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  • 1
    Online Resource
    Online Resource
    Ideas and perspectives: A strategic assessment of methane and nitrous oxide measurements in the marine environment
    Copernicus GmbH ; 2020
    In:  Biogeosciences Vol. 17, No. 22 ( 2020-11-26), p. 5809-5828
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 17, No. 22 ( 2020-11-26), p. 5809-5828
    Abstract: Abstract. In the current era of rapid climate change, accurate characterization of climate-relevant gas dynamics – namely production, consumption, and net emissions – is required for all biomes, especially those ecosystems most susceptible to the impact of change. Marine environments include regions that act as net sources or sinks for numerous climate-active trace gases including methane (CH4) and nitrous oxide (N2O). The temporal and spatial distributions of CH4 and N2O are controlled by the interaction of complex biogeochemical and physical processes. To evaluate and quantify how these mechanisms affect marine CH4 and N2O cycling requires a combination of traditional scientific disciplines including oceanography, microbiology, and numerical modeling. Fundamental to these efforts is ensuring that the datasets produced by independent scientists are comparable and interoperable. Equally critical is transparent communication within the research community about the technical improvements required to increase our collective understanding of marine CH4 and N2O. A workshop sponsored by Ocean Carbon and Biogeochemistry (OCB) was organized to enhance dialogue and collaborations pertaining to marine CH4 and N2O. Here, we summarize the outcomes from the workshop to describe the challenges and opportunities for near-future CH4 and N2O research in the marine environment.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    DOI: 10.5194/bg-17-5809-2020
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2020
    detail.hit.zdb_id: 2158181-2
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  • 2
    Online Resource
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    An intercomparison of oceanic methane and nitrous oxide measurements
    Copernicus GmbH ; 2018
    In:  Biogeosciences Vol. 15, No. 19 ( 2018-10-05), p. 5891-5907
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 15, No. 19 ( 2018-10-05), p. 5891-5907
    Abstract: Abstract. Large-scale climatic forcing is impacting oceanic biogeochemical cycles and is expected to influence the water-column distribution of trace gases, including methane and nitrous oxide. Our ability as a scientific community to evaluate changes in the water-column inventories of methane and nitrous oxide depends largely on our capacity to obtain robust and accurate concentration measurements that can be validated across different laboratory groups. This study represents the first formal international intercomparison of oceanic methane and nitrous oxide measurements whereby participating laboratories received batches of seawater samples from the subtropical Pacific Ocean and the Baltic Sea. Additionally, compressed gas standards from the same calibration scale were distributed to the majority of participating laboratories to improve the analytical accuracy of the gas measurements. The computations used by each laboratory to derive the dissolved gas concentrations were also evaluated for inconsistencies (e.g., pressure and temperature corrections, solubility constants). The results from the intercomparison and intercalibration provided invaluable insights into methane and nitrous oxide measurements. It was observed that analyses of seawater samples with the lowest concentrations of methane and nitrous oxide had the lowest precisions. In comparison, while the analytical precision for samples with the highest concentrations of trace gases was better, the variability between the different laboratories was higher: 36 % for methane and 27 % for nitrous oxide. In addition, the comparison of different batches of seawater samples with methane and nitrous oxide concentrations that ranged over an order of magnitude revealed the ramifications of different calibration procedures for each trace gas. Finally, this study builds upon the intercomparison results to develop recommendations for improving oceanic methane and nitrous oxide measurements, with the aim of precluding future analytical discrepancies between laboratories.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-15-5891-2018
    DOI: 10.5194/bg-15-5891-2018-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2018
    detail.hit.zdb_id: 2158181-2
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  • 3
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    Online Resource
    The marine nitrogen cycle: recent discoveries, uncertainties and the potential relevance of climate change
    The Royal Society ; 2013
    In:  Philosophical Transactions of the Royal Society B: Biological Sciences Vol. 368, No. 1621 ( 2013-07-05), p. 20130121-
    Details
    In: Philosophical Transactions of the Royal Society B: Biological Sciences, The Royal Society, Vol. 368, No. 1621 ( 2013-07-05), p. 20130121-
    Abstract: The ocean's nitrogen cycle is driven by complex microbial transformations, including nitrogen fixation, assimilation, nitrification, anammox and denitrification. Dinitrogen is the most abundant form of nitrogen in sea water but only accessible by nitrogen-fixing microbes. Denitrification and nitrification are both regulated by oxygen concentrations and potentially produce nitrous oxide (N 2 O), a climate-relevant atmospheric trace gas. The world's oceans, including the coastal areas and upwelling areas, contribute about 30 per cent to the atmospheric N 2 O budget and are, therefore, a major source of this gas to the atmosphere. Human activities now add more nitrogen to the environment than is naturally fixed. More than half of the nitrogen reaches the coastal ocean via river input and atmospheric deposition, of which the latter affects even remote oceanic regions. A nitrogen budget for the coastal and open ocean, where inputs and outputs match rather well, is presented. Furthermore, predicted climate change will impact the expansion of the oceans' oxygen minimum zones, the productivity of surface waters and presumably other microbial processes, with unpredictable consequences for the cycling of nitrogen. Nitrogen cycling is closely intertwined with that of carbon, phosphorous and other biologically important elements via biological stoichiometric requirements. This linkage implies that human alterations of nitrogen cycling are likely to have major consequences for other biogeochemical processes and ecosystem functions and services.
