Long-range transport of iron off the Antarctic Peninsula

Science Highlights

7 April 2026

Antarctic continental sediments are an important source of bio-essential elements such as iron (Fe) to the Southern Ocean. However, the longevity of sedimentary Fe signal and Fe cycling in coastal Antarctic waters, remain poorly constrained. By combining measurements of dissolved Fe concentrations ([dFe]) and iron isotope compositions (δ56Fe) along a transect from the Antarctic Peninsula to the central Weddell Sea (GEOTRACES Process Study GApr12), Tian and co-authors show that elevated [dFe] near shelf sediments (up to 7.14 nmol L⁻¹), together with low δ56Fe values (down to -1.38‰), indicate that reductive dissolution of Fe(III) minerals in shelf sediments is the dominant mechanism releasing Fe into the water column. This isotopically light signal persists offshore as a δ56Fe minimum (-0.66 to -0.34‰) at ~200-500 m depth across the continental slope and the central Weddell Sea where Fe is often limited, following a density layer (isopycnal 28.1-28.2 kg m⁻3). The pattern indicates lateral advection of sedimentary Fe from the Antarctic Peninsula shelf into the central Weddell Sea and supports the use of δ56Fe as a tracer of reductive sedimentary Fe inputs to the open ocean. In addition, the study shows that as shelf waters descend along the continental slope to form precursor Weddell Sea Bottom Water, [dFe] decreases by ~60% while δ56Fe increases by ~1‰. This shift reflects mixing with Warm Deep Water and Weddell Sea Deep Water, highlighting the key role of physical mixing in regulating Fe cycling in deep ocean waters.

Figure 1: Conceptual model of isotopic iron (δ56Fe) and dissolved iron [dFe] in the western Weddell Sea. The Weddell Sea continental shelf sediments supply reductive Fe (red arrow) to the shelf waters. The long-range transport of this Fe signal is indicated by the red plume, characterised by a persistent isotopically light signature (-0.66 to -0.34‰) at intermediate depths (~200-500 m) across the continental slope and into the central Weddell Sea. As dense waters form and descend in this region (blue arrows), extensive physical mixing with Warm Deep Water and Weddell Sea Deep Water governs the resulting variations in dissolved Fe concentrations and isotopic compositions in global deep waters.
Figure 2: Map of the study area. Red dots correspond to the sampling stations of cruise PS117 (GEOTRACES Process Study GApr12). Samples were collected during the austral summer (December 2018 to February 2019).

Reference:

Tian, H.-A., van Manen, M., Bunnell, Z. B., Reichart, G.-J., Conway, T. M., & Middag, R. (2026). Iron isotope constraints on source and transport of sediment-derived dissolved Fe in the Weddell Sea region. Geochimica et Cosmochimica Acta. Access the paper: 10.1016/j.gca.2026.01.033

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