Insights into hydrothermal iron flux variability at slow-spreading ridges from deep drilling data and reaction-transport modeling

化学海洋学的最新发现指出，热液铁是全球尺度海洋地球化学循环的重要调节剂，因为铁的可用性往往限制浮游植物的生长，从而限制生物碳泵。有趣的是，GEOTRACES方案的这些新结果再次证实了大洋中脊生物群以前的认识，即热液活动以及因此沿大西洋中脊沿着的热液输出通量远远高于其缓慢扩散速度所显示的水平。然而，热液铁出口的控制，以及如何在镁铁质和超镁铁质地质settings.here之间的变化仍然知之甚少，我们将联合收割机反应输运模型与IODP数据，以确定关键的参数组合，导致在TAG和彩虹热液田的最含盐量和富铁流体的排气。当海水在循环通过热液系统时被加热时，它可能在与两相边界相交时分裂成致密的盐水相和较轻的低盐度蒸气相，金属积聚在盐水相中。因此，在整个循环系统中跟踪向喷口供水的盐水相是改进评估的关键之一。另一个问题是对上升流区周围热液矿物中铁的再沉积进行定量。我们建议返回到独特的ODP 158数据的玄武岩托管断层控制的TAG热液系统，并将其与反应传输模型，以提供新的见解卤水形成和铁的运输。这项工作将得到一项关于超镁铁岩托管的Rainbow热液区的研究的补充，为此，国际社会正在努力提交一份IODP钻探提案。从这两个案例研究中，我们预计基本的新见解的盐水形成和热液铁出口的关键控制因素，在缓慢蔓延的山脊，这是现在意识到是如此重要的全球地球化学循环。

Recent discoveries in chemical oceanography point to hydrothermal iron as an important modulator of global scale biogeochemical ocean cycles, as iron availability often limits phytoplankton growth and thereby the biological carbon pump. Interestingly, these new results from the GEOTRACES program re-confirm the preceding realization within the mid-ocean ridge community that hydrothermal activity and thereby the hydrothermal export flux along the Mid-Atlantic Ridge (MAR) is disproportionally higher than its slow-spreading rate would suggest. Yet, the controls of hydrothermal iron export and how those vary between mafic and ultramafic geological settings remain poorly understood.Here, we will combine reaction-transport models with IODP data to identify the critical combination of parameters that results in the venting of the most saline and iron-rich fluids at the TAG and Rainbow hydrothermal fields. When seawater is heated while cycling through a hydrothermal system, it may split into a dense and saline brine phase and a lighter low salinity vapor phase upon intersecting with the two-phase boundary, with the metals accumulating in the brine phase. Tracking the brine phase throughout the circulation system that feeds the vent sites is therefore one key to an improved assessment. Quantifying the re-deposition of Fe in hydrothermal minerals around the upflow zone is another. We propose to return to the unique ODP 158 data on the basaltic-hosted fault-controlled TAG hydrothermal system and to integrate it with reaction-transport models to provide new insights into brine formation and iron transport. This work will be complemented by a study on the ultramafic-hosted Rainbow hydrothermal field, for which an international effort of submitting an IODP drilling proposal is on the way. From these two case studies, we anticipate fundamental new insights into the key controlling factors of brine formation and hydrothermal iron export at slow-spreading ridges, which is now realized to be so important for global biogeochemical cycles.