Molluscan response to early Pleistocene rapid warming in the Sea of Japan

Major changes occurred in the benthic molluscan fauna of the Sea of Japan c ontinental shelf during the transition from Pleistocene glacial to intergla cial stages, owing to rapid warming associated,vith the inflow of the warm Tsushima Current. Molluscan associations representing this transition occur in the lower Pleistocene Omma Formation in central Japan and suggest that there were two patterns of faunal change. The first was, when warm-water sp ecies migrated into the Sea of Japan and lived along with cold-water specie s, accompanied by a northward shift in species ranges. The second pattern i nvolved the migration of warm-water mollusks shortly after the local extinc tion of cold-water species, In the latter, it is possible that benthic moll uscan communities with very low diversity and density existed temporarily a nd locally at inner shelf depths (<100 m) during the warming phase. Such a community has no modern analogue, but may have resulted from a marine clima te with a higher seasonality than occurs today, These findings show that ep isodes of rapid warming have severe impacts on offshore benthic communities and moluscan species that include patterns not represented by modern fauna l distributions.