scholarly journals No nitrogen fixation in the Bay of Bengal?

2019 ◽  
Author(s):  
Carolin R. Löscher ◽  
Wiebke Mohr ◽  
Hermann W. Bange ◽  
Donald E. Canfield
Keyword(s):  
Primary Production ◽  
Water Column ◽  
Bay Of Bengal ◽  
N2 Fixation ◽  
Carbon Fixation ◽  
Monsoon Season ◽  
Stable Stratification ◽  
Water Column Stratification ◽  
Tropical Oceans ◽  
Subsurface Waters

Abstract. The Bay of Bengal (BoB) has long stood as a biogeochemical enigma with subsurface waters containing extremely low, but persistent, concentrations of oxygen in the nanomolar range which – for some, yet unconstrained reason – are prevented from becoming anoxic. One reason for this may be the low productivity of the BoB waters due to nutrient limitation, and the resulting lack of respiration of organic material at intermediate waters. Thus, the parameters determining primary production are key to understanding what prevents the BoB from developing anoxia. Primary productivity in the sunlit surface layers of tropical oceans is mostly limited by the supply of reactive nitrogen through upwelling, riverine flux, atmospheric deposition, and biological dinitrogen (N2) fixation. In the BoB, a stable stratification limits nutrient supply via upwelling in the open waters, and riverine or atmospheric fluxes have been shown to support only less than one quarter of the nitrogen for primary production. This leaves a large uncertainty for most of the BoB's nitrogen input, suggesting a potential role of N2 fixation in those waters. Here, we present a survey of N2 fixation and carbon fixation in the BoB during the winter monsoon season. We detected a community of N2 fixers comparable to other OMZ regions, with only a few cyanobacterial clades and a broad diversity of non-phototrophic N2 fixers present throughout the water column (samples collected between 10 m and 560 m water depth). While similar communities of N2 fixers were shown to actively fix N2 in other OMZs, N2 fixation rates were below the detection limit in our samples covering the water column between the deep chlorophyll maximum and the OMZ. Consistent with this, no N2 fixation signal was visible in δ15N signatures. We suggest that the absence of N2 fixation may be a consequence of a micronutrient limitation or of an O2 sensitivity of the OMZ diazotrophs in the BoB. To explore how the onset of N2 fixation by cyanobacteria compared to non-phototrophic N2 fixers would impact on OMZ O2 concentrations, a simple model exercise was carried out. We observed that both, photic zone-based and OMZ-based N2 fixation are very sensitive to even minimal changes in water column stratification, with stronger mixing increasing organic matter production and export, which would exhaust remaining O2 traces in the BoB.

scholarly journals No nitrogen fixation in the Bay of Bengal?

2020 ◽  
Vol 17 (4) ◽  
pp. 851-864 ◽  
Author(s):  
Carolin R. Löscher ◽  
Wiebke Mohr ◽  
Hermann W. Bange ◽  
Donald E. Canfield
Keyword(s):  
Primary Production ◽  
Water Column ◽  
Bay Of Bengal ◽  
N2 Fixation ◽  
Carbon Fixation ◽  
Monsoon Season ◽  
Stable Stratification ◽  
Water Column Stratification ◽  
Tropical Oceans ◽  
Subsurface Waters

Abstract. The Bay of Bengal (BoB) has long stood as a biogeochemical enigma, with subsurface waters containing extremely low, but persistent, concentrations of oxygen in the nanomolar range which – for some, yet unconstrained, reason – are prevented from becoming anoxic. One reason for this may be the low productivity of the BoB waters due to nutrient limitation and the resulting lack of respiration of organic material at intermediate waters. Thus, the parameters determining primary production are key in understanding what prevents the BoB from developing anoxia. Primary productivity in the sunlit surface layers of tropical oceans is mostly limited by the supply of reactive nitrogen through upwelling, riverine flux, atmospheric deposition, and biological dinitrogen (N2) fixation. In the BoB, a stable stratification limits nutrient supply via upwelling in the open waters, and riverine or atmospheric fluxes have been shown to support only less than one-quarter of the nitrogen for primary production. This leaves a large uncertainty for most of the BoB's nitrogen input, suggesting a potential role of N2 fixation in those waters. Here, we present a survey of N2 fixation and carbon fixation in the BoB during the winter monsoon season. We detected a community of N2 fixers comparable to other oxygen minimum zone (OMZ) regions, with only a few cyanobacterial clades and a broad diversity of non-phototrophic N2 fixers present throughout the water column (samples collected between 10 and 560 m water depth). While similar communities of N2 fixers were shown to actively fix N2 in other OMZs, N2 fixation rates were below the detection limit in our samples covering the water column between the deep chlorophyll maximum and the OMZ. Consistent with this, no N2 fixation signal was visible in δ15N signatures. We suggest that the absence of N2 fixation may be a consequence of a micronutrient limitation or of an O2 sensitivity of the OMZ diazotrophs in the BoB. Exploring how the onset of N2 fixation by cyanobacteria compared to non-phototrophic N2 fixers would impact on OMZ O2 concentrations, a simple model exercise was carried out. We observed that both photic-zone-based and OMZ-based N2 fixation are very sensitive to even minimal changes in water column stratification, with stronger mixing increasing organic matter production and export, which can exhaust remaining O2 traces in the BoB.

