Sensitivity of the simulated CO2 concentration to inter-annual variations of its sources and sinks over East Asia

The study on how the variations in CO2 sources and sinks can affect the CO2 concentration over East Asia would be useful to provide information for policymaker concerning carbon emission reduction.In this study,a nested-grid version of global chemical transport model(GEOS-Chem)is employed to assess the impacts of variations in meteorological parameters,terrestrial fluxes,fossil fuel emissions,and biomass burning on inter-annual variations of CO2 concentrations over East Asia in 2004—2012.Simulated CO2 concentrations are compared with observations at 14 surface stations from the World Data Centre for Greenhouse Gases(WDCGG)and satellite-derived C 02 column density(XCO,)from the Gases Observing SATellite(GOSAT).The comparison shows that the simulated CO2 column density is generally higher than that of GOSAT by 1.33×10^6(annual mean point by point biases averaged over East Asia).The model reasonably captures the temporal variations of CO2 concentrations observed at the ground-based stations,but it is likely to underestimate the peaks-to-troughs amplitude of the seasonal cycle by 50%or more.The simulated surface CO2 concentration in East Asia exhibits the largest inter-annual variation in December-January—February(DJF).The regional mean absolute deviation(MAD)values over East Asia are within(4.4—5.0)×10^-6 for all seasons.Model sensitivity simulations indicate that the inter-annual variations of surface CO2 concentrations are mainly driven by variations of meteorological parameters,and partly modulated by the inter-annual variations of terrestrial fluxes and fossil fuel emissions in local regions.The variations of the terrestrial fluxes and fossil fuel emissions may account for〜28%of the inter-annual variation of surface CO2 concentration in southern China.The inter-annual variations of the peaks-to-troughs amplitude are dependent on variations of meteorological parameters,terrestrial fluxes and fossil fuel emissions in local regions.The influence of biomass burning emissions is relatively weak.

The distribution and inter-annual variation of water masses on the Bering Sea shelf in summer

On the basis of the CTD data obtained within the Bering Sea shelf by the Second to Sixth Chinese National Arctic Research Expedition in the summers of 2003, 2008, 2010, 2012 and 2014, the classification and interannual variation of water masses on the central Bering Sea shelf and the northern Bering Sea shelf are analyzed. The results indicate that there are both connection and difference between two regions in hydrological features. On the central Bering Sea shelf, there are mainly four types of water masses distribute orderly from the slope to the coast of Alaska： Bering Slope Current Water（BSCW）, MW（Mixed Water）, Bering Shelf Water（BSW） and Alaska Coastal Water（ACW）. In summer, BSW can be divided into Bering Shelf Surface Water（BSW_S） and Bering Shelf Cold Water（BSW_C）. On the northern Bering Sea shelf near the Bering Strait,it contains Anadyr Water（AW）, BSW and ACW from west to east. But the spatial-temporal features are also remarkable in each region. On the central shelf, the BSCW is saltiest and occupies the west of 177°W, which has the highest salinity in 2014. The BSW_C is the coldest water mass and warmest in 2014; the ACW is freshest and mainly occupies the east of 170°W, which has the highest temperature and salinity in 2012. On the northern Bering Sea shelf near the Bering Strait, the AW is saltiest with temperature decreasing sharply compared with BSCW on the central shelf. In the process of moving northward to the Bering Strait, the AW demonstrates a trend of eastward expansion. The ACW is freshest but saltier than the ACW on the central shelf,which is usually located above the BSW and is saltiest in 2014. The BSW distributes between the AW and the ACW and coldest in 2012, but the cold water of the BSW_C on the central shelf, whose temperature less than 0°C, does not exist on the northern shelf. Although there are so many changes, the respond to a climate change is synchronized in the both regions, which can be divided into the warm years（2003 and 2014） and cold years（2008, 2010 and 2012）. The year of 2014 may be a new beginning of warm period.

