A method and system for estimating methane seepage flux of active cold seeps at marine stations

Abstract

The present invention belongs to the technical field of methane leakage monitoring, and discloses a method and system for estimating the methane leakage flux of active cold springs at marine stations. The method obtains the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of the methane gas inside at different depths, and obtains a three-dimensional static molar concentration model of the cold spring plume at the station; calculates the bubble-state methane molar flux and the bubble rising speed to obtain the eruption rate of the seabed cold spring vent; comprehensively considers the three-dimensional static molar concentration model of the cold spring plume at the station, the eruption rate and the bubble rising speed, and combines the periodic leakage characteristics of the cold spring plume to calculate the methane leakage flux of the cold spring at the station throughout the year. The methane flux of the cold spring leakage at the station of the present invention is 6.44×10 5 mol / yr, which is larger than previous estimates. The contribution of methane leakage from cold seep systems to climate change and the carbon cycle has been underestimated.

Description

Technical Field

[0001] The invention belongs to the technical field of methane leakage monitoring, and in particular relates to a method and system for estimating the methane leakage flux of an active cold spring at an ocean station. Background Art

[0002] Methane leakage from cold seeps on the seafloor is an important way for inter-sphere material and energy exchange, an important indicator of the presence of natural gas hydrates, and an important factor leading to seawater acidification and the greenhouse effect. Due to the difficulties in observation range, observation time, sampling, and in-situ environmental laboratory cultivation, the methane flux entering the ocean and atmosphere through cold seeps is still difficult to quantify.

[0003] The study area shows typical surface features of submarine cold seep systems, such as large-scale bubble flows, authigenic carbonate crusts, and chemoautotrophic biological communities. Multi-channel seismic data show that the underlying strata of the southern ridge crest have developed a continuous and nearly symmetrical bottom-like reflector (BSR) at depths ranging from 180 to 460 m, which also provides important evidence that the methane leaked from the cold seeps in this area comes from the unstable decomposition of natural gas hydrates.

[0004] Through the above analysis, the problems and defects of the existing technology are as follows: the traditional cold spring methane seepage flux technology includes: in-situ methane flux observation method at the in-situ sediment-water interface, indoor laboratory analysis and numerical simulation method. Both methods are costly, time-consuming, difficult to operate, and are a local observation method. Summary of the invention

[0005] In order to overcome the problems existing in the related art, the disclosed embodiments of the present invention provide a method and system for estimating the methane leakage flux of an active cold spring at an ocean station, and specifically relate to a method and system for estimating the methane leakage flux of an active cold spring at an ocean station "F". The purpose of the present invention is to take a cold spring at a certain sea station "F" as an example, and preliminarily explore the use of multiple data sets such as multi-beam, side-scan sonar, measured temperature, pressure, salinity and time-series images in the sea area to constrain the physical and chemical properties of the methane leakage bubble plume, and use numerical simulation to establish a molar concentration model of the bubble plume in the cold spring area at the "F" station, and estimate the contribution of methane leaked from the cold spring at the "F" station to the carbon cycle and climate change.

[0006] The technical solution is as follows: A method for estimating the methane seepage flux of active cold seeps at marine stations, comprising the following steps:

[0007] S1, obtain the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of methane gas at different depths, including bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of methane gas;

[0008] S2, based on the acquired data information, obtain the three-dimensional static molar concentration model of the cold spring plume at the station;

[0009] S3, based on the established three-dimensional static molar concentration model of the cold seep plume at the station, the bubble-state methane molar flux and bubble rising velocity are calculated to obtain the time for methane bubbles to rise from the vent to the top of the cold seep plume after the formation of the natural gas hydrate shell; the eruption rate of the submarine cold seep vent is obtained according to the actual duration of the submarine cold seep being affected by tides, ocean currents, and seasonal temperature fluctuations;

[0010] S4, the annual cold spring methane leakage flux at the station is calculated by integrating the three-dimensional static molar concentration model, eruption rate and bubble rise velocity of the cold spring plume at the station, combining the temperature, osmotic pressure, sediment influence and periodic climate changes to cause the periodic leakage characteristics of the cold spring plume.

[0011] In step S1, the bubble radius at different depths is obtained based on the time-series images. The bubble content refers to the percentage of the volume occupied by bubbles in a unit volume, and the expression is:

[0012] (1)

[0013] In the formula, is the bubble content, is the number of bubbles per unit volume, is the radius of the bubble after heat exchange;

[0014] When the gas inside the bubble is considered to be an ideal gas, the state equation of the gas is expressed as:

[0015] (2)

[0016] In the formula, is the ideal gas pressure, is the volume of the ideal gas, represents the amount of substance of an ideal gas, is temperature;

[0017] For an ideal gas, the pressure of methane gas in the bubble is:

[0018] (3)

[0019] In the formula, is the pressure of the surrounding seawater, is the liquid tension, is the initial radius of the bubble, is the pressure of methane gas in the bubble;

[0020] Under in-situ conditions, the Van der-Waals equation is used to describe the behavior of gas under in-situ conditions in real seawater. The expression is:

[0021] (4)

[0022] In the formula, is a constant used to correct for the intermolecular attraction; is a constant used to correct the volume;

[0023] After being corrected by the Van der-Waals equation, the pressure of methane gas in the bubble under in-situ conditions is expressed as:

[0024] (5)

[0025] In the formula, is the pressure of heat exchange under static conditions when the gas is non-ideal gas inside, is the Vander-Waals gas hard core radius. The pressure of methane gas in the bubble of this radius is calculated based on the polynomial equation as follows:

[0026] (6)

[0027] In the formula, is the insulation coefficient;

[0028] According to the thermodynamic properties of gas, the relationship between the molar volume, temperature, Van der-Waals constant, critical temperature and critical volume of gas and gas pressure is established, and the expression is:

[0029] (7)

[0030] In the formula, is the molar volume of methane gas, is a constant used to correct the volume; is the bubble radius;

[0031] is the gas pressure inside the bubble,

[0032] ;

[0033] The methane gas pressure in the bubble at different depths is obtained by formula (5), and combined with the RK equation, the molar volume of methane gas is finally calculated;

[0034] According to Henry's law, the volume molar concentration of a gas dissolved in a solute under different temperature and pressure conditions is proportional to the partial pressure of the gas when the solution-gas reaches equilibrium. The solubility of methane gas is:

[0035] (8)

[0036] In the formula, is the solubility of methane gas, is the Henry constant for methane, is the partial pressure of methane.

