A method for evaluating the regulation factor of dissolved methane in seawater

Abstract

The invention discloses an evaluation method for seawater dissolved CH4 regulation factors, comprising: acquiring data information; preliminarily evaluating the quality of the acquired data based on the basic characteristics of the dissolved CH4 in the shelf marginal sea, analyzing the mutual matching between the data, sorting out the types of the main regulation factors of seawater dissolved CH4 and constructing a preliminary evaluation model; subtracting the sum of the values ​​of the influence of different regulation factors from the actual change of seawater dissolved CH4, taking the difference between the two as the residual term of the preliminary evaluation model, characterizing the residual term as a calculation deviation to obtain a preliminary evaluation result, and correcting and adjusting the preliminary evaluation result through comparative verification; evaluating the proportion of the influence of a single regulation factor on seawater dissolved CH4, and then screening out the main regulation factors; the method can be widely used in the identification and scientific evaluation of the regulation factors of dissolved CH4 in my country's shelf marginal seas, and plays an important role in the scientific evaluation of the spatiotemporal distribution, emission and regional contribution of dissolved CH4 in my country's shelf marginal seas to atmospheric CH4.

Description

Technical Field

[0001] The present invention relates to the technical field of marine environment observation, and in particular to a method for evaluating a seawater dissolved methane regulating factor. Background Art

[0002] Methane (CH4) is the second largest greenhouse gas in the atmosphere after CO2, contributing 18.2% to global warming. CH4 has the characteristics of high warming potential and short life span, so CH4 emission reduction is one of the most powerful means to achieve climate change mitigation in a relatively short period of time. At the 26th United Nations Climate Change Conference in 2021, more than 100 countries signed the Global CH4 Commitment, pledging to reduce CH4 emissions by 30% in each signatory country by 2030. However, the current situation of lack of basic data and limited research technology has led to deviations in the estimation of CH4 emissions at different scales. In order to improve the accuracy of methane emission data, the United States actively uses advanced technical means to carry out methane observation research, which effectively improves the accuracy of CH4 emission data and promotes CH4 emission reduction. The emission control of greenhouse gases such as CH4 faces new challenges. In 2023, the Ministry of Ecology and Environment and 11 other departments jointly issued the "Methane Emission Control Action Plan" to carry out CH4 observation, accounting, reporting and verification work in key industries to promote emission reduction.

[0003] The ocean is the source of atmospheric CH4, releasing about 2.2 to 6.3 Tg of CH4 into the atmosphere each year. The area of ​​the continental shelf marginal sea affected by human activities accounts for only 16% of the global ocean area, but CH4 emissions account for about 75% of the global ocean. my country's continental shelf marginal seas span temperate, subtropical and tropical zones, with significant differences in ecosystem structure. In addition, mesoscale phenomena such as eddies, internal waves and upwelling are significant. The distribution of dissolved CH4 in seawater has significant temporal and spatial differences and is affected by complex physical, chemical and biological factors. It has always been the focus of research by scholars in marine science and environmental science. At present, the evaluation of the regulating factors of dissolved CH4 in seawater usually adopts a qualitative analysis method based on the correlation analysis of a large amount of measured data at sea. This method relies on the acquisition of a large amount of measured data, which is time-consuming, labor-intensive, costly and easily restricted by factors such as sea conditions. In addition, the limited accuracy of qualitative analysis makes it difficult to meet the requirements of the current marine field for quantitative evaluation of CH4 emission reduction in response to climate change. In addition, in recent years, although the quantitative evaluation method based on a single factor can achieve the quantitative evaluation of the factor to a certain extent, such as the quantitative evaluation of the impact of seasonal changes on dissolved CH4 in seawater, it is unable to scientifically clarify the synergistic effect of this factor and other regulatory factors, resulting in greater uncertainty. Therefore, overall, there is still a lack of quantitative evaluation methods for the regulatory factors of dissolved CH4 in seawater, and it is impossible to achieve the coordinated evaluation of different influencing factors and the precise screening of the main controlling factors. It is difficult to scientifically and accurately evaluate the spatiotemporal distribution and emission of dissolved CH4 in my country's continental shelf marginal seas, which limits the effective reduction of CH4 emissions.

