Late Holocene Precipitation Fluctuations in South America Triggered by Variability of the North Atlantic Overturning Circulation

Bahr, André; Kaboth‐Bahr, Stefanie; Jaeschke, Andrea; Chiessi, Cristiano Mazur; Cruz, Francisco W.; Carvalho, Leila M. V.; Rethemeyer, Janet; Schefuß, Enno; Geppert, Philipp; Albuquerque, Ana Luíza Spadano; Pross, Joerg; Friedrich, Oliver

doi:10.1029/2021pa004223

Cited by 6 publications

(5 citation statements)

References 74 publications

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“…Moreover, our data show reduced summer monsoon precipitation during MIS 6. A driver of reduced summer precipitation in the Doce Basin could be a weakened SACZ caused by reduced AMOC during MIS 6, leading to higher temperatures at the SW Atlantic and shifting the sea-land interaction and thus the strength of the convection belts, as previously described for eastern Brazil during reduced AMOC phases of the Holocene (Bahr et al, 2021).…”

Section: High Northern Latitude Temperatures and Local Precipitationmentioning

confidence: 77%

“…Paleoclimate studies from the last glacial period and the Holocene indicate that solar irradiation and high latitude temperature changes affect South American monsoonal precipitation patterns by impacting atmospheric as well as ocean circulation and SST distribution in the tropical South Atlantic (e.g., Bahr et al, 2021;Cruz et al, 2009Cruz et al, , 2005Jaeschke et al, 2007;Kanner et al, 2012;Stríkis et al, 2018Stríkis et al, , 2015. In eastern Brazil, monsoon intensity over the past 300 ka was primarily controlled by precession-forced changes in insolation but also indirectly affected by changing atmospheric greenhouse gas concentrations, which can modify both the interand intrahemispheric temperature gradients (Rind, 1998;Hou et al, 2020a) and thereby intensity of the Hadley circulation and southeast trade winds (Seo et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Spatiotemporal Discharge Variability of the Doce River in SE Brazil During MIS 6 and 5

et al. 2022

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The modern precipitation balance in southeastern (SE) Brazil is regulated by the South American summer Monsoon and threatened by global climate change. On glacial-interglacial timescales, monsoon intensity was strongly controlled by precession-forced changes in insolation. To date, relatively little is known about the spatiotemporal distribution of tropical precipitation in SE Brazil and the resulting variability of fluvial discharge on glacial-interglacial timescales. Here, we present X-ray diffraction-derived mineralogical data for the 150–70 ka period (marine isotope stage (MIS) 6 to MIS 5) from the Doce River basin. This area was sensitive to changes in monsoonal precipitation intensity due to its proximity to the South Atlantic Convergence Zone. The data, obtained from a marine sediment core (M125-55–7) close to the Doce river mouth (20°S), show pronounced changes in the Doce River suspension load’s mineralogical composition on glacial-interglacial and precessional timescales. While the ratio of silicates to carbonates displays precession-paced changes, the mineralogical composition of the carbonate-free fraction discriminates between two assemblages which strongly vary between glacial and interglacial time scales, with precession-forced variability only visible in MIS 5. The first assemblage, dominated by high contents of kaolinite and gibbsite, indicates intensified lowland erosion of mature tropical soils. The second one, characterized by higher contents of the well-ordered illite, quartz and albite, points to intensified erosion of immature soils in the upper Doce Basin. High kaolinite contents in the silicate fraction prevailed in late MIS 6 and indicate pronounced lowland soil erosion along a steepened topographic gradient. The illite-rich mineral assemblage was more abundant in MIS 5, particularly during times of high austral summer insolation, indicating strong monsoonal rainfall and intense physical erosion in the upper catchment. When the summer monsoon weakened in times of lower insolation, the mineral assemblage was dominated by kaolinite again, indicative of lower precipitation and runoff in the upper catchment and dominant lowland erosion.

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Section: High Northern Latitude Temperatures and Local Precipitationmentioning

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Spatiotemporal Discharge Variability of the Doce River in SE Brazil During MIS 6 and 5

et al. 2022

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“…Al, Si, K, Fe, Ti) and Ca, reflecting marine biogenic carbonate. In addition, we utilize ln(K/Al) and ln(Al/Si) ratios, which have been used to infer changes in continental moisture availability favoring chemical weathering in monsoonal dominated realms (Chiessi et al, 2010;Govin et al, 2012;Clift et al, 2014;Croudace and Rothwell, 2015;Bahr et al, 2021). Here, ln(K/Al) represents a measure of the intensification of chemical weathering as K is indicative for minerals (i.e.…”

Section: Bulk Sediment Elemental Analysismentioning

confidence: 99%

“…Modern clay mineral compositions along the eastern and southeastern South American continental shelf clearly reflect the weathering regime of the hinterland as kaolinite is predominant in the southeast and illite increase northward as more arid conditions prevail in ESA (Tintelnot, 1995). Thus, downcore ln(K/Al) of Core M125-35-2 is a pertinent proxy reflecting changes in the clay mineral composition which is strongly dependent on hinterland chemical weathering intensity and hence, moisture availability (Bahr et al, 2021). As related to past hydroclimate, low (high) ln(K/Al) reflect wetter (drier) conditions within the catchment area.…”

Section: Bulk Sediment Elemental Analysismentioning

confidence: 99%

Coupled Oceanic and Atmospheric Controls of Deglacial Southeastern South America Precipitation and Western South Atlantic Productivity

Jaeschke¹,

Rethemeyer²,

Chiessi³

et al. 2022

Front. Mar. Sci.

