末次盛冰期以来印度尼西亚穿越流对东印度洋上部水体结构的影响

INFLUENCE OF INDONESIAN THROUGHFLOW ON EASTERNMOST INDIAN UPPER OCEAN STRUCTURE SINCE LAST GLACIAL MAXIMUM

海洋上部水体垂向结构变化对于理解热带海区在全球气候变化中的作用有着重要意义。通过分析印度尼西亚穿越流(ITF)出口处东印度洋帝汶海区SO18480-3孔中的浮游有孔虫表层种Globigerinoides ruber和温跃层种Pulleniatina obliquiloculata壳体氧碳同位素,并借助12个AMS14C测年数据重建了末次盛冰期(LGM)以来该区温跃层深度和营养盐水平的演化序列。壳体氧同位素(δ18O)记录表明温跃层古海洋学特征的变化幅度要大于表层海水,其差值(Δδ18O(P-G))有效地反映了温跃层深度的变化,即冰消期和晚全新世温跃层较浅,LGM和早中全新世温跃层较深;并揭示出与全新世相比,LGM期间ITF总流量未显著减小,ITF对该区上部水体结构的影响受到了东西太平洋之间不对称性的调节。碳同位素(δ13C)记录则表明该区的古海洋学变化在不同程度上受到了南大洋的影响,并受本区上部水体垂向结构的控制,其差值(Δδ13C(G-P))在一定程度上反映了该区上部水体营养盐水平的变化。

By regulating heat and fresh water budgets between the east Indian and west Pacific oceans, Indonesian throughflow（ITF） leads to significant changes in upper ocean structure of these oceans, which has been proven related to E1 Nino and Indian Ocean Dipole（IOD） phenomena,but the mechanism is still poorly understood. In this study,we present high-resolution records of stable oxygen and carbon isotopes from a gravity sediment core SO18480 -3 （12°3.5＇S, 121°39.0＇E ＆ 2299m water depth）, recovered from the main path of the ITF outflow and hence well documents influences of the ITF on easternmost Indian upper ocean structure. Stable isotopes were measured from shells of mixed-layer dwelling species Globigerinoides tuber and thermocline dwelling species Pulleniatina obliquiloculata. △δ^18O（p obliqulioculatea-G ruber）is utilized as an indicator of depth of thermocline（DOT） and △δ^13C（G,rubar-P obliqulioculatea.）reflects nutrient stratification of upper ocean waters. Age scale of Core SO18480 -3 is constrained by 12 AMS 14C dates measured on shells of G. ruber derived from sediments spanning from present to LGM. Our data show that most significant changes are occurred in thermocline other than in sea surface layer： Firstly,thermocline temperatures increased by ca. 4℃ ,larger than an increase of ca. 3.2℃ in sea surface water temperatures during the last glacial-interglacial transition. Secondly, thermocline species δ^18O has more frequent fluctuations than that of surface species,in particular,on millennial timescale. Changes of DOT in the easternmost Indian Ocean is closely caused by the magnitude of the ITF transports that is modulated by asymmetry between the east and west Pacific,as well as changes in topography induced by sea level. The ITF transport reduced due to the relatively low pressure-head between the easternmost Indian and the west Pacific oceans when E1 Nino happened, resulting in significant shoals of thermocline though sea level increased during 19.2 - 11.0kaB. P. In contrast, in the LGM when sea level kept low stand,thermocline was deep,in a similar fashion as it was in Holocene, supporting that there was no obvious changes in transport of the ITF in this period. The local nutrient stratification is controlled by DOT that affects the nutrient efficiency for photosynthesis, and determined by the nutrient content in thermocline. The upwelling system,which is like Java upwelling system （JUS）in oceanography driven by the southeast Australian monsoon,has strongly influenced local nutrient content. Our data show that this upwelling system provided the higher nutrient levels in LGM,and gradually weakened to the end through Holocene. We also find this upwelling seems to have less relation to DOT,because that it was active while DOT kept relatively deep in LGM.