Acid oceans are shrinking plankton, fuelling faster climate change



Researchers investigated how acidic oceans affect plankton in Prydz Bay, East Antarctica.
Daniel A. Nielsen, Author provided

Katherina Petrou, University of Technology Sydney and Daniel Nielsen, University of Technology Sydney

Increasingly acidic oceans are putting algae at risk, threatening the foundation of the entire marine food web.

Our research into the effects of CO₂-induced changes to microscopic ocean algae – called phytoplankton – was published today in Nature Climate Change. It has uncovered a previously unrecognised threat from ocean acidification.

In our study we discovered increased seawater acidity reduced Antarctic phytoplanktons’ ability to build strong cell walls, making them smaller and less effective at storing carbon. At current rates of seawater acidification, we could see this effect before the end of the century.




Read more:
Ocean acidification is already harming the Great Barrier Reef’s growth


What is ocean acidification?

Carbon dioxide emissions are not just altering our atmosphere. More than 40% of CO₂ emitted by people is absorbed by our oceans.

While reducing the CO₂ in our atmosphere is generally a good thing, the ugly consequence is this process makes seawater more acidic. Just as placing a tooth in a jar of cola will (eventually) dissolve it, increasingly acidic seawater has a devastating effect on organisms that build their bodies out of calcium, like corals and shellfish.

Many studies to date have therefore taken the perfectly logical step of studying the effects of seawater acidification on these “calcifying” creatures. However, we wanted to know if other, non-calcifying, species are at risk.

Diatoms in our oceans

Phytoplankton use photosynthesis to turn carbon in the atmosphere into carbon in their bodies. We looked at diatoms, a key group of phytoplankton responsible for 40% of this process in the ocean. Not only do they remove huge amounts of carbon, they also fuel entire marine food webs.

Diatoms use dissolved silica to build the walls of their cells. These dense, glass-like structures mean diatoms sink more quickly than other phytoplankton and therefore increase the transfer of carbon to the sea floor where it may be stored for millennia.

Diatoms are microscopic plant plankton that collectively remove huge amounts of carbon from the atmosphere.
Alyce M. Hancock, Author provided

This makes diatoms major players in the global carbon cycle. That’s why our team decided to look at how climate-change-driven ocean acidification might affect this process.

We exposed a natural Antarctic phytoplankton community to increasing levels of acidity. We then measured the rate at which the whole community used dissolved silica to build their cells, as well as the rates of individual species within the community.

More acid means less silicone

The more acidic the seawater, the more the diatom communities were made up of smaller species, reducing the total amount of silica they produced. Less silica means the diatoms aren’t heavy enough to sink quickly, reducing the rate at which they float down to the sea bed, safely storing carbon away from the atmosphere.

On examining individual cells, we found many of the species were highly sensitive to increased acidity, reducing their individual silicification rates by 35-80%. These results revealed not only are communities changing, but species that remain in the community are building less-dense cell walls.

Most alarming, many of the species were affected at ocean pH levels predicted for the end of this century, adding to a growing body of evidence showing significant ecological implications of climate change will take effect much sooner than previously anticipated.

Marine diversity is in decline

These losses in silica production could have far reaching consequences for the biology and chemistry of our oceans.

Many species affected are also an important component of the diet of the Antarctic krill, which is central to the Antarctic marine food web.

Fewer diatoms sinking to the ocean floor mean significant changes in silicon cycling and carbon burial. In a time when carbon drawn down by our ocean is crucial to helping sustain our atmospheric systems, any loss from this process will exacerbate CO₂ pollution.

Our new research adds yet another group of organisms to the list of climate change casualties. It emphasises the urgent need to reduce our dependency on fossil fuels.




