by: Swastik Karmakar (Planktons), Anurag Guha (Aerosols)
Planktons and Aerosols might not seem like they have much to do with each other, but they do. And the basis of it plays an understanding on PACE. Planktons
Plankton are a diverse collection of organisms that drift in water, but are unable to propel against a current. Some plankton drift their way throughout their life cycle. Some other species are only classified as plankton only at their youth, and grow large enough to be able to swim against currents. They are cornerstones of aquatic ecosystems, forming the base of food web, as well as contributing to nutrient cycling and energy transfer.
Planktons are broadly classified into trophic levels as phytoplankton and zooplankton. Phytoplankton are the photosynthetic organisms, primarily algae, that convert sunlight into energy through photosynthesis, producing a significant portion of the Earth's oxygen and forming the base of aquatic food webs. Major groups include diatoms, dinoflagellates, and cyanobacteria. While zooplankton, on the other hand, are primarily small, drifting animals that feed on phytoplankton and other zooplankton. This category includes a wide range of organisms, from microscopic protozoa to larger species like jellyfish and small crustaceans such as copepods and krill. Zooplankton serve as a crucial food source for larger marine animals, including fish, whales, and seabirds, facilitating energy transfer through the food chain.
More on Phytoplanktons- the topic of Planktons of interest
Phytoplankton (phyton: plant, planktos: drifter): Phytoplankton are the autotropic (self-feeding) members of the plankton community and a key component of marine ecosystem. Phytoplankton obtain their food through photosynthesis, therefore like trees, they are usually found in the well-lit surface layers of oceans and lakes. Despite amounting to only 1% of the global plant biomass, they account for half the global photosynthetic activity. Though most phytoplankton are microscopic and cannot be seen with the unaided eye, when present in large numbers, some varieties can be observed as colored patches on water surface due to chlorophyll and certain accessory pigments.
Though phytoplankton occurs all across the oceans, their abundance varies horizontally and vertically. This variation can be attributed to sunlight, nutrient availability and wind and ocean currents. Since phytoplankton are driven by solar energy, primary production is observed in the surface waters. Large areas of the tropical and sub-tropical oceans experience relatively low primary production despite an abundance of light, because ocean circulation and water column stratification cause a deficit of nutrients like nitrate, phosphate, silicate and iron. Iron primarily reaches the ocean through the deposition of dust on the sea surface; therefore, abundance of phytoplankton can be observed near arid regions.
A group of phytoplankton named coccolithophorids is responsible for release of dimethyl sulphide (DMS) into the atmosphere. DMS when oxidized to sulphate leads to an increased cloud cover.
Phytoplankton are very diverse in composition, primarily comprising of diatoms, cyanobacteria and dinoflagellates. We shall discuss a few varieties of plankton in this article.
Diatoms: Diatoms are unicellular protists (simple eukaryotic organisms that are neither plants nor animals or fungi) found in both fresh and marine waters and characterized by their unique silica-based cell walls, known as frustules. Diatoms come in a variety of shapes and sizes, ranging from simple cylindrical forms to intricate, ornate patterns. These structures not only provide protection but also contribute to their ability to float and thrive in aquatic environments.
Diatoms play a crucial role in the food web, serving as a primary food source for various marine organisms, including zooplankton and small fish. They are also essential for carbon cycling, absorbing carbon dioxide during photosynthesis and producing a significant portion of the Earth's oxygen—estimated at around 20%.
Diatoms reproduce rapidly through a process called binary fission, where a single cell divides into two. This ability allows them to bloom in favourable conditions, but it can also lead to harmful algal blooms when an excess of nutrients is available. Their fossilized remains, known as diatomaceous earth, are used in a variety of applications, including filtration and as an abrasive in products like toothpaste.
