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  • Proceedings of the National Academy of Sciences  (3)
  • 1
    Online Resource
    Online Resource
    Redox-dependent niche differentiation provides evidence for multiple bacterial sources of glycerol tetraether lipids in lakes
    Proceedings of the National Academy of Sciences ; 2018
    In:  Proceedings of the National Academy of Sciences Vol. 115, No. 43 ( 2018-10-23), p. 10926-10931
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 115, No. 43 ( 2018-10-23), p. 10926-10931
    Abstract: Terrestrial paleoclimate archives such as lake sediments are essential for our understanding of the continental climate system and for the modeling of future climate scenarios. However, quantitative proxies for the determination of paleotemperatures are sparse. The relative abundances of certain bacterial lipids, i.e., branched glycerol dialkyl glycerol tetraethers (brGDGTs), respond to changes in environmental temperature, and thus have great potential for climate reconstruction. Their application to lake deposits, however, is hampered by the lack of fundamental knowledge on the ecology of brGDGT-producing microbes in lakes. Here, we show that brGDGTs are synthesized by multiple groups of bacteria thriving under contrasting redox regimes in a deep meromictic Swiss lake (Lake Lugano). This niche partitioning is evidenced by highly distinct brGDGT inventories in oxic vs. anoxic water masses, and corresponding vertical patterns in bacterial 16S rRNA gene abundances, implying that sedimentary brGDGT records are affected by temperature-independent changes in the community composition of their microbial producers. Furthermore, the stable carbon isotope composition (δ 13 C) of brGDGTs in Lake Lugano and 34 other (peri-)Alpine lakes attests to the widespread heterotrophic incorporation of 13 C-depleted, methane-derived biomass at the redox transition zone of mesotrophic to eutrophic lake systems. The brGDGTs produced under such hypoxic/methanotrophic conditions reflect near-bottom water temperatures, and are characterized by comparatively low δ 13 C values. Depending on climate zone and water depth, lake sediment archives predominated by deeper water/low- 13 C brGDGTs may provide more reliable records of climate variability than those where brGDGTs derive from terrestrial and/or aquatic sources with distinct temperature imprints.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1805186115
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2018
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 2
    Online Resource
    Online Resource
    Nitrogen isotope effects induced by anammox bacteria
    Proceedings of the National Academy of Sciences ; 2013
    In:  Proceedings of the National Academy of Sciences Vol. 110, No. 47 ( 2013-11-19), p. 18994-18999
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 110, No. 47 ( 2013-11-19), p. 18994-18999
    Abstract: Nitrogen (N) isotope ratios ( 15 N/ 14 N) provide integrative constraints on the N inventory of the modern ocean. Anaerobic ammonium oxidation (anammox), which converts ammonium and nitrite to dinitrogen gas (N 2 ) and nitrate, is an important fixed N sink in marine ecosystems. We studied the so far unknown N isotope effects of anammox in batch culture experiments. Anammox preferentially removes 14 N from the ammonium pool with an isotope effect of +23.5‰ to +29.1‰, depending on factors controlling reversibility. The N isotope effects during the conversion of nitrite to N 2 and nitrate are ( i ) inverse kinetic N isotope fractionation associated with the oxidation of nitrite to nitrate (−31.1 ± 3.9‰), ( ii ) normal kinetic N isotope fractionation during the reduction of nitrite to N 2 (+16.0 ± 4.5‰), and ( iii ) an equilibrium N isotope effect between nitrate and nitrite (−60.5 ± 1.0‰), induced when anammox is exposed to environmental stress, leading to the superposition of N isotope exchange effects upon kinetic N isotope fractionation. Our findings indicate that anammox may be responsible for the unresolved large N isotope offsets between nitrate and nitrite in oceanic oxygen minimum zones. Irrespective of the extent of N isotope exchange between nitrate and nitrite, N removed from the combined nitrite and nitrate (NO x ) pool is depleted in 15 N relative to NO x . This net N isotope effect by anammox is superimposed on the N isotope fractionation by the co-occurring reduction of nitrate to nitrite in suboxic waters, possibly enhancing the overall N isotope effect for N loss from oxygen minimum zones.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1310488110
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2013
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
    Location Call Number Limitation Availability
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    Online Resource
  • 3
    Online Resource
    Online Resource
    Nutrient regime shift in the western North Atlantic indicated by compound-specific δ 15 N of deep-sea gorgonian corals
    Proceedings of the National Academy of Sciences ; 2011
    In:  Proceedings of the National Academy of Sciences Vol. 108, No. 3 ( 2011-01-18), p. 1011-1015
    Details
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 108, No. 3 ( 2011-01-18), p. 1011-1015
    Abstract: Despite the importance of the nitrogen (N) cycle on marine productivity, little is known about variability in N sources and cycling in the ocean in relation to natural and anthropogenic climate change. Beyond the last few decades of scientific observation, knowledge depends largely on proxy records derived from nitrogen stable isotopes ( δ 15 N) preserved in sediments and other bioarchives. Traditional bulk δ 15 N measurements, however, represent the combined influence of N source and subsequent trophic transfers, often confounding environmental interpretation. Recently, compound-specific analysis of individual amino acids ( δ 15 N-AA) has been shown as a means to deconvolve trophic level versus N source effects on the δ 15 N variability of bulk organic matter. Here, we demonstrate the first use of δ 15 N-AA in a paleoceanographic study, through analysis of annually secreted growth rings preserved in the organic endoskeletons of deep-sea gorgonian corals. In the Northwest Atlantic off Nova Scotia, coral δ 15 N is correlated with increasing presence of subtropical versus subpolar slope waters over the twentieth century. By using the new δ 15 N-AA approach to control for variable trophic processing, we are able to interpret coral bulk δ 15 N values as a proxy for nitrate source and, hence, slope water source partitioning. We conclude that the persistence of the warm, nutrient-rich regime since the early 1970s is largely unique in the context of the last approximately 1,800 yr. This evidence suggests that nutrient variability in this region is coordinated with recent changes in global climate and underscores the broad potential of δ 15 N-AA for paleoceanographic studies of the marine N cycle.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    URL: Article
    DOI: 10.1073/pnas.1004904108
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2011
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
    Online Resource
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