| 1. |
- Björkman, Leif, et al.
(author)
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Lateglacial and early Holocene vegetation development in the Gutaiului Mountains, northwestern Romania
- 2002
-
In: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:8-9, s. 1039-1059
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Journal article (peer-reviewed)abstract
- Pollen analyses and AMS C-14 measurements were performed on lacustrine sediments and peat sequences from two former crater lakes (Preluca Tiganului, Steregoiu) situated in the Gutaiului Mountains in northwestern Romania, in order to reconstruct the vegetation development during the Lateglacial and Early Holocene. Before c. 14,700 cal. years BP (GS-2) open vegetation with shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae) prevailed in the area. Around c. 14,700 cal. years BP and coinciding with the beginning of GI-le, Pinus expanded, and patchy vegetation with scattered Pinus stands developed. The last 100 years of GI-le (14,150-14,050 cal. years BP) were characterised by an increase in Pinus and Betula and an expansion of open forest communities. This development was shortly interrupted between 14,050 and 13,800 cal. years BP (likely corresponding to the cold phase GI-ld), when the tree cover became reduced and open vegetation with scattered Pinus individuals became frequent. The period with a significant expansion of Betula and Picea and the formation of an open forest (including Pinus and Omits), which took place between 13,800 and c. 12,950 cal. years BP, is tentatively correlated with GI-lc-a. A renewed reduction in tree cover (decrease of Picea and Betula, disappearance of Ulms) started at similar to 12,950 cal. years BP and at 12,600 cal. years BP forest stands were rapidly replaced by open vegetation communities with low shrubs (Salix, Juniperus), grasses and herbs (e.g. Artemisia and Chenopodiaceae). The period between 12,900 and 11,500 is correlated with the cold phase GS-1. At 11,500 cal. years BP, most likely as a response to the warmer climatic conditions at the beginning of the Holocene, an expansion of Betula and Alnus and, slightly later, also of Ulmus can be observed. Between 11,500 and 11,250 cal. years BP, open forests with Betula, Pinus and Ulmus were widespread in the area. At 11,250 cal. years BP dense forests dominated by Ulmus replaced the open forest type. Around 10,700cal. years BP Quercus, Tilia and Fraxinus expanded strongly, and Acer and Corylus became established. Mixed deciduous forest with Picea dominated the upland vegetation between 10,700 and 10, 150 cal. years BP. At 10,150 cal. years BP Corylus increased significantly and between 10,150 and 8500 cal. years BP, dense mixed deciduous forests with Picea and Corylus were abundant in the area. Climatic fluctuations seem to have been the driving force behind vegetation changes during the Lateglacial period, while the forest development during the Early Holocene was mainly driven by migrational and successional processes.
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| 2. |
- Björck, Jonas, et al.
(author)
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An event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden : results from investigations of varved clay and terrestrial sequences
- 2002
-
In: Quaternary Science Reviews. - 0277-3791 .- 1873-457X. ; 21:12/13, s. 1489-1501
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Journal article (peer-reviewed)abstract
- This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the time-span from ca 12,900 to 10,200 cal yr BP. The local event stratigraphy has been linked to the GRIP isotopic event stratigraphy by different correlations. The onset of the Younger Dryas is dated to 12,650 cal yr BP. This cold event lasted for ca 1125 cal yr in the area. The Vedde Ash (ca 12,000 cal yr BP) has been recorded in two terrestrial sequences, which makes it possible to exactly link the event stratigraphy to the GRIP ice-core and to marine cores in the North Atlantic region. The final drainage of the Baltic Ice Lake has been dated to ca 11,560 cal yr BP, which predates the Younger Dryas/Preboreal climatic boundary with ca 35 yr. An early Holocene cold event has been detected both in terrestrial and varved clay sequences at ca 11,305-11,185 cal yr BP. This cold event coincides almost exactly with a brackish water phase in the Baltic Sea. A previously unrecorded early Holocene tephra horizon has been found in lacustrine sediments at ca 10,200 cal yr BP.
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| 3. |
- Haberle, Simon, et al.
