Moussab/ORKG-training-evaluation-set huggingface dataset:
Research field: Oceanography
Title: Ocean carbon cycling in the Indian Ocean: 1. Spatiotemporal variability of inorganic carbon and air-sea CO2gas exchange: INDIAN OCEAN CARBON CYCLE, 1
Abstract: The spatiotemporal variability of upper ocean inorganic carbon parameters and air‐sea CO2 exchange in the Indian Ocean was examined using inorganic carbon data collected as part of the World Ocean Circulation Experiment (WOCE) cruises in 1995. Multiple linear regression methods were used to interpolate and extrapolate the temporally and geographically limited inorganic carbon data set to the entire Indian Ocean basin using other climatological hydrographic and biogeochemical data. The spatiotemporal distributions of total carbon dioxide (TCO2), alkalinity, and seawater pCO2 were evaluated for the Indian Ocean and regions of interest including the Arabian Sea, Bay of Bengal, and 10°N–35°S zones. The Indian Ocean was a net source of CO2 to the atmosphere, and a net sea‐to‐air CO2 flux of +237 ± 132 Tg C yr−1 (+0.24 Pg C yr−1) was estimated. Regionally, the Arabian Sea, Bay of Bengal, and 10°N–10°S zones were perennial sources of CO2 to the atmosphere. In the 10°S–35°S zone, the CO2 sink or source status of the surface ocean shifts seasonally, although the region is a net oceanic sink of atmospheric CO2.
Extracted statement — Average CO2 flux: 0.24
Research field: Oceanography
Title: Nitrous oxide emissions from the Arabian Sea: A synthesis
Abstract: Abstract. We computed high-resolution (1o latitude x 1o longitude) seasonal and annual nitrous oxide (N2O) concentration fields for the Arabian Sea surface layer using a database containing more than 2400 values measured between December 1977 and July 1997. N2O concentrations are highest during the southwest (SW) monsoon along the southern Indian continental shelf. Annual emissions range from 0.33 to 0.70 Tg N2O and are dominated by fluxes from coastal regions during the SW and northeast monsoons. Our revised estimate for the annual N2O flux from the Arabian Sea is much more tightly constrained than the previous consensus derived using averaged in-situ data from a smaller number of studies. However, the tendency to focus on measurements in locally restricted features in combination with insufficient seasonal data coverage leads to considerable uncertainties of the concentration fields and thus in the flux estimates, especially in the coastal zones of the northern and eastern Arabian Sea. The overall mean relative error of the annual N2O emissions from the Arabian Sea was estimated to be at least 65%.
Extracted statement — N2O flux (lower limit): 0.33
Research field: Oceanography
Title: Variabilities in the fluxes and annual emissions of nitrous oxide from the Arabian Sea
Abstract: Extensive measurements of nitrous oxide (N2O) have been made during April–May 1994 (intermonsoon), February–March 1995 (northeast monsoon), July–August 1995 and August 1996 (southwest monsoon) in the Arabian Sea. Low N2O supersaturations in the surface waters are observed during intermonsoon compared to those in northeast and southwest monsoons. Spatial distributions of supersaturations manifest the effects of larger mixing during winter cooling and wind‐driven upwelling during monsoon period off the Indian west coast. A net positive flux is observable during all the seasons, with no discernible differences from the open ocean to coastal regions. The average ocean‐to‐atmosphere fluxes of N2O are estimated, using wind speed dependent gas transfer velocity, to be of the order of 0.26, 0.003, and 0.51, and 0.78 pg (pico grams) cm−2 s−1 during northeast monsoon, intermonsoon, and southwest monsoon in 1995 and 1996, respectively. The lower range of annual emission of N2O is estimated to be 0.56–0.76 Tg N2O per year which constitutes 13–17% of the net global oceanic source. However, N2O emission from the Arabian Sea can be as high as 1.0 Tg N2O per year using different gas transfer models.
