V. Zagorodnov

Annually Resolved Ice Core Records of Tropical Climate Variability over the Past ~1800 Years

Quelccaya Ice Cap Ice cores drilled in the ice sheets of Greenland and Antarctica are some of the most important sources of information about the paleoclimate of high latitudes. Comparable records from the tropics are rare, however, because there are so few locations at which long-lived, undisturbed ice can be found. Thompson et al. (p. 945, published online 4 April) report results obtained from one of the few such sites, the Quelccaya ice cap in the Peruvian Andes. The annually resolved data, extending back 1800 years, provide a detailed chronicle of changes in the isotopic composition of the oxygen in the ice, which are related to the sea surface temperature of the waters source. Analyses of a collection of major ions such as ammonium and nitrate reveal how atmospheric circulation in the region varied over that period. Finally, the radiocarbon content of ancient plants—recently exposed by the retreat of the ice sheet—reveals that Quelccaya has not been smaller for at least six thousand years. A record from the Quelccaya ice cap in Peru shows the variability of climate in the tropical Andes. Ice cores from low latitudes can provide a wealth of unique information about past climate in the tropics, but they are difficult to recover and few exist. Here, we report annually resolved ice core records from the Quelccaya ice cap (5670 meters above sea level) in Peru that extend back ~1800 years and provide a high-resolution record of climate variability there. Oxygen isotopic ratios (δ18O) are linked to sea surface temperatures in the tropical eastern Pacific, whereas concentrations of ammonium and nitrate document the dominant role played by the migration of the Intertropical Convergence Zone in the region of the tropical Andes. Quelccaya continues to retreat and thin. Radiocarbon dates on wetland plants exposed along its retreating margins indicate that it has not been smaller for at least six millennia.

Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.

New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf.

Holocene climate variability archived in the Puruogangri ice cap on the central Tibetan Plateau

Abstract Two ice cores (118.4 and 214.7 m in length) were collected in 2000 from the Puruogangri ice cap in the center of the Tibetan Plateau (TP) in a joint US-Chinese collaborative project. These cores yield paleoclimatic and environmental records extending through the Middle Holocene, and complement previous ice-core histories from the Dunde and Guliya ice caps in northeast and northwest Tibet, respectively, and Dasuopu glacier in the Himalaya. The high-resolution Puruogangri climate record since AD 1600 details regional temperature and moisture variability. The post-1920 period is characterized by above-average annual net balance, contemporaneous with the greatest 18O enrichment of the last 400 years, consistent with the isotopically inferred warming observed in other TP ice-core records. On longer timescales the aerosol history reveals large and abrupt events, one of which is dated ∼4.7 kyr BP and occurs close to the time of a drought that extended throughout the tropics and may have been associated with centuries-long weakening of the Asian/Indian/African monsoon system. The Puruogangri climate history, combined with the other TP ice-core records, has the potential to provide valuable information on variations in the strength of the monsoon across the TP during the Holocene.

Temperature profile for glacial ice at the South Pole: Implications for life in a nearby subglacial lake

Airborne radar has detected ≈100 lakes under the Antarctic ice cap, the largest of which is Lake Vostok. International planning is underway to search in Lake Vostok for microbial life that may have evolved in isolation from surface life for millions of years. It is thought, however, that the lakes may be hydraulically interconnected. If so, unsterile drilling would contaminate not just one but many of them. Here we report measurements of temperature vs. depth down to 2,345 m in ice at the South Pole, within 10 km from a subglacial lake seen by airborne radar profiling. We infer a temperature at the 2,810-m deep base of the South Pole ice and at the lake of −9°C, which is 7°C below the pressure-induced melting temperature of freshwater ice. To produce the strong radar signal, the frozen lake must consist of a mix of sediment and ice in a flat bed, formed before permanent Antarctic glaciation. It may, like Siberian and Antarctic permafrost, be rich in microbial life. Because of its hydraulic isolation, proximity to South Pole Station infrastructure, and analog to a Martian polar cap, it is an ideal place to test a sterile drill before risking contamination of Lake Vostok. From the semiempirical expression for strain rate vs. shear stress, we estimate shear vs. depth and show that the IceCube neutrino observatory will be able to map the three-dimensional ice-flow field within a larger volume (0.5 km3) and at lower temperatures (−20°C to −35°C) than has heretofore been possible.

The Hans Tausen drill: design, performance, further developments and some lessons learned

Abstract In the mid-1990s, excellent results from the GRIP and GISP2 deep drilling projects in Greenland opened up funding for continued ice-coring efforts in Antarctica (EPICA) and Greenland (NorthGRIP). The Glaciology Group of the Niels Bohr Institute, University of Copenhagen, was assigned the task of providing drilling capability for these projects, as it had done for the GRIP project. The group decided to further simplify existing deep drill designs for better reliability and ease of handling. The drill design decided upon was successfully tested on Hans Tausen Ice Cap, Peary Land, Greenland, in 1995. The 5.0m long Hans Tausen (HT) drill was a prototype for the ~11m long EPICA and NorthGRIP versions of the drill which were mechanically identical to the HT drill except for a much longer core barrel and chips chamber. These drills could deliver up to 4m long ice cores after some design improvements had been introduced. The Berkner Island (Antarctica) drill is also an extended HT drill capable of drilling 2 m long cores. The success of the mechanical design of the HT drill is manifested by over 12 km of good-quality ice cores drilled by the HT drill and its derivatives since 1995.

