Layer type: Pressure
Data description: Ocean acidification data were obtained from the East Coast Ocean Acidification Product Suite (ECOAPS)1, which is produced by the NOAA Coral Health and Monitoring Program. This data includes monthly aragonite saturation state (\(\Omega_{arag}\)) values from 2014 - 2017 along the East Coast of the United States in a gridded format with a cell resolution of 0.15 degrees.
Methods summary: The raw data was cropped to our region of interest, reprojected to a US Albers Equal Area Conic projection, resampled using nearest neighbor interpolation to a cell size of 1km2. Mean annual aragonite saturation state concentrations were calculated for each year from the monthly data and then rescaled from 0 to 1 using a step-wise conditional function based on known thresholds for calcifying organisms.
If \(\Omega_{arag}\) is less than or equal to 1, the cell is assigned the highest pressure score of 1. This is a widely accepted saturation lethal threshold for calcifying marine organisms although indivdual responses vary
Cells with \(\Omega_{arag}\) = 1.5 are assigned a pressure value of 0.5. This saturation level is when mild dissolution begins to occur (Bednaršek et al. 2019)
Cells with \(\Omega_{arag}\) = 2.5 are assigned a pressure of 0. This is the lowest saturation level where few organims are affected (Ries et al. 2009).
Functionally this method of rescaling each cell to get a pressure value (\(X\)) between 0 and 1 can be described by the following equation:
\[ X = \begin{cases} 1,& \Omega_{arag} <= 1,\\ -1*\Omega_{arag} + 2,& 1<\Omega_{arag} <= 1.5,\\ -0.5*\Omega_{arag} + 1.25,& 1.5 < \Omega_{arag} <= 2.5,\\ 0,& \Omega_{arag} > 2.5 \end{cases}\]
Pressure layer scores were calculated as the mean of rescaled cell values by region and year.
Gapfilling: Unfortunately this dataset only included the most recent 4 years of data, requiring gapfilling methods for years 2005-2013. Ideally we could have gapfilled from a global dataset used in other Ocean Health Index Assessments (WHOI 2017), but after comparisons between the two datasets for the overlapping years (2014-2017) it became clear that the differences were too significant to justify gapfilling with this dataset. Therefore all values from 2005 - 2013 are gapfilled with the 2014 scores. We recognize this introduces uncertainty to the Index for those years.
References
Bednaršek, Nina, et al. “Systematic Review and Meta-Analysis Toward Synthesis of Thresholds of Ocean Acidification Impacts on Calcifying Pteropods and Interactions With Warming.” Frontiers in Marine Science, vol. 6, 2019, doi:10.3389/fmars.2019.00227.
Ries, J. B., et al. “Marine Calcifiers Exhibit Mixed Responses to CO2-Induced Ocean Acidification.” Geology, vol. 37, no. 12, 2009, pp. 1131–1134., doi:10.1130/g30210a.1.
Signorini, S. R., A. Mannino, R. G. Najjar, Jr., M. A. M. Friedrichs, W.-J. Cai, J. Salisbury, Z. Al-eck Wang, H. Thomas, and E. Shadwick (2013), Surface ocean pCO2 seasonality and sea-air CO2 flux estimates for the North American east coast, J. Geophys. Res. Oceans, 118, 5439–5460, doi:10.1002/jgrc.20369.
Wang, Z. A., G. L. Lawson, C. H. Pilskaln, and A. E. Maas (2017), Seasonal controls of aragonite saturation states in the Gulf of Maine, J. Geophys. Res. Oceans, 122, doi:10.1002/2016JC012373.
Woods Hole Oceanographic Institution (WHOI). 2017 update to data originally published in: Feely, R.A., S.C. Doney, and S.R. Cooley. 2009. Ocean acidification: Present conditions and future changes in a high-CO2 world. Oceanography 22(4):36–47
NOAA Coral Health and Monitoring Program, Ocean Acidification Product Suite, https://www.coral.noaa.gov/accrete/oaps.html↩