Preservation of organic carbon (OC) in marine sediments exerts a major control on the cycling of carbon in the Earth system. In marine sediment, OC preservation may be enhanced by diagenetic reactions in locations where deposition of tephra occurs. While the mechanisms by which this process occurs are well understood, site-specific studies are limited. Here, we report on a study of sediments from the Bering Sea (IODP Site U1339D) to investigate the effects of marine tephra deposition on carbon cycling during the Pleistocene and Holocene. Our results strongly suggest that tephra layers are loci of OC burial with distinct d¹³C values, and that this process is primarily linked to complexation of OC with reactive metals (accounting for ~80% of all OC within tephra layers). In addition, distribution of reactive metals into non-volcanic sediments above and below the tephra layers enhances OC preservation in these sediments, with ~33% of OC bound to reactive phases. Importantly, OC-Fe coupling is evident in sediments >700,000 years old. Thus, these interactions may help explain the preservation of labile OC in older marine sediments.