Plankton layer profiles as determined by shearing, sinking, and swimming

Birch, Daniel A.; Young, W. R.; Franks, Peter J. S.

doi:10.4319/lo.2009.54.1.0397

Cited by 18 publications

(31 citation statements)

References 9 publications

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“…10A; Franks 1995;Birch et al 2008). That is, the same peak should be found on different isopycnals in horizontally separated vertical profiles.…”

Section: Discussionmentioning

confidence: 99%

“…20 mm was almost entirely composed of nonmotile chain diatom species (, 95% on average by number), the most abundant of which belonged to the genera Pseudo-nitzschia, Chaetoceros, Thalassiosira, and Nitzschia. Peaks lying on strong density gradients and composed of passive (nonswimming) particles are consistent with formation by shear (Franks 1995;Stacey et al 2007;Birch et al 2008) or variable sinking rates because of density gradients (Derenbach et al 1979). Observing how the peaks changed horizontally can aid in distinguishing between the relative likelihood of these two mechanisms because formation by shear would be indicated by horizontal layers tilted across isopycnals (Eckart 1948 ;Franks 1995;Birch et al 2008).…”

Section: Discussionmentioning

confidence: 99%

“…9), composed largely of nonmotile chain-forming diatoms, were coherent horizontally and represented part of a layer that was tilted vertically across isopycnals. Thus, the most probable mechanism for their formation is by vertical shearing of existing patches of phytoplankton (Franks 1995;Birch et al 2008).…”

Section: Discussionmentioning

confidence: 99%

“…Many biological and physical mechanisms of layer formation have been proposed (Derenbach et al 1979;Franks 1995;Birch et al 2009), including mechanisms that describe layer formation by straining through vertical shear and by phytoplankton motility or buoyancy (Stacey et al 2007;Birch et al 2008). Several studies have inferred the relative importance of a given mechanism for a particular layer (Gallager et al 2004;Cheriton et al 2009;Sullivan et al 2010).…”

Section: Discussionmentioning

confidence: 99%

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Cryptic peaks: invisible vertical structure in fluorescent particles revealed using a planar laser imaging fluorometer

Prairie

Franks

Jaffe

2010

Limnology & Oceanography

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Small-scale vertical structure in the distribution of phytoplankton could be fundamentally important for zooplankton foraging, trophic coupling, and carbon cycling in planktonic ecosystems. Here, we identify regions of structure in phytoplankton communities that would be undetected by fluorometers by comparing the vertical distribution of chlorophyll fluorescence to the concentration of fluorescent particles over submeter scales. Images acquired with a free-falling planar laser fluorescence imaging system were used to calculate vertical profiles of the concentrations and spatial distributions of fluorescent particles (e.g., eukaryotic phytoplankton, aggregates) and bulk fluorescence. We frequently observed peaks in the concentration of fluorescent particles with no coincident peak in bulk fluorescence: we define these features as cryptic peaks. These cryptic peaks can occur because the integrated fluorescence of the particles that are resolved by the imaging system is a small fraction of the total fluorescence; thus, a dramatic local change in the abundance of fluorescent particles can occur without significantly changing the bulk fluorescence. We also observed bulk fluorescence-only peaks: peaks in bulk fluorescence with no coincident peak in fluorescent particle concentration. These features suggest that peaks in bulk fluorescence or chlorophyll a do not necessarily indicate increases in the concentration of the fluorescent particles resolved by our system, again emphasizing the difference between these two measures of phytoplankton structure. Comparing the relative abundances of two size classes of the fluorescent particles in the images revealed that the size composition of the fluorescent particles also varied over small scales. Phytoplankton less than , 500 mm in length numerically dominated the composition of most (65%) of the cryptic peaks we observed. By comparing vertical profiles of fluorescent particle concentration from two drops separated by less than an hour, we hypothesize that the peaks formed through vertical shearing of existing patches. Cryptic peaks contained almost 20% of the total number of fluorescent particles counted in all drops during our study and thus could represent disproportionately intense regions for important ecological processes relative to the rest of the water column.

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“…10A; Franks 1995;Birch et al 2008). That is, the same peak should be found on different isopycnals in horizontally separated vertical profiles.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Cryptic peaks: invisible vertical structure in fluorescent particles revealed using a planar laser imaging fluorometer

Prairie

Franks

Jaffe

2010

Limnology & Oceanography

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“…Previous papers have applied this idea, (e.g. [5,6,9,13,19]) but have focused more on analytical x-z flows whereas we are interested in flows with complex horizontal structure. As Appendix 1 shows, if the vertical swimming and its random variability overcome the fluid motions and cause clustering around the preferred depth, the biomass density can be represented asb(x, t)F(z) where…”

Section: Concentration Of Depth-keeping Organisms By Fluid Flowmentioning

confidence: 99%

Copepod Aggregations: Influences of Physics and Collective Behavior

Flierl

Woods

2014

J Stat Phys

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Dense copepod aggregations form in Massachusetts Bay and provide an important resource for right whales. We re-examine the processes which might account for the high concentrations, investigating both horizontally convergent flow, which can increase the density of depth-keeping organisms, and social behavior. We argue that the two act in concert: social behavior creates small dense patches (on the scale of a few sensing radii); physical stirring brings them together so that they merge into aggregations with larger scales; it also moves them into areas of physical convergence which retain the increasingly large patch. But the turbulence can also break this apart, suggesting that the overall high density in the convergence zone will not be uniform but will instead be composed of multiple transient patches (which are still much larger than the sensing scale).

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