Table of Contents

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

The data files that makeup this dataset were generated from a flow-through tank experiment conducted at the Schiller Coastal Studies Center. The experiment was designed to examine physiological or environmental responses of multiple bivalve species under controlled conditions using continuously supplied seawater.

Specimens used in the experiment included both field-collected and hatchery-sourced organisms. Juvenile and adult individuals of Arctica islandica were collected offshore of Jonesport, Maine, USA (44°33.247’N, 67°16.183’W) at depths of approximately 76–85 meters. Juvenile Placopecten magellanicus were obtained from PenBay Farmed Scallops. Juvenile Mercenaria mercenaria and Mya arenaria were provided by the Downeast Institute Hatchery.

Four bivalve species were maintained in a fully factorial design with four pH treatments (~7.4, 7.6, 7.8, ~8.0) and three temperature treatments (~6, 9, 12 °C). Environmental conditions were continuously monitored (temperature) and regularly validated (pH, salinity), with all reported values representing tank-level averages. Specimen-level measurements (size, dry weight, buoyant weight) were collected at defined time points and linked to experimental treatment conditions.

Experimental setup:

These four species were grown in four pH treatments (~7.4, 7.6, 7.8, and ambient conditions with a pH=8.0) at three temperature treatments (~6, 9, 12° C). There was one tank at each pH for T=6 and 12° C and two tanks at each pH for T=9° C.

Specimens were randomly assigned to tank conditions with roughly equal numbers of each specimen in each tank condition.

Specimens were in the tank conditions for 20.5 weeks before removed with the following exception. Half of the P. magellanicus were removed in April 2022.

Environmental Conditions:

pH and salinity were measured weekly with a YSI probe. pH was controlled within each tank condition by the Apex control system. Tanks with lower pH conditions than ambient were obtained by bubbling CO2 from compressed cylinders into the water of a mixing chamber before leading to each of the three sets of controlled pH tanks.

Temperature was measured with two Hobo Tidbit devices in each tank throughout the experiment. Temperatures were measured every minute throughout the 20.5 weeks. Temperatures were maintained within the tanks using Inkbird controllers and two (500W/800W) heaters per tank.

All pH measurements are on the total pH scale (pHT).

The reported measurements for temperature, salinity, and pHT are measured tank averages.

Specimen measurements:

All study specimens were measured for maximum height, dry (live) weight, and buoyant weight at the start and end of the experiment. For the P. magellanicus removed in April 2022, height, dry (live) weight, buoyant were measured after removal from the tanks. Photos were taken of each specimen at the conclusion of the experiment.

After the conclusion of the experiment, all specimens were dissected, shells were rinsed with DI water and allowed to air dry prior to sampling for boron isotopes.

Shell sampling:

Organic matter was removed with burring bit (Brasseler #835.11.010) and hand milling with a Dremel tool prior to sampling of the shell. 8 mg of shell was sampled (3-4 mg for P. magellanicus) for boron isotopes with the same bit and Dremel tool.

Boron samples were collected on the shells from the portion of the shell that grew from approximately week 2 to week 10 of the experiment (prior to the spring freshening and second calcein stain line in April 2022) for all species except the adult A. islandica. Due to much slower growth in the adult A islandica, the portion of the shell that grew during the entire tank experiment was sampled. 

For most shells, one sample was collected from each shell. There were two exceptions: a comparison was done between the two halves of the shell for three juvenile A. islandica (g5, g32, g48) and a comparison of the outer shell layer (both inner and outer layers of the outer shell) and the inner shell layer on two juvenile A. islandica (g40 and g52). The samples selected for these comparisons were randomly chosen.

Sample preparation:

All powdered shell samples were subject to two 15-minute leaches in warm 10% (by volume) H2O2 (80 °C; buffered in NH4OH) and a weak acid leach (0.0005 M HNO3) before powders were dissolved in distilled 0.5 M HNO3. Dissolved samples were centrifuged (1 min at 13k rpm), and if there was any visible undissolved non-carbonate material at the bottom of the microcentrifuge tube the dissolved sample was transferred to a clean vial, rejecting the small undissolved fraction.

The burring bit was used to remove all visible organic matter from the outside of the shells. The leaching in H2O2 was performed to remove the remaining organic matter. 

Chemical Processing:

All trace element and boron isotope analyses were performed at the University of Bristol. An aliquot of the dissolved sample was analyzed by Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) using well-characterized, matrix-matched, synthetic standard solutions to give B/Ca and U/Ca ratios. Samples and standards were introduced in 0.5 M HNO3 and an acid wash solution of 0.5 M HNO3 matrix and 0.3 M HF was utilized between samples/standards to aid B wash out.

