South American climatic response to changes in the tropical South Atlantic Ocean hydrography during Termination 1

Rapid climatic reorganizations during the last Termination (i.e. Heinrich Stadials 0-1) had major impacts on the Atlantic Meridional Overturning Circulation (AMOC) strength and on global atmospheric circulation patterns. However, if and how this high-latitude forcing affected low-latitude climate variability is still poorly constrained. Here we present a high-resolution multi-proxy record from marine sediment core M125-3-35 recovered in the western tropical South Atlantic combining foraminiferal Mg/Ca, Ba/Ca ratios, stable oxygen isotope measurements and organic biomarker-based sea surface temperature (SST) proxies (TEX86 and UK&#8217;37). The near-shore core position of M125-3-35 off the Para&#237;ba do Sul river mouth in southeastern Brazil and the means of foraminiferal Ba/Ca ratios, which depends on the quantity of continental freshwater input, enables us to investigate direct coupling of continental hydroclimate and oceanographic changes.The data show a complex interplay of oceanic and atmospheric forcing dominating the tropical South American climate, which is mainly controlled by the strength and position of the Intertropical Convergence Zone (ITCZ) and South Atlantic Convergence Zone (SACZ). During times of weakest AMOC in Heinrich Stadial 1 (HS1) , a distinct SST peak in the tropical South Atlantic points to an enhanced Brazil Current and strong recirculation of heat within the southern hemisphere. Further, wet conditions prevailed during this time in tropical South America caused by a maximum southward shift of the ITCZ. This happened in coincidence with a temperature drop and weakening of the North Brazil Current (NBC) in the tropical North Atlantic (Bahr et al., 2018) as result of maximum AMOC slowdown. Therefore, for the first time, we reveal a clear seesaw-like pattern of the NBC and BC during times of abrupt AMOC variability.While HS1 is generally characterized by a warm and wet anomaly in our record, Ba/Ca ratios and SST show a distinct centennial-scale alternation between warmer (colder) and wetter (drier) phases indicating a distinct climate instability during this climatic phase. A distinct offset exists between SST reconstructed using Mg/Ca, TEX86, and UK&#8217;37 which points to strong seasonal differences in the oceanographic settings and/or changes in the terrestrial input from the south American continent. These findings illustrate the strong sensitivity of hydroclimate variability in tropical South America to oceanic forcing as expected also during future climate change, in line with recent studies that showed a severe impact on modern South American climate by changes in (tropical) South Atlantic SSTs (Rodrigues et al., 2019, Utida et al., 2018).&#160;Bahr, A., Hoffmann, J., Sch&#246;nfeld, J., Schmidt, M. W., N&#252;rnberg, D., Batenburg, S. J., & Voigt, S. (2018). Low-latitude expressions of high-latitude forcing during Heinrich Stadial 1 and the Younger Dryas in northern South America. Global and Planetary Change, 160, 1-9.Rodrigues, R. R., Taschetto, A. S., Gupta, A. S., & Foltz, G. R. (2019). Common cause for severe droughts in South America and marine heatwaves in the South Atlantic. Nature Geoscience, 12(8), 620-626.UTIDA, Giselle, et al. Tropical South Atlantic influence on Northeastern Brazil precipitation and ITCZ displacement during the past 2300 years. Scientific reports, 2019, 9. Jg., Nr. 1, S. 1698.

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The impact of the subtropical South Atlantic SST on South American precipitation

Annales Geophysicae ◽

10.5194/angeo-26-3457-2008 ◽

2008 ◽

Vol 26 (11) ◽

pp. 3457-3476 ◽

Cited By ~ 24

Author(s):

A. S. Taschetto ◽

I. Wainer

Keyword(s):

South America ◽

Southern Oscillation ◽

South Atlantic ◽

Empirical Orthogonal Functions ◽

Convergence Zone ◽

South American ◽

The South ◽

Inter Tropical Convergence Zone ◽

The Impact ◽

Sst Anomalies

Abstract. The Community Climate Model (CCM3) from the National Center for Atmospheric Research (NCAR) is used to investigate the effect of the South Atlantic sea surface temperature (SST) anomalies on interannual to decadal variability of South American precipitation. Two ensembles composed of multidecadal simulations forced with monthly SST data from the Hadley Centre for the period 1949 to 2001 are analysed. A statistical treatment based on signal-to-noise ratio and Empirical Orthogonal Functions (EOF) is applied to the ensembles in order to reduce the internal variability among the integrations. The ensemble treatment shows a spatial and temporal dependence of reproducibility. High degree of reproducibility is found in the tropics while the extratropics is apparently less reproducible. Austral autumn (MAM) and spring (SON) precipitation appears to be more reproducible over the South America-South Atlantic region than the summer (DJF) and winter (JJA) rainfall. While the Inter-tropical Convergence Zone (ITCZ) region is dominated by external variance, the South Atlantic Convergence Zone (SACZ) over South America is predominantly determined by internal variance, which makes it a difficult phenomenon to predict. Alternatively, the SACZ over western South Atlantic appears to be more sensitive to the subtropical SST anomalies than over the continent. An attempt is made to separate the atmospheric response forced by the South Atlantic SST anomalies from that associated with the El Niño – Southern Oscillation (ENSO). Results show that both the South Atlantic and Pacific SSTs modulate the intensity and position of the SACZ during DJF. Particularly, the subtropical South Atlantic SSTs are more important than ENSO in determining the position of the SACZ over the southeast Brazilian coast during DJF. On the other hand, the ENSO signal seems to influence the intensity of the SACZ not only in DJF but especially its oceanic branch during MAM. Both local and remote influences, however, are confounded by the large internal variance in the region. During MAM and JJA, the South Atlantic SST anomalies affect the magnitude and the meridional displacement of the ITCZ. In JJA, the ENSO has relatively little influence on the interannual variability of the simulated rainfall. During SON, however, the ENSO seems to counteract the effect of the subtropical South Atlantic SST variations on convection over South America.

