Ethylene and methane in the upper water column of the subtropical Atlantic

The vertical distributions of ethylene and methane in the upper water column ofthe subtropical Atlantic were measured along a transect from Madeira to the Caribbean andcompared with temperature, salinity, oxygen, nutrients, chlorophyll-a, and dissolved organiccarbon (DOC).Methane concentrations between 41.6 and 60.7 nL L−1 were found in the upper 20 m ofthe water column giving a calculated average flux of methane into the atmosphere of 0.82 µgm−2 h−1. Methane profiles reveal several distinct maxima in the upper 500 m of the watercolumn and short-time variations which are presumably partly related to the vertical migrationof zooplankton.Ethylene concentrations in near surface waters varied in the range of 1.8 to 8.2 nL L−1.Calculated flux rates for ethylene into the atmosphere were in the range of 0.41 to 1.35 µgm−2 h−1 with a mean of 0.83 µg m−2 h−1. Maximum concentrations of up to 39.2 nL L−1were detected directly below the pycnocline in the western Atlantic. The vertical distributionsof ethylene generally showed one maximum at the pycnocline (about 100 m depth) whereelevated concentrations of chlorophyll-a, dissolved oxygen, and nutrients were also found;no ethylene was detected below 270 m depth. This suggests that ethylene release is mainlyrelated to one, probably phytoplankton associated, source, while for methane, enhanced netproduction occurs at various depth horizons. For surface waters, a simple correlation betweenethylene and chlorophyll-a or DOC concentrations could not be observed. No considerablediurnal variation was observed for the distribution and concentration of ethylene in the upperwater column

Letters to Nature: Hydrothermal activity along the southwest Indian Ridge

Twenty years after the discovery of sea-floor hot springs, vast stretches of the global mid-ocean-ridge system remain unexplored for hydrothermal venting. The southwest Indian ridge is a particularly intriguing region, as it is both the slowest-spreading of the main ridges1 and the sole modern migration pathway between the diverse vent fauna of the Atlantic and Pacific oceans2. A recent model postulates that a linear relation exists between vent frequency and spreading rate3 and predicts vent fields to be scarcest along the slowest-spreading ridge sections, thus impeding migration and enhancing faunal diversity2. Here, however, we report evidence of hydrothermal plumes at six locations within two 200-km-long sections of the southwest Indian ridge indicating a higher frequency of venting than expected. These results suggest that fluxes of heat and chemicals from slow-spreading ridges may be greater than previously thought and that faunal migration along the southwest Indian ridge may serve as an important corridor for gene-flow between Pacific and Atlantic hydrothermal fields