Benthic foraminiferal response to carbon loading introduced by “jelly-falls”: An ex-situ experiment using material from Kaldfjord (Northern Norway).

Abstract

Organic carbon (OC) burial in marine sediments plays a key role in long-term carbon sequestration regulating atmospheric CO2 concentration. Fjords, with their deep, narrow basins and high sedimentation rates, have been estimated to account for 11% of the annual marine carbon burial world-wide. So far, research efforts have mainly focussed on quantifying the amount of OC stored in fjord sediments. However, recent changes in quantities and sources of OC, as a consequence of anthropogenic activities, affect the benthic ecosystem structure and function, and can alter the ecological quality status of fjord habitats. The overall aim is to characterise and quantify accumulation rates of OC in northern Norwegian fjord sediments, and describe the associated benthic foraminiferal responses. One aspect is the response of the benthic foraminiferal community to carbon loading by “jelly-falls”. Recently “jelly-falls” have become larger and more frequent but their effect on processing and accumulation of carbon on the sea floor is not known. Study material was collected from Kaldfjord, Norway, in September 2017 and used for an ex-situ carbon-uptake experiment. Experimental chambers were obtained by box- coring in the inner, middle and outer fjord along a fjord to coast gradient. Experimental chambers received δ13C isotope labelled algae and different amounts of jelly fish, to assess the effect of different concentrations of carbon to the benthic foraminiferal assemblages. The δ13C content, representing the incorporation of 13C-labelled algae into foraminiferal cytoplasm, will indicate their response to the OC loading from “jelly-falls”. Impacts of ambient OC inputs, and potential threshold levels for healthy communities along the fjord to coast gradient, will be investigated. Data on sediment TOC, grain size, and sediment isotope signatures from the field provide additional information regarding differences in background environmental conditions within the fjord. Results increase our understanding of the benthic foraminiferal community response to organic carbon and aid towards developing benthic foraminifera as a monitoring tool.