HOLOCENE GLACIAL HISTORY OF YAKOBI SEA VALLEY – CROSS SOUND, SOUTHEAST ALASKA

During the Last Glacial Maximum (LGM) a major ice stream of the Cordilleran Ice Sheet (CIS) issued from fjords like Glacier Bay, down Cross Sound and out across the continental shelf of southeastern Alaska. While the ice extended across the shelf it eroded the Yakobi Sea Valley and built a morainal bank at its seaward end. The ice stream retreated rapidly from the sea valley and concomitant glacial rebound brought the morainal bank at the sea valley mouth into wave base, which transported sediment shoreward into Yakobi Sea Valley. The ice stream terminus of the CIS stabilized at the entrance of Cross Sound and remained long enough to deposit a substantial morainal bank and bank-front fan extending into Yakobi Sea Valley. During this period, glacial ice was reduced from an ice sheet to a valley glacier within Lisianski Inlet, a tributary to Cross Sound, after which the ice stream terminus oscillated within the Sound. Deposition of biogenic sediment of Lisianski began by 11 ka and has continued since. At about that time also, core EW0408-66JC in the Yakobi Sea Valley contains a detailed record of the Bølling–Alleröd and Younger Dryas and indicates that coastal upwelling and biosiliceous productivity were strong during the Bø–Al but declined during the YD (Barron et al., 2009). Sea ice-related diatoms increased in abundance during the YD, indicating cooler, but less productive waters (Barron et al., 2009). During the Hypsithermal all glaciers in the study area had retreated from Cross Sound, but oscillations within Glacier Bay are well known.