[Coral-List] Basic Question. Simple Answer ?

Michael Risk riskmj at univmail.cis.mcmaster.ca
Sun Jul 25 09:07:38 EDT 2004

I had already replied privately to "Fishy" with some comments on his
question, but here is a general response:

The Younger Dryas (about 11,000 years BP, not 15,000) involved a sudden
shift in the climate of (mostly) the North Atlantic. This is believed
to have been caused by a shutdown/cessation/diversion of the Gulf
Stream. At this time, the globe was gradually warming, as we shifted
from glacial to interglacial. During the Y-D, there was a return to
glacial conditions for those regions influenced by the Gulf Stream.

It is true that this reversal took less than 5 years (Smith et al,
Nature 1997)-but that refers to the turnaround, not the entire
temperature range. (Sweden would have felt cooler very quickly, but the
rumble of oncoming glaciers was a few years away...) The entire event
lasted more than 1,000 years.

The reason why this event is so important to us now is that most
theories of origin of the Y-D involve disruption of the thermohaline
circulation of the Atlantic by meltwater-a situation which is perhaps
coming soon.

Greenland in fact has tons of corals-all deepwater. Our work at Orphan
Knoll (in the path of the Gulf Stream Return Flow) suggests that there
was, in fact, a mass death of these deep corals at that time.

It is true that corals/coral reefs are often described as
"resilient"-but all you biologists out there, be careful. Those
descriptions have been written by geologists and paleontologists, such
as Darwin, to whom a million years is a blip. We know that it takes
more than 1,000 years for reefs to colonise newly-flooded continental
shelves-if the water is nice and clean. Similarly, this "resiliant"
behaviour is an ecosystem response. Seen any nice bryozoan reefs
recently? They were common in the Ordovician...the take-home lesson of
the geologic record is that, in fact, corals die like flies.

Finally, although I await the outcome of the survey, I worry that there
may be too much emphasis on the results. I fear that there may be
attempts to use the survey to set policy.(Example: there are probably
100 reef scientists right now working on bleaching for every one doing
research on land-based pollution, yet there is no doubt which of the
two has, to this date, done more damage.)I would be more satisfied by a
study which objectively evaluted the damage to reefs done by the
different sources of stress than I would be by the collected opinions
of those responding to a survey. In fact, this is an excellent time to
consider the fallability of opinion polls...


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