[0004] In recent years, the ocean time series observation technology has been continuously developed, and it can obtain observation data with more regional representativeness, real-time and long time series characteristics. Especially in the fields of marine resources and environmental surveys, it has demonstrated its unique technical advantages. Therefore, using ocean time series observation data, an efficient, scientific and full use of time series observation data to evaluate the regulatory factors of dissolved CH4 in my country's continental shelf marginal seas is established, and the quantitative evaluation of the influence of different regulatory factors including seasonal changes, dilution water input, oxidation process, vertical mixing, sea-air exchange, etc. on dissolved CH4 in seawater and the precise extraction of the main controlling factors are achieved. It is important for scientifically evaluating the spatiotemporal distribution, emissions and regional contribution of dissolved CH4 in my country's continental shelf marginal seas to atmospheric CH4, and can also provide an important technical basis for the precise prevention and control and comprehensive management of CH4 emission reduction in my country's continental shelf marginal seas. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention discloses a method for evaluating a regulating factor of dissolved CH4 in seawater, which specifically comprises the following steps:

[0006] Obtain time series data information for the following items, where the items are divided into at least three items:

[0007] Diluted water: diluted water flow, salinity, temperature, dissolved CH4 of diluted water end members;

[0008] Atmosphere: CH4 concentration, meteorological parameters (temperature, humidity, air pressure, wind direction, wind speed);

[0009] Seawater: depth, temperature, salinity, dissolved oxygen, dissolved CH4, characteristic values ​​of temperature, salinity, dissolved oxygen, and dissolved CH4 of seawater end members;

[0010] Based on the basic characteristics of the spatial and temporal distribution of dissolved CH4 in the shelf marginal sea, the quality of the acquired data was preliminarily evaluated, the mutual matching between the data was analyzed, abnormal data was eliminated, and the data was scientifically evaluated;

[0011] The types of main regulatory factors of dissolved CH4 in seawater were sorted out and a preliminary evaluation model was constructed. The data corresponding to the starting time were used as the original characteristic data. The effects of seasonal changes, diluted water input, oxidation process, vertical mixing, sea-air exchange and changes in various regulatory factors on dissolved CH4 in seawater were analyzed over time.

[0012] The sum of the values ​​of the effects of different regulatory factors is subtracted from the actual change in dissolved CH4 in seawater, and the difference between the two is used as the residual term of the preliminary assessment model. The residual term is characterized as a calculation deviation to obtain a preliminary assessment result, and the preliminary assessment result is corrected and adjusted through comparative verification;

[0013] The magnitude of the impact of different regulatory factors was compared with the actual change in dissolved CH4 in seawater, and the proportion of the impact of a single factor on dissolved CH4 in seawater was evaluated, thereby screening out the main regulatory factors.

[0014] Furthermore, the effect of diluted water input on dissolved CH4 in seawater is calculated using the following algorithm:

[0015]

[0016] In the formula, Δ S CH4 is the change in dissolved CH4 in seawater caused by the input of diluted water; CH 4,Si+1 is the evaluation time t i+1 The amount of dissolved CH4 in seawater only under the influence of dilution water input; S i+1 is the evaluation time t i+1 Seawater salinity; CH 4,Si is the starting time t i The amount of dissolved CH4 in seawater affected only by dilution water input;

[0017]

[0018] f i+1,r +f i+1,sw =1

[0019] S i+1,r ×f i+1,r +S i+1,sw ×f i+1,sw =S i+1

[0020] at the same time:

[0021]

