本文選題：拉森冰架 + 光學(xué)影像�。� 參考：《南京大學(xué)》2016年博士論文

【摘要】：南極冰蓋與全球氣候、生態(tài)環(huán)境及人類社會未來發(fā)展等重大問題密切相關(guān)。在極地地區(qū),氣候變暖的現(xiàn)象會被放大,過去半個世紀(jì)南極半島所有季節(jié)的大氣溫度均已出現(xiàn)明顯升高,其中最為劇烈的增溫出現(xiàn)在冬季。地處南極半島的Faraday/Vernadsky站的氣象數(shù)據(jù)顯示,其年平均氣溫以每十年0.56℃的速度升高,然而冬季的平均氣溫卻以每十年1.09℃的速度升高。南極半島是全球三個氣候變暖最明顯的區(qū)域之一冰架、大氣、海洋三者之間的相互作用系統(tǒng)是全球氣候系統(tǒng)的重要組成部分,同時也是最活躍的部分。冰架面積占南極冰蓋總面積的11%,而且南極內(nèi)陸累積的75%的陸地冰物質(zhì)通過冰架這種特殊形式的“關(guān)口”向海洋輸送,冰山崩解和底部融化構(gòu)成了冰架向海洋輸送物質(zhì)的兩種主要方式。此外,冰架的表面物質(zhì)交換(積雪累積與融化)和底部物質(zhì)交換(附著冰的凍結(jié)與融化等)也會對整個南極冰蓋的物質(zhì)平衡產(chǎn)生一定的影響。本文將重點聚焦在拉森冰架上,系統(tǒng)性地完成了一個較長時間序列的拉森冰架面積、高程及表面流速的監(jiān)測,在此基礎(chǔ)上結(jié)合氣溫、海溫、降水量等數(shù)據(jù)分析了拉森冰架的形態(tài)演變對氣候變化的響應(yīng),探討了冰架物質(zhì)的輸送機制,并基于現(xiàn)有研究成果對拉森冰架未來的穩(wěn)定性進行預(yù)測。主要研究結(jié)果如下：(1)采用多種歷史遙感數(shù)據(jù)源來分析拉森冰架1968-2015年的面積變化,主要包括解密航片(南極單幀數(shù)據(jù))和衛(wèi)星光學(xué)遙感影像(Landsat和MODIS)。得到了一個長時間序列的拉森冰架持續(xù)崩塌與后退的監(jiān)測結(jié)果。直到1980年代中期,拉森冰架北部還沒發(fā)生明顯的面積變化,然而拉森A冰架自從1986年開始便逐步地發(fā)生劇烈的后退。拉森B冰架從1990年代早期也開始步入與拉森A冰架相同的后退模式。拉森冰架北部持續(xù)的后退最終演變成幾次巨型的崩塌事件,當(dāng)前,拉森A冰架已經(jīng)完全消失,拉森B冰架僅存大約2000km2的浮冰殘存于Scar Inlet處。相對于拉森北部冰架在近幾十年發(fā)生劇烈的崩塌與后退,拉森C冰架的表面結(jié)構(gòu)和范圍在過去50年比較穩(wěn)定,并未展現(xiàn)出有關(guān)氣候變暖驅(qū)動的冰架面積退縮的直接證據(jù),其變化遵循的是冰架正常的前緣波動模式。當(dāng)前拉森C冰架仍然保持著監(jiān)測初始周期(1960年代)面積的90%以上,而且仍然呈現(xiàn)出表面形態(tài)的穩(wěn)定性。(2)通過對兩種雷達高度計重合數(shù)據(jù)的比測實驗以及參考橢球系統(tǒng)的轉(zhuǎn)換,可以有效地聯(lián)合T/P和RA-2兩種測高數(shù)據(jù)進行表面高程變化分析。根據(jù)拉森冰架發(fā)生的幾次巨型崩塌事件以及不同時期的冰架范圍,將整個高程變化監(jiān)測分成4個不同監(jiān)測單元及時段(拉森A殘留、拉森B前緣區(qū)域、拉森B殘留以及拉森C冰架)。然后采用共線分析法分別監(jiān)測以上4個監(jiān)測單元的高程變化情況,并在此基礎(chǔ)上探求近20年拉森冰架表面高程的時空變化趨勢。在南極半島氣候變暖的背景下,拉森冰架表面高程日益降低：拉森A殘留呈現(xiàn)出表面高程劇烈降低的趨勢,1992-2001年表面高程降低速率為-0.45m/yr,監(jiān)測周期內(nèi)高程變化波動較大；1992-2001年拉森B冰架前緣區(qū)域的年均高程降幅為-0.19m/yr,該區(qū)域的表面高程變化曲線沒有出現(xiàn)劇烈的波動；拉森B殘留的監(jiān)測周期最長(1992-2010年),觀測周期內(nèi)表面高程降低幅度為-0.07m/yr。出乎意料之外的是,從表面高程變化曲線還可以發(fā)現(xiàn)拉森B殘留在2006年后高程變化趨于穩(wěn)定,表面高程降低的趨勢有所緩解。2002-2010年拉森C冰架表面高程降低幅度為-0.032m/yr,而且該區(qū)域的表面高程變化曲線還體現(xiàn)出波動性較小的特征,這可能與拉森C冰架自1986年以來沒有出現(xiàn)毀滅性的崩塌事件有關(guān)。(3)基于中等分辨率的MODIS和高分辨率的TM影像,采用COSI-Corr模塊(運用IDL語言鑲嵌入ENVI軟件)估算了1986-2012年拉森C冰架和拉森B殘留的冰架表面流速。估算結(jié)果顯示：拉森冰架表面流速特征符合半島模式和裂隙(縫)模式,冰流主要向東流入Weddell海。此外,從表面流速的時間變化趨勢來看,拉森C冰架的大部分區(qū)域體現(xiàn)出持續(xù)但是較為溫和的流速升高趨勢,拉森C冰架表面流速估算區(qū)2006-2012年的整體平均流速比1986-1990年大約升高13.7%。受近20年的幾次冰架崩塌事件地影響,拉森B殘留的表面流速波動更為劇烈,1986-1990年拉森B殘留的總體年平均表面流速略低于拉森C冰架,然而經(jīng)歷幾次崩塌事件之后,拉森B殘留2006-2012年的表面流速比1986-1990年急劇升高了大約32%,此時,其平均表面流速已經(jīng)超過拉森C冰架。總之,近30年拉森冰架大部分區(qū)域的表面流速均出現(xiàn)流速增快的趨勢。(4)通過對NCEP/NCAR夏季月平均氣溫數(shù)據(jù)地分析發(fā)現(xiàn),20世紀(jì)后50年南極半島體現(xiàn)出持續(xù)增溫的趨勢。然而,出乎意料之外的是,從2000年后南極半島氣溫出現(xiàn)略微降溫的現(xiàn)象。雖然近幾十年Weddell海的表面溫度沒有出現(xiàn)明顯的增溫趨勢,但是其深水溫度卻出現(xiàn)顯著的升溫趨勢。通過分析GPCP逐月平均降水量數(shù)據(jù)發(fā)現(xiàn),近幾十年拉森冰架流域范圍內(nèi)年均降水量變化的正負(fù)趨勢不夠顯著。綜上,影響近幾十年拉森冰架表面物質(zhì)平衡變化趨勢最關(guān)鍵的氣象要素是溫度,而非降水。氣溫上升導(dǎo)致冰架表面融水增加以及融池范圍擴大,形態(tài)較為穩(wěn)定的拉森C冰架的表面高程降低被日益增加的表面融化與再凝結(jié)所主導(dǎo),受海洋的影響幾乎可以忽略不計。而持續(xù)后退的拉森A冰架和拉森B冰架的表面高程除了受氣溫升高導(dǎo)致表面融化與再凝結(jié)的驅(qū)動外,同時還受海溫升高導(dǎo)致的冰架底部融化加強的影響。此外,拉森北部冰架的后退甚至消失使得它對內(nèi)陸冰物質(zhì)產(chǎn)生的背向應(yīng)力也隨之減少,導(dǎo)致占冰架物質(zhì)絕大部分的陸地冰向海洋輸送的速度大大加快,直接反映為冰架表面高程的降低和表面流速的加快。南極半島北部冰架的“毀滅性”崩解與消失的主要機制為：近半個世紀(jì)來,隨著全球氣候變暖的加劇,南極半島北部出現(xiàn)了日益擴大的融池范圍以及更多的表面融水。溫暖的表面融水填充入已存在的裂縫,并順著這些裂縫傳播,部分表面融水甚至能穿透了整個冰架厚度,與底部融水共同作用,最終導(dǎo)致冰架的崩塌。綜上所述,氣溫及海溫變暖導(dǎo)致了南極半島北部冰架在冰川學(xué)及流變學(xué)上經(jīng)歷了一系列前所未有的劇烈變化,如拉森冰架北部持續(xù)的崩塌與后退、表面高程持續(xù)的降低以及表面流速的加快等。通過觀察高分辨率的遙感影像就會發(fā)現(xiàn),拉森B殘留冰架表面橫向裂隙(縫)廣泛發(fā)育,而且每年夏季融化季節(jié)都會出現(xiàn)大面積的表面融池,因此基于融水填充冰架裂縫傳播的機制可以預(yù)測拉森B殘留在未來一百年內(nèi)存在完全消失的可能性。拉森C冰架雖然近期形態(tài)較為穩(wěn)定,但是其維持穩(wěn)定的幾種相互關(guān)聯(lián)機制已經(jīng)被打破,因此未來拉森C冰架穩(wěn)定性的威脅也大為增加。近期(2000年以后)區(qū)域性的氣溫變冷在一定程度上會對冰架的冰川學(xué)及流變學(xué)產(chǎn)生積極的影響,但是氣溫略微變冷和冰架局部穩(wěn)定所具有的統(tǒng)計學(xué)意義還尚待進一步論證。
