| 1. |
- Björck, S., et al.
(author)
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Synchronized terrestrial-atmospheric deglacial records around the North Atlantic.
- 1996
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 274:5290, s. 1155-1160
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Journal article (peer-reviewed)abstract
- On the basis of synchronization of three carbon-14 (C-14)-dated lacustrine sequences from Sweden With tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta(14)C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.
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| 2. |
- Hammarlund, Dan, et al.
(author)
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Climate and environment during the Younger Dryas (GS-1) as reflected by composite stable isotope records of lacustrine carbonates at Torreberga, southern Sweden
- 1999
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In: Journal of Quaternary Science. - 1099-1417. ; 14:1, s. 17-28
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Journal article (peer-reviewed)abstract
- Climatic and environmental changes during the Younger Dryas stadial (GS-1) and preceding and following transitions are inferred from stable carbon and oxygen isotope records obtained from the sediments of ancient Lake Torreberga, southern Sweden. Event GS-1 is represented in the sediment sequence by 3.5 m of clay containing lacustrine carbonates of various origins. Comparison of isotopic records obtained on mollusc shells, ostracod valves, and Chara encrustations precipitated during specific seasons of the year supports estimates of relative changes in both lake water and mean annual air temperatures. Variations in soil erosion rates can also be estimated from a simple isotope-mass-balance model to separate allochthonous and autochthonous carbonate contributions to the bulk carbonate content of the sediments. The well-known, rapid climatic shifts characterising the Last Termination in the North Atlantic region are clearly reflected in the isotopic data, as well as longer-term changes within GS-1. Following maximum cooling shortly after the Allerod-Younger Dryas (GI-1-GS-1) transition, a progressive warming and a slight increase in aquatic productivity is indicated. At the Younger Dryas-Preboreal (GS-1-PB) transition mean annual air temperature rapidly increased by more than 5 degrees C and summer lake-water temperature increased by ca. 12 degrees C. The subsequent Preboreal oscillation is characterised by an increase in soil erosion and a slight decrease in mean annual air temperature. These results are in harmony with recent findings about large-scale climate dynamics during the Last Termination. Copyright (C) 1999 John Wiley & Sons, Ltd.
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| 3. |
- Hammarlund, Dan, et al.
(author)
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Multi-component carbon isotope evidence of early Holocene environmental change and carbon-flow pathways from a hard-water lake in northern Sweden
- 1997
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In: Journal of Paleolimnology. - 0921-2728. ; 18:3, s. 219-233
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Journal article (peer-reviewed)abstract
- A 9000-year carbonate-rich sediment sequence from a small hard-water lake in northernmost Sweden was studied by means of multi-component stable carbon isotope analysis. Radiocarbon dating of different sediment fractions provides chronologic control and reveals a rather constant hard-water effect through time, suggesting lake has remained hydrologically open throughout the Holocene. Successive depletion of C-13 in fine-grained calcite and carbonate shells during the early Holocene correlate with a change in catchment vegetation from pioneer herb communities to boreal forest. The vegetational change and associated soil development likely gave rise to an increased supply of C-13-depleted carbon dioxide in groundwater recharging the lake. This process is therefore believed to be the main cause of decreasing values of delta(13)C in dissolved inorganic carbon of the lake and thereby in limnic carbonates. Strongly C-13-depleted sedimentary organic matter may be related to enhanced kinetic fractionation during photosynthetic assimilation by means of proton pumping in Characean algae. This interpretation is supported by a substantial offset between delta(13)C of DIC as recorded by mollusc shells and delta(13)C Of fine-grained calcite.
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| 4. |
- Hammarlund, Dan
(author)
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Ostracod stable isotope records from a deglacial isolation sequence in southern Sweden
- 1999
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In: Boreas. - 1502-3885. ; 28:4, s. 564-574
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Journal article (peer-reviewed)abstract
- A Late Weichselian sediment succession from the Kullen Peninsula, southern Sweden, was studied by means of stable carbon and oxygen isotope analyses of calcitic valves of selected ostracod taxa. The lower part of the record was deposited in a slightly brackish marginal sea close to the receding inland ice, whereas the upper part is lacustrine in origin as a result of glacio-isostatic rebound. The site was deglaciated at c. 17200 cal BP (c. 14500 C-14 BP) within the earliest ice-free area of Sweden, and the isolation took place c. 1100 cal years later. As a result of extensive input of glacial meltwater to the near-shore, shallow basin, the isotopic records predating the isolation give no clear indications of marine conditions. However, the isolation of the lake from the marginal sea is reflected by a distinct depletion of O-18 in ostracod calcite as a response to the changing isotope hydrology of the basin. The change towards a lacustrine environment also fostered a decrease in the input of minerogenic material and a related increase in organic carbon content of the sediments, which may explain a short-lasting depletion of C-13 in dissolved inorganic carbon and ostracod calcite. During the period of c. 14700-13900 cal BP a pronounced warming occurred associated with the onset of the Late Weichselian interstadial complex (Greenland Interstadial I). Based on a distinct enrichment of O-18 in ostracod calcite and applying modern spatial relations between delta(18)O of precipitation and temperature, this climatic shift involved an increase in mean annual air temperature in southernmost Sweden of at least 7 degrees C.
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| 5. |
- Sandgren, Per, et al.
(author)
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Stratigraphic evidence for a high marine shore-line during the Late Weichselian deglaciation on the Kullen Peninsula, southern Sweden
- 1999
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In: Journal of Quaternary Science. - 1099-1417. ; 14:3, s. 223-237
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Journal article (peer-reviewed)abstract
- Mineral magnetic properties and the carbon content of a sediment sequence in Lake Kullatorpssjon on the Kullen Peninsula in northwest Scania, southern Sweden, were investigated. Diatom and ostracod analyses were undertaken for palaeoecological reconstruction and a chronology was constructed from accelerator mass spectrometry (AMS) radiocarbon dating of terrestrial plant remains and mosses. Five stratigraphical units were identified (units 1-5, from oldest to youngest). The two lowermost units consist of clay. The lowest clay unit (1) is strikingly black, 2 m thick and has magnetic properties dominated by high concentrations of authigenic greigite (Fe3S4). In contrast, the overlying clay unit (2) is grey, 1.18 m thick and has magnetic properties dominated by low concentrations of detrital magnetite (Fe3O4). A major palaeoecological change is reflected in the diatom flora and ostracod fauna at the transition from unit 1 to unit 2. The sediment stratigraphy, geochemical, mineral magnetic and palaeoecological analyses also point to a significant change in depositional environment at this transition, which is proposed to represent the isolation of Lake Kullatorpssjon from the Kattegat Sea. Earlier investigations have determined the marine limit to ca. 65 m a.s.l. on the Kullen Peninsula. The separate independent lines of evidence presented here, however, suggest that the Late Weichselian marine limit developed at 85-90 m a.s.l. at the deglaciation ca. 17 200 cal. yr BP (ca. 14 500 yr BP). This limit is ca. 25 m higher than assumed previously. Lake Kullatorpssjon formed ca. 1000 cal. yr later when the basin became isolated from the Kattegat Sea. Copyright (C) 1999 John Wiley & Sons, Ltd.
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