Dissolved nutrient distributions in the Antarctic Cosmonaut Sea in austral summer 2021

Dissolved nutrients are essential to marine productivity and ecosystem structures in the Southern Ocean. The spatial distributions of dissolved nutrients in the Cosmonaut Sea were studied during the 37th Chinese National Antarctic Research Expedition in 2021. The relative standard deviations of the nitrate (NO3-N), nitrite (NO2-N), ammonium (NH4-N), phosphate (PO4-P), and silicate (SiO3-Si) concentrations found in duplicate samples (n=2) were 1.01％, 9.04％, 6.45％, 0.94％, and 0.67％, respectively. The mean NO3-N, NO2-N, NH4-N, PO4-P, and SiO3-Si concentrations in the mixed layer were 26.41±4.13, 0.15±0.09, 0.51±0.22, 1.73±0.23, and 41.48±6.94 μmol·L?1, respectively, and were higher than the relevant limitation concentrations. The concentrations were generally bounded horizontally by the Southern Boundary (SB) of the Antarctic Circumpolar Current, the NO3-N, NO2-N, NH4-N, and PO4-P concentrations being higher northeast than southwest of the SB but the SiO3-Si concentrations being higher southwest than northeast, indicating that the SB dominates nutrient distributions in the mixed layer. The NO3-N, NH4-N, and PO4-P concentrations gradually increased moving vertically down from the mixed layer to 200 m deep and then remained at 33.73±3.51, 0.26±0.13, and 2.28±0.10 μmol·L?1, respectively, to the bottom. The SiO3-Si concentration increased as depth increased and reached a maximum in the bottom layer. The NO2-N concentration decreased rapidly as depth increased and was ～0 μmol·L?1 at >150 m deep. Circumpolar Deep Water upwelling may cause high nutrient concentrations in shallower layers up to the 100 m layer between 62.5°S and 64°S.