Sea Level Budgets And Deep Ocean Warming Based On Satellite Gravity,Altimetry And Temperature-Salinity Data

Ocean absorbs most of the excess heat generated by man-made greenhouse gas emissions,which is an important regulator of global climate change.In recent decades,the accelerated warming of the ocean has had a series of adverse effects on the earth’s climate system and human life.Due to the scarcity of direct observational data in the deep ocean,our understanding of ocean warming is mostly limited to the upper 2000m.Whether the excess heat absorbed by the ocean penetrates the deep ocean has always been one of the most challenging issues in the field of global change.Studying the laws and causes of sea level changes and detecting unknown changes in the deep ocean are of great significance for future climate change predictions and the sustainable development of mankind.With the continuous development of space geodetic technology such as satellite gravity and satellite altimetry,the gradual maturity of the Argo buoy observation network has provided new ideas for the study of deep warming.Combining multi-source spatial geodetic data and ocean data,it is possible to quantitatively study the laws and causes of sea level changes,and it is expected to detect changes in the deep sea that are not covered by data.In the thesis,we fist introduces the background and current situation of deep warming research,and then systematically expounds the method of studying deep steric sea level and ocean heat content changes based on satellite altimetry,satellite gravity and ocean temperature and salinity data.Based on these,we studied sea level budget and deep warming on the global oceans,the four ocean basins,the global coastal region,the coastal of China seas,as well as some sub-basin-scale regions.The thesis mainly includes the research progress in the following aspects:(1)Sea-level budget and deep warming on global and basin scalesWe quantitatively analyzed the sea-level change on global and basin-scales by using multiple sets of satellite altimetry,satellite gravity,and temperature and salinity products.we found that the sea level budget on global and basin scales is closed from 2005 to 2015,which means that deep ocean warming or cooling is not significant under the current observation accuracy.However,the global and Atlantic sea-level budget from 2005 to 2019 are not close significantly.The main reason was the systematic deviation of global salinity data after 2016.The Argo salinity drift after 2016 is global and has the most significant impact on the Atlantic sea level budget.If the global and ocean basin-scale salinity data are corrected,the sea-level budget can be closed on basin scales,but the global-scale sea-level budget is still not closed,which may be due to systematic deviation between GRACE and GRACE-FO.(2)Sea-level budget and deep warming on sub-basin scalesThe regional deep steric sea level changes are usually far exceeded the global and basin scale average.From 2005 to 2015,the indirect method based on "Alt.-Argo-GRACE" detected the deep steric sea level changes in the central and eastern Indian Ocean,the subtropical southwest Pacific,and the northeast Atlantic,while increase and decrease in the Northwest Atlantic.GO-SHIP repeated hydrological observations confirmed these significant deep steric changes,and the steric sea level changes have the same sign as the thermosteric sea level change.However,due to the large discrepancy in temporal and spatial domain between the two methods,the steric trends estimated by the indirect method exceed that from the CTD observations.Therefore,indirect methods based on satellite altimetry,satellite gravity,and upper ocean temperature and salt data can be used to detect deep warming qualitatively,but it is difficult to quantitatively estimate the temperature change of the deep ocean.(3)Coastal sea level budget and deep warmingThe global coastal mean sea level budget is closed from 2005 to 2015,which means that the global coastal deep warming or cooling is not significant.However,the coastal sea level budget is not closed since 2016.The main reason is that the salinity data has drifted after 2016.When the salinity data was revised,the global coastal sea level budget remained closed.China sea level budget is closed from 2005 to 2019.The trend of sea level change is dominated by ocean mass change,while the interannual changes are dominated by steric sea level changes.Sea level budget of the East China Sea and the Yellow Sea are closed,while Sea level budget of the South China Sea and Bohai have significant systematic deviations.This deviation may be due to the low accuracy of altimetry in the coastal regions,the large uncertainty of the temperature and salinity data of ocean models and reanalysis products,and GRACE suffers from leakage errors and GIA effects in small-scale coastal areas.