Intermediate-depth ice coring of high-altitude and polar glaciers with a lightweight drilling system

A total of 11 ice cores to a maximum depth of 460 m have been obtained over the past 3 years from high-altitude glaciers on the saddle of Mount Bona and Mount Churchill in Alaska (designated B-C), and on Quelccaya ice cap and Nevado Coropuna in Peru. Ice coring was conducted using an intermediate-depth drilling system. The system includes an electromechanical drill (EMD) and an ethanol thermal electric drill (ETED). The EMD permitted an average ice-core production rate (ICPR) of 7.0 m h−1 down to 150 m. An average ICPR of 2 m h−1 to 460 m depth was possible with the ETED. The quality of the B-C ice cores is better than that of cores previously drilled with an EMD and ETED system. A new cutter design, drilling with a lubricant/cutting fluid and a new anti-torque assembly were tested in the laboratory and in glacier boreholes. We examine the performance of the drills in cold and temperate ice and in clean and particle-laden ice. The influence of the ethanol drilling fluid on ice-core isotopic, ionic and dust composition is discussed.

Portable system for intermediate-depth ice-core drilling

Alight wcight, portable drilling systcm for coring up to 500 m depths has becn developed and fi eld-tes ted. The drilling system includes four major components: (I) an electromechanical (EM ) dry-hole drill ; (2) an etha nol thcrmal clectric drill; (3) a dri ll se t-up with a 500 m cabl e capacity; a nd (4) a controller unit. The systcm may bc switched quickly from a dry-holc E1V1 drill to an antifreeze thcrmal electric drill. This lightweight sys tem makes icc-co re drilling more cost-efficicnt , and c reates a minimal environmental impact. The new EM drill, which recovers 100 mm dia me ter, I m long pieces o[ ice core, is 3.2 m long and we ighs 35 kg. This drill and the drilling se t-up were recently tes tcd at the R aven (former Dye 2) ite, southcrn Greenl and , where a corc was recovered to 122 m. Thc thermal drill is 2.9 m long and weighs 25 kg. It produccs lOO mm diameter, 2.lm long pieces of ice core, and was tcsted to 315 m in FranzJoscfLand , Eurasian Arctic. The drilling se t-up with a 250 m cable we ighs about 100 kg (or 128 kg for 500 m of cable). After minor adjustments thi s drill system retrieved cores o[ bctter qualit y than those recove rcd by other drill system s under similar glaciologica l condi ti ons. After adjustments to optimi ze its performance, the drill rctri cvcd 5.25 m o[ core pcr hour ovcr the depth range 021m.

Influence of air temperature on a glacier's active-layer temperature

Abstract Seasonal temperature variations occur in the glacier layer about 15–20 m below the surface, while at greater depths the glacier temperature depends on the long-term surface conditions. It is generally accepted that for glaciers without surface melting the temperature at 10 m depth (T 10) is close to the mean annual air temperature at standard screen level (T a), i.e. T 10 =T a. We found that this relationship is not valid for T a above –17˚C and below –55˚C. The goal of our investigation is to find a better temperature transfer function (TTF) between T a and temperature at the boundary of the active layer in accumulation areas of polar and tropical glaciers. Low-precision T 10 temperatures from boreholes, obtained at 41 sites, are compared with air temperatures (T a) measured in the vicinity of these sites for at least a 1 year period. We determine that when T a falls into the temperature range –60 to –7˚C, empirical values can be approximated as T 10 = 1:2T a + 6:7. Analysis of these data suggests that high T 10 occurs in the areas of the glacier that collect meltwater.

Novel monitoring of Antarctic ice shelf basal melting using a fiber‐optic distributed temperature sensing mooring

Measuring basal melting of ice shelves is challenging and represents a critical component toward understanding ocean-ice interactions and climate change. In November 2011, moorings containing fiber-optic cables for distributed temperature sensing (DTS) were installed through the McMurdo Ice Shelf, Antarctica, (~200 m) and extending ~600 m into the ice shelf cavity. The high spatial resolution of DTS allows for transient monitoring of the thermal gradient within the ice shelf. The gradient near the ice-ocean interface is extrapolated to the in situ freezing temperature in order to continuously track the ice-ocean interface. Seasonal melt rates are calculated to be ~1.0 mm d−1 and 8.6 mm d−1, and maximum melting corresponds to the arrival of seasonal warm surface water in the ice shelf cavity between January and April. The development of continuous, surface-based techniques for measuring basal melting represents a significant advance in monitoring ice shelf stability and ice-ocean interactions.

Isolation and Identification of Bacteria from Ancient and Modern Ice Cores

Glacial ice traps and preserves soluble chemical species, gases, and particulates including pollen grains, fungal spores and bacteria in chronologically-deposited archives. We have constructed an ice-core sampling system that melts ice only from the interior of cores, thereby avoiding surface contamination, and using this system we have isolated, cultured and characterized bacteria from ice cores that range from 5 to 20,000 years in age and that originate from both polar and non-polar regions. Low-latitude, high-altitude non-polar ice cores generally contain more culturable bacteria than polar ices, consistent with closer proximities to major biological ecosystems. Direct plating of melt-water from a 200-year old sample of ice from the Guliya ice cap on the Tibetan Plateau (China) generated ~180 bacterial colonies per ml [colony forming units/ml; (cfu/ml)], whereas meltwater from late Holocene ice from Taylor Dome in Antarctica contained only 10 cfu/ml, and <10 cfu/ml were present in ice of the same age from the Antarctic Peninsula and from Greenland. Based on their small-subunit ribosomal RNA-encoding DNA (rDNA) sequences many, but not all of the bacteria isolated are spore-forming species that belong to Bacillus and Actinomycete genera. Non-chronological fluctuations are observed in the numbers of bacteria present, consistent with episodic deposition resulting from attachment to larger particulates.