Drought on the Murray River harms ocean life too



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The mouth of the Murray River delivers vital nutrients to marine life in the ocean beyond.
SA Water, Author provided

Hannah Auricht, University of Adelaide and Kenneth Clarke, University of Adelaide

Drought in the Murray River doesn’t just affect the river itself – it also affects the ecosystems that live in the ocean beyond.

In a study published in Marine and Freshwater Research today, we found that the very low flows in the river over the past decade reduced the abundance of microscopic marine plants called phytoplankton, which are ultimately the base of all marine food webs.

This shows that the health of the Murray River has a much bigger influence on the marine environment than we previously realised. With climate change poised to make droughts more frequent and severe in the river, it will be crucial to monitor the health not just of freshwater species, but of the local marine ones too.


Read more: Is the Murray-Darling Basin Plan broken?


Phytoplankton depend on nutrients, which are often delivered to the ocean by rivers. In turn, these tiny plants are a source of food for almost all marine ecosystems. Worldwide, they are responsible for half the production of organic matter on the planet.

In South Australia, a dry period dubbed the Millennium Drought (2001 to 2010) and overallocation of water resources (primarily for agriculture) meant that very little water was delivered from the Murray Mouth to the coastal ocean. Between 2007 and 2010, no water was discharged at all. The water in the river’s lower reaches became much saltier and cloudier.

We used historical flow records and satellite imagery, taken between early 2002 and late 2016, to figure out how much phytoplankton and other organic matter were in the coastal ocean each month. We broke up the area into incremental zones, venturing up to 130km from the river mouth.

We found that during and after high-flow events, Murray River discharge resulted in a huge increase in phytoplankton concentrations – as far as 60km beyond the river’s mouth. Surprisingly, before our research it wasn’t known that the river played such an important role in stimulating phytoplankton growth over such a large area.

The mouth of the Murray River, where sometimes no water flows into the ocean at all.
CSIRO/Wikimedia Commons, CC BY

Armed with an understanding of how river flows influenced phytoplankton growth, we used historic flow records to estimate phytoplankton concentrations back to 1962. Our results showed that large flows used to occur more often and in greater volumes, and consequently that phytoplankton populations would have gone through more frequent and larger booms.

This in turn would have benefited all of the species that ultimately depend on phytoplankton for food, either directly or indirectly. This food web encompasses almost the whole marine ecosystem.

The past affects the future

Water resource management has greatly altered the volume and timing of freshwater discharges from the Murray. The ocean beyond the Murray mouth now receives small and infrequent deliveries of freshwater.

Rainfall and streamflow are decreasing in this already variable region, while temperatures are rising. This means that South Australia is likely to experience more severe and more frequent droughts, which will cause flows from the Murray mouth to decline still further, ultimately reducing phytoplankton abundance.

Previous research had already established the links between river outflows, phytoplankton and health of marine environments and species. But as far as we can tell, no other research has looked at exactly how extended periods of no or low river outflows affect marine ecosystems. This makes it difficult to predict how these systems will respond to climate change.

We believe that reduced Murray River outflows and reduced phytoplankton concentrations would likely have also placed strain on local mulloway fish and Goolwa cockle populations. Juvenile mulloway use river outflows as habitat and environmental cues, and cockles feed on organic material in the water.


Read more: ‘Tax returns for water’: how satellite-audited statements can save the Murray-Darling


This is why it is so important that the management of the Murray River doesn’t just stop at the river’s mouth, but continues into the ocean beyond. Current plans are focused on restoring flows to support the riparian and wetland ecosystems of the Murray as well as the Lower Lakes and Coorong.

But there has been little recognition of the role of river outflows on the marine environment – let alone in management. Although we might not always think about it, the marine environment is really the end of the river system, and part of a larger global cycle. It would therefore be beneficial if plans extend to monitor the marine ecosystem’s response, both at broad and fine scales, to varying flow events.

The ConversationIt would seem the time is past ripe to call for greater research and consideration on this matter, so that we don’t do further damage to what is actually still a part of the Murray River system, and can improve measures to protect the marine environment.

Hannah Auricht, PhD candidate, University of Adelaide and Kenneth Clarke, Researcher, School of Biological Sciences, University of Adelaide

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

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Mexico: New Ocean Reserve


The link below is to an article reporting on the creation of a new vast ocean reserve by Mexico in the Pacific Ocean.

