Benthic Foraminifera as indicative of Austral Summer monsoon precipitation and winter monsoon wind-driven upwelling

2020 ◽  
Author(s):  
Patricia Eichler ◽  
Katharina Billups ◽  
Ana Christina Ravelo ◽  
Helenice Vital
Keyword(s):  
Organic Matter ◽  
Summer Monsoon ◽  
Radiative Forcing ◽  
Large Scale ◽  
Austral Summer ◽  
Winter Monsoon ◽  
Intermediate Water ◽  
Monsoon Precipitation ◽  
Australian Monsoon ◽  
Monsoon Wind

<p>During IODP Expedition 363, a hemipelagic sediment succession was retrieved for the first time off NW Australia (Site U1483: 13°5.24ʹS, 121°48.25ʹE, water depth: 1733 m, sedimentation rate: ~10 cm/kyr). This carbonate- and clay-rich sequence provides an ideal archive to monitor intensity and variability of the Australian Monsoon (AM) and to better constrain monsoon sensitivity to changes in radiative forcing. Due to the location at the southern edge of the largest amplitude seasonal swing of the Intertropical Convergence Zone (ITCZ) within the large-scale Asian-Australian monsoon system, the AM subsystem is sensitive to tropical hydroclimate variability. However, this sensitivity to changing climate boundary conditions such as ice volume and greenhouse gas concentrations remain poorly understood across the Calabrian, in the Pleistocene Epoch (add ages?). Here we report on benthic foraminiferal assemblages as a tracer for terrigenous runoff (Austral Summer monsoon precipitation). We find shallow, fresh water-tolerant to transitional environments species Bolivina striatula, Buliminella elegantissima, Dentalina spp., Oolina sp., and paleo productivity indicator Melonis spp (winter monsoon wind-driven upwelling) from 1.34 Ma. through 1.61Ma. Principl component analysis (PCA) indicates that Melonis is present in 4 out of 5 PCA axes. It prefers organic matter in a more altered form, and migrates in the sediment depending on the quality of the organic matter supply and remineralization, which indicates surface upwelling during this time. The genera Stilostomella spp. is present in 3 out of 5 axes, and it is indicative of intermediate water temperature. These records will be compared to C org wt (%), TN wt (%) and a benthic foraminiferal stable isotope record to related faunal patterns to carbon cycling and global climate.</p><p> </p><p> </p>

scholarly journals Remote and local drivers of Pleistocene South Asian summer monsoon precipitation: A test for future predictions

2021 ◽  
Vol 7 (23) ◽  
pp. eabg3848
Author(s):  
Steven C. Clemens ◽  
Masanobu Yamamoto ◽  
Kaustubh Thirumalai ◽  
Liviu Giosan ◽  
Julie N. Richey ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
South Asian ◽  
Summer Monsoon ◽  
Large Scale ◽  
Asian Summer Monsoon ◽  
Precipitation Amount ◽  
Monsoon Precipitation ◽  
Orbital Eccentricity ◽  
South Asian Summer Monsoon ◽  
Asian Summer

South Asian precipitation amount and extreme variability are predicted to increase due to thermodynamic effects of increased 21st-century greenhouse gases, accompanied by an increased supply of moisture from the southern hemisphere Indian Ocean. We reconstructed South Asian summer monsoon precipitation and runoff into the Bay of Bengal to assess the extent to which these factors also operated in the Pleistocene, a time of large-scale natural changes in carbon dioxide and ice volume. South Asian precipitation and runoff are strongly coherent with, and lag, atmospheric carbon dioxide changes at Earth’s orbital eccentricity, obliquity, and precession bands and are closely tied to cross-equatorial wind strength at the precession band. We find that the projected monsoon response to ongoing, rapid high-latitude ice melt and rising carbon dioxide levels is fully consistent with dynamics of the past 0.9 million years.

scholarly journals Asian monsoon projection with a new large-scale monsoon definition

