Description: The Cabo Verde Archipelago in the Atlantic Ocean exhibits seamounts and islands in different stages of evolution. Mature islands are well-eroded, exposing early stages of volcanism. However, little is known about the submarine realm of the archipelago. To gain a better understanding of the geological and geodynamic evolution of the archipelago, data and observations from seamounts and islands were combined and different phases of magmatic-tectonic evolution investigated. The thesis provides the first geochronological data for the Cabo Verde Seamounts. A pillow lava from the extinct Nova Holanda (Senghor) Seamount in the NE yields a 40Ar-39Ar weighted mean age of 14.872 ± 0.027 Ma (2sigma). Lava samples from the phonolitic Cadamosto Seamount (SW) were 40Ar-39Ar dated, revealing young eruption ages with a combined weighted mean age of 21.14 ± 0.62 ka (2sigma). This volcanic eruption period can be linked to rapid crustal unloading due to sea level lowstands in the Last Glacial Maximum. Combined with petrological observations a long-lived magmatic plumbing system below Cadamosto is revealed. The evolution of the mature Maio Island was investigated. Uplifted mid-ocean ridge basalts exposed on Maio and overlying deep-sea sedimentary sequences contain Early Cretaceous fossil assemblages and record information on the young Atlantic Ocean. Based on field observations, 40Ar-39Ar geochronology and structural geology the Miocene evolution of Maio was refined, confirming a period of intense igneous growth between ~16 and 8.7 Ma. Extensive polymict conglomerates below Late Miocene lavas are re-interpreted as landslide deposits, confining an erosional period to between 8.7 to 6.7 Ma. A Pleistocene large-scale fossil dune located in the E of Maio records recent uplift and changes in the paleo-environmental conditions. The thesis provides important insights to different phases of the magmatic-tectonic evolution of the archipelago and ocean island evolution worldwide.

Description: The importance of autonomous in situ chemical sensors for ocean observations has increased drastically over the last decades. Yet, the huge potentials of sensor-based data collection remain underutilized by the scientific and regulatory communities, despite wider than ever usage of sensors. This thesis is part of a growing body of work to extend the usability of sensors and is embedded in the Ocean Best Practice approach, which could improve data quality in ocean observation in general. The here presented Ph.D. thesis covers multiple commercial sensors (LOC from ClearWater Sensors, Southampton, UK and OPUS from TriOS GmbH, Germany) for autonomous, high-resolution and in situ measurements of essential biogeochemical parameters (pH and nitrate) in marine waters. It was motivated by the necessity of improving the data quality of autonomous submersible optical sensors and broadening their utility. To achieve this, sensor deployments in various aquatic environments were conducted. Furthermore, the data obtained via sensors based on the same analytical principle was compared with each other, and with benchtop laboratory devices to assess the accuracy of the measurements. The achievements are associated with the acquisition of accurate and temporally well-resolved real-time data. A more reliable sensor-based data collection and improved deployability promotes a broader usage of autonomous sensors in general. Thus, a financially more sustainable ocean monitoring approach can be achieved, since a broader adaptation of autonomous sensors in research yields a higher cost efficiency.