[0037] In step S2, a three-dimensional static molar concentration model of the cold spring plume at the station is obtained, including:

[0038] S201, using the acquired multi-beam acoustic detection information and side-scan sonar information to determine the size and shape of the plume bubble group;

[0039] S202, using random medium theory, a numerical model of bubbling seawater is established;

[0040] S203, using the sea depth, temperature, and salinity parameters of the background seawater provided by the CTD data, a layered model of the surrounding seawater is established;

[0041] S204, based on the methane solubility formula (8), a two-dimensional molar concentration model of the methane plume at the station is established. Combined with the size and morphology of the bubble group determined by the side-scan sonar seabed survey and multi-beam detection, a three-dimensional methane molar concentration model of the seafloor cold seep plume at the station is established based on the established two-dimensional molar concentration model of the methane plume at the station.

[0042] In step S201, the multi-beam acoustic detection information obtained includes:

[0043] A single vent model was selected in the study area, and the near-seafloor depth data obtained by ROV was used to draw a seafloor topographic anomaly map, including the shallowest water depth in the area, the water depth of the circular closed area, the topography of the delineated topographic anomaly area, and the closure amplitude;

[0044] The acquired side-scan sonar information includes: the area of ​​abnormal backscatter signal obtained by side-scan sonar in the study area.

[0045] In step S202, a numerical model of bubbling seawater is established using random medium theory, including:

[0046] (1) Combined with the detection results of the plume scale at the station by multi-beam and side-scan sonar, the overall scale of the plume water body is set; a base value of the bubble radius is set for each layer, and the bubble radius in the layer is randomly varied around the base value based on the random medium theory. The plume water body is gridded using a layered method, and the random medium theory is used to calculate the bubble radius in the layer that randomly varies around the base value;

[0047] (2) Assign a value to the bubble radius.

[0048] In step (2), the bubble radius is assigned, including: the bubble radius of the first cycle is 0.75mm-3.6mm-0.75mm, the bubble radius of the second cycle is 0.8mm-3.9mm-0.9mm, and the bubble radius of the third cycle is 1.0mm-4.2mm-1.4mm;

[0049] The bubble radius at the nozzle is set according to the video image taken by the ROV.

[0050] In step S204, a two-dimensional molar concentration model of the methane plume at the station is established, including:

[0051] Combined with the pressure of the surrounding seawater given by the CTD data, the van der Waals formula (5) is used to calculate the internal pressure of the bubble, and the methane gas partial pressure inside the bubble at different depths is obtained; the molar volume of methane gas at different depths is calculated using formula (7), and the molar concentration of gas in each bubble in the grid of different layers is calculated and applied to the calculation of methane flux;

[0052] After calculating the solubility of methane gas at different depths using formula (8), the solubility at each grid in each layer is compared with the solubility at the vent to obtain the solubility coefficient;

[0053] According to the solubility coefficient, a two-dimensional molar concentration model of the methane plume at the station was established based on the simplified model of the cold spring appearance of the station actually observed.

[0054] In step S3, the calculation of the bubble-state methane molar flux includes:

[0055] The solubility coefficient calculated using CTD data constrains the plume methane flux, and the total number of methane moles contained in the same batch of plume bubbles is linked to the area of ​​the cold seep vent to estimate the methane molar flux of the cold seep plume on a spatial scale. The total number of moles of methane gas produced per second is calculated from the single bubble layer at the vent in the three-dimensional methane molar concentration model of the seafloor cold seep plume at the station, and combined with the methane bubble flow rate, the methane bubble flow rate is finally calculated.

[0056] In step S3, the calculation of the bubble rising speed includes:

[0057] Linear regression equation for bubble rise velocity:

[0058] (9)

[0059] In the formula, is the height of the bubble rising, is the rising speed of the bubble;

[0060] The time for methane bubbles to rise from the vent to the top of the cold seep plume after eruption includes: the time for methane bubbles to rise from the vent to the top of the cold seep plume after the formation of the gas hydrate shell is calculated by using formula (9);

[0061] The eruption rate of the submarine cold seep vent includes the eruption rate of the continuous eruption time of 12 hours per day and the eruption rate of the discontinuous eruption time. The annual cold seep methane leakage flux of the station is 6.44×10 5 mol / yr.

[0062] Another object of the present invention is to provide a system for estimating the methane leakage flux of an active cold seep at an ocean station, the system implementing the method for estimating the methane leakage flux of an active cold seep at an ocean station, the system comprising:

[0063] The module for obtaining the physical state of bubbles and the physical and chemical properties of methane gas is used to obtain the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of methane gas at different depths, including bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of methane gas;

[0064] A module for obtaining a three-dimensional static molar concentration model of a cold spring plume at a station, used for obtaining a three-dimensional static molar concentration model of a cold spring plume at a station based on the acquired data information;

[0065] The bubble rising speed and eruption rate acquisition module is used to calculate the bubble-state methane molar flux and bubble rising speed based on the established station cold spring plume three-dimensional static molar concentration model, and obtain the time for methane bubbles to rise from the vent to the top of the cold spring plume after the formation of the natural gas hydrate shell; according to the actual eruption time of the submarine cold spring, which is affected by tides, ocean currents, and seasonal temperature fluctuations, the eruption rate of the submarine cold spring vent is obtained;

[0066] The module for obtaining the annual cold spring methane seepage flux at the station is used to integrate the three-dimensional static molar concentration model, eruption rate and bubble rise velocity of the cold spring plume at the station, combined with the periodic leakage characteristics of the cold spring plume caused by temperature, osmotic pressure, sediment influence and periodic climate changes, to calculate the annual cold spring methane seepage flux at the station.

