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- Muschitiello, Francesco, et al.
(författare)
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The C20 highly branched isoprenoid biomarker – A new diatom-sourced proxy for summer trophic conditions
- 2015
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Ingår i: Organic Geochemistry. - : Elsevier BV. - 0146-6380 .- 1873-5290. ; 81, s. 27-33
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Tidskriftsartikel (refereegranskat)abstract
- The exact biological source of the C20 highly branched isoprenoid (HBI) present in sediments from aquatic systems is unclear. We therefore examined the relationship between the distribution of fossil diatoms and the concentration of the C20 HBI in a Late Glacial sedimentary record from the Hässeldala Port paleolake in southern Sweden. Using Bayesian multiple linear regression analysis, we show that its concentration is linked primarily to the production of the diatom taxon Gomphonema acuminatum, which accounts for the largest proportion of the temporal variability in the biomarker. By analogy with modern observations, we argue that an increasing amount of G. acuminatum biomass in our sedimentary record reflects increasing oligotrophy in the paleolake during the summer growing season, especially at times defined by subdued hydrologic flow. Our conclusions are corroborated by the δ13C composition of the C20 HBI biomarker, which points to a negative photosynthetic fractionation between atmospheric CO2 and the pool of dissolved inorganic carbon during diatom bloom, a distinct phenomenon at times of inhibited hydrological flow. Accordingly, we suggest that the C20 HBI biomarker can be effectively used to reconstruct the trophic state of the paleolake at Hässeldala Port, while its stable isotope composition can provide physicochemical information about the lake conditions during the dry summer season.Moreover, we note that the major hydrological shifts recorded in the G. acuminatum-C20 HBI stratigraphy do not coincide with the pollen zone boundaries. We thus infer that aquatic and terrestrial environmental responses to climate change are substantially decoupled through the hydrological system, which highlights the necessity for multi-proxy investigations to decipher past climate events.
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| 2. |
- Wohlfarth, Barbara, et al.
(författare)
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Hässeldala – a key site for Last Termination events in southern Sweden
- 2017
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Ingår i: Boreas. - London : John Wiley & Sons. - 0300-9483 .- 1502-3885. ; 46, s. 143-161
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Tidskriftsartikel (refereegranskat)abstract
- The Last Termination (19 000–11 000 a BP) with its rapid and distinct climate shifts provides a perfect laboratory to study the nature and regional impact of climate variability. The sedimentary succession from the ancient lake at Hässeldala Port in southern Sweden with its distinct Lateglacial/early Holocene stratigraphy (>14.1–9.5 cal. ka BP) is one of the few chronologically well-constrained, multi-proxy sites in Europe that capture a variety of local and regional climatic and environmental signals. Here we present Hässeldala's multi-proxy records (lithology, geochemistry, pollen, diatoms, chironomids, biomarkers, hydrogen isotopes) in a refined age model and place the observed changes in lake status, catchment vegetation, summer temperatures and hydroclimate in a wider regional context. Reconstructed mean July temperatures increased between c. 14.1 and c. 13.1 cal. ka BP and subsequently declined. This latter cooling coincided with drier hydroclimatic conditions that were probably associated with a freshening of the Nordic Seas and started a few hundred years before the onset of Greenland Stadial 1 (c. 12.9 cal. ka BP). Our proxies suggest a further shift towards colder and drier conditions as late as c. 12.7 cal. ka BP, which was followed by the establishment of a stadial climate regime (c. 12.5–11.8 cal. ka BP). The onset of warmer and wetter conditions preceded the Holocene warming over Greenland by c. 200 years. Hässeldala's proxies thus highlight the complexity of environmental and hydrological responses across abrupt climate transitions in northern Europe.
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