scholarly journals Glacial changes in tropical climate amplified by the Indian Ocean

2018 ◽  
Vol 4 (12) ◽  
pp. eaat9658 ◽  
Author(s):  
Pedro N. DiNezio ◽  
Jessica E. Tierney ◽  
Bette L. Otto-Bliesner ◽  
Axel Timmermann ◽  
Tripti Bhattacharya ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Climate Changes ◽  
Equatorial Indian Ocean ◽  
Walker Circulation ◽  
Warm Pool ◽  
Pacific Warm Pool ◽  
The Indian Ocean ◽  
The Tropics ◽  
The Last Glacial Maximum ◽  
The Last Glacial

The mechanisms driving glacial-interglacial changes in the climate of the Indo-Pacific warm pool are poorly understood. Here, we address this question by combining paleoclimate proxies with model simulations of the Last Glacial Maximum climate. We find evidence of two mechanisms explaining key patterns of ocean cooling and rainfall change interpreted from proxy data. Exposure of the Sahul shelf excites a positive ocean-atmosphere feedback involving a stronger surface temperature gradient along the equatorial Indian Ocean and a weaker Walker circulation—a response explaining the drier/wetter dipole across the basin. Northern Hemisphere cooling by ice sheet albedo drives a monsoonal retreat across Africa and the Arabian Peninsula—a response that triggers a weakening of the Indian monsoon via cooling of the Arabian Sea and associated reductions in moisture supply. These results demonstrate the importance of air-sea interactions in the Indian Ocean, amplifying externally forced climate changes over a large part of the tropics.

Variations of the Indian Ocean Walker circulation since the Last Glacial Maximum revealed by reconstructed and simulated zonal wind intensity

2021 ◽  
Author(s):  
Xinquan Zhou ◽  
Stéphanie Duchamp-Alphonse ◽  
Masa Kageyama ◽  
Franck Bassinot ◽  
Xiaoxu Shi ◽  
...  
Keyword(s):  
Indian Ocean ◽  
Surface Temperature ◽  
Equatorial Indian Ocean ◽  
Walker Circulation ◽  
Sea Surface ◽  
The Indian Ocean ◽  
Sst Anomaly ◽  
Mean Circulation ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Today, precipitation and wind patterns over the equatorial Indian Ocean and surrounding lands are paced by monsoon and Walker circulations that are controlled by the seasonal land-sea temperature contrast and the inter-annual convection over the Indo-Pacific Warm Pool, respectively. The annual mean surface westerly winds are particularly tied to the Walker circulation, showing interannual variability coupled with the gradient of Sea Surface Temperature (SST) anomaly between the tropical western and southeastern Indian Ocean, namely, the Indian Ocean Dipole (IOD). While the Indian monsoon pattern has been widely studied in the past, few works deal with the evolution of Walker circulation despite its crucial impacts on modern and future tropical climate systems. Here, we reconstruct the long-term westerly (summer) and easterly (winter) wind dynamics of the equatorial Indian Ocean (10°S−10°N), since the Last Glacial Maximum (LGM) based on i) primary productivity (PP) records derived from coccolith analyses of sedimentary cores MD77-191 and BAR94-24, retrieved off the southern tip of India and off the northwestern tip of Sumatra, respectively and ii) the calculation of a sea surface temperature (SST) anomaly gradient off (south) western Sumatra based on published SST data. We compare these reconstructions with atmospheric circulation simulations obtained with the general coupled model AWI-ESM-1-1-LR (Alfred Wegener Institute Earth System Model).</p><p>Our results show that the Indian Ocean Walker circulation was weaker during the LGM and the early/middle Holocene than present. Model simulations suggest that this is due to anomalous easterlies over the eastern Indian Ocean. The LGM mean circulation state may have been comparable to the year 1997 with a positive IOD, when anomalously strong equatorial easterlies prevailed in winter. The early/mid Holocene mean circulation state may have been equivalent to the year 2006 with a positive IOD, when anomalously strong southeasterlies prevailed over Java-Sumatra in summer. The deglaciation can be seen as a transient period between these two positive IOD-like mean states.</p>

Sea-Surface Temperature Estimates for the Tropical Western Pacific during the Last Glaciation and Their Implications for the Pacific Warm Pool

