Seagrass, protector of shipwrecks and buried treasure

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Nature’s bank vault.
Author provided

Oscar Serrano, Edith Cowan University; Carlos Duarte, King Abdullah University of Science and Technology; David John Gregory, National Museum of Denmark; Dorte Krause-Jensen, Aarhus University, and Eugenia Apostolaki, Hellenic Centre for Marine Research

For more than 6,000 years, seagrass meadows in Australia’s coastal waters have been acting as security vaults for priceless cultural heritage.

They’ve locked away thousands of shipwrecks in conditions perfect for preserving the fragile, centuries-old timbers of early European and Asian explorers, and could even hold secrets of seafaring by Aboriginal Australians.

Seagrass meadows accumulate marine sediments beneath their leaves, slowly burying and safeguarding wrecks in conditions that museum curators can only dream of. It’s a process that takes centuries, as mats of seagrass and sediments cover the wrecks and all their buried treasure.

Seagrass sedimentary deposits also hold archives of wider environmental change over millennia and are important sinks for atmospheric carbon dioxide, known as Blue Carbon.

But human development, climate change and storms are threatening fragile seagrass meadows around the world, and that risks the loss of the important cultural heritage they protect as well as some of the world’s most productive marine ecosystems.

Read more:
Dugong and sea turtle poo sheds new light on the Great Barrier Reef’s seagrass meadows

Our research, carried out by an international team of scientists in Australia, Denmark, Saudi Arabia and Greece, shows that seagrass meadows, hidden beneath our oceans, gradually build up the seafloor over millennia by trapping sediments and particles and depositing those materials as they grow.

The organic and chemical structure of seagrass sedimentary deposits is key to its ability to protect shipwrecks and submerged prehistoric landscapes. These structures are extraordinarily resistant to decay, creating thick sediment deposits that seal oxygen away from archaeological sites, preventing ships’ timbers and other materials from rotting away.

Seagrass meadows are under environmental stress due to climate change, storms and human activity. Recent disturbances and losses have exposed shipwrecks and archaeological artefacts that were previously preserved beneath the sediment. Once the protective cover of seagrass is gone, the ships and other sites begin to break down. If you lose seagrass, you lose cultural heritage.

Seagrass meadow losses in the Mediterranean have exposed Phoenician, Greek and Roman ships and cargo, many of which are thousands of years old. Unless these effects can be stemmed, the frequency of exposures is likely to increase. This has already put European archaeologists and marine scientists in a race against the clock.

Roman amphorae from a late Roman shipwreck in South Prasonisi islet, Greece, surrounded by seagrass meadows.
T. Theodoulou., Author provided

Around 7,000 shipwrecks are thought to lie in Australia’s coastal waters. Seagrass disturbance led to the unearthing in 1973 of the James Matthews, a former slave ship that sank in 1841 in Cockburn Sound, Western Australia, and the Sydney Cove, which ran aground off Tasmania’s Preservation Island in 1797, forcing survivors to walk 700km to Sydney.

Artefacts and pieces of the James Matthews’ hull have been recovered and studied at the WA Museum. Meanwhile, the recovery of beer bottles from the Sydney Cove has led, remarkably, to 220-year-old brewing yeast being cultivated and used to create a new beer – fittingly enough called The Wreck.

Revealing wrecks

We and our colleagues are aiming to match shipwreck data with seagrass meadow maps. From there, we hope new acoustic techniques for below-seabed imaging will allow exploration of underwater sites without disturbing the overlying seagrass meadows. Controlled archaeological excavation could then be undertaken to excavate, document and preserve sites and artefacts.

We also believe there’s significant potential to find archaeological heritage of early Indigenous Australians buried and preserved in seagrass meadows. Sea level around Australia rose around 6,000 years ago, potentialy submerging ancient indigenous settlements located in coastal areas, which may now be covered by seagrass.

The danger of not putting these protections in place is evidenced by treasure-hunters off the Florida coast, who have adopted a destructive technique called “mailboxing” to search for gold in Spanish galleons. This involves punching holes into sediment to find and then pillage wrecks, an action that damages seagrass meadows and archaeological remains.

