王 丹, Rashid Harunur

長鏈烯酮在西北大西洋重建全新世氣候變化的研究進展

王 丹, Rashid Harunur

(上海海洋大學(xué)海洋科學(xué)學(xué)院, 上海 201306)

長鏈烯酮; 海洋表層溫度; 冰融水; 烯酮%C37:4; 西北大西洋

全新世西北大西洋古氣候變化的控制因素眾多, 其中3個最主要的變化機制為: 1) 北半球65°N夏季太陽輻射的減弱是導(dǎo)致溫暖的早全新世向較冷的晚全新世氣候轉(zhuǎn)變的主要機制之一[15-17]; 2) 來自極地或陸地殘留冰蓋的淡水輸入通過改變海洋表層溫度和鹽度, 直接影響深層水的形成[18-19]。特別是有研究表明, 勞倫太德冰蓋的Agassiz湖和Ojibway湖崩塌排泄的淡水引發(fā)了10.2 ka、8.2 ka等冷事件, 并削弱了深層水的形成[20-22]; 3) 末次冰期階段, 北極鋒從原本的南部位置撤退, 使得表層洋流(冷而淡的LC和暖而咸的NAC)重組和增強(圖1)。因此, 研究認為SPG強弱狀態(tài)的轉(zhuǎn)換取決于剩余冰蓋排放的淡水量[18-19, 23]。表層洋流的重組顯著影響了加拿大東部邊緣以及更為廣闊的北大西洋北部的SST[24]。而SST的重建有利于評估全新世以來的古氣候變化。

1 長鏈烯酮重建SST的概況

2 西北大西洋長鏈烯酮的研究

在世界各個大洋中, 長鏈烯酮廣泛用于重建古氣候?qū)W變化。這在北大西洋海域已有相當(dāng)多且早的應(yīng)用, 不僅是因為該海域本身的研究意義, 也是因為這里具有不同的環(huán)境特征, 有利于探討長鏈烯酮的應(yīng)用差異。圖1, 表1中列出了北大西洋海域(以西側(cè)為主)烯酮的研究情況, 但圖表中并未列出所有的數(shù)據(jù), 僅列出位于30°N與80°N之間的重要數(shù)據(jù)點, 在文中有所使用。

2.1 烯酮指標的現(xiàn)代過程

圖1 北大西洋區(qū)域地圖

注: LC-拉布拉多洋流; EIC-東冰島洋流; EGC-東格陵蘭洋流; IC-伊爾明厄洋流; SPG-副極地環(huán)流; WGC-東格陵蘭洋流; NAC-北大西洋流; Nfld-紐芬蘭島; 圖中圓形的顏色對應(yīng)年均SST

表1 圖1中各數(shù)據(jù)來源

2.2 低溫海域烯酮的應(yīng)用

3.1 營養(yǎng)鹽對烯酮的影響

圖2 烯酮不飽和度、和分別對年均和春-夏SST的回歸模型[56]

3.2 橫向平流和成巖作用對烯酮的影響

3.3 烯酮合成的季節(jié)性

4 %C37:4對海洋環(huán)境變化的指示作用

研究表明, 海洋環(huán)境中的C37:4主要出現(xiàn)在溫度較低的海水中, Sicre等[65]和Bendle等[31]在北大西洋寒冷的極地海水(Arctic waters)中曾檢測到含量較高的C37:4。Sikes等[69]也曾對大西洋、太平洋和南大洋的水體樣品進行檢測, 發(fā)現(xiàn)C37:4大多存在于鹽度、溫度都較低的水體中。Rosell-Melé等[59]最早提出%C37:4與鹽度之間的函數(shù)關(guān)系; Sicre等[65]指出北大西洋%C37:4與鹽度呈負相關(guān)(2= 0.78)。Bendle等[31]曾對%C37:4能否作為表層海水鹽度指標進行評估, 認為其更適用于指示北大西洋淡水輸入。Filippove等[56]曾推測, 融水輸入導(dǎo)致鹽度改變, 這可能會使藻類離開原本的耐鹽區(qū)(salt tolerance zone), 導(dǎo)致了烯酮生物合成的改變。

在格陵蘭西北岸的迪斯科灣, %C37:4的增加(最高可達28%)指示融水供應(yīng)的增強; 其減少時, 融水通量也有相應(yīng)的減少[32]。該研究區(qū)域海水鹽度較低, 主要受格陵蘭冰蓋融水的影響。相似的, %C37:4在北極的北歐海和巴倫支海區(qū)域亦可指示寒冷北極水的輸入[60]。此外, 在寒冷的拉布拉多海西北部, %C37:4還可用于指示海冰邊緣環(huán)境, 當(dāng)海冰覆蓋減少時, C37:4的占比也有所降低, 與底棲有孔蟲豐度指示的海冰信號相符[33]。在鄰近的拉布拉多陸架南部, Lochte等[4]再次證明了高%C37:4(最高可達20%)指示海冰覆蓋增多, 也可能是融水輸入增強, %C37:4的降低反映海水溫度的回升和海冰覆蓋的減少。盡管此前仍有研究者對此提出異議[69], 但%C37:4指標仍有較為廣泛的應(yīng)用, 尤其是在受海冰影響且鹽度較低的海域[31]。

5 總結(jié)與展望

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Progress in using the long-chain alkenones to reconstruct the Holocene climate changes in northwest Atlantic Ocean

WANG Dan, Rashid Harunur

(College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China)

long-chain alkenones; sea surface temperature; meltwater; alkenone %C37:4; northwest Atlantic Ocean

Dec. 28, 2020

P736.4

A

1000-3096(2022)1-0181-11

10.11759/hykx20201228005

2020-12-28;

2021-01-29

國家自然科學(xué)基金項目(41776064, 41976056)

[National Natural Science Foundation of China, Nos. 41776064; 41976056]

王丹(1996—), 女, 江蘇鹽城人, 碩士研究生, 從事古海洋學(xué)研究, 電話: 15061952053, E-mail: 943795544@qq.com; RASHID Harunur(1969—),通信作者, 男, 教授, 博導(dǎo), 從事海洋地質(zhì)、古海洋學(xué)、低溫地球化學(xué)研究, E-mail: Harunurbhola@gmail.com

(本文編輯: 趙衛(wèi)紅)