Open AccessOceanographic variability in the South Pacific Convergence Zone region over the last 210 years from multi‐site coral Sr/Ca records
Author(s) -
Wu Henry C.,
Linsley Braddock K.,
Dassié Emilie P.,
Schiraldi Benedetto,
deMenocal Peter B.
Publication year - 2013
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2012gc004293
Subject(s) - western hemisphere warm pool , geology , sea surface temperature , oceanography , pacific decadal oscillation , advection , coral , salinity , climatology , physics , thermodynamics
In the South Pacific Convergence Zone (SPCZ), the variability in a sub‐seasonally resolved microatoll Porites colony Sr/Ca record from Tonga and a previously published high‐resolution record from Fiji are strongly influenced by sea surface temperature (SST) over the calibration period from 1981 to 2004 ( R 2 = 0.67–0.68). However, the Sr/Ca‐derived SST correlation to instrumental SST decreases back in time. The lower frequency secular trend (~1°C) and decadal‐scale (~2–3°C) modes in Sr/Ca‐derived SST are almost two times larger than that observed in instrumental SST. The coral Sr/Ca records suggest that local effects on SST generate larger amplitude variability than gridded SST products indicate. Reconstructed δ 18 O of seawater ( δ 18 O sw ) at these sites correlate with instrumental sea surface salinity (SSS; r = 0.64–0.67) but not local precipitation ( r = −0.10 to −0.22) demonstrating that the advection and mixing of different salinity water masses may be the predominant control on δ 18 O sw in this region. The Sr/Ca records indicate SST warming over the last 100 years and appears to be related to the expansion of the western Pacific warm pool (WPWP) including an increasing rate of expansion in the last ~20 years. The reconstructed δ 18 O sw over the last 100 years also shows surface water freshening across the SPCZ. The warming and freshening of the surface ocean in our study area suggests that the SPCZ has been shifting (expanding) southeast, possibly related to the southward shift and intensification of the South Pacific gyre over the last 50 years in response to strengthened westerly winds.