A new study has challenged the long-held notion that a massive ice shelf once sealed the Arctic Ocean during the coldest periods of the last 750,000 years. Researchers from the European Research Council Synergy Grant project Into the Blue — i2B have found no evidence for the presence of a giant ~1km thick ice shelf, instead discovering that seasonal sea ice dominated the region.

The study, published in Science Advances, used sediment cores collected from the seafloor of the central Nordic Seas and Yermak Plateau, north of Svalbard. These cores hold tiny chemical fingerprints from algae that lived in the ocean long ago. Some of these algae only grow in open water, while others thrive under seasonal sea ice.

“Our sediment cores show that marine life was active even during the coldest times,” said Jochen Knies, lead author of the study, based at UiT The Arctic University of Norway and co-lead of the Into The Blue — i2B project. “That tells us there must have been light and open water at the surface. You wouldn’t see that if the entire Arctic was locked under a kilometre-thick slab of ice.”

One of the key indicators the team looked for was a molecule called IP25, which is produced by algae that live in seasonal sea ice. Its regular appearance in the sediments shows that sea ice came and went with the seasons, rather than staying frozen solid all year round.

To test their findings, the research team used the AWI Earth System Model to simulate Arctic conditions during two especially cold periods: the Last Glacial Maximum around 21,000 years ago, and a deeper freeze about 140,000 years ago when large ice sheets covered a lot of the Arctic. The models supported what was found in the sediments – even during these extreme glaciations, warm Atlantic water still flowed into the Arctic gateway.

The study not only reshapes our view of past Arctic climates but also has implications for future climate predictions. Understanding how sea ice and ocean circulation responded to past climate extremes can improve models that project future changes in a warming world.

“These reconstructions help us understand what’s possible — and what’s not — when it comes to ice cover and ocean dynamics,” said Gerrit Lohmann, co-author of this study, based at Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and co-lead of Into The Blue — i2B. “That matters when trying to anticipate how ice sheets and sea ice might behave in the future.”

The full paper, “Seasonal sea ice characterized the glacial Arctic-Atlantic gateway over the past 750,000 years,” is available in Science Advances. This research is part of the European Research Council Synergy Grant project Into the Blue — i2B and the Research Council of Norway Centre of Excellence, iC3: Centre for ice, Cryosphere, Carbon, and Climate.

Climate change is happening at an unprecedented rate, leaving forests behind in its wake. For decades, ecologists have been concerned that forest ecosystems will not be able to keep pace with this rapid warming, ultimately becoming unhealthy and unproductive.

In reality, tree populations in the Northern Hemisphere had adapted to colder and warmer periods over thousands of years before the current climate crisis. During Ice Ages, trees would migrate south to find warmer conditions as global temperatures cooled. However, when the climate warmed again, these same species would adapt by migrating northward to more suitable areas.

Mature trees are long-lived, but their populations cannot migrate quickly enough to keep up with today’s accelerated climate change. The study recently published in Science reveals that forests have a significant lag time of one to two centuries to shift tree populations in response to climate changes.

Lead researcher David Fastovich from Syracuse University’s Paleoclimate Dynamics Lab explains that this research aimed to map the timescales at which tree populations respond to climate change by examining pollen data from lake sediment cores spanning up to 600,000 years ago. The team used spectral analysis – a statistical technique common in fields like physics and engineering – to study long-term ecological data.

Spectral analysis allowed researchers to compare the relationship between tree populations and climate over various timescales, from decades to millennia. This method provided insights into how closely tree population migrations, tree mortality, and forest disturbances match climate changes over time.

The findings indicate that at timescales of years and decades, forests tend to change slowly. However, after about eight centuries, larger changes in the forest become more pronounced, tied to natural climate variability.

Fastovich emphasizes that this new technique can help us understand ecological processes on any timescale and how they are connected. It also highlights the need for nuanced, long-term management strategies to assist forests in adapting to climate change.

One such strategy is assisted migration – the practice of planting warmer-climate trees in traditionally colder locations to help woodlands adapt and flourish despite habitat warming from climate change. Fastovich notes that this approach will be crucial in helping cherished forests thrive in a rapidly changing world.

In conclusion, while forests have a natural lag time in responding to climate change, assisted migration and other human interventions can play a vital role in keeping these ecosystems healthy and productive for longer.

Antarctica’s Ocean Flip: Satellites Reveal Sudden Salt Surge Melting Ice from Below

In a shocking discovery, researchers have found that the Southern Ocean surrounding Antarctica has undergone a dramatic and unexpected shift. Since 2015, the region has lost an astonishing amount of sea ice, equivalent in size to Greenland – the largest environmental change witnessed anywhere on Earth in recent decades.

The ocean’s surface salinity has been rising, while the sea ice is rapidly declining. This sudden turn of events has significant implications for the planet. The findings were published in a study led by the University of Southampton, using European satellite data to reveal the unexpected changes in the Southern Ocean.

For decades, the ocean’s surface had freshened (becoming less salty), helping sea ice grow and thrive. However, this trend has sharply reversed, with scientists detecting a sudden rise in surface salinity south of 50° latitude. This shift has coincided with the dramatic loss of sea ice around Antarctica and the re-emergence of the Maud Rise polynya – a massive hole in the sea ice nearly four times the size of Wales.

The findings were published on June 30 in the Proceedings of the National Academy of Sciences. Dr. Alessandro Silvano, who led the research, warned that this new state could have permanent consequences for the Southern Ocean and the planet as a whole. The effects are already global: stronger storms, warmer oceans, and shrinking habitats for penguins and other iconic Antarctic wildlife.

The research team has attributed the sudden rise in surface salinity to a weakening of stratification between water layers. In the winter, cold, fresh surface water overlays warmer, saltier waters from the deep. As the surface cools and sea ice forms, the density difference weakens, allowing heat to be transported upward, melting the sea ice from below.

The early 1980s saw a strengthening of stratification, trapping heat below and sustaining more sea ice coverage. However, this trend has reversed, with new satellite technology and data from floating robotic devices revealing that surface salinity is increasing, stratification is weakening, and sea ice has reached multiple record lows – with large openings of open ocean in the sea ice (polynyas) returning.

This groundbreaking study highlights the urgent need for continuous satellite and in-situ monitoring to better understand the drivers of recent and future shifts in the ice-ocean system. The project was supported by the European Space Agency, and the paper “Rising surface salinity and declining sea ice: a new Southern Ocean state revealed by satellites” is available online.