Sedimentation and particle dynamics in the seasonal ice zone of the Barents Sea

The Barents Sea seasonal ice zone (SIZ) is one of the most dynamic areas in the world ocean. This biologically productive area undergoes extreme intra- and inter-annual variabilities in sea ice and water mass transport properties. Here, we investigate seafloor burial processes in three regions of the SIZ with different ice-cover frequencies: predominantly open water (POW), marginally ice-covered (MIC), and predominantly ice-covered (PIC) with approximately 0, 10 and 50% sea ice cover, respectively, in 2002–2003. Down-core sediment profiles of the radionuclides 234Th, 210Pb, and 137Cs, along with sediment carbon, nitrogen and phosphorus concentrations are examined in two to three cores from each region. Sedimentation rates and velocities using 210Pbex (excess 210Pb) profiles and assuming negligible mixing below a surface mixed layer are relatively uniform throughout the study area, averaging 558 ± 154 g m− 2 y− 1 and 1.1 ± 0.4 mm y− 1  (n = 7). These sedimentation velocities are confirmed using 137Cs (1.0 ± 0.4 mm y− 1, n = 7). 234Thex (excess 234Th) derived bioturbation rates are positively correlated with number of benthic individuals per 0.5 m2 (R2 = 0.83) and exhibit a pattern of higher rates in the MIC (14.5 ± 2.1 cm− 2 y− 1) relative to both the POW (6.3 ± 2.2 cm− 2 y− 1) and PIC (5.3 ± 1.2 cm− 2 y− 1) (p < 0.01). 234Thex inventories are also significantly higher (p = 0.026) within the MIC, while both 210Pbex and 137Cs sediment inventories are more regionally uniform. Furthermore, organic carbon (Corg) and total nitrogen (Ntot) concentrations are relatively high in both the MIC and PIC compared to POW. For this limited data set, higher bioturbation rate coefficients and higher 234Thex sediment inventories in the MIC relative to the other sampled regions, suggest that the MIC exhibits a greater predominance of marine versus terrestrial sediment sources that support enhanced scavenging and benthic biological activity. These results suggest that a climate-driven northward shift in sea ice will result in a corresponding shift in benthic communities that currently depend upon surface derived fluxes of organic matter associated with the present-day location of the ice edge in the Barents Sea.