Synchronization of Heinrich and Dansgaard-Oeschger Events through
Ice-Ocean Interactions
Abstract
The cause of Heinrich events and their relationship with
Dansgaard-Oeschger (DO) events are not fully understood. Previous
modeling studies have argued that Heinrich events result from either
internal oscillations generated within ice sheets or ocean warming
occurring during DO events. In this study, we present a coupled model of
ice stream and ocean dynamics to evaluate the behavior of the coupled
system with few degrees of freedom and minimal parameterizations. Both
components of the model may oscillate independently, with stagnant
versus active phases for the ice stream model and strong versus weak
Atlantic Meridional Overturning Circulation (AMOC) phases for the ocean
model. The ice sheet and ocean interact through submarine melt at the
ice stream grounding line and freshwater flux into the ocean from ice
sheet discharge. We show that these two oscillators have a strong
tendency to synchronize, even when their interaction is weak, due to the
amplification of small perturbations typical in nonlinear oscillators.
In syn- chronized regimes with ocean-induced melt at the ice stream
grounding line, Heinrich events always follow DO events by a constant
time lag. We also introduce noise into the ocean system and find that
ice-ocean interactions not only maintain a narrow distribu- tion of
timing between Heinrich and DO events, but also regulate DO event
periodic- ity against noise in the climate system. This synchronization
persists across a broad range of parameters, indicating that it is a
robust explanation for Heinrich events and their timing despite the
significant uncertainty associated with past ice sheet conditions.