Description: Some heavy metals e.g., zinc, copper or manganese serve as micronutrients for eukaryotic life and play an important role for the cellular metabolism, growth of organisms, reproduction and enzymatic activity. However, other metals like mercury or lead are not known to have any beneficial effects for organisms and are believed to have a higher toxic potential. Heavy metals occur naturally in the environment. However, in higher concentrations, they become toxic and have hazardous effects on marine biota. Furthermore, they are highly persistent in the marine environment as they are not readily degraded by organisms. Pollution originating from anthropogenic sources, e.g., mining, industry and extensive land use, increased the heavy metal concentration in certain areas above a critical level. Especially temperate and tropical coastal environments act as natural catchment for anthropogenic pollutants because these areas are densely populated and highly affected by industry, agriculture and urban runoff. Therefore, it is vitally important to assess past heavy metal distributions, spatially and temporally and to compare those with recent pollution in order to evaluate contemporary emission reduction measures. The chemistry of the tests of benthic foraminifera and the skeletons of scleractinian corals are widely used for the reconstruction of changes in past environmental conditions including temperature, salinity and carbonate system parameters. Recent studies further demonstrated that the trace metal concentration in the aragonite of corals and the calcite of foraminifera is linked to that in seawater. Therefore, the geochemical analysis of coral skeletons and foraminiferal tests offers the opportunity to gain insights into past heavy metal concentrations in seawater, which can in turn help to improve coastal management. However, it is important to understand distribution patterns, ecological and environmental factors influencing the organism itself and associated species in order to evaluate which species is suitable and representative for a certain area. Therefore, the living and dead foraminiferal assemblage along a transect in the German North Sea was investigated. The results of this study indicate that transport via tidal currents is the dominant environmental factor shaping the foraminiferal assemblages. Haynesina germanica, Ammonia batava and different Elphidium species from the living foraminiferal fauna depict a close linkage between open North Sea areas like Helgoland and the mainland. These species share an opportunistic behaviour and are able to occupy a variety of environments rendering them as possible proxy-carriers for heavy metal contamination in seawater. Nevertheless, an application of the heavy metal concentration in the calcium carbonate of both of the organism groups will only be possible after a calibration of this proxy. Therefore, benthic foraminifera from temperate environments (Ammonia aomoriensis, Ammonia batava and Elphidium excavatum) and tropical corals (Porites lichen and Porites lobata) were exposed to a mixture of dissolved chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), zinc (Zn), silver (Ag), cadmium (Cd), tin (Sn), mercury (Hg) and lead (Pb) over a wide concentration range. High frequency water monitoring in combination with laser ablation ICP-MS measurements of the calcium carbonate, which was precipitated during the culturing period, revealed the uptake of some of these metals mainly depends on its concentration in seawater, which is indicated by strong positive correlations between the metal concentration in seawater and in the calcium carbonate. All three foraminiferal species showed a strong positive correlation between Pb and Ag in the water and their calcite. Ammonia aomoriensis further revealed a correlation with Mn and Cu, Ammonia batava with Mn and Hg and Elphidium excavatum with Cr and Ni, and partially also with Hg. Zinc, Sn and Cd showed no clear trends in all three foraminiferal species studied, which in case of Cd may be due to the exposure to more than one metal at a time. The investigated coral species revealed a positive correlation between the trace metal concentration in seawater and in the coral skeleton for Cr, Mn, Ni, Zn, Ag, Cd and Pb. No correlation was found for Cu, Sn and Hg. The calculated partitioning coefficients (DTE) allow a determination of the heavy metal concentrations in seawater. Therefore, the trace element concentration in benthic foraminifera and in scleractinian corals provides a promising tool for ecosystem status assessments in the future, which can serve as a deciding support for governments and environmental agencies.

Description: Ongoing global climate changes leads to an increased water temperature and a higher probability of extreme events. This thesis focuses on (i) the characterisation of heatwaves and cold-spells in the Kiel Fjord, (ii) using this characterisation for treatment development, (iii) running mesocosm experiments to unravel the importance of frequency, duration, and intensity of environmental stress (i.e., heatwaves, upwelling, and warming) for the impact on the two important species Asterias rubens and Zostera marina, and (iv) the coping mechanisms of these species with (succeeding) environmental stress. Starfish were substantially impacted by heatwaves, with stronger and longer-lasting impacts in amplified and prolonged heatwaves. The impacts reached from 100% mortality (simulated future intensity) to decreased feeding rates, lower growth, and reduced activity (today’s intensity). Upwelling reduced the starfish's activity. However, the succession of extreme events led to an alleviated impact during the second event. Eelgrass was not impacted by short heatwaves or upwelling alone but had less leaves when the heatwave was extended, or a short heatwave was followed by upwelling. The latter combination of stressors also reduced the number of eelgrass shoots. When exposed to long-term warming, aboveground and belowground biomass of non-heat-selected eelgrass was strongly reduced. However, eelgrass individuals from a potentially heat-selected population grew more than those from a non-heat-selected population. Overall, this thesis highlights that extreme events are important drivers of temperate benthic ecosystems but that their impact depends on the nature of the event, their succession, duration, and intensity. Yet, species may have the potential to cope with recurring stress events via an ecological memory or via heat-selection in situ.

