Preprints
https://doi.org/10.5194/bg-2021-329
https://doi.org/10.5194/bg-2021-329

  03 Jan 2022

03 Jan 2022

Review status: this preprint is currently under review for the journal BG.

Contrasting vertical distributions of recent planktic foraminifera off Indonesia during the southeast monsoon: implications for paleoceanographic reconstructions

Raúl Tapia1, Sze Ling Ho1, Hui-Yu Wang1, Jeroen Groeneveld2, and Mahyar Mohtadi3 Raúl Tapia et al.
  • 1Institute of Oceanography, National Taiwan University, No. 1, Sec. 4, Roosevelt Road 10617 Taipei, Taiwan
  • 2Department of Geology, Hamburg University, D-20146 Hamburg, Germany
  • 3MARUM – Center for Marine Environmental Sciences, University of Bremen, D-28334 Bremen, Germany

Abstract. Planktic foraminifera are widely used in palaeoceanographic and paleoclimatic studies. The accuracy of such reconstructions depends on our understanding of the organisms’ ecology. Here we report on field observations of planktic foraminiferal abundances (>150 µm) from 5 depth intervals between 0–500 m water depth at 37 sites in the eastern tropical Indian Ocean. The total planktic foraminiferal assemblage comprises 29 morphospecies; with 11 morphospecies accounting for ~90 % of the total assemblage. Both species composition and dominance in the net samples are broadly consistent with the published data from the corresponding surface sediments.

The abundance and vertical distribution of planktic foraminifera are low offshore west Sumatra, and increase towards offshore south Java and the Lesser Sunda Islands (LSI). Average living depth of Trilobatus trilobus, Globigerinoides ruber, and Globigerina bulloides increases eastward, while that of Neogloboquadrina dutertrei, Pulleniatina obliquiloculata, and Globorotalia menardii remains constant. We interpret the overall zonal and vertical distribution patterns in planktic foraminiferal abundances as a response to the contrasting upper water column conditions during the southeast monsoon, i.e., oligotrophic and stratified offshore Sumatra (non-upwelling) vs. eutrophic and well-mixed offshore Java-LSI (upwelling).

Overall, the inferred habitat depths of selected planktic foraminifera species show a good agreement with those from sediment trap samples and from surface sedimentss off Sumatra, but not with those from surface sediments off Java-LSI. The discrepancy might stem from the different temporal coverage of these sample types. Our findings highlight the need to consider how foraminiferal assemblages and ecology vary on shorter timescales, i.e., from “snapshots” of the water column captured by plankton net to seasonal and interannual variability as recorded in sediment traps and how these changes are transferred and preserved in deep-sea sediments.

Raúl Tapia et al.

Status: open (until 14 Feb 2022)

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  • RC1: 'Comment on bg-2021-329', Anonymous Referee #1, 24 Jan 2022 reply
  • RC2: 'Comment on bg-2021-329', Anonymous Referee #2, 24 Jan 2022 reply

Raúl Tapia et al.

Raúl Tapia et al.

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Short summary
We report census counts of planktic foraminifera in depth-stratified plankton net samples off Indonesia. Our results show that the vertical distribution of foraminifera species routinely used in paleoceanographic reconstructions varies in hydrographically distinct regions, likely in response to food availability. Consequently, the thermal gradient based on mixed layer and thermocline dwellers also differs for these regions, suggesting potential implications for paleoceanographic reconstructions.
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