Cancellation of the Precessional Cycle in δ 18 O Records During the Early Pleistocene

The dominant pacing of glacial‐interglacial cycles in deep‐ocean δ 18 O records changed substantially during the Mid‐Pleistocene Transition. The precessional cycle (∼23 ky) is absent during the Early Pleistocene, which we show can be explained by cancellation of the hemispherically antiphased precessional cycle in the Early Pleistocene interior ocean. Such cancellation develops due to mixing of North Atlantic and Southern Ocean δ 18 O signals at depth, and shows characteristic spatial patterns. We explore the cancellation potential for different North Atlantic and Southern Ocean deep‐water source δ 18 O values using a tracer transport ocean model. Cancellation of precession occurs for all signal strengths and is widespread for a signal strength typical for the Early Pleistocene. Early Pleistocene precessional power is therefore likely incompletely archived in deep‐sea δ 18 O records, concealing the true periodicity of the glacial cycles in the two hemispheres. δ 18 O records from deep‐sea sediments show a pronounced difference in periodicity between the Early (∼2‐1 Million years ago) and Late (∼1‐0 Million years ago) Pleistocene—the Mid‐Pleistocene Transition (MPT). Representing changes in ice volume and temperature, these δ 18 O records are an important source for our understanding of long‐term climate variability. A central conclusion based on these δ 18 O records is that glacial‐interglacial cycles considerably changed their rhythm during the Mid‐Pleistocene. Curiously, the ∼23,000‐year (precessional) cycle of insolation is absent in Early Pleistocene δ 18 O records—despite its presence in insolation forcing to the ice sheets. Climate feedbacks involving (sea) ice, geological processes and carbon cycling may have contributed to the MPT. We, however, show that the absence of an Early Pleistocene precession signal in deep‐sea δ 18 O records could be the result of destructive interference in the deep ocean, caused by the antiphasing of the precessional cycle between the North Atlantic and Southern Ocean deep‐water sources. We explore the potential for cancellation with an ocean model and show that interference can indeed cause widespread cancellation, particularly in the Early Pleistocene. We, therefore, conclude that the δ 18 O incompletely archives climatic cycles, challenging our understanding of long‐term climate variability. Glacial‐interglacial cycles can be incompletely recorded in the ocean due to cancellation of hemispherically antiphased signals