RoSES

Webinar – SO-CHIC: Southern Ocean Carbon and Heat Impact on Climate

The EPB will host the first in a series of webinars for the project Southern Ocean Carbon and Heat Impact on Climate (SO-CHIC) on 15:00 CEST, Tuesday 7th April 2020. This first webinar, given by project coordinator Jean-Baptiste Sallée from Sorbonne Université, will introduce SO-CHIC and its objectives.

The Southern Ocean regulates the global climate by controlling heat and carbon exchanges between the atmosphere and the ocean. Rates of climate change on decadal time scales ultimately depend on oceanic processes taking place in the Southern Ocean, yet too little is known about the underlying processes. Limitations come both from the lack of observations in this extreme environment and its inherent sensitivity to intermittent small-scale processes that are not captured in current Earth system models.

To contribute to reducing uncertainties in climate change predictions, the overall objective of SO-CHIC is to understand and quantify variability of heat and carbon budgets in the Southern Ocean through an investigation of the key processes controlling exchanges between the atmosphere, ocean and sea ice using a combination of observational and modelling approaches.

The SO-CHIC project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement N°821001. For more information on SO-CHIC, please visit http://www.sochic-h2020.eu/.

To register for this webinar, please visit https://zoom.us/webinar/register/WN_Zmuk7prXQciogyJlTMgMeg

CUSTARD research expedition complete, but still more to collect

Dr Adrian Martin, CUSTARD Principal Scientist, National Oceanography Centre, UK

10/01/2020

At present Discovery is back in Punta Arenas with research expedition DY111 complete. We managed to get an enormous amount done and the data should keep us happy making sense of it all for a couple of years. A big reason for the success was the Captain and ship’s company, as well as the fantastic team from NMF, so a huge thank you to them all!

RRS Discovery in Punta Arenas Port preparing for DY112

We were extremely lucky with our timing too, arriving just on the cusp of spring and being there to capture its impact as it a phytoplankton bloom swept across the region. It’ll be frustrating waiting until mid March for our samples to get back to UK on board the RRS Discovery and even then some of them will take several months more to process. Science requires patience sometimes. Hopefully, though, together with the data we collected from the buoy sensors and gliders throughout the year we’ll get exciting new insights into how the Southern Ocean is storing carbon.

Time lapse satellite images above showing Ch-a signal of phytoplankton bloom over 2 week period in Southern Ocean – courtesy of NEODASS

All but three members of the science team (and what a team they were) have now left, but a group from WHOI have joined the remaining trio. DY111 may be done but DY112 is poised to leave and the WHOI team are onboard with the specific task of retrieving the mooring and all the sensors attached to it, hopefully full to the gills with yet more data. Being scientists we also won’t resist the chance to collect a few more samples should we get the chance. You can’t have too much after all.

So stay tuned for updates from DY112 on our blogs and twitter regarding retrieval of the ocean mooring and life onboard the RRS Discovery over the next couple of weeks.

OOI Mooring Buoy being deployed in 2018; pic by Prof Mark Moore, UoS
OOI Buoy in the water with sensors loaded and taking measurements

‘Marine Snow’ – Episode 3

Chelsey Baker, National Oceanography Centre, UK

Cover photograph by Sofia Alexiou, NOC

06/01/2020

EPISODE 3 – Sampling the Sinking Marine Snowstorm

Onboard the RRS Discovery for the past 6 weeks we’ve been waiting for a snowstorm… a marine snowstorm. But what is marine snow? Marine snow is made up of dead algae and plankton poo as discussed in Episodes 1 and 2 (links).

Marine snow, which contains organic carbon, sinks down the water column from the upper ocean. The particles race towards the deep ocean and the faster they sink the less time there is for their carbon to be utilised by marine microbes. This process is similar to leaf litter falling in a forest, except instead of a few metres to fall to the forest floor, marine snow falls for several kilometres before reaching the seafloor. Although, less than 1 % of the algae produced in the upper ocean reaches the seafloor. Marine snow that sinks deeper than 1 kilometre stores carbon in the deep ocean for more than 1000 years, which prevents the carbon returning to the atmosphere. This is an important natural oceanic process that moderates atmospheric carbon dioxide levels.

