現(xiàn)代鈣華沉積的環(huán)境替代指標及其氣候環(huán)境因子控制的研究

1、現(xiàn)代鈣華沉積的環(huán)境替代指標及其氣候環(huán)境因子控制的研究        近2000年氣候與環(huán)境變化研究在全球變化研究中具有特殊的重要性。過去2000年的氣候和環(huán)境變化研究,要求盡可能高的時間分辨率,在此基礎(chǔ)上取得的氣候指標統(tǒng)計基礎(chǔ),才有可能在其中尋找氣候和環(huán)境變化的信息,以尋求氣候演變的規(guī)律,預(yù)測未來發(fā)展趨勢。分布于地表的鈣華沉積物,以其具有的比石筍氣候記錄更高的分辨率和靈敏度的氣候記錄,成為近年來古氣候研究的重要載體。然而,要想利用鈣華進行高分辨率的古氣候重建工作,必須從地球系統(tǒng)科學(xué)思想出發(fā),全面了解鈣華沉積過程中地

2、球化學(xué)指標的變化及其控制機理。只有如此,才能更好地建立鈣華沉積物環(huán)境替代指標與氣候因子之間的定性和定量關(guān)系,才能為利用鈣華記錄重建古氣候環(huán)境奠定堅實可靠的基礎(chǔ)。由于氣候環(huán)境因子對鈣華環(huán)境替代指標的控制機理非常復(fù)雜,地域性很強,這也使得國外已有研究成果的適用范圍有限,并不一定適合中國的情況,而且很多研究主要是針對大氣成因類鈣華的,而對于如本文要研究的深部巖溶動力系統(tǒng)中形成的鈣華,即所謂的地?zé)岢梢蝾愨}華的環(huán)境替代指標與氣候因子之間的關(guān)系則缺乏研究。本文采用水化學(xué)儀器自動記錄、現(xiàn)場測定、取樣進行實驗室測試相結(jié)合的方法,通過水化學(xué)和碳氧穩(wěn)定同位素組成時空動態(tài)的綜合分析,對云南白水臺地區(qū)現(xiàn)代鈣華沉積的環(huán)

3、境替代指標與氣候因子關(guān)系進行了全面系統(tǒng)的研究,得出以下主要結(jié)論:(1)白水臺地區(qū)冬、夏季風(fēng)期間降雨云團可能存在不同的源區(qū),即,夏季降水的源區(qū)主要是印度洋和孟加拉灣,而冬季降水的氣團則主要受大陸內(nèi)部氣團影響。雨水氧同位素與降雨量有很好的線性負相關(guān)關(guān)系,反映了大氣降水的降水量效應(yīng)。(2)通過對白水臺引水渠道及鈣華池內(nèi)鈣華氧同位值(18)O)季節(jié)變化的分析發(fā)現(xiàn),大氣降水的降水量效應(yīng)(P)以及降水云團不同源區(qū)的轉(zhuǎn)換,是控制白水臺熱成因類鈣華中(18)O季節(jié)變化的原因。白水臺地區(qū)的鈣華(18)O的季節(jié)變化是春夏季(雨季)偏負,而秋冬季(早季)偏止。(18)O與P的定量關(guān)系是P每增加100mm,鈣華(18

4、)O偏負0.70;溫度(T)對白水臺鈣華(18)O的影響系數(shù)較O'neil方程小1倍左右,即T每增加1,鈣華(18)O偏負0.1。(3)通過對白水臺引水渠道和鈣華池中鈣華(13)C值的季節(jié)變化分析發(fā)現(xiàn),雨水及雨后形成的坡面流是控制白水臺地區(qū)鈣華(13)C值季節(jié)變化的主要原因。在雨季雨后形成的坡面流(13)C受土壤CO_2的影響,因而偏低)進入引水渠道,對引水渠道水進行了稀釋,因而造成雨季形成的鈣華(13)C值偏負。從而使鈣華(13)C值呈現(xiàn)出春夏季(雨季)偏負,而秋冬(旱季)偏正的季節(jié)變化。(4)通過對白水臺引水渠道和鈣華池內(nèi)鈣華沉積速率的季節(jié)變化研究發(fā)現(xiàn),降雨量是控制白水臺地區(qū)鈣華沉

