Alaska Abyssal Plain

Alaska Abyssal Plain is a vast, flat submarine region in the northeastern Pacific Ocean, forming the deepest part of the Gulf of Alaska. It lies seaward of the Alaska-Aleutian Trench and the complex continental margin of North America. This feature is a classic example of an abyssal plain, created by the deposition of turbidity current sediments that blanket the rugged oceanic crust.

Geography and location

The Alaska Abyssal Plain occupies a significant portion of the deep Gulf of Alaska, bounded to the north and east by the continental slope of Alaska and British Columbia. To the south, it transitions into the general North Pacific Basin, while its western margin is delineated by the towering Alaska Seamount Province and the Kodiak-Bowie Seamount chain. Key adjacent features include the Surveyor Deep-Sea Channel and the Winona Basin, which influence sediment pathways. The plain sits approximately between the Aleutian Islands and the Queen Charlotte Islands, forming a deep, sediment-filled pocket within the larger Pacific Plate system.

Geology and formation

The plain's foundation is oceanic crust of the Pacific Plate, which is being subducted beneath the North American Plate at the adjacent Alaska-Aleutian Trench. Its formation is primarily the result of sedimentation from turbidity currents and pelagic sediment deposition over millions of years, smoothing the original topography of abyssal hills and seamounts. This process is part of the broader plate tectonics evolution of the Northeastern Pacific Ocean. The sediment sources are largely terrigenous, derived from the erosion of the Coast Mountains, the Saint Elias Mountains, and the Alaska Range, transported by systems like the Copper River.

Oceanographic characteristics

The water column over the Alaska Abyssal Plain is dominated by deep, cold water masses, including North Pacific Deep Water and Antarctic Bottom Water that circulate through the global thermohaline circulation. The region is influenced by the Alaska Current and the Alaska Stream at surface levels, which are part of the North Pacific Gyre. Deep-sea conditions are characterized by near-freezing temperatures, high pressure, and complete darkness, similar to other abyssal environments like the Sohm Abyssal Plain. These physical parameters create a stable yet extreme habitat for deep-sea fauna.

Sedimentation and morphology

Morphologically, the Alaska Abyssal Plain is exceptionally flat, with gradients often less than 1:1000, a result of the thick sequence of Holocene and Pleistocene sediments that form a classic abyssal plain stratigraphy. Sedimentation is dominated by hemipelagic muds and distal turbidite deposits originating from the continental shelf via submarine canyons like the Bering Canyon and the Alsek River system. Distinct sedimentary layers, or seismic stratigraphy, reveal sequences from glacial and interglacial periods, influenced by the advance and retreat of the Cordilleran Ice Sheet. The Surveyor Deep-Sea Channel is a major conduit delivering sediment from the Yukon River and the British Columbia coast across the plain.

Economic and scientific significance

Scientifically, the plain is a critical area for studying paleoceanography, paleoclimatology, and marine geology, with research expeditions like those by the R/V Thomas G. Thompson and the Deep Sea Drilling Project having cored its sediments. It serves as a natural laboratory for understanding turbidite systems and deep-sea ecosystem dynamics. Economically, while not a direct hydrocarbon province, its sedimentary record informs exploration in adjacent continental margins. The region is also of interest for potential polymetallic nodule resources and for understanding the geological hazards posed by submarine landslides and their potential to generate tsunamis affecting coastal communities like Anchorage and Juneau.

Category:Abyssal plains Category:Geography of Alaska Category:Landforms of the Gulf of Alaska Category:Physiographic provinces