Investigating the importance of different sources of organic matter as food for the benthos on three Arctic shelves

Benthic communities on Arctic shelves are a key component of food webs, nutrient<br/>cycling, and carbon burial. In ice-covered waters, they are fuelled by a complex assemblage<br/>of organic matter from different sources, especially primary production from overlying<br/>pelagic and sympagic (ice-associated) algae, and from terrestrial inputs in areas of high river<br/>run-off. As the Arctic system is undergoing rapid changes, the relative contributions of these<br/>sources of organic matter to benthic food webs are also changing. It is therefore crucial to<br/>understand what fuels the Arctic benthos, to understand how resilient it can be to these<br/>shifting food sources. Three Arctic shelves were studied: the Barents Sea, the Northeast<br/>Greenland Shelf, and the Beaufort Sea Shelf, representing the often-described inflow,<br/>outflow, and interior shelves, respectively. Highly branched isoprenoids – lipid biomarkers<br/>produced with distinct structures in sea ice and the water column – were used to calculate<br/>the ratio of sympagic-to-pelagic organic matter assimilated by the benthos in the Barents Sea<br/>and Northeast Greenland Shelf. In the Barents Sea, the proportion of organic matter from<br/>sympagic sources ranged from 0.4% to 95.8%. In the summer, a strong spatial pattern<br/>(r2=0.754) associated with sea ice duration was found, with the benthic community feeding<br/>on more sympagic organic matter in areas with longer ice cover. In the winter, the benthos<br/>of the Barents Sea fed mostly on pelagic organic matter. On the Northeast Greenland Shelf,<br/>where sea ice cover is much longer (~10 months) sympagic carbon constituted a larger<br/>portion of diets (90%) throughout the study area, and sea ice duration had very little effect.<br/>In the fjords, assimilation of sympagic carbon was higher (93.7%) than on the open shelf<br/>(83.3%), due to the different type of sea ice (land-fast vs drift ice) and nutrient availability.<br/>On the Beaufort Sea Shelf, stable isotopes were used to investigate seasonal and spatial<br/>trophic structure change and terrestrial influence. Benthic trophic structure remained<br/>seasonally quite stable but changed spatially with the strength of pelagic-benthic coupling.<br/>Stronger pelagic-benthic coupling was found in shallower regions and an area of upwelling<br/>and higher primary productivity. Terrestrial influence did not show many spatial or seasonal<br/>variations in the benthos. The results here indicate that sympagic organic matter can be a<br/>temporally and spatially important food source, and that the delivery of different sources of<br/>organic matter to the Arctic benthos is not controlled by the same environmental factors on<br/>different Arctic shelves. There are still gaps in our understanding of Arctic benthic food<br/>webs, with different methods often showing inconsistent results. Future research should<br/>focus on combining these methods within the same studies, in order to better understand the<br/>roles of different sources of organic matter to the Arctic benthos.

Name dc:type.qualificationname

Doctor of Philosophy (awarded by UHI)

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

University of the Highlands and Islands

Year dc:date.issued

2024

Author dc:creator

• Cautain, Ivan

Advisors dc:contributor.advisor

• Narayanaswamy, Bhavani
• Last, Kim

Language dc:language

eng

Identifier

oai:pure.atira.dk:studenttheses/6424ee46-8646-4c7f-8a62-7408b741d522

OAI identifier oai:identifier

oai:pure.atira.dk:studenttheses/6424ee46-8646-4c7f-8a62-7408b741d522