| 1. |
- Ahmed, Engy, et al.
(författare)
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Archaeal community changes in Lateglacial lake sediments: Evidence from ancient DNA
- 2018
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 181, s. 19-29
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Tidskriftsartikel (refereegranskat)abstract
- The Lateglacial/early Holocene sediments from the ancient lake at Hässeldala Port, southern Sweden provide an important archive for the environmental and climatic shifts at the end of the last ice age and the transition into the present Interglacial. The existing multi-proxy data set highlights the complex interplay of physical and ecological changes in response to climatic shifts and lake status changes. Yet, it remains unclear how microorganisms, such as Archaea, which do not leave microscopic features in the sedimentary record, were affected by these climatic shifts. Here we present the metagenomic data set of Hässeldala Port with a special focus on the abundance and biodiversity of Archaea. This allows reconstructing for the first time the temporal succession of major Archaea groups between 13.9 and 10.8 ka BP by using ancient environmental DNA metagenomics and fossil archaeal cell membrane lipids. We then evaluate to which extent these findings reflect physical changes of the lake system, due to changes in lake-water summer temperature and seasonal lake-ice cover. We show that variations in archaeal composition and diversity were related to a variety of factors (e.g., changes in lake water temperature, duration of lake ice cover, rapid sediment infilling), which influenced bottom water conditions and the sediment-water interface. Methanogenic Archaea dominated during the Allerød and Younger Dryas pollen zones, when the ancient lake was likely stratified and anoxic for large parts of the year. The increase in archaeal diversity at the Younger Dryas/Holocene transition is explained by sediment infilling and formation of a mire/peatbog.
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| 2. |
- John Lowe, J., et al.
(författare)
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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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Ingår i: Quaternary Science Reviews. - 0277-3791. ; 20:11, s. 1175-1187
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Lascu, Ioan, et al.
(författare)
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A Late Glacial paleolake record from an up-dammed river valley in northern Transylvania, Romania
- 2015
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 388, s. 87-96
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Tidskriftsartikel (refereegranskat)abstract
- Lake sediments from the Magherus, Valley in the lowlands of northern Transylvania provide new evidence of paleoenvironmental development in Romania during the Late Glacial. The studied sediments were deposited as a result of the damming of a small river valley following a series of mass wasting events that occurred during the deglaciation period. A continuous sedimentary sequence belonging to the former lake is preserved in the banks of the stream, and contains evidence of paleoenvironmental changes associated with the Late Glacial Interstadial (Bolling-Allerod or Greenland Interstadial 1, GI-1) and the Late Glacial Stadial (Younger Dryas or Greenland Stadial 1, GS-1), implying that the hallmark climatic episodes of northwestern Europe are also expressed in Eastern Europe. We employ a multiproxy approach based on the analysis of sediment composition and texture, mineral magnetism, organic macrofossils, and radiocarbon dating. The reconstructed paleoenvironmental evolution at the site captures the warm and humid conditions associated with GI-1, as well as the subsequent cooling concomitant with the onset of GS-1. These climatic events are paralleled by vegetation shifts in the region, as deduced from comparisons with pollen sequences from Magherus, and neighboring locations in Transylvania and the Carpathians. The Late Glacial Interstadial was warmer and wetter, as evidenced by increased organic matter content in the lake, decreased erosion in the catchment, development of palustrine plant communities in the proximity of the lake, and expansion of spruce during the Allerod (GI-1c-a). The Late Glacial Stadial was colder and dryer, as indicated by low sedimentary organic matter content, an increase in erosion markers, and the decline of spruce and its replacement by birch. The landscape was more open, as herbs and grasses also expanded during this time. These fluctuations imply that Late Glacial climatic events are well expressed not only in upland areas of Romania, but also in lowland regions such as the Transylvanian Basin, where climatic effects are expected to be more muted.
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| 4. |
- Veres, Daniel, et al.
(författare)
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Age, origin and significance of a new middle MIS 3 tephra horizon identified within a long-core sequence from Les Echets, France
- 2008
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 37:3, s. 434-443
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Tidskriftsartikel (refereegranskat)abstract
- A new tephra has been identified within a long core (EC 3) sequence recovered from Les Echets, near Lyon, France. This visible tephra was discovered as part of a high resolution multiproxy re-investigation of the Les Echets sequence. Independent chronological information suggests that the tephra is c. 2 000-45 000 years old, and geochemical analysis indicates that it is of basanitic composition. The latter suggests a possible origin in the Eifel, however, as yet, no other volcanic events or deposits can be correlated to the Les Echets tephra. New sedimentological and chronological data are presented indicating that the tephra falls within an interval that most likely correlates with Dansgaard-Oeschger events 12-9. Thus, this tephra could potentially be an important middle MIS 3 marker horizon in central Europe if it can be traced in other palaeorecords.
