Periodic Reporting for period 3 - SNOWISO (Signals from the Surface Snow: Post-Depositional Processes Controlling the Ice Core IsotopicFingerprint)
Berichtszeitraum: 2021-01-01 bis 2022-06-30
For the past 50 years, our use of ice core records as climate archives has relied on the fundamental assumption that the isotopic composition of precipitation deposited on the ice sheet surface determines the ice core water isotopic composition. Since the isotopic composition in precipitation is assumed to be governed by the state of the climate this has made ice core isotope records one of the most important proxies for reconstructing the past climate. Society is faced with the consequences of climate change. Knowledge about how the past climate has varied before anthropogenic emissions of greenhouse gasses will inform us about the internal dynamics, which govern the climate. Understanding these dynamics better will allow for climate predictions to improve.
New simultaneous measurements of snow and water vapor isotopes have shown that the surface snow exchanges with the atmospheric water vapor isotope signal, altering the deposited precipitation isotope signal. This severely questions the standard paradigm for interpreting the ice core proxy record and gives rise to the hypothesis that the isotope record from an ice core is determined by a combination of the atmospheric water vapor isotope signal and the precipitation isotope signal.
The SNOWISO project will verify this new hypothesis by combining laboratory and field experiments with in-situ observations of snow and water vapor isotopes in Greenland and Antarctica. This will enable us to quantify and parameterize the snow-air isotope exchange and post-depositional processes. SNOWISO will implement these results into an isotope-enabled Regional Climate Model with a snowpack module and benchmarked against in-situ observations. Using the coupled snow-atmosphere isotope model SNOWISO will establish the magnitude of the isotopic shift due to post-depositional processes under different climate conditions. This will facilitate the use of the full suite of water isotopes to infer past changes in the climate system, specifically changes in ocean sea surface temperature and relative humidity.
By establishing how the water isotope signal is recorded in the snow, the SNOWISO project will build the foundation for future integration of isotope-enabled General Circulation Models with ice core records; this opens a new frontier in climate reconstruction.
New simultaneous measurements of snow and water vapor isotopes have shown that the surface snow exchanges with the atmospheric water vapor isotope signal, altering the deposited precipitation isotope signal. This severely questions the standard paradigm for interpreting the ice core proxy record and gives rise to the hypothesis that the isotope record from an ice core is determined by a combination of the atmospheric water vapor isotope signal and the precipitation isotope signal.
The SNOWISO project will verify this new hypothesis by combining laboratory and field experiments with in-situ observations of snow and water vapor isotopes in Greenland and Antarctica. This will enable us to quantify and parameterize the snow-air isotope exchange and post-depositional processes. SNOWISO will implement these results into an isotope-enabled Regional Climate Model with a snowpack module and benchmarked against in-situ observations. Using the coupled snow-atmosphere isotope model SNOWISO will establish the magnitude of the isotopic shift due to post-depositional processes under different climate conditions. This will facilitate the use of the full suite of water isotopes to infer past changes in the climate system, specifically changes in ocean sea surface temperature and relative humidity.
By establishing how the water isotope signal is recorded in the snow, the SNOWISO project will build the foundation for future integration of isotope-enabled General Circulation Models with ice core records; this opens a new frontier in climate reconstruction.
The main tasks of SNOWISO for the period covered by this report have been focused on gathering field data from the top of the Greenland and Antarctic Ice Sheets. The field work has spanned three individual campaigns with two campaigns in Greenland at the EastGRIP station and one campaign in Antarctica at the Kohnen station. The data gathered have consisted of both atmospheric water vapor isotope and snowpack water isotope measurements in addition to measurements of water fluxes between the snow surface and the atmosphere. The snow samples have been transported back to our laboratories for water isotope analysis.
A main goal for the sampling of water isotope data on top of the ice sheets has been focused on closing the water isotope budget i.e. making sure that we are able to link changes in the snow pack isotopes with the flux of water isotopes between the snow surface and atmosphere. To achieve this goal SNOWISO has been developing novel methodology for directly measuring the water isotope flux by combining three-dimensional wind measurements with laser spectroscopy isotope measurements on the water vapor above the snow.
A second goal for the sampling and experiments has been focused on linking the snow surface water isotope signal with the climate signal that is being archived in the snow pack and subsequently is making up the ice core water isotope climate record. To do this, SNOWISO has collected more than ten thousand samples of the snow surface and snowpack in order to have a sufficient dataset to separate the climate process signal from the deposition noise originating when the snow is deposited and redistributed on the surface.
SNOWISO has also started comparing the field observations with climate simulations performed with a regional climate model with the purpose of subsequently include fractionation processes in the exchange between the snow and the atmosphere.
A main goal for the sampling of water isotope data on top of the ice sheets has been focused on closing the water isotope budget i.e. making sure that we are able to link changes in the snow pack isotopes with the flux of water isotopes between the snow surface and atmosphere. To achieve this goal SNOWISO has been developing novel methodology for directly measuring the water isotope flux by combining three-dimensional wind measurements with laser spectroscopy isotope measurements on the water vapor above the snow.
A second goal for the sampling and experiments has been focused on linking the snow surface water isotope signal with the climate signal that is being archived in the snow pack and subsequently is making up the ice core water isotope climate record. To do this, SNOWISO has collected more than ten thousand samples of the snow surface and snowpack in order to have a sufficient dataset to separate the climate process signal from the deposition noise originating when the snow is deposited and redistributed on the surface.
SNOWISO has also started comparing the field observations with climate simulations performed with a regional climate model with the purpose of subsequently include fractionation processes in the exchange between the snow and the atmosphere.
A first step in order to quantify the exchange between the snow surface and the atmosphere is to document whether snow fractionates during sublimation or not. This question is important to answer as it focuses on whether the isotopic composition is conserved or not. One of the hypotheses of SNOWISO is that snow does indeed fractionate during sublimation and that this is one of the processes giving rise to post-depositional alteration of the isotopic climate signal. A paper published last year by SNOWISO showed that isotopic fractionation must occur in order to explain the atmospheric diurnal variations. This paper is therefore a crucial result since it questions the basic premise of ice core climate reconstruction.
The analysis of the snow samples is ongoing, but preliminary results from the analysis indicate that the SNOWISO hypothesis that post-depositional processes are influencing the climate signal in the snow is supported by the data. Further analysis will quantify the importance of this process on the recorded mean climate signal in the ice core records and how to correct for this.
The analysis of the snow samples is ongoing, but preliminary results from the analysis indicate that the SNOWISO hypothesis that post-depositional processes are influencing the climate signal in the snow is supported by the data. Further analysis will quantify the importance of this process on the recorded mean climate signal in the ice core records and how to correct for this.