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  • 1
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    In:  (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 164 pp
    Publication Date: 2019-02-01
    Type: Thesis , NonPeerReviewed
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  • 2
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    In:  (Master thesis), Saint Petersburg State University ; University of Hamburg, Saint Petersburg, Russia ; Hamburg, 98 pp
    Publication Date: 2015-03-19
    Description: Terrestrial dissolved organic matter (DOM) is continuously discharged by rivers into the ocean. The enhanced permafrost thawing and increased arctic river discharges over the last decades have heightened concern about the input of terrestial materials into the Arctic coastal waters. Chromophoric dissolved organic matter (CDOM) is the optically active component of DOM formed by organic compounds that absorb light at both ultraviolet and visible wavelength bands. This DOM fraction has a strong impact in the carbon cycle and other elements mediating photochemical reactions and, hence, modulates light attenuation in the ocean. Therefore, CDOM interferes with satellite estimations of chlorophyll a and primary production. The objective of this work is to analyze the field CDOM data set including: 202 water samples and 18 vertical CDOM fluorescence profiles taken at oceanographic stations carried out during the TRANSDRIFT-XVII expedition to the Laptev Sea, and 15 water samples from the Lena2010 expedition. Thirty satellite images capturing the Laptev Sea region in September 2010 were processed to reveal the spatial distribution of optical parameters in the surface layer and to correlate the field CDOM and turbidity data with remote sensing data. A relationship between salinity, absorption, slopes and CDOM fluorescence was found and conservative CDOM mixing between riverine and marine waters was observed. This implies that strong in situ sources and/or sinks in CDOM concentration are absent. Within the range of salinities from 0 to 22 the spectral slope of the absorption (S) over the wavelength band of absorption coefficients was in the typical range of CDOM of terrestrial origin. Saltier waters with lower CDOM concentration showed high scattering of S. Optical parameters determined by satellite measurements show a significant covariance with the field observations CDOM and salinity observations while turbidity has not shown reliable coincidence. We suggest that the high concentration of CDOM is the reason of the low influence particular matter concentration on the optical properties of the surface water. Linear regressions were obtained between surface CDOM concentrations and satellite parameters helping to trace the spatial distribution of both salinity and CDOM at the sea surface. Anyhow, further investigations are required to develop an algorithm of calculation of CDOM and salinity based on remote sensing data.
    Type: Thesis , NonPeerReviewed
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  • 3
    Publication Date: 2018-12-11
    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
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  • 4
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    Bologna: Alma Mater Studiorum - Università di Bologna, Dipartimento di Scienze Economiche (DSE)
    Publication Date: 2018-02-02
    Description: Online review aggregators, such as TripAdvisor, HotelClub and OpenTable help consumers identify the products and services that best match their preferences. The goal of this study is to understand the impact of online review aggregators on firms and consumers. We adopt Salop's circular city model in which consumers initially do not know the locations of the firms in the product space. The firms decide whether or not to be listed on an online review aggregator's website and choose their prices. When a firm resorts to the aggregator, its location and price become observable to the consumers who visit the website. We consider two different scenarios, depending on the possibility for online firms to offer discounts to the consumers who book online. We show that in equilibrium not all firms will go online – some will remain offline. Online firms attract more customers than their offline counterparts due to reduced mismatch costs, but face a tougher price competition. Comparing the equilibrium prices, profits and the number of firms that go online across the scenarios, we derive interesting conclusions from the private and the social standpoints.
    Keywords: C72 ; D43 ; D61 ; L11 ; L13 ; M31 ; ddc:330
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: English
    Type: doc-type:workingPaper
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  • 5
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    AGU
    In:  Journal of Geophysical Research: Oceans, 121 (11). pp. 7973-7990.
    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
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  • 6
    Publication Date: 2014-11-25
    Description: Enhanced permafrost warming and increased Arctic river discharges have heightened concern about the input of terrigenous matter into Arctic coastal waters. We used optical operational satellite data from the ocean colour sensor MERIS (Medium-Resolution Imaging Spectrometer) aboard the ENVISAT satellite mission for synoptic monitoring of the pathways of terrigenous matter on the shallow Laptev Sea shelf. Despite the high cloud coverage in summer that is inherent to this Arctic region, time series from MERIS satellite data from 2006 on to 2011 could be acquired and were processed using the Case-2 Regional Processor (C2R) for optically complex surface waters 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 C2R parameters with surface water sampling data from the Russian–German ship expeditions LENA2008, LENA2010 and TRANSDRIFT-XVII taking place in August 2008 and August and September 2010 in the southern Laptev Sea. The shallow Siberian shelf waters are optically not comparable to the deeper, more transparent waters of the Arctic Ocean. The inner-shelf waters 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 and coloured dissolved organic matter. We compared the field-based measurements with the satellite data that are closest in time. The match-up analyses related to LENA2008 and LENA2010 expedition data show the technical limits of matching in optically highly heterogeneous and dynamic shallow inner-shelf waters. The match-up analyses using the data from the marine TRANSDRIFT expedition were constrained by several days' difference between a match-up pair