Abstract
Due to the remoteness and difficulty of sampling, the 210Po and 210Pb data are scarce in the Southern Ocean. Here, the activity concentrations of 210Po and 210Pb around Prydz Bay in austral summer were determined to understand their spatial variation and evaluate the dynamics of particle organic matter (POM). The activity concentrations of dissolved 210Po (D210Po) and 210Pb (D210Pb) range from 0.47 to 3.20 Bq⋅m–3 and from 1.15 to 2.97 Bq⋅m–3, respectively, with the lower values in the shelf. The particulate 210Po (P210Po) and 210Pb (P210Pb) are lower in the open ocean and increase to the coastal waters, among which the circumpolar deep water (CDW) is the lowest. The activity concentration of total 210Pb (T210Pb) ranges from 1.26 Bq⋅m–3 to 3.16 Bq⋅m–3, with a higher value in CDW, which is ascribed to radiogenic production from 226Ra and subsequent lateral transport. Occasionally a high value of T210Po occurs in deep water (>3.00 Bq⋅m–3), which may be caused by the remineralization of POM. The disequilibria between T210Po and T210Pb appears throughout the water column at most stations. The average T210Po/T210Pb)A.R. in the euphotic zone is 0.66, reflecting the effect of strong particle scavenging. There is a good positive correlation between the solid-liquid ratio of 210Po and POC, while 210Pb does not, indicating that particulate organic matter regulates the biogeochemical cycle of 210Po around Prydz Bay. Based on the 210Po/210Pb disequilibria, the export flux of POC in the water column is estimated to be 0.8–31.9 mmol m–2 d–1, with the higher values in the shelf.
Highlights
IntroductionThe Southern Ocean divides the polar parts from the warm tropical ocean, including the southern part of the Pacific, Atlantic, and Indian Oceans
210Po (T1/2 = 138.4 days) and 210Pb (T1/2 = 22.3 years) are radionuclides in 238U decay chain
Our results show that Circumpolar Deep Water (CDW) has the highest activity concentrations of 210Po and 210Pb compared with other water masses (p < 0.01, one-way ANOVA, Figure 5)
Summary
The Southern Ocean divides the polar parts from the warm tropical ocean, including the southern part of the Pacific, Atlantic, and Indian Oceans It represents only 10% of the ocean surface area, it accounts for approximately 25% of the oceanic uptake of atmospheric CO2 (Takahashi et al, 2002; Arrigo et al, 2008). The Prydz Bay, located in the Indian sector of the Southern Ocean, is the third largest bay in the Antarctica, following the Weddell Sea and the Ross Sea. Previous studies on 210Po and 210Pb in the Southern Ocean mainly focused on the Antarctic Circumpolar Current (ACC) (Shimmield et al., 1995; Friedrich and Rutgers van der Loeff, 2002), there is still very little research on Prydz Bay. 210Po/210Pb and 234Th/238U disequilibria have been used to estimate POC export flux in the Southern Ocean, but the results obtained by the two methods are sometimes different.
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