pH and Carbon Dioxide Sensors V14

The pH sensor measures pH (total hydrogen scale) in the marine pH range of 7-9.  pH is a measure of the total hydrogen ion concentration in the ocean.  For tens of millions of years, Earth's oceans have maintained a relatively stable pH level.  Since the beginning of the industrial revolution (1800s), however, the surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14. While this may seem to be a very small change in pH, it represents about a 30% in H+ ion concentration and already is impacting marine organisms and in particular the shellfish industry

The pCO2 sensor measures the partial pressure of carbon dioxide (pCO2) from 150-700 μatm in the upper 200 m of the water column on the shallow profiling moorings at the Slope Base and Axial Base sites.  The distribution of pCO2 is dependent on: (1) increases due to gas exchange with the atmosphere at the ocean surface, (2) removal by photosynthesis, (3) removal by calcium carbonate formation, (4) removal by solar heating, (4) increases from breakdown of plant material by microbial processes, and (5) addition due to dissolution of calcium carbonate.  Calcium carbonate minerals are the building blocks for the skeletons and shells of many marine organisms, such as oysters. Carbon dioxide concentrations are increasing in the atmosphere due to the use of fossil fuels.  Currently, the increase in atmospheric CO2 is about 30 times higher than at anytime in the past geological history of the Earth. The oceans are absorbing about 30% of the atmospheric CO2, resulting in a shift in seawater acid-base chemistry and a decrease in ocean pH (more acidic).  These chemical changes are termed “ocean acidification”.

During VISIONS '14, pH sensors are planned for deployment on shallow profilers at Axial Base (SF03A) and Slope Base (SF01A), at the Axial (PC03A) and Endurance offshore (PC01B) 200m platforms, and at the Endurance offshore (LJ01C) and nearshore shelf (LJ01D) benthic packages.

It is anticipated that CO2 sensors will be placed at the Endurance offshore 200m platform (PC01B), benthic package (LJ01C), and shallow profiler (SF01B), as well as the nearshore benthic package (LJ01D), and both the Axial Caldera and Slope Base shallow profilers (SF03A and SF01A, respectively).


pH and CO2 sensors Overview