Infection Dynamics of a Bloom-Forming Alga and Its Virus Determine Airborne Coccolith Emission from Seawater

Abstract

Sea spray aerosols (SSA), have a profound effect on the climate; however, the contribution of oceanic microbial activity to SSA is not fully established. We assessed aerosolization of the calcite units (coccoliths) that compose the exoskeleton of the cosmopolitan bloom-forming coccolithophore, Emiliania huxleyi. Airborne coccolith emission occurs in steady-state conditions and increases by an order of magnitude during E. huxleyi infection by E. huxleyi virus (EhV). Airborne to seawater coccolith ratio is 1:10⁸, providing estimation of airborne concentrations from seawater concentrations. The coccoliths' unique aerodynamic structure yields a characteristic settling velocity of ∼0.01 cm s^-1, ∼25 times slower than average sea salt particles, resulting in coccolith fraction enrichment in the air. The calculated enrichment was established experimentally, indicating that coccoliths may be key contributors to coarse mode SSA surface area, comparable with sea salt aerosols. This study suggests a coupling between key oceanic microbial interactions and fundamental atmospheric processes like SSA formation.

Keywords: Atmospheric Science; Biogeoscience; Earth Sciences; Marine Organism.

Graphical abstract

Figure 1

Dynamics of E. huxleyi and EhV, and Their Impact on Coccolith Release into Seawater (A) E. huxleyi and EhV in seawater: total E. huxleyi cells and calcified cell concentrations (full and empty rectangles, respectively) for infected and control cultures over 10 days. The average viral concentrations are presented in log scale for reference. Error bars represent the standard deviation (SD) of three biological replicates. (B) Percentage of calcified E. huxleyi cells in seawater: calcified cell percentage for infected and control populations. Error bars represent the SD of three biological replicates. (C) Coccoliths and EhV in seawater: coccolith and viral concentrations for infected and control populations. Three biological replicates for infected population are presented: coccolith replicates are presented in circles, error bars represent the SD of technical replicates, viral replicates in diamonds, and the averages of the replicates are shown in dashed black and pink lines for coccoliths and viruses, respectively. The shaded areas around the averages represent the SD of the replicates. Note that viral concentrations are presented in log scale.

Figure 2

Schematic Presentation of the Experimental Setup Using the Bubbling System for Aerosol Production, Enumeration, and Morphological Measurement

Figure 3

Dynamics of Airborne Coccolith Emission Compared with Detachment into Seawater Coccolith airborne concentrations for infected and control populations over 10 days are presented. Three biological replicates for infected populations are shown (blue diamonds) the error bars represent the SD of technical replicates; the replicates' average is shown in dashed black line, and the shaded area around it represents their SD. Seawater coccolith average concentrations for control and infected cases are shown for comparison (circles). Control populations are presented in green, their error bars represent the SD of three biological replicates, and infected populations are shown in blue.

Figure 4

Scanning electron microscopic Images of SSA Collected on Polycarbonate Filters, Focusing on Aerosolized Coccolith Morphologies Images of SSA emitted from non-infected (A–D), and virally infected (E–H) E. huxleyi cultures are presented. Coccolith morphologies appear whole or deformed for both infected and non-infected cultures. Sea salt aerosols are seen in the background (marked in blue circles).