[Abstract]:The Antarctic ice cover is closely related to the global climate, the ecological environment and the future development of human society. In the polar regions, the warming phenomenon will be magnified. In the past half century, the atmospheric temperature of all seasons in Antarctic Peninsula has been significantly increased, of which the most intense temperature increases in winter. It is located in the Faraday/ of Antarctic Peninsula. The meteorological data of the Vernadsky station show that the annual average temperature rises at 0.56 degrees centigrade every ten years, while the average temperature in winter rises at 1.09 degrees centigrade every ten years. Antarctic Peninsula is one of the most obvious regions of the world's three warmer regions. The interaction system between the atmosphere and the three oceans is important for the global climate system. The ice shelf is 11% of the total area of the Antarctic ice cover, and 75% of the land ice material accumulated in the Antarctic is transported to the ocean through the special "gate" of the ice shelf, the disintegration of icebergs and the bottom melting constitute the two main ways of the ice shelves to transport the ocean materials. In addition, the ice shelf The surface material exchange (snow accumulation and melting) and the exchange of the bottom material (the freezing and melting of the attached ice) also have a certain effect on the material balance of the whole Antarctic ice sheet. This paper focuses on the Larsen ice shelf, and systematically completes the monitoring of the area, elevation and surface flow velocity of a long time series of Larsen ice shelves. On the basis of the analysis of the temperature, sea temperature, precipitation and other data, the response of the morphological evolution of Larsen ice shelf to the climate change is analyzed, the transport mechanism of the ice shelf material is discussed, and the future stability of the Larsen ice shelf is predicted based on the existing research results. The main results are as follows: (1) the analysis of Larsen using a variety of historical remote sensing data sources The changes in the area of the ice shelf for 1968-2015 years include decryption aerial (Antarctic single frame data) and satellite optical remote sensing images (Landsat and MODIS). The monitoring results of a long time series of continuous collapse and retreat of the Larsen ice rack have been obtained. Until the mid 1980s, there was no obvious area change in the north of the Larsen ice shelf, but the Larsen A ice shelf The Larsen B ice rack has also stepped into the same backward mode as Larsen's A ice shelf since the early 1990s. The continuing retreat of the northern lalson ice shelf eventually evolved into a number of huge collapse events. At present, the Larsen A ice shelf has been completely lost, and the Larsen B ice shelf remains only about 2000km2 of ice floe residue. Deposited at Scar Inlet, the surface structure and scope of the Larsen C ice shelf has been relatively stable over the past 50 years relative to the severe collapse and retreat of the northern ralson ice shelf over the past few decades. It does not show direct evidence of the shrinking of the ice shelf area driven by climate warming. The change follows the normal front fluctuation pattern of the ice shelf. The C ice rack still maintains