Wednesday, February 28, 2024

‘Spoon worms lick the seabed with a metre-long tongue’: a voyage into a vanishing Arctic world

Polarstern, a German icebreaker, on a ice thickness survey in the Arctic Ocean

From The Guardian by Tim Kalvelage (photos included)

Sea ice around the north pole is disappearing at an alarming rate.
A group of scientists are on a mission to investigate the effects of the climate crisis on the region

It is summer and the air temperature is just below freezing.
Fog has crept in, blurring the outline of Polarstern, the German icebreaker moored to a kilometre-long ice floe at 85 deg N latitude.
Next to a hole we have just drilled through 1.4 metres of ice, Morten Iversen, who studies the flow of carbon around the ocean, has attached several plastic containers to a rope secured by ice screws.
They will be left hanging in the water under the ice for a day to catch marine snow – clumps of dead algae and zooplankton faeces that sink from the upper ocean to the deep sea.

A few metres away, a team of biologists perforate the ice floe with a core drill.
They are looking for algae that grow at the bottom of sea ice, which play an important role in the Arctic Ocean food web.
Metre-long ice cores are pulled up, packed in plastic sleeves and stacked on a sledge to be processed in the ship’s laboratories.

Daniel Scholz, an engineer for the Alfred Wegener Institute, lowers an instrument that measures temperature, salinity and nitrate – an important nutrient for algae and phytoplankton – through an ice hole
Nets are lowred into the water to collect zooplankton
The ship’s helicopter carries a sensor to measure ice thickness
Frederik Bussmann, a marine chemist and PhD student at the Alfred Wegener Institute, measures the salinity at the edge of an ice floe.
Emiliano Cimoli, a researcher at the University of Tasmania, right, and an Alfred Wegener Institute technician Erika Allhusen, drill an ice core to look for sea-ice algae

One of the scientists is keeping watch, with a rifle slung over her shoulder and a flare gun on her belt.
This is, after all, a polar bear habitat – albeit a shrinking one.

Our group is part of a 100-strong expedition – half of them scientists, half ship’s crew – that set out from the Norwegian harbour of Tromsø in early August 2023 to investigate the rapid melting of the Arctic sea ice.
The team is investigating the consequences for the marine ecosystem: from nutrient cycling to ice algae and plankton productivity to seafloor animal communities that live on organic material raining down from the surface ocean.

An ice core drilled from sea ice in the central Arctic Ocean

The central Arctic is heating up much faster than most of the world.
The area covered by sea ice in the Arctic Ocean at the end of summer has shrunk by about 40%, or 2.5m square kilometres – roughly the size of the Mediterranean Sea – since satellite observations began in the late 1970s.
The remaining ice is getting thinner and multi-year floes – ice that has survived at least one summer – are becoming rarer.
The waters around the north pole could be virtually free of ice at the end of the summer as early as the 2030s, according to a recent study.

Shrinking ice cover means not only the loss of hunting grounds of polar bears or resting places and nurseries for seals, but also of an entire under-ice ecosystem: meadows of filamentous ice algae, algae-grazing zooplankton, and juvenile polar cod, which find food and shelter in the cracks and crevices beneath the floes and, when grown up, feed larger predators such as ringed seals or beluga whales.
In the short term, sea ice productivity could increase as more sunlight passes through thinner floes, boosting ice algae growth, but only as long as there is a sufficient supply of nutrients in the overall nutrient-poor central Arctic Ocean.

The same goes for planktonic algae, or phytoplankton, which profit from higher light availability and a longer growth season in the expanding open-water areas, as satellite data shows.
Changes in productivity and a shift from ice algae to phytoplankton at the base of the food web will probably have major effects on the marine ecosystem as whole.
Also, the native flora and fauna are facing new competition from invasive species, from plankton to fish, that are moving in from the Atlantic and Pacific as the oceans warm.
Predictions of the future Arctic Ocean are, however, highly uncertain due to a general lack of observation.
That is why the scientists have come here.
Tiny Arctic life :

A 3cm-long ice amphipod (Onisimus)

A 4cm pelagic sea slug, or sea angel (Clione limacina) found under the sea ice

A 1cm copepod (Paraeuchaeta) caught in aplankton net
A 2cm jellyfish (Botrynema brucei)
The chief scientist of the expedition, Antje Boetius, has been exploring the frigid waters of the Arctic for three decades.
In summer 2012 her team witnessed the lowest sea-ice minimum on record, in the Arctic Ocean’s Eurasian Basin.

