Cosmogenic 10Be and stable 9Be at the land-ocean interface

The land-ocean interface is the most important source or sink for many trace elements in the ocean. Investigating the geochemical behaviour of beryllium (Be) isotopes, encompassing the cosmogenic radionuclide 10Be and the stable nuclide 9Be, and the transfer pathways of Be at this interface is imperative. First, knowing the mechanisms of Be transfer is a prerequisite for the application of the oceanic 10Be/9Be ratio as a sensitive proxy for past continental weathering. Second, understanding the transfer of Be will contribute to our current knowledge of marine biogeochemical cycles of particle-reactive trace metals in general. Third, it helps to expand the potential applications of the 10Be/9Be ratio in coastal marine environments. However, research in this field, particularly on the distribution of 10Be/9Be in coastal seawater, is still lacking due to the analytical challenges in accurately determining ultra-low concentrations of 9Be (at the level of pg/g) and 10Be (at the level of single atoms) in seawater. In this thesis, I propose a new, time-efficient procedure for the simultaneous preconcentration of the exceedingly low levels of 9Be and 10Be from (coastal) seawater based on the iron co-precipitation method. This new procedure contributes towards more time-efficient handling of samples, less risk of sample cross-contamination, and a more accurate 10Be/9Be ratio. I also evaluated the iron co-precipitation method with respect to: i) the impact of major matrix elements on the accuracy of obtained Be concentrations, ii) its extraction efficiency for pg/g-levels Be in the presence and absence of organic matter, and iii) the comparison with existing preconcentration methods. For the determination of 9Be and 10Be in open ocean seawater samples, a precision on the 10Be/9Be ratio of <5% can be attained using less than 3 L of seawater, whereas previously more than 20 L were used to obtain this precision. Even for coastal seawater with extremely low 10Be concentration of only 100 atoms/g, a maximum seawater amount of 10 L is sufficient. I applied this new procedure to measure dissolved 9Be and 10Be along the entire salinity gradient in two of the largest estuaries on Earth: The Changjiang and the Amazon River estuary. In addition, I determined the 10Be and 9Be concentrations in different chemically extractable fractions of the corresponding suspended and bottom sediments. The main objectives were i) to investigate terrigenous 9Be pathways into the ocean under a variety of hydro-chemical estuarine conditions; and ii) to fill the current knowledge gap of the distribution of 10Be/9Be at the land-ocean interface and explore its applications in reconstructing past continental denudation rates of the adjacent river catchments. In both estuaries, dissolved 9Be and 10Be display similar, non-conservative behaviour during estuarine mixing. The removal and release of dissolved 9Be in the Changjiang Estuary and its relationship with corresponding particulate 9Be distribution and hydrochemical data (e.g., dissolved oxygen) suggest three land-to-ocean pathways of 9Be through estuaries. These are: i) riverine dissolved input after coastal scavenging, ii) 9Be desorption from the suspended particulate matter (SPM), and iii) coastal benthic inputs which involve porewater diffusion and/or submarine groundwater discharge. Among these pathways, benthic input potentially presents the most important contributor to the marine 9Be budget and thus likely dominates the paleo-marine 10Be/9Be record. The concentration of dissolved oxygen in coastal bottom seawater may play a role in controlling the benthic 9Be flux through time. Despite the non-conservative behaviour of both dissolved 9Be and 10Be, the 10Be/9Be ratios of dissolved Be exhibit exponential increases along the salinity gradient, generally following the conservative water mixing lines, except where hypoxic bottom