In:
Biogeosciences, Copernicus GmbH, Vol. 19, No. 24 ( 2022-12-21), p. 5927-5952
Abstract:
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. As phytoplankton drift with ocean
currents, rates should be evaluated in a Lagrangian as opposed to an 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 and Eulerian statistics of chlorophyll are sensitive to the
filtering used to compute anomalies. Chlorophyll anomalies about a 31 d
time filter reveal an approximate equivalence of Lagrangian and Eulerian
tendencies, suggesting they are driven by ocean colour pixel-scale processes
and sources or sinks. On the other hand, 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 the magnitude of
velocity fluctuations relative to an evolution speed of the chlorophyll
fields in a manner similar to earlier theoretical results for velocity
scales. The results suggest that stirring by eddies largely sets Lagrangian
time and length scales of chlorophyll anomalies at the mesoscale.
Type of Medium:
Online Resource
ISSN:
1726-4189
DOI:
10.5194/bg-19-5927-2022
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2022
detail.hit.zdb_id:
2158181-2
