Role of eddies and N2 fixation in shaping C:N:P proportions in the Bay of Bengal during spring

2021 ◽  
Author(s):  
Deepika Sahoo ◽  
Himanshu Saxena ◽  
Sipai Nazirahmed ◽  
Sanjeev Kumar ◽  
Athiyarath Sudheer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Bay Of Bengal ◽  
Open Ocean ◽  
Nutrient Concentrations ◽  
Biological Processes ◽  
Biogeochemical Processes ◽  
C:N:P Stoichiometry ◽  
C:N:P Ratio ◽  
Elemental Stoichiometry

<p>Bioavailable nitrogen (N) and phosphorus (P) determine the strength of the ocean’s carbon (C) uptake and variation in their ratio (N:P) is key to phytoplankton growth. A similarity between C:N:P ratio (106:16:1) in plankton and deep-water inorganic nutrients was observed by Alfred C. Redfield, who suggested that biological processes in the surface ocean controlled deep ocean chemistry. Recent studies suggest that the ratio varies geographically. The veracity in C:N:P ratio could be attributed to the characteristic physical and biogeochemical processes, which play an important role in regulating the elemental dynamics in ocean. Basins like the northern Indian Ocean due to its geographic setting and monsoonal wind forcing provide a natural laboratory to explore the role of environmental factors, physical and biogeochemical processes on C:N:P stoichiometry.</p><p>We sampled the Bay of Bengal for its C, N, and P contents in the organic and inorganic pool from surface to 2000 m at 8 stations (5 coastal, 3 open ocean) during spring 2019. Mesoscale anticyclonic eddies were identified in our sampling area, which were associated with low nutrient concentrations in the photic depth. Mean (NO<sub>3</sub><sup>- </sup>+ NO<sub>2</sub><sup>-</sup>):PO<sub>4</sub><sup>3-</sup> ratio was 0.6 at eddy and 4.7 at non eddy stations. On the other hand, C:N:P in the organic matter was same at eddy and non-eddy locations. Mean C:N:P ratio in particulate organic matter was 254:39:1 and 244:37:1 in the photic depth of the coastal and open ocean stations, respectively. Biological N<sub>2</sub> fixation contributed ~0.1-0.4% to the N:P ratio of export flux, which ultimately contributes to the (NO<sub>3</sub><sup>- </sup>+ NO<sub>2</sub><sup>-</sup>):PO<sub>4</sub><sup>3-</sup> ratio in subsurface waters. Our results highlight the importance of physical and biological processes in changing elemental stoichiometry.</p>

scholarly journals Effects of nitrate and phosphate supply on chromophoric and fluorescent dissolved organic matter in the Eastern Tropical North Atlantic: a mesocosm study

2015 ◽  
Vol 12 (10) ◽  
pp. 7209-7255
Author(s):  
A. N. Loginova ◽  
C. Borchard ◽  
J. Meyer ◽  
H. Hauss ◽  
R. Kiko ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Optical Properties ◽  
Amino Acid ◽  
Dissolved Organic Matter ◽  
North Atlantic ◽  
Phytoplankton Biomass ◽  
Open Ocean ◽  
Nutrient Concentrations ◽  
Tropical North Atlantic

Abstract. The Eastern Tropical North Atlantic (ETNA) is an open ocean region with little input of terrestrial dissolved organic matter (DOM), suggesting that pelagic production has to be the main source of DOM. Inorganic nitrogen (DIN) and phosphorus (DIP) concentrations affect pelagic production, leading to DOM modifications. The quantitative and qualitative changes in DOM are often estimated by its optical properties. Colored DOM (CDOM) is often used to estimate dissolved organic carbon (DOC) concentrations by applied techniques, e.g. through remote sensing, whereas DOM properties, such as molecular weight, can be estimated from the slopes of the CDOM absorption spectra (S). Fluorescence properties of CDOM (FDOM) allow discriminating between different structural CDOM properties. The investigation of distribution and cycling of CDOM and FDOM was recognized to be important for understanding of physical and biogeochemical processes, influencing DOM. However, little information is available about effects of nutrient variability on CDOM and FDOM dynamics. Here we present results from two mesocosm experiments conducted with a natural plankton community of the ETNA, where effects of DIP ("Varied P") and DIN ("Varied N") supply on optical properties of DOM were studied. CDOM accumulated proportionally to phytoplankton biomass during the experiments. S decreased over time indicating accumulation of high molecular weight DOM. In Varied N, an additional CDOM portion, as a result of bacterial DOM reworking, was determined. It increased the CDOM fraction in DOC proportionally to the supplied DIN. The humic-like FDOM component (Comp.1) was derived by bacteria proportionally to DIN supply. The bound-to-protein amino acid-like FDOM component (Comp.2) was released irrespectively to phytoplankton biomass, but depending on DIP and DIN concentrations, as a part of an overflow mechanism. Under high DIN supply, Comp.2 was removed by bacterial reworking processes, leading to an accumulation of humic-like Comp.1. No influence of nutrient availability on amino acid-like FDOM component in peptide form (Comp.3) was observed. Comp.3 potentially acted as an intermediate product during formation or degradation Comp.2. Our findings suggest that changes in nutrient concentrations may lead to substantial responses in the quantity and "quality" of optically active DOM and, therefore, might bias results of the applied techniques for an estimation of DOC concentrations in open ocean regions.