waters are affected by submarine groundwater discharge. In contrast, for sediment within the inner-shelf regions (approximately 150 km from the coast), a change in 10Be/9Be ratios of only within a factor of 2 is observed in authigenic (reactive) suspended and bottom sediment phases, indicating that a continent-derived 10Be/9Be signal is largely preserved in this zone. Beyond this zone where boundary currents prevail, reactive 10Be/9Be of outer-shelf/slope sediments markedly increase by a factor of 3 to 30. This increase is likely a result of water-sediment interactions through “boundary exchange” processes. Using the 10Be/9Be ratios of reactive phases of inner-shelf sediments, I calculated the denudation rates for the entire Changjiang and Amazon catchment and compared them with denudation rates derived from in situ cosmogenic beryllium isotopes. The good agreement (within a factor of 2) suggests that in large river-dominated shelves characterized by high sedimentation rates and weakened shoreward diffusion of seawater, the reactive 10Be/9Be ratio of coast-proximal sediments can be a direct recorder of terrigenous denudation of the adjacent river catchments. In summary, with this thesis I demonstrate that the 10Be/9Be ratio in the authigenic phase of open ocean sediments is mainly sensitive to the benthic 9Be flux, while the 10Be/9Be ratio in detrital continental inner-shelf sediments, less affected by “boundary exchange”, can faithfully record the denudation rate of the adjacent river catchments. Thus, both systems are suited to explore past changes of these processes.Die Schnittstelle zwischen Land und Ozean ist die wichtigste Quelle oder Senke für viele Spurenelemente im Ozean. Die Untersuchung des geochemischen Verhaltens von Beryllium (Be)-Isotopen, einschließlich des kosmogenen Radionuklids 10Be und des stabilen Nuklids 9Be, und der Übertragungswege von Be an dieser Schnittstelle ist von entscheidender Bedeutung. Erstens ist die Kenntnis der Mechanismen des Be-Transfers eine Voraussetzung für die Anwendung des ozeanischen 10Be/9Be-Verhältnisses als empfindlicher Indikator für die frühere kontinentale Verwitterung. Zweitens wird das Verständnis des Be-Transfers zu unserem derzeitigen Wissen über marine biogeochemische Zyklen partikelreaktiver Spurenmetalle im Allgemeinen beitragen. Drittens trägt es dazu bei, die Anwendungsmöglichkeiten des 10Be/9Be-Verhältnisses in küstennahen Meeresumgebungen zu erweitern. Die Forschung auf diesem Gebiet, insbesondere zur Verteilung von 10Be/9Be in küstennahem Meerwasser, steht jedoch noch aus, da es schwierig ist, extrem niedrige Konzentrationen von 9Be (auf der Ebene von pg/g) und 10Be (auf der Ebene von einzelnen Atomen) im Meerwasser genau zu bestimmen. In dieser Dissertation stelle ich ein neues, zeiteffizientes Verfahren für die gleichzeitige Anreicherung der äußerst niedrigen 9Be- und 10Be-Gehalte in (Küsten-)Meerwasser vor, basierend auf der Methode der Eisen-Kopräzipitation. Dieses neue Verfahren trägt zu einer zeiteffizienteren Handhabung der Proben, einem geringeren Risiko von Kreuzkontamination und einem genaueren 10Be/9Be-Verhältnis bei. Zudem habe ich die Eisen-Kopräzipitationsmethode im Hinblick auf folgende Aspekte bewertet: i) Einfluss der wichtigsten Matrixelemente auf die Genauigkeit der erhaltenen Be-Konzentrationen, ii) ihre Extraktionseffizienz für pg/g-Konzentrationen von Be in Gegenwart und Abwesenheit von organischem Material, und iii) Vergleich mit bestehenden Anreicherungsmethoden. Für die Bestimmung von 9Be und 10Be in Meerwasserproben aus dem offenen Ozean kann eine Präzision des 10Be/9Be-Verhältnisses von <5% mit weniger als 3 Litern Meerwasser erreicht werden, während vorher mehr als 20 Liter benötigt wurden, um diese Präzision zu erreichen. Selbst für küstennahes Meerwasser mit einer extrem niedrigen 10Be-Konzentration von nur 100 Atomen/g ist eine maximale Meerwassermenge von 10 Litern ausreichend. Ich habe dieses neue Verfahren