Adding water tracers to the UK Earth System Model

What this project does

The project adds water tracers, including stable isotopes, to the UK Earth system model (UKESM2). These tracers follow water through the model’s hydrological cycle.

Why this matters

Stable water isotopes provide long-term records of climate change. Ice core measurements can reveal temperature changes over glacial-interglacial cycles.

Including isotopes in climate models helps establish relationships between isotopic concentrations and climate variables. It also allows evaluation of past climate simulations and improves understanding of the hydrological cycle.

How the project works

The model development project adds code to UKESM2 which will allow users to run with water tracers and isotopes.  This will allow studies into climate and hydrology:

• Relationship assessment: comparing isotopic concentrations with climate variables to improve interpretation of ice core data.
• Palaeoclimate evaluation: comparing model output with ice core measurements to assess model accuracy.
• Hydrological cycle analysis: tracking water pathways, including sources and movement, to better understand model processes.

Stable isotope properties: water molecules contain hydrogen and oxygen. Isotopic variations alter molecular mass from 18 to 22, providing a record that does not decay over time.

Credit: Lesleigh Anderson and Jeremy Havens, USGS

Science objectives

The project aims to:

• Track water and water isotopes through the atmosphere, land, ocean and sea ice model components

• Investigate precipitation sources and how they might change

• Evaluate palaeoclimate simulations against ice core data

Who is involved

The project is led by BAS as part of its National Capability programme (SURFEIT and PRESCIENT), with collaboration with the Met Office plus the SWAIS-2C, ECO-ICE and EU P2F projects.  The work started under the EU-TIPES project.

• The first stage of this work is to add a water tracer to the atmosphere and land surface component models. The tracer will track water through the hydrological cycle of the models.
• The development will be made so that the model can run with a number of different water tracers.
• Isotopic fractionation processes will then be added to allow a water tracer to become a stable water isotope.
• Water tracers/isotopes will also be added to the ocean and sea ice model components.

Update on progress:

• The water tracer code for the atmosphere and land surface components is now complete and being used to investigate sources of precipitation in the atmosphere model.
• Isotopic fractionation processes are currently being added to the atmosphere and land components. We anticipate completion of this stage later in 2025.

External collaborators:

Merve Gorguner – University of Bristol

Simon Wilson – National Centre for Atmospheric Science

Jeff Ridley – Met Office

Paul Valdes – University of Bristol

Grenville Lister – National Centre for Atmospheric Science

Comparison of the oxygen isotope signatures in speleothem records and iHadCM3 model simulations for the last millennium – British Antarctic Survey – Publication

Antarctic Ice Sheet elevation impacts on water isotope records during the Last Interglacial – British Antarctic Survey – Publication

Sea ice feedbacks influence the isotopic signature of Greenland ice sheet elevation changes: Last interglacial HadCM3 simulations – British Antarctic Survey – Publication

Using ice cores and Gaussian process emulation to recover changes in the Greenland Ice Sheet during the last interglacial – British Antarctic Survey – Publication

Ice Cores and Emulation: Learning More About Past Ice Sheet Shapes. – British Antarctic Survey – Publication

Impact of abrupt sea ice loss on Greenland water isotopes during the last glacial period – British Antarctic Survey – Publication

Investigating the 8.2 ka event in northwestern Madagascar: insight from data–model comparisons – British Antarctic Survey – Publication

On recovering Last Interglacial changes in the Antarctic ice sheet – British Antarctic Survey – Publication

Simulating the 128 ka Antarctic climate response to Northern Hemisphere ice sheet melting using the isotope-enabled HadCM3 – British Antarctic Survey – Publication

Simulating the Last Interglacial Greenland stable water isotope peak: the role of Arctic sea ice changes – British Antarctic Survey – Publication

The spatial structure of the 128 ka Antarctic sea ice minimum – British Antarctic Survey – Publication

Antarctic last interglacial isotope peak in response to sea ice retreat not ice-sheet collapse – British Antarctic Survey – Publication

Reconstructing paleosalinity from δ18O: Coupled model simulations of the Last Glacial Maximum, Last Interglacial and Late Holocene – British Antarctic Survey – Publication

Warm climate isotopic simulations: what do we learn about interglacial signals in Greenland ice cores? – British Antarctic Survey – Publication

Differing source water inputs, moderated by evaporative enrichment, determine the contrasting δ18OCELLULOSE signals in maritime Antarctic moss peat banks – British Antarctic Survey – Publication

Antarctic interglacial climate variability and implications for changes in ice sheet topography – British Antarctic Survey – Publication

Sea surface temperature controls on warm climate water isotopes in Greenland ice cores – British Antarctic Survey – Publication

On high-resolution sampling of short ice cores: dating and temperature information recovery from Antarctic Peninsula virtual cores – British Antarctic Survey – Publication

Stable water isotopes in HadCM3: isotopic signature of El Nino-Southern Oscillation and the tropical amount effect – British Antarctic Survey – Publication

Evidence for warmer interglacials in East Antarctic ice cores – British Antarctic Survey – Publication