Achterberg, Eric P. , Zhu, Xunchi, Laufer-Meiser, Katja and Hopwood, Mark J. (2024) Incubation experiments characterize turbid glacier plumes as a major source of Mn and Co, and a minor source of Fe and Si, to seawater. Global Biogeochemical Cycles, 38 (10). e2024GB008144. DOI 10.1029/2024gb008144.

Preview	Text Global Biogeochemical Cycles - 2024 - Zhu - Incubation Experiments Characterize Turbid Glacier Plumes as a Major Source of.pdf - Published Version Available under License Creative Commons: Attribution 4.0. Download (3MB) | Preview
	Text 2024gb008144-sup-0001-supporting information si-s01.docx - Supplemental Material Available under License Creative Commons: Attribution 4.0. Download (3MB)

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.

Key Points

Changing light and temperature had no effect on the net release of Fe, Mn, Co, or Si from glacier rock flour in seawater

A small fraction of labile particulate Fe was soluble in seawater, although this was partially reversible over short (<24 hr) timescales

Mn and Co showed a consistent gradual dissolution behavior with Mn present at dissolved concentrations ∼8× higher than Fe within 24 hr

Plain Language Summary:
Glacier runoff is associated with high sediment loads derived from glacier weathering. Particle surfaces can, depending on ambient conditions, act as a source or sink for dissolved metals in solution. With increasing glacier discharge and ongoing glacier retreat around the Arctic, shifts in the seasonal timing and magnitude of sediment delivery to the coastline are expected. However, the net effect of glacier-derived particles on marine metal and nutrient availability is not clear, especially for elements other than Fe, which are less well studied. Here we used sediment-seawater incubations with different glacier and iceberg sediment samples from Greenland and Svalbard to quantify the change in Fe, Mn, Co, and Si concentrations when particles were suspended in Atlantic seawater. Our results and a comparison with in situ concentrations reveal the significance of particle dissolution on elemental cycles, particularly for Mn.

Actions (login required)

View Item