zur Messung von gelöstem 9Be und 10Be entlang des gesamten Salzgehaltsgradienten in zwei der größten Ästuare der Erde angewandt: dem Changjiang- und dem Amazonas-Ästuar. Darüber hinaus habe ich die 10Be- und 9Be-Konzentrationen in verschiedenen chemisch extrahierbaren Fraktionen der entsprechenden Schwebstoffe und Bodensedimente bestimmt. Die Hauptziele waren i) die Untersuchung der Wege von terrigenem 9Be in den Ozean unter verschiedenen hydrochemischen Bedingungen im Ästuar; und ii) die Schließung der derzeitigen Wissenslücke über die Verteilung von 10Be/9Be an der Land-Ozean-Grenzfläche und die Erkundung ihrer Anwendungsmöglichkeiten bei der Rekonstruktion früherer kontinentaler Denudationsraten der angrenzenden Flusseinzugsgebiete. In beiden Ästuaren zeigen gelöstes 9Be und 10Be während der Vermischung ein ähnliches, nicht konservatives Verhalten. Der Abbau und die Freisetzung von gelöstem 9Be im Changjiang-Ästuar und seine Beziehung zu den entsprechenden partikulären 9Be-Verteilungen und hydrochemischen Wasserdaten (z. B. gelöster Sauerstoff) deuten auf drei Land-Ozean-Wege von 9Be durch Ästuare hin. Diese sind: i) gelöster Eintrag aus Flüssen nach küstennaher Spülung, ii) Desorption von 9Be aus Schwebstoffen (SPM, suspended particulate matter) und iii) benthische Einträge von der Küste, die Porenwasserdiffusion und/oder submarine Grundwasserabflüsse umfassen. Von diesen Wegen ist der benthische Eintrag möglicherweise der wichtigste Beitrag zum marinen 9Be-Budget und damit entscheidend für die Interpretation der paläo-marinen 10Be/9Be-Aufzeichnungen. Die Konzentration von gelöstem Sauerstoff im Meeresbodenwasser der Küstengebiete könnte eine Rolle bei der Kontrolle des benthischen 9Be-Flusses im Laufe der Zeit spielen. Trotz des nicht konservativen Verhaltens von sowohl gelöstem 9Be als auch 10Be zeigen die 10Be/9Be-Verhältnisse einen exponentiellen Anstieg entlang des Salzgradienten. Grundsätzlich folgt dieser Anstieg den konservativen Wassermischungslinien, außer in Bereichen, wo hypoxisches Bodenwasser durch submarine Grundwassereinleitungen beeinflusst wird. Im Gegensatz dazu wird bei Sedimenten der inneren Schelfregionen (ca. 150 km von der Küste entfernt) eine Änderung des 10Be/9Be-Verhältnisses nur von einem Faktor 2 in authigenen (reaktiven) Schwebe- und Bodensedimentphasen beobachtet. Das deutet darauf hin, dass in dieser Zone ein vom Kontinent stammendes 10Be/9Be Signal weitgehend erhalten bleibt. Außerhalb dieser Zone, in der Grenzströmungen vorherrschen, steigt das reaktive 10Be/9Be in den Sedimenten des äußeren Schelfs und des Hangs deutlich um einen Faktor von 3 bis 30 an. Dieser Anstieg ist wahrscheinlich zurückzuführen auf Wasser-Sediment-Wechselwirkungen durch "Grenzaustausch"-Prozesse. Anhand der 10Be/9Be-Verhältnisse reaktiver Phasen an Sedimenten der inneren Schelfregion habe ich die Denudationsraten für das gesamte Einzugsgebiet des Changjiang und des Amazonas berechnet und sie mit Denudationsraten verglichen, die aus in situ-produzierten kosmogenen Berylliumisotopen abgeleitet wurden. Die gute Übereinstimmung (innerhalb eines Faktors 2) deutet darauf hin, dass das reaktive 10Be/9Be-Verhältnis küstennaher Sedimente in großen flussdominierten Schelfgebieten, gekennzeichnet durch hohe Sedimentationsraten und eine schwache küstenwärts gerichtete Diffusion von Meerwasser gekennzeichnet sind, ein direkter Indikator für die terrigene Denudation der angrenzenden Flusseinzugsgebiete sein kann. Zusammenfassend zeige ich in dieser Dissertation, dass das 10Be/9Be-Verhältnis in der authigenen Phase von Sedimenten des offenen Ozeans hauptsächlich auf den benthischen 9Be-Fluss anspricht. Hingegen kann das 10Be/9Be-Verhältnis in detritischen kontinentalen Innenschelfsedimenten, die weniger vom "Grenzaustausch" betroffen sind, die Denudationsrate der angrenzenden Flusseinzugsgebiete genau erfassen. Somit sind beide Systeme geeignet, um frühere Veränderungen dieser Prozesse zu erforschen