(author)
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Postglacial formation and dynamics of North Patagonian Rainforest in the Chonos Archipelago, Southern Chile
- 2004
-
In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 23:23-24, s. 2433-2452
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Journal article (peer-reviewed)abstract
- Pollen analysis of continuous sediment cores from two lakes in the northern Chonos Archipelago (44°S) in southern Chile shows a complete postglacial record of vegetation change. The fossil records indicate that deglaciation was complete in the northern Chonos by at least 13,600 14C yr BP. Ericaceous heath and grassland persisted for more than 600 years after deglaciation under the influence of dry/cold climates and frequent burning. Nothofagus-Pilgerodendron-Podocarpus forest, with modern analogues in the southern Chonos Archipelago, was established across the northern islands by 12,400 14C yr BP under increasingly warm and wet climates. There is no evidence for a return to cooler climates during the Younger Dryas chronozone. The rise of Tepualia stipularis and Weinmannia trichosperma as important forest components between 10,600 and 6000 14C yr BP may be associated with climates that were warmer than present. The collapse of Pilgerodendron communities during this time may have been triggered by a combination of factors related to disturbance frequency including tephra deposition events, fire and climate change. After 6000 14C yr BP Pilgerodendron recovers and Nothofagus-Pilgerodendron-Tepualia forest persists until the present. European logging and burning activity may have increased the susceptibility of North Patagonian Rainforest to invasion by introduced species and to future collapse of the long-lived Pilgerodendron communities.
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| 4. |
- Larocque, I., et al.
(author)
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Holocene temperature estimates and chironomid community composition in the Abisko Valley, northern Sweden
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 23:23-24, s. 2453-2465
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Journal article (peer-reviewed)abstract
- Multi-proxy paleoenvironmental reconstructions are useful to determine the various factors affecting the biological communities of a lake, but to assess if changes in community composition of one indicator organism accurately reconstructs climatic changes through time, it may be more useful to compare temperature reconstructions using the same indicator in several lakes. Here, we compare reconstructions of mean July air temperature using chironomid-based transfer functions from Holocene records at three nearby lakes in the Abisko Valley of northern Sweden to assess if chironomids can be used as indicators of regional temperature changes. The three study lakes experience the same regional climatic conditions, but are located along gradients of elevation (348–999 m a.s.l), temperature (8.1–12°C) and terrestrial vegetation (coniferous to alpine). Chironomid-temperature reconstructions from the three sites indicate a general pattern of temperature decrease (1.5–2.4°C) during the Holocene, consistent with decreases observed from analyses of other proxies in this area, and from other alpine regions in Europe and North America. Similarities between these reconstructions suggest that chironomids can adequately record general patterns of temperature changes through the Holocene, although effects of site-specific factors such as variations in lake water pH can cause deviations in inferred temperature among sites during some periods.
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| 5. |
- Rosqvist, G., et al.
(author)
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Diatom oxygen isotopes in pro-galcial lake sediments from northern Sweden: A 5000 year record of atmospheric circulation.
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 23:7-8, s. 851-859
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Journal article (peer-reviewed)abstract
- We use a pro-glacial oxygen isotope record of diatom silica (δ18Odiatom) and a sedimentary proxy for glacier flutuations to determine centennial-millennial scale climate change during the last 5000 yeras in northern Sweden. We show that the lake water isotopic composition åredominantly reflects the isotopic composition of the precipitation. Superimposed on a general depletion trend of 3.5‰ over the past 5000 years we found that the isotopic composition of precipitation became depleted (> 1‰ excursions) during four occasions centered at 4400, 3000, 2000 and, after 1200 cal yr BP. Climate simultaneously sustained a positive glacier mass balance, taht caused the catchment glacier to advance. A peristan cgange in the atmopheric circulation pattern could potentially have caused the registered chnages in the δ18Odiatom because different air masses hold characteristics δ18O signatures of their precipitation. The glacier mass balance primarily responds to the influence of summer temperature on ablation. We suggest that the most likely cause for the recorded chnages in both these proxies is a steadily increasing but fluctuating dominance of colder and δ18O depleted air masses from the north/northeast during the past 5000 years. Theδ18Odiatom depletion and glacier events all occur at times of relative ice-rafted-debris maxima in the North Atlanic, consistent with cold conditions and changes in surface wind directions. Our results confirm that changes towards a predominace of north/northeasterly winds occured at these time intervals.
