delta N-15 values of settling biogenic particles in the eastern Bransfield Basin (west Antarctic) and their records for the surface-water condition

Abstract

Sediment trap deployments in the eastern Brans-field Basin (west Antarctic) show seasonal and inter-annual variability in particle fluxes, with most of total annual flux at mid-depth occurring during a short period. High seasonality in particle flux may be associated with biological processes (the timing of phytoplankton blooms) and physical factor (sea-ice cover). Inter-annual variability of particle flux may also reflect inter-annual variation of sea-ice cover related to the biological processes. Most notable is that year-round high particle flux is observed in sediment traps moored near the seabed, which is not unexpected, emphasizing the contribution of supplementary transport of lithogenic particles particularly during the unproductive season. In this case, particles in relatively rapid vertical transit, such as aggregates and fecal pellets, are presumably mixed with laterally-transported particles. The relationship between delta N-15 values and biogenic particle flux highlights the contribution of particles in lateral transit to the vertical setting particles downward to the near-bottom sediment trap. Mid-depth sediment trap shows clear seasonal delta N-15 variability, whereas the near-bottom sediment trap shows no distinct seasonal trend, indicating the contamination of low delta N-15, fresh organic material by high delta N-15, regenerated and more refractory material resuspended from shallow continental margin. However, judging from the flux-weight delta N-15 values between the mid-depth and near-bottom sediment traps, biogeochemical components contained in the horizontally delivered particles are not critical to prevent the surface-water condition preserved in those of downward sinking particles. Our results provide the convincing implications from the recovery of paleoclimatic information using sediment cores from the eastern Bransfield Basin (west Antarctic).