1994 ◽  
Vol 41 (3) ◽  
pp. 255-264 ◽  
Author(s):  
Robert Thunell ◽  
David Anderson ◽  
Debrorah Gellar ◽  
Qingmin Miao
Keyword(s):  
Last Glacial Maximum ◽  
Warm Pool ◽  
Glacial Maximum ◽  
Western Pacific ◽  
Last Glacial ◽  
Pacific Warm Pool ◽  
The Tropics ◽  
The Last Glacial Maximum ◽  
The Western Pacific ◽  
The Last Glacial

AbstractTwenty deep-sea sediment cores from the western Pacific between 30°N and 30°S provide evidence of sea-surface temperature (SST) changes throughout the tropics and subtropics. Glacial SSTs were estimated using the modern analog technique (MAT) applied to planktonic foraminifers and planktonic foraminiferal δ18O changes. We used δ18O to identify the last glacial maximum. The MAT method differs from the traditional transfer function approach in that it utilizes a global coretop database, and estimates paleotemperature by finding analogs from the modern coretop samples. In addition, the MAT approach appears to be less susceptible than the transfer function technique to biases introduced by carbonate dissolution. Our results indicate that tropical SSTs differed by less than 2°C from present; away from the tropics (30°N and 30°S) SSTs were at least 3°C cooler. Our results differ from those of previous studies in the western Pacific by using a set of well-preserved, high-sedimentation rate cores from shallow regions. The results of this study clearly indicate that a western Pacific warm pool existed during the last glacial maximum (LGM), providing a heat and moisture source for a Walker Circulation cell similar to that of today. We propose that a steeper lapse rate existed during the last glacial maximum and that this can explain at least part of the discrepancy between marine and terrestrial temperature estimates adjacent to New Guinea for the LGM.

Indian Ocean Variability in the GFDL Coupled Climate Model

2007 ◽  
Vol 20 (13) ◽  
pp. 2895-2916 ◽  
Author(s):  
Qian Song ◽  
Gabriel A. Vecchi ◽  
Anthony J. Rosati
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Deep Convection ◽  
Warm Pool ◽  
Surface Winds ◽  
Pacific Warm Pool ◽  
El Niño Events ◽  
The Indian Ocean ◽  
El Nino Events

Abstract The interannual variability of the Indian Ocean, with particular focus on the Indian Ocean dipole/zonal mode (IODZM), is investigated in a 250-yr simulation of the GFDL coupled global general circulation model (CGCM). The CGCM successfully reproduces many fundamental characteristics of the climate system of the Indian Ocean. The character of the IODZM is explored, as are relationships between positive IODZM and El Niño events, through a composite analysis. The IODZM events in the CGCM grow through feedbacks between heat-content anomalies and SST-related atmospheric anomalies, particularly in the eastern tropical Indian Ocean. The composite IODZM events that co-occur with El Niño have stronger anomalies and a sharper east–west SSTA contrast than those that occur without El Niño. IODZM events, whether or not they occur with El Niño, are preceded by distinctive Indo-Pacific warm pool anomaly patterns in boreal spring: in the central Indian Ocean easterly surface winds, and in the western equatorial Pacific an eastward shift of deep convection, westerly surface winds, and warm sea surface temperature. However, delayed onsets of the anomaly patterns (e.g., boreal summer) are often not followed by IODZM events. The same anomaly patterns often precede El Niño, suggesting that the warm pool conditions favorable for both IODZM and El Niño are similar. Given that IODZM events can occur without El Niño, it is proposed that the observed IODZM–El Niño relation arises because the IODZM and El Niño are both large-scale phenomena in which variations of the Indo-Pacific warm pool deep convection plays a central role. Yet each phenomenon has its own dynamics and life cycle, allowing each to develop without the other. The CGCM integration also shows substantial decadal modulation of the occurrence of IODZM events, which is found to be not in phase with that of El Niño events. There is a weak, though significant, negative correlation between the two. Moreover, the statistical relationship between the IODZM and El Niño displays strong decadal variability.

