PNNL

Abstract

During the “Godzilla” dust storm of June 2020, unusually high fluxes of mineral dust traveled across the Atlantic from the Sahara Desert to reach the Caribbean Basin, Gulf Coast, and southeastern United States. Additionally, an eruption of the La Soufrière volcano on St. Vincent in April 2021—this volcano’s first major explosive eruption in over forty years—generated substantial ashfall in the southeastern Caribbean. While many studies have analyzed mineral dust’s ability to relieve limitation nutrients including phosphorus (P) in the P-depleted North Atlantic, less is known about the impact of extreme events and other natural aerosols like volcanic ash on fluxes of P into seawater and from seawater into marine microbial cells. We quantified P content in mineral dust from the Godzilla dust storm and volcanic ash from the La Soufrière eruption collected at Ragged Point in eastern Barbados. We also performed seawater incubations to assess the marine microbial response to both typical aerosol loading and higher aerosol deposition scenarios like the Godzilla dust storm and volcanic ashfall. Experimental conditions with equal concentrations of mineral dust and volcanic ash enabled direct comparison of the two aerosol types, and using environmentally-relevant concentrations of atmospheric particles allowed us to draw realistic conclusions about how these deposition events impacted P cycling in situ. Volcanic ash has lower P content that is far less soluble (~1%) than assumed in current models (assumed to be up to 100% soluble). However, phosphate uptake rate was stimulated in coastal seawater after either mineral dust or volcanic ash deposition at aerosol concentrations relevant to the Godzilla dust event. Furthermore, high concentrations of both the mineral dust and volcanic ash led to slightly elevated alkaline phosphatase activity (APA) compared to the relevant controls, indicating higher potential for use of dissolved organic phosphorus (DOP) as a P source. These results indicate that input of soluble P alone does not dictate changes in phosphate uptake rate and that bioactive elements released from aerosols besides P can have significant impacts on P cycling. Quantifying these aerosols’ impacts on P cycling is a significant step towards achieving a better understanding of their potential roles in relieving nutrient limitation and fueling the biological carbon pump.