Estuarine Hydrodynamics Under Sea Level Rise

Estuaries provide a wide range of environmental, cultural, social, and economic services. However, sea level rise (SLR) is increasingly threatening these services in estuaries due to their low-lying topography and proximity to the open ocean. As such, the sustainable management of estuaries requires an evidence-based understanding of how different estuaries may respond to SLR over time and space. Assessing SLR impacts in estuaries can either be undertaken on an individual site basis or via broader approaches that may be relevant to many estuaries. This thesis utilises the latter approach and, to this aim, a large ensemble of idealised estuarine hydrodynamic simulations were developed and tested. The results are then analysed, (i) to present a systematic hydrodynamic understanding of different estuary types in present-day and future conditions, (ii) to detail the influence of SLR on tidal energy dynamics, (iii) to establish a framework for assessing SLR impacts on estuaries worldwide, and (iv) to guide decision-makers in establishing holistic, evidence-based management plans for estuaries. Initially, over 2000 idealised estuary models were simulated to determine how SLR influences the tidal dynamics of various systems with different boundary conditions (e.g., different estuary length, depth, convergence, entrance condition, roughness, river discharge). These results indicate that SLR can lead to tidal range amplification in some estuaries, although entrance restriction effects may offset this phenomenon. Further, SLR is likely to alter the distributions and magnitudes of tidal currents, tidal prism, tidal asymmetry, tidal energy, and the location of tidal energy harvesting sites. To link the idealised findings with real-world estuaries, 26 real-world estuaries were simulated and analysed under present-day and future sea level conditions. This information was used to identify sites that are most vulnerable to SLR-induced tidal variations. These results were consistent with the idealised findings and highlighted their transferability to certain estuaries worldwide without an existing, detailed hydrodynamic model. Long, weakly convergent estuaries with higher friction, river inflows and shallower water depths will likely experience significant changes in tidal dynamics due to SLR. The numerical approach and learnings presented in this thesis could be used to assess and predict cumulative SLR impacts on estuaries globally

