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  1. Article ; Online: High-precision measurement of phenylalanine δ15N values for environmental samples: a new approach coupling high-pressure liquid chromatography purification and elemental analyzer isotope ratio mass spectrometry.

    Broek, Taylor A B / Walker, Brett D / Andreasen, Dyke H / McCarthy, Matthew D

    Rapid communications in mass spectrometry : RCM

    2013  Volume 27, Issue 21, Page(s) 2327–2337

    Abstract: Rationale: Compound-specific isotope analysis of individual amino acids (CSI-AA) is a powerful new tool for tracing nitrogen (N) source and transformation in biogeochemical cycles. Specifically, the δ(15)N value of phenylalanine (δ(15)N(Phe)) represents ...

    Abstract Rationale: Compound-specific isotope analysis of individual amino acids (CSI-AA) is a powerful new tool for tracing nitrogen (N) source and transformation in biogeochemical cycles. Specifically, the δ(15)N value of phenylalanine (δ(15)N(Phe)) represents an increasingly used proxy for source δ(15)N signatures, with particular promise for paleoceanographic applications. However, current derivatization/gas chromatography methods require expensive and relatively uncommon instrumentation, and have relatively low precision, making many potential applications impractical.
    Methods: A new offline approach has been developed for high-precision δ(15)N measurements of amino acids (δ(15)N(AA)), optimized for δ(15)N(Phe) values. Amino acids (AAs) are first purified via high-pressure liquid chromatography (HPLC), using a mixed-phase column and automated fraction collection. The δ(15)N values are determined via offline elemental analyzer-isotope ratio mass spectrometry (EA-IRMS).
    Results: The combined HPLC/EA-IRMS method separated most protein AAs with sufficient resolution to obtain accurate δ(15)N values, despite significant intra-peak isotopic fractionation. For δ(15)N(Phe) values, the precision was ±0.16‰ for standards, 4× better than gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS; ±0.64‰). We also compared a δ(15)N(Phe) paleo-record from a deep-sea bamboo coral from Monterey Bay, CA, USA, using our method versus GC/C/IRMS. The two methods produced equivalent δ(15)N(Phe) values within error; however, the δ(15)N(Phe) values from HPLC/EA-IRMS had approximately twice the precision of GC/C/IRMS (average stdev of 0.27‰ ± 0.14‰ vs 0.60‰ ± 0.20‰, respectively).
    Conclusions: These results demonstrate that offline HPLC represents a viable alternative to traditional GC/C/IMRS for δ(15)N(AA) measurement. HPLC/EA-IRMS is more precise and widely available, and therefore useful in applications requiring increased precision for data interpretation (e.g. δ(15)N paleoproxies).
    MeSH term(s) Chromatography, High Pressure Liquid/methods ; Mass Spectrometry/methods ; Nitrogen Isotopes/analysis ; Phenylalanine/analysis
    Chemical Substances Nitrogen Isotopes ; Phenylalanine (47E5O17Y3R)
    Language English
    Publishing date 2013-11-15
    Publishing country England
    Document type Journal Article
    ZDB-ID 58731-x
    ISSN 1097-0231 ; 0951-4198
    ISSN (online) 1097-0231
    ISSN 0951-4198
    DOI 10.1002/rcm.6695
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Closure of the Bering Strait caused Mid-Pleistocene Transition cooling.

    Kender, Sev / Ravelo, Ana Christina / Worne, Savannah / Swann, George E A / Leng, Melanie J / Asahi, Hirofumi / Becker, Julia / Detlef, Henrieka / Aiello, Ivano W / Andreasen, Dyke / Hall, Ian R

    Nature communications

    2018  Volume 9, Issue 1, Page(s) 5386

    Abstract: The Mid-Pleistocene Transition (MPT) is characterised by cooling and lengthening glacial cycles from 600-1200 ka, thought to be driven by reductions in glacial ... ...

    Abstract The Mid-Pleistocene Transition (MPT) is characterised by cooling and lengthening glacial cycles from 600-1200 ka, thought to be driven by reductions in glacial CO
    Language English
    Publishing date 2018-12-19
    Publishing country England
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-018-07828-0
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Out of the tropics: the Pacific, Great Basin lakes, and late Pleistocene water cycle in the western United States.

    Lyle, Mitchell / Heusser, Linda / Ravelo, Christina / Yamamoto, Masanobu / Barron, John / Diffenbaugh, Noah S / Herbert, Timothy / Andreasen, Dyke

    Science (New York, N.Y.)

    2012  Volume 337, Issue 6102, Page(s) 1629–1633

    Abstract: The water cycle in the western United States changed dramatically over glacial cycles. In the past 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation has been hypothesized to result ... ...

    Abstract The water cycle in the western United States changed dramatically over glacial cycles. In the past 20,000 years, higher precipitation caused desert lakes to form which have since dried out. Higher glacial precipitation has been hypothesized to result from a southward shift of Pacific winter storm tracks. We compared Pacific Ocean data to lake levels from the interior west and found that Great Basin lake high stands are older than coastal wet periods at the same latitude. Westerly storms were not the source of high precipitation. Instead, air masses from the tropical Pacific were transported northward, bringing more precipitation into the Great Basin when coastal California was still dry. The changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle.
    MeSH term(s) Climate ; Climate Change ; Ice Cover ; Lakes ; Rain ; United States
    Language English
    Publishing date 2012-09-28
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 128410-1
    ISSN 1095-9203 ; 0036-8075
    ISSN (online) 1095-9203
    ISSN 0036-8075
    DOI 10.1126/science.1218390
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    Zs.MG 77: Show issues

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  4. Article ; Online: Regional climate shifts caused by gradual global cooling in the Pliocene epoch.

