Rare element concentrations measured on filtered seawater of water bottle samples during POLARSTRERN cruise ANT-XXIV/3 (GIPY5)@en

The concentrations of rare earth elements (REEs) in seawater display systematic variations related to weathering inputs, particle scavenging and water mass histories. Here we investigate the REE concentrations of water column profiles in the Atlantic sector of the Southern Ocean, a key region of the global circulation and primary production. The data reveal a pronounced contrast between the vertical profiles in the Antarctic Circumpolar Current (ACC) and those to the south of the ACC in the Weddell Gyre (WG). The ACC profiles exhibit the typical increase of REE concentrations with water depth and a change in the shape of the profiles from near linear for the light REEs to more convex for the heavy REEs. In contrast, the WG profiles exhibit high REE concentrations throughout the water column with only the near surface samples showing slightly reduced concentrations indicative of particle scavenging. Seawater normalised REE patterns reveal the strong remineralisation signal in the ACC with the light REEs preferentially removed in surface waters and the mirror image pattern of their preferential release in deep waters. In the WG the patterns are relatively homogenous reflecting the prevalence of well-mixed Lower Circumpolar Deep Water (LCDW) that follows shoaling isopycnals in the region. In the WG particle scavenging of REEs is comparatively small and limited to the summer months by light limitation and winter sea ice cover. Considering the surface water depletion compared to LCDW and that the surface waters of the WG are replaced every few years, the removal rate is estimated to be on the order of 1 nmol/m3/yr for La and Nd. The negative cerium anomalies observed in deep waters are some of the strongest found globally with only the deepest waters in parts of the Pacific having stronger anomalies. These deep waters have been isolated from fresh continental REE inputs during their long journey through the abyssal Indo-Pacific ocean and suggests that the high REE concentrations found in the ACC and WG reflect contributions from old deep waters.海水中的稀土元素（rare earth elements, REEs）浓度呈现出与风化输入、颗粒清除以及水团演化历史相关的系统性变化。本研究针对南大洋大西洋扇区——全球环流与初级生产的关键区域——的水柱剖面稀土元素浓度展开调查。数据结果显示，南极绕极流（Antarctic Circumpolar Current, ACC）内部的垂直剖面与威德尔海环流（Weddell Gyre, WG）内ACC以南海域的垂直剖面存在显著差异。ACC剖面呈现出典型的稀土元素浓度随水深增加而升高的特征，且配分曲线形态从轻稀土元素的近线性分布转变为重稀土元素的更凸形分布。与之相反，WG剖面的全水柱稀土元素浓度均较高，仅近表层样品浓度略有降低，这一现象反映了颗粒清除作用。海水标准化稀土元素配分模式显示，ACC区域存在强烈的再矿化信号：表层水体优先清除轻稀土元素，而深层水体则呈现出轻稀土元素优先释放的镜像配分模式。WG区域的配分模式相对均一，反映了该区域广泛分布的均一化绕极深层水（Lower Circumpolar Deep Water, LCDW），该水团伴随区域内等密线抬升而形成。WG区域的稀土元素颗粒清除作用相对较弱，且仅在夏季受光照限制与冬季海冰覆盖的影响而发生。相较于LCDW，WG表层水体存在稀土元素亏损，且WG表层水体每数年就会更新一次，据此估算镧（La）与钕（Nd）的稀土元素清除速率约为1 nmol/m³/yr量级。深层水体中观测到的负铈异常是全球范围内最强的一批，仅太平洋部分区域的深层水体可观测到更强的异常。这些深层水体在穿过印度洋-太平洋深海盆的漫长运移过程中，与陆源稀土元素的新鲜输入隔绝，这表明ACC与WG区域的高稀土元素浓度反映了古老深层水的贡献。