Recent Vegetation Cover Dynamics and Climatic Parameters Evolution Study in the Great Green Wall of Senegal

The drought recorded in 1970s and 1980s, particularly in the Sahara and Sahel region has greatly affected the population as well as the economies and the eco-systems of this area. In 2007, the African Union launched a Pan-African program, the Great Green Wall for the Sahara, the Sahel Initiative (GGWSSI) to reverse land degradation and desertification by planting a wall of trees stretching from Dakar to Djibouti. The objective is to improve food security, and support local people to adapt to climate change. This paper aims to evaluate the impacts of the reforestation program in Senegal, fifteen years after it was launched. This study uses a time series of satellite-derived vegetation cover and climatic parameters data to analyze the sustainability of these interventions. Change detection approaches were applied to identify and characterize the drives of the eventual changes. A comparative analysis of reforestation on climatic parameters was explored through the temporal analysis of the vegetation index over the periods 2000-2008 and 2009-2020. An increase in vegetation activity was noted through the NDVI at the interannual (+2% to +8%) and seasonal (+1.5% to 7% for the wet season and 1% to 4% for the dry season) scale and a positive and significant evolution is noted on the trace of the GGW. Also, the period 2009-2020 recorded an increase in rainfall of 2% to 8% of the average value 2000-2020 and 4% to 8% of the rainy season. Soil moisture is the climatic parameter that has increased the most, with an increase of 25% to 54% of the 2000-2020 average, i.e. between 20 mm and 70 mm more. This study shows a significant improvement in the relationship between NDVI and climate parameters after the different reforestation actions of the GGW.

Estimation of the Carbon Sequestration Dynamics of Senegal’s Great Green Wall Based on Land Cover over the Past Three Decades

The severe drought observed in the Sahel during 1970s, 1980s and 1990s has deeply affected the population as well as the economies and the eco-systems of this climatic area. The GGW Initiative spearheaded by Africa Union in 2007 proposed to combat the land degradation and desertification by planting a wall of trees stretching from Dakar to Djibouti. A reforestation was then conducted in the Senegal’s GGW since 2006 as part as other areas in the Sahel. This paper aims to evaluate the carbon sequestration dynamics in the sites of the Senegal’s GGW over the last three decades. The method consists firstly of analyzing the evolution of land cover and land use dynamics based on ESA-CCI LC satellite data. There is an improvement of the surface areas of tree and shrub savanna of 11.40% (Tessekere), 8.25% (Syer) and 2.70% (Loughere-Thioly). The regreening of the different localities and a positive dynamic observed is explained by the return to normal rainfall and to reforestation actions, agroforestry practices, better management of natural resources undertaken. However, some non-reforested sites showed an opposite trend despite of the normal rainfall. Secondly, the results on land mapping are used as a proxy for the assessment of carbon stocks. The dynamic observed in vegetation cover since the beginning of the reforestation made it possible to sequester 5.8 million tons of carbon representing respectively 2.31% of African GGW. This gain in stored carbon is equivalent to 21.2 million tons of CO2 captured in the atmosphere. Through this study, it appears that carbon storage becomes significant 8 to 10 years after the start of reforestation. An urbanization without respect for the environmental factors could be a danger for the climate (case of Ballou).

Towards More Snow Days in Summer since 2001 at the Great Wall Station,Antarctic Peninsula:The Role of the Amundsen Sea Low

The variation in the precipitation phase in polar regions represents an important indicator of climate change and variability.We studied the precipitation phase at the Great Wall Station and Antarctic Peninsula(AP)region,based on daily precipitation,synoptic records and ERA-Interim data during the austral summers of 1985?2014.Overall,there was no trend in the total precipitation amount or days,but the phase of summer precipitation(rainfall days versus snowfall days)showed opposite trends before and after 2001 at the AP.The total summer rain days/snow days increased/decreased during 1985?2001 and significantly decreased at a rate of?14.13 d(10 yr)?1/increased at a rate of 14.31 d(10 yr)?1 during 2001?2014,agreeing well with corresponding variations in the surface air temperature.Further,we found that the longitudinal location of the Amundsen Sea low(ASL)should account for the change in the precipitation phase since 2001,as it has shown a westward drift after 2001[?41.1°(10 yr)?1],leading to stronger cold southerly winds,colder water vapor flux,and more snow over the AP region during summertime.This study points out a supplementary factor for the climate variation on the AP.

Concentration level of heavy metals in the Great Wall Bay， Antarctica in austral summer

Heavy metals in different marine environmental mediums from the Great Wall Bay, Antarctica were determined. Sea water samples from 14 stations, surface sediments from 2 stations and marine organisms from 1 station were analyzed for Cu, Pb, Zn, Cd, Cr, Hg concentrations, The results showed that the terrestrial input characteristics of Cu, Pb and Cr in sea water was evident. Zn concentration in the outlet water was high. The difference of each heavy metal concentration in two sediments was low. The enriching ability of seaweed to Zn was relatively high. Generally speaking, the concentration level of heavy metals in the Great Wall Bay was low.

