Sea-surface temperature records of Termination 1 in the Gulf of California: challenges for seasonal and inter-annual analogues of tropical Pacific climate change

Abstract

Centennial-scale records of sea-surface temperature and opal composition spanning the Last Glacial Maximum and Termination 1 (c. 25 – 6 ka) are presented here from Guaymas Basin in the Gulf of California. Through the application of two organic geochemistry proxies, the UK37' index and the TEXH86 index, we present evidence for rapid, stepped changes in temperatures during deglaciation. These occur in both temperature proxies at 13 ka (~3ºC increase in 270 yr), 10.0 ka (~2ºC decrease over ~250 yr) and at 8.2 ka (3ºC increase in <200 yr). An additional rapid warming step is also observed in TEXH86 at 11.5 ka. In comparing the two temperature proxies and opal content, we consider the potential for upwelling intensity to be recorded and link this millennial-scale variability to shifting inter-tropical convergence zone (ITCZ) position and variations in the strength of the Subtropical High. The onset of the deglacial warming from 17-18 ka is comparable to a “southern hemisphere” signal, although the opal record mimics the ice-rafting events of the north Atlantic (Heinrich events). Neither the modern seasonal cycle nor El Niño/Southern Oscillation (ENSO) patterns provide valid analogues for the trends we observe in comparison with other regional records. Fully-coupled climate model simulations confirm this result, and in combination we question whether the seasonal or inter-annual climate variations of the modern climate are valid analogues for the glacial and deglacial tropical Pacific.