[0067] Combining all the above technical solutions, the beneficial effects of the present invention are as follows: In order to accurately estimate the methane flux of cold spring leakage at the seafloor, the present invention takes the "F" station in a certain sea as an example, explores the application of research data of different scales in multiple disciplines such as multi-beam, side-scan sonar, CTD and time-series imaging, constrains the physical and chemical properties of methane bubbles in seawater, and estimates the methane flux of cold spring leakage at the "F" station through numerical simulation. The research results show that the methane flux of cold spring leakage at the "F" station is 12.06μmol / h in time and 0.5878mol / m in space. 2 , the annual flux is about 6.44×10 5 mol / yr, which is larger than the previous estimated results. This shows that the previous understanding of the contribution of methane leakage from cold seeps to climate change and carbon cycle may be seriously underestimated. The present invention proposes a new method for estimating the methane flux of submarine cold seeps. The present invention obtains the physical state of bubbles at different depths in the cold seep area of ​​the station and the physical and chemical properties of the methane gas inside at different depths; the technical solution of the present invention solves the problem of estimating the methane flux of cold seeps at the "F" station. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The accompanying drawings herein are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the description, serve to explain the principles of the present disclosure;

[0069] Figure 1 It is a method and system diagram for estimating methane leakage flux of cold seeps at marine stations provided by an embodiment of the present invention;

[0070] Figure 2 A diagram of a sea area water depth-temperature curve in a CTD observation result of a northern part of a certain sea provided by an embodiment of the present invention;

[0071] Figure 3 Two graphs of sea depth-temperature curves in CTD observation results of a northern part of a certain sea provided by an embodiment of the present invention;

[0072] Figure 4 A diagram of a water depth-salinity curve of a certain sea area provided by an embodiment of the present invention;

[0073] Figure 5 It is a second diagram of a water depth-salinity curve of a certain sea area provided by an embodiment of the present invention;

[0074] Figure 6 A diagram of a water depth-pressure curve of a certain sea area provided by an embodiment of the present invention;

[0075] Figure 7 It is a graph of water depth-pressure curve of a certain sea area provided by an embodiment of the present invention;

[0076] Figure 8is a schematic diagram of a two-dimensional molar concentration model of a methane plume at the "F" station provided by an embodiment of the present invention;

[0077] Fig. 9 It is a schematic diagram of the three-dimensional methane molar concentration model of the submarine cold seep plume at the "F" station provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0078] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0079] The innovation of the present invention is that the methane flux entering the ocean and atmosphere through cold seeps is still difficult to quantify due to the influence of observation range, observation duration, sampling and in-situ environmental laboratory cultivation difficulties. In order to accurately estimate the methane flux of cold seeps, the present invention takes the "F" station as an example, explores the application of research data of different scales in multiple disciplines such as multi-beam, side-scan sonar, CTD and time-series imaging, constrains the physical and chemical properties of methane bubbles in seawater, and estimates the methane flux of cold seeps at the "F" station through numerical simulation.

[0080] The present invention comprehensively applies data from multiple disciplines and provides a new method for calculating the methane seepage flux of currently active cold springs.

[0081] Embodiment 1, as Figure 1 As shown, the method for estimating the methane seepage flux of active cold seeps at marine stations provided by the embodiment of the present invention comprises the following steps:

[0082] S1, obtain the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of methane gas at different depths, including bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of methane gas;

[0083] S2, based on the acquired data information, obtain the three-dimensional static molar concentration model of the cold spring plume at the station;

[0084] S3, based on the established three-dimensional static molar concentration model of the cold seep plume at the station, the bubble-state methane molar flux and bubble rising velocity are calculated to obtain the time for methane bubbles to rise from the vent to the top of the cold seep plume after the formation of the natural gas hydrate shell; the eruption rate of the submarine cold seep vent is obtained according to the actual duration of the submarine cold seep being affected by tides, ocean currents, and seasonal temperature fluctuations;

[0085] S4, the annual cold spring methane leakage flux at the station is calculated by integrating the three-dimensional static molar concentration model, eruption rate and bubble rise velocity of the cold spring plume at the station, combining the temperature, osmotic pressure, sediment influence and periodic climate changes to cause the periodic leakage characteristics of the cold spring plume.

[0086] Example 2, as a specific implementation of the present invention, the method for estimating the methane seepage flux of active cold seeps at marine stations provided in the embodiment of the present invention includes the following contents.

[0087] 1. Physical and chemical characteristics of bubble plume.

[0088] Simulating the bubble plume state under the in-situ physical and chemical conditions of the cold spring area at the "F" station is the key to improving the accuracy of modeling. It is necessary to accurately describe the physical state of the bubbles at different depths and the physical and chemical properties of the methane gas inside, such as bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of these methane gases.

[0089] 1.1 Bubble content.

[0090] In the modeling process, the bubble radius at different depths is given based on the time series images, and the remaining parameters are calculated by the following equations. The bubble content refers to the percentage of volume occupied by bubbles per unit volume:

[0091] (1)

[0092] In the formula, is the bubble content, is the radius of the bubble after heat exchange; is the number of bubbles per unit volume. The number of bubbles at different depths is different. There are also certain differences in the number of bubbles, mainly due to the dissolution and rupture of bubbles.

[0093] 1.2 Physical and chemical characteristics of methane gas.

[0094] At present, the acoustic model of cold spring bubble plumes is mainly based on the ideal gas state equation. As the depth increases, the hydrostatic pressure increases, which will introduce large errors in the simulation process. Therefore, it is necessary to restore the physical and chemical properties of the methane gas inside the bubble in the original state. When the internal gas of the bubble is considered to be an ideal gas, the state equation of the gas can be expressed as:

[0095] (2)

[0096] In the formula, is the ideal gas pressure, is the volume of the ideal gas, represents the amount of substance of an ideal gas, is temperature;

[0097] For an ideal gas, the pressure of methane gas in the bubble is:

[0098] (3)

[0099] In the formula, is the pressure of the surrounding seawater, and the detection result of CTD is adopted in the present invention; is the liquid tension, is the initial radius of the bubble, is the pressure of methane gas in the bubble;

[0100] Under in-situ conditions, the actual seawater does not meet the ideal state requirements. In order to ensure the accuracy of the model, the present invention uses the Van der-Waals equation to approximately describe the behavior of the gas under in-situ conditions, namely:

[0101] (4)

[0102] In the formula, is a constant used to correct for the intermolecular attraction; is a constant used to correct the volume;

