Abstract

The Patagonia archipelago interior sea (PAIS) of southern Chile is one of the largest fjord systems on earth. These coastal waters include remote and virtually pristine areas where extreme rainfall/runoff and glacial meltwaters intensify the land–ocean interaction impinging on the biological, physical, and chemical characteristics of oceanic subantarctic Surface Water (SAASW) that flood the archipelago basins. The SAASW mix with silicon- and iron-replete continental water and diatom growth would occur concomitantly with a rapid drawdown of SAASW macronutrients. Consequently, phytoplankton metabolism (e.g. macronutrient utilization for primary productivity) in estuaries of southern Patagonian has been previously assumed independent of iron availability (i.e. iron-replete conditions). Experimental results shown here suggest that the nitrate and phosphate drawdown in low salinity (29) water can be enhanced by a 5 nM dissolved iron enrichment (by 13% and 28%, respectively) during the developing phase of a diatom bloom. The simultaneous enrichment in iron (5 nM) and silicic acid (5 μM) in these estuarine waters resulted in a similar macronutrient uptake enhancement, a 119% increment of the production of biogenic silica and a 2-fold rise in the abundance of Pseudo-nitzschia spp (a diatom capable to produce the neurotoxin domoic acid). We suggest that natural freshwater pulses of allochthonous bioavailable forms of iron and silicon to inner waters of the Patagonia archipelago during the onset of the productive season play a potentially significant role modulating macronutrient dynamics (input vs utilization) and influencing coastal phytoplankton assemblages.