“Now, we are following the same route to repeat previous measurements on the ice-ocean system all the way down to the seabed,” says the deep-sea ecologist, who is also director of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany.

The ice-covered Arctic Ocean, especially its deeper realms, is one of the least explored regions on Earth.
To catch a glimpse of larger creatures inhabiting the abyssal plains on the ocean floor and uncharted underwater mountains, the deep-sea ecologists have brought a camera system that is towed behind Polarstern.
Polar bears are an occupational hazard on the Arctic ice

The abundance and diversity of life in this cold, dark and food-scarce environment is truly astonishing: in places, large numbers of sea cucumbers and huge colonies of filter-feeding feather stars appear in the spotlights.
We marvel at basketball-sized sponges flickering across the scientists’ screens, at apricot-coloured anemones and star-shaped patterns extending around the burrows of spoon worms, which lick the seabed for food particles with a metre-long tongue.

Polarstern regularly moors alongside large floes and part of the science team heads out on to the sea ice, pulling sledges heavily loaded with drilling tools and other equipment.

The expedition leader, Antje Boetius, on Polarstern’s bridge

Flags on bamboo poles set up by a scouting party mark routes to different research sites.
Meanwhile, the ship’s helicopter passes over them, with a torpedo-shaped sensor suspended below it that measures the thickness of the sea ice.

The rhythm of life onboard is determined by how fast the ship gets through the ice, the schedule for the research expeditions, and, most reliably, meal times: breakfast at 7.30am, lunch at 11.30am, coffee at 3.30pm, dinner at 5.30pm.

The scientists work around the clock, and often use any time off to catch up on sleep after a long night in the lab or outside on deck in freezing temperatures.
Yet they still find time for social activities in the evenings, be it card games in the cosy red salon, water basketball in the ship’s swimming pool, or a pub quiz in the bar.

Towards the end of the expedition, when Polarstern is going south and the sun disappears below the horizon again after weeks of polar day, powerful spotlights are used to navigate through the ice

Although the sea ice coverage in the study area and in the Arctic Ocean overall is higher in 2023 than in previous years, the expedition makes good progress.
We encounter thicker – but quite old and rotten – ice that Polarstern easily breaks through, and large gaps of open water between the floes.

And so, on 7 September, almost effortlessly, the ship reaches the northernmost point of the planet: the geographic north pole.

For most onboard, it is the first time; for Polarstern it is the seventh time.
In 1991, with the Swedish ship Oden, it was the first conventional icebreaker to reach the latitude 90 deg N.

The Arctic Ocean has changed dramatically since that first arrival, says the captain, Stefan Schwarze.
“Three decades ago, we needed two icebreakers to fight our way through the pack ice,” he says.
“Today, we have reached the north pole with 30% of our engine power.”

Armed guards keep a lookout for polar bears while their colleagues work

Tuesday, February 27, 2024

From the sky to the sea: using satellites to map the world’s unidentified reefs

Coral reefs possess a quarter of all marine life and contribute to the well-being and livelihoods of a billion people worldwide.
Image credit: Chris Roelfsema.
From National Geographic by Elisabeth Marie

Detailed satellite mapping of the world’s reefs has revealed there is more coral reef area across the globe than previously thought – information that’s aiding conservation efforts of these environment

Scientists have identified 348,000 square kilometres of shallow coral reefs up to 20 to 30 metres deep thanks to new technology.

