Moussab/ORKG-training-evaluation-set huggingface dataset:
Research field: Oceanography
Title: An extensive bloom of the N2-fixing cyanobacterium Trichodesmium erythraeum in the central Arabian Sea
Abstract: LVe encountered an extensive surface bloom of the N, fixing cyanobactenum Trichodesrniurn erythraeum in the central basin of the Arabian Sea during the spring ~nter-n~onsoon of 1995. The bloom, which occurred dunng a penod of calm winds and relatively high atmospher~c iron content, was metabollcally active. Carbon fixation by the bloom represented about one-quarter of water column primary productivity while input by h:: flxation could account for a major fraction of the estimated 'new' N demand of pnmary production. Isotopic measurements of the N in surface suspended material confirmed a direct contribution of N, fixation to the organic nltrogen pools of the upper water column. Retrospective analysis of NOAA-12 AVHRR imagery indicated that blooms covered up to 2 X 106 km2, or 20% of the Arabian Sea surface, during the period from 22 to 27 May 1995. In addition to their biogeochemical impact, surface blooms of this extent may have secondary effects on sea surface albedo and light penetration as well as heat and gas exchange across the air-sea interface. A preliminary extrapolation based on our observed, non-bloom rates of N, fixation from our limited sampling in the spring intermonsoon, including a conservative estimate of the input by blooms, suggest N2 fixation may account for an input of about 1 Tg N yr-I This is substantial, but relatively minor compared to current estimates of the removal of N through denitrification in the basin. However, N2 fixation may also occur in the central basin through the mild winter monsoon, be considerably greater during the fall intermonsoon than we observed during the spring intermonsoon, and may also occur at higher levels in the chronically oligotrophic southern basin. Ongoing satellite observations will help to determine more accurately the distribution and density of Trichodesmium in this and other tropical oceanic basins, as well as resolving the actual frequency and duration of bloom occurrence.
Extracted statement — Sampling year: 1995
Research field: Oceanography
Title: An extensive bloom of the N₂-fixing cyanobacterium Trichodesmium erythraeum in the central Arabian Sea
Abstract: LVe encountered an extensive surface bloom of the N, fixing cyanobactenum Trichodesrniurn erythraeum in the central basin of the Arabian Sea during the spring ~nter-n~onsoon of 1995. The bloom, which occurred dunng a penod of calm winds and relatively high atmospher~c iron content, was metabollcally active. Carbon fixation by the bloom represented about one-quarter of water column primary productivity while input by h:: flxation could account for a major fraction of the estimated 'new' N demand of pnmary production. Isotopic measurements of the N in surface suspended material confirmed a direct contribution of N, fixation to the organic nltrogen pools of the upper water column. Retrospective analysis of NOAA-12 AVHRR imagery indicated that blooms covered up to 2 X 106 km2, or 20% of the Arabian Sea surface, during the period from 22 to 27 May 1995. In addition to their biogeochemical impact, surface blooms of this extent may have secondary effects on sea surface albedo and light penetration as well as heat and gas exchange across the air-sea interface. A preliminary extrapolation based on our observed, non-bloom rates of N, fixation from our limited sampling in the spring intermonsoon, including a conservative estimate of the input by blooms, suggest N2 fixation may account for an input of about 1 Tg N yr-I This is substantial, but relatively minor compared to current estimates of the removal of N through denitrification in the basin. However, N2 fixation may also occur in the central basin through the mild winter monsoon, be considerably greater during the fall intermonsoon than we observed during the spring intermonsoon, and may also occur at higher levels in the chronically oligotrophic southern basin. Ongoing satellite observations will help to determine more accurately the distribution and density of Trichodesmium in this and other tropical oceanic basins, as well as resolving the actual frequency and duration of bloom occurrence.
