Abstract
Lithium (Li) and strontium (Sr) are two economically relevant chemical elements whose oceanic biogeochemical cycles are not fully constrained. In particular, how they disperse and behave from hydrothermal sources into the water column is understudied while hydrothermal systems on the global mid-ocean ridge network (∼67,000 km) represent one of the main sources of Li. This study aims to provide new insights on the dissolved Li (DLi) and Sr (DSr) behavior in the water column. Here, we present for the first time the DLi and DSr elemental and isotopic (δ7Li, and 87Sr/86Sr) profiles from six casts distributed over the Lucky Strike hydrothermal vent field (LSHF, Mid-Atlantic Ridge). The DLi and DSr results reflect a hydrothermal contribution to the water column up to ∼300 m above the seafloor that can be quantified by up to 10% based on the DLi dataset. For increasing hydrothermal contribution the δ7Li values of the water column become heavier most likely due to mineral–seawater interactions, i.e., manganese oxide formed during the mixing of hydrothermal fluid and seawater. Contrarily to the DLi, DSr, and δ7Li datasets, the hydrothermal contribution to the water column is not evidenced by the 87Sr/86Sr ratios that fall within the range of oligotrophic oceanic waters. Surprisingly, some geographically distant casts display at the same depth identical DLi and DSr concentrations or similar δ7Li signatures. We attribute these features to the current dynamics above the LSHF, suggesting that the hydrothermal signature of the western casts can overprint those of the eastern and center casts in less than 1 h at the LSHF km-scale. Overall, this study highlights that 1) as for many elements, DLi, DSr, and δ7Li can be used to track the hydrothermal signature to the water column at a km-scale whereas 87Sr/86Sr cannot, 2) local currents play a major role in advecting the hydrothermal contribution away from the hydrothermal sources, and 3) mineral–seawater interaction processes are at play during the mixing between hydrothermal fluid and seawater and impact the δ7Li hydrothermal signature. Our study suggests that chemical tracers of hydrothermal input have to be chosen depending on the spatial scale of the studied area.
Highlights
A better understanding of lithium (Li) and strontium (Sr) oceanic biogeochemical cycles is needed nowadays based on two main issues: 1) their oceanic cycles are still under debate, and 2) they are two economically relevant elements
This study presents Li and Sr elemental and isotopic compositions of six profiles in the water column over the Lucky Strike Hydrothermal Field (LSHF), as well as six current speed intensities and direction profiles
The data were acquired on 30 seawater column samples collected between 1478 and 1722 mbsl at five CTD casts distributed over the LSHF and one at its northern border
Summary
A better understanding of lithium (Li) and strontium (Sr) oceanic biogeochemical cycles is needed nowadays based on two main issues: 1) their oceanic cycles are still under debate, and 2) they are two economically relevant elements. Several studies have notably shown that dissolved metals from hydrothermal origin such as iron and aluminum can be transported over a hundred to thousand kilometers away from their source and can even impact productive layers (Measures et al, 2015; Resing et al, 2015; Guieu et al, 2018). It is questionable whether this type of transport can affect Li and Sr of hydrothermal origin, Li for which hydrothermalism is one of the most dominant sources to the ocean (Araoka et al, 2016; Tomascak et al, 2016, and reference therein)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