    Type of Medium: Online Resource
    ISSN: 0962-8436 , 1471-2970
    URL: Article
    DOI: 10.1098/rstb.2013.0121
    RVK:
    WA 15000
    Language: English
    Publisher: The Royal Society
    Publication Date: 2013
    detail.hit.zdb_id: 1462620-2
    SSG: 12
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  • 4
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    Online Resource
    Global oceanic production of nitrous oxide
    The Royal Society ; 2012
    In:  Philosophical Transactions of the Royal Society B: Biological Sciences Vol. 367, No. 1593 ( 2012-05-05), p. 1245-1255
    Details
    In: Philosophical Transactions of the Royal Society B: Biological Sciences, The Royal Society, Vol. 367, No. 1593 ( 2012-05-05), p. 1245-1255
    Abstract: We use transient time distributions calculated from tracer data together with in situ measurements of nitrous oxide (N 2 O) to estimate the concentration of biologically produced N 2 O and N 2 O production rates in the ocean on a global scale. Our approach to estimate the N 2 O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We estimate that the oceanic N 2 O production is dominated by nitrification with a contribution of only approximately 7 per cent by denitrification. This indicates that previously used approaches have overestimated the contribution by denitrification. Shelf areas may account for only a negligible fraction of the global production; however, estuarine sources and coastal upwelling of N 2 O are not taken into account in our study. The largest amount of subsurface N 2 O is produced in the upper 500 m of the water column. The estimated global annual subsurface N 2 O production ranges from 3.1 ± 0.9 to 3.4 ± 0.9 Tg N yr −1 . This is in agreement with estimates of the global N 2 O emissions to the atmosphere and indicates that a N 2 O source in the mixed layer is unlikely. The potential future development of the oceanic N 2 O source in view of the ongoing changes of the ocean environment (deoxygenation, warming, eutrophication and acidification) is discussed.
    Type of Medium: Online Resource
    ISSN: 0962-8436 , 1471-2970
    URL: Article
    DOI: 10.1098/rstb.2011.0360
    RVK:
    WA 15000
    Language: English
    Publisher: The Royal Society
    Publication Date: 2012
    detail.hit.zdb_id: 1462620-2
    SSG: 12
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  • 5
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    Online Resource
    Nitrous oxide in coastal waters
    American Geophysical Union (AGU) ; 1996
    In:  Global Biogeochemical Cycles Vol. 10, No. 1 ( 1996-03), p. 197-207
    Details
    In: Global Biogeochemical Cycles, American Geophysical Union (AGU), Vol. 10, No. 1 ( 1996-03), p. 197-207
    Abstract: We determined atmospheric and dissolved nitrous oxide (N 2 O) in the surface waters of the central North Sea, the German Bight, and the Gironde estuary. The mean saturations were 104 ± 1% (central North Sea, September 1991), 101 ± 2% (German Bight, September 1991), 99 ± 1% (German Bight September 1992), and 132% (Gironde estuary, November 1991). To evaluate the contribution of coastal areas and estuaries to the oceanic emissions we assembled a compilation of literature data. We conclude that the mean saturations in coastal regions (with the exception of estuaries and regions with upwelling phenomena) are only slightly higher than in the open ocean. However, when estuarine and coastal upwelling regions are included, a computation of the global oceanic N 2 O flux indicates that a considerable portion (approximately 60%) of this flux is from coastal regions, mainly due to high emissions from estuaries. We estimate, using two different parameterizations of the air‐sea exchange process, an annual global sea‐to‐air flux of 11–17 Tg N 2 O. Our results suggest a serious underestimation of the flux from coastal regions in widely used previous estimates.
