Steffen Holzkämper

31. The last and the penultimate interglacial as recorded by speleothems from a climatically sensitive high-elevation cave site in the alps

Abstract Within the greater Alpine region, absolutely dated climate records of the penultimate and the last interglacial are exceptionally rare. Speleothems offer an important and still underutilized source of information about the timing and duration of warm periods during the Middle and Upper Quaternary. The focal point of intense research is Spannagel Cave, a large high-altitude (ca. 2200 to 2500 m a.s.l.) cave system in the Zillertal Alps of Austria. The presently low (1.4 to 2.5°C) cave temperature provides a natural threshold for speleothem growth, i.e. the cave acts as a climatically sensitive archive. U-series dating of calcite speleothems, facilitated by exceptionally high U content in combination with high-resolution stable isotope analyses allow identifying warm climate periods. Calcite growth at 236 to 229kyr, 211 to 206kyr and 199 to 192kyr is in good accordance with U-series dated sea-level records and marine sediments whose chronology was tuned to orbital parameters. Oxygen isotope data show that the climate in the Alps was consistently cooler during the penultimate interglacial than during the last interglacial. Carbon isotope data also show a major difference between the two interglacials: while alpine soil and vegetation was apparently well developed during the last interglacial (and similar as today), high C isotope values testify the lack of pedogenic C input during the penultimate warm periods. Accordingly, the area above the cave was either barren or — more likely — covered by a warm-based glacier. Previously regarded as evidence of ice-free conditions early during the penultimate deglaciation speleothem deposition at 136kyr is now seen as an indication of a major change of the glaciers thermal state most likely as a result of the collapse of ice-stream network at the end of the penultimate glacial maximum. Following a return to stadial conditions not conducive to speleothem formation and marked by a hiatus in speleothem growth, fully interglacial conditions did not commence until 130kyr and prevailed until 119 kyr.

Stable isotopes in tree rings as proxies for winter precipitation changes in the Russian Arctic over the past 150 years

Stable Isotopes in Tree Rings as Proxies for Winter Precipitation Changes in the Russian Arctic over the Past 150 Years We present results from an analysis of tree ring width and stable carbon and oxygen isotopes in tree ring cellulose of Siberian Spruce collected from remote forest islands in the northwestern Russian tundra. Ring width is often considered a proxy for summer temperatures. The aim of this pilot study was to test whether stable isotopes can provide additional information about climate during the growth of trees in this extreme environment. Comparison of δ13C and δ18O with observed meteorological data shows that there is a link between stable isotopes and winter precipitation. This may be explained by the strong influence that snow exerts on the isotopic composition of soil moisture during spring and early summer, when the new cellulose is formed. Our results show that winter precipitation in the study area was increasing from 1865-1900, and thereafter decreasing until ~ 1930. The 1960-1980 period was again rather humid, followed by a drying trend until 1990. The study highlights the potential of stable carbon and oxygen isotopes in tree rings as proxies for winter precipitation.

LONG-TERM SUMMER TEMPERATURE VARIATIONS IN THE PYRENEES FROM DETRENDED STABLE CARBON ISOTOPES

Abstract Substantial effort has recently been put into the development of climate reconstructions from tree-ring stable carbon isotopes, though the interpretation of long-term trends retained in such timeseries remains challenging. Here we use detrended δ13C measurements in Pinus uncinata tree-rings, from the Spanish Pyrenees, to reconstruct decadal variations in summer temperature back to the 13th century. The June-August temperature signal of this reconstruction is attributed using decadally as well as annually resolved, 20th century δ13C data. Results indicate that late 20th century warming has not been unique within the context of the past 750 years. Our reconstruction contains greater am-plitude than previous reconstructions derived from traditional tree-ring density data, and describes particularly cool conditions during the late 19th century. Some of these differences, including early warm periods in the 14th and 17th centuries, have been retained via δ13C timeseries detrending - a novel approach in tree-ring stable isotope chronology development. The overall reduced variance in earlier studies points to an underestimation of pre-instrumental summer temperature variability de-rived from traditional tree-ring parameters.

Effects of Climate, Site Conditions, and Seed Quality on Recent Treeline Dynamics in NW Russia: Permafrost and Lack of Reproductive Success Hamper Treeline Advance?