Extracted statement — N2O flux (lower limit): 0.56
Research field: Oceanography
Title: Dissolved Organic Matter Influences N2 Fixation in the New Caledonian Lagoon (Western Tropical South Pacific)
Abstract: Specialized prokaryotes performing biological dinitrogen (N2) fixation ('diazotrophs') provide an important source of fixed nitrogen in oligotrophic marine ecosystems such as tropical and subtropical oceans. In these waters, cyanobacterial photosynthetic diazotrophs are well known to be abundant and active, yet the role and contribution of non-cyanobacterial diazotrophs are currently unclear. The latter are not photosynthetic (here called 'heterotrophic') and hence require external sources of organic matter to sustain N2 fixation. Here we added the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) to estimate the N2 fixation potential of heterotrophic diazotrophs as compared to autotrophic ones. Additionally, we explored the influence of dissolved organic matter (DOM) on these diazotrophs along a coast to open ocean gradient in the surface waters of a subtropical coral lagoon (New Caledonia). Total N2 fixation (samples not amended with DCMU) ranged from 0.66 to 1.32 nmol N L-1 d-1. The addition of DCMU reduced N2 fixation by >90%, suggesting that the contribution of heterotrophic diazotrophs to overall N2 fixation activity was minor in this environment. Higher contribution of heterotrophic diazotrophs occurred in stations closer to the shore and coincided with the decreasing lability of DOM, as shown by various colored DOM and fluorescent DOM (CDOM and FDOM) indices. This suggests that heterotrophic N2 fixation is favored when labile DOM compounds are available. We tested the response of diazotrophs (in terms of nifH gene expression and bulk N2 fixation rates) upon the addition of a mix of carbohydrates ('DOC' treatment), amino acids ('DON' treatment), and phosphonates and phosphomonesters ('DOP' treatment). While nifH expression increased significantly in Trichodesmium exposed to the DOC treatment, bulk N2 fixation rates increased significantly only in the DOP treatment. The lack of nifH expression by gammaproteobacteria, in any of the DOM addition treatments applied, questions the contribution of non-cyanobacterial diazotrophs to fixed nitrogen inputs in the New Caledonian lagoon. While the metabolism and ecology of heterotrophic diazotrophs is currently elusive, a deeper understanding of their ecology and relationship with DOM is needed in the light of increased DOM inputs in coastal zones due to anthropogenic pressure.
Extracted statement — Volumetric N2 fixation rate (lower limit): 0.66
Research field: Oceanography
Title: Nitrous oxide emissions from the Arabian Sea: A synthesis
Abstract: Abstract. We computed high-resolution (1o latitude x 1o longitude) seasonal and annual nitrous oxide (N2O) concentration fields for the Arabian Sea surface layer using a database containing more than 2400 values measured between December 1977 and July 1997. N2O concentrations are highest during the southwest (SW) monsoon along the southern Indian continental shelf. Annual emissions range from 0.33 to 0.70 Tg N2O and are dominated by fluxes from coastal regions during the SW and northeast monsoons. Our revised estimate for the annual N2O flux from the Arabian Sea is much more tightly constrained than the previous consensus derived using averaged in-situ data from a smaller number of studies. However, the tendency to focus on measurements in locally restricted features in combination with insufficient seasonal data coverage leads to considerable uncertainties of the concentration fields and thus in the flux estimates, especially in the coastal zones of the northern and eastern Arabian Sea. The overall mean relative error of the annual N2O emissions from the Arabian Sea was estimated to be at least 65%.
