The entry gives the Camp Century ice core a few paragraphs. It deserves more, because it is the one result of the camp that is still producing results, and because the way it was nearly lost says as much about how science keeps its records as the camp says about how armies keep theirs. This piece follows the core from the first thermal drill to the jars in Copenhagen.

Bader’s hole

The International Geophysical Year of 1957 to 1958 put the Army’s snow laboratory, SIPRE, to drilling in Greenland, and its chief scientist, Henri Bader, wanted what nobody had: a continuous core from the surface of an ice sheet to the rock beneath it. Hansen and Langway, the two CRREL men who ran the work, wrote in 1966 that the earlier holes “confirmed the desirability of continuous core drilling through the Greenland and antarctic ice sheets. Equipment and techniques for deep core drilling, core analysis, and drill-hole measurements were to be developed and tested in Greenland prior to their use in Antarctica.” Camp Century, with its power, its warm trenches and its sled trains, was the place to test them. Lyle Hansen was in charge; Herbert Ueda and Donald Garfield designed and ran the drills; Chester Langway took charge of the core. The National Science Foundation paid for the drilling and the Army’s Research Support Group kept the field party alive.

The first drill melted its way down. It was a ring of copper six and a half inches across with eighteen cartridge heaters in it, rated at nine kilowatts, under a ten-foot core barrel and a tank for the meltwater, thirty feet long in all and weighing 900 pounds, hung from an armoured cable with twelve conductors in it on a winch that weighed nineteen tons with its 12,000 feet of cable. It sat in a trench at the camp under an aluminium tower. In the 1960 to 1961 season it took a core of 186 metres; a second hole in 1962 gave 238 metres and a third, begun in 1963, 264. In 1964 the third hole was pushed to 535 metres. Below a few hundred metres a hole in ice begins to close under its own weight, as the trenches did, and the drillers filled it with a fluid of the same density as ice, diesel oil and trichloroethylene. The fluid was a solvent. Ueda and Garfield wrote that it “eventually removed a rust inhibiting compound used on the cable, creating a residue which continually settled to the bottom of the hole, impeded the melting rate, clogged the pumping circuit, and ultimately forced the discontinuation of drilling with the thermal method.”

So in 1964 they bought a second-hand oilfield tool. The Electrodrill, invented by Armais Arutunoff of the Reda Pump Company of Bartlesville, Oklahoma, was a submersible electric motor hung on a cable, turning a core barrel and a cutting bit, and it had never been used in ice. Rebuilt, it was eighty-three feet long and weighed 2,650 pounds. The chips it cut could not be bailed out of a fluid as dense as they were, so the drillers dissolved them instead, sending down a charge of ethylene glycol on each run, and the glycol carried the ice chips up as water. In 1965 the Electrodrill took the hole from 535 metres to 1,002, with the core coming up in lengths of eight to fifteen feet, 98 per cent of it recovered.

July 1966

In June 1966 the drill went back down for the last season. Hansen and Langway’s report in the Antarctic Journal that autumn is the primary record of what happened: “On July 2, at a depth of 1,370.5 meters, ice containing silt bands and small pebbles was encountered. On July 4, after drilling through 16.9 meters of this material, the interface at the bottom of the ice cap was reached at a depth of 1,387.4 meters. The bottom material is frozen till; 3.55 meters of this material was recovered. The total depth of the hole is 1,391 meters.” Ueda and Garfield, in feet, say the drill reached the bottom of the ice at 4,450 feet and went on to 4,562, “where a worn bearing in the gear section prevented further penetration”, and that the sub-ice material “consisted of a conglomerate of frozen till and various sized rocks”, in which the drilling rate fell to an inch and a half a minute with 1,800 pounds on the bit. The hole was logged: the ice was coldest at 154 metres, at minus 24.6 degrees, and minus 13 at the bottom. The core, Hansen and Langway wrote, was “in general very good, improving to excellent at great depths”, with unbroken lengths of up to five metres near the bottom. Then the equipment was crated for Antarctica, where the same Electrodrill reached the bed under Byrd Station in January 1968.

Hansen and Langway listed what was to be done with the core: structure, density, dissolved solids, crystal sizes, radioactive fallout horizons, lead-210 dating, ions, silicon-32, carbon-14 from the gas in the bubbles, volcanic dust, cosmic dust, “stable isotope investigations, compositional analyses of fossil atmospheres and climatological correlation of ice core data with historically recorded events”. And they wrote that “this entire profile is currently being studied in detail with immediate emphasis being placed on the sub-ice material.” The emphasis did not last.