Deep ocean marine snow samples from 2000 m deep in the North Atlantic after the spring bloom of algae which is similar to plants blooming on land in spring. Photograph by Chelsey Baker.

During the CUSTARD cruise Emmy McGarry and I, Chelsey Baker, from the National Oceanography Centre in Southampton, UK sampled sinking particles using Marine Snow Catchers. Marine Snow Catchers are 95 litre settling columns that we deploy to different depths in the water column to measure the particles sinking out of the upper ocean. The snow catchers are deployed one at a time and a heavy weight, called a messenger, is sent down the wire to trigger the marine snow catcher to sample seawater at the chosen depth.

A Marine Snow Catcher being deployed in the Southern Ocean. A messenger is sent down the wire to close the snow catcher at the chosen depth. Photograph by Sofia Alexiou and Chelsey Baker.

Marine snow catchers have been used since the 1980’s to capture fast sinking particles that are responsible for the majority of the carbon that sinks deeper than 1 kilometre. More recently marine snow catchers have been used to sample all the non-sinking and sinking particles by allowing the particles to settle in the snow catchers on the ships deck for 2 hours. This settling period allows the particles to be separated into suspended particles, i.e. non-sinking, slow-sinking particles and fast-sinking particles.

A diagram of how particles sink out during the two hour settling period whilst the marine snow catcher is on the ships deck.

Measuring the amount of carbon in the sinking particle pools is important as the faster particles sink the more carbon they will transport deeper than 1 kilometre for long term carbon storage. We will also be measuring other chemical properties of the sinking particles when we are back on dry land. This will aid us in identifying which types of algae contribute heavily to carbon storage. By measuring the chemical content and sinking rates of the particles we can estimate how much carbon is stored at the three stations that we visited during the cruise and understand how this changes as the spring bloom of algae progresses. It’s been a really successful cruise with calm weather and over 60 marine snow catcher deployments! Now to get back into the onshore labs to analyse all our samples…

Setting up a marine snow catcher before deployment. Literally all hands on deck! Photograph by Hugh Venables.
Chelsey sampling the base of the marine snow catcher for slow-sinking and fast-sinking particles. Photograph by Emmy McGarry.

Wildlife we encountered – Southern Ocean

Dr Hugh Venables, British Antarctic Survey, UK

05/01/2020

The main aims of the 2019 CUSTARD expedition have been to look at carbon export from the Southern Ocean, to deep water or even the sediments five kilometres down from the sunlit surface waters where phytoplankton grow. As well as being the start of the biological carbon pump, these microscopic algae are also the base of the food web, being eaten by zooplankton (small animals) which are then food for fish, birds and whales.

Being far from land reduces the amount of wildlife around, but there are normally some birds around and we have seen Fin, Minke and Pilot Whales. The birds are largely either young birds, that have several years to travel away from their colonies (some do complete laps of Antarctica as immature birds) or adult albatross between breeding cycles, which are every other year. Whales are clearly free to be where they like, though for many of them that will be further south, closer to the ice.

The area is very rarely visited so there has been considerable uncertainty what is out here. Several species are well outside their mapped range, but that’s almost certainly because people haven’t looked rather than through any change in behaviour. Late in the cruise there were three Juan Fernandez Petrels – the Juan Fernandez Islands are over a thousand miles to our north, and they are mapped as moving north from there to the equator. Increasingly birds are being tracked with GPS or geolocator tags (the latter record time and light so that day length and timing allow latitude and longitude to be calculated). This is really useful but still hard for immature birds that spend several years at sea, so the old fashioned method of binoculars and a notebook still has value.

