Professor Sarmiento led a team of researchers investigating several aspects of the oceanic "hard tissue pump" under ocean acidification. EarthÆs oceans are salty, and some of the alkaline salts in seawater make the ocean slightly basic, where basic means the opposite of acidic. Organisms in the oceans have adapted to take advantage of the basicity of the oceans. Some organisms form their shells out of calcium carbonate, an alkaline salt. These shells are formed at the ocean surface where there is light for photosynthesis. When the organisms die, the shells sink to depth and dissolve, releasing the alkaline salts. This transport of alkaline salt from the surface to the deep ocean is called the "hard tissue pump." However, the concentration of carbonate ion, needed to form calcium carbonate, is decreasing as CO2 released by man combines with water to form carbonic acid. The response of the hard tissue pump—and the important organisms that keep it going—to these changes is uncertain. Postdoc Eun Young Kwon examined the role that the hard tissue pump plays in the modern ocean. She used global models to quantify the influence of the hard tissue pump on the concentration of CO2 in the atmosphere. This influence is critical for a changing climate because CO2 traps heat and warms the planet when it is in the atmosphere. Her findings help climate scientists better estimate how much a changing hard tissue pump will affect the balance of carbon between the ocean and the atmosphere. She also did research into bygone eras of EarthÆs history to draw insights about the modern ocean. Among other things, she found that ocean circulation changes will be a critical component of understanding how EarthÆs climate changes going forward. Postdoc Brendan Carter and Kwon both examined the challenging problem of determining how deep in the ocean calcium carbonate dissolves. There is a debate among scientists regarding whether calcium carbonate dissolves in the deep ocean where it should be dissolved by corrosive water, or in the shallower ocean where it could be dissolved by acids released by the biological metabolism of organic matter. Kwon found calcium carbonate dissolves deeper than where organic matter is metabolized on average, while Carter showed that a significant fraction dissolves at depths above where the water becomes corrosive. These findings suggest that both possible behaviors are likely occurring to some degree, and Carter has since worked to develop methods for estimating the relative importance of these two mechanisms. The answer is important for modeling the future of EarthÆs climate, especially as one answer means there will be large changes in where carbonate dissolves as the ocean becomes more corrosive, and the other answer suggests the changes would be more strongly related to possible changes in where organic matter is metabolized. Kwon also showed that the depth of dissolution has a large impact on the ocean storage of CO2 and therefore the long term fate of EarthÆs climate with rising CO2. Carter worked with Undergraduate Jeong Do Ahn on the related problem of detecting ocean acidification. Carter refined methods for measuring seawater pH. He then developed a tracer that could be used to directly examine the influence of rivers and the hard tissue pump on the concentrations of alkaline salts in the ocean. Carter used this new tracer to create a riverine alkalinity budget that could be adapted for climate models. In recent yet-unpublished work he plans to show that this tracer could plausibly decrease the length of time required to identify the chemical imprint of a changing hard tissue pump by as much as a factor of 5. Carter was also interested in knowing whether seawater chemistry controls the hard tissue pump or vice versa. He used the tracer he developed to quantify how large of an influence the hard tissue pump has on the concentration of carbonate ions in seawater. He found...
©2020 Biological and Chemical Oceanography Data Management Office.