Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmpp24a..06c&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #PP24A-06
Other
1616 Climate Variability (1635, 3305, 3309, 4215, 4513), 1620 Climate Dynamics (0429, 3309), 3344 Paleoclimatology (0473, 4900), 4914 Continental Climate Records, 4936 Interglacial
Scientific paper
Cave speleothem δ 18O records from southeastern China have been interpreted as the ratio between summer and winter monsoon precipitation (Cheng et al. 2006, Geology v34; Wang et al. 2001, Science v294), the removal of water vapor from air masses between the tropical Indo-Pacific and southeastern China (Yuan et al. 2004, Science v304), and changes in East Asian summer monsoon intensity as a direct response to Northern Hemisphere summer insolation (Wang et al. 2008, Nature v451). The latter two interpretations are inconsistent with a multiproxy phase analysis of 15 other published summer monsoon proxies from the Arabian Sea, the South China Sea, and the Chinese Loess Plateau. The interpretation involving the ratio of summer- and winter-monsoon precipitation (Cheng et al. 2006 and Wang et al. 2001), although simplified, is more consistent with the modern seasonal δ 18O of precipitation in southeastern China and can be reconciled with precession-band phase results from other marine and terrestrial proxy data as follows. Multiproxy analysis of 16 published proxies for late Pleistocene Indian and East Asian summer monsoon strength indicate that 15 of the proxies cluster about a phase of - 124±18° relative to Precession minimum (ω = 90°; maximum NH Summer insolation). One proxy, Hulu-Sanbao cave δ 18O, is an outlier, plotting with phase of -42±5°. This apparent phase discrepancy is reconciled by interpreting the cave δ 18O as a mix of isotopically distinct seasonal precipitation sources. GNIP and NCAR/NCEP reanalysis data indicate three seasonal wind and precipitation regimes, each with a distinct isotopic composition. Summer monsoon months (JJA) are characterized by southerly flow from the South China Sea, account for 51% of the total annual precipitation, and have an average δ 18Oprecip of -9.5 ‰. Spring intermonsoon months (AM) are characterized by easterly flow off the Pacific, account for 14% of the total annual precipitation, and have an average δ 18Oprecip of -3.7 ‰. The remaining fall and winter months (SONDJFM) are characterized by north-northwesterly flow from the continental interior, account for 35% of the total annual precipitation, and have an average δ 18Oprecip of -7.2 ‰. Isotopically-weighted precipitation models indicate that all three seasonal precipitation sources are required to account for the full range exhibited in the Hulu-Sanbao composite δ 18O record. On this basis, interpreting the Hulu-Sanbao δ 18O record as a direct summer monsoon proxy is unjustified (Wang et al., 2008), a conclusion supported by the phase discrepancy between Hulu-Sanbao δ 18O and the 15 other summer monsoon proxies. A simplified vector addition model incorporating the amplitude and phase of summer (-124°) and winter (0°) forcing vectors predicts a precession-band phase of - 63° for the Hulu-Sanbao record when based on modern summer and winter GNIP precipitation weightings (50% each). The measured phase (-42°) indicates a 60% contribution of winter precipitation and 40% summer precipitation, averaged over the past 224,000 years, consistent with the Wang et al. (2001) findings. Thus, the precession-band phase of Hulu-Sanbao δ 18O differs from the 15 other marine and terrestrial summer monsoon proxies because Hulu-Sanbao δ 18O incorporates, at a minimum, both summer and winter monsoon signals, each with different amplitudes and phases.
Clemens Stephan
Prell W.
Sun Yadong
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