Change in seawater chemistry in the Arctic Ocean threatens its ecosystems

Arctic Ecosystem vulnerable to climate change

Our climate is changing and threatening both terrestrial and marine ecosystems at a global scale. Global surface temperature has increased an average of 0.6C1. However, in the Arctic, which is primarily consists of an ocean surrounded by land in the North Pole, the temperature has increased almost two times faster than elsewhere1. This intense temperature changes in the Arctic region is causing reduced ice cover, permafrost thawing, and increased river discharge which altogether alter the ecosystem balance in the Arctic region2. The environmental changes resulting from rising temperature ultimately leave a great deal of plants, birds, animals, and marine species as well as four million people more vulnerable in what already known as one of the most extreme environments on the planet1.

Major Changes in Arctic seawater chemistry

The Arctic Ocean is the smallest and shallowest ocean on earth. Recently a group of scientists led by Woods Hole Oceanographic Institution found that the concentration of radium-228 has almost doubled in surface waters (2m) of the central Arctic Ocean in between 2007 and 2015. The result puzzled the research group and led them to investigate the origin of the increased radium-228 concentration. The group inferred that the excess radium-228 came from shelf derived sediments in the East Siberian Arctic shelf off Russia, the largest Continental Shelf on Earth3(Figure1).Radium-228 is one the naturally occurring isotopes of radium produced by the radioactive decay of thorium in sediment3. Scientists are interested in measuring radium-228 because it can trace the movement of materials from terrestrial and marine sediment such as carbon and other nutrients. Tracing these elements are important because they can impact ecosystem.

Figure 1: Radium-228 activities in surface waters (2m) of the Arctic Ocean in 2015. Cold color(blue) represents low Radium-228 concentration and hot color(red) represents high radium-228 concentration (modified from Kipp et al 2018)

A large mass of ice sheets is prevalent in the Arctic coastal region leaving less area for wind to blow and cause high waves3(Figure2). The scientists suggest large-scale change along the coast, such as melting sea ice due to rising temperatures, has left more open water near the coast for winds to create waves3(Figure2). The wave action reaches down to the shallow shelves and stirs up sediments, causing vertical mixing and releasing radium-228 from the marine sediment. The radium-228 is carried away into the open Arctic Ocean by a powerful current called the ‘Transpolar Drift’.

Figure 2: (Left) More ice sheet leaves less surface area for winds to create waves. (Right) Less ice sheet cover allows wind to create waves that reach down and stirs up sediments, releasing radium-228 and other chemicals into the open Arctic Ocean. (figure credit: source number 3)

The scientists also explored other factors that could have contributed to the increased radium-228 concentrations, such as coastal erosion due to high waves, melting permafrost due to rising temperatures, increasing river and groundwater input carrying more radium, nutrient, carbon, and other land derived materials into the middle on the Arctic Ocean. However, scientists concluded that the wind-driven vertical mixing over the shallow continental shelf has perhaps the greatest potential to affect the radium-228 budget in the Arctic Ocean2.

What does this mean for the Arctic marine ecosystem?

The effects of earth’s rising temperatures are very significant in the Arctic region with the melting of floating ice sheet cover, receding glaciers, and calving of enormous volumes of ice-shelf into the ocean. Excess radium-228 may indicate elevated concentrations of dissolved organic carbon, nutrients and other chemicals from the shelf and land that could marine biological productivity and overall food webs in the Arctic Ocean regions.

For example, phytoplanktons, mostly microscopic single-celled photosynthetic organisms that live suspended in the water, are necessary to the survival of several species found in Arctic marine ecosystems. Phytoplanktons are not abundant in the Arctic Ocean due to both light and nutrient limitations. But decreasing ice coverage and a high input of nutrients from the shelf and land could fuel phytoplankton growth at the bottom of the food chain and that in turn could have significant impacts on fish and marine mammals and change the arctic marine ecosystems. This scientific study provides the first direct evidence of increased shelf materials input in the Arctic shelf-basin systems and serves as an important baseline to assess future chemical changes in the Arctic Ocean.

Sources

  1. https://www.greenfacts.org/en/arctic-climate-change/l-2/1-arctic-global-warming.htm
  2. Kipp, L. E., Charette, M. A., Moore, W. S., Henderson, P. B., & Rigor, I. G. (2018). Increased fluxes of shelf-derived materials to the central Arctic Ocean. Science advances4(1), eaao1302. DOI: 10.1126/sciadv.aao1302
  3. https://www.whoi.edu/news-release/study-finds-surprising-evidence–of-rapid-changes-in-the-arctic

 

 

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Akim Mahmud

Akim Mahmud is a graduate student in the department of Coastal Marine Systems Science at Coastal Carolina University and in the advanced academic program at Johns Hopkins University. His research interest focuses on the interaction between various physical coastal processes and geologic framework in South Carolina. He is also interested in various sea floor mapping techniques and GIS data management and visualization. He received his Bachelor of Science in Earth & Atmospheric Sciences at the City College of New York with a minor in Economics. When not on the water, Akim enjoys hiking, cooking, music concerts, photography, soccer,tennis and sometimes ponders about the universe.

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