Method for quantifying oceanic regenerated nitrogen based on nitrate and water body oxygen isotopes

Abstract

The application discloses a method for quantifying regenerated nitrogen in the ocean based on nitrate and water body oxygen isotopes, and comprises the following steps: collecting seawater samples of different water layers in a target sea area, and determining the concentration of nitrate in the seawater samples; performing isotope sample determination on the seawater samples to obtain the oxygen isotope value of nitrate and the water body oxygen isotope value; determining the original nitrate endmember value based on the concentration of nitrate and hydrological data analysis; linearly combining the water body oxygen isotope value according to a first predetermined proportion and the oxygen isotope value of dissolved oxygen according to a second predetermined proportion to calculate a regenerated nitrate endmember value; and calculating the contribution proportion of regenerated nitrogen based on the oxygen isotope value of nitrate, the original nitrate endmember value and the regenerated nitrate endmember value through an isotope mass balance model.

Description

Technical Field

[0001] This invention belongs to the field of marine biogeochemistry and isotope tracing technology, and particularly relates to a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes. Background Technology

[0002] The marine nitrogen cycle is a crucial process for maintaining the productivity of marine ecosystems. Regenerated nitrogen, as an important source of nitrates in water, requires accurate quantification for understanding marine nutrient structure and biogeochemical cycles. Current techniques for assessing regenerated nitrogen largely rely on biomarkers or indirect estimation methods based on nitrogen isotopes. These methods are either limited by the stability and specificity of the biomarkers or struggle to effectively distinguish the contribution of regenerated nitrogen from nitrates from other sources, thus limiting their application in complex marine environments.

[0003] However, existing methods still face challenges in accurately quantifying the contribution of regenerated nitrogen to nitrate levels in water bodies. On the one hand, traditional methods struggle to directly track the oxygen isotope signal of regenerated nitrogen; on the other hand, there is a lack of a direct, quantitative method that can effectively integrate nitrate oxygen isotope information with water oxygen isotope information and accurately calculate the contribution of regenerated nitrogen. This leads to significant uncertainty in the assessment of marine regenerated nitrogen flux, limiting a deeper understanding of key aspects of the marine nitrogen cycle. Therefore, this invention proposes a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotope data. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes, thereby resolving the issues present in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes, comprising:

[0006] Seawater samples were collected from different water layers in the target sea area, and the nitrate concentration in the seawater samples was determined.

[0007] Isotope analysis was performed on the seawater sample to obtain nitrate oxygen isotope values ​​and water oxygen isotope values.

[0008] The original nitrate endmember values ​​were determined based on the nitrate concentration using hydrological data analysis.

[0009] The oxygen isotope values ​​of the water body are linearly combined according to a first predetermined ratio and the oxygen isotope values ​​of dissolved oxygen are linearly combined according to a second predetermined ratio to calculate the end-member value of regenerated nitrate.

[0010] Based on the nitrate oxygen isotope value, the original nitrate end-member value, and the regenerated nitrate end-member value, the contribution ratio of regenerated nitrogen is calculated using an isotope mass balance model.

[0011] Optionally, the process of determining the oxygen isotope value of nitrate includes: using denitrifying bacteria to convert nitrate in seawater samples into nitrous oxide gas, and using isotope ratio mass spectrometry to determine the nitrogen and oxygen isotope composition of the generated nitrous oxide gas to obtain the oxygen isotope value of nitrate.

[0012] Optionally, the process of determining the oxygen isotope value of water includes: using the carbon dioxide-water balance method or the micro-water injection method, and using an isotope ratio mass spectrometer to determine the oxygen isotope composition of the water in the seawater sample, thereby obtaining the oxygen isotope value of the water.

[0013] Optionally, the process of determining the original nitrate endmember value includes:

[0014] Identify major water masses based on hydrological data analysis of the target sea area;

[0015] Obtain nitrate oxygen isotope values ​​for representative water bodies of each major water mass;

[0016] The value of nitrate oxygen isotope that is least affected by biological activity is determined as the original nitrate endmember value of the corresponding water mass.

[0017] Optionally, the main water masses in the target sea area can be identified based on temperature and salinity data.

[0018] Optionally, the expression for calculating the end-member value of regenerated nitrate is:

[0019] δ 18 O ntr = (5 / 6) ×δ 18 O-H2O + (1 / 6) ×δ 18 O-O2

[0020] In the formula, δ 18 O ntr δ represents the endmember value of regenerated nitrate. 18 O-H2O represents the oxygen isotope values ​​of the water at each sampling point, δ 18 O-O2 represents the oxygen isotope value of dissolved oxygen.

[0021] Optionally, the expression for calculating the contribution ratio of regenerated nitrogen is:

[0022]

[0023] In the formula, δ 18 O obs The measured nitrate oxygen isotope values ​​at the sampling points; δ 18 Opre The corresponding nitrate oxygen isotope endmember values ​​of the original water mass; δ 18 O ntr To calculate the end-member value of the regenerated nitrate, f ntr The proportion of nitrogen contributed by the nitrogen to the regenerated nitrogen.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] This method achieves precise quantification of the contribution ratio of marine regenerated nitrogen by coupling nitrate with water oxygen isotopes. Its key advantages are: by introducing water oxygen isotopes as a conserved tracer and based on the biochemical mechanism of oxygen source ratio in nitrification, it effectively eliminates the interference of biofractionation on nitrate oxygen isotope signals, thus accurately distinguishing the relative contributions of exogenous and regenerated nitrogen in complex marine environments where they coexist. This method effectively overcomes the bottleneck problem of traditional end-member mixing models becoming inaccurate in dynamic marine environments due to intense biological activity, significantly improving the reliability and accuracy of the quantification results. The method is clear, easy to operate, and provides crucial technical support for assessing marine primary productivity structure, nitrogen cycle processes, and carbon sink potential. It is applicable to various marine areas, including nearshore and open ocean regions, that are jointly influenced by water mass mixing and biological activity. Attached Figure Description

[0026] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0027] Figure 1 This is a flowchart of a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes, according to an embodiment of the present invention. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0030] Example 1

[0031] To address the bottleneck problem in existing technologies that struggle to quantify the contribution ratio of regenerated nitrogen to exogenous nitrogen in water bodies, this invention provides a method for accurately quantifying the contribution ratio of regenerated nitrogen based on a combination of nitrate oxygen isotopes and water oxygen isotopes. The purpose of this invention is to effectively isolate the influence of nitrification on nitrate oxygen isotope signals by establishing a novel isotope mixing model, thereby achieving quantitative differentiation and assessment of regenerated nitrogen in water bodies. This provides crucial technical support for studying marine primary productivity structure, carbon export efficiency, and nitrogen cycle processes.

[0032] like Figure 1 As shown, this embodiment provides a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes. This invention is a method that couples nitrate oxygen isotopes (δ¹⁸O₂) to... 18 O-NO3 - ) and water oxygen isotopes (δ) 18 This invention employs a novel method to establish isotopic mixing models using nitrogen (O-H2O), thereby accurately distinguishing and quantifying the relative contributions of regenerated nitrogen from remineralization processes to exogenous nitrogen input in the ocean euphotic zone. This invention is of significant importance for assessing the structure of marine primary productivity, carbon export efficiency, and global carbon cycle research.

[0033] This embodiment specifically includes the following steps:

[0034] Step 1: Sample collection and basic parameter determination: Collect seawater samples from different water layers in the target sea area and determine the nitrate concentration in the seawater samples.

[0035] Water samples were collected from the target study area (such as the Beibu Gulf frontal zone, the Luzon Strait frontal zone, etc.). Specifically, this included:

[0036] 1. Water sampling: Using a Niskin water sampler or similar equipment, seawater samples are collected in the ocean euphotic zone by depth.

[0037] 2. Determination of nitrate concentration ([NO3] - ] obs The concentration of nitrate in each water sample was determined using an automated chemical analyzer, ion chromatograph, or reduction method (such as the cadmium-cadmium column reduction method). The measured value is denoted as [NO3]. - ] obs .

[0038] Step 2: Isotope sample determination: Isotope sample determination of seawater samples to obtain nitrate oxygen isotope values ​​and water oxygen isotope values.

[0039] 1. Determination of nitrate oxygen isotopes (δ¹²) 18 O obsThe denitrifying bacteria method was used to convert nitrates in seawater samples into nitrous oxide gas. The nitrogen and oxygen isotope composition of the generated nitrous oxide gas was determined by isotope ratio mass spectrometry to obtain the oxygen isotope value of nitrates.

[0040] (1) Sample pretreatment: Nitrate in water samples is converted into gases (such as N2O or CO2) that can be analyzed by mass spectrometry through diffusion, denitrifying bacteria or chemical reduction.

[0041] (2) Instrumental analysis: The oxygen isotope ratio of the generated gas was determined using an isotope ratio mass spectrometer coupled with the corresponding interface device.

[0042] (3) Result representation: The measurement result is expressed as a difference of 0.1% (‰) relative to the international standard VSMOW, and the measured value is denoted as δ. 18 O obs .

[0043] 2. Determination of oxygen isotopes (δ¹⁸O) in water. 18 O-H2O): The oxygen isotope composition of the water in the seawater sample is determined by using the carbon dioxide-water balance method or the micro-water injection method and isotope ratio mass spectrometry to obtain the oxygen isotope value of the water.

[0044] (1) The oxygen isotope ratio of the water sample was directly determined by water balance method or carbon dioxide-water balance method using an isotope ratio mass spectrometer.

[0045] (2) The measurement results are expressed as a difference of thousands (‰) relative to VSMOW, which is denoted as δ. 18 O-H2O.

[0046] Step 3: Determine Model Endmember Values: Determine the two key endmember values ​​required for the isotopic mixing model: the original nitrate oxygen isotope value (δ¹⁸O). 18 O pre ) and the theoretically calculated value of oxygen isotopes in regenerated nitrate (δ 18 O ntr ).

[0047] 1. Determine the original nitrate endmember value (δ) 18 O pre The original nitrate endmember value is determined based on hydrological data analysis of nitrate concentration. Specifically, this involves identifying major water masses based on hydrological data analysis of the target sea area; obtaining nitrate oxygen isotope measurements of representative water bodies from each major water mass; and determining the nitrate oxygen isotope value least affected by biological activity as the original nitrate endmember value for the corresponding water mass. Major water masses in the target sea area are also identified based on temperature and salinity data.

[0048] Method: δ 18 O preThe value is the representative δ of each major water mass in the target sea area under study. 18 O-NO3 - Value. It can be determined in the following ways:

[0049] (1) Directly collect and measure the nitrate oxygen isotope values ​​of water bodies considered to be sources of exogenous nitrogen in the research area (such as the nearshore current CC in the Beibu Gulf, the coastal current WGCC in western Guangdong and the South China Sea SCSW).

[0050] (2) By analyzing the hydrological data of the sea area (such as TS curves), the main water masses are identified, and the δ values ​​measured at the stations least affected by biological activity within or at the boundaries of each water mass are determined. 18 O obs The value is used as the endmember value of the water mass.

[0051] Application: In subsequent calculations, based on the hydrological conditions at each sampling point, the corresponding water mass endmember value is selected as the δ value for that point. 18 O-H2O pre .

[0052] 2. Calculate the end-member value of regenerated nitrate (δ). 18 O ntr The oxygen isotope values ​​of the water body are linearly combined according to a first predetermined ratio, and the oxygen isotope values ​​of dissolved oxygen are linearly combined according to a second predetermined ratio to calculate the end-member value of regenerated nitrate.

