Article on the INSU CNRS website
CNRS INSU - 14 April 2020
Following the two oceanographic expeditions carried out in 2015 in the Arctic as part of the international GEOTRACES programme, researchers from the Woods hole oceanographic institution (WHOI) and their international colleagues1 have demonstrated that significant quantities of carbon and trace elements from rivers and sediments on the continental shelf are being brought close to the North Pole by transpolar drift, a major surface current. Combined with global warming, this input of nutrients and contaminants could alter phytoplankton productivity in the Arctic.
Trace elements, such as iron, are essential nutrients for ocean life. They fuel the growth of phytoplankton, the microscopic algae that form the basis of the marine food chain. In general, more phytoplankton leads to more zooplankton (small fish and crustaceans), which can then be eaten by 'top' ocean predators such as seals and whales. Contaminants, particularly mercury, follow the same path and very high levels have been found in Arctic animals.
In 2015, oceanographers conducting research in the Arctic Ocean as part of the international GEOTRACES programme found much higher concentrations of carbon and trace elements in the surface waters near the North Pole than in those on either side of the transpolar drift, a major surface current capable of transporting water from the Siberian continental shelf across the Arctic Ocean via the North Pole.
The many trace elements that enter the global ocean from rivers and continental shelf sediments are generally rapidly eliminated from the water column. However, the researchers showed that in the Arctic Ocean, the trace elements were linked to the abundant organic matter from the rivers, enabling them to be transported by transpolar drift to the central Arctic, more than 1,000 kilometres from their sources.
As a result of global warming, researchers expect that the thawing of the soil will lead to an increase in run-off and therefore in the input of trace elements previously trapped in the permafrost, which could lead to an increase in the quantity of nutrients and contaminants reaching the centre of the Arctic Ocean.
As the Arctic warms and large parts of the ocean become ice-free for long periods, seaweed becomes more productive. A greater supply of nutrients could therefore fuel this algal production even further.
For the moment, although researchers know that the structure of marine ecosystems is determined by the availability of nutrients, they cannot say exactly what changes this could bring about. In the case of mercury, whose biogeochemical cycle is closely linked to photochemistry and major exchange flows at the atmosphere-ocean interface, major changes are also expected with the disappearance of sea ice in summer.
Although an increase in nutrients could boost Arctic marine productivity, the researchers warn that the continued loss of sea ice is exacerbating global warming, which will have a wider impact on ecosystems.
Financing
Funding for Arctic GEOTRACES was provided by the US National Science Foundation, the Alfred-Wegener Institute for polar and marine research (AWI), the Swedish Research Council Formas, the French National Research Agency (ANR) and Labex MER, the Netherlands Organisation for Scientific Research and the Danish Independent Research Fund. The Arctic GEOTRACES expeditions were supported by the captains and crews of the USCGC Healy and the FS Polarstern.
Source
The Transpolar Drift as a Source of Riverine and Shelf-Derived Trace Elements to the Central Arctic Ocean, Matthew A. Charette et al, Journal of Geophysical Research-Oceans. 08 April 2020. https://doi.org/10.1029/2019JC015920