Tracking the extent of the South Pacific Convergence Zone since the early 1600s

Abstract

[1] The South Pacific Convergence Zone (SPCZ) is the largest and most persistent spur of the Intertropical Convergence Zone. At the southeastern edge of the SPCZ near 170°W and 15°-20°S a surface ocean salinity frontal zone exists that separates fresher Western Pacific Warm Pool water from saltier and cooler waters in the east. This salinity front is known to shift east and west with the phase of the El Niño Southern Oscillation. We have generated subannually resolved and replicated coral oxygen isotopic time series from Fiji (17°S, 179°E) and Rarotonga (21.5°S, 160°W) that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front, and eastern extent of the SPCZ, has shifted east-west through 10°to 20°of longitude three times during this interval. The most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites. Our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the SPCZ since the mid 1800s. The expansion of the SPCZ implies a gradual change in the South Pacific to more La Niña-like long-term mean conditions. This observation is consistent with the ocean thermostat mechanism for the Pacific coupled ocean-atmosphere system, whereby exogenous heating of the atmosphere would result in greater warming in the western Pacific and a greater east-west surface temperature gradient.

Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1

“…Our estimates of a reduction in mean SST by 3.5 °C relative to today, using our seasonal Tahiti coral Sr/Ca-SST relationship or by only 2.4 °C, using a possibly more suitable relationship for mean Indo-Pacific SST changes 32 , however, have relatively large uncertainties. As commonly observed at various locations 27,28,33 , between-colony offsets in mean Sr/Ca are evident among the modern Tahiti corals (Supplementary Methods and Supplementary Fig. S9).…”

“…S9). The Sr/Ca ratios in coral skeletons are an established proxy for SST variability 10,11,[25][26][27][28] . Here we present a monthly resolved Sr/Ca-based SST reconstruction for a time window of 22 years generated from our HS1 coral (Fig.…”

Indian Ocean Dipole index recorded in Kenyan coral annual density bands

“…The coral d 18 O range of 0.8% is close to that expected for annual SST cycle of 4°C, and thus we assume that coral d 18 O signal is mainly modulated by SST [Linsley et al, 2006], with additional effect of water d 18 O determined by a balance between precipitation and evaporation [Iijima et al, 2005] or by river discharge [Gagan et al, 1998]. As we assign the heavy and light peaks of d 18 O to the lowest and highest SST peaks (August and April), low-and high-density bands correspond to low and high SST seasons, respectively, which matches with the previous studies [Lough and Barnes, 1997].…”

Spatial linkages between coral proxies of terrestrial runoff across a large embayment in Madagascar

“…However, recently published coral Sr / Ca records covering the past hundreds of years indicate specific problems with the Sr / Ca thermometer, particularly on decadal to secular time scales (e.g. Linsley et al, 2004Linsley et al, , 2006Quinn et al 2006). Pfeiffer et al (2009) showed that the intrinsic variance of the singlecore Sr / Ca time series differs from core to core, limiting their use for absolute estimates of past temperature variations.…”