Late-glacial and early Holocene lake sediments, ground-water formation and climate in the Atacama Altiplano 22–24°S

Precipitation rates in the Atacama Altiplano 22–24°S were 400–500 mm yr−1 during late glacial and early Holocene times as opposed to 200 mm yr−1 today. This humid phase (Tauca phase) was likely due to strengthened tropical (monsoonal) circulation, which brought continental moisture to the Atacama Altiplano. The lake level of Laguna Lejía (23°30′S, 4350 m) at that time was up to 25 m higher than it is today. Mg/Ca and Sr/Ca data from lake sediments show that, what today is a highly saline lake was a freshwater lake at that time. Seasonally-laminated calcareous sediments were deposited between 13 500 and <10 400 yr B.P. indicating the maximum of the humid phase. Climatic changes in the past are important for current groundwater resources.14C and3H data from lake-, ground- and well water suggest that modern groundwater formation (i.e. water <40 years) in the Altiplano is very limited under current arid conditions. We conclude that significant amounts of the water resources in this area originated during the time of the late-glacial and early Holocene humid climate. Tritium data from snow samples show that the moisture in the Altiplano at 22–24°S is mainly of continental origin, whereas precipitation from the westerlies hardly contributes to the water supply in this area. This precipitation pattern matches the paleodata, and we suggest that current precipitation formation may provide an analogue framework for late-glacial circulation in this area

Sources and distribution of trace species in Alpine precipitation inferred from two 60-year ice core paleorecords

International audienceThe Alps represent the largest barrier to meridional air flow in Europe, strongly influencing the weather and hence the distribution of atmospheric trace components. Here for the first time, chemical records from two ice cores retrieved from glaciers located in the northern and southern Swiss Alps were compared in conjunction with an analysis of "weather type", in order to assess geographical and seasonal trends in the deposition of trace species and to identify source regions and transport patterns. Using a correlation analysis, investigated trace species (NH4+, NO3?, SO42?, Ca2+, Mg2+, Na+, K+, and Cl? were grouped into classes of different origin (anthropogenic, sea salt, or Saharan dust). Over the last 60 years, precipitation chemistry at both sites was dominated by NH4+, NO4?, and SO42?, all of anthropogenic origin and deposited mainly in summer by way of convective precipitation. The similarity of the SO42? profiles with historical records of SO4 emissions from France and Italy indicated these two countries as key source areas for the anthropogenic species. In contrast, sea salt and Saharan dust showed major differences in transport pattern and deposition across the Alps. Currently, the sea-salt constituents Na+, K+, and Cl? are transported to the northern site during advective westerly-wind situations, independent of Saharan dust events. At the southern site, sea salt and Saharan dust are deposited simultaneously, indicating a coupled transport active mainly in summer during south-westerly wind situations

Influence of the Tungurahua eruption on the ice core records of Chimborazo, Ecuador

International audienceThe comparison of two shallow ice cores recovered in 1999 and 2000 from the same place on the Chimborazo summit glacier revealed the influence of the coincident Tungurahua volcanic eruption on their stable isotope and chemical records. The surface snow melting and water percolation induced from the ash deposition caused a preferential elution and re-localization of certain ionic species, while the stable isotope records were not affected. Additionally, the comparison of the ionic amount and some selected ion ratios preserved along the ice core column reports under which processes the chemical species are introduced in the snow pack, as snow flake condensation nuclei, by atmospheric scavenging or by dry deposition. This preliminary study is essential for the interpretation of the deep Chimborazo ice core, or for other sites where surrounding volcanic activity influences the glaciochemical records

A 2000 Year Saharan Dust Event Proxy Record from an Ice Core in the European Alps

Dust events originating from the Saharan desert have far reaching environmental impacts but the causal mechanism of magnitude and occurrence of Saharan dust events (SDEs) during the pre‐instrumental era requires further research, particularly as a potential analog for future climate. Using an ultra‐high resolution glacio‐chemical record from the 2013 Colle Gnifetti (CG) ice core drilled in the Swiss‐Italian Alps we reconstructed a 2000 year‐long summer Saharan dust record. We analyzed both modern (1780‐2006) and pre‐modern Common Era (C.E.) major and trace element records to determine air mass source regions to the Colle Gnifetti glacier and assess similarities to modern and reconstructed climate trends in the Northern Hemisphere. This new pSDE (proxy SDE) reconstruction, produced using measurements from a novel, continuous ultra‐high‐resolution (120‐μm) ice core analysis method (laser ablation‐inductively coupled plasma‐mass spectrometer or LA‐ICP‐MS) is comprised of 316,000 data points per element covering the period 1 to 1820 C.E. We found that the CG ice core captures an anomalous increase in Saharan dust transport during the onset of the Medieval Climate Anomaly (870‐1000 C.E.) and records other prominent shorter events (C.E., 140‐170, 370‐450, 1320‐1370, and 1910‐2000), offering a framework for new insights into the implications of Saharan dust variability

Determination of impurities in ice-cores from the Jungfrau-Joch by neutron activation analysis

