A microcosm approach on the potential effects of the vertical mixing of water masses over the primary productivity and phytoplankton biomass in the southern Brazilian coastal region

The vertical mixing between South Atlantic Central Water (SACW) and Coastal Water (CW) was simulated through microcosm experiments using the autochthonous phytoplankton community (fraction < 150 mm), without nutrient enrichments. SACW is cold (T< 18°C) and nutrient rich, while CW is warmer (T> 20°C) and oligotrophic. The phytoplankton growth potential of SACW, CW and an equivalent mixture of both (SACW+CW) was compared, under 100, 30 and 10% of sunlight, at surface seawater temperature, in winter and summer conditions. Results demonstrate the importance of SACW as a natural eutrophication agent for the mixing layer, allowing the occurrence of new production by nutrient input, and also as a biological seeder through the development of its autochthonous phytoplankton community when it reaches the euphotic zone. The time lag for phytoplankton development during winter was around 4-5 days, against 1-2 days in summer. The hypothesis of physiological differences between surface and bottom phytoplankton populations from a deep (80 m) and thermally homogeneous water column (common winter feature) was also tested through the microcosm experiments. Results obtained clearly demonstrate that bottom water presented higher phytoplankton growth potential than the surface one.

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Turbulence measurements suggest high rates of new production over the shelf edge in the north-eastern North Sea during summer

10.5194/bg-2018-385 ◽

2018 ◽

Author(s):

Jørgen Bendtsen ◽

Katherine Richardson

Keyword(s):

North Sea ◽

Vertical Mixing ◽

Euphotic Zone ◽

Shelf Edge ◽

Nutrient Inputs ◽

New Production ◽

The North ◽

North Eastern ◽

The North Sea ◽

Using Data

Abstract. New production, i.e., that driven by allochthonous nutrient inputs, is the only form of primary production that can lead to net increases in organic material and is, therefore, important for understanding energy flow in marine ecosystems. The spatial distribution of new production is generally, however, not well known. Here, using data collected in July 2016, we analyse the potential for vertical mixing to support new production in the upper layers of the north eastern portion of the North Sea. Estimated nitrate fluxes due to turbulent vertical mixing into the euphotic zone were up to 0.5–1 mmol N m−2 d−1 over the shelf-edge (f-ratios > 0.1) while values of

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Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer

Biogeosciences ◽

10.5194/bg-15-7315-2018 ◽

2018 ◽

Vol 15 (23) ◽

pp. 7315-7332 ◽

Cited By ~ 1

Author(s):

Jørgen Bendtsen ◽

Katherine Richardson

Keyword(s):

North Sea ◽

Vertical Mixing ◽

Euphotic Zone ◽

Bottom Layer ◽

Depth Range ◽

Shelf Edge ◽

Nutrient Inputs ◽

New Production ◽

Edge Zone ◽

The North

Abstract. New production, i.e. that driven by allochthonous nutrient inputs, is the only form of primary production that can lead to net increases in organic material and is, therefore, important for understanding energy flow in marine ecosystems. The spatial distribution of new production is generally, however, not well known. Using data collected in July 2016, we analyse the potential for vertical mixing to support new production in the upper layers of the northeastern portion of the North Sea. Relatively large (up to >0.5 mmol N m−2 d−1) nitrate fluxes due to turbulent vertical mixing into the euphotic zone were found at some stations over the shelf edge, while low values (< 0.1 mmol N m−2 d−1) were found in the deeper open area north of the shelf edge. The low vertical mixing rates (dissipation rates of turbulent kinetic energy below 10−8 W kg−1, corresponding to vertical turbulent diffusion coefficients of 10−6–10−5 m2 s−1) implied f ratios of <0.02 in the open waters north of the shelf edge. In the shallow (<50 m) southern and central part of the study area, inorganic nutrients were low and nitrate undetectable, suggesting negligible new production here, despite relatively high concentrations of chlorophyll a being found in the bottom layer. Thus, high rates of new production seem to be concentrated around the shelf-edge zone and in association with localized features exhibiting enhanced vertical mixing. We find that the nutricline depth is significantly deeper at the shelf edge and interference with increased mixing in this deeper depth range can explain the increased diapycnal nitrate fluxes. Overall, this suggests that the shelf-edge zone may be the major nutrient supplier to the euphotic zone in this area during the period of summer stratification.

