Lithogenic Particle Flux to the Subantarctic Southern Ocean: A Multi‐Tracer Estimate Using Sediment Trap Samples

Abstract

Mineral dust is a key source of essential micronutrients, particularly iron (Fe), for phytoplankton in the Southern Ocean. However, observations of dust deposition over the Southern Ocean are sparse, hindering assessments of its influence on marine biogeochemistry. We present a time series (2010–2019) of lithogenic particle flux estimates using sediment trap samples collected at 1,000 m depth at the subantarctic Southern Ocean Time Series (SOTS) site. Lithogenic flux was estimated using individual Fe, aluminium (Al), titanium, and thorium concentrations in sediment trap particles less than 1 mm in size. These tracers showed good agreement with one another, and their average was investigated as a proxy for mineral dust deposition. This multi‐tracer average lithogenic flux exhibited strong seasonality, peaking in late spring and summer. No significant Fe enrichment was observed compared to the average upper continental crust, indicating that lithogenic material dominates particulate Fe flux at SOTS. Similar Fe:Al ratios in our samples compared to those reported in marine aerosols off southern Australia, coupled with particle trajectory analysis, suggested Australian dust constitutes the primary lithogenic source to SOTS sinking particles. Lead enrichment in our samples also highlighted an anthropogenic contribution to sinking particles, which might represent an additional aeolian source of more bio‐available Fe to subantarctic waters. This study contributes a new long‐term estimate of lithogenic particle fluxes and aeolian deposition over the subantarctic Southern Ocean. These estimates may enhance model representation of trace metal contribution to biogeochemical processes in the Southern Ocean.

Mechanistic Constraints on the Drivers of Southern Ocean Meridional Iron Distributions Between Tasmania and Antarctica

“…The observations along SR3 demonstrated characteristic surface dFe depletion across the entire transect (Figure 3c). The mean dFe concentration across the entire transect in the surface 100 m was depleted to 0.14 ± 0.09 nmol/kg ( n = 54) (Figure 3c), indicating that surface external sources of dFe such as atmospheric deposition were minimal, as previously observed based on sinking particle concentrations (Traill et al., 2022). While surface waters (STCW, AASW and SAMW) were very low in dFe, localized sub‐surface regions (∼500 m depth) of high dFe concentrations (>1 nmol/kg) were observed adjacent to the Antarctic and Tasmanian continental shelves (Figure 3c).…”

“…The observations along SR3 demonstrated characteristic surface dFe depletion across the entire transect (Figure 3c). The mean dFe concentration across the entire transect in the surface 100 m was depleted to 0.14 ± 0.09 nmol/kg (n = 54) (Figure 3c), indicating that surface external sources of dFe such as atmospheric deposition were minimal, as previously observed based on sinking particle concentrations (Traill et al, 2022).…”

“…However, the interplay between factors regulating dFe supply to surface waters where productivity occurs is yet to be resolved. These factors include deep winter mixing (Tagliabue, Sallée, et al., 2014), remineralization of sinking particles (Bressac et al., 2019) and external sources of Fe from lithogenic (Bowie et al., 2009; Traill et al., 2022) and hydrothermal inputs (Tagliabue et al., 2022).…”

Different Source Contributions of Bioactive Trace Metals in Sinking Particles in the Northern South China Sea

“…Trace metal compositions in sinking particles retain valuable information to identify their sources and investigate the associated cycling processes. For example, it has been demonstrated that Al, Fe, Ti, and Th are useful indicators for mineral dust deposition [9]. In addition, Cu, Pb, Zn, and V are enriched in sediment trap samples relative to their crustal abundance in the North Pacific Western Subarctic Gyre and Sargasso Sea [10][11][12], suggesting that anthropogenic signals in trace metals can be captured by sinking particles.…”