Sedimentation is the process by which particles sink and accumulate on the seafloor. Layers upon layers of these settled materials tell the story of the oceans and climate from which they originated. Alterations to these sediments from compaction, bioturbation, and microbial respiration form sedimentary rocks through an action termed diagenesis. A better comprehension of diagenesis is needed to translate the sedimentary record into clues that help explain past events. To better understand these processes, students at MLML take the MS 274 “Advanced Topics in Oceanography” course. This class, taught by Dr. Ivano Aiello and Dr. Kenneth Coale, examines the factors that affect sedimentation and subsequent diagenesis in Monterey Bay.
A major driver of sedimentation is the ocean “biological pump.” This is the fixation of carbon by phytoplankton and the subsequent transport of plankton debris to depth. Over time, these sediments undergo diagenesis as more sediments are deposited and compacted or consumed and disturbed by organisms. The process of diagenesis mimics many of the same processes as we observe in a compost pile, but occurs much slower.
To study which organisms drive the biological pump in Monterey Bay, the MS 274 class constructed sediment traps. To build the array, we first mastered the technique of splicing rope together, which held our sediment traps to a mooring approximately 30 feet from the seafloor. Then, we attached a subsurface float that held eight replicate sediment traps just above the sediments. On top of the array, we fastened a surface float to aid in recovery. The purpose of the array was to catch fresh material that we could compare to materials in the sediments.
On September 24, 2012, we boarded the R/V John H. Martin and set a course for a location in Monterey Bay that was approximately 60 feet deep and deployed our sediment trap array. The traps were left for two weeks before they were retrieved on October 8, 2012. In addition, we collected sediment cores from the trap location from the R/V Point Sur in order to retrieve older material from comparison.
Once in the lab, we conducted scanning electron microscopy (SEM), elemental analysis and petrographic microscopy to characterize both fresh and deposited materials. Stay tuned for part two, where we present and interpret our findings!