2021 ◽  
Author(s):  
Xingang Dai ◽  
Yang Yang ◽  
Ping Wang
Keyword(s):  
South Asia ◽  
Summer Monsoon ◽  
Moisture Transport ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Season ◽  
Northwest China ◽  
Winter Monsoon ◽  
Climate Simulation ◽  
Northwestern Part

Abstract This paper focuses on Asian monsoon projection with CMIP5 multi-model outputs. A large-scale monsoon herewith is defined as a vector field of vertically integrated moisture flux from the surface to 500 hPa. Results demonstrate that the model ensemble mean underestimated the summer monsoon and overestimated slightly the winter monsoon over South Asia in both CMIP5 historical climate simulation and the monsoon projection for 2006–2015. The major of the bias is the model climate drift (MCD), which is removed in the monsoon projection for 2016–2045 under scenarios RCP4.5 for reducing the uncertainty. The projection shows that two increased moisture flows northward appeared across the Equator of Indian Ocean, the first is nearby Somalia coast toward northwestern part of South Asia, leading to excess rainfall in where the wet jet could reach, and the second starts from the equatorial Sect. (80°E–100°E) toward northeastern Bay of Bengal, leading to more rainfall spreading over the northwestern coast of Indochina Peninsula. In addition, a westward monsoon flow is intensified over the Peninsula leading to local climate moisture transport belt shifted onto South China Sea, which would reduce moisture transport toward Southwest China on one hand, and transport more moisture onto the southeast coast of the China mainland. The anomalous monsoon would result in a dry climate in Northwest China and wet climate in the coast belt during summer monsoon season for the period. Besides, the Asian winter monsoon would be seemingly intensified slightly over South Asia, which would bring a dry winter climate to Indian subcontinent, Northwest China, but would be more rainfall in southeast part of Arabian Peninsula with global climate warming.

scholarly journals Centennial-scale precipitation anomalies in the southern Altiplano (18° S) suggest an extratropical driver for the South American summer monsoon during the late Holocene

2019 ◽  
Vol 15 (5) ◽  
pp. 1845-1859 ◽  
Author(s):  
Ignacio A. Jara ◽  
Antonio Maldonado ◽  
Leticia González ◽  
Armand Hernández ◽  
Alberto Sáez ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Large Scale ◽  
Southern Oscillation ◽  
Atlantic Coast ◽  
Austral Summer ◽  
High Elevation ◽  
South American ◽  
Tropical Andes ◽  
The South ◽  
Precipitation Anomalies

Abstract. Modern precipitation anomalies in the Altiplano, South America, are closely linked to the strength of the South American summer monsoon (SASM), which is influenced by large-scale climate features sourced in the tropics such as the Intertropical Convergence Zone (ITCZ) and El Niño–Southern Oscillation (ENSO). However, the timing, direction, and spatial extent of precipitation changes prior to the instrumental period are still largely unknown, preventing a better understanding of the long-term drivers of the SASM and their effects over the Altiplano. Here we present a detailed pollen reconstruction from a sedimentary sequence covering the period between 4500 and 1000 cal yr BP in Lago Chungará (18∘ S; 4570 m a.s.l.), a high-elevation lake on the southwestern margin of the Altiplano where precipitation is delivered almost exclusively during the mature phase of the SASM over the austral summer. We distinguish three well-defined centennial-scale anomalies, with dry conditions between 4100–3300 and 1600–1000 cal yr BP and a conspicuous humid interval between 2400 and 1600 cal yr BP, which resulted from the weakening and strengthening of the SASM, respectively. Comparisons with other climate reconstructions from the Altiplano, the Atacama Desert, the tropical Andes, and the southwestern Atlantic coast reveal that – unlike modern climatological controls – past precipitation anomalies at Lago Chungará were largely decoupled from north–south shifts in the ITCZ and ENSO. A regionally coherent pattern of centennial-scale SASM variations and a significant latitudinal gradient in precipitation responses suggest the contribution of an extratropical moisture source for the SASM, with significant effects on precipitation variability in the southern Altiplano.

scholarly journals Will a Warmer World Mean a Wetter or Drier Australian Monsoon?

