Seasonal changes in gaseous elemental mercury in relation to monsoon cycling over the northern South China Sea

© The Author(s), 2012. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Atmospheric Chemistry and Physics 12 (2012): 7341-7350, doi:10.5194/acp-12-7341-2012.The distribution of gaseous elemental mercury (GEM) was determined in the surface atmosphere of the northern South China Sea (SCS) during 12 SEATS cruises between May 2003 and December 2005. The sampling and analysis of GEM were performed on board ship by using an on-line mercury analyzer (GEMA). Distinct annual patterns were observed for the GEM with a winter maximum of 5.7 ± 0.2 ng m−3 (n = 3) and minimum in summer (2.8 ± 0.2; n = 3), with concentrations elevated 2–3 times global background values. Source tracking through backward air trajectory analysis demonstrated that during the northeast monsoon (winter), air masses came from Eurasia, bringing continental- and industrial-derived GEM to the SCS. In contrast, during summer southwest monsoon and inter-monsoon, air masses were from the Indochina Peninsula and Indian Ocean and west Pacific Ocean. This demonstrates the impact that long-range transport, as controlled by seasonal monsoons, has on the Hg atmospheric distribution and cycling in the SCS.Support was provided by the National Science Council (Taiwan, Republic of China) through grant number NSC 97-2745-M-002-001-;98- 2611-M-002-013- and through a thematic research grant titled “Atmospheric Forcing on Ocean Biogeochemistry (AFOBi)” and from the College of Science (COS#1010023540), National Taiwan University (NTU#101R3252) through a grant of the NTU “Aim for Top University Project” under research platform of the “Drunken-Moon Lake” scientific integration

Mapping evapotranspiration variability over a complex oasis-desert ecosystem based on automated calibration of Landsat 7 ETM+ data in SEBAL

Fragmented ecosystems of the desiccated Aral Sea seek answers to the profound local hydrologically- and water-related problems. Particularly, in the Small Aral Sea Basin (SASB), these problems are associated with low precipitation, increased temperature, land use and evapotranspiration (ET) changes. Here, the utility of high-resolution satellite dataset is employed to model the growing season dynamic of near-surface fluxes controlled by the advective effects of desert and oasis ecosystems in the SASB. This study adapted and applied the sensible heat flux calibration mechanism of Surface Energy Balance Algorithm for Land (SEBAL) to 16 clear-sky Landsat 7 ETM+ dataset, following a guided automatic pixels search from surface temperature T-s and Normalized Difference Vegetation Index NDVI (). Results were comprehensively validated with flux components and actual ET (ETa) outputs of Eddy Covariance (EC) and Meteorological Station (KZL) observations located in the desert and oasis, respectively. Compared with the original SEBAL, a noteworthy enhancement of flux estimations was achieved as follows: - desert ecosystem ETa R-2 = 0.94; oasis ecosystem ETa R-2 = 0.98 (P < 0.05). The improvement uncovered the exact land use contributions to ETa variability, with average estimates ranging from 1.24 mm to 6.98 mm . Additionally, instantaneous ET to NDVI (ETins-NDVI) ratio indicated that desert and oasis consumptive water use vary significantly with time of the season. This study indicates the possibility of continuous daily ET monitoring with considerable implications for improving water resources decision support over complex data-scarce drylands

Remote Sensing Supported Sea Surface pCO(2) Estimation and Variable Analysis in the Baltic Sea

Marginal seas are a dynamic and still to large extent uncertain component of the global carbon cycle. The large temporal and spatial variations of sea-surface partial pressure of carbon dioxide (pCO(2)) in these areas are driven by multiple complex mechanisms. In this study, we analyzed the variable importance for the sea surface pCO(2) estimation in the Baltic Sea and derived monthly pCO(2) maps for the marginal sea during the period of July 2002-October 2011. We used variables obtained from remote sensing images and numerical models. The random forest algorithm was employed to construct regression models for pCO(2) estimation and produce the importance of different input variables. The study found that photosynthetically available radiation (PAR) was the most important variable for the pCO(2) estimation across the entire Baltic Sea, followed by sea surface temperature (SST), absorption of colored dissolved organic matter (a(CDOM)), and mixed layer depth (MLD). Interestingly, Chlorophyll-a concentration (Chl-a) and the diffuse attenuation coefficient for downwelling irradiance at 490 nm (Kd_490nm) showed relatively low importance for the pCO(2) estimation. This was mainly attributed to the high correlation of Chl-a and Kd_490nm to other pCO(2)-relevant variables (e.g., a(CDOM)), particularly in the summer months. In addition, the variables' importance for pCO(2) estimation varied between seasons and sub-basins. For example, the importance of a(CDOM) were large in the Gulf of Finland but marginal in other sub-basins. The model for pCO(2) estimate in the entire Baltic Sea explained 63% of the variation and had a root of mean squared error (RMSE) of 47.8 mu atm. The pCO(2) maps derived with this model displayed realistic seasonal variations and spatial features of sea surface pCO(2) in the Baltic Sea. The spatially and seasonally varying variables' importance for the pCO(2) estimation shed light on the heterogeneities in the biogeochemical and physical processes driving the carbon cycling in the Baltic Sea and can serve as an important basis for future pCO(2) estimation in marginal seas using remote sensing techniques. The pCO(2) maps derived in this study provided a robust benchmark for understanding the spatiotemporal patterns of CO2 air-sea exchange in the Baltic Sea

