Plankton dynamics of the open Southern Ocean and surrounding the (Sub)Antarctic islands

The Southern Ocean is a high-nutrient, low-chlorophyll region where primary productivity is limited mainly by iron and light availability, yet it accounts for ~30-40% of global ocean CO2 absorption annually. Marine plankton play a major role in the Southern Ocean CO2 sink as they fix dissolved atmospheric CO2 into organic carbon biomass, much of which supports the ocean food web and a portion of which sinks into the ocean interior, thereby removing atmospheric CO2 on decadal to centennial timescales (i.e., the biological carbon pump). The importance of plankton diversity and dynamics in modulating carbon production and export remains poorly understood, particularly around the many (Sub)Antarctic islands where physical and biogeochemical variability is high. The major motivation for the work presented in this thesis is an improved understanding of the role of the plankton system in Southern Ocean fertility and carbon export, and relatedly, the response of the plankton to environmental forcing such as changes in nutrient dynamics driven by hydrography and island mass effects. To that end, I investigated plankton community diversity and ecological dynamics in the context of nutrient cycling, primary production, and carbon export potential in the open Southern Ocean and in the vicinity of its many island systems. Specifically, I used carbon and nitrogen stable isotope ratios as a tool to quantify carbon export potential and food web dynamics across all major hydrographic zones and basins of the Southern Ocean. Five main findings emerged. Firstly, I developed insights into the major drivers of spatial and temporal variability in the carbon and nitrogen isotope ratios (δ13C and δ15N) of the Southern Ocean's plankton system using circum-Antarctic carbon and nitrogen isoscapes. Along with the drivers commonly invoked by previous studies, I further determined a relationship between the δ13C and δ15N of suspended particulate matter (SPM) and phytoplankton community composition, with diatoms exerting a particularly strong influence on the δ13C and δ15N of the SPM, which is subsequently transferred to the zooplankton. Secondly, I observed that the (Sub)Antarctic islands tend to increase the δ13C and δ 15N of phytoplankton and zooplankton relative to the open Southern Ocean. This trend can be explained by the input of terrestrially-derived iron and other nutrients (e.g., ammonium and/or urea from birds and seals) into the surface layer, which stimulate diatom growth on nitrate and/or exogenous reduced nitrogen sources that are high in δ15N. Thirdly, I applied a new approach using the δ15N of seawater nitrate and SPM to quantify carbon export potential across the summertime Southern Ocean. I found that carbon export potential is highest near the islands and melting sea ice, driven by the input of limiting nutrients (i.e., iron) and by the dominance of diatoms. Fourthly, I found that the δ15N of SPM is a reliable baseline for trophic analysis of the zooplankton system over a large spatial extent of the Southern Ocean (i.e., circum-Antarctic). Since the collection and analysis of SPM samples for δ15N is relatively straightforward, this result should be welcomed by researchers who use such data to reconstruct trophic flows through plankton food webs, as well as the movements and dietary histories of zooplankton in the Southern Ocean. Finally, my new zooplankton δ13C and δ15N isoscapes reveal that during the summer, the primary zooplankton consumers in the Subantarctic waters of the Southern Ocean occupy a low trophic position akin to herbivores, implying that the Subantarctic food web may act to retain organic carbon within the euphotic zone instead of exporting it to depth. By contrast, the primary consumers in Antarctic waters occupy a higher trophic position that suggests they are omnivores and carnivores, which potentially indicates a shorter food chain and thus a stronger biological pump. The work detailed in this thesis suggests new methodological approaches for studying the Southern Ocean plankton system and offers an improved understanding of plankton dynamics and their relationship(s) with the biogeochemical processes that govern the different zones of the Southern Ocean

Reconstructing mid-late Holocene climate and environmental change in Antarctica using Glycerol Dialkyl Glycerol Tetraethers (GDGTs) and pigments in lake sediments

Phd ThesisAssessing the impact of past phases of natural warming on climatically sensitive areas, such as Antarctic and sub-Antarctic regions, will help us better understand the impact that climate warming may have in the future. In recent decades, the Antarctic Peninsula has been one of the fastest warming regions on Earth, warming at a rate of 3.4 °C per century, five times the global mean. Several phases of marked environmental change have occurred on the Antarctic Peninsula during the mid-late Holocene nonetheless, to date quantitative temperature reconstructions of terrestrial climates are not possible. GDGTs are one of few existing quantitative temperature proxies and recent developments of their use in lakes indicates their potential as a temperature proxy. Prior to application the relationship between GDGT-composition and several environmental factors, such as temperature, pH and conductivity, in Antarctic and sub-Antarctic lakes was assessed. Temperature explained a statistically significant independent control on the composition of branched GDGTs in the lakes and a new regional Antarctic and sub-Antarctic GDGT-temperature calibration was developed. Within this calibration, GDGT-IIIb was a statistically significant component indicating its importance in these environments. Applying the new GDGT-temperature calibration to sediment cores from Fan Lake, South Georgia and Yanou Lake, South Shetland Islands allowed the quantitative reconstruction of past temperatures during the Mid to Late-Holocene. The reconstructions showed varied temperatures throughout the records, evidencing the mid-Holocene warm period, and potentially the Medieval Climate Anomaly and Little Ice Age. Neither record, however, reconstructed the recent rapid warming seen in the glacial meltwater and instrumental records. A comparison of Fan Lake and Yanou Lake with other records from Antarctica and Chile showed periods of coherence between records alongside periods of inconsistency. This comparison also enabled potential changes in the PFZ to be considered, suggesting a more poleward position of the PFZ during warmer climates