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| 6. |
- Björck, Svante, et al.
(author)
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Consistently large marine reservoir ages in the Norwegian Sea during the Last Deglaciation
- 2003
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In: Quaternary Science Reviews. - 0277-3791. ; 22:5-7, s. 429-435
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Journal article (peer-reviewed)abstract
- With the exception of the GS-1/Younger Dryas cold period marine reservoir ages for the Last Deglaciation in the North Atlantic-Norwegian Sea are generally assumed to have been around 400-500 radiocarbon years in magnitude (Earth Planet. Sci. Lett. 126 (1994) 275; Radiocarbon 37 (1995) 53; Quat. Res. 52 (1999) 104; Nature 412 (2001) 724). By comparing the climate records obtained from the GRIP ice-core (Nature 359 (1992) 311; J. Quat. Sci. 13(4) (1998) 283) and from North Atlantic/Norwegian Sea cores (Quat. Res. 52 (1999) 104; Geology 23 (12) (1995) 1059; Nature 356 (1991) 757; Nature 356 (1992) 757; Paleoceanography 3(1) (1988) 1; Nature 343 (1990) 612; Earth Planet. Sci. Lett. 126 (1994) 275), with radiocarbon-dated European continental records, we show that marine reservoir ages in the Norwegian Sea were of the order of 1000 C-14 yr, including large uncertainties. This approach rests on the reasonable assumption that climate changes throughout the NE Atlantic and Europe were more or less synchronous at the centennial scale. Fairly large variations in reservoir ages over time may have been caused by changing atmospheric C-14 content. The results indicate that detailed land-sea correlations for the North Atlantic during the Last Deglaciation are not feasible using radiocarbon dating alone. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 7. |
- Hammarlund, Dan, et al.
(author)
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Rapid hydrological changes during the Holocene revealed by stable isotope records of lacustrine carbonates from Lake Igelsjon, southern Sweden
- 2003
-
In: Quaternary Science Reviews. - 0277-3791. ; 22:2-4, s. 353-370
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Journal article (peer-reviewed)abstract
- A Holocene sediment sequence from Lake Igelsjon, south central Sweden, was studied by stable oxygen- and carbon-isotope analyses of different carbonate components. The deposit, which covers the time-span from ca 11,500 cal BP to the present, was laid down in a small, kettle-hole lake, the hydrological balance of which is presently dominated by groundwater flow. Isotopic records obtained on bulk carbonates originating mainly from summer-produced, calcitic algal encrustations exhibit several rapid shifts of more than 2parts per thousand, likely reflecting pronounced hydrological variations. Corresponding isotopic data obtained on calcitic gastropod opercula from parts of the profile show subdued responses to major climatic shifts, probably related to an extended calcification season. The isotopic records were complemented by studies of modern isotope hydrology, and our interpretations are based on a simplistic climate-hydrology model in which variations in groundwater generation within the lake catchment produce changes in groundwater level and related adjustments of lake level and surface/volume ratio of the basin during the ice-free season. Assumed periods of decreased lake volume in a relatively dry climate (low lake level) are characterised by enrichment in O-18 and C-13 resulting from increased evaporation/inflow ratio and atmospheric equilibration, respectively. In clear contrast to this situation, intervals of more humid climatic conditions give rise to increased lake volume (high lake level), possibly surface over flow, and relatively depleted isotopic ratios. Relatively humid conditions, which may correlate to a wide-spread cooling event recorded by various proxies across the North Atlantic region, are indicated by distinct isotopic shifts at ca 8300 and 8000 cal BP, bracketing a period of O-18-depletion. The period between ca 8000 and 4000 cal BP was characterised by relatively dry and stable climatic conditions, whereas the subsequent part of the Holocene experienced a more humid and variable climate following marked and coherent depletions in O-18 and C-13 at ca 4000 cal BP. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 8. |
- John Lowe, J., et al.
