentide ice sheets. It is generally agreed upon that these gently arched, ice-How transverse ridges call be used in reconstructions of paleo-ice-flow patterns and that they indicate a melted-bed or poly-thermal basal ice regime. However, the processes of ridge generation have been contentious. This study proposes a two-stage formation of Rogen moraine, based oil detailed sedimentological and structural investigations in excavated trenches in a Ropen moraine landscape in the province of Dalama, central Sweden. Field data suggest that Rogen moraine ridges are the reshaped remains of pre-existing transverse moraine ridges, originally deposited from ice-cored moraines ill an ice-marginal zone. Due to back- and down-wasting of ice-cores, inter-ridge troughs were filled with debris flow and fluvial deposits, which after landscape inversion were transformed to areas of transverse and hummocky moraines. It is proposed that this primary landscape formation Occurred during an Early Weichselian deglaciation. This relict landscape was later preserved beneath cold-based Mid- to Late-Weichselian ice sheet(s), which turned wet-based during the Preboreal deglaciation phase and re-moulded the precursor landforms into Rogen moraine.
|
|
| 32. |
- Möller, Per, et al.
(author)
-
Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to Late Quaternary
- 2006
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 25:21-22, s. 2894-2936
-
Journal article (peer-reviewed)abstract
- Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79 degrees N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS C-14, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of > 2000m only 200km from the deep Arctic Ocean, consistent with published evidence of ice grounding at similar to 1000m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula.
|
|
| 33. |
- Sommer, Robert S., et al.
(author)
-
Holocene recolonization and extinction of the pond turtle, Emys orbicularis (L., 1758), in Europe
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:25-28, s. 3099-3107
-
Journal article (peer-reviewed)abstract
- We reconstruct the Holocene range fluctuations of the European pond turtle (Emys orbicularis) for northern and Central Europe. Based on 529 subfossil records and radiocarbon dating of critical finds, we provide evidence that E. orbicularis experienced a rapid range expansion with Holocene warming. Phylogeographic data argue for a colonization of northern and Central Europe from a glacial refuge located in the south-eastern Balkans. Already in the Late Preboreal (9100-8600 cal BC) the species occurred in northern Central Europe and was widespread in Denmark and southern Sweden (Skane) during the Boreal (8600-7100 cal BC). The maximum range extension occurred during the Holocene climatic optimum (Atlantic: 7100-3750 cal BC), with records in southern England, middle Sweden, and northern Estonia. After the early Subboreal (3750-1750 cal BC) northern populations collapsed, coinciding with a climatic cooling and oceanization. Northern populations were most likely established via long distance dispersal (rafting using rivers debouching in the North and Baltic Seas); after northern Europe was reached, a minimum dispersal of 50 km per 100 years may be hypothesized for the Boreal. (c) 2007 Elsevier Ltd. All rights reserved.
|
|
| 34. |
- Ukkonen, Pirkko, et al.
(author)
-
MIS 3 mammoth remains from Sweden - implications for faunal history, palaeoclimate and claciation chronology
- 2007
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26, s. 3081-3098
-
Research review (peer-reviewed)abstract
- The distribution of low-arctic megafaunal remains in time and space from the area previously covered by the Scandinavian Ice Sheet(SIS) suggests the presence of breeding mammoth populations in the circum-Baltic region during the time interval from 44 to 26 ka ago. The transport history of 30 mammoth teeth and bones from southern and north-central Sweden was estimated and the remains were subjected to osteological analyses and 14C dating. Oxygen isotope analyses of tooth enamel indicate a palaeoclimate considerably more homogenous than that experienced in Sweden today, showing moderate north–south gradients in the d18O value of precipitation and temperature. In general, the results support the model of restricted ice sheet distribution during the second half of the Middle Weichselian. The clear discrepancy in the inferred absence of glaciation in the central Swedish uplands and the Baltic basin as evidenced by the Swedish mammoth data versus the Danish OSL-based glaciation chronology in the period from 40 to 30 ka ago is discussed in the light of radiocarbon calibration and glacial dynamics. r 2007 Published by Elsevier Ltd.
|
|