Read more:
We desperately need to store more carbon – seagrass could be the answer

The accumulated sediments in seagrass meadows could also help build a record of environmental conditions, including fingerprints of human culture. These archives can be used to reconstruct prehistoric changes in land use and agriculture, mining and metallurgical activities, impacts of human activities on coastal ecosystems, and changes associated with colonisation events by different cultures. Think of it as a coastal equivalent to polar ice cores. Seagrass records could even help us understand, predict and manage the effects of current environmental changes.

But to do all this, we first need to realise what a truly valuable resource seagrass is. Granted, it doesn’t look spectacular, but it can do some pretty spectacular things – from sucking carbon out of the skies, to underpinning entire ecosystems, and even guarding buried treasure.The Conversation

Oscar Serrano, Doctor of Global Change, Edith Cowan University; Carlos Duarte, Adjunct professor, King Abdullah University of Science and Technology; David John Gregory, Senior Researcher, National Museum of Denmark; Dorte Krause-Jensen, Senior Researcher, Marine Ecology, Aarhus University, and Eugenia Apostolaki, Researcher, Institute of Oceanography, Hellenic Centre for Marine Research

This article is republished from The Conversation under a Creative Commons license. Read the original article.


How an alien seaweed invasion spawned an Antarctic mystery

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Southern bull kelp can drift huge distances before washing ashore.
Ceridwen Fraser, Author provided

Adele Morrison, Australian National University; Andy Hogg, Australian National University; Ceridwen Fraser, Australian National University, and Erik van Sebille, Utrecht University

Two small pieces of seaweed found by a Chilean scientist on an Antarctic beach set in train research that may transform our understanding of ocean drift and reveal what the future holds for Antarctic ecosystems affected by climate change.

It all started in January 2017, when sharp-eyed marine biologist Erasmo Macaya spotted two clumps of southern bull kelp washed up on the tide line of an Antarctic beach.

Most of us would have walked right on by, but it stopped Macaya in his tracks. To him it was as if an alien had just landed – and in many ways that was exactly what had happened.

The kelp that washed up on Antarctica’s Prince George Island.
Erasmo Macaya, Author provided

Every piece of science he knew said that this species of kelp should never have ended up in Antarctica. Its home was the regions around New Zealand, Chile and the sub-Antarctic islands. Indeed, a genetic test later confirmed that the pieces he found had travelled tens of thousands of kilometres from the Kerguelen and South Georgia islands.

So how did the kelp get to Antarctica?

The ocean barrier

Many scientists considered such a journey impossible, because of the fierce barrier of winds and currents that encircle Antarctica. These winds – known to sailors as the Roaring Forties – combine with the world’s strongest ocean current, the Antarctic Circumpolar Current, and the Coriolis force generated by Earth’s rotation.

Together, these forces push floating objects east and north, away from Antarctica. Before Macaya’s discovery, this barrier was thought to be impenetrable to floating debris.

Ocean currents in the Southern Ocean push floating objects east and north away from Antarctica.
Author provided

But if kelp and other organisms could make it to Antarctica, this would have profound consequences for Antarctic ecosystems. So was there a way for the kelp to drift through that barrier?

Read more:
Why I’m spending three months sailing right around Antarctica for science

Surfing kelp

We took up the challenge, using our ocean models. The mystery deepened when our first modelling attempts suggested that the Southern Ocean was indeed uncrossable by floating kelp. Even ocean eddies – the “weather” of the ocean – were not able to push floating objects southward away from the main ocean currents.

Yet the kelp had undeniably made the crossing. This led us to think about other influences on ocean drift that could play a role. We decided to add a very small effect known as Stokes drift to our models.

You can think of Stokes drift as deep ocean surfing. Waves can push floating objects in unusual directions. In the kelp’s case, each time a wave passes, the kelp will move a short distance with the wave. This drift is slow when waves are small, but in regions with large waves (such as the Southern Ocean) it can be much faster.

During storms around Antarctica, waves are typically 10-15m high. The largest wave ever recorded in the Southern Hemisphere, more than 23m, was in the Southern Ocean off New Zealand. Stokes drift must be large here.

When we added this factor to our ocean models, the change was instant. The massive waves generated by Antarctic storms pushed a small proportion of floating objects southwards. As we report in Nature Climate Change today, this conceivably explains the kelp’s voyage to Antarctica.

