孫 青, 儲國強, 劉國祥, 王曉華, 劉美美,石麗明, 謝曼曼, 凌 媛

1)國家地質實驗測試中心, 北京 100037;

2)中國科學院地質與地球物理研究所, 北京 100029;

3)中國科學院水生生物研究所, 湖北武漢 430072

湖泊體系中長鏈烯酮研究進展

孫 青1), 儲國強2), 劉國祥3), 王曉華2), 劉美美1),石麗明1), 謝曼曼2), 凌 媛1)

1)國家地質實驗測試中心, 北京 100037;

2)中國科學院地質與地球物理研究所, 北京 100029;

3)中國科學院水生生物研究所, 湖北武漢 430072

長鏈烯酮不飽和度(U37k′)作為定量反映古溫度變化的重要替代指標, 已在海洋中得到廣泛應用, 但在湖泊中長鏈烯酮不飽和度與溫度的關系及其母源研究則很少。課題組研究了中國不同氣候帶、不同水化學環(huán)境湖泊表層沉積物中長鏈烯酮, 發(fā)現(xiàn)多數(shù)湖泊中存在2～4個不飽和鍵的長鏈烯酮, 首次報道硫酸鹽型湖泊中存在長鏈烯酮, 總結了湖泊中長鏈烯酮的分布模式, 探討了分布模式與環(huán)境、母源的關系。研究了湖泊長鏈烯酮不飽和度與溫度的關系, 發(fā)現(xiàn)湖泊長鏈烯酮不飽和度與年均氣溫和春秋季節(jié)溫度高度相關, 建立了中國湖泊表層沉積物中長鏈烯酮不飽和度與溫度的經(jīng)驗函數(shù)關系, 結合文獻中發(fā)表的數(shù)據(jù), 建立了從熱帶的北緣湖光巖瑪珥湖到北極的格陵蘭的湖泊沉積物中長鏈烯酮不飽和度與溫度的經(jīng)驗函數(shù)關系: U37k′= 0.031× T + 0.094 (n=76, r2= 0.67)。首次發(fā)現(xiàn)并成功分離出湖泊中長鏈烯酮母源等鞭金藻Chrysotila lamellosa,通過單藻種控溫培養(yǎng), 建立長鏈烯酮不飽和度與水溫關系方程, 實驗室培養(yǎng)公式與經(jīng)驗公式斜率一致, 驗證了長鏈烯酮不飽和度溫標, 表明長鏈烯酮是可靠的陸地溫標。

湖泊; 長鏈烯酮; 不飽和度; 分布特征; 溫度; 母源

古氣候、古環(huán)境變化研究的關鍵問題之一是古氣候、古環(huán)境變化定量指標的研究, 長鏈烯酮不飽和度溫標, 由于不受碳酸鹽溶解作用、沉積作用、氧化作用及長鏈烯酮豐度等因素的影響(Sikes et al., 1991; Prahl et al., 2003), 已成為繼微體化石(有孔蟲等)、氧同位素之后又一古氣候變化研究的重要替代指標(孫青等, 2002)。盡管有研究表明營養(yǎng)、光照等環(huán)境因素可能影響長鏈烯酮不飽和度溫標(Sikes et al., 2005), 但U37k′溫標仍然廣泛地、成功地應用于定量重建古海表水溫(Rostek et al., 1993; Bard et al., 1997; Sachs et al., 1999; 壟慶杰等, 1999; Zhao et al., 2000; Kienast et al., 2001; Seki et al., 2004)。海洋環(huán)境中長鏈烯酮不飽和度溫標(U37k′)不僅能夠反映地質歷史時期冰期-間冰期較大的溫度變化, 而且能夠定量反映中世紀暖期、小冰期及近代的溫度波動(Abrantes et al. 2005)。

U37k′溫標在全球海洋中得到廣泛應用主要歸功于: 1)長鏈烯酮在海洋中廣泛存在(Müller et al., 1998); 2) 海洋中長鏈烯酮的母源比較清楚, 只有少數(shù)的幾種金藻合成長鏈烯酮: 例如廣海種Emiliania huxleyi、Gephyrocapsa oceanica(Volkman et al., 1980; Marlowe et al., 1984a, b)和濱海種Isochrysis galbana (Marlowe et al., 1984b; Conte et al., 1994; Versteegh et al., 2001)、Chrysotila lamellosa (Marlowe et al., 1984b, 1990; Rontani et al., 2004); 3)通過實驗室對單藻種的控溫培養(yǎng)以及全球海洋表層沉積物的研究,建立了U37k′-溫度(T)的關系方程(Müller et al., 1998; Versteegh et al., 2001; Prahl et al., 1987; Volkman et al., 1995; Conte et al., 1995, 1998, 2001; Sawada et al., 1996; Rosell-Melé et al., 1995; Ternois et al., 1997; Pelejero et al., 1997; Bentaleb et al., 2002)。

長鏈烯酮不僅存在于海洋環(huán)境中, 而且還廣泛存在于湖泊沉積物中(Cranwell et al., 1985; Li et al., 1996; 陽學賢等, 1996; Thiel et al., 1997; Innes et al., 1998; 盛國英等, 1998; Wang et al., 1998; Zink et al., 2001; 張干等, 2000; 孫青等, 2004; Chu et al., 2005)。湖泊地質歷史時期沉積物中長鏈烯酮的研究發(fā)現(xiàn)Steisslingen湖的U37k′能夠反映新仙女木事件前后的溫度變化(Zink et al., 2001); 扎布耶鹽湖的U37k′反映出末次冰期以來的溫度變化(Wang et al., 1998);合同察汗湖U37k′值與δ18O有良好的對應關系, 可能反映出小冰期的降溫事件(張干等, 2000); Titicaca湖(Theissen et al., 2005)的研究結果表明如果長鏈烯酮的母源能夠確定, 長鏈烯酮不飽和度溫標有可能成為湖泊古氣候研究的定量指標。但湖泊中U37k′溫標仍然處于探索中, U37k′能否成為定量重建湖泊古溫度變化的重要替代指標,有待進一步系統(tǒng)研究湖泊體系中長鏈烯酮的分布、母源特征, 通過母源的培養(yǎng)和湖泊沉積物的研究獲得可以被接受的U37k′-T關系方程。

1 湖泊中的長鏈烯酮分布特征

長鏈烯酮廣泛存在于淡水湖(Cranwell et al., 1985; Zink et al., 2001; Chu et al., 2005))、咸水湖(Li et al., 1996; Wang et al., 1998; Abrantes et al., 2005)及堿性咸水湖(Thiel et al., 1997; 盛國英等, 1998;張干等, 2000)的湖泊沉積物中。我們首次報道了硫酸鹽型鹽湖中存在長鏈烯酮(Sun et al., 2004), 比較系統(tǒng)地研究了中國不同氣候帶不同水化學類型的湖泊表層沉積物中的長鏈烯酮分布特征, 這些湖泊鹽度變化很大, 從淡水湖到鹽湖, 湖泊水化學類型包括碳酸鹽型、硫酸鹽型和氯化物型, 長鏈烯酮的含量范圍 0.03-39.00(mg/g 干樣), 其中碳酸鹽型咸水湖夏日淖爾湖的沉積物中長鏈烯酮濃度最高, 硫酸鹽型鹽湖沉積物中長鏈烯酮的濃度最低(Sun et al., 2004, Chu et al., 2005)。

