Seasonal and spatial variability of vertical particle flux along the Beagle Channel (Southern Patagonia)

The Beagle Channel is a 300-km long passage connecting the Pacific and Atlantic Oceans at ~55° S, where glaciers and river streams meet subantarctic waters. Here we present the first evaluation of downward fluxes and composition of particulate matter in the channel. Settling particle fluxes were collected by sequential sediment traps deployed in two contrasting areas: one in the western part of the channel, corresponding to an early post-glacial environment (site A) and a second, fully deglaciated, river-dominated environment (site B) in the eastern part. In early summer, fluxes at both sites are driven by organic matter produced in spring, with peak organic carbon fluxes of 289 and 413 mg C m−2 d−1 at sites A and B, respectively (C:N ratios of 7.3 and 6.3, respectively). During winter, the fluxes of fecal pellets, particulate organic carbon (POC) and particulate nitrogen (PON) were at their minimum. At site A (integrated annual POC flux of 74 g C m−2 yr−1), seasonality was weak and the flux was driven by ballast material (>95% of total particle flux) of glacial origin year-around, which also promotes the POC export. According to isotopic and taxonomic analyses performed at site A, the low seasonality in the organic component of the flux appears to be mainly related to autochthonous production of nano- and picophytoplankton during autumn and winter, later replaced by microphytoplankton fluxes during spring and summer. At site B, ballast material accounted for