An alluvial record of El Niño events from northern coastal Peru

Abstract

Overbank flood deposits of northern coastal Peru provide the potential for the development of a late Quaternary chronology of El Niño events. Alluvial deposits from the 1982–1983 El Niño event are the basis for establishing a type El Niño deposit. Sedimentary structures suggesting depositional processes range from sheet flows to debris flows, with sheet flood deposits being the most common. The 1982–1983 deposits are characterized by a 50‐ to 100‐cm‐ thick basal gravel, overlain by a 10‐ to 100‐cm‐thick sand bed, grading into a 1‐ to 10‐cm‐thick silty sand bed and capped by a very thin layer of silt or clay. The surface of the deposit commonly displays the original shear flow lines crosscut by postdepositional mud cracks and footprints (human and animal). Stacked sequences of flood deposits are present in Pleistocene and Holocene alluvial fill, suggesting that El Niño type events likely occurred throughout the late Quaternary. A relative chronology of the deposits is developed based on terrace and soil stratigraphy and on the degree of preservation of surficial features. A minimum of 15 El Niño events occurred during the Holocene; a minimum of 21 events occurred during the late Pleistocene. Timing of the Holocene events is bracketed by isochrons derived from the archaeologic stratigraphy. Corrected radiocarbon ages from included detrital wood provide the following absolute dates for El Niño events: 1720 ± 60 A.D., 1460 ± 20 A.D., 1380 ± 140 A.D. (error overlaps with the A.D. 1460 event; these may represent a single event), and 1230 ± 60 B.C.

ENSO impact on hydrology in Peru

“…-It can be clearly observed that during SEN years, there are sharp increases in the river discharges in the northern part of the PC, as previously reported in the literature (Waylen and Caviedes, 1986;Wells, 1987;Waylen and Poveda, 2002 and others). Here we show that such relationship between river discharge and ENSO is altered during MEN years; in particular, the discharges are reduced (negative anomalies) during MEN years in the southern part of the PC, the TL and AM being these anomalies, similar to MEN years in the southern PC and in the southern TL (Ilave River) during El Niño years.…”

Late Quaternary hydroclimatology of a hyper-arid Andean watershed: Climate change, floods, and hydrologic responses to the El Niño-Southern Oscillation in the Atacama Desert

“…1000 AD (Rice, 1993) but was abandoned following the catastrophic Miraflores flood of ca. 1330 AD, which has been documented throughout the Atacama Desert and the Pacific (Nunn, 2000;Kumar et al, 2006), with specifically catastrophic effects on certain coastal Chiribaya settlement sites (Wells, 1987(Wells, , 1990Magilligan and Goldstein, 2001;Keefer et al, 2003). This 9.8 m high terrace consists almost entirely of well rounded, large flood-derived boulders (Fig.…”

“…Despite the extensive literature on climatic and atmospheric circulation patterns, minimal focus exists on developing long-term flood chronologies across the Atacama Desert. Most of the previous work on paleofloods comes from Peruvian coastal regions (Wells, 1987(Wells, , 1990Keefer et al, 1998;Fontugne et al, 1999;Sandweiss et al, 2001;Keefer et al, 2003;deFrance and Keefer, 2005) with Andean proximal watersheds receiving far less attention, except for high elevation watersheds in Ecuador or Bolivia (Rodbell et al, 1999;Maas et al, 2001). These inland locations are perfectly situated to capture ENSO signals: the mainstem hydrology of the larger watersheds is broadly controlled by both El Niños and La Niñas and are, thus, sensitive indicators of the spatial variation of the occurrence of these two extreme circulation types.…”

Southern Hemisphere climate scenarios

“…Contrary evidence as to the behaviour of ENSO is found, however, in the eastern equatorial Pacific (Quinn, 1971;Colinvaux, 1972), while the fragmentary evidence extending back through the Little Ice Age (Quinn et al, 1987;Michaelson, 1989) tends to suggest that E1 Nifio statistics are stationary at least within the limited parameter range of climate changes that have occurred within the last several hundred years (Enfield, 1988). There is, indeed, sedimentary evidence that E1 Nifio events occurred during the last glaciation (Wells, 1987). It may well be, then, that the best guess at present for the state of the ENSO phenomenon under warmer Earth conditions is that it will continue to occur quasiperiodically, as it does today.…”