Specifying past climate change through analysis of sand

Paleoclimate and Holocene relative sea-level history of the east coast of India

Study Conducted By: Kakani Nageswara Rao, Shilpa Pandey, Sumiko Kubo, Yoshiki Saito, K. Ch. V. Naga Kumar, Gajji Demudu, Bandaru Hema Malini, Naoko Nagumo, Rei Nakashima, Noboru Sadakata

Summarized by: Scott Martin, a student studying geology at the University of South Florida that will be graduation with a bachelor’s in early December. He plans on working in a government water management position or as a private contractor at an IT firm. He enjoys camping, kayaking, and playing music in his free time.

What data were used: Data from specific kinds of particles, carbon dating, and results of analysis of ancient pollens found within sand columns.

Methods: First, columns of sand were collected from the Kolleru Lake in India. Then, the chemical composition of the sand was identified, carbon dating was done on some of the plant samples and shells within the sand, and the pollen samples within the sand columns were identified. 

Results: It was found that the bottom of the core, which represents about 18,400 years ago, shows signs of being a dried freshwater body that most likely became more arid (i.e., drier) due to a dry spell in the area around that time. We can assume this because in the sand cores, authors found pollen spores from plants that live in arid environments and rocks that are only able to be found in areas where salt water evaporated. The freshwater lakes would have become saltier as they evaporated and eventually start leaving behind evaporite (i.e., rocks and minerals formed during evaporation) deposits. Then, around 8,000 years ago, the climate in the area changed to that of a tidal zone. This is an area that is underwater when the tide is high and above water when the tide is low. The evidence that as found that points to the area being a tidal zone is the color of the sand itself, shells of mollusks that live in tidal areas, and pollen from mangrove trees. At around 4,900 years ago the area changed again and shows evidence of being a completely freshwater area as it is today.

This figure shows the area being studied in relation to the rest of India. The yellow lines are the depth underwater in that spot, so anywhere the line labeled 5 is touching is 5 meters below sea level. The star labeled KK, the triangle labeled DP, and the dots labeled MW and PN are all locations in which sand columns were taken for this study. Note that the yellow lines are not past coastlines but show depth below the current waterline.

Why is this study important?: This study deepened our understanding of the climate of the past in India as well as how the sea level changed in the area as the global climate did. Understanding more of the specifics of how sea level changes with climate allows for more preparation to be done in coastal cities globally. The change in climate that was analyzed during this study is the Earth’s natural cycle of climate change that is in place due to the slight changes in its tilt and path around the sun.

The big picture: The results from this study will allow for climate models being used in the future to be more accurate since the data that was collected covered thousands of years. This allowed for the study of climate change throughout time as well as the potential causes and effects that the changes in climate had on the area. While this study looked at how natural climate change affected the area, human-induced climate change is altering that cycle and the data on how climate change from the past affected specific rehions could better prepare us to handle to affects of the human-driven climate change that is occurring today.

Citation: Nageswara Rao, K., Pandey, S., Kubo, S. et al. Paleoclimate and Holocene relative sea-level history of the east coast of India. J Paleolimnol 64, 71–89 (2020). https://doi.org/10.1007/s10933-020-00124-2

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