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  • 1
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    PANGAEA
    In:  Supplement to: Brandt, Peter; Bange, Hermann Werner; Banyte, Donata; Dengler, Marcus; Didwischus, Sven-Helge; Fischer, Tim; Greatbatch, Richard J; Hahn, Johannes; Kanzow, Torsten; Karstensen, Johannes; Körtzinger, Arne; Krahmann, Gerd; Schmidtko, Sunke; Stramma, Lothar; Tanhua, Toste; Visbeck, Martin (2015): On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic. Biogeosciences, 12(2), 489-512, https://doi.org/10.5194/bg-12-489-2015
    Publication Date: 2020-01-17
    Description: Ocean observations carried out in the framework of the Collaborative Research Center 754 (SFB 754) "Climate-Biogeochemistry Interactions in the Tropical Ocean" are used to study (1) the structure of tropical oxygen minimum zones (OMZs), (2) the processes that contribute to the oxygen budget, and (3) long-term changes in the oxygen distribution. The OMZ of the eastern tropical North Atlantic (ETNA), located between the well-ventilated subtropical gyre and the equatorial oxygen maximum, is composed of a deep OMZ at about 400 m depth with its core region centred at about 20° W, 10° N and a shallow OMZ at about 100 m depth with lowest oxygen concentrations in proximity to the coastal upwelling region off Mauritania and Senegal. The oxygen budget of the deep OMZ is given by oxygen consumption mainly balanced by the oxygen supply due to meridional eddy fluxes (about 60%) and vertical mixing (about 20%, locally up to 30%). Advection by zonal jets is crucial for the establishment of the equatorial oxygen maximum. In the latitude range of the deep OMZ, it dominates the oxygen supply in the upper 300 to 400 m and generates the intermediate oxygen maximum between deep and shallow OMZs. Water mass ages from transient tracers indicate substantially older water masses in the core of the deep OMZ (about 120-180 years) compared to regions north and south of it. The deoxygenation of the ETNA OMZ during recent decades suggests a substantial imbalance in the oxygen budget: about 10% of the oxygen consumption during that period was not balanced by ventilation. Long-term oxygen observations show variability on interannual, decadal and multidecadal time scales that can partly be attributed to circulation changes. In comparison to the ETNA OMZ the eastern tropical South Pacific OMZ shows a similar structure including an equatorial oxygen maximum driven by zonal advection, but overall much lower oxygen concentrations approaching zero in extended regions. As the shape of the OMZs is set by ocean circulation, the widespread misrepresentation of the intermediate circulation in ocean circulation models substantially contributes to their oxygen bias, which might have significant impacts on predictions of future oxygen levels.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 2
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    PANGAEA
    In:  Supplement to: Maltby, Johanna; Steinle, Lea; Löscher, Carolin R; Bange, Hermann Werner; Fischer, Martin A; Schmidt, Mark; Treude, Tina (2018): Microbial methanogenesis in the sulfate-reducing zone of sediments in the Eckernförde Bay, SW Baltic Sea. Biogeosciences, 15(1), 137-157, https://doi.org/10.5194/bg-15-137-2018
    Publication Date: 2020-01-17
    Description: The presence of surface methanogenesis, located within the sulfate-reducing zone (0-30 centimeters below seafloor, cmbsf), was investigated in sediments of the seasonally hypoxic Eckernförde Bay, southwestern Baltic Sea. Water column parameters like oxygen, temperature and salinity together with porewater geochemistry and benthic methanogenesis rates were determined in the sampling area 'Boknis Eck' quarterly from March 2013 to September 2014, to investigate the effect of seasonal environmental changes on the rate and distribution of surface methanogenesis and to estimate its potential contribution to benthic methane emissions. Water column parameters where determined via CTD (temperature, salinity, pressure), as well as gas chromatography (methane) and fluorometric methods (chlorophyll a). For porewater and sediment geochemistry various method were used including photometry (sulfide), ion chromatography (sulfate), N/C Analysis (DIC), Carbo-Elba element analysis (POC, C/N), gas chromatography (methane). Sediment net methanogenesis rates were determined via the methane increase (measured with gas chromatography) over time in sediment slurry batch incubations. Sediment hydrogenotrophic methanogenesis was measured by adding radiotracer (14C-bicarbonate) to sediment samples and measuring the production of 14C-methane (via scintillation counting) after a specific period of time. For further details (sample preparation and analysis) see the related publication (Maltby et al., 2017, Biogeosciences Discussions)
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 3
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    PANGAEA
    In:  Supplement to: Arévalo-Martínez, Damian L; Kock, Annette; Steinhoff, T; Brandt, Peter; Dengler, Marcus; Fischer, Tim; Körtzinger, Arne; Bange, Hermann Werner (2017): Nitrous oxide during the onset of the Atlantic cold tongue. Journal of Geophysical Research: Oceans, 122(1), 171-184, https://doi.org/10.1002/2016JC012238
    Publication Date: 2020-01-17
    Description: Based on a detailed investigation of the distribution and sea-to-air fluxes of N2O in the eastern equatorial Atlantic (EEA), we show that the onset and seasonal development of the ACT can be clearly observed in surface N2O concentrations, which increase progressively as the cooling in the equatorial region proceeds during spring-summer. We observed a strong influence of the surface currents of the EEA on the N2O distribution, which allowed identifying “high” and “low” concentration regimes that were, in turn, spatially delimited by the extent of the warm eastward-flowing North Equatorial Countercurrent and the cold westward-flowing South Equatorial Current.
