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  • 1
    Online Resource
    Online Resource
    Dissolved organic matter cycling in and above oxygen minimum zones (2016)
    Kiel
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (178 Blatt = 7 MB)
    URL: https://oceanrep.geomar.de/35722/
    DDC: 579.817720144
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 2
    Online Resource
    Online Resource
    Chromophoric dissolved organic matter in the Laptev Sea (Siberian Arctic) : a comparison of in-situ observations, laboratory measurements, and remote Sensing (2011)
    Saint Petersburg, Russia, Hamburg
    Details Availability
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (98 Blatt = 7 MB)
    URL: https://oceanrep.geomar.de/28106/
    Language: English
    Note: Zusammenfassung in deutscher und englischer Sprache
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  • 3
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    Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific Oceans (2016)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 13 . pp. 3585-3606.
    Details
    Publication Date: 2019-09-23
    Description: Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs). There are numerous feedbacks between oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. We investigated the pelagic biogeochemistry of OMZs in the eastern tropical North Atlantic and eastern tropical South Pacific during a series of cruise expeditions and mesocosm studies. The following summarizes the current state of research on the influence of low environmental oxygen conditions on marine biota, viruses, organic matter formation and remineralization with a particular focus on the nitrogen cycle in OMZ regions. The impact of sulfidic events on water column biogeochemistry, originating from a specific microbial community capable of highly efficient carbon fixation, nitrogen turnover and N2O production is further discussed. Based on our findings, an important role of sinking particulate organic matter in controlling the nutrient stochiometry of the water column is suggested. These particles can enhance degradation processes in OMZ waters by acting as microniches, with sharp gradients enabling different processes to happen in close vicinity, thus altering the interpretation of oxic and anoxic environments.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-13-3585-2016
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Ocean Colour remote sensing in the Southern Laptev Sea: evaluation and applications (2014)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 11 (15). pp. 4191-4210.
    Details
    Publication Date: 2019-09-23
    Description: Enhanced permafrost warming and increased arctic river discharges have heightened concern about the input of terrigeneous matter into Arctic coastal waters. We used optical operational satellite data from the Ocean Colour sensor MERIS onboard the ENVISAT satellite mission for synoptic monitoring of the pathways of terrigeneous matter in the southern Laptev Sea. MERIS satellite data from 2006 on to 2011 were processed using the Case2Regional Processor, C2R, installed in the open-source software ESA BEAM-VISAT. Since optical remote sensing using Ocean Colour satellite data has seen little application in Siberian Arctic coastal and shelf waters, we assess the applicability of the calculated MERIS parameters with surface water sampling data from the Russian-German ship expeditions LENA2010 and TRANSDRIFT-XVII taking place in August and September 2010 in the southern Laptev Sea. The surface waters of the southern Laptev Sea are characterized by low transparencies, due to turbid river water input, terrestrial input by coastal erosion, resuspension events and, therefore, high background concentrations of Suspended Particulate Matter, SPM, and coloured Dissolved Organic Matter, cDOM. The mapped calculated optical water parameters, such as the first attenuation depth, Z90, the attenuation coefficient, k, and Suspended Particulate Matter, SPM, visualize resuspension events that occur in shallow coastal and shelf waters indicating vertical mixing events. The mapped optical water parameters also visualize that the hydrography of the Laptev Sea is dominated by frontal meanders with amplitudes up to 30 km and eddies and filaments with diameters up to 100 km that prevail throughout the ice-free season. The meander crests, filaments and eddy-like structures that become visible through the mapped MERIS C2R parameters indicate enhanced vertical and horizontal transport energy for the transport of terrigenous and living biological matter in the surface waters during the ice-free season.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-11-4191-2014
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Effects of nitrate and phosphate supply on chromophoric and fluorescent dissolved organic matter in the Eastern Tropical North Atlantic: a mesocosm study (2015)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 12 . pp. 6897-6914.