No N2 fixation in the Bay of Bengal?

2020 ◽  
Author(s):  
Carolin Löscher ◽  
Wiebke Mohr ◽  
Hermann Bange ◽  
Donald Canfield
Keyword(s):  
Primary Production ◽  
Water Column ◽  
Bay Of Bengal ◽  
Carbon Fixation ◽  
Monsoon Season ◽  
Stable Stratification ◽  
Water Column Stratification ◽  
Tropical Oceans ◽  
Matter Production ◽  
Subsurface Waters

<p>The Bay of Bengal (BoB) has long stood as a biogeochemical enigma with subsurface waters containing extremely low, but persistent, concentrations of oxygen (O<sub>2</sub>) in the nanomolar range which - for some, yet unconstrained reason- are prevented from becoming anoxic. One reason for this may be<br>the low productivity of the BoB waters due to nutrient limitation, and the resulting lack of respiration of organic material at intermediate waters. Thus, the parameters determining primary production are key to understanding what prevents the BoB from developing anoxia. Primary productivity in the sunlit surface layers of tropical oceans is mostly limited by the supply of reactive nitrogen through upwelling, riverine flux, atmospheric deposition, and biological dinitrogen (N<sub>2</sub>) fixation. In the BoB, a stable stratification limits nutrient supply via upwelling in the open waters, and riverine or atmospheric fluxes have been shown to support only less than one quarter of the nitrogen for primary production. This leaves a large uncertainty for most of the BoB’s nitrogen input, suggesting a potential role of N<sub>2</sub> fixation in those waters.<br>Here, we present a survey of N<sub>2</sub> fixation and carbon fixation in the BoB during the winter monsoon season. We detected a community of N<sub>2</sub> fixers comparable to other OMZ regions, with only a few cyanobacterial clades and a broad diversity of non-phototrophic N<sub>2</sub> fixers present throughout the water column (samples collected between 10 m and 560 m water depth). While similar communities of N<sub>2</sub> fixers were shown to actively fix N<sub>2</sub> in other OMZs, N<sub>2</sub> fixation rates were below the detection limit in our samples covering the water column between the deep chlorophyll maximum and the OMZ.<br>Consistent with this, no N<sub>2</sub> fixation signal was visible in δ<sup>15</sup>N signatures. We suggest that the absence of N<sub>2</sub> fixation may be a consequence of a micronutrient limitation or of an O<sub>2</sub> sensitivity of the OMZ diazotrophs in the BoB. To explore how the onset of N<sub>2</sub> fixation by cyanobacteria compared to nonphototrophic N<sub>2</sub> fixers would impact on OMZ O<sub>2</sub> concentrations, a simple model exercise was carried out. We observed that both, photic zone-based and OMZ-based N<sub>2</sub> fixation are very sensitive to even minimal changes in water column stratification, with stronger mixing increasing organic matter production and export, which would exhaust remaining O<sub>2</sub> traces in the BoB.       </p>

scholarly journals Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the central Baltic Sea

2013 ◽  
Vol 10 (4) ◽  
pp. 2725-2735 ◽  
Author(s):  
M. Blumenberg ◽  
C. Berndmeyer ◽  
M. Moros ◽  
M. Muschalla ◽  
O. Schmale ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Water Column ◽  
Stable Stratification ◽  
The Baltic Sea ◽  
Allochthonous Input ◽  
The North ◽  
Water Column Stratification ◽  
Gotland Deep ◽  
History Of ◽  
The Baltic

Abstract. The Baltic Sea, one of the world's largest brackish-marine basins, established after deglaciation of Scandinavia about 17 000 to 15 000 yr ago. In the changeable history of the Baltic Sea, the initial freshwater system was connected to the North Sea about 8000 yr ago and the modern brackish-marine setting (Littorina Sea) was established. Today, a relatively stable stratification has developed in the water column of the deep basins due to salinity differences. Stratification is only occasionally interrupted by mixing events, and it controls nutrient availability and growth of specifically adapted microorganisms and algae. We studied bacteriohopanepolyols (BHPs), lipids of specific bacterial groups, in a sediment core from the central Baltic Sea (Gotland Deep) and found considerable differences between the distinct stages of the Baltic Sea's history. Some individual BHP structures indicate contributions from as yet unknown redoxcline-specific bacteria (bacteriohopanetetrol isomer), methanotrophic bacteria (35-aminobacteriohopanetetrol), cyanobacteria (bacteriohopanetetrol cyclitol ether isomer) and from soil bacteria (adenosylhopane) through allochthonous input after the Littorina transgression, whereas the origin of other BHPs in the core has still to be identified. Notably high BHP abundances were observed in the deposits of the brackish-marine Littorina phase, particularly in laminated sediment layers. Because these sediments record periods of stable water column stratification, bacteria specifically adapted to these conditions may account for the high portions of BHPs. An additional and/or accompanying source may be nitrogen-fixing (cyano)bacteria, which is indicated by a positive correlation of BHP abundances with Corg and δ15N.

