Mariko Hatta

Dust deposition in the eastern Indian Ocean: The ocean perspective from Antarctica to the Bay of Bengal

Atmospheric deposition is an important but still poorly constrained source of trace micronutrients to the open ocean because of the dearth of in situ measurements of total deposition (i.e., wet + dry deposition) in remote regions. In this work, we discuss the upper ocean distribution of dissolved Fe and Al in the eastern Indian Ocean along a 95°E meridional transect spanning the Antarctic margin to the Bay of Bengal. We use the mixed layer concentration of dissolved Al in conjunction with empirical data in a simple steady state model to produce 75 estimates of total dust deposition that we compare with historical observations and atmospheric model estimates. Except in the northern Bay of Bengal where the Ganges-Brahmaputra river plume contributes to the inventory of dissolved Al, the surface distribution of dissolved Al along 95°E is remarkably consistent with the large-scale gradients in mineral dust deposition and multiple-source regions impacting the eastern Indian Ocean. The lowest total dust deposition fluxes are calculated for the Southern Ocean (66 ± 60 mg m−2 yr−1) and the highest for the northern end of the south Indian subtropical gyre (up to 940 mg m−2 yr−1 at 18°S) and in the southern Bay of Bengal (2500 ± 570 mg m−2 yr−1). Our total deposition fluxes, which have an uncertainty on the order of a factor of 3.5, are comparable with the composite atmospheric model data of Mahowald et al. (2005), except in the south Indian subtropical gyre where models may underestimate total deposition. Using available measurements of the solubility of Fe in aerosols, we confirm that dust deposition is a minor source of dissolved Fe to the Southern Ocean and show that aeolian deposition of dissolved Fe in the southern Bay of Bengal may be comparable to that observed underneath the Saharan dust plume in the Atlantic Ocean.

Dissolved Fe and Al in the upper 1000 m of the eastern Indian Ocean: A high‐resolution transect along 95°E from the Antarctic margin to the Bay of Bengal

A high-resolution section of dissolved iron (dFe) and aluminum (dAl) was obtained along ~95°E in the upper 1000?m of the eastern Indian Ocean from the Antarctic margin (66°S) to the Bay of Bengal (18°N) during the U.S. Climate Variability and Predictability (CLIVAR) CO2 Repeat Hydrography I08S and I09N sections (February–April 2007). In the Southern Ocean, low concentrations of dAl (

Programmable Fow Injection. Principle, methodology and application for trace analysis of iron in a sea water matrix

Automation of reagent based assays by Flow Injection is based on sample processing, in which a sample flows continuously towards and through a detector for monitoring of its components. There are three drawbacks to using this approach. The constant continuous forward flow: continually consumes reagents and generates chemical waste and necessitates a compromise when optimizing the performance of the reagent based assay. The reason is that individual steps of an assay protocol, i.e., sample and reagent metering, mixing, incubation, monitoring and efficient washout are carried out most efficiently on different time scales and therefore at different flowrates. Programmable Flow Injection (pFI) eliminates all three drawbacks and permits the execution of optimization of the assay protocol by means of a computer. This paper details this novel approach to method development by optimization of an assay of iron at nanomolar levels and its application to its determination in a sea water matrix. The pFI method was developed in two variants: Stop in Holding Coil (SHC) and Stop in Flow cell (SFC). The SHC method has a Limit of Detection (LOD = 3.1ppb or 55nM Fe, precision of 1.9% r.s.d. at ~ 90nM, and sampling frequency of 90 samples/h. The SFC method had LOD = 0.57ppb or 10nM Fe, precision of 0.8% r.s.d. at ~ 90nM, and sampling frequency of 40 samples/h and its sensitivity is independent of the salinity of the matrix. The SFC method, and its manual equivalent, was used for the determination of dissolved Fe (II) that had been spiked into several samples of seawater that had been diluted with various volumes of deionized water to mimic coastal seawater. The results showed good agreement between both the SFC and the manual methods.

Determination of traces of phosphate in sea water automated by programmable flow injection: Surfactant enhancement of the phosphomolybdenum blue response

An assay protocol, based on programmable Flow Injection (pFI), is optimized by tailoring flowrates appropriately to the individual steps of an assay, thus allowing sample and reagent metering, mixing, incubation, monitoring and washout to be carried out more efficiently and in different time frames. This novel approach to flow based methods is applied here to optimize the determination of orthophosphate at nanomolar levels. Programmable Flow Injection was also used to facilitate an investigation of the properties of the phosphomolybdenum blue (PMoB) formed during this assay, by using the stop flow technique - an approach that revealed for the first time the influence of surfactants on the kinetics of formation of PMoB and its spectral characteristics. It was discovered that the two most frequently used surfactants (SDS and Brij) have profound and different influences on the spectra and formation of PMoB and this finding was used to enhance the sensitivity of the phosphate assay at nanomolar levels. The method was applied to the assay of trace levels of phosphate in sea water.