Abstract
Abstract. Using a spectrofluorimeter with 224-nm laser excitation and six emission bands from 300 to 420 nm to measure fluorescence intensities at 0.3-mm depth intervals in ice cores, we report results of the first comparative study of concentrations of microbial cells (using the spectrum of protein-bound tryptophan (Trp) as a proxy) and of aerosols with autofluorescence spectra different from Trp (denoted "non-Trp") as a function of depth in ice cores from West Antarctica (WAIS Divide and Siple Dome) and Greenland (GISP2). The ratio of fluxes of microbial cells onto West Antarctic (WAIS Divide) versus Greenland sites is 0.13±0.06; the ratio of non-Trp aerosols onto WAIS Divide versus Greenland sites is 0.16±0.08; and the ratio of non-sea-salt Ca2+ ions (a proxy for dust grains) onto WAIS Divide versus Greenland sites is 0.06±0.03. All of these are roughly comparable to the ratio of fluxes of dust onto Antarctic versus Greenland sites (0.08±0.05). By contrast to those values, which are considerably lower than unity, the ratio of fluxes of methanesulfonate (MSA) onto Antarctic versus Greenland sites is 1.9±0.4 and the ratio of sea-salt Na2+ ions onto WAIS Divide versus Greenland sites is 3.0±2. These ratios are more than an order of magnitude higher than those in the first grouping. We infer that the correlation of microbes and non-Trp aerosols with non-sea-salt Ca and dust suggests a largely terrestrial rather than marine origin. The lower fluxes of microbes, non-Trp aerosols, non-sea-salt Ca and dust onto WAIS Divide ice than onto Greenland ice may be due to the smaller areas of their source regions and less favorable wind patterns for transport onto Antarctic ice than onto Greenland ice. The correlated higher relative fluxes of MSA and marine Na onto Antarctic versus Greenland ice is consistent with the view that both originate largely on or around sea ice, with the Antarctic sea ice being far more extensive than that around Greenland.
Highlights
In recent years biologists have determined concentrations and taxa of microorganisms at a few depths in polar ice (Miteva et al, 2004; Priscu and Christner, 2004; Price, 2007) and permafrost (Gilichinsky, 2002)
Due to the labor involved in extracting microbes from ice and analyzing them under sterile conditions, no systematic study has heretofore been made of the concentrations of microbes and their rates of deposition onto the two polar caps as a function of depth. Because of their value as monitors of Earth’s climate, atmospheric gases such as CH4, N2O, 18O, and CO2 (Chappellaz et al, 1997; Sowers et al, 2003; Grootes et al, 1993; Bender et al, 1994; Petit et al, 1999), methanesulfonate (MSA) (Legrand et al, 1991; Saltzman et al, 1997), mineral dust (De Angelis et al, 1997; Delmonte et al, 2004) and major elements have been thoroughly studied as a function of depth in a number of ice cores from sites in Antarctica and Greenland
We have recently developed and employed a 224-nm laser scanning spectrofluorimeter to detect and map concentrations of microbes and non-microbial aerosols at depth intervals of 0.3 mm throughout long depth intervals in ice cores
Summary
In recent years biologists have determined concentrations and taxa of microorganisms at a few depths in polar ice (Miteva et al, 2004; Priscu and Christner, 2004; Price, 2007) and permafrost (Gilichinsky, 2002). Due to the labor involved in extracting microbes from ice and analyzing them under sterile conditions, no systematic study has heretofore been made of the concentrations of microbes and their rates of deposition onto the two polar caps as a function of depth. Fluorimetry: microbes and non-Trp aerosols at 1.5 ka (microbes in WAIS ice*) ÷ (microbes in GISP2 ice*) (non-Trp aerosols in WAIS ice*) ÷ (non-Trp aerosols in GISP2 ice*)
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