Latitudinal and Downcore (0–750 ka) Changes in Nalkane Chain Lengths in the Eastern Equatorial Pacific
Latitudinal and Downcore (0–750 ka) Changes in Nalkane Chain Lengths in the Eastern Equatorial Pacific
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DOI：
10.1016/j.yqres.2010.01.001
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发表时间：
2010-05
影响因子：
2.3
通讯作者：
K. Horikawa;M. Murayama;M. Minagawa;Y. Kato;T. Sagawa
中科院分区：
文献类型：
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作者：
K. Horikawa;M. Murayama;M. Minagawa;Y. Kato;T. Sagawa
赤道东太平洋（EEP）表层沉积物中正构烷烃C31/（C29+C31）比值在热带辐合带（ITCZ）南缘（2-4°N）呈现出北高南低的特征。由于植物倾向于合成更长的链长的正构烷烃，在北方的网站更高的C31/（C29+C31）的比例表明在炎热和/或干燥的条件下植被的贡献更大。这与观察结果一致，即北方站点接收由来自南美洲北方的东北信风输送的较高水平的植物蜡，其中炎热和干燥的条件占主导地位。此外，从覆盖过去750 ka的沉积物芯（芯HY 04; 4°N，95°W），我们发现C31/（C29+C31）比值表现出长期下降MIS（海洋氧同位素阶段）17至13。在此期间，赤道太平洋的纬向SST（海表温度）梯度增加，这表明步行者环流的增加。这种增强的步行者环流可能增强了从赤道大西洋暖池到邻近的北方南美洲的水汽平流，导致南美洲北方干旱地区收缩，这可能解释了正烷烃链长的长期减少。
The n-alkane C31/(C29+C31) ratios from surface sediments in the eastern equatorial Pacific (EEP) exhibit higher values to the north and lower values to the south across the southern edge (2–4°N) of the Intertropical Convergence Zone (ITCZ). Since plants tend to synthesize longer chain length n-alkanes in response to elevated temperature and/or aridity, the higher C 31/(C29+C31) ratios at northern sites suggest a higher contribution of vegetation under hot and/or dry conditions. This is consistent with the observation that northern sites receive higher levels of plant waxes transported by northeasterly trade winds from northern South America, where hot and dry conditions prevail. Furthermore, from a sediment core covering the past 750 ka (core HY04; 4°N, 95°W) we found that C31/(C29+C31) ratios exhibit a long-term decrease from MIS (marine oxygen isotope stage) 17 to 13. During this period, the zonal SST (sea-surface temperature) gradient in the equatorial Pacific increased, suggesting an increase in Walker circulation. Such intensified Walker circulation may have enhanced moisture advection from the equatorial Atlantic warm pool to the adjacent northern South America, causing arid regions in northern South America to contract, which may explain long-term decrease in n-alkane chain lengths.