[0022] f i,r +f i,sw =1

[0023] S i,r ×f i,r +S i,sw ×f i,sw =S i

[0024] In the formula, CH 4,i+1,r is the evaluation time t i+1 Characteristic value of dissolved CH4 in dilute water end member, f i+1,r is the evaluation time t i+1 Mixing ratio of diluted water, CH 4,i+1,sw is the evaluation time t i+1 Characteristic value of dissolved CH4 in seawater end member, fi+1,sw is the evaluation time t i+1 Mixing ratio of seawater, S i+1,r is the evaluation time t i+1 Characteristic value of end-member salinity of diluted water, S i+1,sw is the evaluation time t i+1 Characteristic value of seawater end member salinity; CH 4,i,r is the starting time t i Characteristic value of dissolved CH4 in dilute water end member, f i,r is the starting time t i Mixing ratio of diluted water, CH 4,i,sw is the starting time t i Characteristic value of dissolved CH4 in seawater end member, f i,sw is the starting time t i Mixing ratio of seawater, S i,r is the starting time t i Characteristic value of end-member salinity of diluted water, S i,sw is the starting time t i Characteristic values ​​of seawater end-member salinity.

[0025] Furthermore, the effect of the oxidation process on dissolved CH4 in seawater is calculated using the following algorithm:

[0026] Δ Oxi CH4=-(DO i+1 -DO i -Δ AS DO i )÷2

[0027] In the formula, Δ Oxi CH4 is the change in dissolved CH4 in seawater caused by the oxidation process; DO i+1 is the evaluation time t i+1 The amount of dissolved oxygen (DO) in seawater, DO i is the starting time t i The value of dissolved oxygen DO in seawater; Δ AS DO i It is the change in dissolved oxygen in seawater affected by sea-air exchange.

[0028] Furthermore, the effect of vertical mixing on dissolved CH4 in seawater is calculated using the following algorithm: Δ mix CH4=((MLD i+1 -MLD i )÷(t i+1 -t i )+K Z ÷(MLD i+1 -MLD i ))×(CH 4,ss -CH 4,i)÷MLD i

[0029] In the formula, Δ mix CH4 is the change in dissolved CH4 in seawater caused by vertical mixing; MLD i is the starting time t i The depth of the mixing layer MLD, MLD i+1 is the evaluation time t i+1 The depth of the mixed layer MLD, K z is the vertical diffusivity, CH 4,ss is the starting time t i The amount of dissolved CH4 in subsurface seawater, CH 4,i is the starting time t i The amount of dissolved CH4 in surface seawater.

[0030] Furthermore, the effect of air-sea exchange on dissolved CH4 in seawater is calculated using the following algorithm:

[0031] Δ AS CH4=CH 4,i+1 -(F i / k w +CH 4,i,eq )

[0032] In the formula, Δ AS CH4 is the change in dissolved CH4 in seawater due to the air-sea exchange; CH 4,i+1 is the evaluation time t i+1 The amount of dissolved CH4 in seawater; F i is the starting time t i Sea-air CH4 exchange flux, k w is the gas exchange rate, CH 4,i,eq is the starting time t i The amount of dissolved CH4 in seawater when the surface seawater is in equilibrium with the atmosphere.

[0033] Due to the adoption of the above technical scheme, the present invention provides a method for evaluating the regulating factor of dissolved CH4 in seawater, which adopts time series observation data and has the characteristics of greater regional representativeness, real-time and long time series, and can realize the evaluation of the regulating factor of dissolved CH4 in seawater of my country's continental shelf marginal seas with high efficiency and low cost, overcoming the limitation that traditional methods need to rely on a large amount of marine measured data.

[0034] In addition, based on the basic characteristics of dissolved CH4 in my country's continental shelf marginal seas, the present invention classifies different regulatory factors of dissolved CH4 in seawater, enhances the characteristic expression ability of different regulatory factor processes, can scientifically and quantitatively evaluate the influence of different regulatory factors, and accurately extract the main controlling factors. Compared with the traditional correlation qualitative analysis method or single factor quantitative evaluation method, the accuracy is significantly improved, and it can be widely used in the identification and scientific evaluation of the regulatory factors of dissolved CH4 in seawater in my country's continental shelf marginal seas, which is helpful for the accurate evaluation of CH4 emissions in my country's continental shelf marginal seas and the formulation of CH4 emission reduction measures. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0037] In order to make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0038] like Figure 1 A method for evaluating a seawater dissolved CH4 regulating factor is shown, comprising the following steps:

[0039] S1: Obtain time series data of the following items through field investigation or data collection. Specific items include:

[0040] Diluted water: diluted water flow, salinity, temperature, dissolved CH4 of diluted water end members;

[0041] Atmosphere: CH4 concentration, meteorological parameters (temperature, humidity, air pressure, wind direction, wind speed);

[0042] Seawater: depth, temperature, salinity, dissolved oxygen, dissolved CH4, characteristic values ​​of temperature, salinity, dissolved oxygen, and dissolved CH4 of seawater end members;

[0043] S2: Based on the basic characteristics of dissolved CH4 in my country's continental shelf marginal seas, preliminarily evaluate the quality of the acquired data, analyze the mutual matching between the acquired data, eliminate abnormal data, and ensure the scientific nature of the data.

[0044] S3: Based on the basic characteristics of dissolved CH4 in my country's continental shelf marginal seas, the types of main regulatory factors of dissolved CH4 in seawater are sorted out, and an evaluation index is constructed: the change value of dissolved CH4 in seawater is recorded as ΔCH4, and the effects of different regulatory factors including seasonal changes, dilution water input, oxidation process, vertical mixing, and sea-air exchange on dissolved CH4 in seawater are recorded as Δ T CH4, Δ S CH4, Δ Oxi CH4, Δ Mix CH4, Δ As CH4, the residual term of the evaluation model is denoted as Δ Non CH4.

[0045] S4: Set the starting time of the time series data (t i ), the corresponding parameters at this moment are temperature (T i ), salinity (S i ), dissolved CH4(CH 4,i ), CH4 exchange flux at the air-sea interface (F i ), the salinity of the diluted water end member (S i,r ), dissolved CH4(CH 4,i,r ) characteristic value, the salinity of the seawater end member (S i,sw ), dissolved CH4(CH 4,i,SW ) eigenvalue; evaluation time (t i+1 ) and the corresponding parameters are temperature (T i+1 ), salinity (S i+1 ), dissolved CH4(CH 4,i+1 ), the salinity of the diluted water end member (S i+1,r ), dissolved CH4(CH 4,i+1,r ) characteristic value, the salinity of the seawater end member (S i+1,sw ), dissolved CH4(CH 4,i+1,sw ) and construct a one-dimensional model to evaluate the change in dissolved CH4 in seawater:

[0046] ΔCH4=Δ T CH4+Δ S CH4+Δ Oxi CH4+Δ Mix CH4+Δ As CH4+Δ Non CH4

[0047] S5: The sum of the values ​​of the influence of different regulating factors is subtracted from the actual change in the dissolved CH4 in seawater, and the difference between the two is used as the residual term of the preliminary evaluation model. The residual term is characterized as a calculation deviation to obtain a preliminary evaluation result, and the preliminary evaluation result is corrected and adjusted through comparative verification.

[0048] S6: Compare the change in dissolved CH4 in seawater under the influence of different regulatory factors with the actual change in dissolved CH4 in seawater, evaluate the proportion of the influence of a single regulatory factor on dissolved CH4 in seawater, and then screen out the main regulatory factors.

[0049] Example:

[0050] First, obtain the conventional environmental parameter data of seawater in the assessment area and the key parameter data of dissolved CH4; evaluate the data quality based on the basic characteristics of dissolved CH4 in my country's continental shelf marginal seas to ensure the scientific nature of the data; clarify that the change in dissolved CH4 in seawater is recorded as ΔCH4, and the effects of different regulatory factors including seasonal changes, diluted water input, oxidation process, vertical mixing, and sea-air exchange on dissolved CH4 in seawater are recorded as Δ T CH4, Δ S CH4, Δ Oxi CH4, Δ Mix CH4, Δ As CH4, the residual term of the evaluation model is denoted as Δ Non CH4. Set the start time of the time series data to t i The parameters corresponding to this moment are temperature (T i ), salinity (S i ), dissolved CH4(CH 4,i ), CH4 exchange flux at the air-sea interface (F i ), the salinity of the diluted water end member (S i,r ), dissolved CH4(CH 4,i,r ) characteristic value, the salinity of the seawater end member (S i,sw ), dissolved CH4(CH 4,i,SW ) eigenvalue; evaluation time (t i+1 ) and the corresponding parameters are temperature (T i+1 ), salinity (S i+1 ), dissolved CH4(CH 4,i+1 ), the salinity of the diluted water end member (S i+1,r ), dissolved CH4(CH 4,i+1,r ) characteristic value, the salinity of the seawater end member (S i+1,sw ), dissolved CH4(CH 4,i+1,sw ) and construct a one-dimensional model to evaluate the change in dissolved CH4 in seawater:

