Carbonate Chemistry

Measurements of the carbonate chemistry system in seawater are critical in understanding our ocean’s (and the whole Earth’s) response to anthropogenic carbon dioxide emissions. My work aims to make these measurements more accurate and reliable, whether they are made on hydrographic cruises or by someone monitoring seawater quality in coastal Los Angeles. The carbonate system in seawater is typically described by at least two measured variables, chosen from pH, pCO2, total alkalinity, and total dissolved inorganic carbon.  The measurement of each of these variables uses unique chemical techniques and instrumentation, each with its own idiosyncracies and advantages.

One thing that often causes problems with these measurements, is when there are particulates in the seawater sample to be measured. The particle might interfere with an optical measurement, or dissolve and contribute improperly to an acid titration. Filtration is difficult though, because the measurement of pH, pCO2, and dissolved inorganic carbon are all sensitive to gas exchange. I have developed a method for filtering these samples, without unduly exposing them to the atmosphere, and have proven that accurate measurement is possible post filtration. I’d now like to put this method into practice, exploring the differences in our understanding of certain systems given measurement with and without filtration. This could be particularly important along the coast, and in other somewhat complicated environments. Another consideration is whether the use of filtration can reduce the need for preservation of samples in certain circumstances where measurement can be done timely.

Ocean Acidification

Understanding the threat of ocean acidification to oceanic organisms is an important component of understanding our world’s response to anthropogenic climate change. I’ve been lucky to work with many biologists studying a variety of organisms (mussels, abalone, oysters, snails, squid) with a variety of response questions. The ability to perform these types of experiments in the laboratory rests on the ability to control an aquarium at the desired environment, which is where I come in. I built a system capable of controlling the carbon dioxide levels, oxygen levels, and temperature of a multi-tank system. This allows us to reproduce the typical environment that an organism lives in (even a varying one), and modify it as desired. Potentially increasing the carbon dioxide levels, increasing the temperature of the water, and decreasing the oxygen. (It’s less well known that the ocean is becoming less oxygenated with further climate change – a big problem for breathing organisms!) The control of oxygen is also important because it often co-varies with carbon dioxide, as organisms photosynthesize or respire.

MSEAS - An aquarium system at Scripps designed to carefully control carbon dioxide and oxygen levels.

MSEAS – An aquarium system at Scripps designed to carefully control carbon dioxide and oxygen levels.