Precipitation linked to Atlantic moisture transport: clues to interpret Patagonian palaeoclimate

Abstract

Westerlies are the main climatic feature in the mid-latitudes of the Southern Hemisphere (SH), driving the amount and distribution of precipitation. Patagonia is a vast region in South America's mid-latitudes, which encompasses 2 sub regions with highly distinct precipitation features. These two regions include wet Western Patagonia extending from the Pacific coast to the Andean highs (i.e. maximum elevations), and dry Eastern Patagonia situated leeward of the Andes in the Argentine steppe plains. Patagonia is influenced by strong mid-latitude westerlies throughout the year. Westerlies have been considered the unique driver of climate both in Western and Eastern Pata gonia. This research is focused on the Lago Cardiel catchment area in central Eastern Patagonia. A significant link between precipitation in that region and local zonal moisture transport from the Atlantic was established. A fraction of intense precipitation was related to strong local westward moisture transport, partly as a consequence of slow-moving weather systems crossing over Patagonia. As long as a dipolar pattern of long-term precipitation anomaly was observed between dry central Western/Southern Patagonia and wet central Eastern Patagonia, it could be interpreted as due to enhanced synoptic easterly moisture flux from the Atlantic. Thus, the westerlies rule was broken at least under blocking-like flows, which induced moist easterlies. The relatively wet 1940s exemplified this phenomenon. Such a conceptual framework can be applied to palaeoclimatic proxy record reconstructions as well as to general circulation model (GCM) outcomes for the late and mid-Holocene.

Persistent easterly winds leading to precipitation in the Atlantic Coast of Patagonia

“…The previous results show straightforward evidence that strong rainfalls along the eastern coast of Patagonia can happen under stationary easterly air‐mass flows at daily scale, for which there may exist an additional contribution of moisture from the Atlantic (Agosta et al ., ). The latter is prominent for CMR, a locality in which the synoptic‐scale link between persistent easterly winds and strong precipitation occurs more than a half of the times it rains, followed by VMD.…”

Changes in ostracod assemblages and morphologies during lake‐level variations of Lago Cardiel (49°S), Patagonia, Argentina, over the last 15.6 ka

“…The humid nature of the Early Holocene suggests that the SWW were more southerly and weaker than prior to the Early Holocene, allowing more Atlantic Ocean moisture to enter the eastern parts of Patagonia (Agosta et al . ; Franco et al . ; Quade & Kaplan ).…”

“…Therefore, the mean annual precipitation, which occurs primarily during winter (May–August), is about 160 mm near Lago Cardiel and increases to a maximum of 500 mm in the western mountainous area, where the permanent Río Cardiel originates (Heinsheimer ; Agosta et al . ). The total catchment area is about 4500 km 2 but as a result of low precipitation near the modern lake, only a few small permanent and ephemeral streams originate around it (Markgraf et al .…”

“…Thus, lake‐level changes indicate variations in the evaporation/precipitation balance, which in turn can be related to regional climatic changes (Agosta et al . ). A major lake‐level rise starting during the Late Pleistocene reached an Early Holocene highstand of +55 m above present lake level.…”

“…Lago Cardiel sits in a closed basin, located in southern Patagonia (49°S) east of the Andes, and underwent substantial lake-level changes during the Quaternary (Heinsheimer 1959;Stine&Stine1990;Gilliet al2001).Extensiveseismic reflection data from the lake show that the Quaternary sediments are not disturbed by tectonic-related activity. Thus, lake-level changes indicate variations in the evaporation/precipitation balance, which in turn can be related to regional climatic changes (Agosta et al 2015). A major lake-level rise starting during the Late Pleistocene reached an Early Holocene highstand of +55 m above present lake level.…”