Description: Marine ecosystems are subjected to increasing top–down and bottom–up anthropogenic pressures. Top–down pressures affect higher trophic levels (HTL) such as fish, for instance, by harvesting them. Bottom–up pressures affect the ecosystem by changing the environment, which in turn affects lower trophic levels (LTL), such as plankton. The northern Humboldt Current System (NHCS) is the most productive eastern boundary upwelling system in terms of fish catches. In this project, I used physical-biogeochemical and HTL models to understand how the NHCS is affected by top–down and bottom–up drivers. Over four studies, I explored two key questions: How does variability in the biogeochemistry affect fish? And how does fishing pressure affect fish and how does variability in fish affect the biogeochemistry? The first study looks at the impact that fish variability may have on the plankton community. Zooplankton mortality in the physical–biogeochemical model CROCO-BioEBUS was modified to implicitly simulate the change in the biomass of fish which would prey on zooplankton. Large zooplankton was the main driver of the community response. For the second study, the impacts of LTL variability on the HTL of the system were studied by coupling CROCO-BioEBUS with the multispecies HTL model OSMOSE. Interannual variability had an impact on fish biomasses but this was small compared to the high variability seen in observations. Then, I explored the top–down impact of fishing on the Peruvian anchovy and Peruvian hake. I observed a higher resilience of anchovy to increased fishing pressure than hake. Finally, mesopelagic fish in OSMOSE were compared with another model. It was concluded that the life-cycle and trophic interactions in OSMOSE affect the response of simulated mesopelagic fish to changes in LTL. The thesis concludes with a reflection on possible next steps for improving the representation of the NHCS ecosystem.

Description: Clonal species, such as seagrass Zostera marina, have two levels of “population”, an asexual population of ramets belonging to a single clone/genet, which is nested into the population of clones/genets, the “classical”, sexually reproducing population. Although earlier theoretical and conceptual work has repeatedly suggested that somatically generated variation plays an important role in modular species, population genetics of such species has been focused on the “classical” germline genetic variation. This thesis extends the knowledge on the multi-level genetic variation in the model seagrass species Z. marina using whole-genome resequencing. In Chapter 1, I studied the somatic genetic variation (SoGV) in a Z. marina meadow tracing back to one single sexual event. In chapter 2, I studied population genomics of Z. marina, based on the worldwide distribution of the “classical” germline genetic variation. In chapter 3, I proposed the concept of identity by heterozygosity (IBH), meaning that two diploid genomes are identically heterozygous at some genetic markers such as SNPs (single-nucleotide polymorphisms). This was used to detect ramets of the same clone/genet. In summary, two levels of SoGV, namely among cell populations, and among ramets/modules, are nested within “classical” germline genetic variation in clonal species, owing to somatic mutation and somatic genetic drift. This thesis opens up new avenues of studying multi-level genetic variation by using clonal species as model. Further modeling and theoretical work based on clonal species will broaden the current population genetics theory.

Description: Marine ecosystems, particularly productive marine ecosystems, substantially impact global fisheries and are considerably influenced by climate change as an integral component of the earth system. Modelling is an essential tool to understand marine ecosystems and project their possible response to climate change. However, current ecosystem modelling projections have significant uncertainties, which are partially caused by a lack of overall understanding of the underlying physical-biological interactions. This thesis seeks to identify the driving mechanisms of the trophodynamics in productive marine ecosystems in the contemporary climate, which is key to improve future ecosystem projections under climate change.

Description: The current thesis reports a clear understanding of the leaching process of six PAEs from three common consumer plastics, low and high-density polyethylene (LDPE, HDPE) and recycled polyethylene (RP). The effects of salinity, temperature, and ultraviolet irradiation (UVR) on leaching were investigated. Temperature and UVR had a positive effect on the leaching rate while increasing salinity had a negative effect on the leaching rate. The approach used in this study to measure PAEs takes into account the re-adsorption loss of each target compound during the leaching process. Significant re-adsorption of PAEs was observed for all three polymers, which can reduce the amount of actual/total leachate in the dissolved phase by up to 30-80%. This is an important step in understanding the hazards and extent of exposure to additives from plastic pollution. The second major focus of the work is to investigate the relationship between PAEs and PDs in the marine environment. We investigated the abundance of PDs and PAEs in the surface waters of Sharm Obhur Bay and the Red Sea. PAE concentrations in the study area ranged from 0.8 to 1224 ng/L, while the abundance of PDs ranged from (0.0301-0.0374 PDs/m3 ). A positive correlation was observed between the abundance of PDs and the concentration of PAEs, suggesting that a large portion of the dissolved PAE pool may be due to in situ leaching. The calculated ecological risk level (ERL) due to PAEs and PDs for Sharm Obhur and the Red Sea is currently at a low to moderate level. Overall, the work presented in this thesis helps in improving the available knowledge of the leaching process of PAEs from plastics under different environmental conditions. Particularly, in proper assigning the re-adsorption loss in the measurement of total leachates in water. On the other hand, the latest information regarding the distribution of PAEs and plastic waste and their ecological risk in the surface waters of the Red Sea and Sharm Obhur Bay is reported. An improved method for the analysis of PAEs was developed, including the control of blank contamination, and the experimental conditions such as extraction time and temperature were optimized. This information may be useful in the analysis of PAEs where it can be of great importance to obtain a precise determination of plastic additives in the complex environment.