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Quantitative multiproxy assessment of long-term patterns of Holocene environmental change from a small lake near Abisko, northern Sweden
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
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2002 (English)In: The Holocene, ISSN 0959-6836, E-ISSN 1477-0911, Vol. 12, no 4, 481-496 p.Article in journal (Refereed) Published
Abstract [en]

Quantitative reconstructions are made of Holocene changes in climatic and environmental conditions from analyses of pollen, chironomids and diatoms in identical stratigraphic levels of a sediment core from Vuoskku-javri (68degrees20'43 N, 19degrees06'00 E, 348 m a.s.l.) near Abisko in northern Sweden (Lapland). Transfer functions, based on regional calibration sets, are applied to reconstruct Holocene patterns in mean July air temperature (using all three indicators). mean January air temperature (pollen), annual precipitation (pollen) and lakewater pH (diatoms). During periods with 'good' fit to the modern calibration sets all mean July air-temperature inferences based on the three proxy indicators reveal a general trend of decreasing temperature: pollen-inferred mean July air temperature shows a decrease of c, 1.1degreesC since 7500 cal. yrs BP; the chironomids show a decrease of c. 1.2degreesC since the early Holocene whereas the diatoms show a decrease of c. 1.5degreesC since 6000 cal. yrs BP. Pollen-inferred mean January air temperature indicates that winters may have been warmer by c. 3.0degreesC during the early Holocene, followed by a gradual cooling until 8500 cal. yrs BP (c. 1.0degreesC warmer than today) and a subsequent warming until 7000 cal. yrs BP (c. 2.0degreesC warmer than today). Since 7000 cal, yrs BP, a gradual cooling towards the present-day values is inferred. According to the pollen, annual precipitation may have been considerably higher during the early Holocene than today (c. +150 mm) and increased until 7000 cal. yrs BP (c. +320 mm). Since 7000 cal. yrs BP, annual precipitation decreased continuously towards present-day values. Diatom-inferred pH trends show that natural acidification of c. 0.5 pH units followed deglaciation; present-day values were reached c. 5000 cal. yrs BP. The early Holocene is identified as a problematic time period for the application of modern calibration sets. as diatoms show 'poor' fit to the calibration set from 10 600 to 6000 cal. yrs BP. pollen from 10 600 to 7500 cal. yrs BP, and chironomids from 10 250 to 10 000 cal. yrs BP. Compared with estimates from the COHMAP GCM model, mean July air-temperature inferences based on biological proxies at Vuoskkujavri suggest a more moderate decrease in temperature over the past 9000 years.

Place, publisher, year, edition, pages
2002. Vol. 12, no 4, 481-496 p.
Keyword [en]
pollen, chironomids, diatoms, Subarctic, Lapland, precipitation, pH, temperature, multiproxy approach, quantitative inferences, weighted averaging partial least squares (WA-PLS), Holocene
National Category
Physical Geography
Identifiers
URN: urn:nbn:se:umu:diva-2797DOI: 10.1191/0959683602hl559rpISI: 000176583900009OAI: oai:DiVA.org:umu-2797DiVA: diva2:141071
Available from: 2001-11-01 Created: 2001-11-01 Last updated: 2014-08-29Bibliographically approved
In thesis
1. Diatoms as indicators of Holocene climate and environmental change in northern Sweden
Open this publication in new window or tab >>Diatoms as indicators of Holocene climate and environmental change in northern Sweden
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of the thesis was to explore the potential of diatoms (Bacillariophyceae) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions.

Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP).

Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring Fragilaria species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.

Place, publisher, year, edition, pages
Umeå: Ekologi och geovetenskap, 2001. 19 p.
Keyword
Physical geography and sedimentology, diatoms, Holocene, paleolimnology, climate change, lake sediments, transfer functions, quantitative environmental reconstructions, northern Sweden, Abisko, Naturgeografi och sedimentologi
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:umu:diva-144 (URN)91-7305-134-9 (ISBN)
Public defence
2001-12-06, Umeå, 10:00
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Available from: 2001-11-01 Created: 2001-11-01Bibliographically approved

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