claim: The new research showed that [ oxygen isotopes in foraminifera ] can change
evidence: Stable isotopes of oxygen ( δ18O ) and carbon ( δ13C ) are recorded well in speleothems, giving high-resolution data that can show annual variation in temperature ( oxygen isotopes primarily reflect rainfall temperature ) and precipitation ( carbon isotopes primarily reflect C3 / C4 plant composition and plant productivity, but the interpretation is often complicated ).