"Decoding Chemical Evolution and Nucleosynthesis"

I will discuss insights from analytic and numerical models of
galactic chemical evolution and observations of Milky Way
elemental abundances from the SDSS APOGEE survey.  Under
generic model assumptions, abundances and abundance ratios
approach an equilibrium in which element production from
nucleosynthesis is balanced by element depletion from star
formation and outflows.  Reproducing solar abundances requires
outflows with mass-loading factors of 1-3, but one can evade
this conclusion by assuming low stellar yields or metal-enhanced
winds; the high observed deuterium abundance of the local ISM
argues against these alternatives and in favor of outflows.
Starbursts or other sudden transitions can produce temporary
boosts in alpha-to-iron ratios, and other surprising behavior
such as backward evolution of a stellar population from high
metallicity to low metallicity.  APOGEE observations show 
that the distributions of stars in (alpha,iron,age)-space change
steadily across the Milky Way disk.  Given these distributions,
the behavior of other APOGEE abundance ratios can be explained 
by changes in the ratio of core collapse to Type Ia supernova
enrichment.  The separability of "multi-element cartography"
offers a route to empirically constraining supernova yields
in a way that is insensitive to uncertainties in other aspects
of chemical evolution.