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Various mechanisms were proposed as substantial drivers of (sub)tropical South American hydroclimate changes during the last deglaciation. However, the interpretation of past precipitation records from the regions affected by the South American Summer Monsoon, the dominant hydroclimatic system in (sub)tropical South America, still insufficiently consider feedbacks between oceanic and atmospheric processes evident in modern observational data. Here, we evaluate ocean-atmosphere feedbacks active in the region from 19 to 4 ka based on a multi-proxy record comprising lipid biomarker, bulk sediment elemental composition and foraminiferal geochemistry from a sediment core retrieved from the tropical western South Atlantic offshore eastern Brazil at ~22°S. Our proxy data together with existing paleoclimate records show that the consideration of large scale synoptic climatic features across South America is crucial for understanding the past spatio-temporal rainfall variability, especially during the last deglaciation. While the paleohydrological data from our study site show relatively stable precipitation across the deglaciation in the core region of the South Atlantic Convergence Zone, distinct hydroclimatic gradients developed across the continent during Heinrich Stadial 1, which climaxed at ~16 ka. By then, the prevalent atmospheric and oceanic configuration caused more frequent extreme climatic events associated with positive rainfall in the northern portion of eastern South America and in the southeastern portion of the continent. These climatic extremes resulted from substantial warming of the sub(tropical) western South Atlantic sea surface that fostered oceanic moisture transport towards the continent and the reconfiguration of quasi-stationary atmospheric patterns. We further find that enhanced continental precipitation in combination with low glacial sea level strongly impacted marine ecosystems via enhanced terrigenous organic matter input in line with augmented nutrient release to the ocean. Extreme rainfall events similar to those that occurred during Heinrich Stadial 1 are likely to recur in South America as a consequence of global warming, because the projected reduction of the intra-hemispheric temperature gradient may lead to the development of atmospheric patterns similar to those in force during Heinrich Stadial 1.

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“…Previous studies have shown that the Roman Warm Period (300-1 CE), Dark Ages Cold Period (800-300 CE), Medieval Climate Anomaly (1300-800 CE), and Little Ice Age (1900-1300 CE) [16,46,55] were associated with oscillations in orbital dynamics, the release of sulfates during volcanic eruptions, an increase in CO 2 concentrations in the atmosphere, and a displacement of the Intertropical Convergence Zone (ITCZ) [15,46,56]. Furthermore, the colder-warmer climate oscillations presented environmental anti-phases between the Northern and Southern Hemispheres during the Late Holocene.…”

Section: Introductionmentioning

confidence: 99%

Genesis and Distribution of Low Fluvial Terraces Formed by Holocene Climate Pulses in Brazil

Filho

Moreira

Lämmle

et al. 2022

Water

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Low fluvial terraces present azonal spatialization, encompassing several geomorphological compartments and climate zones in Brazil. Their genesis is directly related to river dynamics. When influenced by allogenic forces, such as Holocene climate pulses, it results in channel incision and posterior abandonment of the floodplain. Relatively plain landforms at different altimetric levels identified between the current floodplain and hillslope (low river terraces) are a result of these processes. Previous works using Optically Stimulated Luminescence (OSL) in low terraces of several rivers in Brazil have indicated morpho-chronologic similarities between depositional events, raising the hypothesis of feedbacks and fluvial adjustments relatively simultaneous to Holocene climate events. Considering these dynamics, this study employed OSL to obtain absolute dating information for 114 samples taken from distinct levels of the low river terraces of 30 rivers in Brazil, integrating the database of the IG-UNICAMP laboratory of Geomorphology and Environmental Analysis. Based on the data and statistical analysis (cluster and correlation analysis), this study aimed to identify relationships between different variables which might have controlled spatial homogenous and heterogeneous feedbacks during distinct paleoenvironmental contexts. The proposed methodology tested a fundamental hypothesis of the regional climatic geomorphology, and the results obtained may contribute to future discussions on the relationship between low river terraces and anthropic occupation.

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Late Holocene Precipitation Fluctuations in South America Triggered by Variability of the North Atlantic Overturning Circulation

Cited by 6 publications

References 74 publications

Spatiotemporal Discharge Variability of the Doce River in SE Brazil During MIS 6 and 5

Spatiotemporal Discharge Variability of the Doce River in SE Brazil During MIS 6 and 5

Coupled Oceanic and Atmospheric Controls of Deglacial Southeastern South America Precipitation and Western South Atlantic Productivity

Genesis and Distribution of Low Fluvial Terraces Formed by Holocene Climate Pulses in Brazil

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