TY - JOUR A1 - Heinecke, Liv A1 - Epp, Laura Saskia A1 - Reschke, Maria A1 - Stoof-Leichsenring, Kathleen Rosemarie A1 - Mischke, Steffen A1 - Plessen, Birgit A1 - Herzschuh, Ulrike T1 - Aquatic macrophyte dynamics in Lake Karakul (Eastern Pamir) over the last 29 cal ka revealed by sedimentary ancient DNA and geochemical analyses of macrofossil remains JF - Journal of paleolimnolog KW - Potamogeton/Stuckenia KW - Arid central Asia KW - Paleo-productivity KW - Submerged vegetation composition KW - Metabarcoding KW - Chara/Characeae Y1 - 2017 U6 - https://doi.org/10.1007/s10933-017-9986-7 SN - 0921-2728 SN - 1573-0417 VL - 58 SP - 403 EP - 417 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Reschke, Maria A1 - Kunz, Torben A1 - Laepple, Thomas T1 - Comparing methods for analysing time scale dependent correlations in irregularly sampled time series data JF - Computers & geosciences : an international journal devoted to the publication of papers on all aspects of geocomputation and to the distribution of computer programs and test data sets ; an official journal of the International Association for Mathematical Geology N2 - Time series derived from paleoclimate archives are often irregularly sampled in time and thus not analysable using standard statistical methods such as correlation analyses. Although measures for the similarity between time series have been proposed for irregular time series, they do not account for the time scale dependency of the relationship. Stochastically distributed temporal sampling irregularities act qualitatively as a low-pass filter reducing the influence of fast variations from frequencies higher than about 0.5 (Delta t(max))(-1) , where Delta t(max), is the maximum time interval between observations. This may lead to overestimated correlations if the true correlation increases with time scale. Typically, correlations are underestimated due to a non-simultaneous sampling of time series. Here, we investigated different techniques to estimate time scale dependent correlations of weakly irregularly sampled time series, with a particular focus on different resampling methods and filters of varying complexity. The methods were tested on ensembles of synthetic time series that mimic the characteristics of Holocene marine sediment temperature proxy records. We found that a linear interpolation of the irregular time series onto a regular grid, followed by a simple Gaussian filter was the best approach to deal with the irregularity and account for the time scale dependence. This approach had both, minimal filter artefacts, particularly on short time scales, and a minimal loss of information due to filter length. KW - Irregular sampling KW - Time scale dependence KW - Correlation KW - Resampling methods Y1 - 2018 U6 - https://doi.org/10.1016/j.cageo.2018.11.009 SN - 0098-3004 SN - 1873-7803 VL - 123 SP - 65 EP - 72 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Reschke, Maria A1 - Rehfeld, Kira A1 - Laepple, Thomas T1 - Empirical estimate of the signal content of Holocene temperature proxy records JF - Climate of the past : an interactive open access journal of the European Geosciences Union N2 - Proxy records from climate archives provide evidence about past climate changes, but the recorded signal is affected by non-climate-related effects as well as time uncertainty. As proxy-based climate reconstructions are frequently used to test climate models and to quantitatively infer past climate, we need to improve our understanding of the proxy record signal content as well as the uncertainties involved. In this study, we empirically estimate signal-to-noise ratios (SNRs) of temperature proxy records used in global compilations of the middle to late Holocene (last 6000 years). This is achieved through a comparison of the correlation of proxy time series from nearby sites of three compilations and model time series extracted at the proxy sites from two transient climate model simulations: a Holocene simulation of the ECHAM5/MPI-OM model and the Holocene part of the TraCE-21ka simulation. In all comparisons, we found the mean correlations of the proxy time series on centennial to millennial timescales to be low (R < 0.2), even for nearby sites, which resulted in low SNR estimates. The estimated SNRs depend on the assumed time uncertainty of the proxy records, the timescale analysed, and the model simulation used. Using the spatial correlation structure of the ECHAM5/MPI-OM simulation, the estimated SNRs on centennial timescales ranged from 0.05 - assuming no time