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Infrared spectroscopy as a tool to reconstruct past lake-ecosystem changes: Method development and application in lake-sediment studies
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Natural archives such as lake sediments allow us to assess contemporary ecosystem responses to climate and environmental changes in a long-term context beyond the few decades to at most few centuries covered by monitoring or historical data. To achieve a comprehensive view of the changes preserved in sediment records, multi-proxy studies – ideally in high resolution – are necessary. However, this combination of including a range of analyses and high resolution constrains the amount of material available for analyses and increases the analytical costs. Infrared spectroscopic methods are a cost-efficient alternative to conventional methods because they offer a) a simple sample pre-treatment, b) a rapid measurement time, c) the non- or minimal consumption of sample material, and d) the potential to extract quantitative and qualitative information about organic and inorganic sediment components from a single measurement.

The main objective of this doctoral thesis was twofold. The first part was to further explore the potential of Fourier transform infrared (FTIR) and visible-near infrared (VNIR) spectroscopy in paleolimnological studies as a) an alternative tool to conventional methods for quantifying biogenic silica (bSi) – a common proxy of paleoproductivity in lakes – in sediments and b) as a tool to infer past lake-water total organic carbon (TOC) levels from sediments. In a methodological study, I developed an independent application of FTIR spectroscopy and PLS modeling for determining bSi in sediments by using synthetic sediment mixtures with known bSi content. In contrast to previous models, this model is independent from conventional wet-chemical techniques, which had thus far been used as the calibration reference, and their inherent measurement uncertainties. The second part of the research was to apply these techniques as part of three multi-proxy studies aiming to a) improve our understanding of long-term element cycling in boreal and arctic landscapes in response to climatic and environmental changes, and b) to assess ongoing changes, particularly in lake-water TOC, on a centennial to millennial time scale.

In the first applied study, high-resolution FTIR measurements of the 318-m long sediment record of Lake El’gygytgyn provided a detailed insight into long-term climate variability in the Siberian Arctic over the past 3.6 million years. Highest bSi accumulation occurred during the warm middle Pliocene (3.6-3.3 Ma), followed by a gradual but variable decline, which reflects the first onset of glacial periods and then the finally full establishment of glacial–interglacial cycles during the Quaternary. The second applied study investigated the sediment record of Torneträsk in subarctic northern Sweden also in relation to climate change, but only over the recent post-glacial period (~10 ka). By comparing responses to past climatic and environmental forcings that were recorded in this large-lake system with those recorded in small lakes from its catchment, I determined the significance and magnitude of larger-scale changes across the study region. Three different types of response were identified over the Holocene: i) a gradual response to the early landscape development following deglaciation (~10000-5300 cal yr BP); ii) an abrupt but delayed response following climate cooling during the late Holocene, which occurred c. 1300 cal yr BP – about 1000-2000 years later than in smaller lakes from the area; and iii) an immediate response to the ongoing climate change during the past century. The rapid, recent response in a previously rather insensitive lake-ecosystem emphasizes the unprecedented scale of ongoing climate change in northern Fennoscandia. In the third applied study, VNIR-inferred lake-water TOC concentrations from lakes across central Sweden showed that the ongoing, observed increase in surface water TOC in this region was in fact preceded by a long-term decline beginning already AD 1450-1600. These dynamics coincided with early human land use activities in the form of widespread summer forest grazing and farming that ceased over the past century. The results of this study show the strong impact of past human activities on past as well as ongoing TOC levels in surface waters, which has thus far been underestimated. The research in this thesis demonstrates that infrared spectroscopic methods can be an essential component in high-resolution, multi-proxy studies of past environmental and climate changes.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2015. , 25 p.
Keyword [en]
Fourier transform infrared spectroscopy, visible-near infrared spectroscopy, PLS regression, biogenic silica, climate change, carbon cycling, lake-water quality, geochemistry, paleolimnology, Holocene, Lake El’gygytgyn, Torneträsk
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:umu:diva-111629ISBN: 978-91-7601-372-4 (print)OAI: oai:DiVA.org:umu-111629DiVA: diva2:872271
Public defence
2015-12-11, KBC-huset, Lilla Hörsalen, KB3A9, Umeå universitet, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2015-11-20 Created: 2015-11-18 Last updated: 2016-11-11Bibliographically approved
List of papers
1. Biogeochemical variability during the past 3.6 million years recorded by FTIR spectroscopy in the sediment record of Lake El'gygytgyn, Far East Russian Arctic
Open this publication in new window or tab >>Biogeochemical variability during the past 3.6 million years recorded by FTIR spectroscopy in the sediment record of Lake El'gygytgyn, Far East Russian Arctic
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2014 (English)In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 10, no 1, 209-220 p.Article in journal (Refereed) Published
Abstract [en]

