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In this paper, seasonal variation of the South Equatorial Current (SEC) bifurcation off the Madagascar coast in the upper south Indian Ocean (SIO) is investigated based on a new climatology derived from the World Ocean Database and 19-year satellite altimeter observations. The mean bifurcation integrated over the upper thermocline is around 188S and reaches the southernmost position in June/July and the northernmost position in November/December, with a north-south amplitude of about 18. It is demonstrated that the linear, reduced gravity, long Rossby model, which works well for the North Equatorial Current (NEC) bifurcation in the North Pacific, is insufficient to reproduce the seasonal cycle and the mean position of the SEC bifurcation off the Madagascar coast. This suggests the importance of Madagascar in regulating the SEC bifurcation. Application of Godfrey's island rule reveals that compared to the zero Sverdrup transport latitude, the mean SEC bifurcation is shifted poleward by over 0.88 because of the meridional transport of about 5 Sverdrups (Sv; 1 Sv [ 10 6 m 3 s 21 ) between Madagascar and Australia. A time-dependent linear model that extends the Godfrey's island rule is adopted to examine the seasonal variation of the SEC bifurcation. This time-dependent island rule model simulates the seasonal SEC bifurcation well both in terms of its mean position and peak seasons. It provides a dynamic framework to clarify the baroclinic adjustment processes involved in the presence of an island.

Phosphonate is an important category of highly soluble organophosphorus in contaminated waters, and its oxidative transformation into phosphate is usually a prerequisite step to achieve the in-depth removal of the total phosphorus. Currently, selective oxidation of phosphonate into phosphate is urgently desired as conventional advanced oxidation processes suffer from severe matrix interferences. Herein, we employed 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) as a model phosphonate and demonstrated its efficient and selective oxidation by the Cu­(II)/H2O2 process at alkaline pH. In the presence of trace Cu­(II) (0.020 mM), 90.8% of HEDP (0.10 mM) was converted to phosphate by H2O2 in 30 min at pH 9.5, whereas negligible conversion was observed by UV/H2O2 or a Fenton reaction (pH = 3.0). The oxidation of HEDP by Cu­(II)/H2O2 was insignificantly affected by natural organic matters (10.0 mg TOC/L) and various anions including chloride, sulfate, and nitrate (10.0 mM). The complexation of Cu­(II) with HEDP coupling Cu­(III) produced in situ enabled an intramolecular electron transfer process, which features high selective oxidation. Selective degradation of HEDP was further validated by adding stoichiometric H2O2 into an industrial effluent, where the existing Cu­(II) could serve as the catalyst. This study also provides a successful case to trigger selective oxidation of trace pollutants of concern upon synergizing with the nature of the contaminated water.

Previous studies have suggested that the global ocean density stratification below ∼3000 m is approximately set by its direct connection to the Southern Ocean surface density, which in turn is constrained by the atmosphere. Here the role of Southern Ocean surface forcing in glacial‐interglacial stratification changes is investigated using a comprehensive climate model and an idealized conceptual model. Southern Ocean surface forcing is found to control the global deep ocean stratification up to ∼2000 m, which is much shallower than previously thought and contrary to the expectation that the North Atlantic surface forcing should strongly influence the ocean at intermediate depths. We show that this is due to the approximately fixed surface freshwater fluxes, rather than a fixed surface density distribution in the Southern Ocean as was previously assumed. These results suggest that Southern Ocean surface freshwater forcing controls glacial‐interglacial stratification changes in much of the deep ocean.