Title: Phosphorus
geochemistry in the Luochuan loess section, North China and its
paleoclimatic implications
Source: QUATERNARY
INTERNATIONAL 144: 72-83 FEB 2006
Document Type: Article
Language: English
Abstract: Total
P (P-t) on a carbonate-free basis in an entire loess-paleosol sequence
and P-t, organic P (P-o) and inorganic P (P-i) in the S-0-L-1-S-1
sequence were investigated in detail with different resolutions for the
Luochuan loess section from northern China. P-t content varies between
393 and 786 ppm throughout the loess-paleosol sequence, and is
generally higher in the loess than in interstratified paleosols,
showing fluctuation cycles of 100ka in correspondence to loess-paleosol
alternations. P-t variations on a carbonate-free basis in the
loess-paleosol sequence could indicate variations in atmosphere
precipitation resulting in different leaching loss of P from palcosols.
P-i has an average value of 499 ppm with a range of 324-560 ppm,
accounting for more than 70% of P-t in the S-0-L-1-S-1 sequence, where
the minimum of P-i in the Malan loess is higher than the maximum of P-i
in S-1. P-o ranges between 59 and 233 ppm with an average of 132 ppm in
the S-0-L-1-S-1 sequence. Phosphorus (P) was initially delivered to the
Luochuan loess section via influx of aeolian dust from the northern
desert and Gobi areas by the East Asian winter monsoon, and then was
modified by pedogenesis associated with the East Asian summer monsoon
during the last 130 ka. '' Preserved P-t'' in the loess L-1 is tightly
correlated with grain size without leaching loss of P due to enrichment
of P in fine-grained fractions, as well as '' initial P-t''. ''
Leaching P-t'' data show that paleosol S-1 had lost 15-40% of its ''
initial P-t'', and that there was much more precipitation in S-1 than
in L-1. P-i subject to slightly weak pedogenesis was completely
transformed into P-o without leaching loss of P in loess L-1. By
contrast, much P-i disappeared from paleosol S, due to strong
pedogenesis, partly through leaching and partly through conversion to
organic forms during P cycling processes. P-o variation is similar to
those of MS and the < 7.8 mu m fraction in L-1, but contains more
information on the East Asian winter monsoon due to weak pedogenesis
without leaching of P. P-o in S-1 lower than L1SS1, as a consequence of
strong decomposition of the organic matter kept constantly in the
middle of S-1 where P-i kept at the lowest of 423 ppm, suggesting that
there existed a very warm and humid climate related to the enhanced
summer monsoon during that period. The mean organic P/inorganic P ratio
(P-o/P-i) is lower in the L1LL1 and L1LL2 than in the S-0, S-1, and
L1SS1, indicating that low P-o/P-i ratios coincide with weak
weathering-pedogenesis, and higher P-o/P-i ratios correspond to strong
weathering-pedogenesis. P-o/P-i ratio can eliminate the effect of grain
size on aeolian dust because of chemical uniformity of aeolian dust and
enrichment of P-o and P-i in the fine-grained fractions. Thus, P-o/P-i
ratio is solely linked to pedogenesis of the Luochuan loess section.
Variation in P-o/P-i ratiois similar to those of MS and the Marine
Oxygen Isotope composition, indicating the summer monsoon evolution
during the last 130 ka and providing the biogeochemical evidence for
further understanding the genetic links between the East Asian monsoon
and global climate change. (c) 2005 Elsevier Ltd and INQUA. All rights
reserved.
KeyWords Plus: LAST
130,000 YEARS; SOIL-PHOSPHORUS; MAGNETIC-SUSCEPTIBILITY; SEQUENTIAL
EXTRACTION; ORGANIC PHOSPHORUS; MONSOON VARIATIONS; IRON GEOCHEMISTRY;
PLATEAU; PROVENANCE; CLIMATE
Addresses: Rao
WB (reprint author), Nanjing Univ, Dept Earth Sci, 22 Hankou Rd,
Nanjing, 210093 Peoples R China
Nanjing Univ, Dept Earth Sci, Nanjing, 210093 Peoples R China
Chinese Acad Sci, Key Lab Ore Deposit Geochem, Inst Geochem, Guiyang,
55002 Peoples R China
Publisher: PERGAMON-ELSEVIER
SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB,
ENGLAND
Subject Category: GEOGRAPHY,
PHYSICAL; GEOSCIENCES, MULTIDISCIPLINARY
IDS Number: 002YK
ISSN: 1040-6182