[0053] Based on the biochemical mechanism of nitrification, the newly generated regenerated nitrate (NO3) - ntr The oxygen atoms in the sample are derived from surrounding water molecules in a first predetermined proportion of 5 / 6, and from dissolved oxygen in a second predetermined proportion of 1 / 6. Its oxygen isotope composition is calculated using the following formula:

[0054] δ 18 O ntr = (5 / 6) ×δ 18 O-H2O + (1 / 6) ×δ 18 O-O2 (1)

[0055] Where: δ 18 O-H2O represents the oxygen isotope values ​​of the water at each sampling point measured in step two. δ 18 O-O2 is the oxygen isotope value of dissolved oxygen, taken as a constant value of +23.5‰.

[0056] Step 4: Calculate the contribution ratio of regenerated nitrogen ( f ntr Based on the oxygen isotope values ​​of nitrate, the original nitrate end-member values, and the regenerated nitrate end-member values, the contribution ratio of regenerated nitrogen is calculated using an isotope mass balance model.

[0057] Substitute the data obtained in steps one through three into the isotopic mass balance model established in this invention to calculate the contribution ratio of regenerated nitrogen produced by nitrification to the total nitrate pool.

[0058] 1. Model principle: Based on the law of conservation of mass, the total nitrate at the observation point is composed of a mixture of original nitrate and regenerated nitrate, and its isotopic values ​​also follow the mixing relationship.

[0059] 2. Calculation formula: Contribution ratio of regenerated nitrogen f ntr Calculated using the following formula:

[0060] (2)

[0061] Where, δ 18 O obs The measured nitrate oxygen isotope values ​​at the sampling points (from step two); δ 18 O pre The corresponding original water mass nitrate oxygen isotope end-member values ​​(from step three); δ 18 O ntr The theoretical value of oxygen isotope of regenerated nitrate obtained from step three.

[0062] 3. Interpretation of Results:

[0063] (1) Calculated f ntr It is a value between 0 and 1 (or 0% to 100%), which directly represents the mole fraction of regenerated nitrate in the total nitrate pool.

[0064] f ntr A higher value indicates that the nitrogen in the studied water body is mainly maintained by internal remineralization processes (regenerated nitrogen); a lower value indicates that the input of exogenous nitrogen contributes more.

[0065] Example 2

[0066] This embodiment provides a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes. As another specific implementation of this embodiment, it demonstrates the application of this method in the Beibu Gulf region, where seasonal fronts develop, revealing the dynamic changes in the contribution of regenerated nitrogen from the period without fronts to the period of active fronts. The specific implementation process includes:

[0067] 1. Sample and Data Acquisition: A comprehensive marine survey was conducted in the Beibu Gulf in August 2018 (summer, no frontal period), November 2018 (autumn, early stage of frontal formation), and February 2019 (winter, active frontal period). Seawater samples were collected at different depths within the euphotic zone using the Niskin sampler, and the following measurements were performed:

[0068] Nitrate concentration ([NO3] - ] obs ): Measured by an automated chemical analyzer.

[0069] Nitrate oxygen isotope (δ) 18 O obs ): Nitrate is converted to N2O using denitrifying bacteria, and then measured by isotope ratio mass spectrometry.

[0070] Water oxygen isotopes (δ) 18 O-H2O): Directly determined by water balance method using isotope ratio mass spectrometry.

[0071] The range and average value of the basic data obtained for each voyage are shown in Table 1.

[0072] Table 1

[0073]

[0074] 2. Determine the endmember values ​​of the model:

[0075] Primitive nitrate endmember (δ 18 O pre Based on temperature and salinity (TS) data, the Beibu Gulf was identified as being primarily influenced by three water masses: the Circum-Beibu Gulf Current (CC), the Western Guangdong Coastal Current (WGCC), and the South China Sea Current (SCSW). δ¹⁸O values ​​were selected from stations in the core areas of each water mass where biological activity was minimal. 18 O-NO3 - The measured value is used as its endmember value. For example, δ can be set separately. 18 O pre _CC = 18.5‰, δ 18 O pre _WGCC = 16.0‰, δ 18 O pre _SCSW = 6.5‰. In actual calculations, the δ corresponding to each sampling point is determined by assigning it to a specific water mass based on its TS attribute or by performing linear interpolation. 18 O pre .

