Alejandro Spitzy

Self-organization of dissolved organic matter to micelle-like microparticles in river water.

In aquatic systems, the concept of the ‘microbial loop’ is invoked to describe the conversion of dissolved organic matter to particulate organic matter by bacteria. This process mediates the transfer of energy and matter from dissolved organic matter to higher trophic levels, and therefore controls (together with primary production) the productivity of aquatic systems. Here we report experiments on laboratory incubations of sterile filtered river water in which we find that up to 25% of the dissolved organic carbon (DOC) aggregates abiotically to particles of diameter 0.4–0.8 micrometres, at rates similar to bacterial growth. Diffusion drives aggregation of low- to high-molecular-mass DOC and further to larger micelle-like microparticles. The chemical composition of these microparticles suggests their potential use as food by planktonic bacterivores. This pathway is apparent from differences in the stable carbon isotope compositions of picoplankton and the microparticles. A large fraction of dissolved organic matter might therefore be channelled through microparticles directly to higher trophic levels—bypassing the microbial loop—suggesting that current concepts of carbon conversion in aquatic systems require revision.

Carbon Dioxide: A Biogeochemical Portrait

Carbon dioxide, chemical formula CO2, is a colorless and tasteless gas about 1.5 times as heavy as air. Its specific volume at atmospheric pressure (101, 325 N m-2) and room temperature (21 °C) is 0.546 m3 kg-1. Under natural atmospheric conditions it is a stable, inert, and nontoxic gas. When subjected to higher pressure and temperature, the gas can be liquefied and solidified. For instance at 21 °C and 838 psig (= pounds per square inch gage), CO2 becomes a liquid. Further cooling will result in the formation of dry ice snow, which at atmospheric pressure has a sublimation temperature of — 78 °C.

Experiments on the influence of sediment disturbances on the biogeochemistry of the deep-sea environment

In experiments with large undisturbed sediment cores, stirring the upper centimeters of sediment immediately released dissolved pore-water constituents such as heavy metals and nutrients. Rapid scavenging in the suspension after the disturbance was observed for cationic particle-reactive metals like Mn, Co, Ni, Zn, Cu, Cd, Pb, and Fe, while anionic metal species like Mo, V, and U showed neither strong release nor sorption. Microbial activity, fresh particulate organic carbon and nitrogen, and amino acids and hexosamines increased during the first days after disturbance. The ratios of C and N and of the amino acids also changed with time. Applicability of the results of laboratory experiments to in situ deep-sea conditions supports the necessity of in situ experiments in benthic chambers.

Low-temperature sealed tube combustion of gaseous, liquid and solid organic compounds for 13C/12C and 14C analysis

A new, low-temperature sealed tube technique for combustion of organic carbon prior to subsequent off-line isotope analysis is proposed. Complete oxidation is achieved with potassium peroxodisulfate and silver permanganate as oxidants at temperatures not exceeding 500 °C. The combustion of gaseous (methane), solid (cane sugar, vanilla, N-thiazolyl-2-sulfamide, ascorbic acid, phenanthrene, thiourea, polyethylenefilm, tetrafluoropolyethylene, polyetheretherketone, graphite, and Suwannee River Fulvic Acid), and liquid (tetrachloroethene, toluene, and oil) model compounds and international standards was tested. A 24 h combustion at 500 °C was sufficient for complete oxidation in all cases. The time required for complete oxidation of Suwannee River Fulvic Acid, typical of refractory freshwater dissolved organic carbon, as a function of combustion temperature was 2 h at 500 °C, 6 h at 400 °C, and 24 h at 300 °C. Preparation of saline solution parallels of cane sugar, vanilla, N-thiazolyl-2-sulfanilamide, and ascorbic acid gave consistent results. For reproducible δ13C analyses using a Thermoquest MAT 252 MS, a minimum of 5 µg C had to be combusted. Reliable 14C results, measured at an accelerator mass spectrometer facility, were obtained from coal and from cane sugar combusted for 24 h at 500 °C by the proposed method.