    Type of Medium: Online Resource
    ISSN: 0886-6236 , 1944-9224
    URL: Article
    DOI: 10.1029/95GB03834
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1996
    detail.hit.zdb_id: 2021601-4
    SSG: 12
    SSG: 13
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  • 6
    Online Resource
    Online Resource
    Nitrous oxide and methane in European coastal waters
    Elsevier BV ; 2006
    In:  Estuarine, Coastal and Shelf Science Vol. 70, No. 3 ( 2006-11), p. 361-374
    Details
    In: Estuarine, Coastal and Shelf Science, Elsevier BV, Vol. 70, No. 3 ( 2006-11), p. 361-374
    Type of Medium: Online Resource
    ISSN: 0272-7714
    URL: Article
    DOI: 10.1016/j.ecss.2006.05.042
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2006
    detail.hit.zdb_id: 1466742-3
    detail.hit.zdb_id: 763369-5
    SSG: 21,3
    SSG: 12
    SSG: 14
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  • 7
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    Nitrous oxide and methane in two tropical estuaries in a peat-dominated region of northwestern Borneo
    Copernicus GmbH ; 2016
    In:  Biogeosciences Vol. 13, No. 8 ( 2016-04-26), p. 2415-2428
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 13, No. 8 ( 2016-04-26), p. 2415-2428
    Abstract: Abstract. Estuaries are sources of nitrous oxide (N2O) and methane (CH4) to the atmosphere. However, our present knowledge of N2O and CH4 emissions from estuaries in the tropics is very limited because data are scarce. In this study, we present first measurements of dissolved N2O and CH4 from two estuaries in a peat-dominated region of northwestern Borneo. Two campaigns (during the dry season in June 2013 and during the wet season in March 2014) were conducted in the estuaries of the Lupar and Saribas rivers. Median N2O concentrations ranged between 7.2 and 12.3 nmol L−1 and were higher in the marine end-member (13.0 ± 7.0 nmol L−1). CH4 concentrations were low in the coastal ocean (3.6 ± 0.2 nmol L−1) and higher in the estuaries (medians between 10.6 and 64.0 nmol L−1). The respiration of abundant organic matter and presumably anthropogenic input caused slight eutrophication, which did not lead to hypoxia or enhanced N2O concentrations, however. Generally, N2O concentrations were not related to dissolved inorganic nitrogen concentrations. Thus, the use of an emission factor for the calculation of N2O emissions from the inorganic nitrogen load leads to an overestimation of the flux from the Lupar and Saribas estuaries. N2O was negatively correlated with salinity during the dry season, which suggests a riverine source. In contrast, N2O concentrations during the wet season were not correlated with salinity but locally enhanced within the estuaries, implying that there were additional estuarine sources during the wet (i.e., monsoon) season. Estuarine CH4 distributions were not driven by freshwater input but rather by tidal variations. Both N2O and CH4 concentrations were more variable during the wet season. We infer that the wet season dominates the variability of the N2O and CH4 concentrations and subsequent emissions from tropical estuaries. Thus, we speculate that any changes in the Southeast Asian monsoon system will lead to changes in the N2O and CH4 emissions from these systems. We also suggest that the ongoing cultivation of peat soil in Borneo is likely to increase N2O emissions from these estuaries, while the effect on CH4 remains uncertain.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    DOI: 10.5194/bg-13-2415-2016
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 2158181-2
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  • 8
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    Online Resource
    N〈sub〉2〈/sub〉 fixation in eddies of the eastern tropical South Pacific Ocean
    Copernicus GmbH ; 2016
    In:  Biogeosciences Vol. 13, No. 10 ( 2016-05-18), p. 2889-2899
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 13, No. 10 ( 2016-05-18), p. 2889-2899
    Abstract: Abstract. Mesoscale eddies play a major role in controlling ocean biogeochemistry. By impacting nutrient availability and water column ventilation, they are of critical importance for oceanic primary production. In the eastern tropical South Pacific Ocean off Peru, where a large and persistent oxygen-deficient zone is present, mesoscale processes have been reported to occur frequently. However, investigations into their biological activity are mostly based on model simulations, and direct measurements of carbon and dinitrogen (N2) fixation are scarce.We examined an open-ocean cyclonic eddy and two anticyclonic mode water eddies: a coastal one and an open-ocean one in the waters off Peru along a section at 16° S in austral summer 2012. Molecular data and bioassay incubations point towards a difference between the active diazotrophic communities present in the cyclonic eddy and the anticyclonic mode water eddies.In the cyclonic eddy, highest rates of N2 fixation were measured in surface waters but no N2 fixation signal was detected at intermediate water depths. In contrast, both anticyclonic mode water eddies showed pronounced maxima in N2 fixation below the euphotic zone as evidenced by rate measurements and geochemical data. N2 fixation and carbon (C) fixation were higher in the young coastal mode water eddy compared to the older offshore mode water eddy. A co-occurrence between N2 fixation and biogenic N2, an indicator for N loss, indicated a link between N loss and N2 fixation in the mode water eddies, which was not observed for the cyclonic eddy. The comparison of two consecutive surveys of the coastal mode water eddy in November 2012 and December 2012 also revealed a reduction in N2 and C fixation at intermediate depths along with a reduction in chlorophyll by half, mirroring an aging effect in this eddy. Our data indicate an important role for anticyclonic mode water eddies in stimulating N2 fixation and thus supplying N offshore.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-13-2889-2016
