Subglacior / ERC Ice&Lasers

SUBGLACIOR builds on the substantial technological progress in laser physics provided by the development of an ultra-sensitive trace gas detection technique invented by the LIPhy partner and its applications in the atmospheric monitoring domain (research groups of Romanini, Kassi, and Kerstel). Using near-to-mid infrared laser spectroscopy, it is now possible to accurately and precisely measure trace gas concentrations as well as the water isotopic composition on very small gas flows and with a very compact instrument. The patented methodology (called OFCEAS) relies on optical feedback in a high-finesse cavity, which provides a very high sensitivity in a compact and robust spectrometer.

A promotional video gives a graphic summary of the project.

Background

Ice cores are exceptional archives of past climate dynamics and unique in documenting changes in atmospheric composition, including greenhouse gas concentrations. Ice core data are crucial to characterize carbon cycle–cryosphere–climate feedbacks and test the realism of Earth system models. Since the 1960s, intensive logistical, drilling, technological and scientific efforts have been dedicated to the recovery and analysis of ice cores from polar ice sheets. The Environmental Geosciences and Glaciology Laboratory (LGGE) in Grenoble as well as the Laboratory of Climate Science (LSCE) in Saclay, France, have been among the pionneers of this work. Through European cooperations since the early 1990s, the oldest ice cores in Greenland and Antarctica have been recovered. In Greenland, the international NorthGRIP project, reaching 3085 m of depth, covers one full climatic cycle back to the end of the last interglacial period (North GRIP Project Members 2004). In Antarctica, the European Project for Ice Core drilling in Antarctica (EPICA) has completed in 2004 the Dome C deep drilling, under technical leadership of LGGE, reaching 3260 m of depth and offering an exceptional 800,000-year archive of climate and atmospheric composition evolution (Jouzel, et al., 2007).

Ice cores had iconic contributions to climate change research: they revealed the occurrence of 25 abrupt climate changes (called Dansgaard-Oeschger events) during the last glacial period in Greenland (Dansgaard et al, 1993; North GRIP Project Members, 2004), reaching a magnitude of 8 to 16°C within decades to centuries (Severinghaus et al, 1999; Landais et al, 2004). The synchronisation of Greenland and Antarctic ice cores, made possible thanks to the global methane fluctuations, has evidenced a systematic Antarctic see-saw counterpart of Dansgaard-Oeschger events, reflecting global reorganization in ocean meridional overturning circulation (EPICA Community Members, 2006). Ice cores have revealed the strong glacial-interglacial coupling of climate and carbon cycle, first evidenced from the Vostok ice core over 400,000 years (Petit et al, 1999), and further strengthened by the analysis of the EPICA Dome C ice core over 800,000 years (Lüthi et al, 2008; Loulergue et al., activities on background greenhouse gas levels and many other pollutants in the atmosphere (e.g., 2008; Hansen et al, 2008). Ice core have allowed one to quantify the impact of anthropogenic activities on background greenhouse gas levels and many other pollutants in the atmosphere (see, e.g., MacFalring Meure et al., 2006, and references therein).

Still there is much more to learn from ice sheets, notably by going further back in time. From 1.5 million years ago to 800,000 years ago, the pattern of climate variability has undergone a dramatic reorganization, with a shift from the “obliquity world” characterised by 40,000 year weak glacial - interglacial cycles to the “100,000-year cycles” with longer and stronger glacial interglacial cycles. This insight comes primarily from low temporal resolution marine sediment studies (e.g. Lisiecki and Raymo, 2005). The reasons for this major climate reorganization remain debated and may be intrinsic to the climate – cryosphere - carbon cycle feedbacks. In addition, a longer record may reveal the presence of the 400,000-year excentricity cycle, so far not observed in ice cores, and absent or unexpectedly weak in marine records. In order to evaluate existing hypotheses, there is an urgent need to obtain accurate, high temporal resolution and well-dated records of Antarctic climate and global atmospheric composition. Extending the ice core records back to 1.5 million years ago is thus critical to understand the feedbacks involved in the most recent and unexplained climate transition from the “40-kyr world” to the “100-kyr world”, calling for a changing climate sensitivity.

Such old ice must lie in some places of the lowest 10% of the Antarctic ice sheet. At these depths, ice flow and bedrock topography can produce shearing and mixing of the originally horizontal ice stratigraphic layers, thus rendering impossible any climatic reconstruction from the measured signals, as evidenced for instance by the mixed signals archived in the deepest 60 m of the EPICA Dome C ice core (Jouzel et al., 2007), or by the inclined layers found at Dome Fuji (Goto-Azuma, EGU, EGU2008-A-02971; CL25-1TU3O-001). In addition, warm temperature at the ice/bedrock interface could accelerate the self-diffusion of water isotopes between nearby stratigraphic layers and smooth out the true climatic signal (Pol et al., 2010). Relatively cold interfaces should thus be targeted to recover a suitable climatic archive. Currently available radar measurements from the surface do not allow one to evaluate with confidence the possible occurrence of shearing and folding in the deepest sections of the ice sheet. Using conventional electromechanical drilling systems, it would take at least four (very costly) field seasons to recover such deep ice in a promising place, to eventually and ultimately find out that the target ice prior to the last million years is missing. For instance, the much successful EPICA European drilling at Concordia Station started in December 1999 and reached bedrock at 3260 m of depth five years later. It turned out at that time that the lowest ~80 m of ice were stratigraphically disturbed and not interpretable, although fortunately the upper 3180 m provided a fantastic record. Based on significant technological advances and unconventional approaches, the SUBGLACIOR project aims at projecting forward the ice core research by inventing, constructing and testing a in-situ probe to evaluate, within a single season in Antarctica, if a target site is suitable to recover ice as old as 1.5 million years.

