George T.F. Wong

Exchange of water masses between the East China Sea and the Kuroshio off northeastern Taiwan

Abstract At least six water masses take part in the mixing processes between the East China Sea and the Kuroshio off northeastern Taiwan: the Kuroshio Surface Water (SW), Kuroshio Tropical Water (TW), Kuroshio Intermediate Water (IW), East China Sea Water (ECSW), Coastal Water (CW) and the Taiwan Strait Water (TSW). SW is depleted in nutrients and normalized alkalinity but has the highest temperature and pH of all these waters. TW has relatively high temperature, and the highest salinity of all waters. The salinity maximum in the Kuroshio is usually between 100 and 300 m deep, with large interannual and seasonal variability. IW is characterized by a salinity minimum, high nutrient content and alkalinity, but low pH and oxygen. ECSW is low in salinity, temperature and nutrients, but high in oxygen and normalized calcium and alkalinity. CW has low salinity and nutrient content but is high in normalized alkalinity. TSW is generally depleted in nutrients. The characteristics of the above mentioned waters are discussed. The mixing percentages of SW, TW, IW, and the composite Shelf Surface Water (composed of ECSW, CW and TSW) off the northeast corner of Taiwan in September 1988 and December 1989 are calculated.

A unique seasonal pattern in phytoplankton biomass in low‐latitude waters in the South China Sea

elevated to 0.3 mg/m 3 , 35 mg/m 2 and 300 mg-C/m 2 /d, respectively, in the winter but stayed low, at 0.1 mg/m 3 , 15 mg/m 2 and 110 mg-C/m 2 /d as commonly found in other low latitude waters, in the rest of the year. Concomitantly, soluble reactive phosphate and nitrate+nitrite in the mixed layer also became readily detectable in the winter. The elevationofphytoplanktonbiomasscoincidedapproximately with the lowest sea surface temperature and the highest wind speed in the year. Only the combined effect of convective overturn by surface cooling and wind-induced mixing could have enhanced vertical mixing sufficiently to make the nutrients in the upper nutricline available for photosynthetic activities and accounted for the higher biomass in the winter. Citation: Tseng, C.-M., G. T. F. Wong, I.-I. Lin, C.-R. Wu, and K.-K. Liu (2005), A unique seasonal pattern in phytoplankton biomass in low-latitude waters in the South China Sea, Geophys. Res. Lett., 32, L08608, doi:10.1029/2004GL022111.

Variability of the chemical hydrography at the frontal region between the East China Sea and the Kuroshio north-east of Taiwan

Abstract The hydrography across the frontal region between the East China Sea and the Okinawa Trough north-east of Taiwan, observed during the summer of 1985 and 1988 and the early spring of 1987, was governed mainly by mixing across the front and the topographically induced upwelling of the modified Kuroshio water in the Okinawa Trough during the periodic shelfward migration of the Kuroshio. The location of the front relative to the shelf break seemed to be temporally variable. Topographically induced upwelling was evident during the summer of 1988 and the early spring of 1987 when the front was located close to the shelf break. It might not have occurred in the summer of 1985 when the front was further offshore. The end-member composition of the upwelling water was similar in both seasons. It originated from about 300 m with a temperature and salinity of 13 °C and 34·4 psu. It was rich in nutrients and poor in oxygen with concentrations of nitrate, phosphate, silicate and oxygen of 16, 1, 18 and 160 μM respectively. This upwelling water is potentially a major source of nutrients to the East China Sea. The deep water in the Okinawa Trough at temperatures below 15 C did not participate in cross-shelf mixing. Its chemical characteristics did not change significantly from year to year.

Dissolved organic iodine in marine waters: Determination, occurrence and analytical implications

Abstract An analytical scheme for the determination of dissolved organic I, DOI, in marine waters has been designed. The concentration of total I is determined as IO 3 − or I − after DOI has been oxidized to IO 3 − quantitatively by UV irradiation and all the inorganic I formed and present initially in the sample have been converted to the appropriate form for detection. The concentration of DOI is estimated as (total I−TII) where TII, or total inorganic I, represents the sum of the directly and independently determined concentrations of IO 3 − and I − . The precision for the determination of total I and DOI are ±0.008 and ±0.02 μ M, respectively. DOI was found ubiquitously in coastal waters. It constituted up to 40% of total I and is therefore a significant, and heretofore largely neglected, pool of dissolved I. The concentration of DOI decreased with depth and increased shoreward in the surface waters. The concentration of DOI has probably been underestimated in previously reported analytical schemes. The contribution of DOI to dissolved I may be safely neglected probably only in the deep oceans.

THE UPTAKE OF IODATE BY MARINE PHYTOPLANKTON1

Several studies have suggested that phytoplankton play a role in the iodine cycle. Using a short‐term incubation technique for determining the uptake of iodate by phytoplankton, cultures of Thalassiosira oceanica Hasle, Skeletonema costatum (Greville) Cleve, Emiliania huxleyi (Lohmann) Hay and Mohler, and Dunaliella tertiolecta Butcher were found to be capable of assimilating iodate at rates ranging from 0.003 to 0.24 nmol IO3−·μg chlorophyll a−1·h−1. The kinetics for the uptake of iodate can be modeled, and the similarity between the model and experimental results suggests that there is a steady state between iodate uptake and release of dissolved iodine from the cells, presumably in the form of iodide. Two experiments were conducted in the Sand Shoal Inlet of the Cobb Bay estuary (37°15′N, 75°50′W). The uptake of iodate was 0.26 and 0.08 nmol IO3−·μg chlorophyll a−1·h−1 during high and low tide, respectively. Using field estimates based on measured levels of iodate in the estuary, we estimate that phytoplankton can take up as much as 3% of the ambient pool of iodate on a daily basis and the entire pool in about 1 month. Thus, phytoplankton can be a significant component of the global iodine cycle by mediating changes in the speciation of iodine in the marine environment.