Read more:
Our acid oceans will dissolve coral reef sands within decades


The only course of action to prevent catastrophic climate change is to stop emitting CO₂. We need to cut our emissions soon, if we hope to keep our oceans from becoming too acidic to sustain healthy marine ecosystems.The Conversation

Katherina Petrou, Senior Lecturer in Phytoplankton Ecophysiology, University of Technology Sydney and Daniel Nielsen, Casual Academic, University of Technology Sydney

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

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Climate change may change the way ocean waves impact 50% of the world’s coastlines


Mark Hemer, CSIRO; Ian Young, University of Melbourne; Joao Morim Nascimento, Griffith University, and Nobuhito Mori, Kyoto University

The rise in sea levels is not the only way climate change will affect the coasts. Our research, published today in Nature Climate Change, found a warming planet will also alter ocean waves along more than 50% of the world’s coastlines.

If the climate warms by more than 2℃ beyond pre-industrial levels, southern Australia is likely to see longer, more southerly waves that could alter the stability of the coastline.

Scientists look at the way waves have shaped our coasts – forming beaches, spits, lagoons and sea caves – to work out how the coast looked in the past. This is our guide to understanding past sea levels.




Read more:
Rising seas threaten Australia’s major airports – and it may be happening faster than we think


But often this research assumes that while sea levels might change, wave conditions have stayed the same. This same assumption is used when considering how climate change will influence future coastlines – future sea-level rise is considered, but the effect of future change on waves, which shape the coastline, is overlooked.

Changing waves

Waves are generated by surface winds. Our changing climate will drive changes in wind patterns around the globe (and in turn alter rain patterns, for example by changing El Niño and La Niña patterns). Similarly, these changes in winds will alter global ocean wave conditions.




Read more:
Curious Kids: why are there waves?


Further to these “weather-driven” changes in waves, sea level rise can change how waves travel from deep to shallow water, as can other changes in coastal depths, such as affected reef systems.

Recent research analysed 33 years of wind and wave records from satellite measurements, and found average wind speeds have risen by 1.5 metres per second, and wave heights are up by 30cm – an 8% and 5% increase, respectively, over this relatively short historical record.

These changes were most pronounced in the Southern Ocean, which is important as waves generated in the Southern Ocean travel into all ocean basins as long swells, as far north as the latitude of San Francisco.

Sea level rise is only half the story

Given these historical changes in ocean wave conditions, we were interested in how projected future changes in atmospheric circulation, in a warmer climate, would alter wave conditions around the world.

As part of the Coordinated Ocean Wave Climate Project, ten research organisations combined to look at a range of different global wave models in a variety of future climate scenarios, to determine how waves might change in the future.

While we identified some differences between different studies, we found if the 2℃ Paris agreement target is kept, changes in wave patterns are likely to stay inside natural climate variability.

However in a business-as-usual climate, where warming continues in line with current trends, the models agreed we’re likely to see significant changes in wave conditions along 50% of the world’s coasts. These changes varied by region.

Less than 5% of the global coastline is at risk of seeing increasing wave heights. These include the southern coasts of Australia, and segments of the Pacific coast of South and Central America.

On the other hand decreases in wave heights, forecast for about 15% of the world’s coasts, can also alter coastal systems.

But describing waves by height only is the equivalent of describing an orchestra simply by the volume at which it plays.

Some areas will see the height of waves remain the same, but their length or frequency change. This can result in more force exerted on the coast (or coastal infrastructure), perhaps seeing waves run further up a beach and increasing wave-driven flooding.

Similarly, waves travelling from a slightly altered direction (suggested to occur over 20% of global coasts) can change how much sand they shunt along the coast – important considerations for how the coast might respond. Infrastructure built on the coast, or offshore, is sensitive to these many characteristics of waves.

While each of these wave characteristics is important on its own, our research identified that about 40% of the world’s coastlines are likely to see changes in wave height, period and direction happening simultaneously.

While some readers may see intense waves offering some benefit to their next surf holiday, there are much greater implications for our coastal and offshore environments. Flooding from rising sea levels could cost US$14 trillion worldwide annually by 2100 if we miss the target of 2℃ warming.




