Arsenic (As) causes cancer and non-cancer health effects in humans. Previous research revealed As concentrations over 200 μg g−1 in lake sediments in the south-central Puget Sound region affected by ...the former ASARCO copper smelter in Ruston, WA, and significant bioaccumulation of As in plankton in shallow lakes. Enhanced uptake occurs during summertime stratification and near-bottom anoxia when As is mobilized from sediments. Periodic mixing events in shallow lakes allow dissolved As to mix into oxygenated waters and littoral zones where biota reside. We quantify As concentrations and associated health risks in human-consumed tissues of sunfish pumpkinseed (Lepomis gibbosus) and bluegill (Lepomis macrochirus), crayfish signal (Pacifastacus leniusculus) and red swamp (Procambarus clarkii), and snails Chinese mystery (Bellamya chinensis) from lakes representing a gradient of As contamination and differing mixing regimes. In three shallow lakes with a range of arsenic in profundal sediments (20 to 206 μg As g−1), mean arsenic concentrations ranged from 2.9 to 46.4 μg g−1 in snails, 2.6 to 13.9 μg g−1 in crayfish, and 0.07 to 0.61 μg g−1 in sunfish. Comparatively, organisms in the deep, contaminated lake (208 μg g−1 in profundal sediments) averaged 11.8 μg g−1 in snails and 0.06 μg g−1 in sunfish. Using inorganic As concentrations, we calculated that consuming aquatic species from the most As-contaminated shallow lake resulted in 4–10 times greater health risks compared to the deep lake with the same arsenic concentrations in profundal sediments. We show that dynamics in shallow, polymictic lakes can result in greater As bioavailability compared to deeper, seasonally stratified lakes. Arsenic in oxygenated waters and littoral sediments was more indicative of exposure to aquatic species than profundal sediments, and therefore we recommend that sampling methods focus on these shallow zones to better indicate the potential for uptake into organisms and human health risk.
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•Littoral sediments more indicative of As bioavailability to biota than profundal•Greater human health risk from harvest in As-contaminated shallow lakes•Cancer risk >10−5 from eating crayfish and snails in As-contaminated shallow lakes•Subsistence fishing cancer risk in shallow lake with same As level as deep lake
The Southern Ocean is the largest high-nutrient low-chlorophyll environment in the global ocean, and represents an important source of intermediate and deep waters to lower latitudes. Constraining ...Southern Ocean trace metal biogeochemical cycling is therefore important not just for understanding biological productivity and carbon cycling regionally, but also for understanding trace metal distributions throughout the lower latitude oceans. We present dissolved Fe, Ni, Cu, Zn, Cd, Pb and macronutrient concentrations in the Indian and Pacific sectors of the Southern Ocean from the Antarctic Circumnavigation Expedition (austral summer 2016-17), which included the first opportunities to study trace metal cycling at the Mertz Glacier Polynya and the Balleny Islands, as well as two meridional cross-frontal transects. Dissolved Ni, Cu, Zn, Cd and macronutrient concentrations show similar or greater variability latitudinally within surface waters than vertically through the water column, reflecting the combined influence of circulation and biological drawdown in shaping the distributions of nutrient-type elements in the Southern Ocean. Slopes of Cu-Si(OH)4 and Cd-PO4 increase from the Polar Frontal Zone to south of the Southern ACC Boundary (Cu-Si(OH)4) and from the Subantarctic Zone to the Antarctic Zone (Cd-PO4). Latitudinal differences are also observed for Ni-Si(OH)4 and Zn-PO4, with distinct Subantarctic Zone trends relative to those south of the Polar Front. Similarities between our Zn-Si(OH)4 and Cd-PO4 correlations and global compilations reflect the importance of exported Southern Ocean waters in setting these metal-macronutrient couples globally. Distinct Ni-macronutrient correlations are observed in this dataset relative to the global ocean, which supports a distinct cycling of Ni in the Southern Ocean compared to other basins. Concentrations of Pb are among the lowest observed in the global ocean; however, a local maximum is seen along the density level corresponding with Antarctic Intermediate Water. Concentrations within this isopycnal decrease with increasing latitude, which can be explained by decreasing atmospheric Pb input to more recently subducted waters.
Substantial biological uptake of metals and macronutrients is observed at the Mertz Glacier Polynya. Here, inferred metal:macronutrient uptake ratios are comparable to those found in the Amundsen Sea Polynya, in Southern Ocean phytoplankton, and to metal-macronutrient correlations in our data set as a whole, highlighting the potential of Southern Ocean polynyas as natural systems for trace metal uptake and export studies. The Balleny Islands are a source of Fe to surface waters and the islands also appear to influence distributions of Zn, Cu and macronutrients, which may reflect the combined impact of Fe supply on biological uptake, mixing, and scavenging in deeper waters. The Kerguelen Plateau is also a source of Fe, as previously identified. Throughout our dataset, the ferricline is found deeper than the nitricline, in agreement with existing data and indicating that Fe is less easily entrained into the surface ocean than NO3. Additionally, Fe:NO3 ratios in most samples throughout the water column are Fe-limiting (<0.01 mmol mol−1). Therefore deep mixing, identified previously as the main Fe source to much of the Southern Ocean, would ultimately act to maintain Fe limitation.
