Sedimentation and particle dynamics in the seasonal ice zone of the Barents Sea Kanchan Maiti a,c , JoLynn Carroll b, ⁎, Claudia R. Benitez-Nelson a a Department of Geological Sciences, University of South Carolina, Columbia, SC, USA b Akvaplan-niva AS, Polar Environmental Center, Tromsø, Norway c Woods Hole Oceanographic Institution, Woods Hole MA, 02543, USA abstract article info Article history: Received 22 September 2008 Received in revised form 21 May 2009 Accepted 11 September 2009 Available online 23 September 2009 Keywords: Radioisotopes Sedimentation Bioturbation Seasonal ice zone 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 234 Th, 210 Pb, and 137 Cs, along with sediment carbon, nitrogen and phosphorus concentrations are examined in two to three cores from each region. Sedimentation rates and velocities using 210 Pb ex (excess 210 Pb) 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 137 Cs (1.0 ± 0.4 mm y -1 , n = 7). 234 Th ex (excess 234 Th) derived bioturbation rates are positively correlated with number of benthic individuals per 0.5 m 2 (R 2 = 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). 234 Th ex inventories are also significantly higher (p = 0.026) within the MIC, while both 210 Pb ex and 137 Cs sediment inventories are more regionally uniform. Furthermore, organic carbon (C org ) and total nitrogen (N tot ) concentrations are relatively high in both the MIC and PIC compared to POW. For this limited data set, higher bioturbation rate coefficients and higher 234 Th ex 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. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The Barents Sea is one of the most productive of the Arctic seas with an estimated average annual primary production of 90 gCm -2 y -1 (Wassmann et al., 2006, 2008). A relatively high proportion (∼ 47%) of the sediment burial flux is derived from marine rather than terrestrial sources (Stein and Macdonald, 2004). Depending on the water mass characteristics and physical regimes, between 48 and 96% of primary production in the Barents Sea is estimated to reach the seafloor (Wassmann, 1991; Wassmann and Slagstad, 1993; Wassmann et al., 1999; Carmack and Wassman, 2006). Primary production patterns are strongly correlated with changes in the spatial distribution of sea ice in the Barents Sea. As the seasonal ice zone (SIZ) retreats, pulses of food for higher tropic levels become available to both pelagic and benthic communities (Wassmann et al., 2006). The close relationship between the structure and function of benthic communities and the overlying primary productivity has been well demonstrated throughout this region (Piepenburg et al., 1995; Renaud et al., 2008; Carroll et al., 2008a). Recent studies suggest tight pelagic–benthic coupling within the relatively deep (∼ 200–300 m) northwestern margin of the Barents Sea (Tamelander et al., 2006; Renaud et al., 2008; Morata and Renaud, 2008; Carroll et al., 2008a), similar to the relatively shallow (∼ 30–60 m) regions of the Chukchi Sea (Dunton et al., 2005; Grebmeier et al., 2006). Carroll et al. (2008a) showed that Barents Sea benthic communities are food-limited and hence dependent on episodic delivery of organic matter from the water column. As benthic organisms respond to peaks in food supply, there may be an associated increase in intensity and depth of biological mixing in surface sediment deposits. Sea ice is susceptible to changes in long-term average temperatures and shifts in atmospheric circulation (Polyakov et al., 2005; Deser and Teng, 2008). Over the past 100 years, sea ice extent in the Arctic has diminished by approximately 12 and 40% for April and August, respectively (Vinje, 2001) and the rate of sea ice decline in recent years has accelerated (Serreze et al., 2003; Stroeve et al., 2007; Comiso et al., 2008). Reduced sea ice cover during summer may change the Journal of Marine Systems 79 (2010) 185–198 ⁎ Corresponding author. E-mail address: jc@akvaplan.niva.no (J. Carroll). 0924-7963/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2009.09.001 Contents lists available at ScienceDirect Journal of Marine Systems journal homepage: www.elsevier.com/locate/jmarsys