For more visit:
https://www.theguardian.com/environment/2017/nov/25/mexico-creates-vast-new-ocean-reserve-to-protect-galapagos-of-north-america

Explainer: how does the sea ‘disappear’ when a hurricane passes by?


Darrell Strauss, Griffith University

You may have seen the media images of bays and coastlines along Hurricane Irma’s track, in which the ocean has eerily “disappeared”, leaving locals amazed and wildlife stranded. What exactly was happening?

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These coastlines were experiencing a “negative storm surge” – one in which the storm pushes water away from the land, rather than towards it.


Read more: Irma and Harvey: very different storms, but both affected by climate change


Most people are familiar with the idea that the sea is not at the same level everywhere at the same time. It is an uneven surface, pulled around by gravity, such as the tidal effects of the Moon and Sun. This is why we see tides rise and fall at any given location.

At the same time, Earth’s atmosphere has regions where the air pressure is higher or lower than average, in ever-shifting patterns as weather systems move around. Areas of high atmospheric pressure actually push down on the ocean surface, lowering sea level, while low pressure allows the sea to rise slightly.

This is known as the “inverse barometer effect”. Roughly speaking, a 1 hectopascal change in atmospheric pressure (the global average pressure is 1,010hPa) causes the sea level to move by 1cm.

When a low-pressure system forms over warm tropical oceans under the right conditions, it can intensify to become a tropical depression, then a tropical storm, and ultimately a tropical cyclone – known as a hurricane in the North Atlantic or a typhoon in the northwest Pacific.

As this process unfolds, the atmospheric pressure drops ever lower and wind strength increases, because the pressure difference with surrounding areas causes more air to flow towards the storm.

In the northern hemisphere tropical cyclones rotate anticlockwise and officially become hurricanes once they reach a maximum sustained wind speed of around 120km per hour. If sustained wind speeds reach 178km per hour the storm is classed as a major hurricane.

Surging waters

A “normal” storm surge happens when a tropical cyclone reaches shallow coastal waters. In places where the wind is blowing onshore, water is pushed up against the land. At the same time the cyclone’s incredibly low air pressure allows the water to rise higher than normal. On top of all this, the high waves whipped up by the wind mean that even more water inundates the coast.

The anticlockwise rotation of Atlantic hurricanes means that the storm’s northern side produces winds blowing from the east, and its southern side brings westerly winds. In the case of Hurricane Irma, which tracked almost directly up the Florida panhandle, this meant that as it approached, the east coast of the Florida peninsula experienced easterly onshore winds and suffered a storm surge that caused severe inundation and flooding in areas such as Miami.

The negative surge

In contrast, these same easterly winds had the opposite effect on Florida’s west coast (the Gulf Coast), where water was pushed offshore, leading to a negative storm surge. This was most pronounced in areas such as Fort Myers and Tampa Bay, which normally has a relatively low tide range of less than 1m.

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The negative surge developed over a period of about 12 hours and resulted in a water level up to 1.5m below the predicted low tide level. Combined with the fact that the sea is shallow in these areas anyway, it looked as if the sea had simply disappeared.


Read more: Predicting disaster: better hurricane forecasts buy vital time for residents.


As tropical cyclones rapidly lose energy when moving over land, the unusually low water level was expected to rapidly rise, which prompted authorities to issue a flash flood warning to alert onlookers to the potential danger. The negative surge was replaced by a storm surge of a similar magnitude within about 6 hours at Fort Myers and 12 hours later at Tampa Bay.

The ConversationRising waters are the deadliest aspect of hurricanes – even more than the ferocious winds. So while it may be tempting to explore the uncovered seabed, it’s certainly not wise to be there when the sea comes rushing back.

Darrell Strauss, Senior Research Fellow, Griffith University

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

I have always wondered: why is the sea salty?



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Salt flows down rivers to the ocean.
Shutterstock/Masonjar

Helen Phillips, University of Tasmania

This is an article from I Have Always Wondered, a new series where readers send in questions they’d like an expert to answer. Send your question to alwayswondered@theconversation.edu.au


Why is the sea salty? – Robert Moran, Middlecove


The short answer is that water dissolves the salts contained in rocks, and these salts are carried in the water to the sea.

As raindrops form, they absorb carbon dioxide from the air. The water (H₂O) and carbon dioxide (CO₂) react to form carbonic acid (H₂CO₃). The carbonic acid makes rainwater slightly acidic, with a pH of around 5.6. Pure water has a pH of 7, which is neutral.


