Past climate change to blame for Antarctica’s giant underwater landslides
IMAGE: THE RESEARCH VESSEL JOIDES RESOLUTION SURROUNDED BY SEA ICE AS IT APPROACHES ANTARCTICA'S EASTERN ROSS SEA DURING INTERNATIONAL OCEAN DISCOVERY PROGRAM (IODP) EXPEDITION 374 view more
CREDIT: JENNY GALES/UNIVERSITY OF PLYMOUTH
Scientists have discovered the cause of giant underwater landslides in Antarctica which they believe could have generated tsunami waves that stretched across the Southern Ocean.
An international team of researchers has uncovered layers of weak, fossilised and biologically-rich sediments hundreds of metres beneath the seafloor.
These formed beneath extensive areas of underwater landslides, many of which cut more than 100metres into the seabed.
Writing in Nature Communications, the scientists say these weak layers – made up of historic biological material – made the area susceptible to failure in the face of earthquakes and other seismic activity.
They also highlight that the layers formed at a time when temperatures in Antarctica were up to 3°C warmer than they are today, when sea levels were higher and ice sheets much smaller than at present.
With the planet currently going through a period of extensive climate change – once again including warmer waters, rising sea levels and shrinking ice sheets – researchers believe there is the potential for such incidents to be replicated.
Through analysing the effects of past underwater landslides, they say future seismic events off the coast of Antarctica might again pose a risk of tsunami waves reaching the shores of South America, New Zealand and South East Asia.
The landslides were discovered in the eastern Ross Sea in 2017 by an international team of scientists during the Italian ODYSSEA expedition.
Scientists revisited the area in 2018 as part of the International Ocean Discovery Program (IODP) Expedition 374 where they collected sediment cores extending hundreds of meters beneath the seafloor.
By analysing those samples, they found microscopic fossils which painted a picture of what the climate would have been like in the region millions of years ago and how it created the weak layers deep under the Ross Sea.
The new study was led by Dr Jenny Gales, Lecturer in Hydrography and Ocean Exploration at the University of Plymouth, and part of IODP Expedition 374.
She said: “Submarine landslides are a major geohazard with the potential to trigger tsunamis that can lead to huge loss of life. The landslides can also destroy infrastructure including subsea cables, meaning future such events would create a wide range of economic and social impacts. Thanks to exceptional preservation of the sediments beneath the seafloor, we have for the first time been able to show what caused these historical landslides in this region of Antarctica and also indicate the impact of such events in the future. Our findings highlight how we urgently need to enhance our understanding of how global climate change might influence the stability of these regions and potential for future tsunamis.”
Professor Rob McKay, Director of the Antarctic Research Centre at Victoria University of Wellington and co-chief scientist of IODP Expedition 374, added: “The main aim of our IODP drilling project in 2018 was to understand the influence that warming climate and oceans have had on melting Antarctica’s ice sheets in the past in order to understand its future response. However, when Dr Gales and her colleagues on board the OGS Explora mapped these huge scarps and landslides the year before, it was quite a revelation to us to see how the past changes in climates we were studying from drilling were directly linked to submarine landslide events of this magnitude. We did not expect to see this, and it is a potential hazard that certainly warrants further investigation.”
Laura De Santis, a researcher at the National Institute of Oceanography and Applied Geophysics in Italy, and also co-chief scientist of IODP Expedition 374, said: "The sediment cores we analysed were obtained as part of IODP, the international seafloor scientific drilling project that has been active in the field of geoscience for over 50 years. The project aims to explore the history of planet Earth, including ocean currents, climate change, marine life and mineral deposits, by studying sediments and rocks beneath the seafloor.”
Jan Sverre Laberg, from The Arctic University of Norway, Tromsø, said: “Giant submarine landslides have occurred both on southern and northern high latitude continental margins, including the Antarctic and Norwegian continental margins. More knowledge on these events in Antarctica will also be relevant for submarine geohazard evaluation offshore Norway.”
Dr Amelia Shevenell, Associate Professor of Geological Oceanography at University of South Florida, College of Marine Science, said: “This study illustrates the importance of scientific ocean drilling and marine geology for understanding both past climate change and identifying regions susceptible to natural hazards to inform infrastructure decisions. Large landslides along the Antarctic margin have the potential to trigger tsunamis, which may result in substantial loss of life far from their origin. Further, national Antarctic programs are investigating the possibility of installing submarine cables to improve communications from Antarctic research bases. Our study, from the slope of the Ross Sea, is located seaward of major national and international research stations, indicating that marine geological and geophysical feasibility studies are essential to the success of these projects and should be completed early in the development process, before countries invest in and depend on this communication infrastructure.”
