Seasonal dispersal of fjord meltwaters as an important source of iron and manganese to coastal Antarctic phytoplankton

Glacial meltwater from the western Antarctic Ice Sheet is hypothesized to be an important source of cryospheric iron, fertilizing the Southern Ocean, yet its trace-metal composition and factors that control its dispersal remain poorly constrained. Here we characterize meltwater iron sources in a heavily glaciated western Antarctic Peninsula (WAP) fjord. Using dissolved and particulate ratios of manganese to iron in meltwaters, porewaters, and seawater, we show that surface glacial melt and subglacial plumes contribute to the seasonal cycle of iron and manganese within a fjord still relatively unaffected by climate-change-induced glacial retreat. Organic ligands derived from the phytoplankton bloom and the glaciers bind dissolved iron and facilitate the solubilization of particulate iron downstream. Using a numerical model, we show that buoyant plumes generated by outflow from the subglacial hydrologic system, enriched in labile particulate trace metals derived from a chemically modified crustal source, can supply iron to the fjord euphotic zone through vertical mixing. We also show that prolonged katabatic wind events enhance export of meltwater out of the fjord. Thus, we identify an important atmosphere–ice–ocean coupling intimately tied to coastal iron biogeochemistry and primary productivity along the WAP.

Leaf structural traits of two Restinga plant species with different resistance pattern to iron toxicity

Iron mining activities are a source of particulate iron, which contaminates soil and plants of Restinga biome (Brazil). To investigate the possible effects of iron toxicity to Ipomoea pes-caprae and Canavalia rosea leaves, plants were submitted to different exposure times (12, 36, 108 and 228 hours) and iron concentrations (0.5 or 150 mg L-1, Fe2+ as FeSO4.7H2O). After 108 hours C. rosea leaves were chlorotic while I. pes-caprae leaves presented venal chlorosis and bronzing after 228 hours, both from iron excess treatment. The anatomical alterations in I. pes-caprae were more intense and appeared earlier than in C. rosea, after 36 hours exposed to iron excess. The leaf epidermal cells of I. pes-caprae presented alterations in organization, size and shape and for both species the epicuticular wax was altered and wax rupture occurred close to the stomata. The positive staining for the presence of iron in leaf tissues matches with damaged areas in I. pes-caprae leaves, indicating direct iron toxicity. I. pes-caprae was the species with the most severe symptoms while C. rosea was the most resistant one. The results support that over time, the emission of particulate matter may negatively impact the ecological succession and biodiversity of Restinga.

Soluble, Colloidal, and Particulate Iron Across the Hydrothermal Vent Mixing Zones in Broken Spur and Rainbow, Mid-Atlantic Ridge

The slow-spreading Mid-Atlantic Ridge (MAR) forms geological heterogeneity throughout the ridge system by deep crustal faults and their resultant tectonic valleys, which results in the existence of different types of hydrothermal vent fields. Therefore, investigating MAR hydrothermal systems opens a gate to understanding the concentration ranges of ecosystem-limiting metals emanating from compositionally distinct fluids for both near-field chemosynthetic ecosystems and far-field transport into the ocean interiors. Here, we present novel data regarding onboard measured, size-fractionated soluble, colloidal, and particulate iron concentrations from the 2018 R/V L’Atalante – ROV Victor research expedition, during which samples were taken from the mixing zone of black smokers using a ROV-assisted plume sampling. Iron size fractionation (<20, 20–200, and >200nm) data were obtained from onboard sequential filtering, followed by measurement via ferrozine assay and spectrophotometric detection at 562nm. Our results showed the persistent presence of a nanoparticulate/colloidal phase (retained within 20–200nm filtrates) even in high-temperature samples. A significant fraction of this phase was retrievable only under treatment with HNO3 – a strong acid known to attack and dissolve pyrite nanocrystals. Upon mixing with colder bottom waters and removal of iron in the higher parts of the buoyant plume, the larger size fractions became dominant as the total iron levels decreased, but it was still possible to detect significant (micromolar) levels of nanoparticulate Fe even in samples collected 5m above the orifice in the rising plume. The coolest sample (<10°C) still contained more than 1μM of only nitric acid-leachable nanoparticle/colloidal, at least 200 times higher than a typical Fe concentration in the non-buoyant plume. Our results support previous reports of dissolved Fe in MAR vent plumes, and we propose that this recalcitrant Fe pool – surviving immediate precipitation – contributes to maintaining high hydrothermal iron fluxes to the deep ocean.

Fractionation Analysis of Iron in Coastal Rivers to Yantai Sishili Bay with a Bismuth Microrods-Based Electrochemical Sensor

As an essential metal micronutrient, Fe plays an important role in the marine biogeochemical cycling process, and the bioavailability of Fe has a direct relationship with its fractions in water. The fractionation analysis of iron in main coastal rivers to Yantai Sishili Bay was achieved with an electrochemical sensor based on bismuth microrods (BiMRs). The sensor was characterized by scanning electron microscope and electrochemical methods, and the reliability of the sensor was verified by the determination of the standard samples. Different fractions of iron in coastal river waters, including total iron (TFe), total dissolved iron (TDFe) and particulate iron (PFe), have been determined by combining simple sample pretreatments and cathodic stripping voltammetry with the BiMRs-based sensor. The average concentrations of TFe in Guangdang River, Xin’an River and Yuniao River were 4.02, 3.66 and 4.42 μmol L−1, respectively. The main fractionation of iron in three rivers was PFe, which accounts for 84.46%, 87.56% and 92.34%, respectively. Furthermore, the relationships between iron concentration and tidal action, salinity, dissolved oxygen and other factors were also investigated.

Seasonal dispersal of fjord meltwaters as an important source of iron to coastal Antarctic phytoplankton

Glacial meltwater from the western Antarctic Ice Sheet is hypothesized to be an important source of cryospheric iron, fertilizing the Southern Ocean, yet its trace metal composition and factors which control its dispersal remain poorly constrained. Here we characterize meltwater iron sources in a heavily glaciated western Antarctic Peninsula (WAP) fjord. Using dissolved and particulate ratios of manganese-to-iron in meltwaters, porewaters, and seawater, we show that glacial melt and subglacial plumes contribute to the seasonal cycle of bioavailable iron within a fjord still relatively unaffected by climate change-induced glacial retreat. Organic ligands derived from the phytoplankton bloom and the glaciers bind dissolved iron and facilitate the solubilization of particulate iron downstream. Using a numerical model, we show that plumes generated by outflow from the subglacial hydrologic system, enriched in labile particulate trace metals derived from a chemically-modified crustal source, can supply the surface through vertical mixing, and that prolonged katabatic wind events enhance export of meltwater out of the fjord. Thus, we identify an important atmosphere-ice-ocean coupling intimately tied to coastal iron biogeochemistry and primary productivity along the WAP.

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

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.