Incubation Experiments Characterize Turbid Glacier Plumes as a Major Source of Mn and Co, and a Minor Source of Fe and Si, to Seawater

Abstract

Glaciers are a source of fine-ground rock flour to proglacial and coastal marine environments. In these environments, suspended rock flour may affect light and (micro)nutrient availability to primary producers. Due to high loads of glacier rock flour, the particulate metal load of glacier runoff typically exceeds the dissolved metal load. As glacier rock flour is deposited in downstream environments, short-term exchange between particulate and dissolved metal phases may have a moderating influence on dissolved metal concentrations. Here we compare the behavior of iron (Fe), manganese (Mn), cobalt (Co) and silica (Si) following the addition of different glacier-derived sediments into seawater under conditions of varying sediment load (20–500 mg L⁻¹), time (0.5 hr–21 days), temperature (4–11°C) and light exposure (dark/2,500 Lux). Despite a moderately high labile Fe content across all particle types (0.28–3.50 mg Fe g⁻¹ of dry sediment), only 0.27–7.13 μg Fe g⁻¹ was released into seawater, with less efficient release as sediment load increased. Conversely, Si, Mn, and Co exhibited a more constant rate of release, which was less sensitive to sediment load. Dissolved Si release was equivalent to 17% ± 22% of particulate amorphous Si after 1–2 weeks. Dissolved Mn concentrations in most incubations exceeded dissolved Fe concentrations within 1 hr despite labile Mn content being 12-fold lower than labile Fe content. Our results show the potential for glacier-derived particles to be a large source of Mn and Co to marine waters and add to the growing evidence that Mn may be the bio-essential metal most affected by glacier-associated sources.