(author)
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Inter-regional correlation of palaeoclimatic records for the last Glacial-Interglacial Transition : A protocol for improved precision recommended by the INTIMATE project group
- 2001
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In: Quaternary Science Reviews. - 0277-3791. ; 20:11, s. 1175-1187
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Journal article (peer-reviewed)abstract
- The remit of the INTIMATE project of the INQUA Palaeoclimate Commission is to synthesise marine, terrestrial and ice-core data for the North Atlantic region during the Last Glacial-Interglacial Transition (LGIT: ca 13-1014C kyr BP; ca 15-11.5 ice-core kyr BP). A major problem, however, is the difficulty of effecting correlations at a temporal resolution that are adequate for defining 'leads' and 'lags' between the polar ice, terrestrial, marine, and atmospheric realms. The limitations of the dating and correlation methods currently employed are summarised, and new quality assurance protocols are proposed. These include recommendations on the contextual information that should accompany radiocarbon dates, procedures for radiocarbon calibration, the use of an event-stratigraphic approach in inter-regional correlations, and the more widespread use of time-parallel marker horizons (based on tephra layers, oxygen isotope stratigraphy, palaeomagnetic stratigraphy, and radiocarbon 'wiggle-matching') to underpin the geochronology and correlation of events during the LGIT. These protocols will be adopted by the INTIMATE project in future international, collaborative research and are recommended to other groups working on this important time period.
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| 9. |
- Kjaer, Kurt, et al.
(author)
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What causes till thickness to change over distance? Answers from Myrdalsjokull, Iceland
- 2003
-
In: Quaternary Science Reviews. - 0277-3791. ; 22:15-17, s. 1687-1700
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Journal article (peer-reviewed)abstract
- Many explanations have been provided for variations of the spatial distribution and thickness of till sheets. This paper gives new insight into the architecture of a stratigraphically distinct till sheet as a function of the type of substratum and preadvance topography at a scale of similar to 10 km. This emphasises the sensitivity of the subglacial system to changes in the basal drainage conditions. The study area is the forefield of Slettjokull at the northern margin of the Myrdalsjokull ice cap, central south Iceland. Here, detailed lithostratigraphical and sedimento logical investigations, including mapping of the thickness for two till units, sediment logging, clast fabric and geotechnical measurements provide a basis for interpretations. The results show that the thickness of a stratigraphically distinct till sheet is directly correlated to the type of substratum. Where the substratum consists of sorted sediments the till is thin. Conversely, the till is thick where the substratum consists of till overlying sorted sediments. A sedimentological model is presented in which till thickness is tied to the variable hydraulic conditions experienced in a deforming subglacial bed. (C) 2003 Elsevier Ltd. All rights reserved.
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| 10. |
- Schomacker, Anders, et al.
(author)
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An extensive late Holocene glacier advance of Kotlujokull, central south Iceland
- 2003
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In: Quaternary Science Reviews. - 0277-3791. ; 22:14, s. 1427-1434
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Journal article (peer-reviewed)abstract
- This paper presents data on an extensive late Holocene advance of Kotlujokull, a southeastern outlet glacier from the ice cap Myrdalsjokull, central south Iceland. During the advance, basal till was deposited on top of a volcanic ash layer resting on lava hummocks. Remnants of this landscape are now seen 3.5-5.5 km in front of Kotlujokull as a fragment surrounded by the Myrdalssandur. Electron microprobe analysis of the volcanic ash shows that it is silicic and originates from the volcano Katla underneath Myrdalsjokull. A C-14 AMS date on a twig fragment sampled in the upper part of the volcanic ash layer provides a maximum age of the till of 1610 +/- 40 yr BP, and this is supported by tephrochronological and geochemical analyses of the volcanic ash. It is concluded that Kotlujokull must have advanced more than 5.5 km from its present position after 1.6 kyr 13P. This advance is much more extensive than the Little Ice Age (LIA) advance and took place in a relatively cold period also identified in the Greenland ice cores and the diatom record in the seas surrounding Iceland. In the proglacial environment in front of the Icelandic ice caps, the preservation potential of older end-moraines is strongly restricted due to intense glaciofluvial erosion. Therefore, the LIA end-moraines have in many cases been interpreted as marking the outermost Holocene glacier front position. This study as well as other recent results stresses the fact that the "LIA glacial maximum" in Iceland may not be identical to the Holocene glacial maximum, and that far more case studies with well-constrained dating control are needed. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 11. |
- Thomas, PJ, et al.
