Impact of Mid-Ocean Ridges on the ocean iron cycle

Spearker Dr Ali Lough, University of Southampton. Earth Surface Science Institute seminar.


Supply of Fe from hydrothermal vents to the deep ocean is now known to be extensive, however the longevity of dissolved hydrothermal Fe and its transport through the deep ocean is poorly understood.

Current estimates of hydrothermal Fe flux rely on a fixed dFe/xsHe to predict hydrothermal Fe based on xsHe and as a result Fe inputs reflect ridge spreading rates. This means that current estimates do not account for the variability in Fe concentrations of vents along different ridge axis as a result of different geological settings.

To examine this we conducted a transect following the Mid Atlantic Ridge (MAR). Hydrothermal plumes originating from 10 known vent sites spaced 100’s of km’s apart were sampled, each with differing geochemistry to assess changes in the Fe/xsHe ratio between sites and with transport away from sources of venting.

A new method was devised to aquire accurate Fe/xsHe ratios at each site. Plumes were sampled for total dissolvable Fe (TDFe, unfiltered); dissolved Fe (dFe, <0.2 um); and soluble (sFe, <0.02 um), to asses the exchange of Fe between these different size fractions.

Understanding this exchange and variability in Fe/xsHe between vent sites is critical to constraining the longevity of hydrothermal Fe in the deep ocean and its impact on ocean primary productivity and the ocean-climate system.