10 May 2022
10 May 2022
Status: this preprint is currently under review for the journal BG.

Lagrangian-Eulerian statistics of mesoscale ocean chlorophyll from Bio-Argo floats and satellites

Darren Craig McKee1, Scott C. Doney1, Alice Della Penna2,3, Emmanuel S. Boss4, Peter Gaube5, Michael J. Behrenfeld6, and David M. Glover7 Darren Craig McKee et al.
  • 1Department of Environmental Sciences, University of Virginia, Charlottesville, VA, 22904, USA
  • 2Institute of Marine Science, University of Auckland, Auckland, New Zealand
  • 3School of Biological Sciences, University of Auckland, Auckland, New Zealand
  • 4School of Marine Sciences, University of Maine, Orono, ME, USA
  • 5Applied Physics Laboratory, University of Washington, Seattle, WA, USA
  • 6Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, USA
  • 7Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA

Abstract. Phytoplankton form the base of marine food webs and play an important role in carbon cycling, making it important to quantify rates of biomass accumulation and loss. Since phytoplankton drift with ocean currents, rates should be evaluated in a Lagrangian as opposed to Eulerian framework. In this study, we quantify the Lagrangian (from Bio-Argo floats and surface drifters with satellite ocean colour) and Eulerian (from satellite ocean colour and altimetry) statistics of mesoscale chlorophyll and velocity by computing decorrelation time and length scales and relate the frames by scaling the material derivative of chlorophyll. Because floats profile vertically and are not perfect Lagrangian observers, we quantify the mean distance between float and surface geostrophic trajectories over the time spanned by three consecutive profiles (Quasi-Planktonic Index; QPI) to assess how their sampling is a function of their deviations from surface motion. Lagrangian-Eulerian statistics of chlorophyll are sensitive to the filtering used to compute anomalies. Chlorophyll anomalies about a 31-day time filter reveal approximate equivalence of Lagrangian and Eulerian tendencies, suggesting they are driven by ocean-colour-pixel-scale processes and sources or sinks. Chlorophyll anomalies about a seasonal cycle have Eulerian scales similar to those of velocity, suggesting mesoscale stirring helps set distributions of biological properties, and ratios of Lagrangian to Eulerian timescales depend on observer speed relative to an evolution speed of the chlorophyll fields in a manner similar to earlier theoretical results for velocity scales. By lagging surface chlorophyll patches, floats underestimate the Lagrangian tendency and advective terms, and the Eulerian tendency primarily sets timescales; however, since the QPI increases with profiling interval, frequent profiling can generate more accurate time series of phytoplankton accumulation.

Darren Craig McKee et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-103', Bror Jonsson, 15 Jun 2022
    • AC1: 'Reply on RC1', Darren McKee, 13 Jul 2022
  • RC2: 'Comment on bg-2022-103', Anonymous Referee #2, 22 Jun 2022
    • AC2: 'Reply on RC2', Darren McKee, 13 Jul 2022

Darren Craig McKee et al.

Data sets

DUACS DT2018: 25 years of reprocessed sea level altimetry products Taburet, Guillaume; Sanchez-Roman, Antonio; Ballarotta, Maxime; Pujol, Marie-Isabelle; Legeais, Jean-FranÇois; Fournier, Florent; Faugere, Yannice; Dibarboure, Gerald

GlobColour ACRI-ST GlobColour Team

NOAA Global Drifter Program quality-controlled 6-hour interpolated data from ocean surface drifting buoys Lumpkin, Rick; Centurioni, Luca

NAAMES BGC-Argo Float Data University of Maine In-Situ Sound and Color Lab

Argo float data and metadata from Global Data Assembly Centre (Argo GDAC) - Snapshot of Argo GDAC of February 10st 2021 Argo

Darren Craig McKee et al.


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Short summary
Since phytoplankton (small, drifting photosynthetic organisms) drift with ocean currents, biomass accumulation rates should be evaluated in a Lagrangian (observer moves with a fluid parcel) as opposed to Eulerian (observer is stationary) framework. Here we use profiling floats and surface drifters combined with satellite data to analyze time and length scales of chlorophyll concentrations (a proxy for biomass) and of velocity to quantify how phytoplankton variability is related to water motion.