Award: OCE-1703336

Understanding the magnitude and uncertaintities in the global carbon cycle, and how it will change under a changing climate, requires mechanistic understanding of the links between surface plankton communities and sinking particle flux (export) out of the surface. However, our current methodological paradigms do not directly resolve these mechanisms. This project represented an intesection of perspectives and training introduced by three early career female scientists (a biological, chemical and physical oceanographer), to address this deficiency. Using autonomous technology and ship-based measurements, they made observations who is exported from the surface ocean and how using new, particle-resolving optical and molecular techniques embedded within a sampling scheme that characterizes export events at high resolution (sufficient to even resolve diel pulses). This project formed the foundation of a MS thesis and involved a synthesis of particle- and molecular-level data with interdisciplinary particle flux observations. It directly led to the sucessful funding of this team in the EXPORTS campaign, and also funding to build autonomous Lagrangian RAFOS-style floats that target biological-pump measurements.

Particle export environments were studied at 3 open ocean locations during a cruise from Hawaii to Seattle in January-February 2017. The surface communities were characterized by a combination of satellite observations, sensors attached to a free-drifting, continuously profiling WireWalker, an in situ holographic camera, microscopy, and by sequencing 18S and 16S rRNA gene fragments. Exported particles were be simultaneously captured by various specialized sediment traps and their characteristics will be directly related to their sources in the surface community by identifying the genetic contents of individual particle types. Individual particles will be isolated from gel layers and the 16S and 18S rRNA gene fragments will be amplified and sequenced. This work was the first time that molecular approaches were combined with particle-specific observations to enable simultaneous identification of both which organisms are exported and the mechanisms responsible for their export. These data allowed testing of recent provocative hypotheses about the biological pump, such as the role of cyanobacteria and lesser-studied organisms, and the biological basis of short-term variability in carbon export. In addition, resolving the mechanistic links between surface communities and export is required for the next generation of biological pump models.

Last Modified: 07/10/2019
Modified by: Melissa Omand