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Monday, August 23, 2021
Why is the ocean salty?
No matter how salty you get, you'll never be as salty as the ocean
From ZME Science by Mihai Andrei
Every time you bathe in the sea, you have geology to thank for the extra buoyancy that salty water provides. Large-scale geological processes bring salt into the oceans and then recycle it deep into the planet. The short answer to ‘why is the ocean salty’ sounds something like this:
Salts eroded from rocks and soil are carried by rivers into the oceans, where salt accumulates. Another source of salts comes from hydrothermal vents, deep down on the surface of the ocean floor. We say “salts” — because the oceans carry several types of salts, not just what we call table salt.
But the longer answer (that follows below) is so much more interesting.
Image credits: Olia Nayda.
In the beginning there was saltiness
As it is so often the case in geology, our story begins with rocks and dirt, and we have to go back in time — a lot. Billions of years ago, during a period called the Archean, our planet was a very different environment than it is today. The atmosphere was different, the landscape was different, but as far as ocean saltiness goes, there may have been more similarities than differences.
Geologists look at ancient rocks that preserved ancient water (and therefore, its ancient salinity); one such study found that Earth’s Archean oceans may have been ~1.2 times saltier than they are today.
At first glance, this sounds pretty weird. Since salt in the seas and oceans is brought in by river runoff and erosion, the salts hadn’t yet had time to accumulate in Earth’s earliest days. So what’s going on?
It is believed that while the very first primeval oceans were less salty than they are today, our oceans have had a significant salinity for billions of years. Although rivers hadn’t had sufficient time to dissolve salts and carry them to oceans, this salinity was driven by the oceanic melting of briny rocks called evaporites, and potentially volcanic activity. It is in this water that the first life forms on Earth emerged and started evolving.
“The ions that were put there long ago have managed to stick around,” says Galen McKinley, a UW-Madison professor of atmospheric and oceanic sciences. “There is geologic evidence that the saltiness of the water has been the way that it is for at least a billion years.”
The ancient salinity of oceans is still an area of active research with many unknowns. But while we don’t fully understand what’s going on with the ancient oceans, we have a much better understanding of what drives salinity today.
So how do the oceans get salty today?Salinity map of the world’s oceans. Scale is in parts per thousand. Image credits: NASA.
Oceans today have an average of 3.5% salinity. In other words, 3.5% of the ocean’s weight is made of dissolved salts. Most, but not all of that is sodium chloride (what we call ‘salt‘ in day to day life). Around 10% of the salt ions come from different minerals.
At first glance, 3.5% may not seem that much, but we forget that around 70% of our planet is covered in oceans. If we took all the salt in the ocean and spread it evenly over the land surface, it would form a layer over 500 feet (166 meters) thick — a whopping 40-story building’s height of salt covering the entire planet’s landmass. That’s how much 3.5% means in this particular case.
All these salts come from rocks. Rocks are laden with ionic elements such as sodium, chlorine, and potassium. Much of this material was spewed as magma by massive volcanic eruptions and can form salts under the right conditions.
Because it is slightly acidic, rainwater can slowly dissolve, erode rocks. As it does so, it gathers ions that make up salts and transfers them to streams and rivers. We consider rivers to be “freshwater”, but that’s not technically true: all rivers have some salt dissolved in them, but because they flow, they don’t really accumulate it. Rivers are agents for carrying salts, but they don’t store salts themselves.The main culprit for why oceans are salty: rivers. Image credits: Jon Flobrant.
Rivers constantly gather more salts, but they constantly push it downstream. Influx from precipitation also ensures that the salt concentration doesn’t increase over time.
Meanwhile, the oceans have no outlet, and while they also have currents and are still dynamic, they have nowhere to send the salts to, so they just accumulate more and more salt. Which leads us to an interesting question.
So, are the oceans getting saltier?
Bodies of water can be classified by their salt content.
No, not really. Although it’s hard to say whether oceans will get saltier in geologic time (ie millions of years), ocean salinity remains generally constant, despite the constant influx of salt.
“Ions aren’t being removed or supplied in an appreciable amount,” says McKinley. “The removal and sources that do exist are so small and the reservoir is so large that those ions just stay in the water.” For example, she says, “Each year, runoff from the land adds only 0.00005 percent of total ocean salts.”
A part of the minerals is used by animals and plants in the water and another part of salts becomes sediment on the ocean floor and is not dissolved. However, the main reason why oceans aren’t getting saltier is once more geological.
The surface of our planet is in a constant state of movement — we call this plate tectonics. Essentially, the Earth’s crust is split into rigid plates that move around at a speed of a few centimeters per year. Some are buried through the process of subduction, taking with them the minerals and salts into the mantle, where they are recycled. The movement of tectonic plates constantly recirculates material from and into the mantle. Schematic of subduction (and some other associated processes). Image credits: K. D. Schroeder.
