In this time of festivities the image of snowflakes falling and woolly hats seems a world away from the heat and bustle of the UAE. The thought of being sat around a warm fire with some hot cocoa is somewhat less appealing than being in the firing line of a functioning AC.
The chance of snow here in the UAE this year is minimal to say the least – unless you’re in the peaks of Jebel Jais.We will, however, get snow in the oceans. It’s not the type of snow you would wish to catch on your tongue, make snowmen out of (or women, shouts Eric Idle) or make into a snowball to throw at your friends. Nor is it picturesque snowflakes of ice.
Marine snow is extremely important to the equilibrium of marine ecosystems as well as terrestrial ecosystems and the climate of the earth itself.
To acquire marine snow, first, like the majority of ecosystems, we need the sun. The photic zone is the area of the ocean that sunlight can penetrate down to. In crystal clear water the photic zone can be as deep as 1000m, but realistically this is limited to 200m even in clear water and in coastal waters typically only 50m. Photosynthesis requires light energy, converting it to chemical energy, so in the oceans this means that marine plants (algae) are limited in habitat space to this photic zone, as without light they cannot feed themselves. The majority of the open ocean’s marine algae are microscopic organisms called phytoplankton. These phytoplankton form the foundations of the open ocean’s food webs, fulfilling their roles as primary producers. Primary producers are autotrophs meaning they produce their own energy in contrast to heterotrophs which acquire energy from other organisms normally by means of feeding. Imagine the importance of plants to the terrestrial land ecosystems of the planet and you can understand the significant role of marine algae in the oceans.
Marine snow is organic particulate matter that falls from the upper oceans (photic zone), down into the depths of the aphotic zone where there is no light. These organic, therefore carbon based particulates originate from dead zoo/phytoplankton and waste products from larger marine animals. These particulates are denser than the water column which makes them sink, coagulating on the way to form aggregates which in turn fall faster towards the depths of the abyss.
Down in the abyss the particulates usually remain there and enter food chains. Whales however (particularly sperm whales) dive down from the surface to feed on different organisms, returning to the surface and restoring this energy to the surface waters. Sperm whales (the largest predator on the planet) commonly feed on large squid, which have beaks that are indigestible and precipitate in the whales’ gut to form a substance known as Ambergris. It is a bile duct secretion in the intestines that is excreted by them or found in dead sperm whales. This substance costs more than gold and truffles per gram and its main use, therefore the reason for its high value, is its scarcity and its function as a fixing agent for odours in high end perfumes.
Okay… that’s all well and good, some dead stuff and some “waste” falls from the surface waters to the ocean floor. It doesn’t sound too earth shattering, however this is actually one of the most crucial comnponents of the most important biological and physical pumps on the planet – the carbon cycle; and more relevantly, the oceanic carbon cycle. The oceanic carbon cycle consists of three pumps: the solubility pump, the carbonate pump and the biological pump.
The solubility pump is the dissolution of Atmospheric CO2 into the oceans, forming carbonic acid (the same stuff that makes even plain sparkling water not great for your teeth) and carbonate ions. This dissolved inorganic carbon circulates throughout the whole ocean by means of the thermohaline conveyor belt. The thermohaline conveyor belt is a global system of water movement whereby dense, cold, salty water sinks into the deep oceans driving the thermohaline current and circulation of water throughout the global oceans, as all the Earth’s oceans are connected. The more CO2 that dissolves in the oceans the more acidic it becomes. This is the process known as ocean acidification which could potentially have more of an immediate impact on the oceans and in turn the global climate, than the process of global warming.
The carbonate pump is the process by which the carbonate ions formed from the solubility pump and dissolved calcium in the oceans are utilised by marine fauna and flora to form calcium carbonate. This calcium carbonate is used to form the shells of many marine animals and importantly the plant phytoplankton called coccolithophores. Foraminifera also form calcareous structures but are far less abundant than coccolithophores. Coccolithophores are phytoplankton that form coccoliths, calcium carbonate plates surrounding the organism. Although tiny at 2 – 25 micrometres across, their sheer numbers amount for a huge amount of carbon. For example, the 100m tall, white chalk cliffs of Dover on the south east coast of England are primarily composed of billions of these tiny coccoliths. Coccolithophores are one of the most abundant species in the ocean and are the main primary producers in the marine environment – re-enforcing their importance to planet earth.
