Periodic Reporting for period 3 - DEVOCEAN (Impact of diatom evolution on the oceans)
Período documentado: 2022-10-01 hasta 2024-03-31
Motivated by a series of recent discoveries, DEVOCEAN will provide the first comprehensive evaluation of the emergence of diatoms in the oceans and their impact on the global cycles of silica and carbon, and ultimately on the climate. I propose that the proliferation of phytoplankton that occurred after the Permian-Triassic extinction, in particular the diatoms, fundamentally influenced oceanic environments through carbon export from the settling of diatoms to the ocean floor. Although molecular biologists suggest that diatoms evolved over 200 million years ago, this result has been largely ignored because of the lack of diatoms in the geological fossil record. Therefore, most studies in the past have focused on the diversity of diatoms in the last 66 million years during the Cenozoic when abundant diatom fossils are found. DEVOCEAN will provide evidence on diatom evolution in the geological record by examining older ocean sediments both currently buried on the sea floor and on the continents. The overall objective is to make estimates of the timing and magnitude of dissolved Si drawdown following the origin of diatoms using the isotopic silicon compositions of fossil sponge spicules and radiolarians. The project will also provide new insights into how the evolution of diatoms changed the energy flows and biological communities of the ancient oceans. A deeper knowledge of how diatoms evolved and influenced biological process in the oceans will allow society to make more informed decisions about global challenges especially regarding climate.
Extensive delays in our research were caused by the Covid-19 pandemic, therefore an extension of 18 months was granted to compensate for the time lost to complete this project.
We have searched extensively for diatoms and/or sponge spicules in the early fossil record. This has been one of the biggest challenges we have faced and is one of the high-risk aspects of this research project. We continue to request materials from archives and also to go on field trips to search for siliceous fossils as travel restrictions ease.
We participated in an Integrated Ocean Drilling Program Expedition 391: The Walvis Ridge Hotspot (December 2021 - February 2022). Although the cruise focused on deep drilling to study mantle geodynamics, we were able to collect 2 cores that contain siliceous fossils that will potentially provide the records across the last 80 million years.
Our studies of diatom phylogenies have not progressed until recently because of travel restrictions. We are currently working on reconstructing the evolution of silica transporters (SITs) and its link to the marine-freshwater diatom transition.
We have been testing methods for extracting siliceous fossils (sponges and radiolarians) embedded in cherts in a method that has previously been used by taxonomists. The procedure involves dissolving cherts in 5% HF for 10 minutes, then collecting and washing the materials that are released. Our preliminary analysis suggests that this method my only recover material that has been transformed from opal-A to opal-CT. This change in silica necessitates a dissolution-reprecipitation reaction that is known to fractionate the Si isotopes. Therefore, these materials can not be used to obtain accurate measurements for Si isotopes.
We have observed that many of the siliceous sponge spicules we have collected from the Mesozoic era have been diagenetically altered. We have initiated a study to determine the impacts of varying extents of diagenesis on Si isotopes by comparing modern and fossil sponge spicules. Based on a library of 12 modern sponges and 12 Mesozoic sponge spicules, we have used different techniques to determine extents of diagenesis from opal-A to opal-CT of these samples (Raman spectroscopy, FTIR (on-going), XRD and SEM coupled with element mapping). We also are measuring Si isotopes of these samples using SIMS for individual spicules and liquid mass spectrometry for bulk Si isotopes. This will be a tremendous resource to the geochemical community to verify the status of the materials from the geologic record used to determine their Si isotopic composition.
Biogeochemical models of past ocean chemistry and biology are being used to evaluate the mechanistic links between variations in the global Si and C cycles. We have hired a knowledgeable and highly capable young scientist to carry out this research. We are using the current version of the cGENIE Earth System model that has been configured for Si cycling and Si isotope systematics.
We have searched extensively for diatoms and/or sponge spicules in the early fossil record. This has been one of the biggest challenges we have faced and is one of the high-risk aspects of this research project. We continue to request materials from archives and also to go on field trips to search for siliceous fossils as travel restrictions ease.
We participated in an Integrated Ocean Drilling Program Expedition 391: The Walvis Ridge Hotspot (December 2021 - February 2022). Although the cruise focused on deep drilling to study mantle geodynamics, we were able to collect 2 cores that contain siliceous fossils that will potentially provide the records across the last 80 million years.
Our studies of diatom phylogenies have not progressed until recently because of travel restrictions. We are currently working on reconstructing the evolution of silica transporters (SITs) and its link to the marine-freshwater diatom transition.
We have been testing methods for extracting siliceous fossils (sponges and radiolarians) embedded in cherts in a method that has previously been used by taxonomists. The procedure involves dissolving cherts in 5% HF for 10 minutes, then collecting and washing the materials that are released. Our preliminary analysis suggests that this method my only recover material that has been transformed from opal-A to opal-CT. This change in silica necessitates a dissolution-reprecipitation reaction that is known to fractionate the Si isotopes. Therefore, these materials can not be used to obtain accurate measurements for Si isotopes.
We have observed that many of the siliceous sponge spicules we have collected from the Mesozoic era have been diagenetically altered. We have initiated a study to determine the impacts of varying extents of diagenesis on Si isotopes by comparing modern and fossil sponge spicules. Based on a library of 12 modern sponges and 12 Mesozoic sponge spicules, we have used different techniques to determine extents of diagenesis from opal-A to opal-CT of these samples (Raman spectroscopy, FTIR (on-going), XRD and SEM coupled with element mapping). We also are measuring Si isotopes of these samples using SIMS for individual spicules and liquid mass spectrometry for bulk Si isotopes. This will be a tremendous resource to the geochemical community to verify the status of the materials from the geologic record used to determine their Si isotopic composition.
Biogeochemical models of past ocean chemistry and biology are being used to evaluate the mechanistic links between variations in the global Si and C cycles. We have hired a knowledgeable and highly capable young scientist to carry out this research. We are using the current version of the cGENIE Earth System model that has been configured for Si cycling and Si isotope systematics.
We knew beforehand that there is a paucity of diatom fossils in the geologic record and therefore we have searched widely for diatoms in sediment older than the 124 Ma which contain the oldest known diatoms. We continue to request materials from archives and now we are able to travel to different locations to search for siliceous fossils. We have achieved some success in obtaining material containing sponge spicules and radiolarians to carry out our research. By the end of the project we are confident we will have the necessary material and measurements of Si isotopes to test our hypothesis regarding changes in oceanic dissolved silica during the last 200 million years.