Ice-Ocean Interactions and Heinrich Events

Abstract:

Heinrich events likely represent very strong feedbacks on millennial climate changes, as reviewed here. Ice shelves are debris filters, removing rocks from basal ice before iceberg formation, so ice-shelf loss is the easiest way to make an ice-rafted-debris event when marine-ending ice sheets exist. In turn, ice-shelf loss can be triggered by warmer ocean waters reaching deep grounding lines. Recent work (Marcott et al., 2011, PNAS, etc.) shows subsurface warming in response to “shutdown” of the Atlantic Meridional Overturning Circulation (AMOC) as part of Dansgaard-Oeschger (DO) cycling, whether shutdown was caused by hosing, salt oscillations, or something else. A hybrid model may best fit the data, with a MacAyealian thermal oscillator in Hudson Strait allowing only some Nordic-Seas-triggered DO subsurface warmings to remove a Hudson Strait ice shelf and trigger a Heinrich event, which then extends the “shutdown” into the Labrador Sea to cause longer-lasting, larger far-field climate anomalies. Notable uncertainties remain, however, and the final story is likely to be more involved than this.