Factors controlling nitrate in ice cores: Evidence from the Dome C deep ice core

In order to estimate past changes in atmospheric NOx concentration, nitrate, an oxidation product of NOx, has often been measured in polar ice cores. In the frame of the European Project for Ice Coring in Antarctica (EPICA), a high-resolution nitrate record was obtained by continuous flow analysis (CFA) of a new deep ice core drilled at Dome C. This record allows a detailed comparison of nitrate with other chemical trace substances in polar snow under different climatic regimes. Previous studies showed that it would be difficult to make firm conclusions about atmospheric NOx concentrations based on ice core nitrate without a better understanding of the factors controlling NO3− deposition and preservation. At Dome C, initially high nitrate concentrations (over 500 ppb) decrease within the top meter to steady low values around 15 ppb that are maintained throughout the Holocene ice. Much higher concentrations (averaging 53 ppb) are found in ice from the Last Glacial Maximum (LGM). Combining this information with data from previous sampling elsewhere in Antarctica, it seems that under climatic conditions of the Holocene, temperature and accumulation rate are the key factors determining the NO3− concentration in the ice. Furthermore, ice layers with high acidity show a depletion of NO3−, but higher concentrations are found before and after the acidity layer, indicating that NO3− has been redistributed after deposition. Under glacial conditions, where NO3− shows a higher concentration level and also a larger variability, non-sea-salt calcium seems to act as a stabilizer, preventing volatilization of NO3− from the surface snow layers

The specific surface area and chemical composition of diamond dust near Barrow, Alaska

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95687/1/jgrd17349.pd

Impact of Local Insolation on Snow Metamorphism and Ice Core Records

Local insolation is a major component of the energy balance at the surface of an ice sheet and causes temperature gradient metamorphism (TGM) of snow and firn. TGM is one of the dominant processes changing the structure of dry snow. We present a physically based model that calculates insolation-induced relative changes in TGM in the past. The results indicate that TGM at Dome Fuji varied by up to a factor of 2 over the past 350ka, and is driven predominately by the precession-band variability in local summer solstice insolation. At Dome Fuji, the impact of glacial-interglacial temperature changes on TGM is almost fully compensated by synchronous, opposite changes in accumulation rate, which determines the exposure time of a snow layer to TGM. Even small remaining temperature signals in TGM can cause phase shifts between TGM and local summer solstice insolation of several ka. This directly affects the accuracy of orbitally tuned ice core time scales using O2/N2 or total air content records, as this dating method is based on the assumption of synchronicity between TGM and insolation. It must be assumed that the strong variability in TGM will also be reflected in physical and chemical ice core records by e.g. modulating the volatilization of reversibly deposited species including the stable isotopes of water. Sublimation and thus accumulation rates are also closely linked to TGM, affecting the concentrations also of irreversibly deposited non-volatile impurities. Thus, the effect of a local, post-depositional contribution of TGM on ice core records must be quantified prior to their interpretation in terms of larger scale climate variability in the orbital frequency bands.III. Firn densification, close-off and chronolog

Sensitivity of hydrogen peroxide (H2O2) and formaldehyde (HCHO) preservation in snow to changing environmental conditions: Implications for ice core records

Sensitivity studies with physically based numerical air–snow–firn transfer models for formaldehyde (HCHO) and hydrogen peroxide (H2O2) show that even though nonlinear processes determine the preservation of HCHO and H2O2 in snow and firn, changes in atmospheric mixing ratios are linearly recorded in ice cores under otherwise constant environmental conditions. However, temperature, snowpack ventilation, and rate and timing of snow accumulation also affect the ice core records of reversibly deposited species and must be considered when inferring past atmospheric mixing ratios. The results of the sensitivity studies allow quantitative separation of these factors in ice core records. Past temperatures and accumulation rates are generally determined in ice cores and the preservation of HCHO and H2O2 is not highly sensitive to snowpack ventilation, leaving changes in seasonality of snow accumulation as the main source of uncertainty in a reconstruction of past atmospheric mixing ratios

A new Continuous Flow Analysis (CFA) system for high-resolution field measurements on ice cores

Continuous flow analysis (CFA) is a well-established method to obtain information about impurity contents in ice cores as indicators of past changes in the climate system. A section of an ice core is continuously melted on a melter head supplying a sample water flow which is analyzed online. This provides high depth and time resolution of the ice core records and very efficient sample decontamination as only the inner part of the ice sample is analyzed. Here we present an improved CFA system which has been totally redesigned in view of a significantly enhanced overall efficiency and flexibility, signal quality, compactness, and ease of use. These are critical requirements especially for operations of CFA during field campaigns, e.g., in Antarctica or Greenland. Furthermore,a novel device to measure the total air content in the ice was developed. Subsequently, the air bubbles are now extracted continuously from the sample water flow for subsequent gas measurements

