Liqi Chen

Decrease in the CO2 Uptake Capacity in an Ice-Free Arctic Ocean Basin

Sinking in Slowly As the Arctic warms and its sea ice continues to melt, more of the ocean surface will be exposed, creating the potential for greater uptake of carbon dioxide from the atmosphere. Cai et al. (p. 556, published online 22 July) present results from a series of Arctic Ocean transects that show that the amount of CO2 in the surface waters has increased greatly recently. This will act as a barrier to future CO2 uptake and suggests that the Arctic Ocean will not become the large CO2 sink that some have predicted. The current carbon dioxide levels in the Arctic Ocean basin will limit further uptake under ice-free conditions. It has been predicted that the Arctic Ocean will sequester much greater amounts of carbon dioxide (CO2) from the atmosphere as a result of sea ice melt and increasing primary productivity. However, this prediction was made on the basis of observations from either highly productive ocean margins or ice-covered basins before the recent major ice retreat. We report here a high-resolution survey of sea-surface CO2 concentration across the Canada Basin, showing a great increase relative to earlier observations. Rapid CO2 invasion from the atmosphere and low biological CO2 drawdown are the main causes for the higher CO2, which also acts as a barrier to further CO2 invasion. Contrary to the current view, we predict that the Arctic Ocean basin will not become a large atmospheric CO2 sink under ice-free conditions.

Persistent toxic substances in remote lake and coastal sediments from Svalbard, Norwegian Arctic: Levels, sources and fluxes

Surface sediments from remote lakes and coastal areas from Ny-Alesund, Svalbard, Norwegian Arctic were analyzed for polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs). Relatively high levels of PAHs were encountered from several lakes from Ny-Alesund, which were within the range of levels reported for European high mountain lakes and some urban/industrialized areas in the world, pointing to the role of remote Arctic lakes as potential reservoir of semi-volatile organic compounds. Specific patterns of PBDEs were observed, showing higher concentrations of lower brominated compounds such as BDE-7, 17 and 28. Estimated surface sediment fluxes of PAHs in Ny-Alesund remote lakes were similar to those observed for some European high mountain lakes. The current PAH levels in sediments from three lakes exceeded Canadian sediment quality guidelines, suggesting the presence of possible risks for aquatic organisms and the need for further studies.

Atmospheric non-sea-salt sulfate, nitrate and methanesulfonate over the China Sea

To characterize atmospheric particulate non-sea-salt (nss) sulfate, nitrate, methanesulfonate (MSA), and selected trace elements over the China Sea, aerosol sampling was conducted at Qingdao and Xiamen, which are on the coast of China, and over offshore regions of the East China Sea. The atmospheric concentrations of nss sulfate and nitrate were much higher along the coast of the China Sea than over remote oceans, with mean values of 10 to 12 μg m−3 for nss sulfate and 5.6 to 7.7 μg m−3 for nitrate. The mean concentrations of atmospheric MSA ranged from 0.029 to 0.066 μg m−3 over the China Sea; these are comparable to values from other coastal sites and remote oceans. Both MSA and nss sulfate are concentrated in particles ≤0.5 μm in diameter, while nitrate shows a bimodel distribution. There was no clear correlation between nss sulfate and MSA concentrations, with the ratios of nss sulfate to MSA (60–870) being substantially higher than those over remote oceans. Based on a biogenic nss-sulfate/MSA ratio of 18 obtained from the remote North Pacific, the estimated anthropogenic sulfate accounts for 81–97% of the total nss sulfate over the China Sea. Results of factor analyses suggest that coal combustion is the dominate source for anthropogenic sulfate over the basin of the China Sea. Oil combustion appears to be an additional important contributor for anthropogenic sulfate in the region of the East China Sea, but this feature does not exist in the South China Sea region. Pyrometallurgical nonferrous metal smelting is among the additional sources for nss sulfate in this region.

Spatial and particle size distributions of atmospheric dissolvable iron in aerosols and its input to the Southern Ocean and coastal East Antarctica