As a contrast to the sparse wildlife in the open waters we have also been lucky enough to pass through the Magellan Straits from Punta Arenas where we have been treated to views of Sei and Humpback Whales, Orcas, many fur seals and sea lions and large flocks of birds, with over three hundred Black-browed Albatross together in one area. A non-marine bonus was six Andean Condors soaring over the mountains.

Wildlife encountered during CUSTARD research expedition in the Southern Ocean

Trace Metals on CUSTARD

From Left: Dr Angie Milne, Izzy Turnbull, Dr Antony Birchill, Dr Simon Ussher Plymouth University, UK

04/01/2020

Trace metal team and their role in Custard

Why do we care about trace metals? As the name implies trace metals are the elements with vanishingly low concentrations in seawater. We could make the mistake of thinking that because such little amounts of these elements are found in the ocean that they are not important, but in fact, many have key roles in the most important metabolic ‘chemical machinery’ of phytoplankton. A prime example is their vital part in the photosynthesis process that allows light to be harvested and stored as chemical energy in the surface ocean. On this cruise we are most interested in iron and manganese as these have extremely low concentrations in the surface of the Southern Ocean and can limit the growth of primary producers that support both Southern Ocean and Antarctic ecosystems.

CTD rosette loaded with trace metal free sampling bottles

Trace metal measurements in seawater require a very ‘special’ team of scientists from the University of Plymouth, trained in the dark arts of biogeochemistry. We are dedicated to keeping the sampling equipment and laboratories clean and free from contamination. The central job of the team is to collect seawater from the surface down to 5000m depth in a dedicated sampling rosette that holds metal free sampling bottles. In addition, we provide the Custard scientists with trace metal clean surface seawater collected from a pump and hose that is connected to a special ‘fish’ that is towed alongside (but not too close!) the hull of the RRS Discovery.

The clean ‘fish’ (hiding under the water) being towed next to the hull of the RRS Discovery.

The trace metal team, and their specific roles, include:

Angie on Particles: Once the sampling bottles are full of seawater they are removed from the rosette and brought inside a clean sampling laboratory, where all the air inside is filtered to prevent contamination.  In here,  Angie filters out the suspended particles (often biological cells and very fine silt) and they are collected onto 0.45 micron filters.

Particles are an important vehicle for transporting trace metals (not just in the ocean, but also in the atmosphere and on land). Just like a car, particles can transport trace metals to a different part of the ocean; either as a passenger inside biological cells / lithogenic material, or as free-riders where the metals hop on and off the outside of particles.  In the Southern Ocean, where the amount of trace metals is extremely low, understanding this particle transport network is crucial to understanding how phytoplankton can grow and thrive.  The number of particles in the Southern Ocean are also low, particularly in the deep ocean. To be able to collect enough to analyse requires filtering lots of seawater (up to 9 L) and this can take a long time (several hours). To keep awake requires loud music and chocolate.

Photos from Left: Particle filtration from the trace metal free sampling bottles;
Middle: Angie removing a filter ‘loaded’ with particles for later analysis in Plymouth;
Right: A collection of particle filters collected from deep water on the left to surface water on the right.
Simon in the clean sampling laboratory with the ultra-filtration system, collecting seawater samples with truly dissolved trace metals for later analysis in Plymouth.

Simon on ultrafiltration: Though we filter out all the particles larger than 0.45 microns (less than a thousandth of a millimetre) this still leaves very fine particles called ‘colloids’. To separate these colloids and elements that are truly dissolved (i.e. when you dissolve table salt in water), Simon has a 12 line ‘ultra’ filtration system that removes all colloids down to 20 nanometres of size! This is so small only molecules will pass through it to be analysed. The only problem with this method is it takes ages and Simon has been known to dose off during this procedure.

