Stable isotope data and sedimentary major element concentration of sediment cores from the western equatorial Atlantic

Negative stable carbon isotopic excursions have been observed throughout most of the mid-depth (~1000-3000m) Atlantic Ocean during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). Although there is agreement that these mid-depth excursions were in some way associated with a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), there is still no consensus on the precise mechanism(s). Here, we present benthic stable carbon and oxygen isotopic (d13C and d18O) records from five cores from the western equatorial Atlantic (WEA). Together with published benthic isotopic records from nearby cores, we produced a WEA depth transect (~800-2500m). We compare HS1 and YD data from this transect with data from previously published North- and South Atlantic cores and demonstrate that the largest negative d13C excursions occurred in the WEA during these times. Moreover, our benthic d18O records require the presence of two water masses flowing from the Southern Ocean, bisected by a Northern Component Water (NCW). Given that d18O is a conservative water mass tracer, we suggest that d13C was decoupled from water mass composition and do not correspond to simple alternations between northern and southern sourced waters. Instead, d13C behaved non-conservatively during HS1 and the YD. Consistently with our new 231Pa/230Th record from the WEA transect, that allowed the reconstruction of AMOC strength, we hypothesize that the negative d13C excursions reflect an increase in the residence time of NCW in response to a weakened AMOC, allowing for a marked accumulation of 13C-depleted respired carbon at the mid-depth WEA.

海因里希冷期1（Heinrich Stadial 1，HS1）与新仙女木期（Younger Dryas，YD）期间，大西洋绝大多数中深层（约1000~3000米）海域均记录到负稳定碳同位素偏移事件。尽管学界普遍认为这类中深层同位素偏移与大西洋经向翻转环流（Atlantic Meridional Overturning Circulation，AMOC）的减缓存在关联，但具体驱动机制仍未达成共识。本研究基于西赤道大西洋（western equatorial Atlantic，WEA）5个沉积岩芯的底栖稳定碳、氧同位素（δ¹³C与δ¹⁸O）记录展开分析。结合已发表的邻近岩芯底栖同位素数据，我们构建了WEA海域800~2500米的深度断面序列。将该断面的HS1与YD期数据与此前发表的北大西洋、南大西洋岩芯数据进行对比后证实，上述两段时期内WEA海域的δ¹³C负偏移幅度为区域之最。此外，我们的底栖δ¹⁸O记录显示，当时存在两支源自南大洋的水团，二者被北支水团（Northern Component Water，NCW）分隔。鉴于δ¹⁸O属于保守性水团示踪剂，我们认为δ¹³C并未与水团组成绑定，并非简单反映南北源水团的交替更迭。相反，HS1与YD期的δ¹³C表现出非保守性行为。结合我们在WEA断面获得的新的²³¹Pa/²³⁰Th比值记录（该记录可用于重建AMOC强度），我们提出假说：δ¹³C负偏移反映了AMOC减弱后北支水团停留时间的增加，使得贫¹³C的呼吸代谢碳在WEA中深层海域显著富集。