“The total area of coral reef ecosystems is more extensive than previously thought,” said Dr Mitchell Lyons from the University of Queensland’s School of the Environment, working as part of the Allen Coral Atlas project.
“We can now confidently say there are almost 350,000 square kilometres of coral reef, which is about 50 to 100,000 kilometres more than previous estimations.”
Dive under the waves and explore our global habitat maps.
The maps classify reefs into benthic and geomorphic zones to support reef restoration and protection.
Identify reefs experiencing low, moderate, and severe bleaching with the Atlas monitoring system.
Know when and where to focus restoration efforts.
Monitor changes in water quality over time by identifying turbidity in your area.
Use it to identify sources of land-based pollution and prioritize action.

Dr Mitchell said researchers also found that about 80,000 square kilometres of reefs have a hard bottom, where coral tends to grow, as opposed to soft bottoms like sand, rubble or seagrass.
“This specialised data on area and composition will allow scientists, conservationists and policymakers to better understand and manage reef systems,” he said.
A map showing coral reefs around Australia.
Image credit: Allen Coral Atlas
Making the map

The map, known as the Allen Coral Atlas, was developed by the late Paul Allen’s Vulcan Inc. and is managed by Arizona State University and the University of Queensland along with partners Planet and Coral Reef Alliance.

Using fine-scale, high-resolution pictures from Planet Dove cubesat satellites and scientific-grade information from the Sentinel-2 satellite, scientists processed 100 trillion pixels to produce a global map of coral reefs.

The satellite images were then put through a machine-learning algorithm along with more than 1.5 million training samples curated from data collected by over 480 contributors identifying types of reefs, and the system then predicted any unmapped information to fill in data gaps.
Thousands of people and organisations are using the Allen Coral Atlas to help direct conservation efforts.
Image credit: Chris Roelfsema.

Conserving coral

According to Dr Mitchell, although coral reefs account for only a small proportion of the ocean, they provide tremendous biodiversity that humans rely on for culture, commerce, scientific output and medicine.

“Coral reefs possess a quarter of all marine life and contribute to the wellbeing and livelihoods of a billion people worldwide,” Dr Mitchell said.
“Maps of ecosystems underpin many science and conservation activities, but until recently, there were no consistent high-resolution maps of the world’s coral reefs.
“Hundreds of thousands of people have already accessed the maps, and they are already being used directly around the world for marine spatial planning, marine protected areas, environmental accounting and assessments, restoration, and education.”

In 2022, more than 80,000 people accessed the Allen Coral Atlas, including conservation groups using the technology to advance their initiatives.
From geospatial data scientists to directors of conservation to fisherman, “we are all integrated in this effort”
In Indonesia, teams are using the Allen Coral Atlas to inform the country's reef management strategies.
 Groups include the Coral Reef Rescue Initiative, a global programme of scientists, NGOs and partners working in collaboration with governments and communities to safeguard reefs, food security and livelihoods against climate change; and the Philippine Reef and Rainforest Conservation Foundation, a non-profit organisation focused on environmental conservation on Danjugan Island.

The Coral Triangle Initiative, a multilateral partnership between Indonesia, Malaysia, Papua New Guinea, Philippines, Solomon Islands and Timor-Leste working to sustain marine and coastal resources by addressing food security, climate change and marine biodiversity, is also accessing the Allen Coral Atlas.

The information provided by the map will also have broader uses for Australian researchers and conservationists.
“We tend to be really interested in coral bleaching, so the map can help target locations where we know the reefs have hard substrate for coral to grow,” Dr Mitchell said.
“The Allen Coral Atlas also has a tool that allows pinpointing of areas affected by coral bleaching to help alert to the potentially growing issue.
“It’s more than just maps,” he said. “It’s a tool for positive change for coral reefs, and coastal and marine environments at large.”

Links :

Monday, February 26, 2024

Colossal underwater canyon discovered near seamount deep in the Mediterranean Sea

A newly discovered underwater canyon was carved out of the seabed by extremely salty currents. (Image credit: Jason Edwards via Getty Images)

From LiveScience by Sascha Pare

Researchers have discovered a 33,000-foot-wide (10 kilometers) underwater canyon that was carved out of the Mediterranean seabed shortly before the sea dried up around 6 million years ago.

