Preprints
https://doi.org/10.5194/cp-2024-25
https://doi.org/10.5194/cp-2024-25
15 Apr 2024
 | 15 Apr 2024
Status: this preprint is currently under review for the journal CP.

A sub-fossil coral Sr/Ca record documents meridional variability of the Intertropical Convergence Zone in the eastern Indian Ocean

Miriam Pfeiffer, Hideko Takayanagi, Lars Reuning, Takaaki Konabe Watanabe, Saori Ito, Dieter Garbe-Schönberg, Tsuyoshi Watanabe, Chung-Che Wu, Chuan-Chou Shen, Jens Zinke, Geert-Jan Brummer, and Sri Yudawati Cahyarini

Abstract. Sea surface temperature (SST) variability in the south-eastern tropical Indian Ocean is crucial for rainfall variability in Indian Ocean rim countries. A large body of literature has focused on zonal variability associated with the Indian Ocean Dipole (IOD), but it is unclear whether meridional shifts in the position of the Intertropical Convergence Zone (ITCZ), which at present co-vary with the IOD, may also occur independently. We have developed a new, monthly resolved Sr/Ca record from a sub-fossil coral cored at Enggano Island (Indonesia, 5° S, 102° E). Core sections containing diagenetic phases are omitted from the SST reconstruction. U/Th dating shows that the Sr/Ca-based SST record extends from 1917–1868 and from 1861–1823 with a relative age uncertainty of ±2.4 years (2σ). At Enggano Island, coastal upwelling and cooling in austral spring is coupled to the position of the ITCZ, and impacts SST seasonality. The sub-fossil coral indicates an increase in SST seasonality due to enhanced austral spring cooling between 1917 and 1855, which we attribute to stronger SE winds and a northward shift in the position of the ITCZ in austral spring. A nearby sediment core indicates SST cooling and a shallowing of the thermocline prior to ~1930. These results are consistent with an increase in the North-South SST gradient in the eastern Indian Ocean calculated from historical temperature data, that is not seen in the zonal SST gradient. We conclude that the relationship between meridional and zonal variability in the eastern Indian Ocean is non-stationary and influenced by long-term temperature trends.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Miriam Pfeiffer, Hideko Takayanagi, Lars Reuning, Takaaki Konabe Watanabe, Saori Ito, Dieter Garbe-Schönberg, Tsuyoshi Watanabe, Chung-Che Wu, Chuan-Chou Shen, Jens Zinke, Geert-Jan Brummer, and Sri Yudawati Cahyarini

Status: open (until 10 Jun 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2024-25', Anonymous Referee #1, 18 Apr 2024 reply
  • RC2: 'Comment on cp-2024-25', Anonymous Referee #2, 13 May 2024 reply
  • RC3: 'Comment on cp-2024-25', Anonymous Referee #3, 13 May 2024 reply
Miriam Pfeiffer, Hideko Takayanagi, Lars Reuning, Takaaki Konabe Watanabe, Saori Ito, Dieter Garbe-Schönberg, Tsuyoshi Watanabe, Chung-Che Wu, Chuan-Chou Shen, Jens Zinke, Geert-Jan Brummer, and Sri Yudawati Cahyarini
Miriam Pfeiffer, Hideko Takayanagi, Lars Reuning, Takaaki Konabe Watanabe, Saori Ito, Dieter Garbe-Schönberg, Tsuyoshi Watanabe, Chung-Che Wu, Chuan-Chou Shen, Jens Zinke, Geert-Jan Brummer, and Sri Yudawati Cahyarini

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Short summary
A coral reconstruction of past climate shows changes in the seasonal cycle of sea surface temperature in the SE tropical Indian Ocean. An enhanced seasonal cycle suggests that the tropical rainfall belt shifted northwards between 1855–1917. We explain this with greater warming in the NE Indian Ocean relative to the SE, which strengthens surface winds and coastal upwelling, leading to greater cooling in the eastern Indian Ocean south of the Equator.