A number of studies have shown that Fourier transform infrared spectroscopy (FTIRS) can be applied to quantitatively assess lacustrine sediment constituents. In this study, we developed calibration models based on FTIRS for the quantitative determination of biogenic silica (BSi; n = 420; gradient: 0.9-56.5 %), total organic carbon (TOC; n = 309; gradient: 0-2.9 %), and total inorganic carbon (TIC; n = 152; gradient: 0-0.4 %) in a 318 m-long sediment record with a basal age of 3.6 million years from Lake El'gygytgyn, Far East Russian Arctic. The developed partial least squares (PLS) regression models yield high cross-validated (CV) R-CV(2) = 0.86-0.91 and low root mean square error of cross-validation (RMSECV) (3.1-7.0% of the gradient for the different properties). By applying these models to 6771 samples from the entire sediment record, we obtained detailed insight into bioproductivity variations in Lake El'gygytgyn throughout the middle to late Pliocene and Quaternary. High accumulation rates of BSi indicate a productivity maximum during the middle Pliocene (3.6-3.3 Ma), followed by gradually decreasing rates during the late Pliocene and Quaternary. The average BSi accumulation during the middle Pliocene was similar to 3 times higher than maximum accumulation rates during the past 1.5 million years. The indicated progressive deterioration of environmental and climatic conditions in the Siberian Arctic starting at ca. 3.3 Ma is consistent with the first occurrence of glacial periods and the finally complete establishment of glacial-interglacial cycles during the Quaternary.

Place, publisher, year, edition, pages
European Geosciences Union (EGU), 2014
Keyword
transform infrared-spectroscopy; pliocene sea-level; ne russia; humic substances; oxygen isotopes; biogenic silica; geochemistry; indicator; carbonate; spectra
National Category
Geology Meteorology and Atmospheric Sciences
Identifiers
urn:nbn:se:umu:diva-88687 (URN)10.5194/cp-10-209-2014 (DOI)000333837600015 ()
Available from: 2014-05-15 Created: 2014-05-12 Last updated: 2017-12-05Bibliographically approved
2. Independent measurement of biogenic silica in sediments by FTIR spectroscopy and PLS regression
Open this publication in new window or tab >>Independent measurement of biogenic silica in sediments by FTIR spectroscopy and PLS regression
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2014 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 52, no 3, 245-255 p.Article in journal (Refereed) Published
Abstract [en]

We present an independent calibration model for the determination of biogenic silica (BSi) in sediments, developed from analysis of synthetic sediment mixtures and application of Fourier transform infrared spectroscopy (FTIRS) and partial least squares regression (PLSR) modeling. In contrast to current FTIRS applications for quantifying BSi, this new calibration is independent from conventional wet-chemical techniques and their associated measurement uncertainties. This approach also removes the need for developing internal calibrations between the two methods for individual sediments records. For the independent calibration, we produced six series of different synthetic sediment mixtures using two purified diatom extracts, with one extract mixed with quartz sand, calcite, 60/40 quartz/calcite and two different natural sediments, and a second extract mixed with one of the natural sediments. A total of 306 samples-51 samples per series-yielded BSi contents ranging from 0 to 100 %. The resulting PLSR calibration model between the FTIR spectral information and the defined BSi concentration of the synthetic sediment mixtures exhibits a strong cross-validated correlation ( = 0.97) and a low root-mean square error of cross-validation (RMSECV = 4.7 %). Application of the independent calibration to natural lacustrine and marine sediments yields robust BSi reconstructions. At present, the synthetic mixtures do not include the variation in organic matter that occurs in natural samples, which may explain the somewhat lower prediction accuracy of the calibration model for organic-rich samples.

