New particle formation at the coastal Antarctic site Neumayer in 2012 and 2014

We measured condensation particle (CP) concentrations and particle size distributions at the coastal Antarctic station Neumayer (70°39'S, 8°15'W) during two summer campaigns (from 20 January to 26 March 2012 and 1 February to 30 April 2014) and during polar night between 12 August and 27 September 2014 in the particle diameter (Dp) range from 2.94 nm to 60.4 nm (2012) and from 6.26 nm to 212.9 nm (2014). During both summer campaigns we identified all in all 44 new particle formation (NPF) events. From 10 NPF events, particle growth rates could be determined to be around 0.90±0.46 nm/h (mean ± std; range: 0.4 nm/h to 1.9 nm/h). With the exception of one case, particle growth was generally restricted to the nucleation mode (Dp < 25 nm) and the duration of NPF events was typically around 6.0±1.5 h (mean ± std; range: 4 h to 9 h). Thus in the main, particles did not grow up to sizes required for acting as cloud condensation nuclei. NPF during summer usually occurred in the afternoon in coherence with local photochemistry. During winter, two NPF events could be detected, though showing no ascertainable particle growth. A simple estimation indicated that apart from sulfuric acid, the derived growth rates required other low volatile precursor vapours.

(Table 6) Selenium isotopic composition of sediment samples from ODP Site 185-1149

Multiple-collector inductively coupled plasma mass spectrometry has been used for the precise measurement of the isotopic composition of Se in geological samples. Se is chemically purified before analysis by using cotton impregnated with thioglycollic acid. This preconcentration step is required for the removal of matrix-interfering elements for hydride generation, such as transitional metals, and also for the quantitative separation of other hydride-forming elements, such as Ge, Sb, and As. The analyte is introduced in the plasma torch with a continuous-flow hydride generation system. Instrumental mass fractionation is corrected with a "standard-sample bracketing" approach. By use of this new technique, the minimum Se required per analysis is lowered to 10 ng, which is one order of magnitude less than the amount needed for the N-TIMS technique. The estimated external precision calculated for the 82Se/76Se isotope ratio is 0.25? (2 sigma), and the data are reported as delta notation (?) relative to our internal standard (MERCK elemental standard solution). Measurements of Se isotopes are presented for samples of standard solutions and geological reference materials, such as silicate rocks, soils, and sediments. The Se isotopic composition of selected terrestrial and extraterrestrial materials are also presented. An overall Se isotope variation of 8? has been observed, suggesting that Se isotopes fractionate readily and are extremely useful tracers of natural processes.

Microsensor studies on Padina from a natural CO2 seep: implications of morphology on acclimation to low pH

Low seawater pH can be harmful to many calcifying marine organisms, but the calcifying macroalgae Padina spp. flourish at natural submarine carbon dioxide seeps where seawater pH is low. We show that the microenvironment created by the rolled thallus margin of Padina australis facilitates supersaturation of CaCO3 and calcifi-cation via photosynthesis-induced elevated pH. Using microsensors to investigate oxygen and pH dynamics in the microenvironment of P. australis at a shallow CO2 seep, we found that, under saturating light, the pH inside the microenvironment (pHME) was higher than the external seawater (pHSW) at all pHSW levels investigated, and the difference (i.e., pHME-pHSW) increased with decreasing pHSW (0.9 units at pHSW 7.0). Gross photosynthesis (Pg) inside the microenvironment increased with decreasing pHSW, but algae from the control site reached a threshold at pH 6.5. Seep algae showed no pH threshold with respect to Pg within the pHSW range investigated. The external carbonic anhydrase (CA) inhibitor, acetazolamide, strongly inhibited Pg of P. australis at pHSW 8.2, but the effect was diminished under low pHSW (6.4-7.5), suggesting a greater dependence on membrane-bound CA for the dehydration of HCO3- ions during dissolved inorganic carbon uptake at the higher pHSW. In comparison, a calcifying green alga, Halimeda cuneata f. digitata, was not inhibited by AZ, suggesting efficient bicarbonate transport. The ability of P. australis to elevate pHME at the site of calcification and its strong dependence on CA may explain why it can thrive at low pHSW.