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

364: Chicxulub: Drilling the K-Pg Impact Crater

The location of the Chicxulub Crater, where the meteor struck 66 million years ago, that led to the K-Pg mass extinction. The red circle in the top panel denotes the diameter of the crater on the Yucatan Peninsula and into the Gulf of Mexico. The bottom image indicates the trough created by the impactor, with locations of sinkholes surrounding the impact structure. NASA/JPL-Caltech, modified b – Modified NASA image, with scale and labels to increase clarity by David Fuchs. Original: http://photojournal.jpl.nasa.gov/catalog/PIA03379

The Chicxulub impact crater, located on the Yucatán Peninsula of México, is best known for being the location of a massive meteor impact causing the Cretaceous/Paleocene (K-Pg) mass extinction event. This is a major mass extinction that led to the extinction of 75% of species on Earth (Gulick et al., 2017). The site has been the subject of debate for many years surrounding the extent of the impact and the environmental fallout of the area since. 

Such debates led to a need for further studies and additional information. The main goal of the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Leg 364 was to drill sediments within the impact site to study the peak rings that formed during impact, and how the meteor impact affected the surrounding area. Other expedition objectives included the nature and extent of post-impact hydrothermal circulation, the recovery of life in a sterile zone, and recovery of sediments through the Paleocene/Eocene Thermal Maximum (PETM; Gulick et al., 2017), an event that took place approximately 55 million years ago and was characterized by the Earth heating up by 5–8°C. 

In 2016 the Vessel L/B Myrtle began its voyage for the Yucatán continental shelf.  A single borehole (Hole M0077A) was drilled into the Chicxulub impact crater and 828.99 meters of cored sediments and rock was recovered from below the seafloor. The recovered sediments and rocks allowed scientists to achieve many of the scientific goals that were established for this expedition. 

Figure 2. Image of different impact structures showing the crater rims, peak rings, basins, and troughs. These images are from Venus (upper left and right) and the Moon (bottom). Photo credit: NASA

One of the main goals of the expedition, to core sediments from the peak ring, was successful. Peak rings were formed during the large impact on the Earth’s surface causing the underlying rocks to fracture and overturn onto the impact site. The recovered rocks and sediments allowed scientists to determine that the peak ring is formed from uplifted, shocked, and fractured granitic rocks that overlie older sedimentary rocks. This supported the hypothesis made by Morgan et al. (2016), stating that the dynamic collapse model for peak-ring formation is accurate, and also supported the hypothesis that the rocks are highly porous and fractured from the impact (Gulick et al., 2013). Shipboard studies of microfossils recovered from the sediments indicated that the PETM interval is present in the core sediments, which will allow for the sediments to be studied in greater detail. 

Another objective of the expedition was to understand the hydrothermal system surrounding impacts on Earth. Many scientists hypothesize that microbial life starts on Earth at impact sites. Scientists wanted to study this area for signs of early microbial life. Directly after impact Chicxulub was considered to be a sterile zone, as the impact was so sudden, the area around the impact became super heated and all life in the region was instantly wiped out. Scientists have recently found evidence that cyanobacteria may have bloomed a few months after impact (Schaefer et al., 2020). Small trace fossils and other forms of microbes are believed to have come back within a year after the impact. 

In conclusion, this drilling expedition is considered to be a great success. Many of the predetermined objectives for the expedition were completed, and lots of other promising data was collected for future studies. Drilling into the impact point of the meteor that caused the Cretaceous/Paleocene (K-Pg) mass extinction was a monumental finding for scientists all over the world. This expedition gave scientists evidence for the formation of peak rings, and allowed for the unique study of how life recovers from such an event.

Figure 3. A frame from a simulation of what the Earth’s mantle to upper crust to atmosphere may have looked like at 35 seconds after impact. Dark blue represents the Earth’s mantle; green represents the basement rocks; gray indicates the seafloor sediments and projectiles; light blue represents the atmosphere. The right side of the image is distance, in kilometers, and the bottom axis is distance, in kilometers. Image modified from Artemieva and Morgan (2009). This model indicates that ejecta (sediments from the seafloor) were flung over 200 km (124 miles) into Earth’s atmosphere! In fact, the impact hit Earth so hard, there was very likely dust and sediments shot out into space. The impactor hit Earth so hard, it nearly instantaneously created a 20 mile deep hole in the Earth!



Artemieva, N., and Morgan, J., 2009. Modeling the formation of the K–Pg boundary layer. Icarus, 201(2):768–780. https://doi.org/10.1016/j.icarus.2009.01.021

Collins, G.S., Melosh, H.J., Morgan, J.V., and Warner, M.R., 2002. Hydrocode simulations of Chicxulub crater collapse and peak-ring formation. Icarus, 157(1):24–33. https://doi.org/10.1006/icar.2002.6822

Gulick, S. P., Morgan, J. V., Mellett, C. L., Green, S. L., & Kring, D. A. (2017). Expedition 364 summary. International Ocean Discovery Program.

Gulick, S. P. S., Christeson, G. L., Barton, P. J., Grieve, R. A. F., Morgan, J. V., & Urrutia‐Fucugauchi, J. (2013). Geophysical characterization of the Chicxulub impact crater. Reviews of Geophysics, 51(1), 31-52.

Ivanov, B.A., 2005. Numerical modeling of the largest terrestrial meteorite craters. Solar System Research, 39(5):381–409. https://doi.org/10.1007/s11208-005-0051-0

Kring, D.A., Hörz, F., Zurcher, L., and Urrutia Fucugauchi, J., 2004. Impact lithologies and their emplacement in the Chicxulub impact crater: initial results from the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico. Meteoritics & Planetary Science, 39(6):879–897. https://doi.org/10.1111/j.1945-5100.2004.tb00936.x

Morgan, J. V., Gulick, S. P., Bralower, T., Chenot, E., Christeson, G., Claeys, P., … & Zylberman, W. (2016). The formation of peak rings in large impact craters. Science, 354(6314), 878-882.

Senft, L.E., and Stewart, S.T., 2009. Dynamic fault weakening and the formation of large impact craters. Earth and Planetary Science Letters, 287(3– 4):471–482. https://doi.org/10.1016/j.epsl.2009.08.033