The South American Monsoon Variability over the Last Millennium in  CMIP5/PMIP3 simulations

Abstract. In this paper we assess South American Monsoon System (SAMS) variability throughout the Last Millennium as depicted by the Coupled Modelling Intercomparison Project version 5/Paleo Modelling Intercomparison Project version 3 (CMIP5/PMIP3) simulations. High-resolution proxy records for the South American monsoon over this period show a coherent regional picture of a weak monsoon during the Medieval Climate Anomaly period and a stronger monsoon during the Little Ice Age (LIA). Due to the small forcing during the past 1000 years, CMIP5/PMIP3 model simulations do not show very strong temperature anomalies over these two specific periods, which in turn do not translate into clear precipitation anomalies, as suggested by rainfall reconstructions in South America. However, with an ad-hoc definition of these two periods for each model simulation, several coherent large-scale atmospheric circulation anomalies were identified. The models feature a stronger Monsoon during the LIA associated with: (i) an enhancement of the rising motion in the SAMS domain in austral summer, (ii) a stronger monsoon-related upper-troposphere anticyclone, (iii) activation of the South American dipole, which results to a certain extent in a poleward shift in the South Atlantic Convergence Zone and (iv) a weaker upper-level sub tropical jet over South America, this providing important insights into the mechanisms of these climate anomalies over South America during the past millennium.

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The South American monsoon variability over the last millennium in climate models

Climate of the Past ◽

10.5194/cp-12-1681-2016 ◽

2016 ◽

Vol 12 (8) ◽

pp. 1681-1691 ◽

Cited By ~ 13

Author(s):

Maisa Rojas ◽

Paola A. Arias ◽

Valentina Flores-Aqueveque ◽

Anji Seth ◽

Mathias Vuille

Keyword(s):

South America ◽

Large Scale ◽

Model Simulation ◽

Ice Age ◽

South American ◽

Last Millennium ◽

The South ◽

Model Simulations ◽

South American Monsoon ◽

The Past

Abstract. In this paper we assess South American monsoon system (SAMS) variability in the last millennium as depicted by global coupled climate model simulations. High-resolution proxy records for the South American monsoon over this period show a coherent regional picture of a weak monsoon during the Medieval Climate Anomaly and a stronger monsoon during the Little Ice Age (LIA). Due to the small external forcing during the past 1000 years, model simulations do not show very strong temperature anomalies over these two specific periods, which in turn do not translate into clear precipitation anomalies, in contrast with the rainfall reconstructions in South America. Therefore, we used an ad hoc definition of these two periods for each model simulation in order to account for model-specific signals. Thereby, several coherent large-scale atmospheric circulation anomalies are identified. The models feature a stronger monsoon during the LIA associated with (i) an enhancement of the rising motion in the SAMS domain in austral summer; (ii) a stronger monsoon-related upper-tropospheric anticyclone; (iii) activation of the South American dipole, which results in a poleward shift of the South Atlantic Convergence Zone; and (iv) a weaker upper-level subtropical jet over South America. The diagnosed changes provide important insights into the mechanisms of these climate anomalies over South America during the past millennium.

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Late Quaternary Variations in the South American Monsoon System as Inferred by Speleothems—New Perspectives using the SISAL Database

Quaternary ◽

10.3390/quat2010006 ◽

2019 ◽

Vol 2 (1) ◽

pp. 6 ◽

Cited By ~ 10

Author(s):

Michael Deininger ◽

Brittany Marie Ward ◽

Valdir F. Novello ◽

Francisco W. Cruz

Keyword(s):