scholarly journals The Role of Soil pH in Plant Nutrition and Soil Remediation

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Dora Neina
Keyword(s):  
Plant Growth ◽  
Soil Remediation ◽  
Soil Ph ◽  
Soil Acidification ◽  
Plant Nutrition ◽  
Biomass Yield ◽  
Biological Processes ◽  
Biogeochemical Processes ◽  
Soil Environment

In the natural environment, soil pH has an enormous influence on soil biogeochemical processes. Soil pH is, therefore, described as the “master soil variable” that influences myriads of soil biological, chemical, and physical properties and processes that affect plant growth and biomass yield. This paper discusses how soil pH affects processes that are interlinked with the biological, geological, and chemical aspects of the soil environment as well as how these processes, through anthropogenic interventions, induce changes in soil pH. Unlike traditional discussions on the various causes of soil pH, particularly soil acidification, this paper focuses on relationships and effects as far as soil biogeochemistry is concerned. Firstly, the effects of soil pH on substance availability, mobility, and soil biological processes are discussed followed by the biogenic regulation of soil pH. It is concluded that soil pH can broadly be applied in two broad areas, i.e., nutrient cycling and plant nutrition and soil remediation (bioremediation and physicochemical remediation).

scholarly journals Evidence for surface organic matter modulation of air-sea CO<sub>2</sub> gas exchange

2009 ◽  
Vol 6 (6) ◽  
pp. 1105-1114 ◽  
Author(s):  
M. Ll. Calleja ◽  
C. M. Duarte ◽  
Y. T. Prairie ◽  
S. Agustí ◽  
G. J. Herndl
Keyword(s):  
Organic Matter ◽  
Wind Speed ◽  
Gas Exchange ◽  
Co2 Exchange ◽  
Open Ocean ◽  
Gas Transfer ◽  
Co2 Fluxes ◽  
Transfer Velocity ◽  
Gas Transfer Velocity

Abstract. Air-sea CO2 exchange depends on the air-sea CO2 gradient and the gas transfer velocity (k), computed as a function of wind speed. Large discrepancies among relationships predicting k from wind suggest that other processes also contribute significantly to modulate CO2 exchange. Here we report, on the basis of the relationship between the measured gas transfer velocity and the organic carbon concentration at the ocean surface, a significant role of surface organic matter in suppressing air-sea gas exchange, at low and intermediate winds, in the open ocean, confirming previous observations. The potential role of total surface organic matter concentration (TOC) on gas transfer velocity (k) was evaluated by direct measurements of air-sea CO2 fluxes at different wind speeds and locations in the open ocean. According to the results obtained, high surface organic matter contents may lead to lower air-sea CO2 fluxes, for a given air-sea CO2 partial pressure gradient and wind speed below 5 m s−1, compared to that observed at low organic matter contents. We found the bias in calculated gas fluxes resulting from neglecting TOC to co-vary geographically and seasonally with marine productivity. These results support previous evidences that consideration of the role of organic matter in modulating air-sea CO2 exchange may improve flux estimates and help avoid possible bias associated to variability in surface organic concentration across the ocean.

scholarly journals ROLE OF CARBON CIRCULATION AS A BASIS FOR IMPROVEMENT OF THE SOIL FERTILITY MONITORING SYSTEM

2019 ◽  
Vol 4 (2) ◽  
pp. 124-134
Author(s):  
Yury Larionov
Keyword(s):  
Organic Matter ◽  
Soil Fertility ◽  
Plant Biomass ◽  
Biological Processes ◽  
Huge Amount ◽  
Fixed Amount ◽  
Biochemical Compounds ◽  
Main Indicator ◽  
Carbon Compounds

