Abstract

Heinrich events were collapses of the North American ice sheet during the last ice age that affected the global climate significantly. Their cause is unknown. Some have theorized that the ice sheet grew over time from snow accumulation, while the earth warmed it from below. A victim of its own success, the ice may have thickened enough to insulate heat from the ground until it melted from below, lubricating its slow slide towards the ocean. This would have removed ice from land, starting the process over. However, this theory can not explain why Heinrich events occurred when they did. Later, it was theorized that Dansgaard-Oeschger (DO) events, periods of ocean warming, played a central role by triggering ice sheet collapse through melt at the ice-ocean interface. Unfortunately, we lack robust evidence that conditions were just right for the ocean to trigger these collapses repeatedly. In this paper, we describe a computational model that can reconcile the differences between these two competing theories. We propose that Heinrich and DO events can synchronize, a phenomenon where small influences between interrelated systems can align their timing. We find that this explains many mysterious aspects of the Earth's recent climate history.