Short-term processing of ice algal- and phytoplankton-derived carbon by Arctic benthic communities revealed through isotope labelling experiments

Abstract

Benthic ecosystems play a significant role in the carbon (C) cycle through remineralization of organic matter reaching the seafloor. Ice algae and phytoplankton are major C sources for Arctic benthic consumers, but climate change-mediated loss of summer sea ice is predicted to change Arctic marine primary production by increasing phytoplankton and reducing ice algal contributions. To investigate the impact of changing algal C sources on benthic C processing, 2 isotope tracing experiments on 13 C-labelled ice algae and phytoplankton were conducted in the North Water Polynya (NOW; 709 m depth) and Lancaster Sound (LS; 794 m) in the Canadian Arctic, during which the fate of ice algal (C IA) and phytoplankton (C PP) C added to sediment cores was traced over 4 d. No difference in sediment community oxygen consumption (SCOC, indicative of total C turnover) between the background measurements and ice algal or phytoplankton cores was found at either site. Most of the processed algal C was respired, with significantly more C PP than C IA being released as dissolved inorganic C at both sites. Macroinfaunal uptake of algal C was minor, but bacterial assimilation accounted for 33−44% of total algal C processing, with no differences in bacterial uptake of C PP and C IA found at either site. Overall, the total processing (i.e. assimilation and respiration) of C PP was 33 and 37% higher than processing of C IA in NOW and in LS, respectively, suggesting that the future changes in quality of organic matter sinking to the seafloor could impact the C residence time at the seafloor.

Benthic macrofaunal bioturbation activities from shelf to deep basin in spring to summer transition in the Arctic Ocean

“…centimeters of the sediment (Aller and Aller, 1992;Piot el al., 2014;Aschenbroich et al, 2017;Mäkelä et al, 2018). Therefore, we suggest that also the smaller benthic fractions should be identified in future studies on Arctic deep infaunal activity in order to find better infauna variables for explaining the bioturbation measurements.…”

Organic Carbon Origin, Benthic Faunal Consumption, and Burial in Sediments of Northern Atlantic and Arctic Fjords (60–81°N)

“…Significant correlation to Chl a (but not to C org ) was also documented for benthic fluxes in Skagerrak and for SCOC in Arctic seas reviewed by Bourgeois et al (2017) and oligotrophic Aegean Sea . The fundamental role of the C org origin for short-term benthic carbon processing was also indicated by stable isotope tracer experiments (Mäkelä et al, 2018) and bioturbation response after phytopigment addition (Morata et al, 2015). Grebmeier and McRoy (1989) demonstrated that the amount of labile organic material, rather than temperature, drove enhanced sediment oxygen uptake rates in Arctic sediments.…”

Isotopic and traits-based trophic diversity of Canadian Beaufort Sea benthic communities in relation to food supply

“…Biomass-weighting isotopic indices reduces the influence of less abundant species so that trophic diversity is not erroneously inflated by rare species feeding at the margins of available organic matter sources. Many benthic species can exhibit substantial feeding plasticity, and thus likely derive their carbon from the most readily available sources (Renaud et al 2007;North et al 2014;Mäkelä et al 2018). If this is the case, isotopic diversity (a relative measure) could exhibit low regional variability despite significant differences in the importance of isotopically-distinct organic matter sources to benthic communities in the Canadian Beaufort Sea and Amundsen Gulf (Stasko et al 2018b).…”