Impact of Icebergs on Net Primary Productivity in the Southern Ocean

Productivity in the Southern Ocean (SO) is iron-limited, and supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine environment. However, recent studies show that icebergs could provide a comparable amount of bioavailable iron to the SO as aeolian dust. In addition, small-scale areal studies suggest increased concentrations of chlorophyll, krill, and seabirds surrounding icebergs. Based on previous research, this study aims to examine whether iceberg occurrence has a significant impact on marine productivity at the scale of the SO, using remote sensing data of iceberg occurrences and ocean net primary productivity (NPP) covering the period 2002–2014. The impacts of both large and small icebergs are examined in four major ecological zones of the SO: the continental shelf zone (CSZ), the seasonal ice zone (SIZ), the permanent open ocean zone (POOZ), and the polar front zone (PFZ). We found that the presence of icebergs is associated with elevated levels of NPP, but the differences vary in different zones. Grid cells with small icebergs on average have higher NPP than other cells in most iron-deficient zones: 21 % higher for the SIZ, 16 % for the POOZ, and 12 % for the PFZ. The difference is relatively small in the CSZ where iron is supplied from meltwater and sediment input from the continent. In addition, NPP of grid cells adjacent to large icebergs on average is 10 % higher than that of control cells in the vicinity. The difference is larger at higher latitudes, where most large icebergs are concentrated. From 1992 to 2014, there is a significant increasing trend for both small and large icebergs. The increase was most rapid in the early 2000s and has leveled off since then. As the climate continues to warm, the Antarctic Ice Sheet is expected to experience increased mass loss as a whole, which could lead to more icebergs in the region. Based on our study, this could result in a higher level of NPP in the SO as a whole, providing a possible negative feedback for global warming in near future

Delayed Warming Hiatus over the Tibetan Plateau

A reduction in the warming rate for the global surface temperature since the late 1990s has attracted much attention and caused a great deal of controversy. During the same time period, however, most previous studies have reported enhanced warming over the Tibetan Plateau (TP). In this study we further examined the temperature trend of the TP and surrounding areas based on the homogenized temperature records for the period 1980–2014, we found that for the TP regions lower than 4000 m the warming rate has started to slow down since the late 1990s, a similar pattern consistent with the whole China and the global temperature trend. However, for the TP regions higher than 4000 m, this reduction in warming rate did not occur until the mid‐2000s. This delayed warming hiatus could be related to changes in regional radiative, energy, and land surface processes in recent years

Glaciological observations at Dome Argus, East Antarctica

Dome Argus (Dome A) in East Antarctica is a potentially likely site to meet one of the major objectives of the International Partnerships in Ice Core Sciences (IPICS) on the oldest ice core, and thus has aroused wide public and scientific interest. Since 2004/2005, many glaciological investigations have been conducted in this region. These have included GPS and ground-penetrating radar surveys, snow pit and ice core drilling, stake network measurements, and meteorological observations. In this article, the main results of these glaciological investigations in the Dome A region are summarized. We present details of the surface mass balance on different timescales and its spatial variability, geochemical characteristics of the surface snow, and paleo-environment reconstruction of ice cores. Finally, perspectives on the prospects for future studies are suggested

Snow Accumulation Rate on Qomolangma (Mount Everest), Himalaya: Synchroneity With Sites Across the Tibetan Plateau on 50-100 Year Timescales

Annual-layer thickness data, spanning AD 1534-2001, from an ice core from East Rongbuk Coll on Qomolangma (Mount Everest, Himalaya) yield an age-depth profile that deviates systematically from a constant accumulation-rate analytical model. The profile clearly shows that the mean accumulation rate has changed every 50-100 years. A numerical model was developed to determine the magnitude of these multi-decadal-scale rates. The model was used to obtain a time series of annual accumulation. The mean annual accumulation rate decreased from similar to 0.8 m ice equivalent in the 1500s to similar to 0.3 m in the mid-1800s. From similar to 1880 to similar to 1970 the rate increased. However, it has decreased since similar to 1970. Comparison with six other records from the Himalaya and the Tibetan Plateau shows that the changes in accumulation in East Rongbuk Col are broadly consistent with a regional pattern over much of the Plateau. This suggests that there may be an overarching mechanism controlling precipitation and mass balance over this area. However, a record from Dasuopu, only 125 km northwest of Qomolangma and 700 m higher than East Rongbuk Col, shows a maximum in accumulation during the 1800s, a time during which the East Rongbuk Col and Tibetan Plateau ice-core and tree-ring records show a minimum. This asynchroneity may be due to altitudinal or seasonal differences in monsoon versus westerly moisture sources or complex mountain meteorology

A High‐resolution Atmospheric Dust Record for 1810–2004 A.D. Derived from an Ice Core in Eastern Tien Shan, Central Asia

Centennial‐scale, high‐resolution records of atmospheric dust conditions are rare in the arid and semiarid regions of central Asia, limiting our understanding of the regional climate and environmental changes and their potential driving forces. In this paper, we present an annually resolved atmospheric dust record covering the period of 1810–2004 A.D., reconstructed from an ice core retrieved at 4512 m above sea level from the Miaoergou Glacier in the eastern Tien Shan. The time series of dust flux for the past 195 years shows three periods of relatively low values (i.e., 1810–1829 A.D., 1863–1940 A.D., and 1979–2004 A.D.) and two periods of relatively high values (i.e., 1830–1862 A.D. and 1941–1978 A.D.). Spatial correlation analysis suggests possible regional factors controlling the dust flux, including antecedent summer precipitation, spring soil moisture, and near‐surface wind speed. In addition, the Miaoergou dust flux is closely associated with the winter index of the North Atlantic Oscillation (NAO) over the past two centuries, with high (low) dust periods coinciding with the negative (positive) phases of the NAO. The persistent relationship suggests that the NAO may have been a key driver on dust flux change over the arid regions between the Tien Shan and Kunlun Mountains