5、積速率快慢的主要因素。在雨季,稀釋效應(yīng)造成的鈣華沉積速率的降低超過了溫度升高導(dǎo)致的鈣華沉積速率的增加,從而使白水臺地區(qū)鈣華沉積速率呈現(xiàn)出在雨季(春夏季)降低、秋冬季(旱季)升高的反?，F(xiàn)象,這與在日本大氣成因類鈣華中發(fā)現(xiàn)的規(guī)律正好相反。(5)建立了白水臺鈣華年層的肉眼識別標準,即白水臺地區(qū)一個鈣華年層包括薄的疏松褐色層和厚的致密淺色層。(6)鈣華池內(nèi)水生植物在春夏季(雨季)較強的光合作用使鈣華(13)C值偏正的影響小于雨季雨后形成的坡面流進入鈣華池對池水的稀釋使鈣華(13)C值偏負的影響,因此受水生植物影響的鈣華池內(nèi)的鈣華(13)C值的季節(jié)變化也主要是受降雨量控制,從而呈現(xiàn)出春夏季(雨季)偏負,

6、而秋冬(旱季)偏正的季節(jié)變化。夏季較強的光合作用雖然能夠加快鈣華的沉積速率,但是由于雨季時雨水及坡面流對池水更強的稀釋作用,使得受水生生物影響的各鈣華池內(nèi)的鈣華沉積速率的季節(jié)變化同不受水生生物影響的鈣華池內(nèi)的鈣華沉積速率的季節(jié)變化類似,反映的都主要是降雨量對鈣華沉積速率的控制,均表現(xiàn)為春夏季(雨季)沉積速率低于秋冬季(旱季)The information on climatic and environmental change in the past 2000a is very important to the investigation of the global change.The la

7、tter program requires information with higher time resolution so as to find out how climate and environment change,to reveal the regulation of the climate evolution,and to forecast the future climate change.Travertine and tufa in karst areas are one of the most important geological archives for the

8、study of past climate changes because of their high resolution and sensitive record of climate and environment.However,before one uses the travertine or tufa to reconstruct the paleo-climate changes,one must understand the climatic implication of proxies in travertine or tufa and their controlling m

9、echanisms.The climatic implication of proxies in travertine or tufa and their controlling mechanisms are generally complicated and of site-specific.Therfore,the direct application of previous studies at one site to another site may be problematic.Moreover,the previous studies focused mainly on the m

10、eteogene tufa records and paid little attention to thermogene travertine records.To understand the climatic implication of proxies in travertine and their controlling mechanisms,a case study at Baishuitai of Yunnan was conducted.The methods of one hydrologic year hydrochemical data logging,in-situ t

11、itrating and experiment and laboratory sample analysis were used to understand the spatial-temporal variations in geochemistry and stable isotopes of water and modern travertine at Baishuitai.The following conclusions were obtained through the study:(1) Two vapour sources of precipitation during sum

12、mer and winter monsoon have been recognized at Baishuitai.One is from the Indian Ocean and Bengal Bay during summer,and the other from the inner continent during winter.The precipitation amount effect on rainwater(18)O is significant at Baishuitai.(2) The(18)O of travertine was lower in summer rainy

13、 season and higher in winter dry season.The remarkable seasonal variations in(18)O of travertine were due to the precipitation amount effect and the change of vapour sources of precipitation.The quantitative relationship between the travertine(18)O and the precipitation amount was that the travertin

14、e(18)O decreased by 0.7when the precipitation amount increased by 100mm.The temperature effect coefficient on the travertine(18)O,being -0.1/was smaller than that in O'neil Equation. (3) The lower travertine(13)C values in travertine-depositing canal and travertine-depositing pools during the wa

15、rm and rainy seasons were related to the dilution of overland flows after rainfall,which was mainly influenced by soil water,and so had lower(13)C values.(4) The deposition rate of travertine decreased in warm and rainy seasons because of the dilution of the rainfall and the overland flows after rai

16、nfall,which had lower concentration of Ca(2+)andHCO_3-.Obviously,the dilution effect to decrease the deposition rate of travertine is stronger than the temperature effect to increase the deposition rate of travertine.(5) The seasonal travertine laminas were distinguished with the color change.The thin brown porous lamina was formed in the warm and rainy season,while the thick dense white lamina was formed in the dry season.(6) The effect of aquatic plants to increase the(13)C values