Dataset: Oxygen, carbon, and 13C values from the deep-sea incubator (DSI) and parallel laboratory incubations with mesopelagic water from the same region and depth on May 12, 2023

Cruise/Deployment Information:
Field samples were obtained using R/V Fay Slover (Ocean & Earth Sciences, Old Dominion University).
Deployment date of Deep-Sea Incubator: 2023-05-12
Retrieval date of Deep-Sea Incubator: 2023-05-16
Location: Continental shelf break off Virginia Beach, Virginia, USA
Chief scientist: Alexander B. Bochdansky, Ocean & Earth Sciences, Old Dominion University, abochdan@odu.edu

In situ experiments with the DSI:
The deep-sea incubator (DSI) consists of 24 gas-tight glass syringes and a mechanism that fills the syringes to 42 milliliters (ml) with ambient water set on a timer with a 1-hour delay. This gives the DSI more than sufficient time to settle to the target depth and adjust to the in-situ temperature. The anchor depth was 600 meters (m) and the tether from the anchor to the DSI was 300 m resulting in a deployment depth of 300 m. The syringes were pre-filled with 2 ml of labeled algal phytodetritus from batch cultures of Thalassiosira weissflogii and Tetraselmis sp. The cultures were grown on a f/2+ (T. weissflogii) or f/2 (Tetraselmis) medium enriched with 13C-sodium bicarbonate, frozen at the late exponential stage, and then filtered onto a 0.2-micrometer (um) pore size polycarbonate filter. The particulate material (POC) was resuspended in a 50 ml centrifuge tube filled with the same volume of water as the original culture volume with artificial seawater. The filtrate was used as a source of 13C-labeled dissolved organic carbon (DOC). POC was dislodged from the filter by vigorous vortex mixing and shaking of the centrifuge tube. DOC was the filtrate. Two milliliters of the slurry of POC or the DOC filtrate were then injected into each syringe using an automatic pipette. Controls were poisoned with mercuric chloride (HgCl2). The four treatments were as follows:

1.) 3C labeled POC from Thalassiosira weissflogii (4 replicates)
2.) 13C labeled DOC from Thalassiosira weissflogii (4 replicates)
3.) 13C labeled POC from Tetraselmis sp. (4 replicates)
4.) 13C labeled DOC from Tetraselmis sp. (4 replicates)
5.) 13C labeled POC from Thalassiosira weissflogii with HgCl2 (duplicates)
6.) 13C labeled DOC from Thalassiosira weissflogii with HgCl2 (duplicates)
7.) 13C labeled POC from Tetraselmis sp. with HgCl2 (duplicates)
8.) 13C labeled DOC from Tetraselmis sp. with HgCl2 (duplicates)

The incubation started on May 12, 2023 at 13:09. The syringes were processed (tfinal) on May 16, 2023 (i.e., 4.25 days later).

Parallel laboratory incubations:
The laboratory incubations were set up in parallel using the exact same protocol as with the field incubations except they are filled with seawater from close to the same depth (300 m) as the deep-sea incubator collected with Niskin bottles. The water was returned to lab laboratory in a temperature controlled cool chest (11-12 degrees Celsius (C)) and experiments were started approximately 6.5 hours and after the syringes were filled with labeled material. They were placed in a cold room at 12 degrees C in the dark until retrieval.

The incubation interval for the laboratory experiments was 4 days.

The temperature of the DSI was unknown until retrieval. Because of the highly variable bathymetry at the deployment site (at the continental shelf break), the DSI landed in slightly deeper water than anticipated, which resulted in an average temperature of 8.2 degrees C (range 6.5 – 10.3 degrees C) according to an attached temperature logger.

Oxygen was measured by inserting a Unisense microprobe (a polargraphic oxygen sensor that is drawn out into a capillary) approximately 2 centimeters (cm) into the syringe immediately after removing the Luer-lock valve. A saturated oxygen standard and a NaOH-ascorbic acid standard (zero oxygen) at the same salinity and concentration were used as standards. A two-point calibration suffices as the polarographic sensor signal is strictly linear.

Five ml from each syringe was filtered onto a muffled GF/F filter and frozen until later processing. The filters were dried at 50 degrees C, acidified under HCl fumes to remove inorganic carbon, dried again and sent to the Stable Isotope Facility at UC Davis. There, the filters were encapsulated in tin capsules and processed in an elemental analyzer coupled to an isotope ratio mass spectrometer (EA-IRMS). Only the 13C and bulk particulate organic carbon values (12C + 13C) values were used for this analysis.