Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Location: Two primary stations within the Gulf of Maine's Wilkinson and Jordan basins with sampling depths ranging from surface (~5 meters (m)) to just above gulf bottom (~260 m). Coordinates are as follows: Station 1(42.618 N and 69.6357 W) and Station 2 (43.4868 N and 67.8267 W). The cruise campaign (EN665) was performed aboard the R/V Endeavor. The cruise spanned 6 days in 2021 (4/7 to& 4/12). Dr. Adam Subhas was the Chief Scientist.

General Sampling and storage: McLane pumps were deployed four at a time for a total pumping time of approximately four hours during each deployment. For carbon, nitrogen, and thorium-related measurements, pre-combusted 142-millimeters (mm) filters glass fiber GF/F were used to capture small particles (nominal pore size 0.7 microns (µm)), and acid-washed Nitex screens were used for the large particles (51 micron pore size). Immediately upon pump retrieval, pump filterheads were brought into a custom HEPA-laminar flow hood setup. The GF/F filters were sectioned using a light box and a ceramic plate (slices) or a custom stainless punch. Sample splits or punches were then stored according to best practices for those sample types. For small particle bulk carbon and nitrogen, samples were air-dried for several hours and then stored cool and in the dark until analysis. For large particle carbon, nitrogen, and thorium-234 a half section of the nitex filter was rinsed using filtered seawater onto a pre-combusted 25 mm GF/F, dried in a 50 degree Celsius (C) oven overnight, and then mounted for later beta counting. Small particle thorium-234 was measured using a 25 mm punch of the GF/F that was dried at 50 degrees C overnight and then mounted for beta counting. Photos were taken of all filters in the lab for general assessment of particle loading and color differences. Particulate dipped blanks were collected by attaching a plastic housing (for the dipped blank), containing a 51 µm filter and a 1 µm filter, to the side of the filtration apparatus. The plastic housing allowed for the free exchange of sample water.

Analyses: Small particle carbon and nitrogen filters were analyzed at the UC Davis Stable Isotope Facility following established protocols. Large particle carbon and nitrogen filters were analyzed at the Woods Hole Oceanographic Nutrient Facility following established protocols.

Particulate inorganic carbon samples were analyzed in the Subhas lab using a G-2121i Picarro Cavity Ringdown Spectrometer with an Automate-Liaison front end. The methods were modified from Subhas et al. (2019) for filter samples. The filter slice was placed in an Exetainer vial, put under vacuum, and acidified using 4 mL phosphoric acid (10%). Standardization was done using in-house Iceland Spar and the IAEA C2 standard material.

Size fractionated thorium-234 samples (25 mm GF/F) were mounted with mylar and two aluminum foil layers and beta counted within days of filtration in the Buesseler Radiochemistry Facility at Woods Hole Oceanographic. Second counts were conducted again at least 5 months after filtration. Uncertainties on particulate thorium-234 activities are derived from counting statistics and error propagation from sampling processing. Methods follow those in Black et al. (2018).

RA_P234 is the residual β activity of particulate thorium-234 and behaves in a similar manner to lithophile elements (Lin et al. 2016). The residual β activity is found by beta counting the large and small particle filters well after all the shorter-lived and unsupported isotopes have decayed away (e.g. unsupported thorium-234). These are the 'second count' activities. Data from this study has a method limit for RA_P234 equivalent to 2 times the s.d. of the dipped blank mean value of RA_P234

Processing of Picarro data was completed using home-built MATLAB software to pick sample peaks from the raw data and calculate averages. These data were then passed to a home-built Microsoft Excel spreadsheet for standardization, blank subtraction, and isotope value calculation.

All thorium-234 and large particle datasets were prepared using a custom-built Microsoft Excel spreadsheet for standardization, blank subtraction, and activity calculations.

Quality Flags:
The data flags used are as suggested at www.geotraces.org/geotraces-quality-flag-policy/. Most values were flagged as ‘probably good’ (2), per the suggestion on this website. The (1) flag was not used at all. Standard data flags are used: (2) probably good, (3) probably bad, (4) bad, (6) below detection, (9) missing data. Missing data is only used where the sample was analyzed and there was a subsequent issue with the instrument.

- Imported original file "LVP_Data.xlsx" into the BCO-DMO system.
- Created date-time columns in ISO 8601 format.
- Rounded Latitude values to 5 decimal places and Longitude values to 4 decimal places.
- Saved the final file as "969640_v1_lvp_en665.csv".

NSF Award Abstract:
The ocean actively exchanges carbon dioxide with the atmosphere and is currently absorbing about a third of the carbon dioxide humans emit through fossil fuel burning. Because carbon dioxide is acidic, ocean pH drops as it takes up carbon dioxide, a process known as "ocean acidification". Ocean acidification negatively affects the health of marine ecosystems by making it harder for organisms to grow their calcium carbonate shells. Yet, the dissolution of these calcium carbonate shells in the deep ocean helps neutralize the carbon dioxide we emit as humans. The extent to which this process takes place is a function of the solubility of marine calcium carbonate. This project will evaluate the temperature and pressure effects on the stability of biologically produced calcium carbonate minerals. The results from this study will allow us to better predict where, how much, and how fast, carbon dioxide will be neutralized and stored in the world's ocean. We will also investigate the ways in which small changes in the chemical composition of calcium carbonate shells - such as the incorporation of magnesium - influence their stability. This project will also conduct micro-computed tomography scans of microorganisms' shells to better visualize them in 3-dimensional detail. We will print these 3-dimensional scans for use as educational tools in the classroom and in the Woods Hole Visitor Center. In addition, professional development workshops for high school teacher on ocean acidification and the importance of marine calcification will be held yearly.

The ocean is the ultimate repository for most of anthropogenic carbon dioxide emissions, which in turn is making ocean chemistry less favorable for biogenic carbonate precipitation through the process of ocean acidification. Ocean acidification decreases seawater pH but dissolution of primarily biogenic carbonate minerals has the capacity to buffer this acidification and over thousands of years push whole-ocean pH and atmospheric carbon dioxide to their preindustrial values. Unfortunately, the relationship between seawater chemistry, carbonate mineral solubility, and the kinetics that govern carbonate dissolution and precipitation are not fully understood. Currently, it is clear that relationships based solely on inorganic calcite are insufficient to describe the cycling of biogenic calcites in the ocean. This project will conduct a systematic determination of the solubilities and reaction kinetics of the three most common biogenic carbonates (coccoliths, foraminifera, and pteropods), both in the laboratory and in the field, using spectrophotometric pH saturometry. The saturometer incubates calcium carbonate with seawater in a closed system. During each run, the change in pH within the saturometer traces the progression of calcium carbonate dissolution/precipitation as the system approaches equilibrium. The saturometer therefore has the potential to link mechanistic interpretations of mineral dissolution/precipitation kinetics to measurements of solubility in a single experiment. The spectrophotometric pH method uses well-calibrated indicator dyes, allows solubility and data to be tied to modern pH calibrations and reference materials, and can be used in the laboratory or deployed on a hydrowire at sea. Field experiments will be conducted at multiple depths, elucidating in-situ controls on solubility and kinetics, as well as the sensitivity of biogenic calcite solubility to temperature and pressure. Experiments will be conducted from both sides of equilibrium, allowing for robust determinations of inorganic and biogenic solubilities.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.