•Substantial biological trace metal uptake is observed at the Mertz Glacier Polynya.•The Balleny & Kerguelen Islands and the Antarctic Peninsula are local Fe sources.•Deep mixing supplies NO3 more readily than Fe, and at Fe-limiting Fe:NO3 ratios.•Ni-Si(OH)4, Cu-Si(OH)4, Zn-PO4 and Cd-PO4 relationships vary latitudinally.•Pb decreases from north to south along isopycnals south of Australia.
Particulate Al and Fe and dissolved Al concentrations were analyzed in seawater samples from the upper 1000m of the eastern North Atlantic Ocean along the CLIVAR/CO2 Repeat Hydrography Program ...section A16N in summer 2013, repeating trace metal observations made along the A16N transect a decade earlier. Upper-ocean trace metal distributions in the equatorial and subtropical regions of the North Atlantic are heavily influenced by atmospheric aerosol sources. Using changes in the concentrations of subsurface particulate Al and Fe and mixed-layer dissolved Al in the equatorial North Atlantic, we estimate dust deposition to surface waters in the eastern North Atlantic increased by approximately 15% between 2003 and 2013. Increased concentrations of dissolved Al in subtropical mode waters suggest that dust deposition may have also increased in the western basin. Our observations are consistent with recent reports linking increasing sea surface temperatures in the tropical North Atlantic to increased removal of atmospheric dust via precipitation over the past several decades and highlight the importance of accurate representation of dust deposition processes for modeling Fe biogeochemistry.
•Particulate Al and Fe and dissolved Fe were measured along A16N in 2013.•Trace metal distributions were compared to those measured along A16N in 2003.•Increased trace metal concentrations were found in the tropical North Atlantic.•Changes in trace metal distributions suggest increased aerosol dust deposition.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
5.
Fingerprints of a trace nutrient Resing, Joseph A; Barrett, Pamela M
Nature (London),
07/2014, Letnik:
511, Številka:
7508
Journal Article
Recenzirano
Lack of dissolved iron in the sea limits biological productivity and the uptake of carbon dioxide. The sources of dissolved iron in the North Atlantic Ocean have been identified from isotopic ...variations of this trace nutrient. See Letter p.212
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report water column dissolved iron (dFe) and particulate iron (pFe) concentrations from 50 stations sampled across the Ross Sea during austral summer (January–February) of 2012. Concentrations of ...dFe and pFe were measured in each of the major Ross Sea water masses, including the Ice Shelf Water and off‐shelf Circumpolar Deep Water. Despite significant lateral variations in hydrography, macronutrient depletion, and primary productivity across several different regions on the continental shelf, dFe concentrations were consistently low (<0.1 nM) in surface waters, with only a handful of stations showing elevated concentrations (0.20–0.45 nM) in areas of melting sea ice and near the Franklin Island platform. Across the study region, pFe associated with suspended biogenic material approximately doubled the inventory of bioavailable iron in surface waters. Our data reveal that the majority of the summertime iron inventory in the Ross Sea resides in dense shelf waters, with highest concentrations within 50 m of the seafloor. Higher dFe concentrations near the seafloor are accompanied by an increased contribution to pFe from authigenic and/or scavenged iron. Particulate manganese is also influenced by sediment resuspension near the seafloor but, unlike pFe, is increasingly associated with authigenic material higher in the water column. Together, these results suggest that following depletion of the dFe derived from wintertime convective mixing and sea ice melt, recycling of pFe in the upper water column plays an important role in sustaining the summertime phytoplankton bloom in the Ross Sea polynya.
Key Points
Summertime dissolved and particulate iron concentrations are reported for all Ross Sea water masses and off‐shelf Circumpolar Deep Water
Summertime inventories of dissolved iron and particulate trace elements are strongly influenced by high concentrations near the seafloor
Surface water concentrations of bioavailable iron are approximately doubled if biogenic pFe is considered along with dFe concentrations
Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water column of the ocean (< 1500 m). This study uses the distribution of particulate calcium from high‐resolution ...suspended matter sampling along the Climate Variability and Predictability/CO2 Repeat Hydrography A16N transect in 2003 to estimate CaCO3 dissolution in the top 1000 m of the North Atlantic. Dissolution rates were also approximated using changes in total alkalinity measurements along isopycnal surfaces. Water masses were found to be undersaturated with respect to aragonite at intermediate depths (400–1000 m) in the eastern tropical North Atlantic. The CaCO3 dissolution rate in this region is estimated to be 0.9 mmol CaCO3 m−2 d−1, indicating this region is a hotspot for upper water column CaCO3 dissolution compared to the Atlantic basin as a whole. Dissolution rates calculated from particulate calcium distributions outside of this region were significantly lower (0.2 mmol CaCO3 m−2 d−1) and are comparable to previous estimates of CaCO3 dissolution flux for the Atlantic Ocean. The magnitude of upper water column dissolution rates compared to measured surface ocean CaCO3 standing stocks suggests that biologically mediated CaCO3 dissolution may be occurring in the top 1000 m of the Atlantic.