[1]xa0To characterize atmospheric dissolvable iron over the Southern Ocean (SO) and coastal East Antarctica (CEA), bulk and size-segregated (0.056–18u2009µm in diameter) aerosols were collected from 34°S, 109°E to 69°S, 76°E and between 69°S, 76°E and 66°S, 110°E during a cruise during November 2010 to March 2011. Aerosols were analyzed for total dissolvable Fe and Fe(II) by UV/Visible spectroscopy and total Fe by inductively coupled plasma-mass spectrometry. The average concentrations of total Fe were 19u2009ngu2009m−3 (range: 10–38u2009ngu2009m−3) over the SO and 26u2009ngu2009m−3 (range: 14–56u2009ngu2009m−3) in CEA. The average Fe(II) concentrations were 0.22u2009ngu2009m−3 (range: 0.13–0.33u2009ngu2009m−3) over the SO and 0.53u2009ngu2009m−3 (range: 0.18–1.3u2009ngu2009m−3) over CEA; the total dissolvable Fe followed the same trend. Over the SO, a single-peak size distribution of Fe(II) existed. Over CEA, a bimodal size distribution of Fe(II) appeared, with the first peak at 0.32–0.56u2009µm and the second peak at 5.6–10u2009µm. Higher Fe concentrations over CEA than over the SO and the existence of coarse mode Fe(II) over CEA suggest potential dust sources in Antarctica. The fractional Fe(II) solubility ranged from 0.58% to 6.5% and decreased with total Fe concentration increase. The estimated atmospheric fluxes of Fe(II) were 0.007–0.092u2009mgu2009m−2u2009yr−1 over the SO and 0.022–0.21u2009mgu2009m−2u2009yr−1 in CEA. Total dissolvable Fe fluxes were 0.007–0.52u2009mgu2009m−2u2009yr−1 over the SO. The atmospheric dissolvable Fe input contributes to the dissolved Fe pool in the SO surface waters.

Historical trends of organic pollutants in sediment cores from Hong Kong

Recent studies have indicated the occurrence of a wide range of trace organic contaminants, including polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in the Hong Kong environment. These contaminants are potentially harmful to ecological systems, particularly in coastal areas. In this study, two sediment cores (4m) were collected from southern waters of Hong Kong in 2004 to study the historical trends, distribution patterns, and potential sources of trace organic contaminants. DDTs (p,p-DDT, o,p-DDT, p,p-DDD, o,p-DDD and p,p-DDE), hexachlorohexanes (HCHs) (alpha and gamma), hexachlorobenzene (HCB), and PCBs were detected in the samples, whereas other target compounds were all below detection limits. Many OCPs have not been produced or used for many years due to toxicological or environmental concerns and PCB use is prohibited in Hong Kong. However, some compounds were still detectable in recent years, and were found to be widely distributed in the environment, likely because of pollutant inputs from the highly industrialized Pearl River Delta region. These results provide important information on current and historical contamination in Hong Kong, and help to reconstruct the pollution history of these trace organic pollutants in Hong Kong coastal waters.

Characteristics of water-soluble inorganic and organic ions in aerosols over the Southern Ocean and coastal East Antarctica during austral summer

[1]xa0To characterize the concentrations and size distributions of water-soluble organic and inorganic aerosol species, including Na+, non-sea-salt sulfate (nss SO42−), methane sulfonate (MSA), oxalate, and succinate, over the Southern Ocean (SO) and coastal East Antarctica (CEA), bulk and size-segregated aerosols were collected from 40°S, 100°E to 69°S, 76°E and between 69°S, 76°E and 66°S, 110°E during a cruise from November 2010 to March 2011. Results show that sea salt was the major component of the total aerosol mass, accounting for 72% over the SO and 56% over CEA. The average concentrations of nss SO42− varied from 420u2009ngu2009m−3 over the SO to 480u2009ngu2009m−3 over CEA. The concentrations of MSA ranged from 63 to 87u2009ngu2009m−3 over the SO and from 46 to 170u2009ngu2009m−3 in CEA. The average concentrations of oxalate were 3.8u2009ngu2009m−3 over the SO and 2.2u2009ngu2009m−3 over CEA. The concentrations of formate, acetate, and succinate were lower than those of oxalate. A bimodal size distribution of aerosol mass existed over CEA, peaking at 0.32–0.56u2009µm and 3.2–5.6u2009µm. MSA was accumulated in particles of 0.32–0.56u2009µm over CEA. High chloride depletion was associated with fine-mode particles enriched with nss SO42−, MSA, and oxalate. Higher cation-to-anion and NH4+/nss SO42− ratios in aerosols over CEA compared to that over the SO imply the higher neutralization capacity of the marine atmosphere over CEA.

