Sampling the Sea Surface Microlayer

This is Jim Fiorendino, your host for On the Ocean.

Clouds form when water droplets or ice crystals grow on aerosols in the atmosphere. These aerosols may originate as organic material in the world’s oceans. Breaking waves and the bursting of bubbles propel droplets of water containing organic material into the atmosphere, which may become aerosolized and promote cloud formation. An important source of the organic material in droplets of seawater are marine phytoplankton, which leak exopolymers and organic matter into the surrounding water. Exopolymers are carried to the surface of the ocean by bubbles and become concentrated in the sea surface microlayer, which is a thin skin at the ocean’s surface roughly 50 micrometers thick.

SSM
Figure 1: Exopolymer concentration results from sea surface microlayer sampling.                   Thornton DCO, Brooks SD and Chen J (2016) Protein and carbohydrate exopolymer particles in the sea surface microlayer (SML). Frontiers in Marine Science 3:135.

Studying the sea surface microlayer is important in understanding the transfer of organic material and other particles to the atmosphere. The sea surface microlayer contains higher concentrations of organic material and exopolymers than the water beneath it, and is home to a unique microbial community capable of coping with high amounts of ultra-violet radiation from the sun. Sampling this thin layer of the ocean is difficult, and cannot be done from a research ship. Instead, scientists operate from rigid-hulled inflatable boats to avoid contamination from larger vessels. Sampling is conducted by dipping a large sheet of glass into the ocean. When the glass is pulled up, water from the sea surface microlayer clings to the glass and can be collected and stored for analysis. Results of sea surface microlayer sampling are shown in figure 1. Understanding the relationship between phytoplankton biology and cloud formation requires interdisciplinary research; Dr. Daniel Thornton of the Texas A&M University Department of Oceanography is currently collaborating with Dr. Sarah Brooks of the Department of Atmospheric Sciences on research regarding phytoplankton biology and cloud formation. Ultimately, through careful laboratory experiments and sampling in the field, Dr. Thornton and Dr. Brooks hope to link cloud formation processes to the biology of marine phytoplankton. The research being conducted by Dr. Thornton and Dr. Brooks is funded by the National Science Foundation.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Contributing Professor: Dr. Daniel Thornton

Growing Phytoplankton in a Marine Aerosol Reference Tank (MART)

This is Jim Fiorendino, your host for On the Ocean.

Phytoplankton are microscopic photosynthetic organisms present in all the world’s oceans. They are an abundant and diverse group known to produce organic compounds that may be an important part of cloud formation processes. Waves breaking and bubbles bursting at the surface of the ocean transfer organic material from the ocean to the atmosphere in droplets of water. Dr. Daniel Thornton of the Texas A&M University Department of Oceanography is currently researching how phytoplankton biology influences the chemical composition and production of organic material in the ocean. Certain processes, such as cell death, may be particularly important, as they result in the release of large amounts of organic material into the surrounding water.

Growing phytoplankton within a Marine Aerosol Reference Tank or MART (Figure 1) allows Dr. Thornton to study phytoplankton growth under varying conditions as well as the production of organic material by phytoplankton. The MART is sealed; inside, cultures of phytoplankton are grown in 63 liters of water, with a headspace of atmosphere roughly twice the volume of the water in the MART. Currently, Dr. Thornton is studying the diatom Thalassiosira weisflogii, chosen because it is a cosmopolitan species that grows well in a laboratory setting.

Air and water samples are taken from the tank and analyzed using various instruments to determine the size and chemical composition of both aerosols and organic matter. One of these instruments, known as a cloud condensation counter, determines what proportion of aerosols can form clouds at specific temperatures and relative humidity. Several other analyses are performed as the phytoplankton grow and die, allowing any changes in organic matter and aerosols to be documented. In the future, Dr. Thornton plans to grow additional species from other major groups of phytoplankton to gain a more complete understanding of how the marine phytoplankton community contributes to organic matter production and, consequently, cloud formation. Images of organic material within a MART are shown in figures 2 and 3.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

MART
Figure 1: Marine Aerosol Reference Tank (MART) during an experiment.                              Photo credit: Andrew Whitesell
Thornton_stained_particles
Figure 2: Coomassie stainable particles (CSP) in the Marine Aerosol Reference Tank (MART). These are expolymer particles that contain protein. They have been stained with Coomassie Brillant blue. Image by Andrew Whitesell.
Thornton_Exopolymers
Figure 3: Transparent exopolymer particles (TEP) in the Marine Aerosol Reference Tank (MART). These are expolymer particles that contain polysaccharides. They have been stained with Alcian blue. Image by Andrew Whitesell.

Contributing Professor – Dr. Daniel Thornton

 

 

 

How are Phytoplankton Involved in Cloud Formation?

This is Jim Fiorendino, your host for On the Ocean

Earth’s ocean and atmosphere form a complex interconnected system. With over 71% of Earth’s surface covered by water, the dynamics of the world’s oceans can have considerable impacts on atmospheric processes such as cloud formation. Studying cloud formation is important because clouds influence Earth’s heat budget and, consequently, Earth’s climate and weather. Clouds form when water condenses or ice crystals grow on aerosol particles in the atmosphere. The breaking of waves on the ocean entrains bubbles in the water, which rise and burst. Bubbles bursting and waves breaking launch water droplets containing organic material into the atmosphere, which dry out and form cloud condensation nuclei or ice nucleating particles. A diagram of this process is shown in Figure 1 below.

