Concerns
1. Ecology
Any dam disconnecting Pacific and Arctic waters would create an ecological barrier between the two. This is off course highly undesired. However, concerning this plan, the ecological ‘cost of inaction’ seems much bigger. The Bering Strait does not seem to serve the role of a crucial migration route to Arctic whales, like the beluga and the bowhead.
2. Thermohaline circulation
The big risk of interfering with Artic currents is a disturbance of the world wide thermohaline circulation. However, the stability of the entire worldwide thermohaline circulation is served by sustained cold in the Arctic, as the low temperatures allow for crucial formation of so called deep water. Therefore this plan seems much likelier to increase thermohaline stability.
It should be noted that thermohaline stability also increases with salinity. This plan indeed aims to lower salinity, by increasing fluvial influence. However this effect will most likely be local, in the Chuckchi and around the Arctic coasts of Alaska and eastern Siberia and not in the Greenland Sea, the zone of deep water formation. The only real risk of significantly increasing water sweetness in the Greenland Sea would be melting of sea ice and an increased inflow of melt water from Greenland.
Through albedo effect, this plan may even help decrease Greenland melting and decrease the inflow of Greenland meltwater, again favouring thermohaline stability (although that effect is likely to be small as the geographical distance between most of the Greenland ice cap and the Chuckchi Sea, central focus point of this plan, is rather big).
3. Increased Atlantic influence
Apart from thermohaline concerns, building the St Lawrence dam would decrease the discharge of the Bering Strait inflow. This means the present point of ‘collision’ of inflowing Pacific and Atlantic waters, the ‘ crossroads’, on the edge of the Chukchi plateau and the Amerasian Basin, will disappear. Perhaps this will decrease friction of the Atlantic current that is thereby enabled to extent its flow and influences, mainly the transportation of warmer water, into the Arctic. As the Pacific inflow is already comparably small, and the Amerasian Basin very voluminous, it seems unlikely this will have significant impacts.
4. Overshooting
This plan should help preserve the Arctic climate, not create the onset of global cooling. If it would prove effective to theoretical extremes, feedbacks like the albedo effect could lead to undesired sea ice formation, beyond the original extents of the polar ice cap. This seems very unlikely.
If however calculations should prove inadequate to remove this concern, many engineering options are at hand to prevent overshooting and regulate the process.
5. Practicalities
Building the St Lawrence dam would require thorough scientific research, international cooperation and off course quite a financial investment. On the other hand it does seem very doable. As the length of St Lawrence Island will make up a significant part of the dam, its dimensions can be reduced to a length of some 300 kilometres. Presumed the sea has an average depth of some 50 meters, and the dam would need to be twice as wide as high, around 1.5 billion m³ would be required. How about the carbon credits? (Plan B, the Diomede Threshold, would off course have far smaller material requirements.)
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