Modelling virtual kelp pathways with surface ocean currents and wave motion.

We calculated that the kelp specimens must have drifted at least 20,000km to reach Antarctica – the longest biological rafting events ever recorded.

Our results will also change the way that drift pathways for floating objects – such as plastics, aeroplane crash debris, pumice from volcanoes, driftwood, seaweeds, and messages in bottles – will be calculated, particularly in stormy oceans.

What this means for Antarctica

The implications don’t stop there. Until now, Antarctica was thought to be an isolated ecosystem, largely insulated from environmental change. This is not in fact true.

Southern bull kelp can carry many other species of plants and animals when it detaches and floats out to sea. The discovery that this kelp can raft to Antarctica means we could see major ecological changes in Antarctic marine ecosystems as the climate warms.

So far there is almost no evidence of natural colonisations of Antarctica from northern regions in the past few tens of thousands of years. Many Antarctic plants and animals are distinct from those found on other continents and sub-Antarctic islands.

In fact, the kelp strands Macaya found are the first recorded foreign organisms to have drifted across the Southern Ocean. But our models suggest these are unlikely to be the only ones to have made the trip.

This means that Antarctica’s ecological differences are not really due to physical isolation. It is more likely that the harsh Antarctic climate prevents new plants and animals from establishing themselves.

But Antarctica is changing. Parts of the frozen continent are among the fastest-warming regions on Earth. As Antarctica and the ocean around it warms, the kelp rafts – and other floating organisms, including invertebrates hanging onto the kelp, seeds, driftwood that could harbour insects, and larvae – may one day be able to colonise.

By the end of this century, when parts of Antarctica are expected to be similar to current sub-Antarctic environments, we might see many new species colonising Antarctica, bringing dramatic ecosystem change.

Other human-caused influences may also be felt. If kelp can break through the barrier, then floating plastic debris from the large garbage patches in the South Atlantic and South Pacific, just north of the Southern Ocean, could conceivably make a similar journey.

Read more:
The winners and losers of Antarctica’s great thaw

Plastic litter is still very rare in the waters around Antarctica. But with ever-growing amounts of plastic entering our oceans and the new drift pathways we have discovered, more plastic will likely find its way south to pollute one of our last near-pristine environments.

The ConversationAnd all of this has been revealed through the discovery of two small pieces of kelp on a distant beach, and the application of a relatively insignificant piece of ocean physics. From these small beginnings we now know that one of the world’s last great wildernesses might not escape our influence.

Adele Morrison, Research Fellow, Australian National University; Andy Hogg, Associate Professor, Australian National University; Ceridwen Fraser, Senior lecturer, Australian National University, and Erik van Sebille, Associate Professor in Oceanography and Climate Change, Utrecht University

This article was originally published on The Conversation. Read the original article.

Sea the possibilities: to fight climate change, put seaweed in the mix

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Nadya Peek/Flickr, CC BY-SA

Adam Bumpus, University of Melbourne

The next stage of humanity’s fight to reduce greenhouse emissions may revolve around seaweed, according to tonight’s episode of ABC’s Catalyst, presented by Professor Tim Flannery, which asks the question “can seaweed save the world?”

With the help of me and colleagues around the world, the documentary explores seaweed’s enormous potential to reduce greenhouse gases and draw CO₂ out of the atmosphere. In the case of seaweed, that could include giant kelp farms that de-acidify oceans, or feeding algae to cattle and sheep to dramatically reduce their methane emissions.

Read more: How farming giant seaweed can feed fish and fix the climate

But while these possibilities are exciting, early adopters are dealing with unproven technology and complex international treaties. Globally, emissions are likely to keep rising, which means seaweed-related carbon capture should only be one part of a bigger emissions reduction picture.

Net negative emissions

To stay within the Paris climate agreement’s 2℃ warming threshold, most experts agree that we must remove carbon from the atmosphere as well as reduce emissions. Many scientists now argue that 2℃ will still cause dangerous climate change, and an upper limit of 1.5℃ warming by 2100 is much safer.

To achieve that goal, humanity must begin reducing global emissions from 2020 (in less time than it takes an undergrad enrolling now to finish their degree) and rapidly decarbonise to zero net emissions by 2050.

