Conference Agenda

By our DFG funded project “On sedimentation pattern of the eastern Canary Islands”, we are concentrating on two sediment archives, the dune sequences on Fuerteventura and the Vega sequences on Lanzarote. So called “Vegas” are dammed valleys which act as sediment trap since the damming. The vega sediments consist of redeposited (soil-)sediments from the slopes, volcanic material and dust deposits originating from the northern African continent. In those vegas well differentiated sediment layers can be recognised with alternating pale calcified layers (pcl) and reddish clay dominated layers (rcl). This alternation shows a recurring pattern within the profile. So far we interprete such a sequence of one pcl and one rcl as follows:

A massive deposition of silt dominated dust is followed by a period of de- and recalcification. At the same time, soil formation takes place on slope positions within the catchment due to more humid conditions. With the onset of aridisation, clay dominated material (> 80% clay) from the slopes is transported to the valley floor with a simultaneous increase in dust accumulation. The aridisation culminates in a next massive aggradation of silt dominated dust.

The transition from a pcl to a rcl above is characterised by a quartz and Zr minimum. Within the rcl layer the quartz and Zr contents increase continuously (due to increasing dust input) and reach its peak during the next massive dust event. Whereby massive dust events seem to be linked to terminations of African Humid Periods.

Microfossils as part of multi proxy analyses are a powerful tool to reconstruct environmental changes, sea level fluctuations and coastal development. In combination with datasets, deriving from sedimentological and geochemistry analyses it is possible to follow coastal evolution from open marine to coastal limnic environments. The method is also used in geoarchaeological studies, especially to present an active phase of an ancient harbour, but the infilling of a harbour basin can also use as geo-bio archives. Concerning the microfossil inventory, harbours are very similar to lagoons in habitat type and ecology due to their protected position. In harbour basins, eutrophication is common, caused by the input of human waste and the reduced exchange of water. This is reflected by a ubiquitous faunal association, adapted to temporary deficiency in oxygen. Often, the sedimentation rate is higher than in natural lagoons. Silting up of a harbour leads to the separation from the sea followed by a freshening of the water body with a characteristic freshwater fauna and an increase of organic matter during the final phase. This marked change in the faunal composition, including ostracod freshwater species and the rapid reduction of foraminifer species indicates the disconnection to the sea and the end of the harbour activity. In this study we present the Roman Harbour of Ephesos and the Hellenistic Harbour of Elaia regarding microfossil distribution, sedimentation processes, landscape evolution and human impact. The key difference between the two harbour sites are the various sedimentation rates and the human impact.

Due to their widespread use in high-tech products and processes, the rare earths and yttrium (REY) are nowadays considered as emerging microcontaminants in the environment. Accordingly, a good understanding of their biogeochemistry is highly relevant. Yet, the knowledge gap regarding the incorporation and fractionation of REY in biological and biogenic samples is still surprisingly large.

In contrast to marine and freshwater mollusc shells, only little has been published on REY in terrestrial mollusc shells. This is rather surprising as “Roman snails”, for example, are used for human consumption and considered a delicacy of the “French Cuisine”. The habitat of this land snail (Helix pomatia) extends over many countries in Europe. Its aragonitic shell precipitates from the snail’s mantle epithelium, implying that all REY incorporated into the shell must have been bioavailable to the organism.

We will present complete REY data for Helix pomatia shells from locations with different lithologies from several European countries. The shale-normalised REY (REY_SN) patterns of all shells show a light and/or middle REY enrichment relative to heavy REY. Furthermore, most samples show small positive La_SN, pronounced negative Ce_SN and slightly positive Y_SN anomalies. We will discuss these features and compare the REY_SN patterns with data of ambient substrate (rock or soil), plant samples and Cepaea snails, which are among the most widespread snails in Europe.