Net Community Production and Carbon Exchange From Winter to Summer in the Atlantic Water Inflow to the Arctic Ocean

The eastern Fram Strait and area north of Svalbard, are influenced by the inflow of warm Atlantic water, which is high in nutrients and CO2, influencing the carbon flux into the Arctic Ocean. However, these estimates are mainly based on summer data and there is still doubt on the size of the net ocean Arctic CO2 sink. We use data on carbonate chemistry and nutrients from three cruises in 2014 in the CarbonBridge project (January, May, and August) and one in Fram Strait (August). We describe the seasonal variability and the major drivers explaining the inorganic carbon change (CDIC) in the upper 50 m, such as photosynthesis (CBIO), and air-sea CO2 exchange (CEXCH). Remotely sensed data describes the evolution of the bloom and net community production. The focus area encompasses the meltwater-influenced domain (MWD) along the ice edge, the Atlantic water inflow (AWD), and the West Spitsbergen shelf (SD). The CBIO total was 2.2 mol C m–2 in the MWD derived from the nitrate consumption between January and May. Between January and August, the CBIO was 3.0 mol C m–2 in the AWD, thus CBIO between May and August was 0.8 mol C m–2. The ocean in our study area mainly acted as a CO2 sink throughout the period. The mean CO2 sink varied between 0.1 and 2.1 mol C m–2 in the AWD in August. By the end of August, the AWD acted as a CO2 source of 0.7 mol C m–2, attributed to vertical mixing of CO2-rich waters and contribution from respiratory CO2 as net community production declined. The oceanic CO2 uptake (CEXCH) from the atmosphere had an impact on CDIC between 5 and 36%, which is of similar magnitude as the impact of the calcium carbonate (CaCO3, CCALC) dissolution of 6–18%. CCALC was attributed to be caused by a combination of the sea-ice ikaite dissolution and dissolution of advected CaCO3 shells from the south. Indications of denitrification were observed, associated with sea-ice meltwater and bottom shelf processes. CBIO played a major role (48–89%) for the impact on CDIC.publishedVersio

Ocean Surface Carbon Dioxide Fugacity Observed from Space

We have developed and validated a statistical model to estimate the fugacity (or partial pressure) of carbon dioxide (CO2) at sea surface (pCO2sea) from space-based observations of sea surface temperature (SST), chlorophyll, and salinity. More than a quarter million in situ measurements coincident with satellite data were compiled to train and validate the model. We have produced and made accessible 9 years (2002-2010) of the pCO2sea at 0.5 degree resolutions daily over the global ocean. The results help to identify uncertainties in current JPL Carbon Monitoring System (CMS) model-based and bottom-up estimates over the ocean. The utility of the data to reveal multi-year and regional variability of the fugacity in relation to prevalent oceanic parameters is demonstrated

Kasvuhoonegaaside voogude ajaline ja ruumiline käik looduslikes ja kuivendatud soodes

