Central Andean Pluvial Event

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The Central Andean Pluvial Event is a two-stage climate oscillation in the Central Andes between 18,000 and 9,700 years before present. The first, wetter episode occurred 17,500-15,900 years ago; the second was drier and continued into the early Holocene (until 9,700-8,500 years ago). During this climate oscillation, Lake Tauca formed in the Altiplano and the climate became moister and more conducive to vegetation development.

The CAPE is associated with the formation of Lake Tauca in the Altiplano. During this epoch, major environmental changes occurred in the Atacama as precipitation increased between 18° and 25° degrees south. In some areas, oases formed in the desert and human settlement began.[1] The CAPE chronology is often subdivided into two phases. The first is wetter and begins in the late glacial (17,500-15,900 years ago); the second is drier and continued into the early Holocene (until 9,700-8,500 years ago). Published start and end dates vary by study.[2][3] The dry period separating them[4] coincides with the Ticaña lowstand. The second phase of the Central Andean Pluvial Event has been subdivided further into a wetter earlier and a drier later subphase.[5] During the Coipasa lake cycle, only summer precipitation increased and the increase may have focused on the southern Altiplano (arriving there from the Gran Chaco); the main Tauca cycle may have been accompanied by precipitation from the northeast and a simultaneous increase of summer and winter precipitation.[3][6] A glacial advance in the Turbio valley (a feeder of the Elqui River) between 17,000 and 12,000 years ago has been attributed to the Central Andean Pluvial Event.[7] Other indicators point to dry conditions/lack of glacier advances in central Chile and the central Puna during the highstand of Lake Tauca,[8][9] glaciers had already retreated from their maximum positions by the time it began[10] and the Central Andean Pluvial Event may not have been synchronous between the southern Altiplano and the southern[11] and northern Atacama.[12]

Many explanations link the CAPE to changes in atmospheric circulation during Heinrich event 1,[13] which would have increased moisture transport onto the Altiplano (for example via shifts in the Bolivian High[a] and the summer monsoon[15]) that increased transport of easterly moisture into the Altiplano[16] and a strengthening of the South American Summer Monsoon due to a decrease in the cross-equatorial transport of heat.[15] Earlier highstands of Altiplano lakes may also correlate to earlier Heinrich events.[17] Increased cloud cover probably increased the effective precipitation by reducing evaporation rates.[18] In contrast, insolation rates do not appear to be linked to lake-level highstands in the Altiplano;[19] the lake expansion occurred when summer insolation was low[20] although recently an insolation maximum between 26,000 and 15,000 years ago has been correlated to the Tauca stage.[21] The humidity above the lake has been estimated at 60%, taking into account the oxygen-18 content of carbonates deposited by the lake.[22] Just like the Lake Tauca highstand may have coincided with the first Heinrich event, the Younger Dryas may be associated with the Coipasa highstand,[23][24] one of the Central Andean Pluvial Events with the Antarctic Cold Reversal[25] and the second Central Andean Pluvial Event although the Younger Dryas ended two millennia before the CAPE.[26] The second CAPE was caused either by changes in the South American monsoon or by changes in the atmospheric circulation over the Pacific Ocean, and its end has been attributed to a warming North Atlantic drawing the ITCZ northward.[27]

Increased precipitation during the Tauca phase was probably triggered by the southern movement of the ITCZ and the strengthening of the South America monsoon,[28] possibly caused by chilling in the northern hemisphere[29] and North Atlantic, along with higher water temperatures off Northeastern Brazil.[30] Combined with a southern shift of high pressure zones, increased moisture during late glacial times[31] would have flowed from the Amazon.[32] This change, which occurred from 17,400 to 12,400 years or 18,000 to 11,000 BP, is recorded in Bolivian Chaco and Brazilian cave records.[33] Some 20th century phases of higher water levels in Lake Titicaca have been correlated with episodes of increased snow cover on Northern Hemisphere continents; this may constitute an analogy to conditions during the Lake Tauca phase.[34] The Tauca phase may have been triggered by the southern shift of tropical atmospheric circulation[35] and a weakening of the Atlantic meridional overturning circulation that decreased northward heat transport.[30] An intensification and southward shift of the South Atlantic Convergence Zone[b] may have contributed to the precipitation increase[37] but not all records agree.[38]

Another theory posits that vegetation changes and lake development would have decreased the albedo of the Altiplano, resulting in warming and moisture advection of moisture towards the Altiplano,[39] but such positive feedback mechanisms were considered questionable in a 1998 study.[40] Persistent La Niña climatic conditions may have contributed to the lake's filling[41][42] and also to the onset of the first CAPE.[4] Conversely, a global climatic warming and a northward shift of the monsoon occurred around 14,500 years ago,[43] increased occurrence of El Niño[44] and the northward shift of the ITCZ accompanied the Ticaña lowstand.[45] The ideal conditions for the development of paleolakes in the Altiplano do not appear to exist during maximum glaciation or warm interglacial periods.[46]

Climate and context

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