Antony on Analysis: The concentration of iron in seawater is around 0.000000028 grams per liter. To measure such little amounts of iron, we need a highly sensitive technique. At the University of Plymouth, we use a system called flow injection with chemiluminescence detection. It works in a very similar way to how fireflies and glow worms light up at night. The ‘flow injection’ part describes how the reagents are pumped through very narrow tubes, and the sample is injected into the flow of reagents by a series of valves.

The injection creates a light signal, the ‘chemiluminescence’, that we can measure. This particular chemiluminescence emits blue light. The more iron in the sample, the more light we measure. Part of Antony’s role on the ship is to analyse the samples that we collect. We use this information to improve where and when we sample, and hopefully find interesting features in the iron concentrations deep in the ocean that we didn’t expect to see.

Antony preparing reagents for the flow-injection analysis

Izzy on siderophores: Trace metals are important for the growth of tiny microbes (bacteria) in the ocean. Bacteria play an important role in recycling carbon and other elements from the organic matter produced by phytoplankton. In order to survive on low iron concentrations, they have developed a specific way of transporting iron into their cells. They produce ‘ligands’ (compounds which binds to a metal) called siderophores. These siderophores bind iron from the water column and transports it across bacteria cell membranes for growth. Around 99% of all iron in the oceans is thought to be bound to some form of ligand of unknown origin, and many scientists are working to try and figure out what makes up this ‘ligand soup’.

Photos from Left: Izzy preparing cartridges for her siderophore extraction;
Middle: Keeping an eye on filtering, and
Right: The siderophore filtering set-up.

During experiments carried out in the Southern Ocean previously, it was noted that when iron was added to the seawater, the concentration of ligands also increased. This lead to scientists theorising that these ligands are biologically produced, and at least a portion could be siderophores.

Understanding what makes up these ligands is really important, as it helps improve the accuracy of climate models which are used to predict changes to the ocean and atmosphere under future climate change scenarios. To sample siderophores from the water column, unfiltered seawater is collected from the bottles in the clean laboratory. This is then filtered through a 0.2 micron filter to catch any large particles and collect bacterial cells, before passing over a special column which extracts organic compounds from solution. These are both then frozen for future analysis back in Plymouth. This whole process takes about 4 hours in total, but luckily Izzy does not have to stay in the clean sampling laboratory to do this filtering (where there are no windows!) as things tend to get a little weird in there…

Photo: on the left: The Plymouth Trace Metal Team with visitor, Jo Ainsworth (NOC), in the trace clean sampling laboratory.

Team Moto: Happiness Leads to Negligence 🙂

Favourite sweets: Jelly babies and chocolate orange, though Izzy is also very partial to chocolate eclairs…

Plymouth Uni team measuring trace metals on CUSTARD

Capturing ‘Marine Ninjas’

Dr Katsia Pabortsava, National Oceanography Centre, UK

02/01/2020

Measuring microplastics in the Southern Ocean

‘So, have you found any microplastics in your samples already?’ This is a question that I, Dr Katsia Pabortsava (NOC, UK), often get asked while I am at sea sampling for microplastics. The answer is usually ‘No, but it doesn’t mean that they are not there – they are just way too tiny to be seen … and they are good at hiding. They are like ninjas…the marine particle ninjas!’.

To get an idea of the size of a microplastic particle, look at how thick a single strand of your hair is – microplastics can be even smaller than that! Microplastics also resemble many natural particles: they can look like a dust particle, or a broken-up antenna of a copepod, or a tiny fish scale. Any plastic item can ultimately become a microplastic. For example, the sun and waves can break down plastic bottles, bags and fishing nets into smaller plastic particles; our acrylic clothing inevitably release fibres when we wear and wash them, ships lose bits of paint from their hull as they sail across the oceans, etc.  Furthermore, microplastics are in alliance with marine bacteria, which like to grow on their surfaces and in this way mask microplastics as natural particles. These layers of bacteria, known as biofilms, make microplastics heavier and allow them to sink to the deep ocean. Microplastics also hide within the fluffy marine snow (see previous blog: Marine Snow-Episode 1), which carry them from the ocean surface to the abyss.   

