About this Research Topic
The production of CaCO3 shell material by marine calcifying planktonic organisms produces a surface-to-depth alkalinity gradient, causing CO2 to be released back to the atmosphere. This mechanism is known as the Calcium Carbonate (CaCO3) Counter Pump because, in terms of air-sea CO2 exchange, it is opposite to the process driving the Biological Carbon Pump (where CO2 is consumed by phytoplankton through photosynthesis, leading to a drawdown of CO2 from the atmosphere and to a transport of Particulate Organic Carbon (POC) into the deep ocean).
On the other side, calcifying plankton, through removing calcium (Ca2+) and (bi-) carbonate ions from the ocean surface, can influence the export of Particulate Inorganic Carbon (PIC). Calcifying zooplankton for instance, such as pteropods, ostracods and foraminifera, promote PIC sequestration to the deep ocean because the relatively large mass of their shell makes them sink rapidly. By comparison, calcifying phytoplankton such as the unicellular coccolithophores and their calcite platelets hardly sink individually and have a large range in sinking rates depending on the assimilation into larger biological aggregates and faecal pellets. The burial of CaCO3 in marine sediments (due to the sinking of post-mortem calcifying organisms into to the oceanic depth) is one of the main mechanisms to reduce atmospheric CO2 on geological timescales related to silicate weathering processes.
The Carbonate Counter Pump can, therefore, have very different effects on ocean carbon, alkalinity, and atmospheric CO2 on different spatial and temporal scales. Further, the level of carbonate precipitation, as well as the ability to act as ballast, depends on the composition of calcifying species within the plankton community and the relative balance between PIC: POC export (rain ratio).
The scientific concern about the impact of Ocean Acidification on the calcifying community structure has recently highlighted the importance of understanding the main process regulating the carbonate production.
The objective of this Research Topic is to bring together contributions investigating the biogenic carbonate production, flux and export within the ocean carbon cycle. This Research Topic aims also to better characterize the role of calcifying planktic organisms in driving the stretch of the Carbonate Counter Pump.
We welcome a broad range of contributions (original research articles, methods papers, perspectives, opinions, and reviews), from individual-based process studies, to local and global field observations, and modeling approaches.
Keywords: Carbonate, Flux, PIC, Alkalinity, Calcifying plankton
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