Analysis On Temporal And Spatial Variation Characteristics And Influencing Factors Of PH In The North Pacific Ocean

Ocean acidification is changing the chemical structure of seawater and the marine environment on which marine life depends at an unprecedented speed,which has a more and more far-reaching impact on the scientific and socio-economic levels.Seawater pH value can directly reflect the degree of seawater acidification.Therefore,it is necessary to study and analyze the temporal and spatial variation characteristics of seawater pH.In order to alleviate the problem of seawater acidification,it is still necessary to strengthen the discussion on the influencing factors of pH value.At present,there are few studies on the spatial distribution characteristics of point,line and surface of long-time series of seawater pH and the dynamic variation characteristics of deep seawater pH.The North Pacific is the most typical ocean in the ocean,and the ocean has a wide range,large area and deep water,which plays an important role in global climate change.Therefore,it is of great significance to study the pH change of seawater in the North Pacific,which lays a foundation for the analysis of global ocean acidification.Based on the pH data of surface and bottom seawater in the North Pacific from1995 to 2019 and the data of environmental factors such as carbon dioxide partial pressure,temperature,salinity,chlorophyll and dissolved oxygen,this study uses anomaly analysis and linear regression analysis to explore the inter monthly,seasonal and inter annual temporal variation characteristics of surface seawater pH,and studies the point line surface spatial variation characteristics of surface seawater pH through anomaly percentage analysis,At the same time,the spatial variation characteristics of longitudinal pH at different seawater depths were analyzed.Due to the large temporal and spatial variation of surface seawater pH,the seasonal variation of water pH in Shanghai is significant in time,and there are low latitude and high latitude areas in space.For the reason of studying this characteristic,the influence of various marine physical and chemical parameters on pH is preliminarily discussed by using correlation analysis method.The main achievements are as follows:1)The pH of surface seawater in the North Pacific Ocean shows a linear downward trend with the interannual variation,with the variation range of 8.029-8.070,and the downward rate shows a slow trend first and then fast trend.The pH of surface seawater has obvious seasonal variation characteristics,showing a downward trend.The pH is the highest in winter,followed by spring,and the lowest in autumn and summer.The monthly variation characteristics of surface seawater pH confirmed the difference of seasonal variation.The highest pH value appeared in January and the lowest pH value appeared in August.2)The pH value of surface seawater shows a spatial pattern of high in the northwest and low in the southeast.The acidification degree of central and Western sea areas is particularly obvious,and the acidification areas of other sea areas are merged in a large area.Specifically,in the east-west direction,the pH value in the middle and low latitude sea area(South and middle)decreases from west to East,that is,the west is high and the East is low,and the pH value in the high latitude(North)sea area shows the opposite change trend,that is,the southeast is high and the northwest is low;In the north-south direction,the pH of seawater increases first and then decreases from south to north,that is,it is high in the middle and low in the north-south.The change rate of pH value in the sea area close to land is greater than that in the open sea area.Among them,the pH value of the sea areas near the sea of Japan and the Bohai Sea increased by0.01 as a whole,while the pH value of most other sea areas decreased by 0.04 as a whole.3)The pH value in the North Pacific Ocean varies greatly in time and space with the increase of depth.In the east-west direction,the pH of the middle surface seawater is higher in the West and lower in the East.In the north-south direction,the central sea area is higher than the North-South sea area,and the overall spatial change shows a downward trend.In the east-west direction,the pH in the middle latitude sea area decreases from west to East,while the pH in the high latitude sea area shows the opposite trend.In addition,seawater acidification is more serious in the eastern coastal areas of middle and low latitudes and the western coastal areas of middle and high latitudes.In the north-south direction,the pH value of seawater presents the same spatial variation characteristics,and the pH value in the central sea area is higher than that in the North-South sea area.On the whole,the pH value of deep sea water shows the characteristics of high in the South and low in the north.In some parts,the lowest value occurs in the deep-sea area and high latitude deep-sea area adjacent to the land,the highest value occurs in the deep-sea area of the sea of Japan,and the pH value changes in other sea areas are relatively stable.With the increase of depth,the pH of seawater first decreases rapidly,then rises slowly and then decreases.The decline rate of seawater from the surface to 500 m depth is the fastest.The pH of seawater rises slowly and then decreases from 500 m to 3000 m,but the change range of seawater pH decreases gradually with the increase of depth.4)The correlation between pH and carbon dioxide partial pressure,temperature,salinity,chlorophyll and dissolved oxygen was discussed from the seasonal and regional aspects.The main controlling factor affecting the seasonal and spatial distribution of seawater pH is carbon dioxide partial pressure,followed by temperature,salinity and dissolved oxygen.Chlorophyll has little effect on pH.Salinity has a negative correlation with pH and dissolved pressure,while it has a positive correlation with pH and dissolved pressure,and has a negative correlation with pH and dissolved pressure.