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• The two pathways of Pacific water on the eastern Chukchi shelf are investigated. • In the mean, mass is balanced for both pathways outside of upwelling periods. • The seasonal signal diminishes to the north, where an ice-melt signature is dominant. • Mesoscale variability of the two pathways is diagnosed in the southern Chukchi Sea. The flow of Pacific-origin water across the Chukchi Sea shelf impacts the regional ecosystem in profound ways, yet the two current branches on the eastern shelf that carry the water from Bering Strait to Barrow Canyon – the Alaskan Coastal Current (ACC) and Central Channel (CC) Branch – have not been clearly distinguished or quantified. In this study we use an extensive collection of repeat hydrographic sections occupied at three locations on the Chukchi shelf, together with data from a climatology of shipboard velocity data, to accomplish this. The data were collected predominantly between 2010 and 2020 during the warm months of the year as part of the Distributed Biological Observatory and Arctic Observing Network. The mean sections show that mass is balanced for both currents at the three locations: Bering Strait, Point Hope, and Barrow Canyon. The overall mean ACC transport is 0.34 ± 0.04 Sv, and that of the CC Branch is 0.86 ± 0.11 Sv. The dominant hydrographic variability at Bering Strait is seasonal, but this becomes less evident to the north. At Barrow Canyon, the dominant hydrographic signal is associated with year-to-year variations in sea-ice melt. Farther south there is pronounced mesoscale variability: an empirical orthogonal function analysis at Bering Strait and Point Hope reveals a distinct ACC mode and CC Branch mode in hydrography and baroclinic transport, where the former is wind-driven. Finally, the northward evolution in properties of the two currents is investigated. The poleward increase in salinity of the ACC can be explained by lateral mixing alone, but solar heating together with wind mixing play a large role in the temperature evolution. This same atmospheric forcing also impacts the northward evolution of the CC Branch. [ABSTRACT FROM AUTHOR]

Twenty-four repeat hydrographic transects occupied across Barrow Canyon from 2010 to 2013 are used to study the seasonal evolution of water masses in the canyon from July–October as well as the occurrence of upwelling. The mean sections revealed that the Alaskan coastal water is mainly confined to the eastern flank of the canyon, corresponding to a region of sloped isopycnals indicative of the surface-intensified Alaskan Coastal Current which advects the water. The Pacific-origin winter water is found at depth, banked against the western flank of the canyon. Its isopycnal structure is consistent with a bottom-intensified flow of this dense water mass out of the canyon. For the months that were sampled, the Alaskan coastal water is most prevalent in August and September, while the coldest winter water is observed in the month of August. It is argued that this newly ventilated winter water is delivered to the canyon via pathways on the central Chukchi Shelf, as opposed to the coastal pathway. Roughly a third of the hydrographic sections were preceded by significant up-canyon winds and hence were deemed to be under the influence of upwelling. During these periods, anomalously salty water is found throughout the eastern flank of the canyon, and, on occasion, Atlantic water fills the deepest part of the section. Using atmospheric reanalysis data, it is shown that upwelling occurs when the Beaufort High is strengthened and the Aleutian Low is deepened. Two modes of storm tracks were identified: northward progressing storms (mode 1) and eastward progressing storms (mode 2), both of which can drive upwelling. Mode 1 is prevalent in July–August, while mode 2 is more common in September–October. These seasonal patterns appear to be dictated by regional variations in blocking highs. [ABSTRACT FROM AUTHOR]