1.1 C37:4優(yōu)勢模式

中國的湖泊表層沉積物中長鏈烯酮C37:4含量(C37:4含量占總C37長鏈烯酮含量的百分比)變化范圍是5%～96%,平均值55%(Chu et al., 2005; Sun et al., 2004; Liu et al., 2006; Liu et al. 2008), 在四海龍灣瑪珥湖 1600年的沉積物(王曉華, 2009)中C37:4含量介于57.45%～39.95%, 平均值為46.86%, 青海湖3500年來沉積物(Liu et al., 2006)中C37:4含量介于: 15%～45%, 與世界其它地區(qū)湖泊沉積物中C37:4含量可比, 例如, Titicaca湖沉積物(Theissen et al., 2005)中C37:4含量為 8%～18%, 平均 12.5%, 德國的Steisslingen湖(Zink et al., 2001)為21%～66%, 土耳其的Van湖(Thiel et al., 1997)為20%～72%, 美國的北部平原區(qū)湖泊(Toney, Huang et al. 2010)C37:4含量為62%～69%; 湖泊中分離出的C. lamellosa的培養(yǎng)產(chǎn)物中檢測出C37:4含量為6.3%～24.9%(Sun et al., 2007),分布在湖泊沉積物中長鏈烯酮C37:4含量變化范圍之內。濱海環(huán)境沉積物和物種C. lamellosa和I. galbana的培養(yǎng)產(chǎn)物中檢測出高含量C37:4(Rontani et al., 2004; Marlowe et al., 1984)。在開闊海洋沉積物和物種Emiliania huxleyi、Gephyrocapsa oceanica培養(yǎng)物中C37:4含量很低, 相對高的C37:4含量局限于低溫地區(qū)(Schulz et al., 2000, Mercer et al., 2005, Sikes et al., 1991; Sikes and Volkman, 1993; Rosell-Mel et al., 2002; Harada et al., 2003)。雖然在美國東北部桑德希爾斯湖區(qū)(Toney et al., 2010)發(fā)現(xiàn)一些不含C37:4的湖泊, 但總體上, 濱海和內陸湖泊的沉積物中和母源合成的C37:4含量遠比開闊海洋體系高得多, C37:4優(yōu)勢模式可能是湖泊系統(tǒng)和濱海環(huán)境中長鏈烯酮的普遍分布特征(圖1。Sun et al., 2004; Chu et al., 2005; Cranwell 1985; Li et al., 1996; Zink et al., 2001)。

圖1 湖泊和海洋沉積物中長鏈烯酮的分布特征a-非C37:4優(yōu)勢模式; b-C37:4優(yōu)勢模式Fig. 1 Distribution of long-chain alkenones in lake and marine sediments a-non-C37:4dominant pattern; b-C37: 4 dominant pattern

早期的研究表明, C37:4的百分含量可能受控于溫度(Prahl et al., 1988)。在較冷的海洋環(huán)境中, 當C37:4含量的相對含量低于 5%時, C37:4含量與上覆海水溫度存在很好的線性關系(Rosell-Mel et al.,1998),隨后的研究表明, 在海洋環(huán)境中C37:4的含量與溫度之間不存在線性關系的(Prahl et al., 1988; Freeman and Wakeham, 1992)。但我們對湖泊種C. lamellosa的培養(yǎng)發(fā)現(xiàn), 在其他環(huán)境條件不變的情況下, 當溫度從 22℃降到 10℃時, C37:4由 6.3%增長到 24.9% (Sun et al., 2007), 我們的結果支持溫度是引起C37:4含量變化的重要因素的觀點。

一些學者認為C37:4含量可能作為一種古鹽度的替代指標(Schulz et al., 2000; Rosell-Mel et al., 1998, 2002), Ace湖(Coolen et al., 2004)、青海湖(Liu et al., 2008)中長鏈烯酮的C37:4與鹽度之間具有一定的關系; C37:4可能記錄了青海湖晚全新世湖水鹽度變化(Liu et al., 2006)。但是, 無論湖泊(Chu et al., 2005)、還是海洋環(huán)境(Rosell-Mel et al., 1998; Lopez et al., 2005; Sikes and Sicre, 2002; Mercer et al., 2004)的研究結果都表明C37:4甲基酮與鹽度之間的關系還存在不確定性, 目前, 沒有一個全球性的C37:4和鹽度關系。我們認為在復雜的湖泊體系中, 母源、溫度、營養(yǎng)物質、鹽度等生物、環(huán)境因子多變, 在某一地區(qū)或某一時段內C37:4含量變化可能與鹽度相關, C37:4與鹽度的關系可能不單純是定鞭金藻的單一 屬種對鹽度變化的生理響應, 而是多種合成長鏈烯酮的藻類為適應鹽度的變化發(fā)生種屬間相對豐度 變化(Coolen et al., 2004), 從而導致長鏈烯酮的C37:4變化。

1.2 C37優(yōu)勢模式和C38優(yōu)勢模式

湖泊沉積物中的 C37/C38變化范圍很大(0.02-7.8)(chu et al., 2005), 按鏈長特征, 湖泊中長鏈烯酮分布模式有 C37優(yōu)勢模式(C37＞C38)和 C38優(yōu)勢模式(圖2, C38＞ C37)。

圖2 湖泊中長鏈烯酮分布模式: C38優(yōu)勢模式(a)和C37優(yōu)勢模式(b)Fig. 2 Distribution of long-chain alkenones in lake: C38 dominant pattern (a) and C37 dominant pattern (b)

C37優(yōu)勢模式是湖泊環(huán)境(Cranwell,1985; Li et al., 1996; Thiel et al., 1997; Wang and Zheng, 1998; Zink et al., 2001)、邊緣海環(huán)境(Freeman and Wakeham, 1992; Schulz et al., 2000)和開闊海洋環(huán)境中(Prahl et al., 1988; Sikes and Volkman, 1993)最典型的模式。在開闊海洋環(huán)境的沉積物和物種中C37/C38較低, 多小于2.0(Chu et al., 2005), 而在湖泊沉積物和邊緣海中的C37/C38的比值不乏高值的報道。無論是在中國湖區(qū)(Sun et al., 2004; Chu et al., 2005; Liu et al., 2006; Liu et al., 2008)、英國的湖區(qū)(Cranwell, 1985)、美國的東北桑德希爾斯和北部大平原區(qū)的湖泊(Toney et al., 2010)、Van湖(Thiel et al., 1997), 還是波羅的海 (Schulz et al., 2000) 的沉積物中都有高C37/C38比值的報道。相應的濱海和湖泊環(huán)境長鏈烯酮的母源C .lamellosa和I. galbana合成的長鏈烯酮的 C37/C38變化范圍也較大, C. lamellosa從1.4到9.5(Rontani et al., 2004; Marlowe et al., 1984; Prahl et al., 1988; Sun, 2007), I. galbana從5.4到15.1(Marlowe et al., 1984)。濱海和湖泊的沉積物、相應環(huán)境中母源物種合成的長鏈烯酮的C37/C38烯酮比值整體上高于開闊海洋沉積物和長鏈烯酮的母源合成的C37/C38烯酮比值, 但是大多數(shù)情況下, C37/C38 的變化由藻類細胞的營養(yǎng)、生理和生長溫度貢獻 (Conte et al., 1998), C37/C38很難區(qū)分物種, 只有當C37/C38很高時, 可能合成長鏈烯酮藻類是等鞭金藻 C. lamellosa和I. galbana而非顆石藻 Emiliania huxleyi和 Gephyrocapsa oceanica。

C38優(yōu)勢模式在少數(shù)幾個邊緣海(Cacho et al., 1999; Schulz et al., 2000)、少數(shù)湖泊沉積物(Thiel et al., 1997; Innes et al., 1998; Zink et al., 2001)中出現(xiàn)。C38優(yōu)勢模式在硫酸鈉或硫酸鈉鎂型湖泊沉積物中出現(xiàn)的幾率高于淡水湖、碳酸鹽型和硫酸鎂型鹽湖,例如在西班牙的硫酸鈉或硫酸鈉鎂型湖泊廣泛存在C38優(yōu)勢模式, 在中國的青海的大柴旦、小柴旦、內蒙古的蓮花池等硫酸鈉或硫酸鈉鎂型湖泊沉積物中長鏈烯酮的分布模式也多為C38優(yōu)勢模式。

