Dietmar Wagenbach

Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles

Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial–interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000u2009years ago.Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial–interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000u2009years ago.Its a long story...At over 3 km long, the ice core drilled at Dome C in Antarctica represents a record of 740,000 years, or eight glacial cycles. This will be the longest climate record available for years to come, so information gleaned from it will become a benchmark for Antarctic climate research. An examination of the core shows that sea ice around Antarctica waxed and waned in line with temperature over multimillennial timescales, but less so over shorter periods. During cold periods, larger amounts of dust were produced from a drier Patagonia, landing in the Southern Ocean where they probably affected marine productivity. Oceanic production of sulphur compounds, which might affect cloud nucleation, was remarkably constant throughout the period.Data from the Southern Ocean sea-ice extent, the biological productivity of the ocean, and atmospheric iron flux over the past eight glacial cycles indicate that during glacial terminations, changes in Patagonia apparently preceded Antarctic sea-ice reduction — showing that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations.

Continuous record of microparticle concentration and size distribution in the central Greenland NGRIP ice core during the last glacial period

[1]xa0A novel laser microparticle detector used in conjunction with continuous sample melting has provided a more than 1500 m long record of particle concentration and size distribution of the NGRIP ice core, covering continuously the period approximately from 9.5–100 kyr before present; measurements were at 1.65 m depth resolution, corresponding to approximately 35–200 yr. Particle concentration increased by a factor of 100 in the Last Glacial Maximum (LGM) compared to the Preboreal, and sharp variations of concentration occurred synchronously with rapid changes in the δ18O temperature proxy. The lognormal mode μ of the volume distribution shows clear systematic variations with smaller modes during warmer climates and coarser modes during colder periods. We find μ ≈ 1.7 μm diameter during LGM and μ ≈ 1.3 μm during the Preboreal. On timescales below several 100 years μ and the particle concentration exhibit a certain degree of independence present especially during warm periods, when μ generally is more variable. Using highly simplifying considerations for atmospheric transport and deposition of particles we infer that (1) the observed changes of μ in the ice largely reflect changes in the size of airborne particles above the ice sheet and (2) changes of μ are indicative of changes in long range atmospheric transport time. From the observed size changes we estimate shorter transit times by roughly 25% during LGM compared to the Preboreal. The associated particle concentration increase from more efficient long range transport is estimated to less than one order of magnitude.

DNA signature of thermophilic bacteria from the aged accretion ice of Lake Vostok, Antarctica: implications for searching for life in extreme icy environments

We have used 16S ribosomal genes to estimate the bacterial contents of Lake Vostok accretion ice samples at 3551 m and 3607 m, both containing sediment inclusions and formed 20000–15000 yr ago. Decontamination proved to be a critical issue, and we used stringent ice chemistry-based procedures and comprehensive biological controls in order to restrain contamination. As a result, up to now we have only recognized one 16S rDNA bacterial phylotype with confident relevance to the lake environment. It was found in one sample at 3607 m depth and represents the extant thermophilic facultative chemolithoautotroph Hydrogenophilus thermoluteolus of beta- Proteobacteria , and until now had only been found in hot springs. No confident findings were detected in the sample at 3551 m, and all other phylotypes revealed (a total of 16 phylotypes, 336 clones including controls) are presumed to be contaminants. It seems that the Lake Vostok accretion ice is actually microbe-free, indicating that the water body should also be hosting a highly sparse life. The message of thermophilic bacteria suggests that a geothermal system exists beneath the cold water body of Lake Vostok, what is supported by the geological setting, the long-term seismotectonic evidence from 4 He degassing and the ‘ 18 O shift’ of the Vostok accretion ice. The seismotectonic activity that seems to operate in deep faults beneath the lake could sustain thermophilic chemolithoautotrophic microbial communities. Such a primary production scenario for Lake Vostok may have relevance for icy planets and the approaches used for estimating microbial contents in accretion ice are clearly relevant for searching for extraterrestrial life.

