A long time-series of atmospheric fluxes of trace metals and nutrients to the Canary Basin.

Abstract

Atmospheric inputs of soluble trace elements and nutrients to the ocean are a key component in biogeochemical cycles. Aerosol inputs to the Canary Basin are among the highest in the world, due to its proximity to the Sahara and Sahel desert regions of Africa. However, to date there have been no long- term aerosol studies in the Canary Basin, with only limited data available from sporadic oceanographic research cruises which have crossed the region, generally as part of larger transects of the Atlantic Ocean. In this study, aerosol samples have been collected at three stations on the island of Gran Canaria (Taliarte at sea level, Tafira, 269 m altitude and Pico de la Gorra, 1930 m altitude) since 2002, representing a valuable contribution to the understanding of deposition of these soluble components in the region. We present a 11-year record of total suspended particles (TSP) collected in Gran Canaria, Spain and an 9 year record of wet and dry deposition measurements. The solubility of Fe, Al, Mn, Ti, Cu, Co, N and P in dust deposited to the ocean by the dry and wet deposition processes is also examined. Solubility measurements from acetate buffer leaching experiments showed the same tendency in the percentage of soluble metals in the samples: a higher percentage of soluble metals in anthropogenic aerosols and at lower dust loading. Data were separated into three different groups and results showed that, despite more than 80% of the days having an African component, the fluxes of soluble Fe derived from anthropogenic aerosols represented an important input of this metal to the ocean (more than 28%). Moreover, flux estimates for aerosol-derived soluble metals reveal that phosphate is highly depleted relative to Fe and N when compared to Redfield ratios. Therefore, aerosol deposition may be an important source of N and trace metals (Fe, Co, Mn and Al) to the NE subtropical Atlantic Ocean.