Read more:
Droughts and flooding rains already more likely as climate change plays havoc with Pacific weather


How coastlines respond to future climate change will be a response to a complex interplay of many processes, many of which respond to variable and changing climate. To focus on sea level rise alone, and overlooking the role waves play in shaping our coasts, is a simplification which has great potential to be costly.


The authors would like to acknowledge the contribution of Xiaolan Wang, Senior Research Scientist at Environment and Climate Change, Canada, to this article.The Conversation

Mark Hemer, Principal Research Scientist, Oceans and Atmosphere, CSIRO; Ian Young, Kernot Professor of Engineering, University of Melbourne; Joao Morim Nascimento, PhD Candidate, Griffith University, and Nobuhito Mori, Professor, Kyoto University

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

New research shows that Antarctica’s largest floating ice shelf is highly sensitive to warming of the ocean



Since the last ice age, the ice sheet retreated over a thousand kilometres in the Ross Sea region, more than any other region on the continent.
Rich Jones, CC BY-ND

Dan Lowry, Victoria University of Wellington

Scientists have long been concerned about the potential collapse of the West Antarctic Ice Sheet and its contribution to global sea level rise. Much of West Antarctica’s ice lies below sea level, and warming ocean temperatures may lead to runaway ice sheet retreat.

This process, called marine ice sheet instability, has already been observed along parts of the Amundsen Sea region, where warming of the ocean has led to melting underneath the floating ice shelves that fringe the continent. As these ice shelves thin, the ice grounded on land flows more rapidly into the ocean and raises the sea level.

Although the Amundsen Sea region has shown the most rapid changes to date, more ice actually drains from West Antarctica via the Ross Ice Shelf than any other area. How this ice sheet responds to climate change in the Ross Sea region is therefore a key factor in Antarctica’s contribution to global sea level rise in the future.

Periods of past ice sheet retreat can give us insights into how sensitive the Ross Sea region is to changes in ocean and air temperatures. Our research, published today, argues that ocean warming was a key driver of glacial retreat since the last ice age in the Ross Sea. This suggests that the Ross Ice Shelf is highly sensitive to changes in the ocean.




Read more:
Ice melt in Greenland and Antarctica predicted to bring more frequent extreme weather


History of the Ross Sea

Since the last ice age, the ice sheet retreated more than 1,000km in the Ross Sea region – more than any other region on the continent. But there is little consensus among the scientific community about how much climate and the ocean have contributed to this retreat.

Much of what we know about the past ice sheet retreat in the Ross Sea comes from rock samples found in the Transantarctic Mountains. Dating techniques allow scientists to determine when these rocks were exposed to the surface as the ice around them retreated. These rock samples, which were collected far from where the initial ice retreat took place, have generally led to interpretations in which the ice sheet retreat happened much later than, and independently of, the rise in air and ocean temperatures following the last ice age.

But radiocarbon ages from sediments in the Ross Sea suggest an earlier retreat, more in line with when climate began to warm from the last ice age.

An iceberg floating in the Ross Sea – an area that is sensitive to warming in the ocean.
Rich Jones, CC BY-ND

Using models to understand the past

To investigate how sensitive this region was to past changes, we developed a regional model of the Antarctic ice sheet. The model works by simulating the physics of the ice sheet and its response to changes in ocean and air temperatures. The simulations are then compared to geological records to check accuracy.

Our main findings are that warming of the ocean and atmosphere were the main causes of the major glacial retreat that took place in the Ross Sea region since the last ice age. But the dominance of these two controls in influencing the ice sheet evolved through time. Although air temperatures influenced the timing of the initial ice sheet retreat, ocean warming became the main driver due to melting of the Ross Ice Shelf from below, similar to what is currently observed in the Amundsen Sea.

The model also identifies key areas of uncertainty of past ice sheet behaviour. Obtaining sediment and rock samples and oceanographic data would help to improve modelling capabilities. The Siple Coast region of the Ross Ice Shelf is especially sensitive to changes in melt rates at the base of the ice shelf, and is therefore a critical region to sample.




