Calibration study of bivalve shells : implications for paleoenvironmental reconstruction

The accretionary shells of bivalve mollusks can provide environmental information, such as water temperature, precipitation, freshwater fluxes, primary productivity and anthropogenic activities in the form of variable growth rates and variable geochemical properties, such as stable oxygen and carbon isotopes. However, paleoenvironmental reconstructions are constrained by uncertainties about isotopic equilibrium fractionation during shell formation, which is generally acknowledged as a reasonable assumption for bivalves, but it has been disputed in several species. Furthermore, the variation in shell growth rates is accepted to rely on multiple environmental variables, such as temperature, food availability and salinity, but can differ from species to species. Therefore, it is necessary to perform species-specific calibration studies for both isotope proxies and shell growth rates before they can be used with confidence for environmental interpretations of the past. Accordingly, the principal objective of this Ph.D research is to examine the reliability of selected bivalve species, the long-lived Eurhomalea exalbida (Dillwyn), the short-lived and fast growing species Paphia undulata (Born 1778), and the freshwater mussel Margaritifera falcata (Gould 1850), as paleoenvironmental proxy archives.rnThe first part is focused on δ18Oshell and shell growth history of live-collected E. exalbida from the Falkland Islands. The most remarkable finding, however, is that E. exalbida formed its shell with an offset of -0.48‰ to -1.91‰ from the expected oxygen isotopic equilibrium with the ambient water. If this remained unnoticed, paleotemperature estimates would overestimate actual water temperatures by 2.1-8.3°C. With increasing ontogenetic age, the discrepancy between measured and reconstructed temperatures increased exponentially, irrespective of the seasonally varying shell growth rates. This study clearly demonstrates that, when the disequilibrium fractionation effect is taken into account, E. exalbida can serve as a high-resolution paleoclimate archive for the southern South America. The species therefore provides quantifiable temperature estimates, which yields new insights into long-term paleoclimate dynamics for mid to high latitudes on the southern hemisphere.rnThe stable carbon isotope of biogenic carbonates is generally considered to be useful for reconstruction of seawater dissolved inorganic carbon. The δ13Cshell composition of E. exalbida was therefore, investigated in the second part of this study. This chapter focuses on inter-annual and intra-annual variations in δ13Cshell. Environmental records in δ13Cshell are found to be strongly obscured by changes in shell growth rates, even if removing the ontogenetic decreasing trend. This suggests that δ13Cshell in E. exalbida may not be useful as an environmental proxy, but a potential tool for ecological investigations. rnIn addition to long-lived bivalve species, short-lived species that secrete their shells extremely fast, can also be useful for environmental reconstructions, especially as a high-resolution recorder. Therefore, P. undulata from Daya Bay, South China Sea was utilized in Chapter 4 to evaluate and establish a potential proxy archive for past variations of the East Asian monsoon on shorter time-scales. The δ18Oshell can provide qualitative estimates of the amount of monsoonal rain and terrestrial runoff and the δ13Cshell likely reflect the relative amount of isotopically light terrestrial carbon that reaches the ocean during the summer monsoon season. Therefore, shells of P. undulata can provide serviceable proxy archives to reconstruct the frequency of exceptional summer monsoons in the past. The relative strength of monsoon-related precipitation and associated changes in ocean salinity and the δ13C ratios of the dissolved inorganic carbon signature (δ13CDIC) can be estimated from the δ18Oshell and δ13Cshell values as well as shell growth patterns. rnIn the final part, the freshwater pearl shell M. falcata from four rivers in British Columbia, Canada was preliminarily studied concerning the lifespans and the shell growth rates. Two groups separated by the Georgia Strait can be clearly distinguished. Specimens from the western group exhibit a shorter lifespan, while the eastern group live longer. Moreover, the average lifespan seems to decrease from south to north. The computed growth equations from the eastern and western groups differ as well. The western group exhibits a lower growth rate, while bivalves from the eastern group grow faster. The land use history seems to be responsible for the differences in lifespans of the specimens from the two groups. Differences in growth rate may be induced by differences in water temperature or nutrient input also related to the land use activities.