scholarly journals Spatial Variation in Primary Production in the Eastern Indian Ocean

2021 ◽  
Vol 8 ◽  
Author(s):  
Haijiao Liu ◽  
Yuyao Song ◽  
Xiaodong Zhang ◽  
Guicheng Zhang ◽  
Chao Wu ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Primary Production ◽  
Carbon Fixation ◽  
Monsoon Season ◽  
Biological Data ◽  
Eastern Indian Ocean ◽  
Light Limitation ◽  
Photic Zone ◽  
Production Rates ◽  
Study Region

To examine the spatial pattern and controlling factors of the primary productivity (PP) of phytoplankton in the eastern Indian Ocean (EIO), deck-incubation carbon fixation (a 14C tracer technique) and the related hydrographic properties were measured at 15 locations during the pre-summer monsoon season (February–April 2017). There are knowledge gaps in the field observations of PP in the EIO. The estimated daily carbon production rates integrated over the photic zone ranged from 113 to 817 mgC m–2 d–1, with a mean of 522 mgC m–2 d–1. The mixed-layer integrated primary production (MLD-PP) ranged from 29.0 to 303.7 mgC m–2 d–1 (mean: 177.2 mgC m–2 d–1). The contribution of MLD-PP to the photic zone-integrated PP (PZI-PP) varied between 19 and 51% (mean: 36%). Strong spatial variability in the carbon fixation rates was found in the study region. Specifically, the surface primary production rates were relatively higher in the Bay of Bengal domain affected by riverine flux and lower in the equatorial domain owing to the presence of intermonsoonal Wyrtki jets, which were characterized by a depression of thermocline and nitracline. The PZI-PP exhibited a linear (positive) relationship with nutrient values, but with no significance, indicating a partial control of macronutrients and a light limitation of carbon fixation. As evident from the vertical profiles, the primary production process mainly occurred above the nitracline depth and at high photosynthetic efficiency. Phytoplankton (>5 μm), including dinoflagellates, Trichodesmium, coccolithophores, and dissolved nutrients, are thought to have been correlated with primary production during the study period. The measured on-deck biological data of our study allow for a general understanding of the trends in PP in the survey area of the EIO and can be incorporated into global primary production models.

scholarly journals Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the Central Baltic Sea

2012 ◽  
Vol 9 (12) ◽  
pp. 17139-17165
Author(s):  
M. Blumenberg ◽  
C. Berndmeyer ◽  
M. Moros ◽  
M. Muschalla ◽  
O. Schmale ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Water Column ◽  
Stable Stratification ◽  
The Baltic Sea ◽  
Allochthonous Input ◽  
The North ◽  
Water Column Stratification ◽  
Gotland Deep ◽  
History Of ◽  
The Baltic

Abstract. The Baltic Sea, one of the world's largest brackish-marine basins, established after deglaciation of Scandinavia about 17 000 to 15 000 yr ago. In the changeable history of the Baltic Sea, the initial freshwater system was connected to the North Sea about 8000 yr ago and the modern brackish-marine setting (Littorina Sea) was established. Today, a relatively stable stratification developed in the water column of the deep basins due to salinity differences. Stratification is only occasionally interrupted by mixing events, and controls nutrient availability and growth of specifically adapted microorganisms and algae. We studied bacteriohopanepolyols (BHPs), lipids of specific bacterial groups, in a sediment core from the Central Baltic Sea (Gotland Deep) and found considerable differences between the distinct stages of the Baltic Sea's history. Individual BHP structures indicate contributions from as yet unknown redoxcline-specific bacteria (bacteriohopanetetrol isomer), methanotrophic bacteria (35-aminobacteriohopanetetrol), cyanobacteria (bacteriohopanetetrol cyclitol ether isomer) and, through allochthonous input after the Littorina transgression, from soil bacteria (adenosylhopane), whereas the origin of other BHPs in the core has still to be identified. Notably high BHP abundances were observed in the deposits of the brackish-marine Littorina phase, particularly in laminated sediment layers. Because these sediments record periods of stable water column stratification, bacteria specifically adapted to these conditions may account for the high portions of BHPs. An additional and/or accompanying source may be nitrogen-fixing (cyano)bacteria, which is indicated by a good correlation of BHP abundances with Corg and δ15N.

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