uncertainty - to 0.5 for a time uncertainty of 400 years. On millennial timescales, the estimated SNRs were generally higher. Use of the TraCE-21ka correlation structure generally resulted in lower SNR estimates than for ECHAM5/MPI-OM. As the number of available high-resolution proxy records continues to grow, a more detailed analysis of the signal content of specific proxy types should become feasible in the near future. The estimated low signal content of Holocene temperature compilations should caution against over-interpretation of these multi-proxy and multisite syntheses until further studies are able to facilitate a better characterisation of the signal content in paleoclimate records. Y1 - 2019 U6 - https://doi.org/10.5194/cp-15-521-2019 SN - 1814-9324 SN - 1814-9332 VL - 15 IS - 2 SP - 521 EP - 537 PB - Copernicus CY - Göttingen ER - TY - THES A1 - Reschke, Maria T1 - Signal content of temperature proxy records BT - a correlation-based study Y1 - 2020 ER - TY - JOUR A1 - Reschke, Maria A1 - Kröner, Igor A1 - Laepple, Thomas T1 - Testing the consistency of Holocene and Last Glacial Maximum spatial correlations in temperature proxy records JF - Journal of quaternary science : JQS N2 - Holocene temperature proxy records are commonly used in quantitative synthesis and model-data comparisons. However, comparing correlations between time series from records collected in proximity to one another with the expected correlations based on climate model simulations indicates either regional or noisy climate signals in Holocene temperature proxy records. In this study, we evaluate the consistency of spatial correlations present in Holocene proxy records with those found in data from the Last Glacial Maximum (LGM). Specifically, we predict correlations expected in LGM proxy records if the only difference to Holocene correlations would be due to more time uncertainty and more climate variability in the LGM. We compare this simple prediction to the actual correlation structure in the LGM proxy records. We found that time series data of ice-core stable isotope records and planktonic foraminifera Mg/Ca ratios were consistent between the Holocene and LGM periods, while time series of Uk'37 proxy records were not as we found no correlation between nearby LGM records. Our results support the finding of highly regional or noisy marine proxy records in the compilation analysed here and suggest the need for further studies on the role of climate proxies and the processes of climate signal recording and preservation. KW - Holocene KW - LGM KW - spatial correlation KW - temperature KW - Uk'37 Y1 - 2020 U6 - https://doi.org/10.1002/jqs.3245 SN - 0267-8179 SN - 1099-1417 VL - 36 IS - 1 SP - 20 EP - 28 PB - Wiley CY - New York ER - TY - GEN A1 - Reschke, Maria A1 - Kröner, Igor A1 - Laepple, Thomas T1 - Testing the consistency of Holocene and Last Glacial Maximum spatial correlations in temperature proxy records T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Holocene temperature proxy records are commonly used in quantitative synthesis and model-data comparisons. However, comparing correlations between time series from records collected in proximity to one another with the expected correlations based on climate model simulations indicates either regional or noisy climate signals in Holocene temperature proxy records. In this study, we evaluate the consistency of spatial correlations present in Holocene proxy records with those found in data from the Last Glacial Maximum (LGM). Specifically, we predict correlations expected in LGM proxy records if the only difference to Holocene correlations would be due to more time uncertainty and more climate variability in the LGM. We compare this simple prediction to the actual correlation structure in the LGM proxy records. We found that time series data of ice-core stable isotope records and planktonic foraminifera Mg/Ca ratios were consistent between the Holocene and LGM periods, while time series of Uk'37 proxy records were not as we found no correlation between nearby LGM records. Our results support the finding of highly regional or noisy marine proxy records in the compilation analysed here and suggest the need for further studies on the role of climate proxies and the processes of climate signal recording and preservation. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1222 KW - Holocene KW - LGM KW - spatial correlation KW - temperature KW - Uk’37 Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-538197 SN - 1866-8372 IS - 1 SP - 20 EP - 28 ER -