Extracted statement — Sampling year: 1995
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 — Sampling year: 1995
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 — Sampling year: 1995
Research field: Oceanography
Title: A revised nitrogen budget for the Arabian Sea
Abstract: Despite its importance for the global oceanic nitrogen (N) cycle, considerable uncertainties exist about the N fluxes of the Arabian Sea. On the basis of our recent measurements during the German Arabian Sea Process Study as part of the Joint Global Ocean Flux Study (JGOFS) in 1995 and 1997, we present estimates of various N sources and sinks such as atmospheric dry and wet depositions of N aerosols, pelagic denitrification, nitrous oxide (N2O) emissions, and advective N input from the south. Additionally, we estimated the N burial in the deep sea and the sedimentary shelf denitrification. On the basis of our measurements and literature data, the N budget for the Arabian Sea was reassessed. It is dominated by the N loss due to denitrification, which is balanced by the advective input of N from the south. The role of N fixation in the Arabian Sea is still difficult to assess owing to the small database available; however, there are hints that it might be more important than previously thought. Atmospheric N depositions are important on a regional scale during the intermonsoon in the central Arabian Sea; however, they play only a minor role for the overall N cycling. Emissions of N2O and ammonia, deep‐sea N burial, and N inputs by rivers and marginal seas (i.e., Persian Gulf and Red Sea) are of minor importance. We found that the magnitude of the sedimentary denitrification at the shelf might be ∼17% of the total denitrification in the Arabian Sea, indicating that the shelf sediments might be of considerably greater importance for the N cycling in the Arabian Sea than previously thought. Sedimentary and pelagic denitrification together demand ∼6% of the estimated particulate organic nitrogen export flux from the photic zone. The main northward transport of N into the Arabian Sea occurs in the intermediate layers, indicating that the N cycle of the Arabian Sea might be sensitive to variations of the intermediate water circulation of the Indian Ocean.
Extracted statement — Sampling year: 1995
Research field: Oceanography
Title: Nitrous oxide cycling in the Arabian Sea
Abstract: Depth profiles of dissolved nitrous oxide (N2O) were measured in the central and western Arabian Sea during four cruises in May and July–August 1995 and May–July 1997 as part of the German contribution to the Arabian Sea Process Study of the Joint Global Ocean Flux Study. The vertical distribution of N2O in the water column on a transect along 65°E showed a characteristic double-peak structure, indicating production of N2O associated with steep oxygen gradients at the top and bottom of the oxygen minimum zone. We propose a general scheme consisting of four ocean compartments to explain the N2O cycling as a result of nitrification and denitrification processes in the water column of the Arabian Sea. We observed a seasonal N2O accumulation at 600–800 m near the shelf break in the western Arabian Sea. We propose that, in the western Arabian Sea, N2O might also be formed during bacterial oxidation of organic matter by the reduction of IO3 − to I−, indicating that the biogeochemical cycling of N2O in the Arabian Sea during the SW monsoon might be more complex than previously thought. A compilation of sources and sinks of N2O in the Arabian Sea suggested that the N2O budget is reasonably balanced.
Extracted statement — Sampling year: 1995
Research field: Oceanography
Title: Strong CO2emissions from the Arabian Sea during south-west monsoon
Abstract: The partial pressure of CO2 (pCO2) was measured during the 1995 South‐West Monsoon in the Arabian Sea. The Arabian Sea was characterized throughout by a moderate supersaturation of 12–30 µatm. The stable atmospheric pCO2 level was around 345 µatm. An extreme supersaturation was found in areas of coastal upwelling off the Omani coast with pCO2 peak values in surface waters of 750 µatm. Such two‐fold saturation (218%) is rarely found elsewhere in open ocean environments. We also encountered cold upwelled water 300 nm off the Omani coast in the region of Ekman pumping, which was also characterized by a strongly elevated seawater pCO2 of up to 525 µatm. Due to the strong monsoonal wind forcing the Arabian Sea as a whole and the areas of upwelling in particular represent a significant source of atmospheric CO2 with flux densities from around 2 mmol m−2 d−1 in the open ocean to 119 mmol m−2 d−1 in coastal upwelling. Local air masses passing the area of coastal upwelling showed increasing CO2 concentrations, which are consistent with such strong emissions.