1.3 C38乙基酮模式和C38甲基乙基酮模式

依據(jù) C38長鏈烯酮的組成特征, 湖泊中的長鏈烯酮可以分為C38乙基酮模式和C38甲基乙基酮模式(圖3)。C38乙基酮模式是指C38烯酮由C38乙基酮組成, C38甲基乙基酮模式是指 C38烯酮由C38乙基酮和C38甲基酮組成。綜合研究不同母源藻種培養(yǎng)產(chǎn)物中長鏈系統(tǒng)分布特征(Volkman et al., 1980; Marlowe, Brassell et al. 1984; Rontani et al., 2004; Chu et al., 2005; Sun et al., 2007), 認為E. Huxleyi、G. Oceanic和個別Isochrysis galbana種屬合成的長鏈烯酮為C38甲基乙基酮模式(Chu et al., 2005), 而C. lamellosa單藻種培養(yǎng)產(chǎn)物中未檢出C38甲基酮,為C38乙基酮模式(Sun et al., 2007)。中國的巴里坤湖沉積物中 C38長鏈烯酮為甲基乙基酮模式, 而夏日淖爾湖沉積物中長鏈烯酮為 C38乙基酮模式, 與之相對應, 巴里坤湖沉積物中存在微體古生物化石G. oceanic(Chu et al., 2005), 夏日淖爾湖分離出了合成長鏈烯酮的母源C. lamellosa(Sun et al., 2007), 表明利用C38乙基酮模式和C38甲基乙基酮模式可以區(qū)分長鏈烯酮的母源。但是C38長鏈烯酮分布模式并沒有得到廣泛的重視,在湖泊長鏈烯酮研究的文獻中只有部分文獻給出了 C38長鏈烯酮的組成特征。如英國湖區(qū)Coniston湖(Cranwell, 1985)不同深度的沉積物中 C38長鏈烯酮分布模式不同, 在90～100 cm 為乙基酮模式, 而在 126～145 cm 和153～165 cm的沉積物中為甲基乙基酮模式, 中國的巴里坤湖(Chu et al., 2005)、南美的Titicaca(Theissen et al., 2005)、美國的Crose Mere湖沉積物和Upton Broad湖沉積物(Toney et al., 2010)、南極的Fryxell湖(Jaraula et al., 2010)、格陵蘭的湖泊(D'Andrea et al., 2005)、美國的Brush湖和德國的Steisslingen湖(Zink et al.,2001)沉積物中為甲基乙基酮模式。中國的扎布耶湖(Wang et al., 1998)、俄羅斯的Pichozero湖(Zink et al., 2001)、英國Windermere湖(Cranwell, 1985)、南極的Ace湖(Coolen., 2004)、中國的青海湖的C38長鏈烯酮分布模式為乙基酮模式(Li.,1996; Liu et al., 2008)。如何利用長鏈烯酮的分布特征, 研究長鏈烯酮的母源可能是將來的研究內容。

圖3 C38長鏈烯酮的組成特征: C38乙基酮模式(a)和C38甲基乙基酮模式(b)Fig. 3 Composition of C38 long-chain alkenones: C38 ethylketone pattern (a) and C38 methylethylketone pattern (b)

2 湖泊中長鏈烯酮的母源

自20世紀80年代發(fā)現(xiàn)湖泊沉積物中存在長鏈烯酮以來, 學術界一直不斷地探索湖泊沉積物中長鏈烯酮母源。但是, 由于湖泊長鏈烯酮母源藻類豐度低、個體小, 分離母源難度較大, 學術界一直未能解決此問題。Cranwell等(1985)認為單鞭金藻可能是湖泊沉積物中長鏈烯酮的主要來源。Zink等(2001)根據(jù)湖泊水化學特征和長鏈烯酮的分布特征, 認為湖水的酸堿度控制了產(chǎn)生長鏈烯酮的藻類的生長速度, 研究不同深度的水樣發(fā)現(xiàn)葉綠素含量最高處的水樣和大于 10μm的過濾樣中存在長鏈烯酮, 認為長鏈烯酮來自大于10μm的藻類, 并通過藻類培養(yǎng)、長鏈烯酮和藻類分布的研究明確排除了湖泊中許多藻類是合成長鏈烯酮的母源, 例如: 與海洋定鞭藻綱對應的淡水物種 Chrysochromulina polylepsis 等,其他的還有綠藻門的 Phacotus lenticularis, 藍藻門的 Synechocystis sp. 等, 親堿性的硅藻 Cyclotella meneghiniana等, 但未能發(fā)現(xiàn)長鏈烯酮的母源, 說明長鏈烯酮可能并非來源于湖泊中的優(yōu)勢藻類, Zink等推測Chrychromulina parva有可能是某些湖泊中長鏈烯酮的母源。在我們研究的淡水湖中, 四海龍灣瑪珥湖沉積物中長鏈烯酮含量最高, 而且沉積物中存在高豐度的金藻孢子, 推測淡水湖泊中長鏈烯酮的母源可能為金藻(Chu et al., 2005), 但藻類培養(yǎng)未能獲得四海龍灣瑪珥湖中合成長鏈烯酮的母源。

在中國內陸一些咸化湖, 如巴里坤湖、艾比湖表層沉積物中存在 Gephyrocapsa oceanica、Coccolithus pelagicus等顆石藻化石(徐鈺林和孫鎮(zhèn)城, 1998; 孫鎮(zhèn)城等, 1997; 孫鎮(zhèn)城等, 2002)。Chu等(2005)根據(jù)中國內陸一些咸化湖泊表層沉積物存在Gephyrocapsa oceanica等顆石藻化石、在相應 的湖泊沉積物中檢出長鏈烯酮, 以及巴里坤湖長 鏈烯酮的分布模式與顆石藻G. oceanica培養(yǎng)產(chǎn)物的分布模式一致, 認為一些顆石藻(G. oceanica, C. pelagicus)可能是某些湖泊中長鏈烯酮的母源。在咸化湖泊中, 我們選擇了長鏈烯酮含量高的夏日淖爾湖(碳酸鹽型鹽湖), 采集藻種, 培養(yǎng)分離, 在夏日淖爾湖采集的春秋季節(jié)的藻種培養(yǎng)樣中, 我們(Sun et al., 2007)發(fā)現(xiàn)并成功分離了Chrysotila lamellosa, 單藻種培養(yǎng)表明Chrysotila lamellosa在生長過程中合成長鏈烯酮。

不同類型湖泊、同一湖泊不同發(fā)展階段的沉積物樣品中長鏈烯酮分布特征存在差異, 考慮到湖水物理、化學環(huán)境的巨大差異, 以及前人在長鏈烯酮母源等方面的研究結果, 我們認為湖泊中長鏈烯酮的母源不僅是 Gephyrocapsa oceanica、Chrysotila lamellosa, 可能還存在其他母源。近年來, 一些學者結合長鏈烯酮的分布特征和 18S rDNA序列, 認為Ace湖和 Fryxell湖中長鏈烯酮的可能來源是Isochrysis sp.和 C. lamellosa, 格陵蘭不同湖泊中長鏈烯酮的母源不同, 一些可能來源于 Isochrysis sp.和 C. lamellosa(Coolen et al., 2004; Jaraula et al., 2010), 而另外一些湖泊, 例如美國的東北桑德希爾湖區(qū)的湖泊沉積物中不含 C37:4長鏈烯酮, 與其它湖泊截然不同的烯酮分布模式可能表明這些湖泊中長鏈烯酮的母源不是Isochrysis sp.和C. lamellose.而是其它物種。