Analysis of the inter-annual variability and southward expansion of red tides in the Zhejiang coastal waters from 1981 to 2018

A time series dataset spanning 39 years(1981-2018) on red tide events in Zhejiang coastal waters was used to study the characteristics of inter-annual spatial and temporal variations. A distinct inter-annual pattern characterized by low frequency, explosive growth and fluctuating decline stages was found over the studied time scale. Most red tide events occurred in parallel to the bathymetric contour, and 95.4% were located to the west of the 50 m isobath. Additionally, the high-incidence area of red tides is expanding southward. In this paper, local sea surface temperature(SST), mariculture area and secondary industry growth rate are introduced and identified as the main factors influencing the nutrient and hydrometeorological conditions. A multivariate nonlinear regression equation based on these factors was constructed, and the goodness of fit coefficient was 0.907. The causes of the annual variation and high-frequency area in the southward expansion were quantitatively analyzed based on the proposed regression model. Finally, the results indicated that 68.7% of the annual occurrence variation of red tide was due to the SST and mariculture area, which are the main impact factors;however,secondary industry growth could compensate for the nutrient deficiency caused by the sharp mariculture area reduction and decreased SST. The background nutrient level, which is elevated by coastal economic development, especially secondary industry, is the main determinant of the southward expansion. Although the trend of the southward expansion of high-frequency areas has not changed, the red tide frequency in coastal cities has decreased by half and remained at a stable level after 2010 due to substantial economic restructuring and environmental protection.

Temporal-Spatial Variation of Surface Suspended Matter and Controlling Factors in the Inner Shelf of the East China Sea in Winter

Based on the observed surface suspended matter in the East China Sea in February 2007 and June 2015, an empirical model was established using L1 b's band 4 data to retrieve surface suspended matter from the Moderate Resolution Imagine Spectroradiometer Terra imagery. The squared correlation coefficient is 0.8358, and the root mean square error is 0.4285 mg L-1. The model reflects the distribution characteristics of surface suspended matter in the inner shelf of the East China Sea. In this paper, the satellite images of the study area were retrieved in January from 2001 to 2015, and the monthly distribution of surface suspended matter were obtained. The inter-annual distribution of the study area is similar, and the concentration of surface suspended matter is higher near the shore than offshore. A large amount of surface suspended matter is transported southeast under the influence of Zhejiang and Fujian coastal current and Taiwan warm current. Only a small amount of surface suspension can reach the Kuroshio area. The surface suspended matter concentration changes obviously near the estuary because of the effect of differences in the flux of the Yangtze River. Meanwhile, winter monsoon, temperature front, El Ni?o events, and other factors affect the distribution of surface suspended matter in 100 m isobath to coastal water but minimally influence the distribution in 100 m isobath to deep sea.

Inter-annual variation of the earth rotation and El Nio

The relationship between the inter-annual variations of the earth rotation, atmospheric angular momentum (AAM), sunspot number and El Ni(?)o is analyzed. The result shows that the inter-annual variation of the earth rotation responds to the variation of AAM and the preg-nancy of El Ni(?)o timely. Generally, the inter-annual compo-nent of the earth rotation will reach zero in a changing proc-ess that increases from the negative to the positive extreme before El Ni(?)o occurs about half year or more. And the solar activity may have certain influence on the appearance of El Ni(?)o. We consider that El Ni(?)o will possibly appear around the end of 2001.

Patterns of upper layer circulation variability in the South China Sea from satellite altimetry using the self-organizing map

Patterns of the South China Sea (SCS) circulation variability are extracted from merged satellite altimetry data from October 1992 through August 2004 by using the self-organizing map (SOM). The annual cycle, seasonal and inter-annual variations of the SCS surface circulation are identified through the evolution of the characteristic circulation patterns.The annual cycle of the SCS general circulation patterns is described as a change between two opposite basin-scale SW-NE oriented gyres embedded with eddies: low sea surface height anomaly (SSHA) (cyclonic) in winter and high SSHA (anticyclonic) in summer half year. The transition starts from July—August (January—February) with a high (low) SSHA tongue east of Vietnam around 12°~14° N, which develops into a big anticyclonic (cyclonic) gyre while moving eastward to the deep basin. During the transitions, a dipole structure, cyclonic (anticyclonic) in the north and anticyclonic (cyclonic) in the south, may be formed southeast off Vietnam with a strong zonal jet around 10°~12° N. The seasonal variation is modulated by the interannual variations. Besides the strong 1997/1998 event in response to the peak Pacific El Nio in 1997, the overall SCS sea level is found to have a significant rise during 1999~2001, however, in summer 2004 the overall SCS sea level is lower and the basin-wide anticyclonic gyre becomes weaker than the other years.

