Arndt Schimmelmann

Isotopic fractionation during peptide bond hydrolysis

Abstract Isotopic fractionation of nitrogen and carbon is considered during peptide bond hydrolysis. Theoretical considerations suggest that hydrolysis will enrich residual, unhydrolyzed protein in 15 N while 13 C should be relatively unaffected. Preliminary experimental results support this conclusion, although further studies are required to quantify the magnitude of this effect as a function of protein degradation, in particular under natural environmental conditions.

Evolutionary changes over the last 1000 years of reduced sulfur phases and organic carbon in varved sediments of the Santa Barbara Basin, California

Abstract Sediments from the Santa Barbara Basin (SBB) of the last 1000 years were analyzed for elemental sulfur (Se), mineral sulfide sulfur (Sm), lipid-based organically bound sulfur (Sx), residual organically bound sulfur (So), total organic carbon (TOC) and total nitrogen (TN). The approximate annual resolution of the time-series data permitted us to evaluate the influence of oceanic variables on the benthic environment and the accumulating varved sediment in the SBB. A bacterial mat community at or near the sediment surface is influencing sediment porosity and the production and distribution of Se. Early diagenesis dampens the amplitude of environmental signals in the geochemical time series. The concentrations of Sm and So increase with burial depth, at the expense of decreasing concentrations of Sx and Se. At depths greater than 5.5 cm, corresponding to an age of 7 years, Sm becomes the largest pool of reduced sulfur. It requires approximately 500 years of primarily bacterially mediated diagenesis, equivalent to a burial depth of ~ 1.4 m, for SBB sediments to gradually approach and finally enter the region assumed to represent typical “normal” marine sediments on a plot of weight percent TOC vs. Sm.

Historical oceanographic events reflected in13C/12C ratio of total organic carbon in laminated Santa Barbara Basin Sediment

An 1844-1987 time series of carbon stable isotope ratios from dated sedimentary total organic carbon (TOC) from the center of the Santa Barbara Basin (SBB) is compared with historical climate and oceanographic records. Four isotopically distinct biogeochemical sources of TOC are important: phytoplankton-derived marine biomass, macroalgal biomass from kelp forests, terrigenous biomass (mainly flushed into the SBB via river discharge), and redeposited fossil organic carbon. The significance of the latter two sources is largely limited to a few unusual flood and oil spill events, whereas the combination of 13C-depleted phytoplankton and 13C-enriched macroalgal biomass appears to be responsible for most of the isotopic variance of the marine coastal biomass as recorded in sedimentary TOC. The isotopic response of marine organic carbon in sediments records strong El Nino-Southern Oscillation (ENSO) and the frequently associated severe storm and wave events in SBB varved sediments. The plausible major isotopic mechanisms are (1) increased physical liberation of 13C-enriched kelp carbon from locally abundant giant kelp (Macrocystis spp.) forests during times of physical and environmental stress, and (2) decreased productivity of 13C-depleted phytoplankton during ENSO events.

Moose teeth as monitors of environmental isotopic parameters

SummaryThe radiocarbon activities of amino acids isolated from crown first molar dentin of moose born between 1948 and 1984 on Isle Royale National Park, USA closely follows the bomb radiocarbon signal generated from atmospheric nuclear weapons testing. This demonstrates that these amino acids are metabolically inert and have recorded the isotopic parameters of the environment during the first year or two of the animals life. The moose teeth amino acids provide both carbon and nitrogen isotopic chronologies for Isle Royale for a period of nearly four decades. The carbon isotopic record reflects both anthropogenic alterations of the global atmospheric carbon cycle (the “Suess” effect), and changes in forest ecology and moose feeding habitat. The nitrogen isotopic chronology is more variable than the carbon record and is the result of environmental and biological factors which are poorly understood.