3 長鏈烯酮不飽和度與溫度的關系

孫青等(2004)報道了硫酸鹽型鹽湖中U37k′與湖區(qū)年平均溫度存在較好的相關性, 硫酸鹽型鹽湖的U37k′溫度曲線方程是U37k′=0.028× T +0.166(r2=0.88),此后, 我們(Chu et al., 2005)比較系統(tǒng)的總結了中國不同氣候帶不同水化學成分的 50個湖泊表層沉積物中的長鏈烯酮數(shù)據(jù), 探討了U37k′與年均氣溫、春夏秋冬和7月平均氣溫間的關系, U37k′與年均氣溫相關性最好U37k′= 0.0328 × T + 0.126(r2=0.83), 方程的斜率(0.0328)與實驗室培養(yǎng)的E. huxleyi(0.033, Prahl and Wakeham, 1987)、世界范圍內沉積物的標定(0.033, Müller et al., 1998)、南中國海(0.031, Pelejero and Grimalt, 1997)、圣芭芭拉盆地(0.034, Zhao et al., 2000和南海(0.038, Sikes et al.,1997) 的U37k′-T方程斜率一致(Chu et al., 2005), 結合近年來發(fā)表的北極格陵蘭的湖泊(D'Andrea et al., 2005)、中國青海湖(Liu et al., 2008)、柴達木盆地湖泊(付明義等, 2008)、德國的湖泊(Zink et al., 2001)和美國北部大平原湖區(qū)(Toney et al., 2010)湖泊沉積物中獲得的長鏈烯酮數(shù)據(jù), 獲得新的湖泊體系長鏈烯酮不飽和度與溫度的關系: U37k′= 0.031× T + 0.094 (n=76, r2= 0.67)(圖4)。次相關的是U37k’與春秋季節(jié)溫度間的關系, 與夏冬季節(jié)均溫相關性最差(Chu et al., 2005),可能表明長鏈烯酮的母源在春秋季節(jié)繁盛, 在此期間合成長鏈烯酮, 并記錄了此期間的溫度。湖泊可能的長鏈烯酮的母源是金藻 (Cranwell, 1985; Versteegh et al., 2001), 它們是典型的浮游植物, 以季節(jié)性生長為特征(Duff et al., 1995), 生長季節(jié)是早春和晚秋, 采集夏日淖爾湖藻類樣品, 在4、5、9、10月的藻種培養(yǎng)樣中發(fā)現(xiàn)了合成長鏈烯酮的藻類Chrysotila lamellosa, 而夏季藻類樣品的混合培養(yǎng)樣中雖然含有痕量的長鏈烯酮, 但沒有發(fā)現(xiàn)Chrysotila lamellosa, 也可能說明長鏈烯酮不是在 7月合成的,所以U37k′與春、秋季節(jié)溫度相關性優(yōu)于其它季節(jié)是合理的, 不同湖泊的季節(jié)性藻類繁盛可能是削弱U37k′溫度相關性的重要因素 (Prahl et al., 2001; Bac et al., 2003)。

在溫度較高和溫度較低的區(qū)域, U37k′與溫度之間有明顯的偏離(Sikes and Volkman, 1993; Rosell-Mel et al., 1995; Volkman et al., 1995; Conte et al., 1998; Conte et al., 2001; Versteegh et al., 2001; Mercer et al., 2005)。湖泊沉積物U37k′與溫度間關系的標定方程在溫暖端斜率有變緩趨勢(Chu et al., 2005), 湖泊中長鏈烯酮的母源C. Lamellosa的溫控培養(yǎng)實驗結果表明在低于 14℃時, U37k′與溫度關系方程的斜率也是變小的(Sun et al., 2007)。這種U37k′與溫度間的關系方程在高、低溫端斜率變小現(xiàn)象在海洋沉積物研究和單藻種培養(yǎng)研究中是一種普遍的現(xiàn)象(Sikes and Volkman, 1993; Sonzogni et al., 1997; Conte et al.1998)?？赡苷f明合成長鏈烯酮的藻類細胞在適宜生長溫度范圍之外, 為適應溫度變化調整長鏈烯酮相對含量的能力下降。

圖4 湖泊體系長鏈烯酮不飽和度與溫度的關系Fig. 4 Relationship between unsaturation and temperature of long-chain alkenones in lake system

以前的研究表明海洋體系U37k′-T間的關系可能受物種因素影響較小(Müller et al.,1998)。在海洋體系中, 一般的沉積物標定中U37k′-T具有高的相關系數(shù), 海洋體系中物理化學和生物條件相對均一, 而且沉積物的標定的優(yōu)點在于包含了環(huán)境變化、物種的分布變化、成巖作用的影響, 沉積物中長鏈烯酮的信息中短期的和合成環(huán)境中非溫度的因素影響被平均、被削弱(Müller et al., 1998; Sachs et al., 1999, Conte et al., 2001), 然而, 一些研究表明基因的差異和生理響應的差異確實存在 (Volkman et al., 1995;Versteegh et al., 2001), 而且湖泊體系的水化學、生物物種、季節(jié)性變化遠遠大于海洋體系的變化, 尤其水化學的巨大差異可能導致湖泊體系生物物種發(fā)生重要改變, 考慮到湖泊中長鏈烯酮分布模式的不同, 在研究的湖泊中可能存在生態(tài)迥異、對環(huán)境尤其是溫度變化響應具有很大差異的合成長鏈烯酮的物種, 考慮到當湖水鹽度≤3.0 g/L, 生物區(qū)系沒有明顯差別(Hammer, 1986; Beadle, 1959), 我們將湖泊體系分為兩組: 淡水-微咸水(鹽度≤_3.0 g/L)和咸水湖。淡水-微咸水湖U37k’與年均大氣溫度的關系是U37k′= 0.037× MAAT + 0.108 (n=14, r2= 0.90, Chu et al., 2005), 鹽湖的U37k′與年均大氣溫度的關系是U37k′= 0.025× MAAT + 0.153 (n=24, r2= 0.67, Chu et al., 2005)。淡水-微咸水湖的回歸方程的斜率與咸水湖的差別很大, 斜率的不同可能是因為淡水-微咸水和咸水湖生物區(qū)系發(fā)生明顯的變化, 合成長鏈烯酮的藻類可能有很大的差異。咸水湖回歸方程的斜率與中國硫酸鹽型湖泊U37k′-T 關系方程的斜率(Sun et al, 2004)相似, 與夏日淖爾湖中分離出長鏈烯酮母源(Chrysotila lamellosa)單藻種控溫培養(yǎng)獲得的線性回歸方程: U37k′= 0.0257× T -0.2608 (n = 9, r2= 0.97, Sun et al., 2007)相似, 但與濱海種C. lamellosa的U37k′-T方程斜率相差很大(0.01, Rontani et al., 2004), 斜率的差異可能是由于不同種屬之間對溫度響應的變化不同造成。種屬間遺傳型變化可能是影響生物合成長鏈烯酮對溫度的響應方式的重要因素(Conte et al., 1995; Yamamoto et al., 2000)。這個結果表明在某一湖泊中分布模式不同或奇特時, 利用U37k′重建湖泊古溫度需要謹慎。