    DOI: 10.5194/bg-13-2889-2016-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2016
    detail.hit.zdb_id: 2158181-2
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  • 9
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    Dimethylated sulfur compounds in the Peruvian upwelling system
    Copernicus GmbH ; 2022
    In:  Biogeosciences Vol. 19, No. 3 ( 2022-02-04), p. 701-714
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 19, No. 3 ( 2022-02-04), p. 701-714
    Abstract: Abstract. Our understanding of the biogeochemical cycling of the climate-relevant trace gas dimethyl sulfide (DMS) in the Peruvian upwelling system is still limited. Here we present oceanic and atmospheric DMS measurements which were made during two shipborne cruises in December 2012 (M91) and October 2015 (SO243) in the Peruvian upwelling region. Dimethylsulfoniopropionate (DMSP) and dimethyl sulfoxide (DMSO) were also measured during M91. DMS concentrations were 1.9 ± 0.9 and 2.5 ± 1.9 nmol L−1 in surface waters in October 2015 and December 2012, respectively. Nutrient availability appeared to be the main driver of the observed variability in the surface DMS distributions in the coastal areas. DMS, DMSP, and DMSO showed maxima in the surface layer, and no elevated concentrations associated with the oxygen minimum zone off Peru were measured. The possible role of DMS, DMSP, and DMSO as radical scavengers (stimulated by nitrogen limitation) is supported by their negative correlations with N:P (sum of nitrate and nitrite : dissolved phosphate) ratios. Large variations in atmospheric DMS mole fractions were measured during M91 (144.6 ± 95.0 ppt) and SO243 (91.4 ± 55.8 ppt); however, the atmospheric mole fractions were generally low, and the sea-to-air flux was primarily driven by seawater DMS. The Peruvian upwelling region was identified as a source of atmospheric DMS in December 2012 and October 2015. However, in comparison to the previous measurements in the adjacent regions, the Peru upwelling was a moderate source of DMS emissions at either time (M91: 5.9 ± 5.3 µmol m−2 d−1; SO243: 3.8 ± 2.7 µmol m−2 d−1).
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-19-701-2022
    DOI: 10.5194/bg-19-701-2022-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2022
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  • 10
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    Online Resource
    Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events
    Copernicus GmbH ; 2019
    In:  Biogeosciences Vol. 16, No. 20 ( 2019-10-21), p. 4065-4084
    Details
    In: Biogeosciences, Copernicus GmbH, Vol. 16, No. 20 ( 2019-10-21), p. 4065-4084
    Abstract: Abstract. Ground-based atmospheric observations of CO2, δ(O2∕N2), N2O, and CH4 were used to make estimates of the air–sea fluxes of these species from the Lüderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (±1σ) were 0.65±0.4 µmol m−2 s−1 for CO2, -5.1±2.5 µmol m−2 s−1 for O2 (as APO), 0.61±0.5 nmol m−2 s−1 for N2O, and 4.8±6.3 nmol m−2 s−1 for CH4. A comparison of our top-down (i.e., inferred from atmospheric anomalies) flux estimates with shipboard-based measurements showed that the two approaches agreed within ±55 % on average, though the degree of agreement varied by species and was best for CO2. Since the top-down method overestimated the flux density relative to the shipboard-based approach for all species, we also present flux density estimates that have been tuned to best match the shipboard fluxes. During the study, upwelling events were sources of CO2, N2O, and CH4 to the atmosphere. N2O fluxes were fairly low, in accordance with previous work suggesting that the evasion of this gas from the Benguela is smaller than for other eastern boundary upwelling systems (EBUS). Conversely, CH4 release was quite high for the marine environment, a result that supports studies that indicated a large sedimentary source of CH4 in the Walvis Bay area. These results demonstrate the suitability of atmospheric time series for characterizing the temporal variability of upwelling events and their influence on the overall marine greenhouse gas (GHG) emissions from the northern Benguela region.
    Type of Medium: Online Resource
    ISSN: 1726-4189
    URL: Article
    URL: Article
    DOI: 10.5194/bg-16-4065-2019
    DOI: 10.5194/bg-16-4065-2019-supplement
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2019
    detail.hit.zdb_id: 2158181-2
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