The past : a compass for future earth

Antarctic sea ice impacts on the ocean-atmosphere heat and gas fluxes, the formation of deep and intermediate waters, the nutrient distribution and primary productivity, the so-called &#8216;biological carbon pump&#8217;, one of the most active in the global ocean. In this study, we explore the link between sea ice dynamic, biological production and nutrient cycling during the late Holocene (the last 2,000 yrs) in the Adélie Basin, East Antarctica, from the well-dated sediments of the Ocean Drilling Program (ODP) Site U1357. This archive, composed from ~32 meters of seasonal to annual laminated diatomaceous sequences, allows reconstructions at an unprecedented time resolution (5-10 yrs). Our study combines records of diatom census counts and diatom-specific biomarkers (a ratio (D/T) of di- and tri-unsaturated Highly Branched Isoprenoid lipids (HBI)) as indicators of sea ice and biological production changes, XRF data as markers for terrigenous inputs and bulk nitrogen isotopes (d15N) and d15N on chlorins as proxies for reconstructing nitrogen cycle. The diatom and HBI records reveal five distinct periods. From 0 to 350 yrs AD, decreasing occurrences of sea ice-related diatom species (e.g. Fragilariopsis curta + F. cylindrus) together with low D/T values and increasing open ocean diatom species (large centrics, Chaetoceros Resting Spores (CRS)) document a progressive decline of sea ice presence during the year (>9 months per year) with spring melting occurring earlier in the year and autumn sea ice formation appearing later. In contrast, between 350 and 750 yrs AD, high production of open ocean diatom species and low low D/T values and sea ice related species indicate a short duration of sea ice cover (~10 months per year) is illustrated by a pronounced increase of sea ice-associated diatom species and high D/T values. Between ~1400 and 1850 yrs AD, seasonal sea ice strongly declines (<~7 months per year) as a result of early spring melting (increasing CRS production) and late autumn waxing (high occurrences of Thalassiosira antarctica). Longer growing seasons promoted a substantial development of phytoplankton communities (especially large centric diatoms) that conducted to lower D/T values. Consistent with diatom and HBI reconstructions, XRF data show higher Fe/Al and Zr/Al ratios values during inferred warmer periods and lower ratio values during inferred cooler and icier periods, thus supporting a strong impact of the sea ice seasonal cycle on glacial runoffs. The link between sea ice conditions, biological production and nutrient cycling is still being explored and we will discuss its relationship by combining all the cited records cited above with the d15N records that we are currently generated. Based on our results, we find that sea ice dynamic and associated diatom production in the Adélie Basin revealed an opposite climatic trend than that identified in the Northern Hemisphere for the last 2000 years. The 'Little Ice Age' (1400-1850 yrs AD) or the 'Dark Ages' (400-750 yrs AD) corresponded to warmer climate conditions in the Adélie Basin, while the 'Roman Warm Period' (0-350 yrs AD) or the 'Medieval Warm Period' (900-1200 yrs AD) were associated to colder conditions. We therefore emphasize that Northern and Southern Hemisphere climate evolved in anti-phase seesaw pattern during the late Holocene

Successful invaders are better defended: The example of Gracilaria vermiculophylla

To evaluate the importance of anti-herbivore resistance for algal invasion success we compared resistance traits among specimens of the red macroalga Gracilaria vermiculophylla from six native populations in Korea and China and eight invasive populations in Europe and Mexico that were maintained under identical conditions in the laboratory. Herbivorous snails both from the native range (Littorina brevicula) and from the invaded range (Littorina littorea) consumed significantly less of seaweed specimens originating from non-native populations. Metabolome profiling revealed that this preference was correlated with an increased woundactivated production of deterring prostaglandins and hydroxyeicosatetraenoic acids. Thus, invasive populations of G. vermiculophylla are more strongly defended against challenge by herbivores and other biological enemies that cause local tissue or cell disruption and activate oxylipin production. Anthropogenic distribution of genotypes adapted to resist elevated feeding pressure probably contributed to the invasion success of this species

Molecular support for temporal dynamics of induced anti-herbivory defenses in the brown seaweed Fucus Vesiculosus

Grazing by the isopod Idotea baltica induces chemical defenses in the brown seaweed Fucus vesiculosus. A combination of a 33 day induction experiment, feeding choice assays and functional genomic analyses was used to investigate temporal defense patterns and to correlate changes in palatability to changes in gene expression. Despite permanent grazing, seaweed palatability varied over time. Controls were significantly more consumed than grazed pieces only after 18 and 27 days of grazing. Relative to controls, 562/402 genes were up-/down-regulated in seaweed pieces that were grazed for 18 days, i.e. when defense induction was detected. Reprogramming of the regulative expression orchestra (translation, transcription), up-regulation of genes involved in lipid and carbohydrate metabolism, intracellular trafficking, defense and stress response, as well as downregulation of photosynthesis was found in grazed seaweed. These findings indicate short-term temporal variation in defenses and that modified gene expression patterns arise at the same time when grazed seaweed pieces show reduced palatability. Several genes with putative defensive functions and cellular processes potentially involved in defence, such as reallocation of resources from primary to secondary metabolism, were reveale

