MUCH has been written of late regarding the impending demise of the world’s coral atolls due to sea level rise.Interestingly in the Solomon Islands, the sea level rise has been blamed for salt water intrusion into the subsurface “lens” of fresh water under some atolls.
Beneath the surface of most atolls, there is a lens shaped body of fresh water which floats on the seawater underneath.The claim is that the rising sea levels are contaminating the fresh-water lens with seawater. These claims of blame ignore several facts. The first and most important fact, discovered by none other than Charles Darwin, is that coral atolls essentially “float” on the surface of the sea.
Atolls exist in a delicate balance between new sand and coral rubble being added from the reef, and sand and rubble being eroded by wind and wave back into the sea.When the sea falls, more sand tumbles from the high part, and more of the atoll is exposed to wind erosion. The atoll falls along with the sea level. When the sea level rises, wind erosion decreases. The coral grows up along with the sea level rise.
The flow of sand and rubble onto the atoll continues, and the atoll rises. Since atolls go up and down with the sea level as Darwin discovered, the idea that they will be buried by sea level rises is totally unfounded. They have gone through sea level rises much larger and much faster than the current one.
The weight of the atoll probably augments the barrier between saltwater and fresh. A higher sea would increase pressure from outside the lens–like squeezing an orange between your hands–eventually penetrating the boundary and contaminating the fresh water.
You are correct. Reequilibration could happen, and the atoll could survive. However, not on a timescale relevant to humanity. The immediate concern is the lives of the people who depend on the drinking water–people who wouldn’t be able to wait for the water lens to restabilize following a change in sea level.