The ice

Willi Dansgaard of Copenhagen had not been invited to the drilling trench when he was at the camp in 1964. He had something the Americans did not: a way of reading past temperature from the ratio of heavy to light oxygen in old snow, which he had worked out from rain in the 1950s and tested on Greenland icebergs. In 1967 his colleague Jørgen Møller went to CRREL’s headquarters at Hanover, New Hampshire, where the core was kept in two-metre cardboard tubes, and cut 86 samples at chosen depths; by 1969 Sigfus Johnsen and Henrik Clausen had cut 7,500 more, covering the whole core. The result, Dansgaard wrote forty years later, “was quite surprising. I cannot recall what we had expected, but indeed we did not dare to hope for a d-record that apparently reached throughout the last glaciation, and even farther into the past.”

They presented it with Langway at a CRREL symposium in 1968 and published it in Science on 17 October 1969, four pages under the title “One thousand centuries of climatic record from Camp Century on the Greenland ice sheet”. The abstract: “A correlation of time with depth has been evaluated for the Camp Century, Greenland, 1390 meter deep ice core. Oxygen isotopes in approximately 1600 samples throughout the core have been analyzed. Long-term variations in the isotopic composition of the ice reflect the climatic changes during the past nearly 100,000 years. Climatic oscillations with periods of 120, 940, and 13,000 years are observed.” Near the bottom, at about 1,350 metres, was a peak warmer than anything since, which they read as the last interglacial, and through the glacial ice above it the record swung violently, in jumps that later cores would confirm as changes of ten degrees within a human lifetime. The paper made the ice core a scientific instrument, and the drill a Danish-American partnership that went on to Dye 3, GRIP and the cores that are read today. Dansgaard noted one thing about the bottom: “The deepest 25 metres of ice core consisted of silty ice containing bottom material of increasing coarseness downward from dust to small and larger stones. This indicated that the deepest ice had been in contact with the bedrock farther upstream.” The mud below the ice he did not mention. It was not his.

The freezer

The core stayed with Langway. The paper of 2021 gives its history in one line: “The sediment was stored frozen, initially at University at Buffalo from 1966, until it was transferred to Niels Bohr Institute (NBI) in 1994 and 1996.” Behind the line is a telephone call. Langway had left CRREL for the State University of New York at Buffalo in the 1970s and taken the core with him, in a freezer on Lake Erie, and by the 1990s he was retiring and the university had no use for it. Jørgen Peder Steffensen, who curates the ice-core collection at the University of Copenhagen, has told the University of Vermont’s writer what Langway said to him: “you come over here and get the ice,” and “otherwise it goes into Lake Erie.” The Danes went over and got the ice, and with it, unregarded, the jars of till. The paper of 2021 says the samples “are kept at −30 °C as ∼10 cm thick subsamples stored in individual glass jars.” There were about thirty of them.

In 2017 the Copenhagen collection was being moved to a new freezer, and Steffensen and Dorthe Dahl-Jensen were going through it. In Steffensen’s account there were boxes labelled “Camp Century sub-ice”, and inside them the jars, which he has called the cookie jars. “Well, when you see a lot of cookie jars, you think: who the hell put this in here?” The paper’s version: “The basal material remained in frozen storage for decades until it was rediscovered in 2017.” By then it was the only sample of the ground under the interior of the Greenland ice sheet that anyone had, and there were ways of reading it that had not existed in 1966. In the summer of 2019 two jars, numbered 1059-4 and 1063-7 for their depths in the core, were cut at the institute and the pieces sent to laboratories in the United States, Belgium and France. Paul Bierman of the University of Vermont, who with Joerg Schaefer of Lamont-Doherty led the dating, said in 2019 that the sample might be “the key, the Rosetta Stone”, and when the first numbers came in, “This is tentative,” and “if this first look holds true, this is big-time bad news.”