Assessing spatio-temporal variations of precipitation-use efficiency over Tibetan grasslands using MODIS and in-situ observations

Clarifying the spatial and temporal variations in precipitation-use efficiency （PUE） is helpful for advancing our knowledge of carbon and water cycles in Tibetan grassland ecosystems. Here we use an integrated remote sensing normalized difference vegetation index （NDVI） and in-situ above-ground net primary production （ANPP） measurements to establish an empirical exponen- tial model to estimate spatial ANPP across the entire Tibetan Plateau. The spatial and temporal variations in PUE （the ratio of ANPP to mean annual precipitation （MAP））, as well as the relationships between PUE and other controls, were then investigated during the 2001- 2012 study period. At a regional scale, PUE increased from west to east. PUE anomalies increased significantly （〉 0.1 g.m^-2.mm^-1/10 yr） in the southern areas of the Tibetan Plateau yet decreased （ 〉 0.02 g. m^-2. mm 1/10 yr） in the northeastern areas. For alpine meadow, we obtained an obvious breaking point in trend of PUE against elevation gradients at 3600 m above the sea level, which showed a contrasting relationship. At the inter-annual scale, PUE anomalies were smaller in alpine steppe than in alpine meadow. The results show that PUE of Tibetan grasslands is generally high in dry years and low in wet years.

Coupling textural and stable-isotope variations in fluvial stromatolites:Comparison of Pleistocene and recent records in NE Spain

Textural and stable isotopic features of two middle Pleistocene fluvial stromatolite profiles are compared to a recent stromatolite,both formed in the River Piedra system(NE Spain),to test the reliability of climatic,hydrologic and depositional information derived from ancient records.The Pleistocene stromatolites formed in a multi-domed,highly-inclined cascade-barrage.The recent stromatolite also formed in a highly-inclined cascade of the River Piedra,the sedimentary conditions of which were periodically examined between the years 2000 and 2012.The Pleistocene stromatolites are formed of an alternation of 1) thin large-crystal laminae(type A),with elongated crystals up to 1 mm long,and 2) thick small-crystal laminae(type B),consisting of cyanobacterial fan-and bushshaped bodies.The textural and isotopic comparison with the recent stromatolite shows that each A–B couplet corresponds to one year.The type-A laminae are comparable to the macrocrystalline laminae that occur in the cool-period deposits of the recent stromatolite,and the type-B laminae are comparable to the warm-period deposits of the recent stromatolite.Water temperatures(Tw),calculated from δ^(18)O_(calcite) and present measures of δ^(18)O_(water),were similar in the Pleistocene and recent specimens,and close to the measured river Tw.Thus,the Pleistocene stromatolites formed not far from isotopic equilibrium,as did the recent stromatolite.The Pleistocene δ^(18) O_(calcite) biannual oscillation is wider in amplitude than in the recent stromatolite,which suggests larger differences in Tw through the year in the Pleistocene than at present.The Pleistocene δ^(13)C_(calcite) does not show any pattern;and the values are slightly higher than the recent ones.The co-evolution of δ^(18)O and δ^(13)C is parallel in the Pleistocene stromatolites,matching the recent stromatolite behavior.These results and their comparison with other ancient examples prove that textural and isotopic features in ancient stromatolites are useful tools to infer past depositional,climatic and hydrological conditions.Moreover,interpretations from recent fluvial stromatolites can be extrapolated to past environments to help decipher patterns of past processes,in cases where both recent and ancient stromatolites can be compared within one environmental setting.Such comparisons may be used to help interpretations of ancient stromatolites where the modern ones are not available to study.