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Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer

10.5194/egusphere-egu2020-11427 ◽

2020 ◽

Author(s):

Jørgen Bendtsen ◽

Katherine Richardson

Keyword(s):

North Sea ◽

Vertical Mixing ◽

Euphotic Zone ◽

Bottom Layer ◽

Ecosystem Structure ◽

Depth Range ◽

Shelf Edge ◽

New Production ◽

Edge Zone ◽

Turbulence Measurements

The potential for vertical mixing to support new production in the upper layers of the northeastern portion of the North Sea was analysed from observations obtained during the stratified period in July 2016. Five transects across the shelf edge between the relatively shallow central North Sea and the deep Norwegian trench showed a clear frontal structure in hydrography, turbulent mixing, nutrients and chlorophyll a across the shelf edge. Relatively large (up to >0.5&#8201;mmol&#8201;N&#8201;m&#8722;2&#8201;d&#8722;1) nitrate fluxes due to turbulent vertical mixing into the euphotic zone were found at some stations over the shelf edge, while low values (<&#8201;0.1&#8201;mmol&#8201;N&#8201;m&#8722;2&#8201;d&#8722;1) were found in the deeper open area north of the shelf edge. The low vertical mixing rates implied f ratios less than 0.02 in the open waters north of the shelf edge. In the shallow (<50&#8201;m) southern and central part of the study area, inorganic nutrients were low and nitrate undetectable, suggesting negligible new production here, despite relatively high concentrations of chlorophyll&#160;a being found in the bottom layer. Thus, high rates of new production seem to be concentrated around the shelf-edge zone and in association with localized features exhibiting enhanced vertical mixing. We find that the nutricline depth is significantly deeper at the shelf edge and interference with increased mixing in this deeper depth range can explain the increased diapycnal nitrate fluxes. Overall, this suggests that the shelf-edge zone may be the major nutrient supplier to the euphotic zone in this area during the period of summer stratification. Potential impacts on plankton ecosystem structure are discussed.Reference:Bendtsen, J. and Richardson, K.: Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer, Biogeosciences, 15, 7315&#8211;7332, https://doi.org/10.5194/bg-15-7315-2018, 2018.

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Phytoplankton distribution and nitrogen dynamics in the southwest indian subtropical gyre and Southern Ocean waters

Ocean Science ◽

10.5194/os-7-113-2011 ◽

2011 ◽

Vol 7 (1) ◽

pp. 113-127 ◽

Cited By ~ 20

Author(s):

S. J. Thomalla ◽

H. N. Waldron ◽

M. I. Lucas ◽

J. F. Read ◽

I. J. Ansorge ◽

...

Keyword(s):

Southern Ocean ◽

Austral Summer ◽

Euphotic Zone ◽

Biomass Accumulation ◽

Phytoplankton Growth ◽

Small Cells ◽

New Production ◽

Prince Edward Islands ◽

Chlorophyll Concentrations ◽

Phytoplankton Cells

Abstract. During the 1999 Marion Island Oceanographic Survey (MIOS 4) in late austral summer, a northbound and reciprocal southbound transect were taken along the Southwest Indian and Madagascar Ridge, between the Prince Edward Islands and 31° S. The sections crossed a number of major fronts and smaller mesoscale features and covered a wide productivity spectrum from subtropical to subantarctic waters. Associated with the physical survey were measurements of size fractionated chlorophyll, nutrients and nitrogen (NO3, NH4 and urea) uptake rates. Subtropical waters were characterised by low chlorophyll concentrations (max = 0.27.3 mg m−3 dominated by pico-phytoplankton cells (> 81%) and very low f-ratios (< 0.1), indicative of productivity based almost entirely on recycled ammonium and urea. Micro-phytoplankton growth was limited by the availability of NO3 (< 0.5 mmol m−3 and Si(OH)4 (< 1.5 mmol m−3 through strong vertical stratification preventing the upward flux of nutrients into the euphotic zone. Biomass accumulation of small cells was likely controlled by micro-zooplankton grazing. In subantarctic waters, total chlorophyll concentrations increased (max = 0.74 mg m−3 relative to the subtropical waters and larger cells became more prevalent, however smaller phytoplankton cells and low f-ratios (< 0.14) still dominated, despite sufficient NO3 availability. The results from this study favour Si(OH)4 limitation, light-limited deep mixing and likely Fe deficiency as the dominant mechanisms controlling significant new production by micro-phytoplankton. The percentage of micro-phytoplankton cells and rates of new production did however increase at oceanic frontal regions (58.6% and 11.22%, respectively), and in the region of the Prince Edward archipelago (61.4% and 14.16%, respectively). Here, water column stabilization and local Fe-enrichment are thought to stimulate phytoplankton growth rates. Open ocean regions such as these provide important areas for local but significant particulate organic carbon export and biological CO2 draw-down in an overall high nutrient low chlorophyll Southern Ocean.