[0103] After being corrected by the Van der-Waals equation, the pressure of methane gas in the bubble under in-situ conditions is expressed as:

[0104] (5)

[0105] In the formula, is the pressure of heat exchange under static conditions when the gas is non-ideal gas inside, is the hard core radius of the Vander-Waals gas, is a constant, except and are known parameters, is the radius of the bubble after heat exchange. The pressure of methane gas in the bubble of this radius is calculated based on the polynomial equation:

[0106] (6)

[0107] In the formula, is the adiabatic coefficient, the adiabatic coefficient of methane gas is 1.29;

[0108] To analyze the molar flux of gas in bubbles under in-situ conditions, it is necessary to obtain the molar volume of methane gas at different initial pressures at different depths. During the movement of bubbles, heat exchange occurs with the surrounding seawater. The Redlich-Kwong equation of state is based on the Van der-Waals equation, which takes into account the thermodynamic properties of the gas and gives a state equation that approximately describes the behavior of the real gas. The relationship between the molar volume, temperature, Van der-Waals constant, critical temperature, critical volume, etc. of the gas and the gas pressure is established:

[0109] (7)

[0110] In the formula, is the molar volume of methane gas, is a constant used to correct the volume; is the bubble radius;

[0111] is the gas pressure inside the bubble,

[0112] ;

[0113] The internal pressure of methane bubbles at different depths is obtained by formula (5), which is combined with the RK equation to finally calculate the molar volume of methane gas.

[0114] In addition, Henry's law gives the relationship between gas solubility and environmental conditions such as temperature and pressure, which can be expressed as the volume molar concentration of a gas dissolved in a solute under different temperature and pressure conditions is proportional to the partial pressure of the gas when the solution-gas reaches equilibrium:

[0115] (8)

[0116] In the formula, is the solubility of methane gas, is the methane Henry constant. The size of the Henry constant often depends on environmental conditions such as temperature, solute, pressure, etc. The methane Henry constant of the present invention is derived from the American database NLST; is the partial pressure of methane.

[0117] 2. Methane molar concentration model of cold spring at the “F” station.

[0118] After obtaining the physical and chemical characteristics of methane gas under actual conditions, in order to establish a cold spring molar concentration model, it is also necessary to determine the distribution of bubbles. When a submarine cold spring leaks, free gaseous methane will enter the seawater and form a flame-shaped bubble group, which is also called a plume. By simulating the physical state of bubbles at different depths and the physical and chemical characteristics of methane gas, a cold spring plume methane molar concentration model at the "F" station is established. Specifically, it includes:

[0119] 2.1 Acoustic detection results.

[0120] The multi-beam acoustic detection system is an important means to detect the size and shape of the bubble group of the plume. The multi-beam detection results of the cold spring area at the "F" station show that the cold spring plume has a feather-like shape, with an upper inclination angle of about 15° to 25°. The water depth at the cold spring outlet is about 1175m, the top of the bubble group is located between 450m and 500m deep, and the escape height is about 725m.

[0121] A single nozzle model was selected in the study area to simulate the bubble plume. The seafloor topography anomaly map was drawn using the near-seafloor depth data obtained by ROV. The shallowest water depth in the area was about 1125m, and the circular closed area was located at the depth contour of 1140m. The diameter of the demarcated topography anomaly area was about 100m, and its main performance was mound-shaped positive topography with a closure amplitude of about 25m. The topography anomaly area corresponded well to the side-scan sonar backscatter anomaly area. The cold spring seepage bubble column structure could be clearly identified on the original sonar map. The seafloor reflection signal in the cold spring area was significantly stronger than that in the surrounding area, which was consistent with the backscatter signal anomaly area on the side-scan sonar. Therefore, in the study area, the area of ​​the backscatter signal anomaly area was approximated to the cross-sectional area at the nozzle of the cold spring plume three-dimensional model.

[0122] The shape and overall scale of the model can be determined through multi-beam acoustic detection information, shallow layer profile information and side-scan sonar information. The cold spring vent is located at -1140m. The vent is approximately circular with a radius of 60 to 70m. The top is located at a water depth of about -450m. The total height is about 750m. The overall inclination angle is set to 12°, and the shape is a feather-like semi-ellipse.

[0123] 2.2 Modeling method

[0124] The time-series images taken by ROV show that the bubbles in the cold seepage plume are in a randomly distributed state, so the random medium theory is used to establish a numerical model of bubbling seawater. Based on previous research results, the distribution state of bubbles inside the plume is summarized, and the numerical model of bubbling seawater is set up as follows:

[0125] (1) Although the bubble content and radius change with the depth of seawater, the bubble content and radius will not change much when the depth does not change much. Therefore, combined with the detection results of the plume scale at the "F" station by multi-beam and side-scan sonar, the overall scale of the plume water body is set to 120m horizontally and 750m vertically, and the plume water body is gridded by a layered method. The vertical scale of each layer is about 20m, and a total of 38 layers are set. The grid thickness of each layer is 1m, and the number of grids is 20. A base value of the bubble radius is set in each layer, and the bubble radius in the layer is randomly changed around the base value based on the random medium theory.

[0126] (2) As mentioned above, for the initial state of the numerical model of bubbling seawater, the bubble radius in the numerical model of bubbling seawater needs to be assigned. Under the action of buoyancy, bubbles continue to rise in the water, and as the seawater pressure decreases, the bubble radius gradually increases. After exceeding a certain range, the large bubbles break and become small bubbles, and the radius becomes smaller. Therefore, in the process of bubbles rising from the seabed, both the bubble radius and the bubble content first increase and then decrease as the water depth decreases. This process of changing from small to large and then to small is defined as a cycle. Previous studies have studied the changing law of the size of rising bubbles. Cold spring plumes must undergo at least three processes of "first increasing and then decreasing" within a depth range of 750m. Therefore, within the entire range of the numerical model of bubbling seawater, three cycles are set: the bubble radius of the first cycle is 0.75mm-3.6mm-0.75mm, the bubble radius of the second cycle is 0.8mm-3.9mm-0.9mm, and the bubble radius of the third cycle is 1.0mm-4.2mm-1.4mm. In each cycle, the bubble radius increases first and then decreases. The base values ​​of bubble radius and content in the three cycles are different. The bubble content in the first cycle is 1×10 -7 -1.1×10 -5 -1×10 -7 ; The bubble content in the second cycle is 1.28×10 -7 -1.5×10 -5 -1.83×10 -7 ; The bubble content in the third cycle is 2.67×10 -6 -2×10 -5 -2.67×10 -6 .