Diatoms (pictured) by Motic America
Dinoflagellates: Dinoflagellates are a diverse group of single-celled organisms primarily found in marine environments, although some species inhabit freshwater ecosystems. They belong to the group Alveolata and are known for their distinctive flagella, which allow them to move through water. This motility is aided by two flagella—one encircling the cell in a groove, and another trailing behind, giving them a characteristic spinning motion.
These organisms play a vital role in the marine food web, serving as primary producers that convert sunlight into energy through photosynthesis. Some dinoflagellates are also heterotrophic, feeding on other microorganisms. They are known for their bioluminescence, producing light in response to movement or disturbance, which can create stunning displays in ocean waters.
Dinoflagellates are infamous for causing harmful algal blooms, which can produce toxins harmful to marine life and humans. This phenomenon can lead to events like red tides, where high concentrations of these organisms turn the water reddish-brown.
Dinoflagellates (pictured) by Smithsonian Ocean
Mesodinium: Mesodinium is a genus of marine protists known for its unique characteristics and ecological significance. These single-celled organisms are classified as ciliated dinoflagellates, distinguishing them from typical dinoflagellates due to their cilia, which aid in locomotion and feeding.
One of the most notable species within this genus is Mesodinium rubrum, often recognized for its ability to exhibit a reddish-brown color, especially during blooms. This color is due to the presence of pigments from photosynthetic algae it consumes, leading to a fascinating phenomenon called kleptoplasty. In this process, M. rubrum retains chloroplasts from the algae it ingests, allowing it to photosynthesize and generate energy.
Mesodinium species play a role in marine ecosystems as both consumers and producers, contributing to the complex food web. They can thrive in a range of environments, often blooming in nutrient-rich waters. However, their blooms can sometimes disrupt local ecosystems and contribute to the dynamics of nutrient cycling.
Mesodinium (pictured) by University of Tsukuba, Japan
Dinophysis: Dinophysis is a genus of dinoflagellates known for its ecological importance and potential to produce harmful algal blooms. These single-celled organisms are primarily found in marine environments, often in coastal waters where nutrient levels can be elevated.
One of the most notable features of Dinophysis species is their unique morphology, which includes a distinctive armored cell wall and elongated, somewhat elongated shapes. Many species within this genus are mixotrophic, meaning they can photosynthesize like plants and also consume other microorganisms for nutrition. This dual capability allows them to thrive in diverse conditions.
They are particularly infamous for their role in producing toxins, such as okadaic acid, which can accumulate in shellfish and lead to human health risks through shellfish poisoning. This phenomenon poses significant challenges for fisheries and public health, especially during bloom events.
Despite their potential dangers, Dinophysis also plays a crucial role in marine ecosystems, contributing to nutrient cycling and serving as food for various marine organisms. Their presence in the food web highlights the complex interactions that define marine ecosystems and the importance of monitoring their populations to mitigate harmful effects.
Dinophysis (pictured) by US National Office for Harmful Algal Blooms
Gymnodinium: Gymnodinium is a genus of dinoflagellates, a type of marine and freshwater plankton. It is one of the few naked dinoflagellates, or species lacking armor known as cellulosic plates. Since 2000, the species which had been considered to be part of Gymnodinium have been divided into several genera, based on the nature of the apical groove and partial LSU rDNA sequence data. Amphidinium was redefined later. Gymnodinium belong to red dinoflagellates that, in concentration, can cause red tides as well. The red tides produced by some Gymnodinium, such as Gymnodinium catenatum, are toxic and pose risks to marine and human life, including paralytic shellfish poisoning.
Gymnodynium (pictured) by Kudela Lab
Chlorophytes: Chlorophytes are a diverse group of green algae belonging to the division Chlorophyta. They are primarily found in freshwater environments, but many species also inhabit marine ecosystems and moist terrestrial habitats. Chlorophytes are characterized by their green colour, which comes from the presence of chlorophyll a and b, enabling them to photosynthesize and convert sunlight into energy.