Read more: We need to get rid of carbon in the atmosphere, not just reduce emissions

Zero net carbon emissions can come from radical emissions reductions, and massive geoengineering projects. But it could be vastly helped by what Flannery calls “the third way”: mimicking or strengthening Earth’s own methods of carbon capture.

Studies support the need to remove carbon from the atmosphere, but there are serious technical, economic and political issues with many large-scale plans.

On the other hand, seaweed solutions could be put to work in the biologically desert-like “doldrums” of the ocean, and have positive side effects such as helping to clear up the giant ocean rubbish patches. However, there are many technical problems still to be solved to make this a reality.

We probably haven’t reached peak emissions

Removing carbon from the atmosphere is an attractive proposition, but we can’t ignore the emissions we’re currently pumping out. For any negative emissions technology to work, our global emissions from fossil fuels must start to drop significantly, and very soon.

But wait a second, haven’t we already hit peak emissions? It’s true that for the third year in a row, global carbon dioxide emissions from fossil fuels and industry have barely grown, while the global economy has continued to grow strongly.

This is great news, but the slowdown in emissions growth has been driven primarily by China, alongside the United States, and a general decline of emissions in developed countries.

China’s reductions are impressive. The country peaked in coal consumption in 2014, and tends to under-promise and over-deliver on emissions reductions. However, under the Paris agreement, China has committed to a 60-65% reduction in emissions intensity, which means there’s still room for them to rise in the future.

India’s emissions, on the other hand, are major wild card. With a population of 1.3 billion and rising, about 300 million of whom are still not connected to an electrical grid, and potential increases in coal use to provide energy, India will be vital to stabilising greenhouse gases.

Read more: To slow climate change, India joins the renewable energy revolution

India’s emissions today match those of China in 1990. A study that combined India’s Paris agreement targets with OECD estimates about its long-term economic growth, suggested India’s CO₂ emissions could still grow significantly by 2030 (although per capita emissions would still be well below China and the US).

The emissions reduction relay race

So how do we deal with many competing and interconnected issues? Ideally, we need an array of solutions, with complementary waves of technology handling different problems.

Clearly the first wave, the clean energy transition, is well under way. Solar installations are breaking records, with an extra 75 gigawatts added to our global capacity in 2016, up from 51 gigawatts installed in 2015. But this still represents just 1.8% of total global electricity demand.

In addition to renewable energy generation, limiting warming to below 1.5°C also means we must increase the efficiency of our existing grid. Fortunately, early-stage financiers and entrepreneurs are focusing on a second wave of smart energy, which includes efficiency and optimisation technologies. Others in Australia have also noted the opportunities offered by the increasing use of using small, smart devices connected to the internet that respond to user demand.

Although early user results have been mixed, research shows better system control reduces the emissions intensity of energy generation. These energy efficient devices and optimisation software are on the cusp of becoming widely commercially available.

Critically, these efficiency technologies will be needed to complement structural change in the fossil fuel energy mix. This is especially in places where emissions are set to grow significantly, like India. Building renewable energy capacity, optimising with new software and technologies, and better understanding the opportunity for net negative emissions all play an important part in the emissions reductions relay race over the next 50 years to get us to 1.5°C.

With further research, development, and commercialisation, the possibilities offered by seaweed – outlined in more detail in the Catalyst documentary – are potentially game-changing.

But, as we saw with the development of renewable energy generation technology, it takes a long time to move from a good idea to wide implementation. We must support the scientists and entrepreneurs exploring zero-carbon innovations – and see if seaweed really can save the world.

The ConversationCan Seaweed Save the World? airs on the ABC on Tuesday 22 August at 8.30pm.

Adam Bumpus, Senior Lecturer, Environment & Innovation, University of Melbourne

This article was originally published on The Conversation. Read the original article.

How farming giant seaweed can feed fish and fix the climate

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Giant kelp can grow up to 60cm a day, given the right conditions.
Joe Belanger/

Tim Flannery, University of Melbourne

This is an edited extract from Sunlight and Seaweed: An Argument for How to Feed, Power and Clean Up the World by Tim Flannery, published by Text Publishing.

