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  • 1
    Online Resource
    Online Resource
    The priming effect: can the microbial turn-over of deep-sea organic matter be stimulated? (2018)
    Kiel
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (83 Blatt = 4 MB) , Illustrationen, Graphen, Karten
    URL: http://oceanrep.geomar.de/43559/
    Language: English
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  • 2
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    The priming effect: can the microbial turn-over of deep-sea organic matter be stimulated? (2018)
    In:  (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 58, XIX pp
    Details
    Publication Date: 2019-09-23
    Keywords: Course of study: MSc Biological Oceanography
    Type: Thesis , NonPeerReviewed
    Format: text
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    OceanRep: Thesis - not published by a publisher
  • 3
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    Spatio-temporal variations in community size structure of Arctic protist plankton in the Fram Strait (2021)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: The Arctic Ocean is subject to severe environmental changes, including the massive decline in sea ice due to continuous warming in many regions. Along with these changes, the Arctic Ocean’s ecosystem is affected on various scales. The pelagic microbial food web of the Arctic is of particular interest, because it determines mass transfer to higher trophic levels. In this regard, variations in the size structure of the microbial community reflect changes in size-dependent bottom-up and top-down processes. Here we present analyses of microscopic data that resolve details on composition and cell size of unicellular plankton, based on samples collected between 2016 and 2018 in the Fram Strait. Using the Kernel Density Estimation method, we derived continuous size spectra (from 1 μm to ≈ 200 μm Equivalent Spherical Diameter, ESD) of cell abundance and biovolume. Specific size intervals (3–4, 8–10, 25–40, and 70–100μm ESD) indicate size-selective predation as well as omnivory. In-between size ranges include loopholes with elevated cell abundance. By considering remote sensing data we could discriminate between polar Arctic- and Atlantic water within the Fram Strait and could relate our size spectra to the seasonal change in chlorophyll-a concentration. Our size spectra disclose the decline in total biovolume from summer to autumn. In October the phytoplankton biovolume size-spectra reveal a clear relative shift towards larger cell sizes (〉 30 μm). Our analysis highlights details in size spectra that may help refining allometric relationships and predator-prey dependencies for size-based plankton ecosystem model applications.
    Type: Article , PeerReviewed
    Format: text
    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    A diffusion-based kernel density estimator (diffKDE, version 1) with optimal bandwidth approximation for the analysis of data in geoscience and ecological research (2023)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-03-08
    Description: Probability density functions (PDFs) provide information about the probability of a random variable taking on a specific value. In geoscience, data distributions are often expressed by a parametric estimation of their PDF, such as, for example, a Gaussian distribution. At present there is growing attention towards the analysis of non-parametric estimation of PDFs, where no prior assumptions about the type of PDF are required. A common tool for such non-parametric estimation is a kernel density estimator (KDE). Existing KDEs are valuable but problematic because of the difficulty of objectively specifying optimal bandwidths for the individual kernels. In this study, we designed and developed a new implementation of a diffusion-based KDE as an open source Python tool to make diffusion-based KDE accessible for general use. Our new diffusion-based KDE provides (1) consistency at the boundaries, (2) better resolution of multimodal data, and (3) a family of KDEs with different smoothing intensities. We demonstrate our tool on artificial data with multiple and boundary-close modes and on real marine biogeochemical data, and compare our results against other popular KDE methods. We also provide an example for how our approach can be efficiently utilized for the derivation of plankton size spectra in ecological research. Our estimator is able to detect relevant multiple modes and it resolves modes that are located closely to a boundary of the observed data interval. Furthermore, our approach produces a smooth graph that is robust to noise and outliers. The convergence rate is comparable to that of the Gaussian estimator, but with a generally smaller error. This is most notable for small data sets with up to around 5000 data points. We discuss the general applicability and advantages of such KDEs for data–model comparison in geoscience.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Measuring the smallest - phytoplankton size spectra in a Changing Arctic Ocean (2019)
    In:  EPIC3Changing Arctic Ocean Annual Science Meeting 2109, Birmingham, UK, 2019-01-15-2019-01-17Birmingham
    Details
    Publication Date: 2020-01-20
