Estimation Of Weathering Carbon Sinks In Global Carbonate And Silicate Rocks

Accurate estimation of the magnitude of weathering carbon sinks in continental rocks is of great significance for balancing global carbon budgets.In view of the existing research,the hydrochem-discharge method that is suitable for the estimation of weathering carbon sinks in carbonate rock has not been successfully used in the calculation of global grid scales.The study of long-term chemical weathering carbon sinks in global silicate rocks?CSS?is slightly inadequate.The spatiotemporal evolution trends of CSS are not clear,and the methods of excluding carbonate influences in the estimation of CSS have not been effectively improved.Based on the global major lithological data,hydro-chemical data,and spatial data of main factors?precipitation?P?,runoff?q?,actual evapotranspiration?ET?and soil moisture?SM?,etc.?,using the hydrochem-discharge method,random forest algorithm,forward model,FHCO₃^--RCO₂ model,physical erosion flux model,and West model,this study estimated the weathering carbon sinks of carbonate rocks in major watersheds and extended them to the global spatial grid scale.And from 1992 to 2014,the global weathering cationic carbon sinks and actual weathering carbon sinks of silicate rocks?granite and basalt?were estimated.The weathering carbon sinks of carbonate rocks and weathering carbon sinks of silicate rocks were compared and analyzed.Their spatial distribution patterns and evolution trends at the different scales?grid cell,K?ppen climate types,different continents,countries,and regions scales?were revealed.The main conclusions were as follows:?1?The total amount of carbon sinks of carbonate rock weathering?Tcarb?in the main watershed was 0.12Pg C yr^-1,and the flux?Fcarb?was about 2.16 t km^-2 yr^-1.Tcarb in tropical and warm temperate zones accounted for 62.95%of the main river basins.There were nine critical zones in the longitude and latitude distributions of Fcarb.The average value of Fcarb in the karst outcropping river basins was about three times the average value of Fcarb in the non-karst river basins.?2?q and bicarbonate ion flux?FHCO₃^-?in carbonate rock areas were on the rise.During the study period,the value of Fcarb of weathering carbon sinks in global carbonate rocks was 4.41t km^-2 yr^-1,and the total amount was about 0.1Pg C yr^-1,showing a slight upward trend(5.0×10^-4yr^-1).The value(6.06t km^-2 yr^-1)of Fcarb of warm temperate in the K?ppen climate was slightly higher than the value of Fcarb of tropical(5.85 t km^-2yr^-1).In terms of spatial distribution,Fcarb had two types of changes that were extremely significant increase and extremely significant decrease.The significantly decreased area?59.35%?was slightly higher than the significantly increased area?40.65%?.?3?The average value of global bicarbonate ion flux?FHCO₃^-?from1992 to 2014 was 3.71 t km^-2 yr^-1,and THCO₃^-could reach 0.67Pg C yr^-1,showing an overall upward trend(2.5×10^-3 yr^-1).Although the area increased in spatial change was slightly smaller than the area reduced,the degree of change was about 1.24 times that of the reduced area.Asia's THCO₃^-value accounted for about 30.43%of the world,while Oceania FHCO₃^-(6.20 t km^-22 yr^-1)ranks first among all continents.The latitude distribution of global FHCO₃^-had a similar distribution trend with q,ET and P.FHCO₃^-in basalt area was slightly lower than that in granite area as a whole.?4?The global average physical erosion flux?E?was 204.49 t km^-2 yr^-1,and the average thickness was 7.57 cm ka^-1,showing a rising trend of fluctuation(about 0.26yr^-1).The physical erosion flux of basalt(388.19t km^-2 yr^-1)was slightly higher than the physical erosion flux of granite(379.51 t km^-22 yr^-1).The physical erosion flux in more than two thirds?69.32%?of the world was between 10-500 t km^-2 yr^-1.84.65%of the world's regions were basically stable,but there were 5.15%extremely significant increase regions,and the significantly increased regions were often distributed at the edges of the extremely significantly increased regions.The value of FHCO₃^-in basalt area was slightly lower than that in granite area.?5?The global total amount of weathering cationic carbon sinks of granite?Tcat_gra?was about 32.46Tg C yr^-1,and it showed a slow upward trend(4.8×10^-3 yr^-1).The total amount of weathering carbon sinks from granite cations in Asia ranked first in all continents?36.92%?.There was a significant correlation between E and Fcat_gra flux?R²=0.96?.The flux of actual weathering carbon sinks in global granite was about 2.35 t km^-2yr^-1,and the flux of weathering carbon sinks of about 3/4 of the granite area showed a significant increase trend.The total amount of actual weathering carbon sinks of granite from five countries?Canada,Brazil,Russia,China,and the United States?accounted for 55.15%of the world.?6?The total amount of weathering cationic carbon sinks of basalt?Tcat_bas?was 31.53Tg C yr^-1,showing a downward trend(-0.03 yr^-1)as a whole,and the range of its value range(28.80-34.47Pg C yr^-1)was about Tcat_gra 2.3 times.The correlation between q and Fcat_bas flux in the basalt region?R²=0.72?was much greater than in the granitic region.The actual weathering carbon sinks flux of basalt was about 4.08 t km^-2 yr^-1,and it also showed a slight downward trend(-3×10^-3 yr^-1),with the largest annual variation of 0.35 t km^-2 yr^-1.It was about 70.32%of the flux of the weathering carbon sinks in the basalt region shows a significant increase.The total amount of rock weathering carbon sinks?carbonate and silicate rocks?estimated recently in this study accounted for about 32%of the total amount of terrestrial carbon sinks in the world.This indicated that the weathering carbon sink of rocks,especially the weathering carbon sink of carbonate rocks with fast chemical weathering rate,might play an important role in balancing the global carbon budget.Therefore,this work will have a certain reference value for the global carbon budget,and for the global carbon cycle and climate change research.