Bren Smith, an ex-industrial trawler man, operates a farm in Long Island Sound, near New Haven, Connecticut. Fish are not the focus of his new enterprise, but rather kelp and high-value shellfish. The seaweed and mussels grow on floating ropes, from which hang baskets filled with scallops and oysters. The technology allows for the production of about 40 tonnes of kelp and a million bivalves per hectare per year.

The kelp draw in so much carbon dioxide that they help de-acidify the water, providing an ideal environment for shell growth. The CO₂ is taken out of the water in much the same way that a land plant takes CO₂ out of the air. But because CO₂ has an acidifying effect on seawater, as the kelp absorb the CO₂ the water becomes less acid. And the kelp itself has some value as a feedstock in agriculture and various industrial purposes.

After starting his farm in 2011, Smith lost 90% of his crop twice – when the region was hit by hurricanes Irene and Sandy – but he persisted, and
now runs a profitable business.

His team at 3D Ocean Farming believe so strongly in the environmental and economic benefits of their model that, in order to help others establish similar operations, they have established a not-for-profit called Green Wave. Green Wave’s vision is to create clusters of kelp-and-shellfish farms utilising the entire water column, which are strategically located near seafood transporting or consumption hubs.

Read more: Seaweed could hold the key to cutting methane emissions from cow burps

The general concepts embodied by 3D Ocean Farming have long been practised in China, where over 500 square kilometres of seaweed farms exist in the Yellow Sea. The seaweed farms buffer the ocean’s growing acidity and provide ideal conditions for the cultivation of a variety of shellfish. Despite the huge expansion in aquaculture, and the experiences gained in the United States and China of integrating kelp into sustainable marine farms, this farming methodology is still at an early stage of development.

Yet it seems inevitable that a new generation of ocean farming will build on the experiences gained in these enterprises to develop a method of aquaculture with the potential not only to feed humanity, but to play a large role in solving one of our most dire issues – climate change.

Globally, around 12 million tonnes of seaweed is grown and harvested annually, about three-quarters of which comes from China. The current market value of the global crop is between US$5 billion and US$5.6 billion, of which US$5 billion comes from sale for human consumption. Production, however, is expanding very rapidly.

Seaweeds can grow very fast – at rates more than 30 times those of land-based plants. Because they de-acidify seawater, making it easier for anything with a shell to grow, they are also the key to shellfish production. And by drawing CO₂
out of the ocean waters (thereby allowing the oceans to absorb more CO₂ from the atmosphere) they help fight climate change.

The stupendous potential of seaweed farming as a tool to combat climate change was outlined in 2012 by the University of the South Pacific’s Dr Antoine De Ramon N’Yeurt and his team. Their analysis reveals that if 9% of the ocean were to be covered in seaweed farms, the farmed seaweed could produce 12 gigatonnes per year of biodigested methane which could be burned as a substitute for natural gas. The seaweed growth involved would capture 19 gigatonnes of CO₂. A further 34 gigatonnes per year of CO₂ could be taken from the atmosphere if the methane is burned to generate electricity and the CO₂ generated captured and stored. This, they say:

…could produce sufficient biomethane to replace all of today’s needs in fossil-fuel energy, while removing 53 billion tonnes of CO₂ per year from
the atmosphere… This amount of biomass could also increase sustainable fish production to potentially provide 200 kilograms per year, per person, for 10 billion people. Additional benefits are reduction in ocean acidification and increased ocean primary productivity and biodiversity.

Nine per cent of the world’s oceans is not a small area. It is equivalent to about four and a half times the area of Australia. But even at smaller scales,
kelp farming has the potential to substantially lower atmospheric CO₂, and this realisation has had an energising impact on the research and commercial
development of sustainable aquaculture. But kelp farming is not solely about reducing CO₂. In fact, it is being driven, from a commercial perspective, by sustainable production of high-quality protein.

