NOAA/WDS Paleoclimatology - North Atlantic Deep Water Nd isotope and Rare-Earth Element Data since the Last Glacial Maximum

The Nd isotope composition of seawater has been used to reconstruct past changes in the contribution of different water masses to the deep ocean. In the absence of contrary information, the Nd isotope compositions of endmember water masses are usually assumed constant during the Quaternary. Here we show that the Nd isotope composition of North Atlantic Deep Water (NADW), a major component of the global overturning ocean circulation, was significantly more radiogenic than modern during the Last Glacial Maximum (LGM), and shifted towards modern values during the deglaciation. We propose that weathering contributions of unradiogenic Nd modulated by the North American Ice Sheet dominated the evolution of the NADW Nd isotope endmember. If water mass mixing dominated the distribution of deep glacial Atlantic Nd isotopes, our results would imply a larger fraction of NADW in the deep Atlantic during the LGM and deglaciation than reconstructed with a constant northern endmember.

海水的钕同位素组成（Nd isotope composition）已被应用于重建不同水团对深海贡献的历史变化。在无相反证据的前提下，第四纪期间端元水团的钕同位素组成通常被假定为恒定不变。本研究表明，作为全球大洋翻转环流核心组分的北大西洋深层水（North Atlantic Deep Water, NADW），其钕同位素组成在末次冰盛期（Last Glacial Maximum, LGM）的放射成因水平显著高于现代，并在冰消期向现代值趋近。我们提出，受北美冰盖（North American Ice Sheet）调控的低放射成因钕的风化贡献，主导了北大西洋深层水钕同位素端元的演化过程。若冰川期大西洋深海钕同位素的分布主要由水团混合所主导，则本研究结果意味着，在末次冰盛期及冰消期，北大西洋深层水在深海大西洋中的占比，要高于采用恒定北端元进行重建所得到的结果。