Indo-Pacific warm pool expansion modulates MJO lifecycle

2020 ◽  
Author(s):  
Panini Dasgupta ◽  
Roxy Mathew Koll ◽  
Michael J. McPhaden ◽  
Tamaki Suematsu ◽  
Chidong Zhang ◽  
...  
Keyword(s):  
Life Cycle ◽  
Indian Ocean ◽  
Southern Oscillation ◽  
Average Rate ◽  
Warm Pool ◽  
Dominant Mode ◽  
Maritime Continent ◽  
Pacific Warm Pool ◽  
The Indian Ocean ◽  
The Impact

<p>The Madden–Julian Oscillation (MJO) is the most dominant mode of intraseasonal<br>variability in the tropics, characterized by an eastward propagating zonal circulation pattern<br>and rain bands. MJO is very crucial phenomenon due to its interactions with other<br>timescales of ocean-atmosphere like El Niño Southern Oscillation, tropical cyclones,<br>monsoons, and the extreme rainfall events all across the globe. MJO events travel almost<br>half of the globe along the tropical oceans, majorly over the Indo-Pacific Warm Pool<br>(IPWP) region. This IPWP region has been warming during the twentieth and early twenty-<br>first centuries in response to increased anthropogenic emissions of greenhouse gases and<br>is projected to warm further. However, the impact of the warming of the IPWP region on<br>the MJO life cycle is largely unknown. Here we show that rapid warming over the IPWP<br>region during 1981–2018 has significantly changed the MJO life cycle, with its residence<br>time decreasing over the Indian Ocean by 3–4 days, and increasing over the Indo-Pacific<br>Maritime Continent by 5–6 days. We find that these changes in the MJO life cycle are<br>associated with a twofold expansion of the Indo-Pacific warm pool. The warm pool has<br>been expanding on average by 2.3 × 105 km2 per year during 1900–2018 and at an<br>accelerated average rate of 4 × 105 km2 per year during 1981–2018. The accelerated<br>warm pool expansion has increased moisture in the lower and middle troposphere over<br>IPWP and thereby increased the gradient of lower-middle tropospheric moisture between<br>the Indian Ocean and western Pacific. This zonal gradient of moisture between the Indian Ocean<br>and west Pacific and the increased subsidence over the Indian ocean due to increased<br>convective duration of MJO over maritime continent are likely the reasons behind the<br>changing lifecycle of MJO.</p>

Past and future changes in tropical climate amplified by the Indian Ocean

2020 ◽  
Author(s):  
Pedro DiNezio
Keyword(s):  
Indian Ocean ◽  
Ocean Climate ◽  
Climate Reconstructions ◽  
External Forcings ◽  
Highly Sensitive ◽  
Recent Climate ◽  
Amplifying Effect ◽  
The Indian Ocean ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Presently, the Indian Ocean exhibits a unique climate state with subtle east-west contrasts and weak year-to-year variability. Whether these features could change in response to external forcings remains highly debated, an issue that is critical to predict future climate changes in highly populated neighboring countries. We explored this question combining climate reconstructions and numerical simulations and of the Last Glacial Maximum – the interval ca. 21,000 years ago when the Earth experienced the largest, most recent climate change. We found that the Indian Ocean exhibited radically altered rainfall patterns and oceanographic conditions across the basin, changes that according to our simulations, can only be explained by the amplifying effect of coupled ocean-atmosphere feedbacks. We also find that these changes favored the emergence of an El Niño mode driving significantly stronger climate variability. Despite different triggers in the past and the future, our results show that Indian Ocean climate could also be highly sensitive to future greenhouse forcing.</p>

Millennial-scale trends in west Pacific warm pool hydrology since the Last Glacial Maximum

Nature ◽  
2007 ◽  
Vol 449 (7161) ◽  
pp. 452-455 ◽  
Author(s):  
Judson W. Partin ◽  
Kim M. Cobb ◽  
Jess F. Adkins ◽  
Brian Clark ◽  
Diego P. Fernandez
Keyword(s):  
Last Glacial Maximum ◽  
Warm Pool ◽  
Glacial Maximum ◽  
West Pacific ◽  
Last Glacial ◽  
Pacific Warm Pool ◽  
The Last Glacial Maximum ◽  
The Last Glacial ◽  
Millennial Scale
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