Dissolved iodine in waters overlying and in the Orca Basin, Gulf of Mexico

The distribution and speciation of iodine, a biophilic redox-sensitive trace element, in waters overlying and in the Orca Basin, Gulf of Mexico, which contains hypersaline, anoxic and yet non-sulfide-bearing brine have been determined. The distribution of iodate and iodide in the oxic waters overlying the anoxic brine are similar to those reported in other oceans. However, in the oxic-anoxic mixing zone, iodate disappears while the concentration of iodide reaches a maximum of 8.1 μM, the highest concentration ever reported in open oceans. There is also a maximum in specific iodine of 30.7 nM‰−1 at this depth. Specific iodine in oxic seawater is only about 10–14 nM ‰−1. These features may be explained by the preferential dissolution of biogenic particles that have accumulated in a strong pycnocline. In the anoxic brine proper, the concentration of iodide is 3.8 μM and can be explained almost entirely by the simultaneous mobilization of chloride and iodide during the dissolution of evaporite beds as the specific iodine of 14.5 nM‰−1 is only slightly higher than those observed in the oxic waters.

Optimal conditions and sample storage for the determination of H2O2 in marine waters by the scopoletin–horseradish peroxidase fluorometric method

The conditions presently in use for the fluorometric determination of H(2)O(2) in marine waters, by reacting H(2)O(2) with scopoletin in the presence of horseradish peroxidase (HRP) and measuring the quenching of the fluorescence intensity of scopoletin, are not the optimal conditions. Under the optimized conditions of a pH of 8.5-9.5, an excitation wavelength of 390 nm and an emission wavelength of 460, the sensitivity of the method can be increased significantly, by up to more than a factor of 3 and the variations in the sensitivity from sample to sample can be significantly reduced. Furthermore, the samples need not be analyzed immediately after sample collection as presently prescribed. After scopoletin and HRP have been added to a sample immediately after sample collection, the sample may be stored at room temperature in the dark for up to four days before the quenched fluorescence intensity of scopoletin is read.

The stability of dissolved inorganic species of iodine in seawater

Abstract An oxidation state diagram was used to study the relative stability of inorganic iodine species in an aqueous system. It is shown that although iodate is the most stable form, iodide may exist as a metastable form in a basic solution. Molecular iodine may undergo disproportionation to form iodide and iodate. Results from laboratory studies suggest that molecular iodine is rapidly taken up by seawater, and hypoiodite is probably formed. Hypoiodite is also unstable in seawater, and may react with organic matter or undergo autodecomposition. Direct reactions between molecular iodine and organic matter were not observed.

Dissolved inorganic and organic selenium in the Orca Basin

Abstract The vertical distributions of Se (IV), Se (VI) and dissolved organic Se have been determined in the oxic and non-sulfide-bearing anoxic zones of the Orca Basin. In the oxic waters, the concentration of Se (IV) increases with depth gradually from 0.25 nmole/kg at the surface to a maximum of 0.46 nmole/kg at 750 m and then decreases with depth to a relatively constant concentration of 0.39 nmole/ kg below 1,230 m. The concentration of Se (VI) is rather uniform in the top 250 m at about 0.24 nmole/ kg. Below 250 m it increases with depth to 0.50 nmole/kg at 1.230 m, and it stays relatively constant below this depth. The concentration of organic Se increases from 0.50 nmole/kg at the surface to 1.39 nmole/kg at 78 m. A pronounced broad maximum of organic Se exists between 78 and 250 m. The concentration decreases with depth below 250 m, dropping sharply between 250 and 380 m and more gradually at greater depths. It becomes undetectable at 1,230 m. Organic Se is the dominant species above 250 m. Se (IV) is the most abundant between 250 and 1,000 m while Se (VI) becomes the dominant species below 1,000 m. The distributions of these three species can be explained by the biological uptake of Se in the surface waters and the multi-step regeneration of Se from biogenic particles at greater depths. In suboxic waters at the oxic-anoxic interface, the concentration of Se (IV) increases while that of Se (VI) decreases reflecting a change in redox conditions in the environment. In the anoxic brine, the concentration of Se (IV) is around 0.25 nmole/kg while Se (VI) is undetectable. The concentration of organic Se increases sharply in the suboxic waters and reaches 2.6 nmole/kg in the anoxic brines probably as a result of the decomposition of organic matter and/or a diffusive flux from the underlying sediment.

Fertilization potential of volcanic dust in the low‐nutrient low‐chlorophyll western North Pacific subtropical gyre: Satellite evidence and laboratory study

volcanic particles and a phytoplankton bloom. FLH was found to be ∼9–17 × 10 −3 mW cm −2 mm −1 sr −1 in the patch and ∼3– 5×1 0 −3 mW cm −2 mm −1 sr −1 in the ambient water, indicating that a 2–5‐fold increase in biological activity occurred during the week following the eruption. Satellite altimetry indicated that the bloom took place in the presence of downwelling and was not a result of upwelled nutrients in this oligotrophic ocean. Analysis of satellite ocean color spectra of the bloom region found similar spectra as the reference Trichodesmium spectra. Laboratory experiments further substantiate the satellite observations which show elevated concentrations of limiting nutrients provided by the Anatahan samples, and the averaged soluble nitrate, phosphate, and Fe were 42, 3.1, and 2.0 nM, respectively. Though it was not possible to obtain in situ observations of the ocean biogeochemical responses that followed the Anatahan eruption, this study provided evidence based on remote sensing data and laboratory experiment that fertilization of volcanic aerosols occurred following this eruption in one of the most oligotrophic low‐nutrient low‐chlorophyll ocean deserts on Earth.