06 Jul 2022
06 Jul 2022
Status: this preprint is currently under review for the journal ESSD.

Large salinity gradient and diagenetic changes in the northern Indian Ocean dominate the stable oxygen isotopic variation in Globigerinoides ruber

Rajeev Saraswat1, Thejasino Suokhrie1, Dinesh K. Naik2, Dharmendra P. Singh3, Syed M. Saalim4, Mohd Salman1, Gavendra Kumar1, Sudhira R. Bhadra1, Mahyar Mohtadi5, Sujata R. Kurtarkar1, and Abhayanand S. Maurya3 Rajeev Saraswat et al.
  • 1Micropaleontology Laboratory, National Institute of Oceanography, Goa, India
  • 2Banaras Hindu University, Varanasi, Uttar Pradesh, India
  • 3Indian Institute of Technology, Roorkee, India
  • 4National Center for Polar and Ocean Research, Goa, India
  • 5MARUM, University of Bremen, Bremen, Germany

Abstract. The application of stable oxygen isotopic ratio of surface dwelling Globigerinoides ruber (white variety) (δ18Oruber) to reconstruct past hydrological changes requires precise understanding of the effect of ambient parameters on δ18Oruber. The northern Indian Ocean, with huge freshwater influx and being a part of the Indo-Pacific Warm Pool, provides a unique setting to understand the effect of both the salinity and temperature on δ18Oruber. Here, we use a total of 400 surface samples (252 from this work and 148 from previous studies), covering the entire salinity end member region, to assess the effect of seawater salinity and temperature on δ18Oruber in the northern Indian Ocean. The analyzed surface δ18Oruber very well mimics the expected δ18O calcite estimated from the modern seawater parameters (temperature, salinity and seawater δ18O). We report a large diagenetic overprinting of δ18Oruber in the surface sediments with an increase of 0.18 ‰ per kilometer increase in water depth. The salinity exerts the major control on δ18Oruber (R2 = 0.63) in the northern Indian Ocean, with an increase of 0.29 ‰ per unit increase in salinity. The relationship between temperature and salinity corrected δ18Oruber18Oruber - δ18Osw) in the northern Indian Ocean [T= -0.59*(δ18Oruber - δ18Osw) + 26.40] is different than reported previously based on the global compilation of plankton tow δ18Oruber data. The revised equations will help in better paleoclimatic reconstruction from the northern Indian Ocean.

Rajeev Saraswat et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on essd-2022-107', Anonymous Referee #1, 15 Jul 2022
  • RC2: 'Comment on essd-2022-107', Alberto Sanchez, 09 Sep 2022

Rajeev Saraswat et al.

Data sets

Oxygen isotopic ratio of Globigerinoides ruber (white variety) in the surface sediments of the northern Indian Ocean Saraswat, Rajeev; Suokhrie, T; Naik, Dinesh Kumar; Singh, Dharmendra Pratap; Saalim, S M; Salman, M; Kumar, G; Bhadra, S R; Mohtadi, Mahyar; Kurtarkar, S R; Maurya, A S (2022)

Rajeev Saraswat et al.


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Short summary
A lot of efforts are made to project monsoon changes, by reconstructing the past. The stable oxygen isotopic ratio of marine calcareous organisms is frequently used to reconstruct the past monsoon. Here we use the published and new stable oxygen isotopic data to demonstrate a diagenetic effect and a strong salinity influence on the oxygen isotopic ratio of foraminifera in the northern Indian Ocean. We also provide updated calibration equations to deduce monsoon from the oxygen isotopic ratio.