Dr. Daniel Thornton of the Texas A&M University Department of Oceanography is currently working with a team of scientists to understand the role of oceanic processes in cloud formation. Specifically, Dr. Thornton is studying the production of organic material in the oceans by phytoplankton.

Phytoplankton are microscopic photosynthetic organisms that form the base of oceanic food webs. They are known to form compounds that promote cloud formation, such as exopolymers. Exopolymers are large, irregularly-shaped molecules comprising roughly 10% of the organic matter in the ocean. This material leaks out of cells, particularly when they are eaten or die (Figure 2). Once in the ocean, this material may be carried to the surface by bubbles, where it is concentrated in a thin layer known as the sea surface microlayer. Wave activity can transfer this material to the atmosphere. Dr. Thornton hopes to link the biology of marine phytoplankton to the composition of organic matter in the ocean and the properties of marine organic aerosols in the atmosphere.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Thornton_Aerosols_Diagram
Figure 1. Ecosystem processes affecting the formation of marine aerosol (a) Phytoplankton fix inorganic carbon into organic matter. Phytoplankton productivity is affected by environmental factors such as the availability of energy (sunlight) and nutrients. A web of interactions (green arrows) between organisms affects the formation and transformation of organic matter. Heavy green arrows emphasize processes that produce large amounts dissolved organic matter (DOM) and particulate organic matter (POM). The metagenome represents the genetic potential of the community, including metabolic pathways that affect the fate of organic matter. Labile organic matter is utilized by heterotrophic bacteria, most of which is ultimately remineralized back to inorganic carbon (CO2). A small proportion of the organic matter fixed by photosynthesis may join the large pool of refractory organic matter in the ocean. Organic matter from the ecosystem fluxes to the atmosphere as volatile organic carbon (VOC) compounds and organic-rich primary marine aerosol (red arrows). (b) Volatile organic compounds (such as dimthyl sulfide (DMS)) flux from ocean to atmosphere, where they undergo oxidation reactions leading to the formation of secondary organic aerosol that may act as cloud condensation nuclei. Breaking waves entrain bubbles that scavenge organic matter from the water and burst through the sea surface microlayer (SML), throwing organic-rich primary aerosol into the atmosphere. A proportion of the primary aerosol may act as cloud condensation nuclei (CCN) or ice nucleating particles (INP).                                                                                                                                                                                                                                                                                                                                Brooks SD & Thornton DCO (accepted) Marine aerosols and clouds. Annual Reviews of Marine Science
Thornton_LeakyCells
Figure 2: Cell permeability in the diatom Thalassiosira weissflogii (CCMP 1051) visualized by epifluorescence microscopy. Cells were stained with SYTOX Green (Invitrogen, Life Technologies, Grand Island, U.S.A.), a membrane-imperme- able nucleic acid stain. Chlorophyll autofluorescence is shown in red and SYTOX Green stained nucleic acids are shown in green. A. Intact cell containing chlorophyll but no SYTOX Green staining and therefore intact cell membranes. B. Intact cell containing chlorophyll with compromised cell membranes revealed by the staining of an intact nucleus with SYTOX Green. C. Dying cell with low chlorophyll autofluorescence, a disrupted nucleus and compromised cell membranes. Image courtesy of Jie Chen. Scale bar = 10 μm.                          Thornton (2014) European Journal of Phycology 49: 20-46

Contributing Professor – Dr. Daniel Thornton

The Role of Ocean Biology in Cloud Formation

This is Jim Fiorendino, your host for On the Ocean.

Clouds are composed of water and ice that has adhered to suspended particles in the atmosphere. These particles, and the clouds they help form, are capable of scattering or blocking incoming radiation from the sun and absorbing and emitting heat energy. Studying the processes that control the formation of clouds is therefore essential to our understanding of Earth’s heat budget, weather, and climate.

Cloud formation is a complex process that requires the presence of fine particles suspended in the atmosphere, known as aerosols, which serve as a surface to which water can adhere or freeze. Ice clouds appear wispy, and form high in the atmosphere, while clouds composed of water particles are fluffier and form lower in the atmosphere. Particles conducive to cloud formation are known as either cloud condensation nuclei or ice nucleation particles; the ability of these particles to promote cloud formation depends upon particle size and chemical composition. Pure water in the atmosphere will not form clouds.

The ocean and atmosphere are closely linked; understanding atmospheric processes such as cloud formation requires studying related processes occurring in the ocean. Roughly 71% of Earth’s surface is covered by water, providing a large area over which the ocean and atmosphere interact. At the interface of the atmosphere and ocean, heat, gasses, and other material are exchanged.

Waves break across the entire surface of the ocean; when waves break, droplets of water are thrown into the air. In addition to salt water, these droplets may contain microorganisms, as well as solid and dissolved organic matter. If the particles are small and light enough, they may be carried high into the atmosphere where they become cloud condensation nuclei or ice nucleating particles. Scientists in Texas A&M University’s Department of Oceanography and Department of Atmospheric Sciences are currently working to understand what role oceanic processes, particularly ocean microbiology, play in cloud formation.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

 

Contributing Professor – Dr. Daniel Thornton