ISOTOPES IN CLIMATE ARCHIVES

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Introduction

 

Isotopic and elemental compositions on samples from different environmental archives contain detailed information about climate variability. In particular changes of fluxes between reservoirs (e.g. atmosphere to ocean or atmosphere to biosphere) can be deduced from these measurements, from which net fluxes can be determined, additional isotope ratio measurements allow to calculate gross fluxes.

 

Our research is divided in four subtopics:

• ICE CORES

(more detailed in German )
Polar and alpine ice contains air in bubbles. This air represents the composition of the atmosphere at the time of trapping in the ice (except of some changes due to diffusion in the firn). As the mixing time of the atmosphere is about one year most of the isotopic or elemental ratios represent global climatic parameters.
The air in the bubbles has nearly the age of the ice, hence covering the past 200'000 years for Greenland. This allows us to reconstruct past climatic properties, such as total ice volume (isotope ratio on air oxygen d¹⁸O), biosphere activity (O ₂/N₂ ratio, CO ₂), local temperature and the (local) firn size(both nitrogen and argon isotope ratio, d ¹⁵N and d⁴⁰Ar ), (local) snowfall.
With d ¹⁵N the temperature change during the 8200 event (D T = -5.4 to -11.7 K) (Leuenberger et al., 1999) and the Dansgaard-Oeschger event 19 (70000 years B.P.; DT = 14.3 to 18.1 K) (Lang et al., 1999 ) could be determined.
On the other side anthropogenic (i.e. caused by mankind) changes to atmospheric gas composition (O₂/N ₂ ratio, CO₂, d¹³C of CO₂ etc.) during the last 200 years and its implications on the carbon cycle and greenhouse warming, can be studied.
 
• PRECIPITATION

Isotopes of the water molecules (deuterium, oxygen-18 and tritium) are important tracers to investigate environmental processes. Long term world wide measurements since 1961, coordinated by the International Atomic Energy Agency (IAEA) have proved the usefullness for hydrological and climatological studies.
Our department (KUP) has its own tradition for measurements of oxygen-18 and tritium going back to 1971 for the Bern station. With time more and more stations were added to reach the size of the present swiss network of isotopes in precipitation. The network is run in cooperation with the University of Lausanne (Prof. J. Hunziker) under contract of the Swiss Hydrological and Geological Survey.
 
• TREE RINGS

Carbon in plant material originates from atmospheric CO ₂. During its assimilation through photosynthesis, it undergoes fractionations which depend on temperature and humidity conditions of the site. Hence, after correction for variations in atmospheric carbon isotopic composition (known from direct atmospheric measurements or from ice core measurements, see above ), d¹³C in tree rings allows us to reconstruct large changes in precipitation and temperature on local and regional scales.
On the other hand, oxygen isotopic composition of plant material depends primarily on d¹⁸O of leaf water, which in turn depends on soil water composition and relative humidity. Hence measurements of d¹⁸ O in tree rings allow us to extend the measurements made directely on precipitation water (see above ) into the past, and correspondingly to reconstruct temperature and meteorological situations of the past. This picture shows a part of an oak disk. The pores, seen as white spots, are used for water and nutrient transport. The part of the wood containing pores is built during spring ("early wood") and the other part during summer ("late wood"). This allows us to date the wood by counting the "rings". For clarity reasons we marked the years 1980 ("8") and 1990 ("9") on the wood piece. The scale is given by the line of 1cm. Our studies on tree-rings are made in colaboration with the tree ring departement of the Swiss Federal Institute for Forest, Snow and Landscape Research. Many links on tree ring research are provided by the Laboratory of Tree Ring Research (LTRR) of the University of Tucson, Arizona .
 
• LAKE SEDIMENTS

d¹⁸ O on carbonate lake sediments reflect to some extent temperature changes. We measured sediments from Central Europe (e.g. sediments from lake Gerzensee/Kt. Bern) which exhibit abrupt, characteristic variations. They were identified by a correlation with Greenland's ice core d ¹⁸O_ice records as climate induced variations of the last 15'000 years. Therefore the record includes the well known Younger Dryas cold event.
 

New mass spectrometer laboratory installed in 1999!
 

Project members

PD Dr. Markus Leuenberger (Group leader)
Marc Eyer (d13C in Ice Cores )
Christof Huber (d ¹⁵N, d⁴⁰Ar in Ice Cores )
Patrick Sturm (atmospheric air composition)
 

Peter Nyfeler (technician, Mass Spectrometer)

Dr. Ueli Eicher (Lake sediments )