These organisms range in size from microscopic unicellular forms to large multicellular structures, such as seaweeds. Common examples include Chlorella, Scenedesmus, and Ulva (often referred to as sea lettuce). Chlorophytes are essential contributors to aquatic ecosystems, serving as primary producers that support various food webs.
In addition to their ecological significance, chlorophytes have various practical applications. They are used in biotechnology, biofuels, and as indicators of water quality due to their sensitivity to environmental changes. Some species are also cultivated for human consumption, thanks to their nutritional value.
Ulva intestinalis pictured by The Outer Shores
All of these cases emit green wavelength signatures from absorbing other colors of visible light spectra, but they're not the same shade of green. This is what PACE intends to exploit in identifying specimens when mapping concentrations. Many of these algae aggregate in single type clusters to form algal blooms, and their wavelength signature gives us a clear understanding of closest approximated species, and their presence (size) can be mapped as well with OCI.
Aerosols
What are aerosols, and why should we be freaked out about them?
You might think “aerosol” is just a fancy word for spray cans, but it’s so much more! Aerosols are tiny particles floating around in our atmosphere, and they can come from both natural and man-made sources. Think about smoke from wildfires, dust storms, or even cool ocean spray—PACE is on a mission to measure it all!
Now, here’s a fun (or horrifying) fact: the Aral Sea, once the fourth largest lake in the world, has turned into a giant dust factory! This area has been shrinking since the 1960s because the rivers that fed it were diverted. Now, what used to be a beautiful lake is a dried-up lake bed that sends clouds of dust swirling through the air, reaching far across Asia. Some of that dust is even toxic.
So why should we care? These tiny particles can affect our air quality, our health, and even the climate! By studying aerosols, PACE helps us understand their impact on our planet and find ways to protect our home.
An aerosol is a suspension of fine solid particles or liquid droplets in air or another gas. They are barely visible to the naked eye. They often exhibit what we call the Tyndall Effect, and is often the only way to visibly view Aerosols.
Aerosols range in size from a few tens of nanometers—less than the width of the smallest viruses—to several tens of micrometers—about the diameter of human hair. The size and composition of aerosol particles affects how far they can travel around the world, their interactions with solar and thermal radiation, and their potential effects on health. Aerosols injected into the atmosphere directly are known as 'primary aerosols'. Sea spray, mineral dust, smoke, and volcanic ash are all primary aerosols. Secondary aerosols are aerosols which were emitted in another form (e.g. gases), then become aerosol particles after going through chemical reactions in the atmosphere, such as sulfate aerosols from volcanoes or industrial emissions. All aerosols can also undergo further chemical changes within colloidal suspension.
Mineral Dust
Mineral dust is emitted when wind blows over deserts or otherwise dry soils, lifting the particles get carried off into the atmosphere. Mineral dust is one of the most abundant aerosol types, and dust particles are also very large compared to other aerosols, often a size of several micrometers in diameter.
Sea Spray
Sea spray is largely composed of sea salt, but also consists of organic matter such as dissolved organic carbon, or even bacteria, phytoplankton, and microalgae. It is commonly formed through the bursting of air bubbles over the ocean surface. The properties of sea spray are chiefly dependent on wind speed, near-surface relative humidity, and sea surface temperature.
Biogenic Aerosols
Biogenic aerosols are those which come from living things. This can include organic chemicals such as limonene, which are emitted by plants and react in the atmosphere to form aerosols, as well as other debris such as pollen, spores, and microbes.
Smoke
Smoke is emitted from fires, both natural wildfires and human-caused (for e.g. agricultural practices such as land clearing and waste incineration). These are often also referred to as 'biomass burning' aerosols, and are composed of organic (brown) and black carbon (soot). The composition of smoke is strongly dependent on the fuel source burning, and atmospheric conditions (e.g. moisture) at the time.
Industrial aerosols
Since the start of the Industrial Revolution, the amount of aerosols emitted by human activities has increased greatly. These industrial aerosols may have a wide variety of compositions. Some industrial aerosols include:
Sulfates, which are produced when sulfur dioxide (SO2) reacts with water vapor and other gases in the atmosphere. One source of this is the burning of coal and oil.
