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TL PhD Comprehensive Exam
  • Introduction
  • Tasklist
  • 1. Basics
    • 1.1 Basic Biology Review
    • 1.2 Basic Genetics Review
    • 1.3 Light & Photosynthesis
  • 2. Coral Biology
    • 2.1 Basic Coral Biology
      • 2.1a Food Webs
    • 2.2 Reef Structure
    • 2.3 Growth & Reproduction
    • 2.4 Morphology
    • 2.5 Physiology
    • 2.6 Mixotrophy & Energy
    • 2.7 Symbiosis
    • 2.8 Reef Mortality
      • 2.8a Conservation
  • 3. Ecology & Evolution
    • 3.1 Evolution & Plasticity
    • 3.2 General Ecology
    • 3.3 Species
    • 3.4 Cryptic Species
  • 4. Isotopes
    • 4.1 Isotope Basics
      • 4.1a Instrumentation & methodology
      • 4.1b Environmental O & H
      • 4.1c Environmental C and N
      • 4.1d Organismal Isotopes
    • 4.2 Fractionation in Corals
    • 4.3 Trophic Niche Analysis
    • 4.4 CSIA
      • 4.4a C: Essential vs. Nonessential
      • 4.4b N: Trophic vs. Source
  • 5. Other
    • 5.1 Science & Society
    • 5.2 Stats
  • 6. Summary & Resources
    • 6.1 Glossary
    • 6.2 Resources
    • 6.3 Questions From Exam
    • 6.4 Recommendations & Reflections
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  • Definitions
  • Notation
  1. 4. Isotopes

4.1 Isotope Basics

Most isotope info sourced from URI OCG 550 with Kelton McMahon

Last updated 1 year ago

Definitions

Isotope - atoms of the same element with different numbers of neutrons, differ in mass but have essentialy the same chemical reactivity

  • Stable - do not undergo radioactive decay, but do undergo fractionation

  • Radioactive - unstable isotopes that will decay to other elements by shedding their neutrons / protons to achieve stability

Fractionation - the alteration of the distribution of stable isotopes as a result of chemical, physical, or biological processes

  • Kinetic - Unidirectional reactions due to differences in reaction rate of molecules or atoms containing different masses - light isotope usually reacts faster - includes transport or diffusion processes dealing with flux

    • sometimes there are multiple products, which still have to conserve mass

  • Equilibrium - Isotope exchange reactions driven by changes in vibrational energies of molecules, forward and back reactions reach thermodynamic equilibrium - the heavy isotope accumulates where it is held strongest - phase changes

    • alpha (fractionation rate) decrease with temp

    • fractionation highest for light elements

  • Rayleigh fractionation - products are isolated from reactants immediately after formation, leading to characteristic isotope pattern of evolving phases

  • Conservation of mass - reactant and product must preserve original epsilon when 100% reacted

Most important Isotopes (for me) - O and H are typically associated with environmental fractionation and gradients, while N and C are more important for biological processes

  • 1H vs 2H

  • 12C vs 13C

  • 14N vs 15N

  • 16O vs 18O

Notation

    • positive values = enrichment

    • negative values = depletion

    • very temperature dependent

  • Turnover time - T

References

McMahon, Hamady & Thorrold 2013

Provides a thorough background on ecogeochemistry and the uses of isotopes in marine ecosystems.

Delta Notation - Allows us to compare between samples by standardizing them to international standards. where R is the heavy/light isotope ratio, units are permil ‰.

Big Delta Notation - Isotope separation

Epsilon - Isotope Enrichment

Alpha notation - Isotope Fractionation

As you increase up a mountain slope, the delta18O in clouds becomes increasingly negative. the 18O is being captured in the water / condensation and clouds are getting isotopically lighter. the gradient that is created is called rayleigh fractionation