South America ◽

Late Quaternary ◽

Precipitation Amount ◽

Ice Age ◽

Convergence Zone ◽

South American ◽

The South ◽

South American Monsoon ◽

Monsoon System ◽

South American Monsoon System

Here we present an overview of speleothem δ18O records from South America, most of which are available in the Speleothem Isotopes Synthesis and Analysis (SISAL_v1) database. South American tropical and subtropical speleothem δ18O time series are primarily interpreted to reflect changes in precipitation amount, the amount effect, and consequently history of convection intensity variability of convergence zones such as the Intertropical Convergence Zone (ITCZ) and the South America Monsoon System (SAMS). We investigate past hydroclimate scenarios in South America related to the South American Monsoon System in three different time periods: Late Pleistocene, Holocene, and the last two millennia. Precession driven summertime insolation is the main driver of convective variability over the continent during the last 120 kyrs (from present day to 120 kyrs BP), including the Holocene. However, there is a dipole between speleothem δ18O records from western and eastern South America. Records located in the central region of Brazil are weakly affected by insolation-driven variability, and instead are more susceptible to the variability associated with the South Atlantic Convergence Zone (SACZ). Cold episodic events in the Northern Hemisphere, such as Heinrich and Bond Events, and the Little Ice Age, increase the convective activity of the SAMS, resulting in increased precipitation amount in South America.

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Precipitation Characteristics of the South American Monsoon System Derived from Multiple Datasets

Journal of Climate ◽

10.1175/jcli-d-11-00335.1 ◽

2012 ◽

Vol 25 (13) ◽

pp. 4600-4620 ◽

Cited By ~ 33

Author(s):

Leila M. V. Carvalho ◽

Charles Jones ◽

Adolfo N. D. Posadas ◽

Roberto Quiroz ◽

Bodo Bookhagen ◽

...

Keyword(s):

South America ◽

Large Scale ◽

Austral Summer ◽

Global Precipitation Climatology Project ◽

South American ◽

The South ◽

Frequency Distributions ◽

South American Monsoon ◽

Monsoon System ◽

South American Monsoon System

Abstract The South American monsoon system (SAMS) is the most important climatic feature in South America and is characterized by pronounced seasonality in precipitation during the austral summer. This study compares several statistical properties of daily gridded precipitation from different data (1998–2008): 1) Physical Sciences Division (PSD), Earth System Research Laboratory [1.0° and 2.5° latitude (lat)/longitude (lon)]; 2) Global Precipitation Climatology Project (GPCP; 1° lat/lon); 3) Climate Prediction Center (CPC) unified gauge (CPC-uni) (0.5° lat/lon); 4) NCEP Climate Forecast System Reanalysis (CFSR) (0.5° lat/lon); 5) NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis (0.5° lat/0.3° lon); and 6) Tropical Rainfall Measuring Mission (TRMM) 3B42 V6 data (0.25° lat/lon). The same statistical analyses are applied to data in 1) a common 2.5° lat/lon grid and 2) in the original resolutions of the datasets. All datasets consistently represent the large-scale patterns of the SAMS. The onset, demise, and duration of SAMS are consistent among PSD, GPCP, CPC-uni, and TRMM datasets, whereas CFSR and MERRA seem to have problems in capturing the correct timing of SAMS. Spectral analyses show that intraseasonal variance is somewhat similar in the six datasets. Moreover, differences in spatial patterns of mean precipitation are small among PSD, GPCP, CPC-uni, and TRMM data, while some discrepancies are found in CFSR and MERRA relative to the other datasets. Fitting of gamma frequency distributions to daily precipitation shows differences in the parameters that characterize the shape, scale, and tails of the frequency distributions. This suggests that significant uncertainties exist in the characterization of extreme precipitation, an issue that is highly important in the context of climate variability and change in South America.

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A review of the South American monsoon history as recorded in stable isotopic proxies over the past two millennia

Climate of the Past ◽

10.5194/cp-8-1309-2012 ◽

2012 ◽

Vol 8 (4) ◽

pp. 1309-1321 ◽

Cited By ~ 136

Author(s):

M. Vuille ◽

S. J. Burns ◽

B. L. Taylor ◽

F. W. Cruz ◽

B. W. Bird ◽

...

