TY  - JOUR
A1  - Jambrina-Enriquez, Margarita
A1  - Sachse, Dirk
A1  - Valero-Garces, Blas L.
T1  - A deglaciation and Holocene biomarker-based reconstruction of climate and environmental variability in NW Iberian Peninsula: the Sanabria Lake sequence
JF  - Journal of paleolimnolog
N2  - The molecular biomarker composition of two sediment cores from Sanabria Lake (NW Iberian Peninsula) and a survey of modern plants in the watershed provide a reconstruction of past vegetation and landscape dynamics since deglaciation. During a proglacial stage in Lake Sanabria (prior to 14.7 cal ka BP), very low biomarker concentration and carbon preference index (CPI) values similar to 1 suggest that the n-alkanes could have derived from eroded ancient sediment sources or older organic matter with high degree of maturity. During the Late glacial (14.7-11.7 cal ka BP) and the Holocene (last 11.7 cal ka BP) intervals with higher biomarker and triterpenoid concentrations (high %nC(29) , nC(31) alkanes), higher CPI and average carbon length (ACL), and lower P-aq (proportion of aquatic plants) are indicative of major contribution of vascular land plants from a more forested watershed (e.g. Mid Holocene period 7.0-4.0 cal ka BP). Lower biomarker concentrations (high %nC(27) alkanes), CPI and ACL values responded to short phases with decreased allochthonous contribution into the lake that correspond to centennial-scale periods of regional forest decline (e.g. 4-3 ka BP, Roman deforestation after 2.0 ka, and some phases of the LIA, seventeenth-nineteenth centuries). Human activities in the watershed were significant during early medieval times (1.3-1.0 cal ka BP) and since 1960 CE, in both cases associated with relatively higher productivity stages in the lake (lower biomarker and triterpenoid concentrations, high %nC(23) and %nC(31) respectively, lower ACL and CPI values and higher P-aq). The lipid composition of Sanabria Lake sediments indicates a major allochthonous (watershed-derived) contribution to the organic matter budget since deglaciation, and a dominant oligotrophic status during the lake history. The study constrains the climate and anthropogenic forcings and watershed versus lake sources in organic matter accumulation processes and helps to design conservation and management policies in mountain, oligotrophic lakes.
KW  - Plant n-alkanes
KW  - Lipid biomarker
KW  - Sanabria Lake
KW  - n-Alkanes
KW  - Holocene
KW  - Lateglacial
KW  - Iberian Peninsula
Y1  - 2016
U6  - https://doi.org/10.1007/s10933-016-9890-6
SN  - 0921-2728
SN  - 1573-0417
VL  - 56
SP  - 49
EP  - 66
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Engels, Stefan
A1  - Brauer, Achim
A1  - Buddelmeijer, Nico
A1  - Martin-Puertas, Celia
A1  - Rach, Oliver
A1  - Sachse, Dirk
A1  - Van Geel, Bas
T1  - Subdecadal-scale vegetation responses to a previously unknown late-Allerod climate fluctuation and Younger Dryas cooling at Lake Meerfelder Maar (Germany)
JF  - Journal of quaternary science
N2  - Lake Meerfelder Maar (MFM) is the northernmost Western European sediment record with annual laminations across the Younger Dryas (YD), and the onset of the YD in the record of MFM has previously been defined as an increase in non-arboreal pollen abundance at ca. 12 680 varve a BP. Here we present a palynological record at unprecedented subdecadal resolution for MFM, covering the Allerod-YD transition. Our results show a fluctuation in pollen accumulation rates (PARs) before the onset of the YD, with lower rates between ca. 12 725 and 12 685 varve a BP. The fluctuation in PARs occurs simultaneous with a previously undescribed short fluctuation in sediment composition and varve thickness, as well as with changes in biogeochemical proxies. The combined evidence indicates signs of climatic instability ca. 45 years before the onset of the YD. The PAR records of Betula and Pinus furthermore show earlier and more abrupt changes at the onset of the YD than the percentage-records do. Finally, heliophilous herbaceous taxa show a delayed increase following the onset of the YD of ca. 145 years. This paper illustrates the potential to identify previously unrecognized climate variability and vegetation change when using subdecadal-resolution analyses. Copyright (C) 2016 John Wiley & Sons, Ltd.
KW  - climate instability
KW  - Lateglacial
KW  - Meerfelder Maar
KW  - pollen accumulation rates
KW  - vegetation change
Y1  - 2016
U6  - https://doi.org/10.1002/jqs.2900
SN  - 0267-8179
SN  - 1099-1417
VL  - 31
SP  - 741
EP  - 752
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -