Use of ammonium and other nitrogen tracers to investigate the spreading of shelf waters in the western Arctic halocline

Abstract

The contribution of nutrient regeneration in summer to the nutrient maximum associated with Bering Sea Winter Water (BSWW) is estimated from the ammonium data, which was obtained in the outer shelf region of the Chukchi Sea for the first time by the R/V Mirai in 2002. The contribution rate reaches 20–30%, which is larger than the rate studied earlier inside the Chukchi shelf. Such BSWW influenced by the regeneration spreads to the Chukchi shelf slope up to the isobath of ∼3000 m, however, was not found in the Canada Basin. The ammonium and a nitrogen deficit are also useful tracers to study the spreading of shelf waters that are less saline than BSWW. In the Canada Basin, a small amount of ammonium (<2 μM) was observed east of the Northwind Ridge. This small amount of ammonium would be associated with the spreading of Eastern Chukchi Summer Water via the Barrow Canyon. Around the Chukchi Borderland, a prominent nitrogen deficit layer was found. It would be accompanied by Western Chukchi Summer Water via the Hope Valley–Herald Valley channel. The water flows into the Chukchi Abyssal Plain and then spreads eastward to the west of the Northwind Ridge with the decrease of nitrogen deficit signal.