Southern Ocean carbon export efficiency in relation to temperature and primary productivity.

Satellite remote sensing and numerical models are widely used to estimate large-scale variations in ocean carbon export, but the relationship between export efficiency (e-ratio) of sinking organic carbon out of the surface ocean and its drivers remains poorly understood, especially in the Southern Ocean. Here, we assess the effects of temperature and primary productivity on e-ratio by combining particulate organic carbon export flux from in situ measurements during 1997-2013, environmental parameters from satellite products, and outputs from ocean biogeochemical models in the Southern Ocean. Results show that "High Productivity Low E-ratio" (HPLE) is a common phenomenon in the Subantarctic Zone and the Polar Frontal Zone, but not the Antarctic Zone. The e-ratio shows little dependence on temperature below 6 °C. Our results support the hypothesis that the HPLE phenomenon is due to the large contribution of non-sinking organic carbon. Both temperature and ballast minerals play less important roles in controlling e-ratio than ecosystem structure at low temperatures. These findings suggest that non-sinking organic carbon, ecosystem structure, and region-specific parameterizations of e-ratio are key factors to quantify the carbon export in the Southern Ocean.

Al2O3 nanoparticle impact on the toxic effect of Pb on the marine microalga Isochrysis galbana.

The rapid development and application of nanotechnology have led to increasing concern about the environmental implications of released nanomaterials and potential risks to public health and aquatic ecosystems. Information on the joint effect of nanomaterials and co-existing contaminants such as heavy metals is still inadequate. Our work investigated the effect of Al2O3 nanoparticles (NPs; nano-Al2O3) on the toxic effect of Pb in the unicellular marine phytoplankton Isochrysis galbana. Results showed that a dose-response effect of nano-Al2O3 was found. Significant enhancement of fluorescence in cell cytoplasm rather than cell membrane occurred in the presence of nano-Al2O3, indicating that nano-Al2O3 can penetrate cells and affect the fluorescence emitted from the chloropigments inside them. The presence of nano-Al2O3 has no impact on the toxic effect of Pb at an NP concentration of 1 mg/L but increased that at NP concentrations of 10 mg/L and 100 mg/L. A synergistic effect was also found for the toxic effect of Pb in the presence of 10 mg/L nano-Al2O3. The presence of 100 mg/L nano-Al2O3 significantly increased the bio-uptake of Pb in the range of 0.25 mg/L to 2.0 mg/L Pb, and the maximum accumulated Pb in algae can reach up to 18.22 ng/105 cells with 100 mg/L nano-Al2O3 compared with Pb alone at 2.0 mg/L(12.53 ng/105 cells). Inside cells, Pb loaded onto nano-Al2O3 can be more toxic than the same amount of free Pb species. The results of toxicity tests and accumulated Pb in algae imply that, in addition to the total Pb cell content, the bioavailability of Pb inside algae should be taken into consideration in evaluating the joint toxicity effect. Our work enhances understanding of the combined toxicity of NPs and co-existing heavy metals and is of practical significance in the natural environment.

Source composition and seasonal variation of particulate trace element fluxes in Prydz Bay, East Antarctica.

Particulate fluxes of trace elements (Al, Fe, Mn, Cu, Pb, Zn, Cd and Co) in the polynya area of Prydz Bay were measured using time series sediment trap lasting from December 16th 2010 to December 16th 2011. The comparison of annual fluxes from different regions, the seasonality and sources of trace element, and their association with organic matters were investigated. The fluxes of Cu, Zn and Cd in the polynya area of Prydz Bay are dominated by marine biogenic sources. Their similar seasonality with the export of biological materials (biogenic silica, organic carbon, and calcite carbonate) is strongly related to the ice coverage and biological production. Mineral debris derived from Antarctic continent is suggested to account for the particulate fluxes of Al, Fe, Mn, Pb and Co in the polynya. Their seasonal variations are most likely controlled by ice melting and freezing process. Furthermore, their fluxes are also influenced by scavenging onto biogenic material for Pb and uptake by phytoplankton for Co. The excess fluxes of Cu, Zn and Cd have good relationship with organic carbon export. The coupling patterns are mainly regulated by source composition of trace elements and non-lithogenic input from atmospheric deposition or upwelling, and partly influenced by biological uptake process.