[0076] Regenerated nitrate end-members (δ 18 O ntr ): Calculated according to formula (1). Taking a sampling point from a voyage in February 2019 as an example, its δ18 The measured value of O-H2O (‰) is -0.1‰.

[0077] δ 18 O ntr = (5 / 6) × (-0.1‰) + (1 / 6) × (23.5‰) ≈ 3.8‰

[0078] This value represents the theoretical oxygen isotope value of newly generated nitrates in the water body, solely from nitrification.

[0079] 3. Calculate the contribution ratio of regenerated nitrogen ( f ntr ):

[0080] Taking a sampling point during the active frontal period in February 2019 as an example, its δ 18 O obs The measured value is 10.0‰. Its δ value is determined based on its TS attribute. 18 O pre It is 12.0‰ (representing a mixed water mass), δ 18 O ntr The calculated value is 3.8‰. Substituting into formula (2):

[0081] f ntr = (10.0‰ - 12‰) / (3.8‰ - 12.0‰) = (-2) / (-8.2) ≈ 0.24

[0082] This calculation result indicates that at this specific sampling point, the contribution of regenerated nitrogen is 24%.

[0083] 4. Results and Conclusions:

[0084] After performing the above calculations on all stations and cruise data in the Beibu Gulf, and then averaging by region and cruise, we obtain:

[0085] During the period without fronts (August): Regenerated nitrogen contributes an average of 21%, indicating that nitrogen supply at this time is mainly from external sources.

[0086] In the early stages of frontal formation (November): regenerated nitrogen contributes an average of 26%, while exogenous nitrogen still dominates.

[0087] During the active period of the front (February): the average contribution of regenerated nitrogen increased significantly to 63%.

[0088] This result clearly confirms the effectiveness of the method of the present invention: the formation and intensification of the Beibu Gulf front promotes vertical water exchange and remineralization of organic matter in the euphotic layer, resulting in regenerated nitrogen becoming the main source of nitrogen supply. This also implies that the carbon output and burial efficiency of the Beibu Gulf frontal zone during this period may be relatively low.

[0089] Example 3

[0090] This embodiment provides a method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes. As another specific implementation of this embodiment, it is applied to the quantification of regenerated nitrogen in the Luzon Strait, demonstrating the application of this method in open ocean waters, particularly in persistent frontal zones formed by the mixing of different river systems. The specific implementation process includes:

[0091] 1. Sample and Data Acquisition: From July to August 2019, a cruise was conducted in the Luzon Strait, collecting water samples from the surface to a depth of 3700 meters. This example focuses on analyzing the surface and subsurface (shallower than 300 meters) water. The measurement items are the same as in Example 1, and the data range and average values ​​are as follows:

[0092] δ 18 O-NO3 - Range: -2.8‰ ~ 13.2‰, average 3.6‰

[0093] δ 18 O-H2O range: -0.5‰ ~ 3.1‰, average 0‰

[0094] 2. Determine the endmember values ​​of the model:

[0095] Primitive nitrate endmember (δ 18 O pre Based on the TS chart, the surface and subsurface layers (shallower than 300m) of this sea area are mainly influenced by three water masses: the northern South China Sea nearshore water (SCSCW), the South China Sea water (SCSW), and the Kuroshio Current (KC). Endmember values ​​are set, for example: δ 18 O pre _SCSCW = 8.0‰, δ 18 O pre _SCSW = 2.0‰, δ 18 O pre _KC = 1.0‰. For the frontal zone formed by the mixing of the Kuroshio Current and the South China Sea waters, its δ 18 O pre It can be determined by a linear mixture model of the two end-values.

[0096] Regenerated nitrate end-members (δ 18 O ntr ): with water body δ 18 The average value of O-H2O is calculated to be 0‰.

