TY - JOUR A1 - Kienel, Ulrike A1 - Plessen, Birgit A1 - Schettler, Georg A1 - Weise, Stephan A1 - Pinkerneil, Sylvia A1 - Boehnel, Harald A1 - Englebrecht, Amy C. A1 - Haug, Gerald H. T1 - Sensitivity of a hypersaline crater lake to the seasonality of rainfall, evaporation, and guano supply JF - Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology N2 - The hypersaline crater lake and its catchment on seabird island Isabel (Pacific, off Mexico) was studied to explore the influence of strong seasonal variations in rainfall/evaporation and guano contribution on its limnology. The hypersaline lake water (HSW, 78 %) is up to 2.2-times enriched in inert ions relative to mean seawater. Rainfall during summer dilutes the HSW to form a less saline rainwater body (RWB) above a chemolimnion between 2 and 4 m water depth. The RWB is inhabited first by diatoms and ostracods followed later on by cyanobacteria and ciliates. Evaporation of > 1.5 m depth of lake water over the dry season increases the salinity of the RWB until the water column becomes isohaline at HSW concentrations in the late dry season. Differences in the stable isotope composition of water and primary producers in RWB and HSW reflect this development. Introduction of seabird guano and the decrease of salinity fuel a high primary production in the RWB with higher delta(CDIC)-C-13 and delta(13)Corg of particulate organic matter than in the HSW. The high N supply leads to high delta N-15 NH4 values (+ 39 % in the HSW) as the consequence of ammonia volatilization that is strongest during guano maturation and with evaporative salinity increase from the HSW. Precipitation of carbonate (calcite and aragonite) from the RWB and the HSW is hindered by the high concentration of guano-derived P. This inhibition may be overcome with evaporative supersaturation during particularly dry conditions. Carbonate may also precipitate during particularly wet conditions from the dilute RWB, where the P-concentration is reduced during an active phytoplankton production that raises the pH. Differences in the stable isotope signatures of carbon and oxygen in HSW and RWB (+ 5 % delta(CDIC)-C-13 and -3 % d18OH2O) suggest the processes of carbonate precipitation can be distinguished based on the isotope signature of the carbonates deposited. Changes in the lake system are indicated when lower temperatures and higher rainfall in the 2006 wet season introduced more and less mature guano to the lake. The lower pH was accompanied by lower ammonia volatilization and carbonate precipitation as indicated by an increased concentration of NH4, Ca, Sr and DIC, while delta H-2, delta(NNH4)-N-15, and salinity were lower. According to our results, the observed sediment laminations should reflect the introduction of catchment material (including guano) with runoff, the RWB plankton production, and the carbonate precipitation in relation to its origin and seasonality. KW - ammonia volatilization KW - carbonate precipitation KW - chemocline KW - guano KW - hypersaline lake KW - stable isotopes Y1 - 2013 U6 - https://doi.org/10.1127/1863-9135/2013/0405 SN - 1863-9135 VL - 183 IS - 2 SP - 135 EP - 152 PB - Schweizerbart CY - Stuttgart ER - TY - JOUR A1 - Kienel, Ulrike A1 - Bowen, Sabine Wulf A1 - Byrne, Roger A1 - Park, Jungjae A1 - Boehnel, Harald A1 - Dulski, Peter A1 - Luhr, James F. A1 - Siebert, Lee A1 - Haug, Gerald H. A1 - Negendank, Joerg F. W. T1 - First lacustrine varve chronologies from Mexico : impact of droughts, ENSO and human activity since AD 1840 as recorded in maar sediments from Valle de Santiago N2 - We present varve chronologies for sediments from two maar lakes in the Valle de Santiago region (Central Mexico): Hoya La Alberca (AD 1852-1973) and Hoya Rincn de Parangueo (AD 1839-1943). These are the first varve chronologies for Mexican lakes. The varved sections were anchored with tephras from Colima (1913) and Paricutin (1943/ 1944) and Pb-210 ages. We compare the sequences using the thickness of seasonal laminae and element counts (Al, Si, S, Cl, K, Ti, Mn, Fe, and Sr) determined by micro X-ray fluorescence spectrometry. The formation of the varve sublaminae is attributed to the strongly seasonal climate regime. Limited rainfall and high evaporation rates in winter and spring induce precipitation of carbonates (high Ca, Sr) enriched in C-13 and O-18, whereas rainfall in summer increases organic and clastic input (plagioclase, quartz) with high counts of lithogenic elements (K, Al, Ti, and Si). Eolian input of Ti occurs also in the dry season. Moving correlations (5-yr windows) of the Ca and Ti counts show similar development in both sequences until the 1930s. Positive correlations indicate mixing of allochthonous Ti and autochthonous Ca, while negative correlations indicate their separation in sublaminae. Negative excursions in the correlations correspond with historic and reconstructed droughts, El Nio events, and positive SST anomalies. Based on our data, droughts (3-7 year duration) were severe and centred around the following years: the early 1850s, 1865, 1880, 1895, 1905, 1915 and the late 1920s with continuation into the 1930s. The latter dry period brought both lake systems into a critical state making them susceptible to further drying. Groundwater overexploitation due to the expansion of irrigation agriculture in the region after 1940 induced the transition from calcite to aragonite precipitation in Alberca and halite infiltration in Rincn. The proxy data indicate a faster response to increased evaporation for Rincn, the lake with the larger maar dimensions, solar radiation receipt and higher conductivity, whereas the smaller, steeper Alberca maar responded rapidly to increased precipitation. Y1 - 2009 UR - http://www.springerlink.com/content/100294 U6 - https://doi.org/10.1007/s10933-009-9307-x SN - 0921-2728 ER -