Magnetic signature of vertically migrating aggregations in the ocean

Abstract

The transport of heat and solutes by vertically migrating aggregations of plankton has long been explored as a potentially important source of ocean mixing [1][2][3]. However, direct evidence of enhanced mixing due to these migrations remains challenging to obtain and inconclusive [4]. These shortcomings are due to the limitations of current measurement techniques, i.e., velocimetry techniques, which require a priori knowledge of the precise aggregation location [5] and typically trigger animal avoidance behavior from introducing instrumentation into the migration [6]. Here we develop a new approach to overcome these longstanding limitations by leveraging advancements in modern magnetometry to detect the flow-induced magnetic fields that naturally arise from seawater as it moves through the Earth's geomagnetic field [7]. We derive quantitative predictions showing that these flow-induced magnetic fields in the vicinity of migrating aggregations have a strength proportional to the integrated fluid transport due to the migration. Importantly these magnetic signatures are potentially detectable remotely at a significant distance far from the aggregation and region of moving fluid with emerging quantum-enhanced magnetometry techniques such as Nitrogen-Vacancy centers in diamond [8]. These results provide a new, testable framework for quantifying the significance of fluid transport in the ocean due to swimming organisms that may finally resolve a scientific debate [9] with potentially enormous implications for our understanding of ocean dynamics and climate change.