Alkenones[1] - C Alkenones 13 Allison Ned, Bianca Maibauer,...

Info iconThis preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: C Alkenones 13 Allison Ned, Bianca Maibauer, Laura Santare, Emily Pugh Laura What are Alkenones? What are Alkenones? l l l l l Marine organic molecules used to reconstruct Paleo CO2 in Marine surface waters surface Distinct molecular markers widespread in the photo zone Synthesized by Haptophyte microalgae Presently and in the geologic past Found in Paleogene and Neogene deposits with the oldest Found occurrence in a Mid-Albian black shale occurrence Straight, long-chained, unsaturated ethyl ad methyl Straight, ketones ketones C37 diunsaturated alkenones Alkenone Producers and Isotopic Fractionation Gephyrocapsa Oceanica and Emiliania Huxleyi e Carbon atoms in Alkenones exist in two different isotopic forms: 12 C and 13C l The selective photosynthetic uptake of 12 C is isotopic fractionation l Isotopic fractionation varies depending on dissolved carbon dioxide Emiliania Huxleyi Why does this proxy work? Stable carbon isotope composition is relevant to concentration of dissolved carbon dioxide l εp Photosynthetic carbon fixation of microalgae Shows relationship between cellular growth rate and carbon dioxide concentration Sample Separation Sample Separation Separated from bulk organic matter using traditional adsorption chromatographic techniques (molecules are separated into compound classes) Analyses Analyses Alkenones are identified by GC-MS or by comparison with elution times with a known standard l Analyses performed using a gas chromatograph-combustion system interfaced to an isotope-ratiomonitoring mass spectrometer (GCIRMS) Assumptions Assumptions In the past, alkenones were produced by similar organisms (that act in similar ways) as they are today ways) l Method founded on observation that Method stable carbon isotope composition(δ 13Corg) of marine algae composition( Corg) contains info that is relevant to concentration of dissolved CO2 during concentration algal production algal Assumptions Assumptions Several variables can affect relative expression of δ 13Corg between diff classes of microalgae Not all algae can be used l Criteria needed for δ 13Corg to act as potential CO2(aq) proxy inorganic C used during C fixation is in the form of aqueous CO2 supply of CO2(aq) used during photosynthesis arrives from ambient environment to the site of carboxylation by simple diffusion Assumptions Assumptions Variations in dissolved CO2 concentration of surface waters can result from changes in: partial pressure of CO2 in atmosphere upwelling of deep ocean waters enriched in CO2 Potential Problems Potential Problems • Differing algae species – Cellular growth rate – Cell geometry • Supply and transport mechanisms for inorganic carbon to the site of carbon fixation • • Field based research Limited knowledge of ancient algal physiologies Potential Advantages Potential Advantages You can use this proxy to get paleo CO2 records as far back as the Mid-Albian (Cretaceous ~100Ma) 3 Consistent through geological record Forams don’t always preserve well 3 Lab Based Research/Water Column Reconstruction You can constrain variables like phosphate concentrations and temperature Ideal Environment and Ideal Environment and Conditions • The inorganic carbon used during carbon fixation is in the form of aqueous CO2 • The supply of aq. CO2 used during photosynthesis arrives from the ambient environment to the site of carboxylation by simple diffusion • Low air-to-sea gas disequilibrium characteristic of these oceanic settings reduce uncertainty in the calculation of pCO2 • Culture experiments • Oligotrophic Environments are best – Limiting nutrients means less variables ...
View Full Document

This document was uploaded on 07/08/2011.

Page1 / 12

Alkenones[1] - C Alkenones 13 Allison Ned, Bianca Maibauer,...

This preview shows document pages 1 - 12. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online