Variations in Iron, Aluminium, Beryllium and Barium Concentrations in Surface Waters at Station ALOHA

Sue Vink¹, Kelly Falkner², Vangielynn Tersol³, Jinchun Yuan⁴ and Christopher Measures¹

¹School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822

²COAS, Oregon State University, Corvallis, OR 97331

³Department of Chemistry, Old Dominion University, Norfolk, VA 23529

⁴Institute of Marine Sciences, University of Southem Mississippi, Stennis Space Center, MS 39529

Abstract

An ongoing study to determine the effects of periodic deposition of Asian dust on the trace element budgets of the surface ocean is being conducted at the Hawaii Ocean Time-series (HOT) Station ALOHA. Surface water samples for trace element analyses have been collected using a pole sampler at approximately monthly intervals since July 1992. Al and Fe concentrations in these samples were determined by flow injection analysis and Be concentrations were determined by electron capture gas chromatography. Ba concentrations were determined by isotope dilution-inductively coupled plasma quadrupole mass spectrometry. Both Fe and Al concentrations showed a seasonal cycle. Concentration maxima were observed between February-April, coinciding with the period during which increased deposition of Asian dust has been reported by others. In some years the concentration of these elements also increased between October-November. The concentration of Fe in surface waters at Station ALOHA was generally higher during 1994-1995 compared to previous years. In contrast, Be concentrations did not vary annually, but were relatively constant averaging 11 pM between January 1993 - June 1994. Subsequent to June 1994, Be concentrations were lower on average (8 pM) but likewise have remained relatively constant. The concentrations of Be determined in these samples were higher than values reported for this region between 1980-1985, but were closer to concentrations previously measured in the Western Pacific. These results suggest that either increased deposition of Be to surface waters at Station ALOHA occurred during the initial period of this study or that surface water circulation has varied. Ba concentrations were relatively constant throughout 1994 with maximum concentration in October. In 1995, Ba concentrations were more variable with concentration maxima in both February and October. The Ba:Si ratio in surface water samples varied annually in both 1994 and 1995. The Ba:Si ratio increased throughout the year from minimum values in February-March to maxima in October-November. The Ba:Si ratio was not well correlated with either primary production or the carbon flux reported by others at this site.