Microplastics detected in marine particles samples:
A. visible image of a particle sample (microplastics cannot be seen);
B. the same particle sample imaged under infra-red light;
C. identified polyethylene microplastic particles.

Marine organisms are often deceived by the size and appearance of microplastics. Small zooplankton, such as copepods, mistake them for food and eat them. This sets off the passage of microplastics up the food chain, as marine organisms like krill and fish feed on copepods, and then to larger animals, including seals, whales and humans who eat the fish.

Plastics are very versatile in terms of their chemical composition and often contain substances that can be harmful to an organism’s health if they enter the body.  However, in order to find out how dangerous microplastics are we need to understand two key factors. First one is exposure: how much microplastics are there in the ocean, what are their composition and size, and where and how long do they stay in the water column? The second factor is harm: does the presence of certain amounts and types of microplastics damage the health of marine organisms, and how long would it take for the negative effects to become noticeable.  

SAPs being deployed for microplastic sampling during CUSTARD expedition

The CUSTARD expedition provides a unique opportunity to find out whether microplastics have penetrated the remote Antarctic waters. Here we focus mainly on the exposure aspect of microplastic pollution. We explore how these contaminants are distributed from the surface ocean and throughout the water column all the way down to the seabed. Our deepest samples come from 20 m above the seafloor, which is approximately 5.2 km deep. We also sampled the Antarctic Bottom Waters – a very old water mass that has not been in contact with the atmosphere since before the beginning of the industrial era in the 1850s.  The presence or absence of microplastics in these pre-industrial waters will give us new insights on the spread and the transport pathways of microplastics in the ocean. 

Over the past 6 weeks, we’ve captured marine microplastics using large volume stand-alone in situ pumps, referred to as SAPs, which are also used to collect marine snow (as discussed in Marine Snow Episode 2). We prepared and processed the SAPs’ sample filters in the particle-free cabinet that is free from any air-born microplastics in the ship’s labs.  This allowed us to capture only those microplastics which had already entered the ocean. Once the filters are retrieved, they are kept frozen until they reach our laboratory at National Oceanography Centre in Southampton UK, where we will use an advanced spectroscopic imaging technique to make otherwise invisible marine microplastic ninjas come to light.

CUSTARD Research Expedition Measuring Microplastics in Southern Ocean

Carbon on CUSTARD: Episode 2

Mr Gareth Lee & Dr Maribel García Ibáñez, University of East Anglia, UK

30/12/2019

EPISODE 2: Instruments used for measuring dissolved carbon in the ocean

‘Morning Laurel, morning Lucy’. That’s how the day starts. The same greeting every day, every week and every year. That’s the way they like it. Consistency and repetition. A routine. The same routine… always. Step out of the routine and they start playing up, and boy can they play up when they want to! They have very specific needs too. Seawater, and lots of it. In fact, they drink it by the gallon, one every 7 hours. Sodium chloride solution too. Again, lots of it. About a gallon every 8 hours. Orthophosphoric acid. A dash every half hour or so. Ditto hydrochloric acid and magnesium perchlorate.

You may at this point be wondering who on earth Laurel and Lucy could be? Have we discovered stowaways from a far-away land? Have we encountered a strange kind of chemically fixated sea monster new to science?

VINDTA instrument on board RRS Discovery

Sadly, no. Laurel and Lucy are in fact our ‘Versatile INstruments for the Determination of Total Alkalinity’ or VINDTAs for short. It’s hard not to anthropomorphise such beastly instruments. They are temperamental to say the least and I am convinced that anyone who has used them will say the same. Treat them well and they will shine. Treat them badly and they will punish you. Even the manual states that to operate them you have to ‘like’ them.