Extracted statement — N2O flux (upper limit): 0.7
Research field: Oceanography
Title: Evidence of high N&lt;sub&gt;2&lt;/sub&gt; fixation rates in the temperate northeast Atlantic
Abstract: Abstract. Diazotrophic activity and primary production (PP) were investigated along two transects (Belgica BG2014/14 and GEOVIDE cruises) off the western Iberian Margin and the Bay of Biscay in May 2014. Substantial N2 fixation activity was observed at 8 of the 10 stations sampled, ranging overall from 81 to 384 µmol N m−2 d−1 (0.7 to 8.2 nmol N L−1 d−1), with two sites close to the Iberian Margin situated between 38.8 and 40.7∘ N yielding rates reaching up to 1355 and 1533 µmol N m−2 d−1. Primary production was relatively lower along the Iberian Margin, with rates ranging from 33 to 59 mmol C m−2 d−1, while it increased towards the northwest away from the peninsula, reaching as high as 135 mmol C m−2 d−1. In agreement with the area-averaged Chl a satellite data contemporaneous with our study period, our results revealed that post-bloom conditions prevailed at most sites, while at the northwesternmost station the bloom was still ongoing. When converted to carbon uptake using Redfield stoichiometry, N2 fixation could support 1 % to 3 % of daily PP in the euphotic layer at most sites, except at the two most active sites where this contribution to daily PP could reach up to 25 %. At the two sites where N2 fixation activity was the highest, the prymnesiophyte–symbiont Candidatus Atelocyanobacterium thalassa (UCYN-A) dominated the nifH sequence pool, while the remaining recovered sequences belonged to non-cyanobacterial phylotypes. At all the other sites, however, the recovered nifH sequences were exclusively assigned phylogenetically to non-cyanobacterial phylotypes. The intense N2 fixation activities recorded at the time of our study were likely promoted by the availability of phytoplankton-derived organic matter produced during the spring bloom, as evidenced by the significant surface particulate organic carbon concentrations. Also, the presence of excess phosphorus signature in surface waters seemed to contribute to sustaining N2 fixation, particularly at the sites with extreme activities. These results provide a mechanistic understanding of the unexpectedly high N2 fixation in productive waters of the temperate North Atlantic and highlight the importance of N2 fixation for future assessment of the global N inventory.
Extracted statement — Volumetric N2 fixation rate (lower limit): 0.7
Research field: Oceanography
Title: Variabilities in the fluxes and annual emissions of nitrous oxide from the Arabian Sea
Abstract: Extensive measurements of nitrous oxide (N2O) have been made during April–May 1994 (intermonsoon), February–March 1995 (northeast monsoon), July–August 1995 and August 1996 (southwest monsoon) in the Arabian Sea. Low N2O supersaturations in the surface waters are observed during intermonsoon compared to those in northeast and southwest monsoons. Spatial distributions of supersaturations manifest the effects of larger mixing during winter cooling and wind‐driven upwelling during monsoon period off the Indian west coast. A net positive flux is observable during all the seasons, with no discernible differences from the open ocean to coastal regions. The average ocean‐to‐atmosphere fluxes of N2O are estimated, using wind speed dependent gas transfer velocity, to be of the order of 0.26, 0.003, and 0.51, and 0.78 pg (pico grams) cm−2 s−1 during northeast monsoon, intermonsoon, and southwest monsoon in 1995 and 1996, respectively. The lower range of annual emission of N2O is estimated to be 0.56–0.76 Tg N2O per year which constitutes 13–17% of the net global oceanic source. However, N2O emission from the Arabian Sea can be as high as 1.0 Tg N2O per year using different gas transfer models.
Extracted statement — N2O flux (upper limit): 0.76
Research field: Oceanography
Title: Nitrous oxide emissions from the Arabian Sea
Abstract: Dissolved and atmospheric nitrous oxide (N2O) were measured on the legs 3 and 5 of the R/V Meteor cruise 32 in the Arabian Sea. A cruise track along 65°E was followed during both the intermonsoon (May 1995) and the southwest (SW) monsoon (July/August 1995) periods. During the second leg the coastal and open ocean upwelling regions off the Arabian Peninsula were also investigated. Mean N2O saturations for the oceanic regions of the Arabian Sea were in the range of 99–103% during the intermonsoon and 103–230% during the SW monsoon. Computed annual emissions of 0.8–1.5 Tg N2O for the Arabian Sea are considerably higher than previous estimates, indicating that the role of upwelling regions, such as the Arabian Sea, may be more important than previously assumed in global budgets of oceanic N2O emissions.
Extracted statement — N2O flux (lower limit): 0.8
Research field: Oceanography
Title: Measurements of nitrogen fixation in the oligotrophic North Pacific Subtropical Gyre using a free-drifting submersible incubation device
Abstract: One challenge in field-based marine microbial ecology is to achieve sufficient spatial resolution to obtain representative information about microbial distributions and biogeochemical processes. The challenges are exacerbated when conducting rate measurements of biological processes due to potential perturbations during sampling and incubation. Here we present the first application of a robotic microlaboratory, the 4 L-submersible incubation device (SID), for conducting in situ measurements of the rates of biological nitrogen (N2) fixation (BNF). The free-drifting autonomous instrument obtains samples from the water column that are incubated in situ after the addition of 15N2 tracer. After each of up to four consecutive incubation experiments, the 4-L sample is filtered and chemically preserved. Measured BNF rates from two deployments of the SID in the oligotrophic North Pacific ranged from 0.8 to 2.8 nmol N L?1 day?1, values comparable with simultaneous rate measurements obtained using traditional conductivity–temperature–depth (CTD)–rosette sampling followed by on-deck or in situ incubation. Future deployments of the SID will help to better resolve spatial variability of oceanic BNF, particularly in areas where recovery of seawater samples by CTD compromises their integrity, e.g. anoxic habitats.
