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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Soil Science Society of America journal 63 (1999), S. 1181-1187 
    ISSN: 1435-0661
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 14 C-dated by accelerator mass spectrometry (AMS) and compared with 14C ages of total organic C (TOC) of bulk soils and acid-hydrolyzed residues. In all cases, aliphatic hydrocarbons were significantly older than TOC but comparable with (in some cases older than) hydrolyzed residues, indicating that the 14C content of aliphatic hydrocarbons reflects the age of a passive-fraction C. The age differences between the aliphatic hydrocarbons and TOC increase with the degree of mineralization: thus, up to a 10000 yr difference in age is observed for highly mineralized horizons in podzol and acid brown earth. The leaf-wax n-alkanes (C25 to C33) isolated from a peaty gley core show a virtually linear relationship between their ages and the depth. In contrast to bulk soil organic matter that contains younger C deposited by plant roots and by water leaching, leaf wax n-alkanes are contributed at the soil surface by the leaves of dead plants and are of low mobility due to their extremely low water-solubility. The low biodegradability of long-chain n-alkanes leads to their persistence in the soil horizons where they were originally deposited. Therefore, their ages are ideal as chronological indicators for soils and peats.
    Materialart: Digitale Medien
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  • 2
    Publikationsdatum: 2014-06-25
    Beschreibung: wo commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
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  • 3
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Organic Geochemistry 125 (2018): 70-81, doi: 10.1016/j.orggeochem.2018.08.008.
    Beschreibung: Reconstructions of climate using leaf wax D/H ratios (δDwax) require accounting for the apparent isotopic fractionation (εapp) between plant source water and waxes. There have been conflicting publications on whether plants in the Arctic growing under 24-hour continuous light, fractionate less than temperate and tropical plants. In this study, we examine the effect of diurnal light (DL) versus 24-hour continuous light (CL) on the isotopic composition of leaf n-alkanes and n-acids in greenhouse experiments using two common Arctic plants (Eriophorum vaginatum, or tussock cottongrass and Betula nana, or dwarf birch). For E. vaginatum, the δDwax values of various wax homologues were 5–11‰ more positive for CL plants relative to their DL counterparts, whereas for B. nana, CL waxes were 3–24‰ more negative, suggesting that daylight length is not a unifying control on leaf wax D/H ratios of Arctic plants. The δ13Cwax of B. nana was more negative for plants grown in continuous light compared to diurnal light, reflecting lower water-use efficiency, associated with prolonged stomatal opening in the CL treatment. We modeled the impact of increasing stomatal conductance and effective flow path lengths (mimicking variable leaf morphologies) on the isotopic composition of leaf waters (δDlw) and find that variations in leaf-water enrichment may explain the variable δDwax responses seen between E. vaginatum and B. nana. We suggest that between-species differences in the δDlw response to light, and differences in the utilization of stored carbohydrates, were important for governing δDwax. Our greenhouse results suggest that Arctic plant leaf waxes do not consistently display reduced εapp values as a result of 24-hour day light, providing additional support for field observations.
    Beschreibung: We thank Fred Jackson and Chris Claussen of the Brown University Plant Environmental Center for assistance with growth chambers, Chelsea Parker for assistance in plant care, and Rafael Tarozo for laboratory assistance. We want to thank Trevor Porter and three anonymous reviewers for constructive comments to improve the manuscript. This work was funded by NSF Arctic Natural Sciences grant 1503846 to Yongsong Huang and James Russell and NSF-OPP grant 1603214 to Anne Giblin. We also acknowledge graduate support for Will Daniels from the Brown-MBL joint graduate program and the Institute at Brown for Environment and Society.
    Schlagwort(e): Leaf waxes ; Hydrogen isotopes ; Carbon isotopes ; Growth experiment ; Arctic ; Continuous light
    Repository-Name: Woods Hole Open Access Server
    Materialart: Preprint
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): G03013, doi:10.1029/2005JG000121.
    Beschreibung: The 18S ribosomal DNA (rDNA) sequences of haptophyte algae were successfully amplified using the polymerase chain reaction (PCR) from water filtrate, surface sediments, and a late-Holocene sediment sample (∼1000 years old) from a group of lakes in the Søndre Strømfjord region of west Greenland. The DNA of the algal primary producer is extremely well preserved in the laminated lake sediments which have been deposited in cold (1°–2°C), anoxic, and sulphidic bottom water. Phylogenetic analyses of the Greenland haptophyte rDNA sequences suggest that alkenones in the Greenland lake sediments are produced by haptophyte algae of the class Prymnesiophyceae. The 18S rDNA sequences from the Greenland samples cluster within a distinct phylotype, differing from both marine haptophytes and from those reported previously from Ace Lake, Antarctica. The similarity of haptophyte rDNA sequences among all samples in this study suggests a single alkenone-based temperature calibration may be applied to these lakes for at least the past 1000 years. These sedimentary archives hold great promise for high-resolution, alkenone-based paleotemperature reconstruction of southern west Greenland, a region sensitive to atmospheric-oceanic climate phenomena such as the North Atlantic Oscillation (NAO).