在培養(yǎng)實驗中, C37:4含量從 10°C的 24.9%變至22°C的 6.3%, 表明C37:4在鹽度不變的情況下隨溫度而變化(Sun et al., 2007)。當考慮到指標中引入C37:4,利用U37k指數(shù)(Brassell et al. 1986), 我們可以得到C. lamellosa培 養(yǎng) 產(chǎn) 物 的 U37k與 T線 性 關 系 : U37k=0.0377× T – 0.5992(n=14, r2=0.98, Sun et al, 2007), 顯然生長環(huán)境的水溫控制著U37k, 與海洋物種E. huxleyi和 G. oceanica 的培養(yǎng)結果一致(Conte et al., 1998, Conte et al., 1994); 德國的淡水湖沉積物中U37k與湖水溫度呈線性關系(Zink et al., 2001)。但是C37:4的影響因素較多, 例如可能反映鹽度(Rosell-Mele′et al., 1998; Rosell-Mele′et al., 2002; Liu et al., 2006), 雖然C37:4與鹽度的關系不確定(Chu et al., 2005, Lopez et al., 2005), 而且C37:4較C37:2和C37:3易于氧化, 因此U37k′指標可能比U37k可靠(Sun et al., 2007)。最近, Pearson(2008)在研究西班牙鹽湖中長鏈烯酮時提出了基于C37: 4-2和C38: 4-2長鏈烯酮同系物的新的溫度指標, 西班牙不同鹽湖中 U3K738與溫度的關系是: U3K738= 0.0464×MAutAT- 0.867 (r2=0.80, n=13)。實驗室培養(yǎng)和湖泊表層沉積物中長鏈烯酮溫標的標定方面的研究促進了湖泊古溫度計——長鏈烯酮不飽和度溫標的定量化研究。

4 結論

長鏈烯酮不飽和度(U37k′)作為定量反映古溫度變化的重要替代指標, 已在海洋中得到廣泛應用,但在湖泊中長鏈烯酮不飽和度與溫度的關系及其母源研究則很少。我們課題組研究了中國不同氣候帶、不同水化學環(huán)境湖泊表層沉積物中長鏈烯酮, 發(fā)現(xiàn)多數(shù)湖泊中存在 2～4個不飽和鍵的長鏈烯酮, 認為不同的長鏈烯酮分布模式可能與不同的環(huán)境和物種相關。首次報道硫酸鹽型湖泊中存在長鏈烯酮。研究了湖泊長鏈烯酮不飽和度與溫度的關系, 發(fā)現(xiàn)湖泊長鏈烯酮不飽和度與年均氣溫和春秋季節(jié)溫度高度相關, 結合近年來不同研究者發(fā)表的不同地區(qū)湖泊中長鏈烯酮數(shù)據(jù), 建立了湖泊表層沉積物中長鏈烯酮不飽和度與溫度的經(jīng)驗函數(shù)關系。考慮到湖泊水化學的巨大差異可能導致湖泊體系生物物種發(fā)生重要改變, 我們將湖泊體系分為兩組, 分別建立了兩組不同水化學成分的湖泊: 淡水-微咸水和咸水湖中長鏈烯酮不飽和度與溫度的經(jīng)驗函數(shù)。首次發(fā)現(xiàn)并成功分離出湖泊中長鏈烯酮母源等鞭金藻Chrysotila lamellosa, 通過單藻種控溫培養(yǎng), 建立長鏈烯酮不飽和度與水溫關系方程, 實驗室培養(yǎng)公式與經(jīng)驗公式斜率一致, 驗證了長鏈烯酮不飽和度溫標, 研究表明湖泊環(huán)境和海洋環(huán)境中長鏈烯酮的母源合成烯酮的路徑和對溫度響應的機制一致, 長鏈烯酮有可能成為可靠的陸地溫標, 在陸地古氣候變化研究中將發(fā)揮重要的作用。但是湖泊體系影響因素多, 相對海洋體系復雜, 湖泊長鏈烯酮溫標的選擇與應用需要謹慎, 長鏈烯酮溫標的野外標定和母源分離培養(yǎng)等定量研究有待進一步加強。

付明義, 劉衛(wèi)國, 李祥忠，徐黎明，王政，安芷生. 2008. 青海湖及柴達木盆地地區(qū)現(xiàn)代湖泊沉積物中長鏈烯酮的分布特征[J]. 湖泊科學, 20(3): 285-290.

劉傳聯(lián), 趙泉鴻, 汪品先. 2002. 從化石群及殼體同位素看古近紀東營湖湖水化學[J]. 地球學報, 23: 237-242.

壟慶杰, 吳良基, 吳時國, 羅又郎, .張干. 1999. 南海長鏈烯酮化合物的檢測及U值的應用[J]. 地球化學, 28 (1): 51- 57.

盛國英, 蔡克勤, 陽學賢, 盧家爛, 賈國東, 傅家謨, 彭平安. 1998. 合同察汗淖(堿)湖沉積物中長鏈不飽和烯酮及其古氣候意義[J]. 科學通報, 43 (10): 1090-1094.

時興合, 趙燕寧, 戴升, 徐亮, 李應業(yè), 賈紅莉, 張青梅. 2005.柴達木盆地40多年來的氣候變化研究[J]. 中國沙漠, 25(1): 123-128.

孫青, 儲國強, 李圣強, 呂彩芬, 鄭綿平. 2004. 硫酸鹽型鹽湖中的長鏈烯酮及古環(huán)境意義[J]. 科學通報, 49: 1789-1792.

孫青, 儲國強. 2002. 長鏈烯酮不飽和度溫標研究進展[J]. 地質地球化學, 30(4): 63-67.

孫鎮(zhèn)城, 楊藩, 張枝煥, 李守軍, 李東明, 彭立才, 曾學魯, 徐鈺林, 茅紹智, 王強. 1997. 中國新生代咸化湖泊沉積環(huán)境與油氣生成[M]. 北京: 石油工業(yè)出版社.

孫鎮(zhèn)城, 楊革聯(lián), 喬子真, 楊藩, 李東明, 景民昌. 2002. 我國咸化湖泊沉積中鈣質超微化石特征及其地質意義[J]. 古地理學報, 4: 56-63.

王曉華. 2009. 東北四海龍灣瑪珥湖 1500年來長鏈稀酮不飽和度溫標與古水溫重建[D]. 北京: 中國科學院地址與地球物理研究所.

徐鈺林, 孫鎮(zhèn)城. 1998. 中國西北地區(qū)第四紀鹽湖沉積中鈣質超微化石的發(fā)現(xiàn)及其古環(huán)境意義[J]. 現(xiàn)代地質, 12: 49-55.

陽學賢, 盛國英, 盧家爛, 傅家謨. 1996. 合同查汗淖(堿)湖沉積物中的生物標志物特征及古環(huán)境意義[J]. 地球化學, 25(6): 536-544.

張干, 盛國英, 彭平安, 鄭洪漢, 鄒世春. 2000. 南極喬治王島菲爾德斯半島湖相沉積物的分子有機地球化學特征[J]. 科學通報, 45: 2758-2762.

References:

ABRANTES F., LEBREIRO S., RODRIGUES T., GIL I., BARTELS-JóNSDóTTIR H., OLIVEIRA P., KISSEL C., GRIMALT J O. 2005. Shallow-marine sediment cores record climate variability and earthquake activity off Lisbon (Portugal) for the last 2000 years[J]. Quaternary Science Reviews, 24(23-24): 2477-2494.

BAC M G., BUCK K R., CHAVEZ F P., BRASSELL S C. 2003. Seasonal variation in alkenones, bulk suspended POM, plankton and temperature in Monterey Bay, California: Implications for carbon cycling and climate assessment[J]. Organic Geochemistry, 34: 837-855.

BARD E., ROSTEK F., SONZOGNI C. 1997. Interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry[J]. Nature, 385: 707-710.

BEADLE L. 1959. Osmotic regulation in the relation to the classification of brackish and inland saline waters[J]. Archivo Di Oceanografia E Limnologia, XI: 143-151.

BENTALEB I., FONTUGNE M., BEAUFORT L. 2002. Long-chain alkenones and U variability along a south-north transect in the Western Pacific Ocean[J]. Global Planet Change, 34: 173-183.

BRASSELL S C., EGLINTON G., MARLOWE I T., PFLAUMANN U., SARNTHEIN M. 1986. Molecular stratigraphy: a new tool for climatic assessment[J]. Nature, 320: 129-133.

CACHO I., PELEJERO C., GRIMALT J O., CALAFAT A., CANALS M. 1999. C37 alkenone measurements of sea surface temperature in the Gulf of Lions (NW Mediterranean)[J]. Organic Geochemistry. 30: 557-566.

CHU G Q., SUN Q., LI S Q., ZHENG M P., JIA X X., LU C F., LIU J Q., LIU T S. 2005. Long-chain alkenone distributions and temperature dependence in lacustrine surface sediments from China[J]. Geochimica et Cosmochimica Acta, 69(21): 4985-5003.

CONTE M H., THOMPSON A., EGLINTON G., GREEN J C. 1995. Lipid biomarker diversity in the coccolithophorid Emiliania huxleyi (prymnesiophyceae) and the related species Gephyrocapsa oceanica[J]. Phycology, 31: 272-282.

CONTE M H., THOMPSON A., LESLEY D., HARRIS R P. 1998. Enetic and physiological influences on the alkenone/alkenoate versus growth temperature relationship in Emiliania huxleyi and Gephyrocapsa oceanica[J]. Geochimica et Cosmochimica Acta, 62: 51-68.

CONTE M H., VOLKMAN J K., EGLINTON G. 1994. Lipid biomarkers of the Haptophyta[M]. The Haptophyte Algae (eds. J. C. Green and B. S. C. Leadbeater). Oxford University Press, 351-377.

CONTE M H., WEBER J C., KING L L., WAKEHAM S G. 2001. The alkenone temperature signal in western North Atlantic surface waters[J]. Geochimica et Cosmochimica Acta, 65: 4275-4287.

COOLEN M J L., MUYZER G., RIJPSTRA W I C., SCHOUTEN S., VOLKMAN J K., DAMSTéJ S S. 2004. Combined DNA and lipid analyses of sediments reveal changes in Holocene haptophyte and diatom populations in an Antarctic lake[J]. Earth and Planetary Science Letters, 223(1-2): 225-239.

CRANWELL P A. 1985. Long-chain unsaturated ketones in recent lacustrine sediments[J]. Geochimica et Cosmochimica Acta, 49: 1545-1551.

D'ANDREA W J., HUANG Y. 2005. Long chain alkenones in Greenland lake sediments: Low δ13C values and exceptional abundance[J]. Organic Geochemistry, 36(9): 1234-1241.

DUFF K E., ZEEB B A., SMOL J P. 1995. Atlas of Chrysophycean Cysts[M]. Kluwer Academic Publishers, Dordrecht, the Netherlands.

FREEMAN K H., WAKEHAM S G. 1992. Variations in the distributions and isotopic composition of alkenones in Black Sea particles and sediments[J]. Organic Geochemistry, 19: 277-285.

FU Ming-yi, LIU Wei-guo, LI Zhong-xiang, XU Li-ming, WANG Zheng, AN Zhi-sheng. 2008. The distribution of long-chain alkenones in modern lacustrine sediments in the Lake Qinghai and lakes from the Qaidam Basi[J]. Journal of Lake Science, 20(3): 285-290(in Chinese with English abstract).

HAMMER U T. 1986. Saline lake ecosystems of the world[M]. The Netherlands: Kluwer Academic Publishers Group.

HARADA N., SHIN K. H., MURATA A., UCHIDA M., TOMOKO N. 2003. Characteristics of alkenones synthesized by a bloom of Emiliania huxleyi in the Bering Sea[J]. Geochim. Cosmochim. Acta, 67: 1507– 1519.

INNES H E., BISHOP A N., FOX P A., HEAD I M., FARRIMOND P. 1998. Early diagenesis of bacteriohopanoids in recent sediments of Lake Pollen, Norway[J]. Organic Geochemistry, 29: 1285-1295.

JARAULA C M B., BRASSELL S C., MORGAN-KISS R M., DORAN P T., KENIG F. 2010. Origin and tentative identification of tri to pentaunsaturated ketones in sediments from Lake Fryxell, East Antarctica[J]. Organic Geochemistry, 41(4): 386-397.

KIENAST M., STEINKE S., STATTEGGER K., CALVERT S E. 2001. Synchronous tropical South China Sea SST change andGreenland warming during deglaciation[J]. Science, 291: 2132-2134.

LI J G., PHILP R P., PU F., ALLEN J. 1996. Long-chain alkenones in Qinghai lake sediments[J]. Geochimica et Cosmochimica Acta, 60: 235-241.

LIU Chuan-lian, ZHAO Quan-hong, WANG Pin-xian. 2002. Water Chemistry of the Paleogene Dongying Lake: Evidence from Fossil Assemblages and Shell Isotopes[J]. Acta Geoscientica Sinica, 23: 237-242 (in Chinese with English abstract).

LIU W G., LIU Z H., FU M Y., AN Z S. 2008. Distribution of the C37 tetra-unsaturated alkenone in Lake Qinghai China: A potential lake salinity indicator[J]. Geochimica et Cosmochimica Acta, 72(3): 988-997.

LIU Z H., HENDERSON A C G., HUANG Y S. 2006. Alkenone-based reconstruction of late-Holocene surface temperature and salinity changes in Lake Qinghai, China[J]. Geophysical Research Letters. 33: L09707. doi: 10.1029/2006GL026151.

GONG Qing-jie, WU Liang-ji, WU Shi-guo, LUO You-lang, ZHANG Gan. 1999. Detection of long-chain alkenone compounds and application of U37k values in South China Sea[J]. Geochimica, 28 (1): 51- 57 (in Chinese with English abstract). LOPEZ J F., DE OTEYZA T G., TEIXIDOR P., GRIMALT J O. 2005. Long chain alkenones in hypersaline and marine coastal microbial mats. Organic Geochemistry, 36(6): 861-872.

MARLOWE I T., BRASSELL S C., EGLINTON G., GREEN J C. 1984b. Long chain unsaturated ketones and esters in living algae and marine sediments[J]. Organic Geochemistry, 6: 135-141.

MARLOWE I T., BRASSELL S C., EGLINTON G., GREEN J C. 1990. Long-chain alkenones and alkyl alkenoates and the fossil coccolith record of marine sediments[J]. Chemical Geology, 88: 349-375.

MARLOWE I T., GREEN J C., NEAL A C., BRASSELL C., EGLINTON G., COURSE P A. 1984a. Long chain (n-C37-C39) alkenones in the Prymnesiophyceae Distribution of alkenones and other lipids and their taxonomic significance[J]. British Phycological Journal, 19: 203-216.

MARLOWE I T., BRASSELL S C., EGLINTON G., GREEN J C. 1984b. Long chain unsaturated ketones and esters in living algae and marine sediments[J]. Organic Geochemistry, 6: 135-141.

MERCER J L., ZHAO M X., COLMAN S M. 2004. Seasonal variations of alkenones and UK37 in the Chesapeake Bay water column[J]. Estuarine, Coastal and Shelf Science, 63(4): 675-682

MüLLER P J., KIRST G., RUHLAND G., STORCH I V., ROSELL-MELé A. 1998. Calibration of the alkenone palaeotemperature index U based on core-tops from the eastern South Atlantic and the global ocean(60°C -60°C)[J]. Geochimica et Cosmochimica Acta, 62: 1757-1772.

