Early Pleistocene glacial cycles in marine δ18O exhibit strong obliquity pacing, but there is a
perplexing lack of precession variability despite its important influence on summer insolation
intensity–the presumed forcing of ice sheet growth and decay according to the Milankovitch
hypothesis. This puzzle has been explained in two ways: Northern Hemisphere ice sheets
instead respond to insolation integrated over the summer, which is mostly controlled by
obliquity, or anti‐phased precession‐driven variability in ice volume between the …

Abstract Two decades ago, Joyce (1993) presented a planktonic δ18O record from ODP site
625 in the Gulf of Mexico and interpreted numerous light isotope excursions beginning at 2.5
Ma as reflecting Laurentide Ice Sheet meltwater pulses down the Mississippi River. This
finding implied an extensive early Pleistocene (EP) ice sheet, seemingly at odds with the
smaller global ice volume inferred from benthic δ18O at this time. The till record on land
confirms that ice extended into the central US at least twice during the EP. We are …