Periodic Reporting for period 3 - SNOWISO (Signals from the Surface Snow: Post-Depositional Processes Controlling the Ice Core IsotopicFingerprint)
Periodo di rendicontazione: 2021-01-01 al 2022-06-30
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.
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.
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.