Maintenance of Iron Meromixis by Iron Redeposition in a Rapidly Flushed Monimolimnion

Abstract

Water mass ages determined by the ³H–³He method gave a water renewal time of 2.5 ± 1 yr for the monimolimnion of softwater iron meromictic Lake 120. The water renewal time of the monimolimnion is less than, or equal to, the renewal time of the whole lake. The monimolimnion of Lake 120 was, therefore, not found to be a stratum of "perennially stagnant deep water." The rates of supply to, and degradation of, organic matter in the monimolimnion are responsible, in the first place, for the low redox potential necessary to establish the high concentrations of soluble Fe²⁺ observed (up to 4.2 mmol∙L⁻¹). However, it was found that the major key to maintenance of high monimolimnetic concentrations of Fe, i.e. maintenance of iron meromixis, is recycling of Fe at the chemocline by an "Ferrous Wheel." Up to 90% recycling of iron between chemocline and monimolimnion results in an iron residence time of for the whole lake (greater than 4 times the whole lake water renewal time).Key words: meromixis, iron recycling, ³H–³He water ages, water renewal times, chemical budgets, sediment funneling, redox reactions, Experimental Lakes Area (ELA).