[0127] Table 1 Information about bubbles in the in-situ observation of cold springs at the “F” station

[0128]

[0129] In general, it decreases with increasing depth. The main reason for this setting is that bubbles with small radius are more stable, and bubbles with greater depth are more stable. Since bubbles rise at different depths, their stability varies, so layered gridding is performed during modeling. This principle must be strictly followed when setting the base value of the bubble radius and content of each layer. Among them, the relevant information of the in-situ observation of bubbles in the cold spring at the "F" station is shown in Table 1.

[0130] According to the in-situ observation information, the specific setting method of the bubble radius size of different periods in the numerical model of bubbling seawater is: the bubble radius of the first period is 0.75mm-3.6mm-0.75mm, the bubble radius of the second period is 0.8mm-3.9mm-0.9mm, and the bubble radius of the third period is 1.0mm-4.2mm-1.4mm. At the same time, during the modeling process, the bubble radius at the nozzle was set according to the video images taken by the ROV, ranging from 2.62mm-1.08mm.

[0131] During the rising process of bubbles, they will break and dissolve, and the bubble content will change accordingly, and the number of bubbles will also decrease. Therefore, the methane solubility coefficient is applied to constrain the bubble content. The methane solubility coefficient, that is, the solubility of methane in a specific solvent (usually water), refers to the maximum amount of methane gas that can be dissolved in a unit volume of solvent at a certain temperature and pressure. Solubility limitation: The methane solubility coefficient determines the maximum solubility of methane gas in water. When the concentration of methane gas exceeds this solubility, bubbles will form. Therefore, the solubility coefficient actually sets an upper limit for the formation of bubbles. Control of the number of bubbles: At a given temperature and pressure, the larger the methane solubility coefficient, the more methane gas can be dissolved in water, thereby reducing the number of methane gas that forms bubbles. Conversely, the smaller the solubility coefficient, the easier it is to form bubbles, and the number of bubbles may be relatively large. Influence of bubble stability: The methane solubility coefficient also affects the stability of bubbles. When the solubility coefficient is small, the bubbles formed may be more likely to rise and escape the water surface because the methane concentration in the water is low and the bubbles are subject to greater buoyancy. When the solubility coefficient is larger, the bubbles may be more stable because they are more soluble in water and experience relatively less buoyancy.

[0132] In-situ observation data show that the number of bubbles per unit volume varies in different periods. Based on this, the initial bubble content of each period is set: the bubble content in the first period is 1×10 -7 -1.1×10 -5 -1×10 -7 ; The bubble content in the second cycle is 1.28×10 -7 -1.5×10 -5 -1.83×10 -7 ; The bubble content in the third cycle is 2.67×10-6 -2×10 -5 -2.67×10 -6 .

[0133] 2.3 CTD detection results.

[0134] CTD data can provide relevant parameters of background seawater, which can be used to establish a layered model of the surrounding seawater. Figure 2 The sea depth-temperature curve in the CTD observation results of the northern part of a certain sea and the Figure 3 The second sea depth-temperature curve in the CTD observation results of the northern part of a certain sea shows that salinity, temperature and pressure vary greatly with the depth of seawater. As the depth of seawater increases, the temperature gradually decreases. At a depth of 1150m to 1200m (at the vent), the seawater temperature is about 4°C. From 0 to 400m, the seawater temperature drops rapidly from 30°C to 12°C, with a large rate and amplitude of change. At a depth of more than 400m, the rate of change of seawater temperature slows down, slowly decreasing from 12°C to 4°C. This depth is also the location of the eruption of cold spring plumes.

[0135] The salinity of seawater ranges from 33.7 psu to 34.7 psu. Figure 4 The depth-salinity curve of a certain sea area, as well as Figure 5 The second depth-salinity curve of a certain sea area shows that the salinity has an obvious jump layer phenomenon. From the sea surface to 175m, the salinity increases rapidly with the increase of depth, from 33.7psu to 34.6psu at a very fast rate; between 175m and 400m, the salinity of seawater decreases to 34.4psu; from 400m to 600m, the salinity remains basically stable; above 600m, the salinity of seawater in some areas increases from 34.4psu to 34.7psu. Although the observation results of different stations are slightly different, the trends of water temperature, salinity and change law are basically the same. Different temperature salinity will affect the Henry constant of methane in seawater, and further affect the solubility of methane gas.

[0136] The pressure varies approximately linearly with the depth of seawater, such as Figure 6 The water depth-pressure curve of a certain sea area, as well as Figure 7 The water depth-pressure curve 2 of a certain sea area, and the empirical formula of the pressure related to it can be expressed as: , is the pressure that varies with the depth of the seawater, where Take 1035kg / m 3 , Take 9.8m / s 2 The accurate seawater pressure observation results improve the accuracy of the calculation of the methane gas pressure inside the bubble, the molar volume of methane, and the solubility of methane gas in the cold seep plume molar concentration model.

[0137] 2.4 Molar concentration model.

[0138] Combined with the pressure of the surrounding seawater given by the CTD data, the internal pressure of the bubble can be calculated by applying the van der Waals equation (Formula (5)), and the partial pressure of methane gas inside the bubble at different depths can be obtained. Then, the molar volume of methane gas at different depths can be calculated by applying Formula (7). In this way, the molar concentration of gas in each bubble in the grid of different layers can be calculated and applied to the calculation of methane flux.

[0139] At the same time, bubbles will vibrate, rupture, and merge during the rising process, during which time methane will partially dissolve into the seawater. Therefore, a reasonable solubility coefficient needs to be set to constrain the molar concentration and flux of methane at different depths.