[0051] ΔCH4=Δ T CH4+Δ S CH4+Δ Oxi CH4+Δ Mix CH4+Δ As CH4+Δ Non CH4(1)

[0052] 1. Evaluation of the impact of seasonal changes on dissolved CH4 in seawater (Δ T CH4):

[0053]

[0054] In the formula, Δ T CH4 is the change in dissolved CH4 in seawater caused by seasonal changes; is the evaluation time t i+1 Sea water temperature T i+1 The amount of CH4 dissolved in seawater when the surface seawater is in equilibrium with the atmosphere under certain conditions; is the starting time t i Sea water temperature T i The amount of dissolved CH4 in seawater when the surface seawater is in equilibrium with the atmosphere under certain conditions.

[0055] 2. Evaluation of the impact of dilute water input on dissolved CH4 in seawater (Δ S CH4):

[0056]

[0057] In the formula, Δ S CH4 is the change in dissolved CH4 in seawater caused by the input of diluted water; CH 4,Si+1 is the evaluation time t i+1 The amount of dissolved CH4 in seawater only under the influence of dilution water input; S i+1 is the evaluation time t i+1 Seawater salinity; CH 4,Si is the starting time t i The amount of dissolved CH4 in seawater affected only by dilution water input;

[0058]

[0059] f i+1,r +f i+1,sw =1

[0060] S i+1,r ×f i+1,r +S i+1,sw ×f i+1,sw =S i+1

[0061] at the same time:

[0062]

[0063] f i,r +f i,sw =1

[0064] Si,r ×f i,r +S i,sw ×f i,sw =S i

[0065] In the formula, CH 4,i+1,r is the evaluation time t i+1 Characteristic value of dissolved CH4 in dilute water end member, f i+1,r is the evaluation time t i+1 Mixing ratio of diluted water, CH 4,i+1,sw is the evaluation time t i+1 Characteristic value of dissolved CH4 in seawater end member, f i+1,sw is the evaluation time t i+1 Mixing ratio of seawater, S i+1,r is the evaluation time t i+1 Characteristic value of end-member salinity of diluted water, S i+1,sw is the evaluation time t i+1 Characteristic value of seawater end member salinity; CH 4,i,r is the starting time t i Characteristic value of dissolved CH4 in dilute water end member, f i,r is the starting time t i Mixing ratio of diluted water, CH 4,i,sw is the starting time t i Characteristic value of dissolved CH4 in seawater end member, f i,sw is the starting time t i Mixing ratio of seawater, S i,r is the starting time t i Characteristic value of end-member salinity of diluted water, S i,sw is the starting time t i Characteristic values ​​of seawater end-member salinity.

[0066] 3. Evaluation of the effect of oxidation process on dissolved CH4 in seawater (Δ Oxi CH4):

[0067] Δ Oxi CH4=-(DO i+1 -DO i -Δ AS DO i )÷2 (4)

[0068] In the formula, Δ Oxi CH4 is the change in dissolved CH4 in seawater caused by the oxidation process; DO i+1 is the evaluation time t i+1 The amount of dissolved oxygen (DO) in seawater, DO i is the starting time t i The value of dissolved oxygen DO in seawater; Δ AS DOi It is the change in dissolved oxygen in seawater affected by sea-air exchange.

[0069] 4. Evaluation of the effect of vertical mixing on dissolved CH4 in seawater (Δ mix CH4): Δ mix CH4=((MLD i+1 -MLD i )÷(t i+1 -t i )+K Z ÷(MLD i+1 -MLD i ))×(CH 4,ss -CH 4,i )÷MLD i (5)

[0070] In the formula, Δ mix CH4 is the change in dissolved CH4 in seawater caused by vertical mixing; MLD i is the starting time t i The depth of the mixing layer MLD, MLD i+1 is the evaluation time t i+1 The depth of the mixing layer MLD, K z is the vertical diffusivity, CH 4,ss is the starting time t i The amount of dissolved CH4 in subsurface seawater, CH 4,i is the starting time t i The amount of dissolved CH4 in surface seawater.