A haven for fish.
Daniel Poloha/

What might a kelp farming facility of the future look like? Dr Brian von Hertzen of the Climate Foundation has outlined one vision: a frame structure, most likely composed of a carbon polymer, up to a square kilometre in extent and sunk far enough below the surface (about 25 metres) to avoid being a shipping hazard. Planted with kelp, the frame would be interspersed with containers for shellfish and other kinds of fish as well. There would be no netting, but a kind of free-range aquaculture based on providing habitat to keep fish on location. Robotic removal of encrusting organisms would probably also be part of the facility. The marine permaculture would be designed to clip the bottom of the waves during heavy seas. Below it, a pipe reaching down to 200–500 metres would bring cool, nutrient-rich water to the frame, where it would be reticulated over the growing kelp.

Von Herzen’s objective is to create what he calls “permaculture arrays” – marine permaculture at a scale that will have an impact on the climate by growing kelp and bringing cooler ocean water to the surface. His vision also entails providing habitat for fish, generating food, feedstocks for animals, fertiliser and biofuels. He also hopes to help exploited fish populations rebound and to create jobs. “Given the transformative effect that marine permaculture can have on the ocean, there is much reason for hope that permaculture arrays can play a major part in globally balancing carbon,” he says.

The addition of a floating platform supporting solar panels, facilities such as accommodation (if the farms are not fully automated), refrigeration and processing equipment tethered to the floating framework would enhance the efficiency and viability of the permaculture arrays, as well as a dock for ships
carrying produce to market.

Given its phenomenal growth rate, the kelp could be cut on a 90-day rotation basis. It’s possible that the only processing required would be the cutting of the kelp from the buoyancy devices and the disposal of the fronds overboard to sink. Once in the ocean depths, the carbon the kelp contains is essentially out of circulation and cannot return to the atmosphere.

The deep waters of the central Pacific are exceptionally still. A friend who explores mid-ocean ridges in a submersible once told me about filleting a fish for dinner, then discovering the filleted remains the next morning, four kilometres down and directly below his ship. So it’s likely that the seaweed fronds would sink, at least initially, though gases from decomposition may later cause some to rise if they are not consumed quickly. Alternatively, the seaweed
could be converted to biochar to produce energy and the char pelletised and discarded overboard. Char, having a mineralised carbon structure, is likely to last well on the seafloor. Likewise, shells and any encrusting organisms could be sunk as a carbon store.

Once at the bottom of the sea three or more kilometres below, it’s likely that raw kelp, and possibly even to some extent biochar, would be utilised as a food source by bottom-dwelling bacteria and larger organisms such as sea cucumbers. Provided that the decomposing material did not float, this would not matter, because once sunk below about one kilometre from the surface, the carbon in these materials would effectively be removed from the atmosphere for at least 1,000 years. If present in large volumes, however, decomposing matter may reduce oxygen levels in the surrounding seawater.

Large volumes of kelp already reach the ocean floor. Storms in the North Atlantic may deliver enormous volumes of kelp – by some estimates as much as 7 gigatonnes at a time – to the 1.8km-deep ocean floor off the Bahamian Shelf.

Submarine canyons may also convey large volumes at a more regular rate to the deep ocean floor. The Carmel Canyon, off California, for example, exports large volumes of giant kelp to the ocean depths, and 660 major submarine canyons have been documented worldwide, suggesting that canyons play a significant role in marine carbon transport.

These natural instances of large-scale sequestration of kelp in the deep ocean offer splendid opportunities to investigate the fate of kelp, and the carbon it contains, in the ocean. They should prepare us well in anticipating any negative or indeed positive impacts on the ocean deep of offshore kelp farming.

The ConversationOnly entrepreneurs with vision and deep pockets could make such mid-ocean kelp farming a reality. But of course where there are great rewards, there are also considerable risks. One obstacle potential entrepreneurs need not fear, however, is bureaucratic red tape, for much of the mid-oceans remain a global commons. If a global carbon price is ever introduced, the exercise of disposing of the carbon captured by the kelp would transform that part of the business from a small cost to a profit generator. Even without a carbon price, the opportunity to supply huge volumes of high-quality seafood at the same time as making a substantial impact on the climate crisis are considerable incentives for investment in seaweed farming.

Tim Flannery, Professorial fellow, Melbourne Sustainable Society Institute, University of Melbourne

This article was originally published on The Conversation. Read the original article.

Article: Seagrasses Store Massive Amounts of Carbon

The following link is to an article that looks at how much carbon is stored by seagrasses.

For more visit: