The Holocene history of the North American Monsoon: ‘known knowns’ and ‘known unknowns’ in understanding its spatial and temporal complexity

Abstract

Evidence for climatic change across the North American Monsoon (NAM) and adjacent areas is reviewed, drawing on continental and marine records and the application of climate models.Patterns of change at 12,000, 9000, 6000 and 4000 cal yr BP are presented to capture the nature of change from the Younger Dryas (YD) and through the mid-Holocene. At the YD, conditions were cooler overall, wetter in the north and drier in the south, while moving into the Holocene

8000 years of North Atlantic storminess reconstructed from a Scottish peat record: implications for Holocene atmospheric circulation patterns in Western Europe

“…Further afield, in continental North America and Mexico declining monsoon strength is recorded in several geographically diverse proxies from c . 4200 to 3500 cal a BP (Booth et al , ; Metcalfe et al , ). This is also coincident with the marked southerly migration of the Intertropical Convergence Zone ( c .…”

Latitudinal gradients in tree ring stable carbon and oxygen isotopes reveal differential climate influences of the North American Monsoon System

“…The NAMS is initiated in late spring following heating of the Sierra Madre Occidental and Mexican Plateau [Douglas et al, 1993;Higgins et al, 1997]. Continental heating in these regions creates a sea-land pressure gradient that facilitates the inland movement of low-altitude atmospheric moisture from the eastern tropical Pacific and Gulf of California with an additional source from the Gulf of Mexico in a high-altitude atmospheric circulation [Higgins et al, 1997;Wright et al, 2001;Adams et al, 2014;Metcalfe et al, 2015]. As the Northern Hemisphere summer develops, NAMS rainfall progresses northward in the form of frequent afternoon and evening convective storms.…”

Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka

“…8A–F). There are also similarities between our data and regional reconstructions from neighbouring sites like the southwestern United States and northwestern Mexico, including the deserts of Chihuahua, Mojave and Sonora (Antinao et al ., 2016; Metcalfe et al ., 2015; Quiroz‐Jiménez et al ., 2018; Roy et al ., 2010). During the glacial period, between 28 and 18 ka, summer insolation was at its lowest (Laskar et al ., 2004), the sea level was ~120 m below the present (Bintanja et al ., 2005), and the Intertropical Convergence Zone (ITCZ) was in a southern position (Peterson et al ., 2000) (Fig.…”

“…The entrance of wind‐derived sediment in Bahía Kino (northwestern Mexico) at 6 ka is comparable to the removal of pine forests in the Sierra Madre Occidental coastal region, as the sea level continued to rise (Quiroz‐Jiménez et al ., 2018; Roy et al ., 2010). Current dry conditions could have been established when the scrub vegetation settled in the Sonora desert (Metcalfe et al ., 2015). During the Holocene, even during periods of coarse sediment discharge and flash floods, the sea level and the wide shelf from the western GC (i.e.…”

“…Seasonal warming links the summertime circulation to the North American Monsoon (NAM) intensification, causing intense precipitation (Erfani & Mitchell, 2014). Besides tropical storms and hurricanes, the NAM provides ~50% of the annual rainfall to this arid region, but studies show that it varies over time (Bhattacharya et al ., 2018; Erfani & Mitchell, 2014; Metcalfe et al ., 2015; Mitchell et al ., 2002). Seasonal winds are controlled by the effect of the mountain ranges and changes in the atmospheric pressure cells (Fig.…”