TY  - GEN
A1  - Acevedo, Walter
A1  - Fallah, Bijan
A1  - Reich, Sebastian
A1  - Cubasch, Ulrich
T1  - Assimilation of pseudo-tree-ring-width observations into an atmospheric general circulation model
T2  - Postprints der Universität Potsdam : Mathematisch Naturwissenschaftliche Reihe
N2  - Paleoclimate data assimilation (DA) is a promising technique to systematically combine the information from climate model simulations and proxy records. Here, we investigate the assimilation of tree-ring-width (TRW) chronologies into an atmospheric global climate model using ensemble Kalman filter (EnKF) techniques and a process-based tree-growth forward model as an observation operator. Our results, within a perfect-model experiment setting, indicate that the "online DA" approach did not outperform the "off-line" one, despite its considerable additional implementation complexity. On the other hand, it was observed that the nonlinear response of tree growth to surface temperature and soil moisture does deteriorate the operation of the time-averaged EnKF methodology. Moreover, for the first time we show that this skill loss appears significantly sensitive to the structure of the growth rate function, used to represent the principle of limiting factors (PLF) within the forward model. In general, our experiments showed that the error reduction achieved by assimilating pseudo-TRW chronologies is modulated by the magnitude of the yearly internal variability in themodel. This result might help the dendrochronology community to optimize their sampling efforts.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 627 
KW  - high resolution paleoclimatology
KW  - sparse proxy data
KW  - climate reconstructions
KW  - limiting factors
KW  - Kalman filter
KW  - co-limitation
KW  - ensemble
KW  - variability
KW  - reanalysis
KW  - framework
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-418743
SN  - 1866-8372
IS  - 627
SP  - 545
EP  - 557
ER  - 
TY  - JOUR
A1  - Syrykh, Lydmila S.
A1  - Nazarova, Larisa B.
A1  - Herzschuh, Ulrike
A1  - Subetto, D. A.
A1  - Grekov, I. M.
T1  - Reconstruction of palaeoecological and palaeoclimatic conditions of the Holocene in the south of the Taimyr according to an analysis of lake  sediments
JF  - Contemporary Problems of Ecology
N2  - A sediment core from Khatanga-12 Lake (Taimyr Peninsula, Krasnoyarsk krai) has been studied. The 131.5-cm-long core covers ca. 7100 years of sedimentation. Chironomid analysis, a qualitative reconstruction of the paleoenvironment in the region, and a quantitative reconstruction of variations of the mean July air temperature and in the water depth of the lake have been performed using Northern Russia chironomid-inferred mean July temperature models (Nazarova et al., 2008, 2011, 2015). Khatanga-12 Lake was formed during the Middle Holocene warming as a result of thermokarst processes. The development of the lake ecosystem at different stages of its development was influenced by climatic and cryolithogenic factors. The Middle Holocene warming, which occurred around 7100-6250 cal. years BP, activated thermokarst processes and resulted in the formation of the lake basin. Later, between 6250 and 4500 cal. years BP, a period of cooling took place, as is proved by chironomid analysis. The bottom sediments of the lake during this period were formed by erosion processes on the lake shores. The reconstructed conditions were close to the modern after 2500 cal. years BP.
KW  - Chironomidae
KW  - paleolimnology
KW  - Holocene
KW  - climate reconstructions
KW  - Russian Arctic region
KW  - Khatanga
Y1  - 2017
U6  - https://doi.org/10.1134/S1995425517040114
SN  - 1995-4255
SN  - 1995-4263
VL  - 10
SP  - 363
EP  - 369
PB  - Pleiades Publ.
CY  - New York
ER  -