How the seafloor of the Antarctic Ocean is changing ...and the climate is following suit

From Hydro

Experts have reconstructed the depth of the Southern Ocean at key phases in the last 34 million years of the Antarctic’s climate history.

The glacial history of the Antarctic is currently one of the most important topics in climate research.
Why? Because worsening climate change raises a key question: How did the ice masses of the southern continent react to changes between cold and warm phases in the past, and how will they do so in the future? A team of international experts, led by geophysicists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), has now shed new light on nine pivotal intervals in the climate history of the Antarctic, spread over 34 million years, by reconstructing the depth of the Southern Ocean in each one.
These new maps offer insights into the past courses of ocean currents, for example, and show that, in past warm phases, the large ice sheets of East Antarctica reacted to climate change in a similar way to how ice sheets in West Antarctica are doing so today.
The maps and the freely available article have just been released in the online journal Geochemistry, Geophysics, Geosystems, a publication of the American Geological Union.

The Southern Ocean is one of the most important pillars of the Earth’s climate system.
Its Antarctic Circumpolar Current, the most powerful current on the planet, links the Pacific, Atlantic and Indian Oceans, and has effectively isolated the Antarctic continent and its ice masses from the rest of the world for over 30 million years.
Then and now, ocean currents can only flow where the water is sufficiently deep and there are no obstacles such as land bridges, islands, underwater ridges and plateaus blocking their way.
Accordingly, anyone seeking to understand the climate history and glacial history of the Antarctic needs to know exactly what the depth and surface structures of the Southern Ocean’s floor looked like in the distant past.

Researchers around the globe can now find this information in new, high-resolution grid maps of the ocean floor and data-modelling approaches prepared by a team of international experts led by geoscientists from the AWI, which cover nine pivotal intervals in the climate history of the Antarctic.
“In the course of the Earth’s history, the geography of the Southern Ocean has constantly changed, as continental plates collided or drifted apart, ridges and seamounts formed, ice masses shoved deposited sediments across the continental shelves like bulldozers, and meltwater transported sediment from land to sea,” says AWI geophysicist and co-author Dr Karsten Gohl.
Each process changed the ocean’s depth and, in some cases, the currents.
The new grid maps clearly show how the surface structure of the ocean floor evolved over 34 million years – at a resolution of ca.
5 x 5 kilometres per pixel, making them 15 times more precise than previous models.Southern Ocean 2.65 million years ago – transition from the Pliocene to the Pleistocene.

40 Years of Geoscientific Research in the Antarctic

In order to reconstruct the past water depths, the experts gathered geoscientific field data from 40 years of Antarctic research, which they then combined in a computer model of the Southern Ocean’s seafloor.
The basis consisted of seismic profiles gathered during over 150 geoscientific expeditions and which, when put end-to-end, cover half a million kilometres.
In seismic reflection, sound waves are emitted, penetrating the seafloor to a depth of several kilometres.
The reflected signal is used to produce an image of the stratified sediment layers below the surface – a bit like cutting a piece of cake, which reveals the individual layers.
The experts then compared the identified layers with sediment cores from the corresponding regions, which allowed them to determine the ages of most layers.
In a final step, they used a computer model to ‘turn back time’ and calculate which sediment deposits were already present in the Southern Ocean at specific intervals, and to what depths in the seafloor they extended in the respective epochs.

Antarctic ocean (1890)

 

https://data.aad.gov.au/database/mapcat/20million/edition10/Antarctica_and_the_Southern_Ocean_15310.pdf

see AAD

 

Turning Points in the Climate History

They applied this approach to nine key intervals in the Antarctic’s climate history, including the warm phase of the early Pliocene, five million years ago, which is widely considered to be a potential template for our future climate.
Back then, the world was 2 to 3 degrees Celsius warmer on average than today, partly because the carbon dioxide concentration in the atmosphere was as high as 450 ppm (parts per million).
The IPCC (IPCC Special Report on the Ocean and Cryosphere in a Changing Climate, 2019) has cited this concentration as the best-case scenario for the year 2100; in June 2019, the level was 415 ppm.
Back then, the Antarctic ice shelves now floating on the ocean had most likely completely collapsed.
“Based on the sediment deposits we can tell, for example, that in extremely warm epochs like the Pliocene, the large ice sheets in East Antarctica reacted in a very similar way to what we’re currently seeing in ice sheets in West Antarctica,” reports Dr Katharina Hochmuth, the study’s first author and a former AWI geophysicist, who is now conducting research at the University of Leicester, UK.

Accordingly, the new maps provide data on important climatic conditions that researchers around the world need in order to accurately simulate the development of ice masses in their ice-sheet and climate models, and to produce more reliable forecasts.
Researchers can also download the corresponding datasets from the AWI’s Earth system database PANGAEA.

Links :

• The Guardian : Antarctica: an ecosystem under threat - in pictures

Bedrock modernizes seafloor mapping with autonomous sub and cloud-based data

Image Credits: Bedrock

 

From Techcrunch by devin Coldeway

The push for renewable energy has brought offshore wind power to the forefront of many an energy company’s agenda, and that means taking a very close look at the ocean floor where the installations are to go.

