Surface and deep water variations in the northeast Indian Ocean during 34–6 ka BP: Evidence from carbon and oxygen isotopes of fossil foraminifera
Surface and deep water variations in the northeast Indian Ocean during 34–6 ka BP: Evidence from carbon and oxygen isotopes of fossil foraminifera
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DOI：
10.1016/j.quaint.2012.05.005
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发表时间：
2013-06
影响因子：
2.2
通讯作者：
T. Raza;S. M. Ahmad
中科院分区：
文献类型：
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作者：
T. Raza;S. M. Ahmad
红球孢有孔虫和底栖有孔虫的δ 13 C和δ 18 O记录从孟加拉湾中部采集的深海沉积物岩心（SK 157 -18）中获得。该重力岩心（11°59′N; 90°01′E;水深3069 m;岩心长度230 cm）的年代学是用6个放射性碳年龄建立的。在34-6 ka BP期间，孟加拉湾的表层和深层水的碳和氧同位素的大的变化是暗示的显着变化。SK 157 -18岩芯浮游生物δ 18 O值明显高于孟加拉湾西部和安达曼海岩芯。8-7 kaBP时，孟加拉湾中部表层水δ 18 O显著降低，可能与印度西南季风（ISM）的加强有关。红革藻δ 13 C在34-26和14-7 kaBP期间呈上升趋势，在26 - 15 kaBP期间呈下降趋势。然而，南极有孔虫δ 13 C的变化与冰期-间冰期的变化并不一致，可能是由风引起的地表水δ 13 C的变化引起的。底栖有孔虫的δ 18 O和δ 13 C值在全新世和冰期有较大的变化。底栖有孔虫δ 18 O从末次盛冰期（LGM）到全新世的变化（1.5‰）超过了冰体积效应的0.05 ‰，表明在盐度没有变化的情况下，冰川深层水冷却了0.02 °C。这种冰川深水冷却可能是由于较冷的南大洋深水（SODW）的引入造成的。底栖δ 13 C的大幅度波动是由于全新世和末次冰期期间源水特征的变化。冰川底栖有孔虫的δ 13 C显著降低，表明北大西洋深水（NADW）的贡献减少，SODW的流入增加。此外，在末次盛冰期期间，由于深层水团的通风减少而导致的有机物氧化可能导致δ 13 C的显著降低。
δ13C and δ18O records from planktic (Globigerinoides ruber) and benthic foraminifera (Cibicides spp.) were obtained from a deep sea sediment core (SK157–18) collected in the central Bay of Bengal. The chronology of this gravity core (11°59′N; 90°01′E; water-depth 3069 m; core-length 230 cm) has been established using six radiocarbon ages. Large variations in carbon and oxygen isotopes are suggestive of significant changes in surface and deep water of the Bay of Bengal during 34–6 ka BP. Planktic δ18O values in core SK157–18 are significantly higher compared to cores in the western Bay of Bengal and the Andaman Sea. A marked δ18O decrease at 8–7 ka BP is suggestive of low-salinity surface water in the central Bay of Bengal, probably due to the intensification of the Indian southwest monsoon (ISM). An increasing δ13C trend in G. ruber is seen during ∼34–26 and 14–7 ka BP and decreasing δ13C trend between 26 and 15 ka BP intervals. However these δ13C shifts in planktic foraminifera are not coherent with the glacial–interglacial change and may have been caused by wind-induced variability in surface water δ13C. The δ18O and δ13C values in benthic foraminifera show considerable variations during the Holocene and glacial times. Last Glacial Maximum (LGM) to Holocene δ18O shift in benthic foraminifera (1.5‰) exceeds ice volume effect by ∼0.5‰, suggesting glacial deep water cooling of ∼2 °C, assuming no salinity change. This glacial deep water cooling may have been caused by the introduction of cooler Southern Ocean Deep Water (SODW). Large fluctuations in benthic δ13C are due to the changes in source water characteristics during the Holocene and last glaciation. Glacial benthic foraminifera exhibit pronounced decrease in δ13C suggesting reduced contribution from the North Atlantic Deep Water (NADW) and increased influx of SODW. In addition, oxidation of organic matter due to the reduced ventilation of deep water masses during the LGM may have contributed in the significant decrease in δ13C.