Nitrates, which are often formed when combustion engines (such as vehicles or power plants) release nitrogen oxides (NOx).
Organic and black carbon, again also from combustion.
Together, this combination can be responsible for a visible smog, and heavy exposure can have harmful effects to plant and animal life.
Volcanic aerosols
Volcanoes produce two main aerosols: ash and sulfate. Ash is a dark, large aerosol produced by the pulverization of crystallized magma and contains minerals such as silica and feldspar. The ash clouds can have significant impacts on human health and safety. They pose a significant threat to air traffic, as ash can destroy the engines of planes. Ash deposits, if thick enough, can damage buildings. Volcanic ash also irritates the lungs, and can cause acute respiratory damage or even death if enough is inhaled.
Aerosol Transport and Lifetime:
Aerosol lifetimes range from hours to years, dependent primarily on the size of the particles and the height at which they are injected into the atmosphere. For fine aerosols injected near the surface, the lifetime is typically several days. This increases to weeks or months for particles injected into or transported to the upper troposphere, and fine aerosols in the stratosphere (e.g. volcanic sulfate) can remain there for years. Because of these short lifetimes, many therefore are not usually transported far from their sources.
Aerosols are removed from the atmosphere by either "dry" or "wet" processes:
Dry removal is when particles are deposited on the surface by turbulence or gravity. Movement of small particles is dominated by Brownian motion (random movement), while heavy particles feel the effects of gravitational settling.
Wet removal processes occur when the aerosol is removed in precipitation (water, fog or ice). Aerosol particles may be rained out by collision with falling raindrops ('inertial removal', most effective for heavy particles), or through diffusion of aerosols into falling drops (most efficient for very small particles). The total aerosol amount removed through wet processes does, of course, depend on how much moisture there is. Large aerosol particles are able to act as cloud condensation nuclei (CCN), meaning cloud droplets form by condensing on the aerosol particles. Clouds can form and rain within an hour, and the raindrops remove both the aerosols they formed on and any caught by wet removal processes.
Why do we care about Aerosols though?
Radiation Effects: Aerosols scatter (reflect) a portion of the Sun's incoming light, and, dependent on type, may also absorb some. These are known as 'direct radiative effects' of aerosols. The scattering has a local cooling effect on the surface below, while absorption has a local warming effect on the atmosphere where the aerosols are located. Sometimes these effects can be large and more widespread.
'Indirect effects' or 'Aerosol-Cloud Interactions': Aerosols are largely responsible for the creation of clouds by acting as cloud condensation 'nuclei, or a sort of foundation for clouds to accumulate water on. Increasing the amount of aerosols in the atmosphere can influence factors such as how many clouds there are, how large the cloud droplets are, how high the clouds are, and when or how heavy rainfall is. These are known as 'indirect radiative effects' of aerosols. There is also a `semi-direct effect' whereby local heating of the atmosphere by absorbing aerosols like black carbon can influence whether clouds form at all, or lead to the evaporation of existing clouds. When absorbing aerosols such as soot or dust are deposited on snow or ice, they decrease its reflectivity ('albedo') and cause the surface to absorb more light, which has a warming effect. This can lead to, for example, faster retreat of glaciers.
Health: Aerosols have the capacity to cause damage to plants and animals, including humans. Aerosol particles can irritate the lungs, and in high enough concentrations cause permanent respiratory damage and even death. Chronic exposure to fine particulate matter is associated with adverse health impacts such as decreased life expectancy and higher likelihoods of lung cancer. Fine particulate air pollution has also been determined to have adverse effects on cardiovascular health.
Efficiency of Solar Panels: The efficiency of solar power generation systems is affected by aerosols. Aerosol scattering and absorption reduces the amount of direct sunlight reaching solar panels, by about 4 W for every watt reflected to outer space, decreasing their potential yield.
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