Dana R. Kester

Solubility of hydrous ferric oxide and iron speciation in seawater

Iron solubility equilibria were investigated in seawater at 36.22‰ salinity and 25°C using several filtration and dialysis techniques. In simple filtration experiments with 0.05 μm filters and Millipore ultra-filters, ferric chlorides fluorides, sulfates, and FeOH2+ species were found to be insignificant relative to Fe(OH)2+ at p[H+] = −log [H+] greater than 6.0. Hydrous ferric oxide freshly precipitated from seawater yielded a solubility product of ∗Kso = [Fe3+][H+]−3 = 4.7 · 105. Solubility studies based on the rates of dialysis of various seawater solutions and on the filtration of acidified seawater solutions indicated the existence of the Fe(OH)30 species. The formation constant for this species can be calculated as ∗β3 = [Fe(OH)30] [H+]3/[Fe3+] = 2.4 · 10−14. The Fe(OH)4− species is present at concentrations which are negligible compared to Fe(OH)2+ and Fe(OH)30 in the normal pH range of seawater. However, there is at least one other significant ferric complex in seawater above p[H+] = 8.0 (possibly with bicarbonate, carbonate, or borate ions) in addition to the Fe(OH)2+ and Fe(OH)30 species.

Photochemical redox cycling of iron in coastal seawater

Reduced iron, Fe(II), and hydrogen peroxide, H2O2, were measured in numerous laboratory solar simulation experiments. Under constant irradiation of freshly collected, 0.2 μm filtered water from Narragansett Bay (NBSW), H2O2 accumulates in a linear fashion for at least 2 h at rates from 30 to 59 nM h−1. Our measurements of Fe(II) accumulation in this study provide some of the first direct measurements of photochemical iron reduction in natural seawater at pH 8 in a controlled laboratory setting. At ambient pH, the peak concentration of Fe(II) ranged from 4 to 8% of the total iron concentration. Lowering the pH resulted in increased Fe(II) concentrations over the entire course of the experiment. Measured H2O2 accumulation, published iron oxide solubility products, and published reaction rates for iron oxidation and reduction by oxygen, hydrogen peroxide, and oxygen radicals were used to develop a kinetic model which accounts for the general magnitude and timing of Fe(II) concentration variations observed in our experiments. Our model shows that measured steady state Fe(II) concentrations in irradiated seawater are controlled largely by pH dependent oxidation by oxygen and hydrogen peroxide, and by both oxidation and reduction of iron by photochemically produced Superoxide.

Upwelling in the Taiwan Strait during the summer monsoon detected by satellite and shipboard measurements

The Taiwan Strait is located at the confluence of the East China Sea and the South China Sea in the west Pacific Ocean. Several upwelling zones in the Taiwan Strait are noted for their high fisheries production; these upwelling zones have been studied in the past decade, but we have no overall picture on the size and temporal changes of these upwelling zones due to only limited in situ observation over short periods of time. The present paper investigates upwelling in the Taiwan Strait with satellite remote sensing data of NOAA-derived Sea Surface Temperature (SST) and SeaWiFS-derived Chlorophyll-a (Chl-a) and shipboard measurements during summer 1998. Results reveal five upwelling zones: (1) coastal upwelling near Pingtan Island (PTU), (2) coastal upwelling between Meizhou and Xiaman (MXU), (3) big coastal upwelling near Dongshan Island (DSU), sometimes extending to offshore, (4) small occasional upwelling near the Penghu Island (PHU) and (5) an intensive upwelling in the Taiwan Bank (TBU). TBU was extensively studied over summer 1998. Results showed that the TBU looks like a banana in shape in the southern edge of the Taiwan Bank; it intensifies in its southeastern edge. The size of TBU was about 2500–3000 km 2 , with a mean value of 2796 km 2 . The temperature difference between the upwelling and non-upwelling areas was about 2.5–3.5 jC for early August with a mean value of 2.3 jC on July to October. Series of images indicated a short-term variation of TBU and showed that high Chl-a concentrations (up to 0.8–2 mg m 3 ) zones coincided with low SST (25–26 jC) zones in terms of location, time, and shape. These upwelling zones change with size and intensity center from time to time. Field measurements of water temperature, salinity, and Chl-a in 1998 are consistent with satellite measurements. D 2002 Elsevier Science Inc. All rights reserved.

