Analytical solution of the nitracline with the evolution of subsurface chlorophyll maximum in stratified water columns

Gong, Xuerui; Jiang, Wensheng; Wang, Linhui; Gao, Huiwang; Boss, Emmanuel; Yao, Xiaohong; Kao, Shuh Ji; Shi, Jie

doi:10.5194/bg-14-2371-2017

Cited by 18 publications

(20 citation statements)

References 89 publications

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“…For both floats, the estimated nitracline z NO3 and isolume z 0.415 correlated with z DCM , with the correlation of 0.58 and 0.71 in the northern SCS and of 0.47 and 0.84 in the central basin, respectively (Tables and ). The light‐driven patterns of chlorophyll and nitrate are similar to those in oligotrophic waters (Letelier et al, ) and are consistent with 1‐D steady state modeling (Fennel & Boss, ; Gong et al, ).…”

Section: Resultssupporting

confidence: 82%

“…Our key findings are as follows: Surface variability of chlorophyll‐a at seasonal scale was found to be highly modulated by the photoacclimation process, especially in the central basin, where all bio‐optical properties were nearly constant and most of the observed variability could be explained based on seasonal changes in light. The DCM followed the z 0.415 isolume and the nitracline well, similar to what was found in oligotrophic waters elsewhere (Letelier et al, ) and from the 1‐D model (Gong et al, ). The mixing‐induced entrainment played an important role in the vertical redistribution of particles, especially during the winter bloom period in the northern SCS. Analysis of whole water column properties suggest that the water column bloom started significantly later (~1.5 months) than the “surface” bloom observed by satellite.…”

Section: Discussionsupporting

confidence: 81%

“…2. The DCM followed the z 0.415 isolume and the nitracline well, similar to what was found in oligotrophic waters elsewhere (Letelier et al, 2004) and from the 1-D model (Gong et al, 2017). 3.…”

Section: Discussionsupporting

confidence: 79%

“…This evolution is typical of oligotrophic regions such as the North Pacific subtropical gyre and Mediterranean Sea (Letelier et al, 2004;Mignot et al, 2014) (Tables 2 and 3). The light-driven patterns of chlorophyll and nitrate are similar to those in oligotrophic waters (Letelier et al, 2004) and are consistent with 1-D steady state modeling (Fennel & Boss, 2003;Gong et al, 2017).…”

Section: Chlorophyll-a and Particles At Dcmsupporting

confidence: 77%

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Temporal and Vertical Variations of Particulate and Dissolved Optical Properties in the South China Sea

et al. 2019

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Two Bio‐Argo floats measured the concentration of chlorophyll‐a, the backscattering coefficient, the fluorescence of humic‐like dissolved organic matter, dissolved oxygen, and temperature and salinity in the northern and central basins of the South China Sea for over 2 years. Temporal evolutions of bio‐optical properties were analyzed at surface, subsurface, and in the whole water column, respectively. It was found that (1) The seasonal variability of the surface chlorophyll‐a was highly controlled by photoacclimation, especially in the central basin; (2) backscattering in the upper 150 m was nearly constant, exhibiting no distinct seasonality; (3) with vertical mixing, particles from the deep chlorophyll maxima were entrained into the mixed layer resulting in enhanced surface chlorophyll during the early winter. This phenomenon may mislead a study based on satellite data which is likely to interpret it as blooming rather than a redistribution of phytoplankton within the water column; (4) analysis of a winter bloom and an anticyclonic eddy reveal that physical entrainment and biological photoacclimation modulated the vertical distributions of chlorophyll‐a and particles and potentially also changes of phytoplankton community composition; and (5) fluorescent dissolved organic matter was found to be highly coupled to phytoplankton dynamics in both basins, with a maximum (after removing the contribution of physical convective mixing) located at the depth of chlorophyll‐a subsurface maximum.