Spatial and temporal patterns of mangrove abundance, diversity and functions in the Sundarbans

Mangroves are a group of woody plants that occur in the dynamic tropical and subtropical intertidal zones. Mangrove forests offer numerous ecosystem services (e.g. nutrient cycling, coastal protection and fisheries production) and support costal livelihoods worldwide. Rapid environmental changes and historical anthropogenic pressures have turned mangrove forests into one of the most threatened and rapidly vanishing habitats on Earth. Yet, we have a restricted understanding of how these pressures have influenced mangrove abundance, composition and functions, mostly due to limited availability of mangrove field data. Such knowledge gaps have obstructed mangrove conservation programs across the tropics. This thesis focuses on the plants of Earth’s largest continuous mangrove forest — the Sundarbans — which is under serious threat from historical and future habitat degradation, human exploitation and sea level rise. Using species, environmental, and functional trait data that I collected from a network of 110 permanent sample plots (PSPs), this thesis aims to understand habitat preferences of threatened mangroves, to explore spatial and temporal dynamics and the key drivers of mangrove diversity and composition, and to develop an integrated approach for predicting functional trait responses of plants under current and potential future environmental scenarios. I found serious detrimental effects of increasing soil salinity and historical tree harvesting on the abundance of the climax species Heritiera fomes. All species showed clear habitat preferences along the downstream-upstream gradient. The magnitude of species abundance responses to nutrients, elevation, and stem density varied between species. Species-specific density maps suggest that the existing protected area network (PAN) does not cover the density hotspots of any of the threatened mangrove species. Using tree data collected from different salinity zones in the Sundarbans (hypo-, meso-, and hypersaline) at four historical time points: 1986, 1994, 1999 and 2014, I found that the hyposaline mangrove communities were the most diverse and heterogeneous in species composition in all historical time points while the hypersaline communities were the least diverse and most homogeneous. I detected a clear trend of declining compositional heterogeneity in all ecological zones since 1986, suggesting ecosystem-wide biotic homogenization. Over the 28 years, the hypersaline communities have experienced radical shifts in species composition due to population increase and range expansion of the disturbance specialist Ceriops decandra and local extinction or range contraction of many endemics including the globally endangered H. fomes. Applying habitat-based biodiversity modelling approach, I found historical tree harvesting, siltation, disease and soil alkalinity as the key stressors that negatively influenced the diversity and distinctness of the mangrove communities. In contrast, species diversity increased along the downstream – upstream, and riverbank — forest interior gradients, suggesting late successional upstream and forest interior communities were more diverse than the early successional downstream and riverbank communities. Like the species density hotspots, the existing PAN does not cover the remaining biodiversity hotspots. Using a novel integrated Bayesian modelling approach, I was able to generate trait-based predictions through simultaneously modelling trait-environment correlations (for multiple traits such as tree canopy height, specific leaf area, wood density and leaf succulence for multiple species, and multiple environmental drivers) and trait-trait trade-offs at organismal, community and ecosystem levels, thus proposing a resolution to the ‘fourth-corner problem’ in community ecology. Applying this approach to the Sundarbans, I found substantial intraspecific trade-offs among the functional traits in many tree species, detrimental effects of increasing salinity, siltation and soil alkalinity on growth related traits and parallel plastic enhancement of traits related to stress tolerance. My model predicts an ecosystem-wide drop in total biomass productivity under all anticipated stress scenarios while the worst stress scenario (a 50% rise in salinity and siltation) is predicted to push the ecosystem to lose 30% of its current total productivity by 2050. Finally, I present an overview of the key results across the work, the study’s limitations and proposals for future work