Analyzing biases of nitrogen contents and δ^(15)N values arising from acidified marine sediments with different CaCO_3 concentrations

In some studies, the researchers pretreated and measured organic carbon, nitrogen and their isotopes（δ^（13）C and δ^（15）N） of marine sediment together, to save costs and resources of analysis. However, the procedure of acidification to remove inorganic carbon for analysing δ^（13）C can affect the values of nitrogen and δ^（15）N, and the biases vary a lot depending on the CaCO_3 contents of sediments. In this study, the biases of total nitrogen（TN）and δ^（15）N values arising from acidified sediments were compared between the CaCO_3-poor（1%–16%） and CaCO_3-rich（20%–40%） samples. TN and δ^（15）N values were altered during acid treatment（without centrifugation） that possibly led to N-containing compounds volatilization. For CaCO_3-poor samples, acidification led to a range of 0%–40% TN losses and 0‰–2‰ shift in δ^（15）N values; and 10%–60% TN losses and 1‰–14‰ shift in δ^（15）N values for CaCO_3-rich samples. The biases from most samples exceeded the precision of the instrument（0.002% for TN and 0.08‰ for δ^（15）N）, and high biases could mislead our judgment for the environmental implication of the data. Thus,avoiding co-analysis of organic carbon, nitrogen and their isotopes（δ^（13）C and δ^（15）N） in sediments, even for CaCO_3-poor marine sediments, is necessary.

Experimental Investigation of the Electronic Structure of Ca_(0.83)La_(0.17)Fe_(2)As_(2)

We performed a combined angle-resolved photoemission spectroscopy and scanning tunneling microscopy study of the electronic structure of electron-doped Ca_(0.83)La_(0.17)Fe_(2)As_(2).A surface reconstruction associated with the dimerization of As atoms is observed directly in the real space,as well as the consequent band folding in the momentum space.Besides this band folding effect,the Fermi surface topology of this material is similar to that reported previously for BaFe_(1.85)Co_(0.15)As_(2),with Γ-centered hole pockets quasi-nested to M-centered electron pockets by the antiferromagnetic wave vector.Although no superconducting gap is observed by ARPES possibly due to low superconducting volume fraction,a gap-like density of states depression of 7.7±2.9 meV is determined by scanning tunneling microscopy.