(author)
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Age limit and age underestimation using different OSL signals from lacustrine quartz and polymineral fine grains
- 2003
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In: Quaternary Science Reviews. - 0277-3791. ; 22:10-13, s. 1139-1143
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Journal article (peer-reviewed)abstract
- As part of a systematic palaeohydrological reconstruction of lake level fluctuations during the Last Glacial Maximum, a transect of cores from ancient Lake Xinias in centra Greece has already been studied with respect to pollen, sediment and mineral magnetic analyses. The chronology was based on C-14 AMS dating of terrestrial plant macrofossil remains from peat and clayey peat (Palaeogeog. Palaeoclimatol. Palaeoecol. 158 (2000) 65). This site thus provides an opportunity for the comparison of fine grain optically stimulated luminescence (OSL) ages of water-lain sediments with an independent chronology. We present here infrared (IR), post-IR blue and blue OSL characteristics of the fine grain sediments from Lake Xinias and a preliminary comparison with independent ages. The equivalent doses based on the IR results are about 40% of those based on post-IR blue stimulation, which in turn are 10-15% below those based on quartz OSL. We discuss the ages derived from the 3 signals in terms of the independent chronology, and draw conclusions about initial bleaching of the quartz and feldspar components, and the reliability of the post-IR blue signal as a chronometer. (C) 2003 Elsevier Science Ltd. All rights reserved.
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| 12. |
- Zillén, Lovisa, et al.
(author)
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Calendar year ages of three mid-Holocene tephra layers identified in varved lake sediments in west central Sweden
- 2002
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In: Quaternary Science Reviews. - 0277-3791. ; 21:14-15, s. 1583-1591
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Journal article (peer-reviewed)abstract
- Three intermediate to rhyolitic Icelandic Holocene tephra horizons (Hekla-3, Kebister, and Hekla-4) have been identified in annually laminated (varved) lake sediments in the Province of Varmland, west central Sweden. Calendar year ages were obtained from varve counts and are supported by additional C-14 dating based on terrestrial plant macrofossils. The varve ages of the three tephras are 3295 +/- 95 cal. BP (Hekla-3), 4030 +/- 103 cal. BP (Kebister), and 4390 +/- 107 cal. BP (Hekla-4). The varve age of Hekla-3 refines the former calibrated 14 C age based on studies in the British Isles and Germany. Considering the age-error estimates associated with the varve chronology and calibrated C-14 ages, the ages of Kebister and Hekla-4 are in agreement with former studies. Thus, the age difference between Kebister and Hekla-4 is estimated to be ca 400 +/- 40 varve years (formally estimated to ca 200 C-14 years), between Hekla-3 and Hekla-4 to ca 1135 +/- 55 varve years (formally estimated to ca 1100 calibrated C-14 years) and between Hekla-3 and Kebister, 708 +/- 20 varve years.
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| 13. |
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| 14. |
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| 15. |
- Clague, JJ, et al.
(author)
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Late Holocene environmental change at treeline in the Northern Coast Mountains, British Columbia, Canada
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:23-24, s. 2413-2431
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Journal article (peer-reviewed)abstract
- An integrated stratigraphic, paleoecological, and geochronological study of lake and fen sediments just beyond the terminus of Berendon Glacier provides insights into late Holocene climate, vegetation, and glacier change in the northern Coast Mountains of British Columbia. Cores collected from two small lakes in the foreland of Berendon Glacier and pits dug in a nearby fen record Little lee Age and older glacier advances. The first Little Ice Age advance in this area began more than 500 years ago and peaked in the early 17th century. An earlier Neoglacial advance began about 2800-3000 cal yr ago and may have lasted for hundreds of years. There is also evidence for an intervening advance of even smaller magnitude around 1200-1300 cal yr ago. The advances are broadly synchronous with those in other parts of western North America, indicating that they were caused by regional, possibly global, changes in climate. Plant communities within the study area did not change dramatically during the late Holocene. The ranges of some plants, however, likely retracted or extended near treeline in response to changes in mean temperatures of perhaps 1-2degreesC, as A well as changes in summer snow cover. The greatest changes in vegetation occurred within and just beyond the forefields of Berendon, Frank Mackie, and other nearby glaciers. The largest climate shifts of the last 3000 years took place during the late Little Ice Age and the last century. Climate warmed about 1-2degreesC during the 20th century, accompanied by a rise in treeline, an increase in coniferous tree cover in the subalpine zone, and an increase in the temperature and biological productivity of ponds. These trends are likely to continue if climate, as expected, continues to warm. (C) 2004 Elsevier Ltd. All rights reserved.