Keyword(s):

Time Scales ◽

North Atlantic ◽

Large Scale ◽

Ice Cores ◽

Ice Age ◽

South American ◽

The South ◽

The Past ◽

Se Brazil ◽

Isotopic Proxies

Abstract. We review the history of the South American summer monsoon (SASM) over the past ~2000 yr based on high-resolution stable isotope proxies from speleothems, ice cores and lake sediments. Our review is complemented by an analysis of an isotope-enabled atmospheric general circulation model (GCM) for the past 130 yr. Proxy records from the monsoon belt in the tropical Andes and SE Brazil show a very coherent behavior over the past 2 millennia with significant decadal to multidecadal variability superimposed on large excursions during three key periods: the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the current warm period (CWP). We interpret these three periods as times when the SASM's mean state was significantly weakened (MCA and CWP) and strengthened (LIA), respectively. During the LIA each of the proxy archives considered contains the most negative δ18O values recorded during the entire record length. On the other hand, the monsoon strength is currently rather weak in a 2000-yr historical perspective, rivaled only by the low intensity during the MCA. Our climatic interpretation of these archives is consistent with our isotope-based GCM analysis, which suggests that these sites are sensitive recorders of large-scale monsoon variations. We hypothesize that these centennial-scale climate anomalies were at least partially driven by temperature changes in the Northern Hemisphere and in particular over the North Atlantic, leading to a latitudinal displacement of the ITCZ and a change in monsoon intensity (amount of rainfall upstream over the Amazon Basin). This interpretation is supported by several independent records from different proxy archives and modeling studies. Although ENSO is the main forcing for δ18O variability over tropical South America on interannual time scales, our results suggest that its influence may be significantly modulated by North Atlantic climate variability on longer time scales. Finally, our analyses indicate that isotopic proxies, because of their ability to integrate climatic information on large spatial scales, could complement more traditional proxies such as tree rings or documentary evidence. Future climate reconstruction efforts could potentially benefit from including isotopic proxies as large-scale predictors in order to better constrain past changes in the atmospheric circulation.

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A review of the South American Monsoon history as recorded in stable isotopic proxies over the past two millennia

Climate of the Past Discussions ◽

10.5194/cpd-8-637-2012 ◽

2012 ◽

Vol 8 (1) ◽

pp. 637-668 ◽

Cited By ~ 6

Author(s):

M. Vuille ◽

S. J. Burns ◽

B. L. Taylor ◽

F. W. Cruz ◽

B. W. Bird ◽

...

Keyword(s):

Time Scales ◽

North Atlantic ◽

Large Scale ◽

Ice Cores ◽

Ice Age ◽

South American ◽

The South ◽

The Past ◽

Se Brazil ◽

Isotopic Proxies

Abstract. We review the history of the South American summer monsoon (SASM) over the past ~2000 yr based on high-resolution stable isotope proxies from speleothems, ice cores and lake sediments. Our review is complemented by an analysis of an isotope-enabled atmospheric General Circulation Model (GCM) for the past 130 yr. Proxy records from the monsoon belt in the tropical Andes and SE Brazil show a very coherent behavior over the past 2 millennia with significant decadal to multidecadal variability superimposed on large excursions during three key periods, the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the Current Warm Period (CWP). We interpret these three periods as times when the SASM's mean state was significantly weakened (MCA and CWP) and strengthened (LIA), respectively. During the LIA each of the proxy archives considered contains the most negative δ18O values recorded during the entire record length. On the other hand the monsoon strength is currently rather weak in a 2000-yr historical perspective, rivaled only by the low intensity during the MCA. Our climatic interpretation of these archives is consistent with our isotope-based GCM analysis, which suggests that these sites are sensitive recorders of large-scale monsoon variations. We hypothesize that these centennial-scale climate anomalies were at least partially driven by temperature changes in the Northern Hemisphere and in particular over the North Atlantic, leading to a latitudinal displacement of the ITCZ and a change in monsoon intensity over the tropical continent. This interpretation is supported by several independent proxy archives and modeling studies. Although ENSO is the main forcing for δ18O variability over tropical South America on interannual time scales, our results suggest that its influence may be significantly modulated by North Atlantic climate variability on longer time scales. Finally our analyses indicate that isotopic proxies, because of their ability to integrate climatic information on large spatial scales, could complement more traditional proxies such as tree rings or historical archives. Future climate reconstruction efforts could potentially benefit from including isotopic proxies as large-scale predictors in order to better constrain past changes in the atmospheric circulation.

