A new constraint on the size of Heinrich Events from an iceberg/sediment model

Heinrich Layers, anomalously thick layers of ice-borne sediment in the North Atlantic ocean, have long
been associated with abrupt climate changes in glacial times. However, there is still no consensus on
either the exact amount of ice needed to transport this sediment or how such a large volume of ice could
be produced. Using an iceberg model that includes sediment, we simulate the delivery of sediment to the
North Atlantic during such an event. Our model assumes that sediment is uniformly distributed within
the ice with a concentration of 4%. Unlike sediment models which assume that the sediment lies in a
single layer, this model can carry sediment all the way from the western to the eastern North Atlantic.
We use a variety of different estimates for the total volume of ice released to model the sediment layer
thickness and we show that to best fit the observations 60 × 104 km3 (with a plausible range of 30–120 ×
104 km3 ) of ice needs to be released. This is equivalent to a 0.04 Sv (106 m3 s−1 , with a plausible range
of 0.02–0.08 Sv) release of freshwater over the 500 yr of a typical Heinrich Event. This is a smaller flux
of water than is required to show a significant impact on the global climate in most current “state of the
art” GCMs.