more than 90% of the area of the initial period (1960s), and still shows the stability of the surface morphology. (2) the surface elevation change analysis can be effectively combined with the T/P and RA-2 altimetry data through the comparison test of the reclosing data of the two radar altimeter and the conversion of the reference ellipsoid system. According to the giant collapse events of Larsen ice shelf and the range of ice shelves at different times, the whole elevation change monitoring is divided into 4 different monitoring units and periods (Larsen A residue, ralson B front area, Larsen B residue and Larsen C ice frame). Then the height variation of the above 4 monitoring units is monitored by collinear analysis. On the basis of this, the temporal and spatial variation trend of the surface elevation of Larsen ice shelf for the last 20 years is explored. Under the background of Antarctic Peninsula climate warming, the surface elevation of Larsen ice shelf is decreasing day by day: the remnant of Larsen A shows a tendency to decrease the surface elevation violently, the surface elevation reduction rate of 1992-2001 years is -0.45m/yr, and the fluctuation of elevation changes in the monitoring period is more than that in the monitoring period. The annual average elevation of the leading edge region of the 1992-2001 year B ice shelf is -0.19m/yr, and the surface elevation curve of the region has no violent fluctuations; the remnant B remains the longest (1992-2010 years), and the decrease in the surface elevation is beyond the expectation of the surface elevation, from the surface elevation curve. It is found that the elevation of Larsen B remains stable after 2006, and the trend of surface elevation decreases to be relieved by the reduction of the elevation of the surface elevation of the rson C ice shelf of -0.032m/yr for.2002-2010, and the surface elevation curve of the region is also characterized by less volatility, which may not appear since 1986 in the Larsen C ice shelf. Destructive collapse events are related. (3) based on medium resolution MODIS and high resolution TM images, the COSI-Corr module (embedded in the IDL language embedded in ENVI software) is used to estimate the surface velocity of the 1986-2012 year ralon C ice shelf and the remnant ice shelf of Larsen B. The results show that the surface velocity characteristics of the Larsen ice rack are in accordance with the peninsula model and the fissure. The ice flow mainly flows eastward into the Weddell sea. In addition, in terms of the time change trend of the surface flow velocity, most of the Larsen C ice shelf shows a continuous but relatively mild flow rate rising, and the overall average velocity of the 2006-2012 year overall average velocity of 2006-2012 years in the surface velocity estimation area of the Larsen ice shelf is approximately 20 years higher than that of 1986-1990 years. The residual surface velocity fluctuation of Larsen B is more intense, and the total average annual surface velocity of Larsen B remains slightly lower than the Larsen C ice shelf for 1986-1990 years. However, after several collapse events, the 2006-2012 year surface flow velocity of Larsen B remains about 32% higher than that of 1986-1990 years, and the average surface flow is at this time. The speed has exceeded the Larsen C ice frame. In a word, the surface flow velocity in most of the Larsen ice shelf has increased rapidly in the last 30 years. (4) through the analysis of the monthly mean temperature of NCEP/NCAR in summer, Antarctic