Chuanjin Li

Spatial and temporal variations of total mercury in Antarctic snow along the transect from Zhongshan Station to Dome A

In this study, the concentrations of total mercury (THg) and ions deposited in the surface snow and snow pits in the eastern Antarctic along the 29th inland route of the Chinese National Antarctic Research Expedition were analysed. The THg concentrations in the surface snow ranged from 0.22 to 8.29 ng/L and elevated concentrations were detected in the inland regions of higher altitudes (3000–4000 m). The spatial distribution of the THg in the snow pits showed greater inland concentrations with mean concentrations of <0.2–1.33 ng/L. The THg concentrations in the coastal snow pit (29-A) showed higher concentrations in the summer snow layers than in the winter snow layers. The THg records from the two inland snow pits (29-K and 29-L) spanned decades and indicated elevated THg concentrations between the late 1970s and early 1980s and during the mid-1990s. The temporal variations of THg in the Antarctic snow layers were consistent with anthropogenic emissions around the world. In addition, the Pinatubo volcanic eruption was the primary contributor to the 1992 THg peak that was observed in the inland snow pits.

Factors controlling the nitrate in the DT-401 ice core in eastern Antarctica

Nitrate, an oxidized product of NOx preserved in the polar ice cores, has often been used to estimate past changes of the atmospheric nitrogen cycle. A 102.65 m ice core drilled at DT-401 (79°01′S, 77°00′E) in 1999 provides an opportunity to investigate the possible influencing factors for the nitrate budget in the eastern Antarctica. We studied the relationship between the δ18O (representing the temperature), accumulation rate, volcanic deposition and the astronomical factors (such as the solar activities, supernovae, etc.), and the nitrate variation along the whole duration (2680-year) of the ice core. Prominent impacts of the accumulation rate acting on the nitrate flux rather than the concentration were detected. However, no significant correlation was found between the δ18O and the nitrate deposition characteristics (concentration and the flux variations). Volcanic deposition can significantly affect the deposition of nitrate with a decreasing trend accompanied by the nss-SO4−2 (volcanic signal) peak values. Impacts of the solar activities on the nitrate deposition can be detected at this site, and three prominent periodicities (16.6, 24.0 and 102.0 yr) were found for the nitrate concentration variations. Six climatic events (Dalton Minimum, Maunder Minimum, Sporer Minimum, Wolf Minimum, Oort Minimum and Medieval Maximum) during the past 1150 years were observed with lower nitrate values for the foregoing five events and higher value for the last one.

Re-assessment of recent (2008 - 2013) surface mass balance over Dome Argus, Antarctica

At Dome Argus, East Antarctica, the surface mass balance (SMB) from 2008 to 2013 was evaluated using 49 stakes installed across a 30×30 km area. Spatial analysis showed that at least 12 and 20 stakes are needed to obtain reliable estimates of SMB at local scales (a few hundred square metres) and regional scales (tens of square kilometres), respectively. The estimated annual mean SMB was 22.9±5.9 kg m−2 yr−1, including a net loss by sublimation of −2.22±0.02 kg m−2 yr−1 and a mass gain by deposition of 1.37±0.01 kg m−2 yr−1. Therefore, ca. 14.3% of precipitation was modified after deposition, which should be considered when interpreting snow or ice core records produced by future drilling projects. The surface snow density and SMB in the western portion of Dome Argus are higher than in other areas, and these differences are likely related to the katabatic wind, which is strengthened by topography in this sector. A new digital elevation model (DEM) of Dome Argus was generated, confirming that both peaks of the dome can be considered as the summit of the East Antarctic Ice Sheet. Findings from this study should be valuable for validating SMB estimates obtained from regional climate models and DEMs established using remote-sensing data.