Spectrophotometric determination of iron(II) in seawater at nanomolar concentrations

Abstract Natural Fe(II) concentrations in seawater have been determined by using the colorimeter reagent ferrozine [3-(2-pyridyl)-5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine]. The ferrozine was adsorbed on a C18 Sep-Pak cartridge. Seawater samples ranging in volume from 50 to 400 ml were passed through the Sep-Pak with the Fe(II) being retained as the colored Fe(II)-ferrozine complex. The complex was extracted from the Sep-Pak column with 10 ml of methanol. Up to a 40-fold preconcentration of Fe(II) was possible using this method. The molar absorptivity of the Fe(II)-ferrozine complex in methanol was 28.1 × 103 l mol−1 cm−1 at 562 nm. The recovery of Fe(II) from the Sep-Pak was 91%. The detection limit for Fe(II) in seawater was 0.6 nmol l−1. The precision over the range 0.6–185 nmol l−1 was 2% or 0.2 nmol l−1, whichever is the larger. Copper(I) interference was minimized by complexing Cu(I) with neocuproine added to the methanol Sep-Pak effluent.

Adsorption of copper and cobalt from fresh and marine systems

Abstract The adsorption of copper and cobalt from aqueous solution on to illite and other substrates has been studied as a function of pH, solution composition and solid phase concentration. The results are interpreted in terms of a model whereby the trace metals are adsorbed in exchange for surface bound H + ions. Adsorption varies with solution ionic strength and the concentrations of complex forming ligands; both of these parameters tend to reduce the trace metal adsorption. The Cu 2+ is two orders of magnitude more reactive toward solid surfaces than Co 2+ , which is consistent with the general reactivities of these two metal ions. It is also found that Mg 2+ interferes with adsorption, presumably by competing with the trace metals for the surface sites. A quantitative model was developed which describes adsorption of these metals from natural waters ranging from river water to sea water as a function of pH, complexing ligands and magnesium activity.

In situ and satellite observations of a harmful algal bloom and water condition at the Pearl River estuary in late autumn 1998

Harmful algal blooms (HABs) have posed a serious threat to the aquaculture and fisheries industries in recent years, especially in Asia. During 1998 there were several particularly serious blooms in the coastal waters of south China, which caused a serious damage to aquaculture. We report a massive dinoflagellate bloom near the mouth of Pearl River in November 1998 with analyses of data from both in situ sea water measurements and satellites. A multi-parameter environmental mapping system was used to obtain real-time measurements of water quality properties and wind data through the algal bloom area, which allow us to compare water measurements from inside and outside of the bloom areas. This bloom with high concentrations of algal cells was evident as a series of red colored parallel bands of surface water that were 100–300 m long and 10–30 m wide with a total area of about 20–30 km 2 by visual. The algal density reached 3.8×10 7 cells l −1 and the surface chlorophyll-a (Chl-a) concentration was high. The algal species has been identified as Gymnodiniumcf. catenatumGraham. The water column in the bloom area was stratified, where the surface temperature was 24–25 ◦ C, the salinity was 18–20%, and the northern wind was about 3–4 m s −1 in the bloom area. The SeaWiFS image has shown high Chl-a area coinciding with the bloom area. The sea surface temperature (SST) image of the Pearl River estuary combined with the in situ measurements indicated that the bloom occurred along a mixing front between cooler lower salinity river water and warmer higher saline South China Sea (SCS) water.

AVHRR satellite remote sensing and shipboard measurements of the thermal plume from the Daya Bay, nuclear power station, China

