Abstract

The beginning of the mid-Brunhes event ca. 430 ka coincided with the largest-amplitude change in δ18O in the global ocean over the past 6 m.y. This large δ18O change recorded a major ice-sheet expansion that cannot be explained by small changes in orbital forcing. Our recent studies at Ocean Drilling Program Site 1143 from the South China Sea show that this large δ18O change was preceded by a significant negative δ13C shift. A global survey of long deep-sea records has revealed periodic δ13Cmax episodes (i.e., maximum positive values of δ13C), and both major ice-sheet expansion events in the Pleistocene (the mid-Brunhes event and the middle Pleistocene revolution) were preceded by δ13Cmax episodes followed by negative δ13C shifts. This new finding suggests that disturbance in carbon reservoirs leads to major growth of ice-sheet size and challenges the prevalent concept of Arctic control of glacial cycles. Because Earth is now passing again through a δ13Cmax episode, it is crucial to understand the causal relationship between the successive δ13C changes and ice-sheet growth events.

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