Geology

Biogeochemistry

Sink (geography)

Biology

Sponge spicule

Authigenic

Oceanography

Paleontology

Geography

Ecology

Earth science

Sponge

Diatom

Biogenic silica

Cartography

Sedimentary rock

Biogeochemical cycle

Nature Geoscience

Silicon (Si) is a pivotal element in the biogeochemical and ecological functioning of the ocean. The marine Si cycle is thought to be in internal equilibrium, but the recent discovery of Si entries through groundwater and glacial melting have increased the known Si inputs relative to the outputs in the global oceans. Known outputs are due to the burying of diatom skeletons or their conversion into authigenic clay by reverse weathering. Here we show that non-phototrophic organisms, such as sponges and radiolarians, also facilitate significant Si burial through their siliceous skeletons. Microscopic examination and digestion of sediments revealed that most burial occurs through sponge skeletons, which, being unusually resistant to dissolution, had passed unnoticed in the biogeochemical inventories of sediments. The preservation of sponge spicules in sediments was 45.2 ± 27.4%, but only 6.8 ± 10.1% for radiolarian testa and 8% for diatom frustules. Sponges lead to a global burial flux of 1.71 ± 1.61 TmolSi yr−1 and only 0.09 ± 0.05 TmolSi yr−1 occurs through radiolarians. Collectively, these two non-phototrophically produced silicas increase the Si output of the ocean to 12.8 TmolSi yr−1, which accounts for a previously ignored sink that is necessary to adequately assess the global balance of the marine Si cycle. Inclusion of sponge spicules and radiolarians increases the global ocean biological sink of silicon by 28%, with 95% of that increase attributed to sponges, according to examination of sediments from 17 marine cores.

Sponge skeletons as an important sink of silicon in the global oceans