Modeled seasonality of glacial abrupt climate events

Greenland ice cores, as well as many other paleo-archives from the northern hemisphere, recorded a series of 25 warm interstadial events, the so-called Dansgaard-Oeschger (D-O) events, during the last glacial period. We use the three-dimensional coupled global ocean-atmosphere-sea ice model ECBILT-CLIO and force it with freshwater input into the North Atlantic to simulate abrupt glacial climate events, which we use as analogues for D-O events. We focus our analysis on the Northern Hemisphere. The simulated events show large differences in the regional and seasonal distribution of the temperature and precipitation changes. While the temperature changes in high northern latitudes and in the North Atlantic region are dominated by winter changes, the largest temperature increases in most other land regions are seen in spring. Smallest changes over land are found during the summer months. Our model simulations also demonstrate that the temperature and precipitation change patterns for different intensifications of the Atlantic meridional overturning circulation are not linear. The extent of the transitions varies, and local non-linearities influence the amplitude of the annual mean response as well as the response in different seasons. Implications for the interpretation of paleo-records are discusse

The demand for money in developing countries: Assessing the role of financial innovation

Traditional specifications of money demand have been commonly plagU4:!d by persistent overprediction, implausible parameter estimates, and highly autocorrelated errors. This paper argues that some of those problems stem from the failure to account for the impact of financial innovation. We estimate money demand for ten developing countries employing various proxies for the innovation process and provide an assessment of the relative importance of this variable. We find that financial innovation plays an important role in determining money demand and its fluctuations, and that the importance of this role increases with the rate of inflation.

Nitrous oxide and methane variations covering the last 100,000 years: Insight into climatic and environmental processes

This year, another record-breaking hot and dry summer in large parts of Europe has once more caught the attention of the public and raised questions about climate change and global warming. The evidence is growing that human activities affect the climate system, primarily through the emission of greenhouse gases and aerosols, resulting in significant warming observed over the last century [IPCC, 2001]. In the discussion of climate change, records of climate variations in the past play a crucial role for several reasons. First, paleodata are used to study mechanisms and feedbacks operating in the climate system. Second, attribution of climate change to anthropogenic causes relies on the central finding that the observed trends are unusual. Here, reconstructions of the past climate provide insight into the range of natural climate variability. Third, the simulation of climate variations in the past and the validation with data remain one of the harshest test for the climate models that are used to predict future climate. And fourth, quantifying the effect of anthropogenic emissions of greenhouse gases on the climate requires precise knowledge of the global biogeochemical cycles. The reconstruction of atmospheric greenhouse gas variations in the past offers a unique opportunity to study the key biogeochemical processes. Climate change leaves its traces in a variety of archives, among them marine and lake sediments, tree rings, stalagmites, corals, and others. But many indicators record climate indirectly and/or reflect local as well as large-scale changes. Greenhouse gases are well-mixed over the Earth, reflect large-scale or global changes, and thus are exceptional in this respect. The large ice sheets provide an archive of ancient air trapped in small air bubbles that can be measured directly. Deep ice core drillings in Greenland and Antarctica have provided an often undisturbed record of greenhouse gas concentrations in the past. While atmospheric carbon dioxide (CO2) and methane (CH4) have been reconstructed from ice cores over four glacial cycles, the nitrogen cycle has received little attention, and measurements of nitrous oxide (N2O) have been very sparse until recently. In this thesis, several studies are presented that provide new high resolution records of the evolution of the three greenhouse gases over the last 100,000 years and investigate the processes and changes in the respective ecosystems and biogeochemical cycles. The first introductory chapter presents an overview on atmospheric N2O, CH4 and CO2, their anthropogenic increase over the last 250 years as well as the last glacial-interglacial transition, a time period of increasing greenhouse gas concentrations in parallel to natural climatic changes. In distinct depth intervals of Greenland and Antarctic ice cores, atmospheric N2O records are disturbed by artifacts. The second part of chapter 1 discusses these N2O artifacts and gives an overview of their occurrence, their possible origin and methods to distinguish them from the atmospheric trend. The climate over the last few glacial cycles was dominated by relatively short interglacial warm phases and long ice-ages. Each cycle was about 100,000 years long. The study in chapter 2 gives an overview of the greenhouse gas variations over the last 60,000 years covering part of the last glacial epoch, the last glacial-interglacial transition and the present warm period, the Holocene. The agreement of different records and cores and the reliability of smaller variations found in individual records are discussed. The climate over the last 10,000 years has been exceptionally stable, providing an ideal time period to study the natural variability of the current interglacial warm phase. In chapter 3, high-resolution measurements of N2O and CH4 are presented and compared with CO2 regarding potential processes and changes in sources and sinks of both the ocean and the terrestrial biosphere. The end of last glacial period was characterized by a rather gradual warming in the south. In contrast, a more abrupt warming is seen in the northern hemisphere, interrupted by a return to cold conditions for several centuries. High resolution records of N2O, CH4 and CO2 covering this time period are presented in the two studies of chapters 4 and 5. The different characteristics of the three greenhouse gases reveal important insight and unprecedented details into how the biogeochemical cycles have responded and thereby driven climate change in the two hemispheres. The climate of the last glacial was punctuated by abrupt and large-scale warm events in the northern hemisphere, with local temperature changing by 10◦C or more within a few decades. These so-called Dansgaard-Oeschger (DO) events occurred with remarkable regularity, and their trigger remains unknown. The high-resolution N2O and CH4 records measured over several of these events are presented in chapter 6. Both N2O and CH4 show changes in parallel to DO events, but with different characteristics. The study discusses the amplitudes, timing and duration of these events, as well as different hypotheses of terrestrial and oceanic changes in sources and sinks that might have caused the observed changes. Atmospheric CH4 shows an interhemispheric gradient, caused by the short lifetime of about 10 years and the sources that are located mainly in the northern hemisphere. From the reconstruction of the past CH4 concentration from both Greenland and Antarctic ice cores, the interhemispheric gradient, and thus the source distribution among the tropics and the mid to high northern latitudes can be calculated. In the study presented in chapter 7, CH4 measurements over the last glacial period and the transition to the Holocene are used to reconstruct CH4 source changes in different latitudes for various time intervals as well as for glacial cold and warm events. New ice cores drilled in both Greenland and Antarctica, combined with improved analytical techniques will soon lead to continuous greenhouse gas reconstructions over the last 800,000 years or more, providing insight into how climate has changed in the past. However, it will be a long and challenging task to understand why greenhouse gases changed the way we observe them, and how these changes are related to the large-scale or global environmental and climatic processes. This thesis is one step into this direction