‘Bubble, bubble, toil and trouble’ LEFT: is the DIC purge tube which strips CO2 gas from seawater samples. RIGHT: Coulometry cell measuring concentration of CO2 in our samples

In theory, two simple processes to determine two parameters allow us to understand the dissolved carbon system in the ocean: titration to determine total alkalinity (TA) and coulometry to determine total dissolved inorganic carbon (DIC). In reality it can be challenging. You can spend 23 ½ hours watching the instruments intensely and the moment you leave them they leak all over the floor. Another favourite is regularly stopping when you pop out to make tea. They seem to know you have left them and sit idle until you return. How they know is beyond belief.

During this research expedition, our day starts and ends at midday or mid-night (depending on our shift ). Running a single sample on Laurel or Lucy takes around 23 minutes each and we collect anywhere from 20 to 50 samples per day. so to keep us happy, and sane, we have a good supply of music, books and pod casts. The occasional visitor is a refreshing change too.

Sea water samples are collected from the ocean’s surface with the ‘Continuous Underway Seawater Sampling’ system that is built in to the RRS Discovery (left); and for sampling seawater at various depths of the water column we deploy a CTD rosette (right).

Carbon on CUSTARD: Episode 1

cover pic by Sofia Alexiou, NOC

Dr Maribel García-Ibáñez & Mr Gareth Lee, University of East Anglia, UK

28/12/2019

EPISODE 1: Why we measure carbon dissolved in the ocean

Atmospheric carbon dioxide (CO2) enters the ocean through three “pumps”: the solubility pump (or physical pump), the biological pump, and the carbonate pump. Continuous contact and interaction between the atmosphere and the ocean allows CO2 to be readily absorbed into the surface ocean. This is what is called the solubility pump or physical pump. The biological pump consists of the transformation in the ocean surface of dissolved CO2 into organic matter, whose deposition creates a flow of organic carbon to the deep ocean. Phytoplankton, the base of the oceanic food webs, absorb dissolved CO2 to synthesize organic matter. As it passes through the food web, the organic matter is transported to deeper layers of the oceans, being oxidized and decomposed. Part of this organic material reaches the seafloor, joining seabed sediments. The carbonate pump, on the contrary, releases CO2 in the ocean surface layer through the creation of calcium carbonate external structures by some marine organisms such as coccolithophores and foraminifera. This calcium carbonate precipitates during photosynthesis and sinks.

Schematic of the global carbon cycle. Numbers represent mass reservoirs in PgC (1 PgC = 1015 gC) and annual carbon exchange fluxes (in PgC·yr–1). Black numbers and arrows indicate mass reservoirs and exchange fluxes estimated for the time prior to the Industrial Era (~1750). Red arrows and numbers indicate annual anthropogenic fluxes averaged over the 2000–2009 time period. These fluxes are a perturbation of the carbon cycle during Industrial Era (post 1750). The red arrows parts of Net land flux and Net ocean flux are the uptake of anthropogenic CO2 by the ocean and by terrestrial ecosystems (carbon sinks). Red numbers in the reservoirs denote cumulative changes of anthropogenic carbon over the Industrial Period 1750–2011. By convention, a positive cumulative change means that a reservoir has gained carbon since 1750. Uncertainties are reported as 90% confidence intervals. Source: Ciais et al. (2013).

Understanding how CO2 behaves in the ocean, therefore, gives us information about how the ocean uptakes atmospheric CO2 and how it is the redistributed in the ocean. Human activities have increased atmospheric CO2 concentrations since the industrial revolution. These anthropogenic CO2 emissions occur on top of an active natural carbon cycle that circulates carbon between the atmosphere, ocean and land reservoirs. The ocean dominates the storage of CO2 due to its high solubility in seawater and its sequestration through water sinking away from the surface. In fact, the oceans have absorbed about 30% of the anthropogenic CO2 emitted to the atmosphere since the industrial revolution. But this anthropogenic CO2 is not evenly distributed throughout the oceans. While CO2 concentration in the surface layers of the ocean increases as CO2 increases in the atmosphere, its penetration into the deep ocean depends on the slow vertical mixing of the water column and the circulation of water. About half of the anthropogenic CO2 is found in the first 400 m of the water column. However, in some regions where vertical movements of water are relatively fast, such as the Southern Ocean, the time scale necessary for deep penetration of anthropogenic CO2 is of the order of decades instead of centuries.