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South American Climate during the Early Eocene: Impact of a Narrower Atlantic and Higher Atmospheric CO2

Journal of Climate ◽

10.1175/jcli-d-19-0170.1 ◽

2020 ◽

Vol 33 (2) ◽

pp. 691-706 ◽

Cited By ~ 1

Author(s):

Xiaojuan Liu ◽

David S. Battisti ◽

Rachel H. White ◽

Paul A. Baker

Keyword(s):

South America ◽

Climate Model ◽

Atmospheric Composition ◽

South American ◽

Early Eocene ◽

Tropical Atlantic ◽

State Changes ◽

Climate Model Simulations ◽

South American Climate ◽

Tropical South America

AbstractThe Cenozoic climate of tropical South America was fundamental to the development of its biota, the most biodiverse on Earth. No previous studies have explicitly addressed how the very different atmospheric composition and Atlantic geometry during the early Eocene (approximately 55 million years ago) may have affected South American climate. At that time, the Atlantic Ocean was approximately half of its current width and the CO2 concentration of Earth’s atmosphere ranged from ~550 to ~1500 ppm or even higher. Climate model simulations were performed to examine the effects of these major state changes on the climate of tropical South America. Reducing the width of the Atlantic by approximately half produces significant drying relative to modern climate. Drying is only partly offset by an enhancement of precipitation due to the higher CO2 of the early Eocene. The main mechanism for drier conditions is simple. Low-level air crosses the tropical Atlantic from North Africa in much less time for a narrower Atlantic (2 days) than for the modern Atlantic (~6 days); as a result, much less water is evaporated into the air and thus there is far lower moisture imported to the continent in the Eocene simulation than in the modern control. The progressive wetting (during the mid- to late Cenozoic) of the Amazon due to the widening Atlantic and the rising Andes, only partly offset by decreasing CO2 values, may have been partly responsible for the accumulating biodiversity of this region.

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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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Atmospheric convergence zones stemming from large-scale mixing

Weather and Climate Dynamics ◽

10.5194/wcd-2-475-2021 ◽

2021 ◽

Vol 2 (2) ◽

pp. 475-488

Author(s):

Gabriel M. P. Perez ◽

Pier Luigi Vidale ◽

Nicholas P. Klingaman ◽

Thomas C. M. Martin

Keyword(s):

South America ◽

Large Scale ◽

Hydrological Cycle ◽

Moisture Flux ◽

South Atlantic Convergence Zone ◽

South Atlantic ◽

Convergence Zone ◽

The South ◽

Atmospheric Flow ◽

Convergence Zones

Abstract. Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the finite-time Lyapunov exponent (FTLE), a metric of deformation among neighbouring trajectories, to define convergence zones as attracting Lagrangian coherent structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-Level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in south and southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific–South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

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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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Atmospheric convergence zones stemming from large-scale mixing

10.5194/wcd-2020-57 ◽

2020 ◽

Author(s):

Gabriel M. P. Perez ◽

Pier Luigi Vidale ◽

Nicholas P. Klingaman ◽

Thomas C. M. Martin

Keyword(s):

South America ◽

Large Scale ◽

Hydrological Cycle ◽

Moisture Flux ◽

South Atlantic Convergence Zone ◽

South Atlantic ◽

Convergence Zone ◽

The South ◽

Atmospheric Flow ◽

Convergence Zones

Abstract. Organised cloud bands are important features of tropical and subtropical rainfall. These structures are often regarded as convergence zones, alluding to an association with coherent atmospheric flow. However, the flow kinematics is not usually taken into account in classification methods for this type of event, as large-scale lines are rarely evident in instantaneous diagnostics such as Eulerian convergence. Instead, existing convergence zone definitions rely on heuristic rules of shape, duration and size of cloudiness fields. Here we investigate the role of large-scale turbulence in shaping atmospheric moisture in South America. We employ the Finite-Time Lyapunov Exponent (FTLE), a metric of deformation among neighboring trajectories, to define convergence zones as attracting Lagrangian Coherent Structures (LCSs). Attracting LCSs frequent tropical and subtropical South America, with climatologies consistent with the South Atlantic Convergence Zone (SACZ), the South American Low-level Jet (SALLJ) and the Intertropical Convergence Zone (ITCZ). In regions under the direct influence of the ITCZ and the SACZ, rainfall is significantly positively correlated with large-scale mixing measured by the FTLE. Attracting LCSs in South and Southeast Brazil are associated with significant positive rainfall and moisture flux anomalies. Geopotential height composites suggest that the occurrence of attracting LCSs in these regions is related with teleconnection mechanisms such as the Pacific-South Atlantic. We believe that this kinematical approach can be used as an alternative to region-specific convergence zone classification algorithms; it may help advance the understanding of underlying mechanisms of tropical and subtropical rain bands and their role in the hydrological cycle.

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