Read More: I have always wondered: why are some fruits poisonous?


So, rain dissolves salts out of the rocks and these salts are carried via runoff to streams and rivers and finally to the sea. Rivers carry almost 4 billion tonnes of salt to the sea each year.

But rivers aren’t salty, right? Rivers are definitely not as salty as the sea, but they constantly carry their small salt content into the sea, and as a result the concentration of salt in the sea (which oceanographers call salinity) has built up over millions of years.

In fact, rivers aren’t the only source of sea salt. Rocks in the sea also play a role, and hydrothermal vents in the ocean floor and subsea volcanoes also supply dissolved salts to the sea.

Super-heated molten lava about to explode into the water.
NSF and NOAA

Over millions of years, the concentration of salts has increased from possibly almost fresh in the primeval sea to where it is now – an average of 35 grams of salt in every kilogram of seawater.

If all this salt could be taken out of the ocean and spread over Earth’s land surface, according to the US National Oceanic and Atmospheric Administration, it would form a layer more than 150 metres thick.

Why are some places saltier than others?

Salinity varies from place to place in the sea, depending on how close you are to rivers, how much rain falls, how much evaporation occurs, and whether ocean currents are bringing in saltier or fresher water.

In general, the sea is saltier in the subtropics, where evaporation is high due to warm air temperatures, steady trade winds, and very low humidity related to atmospheric circulation patterns called Hadley Cells.

The sea is fresher close to the Equator where rainfall is high, and in the Southern Ocean and Arctic Ocean, where sea ice melt in the summer adds fresh water.

NASA’s ‘Salt of the Earth’ Aquarius map.
NASA

Enclosed seas, such as the Mediterranean and Red Seas, can be very salty indeed. This is because the removal of fresh water by evaporation is much larger than the addition by rainfall, and lower-salinity waters from the deep sea can’t flow in as easily.

Ocean salinity as a rain gauge

While the total amount of salt in the sea is pretty constant, the distribution of the salt is changing. Broadly speaking, the salty parts of the ocean are becoming saltier, and the fresh parts fresher.

These salinity changes are caused by changing rainfall and evaporation patterns globally, where wet places are generally becoming wetter and dry places are getting drier.


Read More: I have always wondered: when do baby birds begin to breathe?


This amplification of the water cycle is a consequence of rising air temperatures due to climate change. Warm air can hold more moisture, so it can receive more evaporated water from the sea or land surface, and then release more when it rains.

Just how fast the water cycle is amplifying is a topic of current research.

Earth’s water cycle.

Rainfall and evaporation are difficult to measure accurately, particularly over the ocean where 78% of rain falls.

Ocean salinity, on the other hand, is easier to measure now that we have the global Argo program: an armada of profiling floats that measure salinity and temperature from the surface to a depth of 2,000m, and surface salinity measurements via satellite.

The ConversationOcean salinity measurements are not only being used to understand past changes in the water cycle and reduce uncertainty in climate models, they are helping to improve seasonal rain forecasts around the world.


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Helen Phillips, Senior Research Fellow, Institute for Marine and Antarctic Studies, University of Tasmania

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

Sludge, snags, and surreal animals: life aboard a voyage to study the abyss



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The famous “faceless fish”, which garnered worldwide headlines when it was collected by the expedition.
Rob Zugaro, Author provided

Tim O’Hara, Museum Victoria

Over the past five weeks I led a “voyage of discovery”. That sounds rather pretentious in the 21st century, but it’s still true. My team, aboard the CSIRO managed research vessel, the Investigator, has mapped and sampled an area of the planet that has never been surveyed before.

The RV Investigator in port.
Jerome Mallefet/FNRS

Bizarrely, our ship was only 100km off Australia’s east coast, in the middle of a busy shipping lane. But our focus was not on the sea surface, or on the migrating whales or skimming albatross. We were surveying The Abyss – the very bottom of the ocean some 4,000m below the waves.

To put that into perspective, the tallest mountain on the Australian mainland is only 2,228m. Scuba divers are lucky to reach depths of 40m, while nuclear submarines dive to about 500m. We were aiming to put our cameras and sleds much, much deeper. Only since 2014, when the RV Investigator was commissioned, has Australia had the capacity to survey the deepest depths.

