Katrien J. J. Van Landeghem

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. Measured acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the coastal region. Onboard mesocosm experiments simulated resuspension of oxic sediments, rich in highly reactive Fe (2–9 mg g ⁻¹ ), in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. These experiments produced a high sustained bottom water enrichment in dissolved Fe of ∼ 4–12 nM over the 48 h experiment duration. Our observations support a dissolved Fe flux to the water column of 0.18–4.0 µmol m ⁻² d ⁻¹ by resuspension within the glaciated fjords, demonstrating that resuspension of reactive oxic nearshore sediments is a key source of dissolved and reactive particulate Fe to Antarctic shelf waters, the export of which could potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Despite increasing recognition of the importance of polar fjords as an emerging carbon sink, relatively few estimates of organic carbon stocks, deposition and accumulation potential exist for the West Antarctic Peninsula (WAP). We assessed the long-term accumulation of organic carbon in three deglaciating Antarctic fjords by combining total organic carbon (TOC) and 210Pb measurements. These data enabled calculations of carbon flux and sequestration (carbon remaining after 100 years), while the susceptibility of the carbon pool to further degradation was assessed by thermogravimetric analysis (TGA). Organic carbon surface deposition rates were highly variable (11.99 ± 8.27 g C m-2 yr-1), while organic carbon burial rates were more consistent (3.55 ± 1.75 g C m-2 yr-1). Burial efficiencies ranged from 30.59% to 54.44% (mean 39.84%). These results are comparable with previous predictions of carbon sequestration in WAP fjords, highlighting the role of fjords as global hotspots of long-term accumulation, and support the hypothesis that deglaciating polar fjords act as a significant negative (mitigating) feedback on global climate change.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g^-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm^-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm^-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

Southern Ocean primary productivity is often limited by the availability of the essential micronutrient iron (Fe), and sediment-derived fluxes of Fe from the Antarctic shelf have been linked with hotspots of productivity. Glacial meltwater along the West Antarctic Peninsula delivers significant volumes of Fe-rich glacially weathered material to shelf surface sediments. The mechanisms that supply a bioavailable flux of Fe from shelf sediments are not well understood. This study simulated the resuspension of oxic sediments in the nearshore glaciated West Antarctic Peninsula across King George Island, Anvers Island, and Adelaide Island. Glaciomarine surface sediments were rich in highly reactive Fe (2 – 9 mg Fe g-1), and onboard mesocosm resuspensions produced a sustained bottom water enrichment in dissolved Fe of 4 – 12 nM over the 48 h experiment duration. Additional acoustic doppler current profiler and acoustic backscatter turbidity data indicate ongoing resuspension of sediment in the region. Our observations support a flux of highly reactive Fe of 5–20 µmol cm-2 per sediment by resuspension within the glaciated fjords studied, exceeding recent outer shelf estimates of 0.7 µmol cm-2. Reactive oxic nearshore sediments therefore represent an important supply of colloidal and reactive particulate Fe to the Antarctic shelf water column, the export of which can potentially supply bioavailable Fe to Fe-limited Southern Ocean waters.

The drive to cut carbon emissions and harness renewable energy has spurred rapid industrialization of the seas. Current estimates of seabed modification due to offshore windfarms (ca. 1% of a windfarm’s area) do not account for enhanced seabed mobility due to monopile wakes. Here we demonstrate how turbulence emanating from windfarm infrastructure mobilizes seabed sediments. Whilst mean flow conditions in our laboratory experiment could mobilize fine sand, near-bed turbulence from monopile’s wake could mobilize sand 17 monopile diameters ( D ) downstream. Related bedform formation coincided spatially with downwelling of the monopile’s turbulent wake, indicating that the 3D wake flow structure both creates and defines enhanced sediment mobility. We introduce a method for predicting this region of enhanced transport capacity by combining bed shear stress from near-bed turbulence with that from mean flow; and our field evidence at an operational offshore windfarm validates this approach. Our results show bed stress amplification is expected cover 3-8% of a typical windfarm area. Enhanced seabed mobility can alter seabed habitats and should be factored into impact assessment and marine planning.

How will climate change affect the composition of the seabed? Using three-dimensional hydrodynamic and wave models combined with climate projections from the Coupled Model Intercomparison Project phase 5, we investigate and quantify the drivers of seafloor stresses, using a North Western European Shelf case study. This study maps the potential for grain size mobilisation in present-day and future conditions, highlighting areas where transport capacity is likely to change. Sea level rise alters both absolute water depth and tidal dynamics, changing the magnitude and timing of seabed stresses while simultaneously reducing exposure to waves and currents. In contrast, increasing storm intensity in a warming climate is expected to cause more frequent episodic disturbance of an otherwise increasingly stable seabed. These predicted changes and their potential impacts on the benthic environment are discussed in the context of growing anthropogenic pressures and the associated challenges for marine spatial management.