The Importance of Water Mass Transport and Dissolved-Particle Interactions on the Aluminum Cycle in the Subtropical North Atlantic

New dissolved aluminum (dAl) data from the 2017 GEOTRACES process study GApr08 along 22 degrees N in the subtropical North Atlantic are presented. They show an east to west increase in dAl concentration in the surface waters. Simulation of these data with a 1D advection-dust deposition revealed that, (a) advection and dust dissolution are equally important dAl sources, (b) scavenging plays a minor role compared to advection in dAl removal, and (c) in addition to dust dissolution, another dAl source is required at the westernmost stations to fully explain our observations. We attribute this additional source to the dissolution of erosion products delivered to the western subtropical North Atlantic by the Lesser Antilles. For waters deeper than similar to 200-300 m, an optimum multi-parameter analysis allowed to separate the component of the dAl signal derived from water mass transport from its biogeochemical component. This revealed, (a) a major role played by water mass transport, (b) a net dAl removal between 200 and 800 m, attributed to scavenging at the subtropical North Atlantic scale, and (c) internal dAl inputs between 800 m and the seafloor, attributed to reversible scavenging. While the dAl oceanic distribution is usually considered to be dominated by the atmospheric dust input and removal by particle scavenging, this study highlights the important role played by advection, and the need to explicitly take this into account in order to quantitatively reveal the impact of external sources and dissolved-particulate interactions on the Al cycle in the North Atlantic Ocean.

Automated summary

New dissolved aluminum (dAl) data from the 2017 GEOTRACES process study GApr08 show an east to west increase in dAl concentration in the surface waters along 22 degrees N in the subtropical North Atlantic. Results indicate that advection, dust dissolution, and erosion products from the Lesser Antilles contribute to dAl sources, while scavenging, water mass transport, and internal dAl inputs play important roles in dAl removal and distribution in the North Atlantic Ocean. Taking advection into consideration is crucial for understanding the impact of external sources and dissolved-particulate interactions on the Al cycle.