DEVELOPING MARINE BENTHIC EPIPHYTIC DIATOM PRESENCE AND ABUNDANCE AS A TOOL FOR RECONSTRUCTING ANTARCTIC PALEOCEANOGRAPHIC AND PALEOCEANOGRAPHIC HISTORY

Marine epiphytic benthic diatoms grow on seaweed (macroalgae) in the photic zone and provide a rich source of food for herbivores. The macroalgae attach to the marine substrate with a holdfast, a multi-fingered structure that serves as an anchor. Miocene sediments at DSDP Site 269, off Wilkes Land, Antarctica contain variable and discontinuous abundances of such epiphytic genera as Arachnoidiscus, Isthmia, Rhabdonema, Gephyra, Trigonium, Achnanthes, Cocconeis, Grammatophora, and Rhaphoneis. How did these near-shore benthic diatoms get to such a deep water location? We propose that they are transported on the seaweed, when it is uprooted and floats to the deeper ocean. Then, as the diatoms are grazed by herbivores and sink to the seafloor in fecal pellets or decompose outright.

Their discontinuous stratigraphic occurrence within Miocene sediment from Core 9 of DSDP Site 269 suggests environmental changes induced by warm or cold events may have controlled the production and/or release of the macroalgae. One hypothesis is that macroalgae were released during warming when sea ice was retreating, and expanded, sunlit, shallow coastal areas in the Wilkes Basin margin were exposed to high wave activity, thus releasing the buoyant kelp from its substrate and transporting the benthic epiphytic algae into the open sea. Alternatively, their presence could represent a cold interval where ice formation on the macroalgae increased its buoyancy and lifted vast quantities off the substrate allowing it to float to the deeper ocean. Complicating the distinction between warm and cold events is the potential for the transport of sediment within the holdfast, biologically-rafted-debris (BRD). Identifying the abundance and provenance of the terrigeneous sediment may help to distinguish the climate and source-area signal of this complex relationship and refine the use of epiphytic diatoms as a paleoclimate and stratigraphic tool.