353: Indian Monsoon Rainfall

Location map of the six sites drilled during IODP Expedition 353. This map is colored according to topography, with negative numbers and cooler colors indicating depths below sea level. Image from IODP Expedition 353 Summary.

International Ocean Discovery Program (IODP) Expedition 353 was intended to further the understanding of Indian Monsoon circulation changes. Expedition 353 drilled six sites into key regions around the Bay of Bengal, located off the east coast of India. As low atmospheric pressure over the Indo-Asian continent, and high atmospheric pressure over the southern subtropical Indian Ocean changes, this can lead to different weather patterns that affect precipitation over South Asia, the Bay of Bengal, and southeast China. The drillship R/V JOIDES Resolution had previously undergone many drilling voyages to this region to acquire sediments from areas of monsoon impact, however Expedition 353 was the first expedition to drill sediments from the key region of  the northern Bay of Bengal. 

The eastern margin of India was a result of the separation of India and the Australia/Antarctica portion of the ancient supercontinent Gondwanaland during the Early Cretaceous at ~130 million years ago (Powell et al., 1988; Scotese et al., 1988). Six key drill sites were identified to target that would allow scientists to reconstruct changes in Indian monsoon circulation since the Miocene (~23 million years ago) to the present. During the 33 days of operation at sea, over 4,280 meters of sediment cores were recovered from the six sites. 

Images of sediment cores drilled during Expedition 353. A and B are both from Site U1443. The tephra layers, which appear as darker sediments, are from explosive volcanic activity on the island of Sumatra. Image from IODP Expedition 353 Summary.

Some of the main objectives of this expedition were to establish the sensitivity of changes in monsoon circulation relative to the Sun’s location and angle, heat transfer from the Southern Hemisphere, global ice volume, and greenhouse gas effects. Other objectives included determining how long Indian and East Asian monsoon winds and precipitation affected areas based on the geologic history of the area, understanding the effects of climate change and tectonics on erosion and runoff, and to provide targets for paleoclimate models. 

On the northeast Indian margin, Sites U1445 and U1446 records water and salt ratios from precipitation and runoff originating from the Ganges-Brahmaputra river complex and many river basins of peninsular India (Cawthern et al., 2014; Flores et al., 2014). Site U1443 recorded salinity and temperature near the global mean. Sites U1447 and U1448 are located within the Andaman Sea, and as such these sites reveal the precipitation and runoff history from the Irrawaddy and Salween river basins. Future studies of these sediments and oceanic properties can lead to a greater understanding of how this area is affected by the Indian summer monsoon season. 

In conclusion, IODP Expedition 353 helped develop an understanding of the Indian monsoon circulation changes through time. It is important to understand how these monsoonal changes have affected the area through paleo reconstructions of geologic history. This study of the subtropical Indian Ocean helped scientists understand how precipitation changes over South Asia, the Bay of Bengal, and southeast China will change in the future. Understanding what these areas have experienced throughout time during warming and cooling periods can lead us to predictions as to how the area will be affected during increased warming scenarios in the future.


Cawthern, T., Johnson, J.E., Giosan, L., Flores, J.A., Rose, K., and Solomon, E., 2014. A late Miocene–early Pliocene biogenic silica crash in the Andaman Sea and Bay of Bengal. Marine and Petroleum Geology, 58(Part A):490– 501. http://dx.doi.org/10.1016/j.marpetgeo.2014.07.026

Monthly mean salinity for the time period 1955-2006, in which salinity for each month of those years was averaged and plotted (Antonov et al., 2016). Notice how the surface ocean salinity changes seasonally due to the monsoonal rains bringing freshwaters to the ocean. Image from IODP Expedition 353 Summary.

Clemens, S.C., Kuhnt, W., and LeVay, L.J., 2014. iMonsoon: Indian monsoon rainfall in the core convective region. International Ocean Discovery Program Scientific Prospectus, 353. http://dx.doi.org/10.14379/iodp.sp.353.2014

Flores, J.A., Johnson, J.E., Mejía-Molina, A.E., Álverez, M.C., Sierro, F.J., Singh, S.D., Mahanti, S., and Giosan, L., 2014. Sedimentation rates from calcareous nannofossil and planktonic foraminifera biostratigraphy in the Andaman Sea, northern Bay of Bengal, and eastern Arabian Sea. Marine and Petroleum Geology, 58(Part A):425–437. http://dx.doi.org/10.1016/j.marpetgeo.2014.08.011

Johnson, J.E., Phillips, S.C., Torres, M.E., Piñero, E., Rose, K.K., and Giosan, L., 2014. Influence of total organic carbon deposition on the inventory of gas hydrate in the Indian continental margins. Marine and Petroleum Geology, 58(Part A):406–424. http://dx.doi.org/10.1016/j.marpetgeo.2014.08.021

Ponton, C., Giosan, L., Eglinton, T.I., Fuller, D.Q., Johnson, J.E., Kumar, P., and Collett, T.S., 2012. Holocene aridification of India. Geophysical Research Letters, 39(3):L3407. http://dx.doi.org/10.1029/2011GL050722

Powell, C.McA., Roots, S.R., and Veevers, J.J., 1988. Pre-breakup continental extension in East Gondwanaland and the early opening of the eastern Indian Ocean. Tectonophysics, 155(1–4):261–283. http://dx.doi.org/10.1016/0040-1951(88)90269-7

Scotese, C.R., Gahagan, L.M., and Larson, R.L., 1988. Plate tectonic reconstructions of the Cretaceous and Cenozoic ocean basins. Tectonophysics, 155(1–4):27–48. http://dx.doi.org/10.1016/0040-1951(88)90259-4

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