NEW EVIDENCE OF BACTERIAL DEGRADATION IN FOSSIL WHALE FALLS: NOT JUST A BORING TALE!

At whale falls around the world, diverse communities of invertebrates are living off of the nutrient-rich environment provided by sulfate reducing bacteria. Organisms live off of sulfides produced from anaerobic breakdown of lipids found within the bones. Fossil records of microborings indicate that this process has occurred since the evolution of modern cetaceans. Whale fossils from Sekiu River, Washington; Calvert Cliffs, Maryland; coastal Chile; and North and South Carolina were thin-sectioned and analyzed for evidence of microbial activity. A desmostylid fossil from Ojai, California was also thin-sectioned. Assessments of the thin-sections were made using petrographic, reflected light, and cathodoluminescence microscopy. Each thin-section was examined for the presence of bacterial alteration of the bone, formation of authigenic pyrite, and botryoidal aragonitic cements. No evidence of bacteria was found in samples from Calvert Cliffs, Maryland or Ojai, California. The samples from Sekiu River have been heavily altered by bacteria. There are bacterial borings with an average diameter of 8.02 µm. Framboidal pyrite crystals with an average diameter of 61.84 µm in diameter occur within the pore spaces of the bone, in borings, and at the bone-sediment interface. The pyrite crystals are densely packed at the edges of the bone and scattered more randomly throughout the pore spaces. Aragonitic botryoidal cements line pore spaces in samples from Sekiu River. The cements have an average thickness of 90.75 µm and are believed to be linked to bacterial activity. Potential bacterial peloids are rare but observed in pore spaces in the bone. The average size of the potential peloids is 77.45 µm. In the sediment adjacent to the bone, foraminiferal microfossils are observed. Some of the foraminferal tests are also filled with authigenic pyrite, suggesting multiple origins for the sulfide formation. This investigation is yielding new evidence for tracking the record of the bacterial component of whale fall ecosystems through time.