In:
Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 99, No. C5 ( 1994-05-15), p. 9977-9994
Abstract:
Seasonal movements of the Intertropical Convergence Zone (ITCZ) control precipitation patterns and cloud cover throughout the tropics. In this study we have reconstructed seasonal and interannual variability of the eastern Pacific ITCZ from 1984 to 1707 using subseasonal δ 18 O analyses on a massive coral from Secas Island (7°59′N, 82°3′W) in the Gulf of Chiriquí, Panamá. The land area that drains into the Gulf of Chiriquí has served to amplify the rainfall effect on nearshore surface waters and coral δ 18 O composition. During the protracted wet season in Panamá, the δ 18 O of precipitation (δ 18 O ppt ) is reduced on average by 10‰ and sea surface salinity (SSS) along the western coast is reduced up to 11‰. Calibration of the coral δ 18 O from Secas Island against instrumental sea surface temperature (SST), SSS, precipitation and δ 18 O ppt data indicate that seasonal rainfall induced variations in seawater δ 18 O are responsible for ∼80% of the annual δ 18 O variance. Past El Niño‐Southern Oscillation (ENSO) events are recorded as minor 0.2 to 0.4‰ δ 18 O changes superimposed on the dominant annual δ 18 O seawater and salinity variations. The annual cycle in coral δ 18 O (average 0.9‰) accounts for the largest component of variance at 51% and is the direct result of the annual northward expansion of the eastern Pacific ITCZ. The regularity of the reconstructed seasonal ITCZ cycle indicates that over the length of the record the zone of maximum rainfall in the eastern Pacific has always expanded north to at least Panamá in every northern hemisphere summer. Significant interannual and interdecadal δ 18 O oscillations occur at average periods near 9, 3–7 (ENSO band), 17 and 33 years (listed in order of decreasing variance). Over the past 20 years similar decadal shifts are apparent in coral δ 18 O from nearshore in the Gulf of Panamá. SST data spanning the last 40 years show no decadal changes. This indicates that decadal oscillations in the Gulf of Chiriquí δ 18 O record are regional features not related to SST changes, but are caused by ITCZ precipitation effects on the δ 18 O of seawater. A 9‐year period in Panamá precipitation supports this conclusion and provides a potential link between interannual coral δ 18 O variations and ITCZ precipitation. It is also shown that the period of the average 9‐year interannual period in coral δ 18 O varies from ∼7.5 years to ∼11.8 years. Variance near 11 years is strongest throughout the 1800s, however, a poor direct correlation with sunspot number and solar irradiance leaves the origin of this interannual oscillation in question. The δ 18 O time series also contains a long‐term trend of −0.40‰ suggesting an increase in precipitation and/or SST since the early 1800s. As the Gulf of Chiriquí coral δ 18 O time series is the first paleoclimatic record of past variations in the ITCZ, other seasonal‐resolution reconstructions of the past behavior of the ITCZ are required to test whether the interannual and long‐term variability observed in the eastern Pacific ITCZ is more than regional in scale.
Type of Medium:
Online Resource
ISSN:
0148-0227
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1994
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