Organic contamination in the Great Wall bay,Antarctica in austral summer

During 1992/1993 austral summer,oil, BHCs,DDTs,PCBs etc.were determined in the sea water, sediments and organisms samples of the Great Wall bay,Antarctica.In surface sea water,the mean concentrations of oil were 0. 26-0. 93 μg/L.DDTs were all lower than the DL of the method,that was<0.04ng/L. BHCs mean concentrations were<0.69-<1.94 ng/L. In other samples,oil,BHCs,DDTs,and PCBs were all relatively higher in patella than that in sediments and seaweed. PAHs could not be detected in all samples. By comparison,the concentrations level of organic contaminants in the Great Wall bay was low yet.

Seawater nutrient and chlorophyll α distributions near the Great Wall Station, Antarctica

We examined the influences upon nutrient, temperature, salinity and chlorophyll a distributions in Great Wall Cove（GWC） and Ardley Cove（AC）, near the Chinese Antarctic Great Wall Station, using measurements taken in January 2013 and other recent data. Nutrient concentrations were high, with phosphate concentrations of 1.94（GWC） and 1.96（AC） μmol·L-1, DIN（dissolved inorganic nitrogen） concentrations of 26.36（GWC） and 25.94（AC） μmol·L-1 and silicate concentrations of 78.6（GWC） and 79.3（AC） μmol·L-1. However, average concentrations of chlorophyll a were low（1.29 μg·L-1, GWC and 1.08 μg·L-1, AC）, indicating that this region is a high-nutrient and low-chlorophyll（HNLC） area. Nutrient concentrations of freshwater（stream and snowmelt） discharge into GWC and AC in the austral summer are low, meaning freshwater discharge dilutes the nutrient concentrations in the two coves. Strong intrusion of nutrient-rich water from the Bransfield Current in the south was the main source of nutrients in GWC and AC. Low water temperature and strong wind-induced turbulence and instability in the upper layers of the water column were the two main factors that caused the low phytoplankton biomass during the austral summer.

EXPERIMENT OF SHORT WAVE COMMUNICATION AND THE INVESTIGATION OF THE PROPAGATION BEARINGS BETWEEN THE GREAT WALL STATION AND XINXIANG

The distance from the Great Wall Station (62.2°S, 58.9°W) to Xinxiang (35.3°N, 113.8°E) is 16981 km. The path passes through the polar cap absorption region and the auroral absorption zone, and it is across the equator.In this paper firstly the effects of short wave communication and usable time blocks and frequency ranges between the Antarctic Great Wall Station and Xinxiang from December 1985 to March 1986 are introduced. The comparison between the usable frequency ranges with the estimated MUF is made. The upper limit of frequency ranges of communication along the short great circle path basically agrees with the MUF but there is difference between them along the long great circle path.Secondly, the result of the propagation bearings experiment in January to February 1986 is introduced in more detail, The propagation along the great circle path from the Great Wall Station to Xinxiang is the main propagation mode. But the propagation along non great circle paths occurs at times between Great Wall Station and Xinxiang. The non great circle path propagation varies with time because the ionospheric absorption and other conditions which support the non great circle path propagation are the function of the time. So the courses of the non great circle path propagation may be different in the different time. The mechanism of the constructing non great circle path propagation has been analysed. We preliminarily think the main cause of propagation along non great circle path is the ground scatter. The stronger radialization of the side lobes of the antenna and the less absorption of the ionosphere contribute to forming non great circle path propagation.

THE SIGNIFICANCE OF THE GREAT WALL AS A GEOGRAPHIC BOUNDARY

The Great Wall is not only the symbol of the ancient Chinese culture but also an actual and significant geographic boundary. The arrangements of the wall in past dynasties are based on physiographic conditions, and are just consistent with the demarcation line between semi-humid and arid climates in the country. Therefore,the Great Wall becomes an indicator of the demarcation line between the two areas.The extension and retreat of the wall generally reflect the expansion and shrinkage of farming and animal husbandry areas. From the viewpoint of political geography, the Great Wall can be regarded as the balance belt of 'forces' where the political powers of different nationalities histoncally stood facing each other and had repeated trials of strength. On one hand, the man-made wall of 10,000 li had the function of separating two political units, to some extent, the extension and retreat of the wall reflect the changes of relative strength of the two sides. On the other hand,the conflicts of the advanced and backward forces objectively promoted the economic and cultural exchanges as well as the national assimilation. Today, the Great Wall has lost its function of military works for territorial expansion and defense, but it is still the significant indicator as a geographic boundary and a sensitive area for many geographic elements.

