Dataset: DIC and TA sediment fluxes 2017-2018
Deployment: PE18-19

At each site during the R/V Pelican cruises, a box corer was used to collect surface sediment. The box core was subsampled in triplicate using 40 cm acrylic tubes that were pushed into the sediment to refusal, i.e. 20-30 cm. Cores were extracted in the acrylic tubes, capped on the bottom with an acrylic cap and o-ring, and submerged in a dark incubator filled with bottom water collected at the site. Each core was carefully filled with in situ near bottom water with minimum disturbance to the sediment-water interface and closed to ensure no visible headspace or air bubbles at the top. The submerged cores were allowed to equilibrate with the water in the incubator for 12 hours. A control was included that was an acrylic liner filled with bottom water only. Following this equilibration step, the cores were capped on their tops with an acrylic cap and o-ring. The top caps contained two sampling ports that were opened to collect water samples from the water overlying the sediments in the core tubes. The overlying water was mixed by a slowly turning magnetic stir bar suspended from the top cap. All cores were attached to a reservoir containing bottom water for gravity driven replenishment of water inside the core tubes during sampling. After capping, sampling commenced. 

Samples for DIC were taken every 4-8 hours for up to 23 hours (4-6 time points) from the four cores, i.e. one control core with bottom water only (identified as ‘Control’)  and three cores with sediments and bottom water (identified as ‘Rep1’, ‘Rep2’, and ‘Rep3’).  Dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations were analyzed in each sample by Wei Jun Cai’s lab at the University of Delaware. For DIC, 1 ml of water sample was measured in triplicate with an infrared CO2 detector-based DIC analyzer (AS-C3 Apollo Scitech). For TA, a 25 ml water sample was measured in duplicate with the open-cell Gran titration method using a temperature-controlled, semi-automated titrator (AS-ALK2 Apollo Scitech). Certified Reference Materials provided by A. G. Dickson, Scripps Institution of Oceanography, were analyzed for DIC and TA for quality control. 

Detailed methods are provided in Wang et al. (2020) and Lehrter et al. (2012).  

Problem report:  Data for a few time points are missing due to lost or broken sample containers.  For 1801 C6, there is missing data, so assumed depths are presented based on the depths similar to the last sampling on cruise 1710 C6-2.