Galápagos hydroclimate of the Common Era from paired microalgal and mangrove biomarker ² H/ ¹ H values

Abstract

Tropical maritime precipitation affects global atmospheric circulation, influencing storm tracks and the size and location of subtropical deserts. Paleoclimate evidence suggests centuries-long changes in rainfall in the tropical Pacific over the past 2,000 y, but these remain poorly characterized across most of the ocean where long, continuous proxy records capable of resolving decadal-to-centennial climate changes are still virtually nonexistent despite substantial efforts to develop them. Here we apply a new climate proxy based on paired hydrogen isotope ratios from microalgal and mangrove-derived sedimentary lipids in the Galápagos to reconstruct maritime precipitation changes during the Common Era. We show that increased rainfall during the Little Ice Age (LIA) (∼1400-1850 CE) was likely caused by a southward migration of the Intertropical Convergence Zone (ITCZ), and that this shift occurred later than previously recognized, coeval with dynamically linked precipitation changes in South America and the western tropical Pacific. Before the LIA, we show that drier conditions at the onset of the Medieval Warm Period (∼800-1300 CE) and wetter conditions ca. 2 ka were caused by changes in the El Niño/ Southern Oscillation (ENSO). Collectively, the large natural variations in tropical rainfall we detect, each linked to a multicentury perturbation of either ENSO-like variability or the ITCZ, imply a high sensitivity of tropical Pacific rainfall to climate forcings.paleoclimate | hydrogen isotopes | tropical Pacific | ENSO | ITCZ

Seasonal and ENSO Influences on the Stable Isotopic Composition of Galápagos Precipitation

“…Recent efforts to constrain past hydroclimate using proxies for the stable isotopic composition of meteoric waters in the Galápagos focus on an ENSO and ITCZ‐driven amount effect signal (Atwood & Sachs, ; Nelson and Sachs, ; Zhang et al, ). One appeal of proxy records of the stable isotopic composition of precipitation, relative to other types of proxies for rainfall intensity and El Niño in the region, is that they should capture a range of variability, including periods of high and low precipitation.…”

“…In the eastern equatorial Pacific (EEP), several studies have provided the foundation for evaluating the history of ENSO throughout the Holocene and last glacial period using δ 18 O values from corals or mollusks (Carré et al, ; Dunbar et al, ), marine foraminiferal assemblages and δ 18 O values (Koutavas et al, ; Koutavas et al, ; Koutavas et al, ; Lea et al, ; Loubere et al, ), and other lacustrine mineralogical, sedimentological, and biological analyses (Conroy et al, ; Conroy et al, ; Moy et al, ; Riedinger et al, ). More recent Galápagos lacustrine sediment records of biomarker hydrogen isotope ratios derived from aquatic algae, cyanobacteria, and dinoflagellates have provided information on the nature of past Galápagos precipitation (Atwood & Sachs, ; Nelson and Sachs, ; Sachs et al, ; Zhang et al, ). Such records are interpreted to reflect past rainfall amount partly due to the well‐known manifestation of the isotopic “amount effect”: the inverse correlation between precipitation amount and the ratio of heavy to light oxygen and hydrogen isotopes in tropical precipitation (Dansgaard, ; Rozanski et al, ).…”

Southward Shift of the Pacific ITCZ During the Holocene

“…Lipids were purified and quantified following procedures detailed in Nelson and Sachs (, , ). Briefly, sediment subsamples (1 cm‐thick) were removed from split cores or from field‐sectioned material and transferred to combusted glass vials, frozen, then freeze dried.…”

Lipid compound classes display diverging hydrogen isotope responses in lakes along a nutrient gradient

“…as the side-chain in cyanobacterial glycolipids (Sinninghe Damsté et al, 2001;660! Castañeda and Schouten, 2011;Nelson and Sachs, 2016), but are also produced by 661! zooplankton (Sargent et al, 1977;Pearson et al, 2001).…”