of satellite-derived and in situ parameters but are also based on the more stable hydrodynamic conditions of the deeper inner- and the outer-shelf waters. The relationship of satellite-derived turbidity-related parameters versus in situ suspended matter from TRANSDRIFT data shows that the backscattering coefficient C2R_bb_spm can be used to derive a Laptev-Sea-adapted SPM algorithm. Satellite-derived Chl a estimates are highly overestimated by a minimum factor of 10 if applied to the inner-shelf region due to elevated concentrations of terrestrial organic matter. To evaluate the applicability of ocean colour remote sensing, we include the visual analysis of lateral hydrographical features. The mapped turbidity-related MERIS C2R parameters show that the Laptev Sea is dominated by resuspension above submarine shallow banks and by frontal instabilities such as frontal meanders with amplitudes up to 30 km and eddies and filaments with horizontal scales up to 100 km that prevail throughout the sea-ice-free season. The widespread turbidity above submarine shallow banks indicates inner-shelf vertical mixing that seems frequently to reach down to submarine depths of a minimum of 10 m. The resuspension events and the frontal meanders, filaments and eddies indicate enhanced vertical mixing being widespread on the inner shelf. It is a new finding for the Laptev Sea that numerous frontal instabilities are made visible, and how highly time-dependent and turbulent the Laptev Sea shelf is. The meanders, filaments and eddies revealed by the ocean colour parameters indicate the lateral transportation pathways of terrestrial and living biological material in surface waters.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 7
    Publication Date: 2017-06-15
    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), which are connected to the most productive upwelling systems in the ocean. There are numerous feedbacks among 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. In the following, we summarize one decade of research performed in the framework of the Collaborative Research Center 754 (SFB754) focusing on climate–biogeochemistry interactions in tropical OMZs. We investigated the influence of low environmental oxygen conditions on biogeochemical cycles, organic matter formation and remineralization, greenhouse gas production and the ecology in OMZ regions of the eastern tropical South Pacific compared to the weaker OMZ of the eastern tropical North Atlantic. Based on our findings, a coupling of primary production and organic matter export via the nitrogen cycle is proposed, which may, however, be impacted by several additional factors, e.g., micronutrients, particles acting as microniches, vertical and horizontal transport of organic material and the role of zooplankton and viruses therein.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
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    Copernicus Publications (EGU)
    In:  Biogeosciences (BG), 16 . pp. 2033-2047.
    Publication Date: 2019-05-15
    Description: The Eastern Tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZ) in the world ocean where dissolved oxygen (O2) concentrations reach well below 1 µmol kg−1. The high productivity leads to an accumulation of dissolved organic matter (DOM) in the surface layers that may serve as a substrate for heterotrophic respiration. However, the importance of DOM utilization for O2 respiration within the Peruvian OMZ remains unclear so far. Here, we evaluate the diapycnal fluxes of O2, dissolved organic carbon (DOC), dissolved organic nitrogen, dissolved hydrolysable amino acids (DHAA) and dissolved combined carbohydrates (DCCHO) and the composition of DOM in the ETSP off Peru to learn, whether labile DOM is reaching into the core of the OMZ and how important DOM utilization might be for O2 attenuation. The observed diapycnal 2 flux (50 mmol O2 m−2 day−1 at max) was limited to the upper 80 m of the water column, the flux attenuation of ~1 µmol L−1day−1, was comparable to previously published O2 consumption rates for the North and South Pacific OMZs. The diapycnal DOM flux (31 mmol C m−2 day−1 at max) was limited to ~30 m water depth, suggesting that the labile DOM is already utilized within the upper part of the shallow oxycline off Peru. The analyses of DCCHO and DHAA composition support this finding, suggesting that DOM undergoes comprehensive remineralization already within the upper part of the oxycline, as the DOM within the core of the OMZ was found to be largely altered. Estimated by a simple equation for carbon combustion, aerobic respiration of DCCHO and DHAA, supplied by diapycnal mixing (0.46 µmol L−1 day−1 at max), could account for up to 38 % of the diapycnal O2 supply in the upper oxycline, which suggests that DOM utilization may play a significant role for shape of the upper Peruvian oxycline.
    Type: Article , PeerReviewed
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  • 9
    Publication Date: 2019-05-23
    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
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  • 10
    Publication Date: 2019-07-17
    Description: Enhanced permafrost warming and increased arctic river discharges have heightened concern about the input of terrigenous matter into Arctic coastal waters. The IPY project 'ocOC- from Ocean Colour to Organic Carbon' (2008-2010) uses Ocean Colour (OC) data for synoptic monitoring of the input of terrigenous Organic Carbon (OC) from fluvial and coastal sources into Arctic coastal waters. Every late summer, Russian-German ship expeditions take part in the southern Laptev Sea (Arctic Siberia, Russia). The multi-year expedition data are the base for understanding the optico-chemico properties of the coastal waters. The coastal waters are characterized by low transparencies, resuspension events and high cDOM concentrations. The Laptev Sea Region has become an ESA CoastColour investigation site to support the use of the ground data. Ocean Colour MERIS data from 2008 on to 2010 are processed using the VISAT Beam Case2Regional Processor (C2R). The expedition data show that Siberian Arctic coastal waters are highly specific in terms of high cDOM background concentrations. Therefore, all remote sensing chlorophyll products are overestimated by an order of magnitude due to the high cDOM concentrations. The optical C2R parameters such as absorption, attenuation and the first attenuation depth are of immediate value to show the hydrographic dynamics of the Laptev Sea coastal waters
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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