2016 ◽  
Vol 29 (12) ◽  
pp. 4577-4596 ◽  
Author(s):  
Josephine R. Brown ◽  
Aurel F. Moise ◽  
Robert Colman ◽  
Huqiang Zhang
Keyword(s):  
Summer Monsoon ◽  
Climate Models ◽  
Coupled Model ◽  
Equatorial Pacific ◽  
Cold Bias ◽  
Monsoon Precipitation ◽  
Australian Monsoon ◽  
Eastern Equatorial Pacific ◽  
Sst Warming ◽  
The Difference

Abstract Multimodel mean projections of the Australian summer monsoon show little change in precipitation in a future warmer climate, even under the highest emission scenario. However, there is large uncertainty in this projection, with model projections ranging from around a 40% increase to a 40% decrease in summer monsoon precipitation. To understand the source of this model uncertainty, a set of 33 climate models from the Coupled Model Intercomparison Project phase 5 (CMIP5) is divided into groups based on their future precipitation projections (DRY, MID, and WET terciles). The DRY model mean has enhanced sea surface temperature (SST) warming across the equatorial Pacific, with maximum increases in precipitation in the western equatorial Pacific. The DRY model mean also has a large cold bias in present day SSTs in this region. The WET model mean has the largest warming in the central and eastern equatorial Pacific, with precipitation increases over much of Australia. These results suggest lower confidence for projections of reduced monsoon precipitation because of the influence of model SST biases on the SST warming pattern and precipitation response. The precipitation changes for the DRY and WET models are also decomposed into dynamic and thermodynamic components. The component due to spatial shifts in the location of convergence and precipitation is responsible for most of the difference between DRY and WET models. As spatial shifts in precipitation are closely associated with patterns of SST change, reducing uncertainty in model SST warming patterns will be crucial to improved projections of Australian monsoon precipitation.

scholarly journals Asian Monsoon Projection With a New Large-Scale Monsoon Definition

2021 ◽  
Author(s):  
Xingang Dai ◽  
YANG Yang ◽  
WANG Ping
Keyword(s):  
South Asia ◽  
Summer Monsoon ◽  
Moisture Transport ◽  
Large Scale ◽  
Asian Monsoon ◽  
Monsoon Season ◽  
Northwest China ◽  
Winter Monsoon ◽  
Climate Simulation ◽  
Northwestern Part

Abstract This paper focuses on Asian monsoon projection with CMIP5 multi-model outputs. A large-scale monsoon herewith is defined as a vector field of vertically integrated moisture flux from the surface to 500 hPa. Results demonstrate that the model ensemble mean underestimated the summer monsoon and overestimated slightly the winter monsoon over South Asia in both CMIP5 historical climate simulation and the monsoon projection for 2006-2015. The major of the bias is the model climate drift (MCD), which is removed in the monsoon projection for 2016 -2045 under scenarios RCP4.5 for reducing the uncertainty. The projection shows that two increased moisture flows northward appeared across the Equator of Indian Ocean, the first is nearby Somalia coast toward northwestern part of South Asia, leading to excess rainfall in where the wet jet could reach, and the second starts from the equatorial section (80°E-100°E) toward northeastern Bay of Bengal, leading to more rainfall spreading over the northwestern coast of Indochina Peninsula. In addition, a westward monsoon flow is intensified over the Peninsula leading to local climate moisture transport belt shifted onto South China Sea, which would reduce moisture transport toward Southwest China on one hand, and transport more moisture onto the southeast coast of the China mainland. The anomalous monsoon would result in a dry climate in Northwest China and wet climate in the coast belt during summer monsoon season for the period. Besides, the Asian winter monsoon would be seemingly intensified slightly over South Asia, which would bring a dry winter climate to Indian subcontinent, Northwest China, but would be more rainfall in southeast part of Arabian peninsula with global climate warming.

