Recent experimental measurements of fluorescence values and turbulent energy dissipation rates, recorded in weakly stratified boundary layers in the open ocean, have highlighted a significant correlation between the formation of deep chlorophyll maxima (DCM) and turbulent mixing. Specifically, the depth of many DCM are observed to lie below, but within about one standard deviation, of the point at which the energy dissipation rate profile reaches its maximum. This correlation of DCM and turbulent mixing is both exciting and curious, as conventional thinking tends to see the latter as a destructive rather than a constructive agent in regards to the formation of deep biological maxima (DBM), for which DCM data is usually interpreted as a proxy. In order to investigate this phenomenon, a three-dimensional large eddy simulation (LES) of the ocean boundary layer was combined with a generic nutrient-phytoplankton-zooplankton (NPZ) type biological model, in order establish what mechanisms might be driving the experimental observations. Simulations of the LES-NPZ model, based upon various sets of generic biological parameters, demonstrate DCM/DBM formation occurs at normalized depths close to those seen in the experimental observations. The simulations support the hypothesis that the DBM are generated by a combination of zooplankton predation pressure curtailing phytoplankton growth near the surface, and a decline in the strength of the vertical mixing processes advecting nutrient through the boundary layer. In tandem, these produce a region of the water column in which predation pressure is relatively low and nutrient aggregation relatively high, suitable conditions for DBM formation.The presence of deep (or sub-surface) chlorophyll/biological maxima (DCM/DBM) observed in vertical fluorescence profiles is one of the most ubiquitous features of the world's oceans (Macıas et al. 2008), and much research effort has been devoted to understanding the mechanisms behind their formation and dynamics (see Cullen 2015 for a comprehensive review of the subject). Observations of DCM are not just confined to the ocean boundary layer (e.g., Cullen 1982;Estrada et al. 1993;Letelier et al. 2004; Macıas et al. 2013), but are a pervasive feature of the limnology of lakes too (Hamilton et al. 2010;White and Matsumoto 2012; Simmonds et al. 2015). Here, the terminology DCM specifies a broad (10-20 m) region of relatively high chlorophyll concentrations (but weak concentration gradients), usually to be found at or somewhat below the mixed layer depth. This should not be confused with the concept of a rapidly varying biological "thin layer," confined to vertical scales of just a few meters (e.g., Dekshenieks et al. 2001;McManus et al. 2003McManus et al. , 2005Benoit-Bird et al. 2009;Durham et al. 2009;Johnston et al. 2009), which are usually found residing within the top 10 m or so of the water column.A number of different postulates have been advanced to attempt to explain both the formation of DCM, and the reasons as to why they ar...

Phytoplankton patchiness occurs on a plethora of spatial and temporal scales which can be extremely patchy in both horizontal and vertical directions. This patchiness directly affects the dynamics of the overall bloom, so understanding the mechanisms for patchiness to occur on each scale is therefore integral to the understanding of plankton bloom dynamics as a whole. This modelling study aims to introduce a mechanism for patch formations, which has previously had very little exposure, but is ubiquitous to the oceanic mixed layer -patchiness induced by the interaction between nutrient upwelling and Langmuir circulations.

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