Seasonal Variation and Sources of Particulate Matter Induced Air to Sea Nutrient Fluxes in the Eastern Tropical North Atlantic

Abstract

Atmospheric nutrient input to the open ocean is a significant nutrient source that affects biological productivity and marine biogeochemistry. In this study, a 3-year time series (2017 –2019) of aerosol samples collected at a remote ocean site in the eastern tropical North Atlantic (ETNA) was used to investigate the sources and seasonal variation of particulate matter (PM10) derived nutrient inputs to this region. The samples were analysed for soluble major nutrients (NO3-, NH4+, and PO43-) and total trace metals (Al, Fe, Mn, V, Ni, Zn and Cu). The average PM10 mass at the site was 51.8 ± 57.6 μg m−3, with particles transported by air masses from four distinct source regions based on back trajectory analysis. During the sampling period, most of the air masses originated in Europe (55.8%) and the Sahel-Sahara region (26.5%). The nutrients deposited into the ETNA were derived from both natural and anthropogenic emissions, with some of the sources exhibiting strong seasonal variability. Dust dominated the contribution to the fluxes of crustally derived elements Al, Mn, and Fe. Mineral dust was also the primary contributor of P; however, in line with previous studies, emissions from the described source regions indicate that biomass burning contributes a larger soluble fraction of P than dust. From the estimated nutrient fluxes, only the seasonal flux of NO3- showed weak variation. The N to P ratio in PM was higher (ranging from 60 to 486) than the Redfield ratio of 16, indicating that atmospheric deposition was constantly P-deficient relative to phytoplankton requirements. Therefore, atmospheric nutrient fluxes are likely to promote P-limitation in the oligotrophic ETNA ocean. As a result, phytoplankton adapted to P stress will be favoured, potentially triggering a cascade effect that impacts plankton community structure and the biogeochemical cycles of N and C.