Isotopic constraints on past ozone layer in polar ice (ISOL-ICE)

The ozone layer shields all land-based life forms from harmful ultraviolet radiation; and indirectly influences the climate at the Earth's surface, including temperature and winds, particularly near the poles. Man-made halocarbons, used for example in refrigerators and spray cans, were released to the atmosphere and have caused significant destruction of the ozone layer since the late 1970s, especially above Antarctica during spring-time. Because the use of many halocarbons was banned by the 1989 Montreal Protocol, the ozone layer is expected to recover to the conditions of the 1960s and early 1970s within this century.

However, the thickness of the ozone layer is also influenced by natural causes, which are less well understood and which make predictions of future ozone and climate less certain. Natural causes include variations in the sun's activity, volcanic eruptions, release of biogenic halocarbons and atmospheric circulation. Currently there is very little information on the natural variability of the ozone layer over historic time scales, i.e. before direct observations started in the early 20th century. However, understanding the natural variability of the ozone layer and the underlying causes is necessary to evaluate the effectiveness of climate and ozone policy options. It is also necessary in order to improve predictions of ground level UV radiation, which is recognized as an environmental carcinogen and a major concern for human health.

One way to go back in time beyond the era of modern measurements is the use of proxies measured in polar ice cores. Apart from a recently proposed biomarker there are no quantitative proxies of past UV radiation. Here we propose to measure the isotopes of nitrogen and oxygen in the nitrate ion in polar ice to reconstruct past ultraviolet radiation and therefore the ozone layer. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. In the very dry regions of inner Antarctica snow is exposed to sunlight for many months before being buried by snowfall. During that exposure the nitrate in the snow is decomposed by solar UV radiation; during that process the heavier nitrogen isotopes in nitrate are observed to stay preferentially in the snow, whereas the lighter ones escape to the atmosphere above. That fractionation depends on the wavelength and duration of the UV radiation. We hypothesize that once the nitrate in snow is buried at depth, it preserves an isotopic fingerprint of down-welling UV radiation and therefore of the thickness of the ozone layer.

We propose to collect a shallow ice core from East Antarctic Plateau, where low accumulation rates prevail, to develop and apply a new ice core proxy based on the stable isotopes of nitrate, to constrain trends in the ozone layer above Antarctica over the last 1kyr. To do this, we will calibrate the ice core signal with observations of the ozone layer above Antarctica since the 1950s, and then extrapolate that relationship to the more distant past.

Using numerical models we will investigate the underlying causes of the ice core based reconstruction of past variability in the ozone layer. Particular questions we will attempt to answer include: has stratospheric ozone changed in the past; and how did solar variability, natural emissions of halocarbons, or volcanic eruptions contribute to the reconstructed trends?

The main concrete results of this project are (1) the first ever millennial-scale reconstruction of stratospheric ozone and terrestrial UV radiation at high temporal resolution and (2) analysis of underlying causes of the reconstructed variability. Thus, the main immediate beneficiaries of our research are academic ones. We have identified in particular:

a) atmosphere and cryosphere scientists studying air-snow-ice interactions
b) atmospheric scientists studying stratospheric ozone and natural impacts on its variability at global scales
c) paleoclimate scientists developing proxies in ice cores and other archives for past UV radiation
d) solar physicists investigating the sun's activity in the recent and more distant past

Our route to these people is the normal academic one of scientific papers and conference presentations.

Further beneficiaries include also policymakers (e.g. DECC, DEFRA). This is because assessing the natural variability of the ozone layer beyond the instrument era is critical to evaluate the effectiveness of climate and ozone protection policy options. In particular, natural factors controlling the ozone layer still carry significant uncertainties as stated by the WMO 2014 report on ozone. Therefore an improved understanding of the natural background variability of stratospheric ozone will eventually reduce uncertainties in future ozone projections under climate change and recovery scenarios. Furthermore, the IPCC 2013 Working Group 1 report highlights that large climate forcing uncertainties are associated with solar variability. Narrowing these uncertainties will help us to better understand the various contributions to variability in the historical climate record as well as to reduce the uncertainty range in projections.
Such findings will emerge as the sum of inputs from many proposals (including this one) that will be aggregated by BAS and NCAS. PI Frey has started discussions with the current Science Engagement Lead at DECC on how best to present findings from this and related proposals, with one option being a policy briefing paper led by BAS.

Another aspect of impact is that we as scientists play a role in making science accessible and exciting to the wider public and to students. Regarding this project, BAS has a strong track record for public outreach explaining the science and societal relevance of the ozone layer. BAS is part of the network of Ambassadors for Science with particular emphasis on outreach to schools. For such events, scientists often seek material with a wide appeal. We will gather highly visual footage while working on the East Antarctic Plateau, in particular of the drilling work. Film footage as well as photographs will be made available to all staff within BAS as an outreach resource.

PI Frey is an active STEM ambassador with a strong record of outreach activities related to scientific research in the polar regions. He will follow at least three different routes to achieve impact with a broader audience: 1) through school talks and seminars given to school teachers; 2) through skype lessons given to school children of various age groups, and promoted and implemented by the company Digital Explorer; 3) through a display at the annual Cambridge Science Week. This is a major event where literally thousands of people of all ages gain access to Cambridge University departments to learn about scientific research. PI Frey has set up a highly educative classroom experiment he displays during the Cambridge Science Week engaging hundreds of visitors in a discussion about properties of the gas ozone, both life saving at altitude and life threatening at the ground level. This activity will be further expanded as first results emerge from this project.