The months before the trip were frantic, with so much to organise: permits, freight, equipment, flights, medicals, legal agreements, safety procedures, visas, finance approvals, communication ideas, sampling strategies – all the tendrils of modern life (the thought “why am I doing this?” surfaced more than once). But remarkably, on May 15, we had 27 scientists from 14 institutions and seven countries, 11 technical specialists, and 22 crew converging on Launceston, and we were off.

Rough seas

Life at sea takes some adjustment. You work 12-hour shifts every day, from 2 o’clock to 2 o’clock, so it’s like suffering from jetlag. The ship was very stable, but even so the motion causes seasickness for the first few days. You sway down corridors, you have one-handed showers, and you feel as though you will be tipped out of bed. Many people go off coffee. The ship is “dry”, so there’s no well-earned beer at the end of a hard day. You wait days for bad weather to clear and then suddenly you are shovelling tonnes of mud through sieves in the middle of the night as you process samples dredged from the deep.

Shifting through the mud of the abyss on the back deck.
Jerome Mallefet/FNRS

Surveying the abyss turns out to be far from easy. On our very first deployment off the eastern Tasmanian coast, our net was shredded on a rock at 2,500m, the positional beacon was lost, tens of thousands of dollars’ worth of gear gone. It was no one’s fault; the offending rock was too small to pick up on our multibeam sonar. Only day 1 and a new plan was required. Talented people fixed what they could, and we moved on.

I was truly surprised by the ruggedness of the seafloor. From the existing maps, I was expecting a gentle slope and muddy abyssal plain. Instead, our sonar revealed canyons, ridges, cliffs and massive rock slides – amazing, but a bit of a hindrance to my naive sampling plan.

But soon the marine animals began to emerge from our videos and samples, which made it all worthwhile. Life started to buzz on the ship.

Secrets of the deep

Like many people, scientists spend most of their working lives in front of a computer screen. It is really great to get out and actually experience the real thing, to see animals we have only read about in old books. The tripod fish, the faceless fish, the shortarse feeler fish (yes, really), red spiny crabs, worms and sea stars of all shapes and sizes, as well as animals that emit light to ward off predators.

A spiny red lithodid crab.
Rob Zugaro/Museums Victoria
The tripod fish uses its long spines to sit on the seafloor waiting for the next meal.
Rob Zugaro/Museums Victoria

The level of public interest has been phenomenal. You may already have seen some of the coverage, which ranged from the fascinated to the amused – for some reason our discovery of priapulid worms was a big hit on US late-night television. In many ways all the publicity mirrored our first reactions to animals on the ship. “What is this thing?” “How amazing!”

The important scientific insights will come later. It will take a year or so to process all the data and accurately identify the samples. Describing all the new species will take even longer. All of the material has been carefully preserved and will be stored in museums and CSIRO collections around Australia for centuries.

Scientists identifying microscopic animals onboard.
Asher Flatt

On a voyage of discovery, video footage is not sufficient, because we don’t know the animals. The modern biologist uses high-resolution microscopes and DNA evidence to describe the new species and understand their place in the ecosystem, and that requires actual samples.

So why bother studying the deep sea? First, it is important to understand that humanity is already having an impact down there. The oceans are changing. There wasn’t a day at sea when we didn’t bring up some rubbish from the seafloor – cans, bottles, plastic, rope, fishing line. There is also old debris from steamships, such as unburned coal and bits of clinker, which looks like melted rock, formed in the boilers. Elsewhere in the oceans there are plans to mine precious metals from the deep sea.

Rubbish found on the seafloor.
Rob Zugaro/Museums Victoria

Second, Australia is the custodian of a vast amount of abyss. Our marine exclusive economic zone (EEZ) is larger than the Australian landmass. The Commonwealth recently established a network of marine reserves around Australia. Just like National Parks on land, these have been established to protect biodiversity in the long term. Australia’s Marine Biodiversity Hub, which provided funds for this voyage, as been established by the Commonwealth Government to conduct research in the EEZ.

The newly mapped East Gippsland Commonwealth Marine Reserve, showing the rugged end of the Australian continental margin as it dips to the abyssal plain. The scale shows the depth in metres.
Amy Nau/CSIRO

Our voyage mapped some of the marine reserves for the first time. Unlike parks on land, the reserves are not easy to visit. It was our aim to bring the animals of the Australian Abyss into public view.

The ConversationWe discovered that life in the deep sea is diverse and fascinating. Would I do it again? Sure I would. After a beer.

Tim O’Hara, Senior Curator of Marine Invertebrates, Museum Victoria

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