Extracted statement — Sampling year: 1995
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 — Sampling year: 1996
Research field: Oceanography
Title: A revised nitrogen budget for the Arabian Sea
Abstract: Despite its importance for the global oceanic nitrogen (N) cycle, considerable uncertainties exist about the N fluxes of the Arabian Sea. On the basis of our recent measurements during the German Arabian Sea Process Study as part of the Joint Global Ocean Flux Study (JGOFS) in 1995 and 1997, we present estimates of various N sources and sinks such as atmospheric dry and wet depositions of N aerosols, pelagic denitrification, nitrous oxide (N2O) emissions, and advective N input from the south. Additionally, we estimated the N burial in the deep sea and the sedimentary shelf denitrification. On the basis of our measurements and literature data, the N budget for the Arabian Sea was reassessed. It is dominated by the N loss due to denitrification, which is balanced by the advective input of N from the south. The role of N fixation in the Arabian Sea is still difficult to assess owing to the small database available; however, there are hints that it might be more important than previously thought. Atmospheric N depositions are important on a regional scale during the intermonsoon in the central Arabian Sea; however, they play only a minor role for the overall N cycling. Emissions of N2O and ammonia, deep‐sea N burial, and N inputs by rivers and marginal seas (i.e., Persian Gulf and Red Sea) are of minor importance. We found that the magnitude of the sedimentary denitrification at the shelf might be ∼17% of the total denitrification in the Arabian Sea, indicating that the shelf sediments might be of considerably greater importance for the N cycling in the Arabian Sea than previously thought. Sedimentary and pelagic denitrification together demand ∼6% of the estimated particulate organic nitrogen export flux from the photic zone. The main northward transport of N into the Arabian Sea occurs in the intermediate layers, indicating that the N cycle of the Arabian Sea might be sensitive to variations of the intermediate water circulation of the Indian Ocean.
Extracted statement — Sampling year: 1997
Research field: Oceanography
Title: Nitrous oxide cycling in the Arabian Sea
Abstract: Depth profiles of dissolved nitrous oxide (N2O) were measured in the central and western Arabian Sea during four cruises in May and July–August 1995 and May–July 1997 as part of the German contribution to the Arabian Sea Process Study of the Joint Global Ocean Flux Study. The vertical distribution of N2O in the water column on a transect along 65°E showed a characteristic double-peak structure, indicating production of N2O associated with steep oxygen gradients at the top and bottom of the oxygen minimum zone. We propose a general scheme consisting of four ocean compartments to explain the N2O cycling as a result of nitrification and denitrification processes in the water column of the Arabian Sea. We observed a seasonal N2O accumulation at 600–800 m near the shelf break in the western Arabian Sea. We propose that, in the western Arabian Sea, N2O might also be formed during bacterial oxidation of organic matter by the reduction of IO3 − to I−, indicating that the biogeochemical cycling of N2O in the Arabian Sea during the SW monsoon might be more complex than previously thought. A compilation of sources and sinks of N2O in the Arabian Sea suggested that the N2O budget is reasonably balanced.
Extracted statement — Sampling year: 1997
Research field: Oceanography
Title: Enhanced chlorophyllaand primary production in the northern Arabian Sea during the spring intermonsoon due to greenNoctilucascintillansbloom
Abstract: Abstract The surface waters of the northeastern Arabian Sea sustained relatively high chlorophyll a (average 0.81±0.80 mg m–3) and primary production (average 29.5±23.6 mgC m–3 d–1) during the early spring intermonsoon 2000. This was caused primarily by a thick algal bloom spread over a vast area between 17–21°N and 66–70°E. Satellite images showed exceptionally high concentration of chlorophyll a in the bloom area, representing the annually occurring ‘spring blooms’ during February–March. The causative organism of the bloom was the dinoflagellate, Noctiluca scintillans (Dinophyceae: Noctilucidea), symbiotically associated with an autotrophic prasinophyte Pedinomonas noctilucae. The symbiosis between N. scintillans and P. noctilucae is most likely responsible for their explosive growth (average 3 million cells l–1) over an extensive area, making the northeastern Arabian Sea highly productive (average 607±338 mgC m–2 d–1) even during an oligotrophic period such as spring intermonsoon.
Extracted statement — Sampling year: 2000
Research field: Oceanography
Title: Intense blooms of Trichodesmium erythraeum (Cyanophyta) in the open waters along east coast of India
Abstract: Two blooms of Trichodesmium erythraeum were observed during April 2001, in the open waters of Bay of Bengal and this is the first report from this region. The locations of the bloom were off Karaikkal (10°58'N, 81°50'E) and off south of Calcutta (19° 44'N, 89° 04'), both along east coast of India. Nutrients (nitrate, phosphate, silicate) concentration in the upper 30 m of the water column showed very low values. High-integrated primary production (Bloom 1- 2160 mgC m -2 d -1 , Bloom 2-1740 mgC m -2 d -1 ) was obtained in these regions, which indicated the enhancement of primary production in the earlier stages of the bloom. Very low NO3-N concentrations, brownish yellow bloom colour, undisturbed patches and high primary production strongly suggested that the blooms were in the growth phase. Low mesozooplankton biomass was found in both locations and was dominated by copepods followed by chaetognaths.
