TY  - JOUR
A1  - Schirrmeister, Lutz
A1  - Bobrov, Anatoly
A1  - Raschke, Elena
A1  - Herzschuh, Ulrike
A1  - Strauss, Jens
A1  - Pestryakova, Luidmila Agafyevna
A1  - Wetterich, Sebastian
T1  - Late Holocene ice-wedge polygon dynamics in northeastern Siberian coastal lowlands
JF  - Arctic, antarctic, and alpine research : an interdisciplinary journal
N2  - Ice-wedge polygons are common features of northeastern Siberian lowland periglacial tundra landscapes. To deduce the formation and alternation of ice-wedge polygons in the Kolyma Delta and in the Indigirka Lowland, we studied shallow cores, up to 1.3 m deep, from polygon center and rim locations. The formation of well-developed low-center polygons with elevated rims and wet centers is shown by the beginning of peat accumulation, increased organic matter contents, and changes in vegetation cover from Poaceae-, Alnus-, and Betula-dominated pollen spectra to dominating Cyperaceae and Botryoccocus presence, and Carex and Drepanocladus revolvens macro-fossils. Tecamoebae data support such a change from wetland to open-water conditions in polygon centers by changes from dominating eurybiontic and sphagnobiontic to hydrobiontic species assemblages. The peat accumulation indicates low-center polygon formation and started between 2380 +/- 30 and 1676 +/- 32 years before present (BP) in the Kolyma Delta. We recorded an opposite change from open-water to wetland conditions because of rim degradation and consecutive high-center polygon formation in the Indigirka Lowland between 2144 +/- 33 and 1632 +/- 32 years BP. The late Holocene records of polygon landscape development reveal changes in local hydrology and soil moisture.
KW  - Permafrost
KW  - cryolithology
KW  - radiocarbon dating
KW  - paleoecology
KW  - rhizopods
KW  - pollen
KW  - plant macro-fossils
Y1  - 2018
U6  - https://doi.org/10.1080/15230430.2018.1462595
SN  - 1523-0430
SN  - 1938-4246
VL  - 50
IS  - 1
PB  - Institute of Arctic and Alpine Research, University of Colorado
CY  - Boulder
ER  - 
TY  - JOUR
A1  - Kahmen, Ansgar
A1  - Sachse, Dirk
A1  - Arndt, Stefan K.
A1  - Tu, Kevin P.
A1  - Farrington, Heraldo
A1  - Vitousek, Peter M.
A1  - Dawson, Todd E.
T1  - Cellulose delta O-18 is an index of leaf-to-air vapor pressure difference (VPD) in tropical plants
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - Cellulose in plants contains oxygen that derives in most cases from precipitation. Because the stable oxygen isotope composition, delta O-18, of precipitation is associated with environmental conditions, cellulose delta O-18 should be as well. However, plant physiological models using delta O-18 suggest that cellulose delta O-18 is influenced by a complex mix of both climatic and physiological drivers. This influence complicates the interpretation of cellulose delta O-18 values in a paleo-context. Here, we combined empirical data analyses with mechanistic model simulations to i) quantify the impacts that the primary climatic drivers humidity (e(a)) and air temperature (T-air) have on cellulose delta O-18 values in different tropical ecosystems and ii) determine which environmental signal is dominating cellulose delta O-18 values. Our results revealed that e(a) and T-air equally influence cellulose delta O-18 values and that distinguishing which of these factors dominates the delta O-18 values of cellulose cannot be accomplished in the absence of additional environmental information. However, the individual impacts of e(a) and T-air on the delta O-18 values of cellulose can be integrated into a single index of plant-experienced atmospheric vapor demand: the leaf-to-air vapor pressure difference (VPD). We found a robust relationship between VPD and cellulose delta O-18 values in both empirical and modeled data in all ecosystems that we investigated. Our analysis revealed therefore that delta O-18 values in plant cellulose can be used as a proxy for VPD in tropical ecosystems. As VPD is an essential variable that determines the biogeochemical dynamics of ecosystems, our study has applications in ecological-, climate-, or forensic-sciences.
KW  - stable isotopes
KW  - plant-water relations
KW  - paleoecology
KW  - climate change
KW  - Hawaii
Y1  - 2011
U6  - https://doi.org/10.1073/pnas.1018906108
SN  - 0027-8424
VL  - 108
IS  - 5
SP  - 1981
EP  - 1986
PB  - National Acad. of Sciences
CY  - Washington
ER  -