Table of Contents

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

Underway pCO2 from R/V Pelican cruise GOM_UW_1704 conducted in northern Gulf of Mexico in April 2017.

Underway sea surface temperature, salinity, and pCO2 data were collected continuously along the cruise track. Surface seawater was collected from an intake on the port side of the ship at about 4m depth. SST and SSS were measured by an SBE45 (Sea-Bird Electronics) Thermosalino graph installed in the sea chest. Seawater was pumped to the ship's labs. There, underway pCO2 was measured inline by an automated system (Apollo Scitech) with a Li-7000 (LICOR, Inc.) non-dispersive infrared detector at a water flow rate of 3-4L/min; The sampling interval was 2 min. This autonomous system was twice daily against three certified CO2 gas standards (150.62, 404.72, and 992.54 ppm) obtained from NOAA's Earth System Research Laboratory (ESRL), Global Monitoring Division in Boulder, CO. These gas standards are directly traceable to the World Meteorological Organization (WMO) scale. The precision of underway pCO2 measurements of this system is 0.1 μatm, and the overall accuracy is estimated at 2 μatm, as documented by Pierrot et al. (2009). The underway system uses a shower head type equilibrator with ~0.5L headspace volume.

Instruments:
Underway pCO2 was measured inline by an automated system (Apollo Scitech) with a Li-7000 (LICOR, Inc.) non-dispersive infrared detector .

The pCO2 measurement was calibrated twice daily against 3 certified CO2 gas
standards (150.62, 404.72, and 992.54 ppm)

1) Read the data into Excel.
2) Get the data log book and delete any questionable data such as those during instrument failure. Note: data during calibration should be cut and pasted into another worksheet.
3) Correct the CO2 data directly from Li-Cor using the calibration results. Specifically, first get the linear relationship between the known xCO2 from gas cylinders and the Li-Cor reading; then use the correlated equation to correct the raw xCO2 to calibrated xCO2.
4) Calculate the surface water pCO2 at the temperature of equilibration (it will be corrected to in-situ temperature later) [pCO2 (eq), units: μatm][Weiss and Price, 1980].
5) Calculate in-situ pCO2 [pCO2@SST, units: μatm] (Takahashi et al. 1993)

Data Manager processing notes:
- Converted longitude range from 0-360 to -180 - 180
- Added "Z" to end the datetime stamp to indicate it was in UTC time

NSF Award Abstract:

Ocean acidification (OA) refers to the lowering of ocean pH (or increasing acidity) due to uptake of atmospheric carbon dioxide (CO2). A great deal of research has been done to understand how the open ocean is influenced by OA, but coastal systems have received little attention. In the northern Gulf of Mexico (nGOM) shelf region, pH in bottom waters can measure up to 0.45 units less than the pH of the pre-industrial surface ocean, in comparison to the 0.1 overall pH decrease across the entire ocean. Carbonate chemistry in the ocean is greatly influenced by even small changes in pH, so these seemingly minor changes lead to much greater impacts on the biology and chemistry of the ocean. The researchers plan to study coastal OA in the nGOM, a region subject to high inputs of nutrients from the Mississippi River. These inputs of anthropogenic nitrogen mostly derived from fertilizers leads to increased respiration rates which decreases oxygen concentrations in the water column to the point of hypoxia in the summer. This study will inform us how OA in coastal waters subject to eutrophication and hypoxia will impact the chemistry and biology of the region. The researchers are dedicated to outreach programs in the Gulf and east coast regions, interacting with K-12 students and teachers, undergraduate/graduate student training, and various outreach efforts (family workshops on OA, lectures for the public and federal, state, and local representatives). Also, a project website will be created to disseminate the research results to a wider audience.

Increased uptakes of atmospheric carbon dioxide (CO2) by the ocean has led to a 0.1 unit decrease in seawater pH and carbonate mineral saturation state, a process known as Ocean Acidification (OA), which threatens the heath of marine organisms, alters marine ecosystems, and biogeochemical processes. Considerable attention has been focused on understanding the impact of OA on the open ocean but less attention has been given to coastal regions. Recent studies indicate that pH in bottom waters of the northern Gulf of Mexico (nGOM) shelf can be as much as 0.45 units lower relative to pre-industrial values. This occurs because the acidification resulting from increased CO2 inputs (both atmospheric inputs and in-situ respiration) decreases the buffering capacity of seawater. This interactive effect will increase with time, decreasing summertime nGOM bottom-water pH by an estimated 0.85 units and driving carbonate minerals to undersaturation by the end of this century. Researchers from the University of Delaware and the Louisiana Universities Marine Consortium will carry out a combined field, laboratory, and modeling program to address the following questions. (1) What are the physical, chemical, and biological controls on acidification in coastal waters impacted by the large, nutrient-laden Mississippi River?; (2) What is the link between coastal-water acidification, eutrophication, and hypoxia; (3) How do low pH and high CO2 concentrations in bottom waters affect CO2 out-gassing during fall and winter and storm periods when the water column is mixed?; and (4) What are the influences of changing river inputs under anthropogenic forcing on coastal water acidification? Results from this research aim to further our understanding of the processes influencing ocean acidification in coastal waters subject to eutrophication and hypoxia both in the GOM and river-dominated shelf ecosystems globally.

Related Project note:

There are overlapping cruises with the project "Sed Control on OA" https://www.bco-dmo.org/project/815333. Thus, while some water column data can be found under this project "nGOMx acidification", all benthic data can be found under the "Sed Control on OA" project.