    Ravelo, Ana Christina / Andreasen, Dyke H / Lyle, Mitchell / Olivarez Lyle, Annette / Wara, Michael W

    Nature

    2004  Volume 429, Issue 6989, Page(s) 263–267

    Abstract: The Earth's climate has undergone a global transition over the past four million years, from warm conditions with global surface temperatures about 3 degrees C warmer than today, smaller ice sheets and higher sea levels to the current cooler conditions. ... ...

    Abstract The Earth's climate has undergone a global transition over the past four million years, from warm conditions with global surface temperatures about 3 degrees C warmer than today, smaller ice sheets and higher sea levels to the current cooler conditions. Tectonic changes and their influence on ocean heat transport have been suggested as forcing factors for that transition, including the onset of significant Northern Hemisphere glaciation approximately 2.75 million years ago, but the ultimate causes for the climatic changes are still under debate. Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago. Our results suggest that mean low-latitude climate conditions can significantly influence global climate feedbacks.
    MeSH term(s) Animals ; Calcium Carbonate/analysis ; Climate ; Cold Temperature ; Geologic Sediments/chemistry ; Hot Temperature ; Ice ; Oxygen Isotopes ; Pacific Ocean ; Seawater/analysis ; Time Factors ; Tropical Climate
    Chemical Substances Ice ; Oxygen Isotopes ; Calcium Carbonate (H0G9379FGK)
    Language English
    Publishing date 2004-05-20
    Publishing country England
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 120714-3
    ISSN 1476-4687 ; 0028-0836
    ISSN (online) 1476-4687
    ISSN 0028-0836
    DOI 10.1038/nature02567
    Database MEDical Literature Analysis and Retrieval System OnLINE

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    Zs.MO 244: Show issues

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  5. Book ; Online: Holocene sea-surface reconstructions for the Californian margin, supplementary data to: Herbert, Timothy D; Schuffert, J; Andreasen, Dyke; Heusser, Linda E; Lyle, Mitchell W; Mix, Alan C; Ravelo, Ana Christina; Stott, Lowell D; Herguera, Juan Carlos (2001): Collapse of the California current during glacial maxima linked to climate change on land. Science, 293(5527), 71-76

    Herbert, Timothy D / Andreasen, Dyke / Herguera, Juan Carlos / Heusser, Linda E / Lyle, Mitchell W / Mix, Alan C / Ravelo, Ana Christina / Schuffert, J / Stott, Lowell D

    2001  

    Abstract: Time series of alkenone unsaturation indices gathered along the California margin reveal large (4° to 8°C) glacial-interglacial changes in sea surface temperature (SST) over the past 550,000 years. Interglacial times with SSTs equal to or exceeding that ... ...

    Abstract Time series of alkenone unsaturation indices gathered along the California margin reveal large (4° to 8°C) glacial-interglacial changes in sea surface temperature (SST) over the past 550,000 years. Interglacial times with SSTs equal to or exceeding that of the Holocene contain peak abundances in the pollen of redwood, the distinctive component of the temperate rainforest of the northwest coast of California. In the region now dominated by the California Current, SSTs warmed 10,000 to 15,000 years in advance of deglaciation at each of the past five glacial maxima. SSTs did not rise in advance of deglaciation south of the modern California Current front. Glacial warming along the California margin therefore is a regional signal of the weakening of the California Current during times when large ice sheets reorganized wind systems over the North Pacific. Both the timing and magnitude of the SST estimates suggest that the Devils Hole (Nevada) calcite record represents regional but not global paleotemperatures, and hence does not pose a fundamental challenge to the orbital ("Milankovitch") theory of the Ice Ages.
    Language English
    Dates of publication 2001-9999
    Size Online-Ressource
    Publisher PANGAEA - Data Publisher for Earth & Environmental Science
    Publishing place Bremen/Bremerhaven
    Document type Book ; Online
    Note This dataset is supplement to doi:10.1126/science.1059209
    DOI 10.1594/PANGAEA.701440
    Database Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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  6. Article: Millennial–scale CaCO₃ and C[subscript ORG] events along the northern and central California margins : stratigraphy and origins

    Lyle, Mitchell / Mix, Alan C. / Ravelo, A. Christina / Andreasen, Dyke / Heusser, Linda / Olivarez, Annette

    Abstract: Sediments from five Leg 167 drill sites and three piston cores were analyzed for C[subscript ORG] and CaCO₃. Oxygen isotope stratigraphy on benthic foraminifers was used to assign age models to these sedimentary records. We find that the northern and ... ...

    Abstract Sediments from five Leg 167 drill sites and three piston cores were analyzed for C[subscript ORG] and CaCO₃. Oxygen isotope stratigraphy on benthic foraminifers was used to assign age models to these sedimentary records. We find that the northern and central California margin is characterized by k.y.-scale events that can be found in both the CaCO₃ and C[subscript ORG] time series. We show that the CaCO₃ events are caused by changes in CaCO₃ production by plankton, not by dissolution. We also show that these CaCO₃ events occur in marine isotope Stages (MIS) 2, 3, and 4 during Dansgaard/Oeschger interstadials. They occur most strongly, however, on the MIS 5/4 glaciation and MIS 2/1 deglaciation. We believe that the link between the northeastern Pacific Ocean and North Atlantic is primarily transmitted by the atmosphere, not the ocean. Highest CaCO₃ production and burial occurs when the surface ocean is somewhat cooler than the modern ocean, and the surface mixed layer is somewhat more stable.
    Language en_us
    Document type Article
    Database AGRIS - International Information System for the Agricultural Sciences and Technology

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