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Teranes, JL, McKenzie JA.  2001.  Lacustrine oxygen isotope record of 20(th)-century climate change in central Europe: evaluation of climatic controls on oxygen isotopes in precipitation. Journal of Paleolimnology. 26:131-146.   10.1023/a:1011175701502   AbstractWebsite

We report oxygen isotope data from a 108-yr (1885-1993) sequence with annual laminae of bio-induced authigenic calcite in a frozen core from Baldeggersee, a small lake in Central Switzerland. These isotope results provide proxy data on the isotopic composition of past precipitation in the Baldeggersee catchment region and are quantitatively compared with instrumental climate data (i.e. mean annual air temperature and atmospheric circulation pattern indices) to evaluate climatic controls on oxygen isotopes in precipitation. Monitoring the isotope hydrology of Baldeggersee demonstrates that the oxygen isotopic composition of the lake water is controlled by the isotopic composition of local atmospheric precipitation (delta O-18(p)) and that the isotopic signal of precipitation is preserved, albeit damped, in the lake calcite oxygen isotope record (delta O-18(c)). Comparison of the calcite oxygen isotope proxy for delta O-18(p) in the catchment with historical mean annual air temperature measurements from Bern, Switzerland confirms that authigenic calcite reliably records past annual air temperature in the region. This delta O-18(c)/temperature relationship is calculated to be 0.39 parts per thousand/degreesC for the period 1900-1960, based on an isotope mass-balance model for Baldeggersee. An exception is a 0.8 parts per thousand anomalous negative shift in calcite delta O-18 values since the 1960s. Possible explanations for this recent delta O-18(c) shift, as it is not related to mean annual air temperature, include changes in delta O-18(p) due to synoptic circulation patterns. In particular, the 0.8 parts per thousand negative shift coincides with a trend towards a more dominant North Atlantic Oscillation (NAO) index. This circulation pattern would tend to bring more isotopically more negative winter precipitation to the region and could account for the 0.8 parts per thousand offset in delta O-18(c) data.

Teranes, JL, McKenzie JA, Bernasconi SM, Lotter AF, Sturm M.  1999.  A study of oxygen isotopic fractionation during bio-induced calcite precipitation in eutrophic Baldeggersee, Switzerland. Geochimica Et Cosmochimica Acta. 63:1981-1989.   10.1016/s0016-7037(99)00049-6   AbstractWebsite

In order to better understand environmental factors controlling oxygen isotope shifts in autochthonous lacustrine carbonate sequences, we undertook an extensive one year study (March, 1995 to February, 1996) of water-column chemistry and daily sediment trap material from a small lake in Central Switzerland. Comparisons between calculated equilibrium isotope values, using the fractionation equation of Friedman and O'Neil (1977) and measured oxygen isotope ratios of calcite in the sediment-traps reveal that oxygen isotopic values of autochthonous calcite (delta(18)O) are in isotopic equilibrium with ambient water during most of the spring and summer, when the majority of the calcite precipitates. In contrast, small amounts of calcite precipitated in early-spring and again in late-autumn are isotopically depleted in O-18 relative to the calculated equilibrium values, by as much as 0.8 parts per thousand. This seasonally occurring apparent isotopic nonequilibrium is associated with times of high phosphorous concentrations, elevated pH (similar to 8.6) and increased [CO32-] (similar to 50 mu mol/l) in the surface waters. The resulting weighted average delta(18)O Value for the studied period is -9.6 parts per thousand, compared with a calculated equilibrium delta(18)O value of -9.4 parts per thousand. These data convincingly demonstrate that delta(18)O of calcite are, for the most part, a very reliable proxy for temperature and delta(18)O Of the water. Copyright (C) 1999 Elsevier Science Ltd.

Teranes, JL, Geary DH, Bemis BE.  1996.  The oxygen isotopic record of seasonality in Neogene bivalves from the Central American Isthmus. Evolution and Environment in Tropical America. ( Jackson JBC, Budd AF, Coates AG, Eds.).:105-129., Chicago: University of Chicago Press Abstract

How were the tropical Americas formed? This ambitious volume draws on extensive, multidisciplinary research to develop new views of the geological formation of the isthmus linking North and South America and of the major environmental changes that reshaped the Neotropics to create its present-day-marine and terrestrial ecosystems.

Teranes, JL, Bernasconi SM.  2005.  Factors controlling δ13C values of sedimentary carbon in hypertrophic Baldeggersee, Switzerland, and implications for interpreting isotope excursions in lake sedimentary records. Limnology and Oceanography. 50:914-922. AbstractWebsite

We use stable carbon isotope values (delta(13)C) in sedimented organic matter and carbonate as proxy indicators of productivity changes in a highly eutrophic to hypertrophic lake. Stable isotope data from a seasonally sampled sediment core recovered from Baldeggersee, Switzerland were compared with direct and inferred total phosphorus (P) concentrations. Carbon isotope values of sedimentary organic matter (delta(13)C(org)) in both seasonal varves and over the past 100 yr are not linearly related to total P concentrations, nor do they mirror observed trends in carbonate isotope values (delta(13)C(CaCO3)). Baldeggersee delta(13)C(org) values are influenced by both variations in the relative inputs of eukaryotic biomass, which becomes enriched in C-13 with increasing primary productivity, and the contribution of microbial biomass produced in the expanding anoxic bottom waters, which is typically very depleted in C-13. We also examined the fractionation within the organic matter-CO2-CaCO3 system, calculated as epsilon(total organic carbor(TOC)) = 10(3){[(delta(13)C(CaCO3) + 1,000)/(delta(13)C(org) + 1,000)] - 1}. Thresholds within the measured epsilon(TOC) values represent Baldeggersee trophic status more accurately than delta(13)C(org) or delta(13)C(CaCO3) values alone. In alkaline lakes with endogenic carbonate precipitates, STOC values can facilitate accurate interpretation of values and trends in organic carbon isotope data, and can help to better assess trophic history and lake remediation efforts in lake systems that have been heavily affected by cultural eutrophication.