CO2, Kohlenstoff-Kreislauf und Klima: I. Globale Kohlenstoffbilanz

Past and expected emissions of anthropogenic CO 2 stimulate carbon cycle and climate research. Prognoses of future CO 2 levels depend on energy scenarios and on the reaction of the biosphere and hydrosphere to elevated atmospheric CO 2 concentrations. The reaction of the reservoirs vegetation, freshwater and oceans to disturbances of the carbon cycle is reviewed. For the oceans first results of a simple carbon cycle model implanted in a three-dimensional general circulation model are presented. This model allows experiments not possible with previous box models. Das COz-Problem ist in Wissenschaft und 0ffentlichkeit in den letzten zehn Jahren intensiv diskutiert worden. Es geht dabei urn die Frage, ob die zunehmende Emission von anthropogenem CO2 langfristig zu drastischen Ver/inderungen des globalen Klimas f/ihrt. Seit 1958 wird unter anderen auf der Mauna-Loa-Station/Hawaii [1] der Anstieg des CO2-Partialdrucks der Luft gemessen (Pco2, Fig. 1 a). Der Pco2 stieg in diesem Zeitraum exponentiell von 315 auf 340 ppmv, also um etwa 8% (ppmv = Volumensmischungsverhfiltnis in Vielfachen von 10-6). Eine Frage ist, warum der CO2-Gehalt nicht noch h6her stieg, denn alleine der Ausstol3 von CO2 bei der Energieerzeugung ist doppelt so hoch wie der beobachtete Anstieg, ganz abgesehen von m6glichem zusfitzlichem CO z aus der Zerst6rung der Biosphfire. Pro Jahr werden bei der Verbrennung fossiler Kohlenstoffe 5,3 Milliarden Tonnen Kohlenstoff (Gigatonnen = Gt) als CO2 in die Atmosph/ire entlassen. Bisher sind schon 180 Gt C verbraucht. Auch aus der Biosphfire setzt der Mensch grol3e Mengen Kohlenstoff frei. Die Rodung erst der gem/ii3igten (Pioniereffekt) und jetzt der tropischen W/ilder, die Zerst6rung der Savannen und die Abschwemmung und Oxidation der Ackerb6den hat m6glicherweise Kohlenstoff in gleicher Gr613enordnung wie die Verbrennung von Kohle, Ol und Gas mobilisiert. Moore et al. [2] und Houghton et al. [3] errechnen aus Biomasse-Modellen, dab heute zwischen 1,8 und 4,7 Gt Kohlenstoff netto pro Jahr emittiert werden. Das anthropogen erzeugte CO 2 bleibt nicht vollst/indig als COz in der Atmosph/ire, sondern wird durch den natfirlichen Kohlenstoffkreislauf in andere Reservoire gebracht. Entscheidend fiir den CO2-Anstieg ist nut der Anteil der Emission, der in der Luft verbleibt: die air-borne fraction. Fagt man die Entwicklung anthropogener CO 2Emissionen wfihrend der n/ichsten 50-100 Jahre ins Auge, so kann der biosph/irische gegen/iber dem fossilen Eintrag vernachl/issigt werden. Die Absch/itzung zukfinftiger CO2-Emissionsraten mul3 sich daher an Energie-Szenarien orientieren, die die Chancen der Energieoption Kohle im Zusammenhang mit Entwicklungstendenzen des globalen Energiebedarfes diskutieren. Diese ergeben sich aus dem zeitlichen Verlauf und dem Mal3 der Koppelung dreier Faktoren: Bev61kerungswachstum, Wirtschaftswachstum und Effizienz des Energieeinsatzes. Energie-Szenarien sind Versuche, diese drei Faktoren auf der Grundlage demographischer, 6konometrischer und technologischer Analysen zeitabh/ingig zu modellieren. In den Szenarien der letzten Jahre wurden die Pro-