Spatial and temporal scales of chlorophyll variability using high-resolution glider data

Little, Hazel; Vichi, Marcello; Thomalla, Sandy J.; Swart, Sebastiaan

doi:10.1016/j.jmarsys.2018.06.011

Cited by 18 publications

(29 citation statements)

References 32 publications

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“…variation is never negligibly small, and even when the mixed layer is deepest and the turbulence is strongest, it doesn't drop below about 0.5. As expected, the variability is larger during the Austral summer months, when turbulence is weaker than in other seasons, showing an extended peak from spring to autumn, in full agreement with the variability observed through autonomous observations in the SAZ (Little et al, 2018). In the Eulerian simulation, and in Lagrangian simulations with very strong irreversible mixing, the peak is small and occurs in December, when the mixed layer is the shallowest, while the coefficient of variation remains negligibly different from zero in other months.…”

Section: Comparison With Bgc-argo Float Observationssupporting

confidence: 90%

“…Chlorophyll fluctuations are damped, but not completely wiped out. The resolution length scale of observations affects variance estimations, as found when highfrequency sampling instruments are used (Little et al, 2018). In Figure 7B ( Figure S3B for PAPA) we show the monthly average of the coefficient of variation of the simulation data relative to p = 10 −7 , after they underwent this coarse-graining procedure at several resolutions.…”

Section: Comparison With Bgc-argo Float Observationsmentioning

confidence: 98%

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Stirring, Mixing, Growing: Microscale Processes Change Larger Scale Phytoplankton Dynamics

Paparella

Vichi

2020

Front. Mar. Sci.

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Section: Comparison With Bgc-argo Float Observationssupporting

confidence: 90%

Section: Comparison With Bgc-argo Float Observationsmentioning

confidence: 98%

Stirring, Mixing, Growing: Microscale Processes Change Larger Scale Phytoplankton Dynamics

Paparella

Vichi

2020

Front. Mar. Sci.

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“…A SAZ glider study by Little et al (2018) corroborated these findings with summer matchups in small-scale temporal variability (<10 days) in wind stress, mixed-layer depth (MLD) and chlorophyll that emphasizes the interconnectedness between physical drivers and their biological response. Despite the similarity in the scales of variability, no correlation was observed between MLD and Chl a, which is explained by the variable response that MLD adjustments drive, i.e.…”

Section: Discussionmentioning

confidence: 70%

Seasonal development of iron limitation in the sub-Antarctic zone

Ryan‐Keogh

Thomalla

Mtshali³

et al. 2018

Biogeosciences

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Abstract. The seasonal and sub-seasonal dynamics of iron availability within the sub-Antarctic zone (SAZ; ∼ 40-45 • S) play an important role in the distribution, biomass and productivity of the phytoplankton community. The variability in iron availability is due to an interplay between winter entrainment, diapycnal diffusion, storm-driven entrainment, atmospheric deposition, iron scavenging and iron recycling processes. Biological observations utilizing grow-out iron addition incubation experiments were performed at different stages of the seasonal cycle within the SAZ to determine whether iron availability at the time of sampling was sufficient to meet biological demands at different times of the growing season. Here we demonstrate that at the beginning of the growing season, there is sufficient iron to meet the demands of the phytoplankton community, but that as the growing season develops the mean iron concentrations in the mixed layer decrease and are insufficient to meet biological demand. Phytoplankton increase their photosynthetic efficiency and net growth rates following iron addition from midsummer to late summer, with no differences determined during early summer, suggestive of seasonal iron depletion and an insufficient resupply of iron to meet biological demand. The result of this is residual macronutrients at the end of the growing season and the prevalence of the high-nutrient low-chlorophyll (HNLC) condition. We conclude that despite the prolonged growing season characteristic of the SAZ, which can extend into late summer/early autumn, results nonetheless suggest that iron supply mechanisms are insufficient to maintain potential maximal growth and productivity throughout the season.

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“…The euphotic depth was defined as the depth at which the photosynthetically active radiation (PAR) is 1% of surface PAR. Empirical Mode Decomposition (EMD) analysis was performed on glider data according to the methods outlined in Little et al (2018). Briefly, primary signals from glider sea surface temperature (SST), MLD, surface chlorophyll concentration and α NPQ were decomposed into Intrinsic Mode Functions (IMFs) (Rato et al, 2008).…”

Section: Methodsmentioning

confidence: 99%

Deriving a Proxy for Iron Limitation From Chlorophyll Fluorescence on Buoyancy Gliders

Ryan‐Keogh

Thomalla

2020

Front. Mar. Sci.

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Chlorophyll fluorescence, primarily used to derive phytoplankton biomass, has long been an underutilized source of information on phytoplankton physiology. Diel fluctuations in chlorophyll fluorescence are affected by both photosynthetic efficiency and nonphotochemical quenching (NPQ), where NPQ is a decrease in fluorescence through the dissipation of excess energy as heat. NPQ variability is linked to iron and light availability, and has the potential to provide important diagnostic information on phytoplankton physiology. Here we establish a relationship between NPQ sv (Stern-Volmer NPQ) and indices of iron limitation from nutrient addition experiments in the sub-Antarctic zone (SAZ) of the Atlantic Southern Ocean, through the derivation of NPQ max (the maximum NPQ sv value) and α NPQ (the light limited slope of NPQ sv ). Significant differences were found for both F v /F m and α NPQ for iron versus control treatments, with no significant differences for NPQ max . Similar results from CTDs indicated that changes in NPQ were driven by increasing light availability from late July to December, but by both iron and light from January to February. We propose here that variability in α NPQ , which has removed the effect of light availability, can potentially be used as a proxy for iron limitation (as shown here for the Atlantic SAZ), with higher values being associated with greater iron stress. This approach was transferred to data from a buoyancy glider deployment at the same location by utilizing the degree of fluorescence quenching as a proxy for NPQ Glider , which was plotted against in situ light to determine α NPQ. Seasonal increases in α NPQ are consistent with increased light availability, shoaling of the mixed layer depth (MLD) and anticipated seasonal iron limitation. The transition from winter to summer, when positive net heat flux dominates stratification, was coincident with a 24% increase in α NPQ variability and a switch in the dominant driver from incident PAR to MLD. The dominant scales of α NPQ variability are consistent with fine scale variability in MLD and a significant positive relationship was observed between these two at a ∼10 day window. The results emphasize the important role of fine scale dynamics in driving iron supply, particularly in summer when this micronutrient is limiting.

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Spatial and temporal scales of chlorophyll variability using high-resolution glider data

Cited by 18 publications

References 32 publications

Stirring, Mixing, Growing: Microscale Processes Change Larger Scale Phytoplankton Dynamics

Stirring, Mixing, Growing: Microscale Processes Change Larger Scale Phytoplankton Dynamics

Seasonal development of iron limitation in the sub-Antarctic zone

Deriving a Proxy for Iron Limitation From Chlorophyll Fluorescence on Buoyancy Gliders

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