I've read that benthic calcifiers like coral reefs and shellfish are producing most of the carbonate in coastal areas in the ocean. About 2.5 Gt of carbonate a year. Reef calcifiers are the most important which produce about 7,250 t CaCO3 km/yr. Further that corals dominate carbonate production with 73%.
On the other hand we have all the pelagic calcifiers like many zooplankton species using carbonate for building their shells.
Therefore, i would like to know if this is right and if this whole process plays an important role for the second tropic level in the ocean by supplying the oceans with carbonates? If it plays a role reefs should be especially important in times of an acidifying ocean, which is reducing the amount of free carbonates or am i wrong here?
I ask this, because we have already a huge impact on zooplankton in the oceans and i would like to know if dying reefs will also impact the second tropic levels negatively through this diminishing meachanism.
Thanks for any answer
Sheers
Jan
Hi Jan,
Global calcium carbonate production in the world’s oceans has been estimated to be about 5 Gt/year. You are correct, about half of the carbonate accumulates on tropical shelves, banks and coral reefs. Total carbonate production of benthic and planktonic foraminifera amounts to about 1.4 Gt/yr, which is about 25% of the present‐day carbonate production of the oceans.
When it comes to coral reefs it has often been assumed that they are sinks for atmospheric CO2. However, the precipitated of calcium carbonate actually generates CO2. I have attached a paper by Ware et al (1991) that goes into more detail on the question whether coral reefs are sources or sinks of atmospheric CO2.
Another good paper for you to read is by Eyre et al (2014) that looks at coral reef calcium carbonate dissolution in an acidifying ocean. The paper by Iglesias-Rodrigues et al (2002) will give you a nice review of the progress made in our understanding of ocean’s calcium carbonate budget. Finally the paper by Langer (2008) will inform you about the contribution of pelagic calcifiers like foraminifera in the global ocean carbon production.
I hope that some of these papers will lead you to additional literature that will shed more light on this complex issue.
Cheers, Tomas
Thanks a lot Thomas, that was what i needed. Now i can track the scientific discussion ;)
Because i want to include this subject in my book on the changes we observe in the oceans when i address the demise of the coral reefs. And i need better arguments than coral reefs are nice. Because, if they dissolve huge amounts of carbonates or calcium carbonates that would mean that they have an important role for the biogeochemical cycles in the oceans in a sense that they are beneficial to calcifiers which control alga blooms in the oceans. And 5 Gt a year is a huge amount!
The best
Jan
The construction of CaCO3 coccoliths (calcification) leads to additional impacts, over and above those associated with the photosynthesis carried out by all species. The first and perhaps the most important of these is that CaCO3 contains carbon and the vertical downward flux of coccoliths thereby removes carbon from the surface oceans. It might be expected that this would lead to additional removal of CO2 from the atmosphere to the oceans, to replace that taken up into coccoliths, but in fact, because of the complex effect of calcification (CaCO3 synthesis) on seawater chemistry, the production of coccoliths actually increases the partial pressure of CO2 in surface seawater and promotes outgassing rather than ingassing. Determining the exact nature and magnitude of the overall net effect is complicated by a possible additional role of coccoliths as ‘ballast’ (coccoliths are denser than water and hence when incorporated into aggregates of particulate fecal material may drag down extra organic carbon into the ocean interior).
Microscopic examination of seafloor sediments (if shallow enough that the CaCO3 does not dissolve) and of material caught in sediment traps has revealed that much of the calcium carbonate in the samples consists of coccoliths. The flux of coccoliths probably accounts for c. 50% of the total vertical CaCO3 flux in open ocean waters (in other words, about 50% of the inorganic carbon pump), with foraminifera shells responsible for most of the rest. It is usually not the most numerous species (E. huxleyi) but rather larger species (e.g., Calcidiscus quadriperforatus and Coccolithus pelagicus) that make the greatest contributions to the total coccolith flux.
Ref:
Coccolithophore - an overview | ScienceDirect Topics
https://www.sciencedirect.com › topics › agricultural-and-biological-sciences
Dear Abhijit, thanks a lot for your information. I have written the chapter on the organic carbon pump already but wanted to wait to finish it when the issue is more clear because two years ago many issues regarding it were in a kind of transition. At least that was what i had felt.
I think that i have in my pipeline a study that thecosomata are also important contributors to the o.pump in the southern ocean. But that coccoliths and foraminifera are the main actors in the organic carbon pump is now more or less the consent?
My plan was to wait for a new review on the issue, if you know one...
Thanks a lot and all the best
Jan