Distribution and characterization of bacterial communities in diverse Antarctic ecosystems by high-troughput sequencing

Geological events and historical climate changes have eliminated or reduced most life in Antarctica to mainly microbial organisms in relatively simple communities. Due to its exceptional location, millennia long isolations and extreme climatic conditions, the continent offers a spectacular and unique background for fundamental scientific research and the testing of hypotheses. Notwithstanding the fact that Antarctica is still considered by many to be one of the last pristine environments on Earth, it is not only threatened by climate change, which particularly has severe effects on parts of West and Maritime Antarctica, but also by an ever increasing number of tourists and even scientists themselves. Studies on Antarctic biota are relatively scarce, and despite the fact that bacteria are fundamental to the Antarctic ecosystems, only a minority of the studies focus on these organisms. This results in a lacuna in the knowledge about the diversity, distribution and functioning of and the relationships between these organisms under the extreme Antarctic conditions. The recent advent of High-throughput sequencing (HTS) applications enables to sequence millions of DNA-fragments in a very short time, allowing us to visualise bacterial communities at a very high resolution, without the necessity for prior isolation of the organisms. In this PhD-study, we have applied some of these new technologies in order to investigate the bacterial diversity of different habitats throughout the Antarctic. In a first study (Chapter 2), we have compared the results obtained by pyrosequencing and compared these with the results of a previous isolation campaign. As expected, a much larger diversity of bacteria were found with pyrosequencing. While five bacterial phyla were recovered by cultivation, this was the case for 22 phyla with the NGS-approach, and a large amount of unknown diversity was evident. At the same time, it became clear that also the part of the 16S rRNA gene that was sequenced had an impact on the perceived diversity, with the V1-V2 fragments resulting in ~50% more OTUs than the V3-V2 fragments and only a limited amount of overlap in the genera recovered was noticed. In contrast, more chimeric sequences were identified in the V3-V2 amplicons. Notwithstanding the fact that pyrosequencing yielded a higher diversity, there was very little overlap with the cultivation approach, with only about 4 % of the OTUs recovered by cultivation found with pyrosequencing. In contrast, we also noticed that some singleton pyrosequencing OTUs where easily grown on growth media, and hence were not errors in the pyrosequencing data. This study thus showed that several factors could have a large impact on the perceived diversity, and that complementary techniques are necessary to discover the total bacterial diversity. In a second study (Chapter 3), we have examined the effects of both different bedrock types (granite and gneiss) and the presence of macrobiota (mosses, lichens and algae) on the composition of bacterial communities in high-altitude inland soils of different regions if the western Sør Rondane Mountains (Queen Maud Land, East Antarctica), near the Belgian Princess Elisabeth research station. We have used the at present most used HTS-platform, Illumina’s MiSeq, which allows sequencing longer gene fragments and yields more sequences compared to pyrosequencing. We combined this with the ARISA genetic fingerprinting technique. We demonstrated that organic carbon was the most significant parameter in structuring bacterial communities, followed by pH, electric conductivity, bedrock type and moisture content, while spatial distance was of less importance. Diversity showed a positive correlation with moisture content. Acidobacteria and Actinobacteria dominated dry gneiss derived mineral soils, while Proteobacteria, Cyanobacteria, Armatimonadetes and candidate phylum FBP were dominant in samples with a high organic carbon content. A large part of the unexplained variation is probably caused by the absence of data about important nutrients in our dataset (nitrogen and phosphorous), together with microclimatic and topographic differences between sample locations, and noise and stochasticity. In a last study we again used the Illumina MiSeq platform to perform a pan-continental charting of benthic and littoral microbial mats. In total, 138 samples from lakes in eight Antarctic regions and two Sub-Antarctic islands were analysed. We found a significant trend of increasing biodiversity with decreasing latitude from 85° to 54° S, although this than again decreased until 45° S. The mean annual temperature appeared to have a highly significant effect on community structure between Sub-Antarctica and Antarctica, while, besides the geographical distance, electric conductivity, and to a lesser extent pH, was important in explaining differences between samples on the Antarctic continent. In this study, too, a very high unknown diversity was observed. Particularly Cyanobacteria and Alphaproteobacteria dominated freshwater microbial mats, while Bacteroidetes and the alphaproteobacterial Rhodobacteraceae family dominated saline lakes. The Sub-Antarctic Marion Island was highly deviant with very low species richness, dominated by Janthinobacterium (Betaproteobacteria). In conclusion this thesis supports the hypothesis that for Bacteria in the Antarctic Region, too, distinct biogeographic patterns exist and that the environment exerts large selective pressures on community structure and composition, complemented by biotic factors. There is a high amount of heterogeneity at both local and continental scale due to both spatial distance and local differences in environmental variables such as electric conductivity, pH, moisture content, organic carbon and microclimate. Although we only were able sample a fraction of the continent, it is expected that similar patterns hold across the entire continent. However, additional sampling and in depth (metagenomics) sequencing linked to extensive environmental data, combined with phylogenetic analysis is needed to resolve important questions such as within and inter-continental dispersal, functioning and correlation of observed patterns to environmental data

