5:15 PM - 6:45 PM
[MIS12-P32] Detection and Significance of Alkenones during the Cretaceous, and paleocene
Using Gas Chromatography Mass Spectrometry in Selected Ion Monitoring Mode
(GC/MS SIM mode)
Keywords:Alkenone, Isochrysis, Paleotemperture, PETM, GC/MS
Alkenones are long-chain unsaturated ketones specifically produced by the haptophyte Isochrysis, a type of plant plankton. The Order Isochrysidales can be divided into three groups based on genetic analysis: Group I inhabits freshwater, Group II lives in saline lakes or estuaries, and Group III resides in marine environments. Each group produces alkenones with distinctive characteristics. Particularly, Group II uniquely generates C41 (later abbreviated with carbon numbe, or carbon number, unsaturated bond number and functional group) and C42, and produces a considerable amount of C40. Group III mainly produces C37 and uniquely generates C38:2Me. Thus, it is possible to estimate the producing groups of haptophytes from the detected alkenone composition.
The composition of alkenones detected from deep sea sediments varies significantly over time. The oldest record back to 120.5 Ma, where the record shows a high proportion of C37 with no detection of C40, similar to the composition of modern Group III. Subsequently, from the sediments of 105 Ma, C40 and C41 firstly appeared, resembling the composition of modern Group II. Furthermore, previous studies from the sediments of 48.8 Ma, C37:3 and C38:2Me firstly appeared, resulting in an alkenone composition similar to modern times. The emergence of these new alkenones is believed to be related to the environmental perturbation of PETM (Paleocene-Eocene Thermal Maximum). Thus, alkenones have undergone significant changes from the Cretaceous period through the present. This study aims to increase the records of alkenone occurrences to discuss the transition and changes in alkenone producers.
Samples from IODP exp.369 Site U1514 were used for this study. GC/MS-SIM mode was employed for the analysis. This method is typically used to detect small amounts of organic molecules and has been rarely applied to alkenone paleothermometry. This study also verify the efficiency of this technique. Alkenones were detected in five samples. Among them, the oldest C38:2Me was found in a sample dating back to 60.8 Ma. The detection of C38:2Me at 60.8 Ma indicates that its evolution is not related to PETM. It is suggested that the emergence of C38:2Me is related to the haptophyte evolution and changes in the production taxa. This study demonstrates the efficiency of the SIM mode for detection of alkenones.
The composition of alkenones detected from deep sea sediments varies significantly over time. The oldest record back to 120.5 Ma, where the record shows a high proportion of C37 with no detection of C40, similar to the composition of modern Group III. Subsequently, from the sediments of 105 Ma, C40 and C41 firstly appeared, resembling the composition of modern Group II. Furthermore, previous studies from the sediments of 48.8 Ma, C37:3 and C38:2Me firstly appeared, resulting in an alkenone composition similar to modern times. The emergence of these new alkenones is believed to be related to the environmental perturbation of PETM (Paleocene-Eocene Thermal Maximum). Thus, alkenones have undergone significant changes from the Cretaceous period through the present. This study aims to increase the records of alkenone occurrences to discuss the transition and changes in alkenone producers.
Samples from IODP exp.369 Site U1514 were used for this study. GC/MS-SIM mode was employed for the analysis. This method is typically used to detect small amounts of organic molecules and has been rarely applied to alkenone paleothermometry. This study also verify the efficiency of this technique. Alkenones were detected in five samples. Among them, the oldest C38:2Me was found in a sample dating back to 60.8 Ma. The detection of C38:2Me at 60.8 Ma indicates that its evolution is not related to PETM. It is suggested that the emergence of C38:2Me is related to the haptophyte evolution and changes in the production taxa. This study demonstrates the efficiency of the SIM mode for detection of alkenones.