Väitekirja elektrooniline versioon ei sisalda publikatsiooneSoodel on oluline roll kliima reguleerimisel, tulvade leevendamisel ning bioloogilise- ja maastikulise mitmekesisuse säilitamisel. Looduslikud sood seovad õhust süsinikku ja talletavad selle turbana, sest keskkond on veega küllastunud. Soode kuivendamine – peamiselt põllumajanduse ja metsanduse tõttu – on muutnud sood olulisteks kasvuhoonegaaside (CO2 ja dilämmastikoksiidi (N2O) ehk naerugaas) allikaks. Turbaalad katavad maailma maismaast vaid 3%, kuid Eestis lausa 22,3% (~1 009 000 ha), ent jätkuvalt looduslikus seisundis soid leidub Eestis vaid 5,5% territooriumist. Doktoritöö eesmärk oli täpsustada kasvuhoonegaaside ‒ CO2, CH4, N2O ‒ vooge looduslikes ja kuivendatud soodes, analüüsida voogusid mõjutavaid keskkonnaparameetreid ning luua statistilised mudelid, mis võimaldaks kaudsete tunnuste abil gaasivooge hinnata. Turbaaladel mõõdeti kasvuhoonegaaside vooge, mulla- vee- taimkatte ning kaasnevate keskkonnaparameetrite andmeid nii Eestis (26 ala) kui ka mujalt (58 ala). Selgus, et intensiivne turbaalade majandamine muudab mulla süsiniku-lämmastiku tasakaalu, suurendab CO2 ja N2O voogusid ja nende varieeruvust. Kui toitainevaestes rabades olid naerugaasivood hoolimata kuivendusest väikesed, siis siirdesoodes, kus mulla lämmastikusisaldus on suurem, olid need ligi kümme korda kõrgemad. Kuivenduse väga tugev mõju ulatub kuni 50 m kaugusele kuivenduskraavist ning mõju on tugevam toitainerikkamates soodes. Looduslikel aladel on üksikute keskkonnatunnuste mõju kasvuhoonegaaside voogudele väiksem kui majandatavatel aladel, kus ökosüsteemi tasakaal on rikutud ning võtmetegurid (sügavam veetase, kõrgem pinnase temperatuur, hapnikusisaldus, parem lämmastiku kättesaadavus mikroorganismidele) tingivad kõrgemad vood nii lokaalselt kui ka globaalselt. Kuna soode taimkatet mõjutab otseselt veerežiim ja mullaprotsessid, on kaugseire vahenditega tuvastatavate taimkattemuutuste kasutamine KHG voogude uurimisel perspektiivne lahendus. Taimestiku indikaatoreid on maastikutasandil aga seni vähe kasutatud. Tulemuste põhjal võib väita, et turbasammalde katvus, aerolaserskanneerimise teel mõõdetud puude kõrgus ja võrakatvus on olulised indikaatorid, mis aitavad hinnata turbaalade kasvuhoonegaaside vooge. Näiteks kirjeldab turbasammalde katvus, sarnaselt puude võrakatvusega, 42% siirdesoode metaani ja 43% N2O voost. Satelliidilt mõõdetavat maapinna temperatuuri saab kasutada CO2 voo indikaatorina – see kirjeldab täpsemini kuivendatud alade CO2 voogu, näiteks mahajäetud turbatootmisaladel 69%, kuivenduskraavidega alal 65%, kui looduslikus rabas (26%). Töö näitab, et inimtekkelise kuivenduse mõju on CO2, CH4 ja N2O voogudele ulatuslik ning neid mõjutavad peamiselt veetase, mullaniiskus, mulla temperatuur, mulla süsiniku ja lämmastiku sisaldus, seda sõltumata turbaala tüübist, klimaatilisest vööndist või kontinendist.Peatlands are important natural ecosystems with high value for climate regulation, biodiversity conservation and flood control. Intact peatlands bound atmospheric carbon dioxide (CO2) as carbon (C) and accumulate it as peat in water saturated environment. Land use change and associated drainage of mires have turned carbon accumulating peatlands to significant sources of greenhouse gases (GHG) CO2 and N2O. While peatlands cover merely 3% of the world’s land area, they form 22.3% (~1 009 000 ha) of Estonian territory, yet only 5.5% of the territory is covered with mires. The main aim of the study was to quantify GHG ‒ CO2, CH4, N2O ‒ fluxes from natural and drained peatlands, analyse the role of environmental factors on the fluxes and to create statistical models to assess the fluxes using indirect indicators. To conduct the study, 26 peatlands in Estonia and 58 all over the world were sampled for GHG fluxes, soil, water, vegetation, and other accompanying environmental parameters. The results demonstrate that intensive peatland management alters the soil carbon/nitrogen balance, increases emissions of CO2, N2O, and leads to higher variability of GHG emissions. Despite the drainage, emission of N2O was minor in nutrient poor bogs. On the other hand, in transitional bogs with higher soil nitrogen stocks, the emission of N2O was 10 times greater. The effect of drainage is very strong up to 50 m from the ditch and stronger in nutrient rich peatlands. In natural areas, the effect of any single environmental variable on GHG fluxes is smaller and emissions are lower than in managed areas where the ecosystem balance is affected and several key factors e.g. decreased water level, increased soil temperature, oxygen content, nitrogen availability contribute to higher emissions, both in local and global scale. Peatlands’ vegetation composition and structure, relatively easily detectable using remote sensing techniques, is partly controlled by the water level and soil processes. Therefore, vegetation changes are a convenient monitoring tool for the environmental changes related to GHG fluxes. Using vegetation based indicators for estimations of GHG fluxes in landscape level is almost absent in previous studies. The results show that the coverage of Sphagnum mosses, and airborne LIDAR-data based tree layer canopy height and cover are important indicators for assessing the emissions of GHG-s in peatlands. For example, the coverage of Sphagnum mosses alone explains 42% of the CH4 (as does the tree canopy coverage independently) and 43% of N2O flux in transitional bogs. Remotely sensed land surface temperature can be used as indicator for CO2 fluxes. Satellite based land surface temperature is better indicator of CO2 fluxes in drainage affected areas (abandoned peat extraction areas 69%, drained peatland 65%) rather than mires (26%). The results of this dissertation demonstrate the extensive impact of artificial drainage on the fluxes of CO2, CH4 and N2O, and that the leading driving factors of GHG-s such as water table depth or soil water content, soil temperature, soil carbon and nitrogen content are universal despite the type of peatland, climate zone or continent.https://www.ester.ee/record=b546674

