Heinrich Events. Evidence of Atlantic turnover circulaton shutdown...

The other events we have identified as rapid climate changes are Heinrich events (H1-5).

(Rahmstorf, 2002)

In 1988, Hartmut Heinrich noticed extreme layers of ice rafted debris (IRD) in his North Atlantic sediment cores which later became known as Heinrich events. Unlike Dansgaard-Oescher (D/O) events, Heinrich events are characterized to originate from Hudson Straight only (so the Laurentide ice sheet in North America), due to their very low amount of volcanic particles (which normally hints to Iceland) (Heinrich, 1988). 

The extremity of the layers strongly suggests some kind of catastrophic release of ice bergs into the North Atlantic over a period of 250-500 years (Hemming, 2004). MacAyeal’s model (1993) reproduced a released freshwater mass of roughly 1.25 million km³! That is about 55 times the size of the North American Great Lakes (with a Geat Lakes volume of 22,671 km³)! 

However, since it was entered over a time of up to 500 years, is that enough to shut down the THC? Most models say yes (Prange et al., 2004; Rocheet al., 2004; Ganopolski & Rahmstorf, 2001). In fact, some models show even less freshwater input to be enough for a full shutdown (Rahmstorf, 1995).

A more debated question is how that could have happened.

A large amount of scientists believe that it had to do with ice sheet instability. However, did the ice sheet bed become instable (MacAyeal, 1993)? Or was it maybe something like a collective joekulhaup explosion (Johnson and Lauritzen, 1995), similar to that we just had in Iceland? Maybe the simple thickness of ice increased the friction at the bottom which then produced enough heat to melt the bottom of the ice sheet (Clark et al., 1999)? We'll keep our eyes open and see what future scientists will find out!

Even though many questions are still unanswered, there is good evidence for a full shutdown of the THC during Heinrich events! Let's choose a slightly different approach to see whether this is true. Quickly think back to  the heat piracy and bipolar seesaw concept from the last post (heat is always transported northwards in the Atlantic partially via the Gulf Stream). If the THC really "turned off" during Heinrich events, then we should see a cooling in the North and a warming in the South.

Is there any evidence for that??

Yes there is! In the ice cores of Antarctica! And what do we see?? It warmed in the south!!!!! The evidence strongly suggests a full shut down of the THC during Heinrich events!

Seidov & Maslin (2001)

We can now say with fairly high confidence: It is actually possible for the Atlantic thermohaline circulation to stop, inducing an abrupt cooling in the north and a warming in the south.

Slightly scary that it actually is possible to turn off the ocean conveyor belt? Can it happen again?? Can WE make it happen?.......

keep reading the blog ;)