    Beschreibung: This work was supported by grants from the National Science Foundation (NSF0081478, 0318050, 0318123, 0402383, 0520718), NASA (NAG5-10665, NNG04GJ34G) and the American Chemical Society, Petroleum Research Fund (ACS-PRF38878-AC2) to Y. Huang.
    Schlagwort(e): Alkenone ; RDNA ; Haptophyte
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 5
    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): D19108, doi:10.1029/2012JD018060.
    Beschreibung: Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September–November (SON) season is important for hydroclimate in Borneo. The preëminence of the SON season suggests that a seasonally lagged relationship between the Indian
    Beschreibung: J. Tierney acknowledges the NOAA Climate and Global Change Postdoctoral Fellowship for support.
    Beschreibung: 2013-04-04
    Schlagwort(e): Holocene climate ; Indian monsoon ; Indo-Pacific warm pool ; Leaf waxes ; Stable isotopes ; Walker circulation
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: application/pdf
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  • 6
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 5263–5285, doi:10.1002/2013GC004904.
    Beschreibung: Two commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.
    Beschreibung: S.S. thanks the Netherlands Organisation for Scientific Research (NWO) for financial support through a VICI grant and Jaap van der Meer for advice and support on the statistical analysis. A.P. thanks Susan Carter for laboratory assistance and NSF-OCE for funding. A.R.M. thanks Jordi Coello and N uria Moraleda for advice and support on the statistical analysis and Spanish Ministry for research and innovation (MICIIN) for funding. V.G. thanks Xavier Philippon and Carl Johnson for technical assistance. K.G. and M.W. thank the Australian Research Council and John de Laeter Centre for funding toward the LC-MS system, and ARC Fellowship awarded to K.G. C.L.Z. thanks the State Key Laboratory of Marine Geology and the Chinese ‘‘National Thousand Talents’’ program for supporting the LC-MS work performed at Tongji University.
    Beschreibung: 2014-06-20
    Schlagwort(e): TEX86 ; BIT ; GDGT ; Round robin
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
    Format: text/plain
    Format: application/msword
    Format: application/pdf
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  • 7
    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 78 (2012): 51–64, doi:10.1016/j.gca.2011.11.024.
    Beschreibung: Long chain alkenones (LCAs) are potential biomarkers for quantitative paleotemperature reconstructions from lacustrine environments. However, progress in this area has been severely hindered by the lack of culture studies of haptophytes responsible for alkenone distributions in lake sediments: the predominance of C37:4 LCA. Here we report the first enrichment culturing of a novel haptophyte phylotype (Hap-A) from Lake George, ND that produces predominantly C37:4-LCA. Hap-A was enriched from its resting phase collected from deep sediments rather than from water column samples. In contrast, enrichments from near surface water yielded a different haptophyte phylotype (Hap-B), closely related to Chrysotila lamellosa and Pseudoisochrysis paradoxa, which does not display C37:4-LCA predominance (similar enrichments have been reported previously). The LCA profile in sediments resembles that of Hap-A enrichments, suggesting that Hap-A is the dominant alkenone producer of the sedimentary LCAs. In enrichments, excess lighting appeared to be crucial for triggering blooms of Hap-A. Both and indices show a linear relationship with temperature for Hap-A in enrichments, but the relationship appears to be dependent on the growth stage. Based on 18S rRNA gene analyses, several lakes from the Northern Great Plains, as well as Pyramid Lake, NV and Tso Ur, Tibetan Plateau, China contain the same two haptophyte phylotypes. The Great Plains lakes show the Hap-A-type LCA distribution, whereas Pyramid and Tso Ur show the Hap-B type distribution. Waters of the Great Plain lakes are dominated by sulfate, whereas those Pyramid and Tso Ur are dominated by carbonate, suggesting that the sulfate to carbonate ratio may be a determining factor for the competitiveness of the Hap-A and Hap-B phylotypes in natural settings.
    Beschreibung: This work was supported by a grant from the National Science Foundation to Y. Huang (EAR06-02325) and a Brown University Graduate School Dissertation Fellowship to J. L. Toney.
    Repository-Name: Woods Hole Open Access Server
    Materialart: Preprint
    Format: application/pdf
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  • 8
    Publikationsdatum: 2022-05-26
    Beschreibung: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dunlea, A. G., Giosan, L., & Huang, Y. Pliocene expansion of C-4 vegetation in the core monsoon zone on the Indian Peninsula. Climate of the Past, 16(6), (2020): 2533-2546, https://doi.org/10.5194/cp-16-2533-2020.