[0140] In the model, after applying formula (8) to calculate the solubility of methane gas at different depths, the solubility at each grid in each layer is compared with the solubility at the vent to obtain the solubility coefficient. The calculation of the solubility coefficient takes into account the temperature, salinity and pressure of the measured background seawater. The use of the solubility coefficient makes the molar concentration of methane in the entire model more accurate, increasing the authenticity and accuracy of the cold spring molar concentration model.

[0141] According to the above methane solubility formula (8), a two-dimensional molar concentration model of the methane plume at the "F" station was established based on the simplified model of the actual observed cold spring appearance at the "F" station, as shown in Figure 8 As shown in the figure; the methane concentration at the nozzle of the two-dimensional molar concentration model of the methane plume at the "F" station is about 30.15 μmol / L, the concentration at 20m above the nozzle is 16.15 0.3μmol / L. The reason for this difference may be the difference in biological environmental conditions at the vent or the difference in sampling methods. Figure 8 As shown in Table 2, the molar concentration model has a large concentration gradient in the vertical direction, and the methane concentration in the surface seawater is close to 0, which is consistent with the in-situ observation data. This phenomenon further verifies the accuracy of the model. The methane content of the water body near the seafloor vent of the cold spring at the "F" station is shown in Table 2.

[0142] Table 2 Methane content in the water near the seafloor vent of the cold spring at the “F” station

[0143]

[0144] Then, based on the two-dimensional model, a three-dimensional methane molar concentration model of the submarine cold seep plume at the "F" station was finally established, combining the apparent characteristics of the plume determined by the side-scan sonar seabed survey and multi-beam detection. Fig. 9As shown in the figure, the three-dimensional methane molar concentration model of the submarine cold seep plume at the "F" station is 750 meters high and 120 meters in diameter. The methane concentration decreases rapidly with the shallowing of the water depth. The methane concentration decreases by about 80% within 50 meters from the vent, which is also in good agreement with the in-situ detection results.

[0145] 3. Estimation of cold spring seepage flux.

[0146] Under the constraints of the physical and chemical properties of bubble-state methane, a static molar concentration model of the cold spring plume at the "F" station was established. To estimate the experimental cold spring seepage flux, it is also necessary to quantify the temporal variation characteristics of the plume bubbles. The present invention achieves the purpose of describing the temporal evolution characteristics of the plume under the constraints of the research results of in-situ observation data such as multi-beam and time-series images and seepage tents.

[0147] 3.1 Bubble-state methane molar flux.

[0148] The present invention assumes that the methane bubbles in the plume are continuously rising, and also assumes that the methane bubbles are from the same batch from the nozzle to the top of the plume, during which the bubbles may rupture, merge or dissolve. The solubility coefficient calculated using CTD data is used here to constrain the plume methane flux.

[0149] The total number of methane moles contained in the same batch of plume bubbles was related to the area of ​​the cold seep, and the final estimated methane molar flux of the cold seep plume on a spatial scale was 0.5878 mol / m 2 In situ observation data show that the average bubble release rate in the cold spring area at the "F" station is about 11.6 bubbles s -1 , based on the single bubble layer at the nozzle in the model, the total number of moles of methane gas produced per second is calculated, and the production is 0.1967 mol / s, and the bubble flow rate is 0.4 L / h. Fig. 9 As shown in Figure 2, according to the three-dimensional methane molar concentration model of the submarine cold seep plume at the "F" station, the methane molar concentration at the vent is about 30.15 μmol / L, combined with the methane bubble flow rate, the final calculated methane bubble flow rate is 12.06μmol / h. The total number of moles of methane contained in the plume bubble is multiplied by the area of ​​the cold spring nozzle, and the total number of moles of methane gas produced per second is multiplied by the methane bubble flow rate, which is the methane bubble flow rate.

[0150] 3.2 Bubble rising velocity model.

[0151] Similar to the calculation method of estimating the methane flux of cold seep plume bubbles frame by frame using the time series imaging method, the three-dimensional methane molar concentration model of the cold seep plume at the "F" station can be converted into a dynamic evolution model that changes with time, and the methane flux of cold seep plume leakage can be calculated based on this. Previous researchers used the high backscattering oblique line method in multi-beam stack images to depict the movement speed of bubbles in the water body, and gave the linear regression equation for the bubble rise speed:

[0152] (9)

[0153] In the formula, is the height of the bubble rising, is the rising speed of the bubble;

[0154] The results show that the bubble velocity is positively correlated with the water depth. The main reason is inferred to be the decrease in gas concentration in the bubbles during the rise of methane in the water. The increase in the area of ​​high reflections and the decrease in the rising velocity may also be due to the formation of small bubbles by the rupture of large bubbles during the rise. Experiments show that in the deep sea environment, the gas hydrate shell may be formed within 5-10 minutes, and the formation of the gas hydrate shell will significantly reduce the rising velocity of the bubbles. Formula (9) can be used to calculate the time it takes for methane bubbles to rise from the vent to the top of the cold spring plume after the formation of the gas hydrate shell.

[0155] There is a certain time interval between the eruption of methane bubbles in different batches. This time interval is approximately equal to the sum of the time for the formation of the gas hydrate shell and the time for the methane bubbles at the vent to rise to the top of the plume after forming the gas hydrate shell. Formula (9) can be used to calculate the time for the methane bubbles in different batches to rise to the top of the plume, which is about 2.5886h. The time for the formation of the gas hydrate shell is about 0.1h, and the interval between the generation of methane bubbles in the cold spring plume leakage is about 2.6886h.

[0156] 3.3 Calculation of annual methane leakage flux at station “F”.

[0157] The above-mentioned bubble rising speed model establishes a time model for the continuous eruption of cold springs, while the actual eruption duration of submarine cold springs is affected by factors such as tides, ocean currents, and seasonal temperature fluctuations. Therefore, in order to calculate the annual flux of methane leakage from cold springs, in addition to calculating the time intervals between different batches of methane bubble flows, it is also necessary to understand the eruption patterns of submarine cold spring vents.

[0158] Long-term in-situ observations show that tides and waves have a significant control over the leakage of cold springs in the northern part of a certain sea. At the same time, according to the long-term in-situ observations of Di et al., the average tidal range during the entire study period was 1.4 m, the average continuous eruption time was about 12 hours per day, and the eruption rate was about 11.6 bubbles s -1 For the discontinuous eruption time, the lowest value of the eruption rate can be taken, which is about 4 bubbles s -1 .