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| 5. |
- Wohlfarth, Barbara, et al.
(författare)
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Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40-16 ka
- 2008
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 36:5, s. 407-410
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Tidskriftsartikel (refereegranskat)abstract
- We present a high-resolution and independently dated multiproxy lake sediment record from the paleolake at Les Echets in southeastern France that displays synchronous changes in independent limnic and terrestrial ecosystem proxies, in concert with millennial-scale climate oscillations during the last glacial period. Distinct lake-level fluctuations, low lake organic productivity, and open, treeless vegetation indicate cold and dry conditions in response to Heinrich events. Alternating phases of higher and low lake organic productivity, stratified surface waters and long-lasting lake ice cover, decreased or increased catchment erosion, and tree-dominated or herb-dominated vegetation resemble Dansgaard-Oeschger interstadial-stadial variability. Transitions between different ecological states occurred in as little as 40-230 yr and seem to have been controlled by the position of the Polar Front. Ecosystem response after 30 ka suggests that local climate conditions became more important. Our results demonstrate that all parts of the terrestrial system responded to the abrupt and dramatic climatic changes associated with Dansgaard-Oeschger and Heinrich events, and that regional factors modulated ecosystem response.
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| 6. |
- Ampel, Linda, et al.
(författare)
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Abrupt climate change and early lake development - the Lateglacial diatom flora at Hasseldala Port, southeastern Sweden
- 2015
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 44:1, s. 94-102
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Tidskriftsartikel (refereegranskat)abstract
- The fossil diatom record from the Hasseldala Port palaeolake, southeastern Sweden, offers an excellent opportunity to investigate how past climatic shifts influenced catchment conditions and early lake development. The record, dating to between 13900 and 11200 cal. a BP, covers a climatically dynamic period, starting with deglaciation followed by oscillations between warmer and colder climate states. The stratigraphical changes in the fossil diatom assemblages show a trend of less open-water taxa and a successively more complex periphytic community as the lake shallows and the aquatic habitat structure develops. A diatom-based reconstruction of lake water pH indicates a natural acidification trend early in the record from 13900 to 12500 cal. a BP. From 12500 cal. a BP, coincident with the start of climate cooling, to 11300 cal. a BP this trend is disrupted and lake waters become more alkaline. A cooler and drier climate most likely resulted in reduced soil organic matter build-up as well as more frozen ground that impeded hydrological flow and decreased the input of dissolved organic matter and organic acids into the lake system. This study demonstrates the importance of the hydrological system as a link between terrestrial and aquatic ecosystems during early lake ontogeny.
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| 7. |
- Ampel, Linda, et al.
(författare)
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Modest summer temperature variability during DO cycles in western Europe
- 2010
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Ingår i: Quaternary Science Reviews. - : Elsevier. - 0277-3791 .- 1873-457X. ; 29:11-12, s. 1322-1327
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Tidskriftsartikel (refereegranskat)abstract
- Abrupt climatic shifts between cold stadials and warm interstadials, termed Dansgaard-Oeschger (DO) cycles, occurred frequently during the Last Glacial. Their imprint is registered in paleorecords worldwide, but little is known about the actual temperature change both annually and seasonally in different regions. A recent hypothesis based on modelling studies, suggests that DO cycles were characterised by distinct changes in seasonality in the Northern Hemisphere. The largest temperature change between stadial and interstadial phases would have occurred during the winter and spring seasons, whereas the summer seasons would have experienced a rather muted temperature shift. Here we present a temporally high-resolved reconstruction of summer temperatures for eastern France during a sequence of DO cycles between 36 and 18 thousand years before present. The reconstruction is based on fossil diatom assemblages from the paleolake Les Echets and indicates summer temperature changes of ca 0.5–2 °C between stadials and interstadials. This study is the first to reconstruct temperatures with a sufficient time resolution to investigate DO climate variability in continental Europe. It is therefore also the first proxy record that can test and support the hypothesis that temperature changes during DO cycles were modest during the summer season.
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| 8. |
- Fernandez, Marilen, et al.