With these processes, along with the flow of freshwater, precipitation, and a number of other processes, the salinity of the Earth’s oceans remains relatively stable — the oceans have a stable input and output of salts.
But isolated bodies of water, however, can become extra salty.
Why some lakes are freshwater, and some are *very* salty
Lakes are temporary storage areas for water, and most lakes tend to be freshwater. Rivers and streams bring water to lakes just like they do to oceans, so then why don’t lakes get salty?
Well, lakes are usually only wide depressions in a river channel — there is a water input and a water output, water flows in and it flows out. This is called an open lake, and open lakes are essentially a buffer for rivers, where water accumulates, but it still flows in and out, without salts accumulating. Many lakes are also the result of chaotic drainage patterns left over from the last Ice Age, which makes them very recent in geologic time and salts have not had the time to accumulate.Beautiful glacial lakes such as this one are the remains of Ice Age melting. Image credits: K. D. Schroeder.
But when a lake has no water output and it has had enough time to accumulate salts, it can become very salty. This is called a closed lake, and closed lakes (and seas) can be very salty, much more so than the planetary oceans. They accumulate salts and lose water through evaporation, which increases the concentration of salts. Closed lakes are pretty much always saline.
We mentioned that world oceans are 3.5% salt on average. The Mediterranean Sea has a salinity of 3.8%. The Red Sea has some areas with salinity over 4%, and Mono Lake in California can have a salinity of 8.8%. But even that isn’t close to the saltiest lakes on Earth. Great Salt Lake in Utah has a whopping salinity of 31.7%, and the pink lake Retba in Senegal, where people have mined salt for centuries, has a salinity that reaches 40% in some points. The saltiest lake we know of is called Gaet’ale Pond — a small, hot pond with a salinity of 43% — a testament to just how saline these isolated bodies of water can get.Worker digging the salt in Lake Retba. Image in public domain.
It’s important to note that lakes are not stable geologically, and many tend to not last in geologic time. Some of the world’s biggest lakes are drying up, both as a natural process and due to rising temperatures, drought, and agricultural irrigation.
Salt can also come from belowHydrothermal vent. Image credits: NOAA.
We’ve mentioned that rock weathering and dissolving makes oceans salty, but there is another process: hydrothermal vents.
A part of the ocean water seeps deeper into the crust, becomes hotter, dissolves some minerals, and then flows back into the ocean through these vents. The hot water brings large amounts of minerals and salts. It’s not a one-way process — some of the salts react with the rocks and are removed from seawater, but this process also contributes to salinization.
Lastly, underwater volcanic eruptions can also bring salts from the deeper parts to the surface, affecting the salt content of oceans.
Links :
- SurferToday : Why is the ocean salty?
Rain and warmth trigger more melting in Greenland
August 12, 2021
From The Guardian by Damina Carrington
Precipitation was so unexpected, scientists had no gauges to measure it, and is stark sign of climate crisis
Rain has fallen on the summit of Greenland’s huge ice cap for the first time on record.Temperatures are normally well below freezing on the 3,216-metre (10,551ft) peak, and the precipitation is a stark sign of the climate crisis.
Scientists at the US National Science Foundation’s summit station saw rain falling throughout 14 August but had no gauges to measure the fall because the precipitation was so unexpected.
Across Greenland, an estimated 7bn tonnes of water was released from the clouds.
The rain fell during an exceptionally hot three days in Greenland when temperatures were 18C higher than average in places.
As a result, melting was seen in most of Greenland, across an area about four times the size of the UK.
The recent report from the Intergovernmental Panel on Climate Change concluded it was “unequivocal” that carbon emissions from human activities were heating the planet and causing impacts such as melting ice and rising sea level.
The recent report from the Intergovernmental Panel on Climate Change concluded it was “unequivocal” that carbon emissions from human activities were heating the planet and causing impacts such as melting ice and rising sea level.
Air temperature change (August 14 vs August 5-11 average, °C)
In May, researchers reported that a significant part of the Greenland ice sheet was nearing a tipping point, after which accelerated melting would become inevitable even if global heating was halted.
Ted Scambos, a scientist at the National Snow and Ice Data Center at the University of Colorado, which reported the summit rain, told CNN: “What is going on is not simply a warm decade or two in a wandering climate pattern. This is unprecedented. We are crossing thresholds not seen in millennia, and frankly this is not going to change until we adjust what we’re doing to the air.”
Greenland also had a large-scale melting episode in July, making 2021 one of just four years in the past century to see such widespread melting. The other years were 2019, 2012 and 1995.