Teranes, JL, McKenzie JA, Lotter AF.  1999.  Stable isotope response to lake eutrophication: Calibration of a high-resolution lacustrine sequence from Baldeggersee, Switzerland. Limnology and Oceanography. 44:320-333. AbstractWebsite

Stable isotope analyses of discrete seasonal layers from a 108-yr annually laminated freeze-core from Baldeggersee, a small, eutrophic lake in central Switzerland, provide information on the climatological and environmental factors, including lake eutrophication, that control oxygen and carbon isotopic composition of epilimnic biologically induced calcite precipitate. During the last 100 yr, Baldeggersee has undergone major increases in productivity and eutrophication in response to nutrient loading from agriculture and industrialization in the lake's watershed. Calibration of the isotopic signal in Baldeggersec to historical limnological data quantitatively links evidence of isotopic depletion in the sedimented calcite to trophic state of the lake. delta(18)O values from the spring/summer "light" sediment layers steadily diverged to more depleted values in response to historical eutrophication: measured delta(18)O values were up to -1.5 parts per thousand more negative than calculated equilibrium delta(18)O values. Evidence for C-13 depletion in the calcite, relative to equilibrium values, is more difficult to ascertain because of an overall dominance of isotopic enrichment in the dissolved inorganic pool as productivity in Baldeggersee increases. A positive association exists between the degree of oxygen 18 depletion and the calcite crystal size. Thus, large amorphous calcite grains can be used as a proxy for recognizing apparent isotopic nonequilibrium in sediment sequences from highly productive lacustrine environments from all geologic time scales. In contrast to the light layers, the oxygen isotopic composition of the calcite in the late summer/fall "dark" sediment layers is unaffected by the apparent isotope nonequilibrium. Oxygen and carbon isotope values from the dark laminae in the Baldeggersee sediment therefore provide environmental and climatological proxies that can be calibrated with known environmental and regional climate data for the last century.

Teranes, JL, Bernasconi SM.  2000.  The record of nitrate utilization and productivity limitation provided by δ15N values in lake organic matter - A study of sediment trap and core sediments from Baldeggersee, Switzerland. Limnology and Oceanography. 45:801-813. AbstractWebsite

The response of nitrogen isotopic composition of organic matter to changes in nitrate utilization, N-limitation and lake productivity was studied in Baldeggersee, a small eutrophic lake in central Switzerland. Nitrogen isotope ratios were measured on organic matter accumulation in sediment traps, collected daily from March 1995 through October 1996, and on individually sampled light and dark annual laminae from a 108-yr sediment core sequence (1885-1993). Nitrogen accumulation in the sediment traps averaged 0.04 g N m(-2) d(-1). delta(15)N values of the sediment trap material increased from 11 parts per thousand to 13 parts per thousand (atmospheric N-2) as primary productivity decreased surface water [NO3-] from 1.4 to 0.7 mg N L-1 during the seasonal stratified periods. Very small amounts of isotopically enriched organic matter (delta(15)N similar to 15-20 parts per thousand) of heterotrophic and/or detrital origin accumulated in the winter months. Nitrogen accumulation in the core sediments average 4 g N m(-2) per year. delta(15)N values of the sediment core material increased up-core (from delta(15)N similar to 6 parts per thousand to delta(15)N similar to 11 parts per thousand); several abrupt positive isotope shifts (>2 parts per thousand) occur in the upper Dart of the record. Comparison between sediment delta(15)N values and surface water [NO3-] measurements for the period of 1976-1993 reveals that the abrupt positive delta(15)N shifts occurred in years where unusually large phytoplankton blooms depleted surface waters nitrate to concentrations of <0.7 mg N L-1. A 3 parts per thousand negative delta(15)N shift, observed between 1973-1975 at the time of maximum anoxic conditions and meromixis, can be attributed to phytoplankton incorporation of ammonia, which was present in concentrations of up to 0.7 mg L-1 in the epilimnion. Preservation of isotopic shifts in the sediment core which are clearly related to water column processes, and the similarity of core top delta(15)N values to the weighted average N-isotopic composition of sediment trap material indicate that the sediment record reliably reflects the surface-generated delta(15)N signal. Our results from sediment trap and uppermost core samples provide the first conclusive evidence that N-isotopes in lacustrine organic matter record the increasing isotopic enrichment of surface water NO3- due to its utilization by phytoplankton. Artificial aeration of the Baldeggersee bottom water since 1982 has effectively reduced water column anoxia. Thus, water column denitrification, which could considerably increase the isotopic composition of residual nitrate, does not occur in the present lake. Even so, present day nitrogen isotopic values in the sediment core data are higher than most all previous periods suggesting that water column denitrification has never been a dominant influence on sediment delta(15)N values. Instead, the up-core 6 parts per thousand increase in delta(15)N values better corresponds to the documented history of external N-loading from agricultural runoff in the watershed over the last 100 years. These nitrogen sources have characteristically high delta(15)N values (10-20 parts per thousand) and could lead to progressive N-15-enrichment of the Baldeggersee dissolved inorganic nitrogen pool.