Constraining Millennial‐Scale Changes in Northern Component Water Ventilation in the Western Tropical South Atlantic

Abstract

Negative excursions in the stable carbon isotopic composition (δ13C) at Atlantic intermediate to mid‐depths are common features of millennial‐scale events named Heinrich Stadials. The mechanisms behind these excursions are not yet fully understood, but most hypotheses agree on the central role played by the weakening of the Atlantic meridional overturning circulation. Marine records registering millennial‐scale negative δ13C excursions in the Atlantic are mostly restricted to the Heinrich Stadials of the last deglacial, while the Heinrich Stadials of the last glacial are poorly studied. Here, we constrain changes in bottom water ventilation in the western tropical South Atlantic mid‐depth during Heinrich Stadials of the last glacial and deglacial by investigating marine core M125‐95‐3. The concurrent decreases in benthic foraminifera δ13C and increases in bulk sediment sulfur indicate an increased Northern Component Water (NCW) residence time in the western tropical South Atlantic mid‐depth during Heinrich Stadials. Furthermore, a coherent meridional pattern emerges from the comparison of our new data to previously published mid‐depth records from the western South Atlantic. While our record shows the largest negative δ13C excursions during almost all Heinrich Stadials, the western equatorialAtlantic showed medium and the subtropical South Atlantic showed the smallest negative excursions. This meridional pattern supports the notion that during Heinrich Stadials, a reduction in the NCW δ13C source signal together with the accumulation of respired carbon at NCW depths drove the negative δ13C excursions. We suggest that the negative δ13C excursions progressively increase along the NCW southwards pathway until the signal dissipates/dilutes by mixing with Southern Component Water.

A Multi‐Proxy Approach to Unravel Late Pleistocene Sediment Flux and Bottom Water Conditions in the Western South Atlantic Ocean

“…Since δ 13 C of C. wuellerstorfi reflects the δ 13 C of the bottom water dissolved inorganic carbon with no pore water effects (Mackensen et al., 1993; Mackensen & Schmiedl, 2019), we suggest that MTB magnetite production was at least partially controlled by changes in the overlying bottom water. Negative δ 13 C excursions in the western South Atlantic are frequently associated with periods of weak Atlantic Meridional Overturning Circulation (e.g., glacial stages and Heinrich stadials) (Campos et al., 2020; Lund et al., 2015; Santos et al., 2017; Schmittner & Lund, 2015). During these periods of reduced ventilation, increased NADW residence time allowed the accumulation of respired carbon at Atlantic mid‐depths (Campos et al., 2020; Howe et al., 2016; Schmittner & Lund, 2015; Voigt et al., 2017).…”

“…Negative δ 13 C excursions in the western South Atlantic are frequently associated with periods of weak Atlantic Meridional Overturning Circulation (e.g., glacial stages and Heinrich stadials) (Campos et al., 2020; Lund et al., 2015; Santos et al., 2017; Schmittner & Lund, 2015). During these periods of reduced ventilation, increased NADW residence time allowed the accumulation of respired carbon at Atlantic mid‐depths (Campos et al., 2020; Howe et al., 2016; Schmittner & Lund, 2015; Voigt et al., 2017). The carbon accumulated as a result of increased microbial respiration at the expense of oxygen.…”

Meridional changes in the South Atlantic Subtropical Gyre during Heinrich Stadials

“…( b ) Uvigerina spp. stable carbon isotopic composition (δ 13 C) from core M125-95-3 (running average of 3 points) 38 . ( c ) Relative abundance of G. truncatulinoides from core M125-95-3 (this study).…”

Aplicação de isótopos estáveis de carbono no estudo das mudanças climáticas e ambientais

“…O δ 13 C de foraminíferos planctônicos e bentônicos têm sido aplicados de diversas formas para compreender as mudanças paleoambientais no ciclo do carbono. Por exemplo, a composição isotópica de uma ou mais espécies de foraminíferos que calcificam em profundidades distintas e conhecidas é usada em diversas escalas de tempo para reconstituir a concentração de nutrientes ao longo da coluna de água e investigar a distribuição e proporção relativa de massas de água superficiais, intermediárias e profundas (e.g., DUPLESSY et al 1984, MULITZA et al 1998, SANTOS et al 2017aVOIGT et al 2017, CAMPOS et al 2017, 2020.…”

“…Por sua vez, espeleotemas de cavernas podem preservar a assinatura do δ 13 C do solo acima da caverna na sua composição carbonática, que pode ser modificada por efeitos da temperatura e hidrologia, propiciando possíveis indicadores para reconstituições ambientais e climáticas (NOVELLO et al 2019(NOVELLO et al , 2021. Nos oceanos, o δ 13 C do carbono inorgânico dissolvido (δ 13 C CID ) na água do mar é registrado no δ 13 C das conchas de organismos marinhos, tais como foraminíferos, constituindo um importante indicador de mudanças pretéritas no ciclo do carbono e circulação oceânica (e.g., DUPLESSY et al 1984;MULITZA et al 1998;CAMPOS et al 2017CAMPOS et al , 2020SANTOS et al 2017a, b;.…”