Ocean Aerobiology

Abstract

Ocean aerobiology is defined here as the study of biological particles of marine origin, including living organisms, present in the atmosphere and their role in ecological, biogeochemical, and climate processes. Hundreds of trillions of microorganisms are exchanged between ocean and atmosphere daily. Within a few days, tropospheric transport potentially disperses microorganisms over continents and between oceans. There is a need to better identify and quantify marine aerobiota, characterize the time spans and distances of marine microorganisms' atmospheric transport, and determine whether microorganisms acclimate to atmospheric conditions and remain viable, or even grow. Exploring the atmosphere as a microbial habitat is fundamental for understanding the consequences of dispersal and will expand our knowledge of biodiversity, biogeography, and ecosystem connectivity across different marine environments. Marine organic matter is chemically transformed in the atmosphere, including remineralization back to CO₂. The magnitude of these transformations is insignificant in the context of the annual marine carbon cycle, but may be a significant sink for marine recalcitrant organic matter over long (∼10⁴ years) timescales. In addition, organic matter in sea spray aerosol plays a significant role in the Earth's radiative budget by scattering solar radiation, and indirectly by affecting cloud properties. Marine organic matter is generally a poor source of cloud condensation nuclei (CCN), but a significant source of ice nucleating particles (INPs), affecting the formation of mixed-phase and ice clouds. This review will show that marine biogenic aerosol plays an impactful, but poorly constrained, role in marine ecosystems, biogeochemical processes, and the Earth's climate system. Further work is needed to characterize the connectivity and feedbacks between the atmosphere and ocean ecosystems in order to integrate this complexity into Earth System models, facilitating future climate and biogeochemical predictions.

Keywords: aerobiota; air-sea interaction; atmospheric dispersal; biogenic aerosol; cloud condensation nuclei (CCN); ice nucleating particles (INPs); microbial oceanography; sea spray aerosol (SSA).

FIGURE 1

(A) Deposition velocity of varying cell diameters of viruses (blue), prokaryotes (red), and eukaryotes (green). (B) Microscopy images of microorganisms representative of the particle diameter chosen: (1) SARS-CoV-2, (2) Emiliania huxleyi virus, (3) SAR11, (4) Prochlorococcus, (5) Synechococcus, (6) Micromonas pusilla, (7) Emiliania huxleyi, (8) Thalassiosira sp., and (9) Dinophysis acuminata. (1–7) Approximate scale bars were added. The microscopy images in (B) were reproduced under the Creative Commons Attribution International licenses and were captured by (1) NIAID’s Rocky Mountain Laboratories in Hamilton, Montana (2) Wikimedia commons (3) Steindler et al. (2011) (4) Luke Thompson at the Sallie Chisholm Lab and Nikki Watson at Whitehead, MIT (5) Proyecto Agua at Biodiversidad virtual, Cantabria, Spain (6) Manton and Parke (1960) and courtesy of Nordic Microalgae and Aquatic Protozoa (Karlson et al., 2020) (7) Alison R. Taylor, University of North Carolina Wilmington Microscopy Facility (8) Moore et al. (2017) and (9) Plankton Net, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research.

FIGURE 2

Atmospheric transportation of representative marine microorganisms and Coronavirus (SARS-CoV-2) (A) Potential distance traveled (km) and (B) residence time (days) of SARS-CoV-2 (red), Emiliania huxleyi virus (maroon), SAR11 (orange), Prochlorococcus (light green), Synechococcus (dark green), Micromonas pusilla (light blue), Emiliania huxleyi (dark blue), Thalassiosira weissflogii (light purple), and Dinophysis acuminata (dark purple). Values were determined using Stoke’s Law for aerosol particles released at specific altitudes (250–1,000 m) at the average tropospheric temperature (15°C) in a homogeneous atmosphere. Residence time was calculated using a representative average wind speed of 10 m s^–1. Distance traveled and residence time should be considered the upper limit as these estimates do not account for loss processes such as wet deposition.

FIGURE 3

An airmass traveling from the Atlantic to the Pacific was tracked using NOAA Air Resources Laboratory HYSPLIT (Stein et al., 2015; Rolph et al., 2017) forward trajectory ensemble model with a starting point at 0°N, 30°W (black star) over 7 days (04/02/2020 –04/09/2020) with global forecast system (GFS) meteorology data. Each possible trajectory is represented with each point along the trajectory corresponding to a 12-h increment. The estimated mid-boundary layer height was added (345 m) at the starting point (black star) and the height (m) above ground level (AGL) is shown for each trajectory. Multiple colors enables individual trajectories to be visualized.

FIGURE 4

Physical processes associated with the generation of sea spray aerosol (SSA). Breaking waves entrain air, which results in bubbles bursting at the air-sea interface, lofting jet and film drops into the atmosphere, which form SSA. A subset of SSA catalyzes cloud formation by acting as cloud condensation nuclei (CCN) or ice nucleating particles (INPs). Primary marine aerosol formation via sea spray results in the transfer of marine microorganisms and organic matter to the atmosphere, which are transported over the ocean and deposited in a new location via processes such as wet deposition. The vector art used in this figure was downloaded from vecteezy.com.

FIGURE 5

Marine microorganisms are exposed to stressors in the atmosphere that potentially reduce viability: changes in water salinity and pH, temperature change, desiccation, and rehydration, exposure to free radicals and other oxidants, exposure to solar radiation (including UV). Other stressors include the rapid rates of environmental change that can occur on transport across the air-sea interface, and deposition in an unsuitable environment. The vector art used in this figure was downloaded from vecteezy.com.