Potential role of giant marine diatoms in sequestration of atmospheric CO2 during the Last Glacial Maximum: delta C-13 evidence from laminated Ethmodiscus rex mats in tropical West Pacific

• Published in: Global and Planetary Change
• Main Authors: Xiong, Zhifang, Li, Tiegang, Crosta, Xavier, Algeo, Thomas, Chang, Fengming, Zhai, Bin, Li, TG
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Vital Effects; Ethmodiscus Rex Blooms; Surface Stratification; Co2 Sink; Marine Silica Cycle; Late Pleistocene; Eastern Philippine Sea; Physical Geography; Geology; Geography; Physical; Geosciences; Multidisciplinary; Science & Technology; Physical Sciences; CARBON ISOTOPIC FRACTIONATION; SOUTHERN-OCEAN PHYTOPLANKTON; EQUATORIAL PACIFIC; GROWTH-RATE; DEEP-SEA; IRON HYPOTHESIS; BOUND NITROGEN; PHILIPPINE SEA; ORGANIC-CARBON; INDIAN-OCEAN; Indian; Pacific; Southern Ocean
• Online Access: http://ir.qdio.ac.cn/handle/337002/16313; https://doi.org/10.1016/j.gloplacha.2013.06.003

Giant marine diatoms, blooming or aggregating within deep chlorophyll maxima under stratified conditions, can generate substantial production and a large export flux of organic carbon from surface waters. However, their role in regulating glacial-interglacial variation in atmospheric pCO(2) remains unclear. Here, we report the organic carbon isotopic compositions of Ethmodiscus rex diatoms (delta C-13(E.) (rex)) and bulk sediments (delta C-13(org)) from a sediment core in the eastern Philippine Sea dated to similar to 19.5-31.0 kyr B.P. and consisting of (from youngest to oldest) (1) laminated E. rex diatom mats (LDM), (2) diatomaceous clay (DC), and (3) pelagic clay (PC). Our results suggest that delta C-13(E.) (rex) provides a better record of palaeoceanographic processes during LDM and DC deposition than delta C-13(org) because of reduced differential vital effects in near-monospecific E. rex fractions. We used the isotopic composition of the coarse E. rex fraction (delta C-13(E.) (rex) ((>154) (mu m))) to calculate the CO2 partial pressure of eastern Philippine Sea surface waters (pCO(2-sw)) during the Last Glacial Maximum (LGM). Our pCO(2-sw) records suggest that the eastern Philippine Sea switched from being a strong CO2 source during DC deposition to a weak CO2 sink during LDM deposition. The role of the eastern Philippine Sea as a CO2 sink during the LGM was promoted by elevated primary production and, to a lesser extent, intensified water-column stratification. These observations highlight the potential role of giant marine diatoms in the sequestration of atmospheric CO2 during the LGM and, hence, support changes in biogenic silica fluxes as a potential cause of lower glacial atmospheric CO2. Our findings are consistent with an eolian source of silica, as proposed by the 'silica hypothesis' and the 'silicon-induced alkalinity pump hypothesis' but not by the 'silicic acid leakage hypothesis.' (C) 2013 Elsevier B.V. All rights reserved. Giant marine diatoms, blooming or aggregating within deep ...