Climate change: Delayed response in sedimentary discharge to the oceans
Abstract
The neodymium isotopic composition of marine sediments (ɛNd) is often used as a proxy for past climate changes in paleoceanography studies. However, in some parts of the world ocean, the origin of ɛNd variations in seawater over the last Glacial/Interglacial cycles remains unclear. This is particularly true in the Indian Ocean because of its connections with the Atlantic and the Pacific Ocean waters, and because of the huge Himalayan sedimentary discharge that brings low ɛNd into the ocean. The ɛNd variations could result of changes in the global oceanic circulation or be due to changes in the continental input controlled by continental rainfalls. Here we present a simple technique to discriminate these two interpretations at a given site, based on the correlation of δ18O and ɛNd seawater signals. We show in-phase records at site SK129-CR2 [1] (Arabian Sea) and out-of phase records at site ODP-758 [2] (Bay of Bengal), suggesting that the two sites have recorded different phenomena through time. Arabian Site fluctuations were interpreted as changes of the thermohaline circulation and Bay of Bengal Site fluctuations as changes on the Himalayan input. As Himalayan rivers input is linked to the Earth's climate variability, we filtered the time series of δ18O and ɛNd at Site ODP 758 around the three periods related to the three main orbital parameters. We show that the time lag between δ18O and ɛNd, increases from 1000 to 2000 and then to 7000 years for the 23 ky, 41 ky, and 100 ky filtered signals. To explain the delays between temperature changes recorded by δ18O and ɛNd, two models were proposed: diffusive [3] and erosion [4] models of Himalayans. For the first time, we demonstrate that a geochemical dataset can record and thus constrain the time lag in the erosional response of an active mountain belt to climate change. [1] Piotrowski, et al. (2009) Earth Planet. Sci. Lett. 285, 179-189. [2] Gourlan et al. (2010) Quaternary Sci. Rev. 29 (19-20), 2484-2498. [3] Castelltort, S; and Van den Driessche (2003) Sedim. Geol. 157, 3-13. [4] Richter, F. M. and Turkian t1993) Earth Planet. Sci. Lett. 119, 121-131.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMEP23B..01G
- Keywords:
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- 1039 GEOCHEMISTRY Alteration and weathering processes;
- 1040 GEOCHEMISTRY Radiogenic isotope geochemistry;
- 1616 GLOBAL CHANGE Climate variability;
- 3022 MARINE GEOLOGY AND GEOPHYSICS Marine sediments: processes and transport