The most important role in ensuring soil fertility is played by biological processes, and this, above all, the cycles of the main nutrients of plants, animals and microorganisms. Cycles play an important role in the biosphere, providing direct and inverse links in the chains of the agro-ecological system, while maintaining the integrity of the biosphere. To monitor soil fertility it is necessary to determine (find) an integral index and its cycle, which most objectively reflects this property of the soil. Such an indicator, according to our research, is the quantity and qualitative composition of organic matter in the soil, which mainly consists of plant biomass, as well as micro and animal organisms. From the standpoint of chemistry, carbon is a part of the organic matter of the soil in the form of a huge amount of biochemical compounds containing virtually the entire table D.I. Mendeleev, but only about 30 elements (organogenic) have fixed amount and are found in organisms all the time. At the same time, the ratio of organogenic elements in the soil is different, more concentrated, rather than in the crust, established by geochemistry. In this regard, we found that the main indicator of soil fertility (having a closer correlation with it and integrally reflecting it) can be the content and balance of organic matter in it, the activity of which determines the effective and potential soil fertility. As an indicator of the cycle of organic matter it is necessary to use the carbon cycle in the soil on which all organic matter in the biosphere is built. The role of many biochemical carbon compounds in the evolution of living and soil fertility remains is to be seen.

Non-Redfieldian C:N:P ratio in the inorganic and organic pools of the Bay of Bengal during the summer monsoon

2020 ◽  
Vol 653 ◽  
pp. 41-55 ◽  
Author(s):  
D Sahoo ◽  
H Saxena ◽  
N Tripathi ◽  
MA Khan ◽  
A Rahman ◽  
...  
Keyword(s):  
Organic Matter ◽  
Particulate Organic Matter ◽  
Deep Water ◽  
Bay Of Bengal ◽  
N:P Ratio ◽  
Mixed Effect ◽  
Redfield Ratio ◽  
C:N:P Ratio ◽  
P Content ◽  
Water Nutrients

Nitrogen (N) and phosphorus (P) determine the strength of the ocean’s biological carbon (C) pump, and variation in the N:P ratio is key to phytoplankton growth. A fixed C:N:P ratio (106:16:1) in organic matter and deep-water nutrients was observed by Alfred C. Redfield. However, recent studies have challenged the concept of the Redfield Ratio, and its veracity remains to be examined in oceanic basins like the Bay of Bengal. For this purpose, we sampled the water in the Bay of Bengal for C, N, and P content in the organic and inorganic pools from the surface to 2000 m. Overall, the C:N:P ratio deviated greatly from the Redfield Ratio. The C:N:P ratio in particulate organic matter varied from 232:25:1 in the top layer (surface to the depth of the chlorophyll maximum) to 966:72:1 in the deep water (300-2000 m). In dissolved organic matter, the ratio varied from 357:30:1 in the top layer to 245:66:1 in the deep water. The N:P ratio in nutrients varied from 3 in the top layer to 12 in the deep water. The nutrient-depleted top layer (average NO3- + NO2- ~ 0.7 µmol l-1) with a low N:P ratio coupled with reported low primary production rates in the Bay suggested that the production was N limited. Concurrent N2 fixation rates were not sufficient to alter the observed C:N:P ratio. Eddies showed a mixed effect on the C:N:P ratio. Our C:N:P ratios in particulate organic matter are comparable to other tropical basins and supports the nutrient supply hypothesis for low latitude ecosystems.

scholarly journals C : N : P stoichiometry at the Bermuda Atlantic Time-series Study station in the North Atlantic Ocean

2015 ◽  
Vol 12 (12) ◽  
pp. 9275-9305
Author(s):  
A. Singh ◽  
S. E. Baer ◽  
U. Riebesell ◽  
A. C. Martiny ◽  
M. W. Lomas
Keyword(s):  
Time Series ◽  
Organic Matter ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Euphotic Zone ◽  
Redfield Ratio ◽  
The North ◽  
Elemental Stoichiometry ◽  
Series Study

