The fjord estuary ecosystem is one of the richest assemblages of life on earth, but not one of the most well known. Found only in six locations around the planet (Chile, Norway, New Zealand, Alaska, Greenland, and Antarctica), fjord estuaries require just the right combination of events for their construction.
About 27-32,000 years ago, this precise mixture began in Alaska during the Wisconsin glacial period. Snow piled up for years and years, compressing into ice underneath its own weight, and spread across the Kenai Peninsula as the Cordilleran ice sheet. Here in the Kenai Fjords, ice covered the mountains and carved the valleys. The ice etched out a landscape of U-shaped valleys with jagged ridges, known as arêtes, in between. Many of these valleys extended 600-1000 feet below what would become sea level once the warming progressed. Once filled with seawater, these long deep arms of the sea are called fjords; other glacially carved valleys were elevated on mountainsides and appear today as what we call "hanging valleys."
As the ice began to melt about 10,000 years ago, the valleys filled with seawater. Some of the lower glacial features drowned and became beautiful half moon bays. Now, even as they melt, glaciers continue to move downhill under the force of gravity, eroding the bedrock beneath them. The meeting of fresh water and seawater creates an estuary. When the fresh water comes from glaciers, a fjord estuary ecosystem is the result. Glacial run-off colors the saltwater grey with the rock flour it carries. In the park, this sediment accumulates as much as a foot a year at the bottom of the 600- to 1000-foot deep bays. The fresh meltwater provides calcium, iron, magnesium, potassium, and trace elements to the ecosystem.