A seasonally resolved alpine ice core record of nitrate: Comparison with anthropogenic inventories and estimation of preindustrial emissions of NO in Europe

[1]xa0Continuous high-resolution records from Col du Dome (CDD, 4250 m above sea level, French Alps) ice cores were used to investigate the impact of growing NO emissions on the midtroposphere nitrate levels over Europe from 1925 to 1997. The large snow accumulation rate at the CDD site largely minimized diffusional and depositional perturbations of the nitrate record as commonly encountered in ice cores. That permits for the first time examination of the winter and summer trends separately with a high degree of confidence. Being close to 100 ng g−1 in 1925, summer levels increased at a mean rate of 2 ng g−1 per year from 1925 to 1960 and 8.5 ng g−1 yr−1 from 1960 to 1980. These summer nitrate changes follow rather well the course of growing NO emissions from source regions (France, Italy, Spain, and Switzerland, denoted WE4) located 1000 km around the Alps as estimated by NMI and EDGAR-HYDE inventories. After 1980, the summer nitrate levels continue to increase at a slightly weaker rate than during the 1960–1980 time period. Such a lasting increase of nitrate levels is inconsistent with NO emission estimates, which indicate a decrease after 1993. The nitrate record shows a weaker increase (1 ng g−1 yr−1 from 1930 to 1990) in winter than in summer, corresponding to a lower contamination of the European wide midtroposphere as preferentially recorded in CDD winter samples. Using ice core and emission data, we calculate a preindustrial NO emission (including agricultural and natural emissions) of 0.8 ± 0.2 Mt NO2 per year for WE4 countries, which represents 15–20% of the recent NO emissions. These data would help to reduce existing uncertainties in NO inventories which represent key information to assess past and future ozone changes over Europe.

Observations of atmospheric variability and soil exhalation rate of radon-222 at a Russian forest site. Technical approach and deployment for boundary layer studies

Abstract A monitor for continuous observations of the atmospheric 222Rn daughter activity has been improved and successfully implemented in a field study in the European Taiga (Fyodorovskoye Forest Reserve). The α-activity of the short-lived 222Rn and 220Rn (212Pb) decay products, which are attached to aerosols, is accumulated on a quartz aerosol filter and assayed on line by α-spectroscopy. The α-activity from the 212Pb daughters is determined by spectroscopy and corrected for. This monitor is suitable to measure 222Rn activities at hourly resolution down to 0.5 Bq m−3 with an uncertainty well below ±20%. The prototype of this monitor is run in Heidelberg on the roof of the Institutes building about 20 m above ground. For this site, the atmospheric radioactive disequilibrium was determined between the 222Rn daughter 214Po and 222Rn, which has to be known in order to derive the atmospheric 222Rn activity with the static filter method. We derived a mean disequilibrium 214Po/222Rn = 0.704 ± 0.081 for various meteorological conditions through parallel222Rn gas measurements with a slow pulse ionisation chamber. At the Russian field site, continuous activity observations were performed from July 1998 until July 2000 with half a years interruption in summer/fall 1999. During intensive campaigns, a second monitor was installed at Fyodorovskoye at 15.6 m (July/August 1998), and at 1.8 m (July/August 1999 and October 1999) above ground. As expected, pronounced diurnal cycles of the 222Rn daughter activity were observed at all sites, particularly during summer when the vertical mixing conditions in the atmospheric surface layer vary strongly between day and night. The lower envelope of the continuous measurements at Fyodorovskoye and at Heidelberg changes on synoptic timescales by a factor of 4–10 due to long-range transport changes between continental to more maritime situations. Generally, the 222Rn activity at 26.3 m height at Fyodorovskoye is lower by a factor of 2–3 compared to Heidelberg at 20 m above ground. This unexpected result is due to considerably lower 222Rn exhalation rates from the soils measured in the footprint of the Fyodorovskoye Forest tower compared to Heidelberg. With the inverted chamber technique 222Rn exhalation rates in the range 3.3–7.9 Bq m−2 h−1 were determined at Fyodorovskoye for summer 1998 and autumn 1999 (wet conditions with water table depths between 5 and 70 cm). Only during the very dry summer of 1999 the mean222Rn exhalation rate increased by about a factor of five. All measured exhalation rates at the Fyodorovskoye Forest are considerably smaller by a factor of 2–10 compared to observations in the vicinity of Heidelberg (ca. 50–60 Bq m−2 h−1) and generally in Western Europe.

