Zhimin Jian Prof. Zhimin Jian State Key Laboratory of Marine Geology Tongji University China If you would like to interview this scientist, please contact Leah Christen. > biographical information > abstract > paper

Biographical Information:

Zhimin Jian is professor of the School of Ocean and Earth Science at Tongji University. He received his PhD at the Department of Marine Geology and Geophysics, Tongji University in 1993. From 1999-2001, he was an Alexander von Humboldt scholar at Kiel University in Germany. Prof. Jian is mainly engaged in teaching and research work in paleoceanography, paleoclimatology and marine micropaleontology. In recent years, he has been responsible for many research projects, including a key project from the National Natural Science Foundation of China. He has published over 90 papers in academic journals and has participated in several international marine geology cruises, including the Ocean Drilling Program Leg 184 to the South China Sea in 1999.

Abstract:

Millennial-centennial scale climate variability of the low latitude Western Pacific during the Late Quaternary

Zhimin Jian, Xinrong Cheng, Laibin Jiang, David Lea, Wolfgang Kuhnt

Present-day climate is affected significantly by the Western Pacific Warm Pool (WPWP), bounded approximately by the 28ºC surface isotherm, through El Niño-Southern Oscillation (ENSO) phenomena. Here, we present a high-resolution record of sea surface temperature (SST) and depth of thermocline (DOT) in the WPWP at centennial time scale for the last 240 kyr, reconstructed from two sediment cores based on planktonic foraminiferal fauna and their stable isotopes, as well as detailed AMS 14C datings. It has been found that the SST and DOT changed significantly with the amplitudes of ~3-4ºC and ~60-80 m respectively, indicating the climatic instability of the WPWP during the late Quaternary. However, the changes of subsurface water were larger than those of surface water, and these changes mainly took place in the Pacific rather than the Indian side. There was intensified DOT contrast between the equatorial Western Pacific and Eastern Indian during the Holocene rather than during the glacial stage, which hence resulted in weaker Indonesian Throughflow and stronger El Niño during glacials. It is interesting that the difference (Δδ18O) between the oxygen isotope of thermocline-dwelling species Pulleniatina obliquiloculata and mixed-layer-dwelling species Globigerinoides ruber, as a proxy of the DOT change, clearly displays dominant semi-processional cycles and millennial/centennial-scale fluctuations, which center at periodicities of ~1.17 kyr and ~1200 yr, ~700-900 yr, ~500 yr, and ~200 yr, and exist throughout the glacial, deglacial and postglacial stages, even though such short-term climate variability is dominated by centennial-scale cycles in non-glacial sections, instead of millennial-scale cycles in their glacial cousins. Particularly, the timing of the tropical Pacific Mg/Ca-based SST change is similar to the timing of the atmospheric CO2 change, and a little bit ahead of the δ18O change during the last deglaciation. This study further suggests that the WPWP plays an important role in global climate changes on millennial/centennial and orbital timescales through ENSO-like systems.

Xinrong Cheng, Tongji University, China
Laibin Jiang, Tongji University, China
David Lea, University of California, USA
Wolfgang Kuhnt, University of Kiel, Germany

Paper:

Millennial-centennial-scale Climate Variability of the Low Latitude Western Pacific during the Late Quaternary

Present-day climate is affected significantly by the Western Pacific Warm Pool (WPWP), bounded approx. by the 28ºC surface isotherm. However, recent studies suggest that the WPWP also plays an important role in global climate changes on millennial and orbital timescales through a system similar to the way in which the El Niño-Southern Oscillation (ENSO) regulates the poleward flux of heat and water vapor. Here, we present high-resolution records of sea surface temperature (SST) and depth of thermocline (DOT) in the WPWP on a centennial timescale for the last 240 kyr, reconstructed from two sediment cores of the equatorial western Pacific Ocean (MD01-2386: 01º07.80’N, 129º47.56’E; 2,816 m water depth) and easternmost Indian Ocean (MD01-2378: 13º04.95’S, 121º47.27’E; 1,783 m water depth), based on planktonic foraminiferal fauna and their stable isotopes, as well as detailed AMS ¹⁴C datings.

It has been found that the SST and DOT changed significantly with amplitudes of ~5-6ºC and ~70-90 m, respectively during the late Quaternary, indicating the climatic instability of the WPWP. But the changes in δ¹⁸O and fauna-derived temperature of subsurface water were obviously lager than those of surface water. The DOT greatly deepened in the Pacific side during the Holocene, while it changed little in the Indian side since the last glacial maximum. This resulted in a greater DOT contrast between the equatorial western Pacific and eastern Indian Oceans during the Holocene than during the glacial stage. This means that the Indonesian Throughflow was probably stronger during the Holocene than the glacial stage, while ENSO was weaker. It is interesting that the difference (Δδ¹⁸O) between the oxygen isotope of thermocline-dwelling species Pulleniatina obliquiloculata and mixed-layer-dwelling species Globigerinoides ruber, as a proxy of the DOT change, clearly displays dominant semi-processional cycle and typical millennial/centennial-scale fluctuations (Fig. 1) centered at periodicities of approx. 1,170, 1,200, 700-900, 500, and 200 years throughout the glacial, deglacial and postglacial stages, even though such short-term climate variability is dominated by centennial-scale cycles in non-glacial sections, instead of millennial-scale cycles in their glacial cousins. The centennial-scale cycles (e.g., ~200 yr,) of the Holocene are ascribed to solar activity change.

The amplitude of millennial-scale δ¹⁸O changes in the WPWP was muted compared to that in the Greenland ice cores but similar to those in the Antarctic ice cores. The DOT changes in the WPWP apparently correlated to the atmospheric CO₂ and temperature changes in the Antarctic, implying their possible inherent links in climate change. Particularly, the timing of tropical Pacific Mg/Ca-based SST change is similar to that of the atmospheric CO₂ change, and a little ahead of δ¹⁸O change during the last deglaciation. This further supports the tropical greenhouse forcing hypothesis (Lea, 2004) that the tropical SST changes on glacial-interglacial timescales is mainly driven by the changing greenhouse gas (principally CO₂) content of the atmosphere.

Figure 1. δ¹⁸O records of two planktonic foraminiferal species (mixed-layer-dwelling Globigerinoides ruber and thermocline-dwelling Pulleniatina obliquiloculata) in core MD01-2386, with a sampling resolution of ~38-434 years over the last 240 kyr. Numbers with vertical arrows are calendar ages.

Figure 2. The δ¹⁸O difference (Δδ¹⁸Oobl-rub) between the two species, a proxy for the changes in the depth of thermocline (DOT) and its bandpass filter (red curve) at the semi-processional band (1.17 kyr) in core MD01-2386. The DOT change of the low latitude western Pacific displays a dominant semi-processional cycle and clear millennial/centennial-scale fluctuations throughout the glacial, deglacial and postglacial stages.