Planetary Pulse- our weekly departmental seminar series organized by the Geological Institute

This initiative promises to spark dynamic discussions and elevate our academic community’s intellectual vibrancy.

Let’s ignite minds and build connections together!!

Week 1- March 12 , 2025

Did global warming make oyster couples intimate? – Facultative monogamy in oysters.

Prof. Kalyan Halder

Abstract

The living oyster Ostrea puelchana from the Argentine shelf is known by large females carrying dwarf males inside their shells at the anterior end of hinge plate. An identical association was recorded in O. jibananandai from the early Eocene rocks (~54Ma) of Cambay Basin and referred to by ‘facultative monogamy’. Ostrea is a brooding oyster, in which males cast their sperms in water that are brought inside the female shell by inhalant water current, and fertilization takes place internally. The intimate association between the males and females of the carrying/monogamic species of Ostrea reduces the uncertainty involved in this spermcasting process as the males release sperms directly inside the female shells. It is intriguing that in spite of this advantage the phenomenon is rare in the oyster lineage. It is argued here that facultative monogamy reduces evolutionary flexibility as it discourages phenotypic variability. It evolved as a trade-off between morphological variability and successful fertilization in response to environmental perturbations that tend to disrupt sperm transport in open water. Rapid global warming is the most potent environmental stressor because the phenomenon recur at the early stages of global warming events, the early Eocene hyperthermal ETM2 and the current warming crisis.

Week 2- March 26, 2025

Assessment of source, depositional environment and maturity of Ashoknagar crude oil using stable carbon isotope and aromatic hydrocarbon distribution.

Pravat Kumar Behera

Abstract

The Ashoknagar in West Bengal has been the sole oil-producing well in the Indian section of the Bengal Basin. A series of organic geochemical analyses have been performed on crude oil from Ashoknagar, and various organic geochemical proxies have been used to assess the source, depositional environment, and maturity of the oil. The aliphatic and aromatic fractionation from the crude oil is performed using column chromatography and the fractions are analyzed using a quadruple GC-MS/MS. The low sulfur content of the oil (0.03 %) suggests the nonmarine nature of the oil. The low abundance of dibenzothiophene is consistent with the non-marine source. Further, the stable carbon isotope (δ13C) of aliphatic (-24.95‰) and aromatic (-24.63‰) fractions and low abundance of 1,2,5-and 1,2,7-trimethylenapthalenes indicate a terrestrial origin of the source rock organic matter. The low abundance of dibenzothiophene/ phenathrene ratio (0.1) and moderate pristine/phytane ratio (1.9) indicate a lagoonal and sub-oxic depositional environment of the source rock. Vitrine reflectance, calculated from the methylephenathrene index (VRc %) and methyledibenzothiophene ratio (VRm %) using an empirical formula, indicates and early stage of maturation of the Ashoknagan crude oil.

Week 3- April 2, 2025

The Arabian Sea Oxygen Mystery: Connecting Clues to Conclusions

Dr. Shiba Shankar Acharya

Abstract

The Arabian Sea Oxygen Minimum Zone (ASOMZ) presents a paradox: it is more dominant in the eastern Arabian Sea rather than the western part, which is more biologically productive and likely to consume more oxygen. This study investigates the sources and sinks of oxygen in the ASOMZ using extended optimum multiparameter (eOMP) analysis and apparent oxygen utilization (AOU). The analysis identifies Indian Deep Water (dIDW), Indian Central Water (ICW), Persian Gulf Water (PGW), and Red Sea Water (RSW) as key contributors. Notably, PGW and RSW drive the eastward shift of ASOMZ instead of the more voluminous ICW and dIDW. This study further reveals that organic detritus from the highly productive western Arabian Sea is transported eastward, fueling the ASOMZ shift. Seasonal variations show a 30% intensification of ASOMZ and a 5% volume increase during the spring-summer transition. Interestingly, productivity in the Arabian Sea doubles during this period, creating a paradox in oxygen distribution. By analyzing oxygen utilization, primary production, and core depths of water masses, this study highlights a delicate balance between oxygen-rich circulation from the west and organic matter remineralization in the east, ensuring the ASOMZ persists year-round.