The role of the Arctic and Antarctic and their impact on global climate change: Further findings since the release of IPCC AR4, 2007

Changes in the climate of the Arctic and of the Antarctic have been of great concern to the international scientific and social communities since the release in 2007 of the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). Since then, many new findings have been reported from observations and research carried out in the Arctic and Antarctic during the fourth International Polar Year (IPY). There is evidence that global warming is inducing rapid changes in the Arctic and Antarctic, in both a quantitative and qualitative sense, and that these regional changes could be used as indicators of global climate change. Declining Arctic sea ice could affect winter snowfall across much of the Northern Hemisphere by bringing harsher winters. Projections suggest that summertime Arctic sea ice will disappear by 2037. By the 2070s, the Antarctic ozone hole will recover to the level of the early 1980s, following the ban on the production of Freon earlier this century. With the loss of the shielding effect of the ozone hole, Antarctic surface temperatures will increase, ice sheets in East Antarctica will begin to melt, and the Antarctic sea ice will retreat. Therefore, sea level rise will become an increasingly serious issue this century. As sea surface temperature rises, the Southern Ocean will become less effective as a sink for atmospheric CO2 and the increase of surface CO2 will be faster than that in the atmosphere. Increased surface CO2 would lead to ocean acidification and affect ecological systems and food chains

Review of CHINARE chemical oceanographic research in the Southern Ocean during 1984–2016

Between 1984 and 2016, China executed 33 Antarctic cruises with the icebreaker R/V Xuelong, which have provided opportunities for Chinese scientists to investigate the status and changes of the Southern Ocean. Research in chemical oceanography constitutes one of the primary missions of the Chinese National Antarctic Research Expedition (CHINARE). This paper reviews nearly 30 years of Chinese Antarctic expeditions, focusing on the major progress achieved in chemical oceanographic research. Specifically, the sea-surface distributions and air–sea fluxes of CO2 and N2O are considered, and the transport, flux, and budget of organic matter are investigated based on isotopes in the Southern Ocean, especially in Prydz Bay. In addition, the nutrient distribution and deep-water particle export in Prydz Bay and the study of aerosol heavy metal characteristics are considered. Finally, the prospects for future Chinese Antarctic chemical oceanographic research are outlined

Effect of ENSO phase on large-scale snow water equivalent distribution in a GCM

Understanding links between the El Nino-Southern Oscillation (ENSO) and snow would be useful for seasonal forecasting, but also for understanding natural variability and interpreting climate change predictions. Here, a 545-year run of the general circulation model HadCM3, with prescribed external forcings and fixed greenhouse gas concentrations, is used to explore the impact of ENSO on snow water equivalent (SWE) anomalies. In North America, positive ENSO events reduce the mean SWE and skew the distribution towards lower values, and vice versa during negative ENSO events. This is associated with a dipole SWE anomaly structure, with anomalies of opposite sign centered in western Canada and the central United States. In Eurasia, warm episodes lead to a more positively skewed distribution and the mean SWE is raised. Again, the opposite effect is seen during cold episodes. In Eurasia the largest anomalies are concentrated in the Himalayas. These correlations with February SWE distribution are seen to exist from the previous June-July-August (JJA) ENSO index onwards, and are weakly detected in 50-year subsections of the control run, but only a shifted North American response can be detected in the anaylsis of 40 years of ERA40 reanalysis data. The ENSO signal in SWE from the long run could still contribute to regional predictions although it would be a weak indicator onl