1. 18 at 203 25?) was used, with an accuracy of �0.01. The 204 headspace bottle method was used to collect CO 2 205 and CH4 gases in 200 mL gas bags. In the 206 laboratory, the water samples to be tested were 207 filtered through a Whatman GF-F membrane with 208 a diameter of 47 mm and a pore size of 0.45 ?m. 209 After filtration, 100 mL of the filtrate was taken 210 and divided into 50 mL portions for measuring 211 DIC isotopes and content. DIC was determined 212 using a DIC analyzer (AS-C2, Apollo SciTech, 213 USA), and internationally recognized CRMs 214 standard seawater produced by the Scripps 215 Institution of Oceanography, USA, was used for 216 quality control. The precision of duplicate 217 measurements of standard substances was better 218 than 0.1%, and the measurement error of parallel 219 samples was mostly less than 0.05�. The in-situ 220 CO2 partial pressure (pCO2) of the water was 221 calculated using the CO2SYS software, a 222 commonly used carbonate system calculation 223 software;Ohio Spring;The NBS scale (4.00, 6.86, and 9,2015