Extracted statement — Sampling year: 2001
Research field: Oceanography
Title: Nitrogen Uptake in the Northeastern Arabian Sea during Winter Cooling
Abstract: The uptake of dissolved inorganic nitrogen by phytoplankton is an important aspect of the nitrogen cycle of oceans. Here, we present nitrate () and ammonium () uptake rates in the northeastern Arabian Sea using tracer technique. In this relatively underexplored region, productivity is high during winter due to supply of nutrients by convective mixing caused by the cooling of the surface by the northeast monsoon winds. Studies done during different months (January and late February-early March) of the northeast monsoon 2003 revealed a fivefold increase in the average euphotic zone integrated uptake from January (2.3 mmolN ) to late February-early March (12.7 mmolN ). The -ratio during January appeared to be affected by the winter cooling effect and increased by more than 50% from the southernmost station to the northern open ocean stations, indicating hydrographic and meteorological control. Estimates of residence time suggested that entrained in the water column during January contributed to the development of blooms during late February-early March.
Extracted statement — Sampling year: 2003
Research field: Oceanography
Title: Quantification of new production during a winterNoctiluca scintillansbloom in the Arabian Sea
Abstract: We present new data on the nitrate (new production), ammonium, urea uptake rates and f‐ratios for the eastern Arabian Sea (10° to 22°N) during the late winter (northeast) monsoon, 2004, including regions of green Noctilucascintillans bloom. A comparison of N‐uptake rates of the Noctiluca dominated northern zone to the southern non‐bloom zone indicates the presence of two biogeochemical regimes during the late winter monsoon: highly productive north and less productive south. The conservative estimates of photic zone‐integrated total N‐uptake and f‐ratio are high in the north (∼19 mmolNm−2d−1 and 0.82, respectively) during the bloom and low (∼5.5 mmolNm−2d−1 and 0.38 respectively) in the south. The present and earlier data imply persistence of high N‐uptake and f‐ratio during blooms year after year. This quantification of the enhanced seasonal sequestration of carbon is an important input to global biogeochemical models.
Extracted statement — Sampling year: 2004
Research field: Oceanography
Title: Evidence for efficient regenerated production and dinitrogen fixation in nitrogen-deficient waters of the South Pacific Ocean: impact on new and export production estimates
Abstract: Abstract. One of the major objectives of the BIOSOPE cruise, carried out on the R/V Atalante from October-November 2004 in the South Pacific Ocean, was to establish productivity rates along a zonal section traversing the oligotrophic South Pacific Gyre (SPG). These results were then compared to measurements obtained from the nutrient – replete waters in the Chilean upwelling and around the Marquesas Islands. A dual 13C/15N isotope technique was used to estimate the carbon fixation rates, inorganic nitrogen uptake (including dinitrogen fixation), ammonium (NH4) and nitrate (NO3) regeneration and release of dissolved organic nitrogen (DON). The SPG exhibited the lowest primary production rates (0.15 g C m−2 d−1), while rates were 7 to 20 times higher around the Marquesas Islands and in the Chilean upwelling, respectively. In the very low productive area of the SPG, most of the primary production was sustained by active regeneration processes that fuelled up to 95% of the biological nitrogen demand. Nitrification was active in the surface layer and often balanced the biological demand for nitrate, especially in the SPG. The percentage of nitrogen released as DON represented a large proportion of the inorganic nitrogen uptake (13–15% in average), reaching 26–41% in the SPG, where DON production played a major role in nitrogen cycling. Dinitrogen fixation was detectable over the whole study area; even in the Chilean upwelling, where rates as high as 3 nmoles l−1 d−1 were measured. In these nutrient-replete waters new production was very high (0.69±0.49 g C m−2 d−1) and essentially sustained by nitrate levels. In the SPG, dinitrogen fixation, although occurring at much lower daily rates (≈1–2 nmoles l−1 d−1), sustained up to 100% of the new production (0.008±0.007 g C m−2 d−1) which was two orders of magnitude lower than that measured in the upwelling. The annual N2-fixation of the South Pacific is estimated to 21×1012g, of which 1.34×1012g is for the SPG only. Even if our "snapshot" estimates of N2-fixation rates were lower than that expected from a recent ocean circulation model, these data confirm that the N-deficiency South Pacific Ocean would provide an ideal ecological niche for the proliferation of N2-fixers which are not yet identified.
Extracted statement — Sampling year: 2004