The sources of the upper and lower halocline water in the Canada Basin derived from isotopic tracers

Abstract

Seawater samples were collected in the water column from the Canada Basin aboard RV Xuelong in August 1999. Concentrations of δ; D, δ;18 O, nutrients (NO3 -, PO4 3-, SiO3 2-) and dissolved oxygen were measured, along with hydrographic parameters (salinity and temperature). Our results showed that the upper layer of the water column was characterized by the occurrence of the upper halocline water (UHW) and the lower halocline water (LHW). The UHW was associated with a salinity of 33.1 (∼150m depth) and maximums of nutrients, NO and PO*, whereas minimums of NO and PO* (PO* = PO4 3−+ O2/175?1.95 μmol/dm3) occurred at the depth of LHW (~300m depth). Two tracer systems, S-δ;18O-PO* and S-δ D-SiO3 3-, were used to estimate the fractions of the Atlantic water, Pacific water, river runoff and sea ice meltwater in water samples. Combined with the nutrient ratio NO/PO, it was suggested that the UHW was derived from the in-flow of the Pacific water through the Bering Strait. These waters were modified to obtain the high salinity and nutrients in the Chukchi shelf or/and the east Siberian shelf. The LHW was maintained by inflow of the Atlantic water through Barents Sea and subsequent mixing with freshwater in the shelf region to produce the signals of NO and PO* minimums. In study basin, the river runoff signals were confined to water depths less than 300 m and the fractions of river runoff decreased with the increasing depth. Water column inventories of river runoff and sea ice meltwater were calculated between the surface and 300m. The river runoff inventories in the Canada Basin were higher than those in other sea areas, suggesting that the Canada basin is a major storage region for Arctic river water. The sea ice meltwater signals suggested that the Canada Basin is a region of net sea ice formation and the inventories of net sea ice in the upper water column increasing from the south to the north.