The rain and melt on 14-16 August came at the latest point in the year a major event has been recorded.
The cause of the July and August melting was the same – warm air being pushed up over Greenland and held there.
These “blocking” events are not uncommon but seem to be becoming more severe, according to scientists.
Global sea level would rise by about 6 metres if all of Greenland’s ice melted, although this would take centuries or millennia to occur.
But the trillions of tonnes lost from Greenland since 1994 is pushing up sea levels and endangering the world’s coastal cities.
Sea level has already risen by 20cm, and the IPCC said the likely range by the end of the century was a further 28-100cm, though it could be 200cm.
Greenland’s ice is melting faster than any time in the past 12,000 years, scientists have estimated, with the ice loss running at a rate of about 1m tonnes a minute in 2019.
Links :
Sunday, August 22, 2021
Which way will paper maps go in the future? Cartographer says they'll still be crucial, even with GPS
(ABC News: Lincoln Rothall)
From ABC by Bec Whetham
As a test, Anthony Stephens likes to ask "anybody under 30 years old who lives in the city" to name the suburb directly to the north of where they live.
"It is interesting the answers you get," Mr Stephens said.
"Sometimes we even get the question, 'What is north?'"
Our modern dependency on GPS has certainly challenged the cartographer, who has made and sold paper maps for more than 50 years.
His business, The Map Shop, used to produce Adelaide's street directories.
"We stopped printing those four years ago. You will never see a new Fuller's street directory again," Mr Stephens said.
(ABC News: Lincoln Rothall)
Prior to COVID, 40 per cent of his business was overseas maps.
He has sold 10 in the past nine months.
The message that his product is dying doesn't scare him.
He has heard it before.
First at a map conference in the 1970s, where it was predicted that there would be "no such thing as maps" by 1990.
"And then I attended another conference in San Diego in the 1990s and their message was there would be no maps by the year 2000," Mr Stephens said.
"Guess what? It's 2021 and there are still paper maps and we've got 14,500 different ones."
(ABC News: Lincoln Rothall)
Fortunately the shop has been able to fill some of the gap in demand with an increase in local and domestic maps, alongside its longstanding clients looking for topographical maps for commercial, emergency, or farming purposes.
Why maps are important
More than providing a route to travel or indicating where to find the nearest service station, Mr Stephens says maps are an important factor in human empathy.
"What's the use of listening to the news of doom and gloom if you don't know where the doom and gloom is in relation to you?" Mr Stephens said.
"It's as simple as that."
He has genuine concerns for young people who don't use maps, or know how.
"Because they're so used to looking at the screen on their phone, they only see that portion of the world."
He says maps are also an important record of time.
"[With] everything going online, there is then not a snapshot in time.
We're going to become the forgotten generation."
One of the shop's most popular items is a 100-year-old map of Adelaide, which features things like the Sir Ross Smith landing area.
"Of course all those maps were done under 'plane tabling', which involved a man going on top of a hill … triangulating the major features, then going to another hill and checking the coordinates and then sketching between them."
A modern day cartographer
What Mr Stephens once made by hand is now done with computers.
"We used to be known as plastic scratchers because we would actually work over a light table on a material where you would actually scratch out the plastic to mark out the roads and contours and drainage," Mr Stephens said.
"It still takes the same time to make the maps but the updating is a lot easier for us."
It is online mapping that has allowed modern-day cartographer Alex Broers to develop his love of art, culture and fantasy into a profitable business.
He hand draws "bespoke" maps, recreating Australian destinations that resemble maps of The Lord of the Rings' Middle Earth.
"I was making these maps initially as a personal hobby and passion, it was never a business to begin with," he said.
Alex Broers runs Cartography Chronicles, a business that makes old-age maps of Australian destinations.(Supplied: Alex Broers)
Map making an art and a science
In the middle of COVID, Mr Broers started his business Cartography Chronicles in response to commercial interest online.
While it's always preferable to travel to the places he's recreating, the process can be done from his home in Darwin.
"I'm very lucky that we have the internet these days and a lot of the resources that I need to actually make the maps are also online."
It's still a long process though.
"For one of my state maps, it does take me 60-70 hours of drawing and that doesn't factor in the research phase."
(Supplied: Alex Broers)
While the geographical points are accurate, some features — the mountain ranges in particular — are enlarged.
"Obviously they're not in proportion to real life purely because if they were you'd have a little 'x' on a map or a few contour lines.
"With my work I really wanted to bring to the forefront the geography of each region."
Sentimental attachment
Mr Broers is continually taken aback by the interest in — and emotional attachment to — his work.
"I think it's a real testament that Australians in general are very attached and proud of where they come from," he says.
While Mr Broers's maps may not be made for navigation, they do evoke a personal reference for people.
