Evidence for a prolonged retroflection of the North Brazil Current during glacial stages

Wilson, Katy E.; Maslin, Mark; Burns, Stephen J.

doi:10.1016/j.palaeo.2011.01.003

Cited by 32 publications

(22 citation statements)

References 79 publications

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“…6). This hypothesis is supported by the strengthening of the NBC retroflection and oceanward deflection of Amazon freshwater plume suggested during past cold substages and Heinrich events (Maslin, 1998;Rühlemann et al, 2001;Wilson et al, 2011). Larger northern ice sheets during cold substages (or iceberg discharge during Heinrich events) enhanced the Atlantic meridional SST gradient, which strengthened trade winds, shifted the ITCZ southward (Chiang and Bitz, 2005) and curtailed the cross-equatorial export of the NBC (Maslin, 1998).…”

Section: Redistribution By Surface Ocean Currentsmentioning

confidence: 87%

“…This gradient strengthened the North Equatorial Counter Current and the NBC retroflection, that is, a more vigorous eastward flow of surface waters carrying freshwater and suspended particles delivered by the Amazon River (e.g. Maslin, 1998;Zabel et al, 1999;Rühlemann et al, 2001;Wilson et al, 2011). Because it is unlikely that surface-water currents discriminate between the Andean and lowland origin of suspended sediments delivered by the Amazon River, the %-Andes tracer is independent of sediment redistribution by surface ocean currents.…”

Section: Redistribution By Surface Ocean Currentsmentioning

confidence: 99%

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Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka

Chiessi²,

et al. 2014

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Abstract. We investigate changes in the delivery and oceanic transport of Amazon sediments related to terrestrial climate variations over the last 250 ka. We present high-resolution geochemical records from four marine sediment cores located between 5 and 12° N along the northern South American margin. The Amazon River is the sole source of terrigenous material for sites at 5 and 9° N, while the core at 12° N receives a mixture of Amazon and Orinoco detrital particles. Using an endmember unmixing model, we estimated the relative proportions of Amazon Andean material ("%-Andes", at 5 and 9° N) and of Amazon material ("%-Amazon", at 12° N) within the terrigenous fraction. The %-Andes and %-Amazon records exhibit significant precessional variations over the last 250 ka that are more pronounced during interglacials in comparison to glacial periods. High %-Andes values observed during periods of high austral summer insolation reflect the increased delivery of suspended sediments by Andean tributaries and enhanced Amazonian precipitation, in agreement with western Amazonian speleothem records. Increased Amazonian rainfall reflects the intensification of the South American monsoon in response to enhanced land–ocean thermal gradient and moisture convergence. However, low %-Amazon values obtained at 12° N during the same periods seem to contradict the increased delivery of Amazon sediments. We propose that reorganizations in surface ocean currents modulate the northwestward transport of Amazon material. In agreement with published records, the seasonal North Brazil Current retroflection is intensified (or prolonged in duration) during cold substages of the last 250 ka (which correspond to intervals of high DJF or low JJA insolation) and deflects eastward the Amazon sediment and freshwater plume.

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Section: Redistribution By Surface Ocean Currentsmentioning

confidence: 87%

Section: Redistribution By Surface Ocean Currentsmentioning

confidence: 99%

Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka

Chiessi²,

et al. 2014

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“…This higher percentage abundance reflects the influence of the Amazon River freshwater plume at this location Mikkelsen et al, 1997). Moreover, Wilson et al (2011) used planktonic foraminiferal oxygen isotopes and Mg/Ca sea surface temperatures (SSTs) to show that during the late Glacial period, Younger Dryas, mid Holocene and Modern time slices ODP Site 942 and surrounding sites consistently exhibit the most negative oxygen isotope values, suggesting a continual influence of the Amazon River freshwater plume over this part of the Amazon Fan. A comparison of oxygen isotope records either side of the Amazon River outflow also confirms this influence.…”

Section: Methodsmentioning

confidence: 99%

Amazon Fan biomarker evidence against the Pleistocene rainforest refuge hypothesis?

Maslin

Ettwein

Boot

et al. 2012

J Quaternary Science

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Ocean Drilling Program Leg 155 Site 942 on the Amazon Fan is an ideal location for monitoring palaeoclimatic changes within a significant proportion of the Amazon Basin. We present n‐alkane δ13C and taraxerol and laevoglucosan concentration records from this site covering the last 38 ka. The entire n‐alkane δ13C record is constrained between −31‰ and −34‰, which is well within the isotopic range occupied by C3 vegetation. The concentration and relative abundance of taraxerol, a mangrove indicator, varies by over an order of magnitude, but seems to have had no effect on the n‐alkane δ13C record. The laevoglucosan concentrations are extremely low during the last glacial period, suggesting a relatively low occurrence of forest fires. Laevoglucosan concentrations are highest between 13.5 and 12.5 ka, suggesting an increased incidence of Amazon forest fires at the very end of the Younger Dryas. These records, combined with previously published pollen records from Site 932, reveal no evidence for massive incursions of grasslands into Amazonia during the last glacial period, despite evidence of reduced outflow of the Amazon River indicating more arid conditions. We therefore suggest that savannah encroachment, as proposed by the Pleistocene refuge hypothesis, can be refuted as an explanation for high species endemism within the Amazon Basin, and alternative explanations are required. Copyright © 2012 John Wiley & Sons, Ltd.

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“…The North Brazilian current (NBC) runs along the coast from southeast to northwest. Model 2 shows current rings around the Ceará Rise that were described previously by Fratantoni and Richardson (2006) and Wilson et al (2011). Interestingly, for 16,000 years ago there is a significant northward shift of the SEC (Figure 7.3b).…”

Section: Climate and Paleoceanographic Modelssupporting

confidence: 60%

Enviromagnetic response of marine sediments off NE Brazil to paleoclimatic and paleoceanographic changes in the last 85kyr BP

Mathias¹

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Resposta magnética de sedimentos marinhos da margem adjacente ao NE do Brasil às mudanças paleoclimáticas e paleoceanográficas nos últimos 85.000 anos BP) SÃO PAULO 2015 iii GRASIANE LUZ MATHIAS Enviromagnetic response of marine sediments off NE Brazil to paleoclimatic and paleoceanographic changes in the last 85 kyr BP (Resposta magnética de sedimentos marinhos da margem adjacente ao NE do Brasil às mudanças paleoclimáticas e paleoceanográficas nos últimos 85.000 anos BP)

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Evidence for a prolonged retroflection of the North Brazil Current during glacial stages

Cited by 32 publications

References 79 publications

Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka

Terrigenous input off northern South America driven by changes in Amazonian climate and the North Brazil Current retroflection during the last 250 ka

Amazon Fan biomarker evidence against the Pleistocene rainforest refuge hypothesis?

Enviromagnetic response of marine sediments off NE Brazil to paleoclimatic and paleoceanographic changes in the last 85kyr BP

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