BADC Help File: CRYOSTAT Project Data

This file contains background information about the CRYOSTAT Project data held at the BADC.

1. Project Summary of CRYOSTAT: CRYOspheric STudies of Atmospheric Trends in stratospherically and radiatively important gases

Problems to be solved

Two of the most pressing environmental problems of the day are human-induced climate change and stratospheric ozone depletion. The latter itself has profound implications for climate. Both are largely the result of the release of numerous gases to the atmosphere from anthropogenic sources. Some such gases are strong infrared absorbers or “Greenhouse” gases (GHGs), others are ozone-depleting substances (ODSs). Although the Montreal Protocol, to which the EU is committed, has been successful in curtailing the release of some ODSs, others continue to rise. Even more intractable is the rise of GHGs, despite the United Nations Framework Convention on Climate Change, to which the EU is a signatory, and the proposed regulations outlined in the Kyoto agreement. Still others are precursors of tropospheric ozone, itself a powerful GHG, or they may interfere with the natural oxidation cycles responsible for removing many GHGs and ODSs from the atmosphere. Natural emissions of GHGs and ODSs, and natural processes affecting their distribution, are also an important factor. Yet the degree to which the natural chemistry-climate system has been perturbed by human activity is very poorly known. The changing nature of sources, such as soils, wetlands, vegetation, and marine microorganisms, and sinks such as atmospheric oxidation, oceanic and terrestrial uptake, etc. are little understood, yet are themselves sensitive to climate change. By reconstructing the evolution of the present polluted atmosphere from its “clean” pre-industrial beginnings we hope to better test, validate and improve our modelling capability in key aspects of atmospheric change. In this way we will contribute to the scientific underpinning of predicting the climatic effects due to changing emissions, and hence to better plan for the social and economic consequences of such change.

Scientific objectives and approach

CRYOSTAT will undertake the first combined measurements of virtually all significant GHGs (other than water vapour), ODSs, and related trace gases in contiguous firn and ice profiles, spanning as much as 200 years, from both the northern and southern polar ice caps. For many gases these will be their first attempted measurements in early 20th century and pre-industrial air. Using inter-linked computer models of both the transfer of gases from the atmosphere to firn and ice, and the atmospheric transport and chemistry of gases, we will reconstruct the evolution and distribution of these numerous gaseous species in the global atmosphere (hemispheric scale for the shorter-lived gases, inter-hemispheric and tropospheric-stratospheric distributions for the longer-lived gases). Sources and sinks, both natural and anthropogenic, will be identified and quantified using novel multiple-isotope analyses and using trace gas modelling. These reconstructed trends will be further used to determine histories of (a) radiative forcing from the measured GHGs, (b) stratospheric ozone, temperature and halogen loading, and (c) tropospheric ozone and related chemical processes.

Expected impacts

The outputs of CRYOSTAT will consist of a database (ultimately freely and publicly accessible through a central on-line archive) of global trends of numerous key atmospheric gases, including both those measured directly and those derived from models, from pre-industrial times to the present. It will also include assessments of the consequent impacts of these changes on radiative forcing, on stratospheric composition, chemistry, and temperature, on tropospheric chemical reactivity, and on the fluxes of certain key gases between environmental compartments. It will produce a set of refined modelling tools of wider utility to the atmospheric chemistry, global climate and glaciological research communities. It will see the improvement of techniques for determining gaseous composition from firn and ice materials. Finally, and most significantly, it will improve the knowledge base on interactions between atmospheric chemistry and climate, which will in turn improve the predictive capability of climate modellers, with important implications for policy-makers.

2. Scientific/technical objectives

CRYOSTAT aims to reconstruct the histories of virtually all significant radiatively-important “greenhouse” gases (GHGs) (other than water vapour) and stratospheric ozone-depleting substances (ODSs) (Table 1) over the past several decades and up to c. 200 years before the present day. Natural ‘background’ levels of these gases will be assessed, the progressive rise due to anthropogenic releases documented, and the impact on global atmospheric chemistry and climate from these changes examined.

Taking an holistic approach we aim to deconvolute the identity, both natural and man-made, and changing sources strengths of these gases to the atmosphere, by tracing their global atmospheric compositional histories on decadal and longer time scales, by determining correlations between hemispheres and between different gases, and by employing atmospheric models to explore source-sink relationships and to reconstruct other key non-measured chemical species. Powerful interpretive tools arise from the measurements of stable isotopes of important gases, including some novel isotopic measurements of CH4, N2O, and CO (also NMHCs as a pilot project) in ice and firn. Isotope ratios are variously determined by the modes of production of the gases (notably between biological and non-biological origins), and also by atmospheric sink processes. Since sources/sinks to and from the atmosphere are often common to a number of gases (e.g. biomass burning, atmospheric oxidation, etc.), this isotopic information also provides a generic tool with which to help interpret the aforementioned reconstructions of radiatively and stratospherically-important gases.

CRYOSTAT will be implemented through a series of combined firn and shallow ice drilling expeditions, providing the first ever such set of comprehensive gas measurements in contiguous firn and ice profiles from both hemispheres (i.e. Greenland and Antarctica). The extraction and measurement of multiple gas species from ice will be one of the major innovative aspects and technological challenges of the project. Year-round field studies will also take place in Antarctica to study the mechanisms controlling transport of atmospheric chemical constituents across the air-snow interface. This will allow refinement of existing firn air transport models, notably to account for thermal diffusion and convection effects in the upper firn, and so ensure accurate conversion of depth profiles into temporal trends. Year round measurements will also help define the seasonal cycle of shorter-lived gases, crucial for the proper interpretation and validation of firn and atmospheric chemistry models.

