Mesophotic foraminiferal-algal nodules play a role in the Red Sea carbonate budget

Free-living foraminiferal-algal nodules can be over 2000 years old and contribute 980 megatons of calcium carbonate to the mesophotic benthic carbonate budget of the NEOM region of the Saudi Arabian Red Sea, according to radiometric dating of nodule accretion rates and benthic surveys. During two scientific expeditions between 2020 and 2022, direct surveys led to the discovery of free-living mesophotic foraminiferal-algal nodules along the coast of the NEOM region (northern Saudi Arabian Red Sea) where they form an unexpected benthic ecosystem in mesophotic water depths on the continental shelf. Being mostly spheroidal, the nodules are transported en masse down slope, into the deep water of the basin, where they stop accreting. Radiometric dating informs that these nodules can be more than two thousand years old and that they collectively contribute up to 66 g m(-2) year(-1) to the mesophotic benthic carbonate budget and account for at least 980 megatons of calcium carbonate, a substantial contribution considering the depauperate production of carbonate by other means in this light-limited environment. Our findings advance the knowledge of mesophotic biodiversity and carbonate production, and provide data that will inform conservation policies in the Saudi Arabian Red Sea.

Automated summary

According to radiometric dating and benthic surveys, free-living foraminiferal-algal nodules in the NEOM region of the Saudi Arabian Red Sea can be over 2000 years old and contribute 980 megatons of calcium carbonate. Two scientific expeditions between 2020 and 2022 discovered these nodules forming an unexpected benthic ecosystem in mesophotic water depths on the continental shelf. The nodules, mostly spheroidal in shape, are transported en masse down slope into the deep water basin, where they stop accreting. Radiometric dating reveals their age and their significant contribution to the mesophotic benthic carbonate budget.