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Vertical Mixing and its Effects on Phytoplankton Growth in a Turbid Estuary

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f83-285 ◽

1983 ◽

Vol 40 (S1) ◽

pp. s221-s228 ◽

Cited By ~ 18

Author(s):

R. J. Uncles ◽

I. R. Joint

Keyword(s):

Time Scales ◽

Mixing Time ◽

Vertical Mixing ◽

Euphotic Zone ◽

Phytoplankton Growth ◽

Eddy Diffusivities ◽

Generation Times ◽

Mixing Water ◽

Vertical Eddy ◽

Photosynthetic Adaptation

Using a hydrodynamical model, in conjunction with current meter observations, vertical eddy diffusivities, and associated vertical mixing time-scales are estimated for the Bristol Channel, U.K. In this shallow region, the mixing time-scale appears to be more useful than the commonly employed stratification parameter in assessing the potential for thermal stratification of the water column.Chlorophyll a concentrations in the Bristol Channel are observed to be vertically well-mixed throughout the year. This is shown to be a consequence of the short vertical mixing time-scales in comparison with phytoplankton generation times. These time-scales are of particular importance to phytoplankton in the region because the mixed depth is much greater than the depth of the euphotic zone. Photoinhibition is unlikely to occur in the rapidly mixing water column because phytoplankton cells experience high light conditions for only very short periods. In addition, the rapid mixing does not appear to allow time for photosynthetic adaptation of the phytoplankton population of the Bristol Channel.Key words: Bristol channel, phytoplankton growth, vertical mixing, vertical eddy viscosity

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Response of ocean phytoplankton community structure to climate change over the 21st century: partitioning the effects of nutrients, temperature and light

Biogeosciences ◽

10.5194/bg-7-3941-2010 ◽

2010 ◽

Vol 7 (12) ◽

pp. 3941-3959 ◽

Cited By ~ 96

Author(s):

I. Marinov ◽

S. C. Doney ◽

I. D. Lima

Keyword(s):

Climate Change ◽

Community Structure ◽

Sea Ice ◽

Phytoplankton Biomass ◽

Phytoplankton Community ◽

Vertical Mixing ◽

Phytoplankton Community Structure ◽

Marginal Sea ◽

Small Phytoplankton ◽

The Impact

Abstract. The response of ocean phytoplankton community structure to climate change depends, among other factors, upon species competition for nutrients and light, as well as the increase in surface ocean temperature. We propose an analytical framework linking changes in nutrients, temperature and light with changes in phytoplankton growth rates, and we assess our theoretical considerations against model projections (1980–2100) from a global Earth System model. Our proposed "critical nutrient hypothesis" stipulates the existence of a critical nutrient threshold below (above) which a nutrient change will affect small phytoplankton biomass more (less) than diatom biomass, i.e. the phytoplankton with lower half-saturation coefficient K are influenced more strongly in low nutrient environments. This nutrient threshold broadly corresponds to 45° S and 45° N, poleward of which high vertical mixing and inefficient biology maintain higher surface nutrient concentrations and equatorward of which reduced vertical mixing and more efficient biology maintain lower surface nutrients. In the 45° S–45° N low nutrient region, decreases in limiting nutrients – associated with increased stratification under climate change – are predicted analytically to decrease more strongly the specific growth of small phytoplankton than the growth of diatoms. In high latitudes, the impact of nutrient decrease on phytoplankton biomass is more significant for diatoms than small phytoplankton, and contributes to diatom declines in the northern marginal sea ice and subpolar biomes. In the context of our model, climate driven increases in surface temperature and changes in light are predicted to have a stronger impact on small phytoplankton than on diatom biomass in all ocean domains. Our analytical predictions explain reasonably well the shifts in community structure under a modeled climate-warming scenario. Climate driven changes in nutrients, temperature and light have regionally varying and sometimes counterbalancing impacts on phytoplankton biomass and structure, with nutrients and temperature dominant in the 45° S–45° N band and light-temperature effects dominant in the marginal sea-ice and subpolar regions. As predicted, decreases in nutrients inside the 45° S–45° N "critical nutrient" band result in diatom biomass decreasing more than small phytoplankton biomass. Further stratification from global warming could result in geographical shifts in the "critical nutrient" threshold and additional changes in ecology.

