Water column samples were collected by Niskin bottle on a CTD rosette in the Argo basin in the Eastern Indian Ocean/Indonesian throughflow (NW of Australia) on board the R/V Roger Revelle during cruise RR2201 (BLOOFINZ-IO). Samples were collected between February 4th, 2022 and March 2n,d 2022.

14C net primary productivity:
Production measurements were made during quasi‐Lagrangian experiments conducted during RR2201. Samples for net primary productivity, using 14C radio-labeled bicarbonate, were measured in in-situ drift array setups. Four (4) quasi‐Lagrangian experiments (hereafter "cycles") were conducted, during which the cruise track followed a satellite‐tracked Lagrangian drifter (Kranz et al. 2020). Each cycle was initiated during the evening hours by deploying a sediment trap array followed by an array used for in-situ incubations such as 14C primary productivity (Landry et al., 2012; Stukel et al., 2013). Both arrays had a 3 × 1-meter (m) holey sock drogue centered at 15‐m depth in the surface mixed layer.

14C net primary production (NPP14C) was quantified for each day of a cycle at up to six depths spanning the euphotic zone. CTD Niskin bottles from a 2:00 AM (local time) CTD cast were sampled. About 280 milliliters (ml) of seawater from each depth were gently transferred to polycarbonate incubation bottles (triplicate bottles plus a dark bottle) using silicon tubing. Samples were then spiked with H14CO3 and incubated for 24 hours in mesh bags hung below the drift array. Incubations were started and terminated at ~04:00 AM local time (prior to sunrise). NPP14C samples were then filtered onto GF/filters, acidified for 24 hours with 0.5 ml of 10% biological grade HCl, placed in scintillation cocktail, and subsequently counted using a liquid scintillation counter (details in Morrow et al., 2018). Samples were counted after 24 hours and ~3 weeks. Total counts of the radioactivity spiked was measured by pipetting 250 microliters (ul) of the incubated seawater directly into ethanolamide and topped off with scintillation liquid. Total DIC was estimated based on average literature values.