(Figure 3) Dissolved aluminium concentrations during POLARSTERN Cruise ANT-XXIV/3

Dissolved aluminium (Al) occurs in a wide range of concentrations in the world oceans. The concentrations of Al in the Southern Ocean are among the lowest ever observed. An all-titanium CTD sampling system makes it possible to study complete deep ocean sections of Al and other trace elements with the same high vertical resolution of 24 depths as normal for traditional CTD/Rosette sampling. Overall, 470 new data points of Al are reported for 22 full depth stations and 24 surface sampling positions along one transect. This transect consisted of 18 stations on the zero meridian proper from 51°57'S until 69°24'S, and 4 stations somewhat to the northeast towards Cape Town from 42°20'S, 09°E to 50°17'S, 01°27'E. The actual concentrations of Al in the Southern Ocean were lower than previously reported. The concentration of Al in the upper 25 m was relatively elevated with an average concentration of 0.71 nM (n=22; S.D.=0.43 nM), most likely due to atmospheric input by a suggested combination of direct atmospheric (wet and dry) input and indirect atmospheric input via melting sea ice. Below the surface waters there was a distinct Al minimum with an average concentration of 0.33 nM (n=22; S.D.=0.13 nM) at an average depth of 120 m. In the deep southernmost Weddell Basin the concentration of Al increased with depth to ~0.8 nM at 4000 m, and a higher concentration of ~1.5 nM in the ~4500-5200 m deep Weddell Sea Bottom Water. Over the Bouvet triple junction region, where three deep ocean ridges meet, the concentration of Al increased to ~1.4 nM at about 2000 m depth over the ridge crest. In the deep basin north of the Bouvet region the concentration of Al increased to higher deep values of 4-6 nM due to influence of North Atlantic Deep Water. In general the intermediate and deep distribution of Al results from the mixing of water masses with different origins, the formation of deep water and additional input from sedimentary sources at sea floor elevations. No significant correlation between Al and silicate (Si) was observed. This is in contrast to some other ocean regions. In the Southern Ocean the supply of Al is extremely low and any signal from Al uptake and dissolution with biogenic silica is undetectable against the high dissolved Si and low dissolved Al concentrations. Here the Al-Si relation in the deep ocean is uncoupled. This is due to the scavenging and subsequent loss of the water column of Al, whereas the concentration of Si increases in the deep ocean due to its input from deep dissolution of biogenic diatom frustules settling from the surface layer.

全球海洋中，溶解态铝（Al）的浓度分布跨度极大。南大洋的溶解态铝浓度，是全球海洋中观测到的最低值之一。
本研究采用全钛材质的温盐深剖面仪（CTD）采样系统，可实现与传统CTD/罗塞特采水器（Rosette）一致的高垂直分辨率——即每层采样覆盖24个深度层——来获取铝及其他痕量元素的完整大洋深层剖面数据。本数据集共报告了沿一条采样断面的22个全深度站位与24个表层采样点的470组溶解态铝新数据。
该采样断面包含两部分：18个站位位于本初子午线沿线，纬度范围为南纬51°57′至南纬69°24′；另有4个站位位于该区域东北方向朝向开普敦的海域，纬度范围为南纬42°20′、东经9°至南纬50°17′、东经1°27′。
南大洋溶解态铝的实际浓度低于此前文献报道值。表层25米以浅水体的溶解态铝浓度相对偏高，平均浓度为0.71纳摩尔每升（nM，样本量n=22，标准差S.D.=0.43 nM），该现象大概率由大气输入所致——研究认为其来源为大气直接输入（含湿沉降与干沉降）以及海冰融化带来的间接大气输入。表层水体下方存在显著的溶解态铝浓度极小值层，平均浓度为0.33 nM（n=22，S.D.=0.13 nM），对应平均采样深度为120米。
在最南端的威德尔海盆深层水域，溶解态铝浓度随深度增加而升高，在4000米处达到约0.8 nM；而在4500~5200米深度的威德尔海底层水中，浓度进一步升至约1.5 nM。在布韦三重交界区（三处大洋深脊交汇的区域），海脊顶部约2000米深度处的溶解态铝浓度升至约1.4 nM。布韦海域以北的深海盆中，受北大西洋深层水影响，溶解态铝浓度升至4~6 nM的较高深层水体浓度水平。
总体而言，溶解态铝在中层与深层水体中的分布格局，由不同源地水团的混合、深层水形成过程，以及海底隆起区沉积物来源的额外输入共同塑造。观测结果显示，溶解态铝与硅酸盐（Si）之间无显著相关性，这与其他部分海洋区域的研究结论相悖。南大洋中溶解态铝的供给量极低，加之溶解态硅浓度高而溶解态铝浓度低，因此生物硅形成过程中铝的摄取与溶解所产生的信号完全无法被观测到。因此南大洋深层水体中铝与硅的耦合关系被打破：这是因为铝会被水体颗粒吸附并最终从水柱中移除；而硅的浓度则随深度增加而升高，其来源为表层沉降的生物硅藻壳体在深层海域的溶解作用。