A re-assessment of nickel-doping method in iron isotope analysis on rock samples using multi-collector inductively coupled plasma mass spectrometry

Element doping has been proved to be a useful method to correct for the mass bias fractionation when analyzing iron isotope compositions.We present a systematic re-assessment on how the doped nickel may affect the iron isotope analysis in this study by carrying out several experiments.We find three important factors that can affect the analytical results,including the Ni:Fe ratio in the analyte solutions,the match of the Ni:Fe ratio between the unknown sample and standard solutions,and the match of the Fe concentration between the sample and standard solutions.Thus,caution is required when adding Ni to the analyte Fe solutions before analysis.Using our method,theδ56Fe and δ57Fe values of the USGS standards W-2 a,BHVO-2,BCR-2,AGV-2 and GSP-2 are consistent with the recommended literature values,and the long-term(one year) external reproducibility is better than 0.03 and 0.05‰(2 SD) for δ56Fe and δ57Fe,respectively.Therefore,the analytical method established in our laboratory is a method of choice for high quantity Fe isotope data in geological materials.

Performance evaluation of fixed-station sampling design for a fishery-independent survey with multiple objectives

Fixed-station sampling design was widely used in fishery-independent surveys because of its characteristics of convenient sampling station setting,but the non-probabilistic(fixed)nature made it more uncertainty of drawing inferences on population.The performance of fixed-station sampling design for multispecies survey has not been evaluated,and we are uncertain if the design could detect the temporal trends of different populations in multispecies fishery-independent survey.In this study,spatial distribution of abundance indices for three species with different spatial distribution patterns including small yellow croaker(Larimichthys polyactis),whitespotted conger(Conger myriaster)and Fang’s blenny(Enedrias fangi)were simulated using ordinary kriging interpolation as the“true”population distribution.The performance of fixed-station sampling design was compared with simple random sampling design by resampling the simulated“true”populations in this simulation study.The results showed that the fixed-station sampling design had the power to detect the seasonal trends of species abundance.The effectiveness of fixed-station sampling design were different in different species distribution patterns.When the species had even distribution,fixed-station sampling design could get high quality abundance data;when the distribution was uneven with heterogeneity or patchiness,fixed-station sampling design tended to underestimate or overestimate the abundance.Evidently,the estimates of abundance index based on the fixedstation sampling design must be calibrated cautiously while applying them for fisheries stock assessment and management.This study suggested that fixed-station sampling design could catch the temporal dynamics of population abundance,but the abundance estimates from the fixed-station sampling design could not be treated as the absolute estimates of populations.