A Case study of a snowstorm at the Great Wall Station,Antarctica

A case of a snowstorm at the Great Wall Station was studied using data of NCEP（National Centers for Environmental Prediction） analysis,in situ observations and surface weather charts.The storm occurred on August 29th, 2006,and brought high winds and poor horizontal visibility to the region.It was found that the storm occurred under the synoptic situation of a high in the south and a low in the north.A low-level easterly jet from the Antarctic continent significantly decreased the air temperature and humidity.Warm air advection at high level brought sufficient vapor from lower latitudes for the snowstorm to develop. The dynamic factors relating to strong snowfall and even the development of a snowstorm were deep cyclonic vorticity at middle and low levels,the configuration of divergence at high level and convergence at low level,and strong vertical uplift.There was an inversion layer in the low-level atmosphere during the later phase of the storm.This vertical structure of cold air at low levels and warm air at high levels may have been important to the longevity of the snowstorm.

The climate background and synoptic situation of fog at Great Wall Station,Antarctica

Based on the observed and NCEP reanalysis data from 1985 to 2006, the climate background and synoptic situation of fog at Great Wall Station were analyzed.It is shown that the seasonal variation of fog is controlled by the change of general circulation and local pressure field.Three favorable typical synoptic situations for fog development arc found,the Front-of-A-Depression type,the Saddle-Shaped-Field type and the Passing-Weak-Cyclone type.The first one is the most important situation.Advection cooling fog is dominant at Great Wall Station,but there are other kinds of fog as well.As a result,some helpful principles for local fog forecasting are given.

A STUDY ON THE QUANTITY OF SHALLOW SEA BENTHOS IN GREAT WALL BAY, ANTARCTICA

Based on the investigation material acquired during the three cruises of the 4 Chinese Antarctic Research Expedition at 19 quantitative dredging stations and 4 trawling stations from the period December 1987 to March 1988, this paper studies the quantity of the benthos in Great Wall Bay,the distributive characteristics and variations, and points out that the stock number of the benthos in the bay is extremely large and that there are two large ranged high mass area and 2 - 3 low small-ranged mass area. The instability of the sediments is the cause for the low.mass areas. The warm season is the vigorous reproductive period of the various kinds of the benthos and the monthly variation of the quantity is remarkable.

ESTABLISHMENT OF SURVEYING SYSTEM OF THE GREAT WALL STATION

It is the main task of the antarctic surveying expedition to establish the surveying system. In three times of the antarctic surveying research expeditions, a complete and accurate surveying system has been established in the Chinese Great Wall Station area. The surveying system includes geodetic coordinate system, elevation system and gravity reference system. In this paper, the surveying methods and the mathematical models for establishing these systems are discussed, and the accuracy of results is analysed.

MASS MOVEMENT IN THE GREAT WALL STATION AREA, ANTARCTICA

This paper deals with the mass movement processes on the Fildes Peninsula, King George Island. Based on numerous field investigation, the authors consider that the slope mass movement and periglacial form on the peninsula have an internal relationship in genesis, reflecting in there main aspects. 1, All patterns of mass movement are developed on the slope surface; 2, different -order mass movement and periglacial type show their space-time distribution rules (their development stages); 3, The slope mass movement are developed from the periglacio - geomorphic processes. More detailed works have been done, such as fixed reapeated surveying whose results are concord and with the typical characteristics above mentimed very well.

^(210)Pb distribution characteristics in the lake sediment core at Great Wall Station,Antarctica

The results of 210 Pb measurements in the lake sediment core from Antarctica are reported: the relative specific activities of 210 Pb in the lake sediment were found to decrease exponentially with the depth in the study area; the sedimentation rate of the lake is about 0.072 cm/a. This paper shows that 210 Pb method is applicable to Antarctic lake sediment ,and during the 1960's the atmospheric nuclear tests have an effect on the rate of 210 Pb deposition in Antarctica.

Holocene ostracoda and sedimentary environment implication in The core NG93－1 from the Great Wall Bay， Antarctica

the holocene ostracode are analyzed from the core sample ng93-1 collectedIn the great wall bay, antarctica during 1992～1993. Totally 11 genera 21 speciesHave been identified in the sediments, of which the most abundant is loxoreticulatumFallax, the second abundant are xestoleberis keguelenensis, xestoleberis spp., Semicytherura spp., australicythere polylyca, etc. Most species of ostracodes are thoseKnown in antarctic area. Base on the study of ostracodes from the core ng93-1, theirSedimentary environment may be of shore-shallow sea.