    Beschreibung: The expansion of C4 vegetation during the Neogene was one of the largest reorganizations of Earth's terrestrial biome. Once thought to be globally synchronous in the late Miocene, site-specific studies have revealed differences in the timing of the expansion and suggest that local conditions play a substantial role. Here, we examine the expansion of C4 vegetation on the Indian Peninsula since the late Miocene by constructing a ∼6-million-year paleorecord with marine sediment from the Bay of Bengal at Site U1445, drilled during International Ocean Discovery Program Expedition 353. Analyses of element concentrations indicate that the marine sediment originates from the Mahanadi River in the Core Monsoon Zone (CMZ) of the Indian Peninsula. Hydrogen isotopes of the fatty acids of leaf waxes reveal an overall decrease in the CMZ precipitation since the late Miocene. Carbon isotopes of the leaf wax fatty acids suggest C4 vegetation on the Indian Peninsula existed before the end of the Miocene but expanded to even higher abundances during the mid-Pliocene to mid-Pleistocene (∼3.5 to 1.5 million years ago). Similar to the CMZ on the Indian Peninsula, a Pliocene expansion or re-expansion has previously been observed in northwest Australia and in East Africa, suggesting that these tropical ecosystems surrounding the Indian Ocean remained highly sensitive to changes in hydroclimate after the initial spread of C4 plants in late Miocene.
    Beschreibung: This research has been supported by the Ocean and Climate Change Institute Postdoctoral Scholarship at Woods Hole Oceanographic Institution to Ann Dunlea, and the U.S. National Science Foundation to Liviu Giosan (grant no. NSF OCE-0652315). USSSP post-cruise support was provided to Expedition 353 shipboard participants Liviu Giosan and Yongsong Huang.
    Repository-Name: Woods Hole Open Access Server
    Materialart: Article
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  • 9
    Publikationsdatum: 2024-11-22
    Beschreibung: Ratios of glycerol dialkyl glycerol tetraethers (GDGT), which are membrane lipids of bacteria and archaea, are at the base of several paleoenvironmental proxies. They are frequently applied to soils as well as lake‐ and marine sediments to generate records of past temperature and soil pH. To derive meaningful environmental information from these reconstructions, high analytical reproducibility is required. Based on submitted results by 39 laboratories from across the world, which employ a diverse range of analytical and quantification methods, we explored the reproducibility of brGDGT‐based proxies (MBT′5ME, IR, and #ringstetra) measured on four soil samples and four soil lipid extracts. Correct identification and integration of 5‐ and 6‐methyl brGDGTs is a prerequisite for the robust calculation of proxy values, but this can be challenging as indicated by the large inter‐interlaboratory variation. The exclusion of statistical outliers improves the reproducibility, where the remaining uncertainty translates into a temperature offset from median proxy values of 0.3–0.9°C and a pH offset of 0.05–0.3. There is no apparent systematic impact of the extraction method and sample preparation steps on the brGDGT ratios. Although reported GDGT concentrations are generally consistent within laboratories, they vary greatly between laboratories. This large variability in brGDGT quantification may relate to variations in ionization efficiency or specific mass spectrometer settings possibly impacting the response of brGDGTs masses relative to that of the internal standard used. While ratio values of GDGT are generally comparable, quantities can currently not be compared between laboratories.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
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  • 10
    Publikationsdatum: 2025-02-25
    Beschreibung: During the Pleistocene-Holocene transition, the dominant mammoth steppe ecosystem across northern Eurasia vanished, in parallel with megafauna extinctions. However, plant extinction patterns are rarely detected due to lack of identifiable fossil records. Here, we introduce a method for detection of plant taxa loss at regional (extirpation) to potentially global scale (extinction) and their causes, as determined from ancient plant DNA metabarcoding in sediment cores (sedaDNA) from lakes in Siberia and Alaska over the past 28,000 years. Overall, potential plant extinctions track changes in temperature, in vegetation, and in megafauna extinctions at the Pleistocene-Holocene transition. Estimated potential plant extinction rates were 1.7-5.9 extinctions per million species years (E/MSY), above background extinction rates but below modern estimates. Major potential plant extinction events were detected around 17,000 and 9000 years ago which lag maximum vegetation turnover. Our results indicate that herbaceous taxa and taxa contributing less to beta diversity are more vulnerable to extinction. While the robustness of the estimates will increase as DNA reference libraries and ancient sedaDNA data expand, the available data support that plants are more resilient to environmental changes than mammals.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , isiRev
    Format: application/pdf
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