10:15 〜 10:30
[MIS18-16] Large-scale retreat of the Patagonian ice fields during last interglacial period recorded in deep-sea sediments off the Chilean margin
キーワード：パタゴニア氷原、最終間氷期、MIS 5、チリ沖、帯磁率、Ti/K比
In this study, we propose a hypothesis that Patagonian ice fields had significantly retreated compared to the present during the last interglacial period (Marine isotope stage 5e; 13-11.5 ka) based on high magnetic susceptibility peak and changes in major terrigenous elements of deep-sea sediments off Chilean margin, eastern South Pacific.
The northern and southern Patagonian ice fields, which are currently centered on the higher parts of the Andes, have been reported to accelerated retreat during the last decades [1]. Advance and retreat of glaciers during past warm periods provide an essential information to predict future ice fields changes. Among the past warm periods, the last interglacial is the last period showing warm climate comparable to the modern climate. However, there are few ice volume reconstructions in Patagonian ice fields during the last interglacial period. Most glacial deposits on land, such as moraines, could have been modified by subsequent glacier advances. Thus, we focused on deep-sea sedimentary records retrieved from off Chilean margin. Here we use the three hemipelagic sediment cores with wide latitudinal coverage: IODP Site U1543 (54°S; 76°W; ~3860 m water depth), MR16-09 PC04 (50°S; 79°W; 3848 m water depth), and MR16-09 PC03 (46°S; 77°W; 3082 m water depth). We measured the bulk elemental compositions of PC04 and PC03 by the XRF core scanner (ITRAX) and analyzed the downcore variations together with the MSCL data (magnetic susceptibility (MS) and Gamma-ray attenuation (GRA) density) of these cores [2] and the core scanning data (MS, GRA density, and XRF elemental compositions) of U1543 [3]. MS values of all three cores showed a significant peak during the last interglacial period. Since the amount of magnetic minerals controls MS in hemipelagic sediment, these peaks reflect changes in the terrigenous inputs to off Chile. Titanium to potassium ratio (Ti/K), major terrigenous elements, also showed notable peaks simultaneous with the MS peaks, indicating an increased Ti content. Thus, the pronounced MS and Ti/K peaks suggest the rapid inputs of magnetic and Ti-rich materials to the eastern South Pacific between 54°S and 46°S. It was reported that major sources of Ti and K in sediments off Chile are andesitic volcanic rocks and metamorphic rocks, respectively [4]. However, in the southern Andes (south of 45°S), the andesitic volcanic rocks with high Ti content distributed in the limited area around e.g., Lautaro, Aguilera, and Reclus volcanoes, where are now covered by ice (i.e., the southern Patagonian ice field) [5]. Hence it is likely that both peaks of MS and Ti during the last interglacial period represent the Ti enriched andesitic volcanic rock supply from those volcanoes due to the retreat of the Patagonian ice field during the period. We’ll further analyze the grain size distributions of the terrigenous materials in U1543, PC04, and PC03 cores to find the signal of meltwater discharge from the ice field. In addition, the provenance study will be required in the future for the terrigenous sediments in three sediment cores and the rock samples in the potential source regions.
[1] Abdel Jaber et al. (2019), The Cryosphere, 13, pp. 2511–2535
[2] JAMSTEC (2018), MIRAI MR16-09 Leg2 Cruise Data (Accessed 2021-01-30)
[3] Lamy et al. (2019), Exp. 383 Preliminary Report
[4] Stuut et al. (2007), Quat. Int., 161, pp. 67–76
[5] e.g., Motoki et al. (2006), Rev. Geol. Chile, 33, pp. 177–187
The northern and southern Patagonian ice fields, which are currently centered on the higher parts of the Andes, have been reported to accelerated retreat during the last decades [1]. Advance and retreat of glaciers during past warm periods provide an essential information to predict future ice fields changes. Among the past warm periods, the last interglacial is the last period showing warm climate comparable to the modern climate. However, there are few ice volume reconstructions in Patagonian ice fields during the last interglacial period. Most glacial deposits on land, such as moraines, could have been modified by subsequent glacier advances. Thus, we focused on deep-sea sedimentary records retrieved from off Chilean margin. Here we use the three hemipelagic sediment cores with wide latitudinal coverage: IODP Site U1543 (54°S; 76°W; ~3860 m water depth), MR16-09 PC04 (50°S; 79°W; 3848 m water depth), and MR16-09 PC03 (46°S; 77°W; 3082 m water depth). We measured the bulk elemental compositions of PC04 and PC03 by the XRF core scanner (ITRAX) and analyzed the downcore variations together with the MSCL data (magnetic susceptibility (MS) and Gamma-ray attenuation (GRA) density) of these cores [2] and the core scanning data (MS, GRA density, and XRF elemental compositions) of U1543 [3]. MS values of all three cores showed a significant peak during the last interglacial period. Since the amount of magnetic minerals controls MS in hemipelagic sediment, these peaks reflect changes in the terrigenous inputs to off Chile. Titanium to potassium ratio (Ti/K), major terrigenous elements, also showed notable peaks simultaneous with the MS peaks, indicating an increased Ti content. Thus, the pronounced MS and Ti/K peaks suggest the rapid inputs of magnetic and Ti-rich materials to the eastern South Pacific between 54°S and 46°S. It was reported that major sources of Ti and K in sediments off Chile are andesitic volcanic rocks and metamorphic rocks, respectively [4]. However, in the southern Andes (south of 45°S), the andesitic volcanic rocks with high Ti content distributed in the limited area around e.g., Lautaro, Aguilera, and Reclus volcanoes, where are now covered by ice (i.e., the southern Patagonian ice field) [5]. Hence it is likely that both peaks of MS and Ti during the last interglacial period represent the Ti enriched andesitic volcanic rock supply from those volcanoes due to the retreat of the Patagonian ice field during the period. We’ll further analyze the grain size distributions of the terrigenous materials in U1543, PC04, and PC03 cores to find the signal of meltwater discharge from the ice field. In addition, the provenance study will be required in the future for the terrigenous sediments in three sediment cores and the rock samples in the potential source regions.
[1] Abdel Jaber et al. (2019), The Cryosphere, 13, pp. 2511–2535
[2] JAMSTEC (2018), MIRAI MR16-09 Leg2 Cruise Data (Accessed 2021-01-30)
[3] Lamy et al. (2019), Exp. 383 Preliminary Report
[4] Stuut et al. (2007), Quat. Int., 161, pp. 67–76
[5] e.g., Motoki et al. (2006), Rev. Geol. Chile, 33, pp. 177–187