Volatile organic compounds at the air-sea interface : gas exchange rates, oceanic emissions and the effect of ocean acidification

Oceans are key sources and sinks in the global budgets of significant atmospheric trace gases, termed Volatile Organic Compounds (VOCs). Despite their low concentrations, these species have an important role in the atmosphere, influencing ozone photochemistry and aerosol physics. Surprisingly, little work has been done on assessing their emissions or transport mechanisms and rates between ocean and atmosphere, all of which are important when modelling the atmosphere accurately.rnA new Needle Trap Device (NTD) - GC-MS method was developed for the effective sampling and analysis of VOCs in seawater. Good repeatability (RSDs <16 %), linearity (R2 = 0.96 - 0.99) and limits of detection in the range of pM were obtained for DMS, isoprene, benzene, toluene, p-xylene, (+)-α-pinene and (-)-α-pinene. Laboratory evaluation and subsequent field application indicated that the proposed method can be used successfully in place of the more usually applied extraction techniques (P&T, SPME) to extend the suite of species typically measured in the ocean and improve detection limits. rnDuring a mesocosm CO2 enrichment study, DMS, isoprene and α-pinene were identified and quantified in seawater samples, using the above mentioned method. Based on correlations with available biological datasets, the effects of ocean acidification as well as possible ocean biological sources were investigated for all examined compounds. Future ocean's acidity was shown to decrease oceanic DMS production, possibly impact isoprene emissions but not affect the production of α-pinene. rnIn a separate activity, ocean - atmosphere interactions were simulated in a large scale wind-wave canal facility, in order to investigate the gas exchange process and its controlling mechanisms. Air-water exchange rates of 14 chemical species (of which 11 VOCs) spanning a wide range of solubility (dimensionless solubility, α = 0:4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were obtained under various turbulent (wind speed at ten meters height, u10 = 0:8 to 15ms-1) and surfactant modulated (two different sized Triton X-100 layers) surface conditions. Reliable and reproducible total gas transfer velocities were obtained and the derived values and trends were comparable to previous investigations. Through this study, a much better and more comprehensive understanding of the gas exchange process was accomplished. The role of friction velocity, uw* and mean square slope, σs2 in defining phenomena such as waves and wave breaking, near surface turbulence, bubbles and surface films was recognized as very significant. uw* was determined as the ideal turbulent parameter while σs2 described best the related surface conditions. A combination of both uw* and σs2 variables, was found to reproduce faithfully the air-water gas exchange process. rnA Total Transfer Velocity (TTV) model provided by a compilation of 14 tracers and a combination of both uw* and σs2 parameters, is proposed for the first time. Through the proposed TTV parameterization, a new physical perspective is presented which provides an accurate TTV for any tracer within the examined solubility range. rnThe development of such a comprehensive air-sea gas exchange parameterization represents a highly useful tool for regional and global models, providing accurate total transfer velocity estimations for any tracer and any sea-surface status, simplifying the calculation process and eliminating inevitable calculation uncertainty connected with the selection or combination of different parameterizations.rnrn

Chemical interaction between ocean and atmosphere

The exchange of chemical constituents between ocean and atmosphere provides potentially important feedback mechanisms in the climate system. The aim of this study is to develop and evaluate a chemically coupled global atmosphere-ocean model. For this, an atmosphere-ocean general circulation model with atmospheric chemistry has been expanded to include oceanic biogeochemistry and the process of air-sea gas exchange. The calculation of seawater concentrations in the oceanic biogeochemistry submodel has been expanded from DMS, CO₂

