25 May 2023
 | 25 May 2023
Status: this preprint is open for discussion and under review for Climate of the Past (CP).

Glacial-interglacial sea water isotope change near the Chilean Margin as reflected by δ2H of C37 alkenones

Katrin Hättig, Devika Varma, Stefan Schouten, and Marcel T. J. van der Meer

Abstract. Hydrogen isotopic compositions of C37 long chain alkenones (δ2HC37) have been proposed as a proxy for past seawater salinity and applied in several regions. However, previous studies were based solely on a single core and often suggested unlikely large changes in salinity. Here we present a new δ2HC37 record, in combination with oxygen isotopes of benthic foraminifera from the same samples, from a sediment core from the Chilean Margin (ODP site 1235). The observed negative shift in δ2HC37 of 20 ‰ during deglaciation was identical to that of the nearby located, but deeper, ODP core 1234, suggesting a regionally consistent shift in δ2HC37. This shift translates into a hydrogen isotope shift of the surface seawater (∆δ2HSW) of ca. 14 ‰, similar to glacial-interglacial reconstructions based on other δ2HC37 records. The reconstructed bottom seawater oxygen isotope change based on benthic foraminifera during the last deglaciation is approximately 0.8 ‰, in line with previous studies. When translated into ∆δ2HSW using the modern open-ocean waterline this would suggest a shift of ca. 5 ‰, smaller than the reconstructed surface seawater shift based on alkenones. The higher change in surface δ2HSW suggests that the surface water experienced more freshening during the Holocene than bottom waters either due to increased freshwater input or reduced evaporation, or a combination of the two.

Katrin Hättig et al.

Status: open (until 20 Jul 2023)

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Katrin Hättig et al.

Data sets

Age model for ODP Leg 202 Site 1235 and Site 1234. K. Hättig, D. Varma, M. T. J. van der Meer, G.-J. Reichart, and S. Schouten

SST Proxies Chilean (ODP Leg 202 Site 1235 and Site 1234) and Angola Margin (ODP Leg 175 Site 1078 and Site 1079). K. Hättig, D. Varma, M. T. J. van der Meer, G.-J. Reichart, and S. Schouten

Katrin Hättig et al.


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Short summary
Water isotopes correlate with the salt content of the sea. In this study we reconstruct the water isotope signal of the sea surface during the last deglaciation by analyzing the hydrogen isotopes of alkenones, an organic compound preserved in sediment. We compare it to oxygen isotopes analyzed on calcite shells produced in the bottom water. Our results suggest that the surface water experienced more freshening during the last 20.000 years then the bottom waters.