December 15, 2020 — The following was released by NOAA Fisheries:
There are thousands of small islands that comprise Alaska’s Aleutian Island chain, but only a few dozen significant passes among those islands. These passes are important bottlenecks for water exchange among the North Pacific, Gulf of Alaska, and the Bering Sea. However, until now there has been limited detail on estimates of pass location, size, shape, length, and depth.
“Flow estimates have been based on rough pass size estimates from over 50 years ago,” said Mark Zimmermann, fisheries biologist from the Alaska Fisheries Science Center. “We have updated information for eastern, western and central passes along the Aleutian Island chain. This new information will help oceanographers and ecologists better quantify impacts of water flow on Alaska marine ecosystems and better understand environmental and ecological changes that are taking place.”
Two new NOAA Fisheries’ studies provide more detail on the size and extent of the passes and the shoreline around the Aleutian Islands.
One study showed that all of the western-most Aleutian passes, from Kavalga to Semichi, are larger (18 to 71 percent) than previously reported. The last study was conducted for this area in the 1960s. This includes Amchitka Pass (+23 percent), the largest in the Aleutians.
The other study focused on the easternmost pass, False Pass, which posed a particular challenge for co-author Zimmermann. False Pass is unusual: it’s the only Aleutian pass that directly connects the shallow shelves of the western Gulf of Alaska and eastern Bering Sea. It is also the only pass with constricted southern and northern openings. We found this pass to have a single northern inlet to the Bering Sea—however, until recently it had two. This conflicts with current navigational charts, depicting two inlets to the Bering Sea now, compared to just one on the older charts (1926–1943).
“Our analysis of eastern pass sizes compared to the results of the 1960s study generated mixed results,” said Zimmermann. “In some cases, our pass size estimates were larger while in other cases they were smaller than previous estimates.”
In 2005, NOAA scientists updated information on some of the eastern and central passes. When Zimmermann looked at the two eastern passes from that study, he found that they were actually larger than previously thought. He also found that five central Aleutian passes were smaller than reported. The earlier study did not examine western pass sizes. The new studies include much more detailed information about the seafloor and shoreline that was not available at the time of the earlier analyses. As a result, they will be a great new resource for oceanographers and ecologists studying marine systems.