Atmosphere-to-snow-to-firn transfer studies of HCHO at Summit, Greenland

. Formaldehyde (HCHO) measurements in snow, firn, atmosphere, and air in the open pore space of the firn (firn air) at Summit, Greenland, in June 1996 show that the top snow layers are a HCHO source. HCHO concentrations in fresh snow are higher than those in equilibrium with atmospheric concentrations, resulting in HCHO degassing in the days to weeks following snowfall. Maximum HCHO concentrations in firn air were 1.5-2.2 ppbv, while the mean atmospheric HCHO concentration 1 m above the surface was 0.23 ppbv. Apparent HCHO fluxes out of the snow are a plausible explanation for the discrepancy between the 0.1 ppbv atmospheric concentration predicted by photochemical modeling and the measurements. HCHO in deeper firn is near equilibrium with the lower tropospheric HCHO concentration at the annual average temperature. Thus HCHO in ice may in fact be linearly related to multiyear average atmospheric concentrations through a temperature dependent partition coe#cient. Introduction The main..

Past atmospheric composition and chemistry from ice cores - progress and prospects

Ice cores provide the most direct evidence available about the past atmosphere. For long-lived trace gases, ice cores have provided clear evidence that in the last two centuries, concentrations of several greenhouse gases have risen well outside the natural range observed in the previous 650 000 years. Major natural changes are also observed between cold and warm periods. Aerosol components have to be interpreted in terms of changing sources, transport and deposition. When this is done, they can also supply evidence about crucial aspects of the past environment, including sea ice extent, trace element deposition to the ocean, and about the aerosols available for cloud nucleation, for example. It is much more difficult to extract information about shorter-lived chemical species. Information may be available in components such as nitrate and formaldehyde, but to extract that information, detailed modern atmospheric studies about air to snow transfer, preservation in the ice, and the link between the polar region boundary layer and other parts of the atmosphere are urgently required

Measurements of hydrogen peroxide and formaldehyde exchange between the atmosphere and surface snow at Summit, Greenland

Tower-based measurements of hydrogen peroxide (H2O2) and formaldehyde (HCHO)exchange were performed above the snowpack of the Greenland ice sheet. H2O2 andHCHO fluxes were measured continuously between June 16 and July 7, 2000, at theSummit Environmental Observatory. The fluxes were determined using coilscrubber-aqueous phase fluorometry systems together with micrometeorologicaltechniques. Both compounds exhibit strong diel cycles in the observed concentrationsas well as in the fluxes with emission from the snow during the day and the eveningand deposition during the night. The averaged diel variations of the observed fluxeswere in the range of +1.3 · 10^13 molecules m^-2 s^-1 (deposition) and-1.6 · 10^13 molecules m^-2 s^-1 (emission) for H2O2 and +1.1 · 10^12molecules m^-2 s^-1 and -4.2 · 10^12 molecules m^-2 s^-1 for HCHO, while the netexchange per day for both compounds were much smaller. During the study period of22 days on average 0.8 (+4.6/-4.3) · 10^17 molecules m^-2 of H2O2 were depositedand 7.0 (+12.6/-12.2) · 10^16 molecules m^-2 of HCHO were emitted from the snowper day. A comparison with the inventory in the gas phase demonstrates that theexchange influences the diel variations in the boundary layer above snow covered areas.Flux measurements during and after the precipitation of new snow shows that less than16 % of the H2O2 and more than 25 % of the HCHO originally present in the new snowwere available for fast release to the ABL within hours after precipitation. This releasecan effectively disturb the normally observed diel variations of the exchange betweenthe surface snow and the atmosphere, thus perturbing also the diel variations ofcorresponding gas phase concentrations

Dust and calcium record in calculated for ice core EPICA Dome C

Ice core data from Antarctica provide detailed insights into the characteristics of past climate, atmospheric circulation, as well as changes in the aerosol load of the atmosphere. We present high-resolution records of soluble calcium (Ca2+), non-sea-salt soluble calcium (nssCa2+), and particulate mineral dust aerosol from the East Antarctic Plateau at a depth resolution of 1 cm, spanning the past 800 000 years. Despite the fact that all three parameters are largely dust-derived, the ratio of nssCa2+ to particulate dust is dependent on the particulate dust concentration itself. We used principal component analysis to extract the joint climatic signal and produce a common high-resolution record of dust flux. This new record is used to identify Antarctic warming events during the past eight glacial periods. The phasing of dust flux and CO2 changes during glacial-interglacial transitions reveals that iron fertilization of the Southern Ocean during the past nine glacial terminations was not the dominant factor in the deglacial rise of CO2 concentrations. Rapid changes in dust flux during glacial terminations and Antarctic warming events point to a rapid response of the southern westerly wind belt in the region of southern South American dust sources on changing climate conditions. The clear lead of these dust changes on temperature rise suggests that an atmospheric reorganization occurred in the Southern Hemisphere before the Southern Ocean warmed significantly