Peninsula showed a trend of continuous warming in the last 50 years. However, unexpectedly, from 2000 after 2000. The temperature appears slightly cooling. Although the surface temperature of the Weddell sea has no obvious warming trend in the last few decades, its deepwater temperature has a significant warming trend. By analyzing the monthly mean precipitation data of GPCP, the positive and negative trend of the annual average annual precipitation in the range of the Larsen ice shelf basin is not obvious enough in recent decades. To sum up, the most important meteorological factors that affect the surface material balance of the Larsen ice shelf in recent decades are temperature, not precipitation. The rise of temperature leads to the increase of the surface melting water and the expansion of the melting pool. The surface elevation reduction of the relatively stable C ice shelf is dominated by the increasing surface melting and recondensation, and the sea is subject to the sea. The impact of the ocean is almost negligible. The surface elevation of the Larsen A ice rack and the Larsen B ice shelf is influenced by the increase of the surface melting and recondensation, as well as the melting of the bottom of the ice shelf, which is caused by the increase of sea temperature. The back stress produced by the material also decreases, which leads to the speed of transportation of the land ice to the vast majority of the ice shelf, which is directly reflected as the reduction of the surface elevation of the ice shelf and the acceleration of the surface velocity. The main mechanism of the "devastating" disintegration and disappearance of the ice shelves in the northern part of Antarctic Peninsula is for nearly half a century. The increasing warming of the ball climate, the increasing melting pool area and more surface melt water in northern Antarctic Peninsula. Warm surface melting water filled with existing cracks and spread along these cracks. Some surface melting water even penetrated the thickness of the whole ice frame, combined with the melting of the bottom, eventually leading to the collapse of the ice frame. The temperature and the warming of sea temperature have caused a series of unprecedented dramatic changes in Glaciology and rheology in northern Antarctic Peninsula, such as the continuous collapse and retreat in the north of the Larsen ice shelf, the continuous reduction of the surface elevation and the acceleration of surface flow velocity. The transverse fissure (SEW) of the surface of the B residual ice shelf is widely developed, and a large area of surface melting pool will appear every summer in the summer melting season. Therefore, the possibility of completely disappearing of Larsen's B residue in the next one hundred years can be predicted based on the mechanism of the crack propagation of the ice shelves filled with melt water. The Larsen C ice shelf is more stable in recent years, but it is more stable. Some of the stable interrelated mechanisms have been broken, so the threat of the stability of the C ice shelf is also increased in the future. In the near future, the regional temperature cooling will have a positive effect on the Glaciology and rheology of the ice shelf to a certain extent, but the temperature is slightly cold and the local stability of the ice shelf has the statistics. The significance of the study is yet to be further demonstrated.

【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：P343.6
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本文編號：1844984