An ice-core of 4 m length was drilled at the Jungfraujoch. It was divided into 18 sections and analyzed for solid and dissolved material by neutron activation analysis using nondestructive counting as well as chemical group separations. The solid material was identified as stone dust. Part of the dissolved material seems to originate from dissolved limestone, whereas many elements can not be accounted for by this hypothesis and must be due to atmospheric fallout

Temporal Changes of the 14C Reservoir Effect in Lakes

From the 16th International Radiocarbon Conference held in Gronigen, Netherlands, June 16-20, 1997.Conventional radiocarbon dates for sediment samples from aquatic systems and of coeval terrestrial samples deviate from each other due to the reservoir effect. The reservoir correction is usually assumed to be constant with time for a specific aquatic system. Our studies confirm that seasonal and secular changes are frequent and are governed by the limnological conditions. Lakes have two principal sources of 14C: atmospheric CO2 and the total dissolved inorganic carbon (TDIC) of the entering groundwater and runoff. The former has values of ca. 100 pMC; the latter usually has a 14C value well below 100 pMC. Atmospheric CO2 enters the lake by exchange via its surface. The proportions of these two kinds of input determine the magnitude of the reservoir correction in freshwater lakes. It is mainly a function of the volume/surface ratio of the lake and, consequently a function of the water depth. The surface of lakes with outflow does not change when sedimentation decreases the depth of the water. The depth of Schleinsee Lake in southern Germany has decreased from 30 to 15 m since ca. 9000 BP. As a result, the reservoir correction has decreased from ca. -1550 to -580 yr. In contrast, the depth of Lake Proscansko in Croatia increased with growth of the travertine dam and the reservoir correction changed from ca. -1790 to -2650 yr during the last 8800 yr. The largest fluctuations of lake levels occur in closed lakes in arid regions when the climate changes from humid to arid and vice versa. As a result, the reservoir correction of the 14C dates for the total organic fraction from Lejía Lake in the Atacama Desert of Chile varied between <-1800 yr and -4700 yr over a period of only 1800 yr between 11,500 and 9700 BP. The corresponding reservoir correction for the marl fraction is much higher. In summary, accurate and reliable 14C dating of lake sediments requires a study of the temporal changes of the reservoir effect by analysis of both the organic and marl fractions. The most reliable 14C dates are obtained from terrestrial plant remains.This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

A historical record of ammonium concentrations from a glacier in the Alps

Ammonia is the primary gaseous alkaline species in the atmosphere over Europe, neutralising up to 70% of the original acidity in precipitation [Buijsman et al., 1987]. It is directly involved in the conversion of sulphur dioxide and nitrogen oxides into the aerosol phase. Furthermore, ammonium contributes considerably to the nitrogen deposition and soil acidification which causes extensive changes in plant communities in many ecosystems [Moore, 1995; Rohde et al., 1995]. However, in Europe continuous long-term measurements of atmospheric ammonia or ammonium in precipitation are lacking. Here, we present a continuous, high-resolution record of ammonium in precipitation for the time period 1780 to 1980 deduced from an ice core recovered from a high-altitude glacier in the Alps. The ammonium level remained constant from 1780 to 1870 and increased afterwards by a factor of three. This trend shows that ammonia emissions in Europe have substantially increased in the last 100 years

A box diffusion model to study the carbon dioxide exchange in nature

Phenomena related to the natural carbon cycle as the 14C distribution between atmosphere and ocean and the atmospheric response to the input of fossil fuel CO2 and of 14C produced in nuclear weapon tests have been quantitatively discussed by other authors using box models. However the exchange coefficients derived from the natural 14C distribution do not agree with those valid to describe the short-term phenomena. A model consisting of a well mixed atmospheric box coupled to a long-term biosphere, of an ocean surface box and a diffusive deep ocean is discussed. The dynamic parameters were derived from the preindustrial 14C distribution in atmosphere and ocean. A consistent description of phenomena with completely different characteristic times is possible, because in the box diffusion model the flux from mixed layer to deep sea increases for decreasing time constants of the perturbations. This is in contrary to box models where it is essentially independent of the time constants if they are smaller than a few hundred years. Due to this fact our model is valid for predictions of the atmospheric CO2 response to the various possible future CO2 input time functions

Radiocarbon reservoir effect and the timing of the late-glacial/early holocene humid phase in the Atacama Desert (Northern Chile)

We revise substantially the regional chronology of lake-level fluctuations from the late-glacial/early Holocene humid phase along a high altitude transect (3500 to 4500 m) between 18°S and 28°S in the Southwestern Altiplano of Northern Chile. Radiocarbon dates and 210Pb profiles for limnic and terrestrial materials allow us to estimate and justify reservoir correction values for conventional 14C dates. Our chronology suggests that the latest Pleistocene/early Holocene humid phase started between 13,000 and 12,000 14C yr B.P., and that maximum lake levels were reached between 10,800 and 9200 14C yr B.P. This is significantly younger than what has been established so far for the Titicaca–Uyuni Basin in Bolivia. The paleolakes disappeared sometime between 8400 and 8000 14C yr B.P. Our revised chronology agrees with the regional history of human occupation, and is broadly synchronous with vegetation changes in subtropical continental South America, and with the onset of wetland expansion in the northern hemisphere tropics