Abstract

Alkenone signatures preserved in marine sedimentary records are considered one of the most robust paleothermometers available, and are often used as a proxy for paleoproductivity. However, important gaps remain on the provenance and fate of alkenones, and their impact on derived environmental signals in marine sediments. Here, we analyze the abundance, distribution, and radiocarbon (14C) age of alkenones in bulk sediments and corresponding grain-size fractions in surficial sediments from seven continental margin settings in the Pacific and Atlantic Oceans in order to evaluate the impact of organo-mineral associations and hydrodynamic sorting on sedimentary alkenone signals. We find that alkenones preferentially reside within fine-grained mineral fractions of continental margin sediments, with the preponderance of alkenones residing within the fine silt fraction (2–10 µm), and most strongly influencing alkenone 14C age, and SST signals from bulk sediments as a consequence of their proportional abundance and higher degree of OM protection relative to other fractions. Our results demonstrate that selective association of alkenones with mineral surfaces and associated hydrodynamic mineral sorting processes can alter alkenone signals encoded in marine sediments (14C age, content, and distribution) and confound corresponding proxy records (productivity and SST) in the spatial and temporal domain.

Highlights

  • Since the initial discovery of alkenones (Boon et al, 1978; Volkman et al, 1980), these molecular biomarkers have become one of the most applied and well-established paleoclimate proxies, allowing estimation of sea surface temperature (SST) and 25 primary productivity in most oceanographic settings (Sachs et al, 2000; Raja and Rosell-Melé, 2021)

  • We analyze the abundance, distribution, and radiocarbon (14C) age of alkenones in bulk sediments and corresponding grain-size fractions in surficial sediments from seven continental margin settings in the Pacific and Atlantic Oceans in order to evaluate the impact of organo-mineral associations and hydrodynamic sorting on sedimentary alkenone signals

  • We find that alkenones preferentially reside within fine-grained mineral fractions of continental margin sediments, with the preponderance of 15 alkenones residing within the fine silt fraction (2-10 μm), and most strongly influencing alkenone 14C age, and SST signals from bulk sediments as a consequence of their proportional abundance and higher degree of OM protection relative to other fractions

Read more

Summary

Introduction

Since the initial discovery of alkenones (Boon et al, 1978; Volkman et al, 1980), these molecular biomarkers have become one of the most applied and well-established paleoclimate proxies, allowing estimation of sea surface temperature (SST) and 25 primary productivity in most oceanographic settings (Sachs et al, 2000; Raja and Rosell-Melé, 2021). This signal can be altered in marine sediments by the significant loss of alkenones that occurs during their export to and deposition on the seafloor. This “flux attenuation” is site-dependent and generally higher during periods of maximum flux (Rosell-Melé and Prahl, 2013). Given the propensity for preferential mobilization and redistribituion of specific grain sizes (McCave et al, 1995; McCave and Hall, 2006a; Pedrosa-Pàmies et al, 2013; Bao et al, 2016) this information is crucial for assessing potential impacts on sedimentary alkenone signals

Methods
Results
Discussion
Conclusion

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.