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South Atlantic Surface Boundary Current System during the Last Millennium in the CESM-LME: The Medieval Climate Anomaly and Little Ice Age

Geosciences ◽

10.3390/geosciences9070299 ◽

2019 ◽

Vol 9 (7) ◽

pp. 299

Author(s):

Fernanda Marcello ◽

Ilana Wainer ◽

Peter R. Gent ◽

Bette L. Otto-Bliesner ◽

Esther C. Brady

Keyword(s):

Little Ice Age ◽

South Atlantic ◽

Subtropical Gyre ◽

Ice Age ◽

Surface Boundary ◽

South American ◽

Last Millennium ◽

Medieval Climate Anomaly ◽

The South ◽

Gyre Circulation

Interocean waters that are carried northward through South Atlantic surface boundary currents get meridionally split between two large-scale systems when meeting the South American coast at the western subtropical portion of the basin. This distribution of the zonal flow along the coast is investigated during the Last Millennium, when natural forcing was key to establish climate variability. Of particular interest are the changes between the contrasting periods of the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The investigation is conducted with the simulation results from the Community Earth System Model Last Millennium Ensemble (CESM-LME). It is found that the subtropical South Atlantic circulation pattern differs substantially between these natural climatic extremes, especially at the northern boundary of the subtropical gyre, where the westward-flowing southern branch of the South Equatorial Current (sSEC) bifurcates off the South American coast, originating the equatorward-flowing North Brazil Undercurrent (NBUC) and the poleward Brazil Current (BC). It is shown that during the MCA, a weaker anti-cyclonic subtropical gyre circulation took place (inferred from decreased southern sSEC and BC transports), while the equatorward transport of the Meridional Overturning Circulation return flow was increased (intensified northern sSEC and NBUC). The opposite scenario occurs during the LIA: a more vigorous subtropical gyre circulation with decreased northward transport.

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Projected End-of-Century Changes in the South American Monsoon in the CESM Large Ensemble

Journal of Climate ◽

10.1175/jcli-d-19-0645.1 ◽

2020 ◽

Vol 33 (18) ◽

pp. 7859-7874

Author(s):

Ana Claudia Thome Sena ◽

Gudrun Magnusdottir

Keyword(s):

South America ◽

South Atlantic ◽

Northeastern Brazil ◽

Southeastern Brazil ◽

South American ◽

The South ◽

Wet Season ◽

Large Ensemble ◽

South American Monsoon ◽

The Mean

AbstractProjected changes in the South American monsoon system by the end of the twenty-first century are analyzed using the Community Earth System Model Large Ensemble (CESM-LENS). The wet season is shorter in LENS when compared to observations, with the mean onset occurring 19 days later and the mean retreat date 21 days earlier in the season. Despite a precipitation bias, the seasonality of rainfall over South America is reproduced in LENS, as well as the main circulation features associated with the development of the South American monsoon. Both the onset and retreat of the wet season over South America are delayed in the future compared to current climate by 3 and 7 days, respectively, with a slightly longer wet season. Central and southeastern Brazil are projected to get wetter as a result of moisture convergence from the strengthening of the South Atlantic low-level jet and a weaker South Atlantic subtropical high. The Amazon is projected to get drier by the end of the century, negatively affecting rain forest productivity. During the wet season, an increase in the frequency and intensity of extreme precipitation events is found over most of South America, and especially over northeastern and southern Brazil and La Plata. Meanwhile, during the dry season an increase in the maximum number of consecutive dry days is found over northeastern Brazil and the northern Amazon.

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Floristics of the South American Páramo Moss Flora

Bryophyte Diversity and Evolution ◽

10.11646/bde.2.1.10 ◽

1990 ◽

Vol 2 (1) ◽

pp. 127-132

Author(s):

Dana Griffin III

Keyword(s):