Read more:
Climate scientists explore hidden ocean beneath Antarctica’s largest ice shelf


Implications for the future

Understanding processes that were important in the past allows us to improve and validate our model, which in turn gives us confidence in our future projections. Through its history, the ice sheet in the Ross Sea has been sensitive to changes in ocean and air temperatures. Currently, ocean warming underneath the Ross Ice Shelf is the main concern, given its potential to cause melting from below.

Challenges remain in determining exactly how ocean temperatures will change underneath the Ross Ice Shelf in the coming decades. This will depend on changes to patterns of ocean circulation, with complex interactions and feedback between sea ice, surface winds and melt water from the ice sheet.

Given the sensitivity of ice shelves to ocean warming, we need an integrated modelling approach that can accurately reproduce both the ocean circulation and dynamics of the ice sheet. But the computational cost is high.

Ultimately, these integrated projections of the Southern Ocean and Antarctic ice sheet will help policymakers and communities to develop meaningful adaptation strategies for cities and coastal infrastructure exposed to the risk of rising seas.The Conversation

Dan Lowry, PhD candidate, Victoria University of Wellington

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

Eelgrass keeps the oceans alive and preserves shipwrecks, so just cope when it tickles your feet



Sea grass meadows at Bonna Point.
Valentina Hurtado-McCormick, Author provided

Valentina Hurtado-McCormick, University of Technology Sydney

Sign up to the Beating Around the Bush newsletter here, and suggest a plant we should cover at batb@theconversation.edu.au.


Have you ever walked into the ocean from a stunning Australian beach and realised the sand was covered with hundreds of ticklish leaves? This submerged canopy is a seagrass meadow, and while you might see them as a nuisance to swim past, they’re a hidden treasure.

Seagrasses are the only group of flowering plants that have adapted to the marine environment. This group comprises nearly 60 species, which typically occupy tropical and temperate regions of the world distributed across 1,646,788 km2.

There is a disproportionately large number of temperate seagrass species in southern Australia, with Zostera species dominating extensive and very diverse meadows.

Eelgrass (Zostera muelleri) is one of the dominant meadow-forming species in Australia. It has the widest distribution of its family (Zosteraceae) in temperate Australian waters, and is vital to our oceans’ health.



The Conversation

Don’t call me weedy!

These aquatic plants have evolved myriad adaptations to survive in the seas, and contrary to what many people think, seagrasses are very different from seaweeds.

Seaweeds are comparatively simple organisms: they are macroalgae with no vascular tissue, which is what conducts water and nutrients throughout a plant. In comparison, eelgrass has leaves, root and rhizomes, with flowers, fruits and seeds for reproduction.


J. Maughn/Flickr, CC BY-SA

They do, however, share one thing. Seagrasses and seaweeds are “holobionts” – meaning that they each play host to a range of microorganisms such as bacteria, fungi and microalgae that help to support their health and survival.

Research has shown that these crucial host-microbe relationships can be easily disrupted.

Climate change is not just affecting the seagrass host; the entire holobiont and even the environment it occupies are suffering from rising temperatures.

Purple plants in warm waters

My research involves studying the response of seagrass and their associated microbes to environmental degradation. I realised how much warming oceans were affecting eelgrass when I suddenly came across purple shoots in a meadow I was sampling once a month.

I was shocked. I had never seen anything like it.

While previous research has described the phenomenon of seagrass leaf reddening, I’d never heard of seagrass going purple in this specific black-purple-white pattern.

We already knew that the eelgrass accumulates red pigments as a sunscreen against the increased UV radiation that results from ozone depletion and related consequences of climate change. My PhD (soon to be published) has found that this colour change has a strong effect on the microbial communities that live on seagrass leaves.

Seagrasses establish and maintain fundamental relationships with the microbes that live among them.
Valentina Hurtado McCormick, Author provided

Why should we care?

