Spatial and temporal organic carbon burial along a fjord to coast transect: A case study from Western Norway

Abstract

We investigated spatial and temporal changes in accumulation rate and source of organic carbon on a gradient along the Lysefjord and the more coastal Høgsfjord, Western Norway. This was achieved through analysis of total organic carbon and nitrogen content of sediment cores, which were radiometrically dated to the early 19th and 20th centuries for the Høgsfjord and Lysefjord, respectively. Benthic foraminifera (protists) were utilized to determine changes in organic carbon supply and Ecological Quality Status (EcoQS) by their accumulation rate (benthic foraminiferal accumulation rate (BFAR)), assemblage composition, species diversity, individual species responses and the composition of stable carbon isotopes of the tests (shells) of Cassidulina laevigata, Hyalinea balthica and Melonis barleeanus. Organic carbon accumulation rates were greatest closest to the river Lyse at the head of the Lysefjord (83-171 g C m −2 yr −1 ). The organic carbon at the head of the fjord is mainly terrestrial in origin, and this terrestrial influence becomes progressively less seaward. The δ 13 C in H. balthica tests as well as the benthic foraminiferal assemblage composition also showed a clear fjord to coast gradient. Organic carbon accumulation rates were lower and less variable at the seaward study sites (13-61 g C m −2 yr −1 ). We observe no temporal trend in organic carbon, carbon isotopes, EcoQS or foraminiferal assemblage composition in the Lysefjord. In contrast, in the Høgsfjord, there seems to have been an increase in organic carbon accumulation rates during the 1940s. Subsequent accumulation rates are stable. The foraminiferal assemblages in the surface sediments reflect a recent transition from good/moderate to moderate/bad EcoQS.

Environmental and coastline changes controlling Holocene carbon accumulation rates in fjords of the western Strait of Magellan region

“…European Artic Fjords (20.3-40.5 g m À 2 yr À 1 ; Koziorowska et al, 2018). Other fjord regions present mean values that are in a similar range, but the upper values are half to one order of magnitude higher than our estimations, e.g., Northern Patagonia (1.9-82.5 g m -2 y -1 ; Sepúlveda et al, 2011), New Zealand (9.1-68.0 g m À 2 y -1; Cui et al, 2016;Hinojosa et al, 2014;Knudson et al, 2011;Smith et al, 2015), Norway (13-171 g m À 2 yr À 1 ; Duffield et al, 2017;Faust and Knies, 2018) and Canada (20-290 g m À 2 yr À 1 ; St-Onge and Hillaire-Marcel, 2001). These values should reflect the spatial heterogeneity of AR OC between fjord systems, which has been linked with the sediment type and particle size of the seabed (Smeaton and Austin, 2019).…”

Organic Matter Sources in North Atlantic Fjord Sediments

“…These parameters have been extensively investigated and successfully utilized in previous studies to differentiate marine from terrigenous OM in fjord and ocean surface sediments (Bertrand et al, 2012;Faust, Knies, Slagstad, et al, 2014;Goñi et al, 1997;Karageorgis et al, 2005;Knies et al, 2007;Knies & Martinez, 2009;Knudson et al, 2011;Perdue & Koprivnjak, 2007;Sepúlveda et al, 2011;Sepúlveda et al, 2009;Stein & MacDonald, 2004;Winkelmann & Knies, 2005). Previous investigations of fjord surface sediments from Chile, New Zealand, and Norway found clear gradients of terrigenous versus marine OM from the inner fjords toward the open ocean (Duffield et al, 2017;Faust, Knies, Slagstad, et al, 2014;Faust et al, 2017;Knudson et al, 2011;Sepúlveda et al, 2011;Silva et al, 2011). These geochemical gradients were associated with two opposing and fundamental processes: the inflow of oceanic water versus the inflow of freshwater from the fjord drainage area Faust, Knies, Slagstad, et al, 2014;Faust et al, 2017).…”

Organic-carbon-rich sediments: benthic foraminifera as bio-indicators of depositional environments

“…A recent study by Smeaton et al (2017) estimated that the sediments of Scotland's 111 major fjords hold 295 ± 52 Mt OC. In Shetland, these fjordic systems are different from their mainland counterparts, notably in that they are shallower and less glaciated (Edwards and Sharples, 1986) and peat or peaty soils dominate their catchments (Soil Survey of Scotland, 1981). The erosion of terrestrial organic matter (OM) is known to be a major source of OC in fjordic sediments (Cui et al, 2017), and Scottish peatlands hold 1620 Mt of OC (Chapman et al, 2009).…”

“…Benthic foraminiferal assemblages have long been used as indicators of environmental change and to reconstruct the intrinsic characteristics of marine ecosystems. A recent study (Duffield et al, 2017) explored the relationship between foraminiferal assemblages and variations in OC content in the surficial and recent sediments of Norwegian fjords, highlighting temporal trends in OC fluxes and ecological quality status. In this study, we evaluate the use of modern benthic foraminifera as bio-indicators of OC content in six voes (fjords) on the west coast of Shetland whose sedimentation dynamics are likely influenced by the erosion of OC-rich peat from the surrounding catchments ( Fig.…”