Abstract. Nitrogen (N) and phosphorus (P) availability determine the strength of the ocean's carbon (C) uptake, and variation in the N : P ratio in inorganic nutrients is key to phytoplankton growth. A similarity between C : N : P ratios in the plankton biomass and deep-water nutrients was observed by Alfred C. Redfield around 80 years ago and suggested that biological processes in the surface ocean controlled deep ocean chemistry. Recent studies have emphasized the role of inorganic N : P ratios in governing biogeochemical processes, particularly the C : N : P ratio in suspended particulate organic matter (POM), with somewhat less attention given to exported POM and dissolved organic matter (DOM). Herein, we extend the discussion on ecosystem C : N : P stoichiometry but also examine temporal variation of stoichiometric relationships. We have analysed elemental stoichiometry in the suspended POM and total (POM + DOM) organic matter (TOM) pools in the upper 100 m, and in the exported POM and sub-euphotic zone (100–500 m) inorganic nutrient pools from the monthly data collected at the Bermuda Atlantic Time-series Study (BATS) site located in the western part of the North Atlantic Ocean. C : N : P ratios in the TOM pool were more than twice that in the POM pool. Observed C : N ratios in suspended POM were approximately equal to the canonical Redfield Ratio (C : N : P = 106 : 16 : 1), while N : P and C : P ratios in the same pool were more than twice the Redfield Ratio. Average N : P ratios in the subsurface inorganic nutrient pool were ~ 26 : 1, squarely between the suspended POM ratio and the Redfield ratio. We have further linked variation in elemental stoichiometry with that of phytoplankton cell abundance observed at the BATS site. Findings from this study suggest that the variation elemental ratios with depth in the euphotic zone was mainly due to different growth rates of cyanobacterial cells. These time-series data have also allowed us to examine the potential role of climate variability on C : N : P stoichiometry. This study strengthens our understanding of elemental stoichiometry in different organic matter pools and should improve biogeochemical models by constraining the range of non-Redfield stoichiometry.

scholarly journals Factors controlling plankton productivity, particulate matter stoichiometry, and export fluxin the coastal upwelling system off Peru

2020 ◽  
Author(s):  
Lennart Thomas Bach ◽  
Allanah Joy Paul ◽  
Tim Boxhammer ◽  
Elisabeth von der Esch ◽  
Michelle Graco ◽  
...  
Keyword(s):  
Organic Matter ◽  
Particulate Matter ◽  
Inorganic Nitrogen ◽  
Phytoplankton Growth ◽  
Water Bodies ◽  
Biogeochemical Processes ◽  
C:N:P Stoichiometry ◽  
Upwelling System ◽  
Phytoplankton Communities ◽  
Ecological Regime

Abstract. Eastern boundary upwelling systems (EBUS) are among the most productive marine ecosystems on Earth. The high productivity in surface waters is facilitated by upwelling of nutrient-rich deep waters, with high light availability enabling fast phytoplankton growth and nutrient utilization. However, there are numerous biotic and abiotic factors modifying productivity and biogeochemical processes. Determining these factors is important because EBUS are considered hotspots of climate change, and reliable predictions on their future functioning requires understanding of the mechanisms driving biogeochemical cycles therein. In this study, we used in situ mesocosms to obtain mechanistic understanding of processes controlling productivity, organic matter export, and particulate matter stoichiometry in the coastal Peruvian upwelling system. Therefore, eight mesocosm units with a volume of ~50 m3 were deployed for 50 days ~6 km off Callao during austral summer 2017, coinciding with a coastal El Niño event. To compare how upwelling of different water bodies influences plankton succession patterns, we collected two subsurface waters at different locations in the regional oxygen minimum zone (OMZ) and injected these into four replicate mesocosms, respectively (mixing ratio ≈ 1.5:1 mesocosm: OMZ water). The differences in nutrient concentrations between the collected water bodies were relatively small, and therefore we do not consider treatment differences in the present paper. The phytoplankton communities were initially dominated by diatoms but shifted towards a pronounced dominance of the mixotrophic harmful dinoflagellate (Akashiwo sanguinea) when inorganic nitrogen was exhausted in surface layers. The community shift resulted in a major short-term increase in productivity during A. sanguinea growth which left a pronounced imprint on organic matter C:N:P stoichiometry. However, C, N, and P export fluxes were not affected by this ecological regime shift because A. sanguinea persisted in the water column and did not sink out during the experiment. Accordingly, ongoing export fluxes during the study were maintained mainly by a remaining “background” plankton community. Overall, biogeochemical pools and fluxes were surprisingly constant in between the ecological regime shifts. We explain this constancy by light limitation through self-shading by phytoplankton and inorganic nitrogen limitation which constrained phytoplankton growth. Thus, gain and loss processes seemed to be relatively well balanced and there was little opportunity for blooms, which represents an event where the system becomes unbalanced. The mesocosm study revealed key links between ecological and biogeochemical processes for one of the economically most important regions in the oceans.

