Gloria Jimenez Abstracts

Gloria Jimenez Abstracts

 

Gloria Jimenez
  Ph.D. Student
  Global Change GIDP Minor

  American Geophysical Union Fall Meeting
  San Francisco, California
  December 14-18, 2015

 

Professional Abstract
Lay Audience Abstract

Changing trends and variance in eastern equatorial Pacific sea surface temperatures over the twentieth century

Abstract

Global climate models and instrumental datasets often disagree regarding sea surface temperature (SST) trends in the tropical Pacific. Coral Sr/Ca records with sub-seasonal resolution provide SST proxies that complement and extend limited instrumental records. We present a new partially replicated Sr/Ca-SST record from two Galápagos corals (Isla Wolf, at 1°24’N, 91°48’W) that spans 1937-2010. The record shows high SST variance in the region, which increases nearly twofold after the late 1970s. Similarly,  there is little trend in the mean until 1976, after which SSTs warm during all seasons. Both  the increase in variance and the trend are strongest during the warm season, leading to progressively more anomalous conditions during El Niño events.

To investigate recent changes in the eastern equatorial Pacific since the 1976/1977 climate transition, we compare the Galápagos record to a published coral Sr/Ca-SST record from Clipperton Atoll (10°18’N, 109°13’W, spanning 1874-1993; Wu et al., 2014, Palaeogeogr. Palaeoclimatol. Palaeoecol.). As in the Galápagos, Clipperton corals show increasing SSTs in all seasons after 1976. The trend at Clipperton is greater than in the Galápagos, though the variance is smaller and does not change significantly throughout the record. Finally, the north-south temperature gradient between Clipperton  and Galápagos has increased slightly over the interval in which the two records overlap (1937- 1993). Gridded instrumental SST data generally agree with the coral Sr/Ca-SST results, though the gridded data suggest lower variance at both sites. In sum, we show that an increase in the mean and variance of SSTs in the eastern equatorial Pacific is associated with an enhanced meridional SST gradient over the twentieth century, and especially since 1976. These results contrast with recent suggestions that a weakened meridional SST gradient in the equatorial Pacific may be leading to stronger El Niño events. Our results support the consensus that the 1976/1977 climate transition was a key turning point in the state of the tropical Pacific.

Abstract (for Lay Audience)

The research I will present at the American Geophysical Union (AGU) Fall Meeting aims to improve our understanding of the El Niño-Southern Oscillation (ENSO). Few natural climate phenomena impact societies and the environment as pervasively as ENSO. Defined as an alternating pattern of warm and cool sea surface temperatures (SSTs) in the tropical Pacific, ENSO gives rise to warm El Niño and cool La Niña episodes that modify global temperature and rainfall patterns. In fact, ENSO is regarded as the strongest source of global climate variability from year to year. This ubiquitous influence on climate translates to profound effects on human health, economies, and natural ecosystems.

To predict ENSO and its global effects, especially in a changing climate, we need to answer several fundamental questions. First, few observational climate records span the 20th century in the tropical Pacific, so it is difficult  to define the “normal” distribution of SSTs there. Second, scientists are still trying to determine how intense past El Niño and La Niña episodes were, how frequently they occurred, and what their SST patterns looked like. Finally, ENSO’s response to climate change is uncertain, largely because its behavior  is shifting in unprecedented ways.

The research I will present at the AGU Fall Meeting helps to address these questions. I use a coral-based dataset from the Galápagos Islands to construct a new record of twentieth century SSTs in the eastern equatorial Pacific. Both my data and a previously published record from Clipperton Atoll, northwest of the Galápagos, show that SSTs began to increase markedly after 1976. The amount of variability in the Galápagos record also increases after 1976—meaning high temperatures have become higher and lows have become lower—while variability at Clipperton does not change. Comparing the two sites suggests an enhanced north-south temperature gradient in the eastern equatorial Pacific over the twentieth century, and particularly since 1976.

These results are striking because previous work has proposed that Pacific Ocean climate underwent a major change in 1976/1977. However, my results are some of the first to document this transition in the eastern equatorial Pacific. In addition, my results represent an important addition to records of 20th century climate in the Pacific, and they will help determine the average distribution of Pacific  SSTs as well as better defining ENSO’s history. Finally, my research emphasizes changes in the eastern equatorial Pacific since 1976, which may help unravel the mechanism behind the recent shifts in ENSO’s behavior.