Table of Contents

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

These data were collected on R/V Endeavor cruise EN665 from three stations in the Wilkinson and Jordan Basins of the Gulf of Maine (approximately 42.6 North, 69.6 West, depth 0-260 meters). Water samples were collected using Niskin bottles on the CTD rosette.

Nutrients:
Nutrient samples were collected directly from Niskin bottles using clean 60-milliliter (mL) plastic syringes. Samples were then passed through a 25-millimeter (mm) 0.2-micron filter (either polycarbonate or PTFE) into clean, 60-mL HDPE bottles. Bottles were rinsed 3 times with filtered water before filling and capping. Bottles were then frozen at -20 degrees Celsius for approximately 30 days until analysis. Analyses were performed at the WHOI Nutrient Analytical Facility on a SEAL Analytical AA3 HR following established procedures.

Total Alkalinity, Dissolved Inorganic Carbon (DIC), and d13C-DIC:
Samples for total alkalinity (TA), dissolved inorganic carbon (DIC), and d13C-DIC were collected simultaneously. Water from the Niskins was passed through a 0.45-micron cartridge filter and all bubbles were removed from the line. Ground-glass stoppered 250-mL were rinsed 3 times with flowing, filtered seawater and then filled. Each sample bottle was left to overflow for approximately double the amount of time it took to fill the bottle. Excess water was gently dumped out to leave a ~2-3 mL headspace below the ground glass fitting. Following collection, samples were poisoned with 100 microliters of saturated mercuric chloride solution. Bottles were sealed with a greased stopper (Apiezon-L). A rubber band was placed over the stopper to ensure sample closure. Samples were stored cool and in the dark prior to analysis at the Woods Hole Oceanographic Institution.

DIC and d13C analyses were performed first immediately after opening the bottle. DIC and d13C-DIC were determined simultaneously using an Apollo AS-D1 analyzer connected to a Picarro G-2121i cavity ringdown system on a 5 mL sample of seawater. Samples were run in at least triplicate and calibrated against seawater Certified Reference Materials. Isotopic values were calibrated against an in-house seawater standard that was intercalibrated against known solid materials (NBS-19, IAEA-C2, and NBS-20). Intercalibration was performed on the same Picarro instrument using an Automate-Liaison front-end unit. Total alkalinity was determined using an open-system Gran titration on 5-mL samples in triplicate, using a Metrohm 805 Dosimat and a robotic Titrosampler, calibrated against seawater Certified Reference Materials.

pH:
pH samples were measured on the total scale with pure meta cresol purple indicator (mCP) at 25C +/- 0.1C on an Agilent 8453 spectrophotometer. A subset of the samples (18 out of 30 total) was used to derive the R-value perturbation by the indicator, for which all of the samples were then corrected.

Data Quality Flags:
Quality flags were applied according to the definitions described in Jiang et al., 2022, as follows:
0 = interpolated data;
1 = not evaluated / quality unknown;
2 = acceptable;
3 = questionable;
4 = known bad;
6 = median of replicates;
9 = missing value.

BCO-DMO Processing:
- replaced "NaN" with "nd" ("no data");
- converted date to ISO 8601 format;
- added column for date-time in UTC;
- renamed fields to comply with BCO-DMO naming conventions;
- converted longitude values from positive degrees West to negative degrees East;
- replaced the wrong cruise ID of EN669 with EN665.

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.