Climatological Significance of δ\u3csup\u3e18\u3c/sup\u3eO in Precipitation and Ice Cores: a Case Study at the Head of the Ürütnqi River, Tien Shan, China

Stable-oxygen-isotope ratios (δ18O) collected from the headwaters of the Ürümqi river, Tien Shan, China, were used to test the relationship between δ18O temporal relationship is found between δ18O monthly averages which remove synoptic-scale influences such as changes in condensation level, condensation temperature and moisture sources (Yao and others, 1996). Linear fits as high as 0.95‰°C-1 for precipitation events and 1.23‰°C-1 for monthly averages are found. Although the δ18O (∼2 km from the precipitation sampling site) decreased dramatically compared to the precipitation samples , the ice-core records of annually averaged δ18O with contemporaneous air temperature, especially summer air temperature, at the nearby Daxigou meteorological station. Nevertheless, the relationship between the ice core δ18O records and contemporaneous air temperature is less significant than that [or the precipitation samples due to depositional and post-depositional modification processes, which are highlighted by the successive snow-pit δ18O No. 1. Our results might extend the application of high-altitude and subtropical ice-core δ18

The evaluation of biological productivity by triple isotope composition of oxygen trapped in ice-core bubbles and dissolved in ocean: a review

The 17O anomaly of oxygen (Δ17O, calculated from δ17O and δ18O) trapped in ice-core bubbles and dissolved in ocean has been respectively used to evaluate the past biosphere productivity at a global scale and gross oxygen production (GOP) in the mixed layer (ML) of ocean. Compared to traditional methods in GOP estimation, triple oxygen isotope (TOI) method provides estimates that ignore incubation bottle effects and calculates GOP on larger spatial and temporal scales. Calculated from TOI of O2 trapped in ice-core bubbles, the averaged global biological productivities in past glacial periods were about 0.83–0.94 of the present, and the longest time record reached 400 ka BP (thousand years before the present). TOI-derived GOP estimation has also been widely applied in open oceans and coastal oceans, with emphasis on the ML. Although the TOI method has been widely used in aquatic ecosystems, TOI-based GOP is assumed to be constant at a steady state, and the influence of physical transports below the ML is neglected. The TOI method applied to evaluate past total biospheric productivity is limited by rare samples as well as uncertainties related to O2 consumption mechanisms and terrestrial biosphere’s hydrological processes. Future studies should take into account the physical transports below the ML and apply the TOI method in deep ocean. In addition, study on the complex land biosphere mechanisms by triple isotope composition of O2 trapped in ice-core bubbles needs to be strengthened

Possible Recent Warming Hiatus on the Northwestern Tibetan Plateau Derived from Ice Core Records

Many studies have reported enhanced warming trend on the Tibetan Plateau (TP), even during the warming hiatus period. However, most of these studies are based on instrumental data largely collected from the eastern TP, whereas the temperature trend over the extensive northwestern TP remains uncertain due to few meteorological stations. Here we combined the stable isotopic δ18O record of an ice core recovered in 2012 from the Chongce glacier with the δ18O records of two other ice cores (i.e., Muztagata and Zangser Kangri) in the same region to establish a regional temperature series for the northwestern TP. The reconstruction shows a significant warming trend with a rate of 0.74 ± 0.12 °C/decade for the period 1970–2000, but a decreasing trend from 2001 to 2012. This is consistent with the reduction of warming rates during the recent decade observed at the only two meteorological stations on the northwestern TP, even though most stations on the eastern TP have shown persistent warming during the same period. Our results suggest a possible recent warming hiatus on the northwestern TP. This could have contributed to the relatively stable status of glaciers in this region

Recent Increases in Atmospheric Concentrations of Bi, U, Cs, S and Ca from a 350-Year Mount Everest Ice Core Record

High-resolution major and trace elements (Sr, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, U, Tl, Al, S, Ca, Ti, V, Cr, Mn, Fe, and Co) quantified in a Mount Everest ice core ( 6518 m above sea level) spanning the period 1650-2002 AD provides the first Asian record of trace element concentrations from the pre-industrial era, and the first continuous high-resolution Asian record from which natural baseline concentrations and subsequent changes due to anthropogenic activities can be examined. Modern concentrations of most elements remain within the pre-industrial range; however, Bi, U, and Cs concentrations and their enrichment factors (EF) have increased since the similar to 1950s, and S and Ca concentrations and their EFs have increased since the late 1980s. A comparison of the Bi, U, Cs, S, and Ca data with other ice core records and production data indicates that the increase in atmospheric concentrations of trace elements is widespread, but that enrichment varies regionally. Likely sources for the recent enrichment of these elements include mining, metal smelting, oil and coal combustion, and end uses for Bi, and mining and refinement for U and Cs. The source of the synchronous enrichment of Ca and S is less certain, but may be related to land use and environmental change