PEARSON E J., JUGGINS S., FARRIMOND P. 2008. Distribution and significance of long-chain alkenones as salinity and temperature indicators in Spanish saline lake sediments[J]. Geochimica et Cosmochimica Acta, 72(16): 4035-4046.

PELEJERO C., GRIMALT J O. 1997. The correlation between the U index and sea surface temperatures in the warm boundary: The South China Sea[J]. Geochimica et Cosmochimca Acta, 61: 4789-4797.

PRAHL F G., PILSKALN C H., SPARROW M A. 2001. Seasonal record for alkenones in sedimentary particles from the Gulf of Maine[J]. Deep Sea Research: part I, 48: 515-528.

PRAHL F G., WAKEHAM S G. 1987. Calibration of unsaturation patterns in long-chain ketone compositions for paleotemperature assessment[J]. Nature, 330: 367-369.

PRAHL F G., MUEHLHAUSEN L A., ZAHNLE D L. 1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions[J]. Geochimica et Cosmochimica Acta, 52: 2303–2310.

PRAHL F G., COWIE G L., DE LANGE G J., SPARROW M A. 2003. Selective organic matter preservation in 'burn-down' turbidites on the Madeira abyssal plain[J]. Paleoceanography, 18(2): 1052.

RONTANI J F., BEKER B.,VOLKMAN J. 2004. Long-chain alkenones and related compounds in the benthic haptophyte Chrysotila lamellosa Anand HAP17[J]. Phytochemistry, 65: 117-126.

ROSELL-MELE’A. 1998. Interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in highlatitude locations[J]. Paleoceanography, 13: 694-703.

ROSELL-MELE’A., JANSEN E., WEINELT M. 2002. Appraisal of a molecular approach to infer variations in surface ocean freshwater inputs into the North Atlantic during the last glacial[J]. Global and Planetary Change, 34: 143-152.

ROSELL-MELé A., COMES P., MüLLER P., ZIVERI P. 2000. Alkenone fluxes an anomalous UK37′ values during 1989-1990 in the Northeast Atlantic (48°N 21°W)[J]. Marine Chemistry, 71: 251-264.

ROSELL-MELé A., EGLINTON G., PFLAUMANN U., SARNTHEIN M. 1995. Atlantic core-top calibration of the UK37′ index as a sea-surface paleotemperature indictor[J]. Geochimica et Cosmochimica Acta, 59: 3099-3107.

ROSTEK F., RUHLAND G., BASSINOT F C., MULLER P J., LABEYRIE L D., LANCELOT Y., BARD E. 1993. Resconstructing sea surface temperature and salinity using18O and alkenone records[J]. Nature, 364: 319-321.

SACHS J P., LEHMAN S J. 1999. Subtropical North Atlantic temperatures 60,000 to 30,000 years ago[J]. Science, 286: 756-759.

SAWADA K., HANDA N., SHIRAIWA Y., DANBARA A., MONTANI S. 1996. Long-chain alkenones and alkyl alkenoates in the coastal and pelagic sediments of the northwest North Pacific with special reference to the reconstruction of Emiliania huxleyi and Gephyrocapsa oceanica ratios[J]. Organic Geochemistry, 24: 751-764.

SCHULZ H M., SCH?NER A., EMEIS K C. 2000. Long-chain alkenone patterns in the Baltic Sea—An ocean-freshwater transition[J]. Geochimica et Cosmochimca Acta, 64: 469–477.

SEKI O., KAWAMURA K., IKEHARA M., NAKATSUKA T., OBA T. 2004. Variation of alkenone sea surface temperature in the Sea of Okhotsk over the last 85 kyrs[J]. Organic Geochemistry, 35(3): 347-354.

SHENG G Y., CAI K Q., YANG X X., LU J L., JIA G D., PENG P A., FU J M. 1998. Long-chain alkenones in Hotong Qagan Nur Lake sediments and its paleoclimatic implications[J]. Chinese Science Bulletin, 44(3): 259-263.

SHI Xing-he, ZHAO Yan-ning, DAI Sheng, XU Liang, LI Ying-ye, JIA Hong-li, ZHANG Qing-mei. 2005. Research on climatic change of Qaidam Basin since 1961[J]. Journal of Desert Research, 25(1): 123-128 (in Chinese with English abstract).

SIKES E L., FARRINGTON J W., KEGWIN L D. 1991. Use of alkenone unsaturation ratio (UK37′) to determine past sea surface temperatures: Core-top SST calibrations and methodology considerations[J]. Earth and Planetary Science Letters, 104: 36-47.

SIKES E L., LEARY T O., NODDER S D., VOLKMAN J K. 2005. Alkenone temperature records and biomarker flux at the subtropical front on the chatham rise, SW Pacific Ocean[J]. Deep Sea Research, Part I: Oceanographic Research Papers, 52(5): 721-748.

SIKES E L., VOLKMAN J K. 1993. Calibration of alkenone unsaturation ratios (Uk'37) for paleotemperature estimation in cold polar waters[J]. Geochimica et Cosmochimica Acta, 57(8): 1883-1889.

SIKES E. L, VOLKMAN J K., ROBERTSON L G., PICHON J J. 1997. Alkenones and alkenes in surface water and sediments of the Southern Ocean: Implications for paleotemperature estimation in polar regions[J]. Geochimica et Cosmochimica Acta, 61: 1495–1505.

SIKES E L., SICRE M A. 2002. Relationship of the tetra-unsaturated C37alkenone to salinity and temperature: Implications for paleoproxy applications[J]. Geochemistry Geophysics Geosystems, 3: 1063.

SONZOGNI C., BARD E., ROSTEK F., LAFONT R., ROSELL-MELE A., EGLINTON G. 1997. Core-top calibration of the alkenone index vs sea surface temperature in the Indian Ocean[J]. Deep Sea Research Part II: Topical Studies in Oceanography, 44: 1445-1460.

SUN Qing, CHU Guo-qiang. 2002. Progress in the study of temperature proxy of alkenone unsaturation[J]. Geology Geochemistry, 30(4): 63-67 (in Chinese with English abstract).

SUN Q., CHU G Q., LIU G X., LI S., WANG X H. 2007. Calibration of alkenone unsaturation index with growth temperature for a lacustrine species, Chrysotila lamellose (Haptophyceae)[J]. Organic Geochemistry, 38(8): 1226-1234.

SUN Q., CHU G Q., LI S Q., LV C F., ZHENG M P. 2004. Long-chain alkenones in sulfate lakes and its paleoclimatic implications[J]. Chinese Science Bulletin, 49(19): 2082-2086. SUN Zhen-cheng, YANG Ge-lian, QIAO Zi-zhen, YANG Fan, LI Dong-ming, JING Min-chang. 2002. Characteristics and geologic significance of calcareous nanofossils in sediments of terrestrlal salinized lakes[J]. Journal of Palaeogeography, 4: 56-63 (in Chinese with English abstract).

TERNOIS Y., SICRE M A., BOIREAU A., CONTE M H., E G. 1997. Evaluation of long-chain alkenones as paleo-temperature indicators in the Mediterranean Sea[J]. Deep Sea Research, 44: 271-286.

THEISSEN K M., ZINNIKER D A., MOLDOWAN J M., DUNBAR R B., ROWE H D. 2005. Pronounced occurrence of long-chain alkenones and dinosterol in a 25,000-year lipid molecular fossil record from Lake Titicaca, South America[J]. Geochimica Cosmochimica Acta, 69: 623-636.

THIEL V., JENISCH A., LANDMANN G., REIMER A., MICHAELIS W. 1997. Unusual distributions of long-chain alkenones and tetrahymanol from the highly alkaline Lake Van, Turkey[J]. Geochimica Cosmochimica Acta, 61: 2053-2064.