Besides producing weird sensations on human feet, eelgrass and its counterparts are a crucial part of our coastal ecosystems. Probably the best example is their nursery role in supporting juvenile fish and crustaceans.

They also provide food for a wide range of grazers, from dugongs to the green sea turtle (as featured in the movie Finding Nemo), which feed on bounteous seagrass meadows.

Finally, we can also thank them for sequestering huge amounts of organic carbon that would otherwise contribute enormously to the greenhouse effect. Referred to as “blue carbon sinks”, researchers have calculated seagrass meadows could store 19.9 gigatonnes of organic carbon worldwide.

I could keep writing about the virtues of Zostera species (and seagrasses in general) for much, much longer, but I will leave you with a single thought: we breathe and eat from a healthy ocean, and the ocean is not healthy without seagrass.

Not just grass under your feet

Seagrass is so protective, I think of them as one of the most altruistic plants on the planet. They keep waterborne pathogens in check and neutralise harmful bacteria, keeping coral reefs healthy, and acting as an important part of the ocean’s well-being.

On the other hand, these aquatic plants also help preserve human heritage. They create a thick sediment layer on the seafloor, beneath which shipwrecks and other treasures are buried and protected from decomposition.




Read more:
Seagrass, protector of shipwrecks and buried treasure


For some 400 million years, eelgrass and other seagrass species have protected the ocean, our planet, and the creatures who live here.

In return, we have managed to create uncountable ways to directly or indirectly threaten seagrass-based ecosystems. As a result, meadows have declined globally at the accelerated rate of 7% per year.

For many of us, seagrass meadows are simply an obstacle to get past on the way to the waves. But for those of us who spend our days with a snorkel and collection tubes, these little watery plants mean far more. When I look at a single seagrass leaf, I see an entire microcosm of interacting entities.


Sign up to Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian.The Conversation

Valentina Hurtado-McCormick, PhD Candidate, University of Technology Sydney

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

Will the discovery of another plastic-trashed island finally spark meaningful change?


Jennifer Lavers, University of Tasmania and Annett Finger, Victoria University

Today we learnt of yet another remote and formerly pristine location on our planet that’s become “trashed” by plastic debris.

Research published today in Scientific Reports shows some 238 tonnes of plastic have washed up on Australia’s remote Cocos (Keeling) Islands.

It’s not the first time the world has been confronted with an island drowning under debris. Perhaps it’s time to take stock of where we’re at, what we’ve learnt about plastic and figure out whether we can be bothered, or care enough, to do something meaningful.




Read more:
This South Pacific island of rubbish shows why we need to quit our plastic habit


Taking stock

In 2017, the world was introduced to Henderson Island, an exceptionally remote uninhabited island in the South Pacific. It has the dubious honour of being home to the beach with the highest ever recorded density of plastic debris (more than 4,400 pieces per metre squared).

What’s more, a single photo taken in 1992 showed Henderson Island had gone from pristine to trashed in only 23-years.

Now, the Cocos (Keeling) Islands off the coast of Australia are set to challenge that record, despite being sparsely populated and recognised for having one of Australia’s most beautiful beaches.

A recent, comprehensive survey of the Cocos (Keeling) Islands revealed mountains of plastic trash washed up on the beaches.




Read more:
Plastic warms the planet twice as much as aviation – here’s how to make it climate-friendly


While the density of debris on Cocos (a maximum of 2,506 items per square metre) was found to be less than that on Henderson Island, the total amount of debris Cocos must contend with is staggering: an estimated 414 million debris items weighing 238 tonnes.

A quarter of the identifiable items were found to be “single-use”, or disposable plastics, including straws, bags, bottles, and an estimated 373,000 toothbrushes.

At only 14 kilometres squared, the entire Cocos (Keeling) Island group is a little more than twice the size of the Melbourne CBD. So it’s hard to envision 414 million debris items in such a small area.

