[Journal of Geophysical Research: Oceans] Supporting Information for Changes in anthropogenic carbon storage in the Northeast Pacific in the last decade Sophie N Chu1,2, Zhaohui Aleck Wang2*, Scott C Doney2, Gareth L Lawson3, and Katherine A Hoering2 Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography/Applied Ocean Science and Engineering, 77 Massachusetts Avenue, Cambridge, MA 02139, USA Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA Biology Department, Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA *Corresponding author: Zhaohui Aleck Wang, zawang@whoi.edu Contents of this file Text S1 Figures S1 to S2 Introduction The supporting information provides Text and Figures Text S1 presents the sample analysis procedures for dissolved oxygen and salinity samples Figure S1 presents the deep crossover analyses used to correct the offsets of various parameters between 2001 and 2012 P17N cruises Figure S2 presents the multiple linear regression residuals for the 2012 P17N cruise Text S1 Sample analysis procedures for dissolved oxygen and salinity Dissolved oxygen (DO) samples were collected from CTD Niskin bottles into 150 mL brown glass tincture bottles Sodium iodide-sodium hydroxide mixture and manganese chloride were added sequentially to the sample immediately after collection and mixed thoroughly One mL of sulfuric acid was added and mixed into the sample prior to measurement DO samples were measured after temperature equilibration, within days, on an automated dissolved oxygen titrator developed at Woods Hole Oceanographic Institution [Knapp et al 1990] The system is based on the Winkler technique This method has an accuracy of 1.0 μmol kg -1 and precision of 0.2 μmol kg-1 The titrator was standardized with sodium thiosulfate for each group of analyses, usually about 30 samples A custom procedure was developed and implemented to detect concentrations of dissolved oxygen < 90 μmol kg -1 In situ temperature was used to calculate potential density in order to convert from mL L -1 to μmol kg-1 for bottle samples Ideally, the conversion temperature should be the temperature measured at the time of sample drawing, but those were not measured Bottle values were used to calibrate CTD values Salinity samples were collected into 250 mL square cross-sectioned, borosilicate glass bottles and measured on an Autosal Salinometer (Guildline 8400B) PSS-78 salinity was calculated from measured conductivity ratios Measurements were performed after samples had equilibrated to laboratory temperature, within days after collection The machine was standardized for each group of analyses, approximately 50 samples International Association for the Physical Sciences of the Oceans (IAPSO) Standard Seawater Batch P-152 was used for standardization This method has an accuracy of ±0.003 and precision of ± 0.0002 Bottle analyses were used to calibrate CTD salinity values Figure S1 Deep isopycnal crossover analyses were used to correct systematic offsets between different cruise occupations of similar locations Results from the analysis are shown in Table in the main paper Data from >2000 m for CLIVAR 2001 (red) and NH1208 2012 (blue) was plotted against potential density referenced to 3000 dbar (σ3) and fit by a second-order polynomial If an offset was found, NH1208 2012 cruise data was corrected to the CLIVAR 2001 data The corrected data is plotted in green a) salinity vs σ3 b) phosphate vs σ3 c) nitrate vs σ3 d) silicate vs σ3 e) dissolved oxygen vs σ3 f) dissolved inorganic carbon vs σ3 g) total alkalinity vs σ3 a 34.67 CLIVAR 2001 NH1208 2012 Salinity[PSS] 34.65 34.63 34.61 34.59 34.57 41.33 41.38 σ3[kgm-3] 41.43 41.48 Phosphate[μmol kg-1] b 3.2 CLIVAR 2001 3.1 NH1208 2012 NH1208 2012 corrected 2.9 2.8 2.7 2.6 2.5 41.33 41.38 41.43 σ3 41.48 [kgm-3] c 45 CLIVAR 2001 44 NH1208 2012 Nitrate[μmol kg-1] 43 42 41 40 39 38 37 36 41.33 41.38 σ3[kgm-3] 41.43 41.48 d 190 CLIVAR 2001 185 NH1208 2012 Silicate[μmol kg-1] 180 NH1208 2012 corrected 175 170 165 160 155 150 145 140 41.33 41.38 σ3[kgm-3] 41.43 41.48 41.43 41.48 Dissolvedoxygen[μmol kg-1] e 120 CLIVAR 2001 110 NH1208 2012 100 NH1208 2012 corrected 90 80 70 60 50 40 41.33 41.38 σ3[kgm-3] DissolvedInorganicCarbon[μmol kg-1] f 2400 CLIVAR 2001 2390 NH1208 2012 2380 NH1208 2012 corrected 2370 2360 2350 2340 2330 2320 41.33 41.38 σ3[kgm-3] 41.43 41.48 g 2460 Total alkalinity[μmol kg-1] 2450 2440 CLIVAR 2001 NH1208 2012 NH1208 2012 corrected 2430 2420 2410 2400 2390 41.33 41.38 σ3[kgm-3] 41.43 41.48 Figure S2 Residuals between the DIC MLR model and measured values from the 2012 NH1208 cruise plotted against potential density, latitude, and depth show no significant trends, confirming that binning the dataset by potential density or latitude would not affect MLR results ... Residuals between the DIC MLR model and measured values from the 2012 NH1208 cruise plotted against potential density, latitude, and depth show no significant trends, confirming that binning the dataset... corrected to the CLIVAR 2001 data The corrected data is plotted in green a) salinity vs σ3 b) phosphate vs σ3 c) nitrate vs σ3 d) silicate vs σ3 e) dissolved oxygen vs σ3 f) dissolved inorganic carbon. .. within days after collection The machine was standardized for each group of analyses, approximately 50 samples International Association for the Physical Sciences of the Oceans (IAPSO) Standard