South America ◽

Southern Hemisphere ◽

Cloud Forest ◽

South American ◽

Long Distance Dispersal ◽

The South ◽

Long Distance ◽

Late Pliocene ◽

Northern Andes ◽

The Past

The South American paramos appeared in Pliocene times and persist to the present day. The moss flora of this habitat consists of an estimated 400 species that comprise 8 floristic groups. In Venezuela these groups and their percent representation are as follows: neotropical 37%, Andean 26%, cosmopolitan 18%, Andean-African 8%, neotropical-Asiatic 3%, neotropical-Australasian 2%, temperate Southern Hemisphere 2% and northern boreal-temperate 2%. Acrocarpous taxa outnumber pleurocarps by nearly 3:1. The neotropical and Andean floristic stocks likely were present prior to late Pliocene orogenies that elevated the cordillera above climatic timberlines. These species may have existed in open, marshy areas (paramillos) or may have evolved from cloud forest ancestors. Taxa of northern boreal- temperate affinities, including those with Asiatic distributions, probably arrived in the paramos during the Pleistocene, a period which may also have seen the establishment in the Northern Andes of some cosmopolitan elements. Species with temperate Southern Hemisphere and Australasian affinities likely spread first to austral South America thence migrated northward during a cool, moist interval sometime over the past 2.5-3 million years or may have become established in the paramos as a result of long- distance dispersal.

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Daily Precipitation Statistics for South America: An Intercomparison between NCEP Reanalyses and Observations

Journal of Hydrometeorology ◽

10.1175/2010jhm1303.1 ◽

2011 ◽

Vol 12 (1) ◽

pp. 101-117 ◽

Cited By ~ 33

Author(s):

Viviane B. S. Silva ◽

Vernon E. Kousky ◽

R. Wayne Higgins

Keyword(s):

South America ◽

Large Scale ◽

Atmospheric Model ◽

Northeastern Brazil ◽

South American ◽

The South ◽

Wet Season ◽

Central Brazil ◽

Monsoon System ◽

Dry Bias

Abstract In this study, the authors document the extent to which the precipitation statistics of the new CFS reanalysis (CFSR) represent an improvement over the earlier reanalyses: the NCEP–NCAR reanalysis (R1) and the NCEP–DOE Second Atmospheric Model Intercomparison Project (AMIP-II) reanalysis (R2). An intercomparison between the CFSR, R1, R2, and observations over South America was made for the period 1979–2006. The CFSR shows notable improvements in the large-scale precipitation patterns compared with the previous reanalyses (R1 and R2). In spite of these improvements, the CFSR has substantial biases in intensity and frequency of occurrence of rainfall events. Over west-central Brazil, the core region of the South American monsoon system (SAMS), the CFSR displays a dry bias during the onset phase of the SAMS wet season and a wet bias during the peak and decay phases of the SAMS wet season. The CFSR also displays a dry bias along the South American coast near the mouth of the Amazon and along the east coast of northeastern Brazil. A wet bias exists in all seasons over southeast Brazil and over the Andes Mountains.

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Unenlagiinae revisited: dromaeosaurid theropods from South América

Anais da Academia Brasileira de Ciências ◽

10.1590/s0001-37652011000100009 ◽

2011 ◽

Vol 83 (1) ◽

pp. 163-195 ◽

Cited By ~ 22

Author(s):

Federico A. Gianechini ◽

Sebastian Apesteguia

Keyword(s):

South America ◽

South American ◽

The South ◽

Important Data ◽

The Past

Over the past two decades, the record of South American unenlagiine dromaeosaurids was substantially increased both in quantity as well as in quality of specimens. Here is presented a summary review of the South American record for these theropods.Unenlagia comahuensis, Unenlagia paynemili, and Neuquenraptor argentinus come from the Portezuelo Formation, the former genus being the most complete and with putative avian features. Neuquenraptor is more incomplete and exhibits pedal features resembling those of Unenlagia. The earliest and most complete South American dromaeosaurid is Buitreraptor gonzalezoru, whose preserved cranial remains, provides important data in the characterization of unenlagiines. The most recently described,Austroraptor cabazai also with cranial remains, allows further comparisons with Laurasian lineages and a better characterization of unenlagiines. The possible synonymy between nenlagia and Neuquenraptor is discussed. Additional evidences from Brazil and Colombia show that dinosaurs with similar dentition to that of unenlagiines were present in the whole South America. However, it is not possible to discart that these remains may belong to other unknown maniraptoran lineages, considering the increasing number of taxa of this group found in South America.

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