Mahadevan, Amala: WHOI (Project Lead)
Project Funding:
2016 - 2018
NRA: 2015 NASA: Ocean Biology and Biogeochemistry
Funded by NASA
Abstract:
Particulate organic matter (POM) in the upper ocean is subject to advection by near-surface velocities related to the dynamics of eddies, fronts and mixed layer instabilities. This advection influences both the horizontal and vertical distributions of POM. When advective motion is coupled to the differential sinking rates of various classes of POM, a sorting effect emerges. Slower sinking or neutrally buoyant particles are advected with the water, while faster sinking particles are quicker to descend from the surface ocean that typically has higher velocities. In order to relate the surface production of POM to its export flux at depth, we will consider the interaction between a submesoscale-resolving flow field and particles characterized by a spectrum of sinking velocities. As the particles sink, their mass and sinking velocity may be transformed by remineralization, aggregation and disaggregation.
Our objectives are: (1) To characterize the vertical transport of POM as a function of the
flow field, the POM mass and sinking distributions, and the patchiness of productivity; and (2) To assess the ability of various configurations of an observing system (autonomous and ship-based) to characterize these fluxes. Our results will improve our ability to interpret observational data and to suggest strategies for employing a system of observing assets for the EXPORTS field campaigns.
We will use a three-dimensional, submesoscale-resolving Process Study Ocean Model (PSOM) configured for 3 regions where observational Seaglider datasets can be mined. These are the 2008 North Atlantic Bloom experiment (NAB08; 61◦N, 26◦W), the OSMOSIS field campaign at the site of the Porcupine Abyssal Plain (PAP; 49◦N, 16◦W) and Ocean Station Papa (OSP; 50◦N, 145◦W) in the North Pacific. Datasets from each of these regions will be used to initialize the model with realistic vertical and horizontal density gradients, nutrient fields, and seasonally appropriate wind stresses, heat fluxes and light. The production of POM from an NPZD model will be used to seed virtual particles with a spectrum of characteristics (masses and sinking velocities) to represent the diversity of the particulate pool. We will characterize the depth-dependent export flux in different particle classes in relation to physical conditions and the upper ocean detrital particle production. We will characterize the sensitivity of model POM export to (1) a spectrum of particle characteristics and the transformation of these
characteristics (e.g. sinking speed and mass) with time, (2) the surface supply of POM from patchy productivity, and (3) variable physical settings (seasonally dependent stratification and mixed layer properties, fronts and eddies) at each of the field sites.
An integrated suite of Observing System Simulation Experiments (OSSEs) will enable us to test the ability of a suite of mixed autonomous assets, including floats, gliders, towed profilers and sediment traps to accurately characterize export pathways at submesoscale resolution. OSSEs will be designed to test adaptive sampling of frontal features guided by surface properties accessible by remote sensing, and to determine the optimal deployment of sediment traps based on the statistical funnel of particles sampled by a trap at depth. Our activities will address a number of the fundamental mechanisms of POM export identified by the EXPORTS Science Plan and will inform the design and implementation of EXPORTS field campaigns in a number of ways, ranging from a mechanistic understanding of processes, characterization of export, and planning of observational strategies.
More details may be found in the following project profile(s):