Als Eisforscher in Dome C - ein Tagebuch

Seit 1997 sind Wissenschafter und Techniker aus zehn europäischen Ländern in Dome Concordia daran, den rund 3250 Meter mächtigen antarktischen Eisschild zu durchbohren. Die Untersuchungen an den Eisbohrkernen sollen die längste Klimarekonstruktion dieser Art ermöglichen. Insbesondere möchte man die Zusammenhänge im Klimasystem und die Ursachen von vergangenen natürlichen Klimaschwankungen besser verstehen – wesentliche Voraussetzungen, um Klimamodelle weiterentwickeln und immer genauere Klimaprognosen für die Zukunft erstellen zu können. Im Südsommer 2001/2002 haben erneut Berner Wissenschafter der Abteilung für Klima- und Umweltphysik an den Feldarbeiten in der Antarktis teilgenommen. Ein Tagebuch

The EPICA deep ice cores: first results and perspectives

Two deep ice cores are being drilled in Antarctica in the frame of the European Project for Ice Coring in Antarctica (EPICA). The Dome C ice core will provide more information about mechanisms of global climatic changes over several climatic cycles. The DML core, drilled at Kohnen station, will provide a detailed record over the last climatic cycle, which can be compared with Greenland records. The drilling at Dome C reached 3200 m depth during field season 2002/03, and the age of the ice at the bottom of the hole could be 900 000 years according to preliminary estimates. The depth at Kohnen station is 1564.6 m at present, corresponding to an age of about 55 000 years. Analyses along the top parts of both ice cores have provided interesting first results. A few selected results from these parts, mostly published already, are summarized. Only a few measurements are available from the deeper parts of both cores. Dielectric profiling and electrical conductivity measurements, performed in the field, provide continuous and high-resolution records concerning the acidity and the salt concentration of the ice. Continuous flow analyses and Fast Ion Chromatography also provide high-resolution records of several chemical compounds. These records give some clues as to the age scale of the EPICA Dome C ice core, but they also leave us with many open questions

High-resolution Holocene N2O ice core record and its relationship with CH4 and CO2

Nitrous oxide (N2O) concentration records exist for the last 1000 years and for time periods of rapid climatic changes like the transition from the last glacial to today's interglacial and for one of the fast climate variations during the last ice age. Little is known, however, about possible N2O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high-resolution N2O record measured along the European Project for Ice Coring in Antarctica (EPICA) Dome C Antarctic ice core. On the same ice we obtained high-resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapor) without any uncertainty in their relative timing. The CO2 and CH4 records are in good agreement with previous measurements on other ice cores. The N2O concentration started to decrease in the early Holocene and reached minimum values around 8 ka (<260 ppbv) before a slow increase to its preindustrial concentration of ∼265 ppbv

Atmospheric CO2, CH4 and N2O records over the past 60 000 years based on the comparison of different polar ice cores

Analyses of air extracted from polar ice cores are the most straightforward method of reconstructing the atmospheric concentrations of greenhouse gases and their variations for past climatic epochs. These measurements show that the concentration of the three most important greenhouse gases (other than water vapour) CO2, CH4 and N2O have steadily increased during the past 250 years due to anthropogenic activities (Prather and others, 2001; Prentice and others, 2001). Ice-core results also provided the first evidence of a substantial increase in the concentration of the three gases during the transition from the last glacial epoch to the Holocene (Raynaud and others, 1993). However, results from different cores are not always in agreement concerning details and small, short-term variations. the composition of the air enclosed in bubbles can be slightly changed by fractionation during the enclosure process, by chemical reactions and/or biological activity in the ice and by fractionation during the air extraction. We compile here several records with short-term variations or anomalies and discuss possible causes, taking into account improved analytical techniques and new results