Toward an improved understanding of the Southern Ocean's biological pump: phytoplankton group-specific contributions to nitrogen and carbon cycling across the Subantarctic Indian Ocean

Iron (and silicate) (co-)limitation of phytoplankton is considered a primary cause of the Southern Ocean's inefficient biological pump. However, the role of phytoplankton community structure and response to nutrient cycling remains poorly understood. In a mass balance sense, phytoplankton consumption of new nitrogen (N; e.g., allochthonous nitrate) is proportional to net carbon (C) export, while growth fueled by recycled N (e.g., ammonium) yields no net C flux. The N isotope ratio (δ15N) of surface biomass has long been used as an integrative tracer of new versus regenerated uptake. This approach is rendered more accurate by coupling either fluorescence-activated cell sorting (FACS; of nano- and picophytoplankton; 0.4-20 μm) or microscopy (for microphytoplankton; >20 um) with groupspecific δ15N measurements. Samples were collected for the analysis of nutrients and nitrate-, FACS-, and microscopy-δ15N on a mid-summer transect of the Subantarctic Indian basin during the 2016/17 Antarctic Circumnavigation Expedition (ACE) cruise. The data show that all phytoplankton populations preferentially utilize nitrate (≥55%) across the Indian Sector of the Subantarctic, potentially driving higher C export potential than previously estimated. Indeed, near the Subantarctic islands, 72% of microand >80% of nano- and picophytoplankton growth is supported by nitrate. This is likely due to the partial alleviation of phytoplankton iron and silicate stress, largely as a result of bathymetric upwelling, which constitutes a manifestation of the island mass effect. C export potential is lower in the open ocean region away from the islands where iron stress has been shown to be higher; here, nitrate supports >55% of micro- and picophytoplankton and 7 to 79% of nanophytoplankton growth. In terms of relative abundance (RA), the open Subantarctic is dominated by picoeukaryotes (64%), although there exists a large disconnect between relative abundance and potential contribution to C export. The three largest surface-ocean phytoplankton populations included in this study – microphytoplankton, cryptophytes, and nanoeukaryotes – each contribute ~30% to the total C export potential across the Subantarctic Indian sector while picophytoplankton contribute ~5%. Thus, as has been concluded previously, the larger phytoplankton size classes are disproportionately important drivers of the Subantarctic biological pump. Other interesting ecological findings include diatom-dominated microphytoplankton populations apparently fueled by a significant fraction of regenerated N, even in areas of iron supply, and Synechococcus relying near-exclusively on new N, in contrast to subtropical observations. Additionally, the abundance of Synechococcus appears to be controlled by the availability of iron across the Subantarctic, with silicate and temperature playing a supporting role

Biogeografická pozice souostroví Tristan da Cunha z pohledu floristických studií.

