DOI: 10.5061/dryad.fbg79cnvp
title: Data for contribution of marine phytoplankton and bacteria to ocean alkalinity

description: The contributions of phytoplankton and bacteria cells to alkalinity (AT)
 were measured in seawater samples obtained from 205 locations including
 the East Sea, the North Pacific Ocean, the Bering Sea, the Chukchi Sea,
 and the Arctic Ocean. We attributed the differences in AT values measured
 for unfiltered versus filtered samples to AT components contributed by
 phytoplankton (retained on a 0.7 µm filter) and by phytoplankton and
 bacteria combined (AT-BIO; retained on a 0.45 µm filter). The AT-BIO
 values reached 10-19 μmol kg-1 in the East Sea and the North Pacific
 Ocean, and progressively decreased to a level of 1 μmol kg-1 with distance
 towards the Arctic Ocean. The study shows that the AT-BIO values are
 non-negligible in coastal and open ocean environments and need to be
 considered when assessing the accuracy of carbon parameters calculated
 using the thermodynamic models that use measured AT as an input parameter.
description: <strong>Sampling locations</strong>
 Sampling was carried out on board the R/V ARAON during the study
 from 17 July 2020 to 15 September 2020. The sampling locations were
 approximately evenly spaced along a transect from the East Sea to the
 North Pacific Ocean, the Bering Sea, the Chukchi Sea, and the Arctic
 Ocean. A total of 205 surface seawater samples were collected in 4-L
 polycarbonate bottles from the underway clean seawater line. To obtain
 depth profiles, a total 24 discrete samples were collected in 1-L high
 density polyethylene bottles using a rosette sampler (SeaBird Electronics,
 SBE 911 plus) at two sites (76.003ºN, 170.588ºW; 74.499ºN, 162.262ºW) in
 the Arctic Ocean. <strong>Determination of
 A<sub>T</sub>, A<sub>T-BIO</sub>,
 A<sub>T-PLANKTON</sub>, and
 A<sub>T-BACTERIA</sub></strong>
 For each seawater
 sample the A<sub style="text-indent:24pt;">T</sub> values of an unfiltered and a
 filtered (0.7 μm and 0.45 μm) sample were measured within 12 h of
 collection. The total contribution of all biogenic particles to the
 A<sub style="text-indent:24pt;">T</sub> of the unfiltered seawater
 (A<sub style="text-indent:24pt;">T</sub><sub style="text-indent:24pt;">-</sub><sub style="text-indent:24pt;">BIO</sub>; Equation 2) was determined as the
 difference between the measured A<sub style="text-indent:24pt;">T</sub> values of the unfiltered sample
 and the 0.45 μm-filtered sample, followed by subtraction of the
 CaCO<sub style="text-indent:24pt;">3</sub> contribution
 (A<sub style="text-indent:24pt;">T</sub><sub style="text-indent:24pt;">-</sub><sub style="text-indent:24pt;">PIC</sub>), which was calculated from the
 particulate inorganic carbon (PIC) concentration determined as described
 in Text S1. In this calculation we assumed that the particulate matter
 contribution to A<sub style="text-indent:24pt;">T</sub> mostly comprised phytoplankton and
 bacteria cells, and CaCO<sub style="text-indent:24pt;">3</sub> shells. The contribution of
 phytoplankton cells to A<sub style="text-indent:24pt;">T</sub> (A<sub style="text-indent:24pt;">T</sub><sub style="text-indent:24pt;">-</sub><sub style="text-indent:24pt;">PLANKTON</sub>; Equation 3) was determined as the
 difference in measured A<sub style="text-indent:24pt;">T</sub> between the unfiltered sample and
 the 0.7 μm-filtered sample, followed by subtraction of
 A<sub style="text-indent:24pt;">T</sub><sub style="text-indent:24pt;">-</sub><sub style="text-indent:24pt;">PIC</sub>. The contribution of bacteria
 (A<sub style="text-indent:24pt;">T</sub><sub style="text-indent:24pt;">-</sub><sub style="text-indent:24pt;">BACTERIA</sub>; Equation 4) was determined by
 calculating the difference in measured A<sub style="text-indent:24pt;">T</sub> values between the 0.7 μm-filtered
 sample and the 0.45 μm-filtered sample.
          
 A<sub>T</sub><sub>-</sub><sub>BIO</sub> = A<sub>T</sub><sub>-</sub><sub>PLANKTON </sub>+ A<sub>T</sub><sub>-</sub><sub>BACTERIA</sub> = A<sub>T</sub><sub>-</sub><sub>unfiltered</sub> – A<sub>T</sub><sub>-</sub><sub>0.45 </sub><sub>μm-filtered</sub> – A<sub>T</sub><sub>-</sub><sub>PIC</sub>      (2)           A<sub>T</sub><sub>-</sub><sub>PLANKTON</sub> = A<sub>T</sub><sub>-</sub><sub>unfiltered</sub> – A<sub>T</sub><sub>-</sub><sub>0.7 </sub><sub>μm-filtered</sub> – A<sub>T</sub><sub>-</sub><sub>PIC</sub>                                      (3)           A<sub>T</sub><sub>-</sub><sub>BACTERIA</sub> = A<sub>T</sub><sub>-</sub><sub> </sub><sub>0.7 </sub><sub>μm-filtered</sub> – A<sub>T</sub><sub>-</sub><sub>0.45 </sub><sub>μm-filtered</sub>                                           (4) The precisions of measurements for three biological A<sub>T </sub>components were estimated from the root sum square of the standard deviations of all parameters involved ( ; see those relevant parameters in Equations 2, 3, 4, and Text S2) and were found to be 1.1 μmol kg<sup>-</sup><sup>1</sup> for A<sub>T</sub><sub>-</sub><sub>BIO</sub>, A<sub>T</sub><sub>-</sub><sub>PLANKTON</sub>, and A<sub>T</sub><sub>-</sub><sub>BACTERIA</sub>. Note that the A<sub>T</sub><sub>-</sub><sub>PIC</sub> component was not considered in the estimation of the precisions for A<sub>T</sub><sub>-</sub><sub>BIO </sub>and A<sub>T</sub><sub>-</sub><sub>PLANKTON </sub>because measurable PIC values were found only for 6 of the 205 samples. For more details, see the methods section in the manuscript "Contribution of marine phytoplankton and bacteria to ocean alkalinity: an uncharacterized component".