The remaining sample containing between 4 and 40 ng of B was separated from the carbonate matrix using 20 μl micro-columns containing Amberlite IRA 743 boron-specific anionic exchange resin. The boron separation from the matrix was performed only on the day preceding Multi Collector-ICP-MS (MC-ICP-MS) analysis. All samples, blanks, and standard solutions were introduced to the instrument in a 0.5 M HNO3 and 0.3 M HF acid matrix again to ensure optimal B wash out.

A total of 108 samples were prepared for boron isotope analysis. There were two samples that did not produce useful results due to blocked columns (one adult A. islandica and one juvenile P. magellanicus). 

See Thatcher et al., (2026; GCA) and McMahon et al. (2024; PLOS Climate) for full details on the methods.

- Loaded sheet 1 from "Thatcher et al_summary data.xlsx" in xlsx format, using row 1 as header, with missing values defined as empty strings, "nd", "**", "Column blocked", and "N/A". These various missing data values are retained within the dataset to differentiate between types of data flags, as they differ between columns.
- Renamed fields: "Average temperature (°C)" to Average_temperature, "Average salinity (psu)" to Average_salinity, "Average pHT" to Average_pHT, "Sample species" to Sample_species, "Sample description" to Sample_description, "δ11B Borate (‰, water)" to boron_isotope_value_borate_ion, "δ11B (‰)" to boron_isotope_value_shell, "B/Ca (µmol/mol)" to boron_calcium_ratio, "ΔpH" to delta_pH
- Set data columns to the following data types: Average_temperature, Average_salinity, Average_pHT, boron_isotope_value_borate_ion, boron_isotope_value_shell, delta_pH as number; boron_calcium_ratio as integer; SampleID, Sample_description, Sample_species as string
- Renamed resource from "thatcher_et_al_summary_data-1" to "995690_v1_bivalve_boron_isotopes"
- Output written to 995690_v1_bivalve_boron_isotopes.csv

NSF Award Abstract:

The Gulf of Maine is located in the Northwestern Atlantic Ocean. Its waters serve as home to the economically important Atlantic Cod and shellfish industry. But recent changes to this environment pose a threat to the ecosystem and the commercial fishing industry. However, only a few long-term records of the environment exist in this area making it difficult to tell exactly when these changes started and how much is related to human activities. In this project, a team of researchers from three universities will construct a 250-year history of the regional environment by measuring yearly growth bands in local clams and algae. Chemical fingerprints in these growth bands will be used to determine the water temperature, salinity, biological productivity and pH conditions. This allow scientists to study how natural changes have affected the environment and compare these to changes caused by greenhouse global warming. This information will inform policy decisions of the newly-formed Maine Climate Council on how to better manage this area. The proposed work will also support training for early career scientists, broaden participation in science programs, and support undergraduate research opportunities.

Specifically, the team will use a multi-pronged approach using geochemical proxies in two types of high-resolution marine climate archives (clams and crustose coralline algae) to reconstruct past changes in oceanographic conditions, including near surface seawater temperatures, salinity, and pH in the Gulf of Maine through the last 250 years. Geochemical fingerprints (or proxies) preserved in the annual growth bands of clam shells and skeletons of long-lived marine calcifiers have been used extensively as archives of past ocean conditions. Discrete calcium carbonate layers can be sampled from the growth bands of clams and crustose coralline algae for geochemical analysis, generating proxy archive records. These reconstructions of past environmental conditions fill data gaps prior to instrumental records. Hence, the proposed research will potentially yield several multi-centennial, annually-resolved, absolutely-dated datasets of oceanographic variability in the Northwestern Atlantic, including the Gulf of Maine, prior to the Industrial Revolution, which will be used to evaluate the role of Atlantic meridional overturning circulation, and other climate forcings, on observed changes. By combining new data derived from traditional and novel proxies with existing hydrographic records, the relative contributions of source waters into the Gulf of Maine through time will be characterized to better understand the drivers of variability within the Gulf of Maine. Understanding past oceanographic variability in the Gulf of Maine is therefore critical for predicting the likely extent and magnitude of future change, and for planning to safeguard ecosystems and fisheries. Results will be widely disseminated to science and non-science audiences through publications, conference presentations, mentoring programs, coursework, and outreach activities at area schools, museums, and science centers.

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.