    Details
    Publication Date: 2020-10-20
    Description: In open-ocean regions, as is the Eastern Tropical North Atlantic (ETNA), pelagic production is the main source of dissolved organic matter (DOM) and is affected by dissolved inorganic nitrogen (DIN) and phosphorus (DIP) concentrations. Changes in pelagic production under nutrient amendments were shown to also modify DOM quantity and quality. However, little information is available about the effects of nutrient variability on chromophoric (CDOM) and fluorescent (FDOM) DOM dynamics. Here we present results from two mesocosm experiments ("Varied P" and "Varied N") conducted with a natural plankton community from the ETNA, where the effects of DIP and DIN supply on DOM optical properties were studied. CDOM accumulated proportionally to phytoplankton biomass during the experiments. Spectral slope (S) decreased over time indicating accumulation of high molecular weight DOM. In Varied N, an additional CDOM portion, as a result of bacterial DOM reworking, was determined. It increased the CDOM fraction in DOC proportionally to the supplied DIN. The humic-like FDOM component (Comp.1) was produced by bacteria proportionally to DIN supply. The protein-like FDOM component (Comp.2) was released irrespectively to phytoplankton or bacterial biomass, but depended on DIP and DIN concentrations. Under high DIN supply, Comp.2 was removed by bacterial reworking, leading to an accumulation of humic-like Comp.1. No influence of nutrient availability on amino acid-like FDOM component in peptide form (Comp.3) was observed. Comp.3 potentially acted as an intermediate product during formation or degradation of Comp.2. Our findings suggest that changes in nutrient concentrations may lead to substantial responses in the quantity and quality of optically active DOM and, therefore, might bias results of the applied in situ optical techniques for an estimation of DOC concentrations in open-ocean regions.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.5194/bg-12-6897-2015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Distribution and potential impacts of coloured dissolved organic matter (CDOM) in the Laptev Sea (Siberian Arctic) (2012)
    In:  [Poster] In: TOS/ASLO/AGU 2012 Ocean Sciences Meeting, 19.02.-24.02.2012, Salt Lake City, USA .
    Details
    Publication Date: 2019-09-23
    Description: The Lena River strongly influences physical, biological and chemical processes on the Laptev Sea shelf through vast amounts of freshwater runoff. The Lena river water is poor in nutrients and carries high concentrations of dissolved organic matter (DOM) and colored dissolved organic matter (CDOM). Here we present CDOM absorption complemented by profiles obtained with an in situ WETstar fluorometer during expeditions in August 2010 and 2011, in order to study the vertical and horizontal CDOM distribution on this shelf. The results show that the river Lena dominates the supply of CDOM which exhibits a conservative mixing behavior over a wide range of salinities. The low light penetration of the CDOM-rich river water in conjunction with low concentrations of dissolved phosphate and nitrate and a strong density stratification of the water column result in low chlorophyll a concentrations within and beneath the river plume. Outside of the river plume increased water transparency and the upward transport of phosphate and nitrate from nutrient enriched bottom waters lead to the formation of deep chlorophyll maxima at the pycnocline.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 7
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    Distribution of transparent exopolymer particles in the easter tropical south Pacific (2014)
    In:  [Poster] In: Ocean Sciences Meeting 2014, 23.-28.02.2014, Honululu, Hawaii, USA .
    Details
    Publication Date: 2019-09-23
    Description: Important for the carbon export to the Deep Sea, Transparent Exopolymer Particles (TEP) also serve as nutritional substrate and attachment surfaces for bacteria, supporting biological oxygen consumption. Spatial distribution of TEP in the Eastern South Pacific Ocean (ESP), an area influenced by a highly productive upwelling system and underlying extensive Oxygen Minimum Zone (OMZ), is largely unknown. In attempt to recognize how TEP stocks are affected by complex biogeochemistry of ESP and vice versa, we determined TEP distribution in the ESP (12°-14°S, 76°-79°W) during the Meteor 93 cruise (February - March 2013). Highest TEP concentrations (〉1900µgXeq/l) were observed close to the coast, coinciding with upwelling of nutrient-rich waters. Generally TEP accumulated in the oxygenated photic layer and correlated significantly with chlorophyll-a-fluorescence (r=0.7, n=323, P〈0.05). At the upper boundary the OMZ (70 m), TEP concentrations were moderate (〈80µgXeq/l), slightly attenuating toward its lower border (〈60µgXeq/l; 500m depth). The role of TEP for organic matter cycling in the ESP and their potential influence on oxygen and carbon fluxes in the OMZ are discussed.
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Poster
  • 8
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    Effects of varied nitrate and phosphate supply on polysaccharidic and proteinaceous gel particles production during tropical phytoplankton bloom experiments (2015)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 12 . pp. 5647-5665.
    Details
    Publication Date: 2020-10-20
    Description: Gel particles such as the polysaccharidic transparent exopolymer particles (TEP) and the proteinaceous Coomassie stainable particles (CSP) play an important role in marine biogeochemical and ecological processes like particle aggregation and export, or microbial nutrition and growth. So far, effects of nutrient availability or of changes in nutrient ratios on gel particle production and fate are not well understood. The tropical ocean includes large oxygen minimum zones, where nitrogen losses due to anaerobic microbial activity result in a lower supply of nitrate relative to phosphate to the euphotic zone. Here, we report of two series of mesocosm experiments that were conducted with natural plankton communities collected from the eastern tropical North Atlantic (ETNA) close to Cape Verde in October 2012. The experiments were performed to investigate how different phosphate (experiment 1, Varied P: 0.15–1.58 μmol L−1) or nitrate (experiment 2, Varied N: 1.9–21.9 μmol L−1) concentrations affect the abundance and size distribution of TEP and CSP. In the days until the bloom peak was reached, a positive correlation between gel particle abundance and Chl a concentration was determined, linking the release of dissolved gel precursors and the subsequent formation of gel particles to autotrophic production. After the bloom peak, gel particle abundance remained stable or even increased, implying a continued partitioning of dissolved into particulate organic matter after biomass production itself ceased. During both experiments, differences between TEP and CSP dynamics were observed; TEP were generally more abundant than CSP. Changes in size distribution indicated aggregation of TEP after the bloom, while newly formed CSP decomposed. Abundance of gel particles clearly increased with nitrate concentration during the second experiment, suggesting that changes in [DIN] : [DIP] ratios can affect gel particle formation with potential consequences for carbon and nitrogen cycling as well as food web dynamics in tropical ecosystems.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/bg-12-5647-2015
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Chromophoric and fluorescent dissolved organic matter in and above the oxygen minimum zone off Peru (2016)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 121 (11). pp. 7973-7990.