Lessons learned

Islands “filter” debris from the ocean. Items flow past and accumulate on beaches, providing valuable information about the quantity of plastic in the oceans.

So, what have these two studies of remote islands taught us?

South Island. A quarter of the identifiable items were found to be disposable plastics.
Cara Ratajczak, Author provided

On Cocos, the overwhelming quantity of debris you can see on the surface accounts for just 7% of the total debris present on the islands. The remaining 93% (approximately 383 million items) is buried below the sediment. Much like the proverbial iceberg, we’re only seeing the very tip of the problem.

Henderson Island, on the other hand, highlighted the terrifying pace of change, from pristine, tropical oasis to being inundated with 38 million plastic items in just two decades.

In the past 12 months alone, scientists have made other, ground-breaking discoveries that have emphasised how little we understand about the behaviour of plastic in the environment and the myriad consequences for species and habitats – including ourselves.




Read more:
Eight million tonnes of plastic are going into the ocean each year


Here are a few of the shocking discoveries:

  • microplastics were reported in bottled water, salt and beer

  • chemicals from degrading plastic in the ocean were found to disrupt photosynthesis in marine bacteria that are important to the carbon cycle, including producing the oxygen for approximately every tenth breath we take

  • degrading plastic exposed to UV sunlight (such as those on beaches) was reported to produce greenhouse gas emissions, including methane. This is predicted to increase significantly over the next 20 years in line with plastic production trends

  • microplastic particles are ingested by krill at the base of the marine food web, then fragmented into nano-sized particles

  • plastic items recovered from the ocean were found to be reservoirs and potential vectors for microbial communities with antibiotic resistant genes

  • tiny nanoplastics are transported via wind in the atmosphere and deposited in cities and even remote areas, including mountain tops

Meaningful action

Clean-ups on near-shore islands and coastal areas around cities are fantastic.

The educational component is invaluable and they provide an important sense of community. They also prevent large items, like bottles, from breaking up into hundreds or thousands of bite-sized microplastics.

But large-scale clean-ups of the Cocos (Keeling) Islands, and most other remote islands, are challenging for a variety of reasons. Getting to these locations is expensive, as would be shipping the plastic off for recycling or disposal.

There are also serious biosecurity issues relating to moving plastic debris off islands. Even if we did somehow manage to clean these remote islands, it would not be long before the beaches are trashed again, as it was estimated on Henderson Island that more than 3,500 new pieces of plastic wash up every single day.

As Heidi Taylor from Tangaroa Blue, an Australian initiative tackling marine debris, puts so aptly:

if all we ever do is clean up, that is all we will ever do.

For our clean-up efforts to be effective, they must be paired with individual behaviour change, underpinned by legislation that mandates producers to take responsibility for the entire lifecycle of their products.

Single-use items, such as razors, cutlery, scoops for coffee or laundry powder and toothbrushes were very common on the beaches of Cocos. Clearly this is an area where extended product stewardship laws (following the principles of a circular economy), coupled with informed consumer choices can lead to better decisions about the types of products we use and how and when we dispose of them.




Read more:
There’s no ‘garbage patch’ in the Southern Indian Ocean, so where does all the rubbish go?


The global plastic crisis requires immediate and wide-ranging actions that drastically reduce our plastic consumption. And large corporations and government need to adopt a leadership role.

In the EU, for instance, governments voted in March 2019 to implement a ban on the ten most prolific single-use plastic items by 2021. The rest of the world urgently needs to follow suit. Let’s stop arguing about how to clean up the mess, and start implementing meaningful preventative actions.The Conversation

Jennifer Lavers, Research Scientist, University of Tasmania and Annett Finger, Adjunct Research Fellow, Victoria University

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

Plastic and Marine Life


The link below is to an article reporting on how plastic is leading to reproductive problems for marine wildlife.

For more visit:
https://www.theguardian.com/environment/2019/feb/27/plastics-leading-to-reproductive-problems-for-wildlife