Natural variability of benthic foraminiferal assemblages and metal concentrations during the last 150years in the Ingøydjupet trough, SW Barents Sea

Abstract

While today the SW Barents Sea is a relatively un-impacted and uncontaminated area, industrial activities related to the petroleum industry are projected to increase in the coming decades. This makes the area a valuable natural laboratory to establish pre-impacted baselines as a precursor for future seabed monitoring programs. Here we present benthic foraminiferal assemblages and metal concentrations in four sediment cores from the Ingøydjupet trough, SW Barents Sea, covering approximately the last 150 years. This information supports the application of foraminiferal assemblages as a bio-monitoring tool applicable in high latitudes. At all stations, metal concentrations in the sediment correspond to no effect concentrations. The downcore metal concentrations are mainly attributed to natural variability of the clay fraction and total organic content of the sediments. Agglutinated foraminifera are poorly preserved down-core. Patterns in the calcareous foraminiferal assemblages suggest an enhanced food supply as a result of increased Atlantic Water inflow through the region during the last 150 years. At near-shore stations, the Norwegian Coastal Current additionally influences assemblages. Decadal scale climatic oscillations are indicated by increased calcareous fluxes and are attributed to variability in the food-rich Atlantic Water. This study serves as an important baseline data set prior to increasing industrial activities in the SW Barents Sea, and thereby contributes to a better understanding of natural environmental variability. AbstractWhile today the SW Barents Sea is a relatively un-impacted and uncontaminated area, industrial activities related to the petroleum industry are projected to increase in the coming decades. This makes the area a valuable natural laboratory to establish pre-impacted baselines as a precursor for future seabed monitoring programs. Here we present benthic foraminiferal assemblages and metal concentrations in four sediment cores from the Ingøydjupet trough, SW Barents Sea, covering approximately the last 150 years. This information supports the application of foraminiferal assemblages as a bio-monitoring tool applicable in high latitudes.At all stations, metal concentrations in the sediment correspond to no effect concentrations.The down-core metal concentrations are mainly attributed to natural variability of the clay fraction and total organic content of the sediments. Agglutinated foraminifera are poorly preserved down-core. Patterns in the calcareous foraminiferal assemblages suggest an enhanced food supply as a result of increased Atlantic Water inflow through the region during the last 150 years. At near-shore stations, the Norwegian Coastal Current additionally influences assemblages. Decadal scale climatic oscillations are indicated by increased calcareous fluxes and are attributed to variability in the food-rich Atlantic Water. This study serves as an important baseline data set prior to increasing industrial activities in the SW Barents Sea, and thereby contribu...

Variability of present and past PAH (polyaromatic hydro carbons) concentrations in sediments of the SW Barents Sea

“…5). Other studies have also reported an increase in PAH as well as heavy-metal concentrations which correlates with an increase in TOC and the fraction of fine-grained material (Boitsov et al, 2009a;Dijkstra et al, 2013Dijkstra et al, , 2015. This supports the idea that PAH concentrations respond to natural variability in the transportation of sediments by bottom currents (Junttila et al, 2014).…”

“…Bottom current transportation of fine-grained sediments and heavy-metal concentrations based on the same sample material as presented in this paper has been studied previously (Dijkstra et al, 2013(Dijkstra et al, , 2015Junttila et al, 2014). Through these earlier studies, there is a clear connection between bottom current strength, fine particle deposition, and heavy-metal concentrations.…”

“…All samples were sieved (>1 mm, >100 μm, >63 μm) to perform grain-size analyses on the coarse fraction and to collect foraminifera for further studies ( Dijkstra et al, 2013( Dijkstra et al, , 2015. Smaller fractions (<63 μm) were further analyzed by using the sedigraph technique (Coakley & Syvitski, 1991).…”

“…These sediments are preferentially deposited northeast of Tromsøflaket in the deeper and calmer areas of Ingøydjupet. Further, Dijkstra et al (2015) analyzed the metal contents (Ba, Zn, Cr, Hg, Pb, Cd, Cu, Ti) and benthic foraminifera on the same four cores from Ingøydjupet as in this paper. They observed the highest metal concentrations in core 154.…”

“…These were collected as part of the Norwegian offshore monitoring program and it is required by the operator (Statoil) to take three replicate samples at each site (see Mannvik et al, 2011). In the summer of 2011, multicore samples were collected from different locations in Ingøydjupet ( University of Tromsø (UiT) set), as described in Junttila et al (2014) and Dijkstra et al (2015).…”