Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Rajiv Nigam ¹, Afimjit Mazumder ¹, Pravin J. Henriques ², Rajeev Saraswat ¹

Affiliations
1 Geological Oceanography Division, National Institute of Oceanography, Dona Paula - 403 004, IN
2 Geology Department, St. Xaviers College, Mumbai- 400 001, IN

Abstract

In order to study the response of benthic foraminifera, especially the rectilinear bi- and Tri-Serial benthic foraminifera (RBF) to oxygen-Depleted conditions from the Arabian Sea off central west coast of India, 103 surface sediment samples collected from a water depth of 15m to 3300m were studied for the benthic foramini feral content. A total of 383 recent benthic foraminiferal species were identified. Out of the total 383 benthic foraminiferal species identified in the study area, 65 species belong to 18 rectilinear bi- and tri-serial benthic foraminifer genera. The RBF abundance remains consistently high (>40%) between 90 m to ∼1200 m water depth. The intermediate depth zone of increased abundance of RBFs coincides with the prominent intermediate water oxygen minimum zone of the Arabian Sea (upper boundary ∼100 m and lower boundary ∼1000 to 1250 m). The other significant abundance (>40%) of rectilinear benthic foraminiferal forms is reported from the water depth range &#∼60 m with the maximum abundance reaching ˜78% at the water depth of 56 m. This zone has also been reported to be affected by seasonal severe Oxygen-Depleted conditions. Therefore, we propose that the increased abundance of RBF may be used as an indicator of Oxygen-Depleted conditions in the Arabian Sea. This benthic foraminiferal response to oxygen-depleted conditions, especially from the shallow water depths is significant as it can be applied to document the geologic extent of shallow water Oxygen-Depleted conditions that have been suggested as a consequence of spurt in the anthropogenic activities in the coastal regions.

Keywords

Oxygen Minima Zone, Rectilinear Benthic Foraminifera, Deep And Shallow Water OMZ, Central West Coast Of India.

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Rajiv Nigam ¹, Rajeev Saraswat ¹, Sujata R. Kurtarkar ¹

Affiliations
1 Micropaleontology Laboratory, Geological Oceanography Division, National lnstitute of Oceanography, Dona Paula - 403 004, Goa, IN

Abstract

Culture experiment has been carried out to observe the response of Pararotalia nipponica (Asano) to different salinities and its salinity tolerance limits. The specimens of P nipponica kept in 33%0 saline water achieved optimum growth, while rest of the specimens maintained under either higher or lower salinities showed comparatively lower growth Pararotalia nipponica specimens kept at 10%0 and 15% salinity started becoming opaque and later their test dissolved, within a span of 25 days. Towards the end of experiment in order to find the maximum salinity tolerance limit, the salinity was gradually increased to 100%o, in the culture dishes having specimens at 40%0 saline water and it was noted that P nipponica specimens were alive even at 100%o salinity. It is concluded that comparatively lower sallinities are much more detrimental to the foraminiferal tests than higher salinities. Results are significant as the salinity response of benthic foraminifera is being used for environmental assessment.

Keywords

Benthic Foraminifera, Salinity Tolerance, Pararotalia nipponica, Culture Experiment, Retarded Growth, Dissolution, pH.

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Rajeev Saraswat ¹

Affiliations
1 Geological Oceangraphy Division, National Institute of Oceangraphy, Dona Paula - 403 004, Goa, IN

Abstract

No Abstract.

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