The SUBGLACIOR probe will make its own way into the ice and, relying on innovative French laser technology, will measure in real time and down to bedrock the depth profiles of the ice dD water isotopes, as well as the trapped gas CH₄ concentration, and possibly other gas signals depending on progresses of this laser technology. dD of the melted ice will deliver the baseline climatic signal in the deep ice. Its evolution with depth will allow us to differentiate ice corresponding to interglacial or glacial conditions, to basically “count” the climatic cycles back in time, and to compare them to marine reference records (e.g. Lisiecki and Raymo, 2005). Atmospheric CH₄ shows large changes between glacial and interglacial states (typically from 350 to 800 ppbv). It is an indirect tracer of northern hemisphere climate. Being recorded in trapped bubbles and clathrates, its changes are shifted with depth compared with concomitant climatic changes recorded in dD of the ice because of firnification processes. The observation of such a depth shift makes a primary indicator that the ice layers are still in good stratigraphic order (Chappellaz et al., 1997). Therefore with these two signals, we will already obtain three relevant pieces of information:

(1) the time span of the ice depth,

(2) the integrity of the ice record, and

(3) key climate and atmospheric signals back to 1.5 Myr ago.

The Partners

SUBGLACIOR will build on the unique experience of four partners. The LGGE has decades of experience with ice-core drilling technology, instrument integration and remote operation in ice sheets, while the LIPhy is the inventor of the ultra-sensitive laser OFCEAS technique to measure atmospheric trace gases and isotopic composition. The LSCE is a world leader in measuring water isotopes and will be a key partner to deal with possible isotopic fractionation during water sample handling. The DT-INSU is a central operator in France for developing unique scientific instruments and prototypes for marine and atmospheric sciences. Together, we will build a novel probe, able to make its own way into the ice, in an energy efficient manner, at a relatively fast pace, and in a way that the probe can be recovered back to the surface after the measurement campaign. The probe will include an electromechanical drilling head and a small thermal head to melt the ice which will be introduced into the laser spectrometer after membrane separation of the gases. Embarked electronics will transmit the processed data to the surface. The complete equipment will be small enough to enable its transportation into the field with a medium size aircraft. The probe will be designed to be able to reach a depth of up to 4000 m in less than 90 days in the field. In the framework of SUBGLACIOR, the probe will be validated at Concordia station on the Antarctic plateau, where the deployment will profit of the reliable French and Italian logistics, and the signals obtained would be directly compared to the existing data from the EPICA deep drilling operation.

In a high gain/high risk comprehensive approach, SUBGLACIOR will thus put together two different scientific communities (ice core scientists and laser physicists) for a major step forward in experimental development for ice core science and a much increased efficiency of the expensive field work in particular.

Over the next years, improved glaciological information obtained during the International Polar Year 2007-2009 will help to characterize the best suited sites for finding well preserved very old ice. In a perfectly timely agenda with respect to the international context, it will provide a unique instrument for the international ice core research community, which could then be deployed to qualify the best Antarctic drilling sites. This “oldest ice” challenge is currently the main long-term target of the International Partnerships in Ice Core Sciences (IPICS, involving 25 nations, and endorsed by IGBP/PAGES).

Challenges

Several technical difficulties will have to be dealt with in the probe's conception:

• Drill head: it will combine two existing technologies, electromechanical and thermal drilling.

• Borehole pressure: avoiding borehole closure due to ice flow will save time as it avoids bringing back the probe at the surface to empty a chip reservoir.

• Surface - probe communication: we will use multiplexing communication between the drilling device and the driving unit at the surface to control the power supply, flow handling, and to acquire the pre-processed signal of the OF-CEAS laser system, as well as other information from the probe.

• Flow handling: the pressurized (up to 400 bars) water/gas mixture produced from the melt head will travel through a custom-made membrane system, from where the gas phase will be pumped through the OF-CEAS cavity at much lower absolute pressure.

• Stability of the laser system : it is crucial to control the OF-CEAS temperature to better than 0.1 K for best performance; vibrations due to the electromechanical drilling must also be filtered to keep the optical path undisturbed.

• Integration of the instrument into the probe : the OF-CEAS architecture will be adapted to the probe dimensions, in order to obtain the smallest possible probe diameter ; embarked electronics will pre-process the signal before communication with the surface.

Funding

The Subglacior project is funded through the ERC Advanced Grant ICE&LASERS (submitted by Jerome Chappellaz of the LGGE, Grenoble), the French ANR research proposal "Subglacior", as well as by BNP Paribas.