Place, publisher, year, edition, pages
Springer Netherlands, 2014
Keyword
biogenic silica, Fourier transform infrared spectroscopy (FTIRS), bioproductivity, silicon cycle, paleoceanography, paleolimnology
National Category
Oceanography, Hydrology, Water Resources
Identifiers
urn:nbn:se:umu:diva-95265 (URN)10.1007/s10933-014-9791-5 (DOI)000342338700009 ()
Available from: 2014-10-31 Created: 2014-10-27 Last updated: 2017-12-05Bibliographically approved
3. Regional Holocene climate and landscape changes recorded in the large subarctic lake Torneträsk, N Fennoscandia
Open this publication in new window or tab >>Regional Holocene climate and landscape changes recorded in the large subarctic lake Torneträsk, N Fennoscandia
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2017 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 487, 1-14 p.Article in journal (Refereed) Published
Abstract [en]

Understanding the response of sensitive Arctic and subarctic landscapes to climate change is essential to determine the risks of ongoing and projected climate warming. However, these responses will not be uniform in terms of timing and magnitude across the landscape because of site-specific differences in ecosystem susceptibility to climate forcing. Here we present a multi-proxy analysis of a sediment record from the 330-km2 lake Torneträsk to assess the sensitivity of the Fennoscandian subarctic landscape to climate change over the past ~ 9500 years. By comparing responses of this large-lake system to past climatic and environmental changes with those in small lakes in its catchment, we assessed when the magnitude of change was sufficient to affect an entire region rather than only specific sub-catchments that may be more sensitive to localized environmental changes such as, e.g., tree-line dynamics. Our results show three periods of regional landscape alteration with distinct change in sediment composition: i) landscape development following deglaciation and through the Holocene Thermal Maximum, ~ 9500–3400 cal yr BP; ii) increased soil erosion during the Little Ice Age (LIA); and iii) rapid change during the past century coincident with ongoing climate change. The gradual landscape development led to successive changes in the lake sediment composition over several millennia, whereas climate cooling during the late Holocene caused a rather abrupt shift occurring within ~ 100 years. However, this shift at the onset of the LIA (~ 750 cal yr BP) occurred > 2000 years later than the first indications for climate cooling recorded in small lakes in the Torneträsk catchment, suggesting that a critical ecosystem threshold was not crossed until the LIA. In contrast, the ongoing response to recent climate change was immediate, emphasizing the unprecedented scale of ongoing climate changes in subarctic Fennoscandia.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Inorganic geochemistry, Soil erosion, Climate change, Oxygen and silicon isotopes, Holocene, Scandinavia
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-111628 (URN)10.1016/j.palaeo.2017.08.001 (DOI)000414881100001 ()
Note

Originally published in thesis in manuscript form 2015 with the title "Holocene ecosystem ontogeny and element cycling in the subarctic catchment of lake Torneträsk, NW Sweden : large lake sensitivity to climate change" by authors Carsten Meyer-Jacob, Richard Bindler, Christian Bigler, Melanie J. Leng and Hendrik Vogel.

Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2017-12-06Bibliographically approved
4. Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring
Open this publication in new window or tab >>Early land use and centennial scale changes in lake-water organic carbon prior to contemporary monitoring
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2015 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 112, no 21, 6579-6584 p.Article in journal (Refereed) Published
Abstract [en]

Organic carbon concentrations have increased in surface waters across parts of Europe and North America during the past decades, but the main drivers causing this phenomenon are still debated. A lack of observations beyond the last few decades inhibits a better mechanistic understanding of this process and thus a reliable prediction of future changes. Here we present past lake-water organic carbon trends inferred from sediment records across central Sweden that allow us to assess the observed increase on a centennial to millennial time scale. Our data show the recent increase in lake-water carbon but also that this increase was preceded by a landscape-wide, long-term decrease beginning already A. D. 1450-1600. Geochemical and biological proxies reveal that these dynamics coincided with an intensification of human catchment disturbance that decreased over the past century. Catchment disturbance was driven by the expansion and later cessation of widespread summer forest grazing and farming across central Scandinavia. Our findings demonstrate that early land use strongly affected past organic carbon dynamics and suggest that the influence of historical landscape utilization on contemporary changes in lake-water carbon levels has thus far been underestimated. We propose that past changes in land use are also a strong contributing factor in ongoing organic carbon trends in other regions that underwent similar comprehensive changes due to early cultivation and grazing over centuries to millennia.

Place, publisher, year, edition, pages
National Academy of Sciences, 2015
Keyword
lake-water quality, carbon cycling, land use, Holocene, paleoecology
National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-105255 (URN)10.1073/pnas.1501505112 (DOI)000355213200034 ()25964363 (PubMedID)
Available from: 2015-06-24 Created: 2015-06-22 Last updated: 2017-12-04Bibliographically approved

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