A 2680-year record of sea ice extent in the Ross Sea and the associated atmospheric circulation derived from the DT401 East Antarctic ice core

Long time series of Antarctic sea ice extent (SIE) are important for climate research and model forecasting. A historic ice extent in the Ross Sea in early austral winter was rebuilt through sea salt ions in the DT401 ice core in interior East Antarctica. El Niño-Southern Oscillation (ENSO) had a significant influence on the sea salt deposition in DT401 through its influence on the Ross Sea SIE and the transport of sea salt inland. Spectral analysis also supported the influence of ENSO with a significant 2–6 a periodicity band. In addition, statistically significant decadal (10 a) and pentadecadal (50–70 a) periodicities suggested the existence of a teleconnection from the Pacific decadal oscillation (PDO), which originated from sea surface temperature anomalies in the tropical Pacific Ocean. The first eigenvector of the empirical orthogonal function analysis (EOF1) showed lower values during the Medieval Warm Period (MWP), while higher values were found in the Little Ice Age (LIA). A higher frequency of ENSO events were found in the cold climatic stage. The post 1800 AD period was occupied by significant fluctuations of the EOF1, and PDO may be one of the influencing factors. The EOF1 values showed moderate fluctuations from 680 BC to 1000 AD, showing that the climate was relatively stable in this period.

Chinese First Deep Ice-Core Drilling Project DK-1 at Dome A, Antarctica (2011-2013): progress and performance

Abstract The Chinese First Deep Ice-Core Drilling Project DK-1 has commenced at Kunlun station in the Dome A region, the highest plateau in Antarctica. During the first season, within the 28th Chinese National Antarctic Research Expedition (CHINARE) 2011/12 the pilot hole was drilled and reamed in order to install a 100 m deep fiberglass casing. In the next season, 29th CHINARE 2012/13, the deep ice-core drilling system was installed, and all the auxiliary equipment was connected and commissioned. After filling the hole with drilling fluid (n-butyl acetate), three runs of ‘wet’ ice-core drilling were carried out and a depth of 131.24 m was reached. Drilling to the bedrock at the target depth of ∼3100 m is planned to be completed during a further four seasons. We describe the work in progress and the status of equipment for the Dome A drilling project.

Dating a 109.9 m ice core from Dome A (East Antarctica) with volcanic records and a firn densification model

A 109.9 m ice core was extracted at a location about 300 m away from the Dome A summit (80°00′S, 77°21″E) by the Chinese team of the International Trans-Antarctic Science Expedition (ITASE) during the 21st Chinese National Antarctica Research Expedition (CHINARE) in January 2005. Two independent methods were used for dating the ice core, volcanic event markers shown by prominent non-sea-salt sulfate (nss-SO42−) and the Herron and Langway (H-L) firn densification model. Six prominent volcanic events (Agung 1963 AD, Tambora 1815 AD, Kuwae 1453 AD, Unknown 1259 AD, Taupo 186 AD and Pinatubo 1050 BC) were identified by comparison with other Antarctic ice cores. Based on the mean accumulation rates between adjacent events, we estimate the age at the firn pore close-off depth (102 m) was 3516±100 a BP. This is the oldest close-off age ever reported from the Antarctic and the Greenland ice sheets. Calculations using the H-L model show that the age at the same depth is 3581±100 a BP. The two dating techniques differ by 65 years, or ∼1.8% of the record. We calculated the bottom age of the ice core as 4009±150 a BP using the volcanic dating method and 4115±150 a BP using the H-L model method.

Nitrate deposition and preservation in the snowpack along a traverse from coast to the ice sheet summit (Dome A) in East Antarctica

Antarctic ice core nitrate (NO−3 ) can provide a unique record of the atmospheric reactive nitrogen cycle. However, the factors influencing the deposition and preservation of NO−3 at the ice sheet surface must first be understood. Therefore, an intensive program of snow and atmospheric sampling was made on a traverse from the coast to the ice sheet summit, Dome A, East Antarctica. Snow samples in this observation include 120 surface snow samples (top ∼ 3 cm), 20 snow pits with depths of 150 to 300 cm, and 6 crystal ice samples (the topmost needle-like layer on Dome A plateau). The main purpose of this investigation is to characterize the distribution pattern and preservation of NO−3 concentrations in the snow in different environments. Results show that an increasing trend of NO−3 concentrations with distance inland is present in surface snow, and NO−3 is extremely enriched in the topmost crystal ice (with a maximum of 16.1 μeq L−1). NO−3 concentration profiles for snow pits vary between coastal and inland sites. On the coast, the deposited NO−3 was largely preserved, and the archived NO−3 fluxes are dominated by snow accumulation. The relationship between the archived NO−3 and snow accumulation rate can be depicted well by a linear model, suggesting a homogeneity of atmospheric NO−3 levels. It is estimated that dry deposition contributes 27–44 % of the archived NO−3 fluxes, and the dry deposition velocity and scavenging ratio for NO−3 were relatively constant near the coast. Compared to the coast, the inland snow shows a relatively weak correlation between archived NO−3 and snow accumulation, and the archived NO−3 fluxes were more dependent on concentration. The relationship between NO−3 and coexisting ions (nssSO2− 4 , Na + and Cl) was also investigated, and the results show a correlation between nssSO2− 4 (fine aerosol particles) and NO−3 in surface snow, while the correlation between NO−3 and Na + (mainly associated with coarse aerosol particles) is not significant. In inland snow, there were no significant relationships found between NO−3 and the coexisting ions, suggesting a dominant role of NO−3 recycling in determining the concentrations.

