Variations in the South Atlantic Convergence Zone over the mid-to-late Holocene inferred from speleothem δ18O in central Brazil

Long‐and short‐term vegetation change and inferred climate dynamics and anthropogenic activity in the central Cerrado during the Holocene

“…At Lake Feia, regular sedimentation and the establishment of the Cerrado started around 6000 cal a bp , suggesting regular regional precipitation. Rainfall stability has also been reported at 7000 a bp in south‐eastern Brazil (27°S, 49°W) (Bernal et al , 2016), at 6800 a bp in central Brazil (13°S, 46°W) (Wong et al , 2021) and since the mid‐Holocene in northern Brazil (4°S, 55°W) (Wang et al , 2017), as a response to the increase in insolation (Deininger et al , 2019). However, regional differences in the expression of drivers have also been observed, such as the strengthening of the SASM system in the south, which increased rainfall, while in the north the increased rainfall was not directly linked to the SASM but driven by humid convection from the eastern Amazonia (Wong et al , 2021).…”

“…The percentages of terrestrial and water level‐related taxa, normalized Ti/K ratios, charcoal influxes (CHARarea) and L:W ratio (Vachula et al , 2021) are indicated. The speleothem records come from southern (Botuverá cave; Bernal et al , 2016), northern (Paraiso cave; Wang et al , 2017) and central (Angelica cave; Wong et al , 2021, Wortham et al , 2017) Brazil, with an insolation curve at 15°S (Laskar et al , 2011). The blue dotted line shows the main vegetation observed in the central Cerrado; the gray bands represent dry intervals.…”

“…Speleothem records in central Brazil (Fig. 4) show apparently stable climatic conditions during the last 6000 years (Deininger et al , 2019; Wong et al , 2021), compared with southern and northern regions of Brazil at the margins of the monsoon domain, where the establishment of a SW–NE dipole (Novello et al , 2012 and 2019; Deininger et al , 2019) led to abrupt changes in the extent of the monsoon and consequently in seasonality and precipitation (Campos et al , 2019). At Lake Feia, regular sedimentation and the establishment of the Cerrado started around 6000 cal a bp , suggesting regular regional precipitation.…”

“…During the early and mid‐Holocene, the presence of a precipitation dipole between NEB and SEB in response to northern/southern hemisphere summer insolation was characterized by longer wet and dry seasons, respectively (Cruz et al , 2009). However, speleothem records have also revealed that the central Cerrado underwent numerous fluctuations in wet and dry episodes between 11 000 and 4000 cal a bp (Ward et al , 2019; Azevedo et al , 2021, Wong et al , 2021), with longer wetter episodes in the last 4000 cal a bp (Strikis et al , 2011; Campos et al , 2019), implying both regional and local influences on seasonality. Paleoecologic studies of the Cerrado are rare and discontinuous in space and time.…”

The Changing Amazon Hydrological Cycle—Inferences From Over 200 Years of Tree‐Ring Oxygen Isotope Data

“…Proxy climate data, such as oxygen isotope ratios (δ 18 O), can potentially provide some insight on past hydrological variation (Vuille et al., 2012). For example, there have been a growing number of speleothem δ 18 O records from the Amazon in recent years (Kanner et al., 2013; Moquet et al., 2016; Novello et al., 2016; Wang et al., 2017; Ward et al., 2019; Wong et al., 2021), though these often have low replication and highly variable temporal resolution (e.g., <1–150 years). Therefore, there is a need to identify other tropical proxies that can provide a reliable record of on‐going change, as well as helping to improve our understanding of past hydrological cycle variation.…”