Search results for "klimat"

Meteorological validation of chironomids as a paleotemperature proxy using varved lake sediments

2016

In order to improve the reliability of climate models in their projections for the future, spatially and temporally detailed paleoclimate proxy data are needed. In this study, we examined annually laminated sediments from Lake Nurmijärvi (Finland) for their fossil Chironomidae assemblages over a time period with available meteorological observational data (since 1830s). In doing so, we correlated chironomid-based inferences of summer air temperatures against instrumentally measured values using two different reconstruction approaches, namely, calibration-in-space (CiS, multilake training set) and calibration-in-time (CiT, calibration of time series data against meteorological data). The re…

The SISAL database: a global resource to document oxygen and carbon isotope records from speleothems

2018

Stable isotope records from speleothems provide information on past climate changes, most particularly information that can be used to reconstruct past changes in precipitation and atmospheric circulation. These records are increasingly being used to provide “out-of-sample” evaluations of isotope-enabled climate models. SISAL (Speleothem Isotope Synthesis and Analysis) is an international working group of the Past Global Changes (PAGES) project. The working group aims to provide a comprehensive compilation of speleothem isotope records for climate reconstruction and model evaluation. The SISAL database contains data for individual speleothems, grouped by cave system. Stable isotopes of oxyg…

Rereading a tree-ring database to illustrate depositional histories of subfossil trees

2017

Late Quaternary tree-ring chronologies have been constructed using data collected from subfossil trees preserved under favourable conditions in lake sediments and peat deposits. Tree-ring widths and densities are commonly used for reconstructions of past climate variability. An alternative way of using these data is to explore the replication curves of these chronologies. Here, we make use of previously collected data that is currently available from tree-ring databases to demonstrate the depositional histories of pine trees once accumulated into the sediment in lake (i.e., riparian trees) and peatland sites. Divergent courses of depositional histories were obtained for different sedimentar…

Stratification strength and light climate explain variation in chlorophyll a at the continental scale in a European multilake survey in a heatwave su…

2021

The authors acknowledge COST Action ES 1105 "CYANOCOST Cyanobacterial blooms and toxins in water resources: Occurrence impacts and management" and COST Action Global Change Biology ES 1201 NETLAKE -Networking Lake Observatories in Europe" for contributing to this study through networking and knowledge sharing with European experts in the field. We acknowledge the members of the Global Lake Ecological Observatory Network (GLEON) for their collaborative spirit and enthusiasm that inspired the grassroots effort of the EMLS. E.M. was supported by a grant from the Swiss State Secretariat for Education, Research and Innovation to Bas Ibelings and by supplementary funding from University of Geneva…

Comparison of quantitative Holocene temperature reconstructions using multiple proxies from a northern boreal lake

2017

Four biotic proxies (plant macrofossils, pollen, chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures ( Tjul) at Lake Loitsana (northern Finland) during the Holocene. The aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest Tjul in the individual reconstructions. The reconstructed Tjul values are evaluated in relation to local-scale/site-specific processes associated with the Holocene lake development at Loitsana as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. While pollen-based temperatures follow…

Zemes un vides zinātnes: Bioģeogrāfija

2003

Klimats un ilgtspējīga attīstība

2016

Amatas upes hidroloģiskā režīma ilgtermiņa un sezonālās izmaiņas

2017

Darba mērķis ir izvērtēt Amatas upes hidroloģiskā režīma sezonālās un ilgtermiņa izmaiņas mainīga klimata apstākļos. Darbā raksturots Gaujas baseina upju hidroloģiskais režīms un to ietekmējošie faktori, aplūkoti hidroloģiskā režīma pētījumi Latvijā un Baltijā. Veikts Amatas upes baseina fizioģeogrāfiskais raksturojums. Analizēti rezultāti par Amatas upes hidroloģiskā režīma raksturojošo parametru (caurplūdums, temperatūra, ledus izveidošanās un uzlūšanas datumi, ledstāves ilgums) sezonālajām un ilgtermiņa izmaiņām un to savstarpējo korelāciju ar meteoroloģiskajiem parametriem (gaisa temperatūra un atmosfēras nokrišņi) laika periodā no 1921.-2015. gadam. Noteces režīms raksturots, analizējo…

Kopīgo resursu pārvaldība krīžu saplūšanas laikā

2022

Kolektīvā monogrāfija “Kopīgo resursu pārvaldība krīžu saplūšanas laikā” apkopo galvenās pētnieciskā projekta “Gatavi pārmaiņām? Kopīgo dabas resursu ilgtspējīga pārvaldība” (LZP-2019/1-0319) (projekta vadītājs LU SZF SPPI vadošais pētnieks Jurijs Ņikišins) atziņas.

Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw

2020

Significance Over many millennia, northern peatlands have accumulated large amounts of carbon and nitrogen, thus cooling the global climate. Over shorter timescales, peatland disturbances can trigger losses of peat and release of greenhouses gases. Despite their importance to the global climate, peatlands remain poorly mapped, and the vulnerability of permafrost peatlands to warming is uncertain. This study compiles over 7,000 field observations to present a data-driven map of northern peatlands and their carbon and nitrogen stocks. We use these maps to model the impact of permafrost thaw on peatlands and find that warming will likely shift the greenhouse gas balance of northern peatlands. …