A coral-based reconstruction of sea surface salinity at Sabine Bank, Vanuatu from 1842 to 2007 CE

Abstract

Climate variability associated with the El Niño Southern Oscillation (ENSO) results in large sea-surface temperature (SST) and sea-surface salinity (SSS) anomalies in many regions of the tropical Pacific Ocean. We investigate interannual changes in SSS driven by ENSO in the southwestern Pacific at Sabine Bank, Vanuatu (SBV, 166.04°E, 15.94°S) using monthly variations in coral δ 18 O from 1842 to 2007 CE. We develop and apply a coral δ 18 O-SSS transfer function, which is assessed using a calibration-verification exercise (1970-2007 CE). The 165-year reconstructed SSS record contains a prominent trend toward freshening from 1842 to 2007 CE; mean SSS for 1842-1872 CE is 35.46 ± 0.28 psu, which contrasts with a mean value of 34.85 ± 0.31 psu for 1977-2007 CE, with a freshening trend during the latter part of the 20th century that is not unprecedented with respect to the overall record. Variance in the record is concentrated in the interannual (42%) and interdecadal (29%) bands. The SBV-SSS record matches well with a similarly reconstructed SSS time series at Malo Channel, Vanuatu, which is located ∼120 km to the east of SBV. This regional signal is likely driven by ENSO-related changes in the SPCZ and interdecadal changes in surface water advection. The pattern of interdecadal variability at SBV agrees reasonably well with coral records of interdecadal variability from Fiji and Tonga, especially in the pre-1940 portions of the records, further evidence for the regional extent of the salinity signal at Sabine Bank, Vanuatu. © 2012. American Geophysical Union. All Rights Reserved.