Subantarctic zone oceanography - SAZ Project 1997-1998 - Arsenic Data

This method shows a number of advantages over a previously reported manual HG-AFS method including, shorter sample throughput time, increased precision and most significantly, ease of use under shipboard conditions. The semi-automated method was operated on the RSV Aurora Australis during a Southern Ocean voyage in March 1998. Arsenic measurements from a surface transect between 42 and 55 degrees S along 141 degrees 30 minutes E, are presented.

Application of the method to more routine laboratory use is also discussed. Distribution of the arsenic species total inorganic arsenic [As(V+III)], arsenite [As(III)], monomethyl arsenic(MMA), andd dimethyl arsenic (DMA) was studied in the Subantarctic Zone (SAZ) of the Southern Ocean, south of Australia, during the austral autumn (March 1998). As (V) was the dominant arsenic species in both vertical profiles and surface waters along the meridional transect 42-55 degrees S, 141 degrees 30' E. It was also the only species observed at depths greater than 600 m.

Concentrations of the reduced arsenic species (As(III), MMA, and DMA) were low in these waters compared with other oceanic sites with similar concentrations of chlorophyl a. As(III) concentrations could not be reliably quantified at any sites (less than 0.04 nM). The greatest conversion of As(V) to "biological" species was found at the surface in the Subtropical Convergence Zone(2.5%) and decreased heading southward to 1% in the Polar Front (PF).

While the decline in methyl arsenic concentrations was broadly associated with water temperature and measures of biological production, slightly different trends were found in the SAZ and PF. North of the Subantarctic Front (SAF), methyl arsenic concentrations were well correlated with water temperature, while south of the front, no such relation existed. In addition, the ratio DMA/MMA increased south of the SAF, associated with a change in the microalgal community composition.

Low water temperature, phosphate replete conditions, and low biological productivity in the Southern Ocean all contribute to the concentrations of biologically produced arsenic species in this region being among the lowest reported for oceanic waters.