Dataset: Size fractionated organic carbon and 13C at Bermuda Atlantic Time Series (BATS) from samples collected on R/V Atlantic Explorer cruise AE1920 in August 2019

For size fractionated suspended particulate organic matter in August 2019, samples were obtained from Niskin bottles but were collected by opening the bottom of the Niskin bottle into an acid cleaned bucket. This ensured that particles that had sunk below the spigot of the Niskin bottle were included. 120 liters (L) of water was gravity filtered, in sequence, through nylon mesh (142-millimeter (mm) diameter) of decreasing pore size (500, 180, 53, 20 micrometers (µm)) and a subset of this 20 µm filtered water (~20 L) was then filtered through a 5 µm mesh. For mesh sizes 20 µm and above, the large diameter of the mesh and abundance of functional pore-space prevented clogging, and water flowed through the mesh quickly, indicating that clogging did not occur. Water filtered more slowly through the 5 µm mesh (on the order of 30 minutes). After filtration, each nylon mesh was back-rinsed with ~500 milliliters (mL) of prefiltered 60 kd filtered seawater to produce a resuspension of particulate matter from particles from each size class. The 60 kd filtered seawater had been produced by tangential flow filtration as a byproduct of virus isolation experiments on the same cruise. After back-rinsing, the resuspended particles were split with one half used for particulate matter measurements. In all cases, the actual volumes were carefully recorded and used for normalization during analysis. The resuspended particulate matter from each sample and size class was collected by vacuum filtration through a 1.2 µm nominal pore size, 25 mm diameter, GF/C glass fiber filter (Whatman WHA1822025). These filters had been previously pre-combusted for at least two hours at 400 degrees Celsius (°C). Two depths were sampled per cast, and multiple casts were combined to represent the station. Samples were immediately frozen.

At Horn Point, samples were dried at 40°C and stored in a desiccator. For processing, they were wafted with HCl overnight to remove carbonate, dried at 40°C, packed in both silver and tin capsules, and sent to the UC Davis Stable Isotope Facility for C and N analysis utilizing an Elemental Analyzer (Elementar Vario EL Cube) attached to an Isotope Ratio Mass Spectrometer (Isoprime VisION). Blank combusted GF/C filters were included in analyses and did not show measurable material.

For the 90-meter (m) sample, the entire Niskin rosette was fired at the same depth. Particles were fractionated for both size and sinking. In this case, the CTD sat on deck for one hour while the particles were allowed to settle. After one hour, the top ⅔ of each Niskin bottle were siphoned off and saved. Then the bottom ⅓ of each bottle was collected by opening the bottom of the Niskin bottle into an acid-cleaned bucket. The upper and lower fractions were then filtered using the size fractionation method described above.