[0071] 5. Evaluation of the impact of air-sea exchange on dissolved CH4 in seawater (Δ AS CH4):

[0072] Δ AS CH4=CH 4,i+1 -(F i / k w +CH 4,i,eq ) (6)

[0073] In the formula, Δ AS CH4 is the change in dissolved CH4 in seawater due to the air-sea exchange; CH 4,i+1 is the evaluation time t i+1 The amount of dissolved CH4 in seawater; F i is the starting time t i Sea-air CH4 exchange flux, k w is the gas exchange rate, CH 4,i,eq is the starting time t i The amount of dissolved CH4 in seawater when the surface seawater is in equilibrium with the atmosphere.

[0074] 6. Calculation of the proportion of the effects of different regulatory factors on dissolved CH4 in seawater, taking the calculation of the proportion of the effects of vertical mixing on dissolved CH4 in seawater as an example:

[0075] Δ mix CH4 / ΔCH4×100% (7)

[0076] 7. Screening of master controlling factors

[0077] The influence ratios of seasonal changes, diluted water input, oxidation process, vertical mixing, air-sea exchange and changes in various regulating factors on dissolved CH4 in seawater were calculated and compared in turn, and the main controlling factors were extracted.

[0078] Example

[0079] Based on the measured data of the North Yellow Sea time series station, the result obtained by the traditional correlation analysis method is that except for February throughout the year, river input is the main controlling factor of the seasonal variation of dissolved CH4 in seawater; based on the invented method, a quantitative evaluation of the regulating factors of dissolved CH4 in seawater was carried out, and the results showed that the spring oxidation process, summer dilution water input, autumn vertical mixing, and winter seasonal changes are the main controlling factors of dissolved CH4 in seawater, as shown in Table 1. This conclusion is in line with objective reality and is more scientific and accurate. Therefore, it can be seen that the invented method can more scientifically and efficiently evaluate the influence of different regulating factors of dissolved CH4 in seawater and accurately extract the main controlling factors.

[0080] Table 1 Evaluation results of seawater dissolved CH4 regulation factors at the Northern Yellow Sea time series station

[0081]

[0082] The present invention adopts time series observation data, which is more representative of the region, real-time and with long time series, and can realize the evaluation of the regulation factors of dissolved CH4 in my country's continental shelf marginal seas with high efficiency and low cost, overcoming the limitation that traditional methods need to rely on a large amount of measured data at sea.

[0083] The present invention classifies different regulatory factors of dissolved CH4 in seawater based on the basic characteristics of dissolved CH4 in my country's continental shelf marginal seas, enhances the characteristic expression ability of different regulatory factor processes, can scientifically and quantitatively evaluate the influence of different regulatory factors, and accurately extract the main controlling factors. Compared with the traditional correlation qualitative analysis method or single factor quantitative evaluation method, the accuracy is significantly improved.

