Holocene land–sea climatic links on the equatorial Pacific coast (Bay of Guayaquil, Ecuador)

Abstract

Abstract:We analyzed the pollen content of a marine core located near the bay of Guayaquil in Ecuador to document the link between sea surface temperatures (SST) and changes in rainfall regimes on the adjacent continent during the Holocene. Based on the expansion/regression of five vegetation types, we observe three successive climatic patterns. In the first phase, between 11,700 and 7700 cal yr BP, the presence of a cloud (Andean) forest in the mid altitudes and mangroves in the estuary of the Guayas Basin, were associated with a maximum in boreal summer insolation, a northernmost position of the Intertropical Convergence Zone (ITCZ), a land-sea thermal contrast, and dryness. Between 7700 and 2850 cal yr BP, the expansion of the coastal herbs and the regression of the mangrove indicate a drier climate with weak ITCZ and low ENSO variability while austral winter insolation gradually increased. The interval between 4200 and 2850 cal yr BP was marked by the coolest and driest climatic conditions of the Holocene due to the weak influence of the ITCZ and a strengthening of the Humboldt Current. After 2850 cal yr BP, high variability and amplitude of the Andean forest changes occurred when ENSO frequency and amplitude increased, indicating high variability in land-sea connections. The ITCZ reached the latitude of Guayaquil only after 2500 cal yr BP inducing the bimodal precipitation regime we observe today. Our study shows that besides insolation, the ITCZ position and ENSO frequency, changes in eastern equatorial Pacific SSTs play a major role in determining the composition of the ecosystems and the hydrological cycle of the Ecuadorian Pacific coast and the Western Cordillera in Ecuador. We analyzed the pollen content of a marine core located near the bay of Guayaquil in Ecuador to document the link 30

Pollen from the Deep-Sea: A Breakthrough in the Mystery of the Ice Ages

“…We have performed a literature survey to compile pollen records from deep-sea cores spanning the last 1 million years, finding 129 sites all over the world ( Supplementary Table S1 and Figure 4 ). This compilation shows that there are 74 high-resolution pollen sequences (better than 1000 years between adjacent samples) and highlights the paucity of pollen records from the Indian (e.g., Rossignol-Strick, 1983 ) and the South Pacific (e.g., Montade et al, 2013 ; Seillès et al, 2016 ) Oceans. Likewise, almost half of the records ( n = 57) do not cover periods older than the Last Glacial Maximum, and few sequences ( n = 19) record several orbital climatic cycles.…”

Late Quaternary environmental dynamics in the Atacama Desert reconstructed from rodent midden pollen records

“…A decrease in Southern Hemisphere insolation during the mid‐Holocene drives coupled ocean–atmosphere simulations to minimum values at subtropical latitudes during the austral summer, which result in a northward position of the ITCZ at millennial timescales (Braconnot et al ., ). Multiple evidence from the equatorial Pacific Ocean (Reimi and Marcantonio, ; Seillès et al ., ), the Cariaco Basin (Haug et al ., ) and the Amazonian basins (Wang et al ., ) lends further support to a northwardly displaced ITCZ during the early Holocene (∼9 ka), which would have reached its position furthest north during the mid‐Holocene (∼7 ka). As a consequence, a weakened tropical rainfall system together with a northward shift of the mid‐level westerly flow and more frequent cold surges in summer and autumn at 20°S (Vuille and Keimig, ) could be one of the mechanisms that led to the mid‐Holocene dry conditions in the Central Andes and adjacent Atacama Desert.…”

Enhanced mercury deposition by Amazonian orographic precipitation: Evidence from high-elevation Holocene records of the Lake Titicaca region (Bolivia)

“…Hence, as observed in lakes of the Altiplano, precipitation fluctuations in the eastern Andean cordillera occurred in phase with North Atlantic cold climate events during the late Holocene (Baker and Fritz, 2015;Baker et al, 2009Baker et al, , 2005Bond et al, 2001;Vuille et al, 2012). The resulting SASM intensification related to a southward displacement of the Intertropical Convergence Zone (ITCZ) likely acted as the main driver for summer moisture (Haug et al, 2001;Seillès et al, 2016). Over the middle Holocene, precipitations are unlikely to be simply related to the same mechanism.…”

“…Such anomalously strong northeasterly trades could bring about increased precipitation in the southern tropics of South America, including much of the Amazon and tropical Andes (Baker et al, 2009). Ocean-atmosphere-vegetation coupled models (Braconnot et al, 2007a(Braconnot et al, , 2007b and palaeodata syntheses (Prado et al, 2013a(Prado et al, , 2013b have also established that changes in tropical Atlantic SST gradient and in summer insolation weakened the SAMS circulation over the South Atlantic Convergence Zone area during the Middle Holocene compared to the Late Holocene (Seillès et al, 2016).…”