Analysis On Global Oceanic Dissolved Oxygen Based On A Comprehensive Dataset During 1960-2019

Most creatures in the ocean rely on oxygen to breathe,including higher plants and phytoplankton,which consume oxygen by respiration as well as producing oxygen by photosynthesis.Hypoxia in the ocean may pose a threat to many creatures and cause death.Marine creatures may also be indirectly affected by hypoxia,such as changes in their behavior,reproduction,and growth.According to existing research,deoxygenation is very common in many oceans,and it is reported that the global oceanic oxygen content has decreased by more than 2%.Dissolved oxygen in the ocean is of great significance to the whole marine ecosystem and is the key environmental factor to maintain steady state of the marine ecosystem.In recent years,people have begun to pay attention to the influence of oceanic dissolved oxygen.However,the related research and observation are insufficient.It is urgent to collate and explore observational data covering more time and space.Most existing analysis on dissolved oxygen focuses on regional data or specific depths instead of global dissolved oxygen in all depths.This paper integrates seven existing dissolved oxygen datasets:Southern Ocean dataset,Global Ocean data Analysis Project version 2(GLODAP v2)dataset,HydroBase 3 dataset,World Ocean Database 2018(WOD 18)dataset,OceanSITES dataset,Climate Variability and Predictability(CLIVAR)Carbon and Hydrographic Data Office(CCHDO)dataset and Argo dataset.They are used to obtain a new dissolved oxygen dataset with more comprehensive spatio-temporal coverage.The main research contents and conclusions of this paper are as follows:(1)After integrating and analyzing seven datasets,it is found that the data of WOD 18 dataset is the most comprehensive and complete.The dataset has been constantly updated,well maintained and supported to form a long-term data system.Although Argo data started relatively late and its observational data begun after 2000,it has great advantage from the point of view of future development.The observational data of the northern hemisphere is a little more than that of the southern hemisphere.This dataset covers dissolved oxygen data from 1960 to 2019,especially expands and updates the data during last decade,which is of great significance to the later research and analysis.(2)In this paper,the observational data are interpolated into the global ocean with fixed rank smoothing to obtain spatio-temporal distribution of dissolved oxygen in the upper and middle layers of the global ocean(0-1000 m).Furthermore,we analyse the spatio-temporal]change of minimum,median and maximum with quantile regression.The study indicates that the concentration of global dissolved oxygen in the upper and middle ocean increases with latitude.The main hypoxic regions are located in the eastern equatorial Pacific,the southeast of northern Pacific,the northeast of southern Pacific,the gulf of Mexico,the eastern and central part of equatorial Atlantic and the equatorial Indian Ocean.During 1960-2009,dissolved oxygen generally shows a downward trend,with the fastest decline in Arctic Ocean.However,dissolved oxygen in the sea near the western coast of South America increases,which may be affected by the change in the intensity of upwelling,Peruvian current.(3)On the basis of this new dataset,we study numerous vertical profiles to get the most typical and common form of profiles.The concentration of dissolved oxygen on the sea surface is more than 200 ?mol/kg,and then it gradually decreases to the minimum.Oxygen minimum zone is usually in depth of 100-1500 m.Then the concentration of dissolved oxygen gradually rises and keeps stable in depth deeper than 1000 m.The main configuration of profiles summarized is helpful for the follow-up study on the vertical state and change of dissolved oxygen.The main innovation of this paper is that under the background of the increase of dissolved oxygen observation and the improvement of data quality in recent 10 years,we integrate many datasets and add new data sources,especially the global dissolved oxygen data in last deacade.This is of great significance to the later research and analysis.In this paper,the variation of dissolved oxygen in the 0-1000 m global ocean is analyzed on the basis of the updated dataset,and the main morphology of the vertical profiles is summarized,which has not been discussed in previous study.In particular,the main morphology of profiles is helpful to understand the specific variation of dissolved oxygen in the vertical direction.