Sulphate record from a Northeast Greenland ice core over the last 1200 years based on continuous flow analysis

Abstract A 150 m deep ice core from the low-accumulation area of northeast Greenland was analyzed for sulphate, calcium, sodium and electrolytical meltwater conductivity at a depth resolution of approximately 1 cm by continuous flow analysis (CFA). the calcium and sodium profiles are used to establish a relatively precise ice-core chronology by annual-layer counting back to AD 830. Inspection of the novel CFA method for sulphate revealed relative errors typically around 15%, but at least ±20 ng g–1, for concentrations 5130 ng g–1, and a current detection limit for routine ice-core analyses of 40 ng g–1. Annual sulphate peaks are shown to occur over almost the entire core, with only a small shift in seasonality between the modern and pre-industrial sections. Inspection of volcanic horizons allowed more accurate timing of these peaks and clear identification of calcium-rich events. Disregarding clear volcanic peaks, significant long-term changes of sulphate are only seen over the industrial period. However, a higher frequency of important volcanic inputs was identified around AD 1200.

Alpine ice cores and ground penetrating radar: combined investigations for glaciological and climatic interpretations of a cold Alpine ice body

Accurate interpretation of ice cores as climate archives requires detailed knowledge of their past and present geophysical environment. Different techniques facilitate the determination and reconstruction of glaciological settings surrounding the drilling location. During the ALPCLIM1 project, two ice cores containing long-term climate information were retrieved from Colle Gnifetti, Swiss-Italian Alps. Here, we investigate the potential of ground penetrating radar (GPR) surveys, in conjuction with ice core data, to obtain information about the internal structure of the cold Alpine ice body to improve climatic interpretations. Three drill sites are connected by GPR profiles, running parallel and perpendicular to the flow line, thus yielding a three-dimensional picture of the subsurface and enabling the tracking of internal reflection horizons between the locations. As the observed reflections are of isochronic origin, they permit the transfer of age—depth relations between the ice cores. The accuracy of the GPR results is estimated by comparison of transferred timescales with original core datings, independent information from an older ice core, and, based on glaciological surface data, findings from flow modeling. Our study demonstrates that GPR is a mandatory tool for Alpine ice core studies, as it permits mapping of major transitions in physical-chemical properties, transfer of age—depth relations between sites, correlate signals in core records for interpretation, and establish a detailed picture of the flow regime surrounding the climate archive. Environmental and Climate Records from High Elevation Alpine Glaciers.

A historical record of formate and acetate from a high‐elevation Alpine glacier: Implications for their natural versus anthropogenic budgets at the European scale

[1]xa0High-resolution records of formate and acetate from a Col du Dome (CDD, 4250 m elevation, French Alps) ice core were used to investigate the impact of man-made activities on the midtropospheric levels of these species over Europe since 1925. Formate whose summer levels remained unchanged (80 ± 20 ng g−1) over the 1925–1995 time period is the major monocarboxylate present in summer CDD snow layers. In contrast, the acetate summer level being close to 15 ng g−1 prior to 1950 increased by a factor of 3 from 1950 to 1975 and declined during the 1980s. The difference in past changes of these monocarboxylates is due to recent acidification of the atmosphere which has lowered the scavenging efficiency in a larger extent for formate than for acetate. Formate levels corrected from effect of past acidity changes show a long-term trend similar to the acetate one. These past changes are likely related to vehicle emissions (direct emissions and secondary production from alkenes) which strongly increased from 1950 to 1980. Because of improvement of engines and more stringent emission standards the CDD summer levels of monocarboxylates declined in the 1980s, and the 1990 levels are only slightly higher than their preindustrial levels. Therefore, except at the end of the 1970s when the anthropogenic input was as high as the natural one, natural sources appear to dominate the budget of the two monocarboxylates in the European midtroposphere. It is shown that natural sources include direct emissions by vegetation, oxidation of isoprene and monoterpenes, and possibly in-cloud oxidation of formaldehyde into formic acid and gas phase oxidation of peroxyl acetyl radical into acetic acid.

