Sentences with phrase «firn air concentrations»

To infer the atmospheric record of GEM from firn air concentrations presented in Fig. 1, we determined a site specific, diffusivity - depth relationship.

Not exact matches

please read Z. Jaworowski's (with Segalstad and Ono) many papers on this subject of trapped gases in glaciers, where he discusses the over 20 mechanical and chemical processes that make accurate measurements impossible; even in shallow cores above the point where co2 is supposedly permanently trap in ice cavities in the firn, co2 concentrations are already 20 - 40 % lower than those measured in air at mauna loa.

Atmospheric gas concentrations over the past century measured in air from firn at the South Pole

However, both sediment records of atmospheric deposition of Hg2 + species at high northern latitudes and atmospheric GEM concentrations inferred from Greenland firn air support the conclusion that transfer of anthropogenic inorganic mercury through the atmosphere to terrestrial and marine reservoirs occurs on a large scale.

(A) Envelope of modeled concentrations for atmospheric GEM inferred from Summit firn air, central Greenland, during the last 66 years (gray area).

Thus, we conclude the firn air is a reliable archive to investigate historical changes of GEM atmospheric concentrations during the last ≈ 70 years.

We next applied a one - dimensional firn diffusion model (24) to reconstruct GEM concentrations at all depths in the firn air from different atmospheric histories.

Gaseous elemental mercury (GEM; Hg °) concentrations measured in firn air at Summit Station from 15 to 79.5 m depth.

Atmospheric GEM concentrations inferred from Greenland firn air reproduce the scarce GEM measurements reported from 1977 to 1980 across the Atlantic Ocean at mid-northern latitudes (7)(see Fig.

Hence, atmospheric GEM concentrations inferred from Greenland firn air and global anthropogenic Hg emissions have exhibited consistently similar trends during the most recent decades (Fig. 2), suggesting that the atmospheric reservoir of mercury at mid - and high - northern latitudes has been driven mainly by anthropogenic emissions during the last decades.

Atmospheric GEM concentrations, reconstructed from Greenland firn air and the worldwide production of mercury, peak at roughly the same time during the 1970s (Fig. 2).

While atmospheric GEM concentrations reconstructed from Summit firn air are higher than mean hemispheric values, they reproduce GEM levels observed shipboard between 40 ° and 50 ° N (see Fig.

Processes taken into account included (i) air mixing by pressure and temperature gradients down to a few meters below the surface (i.e., the so - called convection zone); (ii) molecular diffusion in the open pore space and gravitational fractionation (entrainment toward the deeper firn depends on concentration gradients, diffusivities, and molar mass); and (iii) a downward air flux in the open porosity zone due to bubble closure removing air from the open pores.

[71][72] Because of the way air is trapped in ice (pores in the ice close off slowly to form bubbles deep within the firn) and the time period represented in each ice sample analyzed, these figures represent averages of atmospheric concentrations of up to a few centuries rather than annual or decadal levels.