A couple of fascinating topics regarding marine plankton, coccolithophores and their role in sequestering excess atmospheric carbon is the CLAW hypothesis and iron fertilisation. Starting with iron fertilisation, plankton blooms are restricted in growth by limiting nutrients in the oceans, primarily iron, so the addition of solute iron to the ocean promotes and allows growth. The natural process where winds blow westerly across the Sahara and northern Africa gathers dust containing iron along the way, before depositing it into the mid-Atlantic Ocean. This fertilises the oceans and allows for a naturally occurring bloom of phytoplankton and subsequently the organisms which thrive on them. This increase in phytoplankton decreases the amount of dissolved CO2 in the oceans and causes more atmospheric CO2 to be removed from the atmosphere by dissolution into the ocean. A prospective answer to climate change would be to artificially add dissolved iron into the seas to trigger a bloom increasing the amount of carbon sequestration.
The other topic is the CLAW hypothesis, Coccolithopores produce a chemical called dimethyl sulphide (DMS) as a metabolic waste product, this is released into the atmosphere forming aerosols which act as cloud condensation nuclei, similar to the cloud seeding undertaken here in the UAE. Therefore an increase in atmospheric CO2 would increase the abundance of coccolithophores and the production of DMS which would in turn increase the amount of cloud formation to block more of the sun’s rays, decreasing the global temperature. This suggests that phytoplankton play a huge role in the Earth’s homeostasis. This is still a hypothesis and should not be considered as a hard fact that climate change does not exist.
The last system in the oceanic carbon cycle is the biological pump. The biological pump is the process by which energy is transferred in the form of organic carbon from one organism to the other. This energy is cycled between organisms through feeding, excretion, death and decay, remaining in a semi-closed system. A large proportion of the organic material will remain in this cycle for considerable periods of time until it falls out of the system in the form of marine snow.
This is where the marine snow comes into its own with regards to the importance of maintaining the earth’s thermal equilibrium. Marine snow acts as a carbon sink through the loss of this organic material from the food chain though death, fecal matter or waste which are the main contributors to marine snow. This falls down into the abyss, becoming sequestered into the sediments and acts as a major energy source for the base of food chains in the depths, where autotrophic self feeding is impossible due to lack of sunlight. Once in the ocean depths, the organic material can remain there for more than 1,000 years, negating its detrimental effects on the earth’s climate.
This organic sequestered material, formed from large quantities of marine snow, is then buried underneath further sediments. Over millennia, subjected to intense heat and pressure, it forms oil or specifically petroleum. Once upon a time the fuel you put in your car this morning was plankton and whale poop, fuel for more than thought. It’s through this process that marine snow plays a vital role in the carbon pump. It removes carbon dioxide from our atmosphere and reduces the effects of our impacts from burning the fossil fuels, which releases the carbon from oil, leading to climate change.
Climate change is something that I hope everyone is aware of, especially in the diving community, with the impacts of rising sea surface temperatures and ocean acidification directly damaging the coral reefs we love. Increasing levels of Carbon Dioxide is a leading cause of the greenhouse effect, raising the temperature of the planet and in turn driving the rising sea surface temperatures. Our burning of fossil fuels should be exactly that – fossilised, antiquated, left to ancient history. Unfortunately we’re not there yet. However, the world is changing and leaning more on renewable energy sources and collectively the human race is becoming more conscious of climate change and the impacts humans are having upon the environment
So this Christmas let’s be thankful for marine snow – it’s our greatest safeguard against global warming – without marine snow there would be no more white Christmases. Merry Christmas!
Written by James Campbell, our resident marine biologist
Article first published in the December 2020 EDA Divers for the Environment magazine.