Seasonally resolved Alpine and Greenland ice core records of anthropogenic HCl emissions over the 20th century

[1]xa0The continuous highly resolved records of Cl−, Na+, and Ca2+ in ice cores from Col du Dome (4250 m elevation, French Alps) and Summit (3240 m elevation, central Greenland) are used to reconstruct the history of atmospheric HCl pollution over Europe and Greenland since the early 20th century. The evaluation of the HCl amount in summer snow deposits at high-elevation Alpine sites is complex since continental emissions (soils, halide evaporites, and possibly manure-fertilized fields) account for 80% of the chloride budget and only one fifth of Cl− is related to HCl. During the preindustrial era the HCl content of summer Alpine snow layers fluctuated between 0 and 6 ng g−1, likely in relation with a highly variable interannual biomass burning activity in western Europe. From 1925 to 1960 the HCl levels were slightly higher (3–9 ng g−1), mainly due to growing coal burning emissions in western Europe. In the late 1960s a sharp increase of HCl levels (up to 17 ng g−1) took place as a result of the setup of waste incineration in western Europe, this process contributing 3–4 times more than coal combustion to the HCl budget of summer Alpine snow layers deposited between 1970 and 1990. In winter, sea spray emissions dominate (∼78%) the total Cl− level of Alpine snow layers. The HCl trend in these snow layers remained limited to ∼2 ng g−1 over the 20th century, likely in relation to waste incineration after 1965. In Greenland snow layers most of particulate Cl− originates from sea spray, 1/3 to 2/3 of Cl− being present as HCl in spring and summer, respectively. The Greenland HCl ice core records indicate a preindustrial HCl level close to 4 ng g−1, which is found to be mainly due to the sea-salt dechlorination, while the contribution of passive volcanic HCl emissions at high northern latitudes can be neglected. The input from sea-salt dechlorination has been enhanced by a factor of 2–3 during the second half of the 20th century similarly to the increase of the atmospheric acidity in response to growing NOx and SO2 anthropogenic emissions.

Atmospheric year‐round records of dicarboxylic acids and sulfate at three French sites located between 630 and 4360 m elevation

[1]xa0An atmospheric year-round study of C2–C5 dicarboxylic acids (oxalic, malonic, succinic, malic, and glutaric) and sulfate was conducted in 2002 and 2003 at three remote western Europe continental sites located at different elevations (from 630 to 4360 m asl). Whatever the site and the season, oxalic acid is always the dominant diacid (average 64% of total dicarboxylic acids) followed by malonic acid (15% of total dicarboxylic acids). High correlation coefficients are observed between C3 (malonic), C4 (malic and succinic), and C5 (glutaric) acids and oxalic acid. These strong relationships between C2–C5 diacids support the hypothesis of a common production of these diacids through the aqueous phase chemistry of glutaric acid. Data gained at different elevations are here useful to compare the mass formation rates of sulfate and dicarboxylic acids. It is shown that in summer the decrease of the sum of dicarboxylic acids with height is far less pronounced than the decrease of sulfate (a factor of 2 instead of 6.8 from 630 to 4360 m asl). That demonstrates that the production of dicarboxylic acids occurs at up to 4300 m elevation while the production of sulfate from SO2 mainly takes place between the boundary layer and 3000 m elevation. With respect to summer 2002 the sum of dicarboxylic acids was enhanced in summer 2003 (from 136 to 331 ng m−3 STP at 2870 m asl, for instance) whereas a weaker increase is observed for sulfate (from 1700 to 2500 ng m−3 STP at 2870 m asl). These changes are attributed to the particular summer 2003 conditions which led to enhanced level of oxidants (strengthened secondary productions) and warmer temperatures (enhanced emissions of biogenic precursors of diacids).