Samples for dissolved trace metal concentrations were collected during GEOTRACES expedition GA04-N in summer/spring in the Mediterranean Sea, starting in the Atlantic Ocean and sampling both deep basins of the Mediterranean Sea. Outflow of Mediterranean Outflow Water leads to elevated concentrations of Mn, Ni and Zn in the Atlantic Ocean, but a concentration minimum in the Atlantic distribution of Cd. Nevertheless, when comparing the in- and outflow, the Mediterranean is a net source of Cd to the Atlantic Ocean. Surface concentrations of Mn, Ni, Zn and Cd are elevated in the Mediterranean relative to the Atlantic Ocean where Ni and Cd gradually increased along the eastward surface water flow path, Zn reached a homogenous concentration in the order of 1 to 1.5 nM, and Mn displayed a patchy surface distribution. The observed differences are attributable to the different dynamics of their biogeochemical cycling, notably the partitioning between the dissolved and particulate phases due to biological uptake, scavenging and possibly organic complexation. The elevated surface concentrations of Mn, Ni, Zn and Cd in the Mediterranean are derived from atmospheric deposition, where most likely Zn and Cd are mainly sourced from anthropogenic origin, Mn mostly from lithogenic origin and Ni from both anthropogenic and lithogenic origin. Dissolved Zn and Cd, as well as phosphate and nitrate, display striking inter-basin fractionations with elevated concentrations in the deep water of the western basin compared to the deep eastern basin, without a coinciding increase in the apparent oxygen utilization. Given that physical circulation or contribution from biogenic particulate metals cannot explain the elevated dissolved concentrations, an external non-biological source is required. This source is most likely a vertical flux of metal laden particles dissolving through the water column of the western Mediterranean where these particles, most likely from anthropogenic origin, are derived from either atmospheric deposition or particulate material deposited on the continental shelves that makes its way into the deep basin. To confirm or detect trends in dissolved metal concentrations in the deep basin, regular basin wide assessments of the trace metal distributions in the Mediterranean are needed. The distributions of Mn, Ni, Zn and Cd in the Sea of Marmara illustrate that all of these metals can be affected by anthropogenic surface sources and highlight the different susceptibilities of the dissolved metal distributions to supply from remineralization, and to removal through scavenging. This study provides a first baseline to assess future changes and underlines that the Mediterranean marine environment is susceptible to anthropogenic disturbances, with varying effects for different metals due to differing source strengths and biogeochemical cycles.

GEOTRACES 探险队 GA04-N 在地中海夏季/春季期间收集了溶解痕量金属浓度的样品，从大西洋开始，对地中海的两个深海盆地进行采样。地中海流出水的流出导致大西洋中锰、镍和锌的浓度升高，但在大西洋分布的镉浓度最低。然而，当比较流入和流出时，地中海是大西洋 Cd 的净来源。相对于大西洋，地中海的 Mn、Ni、Zn 和 Cd 的表面浓度升高，其中 Ni 和 Cd 沿地表水流向东逐渐增加，Zn 达到 1 至 1.5 nM 的均匀浓度，Mn显示出不规则的表面分布。观察到的差异归因于它们的生物地球化学循环的不同动力学，特别是由于生物吸收、清除和可能的有机络合导致溶解相和颗粒相之间的分配。地中海地区 Mn、Ni、Zn 和 Cd 的地表浓度升高源于大气沉积，其中最有可能的 Zn 和 Cd 主要来自人为来源，Mn 主要来自岩源，而 Ni 则来自人为和岩源。溶解的 Zn 和 Cd，以及磷酸盐和硝酸盐，在西部盆地的深水中显示出显着的跨盆地分馏，与东部深部盆地相比，其浓度升高，但表观氧利用率没有同时增加。鉴于物理循环或生物颗粒金属的贡献无法解释溶解浓度升高，因此需要外部非生物来源。这个来源很可能是通过地中海西部水柱溶解的含金属颗粒的垂直通量，这些颗粒很可能来自人为来源，来自大气沉积或沉积在大陆架上的颗粒物质，这些颗粒物质进入深盆地。为了确认或检测深盆中溶解金属浓度的趋势，需要对地中海的痕量金属分布进行定期的盆地范围内评估。Mn、Ni、马尔马拉海中的锌和镉表明所有这些金属都可能受到人为表面源的影响，并突出了溶解金属分布对再矿化供应和通过清除去除的不同敏感性。该研究提供了评估未来变化的第一个基线，并强调地中海海洋环境容易受到人为干扰，由于来源强度和生物地球化学循环不同，对不同金属的影响也不同。