Quantifying the Impact of Atmospheric Deposition on the Biogeochemistry of Fe and Al in the Upper Ocean: A Decade of Collaboration with the US CLIVAR-CO2 Repeat Hydrography Program

Abstract

The aerosol deposition of continental material and its partial dissolution in the surface ocean exerts an important control on the distribution of iron and other potentially limiting trace metal (TM) micronutrients in the open ocean. This dust deposition has implications for the regulation of global climate through the coupling of biolimiting TM cycles, marine productivity, and the global carbon cycle. Thus, it is important to determine the locations of dust deposition in the open ocean and to quantify the magnitude and subsequent dissolution of the dust. At present, there are too few dust deposition estimates and solubility measurements in the open ocean to adequately constrain this key source term in global biogeochemical models. While early sampling efforts were invaluable in highlighting the importance of TMs in regulating nutrient cycling and phytoplankton productivity in vast ocean regions, they lacked the spatial resolution and global coverage required to constrain model simulations and identify features that illuminate the processes controlling TM distributions. Starting in 2003, the US Climate Variability and Predictability (CLIVAR)-CO2 Repeat Hydrography Program provided an hour of ship time for dedicated TM sampling at every degree of latitude or longitude along selected cruise tracks. The principal goals for CLIVAR TM sampling were to produce a high-resolution dissolved iron (Fe) and aluminum (Al) data set with global coverage to better understand upper-ocean Fe biogeochemistry, determine patterns of atmospheric dust deposition based on surface dissolved Al levels, and improve our estimates of the fractional solubility of aerosol TMs using a dedicated shipboard aerosol sampling program. This paper describes recent advances in our understanding of dust deposition and the solubility of aerosol material resulting from 10 years of collaborative work under the US CLIVAR-CO2 Repeat Hydrography Program.