(författare)
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Diatom assemblage changes in lacustrine sediments from Isla de los Estados, southernmost South America, in response to shifts in the southwesterly wind belt during the last deglaciation
- 2013
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Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 50:4, s. 433-446
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Tidskriftsartikel (refereegranskat)abstract
- Isla de los Estados (54A degrees 45'S, 63A degrees 10'aEuro64A degrees 46'W) lies east of the main island of Tierra del Fuego and is the southeastern-most point in Argentina. Because of its geographic position near the latitudes of the Southern Hemisphere Westerlies and the strong influence of the Antarctic Circumpolar Current (ACC), the area is suitable for paleoecological and paleoclimate research. The island is not far north of the Subantarctic Front, which limits the northern boundary of the ACC. Paleoenvironmental study in this geographic location can shed light on past changes in atmospheric and marine circulation patterns. Diatom analysis of the lower part of a sediment sequence from Laguna Cascada (54A degrees 45' 51.3''S, 64A degrees 20' 20.07''W) enabled inference of changing lake conditions between 16 and 11.1 cal ka BP. Between 16 and 14.4 cal ka BP fragilarioid diatom species, often a pioneer group, dominated the record. Their presence shows seasonally open-water conditions from the onset of sedimentation. In zone II (14.4-12.8 cal ka BP), the dominance of planktonic/tychoplanktonic Aulacoseira spp. might represent longer ice-free periods and windier conditions, which would have kept this heavy species suspended in the water column. This period corresponds to the Antarctic Cold Reversal, when the Southern Hemisphere Westerlies were possibly centered on the latitudes of Tierra del Fuego, resulting in windy and wet conditions. Zone III (12.8-11.1 cal ka BP) is dominated by benthic diatom taxa that are mainly associated with peat and wetland vegetation. This suggests that climate conditions had become milder and less windy, favoring aquatic productivity and terrestrial vegetation development. This change in environmental conditions may have been a consequence of the southward movement of the Southern Hemisphere Westerlies at the start of the Antarctic Holocene thermal optimum.
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| 9. |
- Muschitiello, Francesco, et al.
(författare)
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New evidence of Holocene atmospheric circulation dynamics based on lake sediments from southern Sweden : a link to the Siberian High
- 2013
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 77, s. 113-124
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen (delta O-18) and carbon (delta C-13) isotope records of calcitic carbonate components (Chara sp. algal encrustations and Bithynia tentaculata gastropod opercula) from a lake-sediment succession on the Baltic Sea island of Gotland, south-eastern Sweden, have been obtained to investigate regional climate dynamics during the Holocene. The hydrological sensitivity of the small lake, particularly in terms of spring snowmelt contribution to the local water budget, provides a means of tracing past changes in the influence of snow-bearing easterly winds across the Baltic Sea Proper, which signifies the wintertime strength of the Siberian High. Repeated episodic depletions in O-18 at the centennial scale correlate with events of increased potassium concentration in the GISP2 ice-core record from Greenland, which indicates a coupling to large-scale fluctuations in atmospheric circulation patterns. A corresponding correlation with simultaneous depletions in C-13 suggests repeated responses of the local lake hydrology to snow-rich winters through decreasing water residence time, perhaps augmented by methanogenesis due to prolonged ice-cover seasons under the influence of an expanding Siberian High. Frequency analysis of the isotopic records reveals well-defined fluctuations at quasi-500-520-, 670-, 830- and 1430-yr periodicities, and a gradually stronger impact of Polar air outbreaks across the southern Baltic Sea region with time after ca 6000 cal. BP.
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| 10. |
- Steinthorsdottir, Margret, et al.
(författare)
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Synchronous records of pCO(2) and Delta C-14 suggest rapid, ocean-derived pCO(2) fluctuations at the onset of Younger Dryas
- 2014
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 99, s. 84-96
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Tidskriftsartikel (refereegranskat)abstract
- Just before the onset of the Younger Dryas (YD) cold event, several stomatal proxy-based pCO(2) records have shown a sharp increase in atmospheric CO2 concentration (pCO(2)) of between ca 50 and 100 ppm, followed by a rapid decrease of similar or even larger magnitude. Here we compare one of these records, a high-resolution pCO(2) record from southern Sweden, with the IntCal13 record of radiocarbon (Delta C-14). The two records show broadly synchronous fluctuations at the YD onset. Specifically, the IntCal13 record documents decreasing Delta C-14 just before the YD onset when pCO(2) peaks, consistent with a source of old CO2 from the deep ocean. We propose that this fluctuation occurred due to a major ocean flushing event. The cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor. We confirm that the earth system can produce such large multi-decadal timescale fluctuations in pCO(2) through simulating an artificial ocean flushing event with the GENIE Earth System Model. We suggest that sharp transitions of pCO(2) may have remained undetected so far in ice cores due to inter-firn gas exchange and time-averaging. The stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change.
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