Potential Sources of Particulate Iron in Surface and Deep Waters of the Terra Nova Bay (Ross Sea, Antarctica)

Paola Rivaro,Pierpaolo Falco,Francisco Ardini,Olga Mangoni,Davide Vivado,Pasquale Castagno,Roberto Cabella

doi:10.3390/w12123517

Abstract

The distribution of particulate Fe (pFe), suspended particulate matter (SPM), and other particulate trace metals were investigated in Terra Nova Bay as part of CDW Effects on glaciaL mElting and on Bulk of Fe in the Western Ross sea (CELEBeR) and Plankton biodiversity and functioning of the Ross Sea ecosystems in a changing Southern Ocean (P-ROSE) projects. Variable concentrations of SPM (0.09–97 mg L−1), pFe (0.51–8.70 nM) and other trace metals were found in the Antarctic Surface waters (AASW) layer, where the addition of meltwater contributed to the pool with both lithogenic and biogenic forms. The deeper layer of the water column was occupied by High Salinity Shelf Water (HSSW) and Terra Nova Bay Ice Shelf Water (TISW) encompassing glacial water as confirmed by the lightest δ18O measured values. The concentration of pFe in TISW (11.7 ± 9.2 nM) was higher than in HSSW samples (5.55 ± 4.43 nM), suggesting that the drainage of material released from glaciers surrounding the area is relevant in terms of pFe contribution. Particulate Fe/Al and Mn/Al ratios were substantially in excess compared with the mean crustal ratios. Microscopic analyses confirmed that more labile Fe oxyhydroxides and authigenic MnO2 phases were present together with biogenic sinking material. Future expected increasing melt rates of these glaciers enlarge Fe input, thus having a greater role in supplying iron and counteracting the reductions in sea ice cover around Terra Nova Bay.

Highlights

In recent years, iron has been recognized as a key element in ocean biogeochemical cycles, in High Nutrient Low Chlorophyll areas
The contribution of sea ice meltwater to surface waters (MW%) is obviously greater at the surface (1.20 ± 0.59%) than at the subsurface depth sampled for particulate metals (0.89 ± 0.62%), but the difference is not statistically significant (Student’s t-test, p < 0.05)
This study provides insight into the biogeochemistry of the Terra Nova Bay area, highlighting the spatial heterogeneity of both suspended particulate matter (SPM) and particulate metals concentration in the water masses

Summary

Introduction

Iron has been recognized as a key element in ocean biogeochemical cycles, in High Nutrient Low Chlorophyll areas. Water 2020, 12, 3517 four potential sources of dFe in Ross Sea surface waters: Circumpolar Deep Water (CDW) originating from the shelf edge, sediments from shallow banks and near shore areas, melting sea ice around the perimeter of polynya and glacial meltwater from the Ross Ice Shelf (RIS) [3]. Fewer measurements of particulate Fe (pFe) than dFe have been reported in the Ross Sea. Despite this, the study of pFe is essential to better constrain the iron biogeochemical cycle [4,5,6]. Sea ice meltwater contributes to pFe in Ross Sea surface waters near the receding ice edge during the austral summer [7], while terrestrial material may influence metal distribution more than aeolian input in coastal areas [8]. De Jong et al, (2013) [4] acknowledged the importance of dust and sea ice melt as sources of iron in coastal surface waters, along with sediment re-suspension and the melting of icebergs and ice sheets

Methods

Results

Discussion

Conclusion