Distribution And Genesis Of Stable Hydrogen And Oxygen Isotopes In Global Ocean Surface Waters

Hydrogen and oxygen are constituent elements of water molecule（H₂O）,and like salinity,the hydrogen and oxygen stable isotope ratios(δ¹⁸O andδD)of water are effective tracers of water bodies.The spatial distribution characteristics of seawater hydrogen and oxygen stable isotope ratio and its relationship with salinity can effectively trace modern ocean physical processes（precipitation and evaporation,sea ice formation and melting,river runoff,advection,upwelling and seawater mixing）.Due to the limitation of scientific investigation,the measured values of stable isotope ratio of hydrogen and oxygen can only be used to study the ocean physical processes in local areas,but not in a wide range.In this study,the spatial distribution characteristics and influencing factors of stable hydrogen and oxygen isotope ratios of surface sea water were revealed based on the measured values of stable hydrogen and oxygen isotope ratios of surface sea water in different regions of global oceans.The results are as follows:（1）The spatial distribution characteristics of hydrogen and oxygen stable isotope ratio of global ocean surface water was obtained by selecting data of 15m as surface water data.The spatial distribution ofδ¹⁸O andδD of global ocean surface waters is consistent and decreases with increasing latitude.Theδ¹⁸O andδD of river surface waters are obviously poorer than that of open oceans.Theδ¹⁸O andδD of surface sea water are more abundant than those near the equator.Theδ¹⁸O andδD of surface sea water in the northern and Southern hemispheres are not symmetrically distributed due to the location of sea and land in the southern and northern hemispheres and the runoff of continental rivers.Theδ¹⁸O andδD of surface sea water in the northern hemispheres is larger than that in the southern hemispheres.（2）The global ocean is divided into the Pacific Ocean,The Indian Ocean,the Atlantic Ocean,the Arctic Ocean and the Southern Ocean to represent the spatial distribution characteristics of surface waterδ¹⁸O andδD in different oceans.Theδ¹⁸O andδD of surface sea water in the Pacific presents a"double peak"distribution,and theδ¹⁸O andδD of surface sea water in the Subtropical region of the South Pacific are the most abundant.Theδ¹⁸O of surface sea water in the Indian Ocean is small,but theδ¹⁸O of surface sea water in the Western Indian Ocean is enriched in the eastern Indian Ocean,and theδD of surface sea water in the Indian Ocean increases from the northern ocean to the Southern Ocean.The distribution ofδ¹⁸O andδD in the Surface waters of the Atlantic Ocean is"double peak",and the range ofδ¹⁸O andδD in the surface waters of the North Atlantic Ocean is larger than that in the South Atlantic Ocean.Hydrogen and oxygen stable isotope ratios are most abundant in subtropical seas and Mediterranean Sea surface waters,while depleted in northern North Atlantic Sea surface waters.Theδ¹⁸O andδD of surface sea water in the Arctic Ocean are the most depleted in the world,and the"zonal distribution"is not obvious.Theδ¹⁸O andδD of surface sea water in the Southern Ocean are depleted,and the"zonal distribution"is not obvious.Theδ¹⁸O andδD of surface sea water increase from the coastal to the north due to the influence of ice and snow meltwater.（3）Correlation analysis ofδ¹⁸O-δD,δ¹⁸O-S andδD-S in surface seawater was conducted to determine the influence of precipitation and evaporation on the ratio of stable hydrogen and oxygen isotopes in surface seawater.The slopes ofδ¹⁸O-S,δD-S andδ¹⁸O-δD in surface waters of the Pacific,Indian and Atlantic oceans are lower than those of the global oceans,indicating that evaporation in these three oceans is relatively obvious.The slopes ofδ¹⁸O-S,δD-S andδ¹⁸O-δD in the surface waters of the Arctic Ocean and the Southern Ocean are higher than those of the global ocean,indicating that evaporation is weak in the Southern Ocean and the Arctic Ocean.The lack of precipitation in the polar regions may be due to the influence of sea ice melt water and continental glacier melt water.Based on theδ¹⁸O-S relationship between the Amazon Continental shelf and the Guayaquil Bay,and combined with the spatial distribution characteristics ofδ¹⁸O,the influence of runoff on the stable isotope ratio of hydrogen and oxygen in the surface seawater was analyzed.With the increase of the distance from the shore,the influence of river runoff gradually decreases.In addition,the influence of high river runoff on seawater is larger and wider than that of low river runoff.Based on the ternary mixing model（Atlantic water,river water and sea ice melt water）,the effects of sea ice freezing and melting on the stable isotopes of hydrogen and oxygen in surface seawater are determined.The melting water ratio of sea ice is less than 0,indicating the effect of sea ice freezing onδ¹⁸O of surface sea water.According to the spatial distribution characteristics of sea ice melt water ratio,it is concluded that the coastal and northern part of Laptev Sea are affected by sea ice melt water,and the central part is affected by sea ice freezing.Based on the term-mixing model,the mixing ratio of surface water in the Laptev Sea is calculated.The results show that the mixing ratio of Atlantic deep water is81.36%,river water is 26.5%,and sea ice meltwater is-0.83%.According to the spatial distribution characteristics ofδ¹⁸O and salinity of Atlantic deep water ratio,river water ratio and sea ice melt water ratio of raptev’s surface sea water,it is concluded that theδ¹⁸O and salinity of surface sea water are higher when Atlantic deep water is dominant,and lower when river water is dominant.It shows that when water masses mix,the surface water will show the hydrologic characteristics of which water masses are in greater proportion.