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Section: Resultssupporting

confidence: 82%

Section: Discussionsupporting

confidence: 81%

Section: Discussionsupporting

confidence: 79%

Section: Chlorophyll-a and Particles At Dcmsupporting

confidence: 77%

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Temporal and Vertical Variations of Particulate and Dissolved Optical Properties in the South China Sea

et al. 2019

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“…A statistical method based on the singular value decomposition (SVD) algorithm (Golub and Van Loan, 1996) was used to identify the different types of SCMs in the Mediterranean Sea. The approach allowed us to tackle the large amount of data provided by the BGC-Argo floats and to simultaneously classify the Chl a and b bp vertical profiles of the database.…”

Section: Statistical Methods Of Classification Of the Vertical Profilementioning

confidence: 99%

Bio-optical characterization of subsurface chlorophyll maxima in the Mediterranean Sea from a Biogeochemical-Argo float database

et al. 2019

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Abstract. As commonly observed in oligotrophic stratified waters, a subsurface (or deep) chlorophyll maximum (SCM) frequently characterizes the vertical distribution of phytoplankton chlorophyll in the Mediterranean Sea. Occurring far from the surface layer “seen” by ocean colour satellites, SCMs are difficult to observe with adequate spatio-temporal resolution and their biogeochemical impact remains unknown. Biogeochemical-Argo (BGC-Argo) profiling floats represent appropriate tools for studying the dynamics of SCMs. Based on data collected from 36 BGC-Argo floats deployed in the Mediterranean Sea, our study aims to address two main questions. (1) What are the different types of SCMs in the Mediterranean Sea? (2) Which environmental factors control their occurrence and dynamics? First, we analysed the seasonal and regional variations in the chlorophyll concentration (Chl a), particulate backscattering coefficient (bbp), a proxy of the particulate organic carbon (POC) and environmental parameters (photosynthetically active radiation and nitrates) within the SCM layer over the Mediterranean Basin. The vertical profiles of Chl a and bbp were then statistically classified and the seasonal occurrence of each of the different types of SCMs quantified. Finally, a case study was performed on two contrasted regions and the environmental conditions at depth were further investigated to understand the main controls on the SCMs. In the eastern basin, SCMs result, at a first order, from a photoacclimation process. Conversely, SCMs in the western basin reflect a biomass increase at depth benefiting from both light and nitrate resources. Our results also suggest that a variety of intermediate types of SCMs are encountered between these two endmember situations.

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Deep chlorophyll maxima across a trophic state gradient: A case study in the Laurentian Great Lakes

Scofield

Watkins

Osantowski

et al. 2020

Limnology & Oceanography

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Deep chlorophyll maxima (DCM) are common in stratified lakes and oceans, and phytoplankton growth within DCM often contributes significantly to total system production. Theory suggests that properties of DCM should be predictable by trophic state, with DCM becoming deeper, broader, and less productive with greater oligotrophy. However, rigorous tests of these expectations are lacking in freshwater systems. We use data generated by the U.S. EPA from 1996 to 2017, including in situ profile data for temperature, photosynthetically active radiation (PAR), chlorophyll, beam attenuation (c p), and dissolved oxygen (DO), to investigate patterns in DCM across lakes and over time. We consider trophic state, 1% PAR depth (z 1%), thermal structure, and degree of photoacclimation as potential drivers of DCM characteristics. DCM depth and thickness generally increased while DCM chlorophyll concentration decreased with decreasing trophic state index (greater oligotrophy). The z 1% was a stronger predictor of DCM depth than thermal structure. DCM in meso-oligotrophic waters were closely aligned with maxima in c p and DO saturation, suggesting they are autotrophically productive. However, the depths of these maxima diverged in ultra-oligotrophic waters, with DCM occurring deepest. This is likely a consequence of photoacclimation in high-transparency waters, where c p can be a better proxy for phytoplankton biomass than chlorophyll. Our results are generally consistent with expectations from DCM theory, but they also identify specific gaps in our understanding of DCM in lakes, including the causes of multiple DCM, the importance of nutriclines, and the processes forming DCM at higher light levels than expected.

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Analytical solution of the nitracline with the evolution of subsurface chlorophyll maximum in stratified water columns

Cited by 18 publications

References 89 publications

Temporal and Vertical Variations of Particulate and Dissolved Optical Properties in the South China Sea

Temporal and Vertical Variations of Particulate and Dissolved Optical Properties in the South China Sea

Bio-optical characterization of subsurface chlorophyll maxima in the Mediterranean Sea from a Biogeochemical-Argo float database

Deep chlorophyll maxima across a trophic state gradient: A case study in the Laurentian Great Lakes

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