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| 16. |
- Hubberten, HW, et al.
(author)
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The periglacial climate and environment in northern Eurasia during the Last Glaciation
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:11-13, s. 1333-1357
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Research review (peer-reviewed)abstract
- This paper summarizes the results of studies of the Late Weichselian periglacial environments carried out in key areas of northern Eurasia by several QUEEN teams (European Science Foundation (ESF) programme: "Quaternary Environment of the Eurasian North"). The palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the EU funded project "Eurasian Ice Sheets". These data prove beyond any doubt, that with the exception of the northwestern fringe of the Taymyr Peninsula, the rest of the Eurasian mainland and Severnaya Zemlya were not affected by the Barents-Kara Sea fee Sheet during the Last Glacial Maximum (LGM). Inversed modelling based on these results shows that a progressive cooling which started around 30 ka BP, caused ice growth in Scandinavia and the northwestern areas of the Barents-Kara Sea shelf, due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets. In the rest of the Eurasian Arctic extremely low precipitation rates (less than 50 mm yr(-1)), did not allow ice sheet growth in spite of the very cold temperatures. Palaeoclimatic and palaeoenvironmental conditions for the time prior to, during, and after the LGM have been reconstructed for the non-glaciated areas around the LGM ice sheet with the use of faunal and vegetation records, permafrost, eolian sediments, alluvial deposits and other evidences. The changing environment, from interstadial conditions around 30 ka BP to a much colder and drier environment at the culmination of the LGM at 20-15 ka BP, and the beginning of warming around 15 ka BP have been elaborated from the field data, which fits well with the modelling results. (C) 2003 Elsevier Ltd. All rights reserved.
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| 17. |
- Mangerud, J, et al.
(author)
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Ice-dammed lakes and rerouting of the drainage of northern Eurasia during the Last Glaciation
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:11-13, s. 1313-1332
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Journal article (peer-reviewed)abstract
- During the Quaternary period, ice sheets centred over the Barents and Kara seas expanded several times onto mainland Russia and blocked northflowing rivers, such as the Yenissei, Ob, Pechora and Mezen. Large ice-dammed lakes with reversed outlets, e.g. toward the Caspian Sea, formed south of these ice sheets. Some lakes are reconstructed from shorelines and lacustrine sediments, others mainly from ice-sheet configuration. Ice-dammed lakes, considerably larger than any lake on Earth today, are reconstructed for the periods 90-80 and 60-50 ka. The ages are based on numerous optically stimulated luminescence (OSL) dates. During the global Last Glacial Maximum (LGM, about 20 ka) the Barents-Kara Ice Sheet was too small to block these eastern rivers, although in contrast to the 90-80 and 60-50 ka maxima, the Scandinavian Ice Sheet grew large enough to divert rivers and meltwater across the drainage divide from the Baltic Basin to the River Volga, and that way to the Caspian Sea. Climate modelling shows that the lakes caused lower summer temperatures on the continent and on the lower parts of the ice sheet. The final drainage of the best mapped lake is modelled, and it is concluded that it probably emptied within few months. We predict that this catastrophic outburst had considerable impact on sea-ice formation in the Arctic Ocean and on the climate of a much larger area. (C) 2003 Elsevier Ltd. All rights reserved.
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| 18. |
- Moros, M, et al.