Drilling into the seabed of Antarctica [VIDEO] |Professor Rob McKay (Director of the Antarctic Research Centre at Victoria University of Wellington and co-chief scientist of IODP Expedition 374) and Dr Jenny Gales (Lecturer in Hydrography and Ocean Exploration at the University of Plymouth) examine the half-section of a core recovered from the Antarctic seabed
CREDIT
Justin Dodd
JOURNAL
Nature Communications
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Climate-controlled submarine landslides on the Antarctic continental margin
ARTICLE PUBLICATION DATE
18-May-2023
Why Antarctic ice shelves are losing their mass and how it leads to global sea level rise
There are many nuances that factor into the behavior of large ice sheets in the Earth’s oceans; these nuances and the progress toward understanding and accurately simulating these behaviors are being reviewed in this study
IMAGE: FROM FIGURE 1 OF WANG Z, LIU C, CHENG C, QIN Q, YAN L, QIAN J, SUN C, ZHANG L. ON THE MULTISCALE OCEANIC HEAT TRANSPORTS TOWARD THE BASES OF THE ANTARCTIC ICE SHELVES. OCEAN-LAND-ATMOS. RES. 2023;2:ARTICLE 0010. view more
CREDIT: WANG Z, LIU C, CHENG C, QIN Q, YAN L, QIAN J, SUN C, ZHANG L.
The Greenland ice sheet (GIS) and Antarctic ice sheet (AIS) contribute largely to global mean sea level (GMSL) changes, though the seas surrounding the Antarctic like the Bellinghausen-Amundsen Seas and the Indian Ocean sector are seeing significantly more warming than the rest of the marginal seas, with immediate noticeable effects on the mass balance (net weight of the glacier mainly accounting for ice gained by snow and lost by melting and calving) of the AIS. The level AIS will contribute to the overall increase in sea level is unknown, and current models vary drastically, leaving a major question regarding future sea levels unanswered. The development of accurate modeling and technology that can help predict the future state of the Earth’s oceans and ice sheets will be helpful in answering these questions.
Researchers’ findings were published in Ocean-land-Atmosphere Research on May 9.
“In this paper, we identify key multiscale oceanic processes that are responsible for heat delivery to the bases of the Antarctic ice shelves and review our current understanding of these processes,” said Zhaomin Wang, professor and first author of the study.
One of these processes responsible for heat delivery is circumpolar deep water (CDW).
CDW is a mix of the ocean’s water masses from different ocean basins, culminating in a warm, salty mass of water in the Southern Ocean. This water can cut through the base of ice shelves rapidly, leading to “cavities”, or cleaves in a glacier due to warm water currents. These cavities are then filled with warm-modified CDW and high salinity shelf water which eventually leads to loss of chunks from the tip of the glacier, known as “calving”. CDW and cavity development are substantial processes, along with basal melting and calving, in which the AIS loses its mass and consequently is a significant contributor to the rise in GMSL.
The effects CDW has on melting of Antarctic ice shelves, along with other mechanisms contributing to warm air and water circulation, are generally understood though they are poorly modeled with consistency. This may be due to not understanding small-scale processes, particularly when it comes to the effects eddies (short-lived oceanic circulation patterns) and the topography of cavities in the glacier have on melting.
“Both eddies and the dynamic effects of bottom topography have been proposed to be crucial in heat transport toward the fronts of ice shelves, in addition to heat transport by coastal currents,” Wang said.
These topographical subtleties help with understanding the transport of CDW and how coastal currents, surface winds, and bottom pressure torque all play into the interactions of these warm water currents with glacial masses and ice sheets.
In review, ice melting thanks to warm water isn’t as simple as it seems on the surface. Researchers surmised that while progress in learning the mechanisms in which oceanic warming is affecting the AIS is occurring, there needs to be improvement and innovation to assess where the continued melting of ice shelves in the Antarctic will leave humanity in the future. Retreating coastlines and GMSL rise are anticipated, though the levels to be expected are poorly understood.
Researchers suggest priorities are made, starting with improving cavity geometry, bathymetry (measuring the depth of water) and future projections of the mass balance of ice sheets. Spending time investigating small-scale processes may also provide valuable information leading to better future models being developed, and critically, determining what the mass loss of the AIS means for atmospheric, oceanic, and sea ice circulations.
China National Natural Science Foundation Projects, The Independent Research Foundation of Southern Marine Science and Engineering Guangdong Laboratory, and the National Science Foundation of Jiangsu Province made this research possible through funding.
Zhaomin Wang, Chengyan Liu, and Chen Cheng of Southern Marine Science and Engineering Guangdong Laboratory（Zhuhai）, Qing Qin, Liangjun Yan, Jiangchao Qian, and Chong Sun of College of Oceanography at Hohai University, and Li Zhang of the School of Atmospheric Sciences at Sun Yat-sen University contributed to this research.
JOURNAL
Ocean-Land-Atmosphere Research
METHOD OF RESEARCH
Literature review
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
On the Multiscale Oceanic Heat Transports Toward the Bases of the Antarctic Ice Shelves
ARTICLE PUBLICATION DATE
9-May-2023
No comments:
Post a Comment