scholarly journals Changes in the in-phase relationship between the Indian and subsequent Australian summer monsoons during the past five decades

2007 ◽  
Vol 25 (9) ◽  
pp. 1929-1933 ◽  
Author(s):  
J.-Y. Yu ◽  
M. A. Janiga
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Phase Relationship ◽  
Austral Summer ◽  
Australian Monsoon ◽  
The Past ◽  
The Pacific ◽  
Australian Summer Monsoon ◽  
Sst Anomalies ◽  
Australian Summer

Abstract. This study examines the decadal changes in the in-phase relationship between Indian summer monsoon and the subsequent Australian summer monsoon using observational data from 1950–2005. The in-phase relationship is the tendency for a strong Indian summer monsoon to be followed by a strong Australian summer monsoon and vice versa. It is found that the in-phase relationship was weak during the late 1950s and early 1960s, strengthened to a maximum in the early 1970s just before the 1976/77 Pacific climate shift, then declined until the late 1990s. Pacific SST anomalies are noticed to have strong persistence from boreal to austral summer, providing the memory to connect the Indian and subsequent Australian summer monsoon. The simultaneous correlation between the Pacific SST anomalies and the Indian summer monsoon is always strong. It is the weakening and strengthening of the simultaneous correlation between the Australian summer monsoon and the Pacific SST anomalies that contributes to the decadal variations of the in-phase monsoon relation. This study suggests that the interaction between the Australian monsoon and the Pacific Ocean is crucial to tropical climate variability and has experienced significant changes over the past five decades.

VARIABILITY IN THE INDIAN SUMMER MONSOON PRECIPITATION AND LAKE LEVELS IN EASTERN TIBET

2016 ◽  
Author(s):  
Melanie Perello ◽  
◽  
Broxton W. Bird ◽  
Yanbin Lei ◽  
Pratigya J. Polissar ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Indian Summer Monsoon ◽  
Monsoon Precipitation ◽  
Lake Levels ◽  
Eastern Tibet

scholarly journals Subseasonal Forecasts of the Northern Queensland Floods of February 2019: Causes and Forecast Evaluation

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 758
Author(s):  
Wayne Yuan-Huai Tsai ◽  
Mong-Ming Lu ◽  
Chung-Hsiung Sui ◽  
Yin-Min Cho
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Austral Summer ◽  
Rainfall Event ◽  
Monsoon Depression ◽  
Forecast Skill ◽  
Sea Surface ◽  
Central Pacific ◽  
Percentile Rank ◽  
Extended Range

During the austral summer 2018/19, devastating floods occurred over northeast Australia that killed approximately 625,000 head of cattle and inundated over 3000 homes in Townsville. In this paper, the disastrous event was identified as a record-breaking subseasonal peak rainfall event (SPRE). The SPRE was mainly induced by an anomalously strong monsoon depression that was modulated by the convective phases of an MJO and an equatorial Rossby (ER) wave. The ER wave originated from an active equatorial deep convection associated with the El Niño warm sea surface temperatures near the dateline over the central Pacific. Based on the S2S Project Database, we analyzed the extended-range forecast skill of the SPRE from two different perspectives, the monsoon depression represented by an 850-hPa wind shear index and the 15-day accumulated precipitation characterized by the percentile rank (PR) and the ratio to the three-month seasonal (DJF) totals. The results of four S2S models of this study suggest that the monsoon depression can maintain the same level of skill as the short-range (3 days) forecast up to 8–10 days. For precipitation parameters, the conclusions are similar to the monsoon depression. For the 2019 northern Queensland SPRE, the model forecast was, in general, worse than the expectation derived from the hindcast analysis. The clear modulation of the ER wave that enhanced the SPRE monsoon depression circulation and precipitation is suspected as the main cause for the lower forecast skill. The analysis procedure proposed in this study can be applied to analyze the SPREs and their associated large-scale drivers in other regions.

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