title: An Optical Dye Method for Continuous Determination of Acidity in Ice Cores.
abstract: The pH of polar ice is important for the stability and mobility of impurities in ice cores and can be strongly influenced by volcanic eruptions or anthropogenic emissions. We present a simple optical method for continuous determination of acidity in ice cores based on spectroscopically determined color changes of two common pH-indicator dyes, bromophenol blue, and chlorophenol red. The sealed-system method described here is not equilibrated with CO2, making it simpler than existing methods for pH determination in ice cores and offering a 10-90% peak response time of 45 s and a combined uncertainty of 9%. The method is applied to Holocene ice core sections from Greenland and Antarctica and compared to standard techniques such as electrical conductivity measurement (ECM) conducted on the solid ice, and electrolytic meltwater conductivity, EMWC. Acidity measured in the Greenland NGRIP ice core shows good agreement with acidity calculated from ion chromatography. Conductivity and dye-based acidity Hdye+are found to be highly correlated in the Greenland NEGIS firn core (75.38° N, 35.56° W), with all signals greater than 3σ variability coinciding with either volcanic eruptions or possible wild fire activity. In contrast, the Antarctic Roosevelt Island ice core (79.36° S, 161.71° W) features an anticorrelation between conductivity and Hdye+, likely due to strong influence of marine salts.
authors: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen , Copenhagen, Denmark.
authors: Helle Astrid
authors: HA
authors: Kjær
authors: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen , Copenhagen, Denmark.
authors: Paul
authors: P
authors: Vallelonga
authors: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen , Copenhagen, Denmark.
authors: Anders
authors: A
authors: Svensson
authors: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen , Copenhagen, Denmark.
authors: Magnus
authors: M
authors: Elleskov L Kristensen
authors: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen , Copenhagen, Denmark.
authors: Catalin
authors: C
authors: Tibuleac
authors: Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen , Copenhagen, Denmark.
authors: Mai
authors: M
authors: Winstrup
authors: Alfred Wegener Institute , Bremerhaven, Germany.
authors: Sepp
authors: S
authors: Kipfstuhl
mesh_terms: D000864:Antarctic Regions; D002845:Chromatography; D006116:Greenland; D006863:Hydrogen-Ion Concentration; D007053:Ice; D018707:Volcanic Eruptions
chemical_list: D007053:Ice