By Ben Gustafson
Ocean carbon is important to understand because climate change is affecting the world today and the ocean plays a major role, taking up so much of the world’s carbon. Thus, understanding the carbon processes in the ocean will greatly help us mitigate climate change. On a personal note, I think the ocean is a beautiful ecosystem with so many different fascinating organisms, and it is important to understand how to protect them. Furthermore, it is important to understand how ocean acidification will play a role in potentially changing these systems.
Ocean acidification affects all parts of the ocean, from the shallow coastal ocean to the deep sea. Specifically impactful are its effects on shell-forming organisms. Pelagic, or open ocean calcifiers are a major group that are anticipated to be impacted by climate change. Similar to corals, pelagic calcifiers make their shells from calcium carbonate (CaCO3). Shells made of CaCO3 are susceptible to dissolution and will experience some form of dissolution either at the surface or over time as they sink into the deep ocean.
However, not all calcifiers experience dissolution at the same rate due to the structure of CaCO3, or the polymorph. Aragonite, for example, is more susceptible to dissolution than calcite. A third form, High-Mg calcite, is also more susceptible to dissolution.
Different pelagic calcifiers produce different CaCO3 polymorphs. Coccolithophores are phytoplankton that make a series of coccoliths, or spheres surrounding their cell, from calcite. Foraminifera, another single-celled organism (but not a primary producer), also make a calcite shell known as a test.
On the other hand, shelled pteropods, a swimming snail of the sea, creates a shell of aragonite. Finally, pelagic fish create a carbonate in their gut that they excrete that is made from high-Mg calcite. While high-Mg calcite is very soluble, the excreta are surrounded by an organic coating that limits dissolution while the quick-sinking particles descend in the ocean.
I have been surprised in the diversity of the calcifiers. It’s so fascinating to see this one common trait that unite calcifiers, while their life cycles can be so different from one another.
Given the great diversity in shell type and shell-forming organisms, most studies only evaluate one or two calcifiers together. It makes sense that a microscopic photosynthesising coccolithophore and a 100cm free-swimming fish might not behave in the same way. However, to understand the ocean as a whole, it is important to synthesise the information on pelagic calcifiers. Part of my PhD project is to understand the multi-stressors of climate change, including ocean acidification, ocean warming, and loss of oxygen and how they will affect each calcifier. Putting together these key pieces will provide us context and inform on the future of our oceans under climate change.
Ben Gustafson
Ben’s research in OceanICU is focused on global and regional assessments of the contribution of different organisms to the ocean’s carbonate pump and examining the role of biology in the marine carbon cycle. Raised in Ely, MN, USA, Ben holds a BA in environmental science and biology from Colby College.