Scientists have discovered a giant underwater canyon in the eastern Mediterranean Sea that likely formed just before the sea transformed to a mile-high salt field.

The canyon formed around 6 million years ago, at the onset of the Messinian salinity crisis (MSC), when the Gibraltar gateway between the Atlantic Ocean and Mediterranean Sea narrowed and eventually pinched shut due to shifts in tectonic plates.
The Mediterranean Sea became isolated from the world's oceans and dried up for roughly 700,000 years, leaving behind a vast expanse of salt up to 2 miles (3 kilometers) thick in some places.

As sea levels dropped, increasingly salty currents eroded the seabed and incised gullies several hundred feet deep along the steepest edges of the Mediterranean Sea.
In a study published in the January issue of the journal Global and Planetary Change, researchers now describe a giant U-shaped canyon located 75 miles (120 km) south of Cyprus, in the depths of the Mediterranean's Levant Basin.

The 1,640-foot-deep (500 meters) and 33,000-foot-wide (10 km) canyon, which the researchers named after the nearby Eratosthenes seamount, likely formed underwater shortly before salt piled onto the seabed.
Unlike the more coastal gullies, the canyon had no older "pre-salt" roots, according to the study."
To explain the submarine formation of the Eratosthenes Canyon, we suggest incision by dense gravity currents scratching and carving the deep-water seafloor," the researchers wrote in the study.

The newly discovered Eratosthenes Canyon sits close to the Eratosthenes seamount in the eastern Mediterranean sea.
(Image credit: Geological Survey of Israel)
STRM bathymetry off of the Levant Basin with  the GeoGarage platform
Visualization with nautical map (SHOM)

Weighed down with salt and sediment, these currents rushed along faster than the surrounding water and gradually scooped out enough of the seabed to form the colossal canyon.
Precisely when this occurred remains unclear, but it likely coincided with the beginning of the MSC — between 5.6 million and 6 million years ago, according to the study.
The incision process may have lasted anywhere from tens of thousands to half a million years.

The discovery sheds light on a decades-long debate over whether Messinian gullies and canyons that now lie underwater formed above or below the sea surface.
"This new evidence strengthens the arguments that at least part of the erosion across continental margins occurred [below water]," the researchers wrote.

The newly discovered canyon sits within a wider network of canyons and channels in an area known as the Levant Basin, which extends from the coast of Syria in the north to Gaza in the south, and northwest toward Cyprus.

To the northwest of the canyon, beyond the Eratosthenes seamount, sits the much deeper and older Herodotus basin, which receives currents loaded with sediment from the southeast.
These currents may have crossed the area that now boasts the Eratosthenes Canyon long before it was incised, according to the study.

"The absence of older roots under the Eratosthenes Canyon does not rule out the possibility that a shallow pre-MSC channel system predated the Eratosthenes Canyon," the researchers wrote.

Links :

Sunday, February 25, 2024

Mesoscale Convective Systems : Lightning megaflash

A continuous mesoscale lightning flash (MSC) with a horizontal path length of approximately 100 km or greater.
The tremendous distances covered by megaflashes necessitate long flash durations as well, typically 5 s or greater.

Megaflashes typically occur in the stratiform regions of mesoscale convective systems (MCSs).
These expansive flashes can produce one or more cloud-to-ground (CG) strikes along their paths.
Some CGs associated with megaflashes have large charge moment changes and/or peak currents resulting in lightning superbolts, sprites, and/or lightning-triggered upward lightning discharges (LTULs) from tall structures.

A World Meteorological Organization (WMO) committee of experts has established two new world records for the longest reported distance and the longest reported duration for a single lightning flash in, respectively, Brazil and Argentina
In June 2020 the World Meteorological Organization announced the certification of new global lightning extreme records for megaflashes after the identification of megaflashes in excess of 700 km in length and 16 s in duration over Argentina and southern Brazil.

Links :

Saturday, February 24, 2024

Image of the week : whales bones

Incredibly moving photograph of a whale skeleton in Greenland. 
Alex Dawson, winner of the Underwater Photographer of the Year 2024