Treeline advance alters albedo and carbon storage and is an important feedback mechanism to the global climate system. Establishment of trees north of the treeline requires favorable climate, suitable microsites, and viable seeds. Here we studied the influence of climate and microsite conditions on tree and seedling growth at four transects from forest through woodland to tundra in NW Russia, and tested the viability of seeds from the region. General growth patterns and establishment periods of the treeline species Picea obovata are similar across the study sites suggesting a regional driver (for example, climate). Individuals established as early as the 1640s, but mainly between 1850 and 1880, and during a major and continental scale establishment wave in the 1950s and 1960s. No establishment occurred after 1982. Older trees mainly showed significant and stable positive relationships to growing year summer temperatures and significant stable negative correlations to previous year summer temperatures in nearly all plots. Trees from the last establishment wave showed more mixed responses, but current year summer temperature positively affected growth. Active layer depth was similar in all plots with trees but decreased sharply in treeless tundra. A major role for the lack of recent establishment seems to be very low seed viability, possibly combined with early strong fall frosts, which might have severely limited successful recruitment in the last decades of the twentieth century. For a successful establishment of P. obovata in tundra areas of NW Russia, permafrost degradation and (generally) warmer winters might be a prerequisite.

A 2000-year record of lake ontogeny and climate variability from the north-eastern European Russian Arctic

A lake sediment record from the north-eastern European Russian Arctic was examined using palaeolimnological methods, including subfossil chironomid and diatom analysis. The objective of this study is to disentangle environmental history of the lake and climate variability during the past 2000 years. The sediment profile was divided into two main sections following changes in the lithology, separating the limno-telmatic phase between ~2000 and 1200 cal. yr BP and the lacustrine phase between ~1200 cal. yr BP and the present. Owing to the large proportion of semi-terrestrial chironomids and poor modern analogues, a reliable chironomid-based temperature reconstruction for the limno-telmatic phase was not possible. However, the lacustrine phase showed gradually cooling climate conditions from ~1200 cal. yr BP until ~700 cal. yr BP. The increase in stream chironomids within this sediment section indicates that this period may also have had increased precipitation that caused the adjacent river to overflow, subsequently transporting chironomids to the lacustrine basin. After a short-lived warm phase at ~700 cal. yr BP, the climate again cooled, and a progressive climate warming trend was evident from the most recent sediment samples, where the biological assemblages seem to have experienced an eutrophication-like response to climate warming. The temperature reconstruction showed more similarities with the climate development in the Siberian side of the Urals than with northern Europe. This study provides a characteristic archive of arctic lake ontogeny and a valuable temperature record from a remote climate-sensitive area of northern Russia.

Stable isotopes in Sphagnum fuscum peat as late-Holocene climate proxies in northeastern European Russia

The environment of the northern taiga to tundra transition is highly sensitive to climate fluctuations. In this study from northeastern European Russia, stable carbon and oxygen isotope ratios (δ13C, δ18O) in α-cellulose of Sphagnum fuscum stems subsampled from hummocks and peat plateau profiles have been used as climate proxies. The entire isotope time series, dated by lead (210Pb), caesium (137Cs) and AMS-radiocarbon (14C) dating, spans the past 2500 years. Plant macrofossil analyses were used as an aid in single species selection, but are also helpful in identifying past surface moisture conditions. The most significant relationships were found between the recent δ13C record and summer (July–August) temperatures (R2 = 0.58, p < 0.01), and the recent δ18O record and winter (October–May) precipitation anomalies in the tundra region (R2 = 0.36, p < 0.01). The study demonstrates that stable isotopes preserved in northern peat deposits are useful indicators for summer temperature and winter precipitation at decadal to millennial timescales.

Site-specific climatic signals in stable isotope records from Swedish pine forests

Key messagePinus sylvestris tree-ring δ13C and δ18O records from locally moist sites in central and northern Sweden contain consistently stronger climate signals than their dry site counterparts.AbstractWe produced twentieth century stable isotope data from Pinus sylvestris trees near lakeshores and inland sites in northern Sweden (near Kiruna) and central Sweden (near Stockholm) to evaluate the influence of changing microsite conditions on the climate sensitivity of tree-ring δ13C and δ18O. The data reveal a latitudinal trend towards lower C and O isotope values near the Arctic tree line (− 0.8‰ for δ13C and − 2.4‰ for δ18O relative to central Sweden) reflecting widely recognized atmospheric changes. At the microsite scale, δ13C decreases from the dry inland to the moist lakeshore sites (− 0.7‰ in Kiruna and − 1.2‰ in Stockholm), evidence of the importance of groundwater access to this proxy. While all isotope records from northern and central Sweden correlate significantly against temperature, precipitation, cloud cover and/or drought data, climate signals in the records from moist microsites are consistently stronger, which emphasizes the importance of site selection when producing stable isotope chronologies. Overall strongest correlations are found with summer temperature, except for δ18O from Stockholm correlating best with instrumental drought indices. These findings are complemented by significant positive correlations with temperature-sensitive ring width data in Kiruna, and inverse (or absent) correlations with precipitation-sensitive ring width data in Stockholm. A conclusive differentiation between leading and co-varying forcings is challenging based on only the calibration against often defective instrumental climate data, and would require an improved understanding of the physiological processes that control isotope fractionation at varying microsites and joined application of forward modelling.