Phytoplankton community response to episodic wet and dry aerosol deposition in the subtropical North Atlantic

Abstract

Atmospheric aerosol deposition into the low latitude oligotrophic ocean is an important source of new nutrients for primary production. However, the resultant phytoplankton responses to aerosol deposition events, both in magnitude and changes in community composition, are poorly constrained. Here, we investigated this with 19 d of field and satellite observations for a site in the subtropical North Atlantic. During the observation period, surface dissolved aluminum concentrations alongside satellite‐derived aerosol and precipitation data demonstrated the occurrence of both a dry deposition event associated with a dust storm and a wet deposition event associated with strong rainfall. The dry deposition event did not lead to any observable phytoplankton response, whereas the wet deposition event led to an approximate doubling of chlorophyll a, with Prochlorococcus becoming more dominant at the expense of Synechococcus. Bioassay experiments showed that phytoplankton were nitrogen limited, suggesting that the wet deposition event likely provided substantial aerosol‐derived nitrogen, thereby alleviating the prevalent nutrient limitation and leading to the rapid observed phytoplankton response. These findings highlight the important role of wet deposition in driving rapid responses in both ocean productivity and phytoplankton community composition.

Switches between nitrogen limitation and nitrogen–phosphorus co‐limitation in the subtropical North Atlantic Ocean

“…Concentrations of dissolved Fe were analyzed following preconcentration on a SeaFAST device using inductively coupled plasma mass spectrometry (ICP‐MS; Element XR, Thermo Scientific), with quantification by isotope dilution (Rapp et al 2017). Certified values for GEOTRACES standards GSP and GSC matched well with our measured values (Yuan et al 2023).…”

“…In this event, atmospheric aerosols, typically characterized by an N : P ratio of > 500 (Baker et al 2010; Zamora et al 2013), were deposited into surface seawater. Yuan et al (2023) showed that this extra N supply was quickly exhausted to support a ~ 2‐fold increase in Chl a biomass (also see Table 1). Making the reasonable assumption that P supply from the rainfall event was minimal (Baker et al 2010; Zamora et al 2013), we hypothesize that this external N supply and the subsequent phytoplankton biomass enhancement depleted bioavailable P in seawater (including phosphate and bioavailable dissolved organic P).…”

“…Experiments were repeatedly conducted at a quasi‐fixed site in September 2021 (M176/2 cruise; Fig. 1a; Yuan et al 2023). Surface (~ 2–3 m depth) seawater was sampled from a custom‐built towed‐fish fitted with acid‐washed tubing with suction provided by an acid‐washed Teflon bellows pump (Dellmeco).…”

“…One “standard” nutrient addition experiment followed published protocols, as described in Yuan et al (2023). Briefly, the experiment was carried out in 1‐liter trace‐metal‐clean polycarbonate bottles (Nalgene).…”

“…( b ) Chl a responses to nutrient additions. Data were previously reported in Yuan et al (2023). Responses of cell abundances of ( c ) Prochlorococcus and ( d ) Synechococcus , and intracellular red fluorescence (F cell −1 ; arbitrary units; a.u.…”