Iron organic speciation determination in rainwater using cathodic stripping voltammetry

A sensitive method using Competitive Ligand Exchange-Adsorptive Cathodic Stripping Voltammetry (CLE-ACSV) has been developed to determine for the first time iron (Fe) organic speciation in rainwater over the typical natural range of pH. We have adapted techniques previously developed in other natural waters to rainwater samples, using the competing ligand 1-nitroso-2-naphthol (NN). The blank was equal to 0.17 ± 0.05 nM (n = 14) and the detection limit (DL) for labile Fe was 0.15 nM which is 10–70 times lower than that of previously published methods. The conditional stability constant for NN under rainwater conditions was calibrated over the pH range 5.52–6.20 through competition with ethylenediaminetetraacetic acid (EDTA). The calculated value of the logarithm of β′Fe3+3(NN)β′Fe3+(NN)3 increased linearly with increasing pH according to log β′Fe3+3(NN)=2.4±0.6×pH+11.9±3.5log β′Fe3+(NN)3=2.4±0.6×pH+11.9±3.5 (salinity = 2.9, T = 20 °C). The validation of the method was carried out using desferrioxamine mesylate B (DFOB) as a natural model ligand for Fe. Adequate detection windows were defined to detect this class of ligands in rainwater with 40 μM of NN from pH 5.52 to 6.20. The concentration of Fe-complexing natural ligands was determined for the first time in three unfiltered and one filtered rainwater samples. Organic Fe-complexing ligand concentrations varied from 104.2 ± 4.1 nM equivalent of Fe(III) to 336.2 ± 19.0 nM equivalent of Fe(III) and the logarithm of the conditional stability constants, with respect to Fe3+, varied from 21.1 ± 0.2 to 22.8 ± 0.3. This method will provide important data for improving our understanding of the role of wet deposition in the biogeochemical cycling of iron.

Estimation of atmospheric nutrient inputs to the Atlantic Ocean from 50°N to 50°S based on large-scale field sampling: Iron and other dust-associated elements

Atmospheric inputs of mineral dust supply iron and other trace metals to the remote ocean and can influence the marine carbon cycle due to iron's role as a potentially limiting micronutrient. Dust generation, transport, and deposition are highly heterogeneous, and there are very few remote marine locations where dust concentrations and chemistry (e.g., iron solubility) are routinely monitored. Here we use aerosol and rainwater samples collected during 10 large-scale research cruises to estimate the atmospheric input of iron, aluminum, and manganese to four broad regions of the Atlantic Ocean over two 3 month periods for the years 2001–2005. We estimate total inputs of these metals to our study regions to be 4.2, 17, and 0.27 Gmol in April–June and 4.9, 14, and 0.19 Gmol in September–November, respectively. Inputs were highest in regions of high rainfall (the intertropical convergence zone and South Atlantic storm track), and rainfall contributed higher proportions of total input to wetter regions. By combining input estimates for total and soluble metals for these time periods, we calculated overall percentage solubilities for each metal that account for the contributions from both wet and dry depositions and the relative contributions from different aerosol types. Calculated solubilities were in the range 2.4%–9.1% for iron, 6.1%–15% for aluminum, and 54%–73% for manganese. We discuss sources of uncertainty in our estimates and compare our results to some recent estimates of atmospheric iron input to the Atlantic.

Volcanic ash supply to the surface ocean – remote sensing of biological responses and their wider biogeochemical significance

Transient micronutrient enrichment of the surface ocean can enhance phytoplankton growth rates and alter microbial community structure with an ensuing spectrum of biogeochemical feedbacks. Strong phytoplankton responses to micronutrients supplied by volcanic ash have been reported recently. Here we: (i) synthesize findings from these recent studies; (ii) report the results of a new remote sensing study of ash fertilization; and (iii) calculate theoretical bounds of ash-fertilized carbon export. Our synthesis highlights that phytoplankton responses to ash do not always simply mimic that of iron amendment; the exact mechanisms for this are likely biogeochemically important but are not yet well understood. Inherent optical properties of ash-loaded seawater suggest rhyolitic ash biases routine satellite chlorophyll-a estimation upwards by more than an order of magnitude for waters with <0.1 mg chlorophyll-a m-3, and less than a factor of 2 for systems with >0.5 mg chlorophyll-a m-3. For this reason post-ash-deposition chlorophyll-a changes in oligotrophic waters detected via standard Case 1 (open ocean) algorithms should be interpreted with caution. Remote sensing analysis of historic events with a bias less than a factor of 2 provided limited stand-alone evidence for ash-fertilization. Confounding factors were poor coverage, incoherent ash dispersal, and ambiguity ascribing biomass changes to ash supply over other potential drivers. Using current estimates of iron release and carbon export efficiencies, uncertainty bounds of ash-fertilized carbon export for 3 events are presented. Patagonian iron supply to the Southern Ocean from volcanic eruptions is less than that of windblown dust on thousand year timescales but can dominate supply at shorter timescales. Reducing uncertainties in remote sensing of phytoplankton response and nutrient release from ash are avenues for enabling assessment of the oceanic response to large-scale transient nutrient enrichment.

