A little about chemistry on the RV Oceanus

Hello, I am Jacinta Edebeli. I am a summer student fellow on board the RV Oceanus on this ocean acidification- pteropod cruise. I am on the Chemistry half of the team. I am going to give you some insight into what the chemistry team is doing - what we sample for and how we measure them. When we send the CTD rosette down to 1000m or 3000m, we most often collect water samples. We commonly collect samples from 16 Niskin bottles for the 1000m cast and 24 Niskin bottles from the 3000m depth. We collect these samples to measure inorganic carbon (carbon dioxide (CO₂)) parameters, nutrients and salinity. The CO₂ parameters give us information about ocean acidification. 
 

Katherine Hoering drawing water from the CTD for analysis

Three of these parameters include alkalinity, dissolved inorganic carbon (DIC) and pH. We measure these three in the lab on the boat using separate measuring instruments (please refer to pictures). We also have the MICA (Multi-Parameter Inorganic Carbon Analyzer), an underway seawater inorganic carbon measuring instrument which measures sea surface water DIC, pH and the fourth sea water inorganic carbon parameter, CO₂ fugacity (partial pressure of CO₂ in sea water, also known as fCO₂). The MICA also measures atmospheric CO₂ (or pCO₂). We also measure salinity on the boat. The nutrient samples are frozen till we get to land. 

Mohammad Uddin measuring salinity

Cris Luttazi setting up the DIC analyzer

How is the information from the chemistry measurements relevant to pteropods and ocean acidification?  Researchers have shown that ocean acidification is closely related to the amount of CO₂ in the atmosphere and in the water (please refer to previous posts by Cris Lutazzi for more details). DIC and fCO₂ provide information about concentrations of CO­₂ in water while pCO_2­ tells us the concentration of CO_{2 ­} in the atmosphere. Alkalinity tells us about the excess of concentration of chemical species present in sea water that could take up hydrogen ions over those that donate hydrogen ions. 

Jacinta Edebeli working with the alkalinity titrator

The presence of hydrogen ions implies some level of acidity, hence, we also measure pH. The higher the concentration of hydrogen ions, the lower the pH, and vice versa. Comparing these present measurements with previous ones, we can tell whether or not there are changes occurring that we can relate to physiological and geographical patterns observed in the pteropods.