During the CUSTARD cruise, we, the UEA CO2 team, are quantifying two variables of the carbon system in the water of the Southern Ocean to help in answering the question of how deep in the ocean the CO2 is stored and, therefore, for how long it is kept out of the atmosphere. Understanding how the ocean uptakes the atmospheric CO2, which processes are responsible for this uptake, and where in the water column the CO2 is stored will allow us to understand how the ocean will continue this task, favourable to us all, in the future.

Please see our next blog post ‘Carbon on CUSTARD- EPISODE 2’ to learn more about how we go about measuring dissolved carbon in the ocean.

Scientists measure Carbon on CUSTARD research expedition, here’s why

‘Marine Snow’ Trilogy: Episode 2

Dr Frédéric Le Moigne (CNRS, Marseille, France) and Dr Katsia Pabortsava (NOC, Southamtpon, UK)

20/12/2019

EPISODE 2: What is the ocean’s biological carbon pump?

Currents and biological activity play a critical role in controlling the uptake of atmospheric carbon dioxide by the oceans. This affects marine life from microbes to large fishes everywhere in the ocean, including the remote waters around Antarctica. And this is where we currently are, in the Southern Ocean, aboard the RRS DISCOVERY trying to understand how and why this process works.

‘Marine Snow’ courtesy of Dr N Briggs, NOC

Dr Katsia Pabortsava (NOC, Southamtpon, UK) and I, Dr Frédéric Le Moigne (CNRS, Marseille, France), are investigating the important process of the oceanic carbon uptake, called the “biological carbon pump”. In essence, it represents the amount of carbon that marine particles transport from the surface ocean to depths greater than 1 km as they sink by gravity. We call these sinking particles “marine snow” because they often resemble flocs of snow, as shown in the picture on the right.

Marine snow forms mainly when phytoplankton and zooplankton die and due to the motion of water collide and stick to each other. Eventually marine snow sinks down into the deep ocean carrying along all the organic carbon that originated from photosynthetic plankton. This mechanism is essential for the ocean because it “pumps” carbon from the surface ocean and transfers it to the deep ocean for long periods of time. The deeper marine snow sinks, the longer carbon remains locked at depth and the longer it takes for it to get back to the atmosphere. The central question of our CUSTARD expedition is how deep does this carbon sink?

SAPS being deployed, photo by S Alexiou, NOC

There are multiple ways of collecting and studying marine snow particles. In ‘Marine Snow Episode 1’, Dr Nathan Briggs described various cameras that he uses to detect and describe marine snow. We, however, directly capture marine snow from the ocean to primarily investigate their chemical composition. We are most interested in how much organic carbon these particles contain as this will tell us how strong the biological carbon pump is. We collect sinking particles using 6 water pumps, called  Stand Alone Pumps or SAPS (as shown on the left). We attach the SAPS to the ship’s wire and send them to different depths to pump seawater at the same time. The SAPS usually filter around 1500 L of seawater during just one hour of pumping.

On this CUSTARD expedition, we are deploying SAPS every other day at the three main research sites in order to collect the crucial information on the amount of carbon sinking at various depths and how it may change as phytoplankton grow in the surface. So far, we have deployed the SAPS ten times and collected particles from approximately 50,000 liters of water! That’s equivalent to 71,428 bottles of mulled wine!

‘Marine Snow’ Trilogy: Episode 2 – What is the Ocean’s Biological Carbon Pump?

‘Marine Snow’ Trilogy: Episode 1

Dr Nathan Briggs, National Oceanography Centre, UK

16/12/2019

EPISODE 1: What is “Marine Snow” and how does it help keep the earth cooler?

