PhD defense on mercury in Arctic marine plankton under climate change

The levels of toxic heavy metals have increased in our natural environment because of mining, coal burning, industrial manufacturing and other human activities. Heavy metals such as mercury have a special ability to stay longer in the atmosphere when released and can, therefore, be transported over longer distances. Due to this, some of the mercury released in other parts of the world eventually ends up in the Arctic, where it is trapped in the cryosphere (sea ice, glaciers, snow and permafrost soils). 

Considering the melting of the Arctic cryosphere due to rising temperatures, it is likely that the mercury trapped in the cryosphere will be released into rivers, fjords and oceans. In the aquatic environment, inorganic mercury can be transformed into an organic mercury form, which is more bioavailable and toxic to wildlife. This facilitates its uptake by phytoplankton, which are eaten by zooplankton, starting the process of mercury bio-accumulation and magnification in the food web.

In his PhD project, Delove Asiedu from DTU Aqua has examined the level of mercury in phytoplankton and zooplankton in Arctic regions as well as the effects of inorganic and organic mercury on key Arctic and subarctic zooplankton. The aim was to improve our understanding of the dynamics and impact of mercury in the Arctic marine environment. 

Delove Asiedu’s findings show a higher mercury concentration in planktonic organisms on the west and east Greenland coast compared to other Arctic regions. The mercury levels in plankton are higher in the fjords than in the open sea, which may highlight the impact of mercury released from the glacier melts into the fjords. 

The results also show that different zooplankton organisms have different tolerances to mercury. Particularly, large zooplankton with a lot of fat are more tolerant than smaller zooplankton with lower fat content. In addition, the transformed mercury (methyl mercury) has a greater effect on zooplankton than inorganic mercury (IHg). However, the concentrations that result in elevated mortality or reduced reproduction or feeding are several-fold higher than the current concentrations of mercury in the Arctic marine environment. Therefore, mercury at the current concentrations is considered to have limited direct impact on Arctic zooplankton, although they can still act as a vector transfering mercury in the food web.

About the defense

Delove Asiedu will defend his PhD thesis, “Effect and bioaccumulation of mercury in Arctic marine plankton under climate change”, on Friday, 23 February 2024 at 13:00. The defense can be followed online or in person at DTU Lyngby Campus (find more info in the box below).

Examiners

• Professor Thomas Kiørboe, DTU Aqua (chair)
• Professor Ingela Dahllöf, University of Gothenburg, Sweden
• Senior Researcher Enric Saiz, Institut de Ciències del Mar, Spain

Chair at the defense

• Professor Torkel Gissel Nielsen, DTU Aqua

Supervisors

• Principal supervisor: Professor Marja Koski, DTU Aqua
• Co-supervisor: Senior Researcher Sigrun Jónasdóttir, DTU Aqua

Learn more

A copy of the thesis is available for reading at DTU Aqua. Please contact PhD Coordinator Susan Zumbach Johannesen, szjo@aqua.dtu.dk