Dataset: Sulfur hexafluoride and rhodamine WT from a tracer release experiment in August 2022 in the Kāne'ohe Bay

We conducted tracer release experiments using SF₆ and a dye. We bubbled SF₆ into a 2-liter (L) plastic bottle that was half-filled with seawater from the bay. After adding 2 L of Rhodamine WT (20% solution) to a 20-L carboy, we filled the carboy with bay water and the SF₆-infused water. We gently released this tracer-enriched water into the Kāne'ohe Bay at the study site in the morning (~19:30 UTC; ~9:30 local time) from 15 to 19 August (year day (YD) 227 to 231) 2022.

We slowly traversed the tracer patch multiple times, collecting discrete water samples for SF₆ while continuously measuring Rhodamine WT within the patch. Following the procedures of Ho et al. (2000), we collected each SF₆ sample using a 50 milliliter (mL) glass syringe, with 30 mL of water drawn into the syringe. We submerged the syringes in a water-filled cooler for later measurements in the laboratory. We collected ~4 discrete SF₆ samples during each transect. We measured Rhodamine WT every 5 seconds using a YSI EXO1 sonde with a Rhodamine sensor. The sensor has a detection range of 0 to 1,000 micrograms per liter (μg L⁻¹), with an accuracy of 0.1 μg L⁻¹. We recorded data from the Rhodamine sensor using a GPS-equipped computer to track the precise time and location of each measurement. Sampling continued until the tracer patch exited the area of interest (~5 hours).

In the laboratory, we created a headspace in each syringe with UHP nitrogen gas (N₂) and shook each one for at least 3 minutes to achieve equilibration. After equilibration, we injected the sample gas into a sample loop, using magnesium perchlorate (Mg(ClO₄)₂) to remove water vapor. We then transferred the loop contents to a mol sieve 5A column at 60 degrees Celsius (°C) to separate SF₆ and other gases, and measured SF₆ concentrations using a gas chromatograph equipped with an electron capture detector (GC-ECD; Shimadzu GC-8A). Measurement reproducibility was within 4%.