The 1800 MW Daya Bay Nuclear Power Station (DNPS), Chinas first nuclear power station, is located on the coast of the South China Sea. DNPS discharges 29 10 x 10(5) m(3) year(-1) of warm water from its cooling system into Daya Bay, which could have ecological consequences. This study examines satellite sea surface temperature data and shipboard water column measurements from Daya Bay. Field observations of water temperature, salinity, and chlorophyll a data were conducted four times per year at 12 sampling stations in Daya Bay during January 1997 to January 1999. Sea surface temperatures were derived from the Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites during November 1997 to February 1999. A total of 2905 images with 1.1 x 1.1 km resolution were examined; among those images, 342 have sufficient quality for quantitative analysis. The results show a seasonal pattern of thermal plumes in Daya Bay. During the winter months (December to March), the thermal plume is localized to an area within a few km of the power plant, and the temperature difference between the plume and non-plume areas is about 1.5 degreesC. During the summer and fall months (May to November), there is a larger thermal plume extending 8-10 kin south along the coast from DNPS, and the temperature change is about 1.0 degreesC. Monthly variation of SST in the thermal plume is analyzed. AVHRR SST is higher in daytime than in nighttime in the bay during the whole year. The strong seasonal difference in the thermal plume is related to vertical mixing of the water column in winter and to stratification in summer. Further investigations are needed to determine any other ecological effects of the Daya Bay thermal plume

Stopped flow luminol chemiluminescence determination of Fe(II) and reducible iron in seawater at subnanomolar levels

Abstract A highly sensitive stopped flow chemiluminescence method has been developed for the analysis of Fe(II) at subnanomolar levels in seawater. Oxidation of Fe(II) by O 2 in the absence of H 2 O 2 is used to catalyze luminol chemiluminescence. The sample and luminol reagent are pneumatically injected into a 1 cm flow cell positioned in front of a photomultiplier tube. The luminescence intensity is measured with a picoammeter and recorded on a personal computer. Fe(II) can be determined directly in open ocean and coastal waters with 5 ml of sample. Interference studies were conducted with Cr(III), Fe(III), Cu(II), Mn(II), Zn(II), Co(II), and Ni(II). Ni(II), Cr(III), and Fe(III) did not exhibit a significant interference over the concentration range 5 to 500 nmol/kg. Mn(II) and Cu(II) caused a reduction in signal at all levels greater than 5 nmol/kg. Zn(II) and Co(II) produced an interference only when their concentrations were 100 times or more that of Fe(II), resulting in an enhanced signal. Dissolved organic matter reduced the sensitivity of the method in coastal waters relative to open ocean waters. The detection limit for Fe(II) with a 200 μl sample injection volume is 0.06 nmol/kg in open ocean waters and 0.15 nmol/kg in coastal waters. The relative standard deviation of three replicates is ±8%. Direct application to seawater is accomplished with a minimum of post-sampling manipulations or chemical treatments. In addition the reducible iron concentration can be determined by reduction with sulfite. The instrumentation required is easily adapted for field use.

Peroxide variations in the Sargasso Sea

Abstract This paper presents a time series study of H 2 O 2 distributions and variability at an oligotrophic station in the North Atlantic. Hydrogen peroxide was examined over eleven consecutive days at 1 and 3 m. The average concentration exceeded 100 nM with daily variations of about 40 nM at both depths. Surface water peroxide concentrations increased following an evening rain shower and remained elevated by about 40 nM throughout the remainder of the study. Atmospheric input of H 2 O 2 appears to represent a disturbance to the kinetic balance of H 2 O 2 production and loss and thus produces long term H 2 O 2 trends while the system approaches the steady state concentrations dictated by mixing regime and in situ processes. Vertical profiles showed H 2 O 2 distributions which closely follow density profiles with concentrations dropping rapidly to less than 5 nM below the thermocline when a distinct seasonal mixed layer was present. Results suggest H 2 O 2 as a useful tracer for freshwater input and mixing processes in the upper ocean.

Copper(II) ion hydrolysis in aqueous solution

A copper(II) ion-selective-electrode potentiometric method was used to determine the first and second hydrolysis constants of Cu2+. Special techniques prevented copper(II) hydroxide precipitation, and copper(II) carbonate and cipper(II) organic complexation during the titration of the experimental solution over the pH range 6.8–8.4. The large change in the total copper concentration during the titration due to adsorption of copper onto the vessel walls was accounted for by measuring the total copper concentration at each pH by atomic absorption spectrophotometry. The two hydrolysis constants were determined at 25°C in 0.7 and 0.05m NaClO4 media. The measured stability constants are independent of the copper concentration and yield similar zero ionic strength values. Also, the stepwise equilibrium constants decrease as the ligand number increases.