3. Chemical species measured

Table 1. Overview of principal GHGs, ODSs, and related gases to be directly measured in CRYOSTAT

*1. Indirect effects via changes in tropospheric ozone and oxidative lifetimes of key gases

4. Measurement locations

Details of the sampling sites are given in Table 2. Firn air, ice cores and ambient air samples will be collected at a northern hemispheric (NH) site (North GReenland Ice coring Project, NGRIP, site), and an Antarctic sites (Berkner Island). In addition to the Berkner Island samples either archived ice from Law Dome, Antarctica or, if a new field campaign transpires during the course of CRYOSTAT, firn and ice samples from this site, will be examined to compare and contrast with Berkner Island. NGRIP has one of the lowest mean annual temperatures of any location in the NH, and an absence of summer melting. This makes it one of the most ideal NH locations to retrieve air from firn and ice with minimal in situ chemical effects, and oldest possible air ages in firn. Berkner Island and Law Dome in Antarctica are sites with quite different characteristics. Berkner Island is located in the Atlantic sector whilst Law Dome is located on the opposite side of the continent in the Pacific sector. They are therefore influenced by quite different air masses, which will provide a valuable comparison and test of uniformity of atmospheric signals in the southern hemisphere (SH). More significantly, Law Dome experiences very high accumulation rates compared with Berkner Island. As a result, close-off of air occurs on a very short time scale at Law Dome. It is, therefore, possible to find ‘young’ air in ice at Law Dome with which to compare firn records at Berkner Island, whilst air extracted from ice at Law Dome should have narrow age spectra (predicted to be less than a decade at ‘ideal’ sites), yielding high resolution records.

Year-round sampling will take place at Halley. This is geographically ‘close’ to Berkner Island, but is essentially at sea level (ice shelf site). A new over-wintering “clean air” station (CASLAB) is being constructed at Halley enabling year-round collection of air and shallow firn air samples. Summer melting is rare and transitory at Halley making it acceptable for firn transport studies.

Table 2. Field site information

New CASLAB station and science team, Halley Bay

5. Modelling activities

Combining firn modelling with atmospheric modelling we will convert concentration-depth profiles at single geographic points (i.e. the drill sites) into

• local time trends (for all measured species)

• global time-varying latitudinal and altitudinal (troposphere and stratosphere) distributions for species with significant lifetimes relative to the inter-hemispheric exchange time, and with a primary focus on halocarbons.

The reconstructed time trends will then be used to gain knowledge on past budgets and lifetimes of the measured species. In particular, the CH4-CO-OH chemistry coupling will be examined in the light of the novel isotopic information. Histories of global emission rates (which compensate for the modelled trace gas sinks) and atmospheric lifetimes of medium and long-lived species will be determined, with a special focus on the halocarbons.

Using the reconstructed trends as constraints, the work will also be extended to gaseous species that cannot be measured in firn and ice, such as stratospheric and tropospheric ozone, and their reactive precursors (e.g. Cly, Bry, NOx, OH, etc.). Existing simulations of the pre-industrial atmosphere will be improved using the important new constraints provided by CRYOSTAT measurements. A fast 2-D model, with full coupling between radiation, dynamics and chemistry in the middle atmosphere will be used in an innovative attempt to continuously simulate the impacts of CO2, CH4, N2O, and halocarbon increases on stratospheric Cly, Bry, ozone, and temperature over the last century or more. A second 2-D model (no explicit treatment of the stratosphere but incorporating ocean-atmosphere cycling) will be used in addition, notably for short-lived gases with significant air-sea exchange. An eight-box global Eulerian transport model will be used specifically to help interpret the CH4 isotope measurements.

In a further modelling activity the CRYOSTAT reconstructions will be used, along with available archived in situ and satellite data, to validate and constrain a chemistry-general circulation model (GCM) and hence calculate trace gas trends on a global scale. These will include gaseous precursors of tropospheric ozone and acidifying compounds (e.g. NMHC, NOx, OH, etc.). Of particular utility will be a recently-established database of gridded emissions estimates that covers the 20th century at 10-year intervals up to 1970 and 5-year intervals thereafter. For the 1960-2000 period, European Centre for Medium-range Weather Forecasts (ECMWF) re-analyses will be used to assimilate meteorological data into the chemistry-GCM, to represent both meteorological and atmospheric chemical changes during this period. Climatological data will be used for earlier periods where appropriate.

As a final step in this sequence of interpretive studies, the potential impact of these changes on the radiative forcing of climate during the period of 19th and 20th century industrialisation will be determined. Radiative forcing due to individual target molecules will be assessed using detailed line-by-line and narrow band radiative transfer codes. Based on these calculations, the radiative forcing of climate change will be calculated with the coupled chemistry-GCM.

The outputs of CRYOSTAT will consist of a database (ultimately freely and publicly accessible) of depth-concentration profiles, local and global trends of numerous key atmospheric gases, including both those measured directly and those derived from models, from pre-industrial times to the present. It will also include assessments of the consequent impacts of these changes on radiative forcing, on stratospheric composition and chemistry, on tropospheric chemical reactivity, and on the fluxes of certain key gases between environmental compartments. It will produce a set of refined modelling tools of wider utility to the atmospheric chemistry, global climate and glaciological research communities. Finally, and perhaps most significantly, it will improve the knowledge base on interactions between atmospheric chemistry and climate, which will in turn improve the predictive capability of climate modellers, with important implications for policy-makers.

6. More details

For further details on firn sampling, etc., follow this link to the FIRETRACC/100 page.

Or return to the CRYOSTAT Home Page.