Forschung (research)


Trace element incorporation and isotopic fractionation in calcium carbonate phases (calcite, aragonite, vaterite, monohydrocalcite, ikaite and ACC)
In sediments calcium carbonates (CaCO3) is one of the most common phases. Calcium carbonate has three polymorphs (aragonite, calcite and vaterite) and three other hydrous phases (monohydrocalcite, ikaite and amorphous calcium carbonate ACC). Later are seldom in nature, nevertheless they might play an important role during first CaCO3 precipitation and especially during biogenic calcium carbonate formation. We study the trace element incorporation and isotopic fractionation during formation and transformation processes of these six CaCO3 phases under controlled and well known experimental conditions. Besides to the transformation of the CaCO3 polymorphs, the thermodynamic and kinetic effects on trace element incorporation and isotopic fractionations during CaCO3 formation are investigated to improve the understanding of paleoproxies. Staff involved: A. Niedermayr, A. Immenhauser.

Evaluating the impact of Toarcian environmental changes on neritic carbonate systems in NW Africa
The Toarcian is characterized by the occurrence of the first Mesozoic Oceanic Anoxic Event (OAE). This event (T-OAE) is associated with a very significant and complex perturbation of the Early Jurassic ocean-atmosphere system. In Toarcian research, much attention has previously been paid to open oceanic settings. In contrast, field and geochemical evidence from shallow-water environments is surprisingly scarce. This forms a strong motivation for this, aiming to assess the impact of Late Pliensbachian-Toarcian palaeoenvironmental perturbations in the High Atlas Basin of Morocco. The High Atlas of Morocco offers an exceptional natural laboratory for this purpose. This, as not only basinal sediments, but also their coeval platform equivalents, are well exposed. In this region, the carbonate platform ecosystem is marked by repeated disruption and re-installation episodes. They are probably linked to the Toarcian environmental changes but a better understanding of their timing and causes is needed. A high-resolution, multi-proxy approach (C, O and Sr isotopes, phosphorus) is applied in this study. Geochemical analyses are to be coupled with a detailed sedimentological and paleo-ecological assessment of carbonate platform successions. These tools are applied both to platform and coeval basinal successions in order to characterize the differential response mechanisms of neritic versus basinal responses to Early Jurassic carbon cycle perturbations along the southwestern Tethyan margin. Staff involved: S. Bodin, F.-N. Krencker, A. Immenhauser, U. Heimhofer (LU Hannover).

BIOACID − National collaborative research project of the Federal Ministry of Education and Research
This project forms part of a national research initiative coordinated by Prof. U. Riebesell (Kiel). The Bochum component includes collaboration between Prof. Tollrian (Biology), Prof. Mutterlose (Paleontology) and Prof. Immenhauser (Sedimentary Geochemistry). Collaboration with the LMU Munich (Prof. Schmal) is a key component. The main aim of our research project is a detailed assessment of the past and future performance (metabolism, biomineralization and biodiversity) of coastal/sessile and oceanic/planktonic calcifyers exposed to CO2-induced ocean acidification. Tools applied involve the investigation of shell ultrastucture combined with non-conventional isotope systems sensitive to metabolic effects. With the interdisciplinary approach applied here we will address the following six key questions: (1) How sensitive are coastal calcifyers (here bivalves) to changing seawater pH? (2) What are the pH threshold limits and are these limits universal or species dependent? (3) What is the impact of changing seawater pH on biodiversity? (4) What is the adaptational potential of coastal ecosystems in the time-scale of decennia to few centuries? (5) Are short-term (culturing) experiments with calcifying organisms suitable analogues for pH/CO2 conditions predicted for the end of the 21. century? (6) To which degree are Cenozoic acidification events suitable analogues for predicted anthropogenic CO2 rise by 2100? Staff involved: A. Immenhauser, D. Buhl, S. Hahn, W. Schmahl (LMU Munich) and E. Griesshaber (LMU Munich).

Holocene and Pleistocene climate evolution of NW Africa
This DFG sponsored research initiative deals with speleothem-based climate records from the Atlas Mountain range in Morocco. Our regional focus is on the contrast comparison of speleothems from the Middle Atlas, the High Atlas and the Anti-Atlas. Research questions include the desertification of NW Africa and the role of the shifting ITCZ during the last 200 kyr. This project is undertaken in collaboration with Moroccan colleagues from the universities of Fez and Er-Rachidia. Staff involved: A. Immenhauser, J. Wasserburg, D. Richter, D. Buhl and U. Schulte.

Establishing Mg isotopes as new proxy in speleothem research
We combine interdisciplinary collaboration and continuation of Bunker cave monitoring in the context of DAPHNE II with MC-ICP-MS analysis of the novel δ26Mg isotope proxy. Phase II of DAPHNE offers a unique opportunity for this aim. This because of the concerted effort combining well-established (monitoring, C, O, trace elements) and novel methods (FLINCS, noble gas, modelling). Caves selected include well documented ones (Spannagel Cave, Austria; and Ernesto Cave, Italy), as well as caves investigated in the context of DAPHNE II (Korallgrottan, Sweden; and Giazzera Cave, Italy). Staff involved: S. Riechelmann, A. Immenhauser, D. Buhl, D. Richter

Magnesium isotope signature of dolomites
The goal of this research project is an improved understanding of the controlling factors of magnesium isotope (δ26Mg) fractionation in for instance speloan carbonates or bivalve hardparts. The main focus is on the potential of this novel isotope system as a paleo-climatological, paleo-ecological and paleo-oceanographic proxy. Staff involved: A. Geske, D. Buhl, A. Immenhauser, D.K. Richter

Cryogenic cave calcites
Cryogenic cave calcites (CCC) grow from freezing cave waters where slow freezing leads to a very light O-isotope composition and quick freezing leads to higher O-isotope composition. Calcites of the first group have formed in Middle European caves in water pools on ice during the transition from cold to warm periods. After the ice had molten, a polymict "crystal sand" of cryogenic calcite particles is found as a residue on the cave ground. According to morphological and structural criteria these particles can be distinguished as spherolitic, rhombohedral crystal, plait and skeletal crystal sinters. Our investigations focus on occurrences of CCC in different european caves. Staff involved: D.K. Richter, R.D. Neuser.

Crystallographic orientation of calcite crystalls in speleothems
Calcitic speleothems are known as monocrystalline (most soda straws and helictites) or polycrystalline (most stalagmites and flowstones) compositions. Crystal formation such as crystal surface limitations, crystal elongation and crystal arrangement allow a further differentiation of the speleothem patterns, but the internal crystal structure has been taken into consideration insufficiently with respect to that. Today, Electron-Backscatter-Diffraction allows the evaluation of crystal orientation parameters on oriented chemically polished thin sections. Our systematic investigations should gain new information on the in many kinds not understood genesis of speleothems. Staff involved: R.D. Neuser, D.K. Richter