As a result of their widespread use in various high-tech applications, Rare Earths and Yttrium (REY) have become microcontaminants in freshwater systems. However, their biogeochemical behavior, particularly their uptake by aquatic organisms, remains poorly understood. In this study, we investigated the distribution of REY in different soft tissues and shells of freshwater bivalve A. anatina, along with REY levels in ambient water from the Danube River in Hungary and the Vistula River in Poland, as well as in their potential food sources. Regardless of the origin of the samples, all compartments of the mussels exhibit very similar shale-normalized REY patterns. Despite Gd contamination of the river waters from MRI contrast agents, no anthropogenic positive Gd anomalies were observed in any mussel sub-samples. This suggests that anthropogenic Gd from MRI contrast agents may not be bioavailable in freshwater, or that REY from ambient river water do not significantly contribute to the REY uptake of freshwater mussels.

Compared to ambient water, bivalves accumulate REY, particularly Ce and light REY. However, REY concentrations in mussels are generally lower than those in their potential food sources, with minor fractionation along the REY series, except for preferential uptake of La and Y. Comparison of shells and tissues does not indicate any major fractionation during transfer within the mussels or shell formation. Mussel shells, therefore, may serve as convenient indicators for environmental monitoring of REY, without significant interference from vital effects.

The Great Barrier Reef (GBR)is a unique environment almost 300 times bigger than the next biggest barrier reef system. One of the key questions about this system is what conditions allowed the formation of this environment. Given the influence of Sea Surface Temperature (SST) on modern reef environments, it was originally assumed that it was related to changes in SST. However, there is a lack of SST records for the late Pleistocene for the area around the Great GBR. We used TEX₈₆^H to produce a new SST record starting at 900 ka from ODP Site 820 next to the northern GBR. Before MIS 17, summer SSTs were as low as 26-24 degrees during glacials. While reefs can persist at these temperatures, reef expansion is limited by the cold conditions. Then, there is an increase in temperature around MIS 17. This is followed by a period of relatively of stable SST between MIS 17-13, with glacial summer SSTs above 27 degrees. This period matches the establishment of the GBR at MIS 17 (700 ka) and then the development of the permanent reef system around MIS 13 (500 ka). This period of relatively stable SSTs might have allowed the system to develop and expand within a narrow window ideal for coral Reef growth, even during glacials. Therefore, our research suggests that major steps in the development of the Great Barrier Reef system are linked to changes in the SSTs.

Oxygen isotopes (δ¹⁸O) from biogenic apatite are used for the calculation of seawater temperatures in paleoclimatic reconstructions. While conventional δ¹⁸O analyses by IRMS (isotope ratio mass spectrometry) requires sample quantities of more than 1 mg, in situ SIMS (secondary ion mass spectrometry) minimizes sample size and thus the risk of contamination of the primary δ¹⁸O signal. Despite this obvious advantage, there are some critical points that could influence the final δ¹⁸O values and their interpretation: (1) The conventional IRMS method exclusively measures the δ¹⁸O from the isolated PO₄³⁻ group of biogenic apatite (Ca₅(PO₄, CO₃, F)₃(OH, F, Cl, CO₃)). In contrast, SIMS releases the oxygen from all molecular groups and from organics. But, to what extent do these non-PO₄³⁻ bound oxygen isotopes bias the final δ¹⁸O values? (2) Thermometer equations are based on IRMS analyses. Are these equations also applicable to SIMS data? (3) Thermometer equations assume, that the δ¹⁸O of seawater signature is –1‰ or 0‰ (VSMOW) for ice-free or ice-covered oceans, respectively. These data are based on sub-recent glacial-interglacial cycles and the associated δ¹⁸O seawater signatures. Whether the oxygen isotopic composition of seawater has changed during the earth history is still under debate.

Clarification of these aspects is crucial for a reliable assessment of δ¹⁸O values and the calculation of seawater temperatures. For this reason, we compare δ¹⁸O data of recent shark teeth analyzed by IRMS and SIMS. Our sharks lived during documented seawater temperatures, ph-values, and δ¹⁸O signatures and are therefore the ideal subjects for our study.