    Description: Phytoplankton species composition and the associated community size structure are expected to change with a warming and freshening of the Arctic Ocean. Cell size controls many physiological (bottom-up) processes, such as nutrient uptake, photosynthesis and growth, thereby affecting the functioning of the planktonic ecosystem as a whole. Furthermore, predator-prey interaction (top-down control) is highly size dependent. The size structure of the phytoplankton community in the Fram Strait has been analysed, based on observations of cell abundance and size. Non- parametric size spectra are obtained from microscopic observations, using a statistical approach that also provides respective confidence intervals. A bootstrap approach is applied, with cell counts and size measurements being resampled respectively. Kernel density estimates (KDE) are derived for all resampled data sets. The collection of KDEs yield robust continuous descriptions of cell density versus cell size together with their confidence limits. With this approach we resolve detailed changes in community size structure that shall be used to improve and constrain results of a size-based plankton ecosystem model. Size dependencies of bottom-up and top-down effects on biogeochemical mass flux will be investigated. The calibrated model can then be applied for deriving reliable projections of how the planktonic ecosystem in the Arctic may be affected by climate change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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    PAPER (OA)
  • 6
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    Spatio-temporal variations in community size structure of Arctic protist plankton in the Fram Strait (2021)
    In:  EPIC3Front. Mar. Sci., 7(579880), pp. 1-18
    Details
    Publication Date: 2021-09-21
    Description: The Arctic Ocean is subject to severe environmental changes, including the massive decline in sea ice due to continuous warming in many regions. Along with these changes, the Arctic Ocean’s ecosystem is affected on various scales. The pelagic microbial food web of the Arctic is of particular interest, because it determines mass transfer to higher trophic levels. In this regard, variations in the size structure of the microbial community reflect changes in size-dependent bottom-up and top-down processes. Here we present analyses of microscopic data that resolve details on composition and cell size of unicellular plankton, based on samples collected between 2016 and 2018 in the Fram Strait. Using the Kernel Density Estimation method, we derived continuous size spectra (from 1μm to ≈ 200 μm Equivalent Spherical Diameter, ESD) of cell abundance and biovolume. Specific size intervals (3–4, 8–10, 25–40, and 70–100 μm ESD) indicate size-selective predation as well as omnivory. In-between size ranges include loopholes with elevated cell abundance. By considering remote sensing data we could discriminate between polar Arctic- and Atlantic water within the Fram Strait and could relate our size spectra to the seasonal change in chlorophyll-a concentration. Our size spectra disclose the decline in total biovolume from summer to autumn. In October the phytoplankton biovolume size-spectra reveal a clear relative shift toward larger cell sizes (〉30μm). Our analysis highlights details in size spectra that may help refining allometric relationships and predator-prey dependencies for size-based plankton ecosystem model applications.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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    PAPER (OA)
  • 7
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    Phytoplankton functional types from multi-sensor satellite observations – towards a long-term monitoring (2002-2020) (2022)
    In:  EPIC3Ocean Science Meeting 2022, 2022-02-24-2022-03-04
    Details
    Publication Date: 2023-06-21
    Description: Phytoplankton in the sunlit layer of the ocean act as the base of the marine food web fueling fisheries, and also regulate key biogeochemical processes such as exporting carbon to the deep ocean. Phytoplankton composition structure varies in ocean biomes and different phytoplankton groups drive differently the marine ecosystem. As one of the algorithms deriving phytoplankton composition from space borne data, within the framework of the EU Copernicus Marine Service (CMEMS), OLCI-PFT algorithm was developed using multi-spectral satellite data collocated to an extensive in-situ PFT data set based on HPLC pigments and sea surface temperature data (Xi et al. 2020, 2021). It provides global PFT retrievals including chlorophyll a estimations of diatoms, haptophytes, dinoflagellates, chlorophytes and prokaryotic phytoplankton spanning the period from 2002 until today, by using multi-sensor merged products and OLCI data. These PFT products with per-pixel uncertainty are publicly available on the CMEMS. Due to different lifespans and radiometric characteristics of the ocean color sensors, it is crucial to evaluate the CMEMS PFT products to provide quality-assured data for a consistent long-term monitoring of the phytoplankton community structure. In this study, using in-situ phytoplankton data (HPLC pigment data further evaluated with microscopic, flow cytometry, molecular and hyperspectral optical data) collected from expeditions since 2009 in the tropical, temperate and polar (mainly Fram Strait within the PEBCAO network) regions, we aim to 1) validate the CMEMS PFT products and investigate the continuity of the PFTs data derived from different satellites, and 2) deliver two-decade consistent PFT products for times series analysis. For the latter we determine inter-annual trends and variation of the surface phytoplankton community structure targeting some key sub-regions (e.g.,east Fram Strait) that have been observed being influenced by the changing marine environment.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev , info:eu-repo/semantics/conferenceObject
    Format: application/pdf
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