Simulating atmospheric d13CO2 during the last 740,000 years: Model-based estimates in the context of ice core measurements

The ratio of the stable carbon isotopes of atmospheric CO2 (δ 13 CO2 ) contains valuable information on the processes which are operating on the global carbon cycle. However current δ 13 CO2 ice core records are still limited in both resolution, temporal coverage as well as precision. To make optimal use of the existing and future δ 13 CO2 ice core records an estimate of the expected temporal variability would help to constrain for the acceptable measurement uncertainty and resolution to successfully retrieve the characteristic variability in δ 13 CO2 . In this study we performed simulations with the carbon cycle box model BICYCLE with special emphasis on atmospheric δ 13 CO2, proposing how changes in δ 13 CO2 might have evolved over the last 740,000 years. The overall model dynamic is validated with reconstructions of δ 13 C in benthic foraminifera in thedeep Pacific and with atmospheric CO2 ice core data. On glacial/interglacial timescales lower surface ocean temperature is most important for lower glacial δ 13 CO2 , followed by the release of isotopically lighter terrestrial carbon. In addition, changes in the terrestrial biosphere also dominate deep ocean δ 13 CO2 but have only a limited effect on atmospheric pCO2 . All other oceanic processes lead to higher than present glacial δ 13 CO2 . Taken all processes together the effects nearly cancel each other and there are nearly no glacial/interglacial amplitudes in δ 13 CO2 in line with ice core data. However faster variations of up to 0.3 occur throughout the whole simulation period. Due to our model configuration, terrestrial carbon storage is very sensitive to temperature changes over northern hemispheric lands, which accompany the reorganization of the Atlantic meridional ocean circulation during fast climate fluctuations (Dansgaard/Oeschger events). These fast events intensify the frequency and amplitude in δ 13 CO2 . However, due to ocean uptake of additional carbon as well as the signal attenuation in ice cores, the amplitudes of such events are strongly time scale dependent

Musée imaginaire: Fontane's picture gallery

This paper tends to explore ,Fontane's picture gallery' referring to its genesis, characteristic and effect. In doing so the art critic Fontane is improving a distinctive image as an expert especially of English art und of the at that time in Germany leading Dusseldorf School of Painting (Düsseldorfer Malerschule). Furthermore it will be set out how the writer Fontane is acting in his work with pictures and pictorial perception. Eventually there is a suggestion for recovering ,Fontane's picture gallery' to make it possible for the contemporary audience to read Fontane's works in a wider and subtly differentiated manner.This paper tends to explore ,Fontane's picture gallery' referring to its genesis, characteristic and effect. In doing so the art critic Fontane is improving a distinctive image as an expert especially of English art und of the at that time in Germany leading Dusseldorf School of Painting (Düsseldorfer Malerschule). Furthermore it will be set out how the writer Fontane is acting in his work with pictures and pictorial perception. Eventually there is a suggestion for recovering ,Fontane's picture gallery' to make it possible for the contemporary audience to read Fontane's works in a wider and subtly differentiated manner

How does the local wind field control the aerosol distribution in coastal Dronning Maud Land?

Atmospheric circulation patterns and chemical concentrations in firn cores are highly related to each other. Atmospheric winds transport aerosols like sea salt and mineral dust over the globe and redistribute them. Because of this, it is possible to reconstruct atmospheric circulation bringing aerosol to Antarctica by analyzing chemical impurities in firn and ice. With these analyses, the gap caused by sparse atmospheric measurements can be filled and this knowledge can then be used to improve the understanding of local and global circulation patterns.Due to a very high accumulation rate (~600 kg/m²*a), coastal Dronning Maud Land (CDML) is a perfect site to conduct these studies.Here, the upper 6m of two firn cores drilled on Halvfaryggen and Sörasen (covering the time interval from 2002- 2007) were analyzed on ionic concentrations. This data was then contrasted to measurements from the air chemistry laboratories at Neumayer (NM) and Kohnenstation (KS), and synoptic measurements from automatic weather stations (distributed in CDML and at NM).The analyses show very different results: Sea salt ions (e.g. Na+) are higher correlated to ions measured in aerosol samples at the air chemistry laboratory at KS than to the one located at NM. In contrast, ions representing mineral dust (e.g. nss-Ca2+) only have a weak correlation over the whole area and time period. Accordingly, the deposition of aerosol is highly dependent on its origin and the topography in coastal Antarctica suggesting different transport pathways for sea level and higher altitude sites

Glacial/interglacial changes in mineral dust and sea-salt records in polar ice cores: sources, transport, and deposition

Sea salt and mineral dust records as represented by Na+ and Ca2+ concentrations, respectively, in Greenland and Antarctic ice cores show pronounced glacial/interglacial variations. For the Last Glacial Maximum (LGM) mineral dust (sea salt) concentrations in Greenland show an increase of a factor of approximately 80 (15) compared to the Holocene and significant shifts by a factor of 15 (5) during Dansgaard Oeschger events. In Antarctica, the dust (sea salt) flux is enhanced by a factor of 15 (3) during the LGM compared to the Holocene and variations by approximately a factor of 8 (1-2) exist in parallel to Antarctic warm events. Primary glacial dust sources are the Asian deserts for Greenland and Patagonia for Antarctica. Ice core evidence and model results show that both changes in source strength as well as atmospheric transport and lifetime contributed to the observed changes in Greenland ice cores. In Antarctica changes in ice core fluxes are in large parts related to source variations both for sea salt and dust, where the formation of sea salt aerosol from sea ice may play a pivotal role. Summarizing our latest estimates on changes in sources, transport and deposition these processes are roughly able to explain the glacial increase in sea salt in both polar regions while they fall short by at least a factor of 4-7 for mineral dust. Future improvements in model resolution and in the formulation of source and transport processes together with new ice core records, e.g. on dust size distributions, will eventually allow to converge models and observations

Reconstruction of glacial/interglacial changes in the global carbon cycle from CO2 and d13 CO2 in Antarctic ice cores (scientific paper)

High-resolution CO2 and δ13CO2 records from the Taylor Dome ice core, Antarctica, reveal significant changes in the global carbon cycle over the last 30,000 yrs. CO2 concentrations increase from 180 ppmv at 20 kyr before present to 275 ppmv at the start of the Holocene with an intermittent decline during the Antarctic Cold Reversal. δ13C shows a net increase from the average glacial level of -6.7‰ to mean Holocene values of around -6.5‰. However, the transition period is initiated by an 0.5‰ drop at 20 kyr before present followed by an 0.7 ‰ increase which is interrupted by an 0.2‰ decline during the Antarctic Cold Reversal. Isotope budget considerations show that during the Holocene and the Last Glacial Maximum changes in the size of terrestrial biosphere can account for the observed changes in CO2 and δ13C. In contrast changes in the atmosphere/ocean system are dominant during termination I. The size of the CO2 increase cannot be explained by variations in ocean temperature, salinity or net transfer of carbon into the terrestrial biosphere alone. The strong temporal correlation of CO2 and Antarctic isotope temperatures is in conflict with hypotheses to account for the missing CO2 which are connected to sea level change or a dust induced change in the biological productivity in the Southern Ocean. Changes in the Southern Ocean sea ice cover, however, may provide a direct link to temperature which appears to be able to account for the observed changes in atmospheric CO2 and δ13C