Dorothee Wilhelms-Dick

Coexistence of three calcium carbonate polymorphs in the shell of the Antarctic clam Laternula elliptica

We analyzed shell cuts of the Antarctic bivalve Laternula elliptica collected at King George Island by means of Confocal Raman Microscopy (CRM) as well as Electron Microprobe (EMP). Large area CRM scans (5 mm x 2 mm) reveal that three polymorphs of calcium carbonate ‐ aragonite, calcite, vaterite ‐ are present in the umbo region, the connection of both shell valves. Until now the shell of L. elliptica was believed to be exclusively composed of aragonite. Annual shell growth layers continued through aragonite and vaterite, suggesting simultaneous mineralization of both polymorphs. Spatially congruent EMP scans showed that the calcium carbonate polymorph affects the distribution of magnesium and strontium within the umbo. Mg was distinctly enriched in the vaterite layers deposited during winter. To the contrary Sr was enriched in the aragonite layers, also deposited during winter. This is, to our knowledge, the first report of the coexistence of three calcium carbonate polymorphs within the mineralized structures of a marine calcifying organism, including foraminifera, bivalves, and corals. Particularly the significant amounts of vaterite are quite unusual. The strong effect of the calcium carbonate polymorph on trace element fractionation restricts the suitability of Mg and Sr based proxies in shells of Laternula elliptica. Further analyses will show whether this is a unique finding typical for L. elliptica, or if this also applies to other bivalve species.

Oxygen-dependent niche formation of a pyrite-dependent acidophilic consortium built by archaea and bacteria

Biofilms can provide a number of different ecological niches for microorganisms. Here, a multispecies biofilm was studied in which pyrite-oxidizing microbes are the primary producers. Its stability allowed not only detailed fluorescence in situ hybridization (FISH)-based characterization of the microbial population in different areas of the biofilm but also to integrate these results with oxygen and pH microsensor measurements conducted before. The O2 concentration declined rapidly from the outside to the inside of the biofilm. Hence, part of the population lives under microoxic or anoxic conditions. Leptospirillum ferrooxidans strains dominate the microbial population but are only located in the oxic periphery of the snottite structure. Interestingly, archaea were identified only in the anoxic parts of the biofilm. The archaeal community consists mainly of so far uncultured Thermoplasmatales as well as novel ARMAN (Archaeal Richmond Mine Acidophilic Nanoorganism) species. Inductively coupled plasma analysis and X-ray absorption near edge structure spectra provide further insight in the biofilm characteristics but revealed no other major factors than oxygen affecting the distribution of bacteria and archaea. In addition to catalyzed reporter deposition FISH and oxygen microsensor measurements, microautoradiographic FISH was used to identify areas in which active CO2 fixation takes place. Leptospirilla as well as acidithiobacilli were identified as primary producers. Fixation of gaseous CO2 seems to proceed only in the outer rim of the snottite. Archaea inhabiting the snottite core do not seem to contribute to the primary production. This work gives insight in the ecological niches of acidophilic microorganisms and their role in a consortium. The data provided the basis for the enrichment of uncultured archaea.

The EPICA Dronning Maud Land deep drilling operation

Abstract We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. core-break force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run.