Souostroví Tristan da Cunha je jedním z nejméně porušených temperátních ostrovů světa, s mnoha druhy endemické flory a fauny, nacházející se v Jižním Atlantickém oceánu, přibližně uprostřed mezi Jižní Amerikou a nejjižnějším výběžkem Jižní Afriky. Ačkoliv se jedná o tak zajímavou lokalitu, v mnoha směrech zůstává stále neprobádanou. Bakalářská práce představuje souhrn veškeré dostupné literatury o bezcévných rostlinách vyskytujících se na zmíněném souostroví. Jedná se o značně diversifikované skupiny, přesto vědci mnohdy přehlížené. V rámci bakalářské práce je vytvořen list jednotlivých zástupců. Nakonec je diskutována schopnost bezcévných rostlin se šířit na dlouhé vzdálenosti, jakožto i charakter jejich rozšíření. KLÍČOVÁ SLOVA: Tristan da Cunha; oceánské ostrovy; botanika; distribuce; ostrovní biogeografie; lišejníky; mechy; játrovky; hlevíky; rozsivky;The archipelago Tristan da Cunha is situated in the South Atlantic Ocean, about midway between South America and southern tip of Africa. It represents one of the least disturbed temperate island systems in the world, supports many endemic plant and animal species. Although the locality is interesting by many aspects, many fields still remain under-studied. This bachelor thesis presents a synthesis of available literature about the archipelagos non-marine non-vascular floras, which are of a great diversity, but mostly still overlooked by scientist. For some of them were made lists of taxa present. Further, the distributional ability and patterns of this plant groups are discussed. KEYWORDS: Tristan da Cunha; Oceanic islands; Botanic; Distribution; Island Biogeography; Lichens; Mosses; Liverworts and Hornworts; Diatoms;Department of EcologyKatedra ekologiePřírodovědecká fakultaFaculty of Scienc

Hydrochemical dynamics on sub-Antarctic Marion Island

Although sub-Antarctic maritime environments are some of the most sensitive regions to climate change, investigations into isotopic and hydrochemical dynamics on sub-Antarctic islands are limited. To address this, the Soft Plume River on sub-Antarctic Marion Island was sampled daily along an altitudinal gradient during an intense high-resolution 16-day field campaign in April/May 2015. Samples were analysed for stable isotopes (δ²H and δ¹⁸O) and major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl⁻ , SO4²⁻, NO³⁻). In addition, stream water physicochemistry (pH, water temperature, dissolved oxygen and total dissolved solids) was monitored in situ at a single site in the stream at 5 minute resolution for the duration of the field campaign. Monthly precipitation δ²H and δ¹⁸O had mean values of -27.51‰ and -4.67‰ respectively. Stream water δ²H and δ¹⁸O values were significantly different to that of precipitation, with values ranging from -48.0‰ to -33.6‰ and from -7.6‰ to -5.6‰, respectively. Major ion concentrations were dominated by Na⁺ and Cl⁻, reflecting the overwhelming influence of the surrounding ocean on the island's stream water chemistry. This finding is consistent with previous studies on Marion Island and other maritime sub-Antarctic islands. Temporal variability in stream chemistry was assessed through daily sampling. Findings show that variation was predominantly controlled by precipitation. Following high precipitation amounts low stream water δ²H and δ¹⁸O values were recorded. This was likely the result of the "amount effect". Similarly, a decrease in ion concentrations was also observed following high rainfall amounts. This was because of stream dilution. Sampling along the stream revealed that variation in δ²H and δ¹⁸O and most major ions was largest at the highest site. This pattern is likely the result of an altitudinal precipitation gradient, with higher amounts of precipitation falling at the highest altitude site. High-frequency monitoring of stream water physicochemistry revealed the presence of diel oscillations. Stream pH, temperature and dissolved oxygen concentrations all exhibited diel cycles. Stream pH and temperature were characterised by afternoon maxima and night time minima, with dissolved oxygen following an inverse cycle. These results are the first time diel cycles have been observed for stream water on Marion Island. Taken together, results from this study revealed that the Soft Plume River exhibited a noticeable degree of variability and complexity, especially as results only represent stream water chemical dynamics over a limited range of annual hydroclimatic variation

Improved pre-treatment protocol for scanning electron microscopy coupled with energy dispersive X-ray spectroscopy analysis of selected tropical microalgae

Suitable protocol for identification and classification of microalgae using scanning electron microscopy, coupled with energy dispersive X-ray spectroscopy (SEM-EDX), is important to obtain accurate information of their ultrastructure description. The objective of this study was to modify microalgae pre-treatments for reliable SEM-EDX analysis. Sixteen cultured tropical microalgae were subjected to two-step chemical fixation of glutaraldehyde and osmium tetroxide, sample washing in sodium cacodylate, ethanol and acetone dehydration, critical point-drying, mounting and gold sputter-coating prior to SEM visualisation and elemental characterisation. In this study, short period of chemical fixation and optimum separation forces, at 3213 x g for 3 min during every chemical solution change, were successfully established with high quality SEM images. Ultrastructure, particularly clear and useful images of cell wall ornamentation in Scenedesmus spp. and Desmodesmus sp.; areola patterns in Biddulphia sinensis and Thalassiosira sp. and morphological appearances such as interconnecting structures in Coelastrum sp. and Crucigenia sp., were obtained. Twelve elements of Y, Nb, Fe, Ca, Cl, K, Cu, F, Ir, P, Mg and Si were detected within the 16 investigated microalgae species. This study illustrated that microalgae identification and classification, as well as their elemental characterisation, could be simultaneously and effectively analysed by SEM-EDX using a modified pre-treatment protocol