Evidence for a Northern Hemispheric trigger of the 100,000-y glacial cyclicity.

The causes of the Mid-Pleistocene Transition, the shift from ∼41-ky to 100-ky interglacial-glacial cycles and more intense ice ages, remain intensely debated, as this fundamental change occurred between ∼1,250 and 650 ka without substantial changes in astronomical climate forcings. Recent studies disagree about the relative importance of events and processes in the Northern and Southern Hemispheres, as well as whether the shift occurred gradually over several interglacial-glacial cycles or abruptly at ∼900 ka. We address these issues using a north-to-south reconstruction of the Atlantic arm of the global meridional overturning ocean circulation, a primary means for distributing heat around the globe, using neodymium (Nd) isotopes.

Causes and timing of recurring subarctic Pacific hypoxia.

Several North Pacific studies of the last deglaciation show hypoxia throughout the ocean margins and attribute this phenomenon to the effects of abrupt warming and meltwater inputs. Yet, because of the lack of long records spanning multiple glacial cycles and deglaciation events, it is unclear whether deoxygenation was a regular occurrence of warming events and whether deglaciation and/or other conditions promoted hypoxia throughout time. Here, subarctic Pacific laminated sediments from the past 1.