Distribution of dissolved methane and nitrous oxide in Chilean coastal systems of the Magellanic Sub-Antarctic region (50°–55°S)

Abstract

Nitrous oxide (N2O) and methane (CH4) are greenhouse gases and active in the depletion of the ozone layer. These gases, originating from both anthropogenic and natural sources, are mainly released to the atmosphere from coastal areas, including continental shelves, estuaries and fjords. Surface distribution of dissolved N2O and CH4 during the austral spring were described within the Magellanic Sub-Antarctic region (50–55°S, Chile) with a coastal area that has a complex system of fjords, channels, gulf and, bays. A narrow range of N2O concentrations were observed from under-saturations (∼65%), as result of freshwater/glacial flow into fjord heads, to slight super-saturations (∼120–150%) in fjord mouths and adjacent marine zones. One exception was Otway Sound, where a penguin colony is situated, with N2O levels of up to 218%. In contrast, CH4 concentrations presented a wide range of saturations between 47.9% and 483%, with a spatial distribution that mainly corresponded to the type of hydrographic/geomorphologic basin; in the southern Patagonian Andes (mostly covered by the southern Ice Fields) CH4 levels varied between 65 and 80% in the marine area, and 180% saturation in the channels and fjords; whereas in the southern Patagonian tableland (Magellan Strait) higher CH4 concentrations, up to 483% saturation, were observed apparently associated with continental inputs (peatland and tundra vegetation). N2O concentrations were positively correlated with salinity and nutrients, indicating that the majority of N2O and nutrients (except silicate) originated from the Sub-Antarctic Water Mass (SAAW), which mixes with N2O-depleated freshwater. However, CH4 concentrations did not correlate with any oceanographic variables, suggesting that they originate from local marine/terrestrial interactions. The Magellanic Sub-Antarctic region acts as a modest source of N2O and CH4, to the atmosphere with effluxes of 6.20 ± 10.13 and 16.88 ± 27.04 μmol m−2 d−1 respectively. Due to climate change and a growth in anthropogenic activities such as salmon farming, future emissions of N2O and CH4 within this remote region remain uncertain.