TONEY J L., HUANG Y S., FRITZ S C., BAKER P A., GRIMM E., NYREN P. 2010. Climatic and environmental controls on the occurrence and distributions of long chain alkenones in lakes of the interior United States[J]. Geochimica et Cosmochimica Acta, 74(5): 1563-1578.

VERSTEEGH G J M., RIEGMAN R., DE LEEUW J W., (FRED) JANSEN J H F. 2001. Uk37′ value for Isochrysis galbana as a function of culture temperature, light intensity and nutrient concentrations[J]. Organic Geochemistry, 32: 785-794.

VOLKMAN J K., BARRETT S M., BLACKBURN S I., SIKES E L. 1995. Alkenone in Gephyrocapsa oceanica: implications for studies of paleoclimate[J]. Geochimica Cosmochimica Acta, 59: 513-520.

VOLKMAN J K., EGLINTON G., CORNER E D S. 1980. Novel unsaturated straight-chain C37-C39 methyl and ethyl ketones in marine sediments and a coccolithophorid Emiliania huxleyi[M]. Advances in Organic Geochemistry (eds. A. G. Doulkas and J. R. Maxwell), Pergamon, New York, 219-227.

VOLKMAN J K , EGLINTON G., CORNER E D S., SARGENT J R. 1980. Novel unsaturated straight-chain C37-C39 methyl and ethyl ketones in marine sediments and a coccolithophore Emiliania huxleyi[J]. Physics and Chemistry of the Earth 12: 219-227.

WANG R L., ZHENG M P. 1998. Occurrence and environmental significance of long-chain alkenones in Tibetan Zabuye salt lake, S W China[J]. Int. Salt Lake Research, 6: 281-302.

WANG X H. 2009. Use of the Alkenone Unsaturation Ratio U37k’to Determine Past Temperature for Sihailongwan Maar(Northeast China) During the Last 1500 Years[D]. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing.

XU Yu-lin, SUN Zhen-cheng. 1998. Discovery of the quaternary calcareous nannofossils in the deposits of interior saline lakes from northwestern China and its paleoenvironmental significance[J]. Journal of Graduate School. China University of Geosciences, 12: 49-55 (in Chinese with English abstract).

YANG Xue-xian, SHENG Guo-ying, LU Jia-can, FU Jia-mo. 1996. Characteristics and paleoenvironmental significance of biomarks in sediments from Hotong Qagan Num (soda lake)[J]. Geochimica, 25(6): 536-544(in Chinese with English abstract).

YAMAMOTO M., SHIRAIWA Y., INOUYE I. 2000. Physiological responses of lipids in Emiliania huxleyi and Gephyrocapsa oceanica (Haptophyceae) to growth status and their implications for alkenone paleothermometry[J]. Organic Geochemistry, 31(9): 799-811.

ZHANG G., SHENG G Y., PENG P A., ZHENG H H. 2000. Molecular organic geochemical peculiarities of lacustrine core sediments in Fildes Peninsula, King George Island, Antarctica[J]. Chinese science bulletin, 45: 67-70.

ZHAO M X, EGLINTON G., READ G. 2000. An alkenone (U) quasi-annual sea surface temperature record (A.D.1440 to 1940) using varved sediments from the Santa Barbara Basin[J]. Organic Geochemistry, 31: 903-917.

ZINK K G., LEYTHAEUSER D., MELKONIAN M., SCHWARK L. 2001. Temperature dependency of long-chain alkenone distributions in recent to fossil limnic sediments and in lake waters[J]. Geochimica et Cosmochimica Acta, 65: 253-265.

The Occurrence and Distribution of Long Chain Alkenones in Lakes

SUN Qing1), CHU Guo-qiang2), LIU Guo-xiang3), WANG Xiao-hua2), LIU Mei-mei1), SHI Li-ming1), XIE Man-man2), LIN Yuan1)
1) National Research Center of Geoanalysis, Beijing 100037;
2) Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
3) Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072

The alkenone unsaturation paleothermometer has been successfully and widely applied to reconstructing SST in most oceanographic settings. The utility of the alkenone unsaturation index in the marine system has stirred the interest in the study of LCK in the limnic system, in the hope that it can also be used as a paleotemperature proxy in lacustrine sediments. A suite of long-chain di-, tri- and tetra-unsaturated ketones whose chain lengths range from C37 to C39 with variable patterns of LCK were detected in the lake sediment samples. The ratio of C37:4methyl ketone to the sum of C37 alkenones observed in different lakes is highly variable, and higher than that seen in marine systems. Different distribution patterns of LCK were detected in the surface sediment samples. The very high ratio of C37 / C38 may imply that dominant LCK-producing algae are probably similar to the species C. lamellosa and I. galbana. The detection of C38:4-2 ethyl alkenones suggests that the precursor organism might be similar to E. huxleyi G. oceanica and some species of Isochrysis galbana. However, if only C38:4-2 ethyl alkenonewas identified, the precursor organism may be or closely related species to Chrysotila lamellosa or some species of Isochrysis galbana. Empirical relationships between the alkenone unsaturation index U37k’and different temperature sets (mean annual air temperature, mean annual air temperature in different seasons, and lake surface water temperature of July) were tested. The better correlation between U37k’and temperature was obtained using mean annual air temperature, mean air temperatures of spring and autumn. Based on the new data from the reference the authors fit a new global linear regression of U37k’and MAAT can be expressed as U37k’= 0.031× T + 0.094 (n=76, r2= 0.67), it covers the lake system from the lakes in Greenland to the lakes in the northern part of tropical area in China. Although problems such as species-uncertainty and other unknown factors for U37k’temperature dependence remain existent, the equation might be the representative of the average contribution of LCK to sediments for these data over a wide range of surface temperatures, water chemistry and different alkenones-producer algal populations. A lacustrine source, the non-calcifying species Chrysotila lamellosa Anand (Haptophyceae), was collected and isolated from an inland saline water body, Lake Xiarinur (Inner Mongolia). Its alkenone distribution pattern is similar to that of coastal marine strains of C. lamellosa, but the relationship between U37k’index and culture temperature for the lacustrine species is quite different from that of the coastal species. A significant feature of the alkenones in this strain of C. lamellosa is the lack of C38 methyl alkenones, which might be used to distinguish the species from the marine haptophyte species Emiliania huxleyi and Gephyrocapsa oceanica. The authors examined U37k’and U37kvalues for C. lamellosa as a function of culture temperature in a batch culture experiment. The calibration for U37k’versus culture temperature (T) was U37k’= 0.0257× T -0.2608 (n = 9, r2= 0.97), from 14°C to 22°C. The slope of the equation is similar to the empirical relationship between U37k’and mean annual air temperature in saline lakes. The authors’ studies show that the alkenone unsaturation index U37k’is strongly controlled by environmental temperature the precursor organisms live in, and can be used for palaeoclimate reconstruction. This supports the suggestion that the biosynthetic pathway of alkenones and the mechanism of their temperature signal may be similar in both marine and limnic systems. LCK might be used as an important paleotemperature proxy in the limnic environment.

lake; alkenone; U37k’; distribution pattern; temperature; precursor organism

K928.43; O622

A

1006-3021(2010)04-485-10

本文由國家自然科學基金項目(編號: 40572101; 40972121; 40102016)和國土資源部百人計劃項目聯(lián)合資助。獲中國地質科學院2009年度十大科技進展第四名。

2010-06-10; 改回日期: 2010-07-08。

孫青, 女，1967年生。研究員。主要從事古氣候變化研究。通訊地址: 100037, 北京市西城區(qū)百萬莊大街26號。電話: 010-68999590。E-mail:sunqingemail@yahoo.com.cn。