Carbon reservoir changes preceded major ice-sheet expansion at the mid-Brunhes event

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 δ¹³C_max 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 δ¹³C_max 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 δ¹³C_max episode, it is crucial to understand the causal relationship between the successive δ¹³C changes and ice-sheet growth events.