Contrasting Scenarios for Upper Ocean Temperature Changes at the Last Glacial Maximum Inferred From Inorganic and Organic Paleothermometers: A Case Study From the Eastern Tropical Indian Ocean
Journal
Paleoceanography and Paleoclimatology
Journal Volume
40
Journal Issue
8
ISSN
2572-4517
2572-4525
Date Issued
2025-08
Author(s)
Makarova, M.
Tapia, R.
Mohtadi, M.
Hou, A.
Groeneveld, J.
Meckler, A. N.
Huang, K.‐F.
Tung, R.‐Y.
Iizuka, Y.
Ho, S. L.
Abstract
Reconstructing paleo seawater temperatures is essential for understanding past climate changes, yet different paleotemperature proxies can yield divergent signals with opposing climatic interpretations. This study reconstructs the upper ocean thermal structure in the eastern tropical Indian Ocean offshore southwest Sumatra across two 2-kyr periods during the Last Glacial Maximum (LGM, 19–21 ka) and the Late Holocene (LH, 0–2 ka). Our multiproxy approach combines updated, published results from organic paleothermometers ((Formula presented.), TEX86), published and newly generated Mg/Ca data from four species of surface and thermocline dwelling planktic foraminifera, alongside new data from clumped isotope analysis (Δ47) on the same foraminiferal species. The new Δ47 data suggest surface dwellers experienced more pronounced cooling (6.1°C; 95% confidence interval 4.7–7.5°C) than the thermocline dwellers (1.6°C; 1.1–2.1°C) during the LGM compared to the LH, resulting in a weaker LGM vertical temperature gradient in the upper ocean and a deeper thermocline. While this weaker thermal gradient is generally consistent with previous Mg/Ca reconstructions, our new Δ47 data for the LH suggest a higher thermocline temperature than the Mg/Ca-based data, which may have been affected by dissolution effects as indicated by the correlation between Mg/Ca values and shell weights of thermocline dwellers. In contrast, paired (Formula presented.) and TEX86 suggest a stronger or similar upper ocean thermal gradient during the LGM. Based on our analysis of modern data, we propose that the apparent discrepancy between the foraminiferal and biomarker approaches might have stemmed from proxies reflecting different depths with different sensitivities to upwelling dynamics.
Subjects
clumped isotopes
eastern tropical Indian Ocean
Late Holocene
LGM
multiproxy
vertical thermal gradient
SDGs
Publisher
American Geophysical Union (AGU)
Type
journal article