St. Petersburg Coastal and Marine Science Center

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Ocean Acidification

2015 Davis Strait - Arctic Circle Cruise

Questions & Answers

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Q: Are the carbonate mineral saturation states also affected by temperature?

A: Yes, carbonate mineral saturation states are affected by temperature. In general, carbonate mineral saturation states decrease with decreasing temperature. For example, a drop in temperature from 25 to 0 degrees C at constant dissolved inorganic carbon (DIC) concentration of 2000 micromoles kg-1 and total alkalinity of 2440 micromoles kg-1 at a salinity of 35 would cause a decrease in carbonate mineral saturation state of approximately 0.5 micromoles kg-1. Zeebe and Wolf-Gladrow (2001) provide an excellent discussion of the effects of temperature, salinity, and pressure on the carbonate system parameters in seawater.

Q:  How do you measure the impact of Ocean Acidification on your location?

A: One of the effects of ocean acidification is a decrease in carbonate mineral saturation states. We are measuring carbonate chemistry in seawater at a very high spatial resolution and very accurately so we can calculate the variation in carbonate mineral saturation states across the Arctic Ocean. These data provide a baseline to compare to past and future measurements of seawater carbonate mineral saturation states so we can quantify the effects of increasing atmospheric CO2 and ocean acidification on this parameter.

Q: What kinds of samples are you collecting  (air, water, plants, animals) and what are you looking for in the samples that you collect?

A: We are collecting seawater samples and measuring carbonate system parameters including temperature, salinity, total alkalinity, dissolved inorganic carbon, pCO2, and pH. In addition, we are measuring oxygen isotopes of seawater. These data allow us to very accurately determine the concentrations of CO2 and pH of the water and the exchange of CO2 from air to water or vice versa in areas that are covered with sea ice and where sea ice has melted away. Furthermore, these data provide information about the different sources of water in an area–which allows us to evaluate input of freshwater. Finally, the data also allow us to calculate carbonate mineral saturation state of seawater, which is an important indicator of ocean acidification. Low saturation state of seawater may be deleterious on marine organisms that produce their skeletons from calcium carbonate minerals.

Some of the samples are acquired by instruments that are autonomous flow though systems, connected directly to seawater in the ships lab, and can collect surface seawater data constantly while the ship is in transit. Other samples require discrete water samples in order to measure parameters back onshore. These samples are collected by lowering a CTD and rosette of water sampling containers into the icy waters in order to bring up water column samples for analysis in a laboratory.

pH spectrophotometer for shipboard discrete water sample analysis.
pH spectrophotometer for shipboard discrete water sample analysis.

 

CTD rosette with Niskin bottles filled with seawater.
CTD rosette with Niskin bottles filled with seawater. The rosette with open bottles was lowered down the water column and on its journey down, certain bottles were “triggered” remotely to be closed- capturing water at specific depths.

 

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