[BCG06-P03] Reconstruction of key ecological responses leading to the most recent dead zone formations in Japan Sea through ancient DNA metabarcodring
Keywords:global warming paleo-analogue, hypoxemia expansion, molecular paleoecologcail dynamics, biogeochemical cycling
Stage1: Under oxygenated bottom conditions, the most dominant taxonomic group was Marine Stramenopiles Group 9 (MAST-9). MAST-9 encompasses diverse uncharacterized planktonic species, 18S rRNA gene sequences of which were detected from both anoxic and oxic water bodies in Pacific and Atlantic Oceans, Mediterranean Sea and South China Sea.
Stage 2: Before the onset of dead zone formation, the sharp decline of MAST-9 was accompanied with the expansion of marine diatom species of the genus Skeletonema, many members of which are known to be a cause of red tide around the world.
Stage 3: The dead zone formation was synchronized with the expansion of marine radiolarians of the order Chaunacanthida, the members of which are encrusted within SrSO4.
Stage 4: Stages 2 was repeated, whereas the expansion of the Chaunacanthida radiolarians was not evident.
Stage 5: The uncharacterized MAST-9 that was dominant before the dead zone formation was gradually recovered towards oxygenated bottom conditions.
From these results, it is suspected that the expansion of Radiolaria species encrusted with SrSO4 triggered dead zone formation by the accelerated downward transport of dead cells and subsequent heterotrophic consumption of O2. From bioturbated sediment samples from a maximum depth of 31 mbsf with a depositional age of 100 ka, the Chaunacanthida sequences closely related to that from the laminated sediments have been previously detected.It is therefore suggested the record of the Chaunacanthida species can be reconstructed from sediments with great depth and age.