A new statistical approach for interpreting oceanic fCO(2) data

作者：Wang Hongjie; Sterba Boatwright Blair; Hu Xinping

来源：Marine Chemistry, 2016, 183: 41-49.

DOI：10.1016/j.marchem.2016.05.007

• Surface ocean fCO(2)
• Ocean margin
• Generalized Additive Mixed Modeling
• Heteroscedasticity

Surface ocean CO2 fugacity ((CO2) often exhibits large fluctuations and heterogeneity because of multiple controlling factors that pose a challenge for trend analysis, especially in the ocean margins. We propose a new statistical approach, Generalized Additive Mixed Modeling (GAMM), to interpret oceanic fCO(2) data in two ocean margins (Japan and Europe) and two open ocean areas. The latter included areas near the Hawaii Ocean Time-series (HOT) and the Bermuda Atlantic Time-series (BATS). This method utilizes day of year, sea surface salinity (SSS), sea surface temperature (SST), and sampling date as predictors. Using this method, we were able to derive multidecadal fCO(2) trends with both improved precision and greater robustness to data gaps compared to an existing deseasonalization method used in the open ocean. The fCO(2) trend derived by our method for the Japanese margin (1992-2013), the European margin (1989-2014), and the open ocean near HOT (1983-2013) were 2.1 +/- 0.6, 1.9 +/- 0.7, and 2.0 +/- 0.5 mu atm year(-1) (mean +/- standard deviation of multiple 1 degrees x 1 degrees grids in margins and 5 degrees x 5 degrees grids in open ocean), respectively, and the fCO(2) trends were all close to the atmosphere CO2 trend (1.7-1.9 mu atm year(-1)). Our analysis produced generally smaller standard errors (paired t-test, p << 0.001) than those obtained using the existing method based on the same dataset. In addition, our method was less sensitive to data gaps compared to this existing method. However, for regularly spaced fCO(2) times-series data, for example, discrete bottle data collected in the BATS station in 1991-2011, this method was not advantageous over the existing method (1.9 +/- 02 vs. 2.0 +/- 0.2 mu atm year(-1)) To test the broader applicability of this method, we compared fCO(2) trends in the Southern Ocean derived using our method with those from a recently reported Markov Chain Monte Carlo method and found no significant difference between the two sets of values. Therefore, we recommend the application of our method in interpreting fCO(2) data in different oceanic environments.

• 出版日期2016-7-20