On land, plants use sunlight to take carbon dioxide from the air and convert it into organic matter as they go through photosynthesis. In the ocean, tiny, plant-like cells called “phytoplankton” do the same thing, taking carbon dioxide out of the water as they drift in the sunlit upper ocean. As long as this organic matter is “stored” in the phytoplankton, this means there is less carbon dioxide in the ocean. The upper ocean is closely connected with our atmosphere, thus carbon storage in phytoplankton leads to less carbon dioxide in the atmosphere as well.

So, does this mean that phytoplankton are like the trees of the ocean, locking up large amounts of carbon dioxide, keeping our planet cooler and our oceans less acidic?

Well, not exactly…

On land, trees can grow for centuries, storing more carbon each year, but in the ocean, tiny, single-celled phytoplankton do not. The organic matter in phytoplankton is usually consumed within days to weeks, either by the phytoplankton themselves or by the various, and tiny, “zooplankton” that eat them. When organic matter is consumed, its carbon is converted back to carbon dioxide, which makes its way back into the ocean (and atmosphere). Nevertheless, phytoplankton play an important role in carbon storage.

How? One important answer to this question has to do with the deep ocean… and “marine snow”.

Take a look at the photo below. Does it remind you of falling snow? This “marine snow” is in fact organic matter, originally produced by phytoplankton, which has aggregated into larger particles that sink slowly from the surface to the deep ocean. This marine snow is one of the reasons we have travelled 1000 km west of the southern tip of Chile. Specifically, we want to know how much marine snow is produced here and how deep it sinks before it is consumed. Here in the Southern Ocean, below the sunlit surface waters, currents drive some water back to the surface and other water deeper still, where it will remain out of contact with the surface for 100s to 1000s of years.

The image on the left is an example of the large clump of marine snow we are finding in the Southern Ocean during the CUSTARD research expedition. It will most likely be consumed within a few days. In that time, which current will it sink to? The upwards current? In this case, the carbon dioxide locked within it will be released back into the atmosphere. But if it is consumed within the downward current, the carbon dioxide it releases will be “stored” in the deep ocean, keeping it out of the atmosphere for centuries, and keeping the planet a little bit cooler (or reducing its warming) during that time.

The various research teams on board are trying to learn more about the formation, sinking, and consumption of marine snow in different ways.

My team’s role is to study marine snow in its “natural habitat” by lowering cameras into the water and counting the number, shapes and sizes marine snow particles that we see at different locations and different depths. We also look for the zooplankton that may eat the marine snow, or may eat phytoplankton and produce “fecal pellets” (plankton poo) that sink, adding to the marine snow. On the right is our “Red Camera Frame” being lowered into the water.

What have we found so far?

Two different research sites, with very different amounts and types of marine snow. At our southern site (60°S), where we took the marine snow picture above, we found lots of aggregates, they were big (some over centimeters across!), and we found them deep (well past 1000 m). This means they were either sinking fast or they were consumed less quickly than usual.

We also found some odd shapes. Many of the marine snow aggregates photographed with our “Underwater Vision Profiler” system, like the picture on the left, appeared to be “ring” or “donut” shaped! We are not sure whether these shapes are natural or caused by water flow around our camera, but either way these shapes might tell us something about how marine snow forms and interacts with ocean turbulence.

In our northern site (54°S) we have seen very few aggregates so far, but we have seen one smaller (less than 1 mm) aggregate with a half-millimeter zooplankton attached, presumably eating. We will continue to monitor marine snow at these sites over the next four weeks. Any changes in conditions, combined with the many other measurements on board, from turbulence to photosynthetic rates, may help us understand the cause of our southern “snowstorm”. And, who knows, we may also solve the mystery of the marine “snonuts”!

All photographs courtesy of Dr Nathan Briggs, NOC

#CUSTARDcruise 2019 #blog 4 – ‘Marine Snow’ Trilogy: Episode 1