Spatial and temporal variability of marine-origin matter along a transect from Zhongshan Station to Dome A, Eastern Antarctica

The spatiotemporal distribution pattern of marine-origin matter on the Antarctica ice sheet was used to study variations in the source regions, transport mechanisms and post-depositional influences. We present data on sea salt ions, sulfur components and stable isotopes from surface and snow pit samples collected along the transect route from Zhongshan Station to Dome A during the austral summer in 2012-2013. A general decreasing trend in the accumulation, sea salt ions and sulfur components occurred with increasing distance from the coast and increasing elevation. However, different sources of the marine components, transport pathways and post-depositional influences were responsible for their different spatial distribution patterns. The marine ions in the coastal snow pit varied seasonally, with higher sea salt ion concentrations in the winter and lower concentrations in the summer; the opposite pattern was found for the sulfur compounds. The sea ice area surrounding Antarctica was the main source region for the deposited sea salt and the open sea water for the sulfur compounds. No significant trends in the marine-origin components were detected during the past 3 decades. Several periods of elevated deposition of sea salt ions were associated with lower temperatures (based on δD and δ(18)O) or intensified wind fields. In comparison to the sea salt ions, the sulfur concentrations exhibited the opposite distribution patterns and were associated with changes in the surrounding sea ice extent.

Spatial distribution of marine chemicals along a transect from Zhongshan Station to the Grove Mountain area, Eastern Antarctica

This study investigates the regional distribution of marine aerosol originated species (Na+, Cl−, nss-SO42− and MSA) in the snow pits (or firn cores) collected along a transect between Zhongshan Station and the Grove Mountain area (450 km inland) on the eastern side of the Lambert Glacier Basin. Concentrations of Na+ and Cl− decrease exponentially with distance from the coast to 100 km inland (i.e., 1500 m a.s.l.). Statistical results demonstrate that distance from the coast inland and elevation affect the concentration of sea-salt originated ions in inland areas significantly. Increase of Cl-/Na+ ratio and higher variability in its standard deviation suggest that there are other sources of ions in addition to sea-salt in inland areas of the Antarctic continent. The concentrations of Na+ and Cl− from nine sampling sites in the Grove Mountain area are relatively higher than those from sites along CHINARE transect, although all sites are at similar distance inland. This phenomenon indicates that the barrier effect of the mountain may be the most important factor influencing ion deposition. In addition, nss-SO42− and MSA vary differently, with nss-SO42− decreasing with distance more significantly. This implies that sources and transporting pathways influence the deposition of the two sulfur compounds considerably, being supported by the spatial pattern of correlation coefficients between the nss-SO42− and MSA.

Snowdrift effect on snow deposition: Insights from a comparison of a snow pit profile and meteorological observations in east Antarctica

A high-frequency and precise ultrasonic sounder was used to monitor precipitated/deposited and drift snow events over a 3-year period (17 January 2005 to 4 January 2008) at the Eagle automatic weather station site, inland Antarctica. Ion species and oxygen isotope ratios were also generated from a snow pit below the sensor. These accumulation and snowdrift events were used to examine the synchronism with seasonal variations of δ18O and ion species, providing an opportunity to assess the snowdrift effect in typical Antarctic inland conditions. There were up to 1-year differences for this 3-year-long snow pit between the traditional dating method and ultrasonic records. This difference implies that in areas with low accumulation or high wind, the snowdrift effect can induce abnormal disturbances on snow deposition. The snowdrift effect should be seriously taken into account for high-resolution dating of ice cores and estimation of surface mass balance, especially when the morphology of most Antarctic inland areas is similar to that of the Eagle site.