Alex Broers (pictured) and Anthony Stephens are travellers.
Mr Broers grew up in Bahrain and then lived in UK and Oman before moving to Australia.
Mr Broers grew up in Bahrain and then lived in UK and Oman before moving to Australia.
(Supplied: Alex Broers)
"[They] almost connect the dots for people … [the map] triggers different memories depending on what area you look at."
The future of map making
While Mr Broers's personal style of map making may be keeping the art of cartography alive, Mr Stephens hopes traditional topographical maps will continue into the future.
"[Companies] … like Google rely on that base data so you can have your electronic version.
If that base data is not being developed then your electronic data is going to get out of date as well," Mr Stephens said.
"How can you develop a country if you haven't got up-to-date maps?"
It's a skill Mr Broers appreciates too.
"I don't know many people who are making cartography maps like the likes of Anthony," he said.
While GPS is an aid to a map, he says it's not a replacement.(ABC News: Lincoln Rothall)
"I do feel like it's a slowly dying art because of GPS, Google Maps and everything else [but] I still think there's a need for those handmade accurate maps."
The amazing life of sand : deep look
There's a story in every grain of sand: tales of life and death, fire and water.
If you scooped up a handful of sand from every beach, you'd have a history of the world sifting through your fingers.
See the unseen at the very edge of our visible world.
If you scooped up a handful of sand from every beach, you'd have a history of the world sifting through your fingers.
See the unseen at the very edge of our visible world.
How does sand form?
Sand can be anything that has been worn down until it’s reduced to some tiny, essential fragment of what it once was: a granite pebble from the mountains; coral from the sea; obsidian from a volcano; even skeletons of microscopic sea animals.
It's also a technical term.
Bigger than sand, that’s gravel, smaller? Silt.
It's also a technical term.
Bigger than sand, that’s gravel, smaller? Silt.
By studying the composition and texture of sand, geologists can reconstruct its incredible life history.
“There’s just a ton of information out there, and all of it is in the sand,” said Mary McGann, a geologist at the United States Geological Survey in Menlo Park, CA. McGann recently took part in a comprehensive research project mapping sand’s journey into and throughout San Francisco Bay.
Patrick Barnard, another USGS geologist who helped oversee the project, said that it will help scientists understand how local beaches are changing over time.
In particular, Barnard wants to understand why beaches just south of San Francisco Bay are among the most rapidly eroding beaches in the state.
In particular, Barnard wants to understand why beaches just south of San Francisco Bay are among the most rapidly eroding beaches in the state.
From 2010-2012, Barnard and his team sampled beaches, outcrops, rivers and creeks to track sand’s journey around the bay.
They even collected sand from the ocean floor.
The researchers then carefully analyzed the samples to characterize the shapes, sizes, and chemical properties of the sand grains.
They even collected sand from the ocean floor.
The researchers then carefully analyzed the samples to characterize the shapes, sizes, and chemical properties of the sand grains.
Barnard said the information provides a kind of fingerprint, or signature, for each sample that can then be matched to a potential source.
For example, certain minerals may only come from the Sierra Mountains or the Marin Headlands.
For example, certain minerals may only come from the Sierra Mountains or the Marin Headlands.
“If we’ve covered all of the potential sources, and we know the unique signature of the sand from these different sources, and we find it on a beach somewhere, then we basically know where it came from,” explained Barnard.
And those species aren’t the only things finding their way into the sand.
Manmade materials can show up there, too.
Manmade materials can show up there, too.
McGann has found metal welding scraps and tiny glass spheres (commonly sprinkled on highways to make road stripes reflective) in sand samples from around the bay.
“All of these things can get washed into our rivers or our creeks, or washed off the road in storm drains,” explained McGann.
“Eventually they end up in, for example, San Francisco Bay.”
“Eventually they end up in, for example, San Francisco Bay.”
By piecing together all of these clues – the information found in the minerals, biological material and man made objects that make up sand – the researchers ended up with a pretty clear picture of how sand travels around San Francisco Bay.
Some sands stay close to home.
Rocky sand in the Marin Headlands comes from nearby bluffs, never straying far from its source.
Rocky sand in the Marin Headlands comes from nearby bluffs, never straying far from its source.
Other sands travel hundreds of miles.
Granite from the Sierra Nevada mountains careens down rivers and streams on a century-long sojourn to the coast.
Granite from the Sierra Nevada mountains careens down rivers and streams on a century-long sojourn to the coast.
In fact, much of the sand in the Bay Area comes from the Sacramento and San Joaquin rivers, with local watersheds also playing an important role in transporting sand to the beach.
Although this project focused on San Francisco Bay, the same techniques could be used to study other coastal systems, he added, revealing the incredible life stories of sand from around the world.
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