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Cold Room Core Jamboree: Scientists Work on NGEE Arctic Cores

Sources: Yuxin Wu, Susan Hubbard, Tim Kneafsey, Dan Hawkes

Figure 1: NGEE researchers working on Arctic cores. Right to left: Craig Ulrich (LBL), Alex Kholodov (UAF), Heather Throckmorton (LANL)

The DOE Next-Generation Ecosystem Experiment (NGEE) is developing a predictive understanding of terrestrial ecosystem dynamics across scales and their feedbacks to climate, with a focus on the vulnerable Arctic system. As part of the NGEE effort, a team of LBNL-ESD scientists (including Yuxin Wu, Craig Ulrich, Tim Kneafsey, and Catherine McKnight ) recently worked with a team of scientists from Los Alamos National Laboratory (Cathy Wilson and Heather Throckmorton) and University of Alaska-Fairbanks (Alexander Kholodov) to study several dozen permafrost cores collected from different regions of the NGEE Barrow (Alaska) Environmental Observatory (BEO) study site.

Figure 2: Tim Kneafsey working on NGEE cores with the CT Scanner.

Much of their work was conducted at the Richmond Field Station, where Wu and Ulrich have developed a new cold lab, enabling analysis at -15°C conditions (Figure 1), as well as in the Earth Sciences Division CT-scanning Rock Physics Laboratory (Figure 2). The core research was performed to gain an understanding of the structure of the subsurface, and particularly the physicochemical properties of the shallow active layer and the deeper permafrost zones. Understanding the structure and the physiochemical properties of the Arctic soils is essential for developing process-rich climate models of greenhouse gas fluxes in and through Arctic soils.

Much of the surface at the BEO is polygonal ground, featuring high, low, and transitional polygons, with troughs in between. Cores have been strategically gathered from all of these ground types to aid in our understanding of the Arctic subsurface. At the Barrowstudy site, the top-surface 30 cm (or so) is typically called the active layer (the region that thaws and refreezes every year). This active layer is underlain by permafrost. An unfrozen saline-rich zone of varying thickness has also been identified beneath the permafrost layer at the site. This saline-rich zone is a region of potential microbial respiration and carbon turnover even during the winter season.

Figure 4: NGEE core sampling team. Left to Right: Catherine McKnight (LBNL-ESD), Heather Throckmorton (LANL), Alex Kholodov (UAF), Craig Ulrich (LBNL-ESD), Cathy Wilson (LANL) and Yuxin Wu (LBNL-ESD).
Figure 3: CT image of a ~1m NGEE core. Left: entire core. Right: cross sections of the core at successive depths.

After CT-scanning the cores (Figure 2 and 3), the team (Figure 4) sectioned the cores (Figure 5), logged the soil profile, and prepared samples to allow measurement of parameters such as permeability, thermal conductivity, water retention, water chemistry, soil texture, and organic carbon content. This information

Figure 5: Sectioned NGEE core-sampling showing ice-lens within the soil.

will be combined with other datasets collected in the project (including metagenomic, geophysical, and eddy covariance data; see links below) and integrated into multiscale models being developed to predict Arctic tundra-climate feedbacks.

To read about related work regarding acquisition of geophysical data, go to: