EDML1: a chronology for the EPICA deep ice core from Dronning Maud Land, Antarctica, over the last 150 000 years

A chronology called EDML1 has been developed for the EPICA ice core from Dronning Maud Land (EDML). EDML1 is closely interlinked with EDC3, the new chronology for the EPICA ice core from Dome-C (EDC) through a stratigraphic match between EDML and EDC that consists of 322 volcanic match points over the last 128 ka. The EDC3 chronology comprises a glaciological model at EDC, which is constrained and later selectively tuned using primary dating information from EDC as well as from EDML, the latter being transferred using the tight stratigraphic link between the two cores. Finally, EDML1 was built by exporting EDC3 to EDML. For ages younger than 41 ka BP the new synchronized time scale EDML1/EDC3 is based on dated volcanic events and on a match to the Greenlandic ice core chronology GICC05 via 10Be and methane. The internal consistency between EDML1 and EDC3 is estimated to be typically ~6 years and always less than 450 years over the last 128 ka (always less than 130 years over the last 60 ka), which reflects an unprecedented synchrony of time scales. EDML1 ends at 150 ka BP (2417 m depth) because the match between EDML and EDC becomes ambiguous further down. This hints at a complex ice flow history for the deepest 350 m of the EDML ice core.

A High-Altitude Snow Chemistry Record from Amundsenisen, Dronning Maud Land, Antarctica

In this paper a detailed record of major ions from a 20 in deep firn core from Amundsenisen, western Dronning Maud Land, Antarctica, is presented. The core was drilled at 75degreesS, 2degrees E (2900 m.a.s.l.) during austral summer 1991/92. The following ions were measured at 3 cm resolution: Na+, Mg2+, Ca2+, Cl-, NO3-, SO42- and CH3SO3H (MSA). The core was dated back to 1865 using a combination of chemical records and volcanic reference horizons. The volcanic eruptions identified in this core are Mount Ngauruhoe, New Zealand (1974-75), Mount Agung, Indonesia (1963), Azul, Argentina (1932). and a broad peak that corresponds in time to Tarawera, New Zealand (1886), Falcon Island, South Shetlands, Southern Ocean (1885), and Krakatau, Indonesia (1883). There are no trends in any of the ion records, but the annual to decadal changes are large. The mean concentrations of the measured ions are in agreement with those from other high-altitude cores from the Antarctic plateau. At this core site there may be a correspondence between peaks in the MSA record and major El Nino-Southern Oscillation events.

A climatological analysis of high-precipitation events in Dronning Maud Land, Antarctica, and associated large-scale atmospheric conditions

The link between high precipitation in Dronning Maud Land (DML), Antarctica, and the large-scale atmospheric circulation is investigated using ERA-Interim data for 1979–2009. High-precipitation events are analyzed at Halvfarryggen situated in the coastal region of DML and at Kohnen Station located in its interior. This study further includes a comprehensive comparison of high precipitation in ERA-Interim with precipitation data from the Antarctic Mesoscale Prediction System (AMPS) and snow accumulation measurements from automatic weather stations (AWSs), with the limitations of such a comparison being discussed. The ERA-Interim and AMPS precipitation data agree very well. However, the correspondence between high precipitation in ERA-Interim and high snow accumulation at the AWSs is relatively weak. High-precipitation events at both Halvfarryggen and Kohnen are typically associated with amplified upper level waves. This large-scale atmospheric flow pattern is preceded by the downstream development of a Rossby wave train from the eastern South Pacific several days before the precipitation event. At the surface, a cyclone located over the Weddell Sea is the main synoptic ingredient for high precipitation both at Halvfarryggen and at Kohnen. A blocking anticyclone downstream is not a requirement for high precipitation per se, but a larger share of blocking occurrences during the highest-precipitation days in DML suggests that these blocks strengthen the vertically integrated water vapor transport (IVT) into DML. A strong link between high precipitation and the IVT perpendicular to the local orography suggests that IVT could be used as a “proxy” for high precipitation, in particular over DML's interior.

The EPICA Dronning Maud Land deep drilling operation

We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. core-break force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run.

The role of seasonality of mineral dust concentration and size on glacial/interglacial dust changes in the EPICA Dronning Maud Land ice core

We present a record of particulate dust concentration and size distribution in subannual resolution measured on the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice core drilled in the Atlantic sector of the East Antarctic plateau. The record reaches from present day back to the penultimate glacial until 145,000 years B.P. with subannual resolution from 60,000 years B.P. to the present. Mean dust concentrations are a factor of 46 higher during the glacial (~850–4600 ng/mL) compared to the Holocene (~16–112 ng/mL) with slightly smaller dust particles during the glacial comparedto the Holocene and with an absolute minimum in the dust size at 16,000 years B.P. The changes in dust concentration are mainly attributed to changes in source conditions in southern South America. An increase in the modal value of the dust size suggests that at 16,000 years B.P. a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the EDML drill site. We find a clear in-phase relation of the seasonal variation in dust mass concentration and dust size during the glacial (r(conc,size) = 0.8) but no clear phase relationship during the Holocene (0

Chronology for the EDML ice core from Dronning Maud Land, Antarctica, over the last 150 000 years

A chronology called EDML1 has been developed for the EPICA ice core from Dronning Maud Land (EDML). EDML1 is closely interlinked with EDC3, the new chronology for the EPICA ice core from Dome-C (EDC) through a stratigraphic match between EDML and EDC that consists of 322 volcanic match points over the last 128 ka. The EDC3 chronology comprises a glaciological model at EDC, which is constrained and later selectively tuned using primary dating information from EDC as well as from EDML, the latter being transferred using the tight stratigraphic link between the two cores. Finally, EDML1 was built by exporting EDC3 to EDML. For ages younger than 41 ka BP the new synchronized time scale EDML1/EDC3 is based on dated volcanic events and on a match to the Greenlandic ice core chronology GICC05 via 10Be and methane. The internal consistency between EDML1 and EDC3 is estimated to be typically ~6 years and always less than 450 years over the last 128 ka (always less than 130 years over the last 60 ka), which reflects an unprecedented synchrony of time scales. EDML1 ends at 150 ka BP (2417 m depth) because the match between EDML and EDC becomes ambiguous further down. This hints at a complex ice flow history for the deepest 350 m of the EDML ice core.

Accumulation rates for western Dronning Maud Land from firn cores and snow pits

As a result of intensive field activities carried out by several nations over the past 15 years, a set of accumulation measurements for western Dronning Maud Land, Antarctica, was collected, based on firn-core drilling and snow-pit sampling. This new information was supplemented by earlier data taken from the literature, resulting in 111 accumulation values. Using Geographical Information Systems software, a first region-wide mean annual snow-accumulation field was derived. In order to define suitable interpolation criteria, the accumulation records were analyzed with respect to their spatial autocorrelation and statistical properties. The resulting accumulation pattern resembles well known characteristics such as a relatively wet coastal area with a sharp transition to the dry interior, but also reveals complex topographic effects. Furthermore, this work identifies new high-return shallow drilling sites by uncovering areas of insufficient sampling density.

Physical properties and accumulation rates in Dronning Maud Land, Antarctica

The European Programme for Ice Coring in Antarctica includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land, Antarctica. The German glaciological programme during the 1997/98 field season was carried out along a 1200 km traverse on Amundsenisen and involved sampling the snow cover in pits and by shallow firn cores. This paper focuses on the accumulation studies. The cores were dated by dielectric-profiling and continuous-flow analysis. Distinct volcanogenic peaks and seasonal signals in the profiles served to establish a depth time-scale. The eruptions of Krakatoa, Tambora, an unknown volcano, Kuwae and El Chichon are well-documented in the ice. Variations of the accumulation rates over different times were inferred from the depth time-scales. A composite record of accumulation rates for the last 200 years was produced by stacking 12 annually resolved records. According to this, accumulation rates decreased in the 19th century and increased in the 20th century. The recent values are by no means extraordinary, as they do not exceed the values at the beginning of the 19th century. Variations in accumulation rates are most probably linked to temperature variations indicated in d18O records from Amundsenisen.

Seasonally resolved chemical records of six ice cores from the Dronning Maud Land, Antarctica

The ammonium, calcium, and sodium concentrations from three intermediate depth ice cores drilled in the area of Dronning Maud Land, East Antarctica, have been investigated. Since all measurements were performed by a high-resolution Continuous Flow Analysis system, for the first time seasonal signals of chemical trace species could be obtained from the interior of central Antarctica over a period of approximately 2 millennia. Although the elevation as well as the accumulation rate differ between the drilling sites, similar values were obtained by comparing mean concentrations spanning the last 900 years. However, a distinct lack of intersite correlation was found on decadal timescales. Despite a noticeable accumulation change, apparent in one core, no significant concentration change of all three species has occurred. All the measured ions show clear seasonal signals over the whole records. While the sea-salt-related component sodium peaks simultaneously with calcium, the maximum ammonium concentration occurs in the snow with a time lag of 2 months after the sea-salt peak. More than 60% of the calcium concentration can be attributed to an ocean source. Elevated sodium concentrations were found within this millennium compared to mean values of the whole records, but the spatially varying shape of the increase suggests that a possible climatic signal is biased by local deposition effects.

Stable-isotope records from Dronning Maud Land, Antarctica

The European Project for Ice Coring in Antarctica (EPICA) includes a comprehensive pre-site survey on the inland ice plateau of Dronning Maud Land. This paper focuses on the investigation of the 18O content of shallow firn and ice cores. These cores were dated by profiles derived from dielectric-profiling and continuous flow analysis measurements. The individual records were stacked in order to obtain composite chronologies of 18O contents and accumulation rates with enhanced signal-to-noise variance ratios.These chronologies document variations in the last 200 and 1000 years.The 18O contents and accumulation rates decreased in the 19th century and increased during the 20th century.Using the empirical relationships between stable isotopes, accumulation rates and the 10m firn temperature, the variation of both parameters can be explained by the same temperature history.But other causes for these variations, such as the build-up of the snow cover, cannot be excluded. A marked feature of the 1000 year chronology occurs during the period AD 1180-1530 when the 18O contents remains below the long-term mean. Cross-correlation analyses between five cores from the Weddell Sea region and Dronning Maud Land show that 18O records can in some periods be positively correlated and in others negatively correlated, indicating a complex climatic history in time and space.