NOAA/WDS Paleoclimatology - Brazil Margin Deglacial Benthic Stable Isotope Data

The initial rise in atmospheric CO2 during the last deglaciation was likely driven by input of carbon from a 13C-depleted reservoir [Schmitt et al., 2012]. Here we show that high resolution benthic foraminiferal records from the mid-depth Brazil Margin display an abrupt drop in d13C during Heinrich Stadial 1 (HS1) that is similar to but larger than in the atmosphere. Comparing the Brazil Margin results to published records from the North Atlantic, we are unable to account for the South Atlantic d13C data with conservative mixing between northern and southern component water masses. Rapid input of abyssal water from the Southeast Atlantic could account for deglacial d13C anomalies at the Brazil Margin but it would require a reversal in deep water flow direction compared to today. A new mid-depth water mass may explain similar HS1 d13C values in both the North and South Atlantic, but contrasting oxygen isotopic values between the two basins do not support the presence of a single dominant water mass at mid-depths. Instead, it appears that d13C behaved non-conservatively during the deglaciation, possibly reflecting the input of carbon from an isotopically depleted source.

末次冰消期大气二氧化碳的初始上升，大概率由贫13碳储库（13C-depleted reservoir）的碳输入所驱动[Schmitt等，2012]。本研究显示，源自巴西陆缘中深层的高分辨率底栖有孔虫记录，呈现出海因里希停滞期1（Heinrich Stadial 1，HS1）期间碳同位素比值（δ13C）的急剧下降，其幅度大于大气中的对应变化。将巴西陆缘的观测结果与已发表的北大西洋记录对比后，我们发现无法通过南北端元水团间的保守混合来解释南大西洋的δ13C数据。南大西洋东部的深渊水快速输入，或可解释巴西陆缘处冰消期的δ13C异常，但这要求深层水流方向与现今完全相反。一种新的中深层水团假说，可解释北大西洋与南大西洋HS1时期相似的δ13C值，但两盆地间存在差异的氧同位素值，并不支持中深层存在单一主导水团的结论。与此相反，研究发现δ13C在冰消期表现出非保守性变化，这或许反映了同位素贫化碳源的输入。