[0159] Based on the above analysis, the present invention draws on the calculation method of calculating the methane flux of cold spring plume leakage based on time series images frame by frame, combines the three-dimensional static molar concentration model of the cold spring plume at the "F" station, the eruption rate (continuous eruption time rate and discontinuous eruption time eruption rate) and the bubble rise rate, and considers the periodic leakage characteristics of the cold spring plume. The comprehensive calculation results show that the annual cold spring methane leakage flux at the "F" station is about 6.44×10 5 mol / yr, the comprehensive calculation is to multiply the eruption rate by the area of ​​the cold spring vent, add the bubble rise speed factor, and use real-time monitoring or appropriate statistical methods to estimate the bubble rise speed. Although this amount is consistent with previous studies in terms of order of magnitude, it is much larger than previous calculations, so the previous understanding of the contribution of methane leakage from cold spring systems to climate change and carbon cycle has been seriously underestimated.

[0160] Embodiment 3, another object of the present invention is to provide a system for estimating methane seepage flux of active cold seeps at marine stations, comprising:

[0161] The module for obtaining the physical state of bubbles and the physical and chemical properties of methane gas is used to obtain the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of methane gas at different depths, including bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of methane gas;

[0162] A module for obtaining a three-dimensional static molar concentration model of a cold spring plume at a station, used for obtaining a three-dimensional static molar concentration model of a cold spring plume at a station based on the acquired data information;

[0163] The bubble rising speed and eruption rate acquisition module is used to calculate the bubble-state methane molar flux and bubble rising speed based on the established station cold spring plume three-dimensional static molar concentration model, and obtain the time for methane bubbles to rise from the vent to the top of the cold spring plume after the formation of the natural gas hydrate shell; according to the actual eruption time of the submarine cold spring, which is affected by tides, ocean currents, and seasonal temperature fluctuations, the eruption rate of the submarine cold spring vent is obtained;

[0164] The module for obtaining the annual cold spring methane seepage flux at the station is used to integrate the three-dimensional static molar concentration model, eruption rate and bubble rise velocity of the cold spring plume at the station, combined with the periodic leakage characteristics of the cold spring plume caused by temperature, osmotic pressure, sediment influence and periodic climate changes, to calculate the annual cold spring methane seepage flux at the station.

[0165] To further illustrate the effects of the embodiments of the present invention, the following experiment was conducted: Undersea cold seep methane leakage is an important part of the global carbon cycle and an important factor affecting seawater acidification and climate warming. By combining multiple data sets such as multi-beam, side-scan sonar, CTD and time-series images of the cold seep area at the "F" station in a certain sea, the present invention determines the methane flux of cold seep plume leakage through numerical simulation, and more accurately estimates the contribution of the cold seep system to the organic carbon mass balance of the marine ecosystem.

[0166] The physical and chemical properties of the cold seep plume were constrained by using the multi-beam, CTD and time-series imaging research results. Based on the three-dimensional molar concentration model of the plume, the methane flux of the cold seep at the "F" station in a certain sea was estimated to be 12.06μmol / h and 0.5878mol / m 2 The annual seepage flux is 6.44×105mol / yr, which is larger than the previous estimated results. The experimental results show that the existing technology may seriously underestimate the contribution of methane leakage from cold spring systems to climate change and carbon cycle.

[0167] The present invention combines the research results of multiple disciplines at different scales, and constrains the plume numerical model by linking the data of different disciplines with the physical and chemical properties of methane bubbles in seawater, which can achieve a more accurate and efficient description of the methane seepage flux of submarine cold seeps.

[0168] 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 modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for estimating the methane seepage flux of active cold seeps at marine stations, characterized in that: The method comprises the following steps: S1, obtain the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of methane gas at different depths, including bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of methane gas; S2, based on the acquired data information, obtain the three-dimensional static molar concentration model of the cold spring plume at the station; S3, based on the established three-dimensional static molar concentration model of the cold seep plume at the station, the bubble-state methane molar flux and bubble rising velocity are calculated to obtain the time for methane bubbles to rise from the vent to the top of the cold seep plume after the formation of the natural gas hydrate shell; the eruption rate of the submarine cold seep vent is obtained according to the actual duration of the submarine cold seep being affected by tides, ocean currents, and seasonal temperature fluctuations; S4, the annual cold spring methane leakage flux at the station is calculated by integrating the three-dimensional static molar concentration model, eruption rate and bubble rise velocity of the cold spring plume at the station, combining the temperature, osmotic pressure, sediment influence and periodic climate changes to cause the periodic leakage characteristics of the cold spring plume.

2. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 1, characterized in that: In step S1, the bubble radius at different depths is obtained based on the time-series images. The bubble content is the percentage of the volume occupied by bubbles in a unit volume, and the expression is: （1） In the formula, is the bubble content, is the number of bubbles per unit volume, is the radius of the bubble after heat exchange; For an ideal gas, the state equation of the gas is expressed as: （2） In the formula, is the pressure of the ideal gas, is the volume of the ideal gas, is the amount of substance of the ideal gas, is temperature; For an ideal gas, the pressure of methane gas in the bubble is: （3） In the formula, is the pressure of the surrounding seawater, is the liquid tension, is the initial radius of the bubble, is the pressure of methane gas in the bubble; Under in-situ conditions, the Van der-Waals equation is used to describe the behavior of gas under in-situ conditions in real seawater. The expression is: （4） In the formula, are all constants; After being corrected by the Van der-Waals equation, the pressure of methane gas in the bubble under in-situ conditions is expressed as: （5） In the formula, is the pressure of heat exchange under static conditions when the gas is non-ideal gas inside, is the hard core radius of the Van der-Waals gas. The pressure of methane gas in the bubble of this radius is calculated based on the polynomial equation as follows: （6） In the formula, is the insulation coefficient; According to the thermodynamic properties of gas, the relationship between the molar volume, temperature, Van der-Waals constant, critical temperature and critical volume of gas and gas pressure is established, and the expression is: （7） In the formula, is the molar volume of methane gas, is the bubble radius; is the gas pressure inside the bubble, ； The methane gas pressure in the bubble at different depths is obtained by formula (5), and combined with the RK equation, the molar volume of methane gas is calculated; According to Henry's law, the volume molar concentration of a gas dissolved in a solute under different temperature and pressure conditions is proportional to the partial pressure of the gas when the solution-gas reaches equilibrium. The solubility of methane gas is: （8） In the formula, is the solubility of methane gas, is the Henry constant for methane, is the partial pressure of methane.

3. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 2, characterized in that: In step S2, a three-dimensional static molar concentration model of the cold spring plume at the station is obtained, including: S201, using the acquired multi-beam acoustic detection information and side-scan sonar information to determine the size and shape of the plume bubble group; S202, using random medium theory, a numerical model of bubbling seawater is established; S203, using the sea depth, temperature, and salinity parameters of the background seawater provided by the CTD data, a layered model of the surrounding seawater is established; S204, based on the methane solubility formula (8), a two-dimensional molar concentration model of the methane plume at the station is established. Combined with the size and morphology of the bubble group determined by the side-scan sonar seabed survey and multi-beam detection, a three-dimensional methane molar concentration model of the seafloor cold seep plume at the station is established based on the established two-dimensional molar concentration model of the methane plume at the station.

4. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 3, characterized in that: In step S201, the multi-beam acoustic detection information obtained includes: A single vent model was selected in the study area, and the near-seafloor depth data obtained by ROV was used to draw a seafloor topographic anomaly map, including the shallowest water depth in the area, the water depth of the circular closed area, the topography of the delineated topographic anomaly area, and the closure amplitude; The acquired side-scan sonar information includes: the area of ​​abnormal backscatter signal obtained by side-scan sonar in the study area.

5. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 3, characterized in that: In step S202, a numerical model of bubbling seawater is established using random medium theory, including: (1) Combined with the detection results of the plume scale at the station by multi-beam and side-scan sonar, the overall scale of the plume water body is set; a base value of the bubble radius is set for each layer, and the bubble radius in the layer is randomly varied around the base value based on the random medium theory. The plume water body is gridded using a layered method, and the random medium theory is used to calculate the bubble radius in the layer that randomly varies around the base value; (2) Assign a value to the bubble radius.

6. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 5, characterized in that: In step (2), the bubble radius is assigned, including: the bubble radius of the first cycle is 0.75mm-3.6mm-0.75mm, the bubble radius of the second cycle is 0.8mm-3.9mm-0.9mm, and the bubble radius of the third cycle is 1.0mm-4.2mm-1.4mm; The bubble radius at the nozzle is set according to the video image taken by the ROV.

7. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 3, characterized in that: In step S204, a two-dimensional molar concentration model of the methane plume at the station is established, including: Combined with the pressure of the surrounding seawater given by the CTD data, the van der Waals formula (5) is used to calculate the internal pressure of the bubble, and the methane gas partial pressure inside the bubble at different depths is obtained; the molar volume of methane gas at different depths is calculated using formula (7), and the molar concentration of gas in each bubble in the grid of different layers is calculated and applied to the calculation of methane flux; After calculating the solubility of methane gas at different depths using formula (8), the solubility at each grid in each layer is compared with the solubility at the vent to obtain the solubility coefficient; According to the solubility coefficient, a two-dimensional molar concentration model of the methane plume at the station was established based on the simplified model of the cold spring appearance of the station actually observed.

8. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 1, characterized in that: In step S3, the calculation of the bubble-state methane molar flux includes: The solubility coefficient calculated using CTD data constrains the plume methane flux, and the total number of methane moles contained in the same batch of plume bubbles is linked to the area of ​​the cold seep vent to estimate the methane molar flux of the cold seep plume on a spatial scale. The total number of moles of methane gas produced per second is calculated from the single bubble layer at the vent in the three-dimensional methane molar concentration model of the seafloor cold seep plume at the station, and combined with the methane bubble flow rate, the methane bubble flow rate is finally calculated.

9. The method for estimating methane seepage flux of active cold seeps at marine stations according to claim 1, characterized in that: In step S3, the calculation of the bubble rising speed includes: Linear regression equation for bubble rise velocity: （9） In the formula, is the height of the bubble rising, is the rising speed of the bubble; The time for methane bubbles to rise from the vent to the top of the cold seep plume after eruption includes: the time for methane bubbles to rise from the vent to the top of the cold seep plume after the formation of the gas hydrate shell is calculated by using formula (9); The eruption rate of the submarine cold seep vent includes the eruption rate of the continuous eruption time of 12 hours per day and the eruption rate of the discontinuous eruption time. The annual cold seep methane leakage flux of the station is 6.44×10 5 mol / yr.

10. A system for estimating methane seepage flux of active cold seeps at marine stations, characterized in that: The method for estimating the methane seepage flux of an active cold seep at an ocean station as claimed in any one of claims 1 to 9 is implemented, the system comprising: The module for obtaining the physical state of bubbles and the physical and chemical properties of methane gas is used to obtain the physical state of bubbles at different depths in the cold spring area of ​​the station and the physical and chemical properties of methane gas at different depths, including bubble radius, bubble content, solubility of methane gas, pressure of methane gas in bubbles, and molar volume of methane gas; A module for obtaining a three-dimensional static molar concentration model of a cold spring plume at a station, used for obtaining a three-dimensional static molar concentration model of a cold spring plume at a station based on the acquired data information; The bubble rising speed and eruption rate acquisition module is used to calculate the bubble-state methane molar flux and bubble rising speed based on the established station cold spring plume three-dimensional static molar concentration model, and obtain the time for methane bubbles to rise from the vent to the top of the cold spring plume after the formation of the natural gas hydrate shell; according to the actual eruption time of the submarine cold spring, which is affected by tides, ocean currents, and seasonal temperature fluctuations, the eruption rate of the submarine cold spring vent is obtained; The module for obtaining the annual cold spring methane seepage flux at the station is used to integrate the three-dimensional static molar concentration model, eruption rate and bubble rise velocity of the cold spring plume at the station, combined with the periodic leakage characteristics of the cold spring plume caused by temperature, osmotic pressure, sediment influence and periodic climate changes, to calculate the annual cold spring methane seepage flux at the station.

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