scholarly journals Effects of nitrate and phosphate supply on chromophoric and fluorescent dissolved organic matter in the Eastern Tropical North Atlantic: a mesocosm study

2015 ◽  
Vol 12 (23) ◽  
pp. 6897-6914 ◽  
Author(s):  
A. N. Loginova ◽  
C. Borchard ◽  
J. Meyer ◽  
H. Hauss ◽  
R. Kiko ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
North Atlantic ◽  
Inorganic Nitrogen ◽  
Bacterial Biomass ◽  
Open Ocean ◽  
Nutrient Concentrations ◽  
Fluorescent Dissolved Organic Matter ◽  
Tropical North Atlantic ◽  
Mesocosm Experiments

Abstract. In open-ocean regions, as is the Eastern Tropical North Atlantic (ETNA), pelagic production is the main source of dissolved organic matter (DOM) and is affected by dissolved inorganic nitrogen (DIN) and phosphorus (DIP) concentrations. Changes in pelagic production under nutrient amendments were shown to also modify DOM quantity and quality. However, little information is available about the effects of nutrient variability on chromophoric (CDOM) and fluorescent (FDOM) DOM dynamics. Here we present results from two mesocosm experiments ("Varied P" and "Varied N") conducted with a natural plankton community from the ETNA, where the effects of DIP and DIN supply on DOM optical properties were studied. CDOM accumulated proportionally to phytoplankton biomass during the experiments. Spectral slope (S) decreased over time indicating accumulation of high molecular weight DOM. In Varied N, an additional CDOM portion, as a result of bacterial DOM reworking, was determined. It increased the CDOM fraction in DOC proportionally to the supplied DIN. The humic-like FDOM component (Comp.1) was produced by bacteria proportionally to DIN supply. The protein-like FDOM component (Comp.2) was released irrespectively to phytoplankton or bacterial biomass, but depended on DIP and DIN concentrations. Under high DIN supply, Comp.2 was removed by bacterial reworking, leading to an accumulation of humic-like Comp.1. No influence of nutrient availability on amino acid-like FDOM component in peptide form (Comp.3) was observed. Comp.3 potentially acted as an intermediate product during formation or degradation of Comp.2. Our findings suggest that changes in nutrient concentrations may lead to substantial responses in the quantity and quality of optically active DOM and, therefore, might bias results of the applied in situ optical techniques for an estimation of DOC concentrations in open-ocean regions.

Impact of glacial meltwater on biogeochemical cycling in coastal and shelf waters off South West Greenland: Insights from ship-board and glider observations

2020 ◽  
Author(s):  
Katharine Hendry ◽  
Nathan Briggs ◽  
Jacob Opher ◽  
J. Alexander Brearley ◽  
Michael Meredith ◽  
...  
Keyword(s):  
Organic Matter ◽  
Environmental Changes ◽  
Mixed Layer Depth ◽  
Greenland Ice Sheet ◽  
Organic Content ◽  
Open Ocean ◽  
Storm Events ◽  
Ocean Stratification ◽  
Buoyancy Forcing

&lt;p&gt;The high-latitude regions are experiencing some of the most rapid environmental changes observed anywhere on Earth, especially in recent years.&amp;#160;The Greenland Ice Sheet, for example,&amp;#160;is experiencing significant mass loss largely through surface melting, but also via ice discharge at glacier fronts. As well as changing&amp;#160;freshwater budgets and ocean stratification and mixing, there has been increasing focus on the role of glaciers and ice sheets in supplying particulate and dissolved organic material and inorganic nutrients to marine systems.&amp;#160;Here, we explore how a combination of ship-board and high-resolution ocean glider observations in shelf waters off SW Greenland inform on how these nutrients reach the coastal oceans and, eventually, mix off the shelf and into the open ocean. We find that the proportion of meltwater calculated using salinity and oxygen isotope mass balance agrees well with estimates from glider sensors. These meltwaters contain low dissolved macronutrients, but are characterised by high particulate and high dissolved organic content. Bio-optic sensors on the gliders reveal strong meltwater signals in fluorescing dissolved organic matter (FDOM), and a detectable signal in optical backscatter; these signals can be now observed extending further out into the open ocean in compiled biogeochemical (BGC) argo float data. The mixing of both dissolved and particulate macronutrients and organic matter off the shelf is likely driven by advection in geostrophic currents, tidal and buoyancy forcing, and is also impacted by storm events via wind-driven changes in mixed layer depth and resuspension.&lt;/p&gt;

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