[0097] δ 18 O ntr = (5 / 6) × (0‰) + (1 / 6) × (23.5‰) ≈ 3.9‰

[0098] 3. Calculate the contribution ratio of regenerated nitrogen ( f ntr Conclusion:

[0099] Calculations were performed on different areas of the Luzon Strait, and the results showed that:

[0100] Northwest Pacific side (dominated by the Kuroshio Current): Regenerated nitrogen contributes an average of 38%.

[0101] South China Sea side (dominated by South China Sea water): Regenerated nitrogen contributes an average of 41%.

[0102] The persistent frontal zone in the Kuroshio-Nankai region: Regenerated nitrogen contributes an average of up to 67%.

[0103] This result strongly demonstrates that even in nutrient-poor oligotrophic ocean areas, persistent fronts formed by the interaction of different water systems are also "hotspots" for nitrogen regeneration. The method of this invention successfully identifies regions in the seemingly homogeneous ocean water that exhibit distinctly different nitrogen cycle functions due to the coupling of physical and biological processes.

[0104] In summary, this embodiment fully demonstrates its powerful ability and versatility in quantifying the contribution of regenerated nitrogen in different marine environments, from nearshore to open ocean and from seasonal to persistent conditions, providing an irreplaceable technical tool for accurately assessing the potential of marine nitrogen cycle and carbon sink.

[0105] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes, characterized in that, Includes the following steps: Seawater samples were collected from different water layers in the target sea area, and the nitrate concentration in the seawater samples was determined. Isotope analysis was performed on the seawater sample to obtain nitrate oxygen isotope values ​​and water oxygen isotope values. The original nitrate endmember values ​​were determined based on the nitrate concentration using hydrological data analysis. The process of determining the original nitrate endmember value includes: identifying the main water masses based on hydrological data analysis of the target sea area; obtaining the nitrate oxygen isotope values ​​of representative water bodies of each main water mass; and determining the value of the nitrate oxygen isotope value that is least affected by biological activity as the original nitrate endmember value of the corresponding water mass. The oxygen isotope values ​​of the water body are linearly combined according to a first predetermined ratio, and the oxygen isotope values ​​of dissolved oxygen are linearly combined according to a second predetermined ratio to calculate the regenerated nitrate end-member value; the expression for calculating the regenerated nitrate end-member value is: δ 18 THE ntr = (5 / 6) ×δ 18 O-H2O + (1 / 6) ×δ 18 O-O2 In the formula, δ 18 O ntr For the regenerated nitrate endmember value, δ 18 O-H2O represents the oxygen isotope values ​​of the water at each sampling point, δ 18 O-O2 represents the oxygen isotope value of dissolved oxygen; Based on the nitrate oxygen isotope value, the original nitrate end-member value, and the regenerated nitrate end-member value, the contribution ratio of regenerated nitrogen is calculated using an isotope mass balance model. The expression for calculating the contribution ratio of regenerated nitrogen is: In the formula, δ 18 O obs The measured nitrate oxygen isotope values ​​at the sampling points; δ 18 O pre The corresponding nitrate oxygen isotope endmember values ​​of the original water mass; δ 18 O ntr To calculate the end-member value of the regenerated nitrate, f ntr The proportion of nitrogen contributed by the nitrogen to the regenerated nitrogen.

2. The method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes according to claim 1, characterized in that, The process of determining the oxygen isotope value of nitrate includes: using denitrifying bacteria to convert nitrate in seawater samples into nitrous oxide gas, and using isotope ratio mass spectrometry to determine the nitrogen and oxygen isotope composition of the generated nitrous oxide gas to obtain the oxygen isotope value of nitrate.

3. The method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes according to claim 1, characterized in that, The process of determining the oxygen isotope value of water includes: using the carbon dioxide-water balance method or the micro-water injection method, and using an isotope ratio mass spectrometer to determine the oxygen isotope composition of the water in the seawater sample, thereby obtaining the oxygen isotope value of the water.

4. The method for quantifying marine regenerated nitrogen based on nitrate and water oxygen isotopes according to claim 1, characterized in that, Identify the main water masses in the target sea area based on temperature and salinity data.

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