Extracted statement — Volumetric N2 fixation rate (lower limit): 0.8
Research field: Oceanography
Title: Evidence of active dinitrogen fixation in surface waters of the eastern tropical South Pacific during El Niño and La Niña events and evaluation of its potential nutrient controls: N2FIXATION IN THE ETSP
Abstract: Biological N2 fixation rates were quantified in the Eastern Tropical South Pacific (ETSP) during both El Niño (February 2010) and La Niña (March–April 2011) conditions, and from Low‐Nutrient, Low‐Chlorophyll (20°S) to High‐Nutrient, Low‐Chlorophyll (HNLC) (10°S) conditions. N2 fixation was detected at all stations with rates ranging from 0.01 to 0.88 nmol N L−1 d−1, with higher rates measured during El Niño conditions compared to La Niña. High N2 fixations rates were reported at northern stations (HNLC conditions) at the oxycline and in the oxygen minimum zone (OMZ), despite nitrate concentrations up to 30 µmol L−1, indicating that inputs of new N can occur in parallel with N loss processes in OMZs. Water‐column integrated N2 fixation rates ranged from 4 to 53 µmol N m−2 d−1 at northern stations, and from 0 to 148 µmol m−2 d−1 at southern stations, which are of the same order of magnitude as N2 fixation rates measured in the oligotrophic ocean. N2 fixation rates responded significantly to Fe and organic carbon additions in the surface HNLC waters, and surprisingly by concomitant Fe and N additions in surface waters at the edge of the subtropical gyre. Recent studies have highlighted the predominance of heterotrophic diazotrophs in this area, and we hypothesize that N2 fixation could be directly limited by inorganic nutrient availability, or indirectly through the stimulation of primary production and the subsequent excretion of dissolved organic matter and/or the formation of micro‐environments favorable for heterotrophic N2 fixation.
Extracted statement — Volumetric N2 fixation rate (upper limit): 0.88
Research field: Oceanography
Title: Dissolved Organic Matter Influences N2 Fixation in the New Caledonian Lagoon (Western Tropical South Pacific)
Abstract: Specialized prokaryotes performing biological dinitrogen (N2) fixation ('diazotrophs') provide an important source of fixed nitrogen in oligotrophic marine ecosystems such as tropical and subtropical oceans. In these waters, cyanobacterial photosynthetic diazotrophs are well known to be abundant and active, yet the role and contribution of non-cyanobacterial diazotrophs are currently unclear. The latter are not photosynthetic (here called 'heterotrophic') and hence require external sources of organic matter to sustain N2 fixation. Here we added the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) to estimate the N2 fixation potential of heterotrophic diazotrophs as compared to autotrophic ones. Additionally, we explored the influence of dissolved organic matter (DOM) on these diazotrophs along a coast to open ocean gradient in the surface waters of a subtropical coral lagoon (New Caledonia). Total N2 fixation (samples not amended with DCMU) ranged from 0.66 to 1.32 nmol N L-1 d-1. The addition of DCMU reduced N2 fixation by >90%, suggesting that the contribution of heterotrophic diazotrophs to overall N2 fixation activity was minor in this environment. Higher contribution of heterotrophic diazotrophs occurred in stations closer to the shore and coincided with the decreasing lability of DOM, as shown by various colored DOM and fluorescent DOM (CDOM and FDOM) indices. This suggests that heterotrophic N2 fixation is favored when labile DOM compounds are available. We tested the response of diazotrophs (in terms of nifH gene expression and bulk N2 fixation rates) upon the addition of a mix of carbohydrates ('DOC' treatment), amino acids ('DON' treatment), and phosphonates and phosphomonesters ('DOP' treatment). While nifH expression increased significantly in Trichodesmium exposed to the DOC treatment, bulk N2 fixation rates increased significantly only in the DOP treatment. The lack of nifH expression by gammaproteobacteria, in any of the DOM addition treatments applied, questions the contribution of non-cyanobacterial diazotrophs to fixed nitrogen inputs in the New Caledonian lagoon. While the metabolism and ecology of heterotrophic diazotrophs is currently elusive, a deeper understanding of their ecology and relationship with DOM is needed in the light of increased DOM inputs in coastal zones due to anthropogenic pressure.