    Type: Dataset
    Format: application/zip, 4 datasets
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  • 4
    Publication Date: 2020-01-17
    Description: Continuous Surface Ocean and related atmospheric N2O measurements from M90 cruise measured with LGR OA-ICOS N2O Analyzer DLT 100 coupled to Weiss-type showerhead equilibrator.
    Type: Dataset
    Format: text/tab-separated-values, 102897 data points
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  • 5
    Publication Date: 2020-01-17
    Description: Continuous Surface Ocean and related atmospheric N2O measurements from M91 cruise measured with LGR OA-ICOS N2O Analyzer DLT 100 coupled to Weiss-type showerhead equilibrator.
    Type: Dataset
    Format: text/tab-separated-values, 138732 data points
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  • 6
    Publication Date: 2020-01-17
    Description: Continuous Surface Ocean and related atmospheric N2O measurements from M91 cruise measured with LGR OA-ICOS N2O Analyzer DLT 100 coupled to Weiss-type showerhead equilibrator.
    Type: Dataset
    Format: text/tab-separated-values, 104049 data points
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  • 7
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    PANGAEA
    In:  Supplement to: Kock, Annette; Gebhardt, Sarah; Bange, Hermann Werner (2008): Methane emissions from the upwelling area off Mauritania (NW Africa). Biogeosciences, 5(4), 1119-1125, https://doi.org/10.5194/bg-5-1119-2008
    Publication Date: 2020-01-17
    Description: Coastal upwelling regions have been identified as sites of enhanced CH4 emissions to the atmosphere. The coastal upwelling area off Mauritania (NW Africa) is one of the most biologically productive regions of the world's ocean but its CH4 emissions have not been quantified so far. More than 1000 measurements of atmospheric and dissolved CH4 in the surface layer in the upwelling area off Mauritania were performed as part of the German SOPRAN (Surface Ocean Processes in the Anthropocene) study during two cruises in March/April 2005 (P320/1) and February 2007 (P348). During P348 enhanced CH4 saturations of up to 200% were found close to the coast and were associated with upwelling of South Atlantic Central Water. An area-weighted, seasonally adjusted estimate yielded overall annual CH4 emissions in the range from 1.6 to 2.9 Gg CH4. Thus the upwelling area off Mauritania represents a regional hot spot of CH4 emissions but seems to be of minor importance for the global oceanic CH4 emissions.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 8
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    PANGAEA
    In:  Supplement to: Steinle, Lea; Maltby, Johanna; Treude, Tina; Kock, Annette; Bange, Hermann Werner; Engbersen, Nadine; Zopfi, Jakob; Lehmann, Moritz F; Niemann, Helge (2017): Effects of low oxygen concentrations on aerobic methane oxidation in seasonally hypoxic coastal waters. Biogeosciences, 14(6), 1631-1645, https://doi.org/10.5194/bg-14-1631-2017
    Publication Date: 2020-01-17
    Description: Coastal seas may account for more than 75% of global oceanic methane emissions. There, methane is mainly produced microbially in anoxic sediments from where it can escape to the overlying water column. Aerobic methane oxidation (MOx) in the water column acts as a biological filter reducing the amount of methane that eventually evades to the atmosphere. The efficiency of the MOx filter is potentially controlled by the availability of dissolved methane and oxygen, as well as temperature, salinity, and hydrographic dynamics, and all of these factors undergo strong temporal fluctuations in coastal ecosystems. In order to elucidate the key environmental controls, specifically the effect of oxygen availability, on MOx in a seasonally stratified and hypoxic coastal marine setting, we conducted a 2-year time-series study with measurements of MOx and physico-chemical water column parameters in a coastal inlet in the southwestern Baltic Sea (Eckernförde Bay). We found that MOx rates generally