What the mud said

The paper came out in the Proceedings of the National Academy of Sciences in March 2021 with eighteen authors, Andrew Christ of Vermont first among them: “A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century”. It used everything on the jars that could be used. Under the microscope the upper sample held “twigs (possibly including Empetrum), moss leaves and stems of Tomentypnum nitens and Polytrichum juniperinum”, crowberry and two mosses of the tundra, and a twig gave a radiocarbon age beyond the method’s reach, more than 50,000 years. The pore ice in the sediment carried oxygen and hydrogen isotopes that spoke of precipitation falling at a low elevation, that is, with no ice sheet on top. Lipids from the plants were still there. And two clocks gave the dates. Beryllium-10 and aluminium-26 are made in quartz by cosmic rays only while the rock is at the surface, and they decay at different rates once it is buried, so their ratio says how long it has been dark. Luminescence in feldspar grains builds up in the dark and is reset by sunlight, so it says when the grain last saw the sun.

The answers: “In the upper-most sediment, cosmogenic 26Al/10Be data require exposure within the last 1.0 ± 0.1 My.” For the lower sample, the two clocks together “bracket the burial of the lower-most sediment between <3.2 ± 0.4 Ma and >0.7 to 1.4 Ma”. The sediment, the authors wrote, “documents at least two episodes of ice-free, vegetated conditions, each followed by glaciation”, and their conclusion was that the ice sheet “persisted through much of the Pleistocene but melted and reformed at least once since 1.1 Ma”. The place where the Army had built its camp on 1,387 metres of ice had, within the last million years, been open ground with moss and crowberry on it, and an ice sheet that had gone once under a climate not very different from the present could go again.

The jars had more in them. In July 2023 the same group, with the Geological Survey of Denmark and Greenland, reported in Science that luminescence dating of the sediment just beneath the ice “shows that sediment just beneath the ice sheet was deposited by flowing water in an ice-free environment 416 ± 38 thousand years ago”, in the long warm interglacial known as Marine Isotope Stage 11, and that “ice sheet modeling indicates that ice-free conditions at Camp Century require at least 1.4 meters of sea level equivalent contribution from the Greenland Ice Sheet.” That interglacial was warm for a long time rather than very warm, and the ice at Camp Century did not survive it.

What it keeps

Nothing in this story was planned, except the drilling. The Army wanted to know how ice flows; Bader wanted a core; Hansen’s drillers were told to reach the rock, and did, and brought up what was under it because that is what a drill does. The mud was packed, labelled, frozen and forgotten, carried across an ocean by people who wanted the ice above it, and found by a curator moving house. Fifty-one years after it came out of the ground it answered a question about the next century that nobody could have asked in 1966. The lesson the entry draws from it is short: keep the sample you cannot yet read, label it, and do not let it go into the lake.

Sources

• B. Lyle Hansen and Chester C. Langway Jr., “Deep core drilling in ice and core analysis at Camp Century, Greenland, 1961–1966”, Antarctic Journal of the United States 1 (5), 207–208, September–October 1966. The seasons, the depths, 2 and 4 July 1966, the till, the hole temperatures, the list of analyses and “immediate emphasis”. icedrill.org
• Herbert T. Ueda and Donald E. Garfield, Drilling Through the Greenland Ice Sheet, CRREL Special Report 126, November 1968. The thermal drill and its failure, the Electrodrill, the glycol method, the bit loads and the worn bearing. icedrill.org
• W. Dansgaard, S. J. Johnsen, J. Møller and C. C. Langway Jr., “One thousand centuries of climatic record from Camp Century on the Greenland ice sheet”, Science 166 (3903), 377–380, 17 October 1969. Paywalled; the abstract is quoted from PubMed. pubmed.ncbi.nlm.nih.gov
• Willi Dansgaard, Frozen Annals: Greenland Ice Cap Research, Niels Bohr Institute, 2005, chapter 6, “The deep ice core”. Møller’s 86 samples, the 7,500 that followed, the surprise, the symposium of 1968, the Eemian peak and the silty bottom ice. nbi.ku.dk
• Andrew J. Christ and others, “A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century”, Proceedings of the National Academy of Sciences 118 (13), e2021442118, 2021. The storage history, the jars, the samples cut in 2019, the methods, the fossils and the dates. pmc.ncbi.nlm.nih.gov
• Andrew J. Christ, Tammy M. Rittenour, Paul R. Bierman and others, “Deglaciation of northwestern Greenland during Marine Isotope Stage 11”, Science 381 (6655), 330–335, 21 July 2023. Paywalled; the abstract is quoted from PubMed. pubmed.ncbi.nlm.nih.gov
• Joshua E. Brown, “Secrets Under the Ice”, University of Vermont, 2019. Steffensen on Langway’s call and the cookie jars; Bierman’s remarks on the first results. uvm.edu