Dr. Èric Jordà Molina (left) and Dr. Ivan Cautain (right)
The seafloor of the Barents Sea shelf hosts one of the most productive benthic communities of the Arctic seas. They play critical roles in the recycling of organic matter that sinks from the overlying waters to the seafloor. Organisms that live in or on the sea floor are highly spatially structured by the environmental conditions and processes in the waters above. Climatic changes such as ocean temperature rise or sea-ice decline can therefore cause shifts in benthic communities in the coming decades. In his work, Dr. Èric Jordà Molina investigated the spatial and temporal variability in communities of the larger benthic organisms (macrofaunal communities) on the northern Barents Sea shelf and in the deep Nansen Basin, and at different times of the year.
He found that increased occurrence of warmer Atlantic water inflow in an Arctic fjord north of Svalbard resulted in fluctuations in macrofaunal composition throughout 2003-2017. However, macrofauna communities did not respond to seasonal variations in the adjacent open Barents Sea shelf. At the same time, experimental incubations of seafloor sediments revealed that benthic degradation of organic matter will most likely increase in a predicted warmer and more productive Barents Sea. This has impacts on carbon cycling and biogeochemical processes taking place at the seafloor. Overall, his thesis contributes to a better understanding of benthic ecosystems and their function in the Arctic relevant to the effective management of the Barents Sea ecosystem.
Benthic organisms collected from the Barents Sea floor (©Christian Morel www.christianmorel.net)
Another way that rapid climatic changes impact benthic communities is through their food supply. In the research by Dr. Ivan Cautain the importance of different sources of organic matter as food for the benthos on three Arctic shelves was investigated. He calculated the amount of organic matter originating from sea ice flora and water column algae that was taken up by the benthic communities in the Barents Sea and Northeast Greenland Shelf, using different biomarkers (highly branched isoprenoids, which are lipids) produced by algae in sea ice and the water column.
The results indicate that sea ice-originating organic matter can be an important food source at times of the year or specific regions, and that the share of different sources of organic matter to the Arctic benthos is not controlled by the same environmental factors on different Arctic shelves. In the Barents Sea, the benthic community feeds on more ice-associated organic matter in areas with longer ice cover in the summer, while they fed mostly on pelagic organic matter in winter. On the Northeast Greenland Shelf, where sea ice cover duration is longer, a higher portion of diets came from ice-associated carbon throughout the study area. Here, the sea ice duration was not related to the proportion of ice associated carbon in the benthos. Sea ice-associated carbon was more important in the fjords of Greenland than on the open shelf, due to the different type of sea ice (land-fast vs drift ice) and nutrient availability. On the Beaufort Sea Shelf, closer to the Pacific side of the Arctic Ocean, benthic food web structure did not change with season, but was impacted by how tightly it was linked to the pelagic food web. Dr. Cautain’s work fills in some important gaps in our understanding of Arctic benthic food webs and their response to the overlaying sea ice and water column dynamics.
We congratulate Dr. Èric Jordà Molina (Nord University) and Dr. Ivan Cautain (Scottish Association for Marine Science (SAMS), UK) with their well-deserved degrees and excellent work.
Dr. Èric Jordá Molina’s thesis was entitled “Spatio-temporal dynamics of soft-bottom macrobenthic communities in a rapidly changing Arctic: a case study of the Northwestern Barents Sea”, and was supervised by Professor Henning Reiss (Nord), Professor Arunima Sen (UNIS, Nord), Dr. Paul Renaud (Akvaplan-NIVA), Professor Bodil Bluhm (UiT the Arctic University of Norway) and Dr. Marc Silberberger (Institute of Oceanology PAN, Poland).
Dr. Ivan Cautain’s thesis was entitled “Investigating the importance of different sources of organic matter as food for the benthos on three Arctic shelves”, and was supervised by Dr Bhavani Narayanaswamy and Dr. Kim Last (SAMS, UK), Dr. David McKee (University of Strathclyde, UK), Dr. Paul Renaud (Akvaplan-NIVA), and Professor Bodil Bluhm (UiT the Arctic University of Norway).
Dr. Èric Jordà Molina with his supervisors
Dr. Ivan Cautain with his primary supervisor and defense committee