Oxygen- and carbon-isotopic signatures of benthic ostracodes from lake sediments from climate sensitive regions in the Alpine region, Central Europe, the north-central USA, the Chilean Altiplano and Patagonia, Argentina, are used to characterize lake system processes and to reconstruct climate patterns of the past 16,000 years. The case studies provide examples that highlight different aspects of the broad application of isotope stratigraphies, and provide keys for the interpretation of complex lacustrine records. The integration of stable-isotope stratigraphy, sedimentology, and ecological information from ostracode assemblages is a new tool that acquires climate information from the indirect views of climate series provided by lake sediments. This tool (1) identifies lake system characteristics, (2) confines which isotopic signatures are controlled by which processes in the lake system and/or in the catchment, and (3) defines which signatures are ultimately controlled by climate change. If sudden shifts in the isotopic composition occur concomitantly with changes between sedimentological units, then the isotopes reflect first of all changes in catchment hydrology that may be ultimately controlled by climate. Also, if ostracode δ18O and δ13C values show the same timing and direction of shifts, then this indicates a major change in the hydrological budget of the lake. The case studies presented here show that coupled isotopic signatures may be used to track hydrological changes related to meltwater and deglaciation, shifting rivers and ground water sources, and changes in precipitation mechanisms and patterns. Values of δ18O from large lakes with short water residence time, low evaporation rates and homothermic bottom waters provide records of past temperatures of precipitation. The δ13C values reflect changes in the ratio of C3:C4 plants in the catchment. They indicate shifts in modes of organic decay in the surface sediments that can be linked to a change in hydrodynamics within a lake. The δ13C values also allow detection of the input of volcanically charged ground waters providing large quantities of 14C-free CO2 that hinders accurate 14C chronology. General climate trends for the sites in the Americas indicate a dry mid-Holocene punctuated by moist spells, and show a general increase in moisture during the past approximately 4000 years, interrupted by recurring droughts. This hints at an interhemispheric connection and a common driving mechanism. Environmental isotopes from high-resolution lake sediments thus provide an ideal tool to identify and characterize the regional impact and magnitude of global climate change. This tool contributes to a better understanding of regional climate change and its driving mechanisms and thus provides the type of information needed to improve climate models. Environmental isotopes provide more information than just moisture balance and airmass history if they are integrated with the detailed sedimentological and ostracode ecological evidence, and understanding for the component system. Thus environmental isotopes serve to a better understanding of the climate signal archived in lake records and represent an essential contribution to Global Change research and Earth System Science.
Bibliographical noteFunding Information:
The base of this paper, representing my ‘Habilitations-schrift’, submitted to the Universität Göttingen in 2001, was prepared during a postdoctoral visit (1993–1996) at the Limnological Research Center, LRC, University of Minnesota, Minneapolis, funded by 2 post-doctoral fellowships from the Swiss National Science Foundation (‘chercheur débutant’ and ‘chercheur avancé’, total 2.5 years). The second major funding source was a fellowship from the Deutsche Forschungs-gemeinschaft, DFG (Habilitanden-Stipendium, 2 years). Additional funding of a couple of months each came from the National Science Foundations in Switzerland and the USA, as well as the DFG through grants to Bruno Messerli, Universität Bern (4 months); Herb Wright and Emi Ito, University of Minnesota (3 months); Dieter Meischner and Eberhard Grüger, Universität Göttingen (7 months); Vera Markgraf, University of Colorado, and Kerry Kelts, University of Minnesota (6 months); the Deutscher Akademischer Austauschdienst, DAAD (British German Academic Research Collaboration Programme, travel grant) and last but not least from the German Federal Office of Employment (5 months).
Copyright 2008 Elsevier B.V., All rights reserved.
- Environmental dynamics
- Non-marine ostracodes
- Stable isotopes