Latitudinal distributions of atmospheric MSA and MSA/nss-SO42− ratios in summer over the high latitude regions of the Southern and Northern Hemispheres

high-latitude regions, bulk aerosol samples were collected during eight cruises during the Chinese National Antarctic and Arctic Research Expeditions from 1998 to 2008. The concentrations of MSA (an indicator of marine biogenic sulfur production), sulfate, sodium and chloride in samples were analyzed using ion chromatography. Increases in the aerosol MSA concentrations and MSA/nss-SO4 ratios were observed as functions of latitudes in the Pacific Ocean, more abruptly near high southern latitudes as compared to those in high northern latitudes. The MSA concentrations increased from 0.011 m gm 3 near the equator to 0.26 m gm 3 at 63S, 23W and from 0.0013 m gm 3 at northern midlatitudes to 0.19 m gm 3 at 58N, 175E. However, MSA decreased in the latitudes north of 58N in the Pacific, where air temperature was lower. MSA/nss-SO4 ratios increased from 0.024 near the equator to 0.93 at 62S, 4E and from 0.0031 around northern midlatitudes to 0.39 at 68N, 169W. The MSA concentrations were more correlated with MSA/nss-SO4 (R 2 = 0.43, n = 60) in Southern Hemisphere than Northern Hemisphere (R 2 = 0.091, n = 40). No significant correlation was found between MSA/nss-SO4 and air temperature at high latitudes, indicating latitudinal temperature variations were not a main factor responsible for the MSA/nss-SO4 variation in those regions. Substantial increases in the concentrations of MSA in coastal Antarctica may indicate additional sources of biogenic S besides the emissions of dimethylsulfide from the sea.

Effects of ship emissions on summertime aerosols at Ny–Alesund in the Arctic

Abstract Selected trace elements, ionic species and organic/elemental carbon in aerosols were measured in summer at Ny–Alesund in the Arctic, and an interpreted approach combining elemental ratios, back–trajectories and enrichment factors was used to assess the sources of aerosols observed at this location. Aerosol samples influenced by ship emissions were featured by elevated concentrations of non–crustal (nc) vanadium (V), nc–nickel (nc–Ni), non–sea salt (nss) sulfate (SO42−) and ratios of nc–Ni/nc–V (1.7) and nss–SO42−/nc–V (200). When two cruise ships with more than 1 500 passengers visited Ny–Alesund in July 2012, the total suspended particulate (TSP) mass reached 2 290xa0ng m−3, almost three times the median TSP concentration (609xa0ng m−3) measured during the study period. The nc–V concentration reached 0.976xa0ng m−3, about 38–fold higher compared to the mean value of the sampling period, and this value was even higher than the annual mean value observed at Zeppelin station and the values measured during Haze events at North American Arctic and Norwegian Arctic. The concentrations of nc–Ni and nss–SO42− were 0.572xa0ng m−3 and 203xa0ng m−3, which were 8–fold and 2–fold higher than the median values of the sampling period. While in the few–ship period, defined as the period with none or only one cruise ship with less than 1 000 passengers being present, aerosols at this location could be affected by a mixed impact of local emissions and long–range transport, reflected by the nc–Mn/nc–V ratios and element enrichment factors often found in the air masses from North America Arctic, Iceland and North Eurasia. Results from this study suggest that cruise ship emissions contributed significantly to atmospheric particulate matter at Ny–Alesund in the summer, effecting air quality in this area.

A system for the automated static headspace analysis of dissolved N2O in seawater

A new automated static headspace N2O analysis technique has been developed that includes a CTC autosampler composed of agitator and headspace modules, a combined-valve switching system and ECD Gas Chromatography. This new CTC autosampling technique is more efficient for sample analysis than similar systems and takes approximately 10 mins to analyze each sample without pre-equilibration. The accuracy and precision of this method are approximately 2% each. Laboratory and field results demonstrate that this technique is suitable for seawater sample analysis.

Distributions of N2O and its air‐sea fluxes in seawater along cruise tracks between 30°S–67°S and in Prydz Bay, Antarctica

[1] Air and surface seawater samples were taken during the 22nd Chinese National Antarctic Research Expedition, November 2005 to March 2006, and analyzed for N 2 O concentrations. The results show that the concentration of N 2 O in surface seawater increased from 8.9 ± 0.2 nM to 17.9 ± 0.3 nM along the cruise tracks southward from 30°S-67°S latitude and correlated well with sea surface temperature (SST). The saturation anomaly along the cruise tracks changed from negative (south) to positive (north) with the turning point located between 50 and 55°S latitude coincident with the location of the Subantarctic Front (SAF). Positive saturation found north of the SAF is due to the seasonal SST variation, while the undersaturation of N 2 O south of the SAF may be due to a combination of SST variation and intrusion of N 2 O-depleted ice meltwater during summer. Air-sea fluxes measured on the cruise tracks north of the SAF were positive, ranging between 5 and 10 μmol m -2 d -1 , while fluxes south of the SAF were close to zero. N 2 O in the surface water of Prydz Bay was in near equilibrium with the atmosphere: the corresponding air-sea flux was about -0.3 ± 0.8 μmol m -2 d -1 , not different from zero.