    Details
    Publication Date: 2019-02-01
    Description: Key Points: - Two amino acid-like and three humic-like FDOM components were found in and above the oxygen minimum zone off the coast of Peru - The distribution of CDOM and amino acid-like FDOM covaried with chl a, suggesting phytoplankton as their major source - Presence of DOM microbial reworking and DOM release by anoxic sediment was illustrated by the distribution of humic-like FDOM As a result of nutrient upwelling, the Peruvian coastal system is one of the most productive regions in the ocean. Sluggish ventilation of intermediate waters, characteristic for the Eastern Tropical South Pacific (ETSP) and microbial degradation of a high organic matter load promotes deoxygenation at depth. Dissolved organic matter (DOM) plays a key role in microbial respiration and carbon cycling, but little is known on DOM distribution and cycling in the ETSP. DOM optical properties give important insights on DOM sources, structure and biogeochemical reactivity. Here, we present data and a conceptual view on distribution and cycling of chromophoric (CDOM) and fluorescent (FDOM) DOM in and above the oxygen minimum zone (OMZ) off Peru. Five fluorescent components were identified during PARAFAC analysis. Highest intensities of CDOM and of the amino acid-like fluorescent component (C3) occurred above the OMZ and coincided with maximum chl a concentrations, suggesting phytoplankton productivity as major source. High intensities of a marine humic-like fluorescent component (C1), observed in subsurface waters, indicated in situ microbial reworking of DOM. FDOM release from inner shelf sediment was determined by seawater analysis and continuous glider sensor measurement and included a humic-like component (C2) with a signature typical for terrestrially derived humic acids. Upwelling supplied humic-like substances to the euphotic zone. Photo-reactions were likely involved in the production of a humic-like fluorescent component (C5). Our data show that variable biological and physical processes need to be considered for understanding DOM cycling in a highly dynamic coastal upwelling system like the ETSP off Peru.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016JC011906
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Oxygen Utilization and Downward Carbon Flux in an Oxygen-Depleted Eddy in the Eastern Tropical North Atlantic (2016)
    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 13 . pp. 5633-5647.
    Details
    Publication Date: 2021-04-21
    Description: The occurrence of mesoscale eddies that develop suboxic environments at shallow depth (about 40–100 m) has recently been reported for the eastern tropical North Atlantic (ETNA). Their hydrographic structure suggests that the water mass inside the eddy is well isolated from ambient waters supporting the development of severe near-surface oxygen deficits. So far, hydrographic and biogeochemical characterization of these eddies was limited to a few autonomous surveys, with the use of moorings, underwater gliders and profiling floats. In this study we present results from the first dedicated biogeochemical survey of one of these eddies conducted in March 2014 near the Cape Verde Ocean Observatory (CVOO). During the survey the eddy core showed oxygen concentrations as low as 5 µmol kg−1 with a pH of around 7.6 at approximately 100 m depth. Correspondingly, the aragonite saturation level dropped to 1 at the same depth, thereby creating unfavorable conditions for calcifying organisms. To our knowledge, such enhanced acidity within near-surface waters has never been reported before for the open Atlantic Ocean. Vertical distributions of particulate organic matter and dissolved organic matter (POM and DOM), generally showed elevated concentrations in the surface mixed layer (0–70 m), with DOM also accumulating beneath the oxygen minimum. With the use of reference data from the upwelling region where these eddies are formed, the oxygen utilization rate was calculated by determining oxygen consumption through the remineralization of organic matter. Inside the core, we found these rates were almost 1 order of magnitude higher (apparent oxygen utilization rate (aOUR); 0.26 µmol kg−1 day−1) than typical values for the open North Atlantic. Computed downward fluxes for particulate organic carbon (POC), were around 0.19 to 0.23 g C m−2 day−1 at 100 m depth, clearly exceeding fluxes typical for an oligotrophic open-ocean setting. The observations support the view that the oxygen-depleted eddies can be viewed as isolated, westwards propagating upwelling systems of their own, thereby represent re-occurring alien biogeochemical environments in the ETNA.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.5194/bg-13-5633-2016
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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