Contribution of Large Marine Aerosols in Phytoplankton Dispersal

Abstract

Sea-spray aerosol (SSA) plays a crucial role in climate processes by influencing radiative forcing, cloud formation, and precipitation. While SSA particles with diameters between 0.1 and 10 μm are commonly studied, larger aerosols (>20 μm) have been observed over terrestrial and oceanic regions but are generally overlooked. Large bioaerosols can be formed by pollen, fungal spores, and cell debris. However, the abundance, dynamics, and composition of large marine aerosols remain poorly understood. This study observed wave and atmospheric conditions driving aerosol production, the resulting SSA abundance, and sizes (up to 90 μm), and collected collocated SSA samples for microscopy analysis during a two-month time period. SSA above 20 μm were frequently observed, containing a diverse range of intact phytoplankton cells, including small flagellates (2 μm), to diatoms, and colonial cells (above 40 μm). The abundance of small flagellates suggests that sea-to-air transfer may be an important, yet overlooked, dispersal mechanism for these groups. To the best of our knowledge, this is the first evidence of direct airborne observation (rather than deposition) of large intact phytoplankton cells. These findings highlight the ubiquity of large marine aerosols and their capacity to carry intact phytoplankton cells.

Keywords: aerosols; bioaerosols; large aerosols; phytoplankton; sea-spray; transport.

Figure 1

Instrument deployment configuration for this study at the SIO Pier end. Instruments were deployed side-by-side (inset) approximately 10 m above mean sea level on a retractable boom arm 6 m away from the SIO Pier structure.

Figure 2

HYSPLIT 3 h hindcast trajectories for each sample day with origin at the SIO Pier experiment location.

Figure 3

Background conditions during sampling periods spanning June 27, 2024 to August 27, 2024, including (a) significant wave height H_s, (b) wave peak period T_p, (c) wind speed 10 m above the mean ocean surface U₁₀, (d) wind direction θ with directional limits as black lines for reference, and (e) measured aerosol lwc observed during sample periods. Biologically interesting organisms were observed during most sample periods and are highlighted in red if they contain cell images presented in this paper. Note that some days had multiple sampling periods.

Figure 4

Aerosol number distribution as a function of binned diameter D_i for all sample periods. A common wind-dependent aerosol source parametrization (black line) is fit for reference using the average U₁₀ over all observations. Aerosol observations from the 2023 EPCAPE experiment during the same June–August period (gray) are shown for additional context. U₁₀ during each sampled period is indicated by color.

Figure 5

Epifluorescence microscope images of putative colonial Phaeocystis sp. observed in air samples collected on 07/01/24 (a) and 08/02/24 (b). Red indicates autofluorescence of photosynthetic pigments, and blue indicates DAPI staining of DNA. Note 10 μm scale in (a).

Figure 6

Epifluorescence microscope images of nanophytoplankton cells observed in the seawater (left) and sea spray aerosol air samples (right). (a–f) Collected on 08/07/24, 07/18/24, 07/23/24, 07/16/24, 07/16/24, and 07/18/24 respectively. Red indicates autofluorescence of photosynthetic pigments, and blue indicates DAPI staining of DNA. Note 10 μm scale in (a).

Figure 7

Epifluorescence microscope images of putative diatoms observed in seawater (a,c,e) and air (b,d,f) samples collected around 07/23/24 and 07/29/24. Red indicates autofluorescence of photosynthetic pigments, and blue indicates DAPI staining of DNA. Note 10 μm scale in (a) for (a,b), in (d) for (c,d) and in (e) for (e,f).