Seasonal Depletion of the Dissolved Iron Reservoirs in the Sub-Antarctic zone of the Southern Atlantic Ocean

Seasonal progression of dissolved iron (DFe) concentrations in the upper water column were examined during four occupations in the Atlantic sector of the Southern Ocean. DFe inventories from euphotic and aphotic reservoirs decreased progressively from July to February, while dissolved inorganic nitrogen (DIN) decreased from July to January with no significant change between January and February. Results suggest that between July and January, DFe loss from both euphotic and aphotic reservoirs were predominantly in support of phytoplankton growth (Iron to carbon (Fe:C) uptake ratio of 16±3 μmol mol‐1) highlighting the importance of the “winter DFe‐reservoir” for biological uptake. During January to February, excess loss of DFe relative to DIN (Fe:C uptake ratio of 44±8 μmol mol‐1 and aphotic DFe loss rate of 0.34±0.06 μmol m‐2 d‐1) suggests that scavenging is the dominant removal mechanism of DFe from the aphotic, while continued production is likely supported by recycled nutrients. Plain Language Summary Trace metal iron is one of the limiting nutrients for primary productivity in the Southern Ocean; however the relative importance of seasonal iron supply and sinks remains poorly understood, due to sparse data coverage across the seasonal cycle and lack of high‐resolution dissolved iron (DFe) measurements. Here, we present four “snap‐shots” of DFe measurements at a single station in the south‐east Southern Atlantic Ocean (one in winter and three in late spring‐summer), to address the seasonal evolution of DFe and dissolved inorganic nitrogen (DIN) concentrations within the biologically active sunlit and subsurface reservoirs. We observed a seasonal depletion of DFe inventories from July‐February, while DIN inventories decreases from July‐January with no concomitant changes between January‐February. This suggests that, in addition to biological uptake in the sunlit layer, the observed decrease in DFe inventories below this (relative to DIN) is driven by aggregation and incorporation of iron particles into larger "marine snow" sinking particles, while nutrient recycling is driving the observed continuation of primary productivity during late summer. Our results provide insight into seasonal change of DFe availability in different reservoirs where interplay between removal and supply processes are controlling its distributions and bioavailability to support upper surface primary production

The influence of wax content on the physical properties of low-density polyethylene-wax blends

\The influence of wax content on the thermal, mechanical and viscoelastic properties of low-density polyethylene (LDPE)-oxidized wax miscible blends have been investigated. It was found that small concentrations of wax improved physical properties such as thermal stability, elastic modulus and yield stress. At higher concentrations, however, due to crystal phase separation, wax deteriorates the thermal as well as the mechanical properties. It was also shown that a formerly established two-process model for the stress relaxation in semicrystalline polymers could be used for the explanation of the viscoelastic behaviour of the blends. (C) 2003 Society of Chemical Industry

Binary mixtures of polyethylene and oxidized wax: Dependency of thermal and mechanical properties upon mixing procedure

The influence of the preparation procedure on the thermal and mechanical properties of linear low-density polyethylene (LLDPE)- and LDPE-oxidized wax blends was investigated. It was found that mechanically mixed blends show reduced thermal stability as well as ultimate mechanical properties (stress and strain at break) compared to that of extrusion mixed blends. However, the structure of the blend and consequently its thermal and mechanical behavior also depend on the initial morphology of polyethylene. DSC measurements show miscibility up to high wax contents in both blend types, but increasing the amount of wax in LDPE blends induces increasing crystallinity. As a result, the LDPE/wax blends show improved thermal stability of between 20 and 50degreesC at low wax concentrations. Although the elasticity modulus of the blends increases, increasing the amount of wax generally degrades the mechanical properties. The main reason for this is the reduced number of tie chains. Changes in the average concentration of tie chains with increasing wax content were calculated and a correlation was made with the ultimate properties of the blends. (C) 2003 Wiley Periodicals, Inc

Chemically and Geographically distinct solid-phase iron pools in the Southern Ocean

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