Key Points
Carbonate dissolution is estimated from particulate Ca distributions
Carbonate‐undersaturated waters result in attenuated particulate Ca signal
High dissolution rates observed in tropical North Atlantic at depths < 1000 m
Recent analyses suggest that considerable CaCO3 dissolution may occur in the upper water column of the ocean (<1500m). This study uses the distribution of particulate calcium from high-resolution ...suspended matter sampling along the Climate Variability and Predictability/CO2 Repeat Hydrography A16N transect in 2003 to estimate CaCO3 dissolution in the top 1000m of the North Atlantic. Dissolution rates were also approximated using changes in total alkalinity measurements along isopycnal surfaces. Water masses were found to be undersaturated with respect to aragonite at intermediate depths (400-1000m) in the eastern tropical North Atlantic. The CaCO3 dissolution rate in this region is estimated to be 0.9mmol CaCO3 m-2 d-1, indicating this region is a hotspot for upper water column CaCO3 dissolution compared to the Atlantic basin as a whole. Dissolution rates calculated from particulate calcium distributions outside of this region were significantly lower (0.2mmol CaCO3 m-2 d-1) and are comparable to previous estimates of CaCO3 dissolution flux for the Atlantic Ocean. The magnitude of upper water column dissolution rates compared to measured surface ocean CaCO3 standing stocks suggests that biologically mediated CaCO3 dissolution may be occurring in the top 1000m of the Atlantic. Key Points Carbonate dissolution is estimated from particulate Ca distributions Carbonate-undersaturated waters result in attenuated particulate Ca signal High dissolution rates observed in tropical North Atlantic at depths <1000 m
The mechanisms delivering iron (Fe) to Southern Ocean surface waters and resulting capacity for the oceanic drawdown of CO2 are important to constrain in a changing climate. The East Australian ...Current (EAC) is a major western boundary current flowing south along the eastern margin of Australia, hypothesized to play an important role in entraining Fe from a variety of potential sources and supplying Fe to large annual spring phytoplankton blooms in HNLC waters. We report Fe concentration and Fe isotope (δ56Fe) profiles for both dissolved and particulate phases at stations within the EAC, in the frontal mixing zone, and in subantarctic waters along the southward flowpath of the EAC in early spring. Mixed layer dFe concentrations declined from EAC source waters (0.32–0.53 nmol kg−1) into subantarctic waters (0.27–0.42 nmol kg−1) with a concurrent deepening of the ferricline. Particulate trace metal concentrations indicate robust inputs of lithogenic particles to subtropical EAC waters, potentially impacted by advection of shelf sedimentary particles and evidence of a significant supply from local aerosol deposition. The isotopic composition of pFe in the EAC (0.3 ± 0.1‰) is similar to prior reports of aerosol δ56Fe and upper ocean δ56pFe in the western Pacific and isotopically heavier than average values for the bulk continental crust. In EAC surface waters, isotopically light δ56dFe values (0.11–0.16‰) are observed likely due to reductive release of dFe from lithogenic particles in the photic zone with a particle-dissolved phase fractionation (Δ56FedFe–pFe) of −0.1 to −0.4‰. At depth, elevated dFe concentrations and a heavy δ56dFe signature suggest a non-reductive release of dFe from lithogenic particles via desorption or dissolution processes with a Δ56FedFe–pFe of +0.3‰. During southward transit of EAC waters, mixed layer dFe pools become increasingly heavy due to biological uptake through the frontal mixing zone and into subantarctic waters. We also observe differences in particulate trace metal concentrations in intermediate waters between subantarctic stations that could result from entrainment of sedimentary particles during transit over the relatively shallow South Tasman Rise.
•The EAC is thought to supply Fe fueling large subantarctic phytoplankton blooms.•Concentrations and isotope ratios of dissolved and particulate Fe are presented.•Box model calculations suggest aerosols may dominate Fe supply during this study.•Both reductive and non-reductive dissolution from particles releases dFe.•Biological uptake along the EAC flowpath shifts to isotopically heavier dFe.
A series of three- and four-coordinate iron(II) complexes with nitrogen, chlorine, oxygen, and sulfur ligands is presented. The electronic variation is explored by measuring the association constant ...of the neutral ligands and the reduction potential of the iron(II) complexes. Varying the neutral ligand gives large changes in K eq, which decrease in the order CNtBu > pyridine >2-picoline > DMF > MeCN > THF > PPh3. These differences can be attributed to a mixture of steric effects and electronic effects (both σ-donation and π-backbonding). The binding constants and the reduction potentials are surprisingly insensitive to changes in an anionic spectator ligand. This suggests that three-coordinate iron(II) complexes may have similar binding trends as proposed three-coordinate iron(II) intermediates in the FeMoco of nitrogenase, even though the anionic spectator ligands in the synthetic complexes differ from the sulfides in the FeMoco.
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