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Photoinhibition of DCMU-Enhanced Fluorescence in Lake Ontario Phytoplankton

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f87-263 ◽

1987 ◽

Vol 44 (12) ◽

pp. 2144-2154 ◽

Cited By ~ 8

Author(s):

M. Putt ◽

G. P. Harris ◽

R. L. Cuhel

Keyword(s):

Vertical Mixing ◽

Natural Populations ◽

Bright Light ◽

Euphotic Zone ◽

Lake Ontario ◽

Enhanced Fluorescence ◽

Low Light ◽

Light Levels ◽

Phosphorus Status

Measurement of 1-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) enhanced fluorescence (FDCMU) suggested that photoinhibition of photosynthesis was frequently an artifact of in situ bottle incubations in Lake Ontario phytoplankton. In a seasonal study, FDCMU of all populations was depressed by bright light in an incubator. However, when the euphotic zone did not exceed the depth of the mixed layer, vertical transport of phytoplankton into either low-light or dark regions apparently allowed reversal of photoinhibition of FDCMU. Advantages of FDCMU as a bioassay of vertical mixing include rapidity of response time, ease of measurement in the field, and insensitivity of this parameter to changes in phosphorus status of the population. Because of seasonal changes in the photoadaptive response of natural populations, the rate constants and threshold light levels required to cause the response must be determined at each use if the method is to be quantitative.

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Determinants of pelagic metabolism in the Timor Sea during the inter-monsoon period

Marine and Freshwater Research ◽

10.1071/mf10170 ◽

2011 ◽

Vol 62 (2) ◽

pp. 130 ◽

Cited By ~ 7

Author(s):

A. D. McKinnon ◽

J. H. Carleton ◽

S. Duggan

Keyword(s):

Gross Primary Production ◽

Vertical Mixing ◽

Community Respiration ◽

New Production ◽

Net Community Production ◽

Monsoon Period ◽

Hydrocarbon Seeps ◽

Timor Sea ◽

Waves And Tides ◽

High Production

The Timor Sea is a major conduit of the Indonesian Throughflow characterised by large internal waves and tides. To ascertain whether these result in high pelagic productivity, we conducted experiments to determine the metabolic balance between net community production (NCP) and community respiration (CR) on the Sahul Shelf, the Sahul Shoals and the Yampi Shelf, an area of active hydrocarbon seeps. The barrier to vertical mixing of subthermocline nutrients represented by the halocline allowed new production to dominate in March 2004, whereas production in June 2005 depended on recycled nutrients. CR was correlated with dissolved organic carbon (DOC) in 2004, but with chlorophyll in 2005, suggesting that respiration was dominated by microheterotrophs in 2004 but by autotrophs in 2005. Overall, area-specific CR averaged 120 ± 92 (s.d.), 101 ± 52 and 61 ± 6 mmol O2 m–2 day–1, NCP averaged 109 ± 85 (s.d.), 32 ± 41 and 57 ± 10 mmol O2 m–2 day–1, and average gross primary production (= CR+NCP) : R ratios were 1.9, 1.4 and 1.9 on the shelf, at the Sahul Shoals and the Yampi Shelf, respectively. We suggest that differences in water column structure and internal wave activity drive intermittent high production events in a predominantly oligotrophic sea.

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