Observations from moorings in the Aleutian Passes: temperature, salinity and transport

Abstract

Between May 2001 and September 2003, a series of moorings were deployed in four of the Aleutian Passes – Tanaga Pass (12 months of data), Akutan Pass and Seguam Pass (18 months), and Amukta Pass (36 months). Instruments on each mooring measured temperature, salinity and current velocity. Tidal currents dominated the flow in each pass, including a strong fortnightly component in the three deeper passes (Tanaga, Seguam, and Amukta). Net transport in each of the passes was northward, varying from 0.1 × 106 m3 s−1 in Akutan Pass and 0.4 × 106 m3 s−1 in Seguam to >4.0 × 106 m3 s−1 in Amukta Pass. The transport in Amukta Pass, calculated from current meters, was approximately five times as large as previously estimated from hydrographic surveys. At monthly and longer periods, the variability in transport in Amukta Pass was related to the position and strength of the Alaskan Stream southeast of the pass. Vertical mixing was examined in Akutan and Seguam Passes. Strong tidal currents mix the water column top‐to‐bottom over the shallow sills in the passes, a depth of 80 m in Akutan and 140 m in Seguam Pass, providing a critical source of nutrients to the Bering Sea ecosystem.

Vertical turbulent iron flux sustains the Green Belt along the shelf break in the southeastern Bering Sea

“…The distribution of this layer ( Figure 1b) corresponds well to the extent of the GB, and is associated with high surface Chl-a distribution in summer ( Figure 1a). Water near the Aleutian Passes also has greater H (Figure 1b), probably because of intense vertical mixing in this area [Ladd et al, 2005;Stabeno et al, 2005], while water in the basin has smaller H than water along the GB and Aleutian Passes.…”

Summer transport estimates of the Kamchatka Current derived as a variational inverse of hydrophysical and surface drifter data

“…The circulation in the BS basin is driven by the atmospheric forcing and the inflow/outflow transports through four primary passes: Kamchatka Strait, Near Strait, Amchitka Pass and Amukta Pass [Stabeno et al, 2005]. The currents in the Bering Strait are relatively well monitored by velocity moorings [Woodgate et al, 2005], while the water transports through the straits and passages of the Aleutian Arc have been mainly explored through the estimates of the baroclinic currents by dynamical method [Verhunov and Tkachenko, 1992;Stabeno and Reed, 1992].…”

“…The estimates of the Kamchatka Current (KC) transport are based mainly on the hydrophysical data and range from 5 Sv [Verkhunov and Tkachenko, 1992] to 15 Sv [Ohtani, 1970] in dynamical calculations and 8 -13 Sv in numerical modelling studies [Overland et al, 1994]. Unfortunately, the results of both these methods depend on a number unknown parameters, such as the level of no motion or poorly known boundary conditions and tidal rectification through many of the passes that are often not resolved in models [Stabeno et al, 2005].…”

Persistent annual migration patterns of a specialist seabird

“…In the western Bering Sea, fronts are often closer to each other than in the east due to the narrow continental shelf (Belkin 2016), perhaps limiting foraging opportunities. Instead, core areas associated with lower stress levels were located over the deep waters of Kamchatka Pass and Near Straight, where surface currents move out of the Bering Sea at up to 100 cm s −1 , some of the fastest current speeds in the Bering Sea (Stabeno et al 1999(Stabeno et al , 2005. This region was a consistent hotspot, and due to its proximity to colonies in the western Aleutians and Commander Islands, there is the potential for high overlap between birds from multiple colonies.…”