Fortunately Bedrock is here to drag that mapping process into the 21st century with its autonomous underwater vehicle and modern cloud-based data service.

The company aims to replace the standard “big ship with a big sonar” approach with a faster, smarter, more modern service, letting companies spin up regular super-accurate seafloor imagery as easily as they might spin up a few servers to host their website.

“We believe we’re the first cloud-native platform for seafloor data,” said Anthony DiMare, CEO and cofounder (with CTO Charlie Chiau) of Bedrock. 

“This is a big data problem — how would you design the systems to support that solution? We make it a modern data service, instead of like a huge marine operation — you’re not tied to this massive piece of infrastructure floating in the water. Everything from the way we move sonars around the ocean to the way we deliver the data to engineers has been rethought.”

The product Bedrock provides customers is high-resolution maps of the seafloor, made available via Mosaic, a familiar web service that does all the analysis and hosting for you — a big step forward for an industry where “data migration” still means “shipping a box of hard drives.”

Normally, DiMare explained, this data was collected, processed, and stored on the ships themselves.

Since they were designed to do everything from harbor inspections to deep sea surveys, they couldn’t count on having a decent internet connection, and the data is useless in its raw form.

Like any other bulky data, it needs to be visualized and put in context.

Image Credits: Bedrock

“These datasets are extremely large, tens of terabytes in size,” said DiMare. 

“Typical cloud systems aren’t the best way to manage 20,000 sonar files.”

The current market is more focused on detailed, near-shore data than the deep sea, since there’s a crush to take part in the growing wind energy market.

This means that data is collected much closer to ordinary internet infrastructure and can be handed off for cloud-based processing and storage more easily than before.

That in turn means the data can be processed and provided faster, just in time for demand to take off.

As DiMare explained, while there may have been a seafloor survey done in the last couple decades of a potential installation site, that’s only the first step.

An initial mapping pass might have be made to confirm the years-old maps and add detail, then another for permitting, for environmental assessments, engineering, construction, and regular inspections.

If this could be done with a turnkey automated process that produced even better results than crewed ships for less money, it’s a huge win for customers relying on old methods.

And if the industry grows as expected to require more active monitoring of the seafloor along every U.S. coast, it’s a win for Bedrock as well, naturally.

Image Credits: Bedrock

To make this all happen, of course, you need a craft that can collect the data in the first place.

 “The AUV is a piece of technology we built solely to enable a data product,” said DiMare, but noted that, originally, “we didn’t want to do this.”

“We started to spec out what it looked like to use an off the shelf system,” he explained.

“But if you want to build a hyper-scalable, very efficient system to get the best cost per square meter, you need a very specific set of features, certain sonars, the compute stack… by the time we listed all those we basically had a self-designed system. It’s faster, it’s more operationally flexible, you get better data quality, and you can do it more reliably.”

And amazingly, it doesn’t even need a boat — you can grab it from the back of a van and launch it from a pier or beach.

“From the very beginning one of the restrictions we put on ourselves was ‘no boats.’ And we need to be able to fly with this thing. That totally changed our approach,” said DiMare.

Image Credits: Bedrock

The AUV packs a lot into a small package, and while the sensor loadout is variable depending on the job, one aspect that defines the craft is its high-frequency sonar.

Sonars operate in a wide range of frequencies, from the hundreds to the hundreds of thousands of hertz. Unfortunately that means that ocean-dwelling creatures, many of which can hear in that range, are inundated with background noise, sometimes to the point where it’s harmful or deters them from entering an area.

Sonar operating about 200 kHz is safe for animals, but the high frequency means the signal attenuates more quickly, reducing the range to 50-75 meters.

That’s obviously worthless for a ship floating on the surface — much of what it needs to map is more than 75 meters deep.

But if you could make a craft that always stayed within 50 meters of the seabed, it’s full of benefits. And that’s exactly what Bedrock’s AUV is designed to do.

 

The increased frequency of the sonar also means increased detail, so the picture its instruments paint is better than what you’d get with a larger wave.

And because it’s safe to use around animals, you can skip the (very necessary but time-consuming) red tape at wildlife authorities.

Better, faster, cheaper, and safer is a hell of a pitch.

Today marks the official launch of Mosaic, and to promote adoption Bedrock is offering 50 gigs of free storage — of any kind of compatible map data, since the platform is format-agnostic.

There’s a ton of data out there that’s technically “public” but is nevertheless very difficult to find and use.

It may be a low-detail survey from two decades ago, or a hyper-specific scan of an area investigated by a research group, but if it were all in one place it would probably be a lot more useful, DiMare said.
“Ultimately we want to get where we can do the whole ocean on a yearly basis,” he concluded. “So we’ve got a lot of work to do.”

 

Links :

• Techcrunch : Ocean floor mapping robotics startup Bedrock announces an $8M raise
• GeoGarage blog : The future of ocean exploration

New Zealand (Linz) layer update in the GeoGarage platform

6 nautical raster charts updated

see GeoGarage news

Canada (CHS) layer update in the GeoGarage platform

42 nautical raster charts updated 

see GeoGarage news

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?