increased toward the seafloor, but were not directly linked to methane concentrations. MOx exhibited a strong seasonal variability, with maximum rates (up to 11.6 nmol l-1 d-1) during summer stratification when oxygen concentrations were lowest and bottom-water temperatures were highest. Under these conditions, 70-95% of the sediment-released methane was oxidized, whereas only 40-60% were consumed during the mixed and oxygenated periods. Laboratory experiments with manipulated oxygen concentrations in the range of 0.2-220 µmol l-1 revealed a sub-micromolar oxygen-optimum for MOx at the study site. In contrast, the fraction of methane-carbon incorporation into the bacterial biomass (compared to the total amount of oxidised methane) was up to 38-fold higher at saturated oxygen concentrations, suggesting a different partitioning of catabolic and anabolic processes under oxygen-replete and oxygen-starved conditions, respectively. Our results underscore the importance of MOx in mitigating methane emission from coastal waters and indicate an organism-level adaptation of the water column methanotrophs to hypoxic conditions.
    Type: Dataset
    Format: text/tab-separated-values, 478 data points
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  • 9
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    PANGAEA
    In:  Supplement to: Stramma, Lothar; Fischer, Tim; Grundle, Damian; Krahmann, Gerd; Bange, Hermann Werner; Marandino, Christa A (2016): Observed El Niño conditions in the eastern tropical Pacific in October 2015. Ocean Science, 12(4), 861-873, https://doi.org/10.5194/os-12-861-2016
    Publication Date: 2020-01-17
    Description: A strong El Niño developed in early 2015. Measurements from a research cruise on the RV Sonne in October 2015 near the equator east of the Galapagos Islands and off the shelf of Peru, are used to investigate changes related to El Niño in the upper ocean in comparison with earlier cruises in this region. At the equator at 85°30' W, a clear temperature increase leading to lower densities in the upper 350 m, despite a concurrent salinity increase from 40 to 350 m, developed in October 2015. Lower nutrient concentrations were also present in the upper 200 m, and higher oxygen concentrations were observed between 40 and 130 m. Except for the upper 60 m at 2°30' S, however, there was no obvious increase in oxygen concentrations at sampling stations just north (1° N) and south (2°30' S) of the equator at 85°30' W. In the equatorial current field, the Equatorial Undercurrent (EUC) east of the Galapagos Islands almost disappeared in October 2015, with a transport of only 0.02 Sv in the equatorial channel between 1° S and 1° N, and a weak current band of 0.78 Sv located between 1° S and 2°30' S. Such near-disappearances of the EUC in the eastern Pacific seem to occur only during strong El Niño events. Off the Peruvian shelf at ~9° S, where the sea surface temperature (SST) was elevated, upwelling was modified, and warm, saline and oxygen rich water was upwelled. Despite some weak El Niño related SST increase at ~12 to 16° S, the upwelling of cold, low salinity and oxygen-poor water was still active at the easternmost stations at three sections at ~12° S, ~14° S and ~16° S, while further west on these sections a transition to El Niño conditions appeared. Although in early 2015 the El Niño was strong and in October 2015 showed a clear El Niño influence on the EUC, in the eastern tropical Pacific the measurements only showed developing El Niño water mass distributions. In particular the oxygen distribution indicated the ongoing transition from 'typical' to El Niño conditions progressing southward along the Peruvian shelf.
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 10
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    PANGAEA
    In:  IFM-GEOMAR Leibniz-Institute of Marine Sciences, Kiel University
    Publication Date: 2020-01-17
    Type: Dataset
    Format: text/tab-separated-values, 212514 data points
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