Changes in biological pump by 230Th-normalized flux of biogenic components recorded in the Chilean margin sediment during the past 22kyr.

• Main Authors: Fukuda Miho, Harada Naomi, Kawakami Hajime, et.al
• Format: Conference Object
• Language: English
• Published: 2019
• Subjects: Patagonia; Drake Passage; Pacific
• Online Access: https://repo.qst.go.jp/?action=repository_uri&item_id=71233; http://id.nii.ac.jp/1657/00071221/

During the last glacial maximum, the atmospheric partial pressure of CO2 (pCO2atm) was very low, 180-190 ppm and rapidly increased to 280 ppm during the last deglacation [1]. During glacial periods, strengthened productivity and an efficient biological pump in the North Pacific, equatorial Pacific, and Southern Oceans may have contributed to low pCO2atm[2]. However, there is still some controversy as to whether marine productivity was high everywhere during glacial periods. To resolve this controversy, more data are required from many regions regarding temporal changes in past export fluxes of biogenic materials. The eastern South Pacific Ocean including the Chilean marginal region, where active biological production is observed at present is target area of this study. The aim of this study is to identify changes in the 230Th-normalized export flux of biogenic components commonly used as proxies for paleoproductivity-namely total organic carbon (TOC), total nitrogen (TN) and biogenic opal (Siopal) from two sediment cores collected at 36S, off central-south Chilean covering the past 22 kyr (PC-1) and at 52S near the mouth of Strait of Magellan, Pacific side over the past 13 kyr (PC-3). 230Th-normalized fluxes of biogenic components of sediments at 36S and 52S off the Chilean coast imply that the biological pump was effective during 14-8 kyr BP off central Chile, and after 5 kyr BP off central and southernmost Chile; and less effective during 22-14 kyr BP off central Chile and during 13-6 kyr BP off southernmost Patagonia [3]. That is to say, off central Chile, the weakness of the biological pump during the LGM contributed to the global rise of pCO2atm at that time. During 14-8 kyr BP, the increasing effectiveness of the biological pump at the PC-1 site off central Chile contributed to the global rise of pCO2atm. At the PC-3 site, the weakening of biological pump contributed to the rise of pCO2atm during 13-6 kyr BP. After 6 kyr BP, the active biological pump did not contribute to the rise of pCO2atm. In this presentation, we will also report 230Th-normalized fluxes of biogenic components at the 55S collected from the Drake Passage sediment.\n[1] Monnin et al. (2001) Science 291, 112-114. [2] Kohfeld et al. (2005) Science 308, 74-78. [3] Fukuda et al., Geochemical Journal (in press) Goldschmidt 2013 Conference