Extracted statement — Volumetric N2 fixation rate (upper limit): 1.32
Research field: Oceanography
Title: Nitrous oxide emissions from the Arabian Sea
Abstract: Dissolved and atmospheric nitrous oxide (N2O) were measured on the legs 3 and 5 of the R/V Meteor cruise 32 in the Arabian Sea. A cruise track along 65°E was followed during both the intermonsoon (May 1995) and the southwest (SW) monsoon (July/August 1995) periods. During the second leg the coastal and open ocean upwelling regions off the Arabian Peninsula were also investigated. Mean N2O saturations for the oceanic regions of the Arabian Sea were in the range of 99–103% during the intermonsoon and 103–230% during the SW monsoon. Computed annual emissions of 0.8–1.5 Tg N2O for the Arabian Sea are considerably higher than previous estimates, indicating that the role of upwelling regions, such as the Arabian Sea, may be more important than previously assumed in global budgets of oceanic N2O emissions.
Extracted statement — N2O flux (upper limit): 1.5
Research field: Oceanography
Title: Measurements of nitrogen fixation in the oligotrophic North Pacific Subtropical Gyre using a free-drifting submersible incubation device
Abstract: One challenge in field-based marine microbial ecology is to achieve sufficient spatial resolution to obtain representative information about microbial distributions and biogeochemical processes. The challenges are exacerbated when conducting rate measurements of biological processes due to potential perturbations during sampling and incubation. Here we present the first application of a robotic microlaboratory, the 4 L-submersible incubation device (SID), for conducting in situ measurements of the rates of biological nitrogen (N2) fixation (BNF). The free-drifting autonomous instrument obtains samples from the water column that are incubated in situ after the addition of 15N2 tracer. After each of up to four consecutive incubation experiments, the 4-L sample is filtered and chemically preserved. Measured BNF rates from two deployments of the SID in the oligotrophic North Pacific ranged from 0.8 to 2.8 nmol N L?1 day?1, values comparable with simultaneous rate measurements obtained using traditional conductivity–temperature–depth (CTD)–rosette sampling followed by on-deck or in situ incubation. Future deployments of the SID will help to better resolve spatial variability of oceanic BNF, particularly in areas where recovery of seawater samples by CTD compromises their integrity, e.g. anoxic habitats.
Extracted statement — Volumetric N2 fixation rate (upper limit): 2.8
Research field: Oceanography
Title: Environmental controls on the seasonal carbon dioxide fluxes in the northeastern Indian Ocean
Abstract: Total carbon dioxide (TCO 2) and computations of partial pressure of carbon dioxide (pCO 2) had been examined in Northerneastern region of Indian Ocean. It exhibit seasonal and spatial variability. North-south gradients in the pCO 2 levels were closely related to gradients in salinity caused by fresh water discharge received from rivers. Eddies observed in this region helped to elevate the nutrients availability and the biological controls by increasing the productivity. These phenomena elevated the carbon dioxide draw down during the fair seasons. Seasonal fluxes estimated from local wind speed and air-sea carbon dioxide difference indicate that during southwest monsoon, the northeastern Indian Ocean acts as a strong sink of carbon dioxide (-20.04 mmol m –2 d -1 ). Also during fall intermonsoon the area acts as a weak sink of carbon dioxide (-4.69 mmol m –2 d -1 ). During winter monsoon, this region behaves as a weak carbon dioxide source with an average sea to air flux of 4.77 mmol m -2 d -1 . In the northern region, salinity levels in the surface level are high during winter compared to the other two seasons. Northeastern Indian Ocean shows significant intraseasonal variability in carbon dioxide fluxes that are mediated by eddies which provide carbon dioxide and nutrients from the subsurface waters to the mixed layer.
Extracted statement — CO2 flux (upper limit): 4.77