Temperature variation and abrupt change analysis in the Three-River Headwaters Region during 1961-2010

In this study, a monthly dataset of temperature time series （1961-2010） from 12 meteorological stations across the Three-River Headwater Region of Qinghai Province （THRHR） was used to analyze the climate change. The temperature variation and abrupt change analysis were examined by using moving average, linear regression, Spline interpolation, Mann-Kendall test and so on. Some important conclusions were obtained from this research, which mainly contained four aspects as follows. （1） There were several cold and warm fluctuations for the annual and seasonal average temperature in the THRHR and its three sub-headwater regions, but the temperature in these regions all had an obviously rising trend at the statistical significance level, especially after 2001. The spring, summer, autumn and annual average temperature increased evidently after the 1990s, and the winter average temperature exhibited an obvious upward trend after entering the 21st century. Except the standard value of spring temperature, the annual and seasonal temperature standard value in the THRHR and its three sub-headwater regions increased gradually, and the upward trend for the standard value of winter average temperature indicated significantly. （2） The tendency rate of annual average temperature in the THRHR was 0.36℃ 10a^-1, while the tendency rates in the Yellow River Headwater Region （YERHR）, Lancangjiang River Headwater Region （LARHR） and Yangtze River Headwater Region （YARHR） were 0.37℃ 10a^-1, 0.37℃ 10a^-1 and 0.34℃10a^-1 respectively. The temperature increased significantly in the south of Yushu County and the north of Nangqian County. The rising trends of temperature in winter and autumn were higher than the upward trends in spring and summer. （3） The abrupt changes of annual, summer, autumn and winter average temperature were found in the THRHR, LARHR and YARHR, and were detected for the summer and autumn average temperature in the YERHR. The abrupt changes of annual and summer average temperatures were mainly in the late 1990s, while the abrupt changes of autumn and winter average temperatures appeared primarily in the early 1990s and the early 21st century respectively. （4） With the global warming, the diversities of altitude and underlying surface in different parts of the Tibetan Plateau were possibly the main reasons for the high increasing rate of temperature in the THRHR.

Precipitation and seasonality affect grazing impacts on herbage nutritive values in alpine meadows on the Qinghai-Tibet Plateau

Aims Grasslands used for animal husbandry are chosen depending on the nutritive values of dominant herbage species.However,the influence of grazing in combination with precipitation and growing season on the nutritive values of dominant species has not been explicated.Methods To unveil the influence of the different grazing intensities on the nutritional values,an ecological study was formulated,namely fencing(G0),light grazing(G1),moderate grazing(G2)and high grazing(G3).This ambitious study was undertaken on the nutritive values of the four dominant species of herbage in an alpine meadow on the Qinghai-Tibet Plateau(QTP)during growing season(June–September)for two successive years,namely 2015(rainy year)and 2016(droughty year).Important Findings We found that(i)the nutritive value of Kobresia capillifolia,Polygonum viviparum and Caragana sinica was noticeably increased by grazing,but negligible effect on Potentilla fruticosa nutritive value was recorded.(ii)During the rainy year(2015),compared with G0,Polygonum viviparum and Potentilla fruticosa displayed 5.4 and 1.5%increases in the crude protein(CP)content and 8.5 and 2.4%increases in vitro true digestibility(IVTD),respectively,while the neutral detergent fibre(NDF)decreased by 13.5 and 0.9%,respectively.During the droughty year(2016),compared with G0,C.sinica and Potentilla fruticosa showed increases in the CP content by 4.3 and 1.3%and increases in the IVTD by 10.7 and 0.4%,respectively,during G3,while the NDF decreased by 6.0 and 1.0%,respectively.(iii)The nutritive values of all species were higher in the years when the rains were good.However,the nutritive values suffered heavily during drought conditions.Besides,the highest and lowest values of nutrition were detected in June and in September,respectively.The inter-seasonal and the inter-annual changes in the nutritional values of species were higher for K.capillifolia and Polygonum viviparum than for Potentilla fruticosa and C.sinica,suggesting that Potentilla fruticosa and C.sinica had higher water-use efficiency.(iv)Grazing clearly reduced the drought tolerance of three species and showed no effects on Potentilla fruticosa.(v)Grazing clearly increased the inter-month variation in the nutritional value of K.capillifolia and Polygonum viviparum but showed no effects on Potentilla fruticosa or C.sinica.Evidently,the grazing effects impacting the nutritional value of the dominant species of herbage exhibited conspicuous inter-annual and seasonal variations with species-specific influences and responses.Our findings are expected to have far-reaching implications enabling the authorities to arrive at strategic decisions and designing of relevant policies for the efficient management of the ecosystems ensuring the speed restoration of the QTP under severe grazing and extreme climatic circumstances.