(author)
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Sea surface temperatures and ice rafting in the Holocene North Atlantic: climate influences on Northern Europe and Greenland
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:20-22, s. 2113-2126
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Journal article (peer-reviewed)abstract
- The oceanographic conditions in the high-latitude North Atlantic ocean during the Holocene were reconstructed through analyses of sea surface temperature (SST; alkenone unsaturation ratios) and ice rafting (mineralogy and grain size) from two sediment sequences, one recovered from the Reykjanes Ridge at 59degreesN and the other from the Norwegian Sea at 68degreesN. Comparison of our records to published ice core and terrestrial proxy-climate data sets suggests that atmospheric temperature changes over Northern Europe and Greenland were coupled to SST variability and ice rafting. The records outline four major climatic phases: (i) an early-Holocene Thermal Maximum that lasted until approximately 6.7 kyr BP, (ii) a distinctly cooler phase associated with increased ice rafting between 6.5 and 3.7 kyr BP, (iii) a transition to generally warmer, but relatively unstable climate conditions between 3.7 and 2 kyr BP and (iv) a second distinct SST decline that took place between 2 and 0.5 kyr BP. In contrast to the dominant control of Northern Hemisphere summer insolation on early-Holocene climate development (via strong seasonality), the trigger for the onset of relatively unstable climatic conditions in the North Atlantic at 3.7 kyr BP is not straightforward. However, it is possible that this change was triggered by late-Holocene winter insolation increase at high northern latitude and/or by inter-hemispheric changes in orbital forcing. The late-Holocene Neoglaciation trend, which is characteristic of numerous terrestrial archives in northern Europe, may not only be attributed to a gradual decrease in orbitally forced summer temperature, but also to increase snow precipitation at high northern latitudes during generally milder winters. (C) 2004 Elsevier Ltd. All rights reserved.
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| 19. |
- Muscheler, Raimund, et al.
(author)
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Causes and timing of the 8200 yr BP event inferred from the comparison of the GRIP Be-10 and the tree ring Delta C-14 record
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:20-22, s. 2101-2111
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Journal article (peer-reviewed)abstract
- We analyse the 8200 yr BP cold event by comparing the high-resolution Be-10 record from the GRIP ice core from Central Greenland with the well-known tree ring Delta(14)C record. By transferring the absolute dated tree ring chronology to the ice core time scale, we show that the coldest phase in the GRIP record occurred around 8150 yr BP. Furthermore, this method allows us to disentangle production and climate effects on Be-10 and C-14 with important implications for the reconstruction of past solar activity, and changes in the carbon cycle and Be-10 transport. We show that, in principle, it is possible to infer changes in ocean circulation by comparing Be-10 and C-14 records. However, the duration of the 8200 yr BP event is too short to assign unambiguously a significant change in atmospheric C-14 concentration to changes in the global ocean circulation. Based on the comparison of Be-10 with climate records, one could argue that the 8200 yr BP cold event is triggered by a change towards lower solar activity. However, this link is questioned by the fact that around this period there are other similar and even stronger changes in solar activity that have no apparent connection to climate changes. (C) 2004 Elsevier Ltd. All rights reserved.
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| 20. |
- Svendsen, JI, et al.
(author)
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Late quaternary ice sheet history of northern Eurasia
- 2004
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In: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 23:11-13, s. 1229-1271
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Research review (peer-reviewed)abstract
- The maximum limits of the Eurasian ice sheets during four glaciations have been reconstructed: (1) the Late Saalian (> 140 ka), (2) the Early Weichselian (100-80 ka), (3) the Middle Weichselian (60-50 ka) and (4) the Late Weichselian (25-15 ka). The reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in Russia and Siberia, and with marine seismic- and sediment core data. The Barents-Kara Ice Sheet got progressively smaller during each glaciation, whereas the dimensions of the Scandinavian Ice Sheet increased. During the last Ice Age the Barents-Kara Ice Sheet attained its maximum size as early as 90-80,000 years ago when the ice front reached far onto the continent. A regrowth of the ice sheets occurred during the early Middle Weichselian, culminating about 60-50,000 years ago. During the Late Weichselian the Barents-Kara Ice Sheet did not reach the mainland east of the Kanin Peninsula, with the exception of the NW fringe of Taimyr. A numerical ice-sheet model, forced by global sea level and solar changes, was run through the full Weichselian glacial cycle. The modeling results are roughly compatible with the geological record of ice growth, but the model underpredicts the glaciations in the Eurasian Arctic during the Early and Middle Weichselian. One reason for this is that the climate in the Eurasian Arctic was not as dry then as during the Late Weichselian glacial maximum.
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