[0084] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for evaluating the regulating factor of dissolved CH4 in seawater, characterized in that include: Obtain information on characteristic parameters of diluted water, atmosphere and seawater; Based on the basic characteristics of dissolved CH4 in the shelf marginal sea, the quality of the acquired data was preliminarily evaluated, the mutual matching between the acquired data was analyzed, the scientific evaluation of the acquired data was carried out, and the abnormal data was eliminated; The types of regulating factors of dissolved CH4 in seawater were sorted out and a preliminary evaluation model was constructed. The seawater temperature, seawater salinity, and concentration of dissolved CH4 in seawater corresponding to the starting time were used as the original characteristic data. The effects of seasonal changes, dilute water input, oxidation process, vertical mixing, air-sea exchange, and changes in various regulating factors on dissolved CH4 in seawater were analyzed over time. The sum of the values ​​of the effects of different regulatory factors is subtracted from the actual change in dissolved CH4 in seawater, and the difference between the two is used as the residual term of the preliminary assessment model. The residual term is characterized as a calculation deviation to obtain a preliminary assessment result, and the preliminary assessment result is corrected and adjusted through comparative verification; Compare the magnitude of the effects of different regulatory factors with the actual changes in dissolved CH4 in seawater, evaluate the proportion of the effect of a single factor on dissolved CH4 in seawater, and screen out the final regulatory factor; The following algorithm is used to analyze the effect of diluted water input on dissolved CH4 in seawater: In the formula, Δ S CH4 is the change in dissolved CH4 in seawater caused by the input of dilute water; is the evaluation time t i+1 The amount of dissolved CH4 in seawater under the influence of dilution water input only; S i+1 is the evaluation time t i+1 Seawater salinity; is the starting time t i The amount of dissolved CH4 in seawater affected only by dilution water input; f i+1,r +f i+1,sw =1 S i+1,r ×f i+1,r +S i+1,sw ×f i+1,sw =S i+1 at the same time: f i,r +f i,sw =1 S i,r ×f i,r +S i,sw ×f i,sw =S i In the formula, CH 4,i+1,r is the evaluation time t i+1 Characteristic value of dissolved CH4 in dilute water end member, f i+1,r is the evaluation time t i+1 Mixing ratio of diluted water, CH 4,i+1,sw is the evaluation time t i+1 Characteristic value of dissolved CH4 in seawater end member, f i+1,sw is the evaluation time t i+1 Mixing ratio of seawater, S i+1,r is the evaluation time t i+1 Characteristic value of end-member salinity of diluted water, S i+1,sw is the evaluation time t i+1 Characteristic value of seawater end member salinity; CH 4,i,r is the starting time t i Characteristic value of dissolved CH4 in dilute water end member, f i,r is the starting time t i Mixing ratio of diluted water, CH 4,i,sw is the starting time t i Characteristic value of dissolved CH4 in seawater end member, f i,sw is the starting time t i Mixing ratio of seawater, S i,r is the starting time t i Characteristic value of end-member salinity of diluted water, S i,sw is the starting time t i Characteristic values ​​of seawater end-member salinity; The following algorithm is used to analyze the effect of oxidation process on dissolved CH4 in seawater: Δ Oxi CH4=-(DO i+1 -DO i -Δ AS DO i )÷2 In the formula, Δ Oxi CH4 is the change in dissolved CH4 in seawater caused by the oxidation process; DO i+1 is the evaluation time t i+1 The amount of dissolved oxygen (DO) in seawater, DO i is the starting time t i The value of dissolved oxygen DO in seawater; Δ AS DO i is the change in dissolved oxygen in seawater affected by air-sea exchange; The following algorithm is used to analyze the effect of vertical mixing on dissolved CH4 in seawater: Δ mix CH4=((MLD i+1 -MLD i )÷(t i+1 -t i )+K Z ÷(MLD i+1 -MLD i ))×(CH 4,ss -CH 4,i )÷MLD i In the formula, Δ mix CH4 is the change in dissolved CH4 in seawater caused by vertical mixing; MLD i is the starting time t i The depth of the mixing layer MLD, MLD i+1 is the evaluation time t i+1 The depth of the mixed layer MLD, K z is the vertical diffusivity, CH 4,ss is the starting time t i The amount of dissolved CH4 in subsurface seawater, CH 4,i is the starting time t i The amount of dissolved CH4 in surface seawater; The following algorithm is used to analyze the effect of air-sea exchange on dissolved CH4 in seawater: Δ AS CH4=CH 4,i+1 -(F i / k w +CH 4,i,eq ) In the formula, Δ AS CH4 is the change in dissolved CH4 in seawater due to the air-sea exchange; CH 4,i+1 is the evaluation time t i+1 The amount of dissolved CH4 in surface seawater; F i is the starting time t i Sea-air CH4 exchange flux, k w is the gas exchange rate, CH 4,i,eq is the starting time t i The amount of dissolved CH4 in seawater when the surface seawater is in equilibrium with the atmosphere.

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