CONTRIBUTION OF A SPERM PROTEIN, PAWP, TO THE SIGNAL TRANSDUCT PATHWAY DURING VERTEBRATE FERTILIZATION

PAWP, postacrosomal sheath WW domain binding protein, is a novel sperm protein identified as a candidate sperm borne, oocyte-activating factor (SOAF). PAWP induces both early and later egg activation events including meiotic resumption, pronuclear formation and egg cleavage. Based on the fact that calcium increase is universally accepted as the sole requirement for egg activation, we hypothesized that PAWP is an upstream regulator of the calcium signaling pathway during fertilization. Intracellular calcium increase was detected by two-photon laser scanning fluorescence microscopy following microinjection of recombinant PAWP into Xenopus oocytes, bolstering our hypothesis and suggesting the involvement of a novel PAWP-mediated signaling pathway during fertilization. The N-terminal of PAWP shares a high homology to WW domain binding protein while the C-terminal half contains a functional PPXY motif, which allows it to interact with group I WW domain proteins. These structural considerations together with published data indicating that PPXY synthetic peptide derived from PAWP inhibits ICSI-induced fertilization led to the hypothesis that PAWP triggers egg activation by binding to a group I WW domain protein in the oocyte. By far-Western analysis of oocyte cytoplasmic fraction, PAWP was found to bind to a 52 kDa protein. The competitive inhibition studies with PPXY synthetic peptide, WW domain constructs, and their point mutants demonstrated that the interaction between PAWP and its binding partner is specifically via the PPXY-WW domain module. The 52 kDa protein band crossreacted with antibodies against group I WW domain protein YAP in Western blot assay, indicating that this 52 kDa PAWP binding partner is either YAP or a YAP-related protein. In addition, the far-Western competitive inhibition studies with recombinant GST fusion protein YAP and another WW domain-containing protein, TAZ, demonstrated that the binding of PAWP to its binding partner was significantly reduced by TAZ, providing evidence that TAZ could be the 52 kDa protein candidate. Mass spectrometry was employed to identify this PAWP binding partner candidate. However, due to the low abundance of the candidate protein and the complexity of the sample, several strategies are still needed to enrich this protein. This study correlates PAWP induced meiotic resumption and calcium efflux at fertilization and uncovers a 52 kDa candidate WW domain protein in the oocyte cytoplasm that most likely interacts with PAWP to trigger egg activation.

THE IDENTIFICATION AND CHARACTERIZATION OF AN INNER ACROSOMAL MEMBRANE ASSOCIATED PROTEIN, IAM38, RESPONSIBLE FOR SECONDARY SPERM-ZONA BINDING DURING FERTILIZATION

During mammalian fertilization, the exposure of the inner acrosomal membrane (IAM) after acrosomal exocytosis is essential for the secondary binding between sperm and zona pellucida (ZP) of the oocyte, a prerequisite for sperm penetration through the ZP. The identification of the sperm protein(s) responsible for secondary binding has posed a challenge for researchers. We were able to isolate a sperm head fraction in which the IAM was exposed. Attached to the IAM was an electon dense layer, which we termed the IAM extracellular coat (IAMC). The IAMC was also observable in acrosome reacted sperm. High salt extraction removed the IAMC including a prominent 38 kDa polypeptide, referred to as IAM38. Antibodies raised against IAM38 confirmed its presence in the IAMC of intact, sonicated, and acrosome-reacted sperm. Sequencing of IAM38 revealed it as the ortholog of porcine SP38, a protein that was found to bind specifically to ZP2 but whose intra-acrosomal location was not known. We showed that IAM38 occupied the leading edge of sperm contact with the zona pellucida during fertilization, and that secondary binding and fertilization were inhibited in vitro by antibodies directed against IAM38. As for the mechanism of secondary sperm-zona binding by IAM38, we provided evidence that the synthetic peptide derived from the ZP2-binding motif of IAM38 had a competitive inhibitory effect on both sperm-zona binding and fertilization while its mutant form was ineffective. In summary, our study provides a novel approach to obtain direct information on the peripheral and integral protein composition of the IAM and consolidates IAM38 as a genuine secondary sperm-zona binding protein. In addition, our investigation also provides an ultrastructural description of the origin, expression and assembly of IAM38 during spermatogenesis. It shows that IAM38 is originally secreted by the Golgi apparatus as part of the dense contents of the proacrosomic granules but later, during acrosome capping phase of spermiogenesis, is redistributed to the inner periphery of the acrosomal membrane. This relocation occurs at the time of acrosomal compaction, an obligatory structural change that fails to occur in Zpbp1-/- knockout mice, which do not express IAM38 and are infertile.

Diatom carbon export enhanced by silicate upwelling in the North East Atlantic.

Diatom carbon export enhanced by silicate upwelling in the northeast Atlantic John T. Allen1,2, Louise Brown1,3, Richard Sanders1, C. Mark Moore1, Alexander Mustard1, Sophie Fielding1, Mike Lucas1, Michel Rixen4, Graham Savidge5, Stephanie Henson1 and Dan Mayor1 Top of pageDiatoms are unicellular or chain-forming phytoplankton that use silicon (Si) in cell wall construction. Their survival during periods of apparent nutrient exhaustion enhances carbon sequestration in frontal regions of the northern North Atlantic. These regions may therefore have a more important role in the 'biological pump' than they have previously been attributed1, but how this is achieved is unknown. Diatom growth depends on silicate availability, in addition to nitrate and phosphate2, 3, but northern Atlantic waters are richer in nitrate than silicate4. Following the spring stratification, diatoms are the first phytoplankton to bloom2, 5. Once silicate is exhausted, diatom blooms subside in a major export event6, 7. Here we show that, with nitrate still available for new production, the diatom bloom is prolonged where there is a periodic supply of new silicate: specifically, diatoms thrive by 'mining' deep-water silicate brought to the surface by an unstable ocean front. The mechanism we present here is not limited to silicate fertilization; similar mechanisms could support nitrate-, phosphate- or iron-limited frontal regions in oceans elsewhere.