B3a km 19 - ein linienbandkeramischer Fundplatz bei Friedberg, Wetteraukreis

Durch den Straßenbau an der Bundesstraße B3a veranlasst, wurden im Zeitraum vom 13.08.2007 bis zum 07.12.2007 archäologische Untersuchungen im Bereich der Streckenkilometer 19 bis 22 durch die Firma Archbau Essen, unter Kontrolle des Landesamtes für Denkmalpflege Hessen und der Kreisarchäologie Wetteraukreis durchgeführt. Bei km 19 wurde dabei eine Siedlung mit angrenzendem Gräberfeld aus der Linienbandkeramik (im Folgenden als LBK bezeichnet) festgestellt. Daneben ergaben sich eine Bestattung und ein Erdwerk der Michelsberger Kultur, Grubenkomplexe und ein Bronzehort aus der Urnenfelderkultur sowie eine mittelalterliche Straße.Heute liegt die Fundstelle Friedberg B3a km 19 in der südlichen Wetterau 30 km nördlich von Frankfurt am Main in Hessen an der Wetter 140 m über NN und gehört zum Wetteraukreis. rnDie 21 ha messende Ausgrabungsfläche umfasste insgesamt 344 Befunde. Die Identifikation der bandkeramischen Strukturen erfolgte hierbei vorwiegend durch die vergesellschaftete Keramik. Von zentraler Bedeutung sind die fünf Hausgrundrisse A bis E im nördlichen Sektor der Fundstelle, wobei die Präsenz zahlreicher „Dreipfostenriegel“ sowie die Nordost-Südwest Ausrichtung der Strukturen als Belege für eine Zeitstellung innerhalb der LBK angesehen werden. Über die Korrespondenzanalyse der bei den Siedlungsstrukturen angetroffenen Keramik konnte darüber hinaus eine Abfolge von Hausgenerationen erstellt werden. Daneben existierten eine Reihe weiterer Befunde von LBK-zeitlichen Pfostenstellungen, bei denen es sich um Zäune oder Palisaden gehandelt haben könnte. Südwestlich dieser Hausgrundrisse wurde bei den Ausgrabungen eine Grabenstruktur geschnitten, für die eine Funktion als Einfassung der bandkeramischen Siedlungsstrukturen möglich ist. Südlich dieser Grabenstruktur konnten sechs Hockerbestattungen der LBK festgestellt werden. Die räumliche Anordnung im Bereich der westlichen Grabungsgrenze lässt den Schluss zu, dass es sich hierbei um ein Gräberfeld handelt, welches bisher nur zu einem geringen Teil ergraben wurde. Ein Zusammenhang zu den Hausgrundrissen A bis E kann erwogen werden. Der nördliche Sektor der Fundstelle umfasste außerdem zahlreiche Grubenbefunde der LBK sowie einige Grubenkomplexe, wobei letztere als Lehmentnahmegruben anzusprechen sind. Abschließend soll hier noch auf die Existenz zweier bandkeramischer Öfen, darunter ein Grubenofen, im Südosten von Friedberg B3a km 19 hingewiesen werden. rnDen mit Abstand größten Anteil am bandkeramischen Fundmaterial aus Friedberg B3 km 19 hatte die Keramik mit 3428 Elementen. An Steingeräten konnten nur 12 Silices sowie 4 Beile und 14 Mahlsteine über die Typologie und die vergesellschaftete Keramik in die LBK eingeordnet werden. Bei den Knochengeräten zeigte sich ein einzelner beschädigter Kamm. Der Fokus der Analysen des bandkeramischen Fundmaterials aus Friedberg B3a km 19 lag auf der Keramik und deren Auswertung innerhalb von Seriation und Korrespondenzanalyse. Um den Untersuchungen mehr Validität zu verleihen und eine optimale Einordnung zu erreichen, wurden die Keramik-Daten aus Friedberg B3a km 19 mit anderen Datensätzen aus Südhessen kombiniert. Dabei war nicht nur die räumliche Nähe der Fundstellen entscheidend, sondern auch die stilistisch-typologische Nähe der Inventare. In Friedberg B3a km 19 waren die Phasen nach Meier-Arendt von einem frühen III bis zum Ende der Phase V anwesend. Phase II kann nur als marginal angesprochen werden. Es ließ sich kein Übergang zum Mittelneolithikum fassen. Nach der Interpretation aller relativchronologischer Daten könnte es sich in Friedberg B3a km 19 um eine Hausentwicklung mit sieben Phasen à 25 Jahren über 175 bis zu 200 Jahren handeln, die eine kontinuierliche Belegung des Platzes von der mittleren bis zum Ende der jüngsten LBK beschreibt. Insgesamt pflegt sich die Fundstelle Friedberg B3a km 19 so in die bandkeramische Siedlungslandschaft der südlichen Wetterau ein.