Species composition and quantitative variation of zooplankton in the Great Wall Bay and its adjacent waters，Antarctica

A preliminary identification has been made of 35 species of the zooplankton in the Great Wall Bay and its adjacent waters,Antarctica. The dominant species in the investigated area are Calanus propinquus, Calanoides acutus, Metrdia gerlachei and the larvae of antarctic krill.The results indicated that the zooplankton in the investigated waters were simple in species number, which conforms to the general pattern of the distribution of the zooplankton in antarctic waters.The total biomass and number of individuals of the zooplankton in the investigated waters showed obvious seasonal variation. In summer there were Calaninioides acutus and the larvae of antarctic krill; in winter there were Metrdia gerlacher, Calanus propinquus, Oithon similis, O. frigda and the larvae of antarctic krill. The quantity of Copepoda occupied a considerable proportion in each month. The water temperature is an important factor in controling the biomass of zooplankton.

Surface ozone variations at the Great Wall Station,Antarctica during austral summer

Surface ozone(O3)is a secondary pollutant harmful to human health and a greenhouse gas which is one of the prime climate forcers.Due to the clean atmospheric environment of the Antarctic region and given the complexity of O3 chemistry,the observation of surface O3 variability in this region is necessary in the quest to better understand the potential sources and sink of polar surface O3.In this paper,we highlighted our observations on O3 variability at the Great Wall Station(GWS)during austral summer in December 2018 and January 2019.The continuous surface O3 measurement at the GWS,Antarctica was carried out using the Ecotech Ozone analyzer.To understand the roles of the meteorological conditions on the temporal variations of O3,meteorological data was obtained from the conventional auto-observational station at the GWS.The Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model was employed to investigate the air mass transport over the region.The observed austral summer surface O3 concentrations at the GWS exhibited variability and were significantly lower than those previously observed at other permanent coastal stations in Antarctica.The surface ozone variability at the GWS was strongly influenced by the synoptic change of air mass origin although the roles of photochemistry production and destruction were still uncertain.Marine characteristics and stable surface O3 characterized the air masses that reached the GWS.The unique characteristic of surface O3 at the coastal site of GWS was emphasized by its synoptic air mass characteristics,which displayed a significant influence on surface O3 variability.Air mass that traveled over the ocean with relatively shorter distance was linked to the lower O3 level,whereby the marine transport of reactive bromine(Br)species was thought to play a significant role in the tropospheric chemistry that leads to O3 destruction.Meanwhile,the diurnal variation indicated that the O3 background concentration levels were not strongly associated with the local atmospheric conditions.

The preliminary study of the phytoplankton ecology in the Great Wall Bay，Antarctica

This paper presents the identification and quantitative analysis of the phytoplankton samples collected in the Great Wall Bay, Antarctica from March 1988 to February 1989. The results indicate that the specific composition of phytoplankton clearly shows their ecological characteristics. That is the community mainly composed of cold-water species and neritic-eurythermal species. The dominant species altered with seasonal variation, their number showed the high-peak in the austral summer and the abundance of phytoplankton in each month mainly depended upon the dominant species. The distribution of phytoplankton is influenced by many environmental factors. Among them the hours of sunshine are the main factor.

ON CHEMICAL WEATHERING OF WEATHERING CRUST AT THE GREAT WALL STATION REGION, ANTARCTICA

The chief aim of this study is to investigate the chemical weathering process of the weathering crust in Great Wall Station region of China (in Fildes Peninsula), Antarctica by the method of sedimentology.CW,SW,GW,TW,WE weathering crusts developed on volcanic clastic rock, gray aptitic basalt with tuff or basaltic bedrock. On change of minerals, geochemical behaviors of elements, migration and enrichment regularities of elements, Correlation between element geochemical behaviors, change of weathering potential of rocks in chemical weathering process are studied by us.We can see that the sequence fo weathering strengths of the abovementioned sections, from high to low, should reflected in TW, GW, CW and SWT and basical correspond with that calculated from the enrichment and differentiation indexes.

A preliminary analysis of the pigments from ice algae in theadjacentwatersofGreatWallStation，Antarctica

This paper reports the results of separation and identification of the pigments from ice algae in the adjacent waters (62°12′30″S～62°14′30″S, 58°53′W～ 58°57′W) of Great Wall Station, Antarctica during the icing Pened (from June 1988～ December 1988) and the discussion is also made on the composition and seasonal variations of the pigments of ice algae in that area as well as their roles in marine ecosystems. The results indicate that 15 kinds of pigments have been separated from ice algae, of which 13 kinds can be identified. They are respeCtively: carotene, pheophytin-a, chlorophyll-a, -b, -c, xanthophyll, fucoxanthin, chlorophyllide-a, violaxanthin, pheophorbide-a, chlorophyllin-a, derivative of chlorophyll-c (diadinoxanthin), but two kinds of pigments can not be identified. There are distinct seasonal variations in the pigments of ice algae at that sea area.