Marine algae are ‘taught’ the basics of angular momentum

Abstract

Advanced modelling studies and high-resolution observations have shown that flows related to instability of the mesoscale (~1-10 km scale) may provide both the fertilisation mechanism for nutrient-depleted (oligotrophic) surface waters and a subduction mechanism for the rapid export of phytoplankton biomass to the deep ocean. Here, a detailed multidisciplinary analysis of the data from an example high-resolution observational campaign is presented. The data provide direct observations of the transport of phytoplankton through baroclinic instability. Furthermore, the data confirm that this transport is constrained by the requirement to conserve angular momentum, expressed in a stratified water column as the conservation of potential vorticity. This constraint is clearly seen to produce long thin filaments of phytoplankton populations strained out along isopycnal vorticity annuli associated with mesoscale frontal instabilities.

Frontal Dynamics in the Alboran Sea: 1. Coherent 3D Pathways at the Almeria‐Oran Front Using Underwater Glider Observations

“…Our simple estimate for the potential biological export associated with filaments of the AO front is of a similar order of magnitude but less than that estimated for a similar filament in the northern North Atlantic (Allen, 2017); this indicates how important small cells may be in terms of carbon export to the deeper water column. The coherent pathways provided by filaments of instability contribute to a flux of carbon out of the euphotic zone, which is not captured by satellite imagery.…”

“…with a high C:CHL ratio ∽ of 46:1 (Gould & Wiesenburg, 1990; Jacquet, 2002). Following the simple geometrical approach of Allen (2017), the elliptical cross section area of observed CHL filament in both north and central glider line is approximately 1.7 × 10 5 m 2 assuming, by inspection (Figures 10a and 10c), the short and long radii of the ellipse to be 9 and 6,000 m. From the ADCP of the north glider, we see the characteristic along front velocity of 25 cm s −1 (Figure S4 in Supporting Information ). If we estimate the difference in depth of the chl filament seen in both the north and central glider lines to be 18 m, from inspection of (Figures 10a and 10c), then bearing in mind the distance between the two lines of approximately 17500 m we have a gradient of approximate 0.001.…”

“…We examine the variability of the AO front from a vertical scale of 10 m, a horizontal scale of 10–100 km, and a temporal scale of a week. Previous high‐resolution modeling and in‐situ studies have found that submesoscale three‐dimensional flow (∼1–10 km scale) is associated with heavily perturbed unstable fronts (Allen, 2017; Lévy & Klein Patriece, 2001; Mahadevan, 2016), which may provide stratification within the pycnocline.…”

The 48th Liege colloquium: submesoscale processes: mechanisms, implications, and new frontiers

“…Another high-resolution observational study addresses the transport of phytoplankton through baroclinic instability (Allen 2017) and the importance of the conservation of potential vorticity in producing long, thin filaments of phytoplankton populations is highlighted.…”