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

2018 ◽  
Vol 15 (23) ◽  
pp. 7315-7332 ◽  
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.

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

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

&lt;p&gt;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 &gt;0.5&amp;#8201;mmol&amp;#8201;N&amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt;&amp;#8201;d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) nitrate fluxes due to turbulent vertical mixing into the euphotic zone were found at some stations over the shelf edge, while low values (&lt;&amp;#8201;0.1&amp;#8201;mmol&amp;#8201;N&amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt;&amp;#8201;d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) 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 (&lt;50&amp;#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&amp;#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.&lt;/p&gt;&lt;p&gt;Reference:&lt;/p&gt;&lt;p&gt;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&amp;#8211;7332, https://doi.org/10.5194/bg-15-7315-2018, 2018.&lt;/p&gt;

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

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

scholarly journals 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

2004 ◽  
Vol 52 (3-4) ◽  
pp. 167-182 ◽  
Author(s):  
Flávia Marisa Prado Saldanha-Corrêa ◽  
Sônia Maria Flores Gianesella
Keyword(s):  
Phytoplankton Community ◽  
Seawater Temperature ◽  
Time Lag ◽  
Mixing Layer ◽  
Vertical Mixing ◽  
Coastal Region ◽  
Euphotic Zone ◽  
Phytoplankton Growth ◽  
Growth Potential ◽  
New Production

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.

Rapid turnover of dissolved DMS and DMSP by defined bacterioplankton communities in the stratified euphotic zone of the North Sea

2002 ◽  
Vol 49 (15) ◽  
pp. 3017-3038 ◽  
Author(s):  
Mikhail V. Zubkov ◽  
Bernhard M. Fuchs ◽  
Stephen D. Archer ◽  
Ronald P. Kiene ◽  
Rudolf Amann ◽  
...  
Keyword(s):  
North Sea ◽  
Euphotic Zone ◽  
Rapid Turnover ◽  
The North ◽  
The North Sea ◽  
Bacterioplankton Communities

scholarly journals Noctiluca scintillans: Dynamics, Size Measurements and Relationships With Small Soft-Bodied Plankton in the Belgian Part of the North Sea

2021 ◽  
Vol 8 ◽  
Author(s):  
Anouk Ollevier ◽  
Jonas Mortelmans ◽  
Anaïs Aubert ◽  
Klaas Deneudt ◽  
Michiel B. Vandegehuchte
Keyword(s):  
North Sea ◽  
Temporal Dynamics ◽  
Negative Impact ◽  
Large Cell ◽  
Nutrient Inputs ◽  
Anthropogenic Pressures ◽  
Noctiluca Scintillans ◽  
The North ◽  
The North Sea ◽  
The Relationship

Climate driven changes and anthropogenic pressures on the marine environment have been shown to favor the increase in certain potentially harmful species. Among them, Noctiluca scintillans, a common dinoflagellate, often blooms during warm summers and is known to affect plankton communities. In this study, we assessed the dynamics in abundance and cell size of N. scintillans as well as the relationship between N. scintillans and small soft-bodied zooplankton in the Belgian part of the North Sea (BPNS), since negative correlations between these plankton groups have been previously reported for nearby regions. This study is the first to present consistently counted N. scintillans cell numbers and measured cell lengths, through the analysis of ZooScan images from samples taken monthly at stations throughout the coastal zone of the BPNS. The results show that N. scintillans demonstrated clear seasonal dynamics with both high densities and large cell sizes in spring/summer (May-July). The occurrence of N. scintillans in the analyzed plankton samples and the abundance of N. scintillans at the observed peak intensities nearly tripled over a period of 5 years. A zero-inflated model showed a correlation of N. scintillans abundance with temperature as well as with phosphate concentrations, suggesting that anthropogenic influences such as climate change and riverine nutrient inputs could affect the temporal dynamics of the species. The results, on the other hand, did not show any negative impact of N. scintillans on the soft-bodied plankton community.

scholarly journals Composition and vertical flux of particulate organic matter to the oxygen minimum zone of the central Baltic Sea: impact of a sporadic North Sea inflow

2019 ◽  
Vol 16 (4) ◽  
pp. 927-947 ◽  
Author(s):  
Carolina Cisternas-Novoa ◽  
Frédéric A. C. Le Moigne ◽  
Anja Engel
Keyword(s):  
Organic Matter ◽  
North Sea ◽  
Euphotic Zone ◽  
Vertical Flux ◽  
The North ◽  
Vertical Fluxes ◽  
Deep Waters ◽  
Sinking Particles ◽  
Minimum Zone ◽  
The North Sea

Abstract. Particle sinking is a major form of transport for photosynthetically fixed carbon to below the euphotic zone via the biological carbon pump (BCP). Oxygen (O2) depletion may improve the efficiency of the BCP. However, the mechanisms by which O2 deficiency can enhance particulate organic matter (POM) vertical fluxes are not well understood. Here, we investigate the composition and vertical fluxes of POM in two deep basins of the Baltic Sea (GB: Gotland Basin and LD: Landsort Deep). The two basins showed different O2 regimes resulting from the intrusion of oxygen-rich water from the North Sea that ventilated the water column below 140 m in GB, but not in LD, during the time of sampling. In June 2015, we deployed surface-tethered drifting sediment traps in oxic surface waters (GB: 40 and 60 m; LD: 40 and 55 m), within the oxygen minimum zone (OMZ; GB: 110 m and LD: 110 and 180 m) and at recently oxygenated waters by the North Sea inflow in GB (180 m). The primary objective of this study was to test the hypothesis that the different O2 conditions in the water column of GB and LD affected the composition and vertical flux of sinking particles and caused differences in export efficiency between those two basins. The composition and vertical flux of sinking particles were different in GB and LD. In GB, particulate organic carbon (POC) flux was 18 % lower in the shallowest trap (40 m) than in the deepest sediment trap (at 180 m). Particulate nitrogen (PN) and Coomassie stainable particle (CSP) fluxes decreased with depth, while particulate organic phosphorus (POP), biogenic silicate (BSi), chlorophyll a (Chl a) and transparent exopolymeric particle (TEP) fluxes peaked within the core of the OMZ (110 m); this coincided with the presence of manganese oxide-like (MnOx-like) particles aggregated with organic matter. In LD, vertical fluxes of POC, PN and CSPs decreased by 28 %, 42 % and 56 %, respectively, from the surface to deep waters. POP, BSi and TEP fluxes did not decrease continuously with depth, but they were higher at 110 m. Although we observe a higher vertical flux of POP, BSi and TEPs coinciding with abundant MnOx-like particles at 110 m in both basins, the peak in the vertical flux of POM and MnOx-like particles was much higher in GB than in LD. Sinking particles were remarkably enriched in BSi, indicating that diatoms were preferentially included in sinking aggregates and/or there was an inclusion of lithogenic Si (scavenged into sinking particles) in our analysis. During this study, the POC transfer efficiency (POC flux at 180 m over 40 m) was higher in GB (115 %) than in LD (69 %), suggesting that under anoxic conditions a smaller portion of the POC exported below the euphotic zone was transferred to 180 m than under reoxygenated conditions present in GB. In addition, the vertical fluxes of MnOx-like particles were 2 orders of magnitude higher in GB than LD. Our results suggest that POM aggregates with MnOx-like particles formed after the inflow of oxygen-rich water into GB, and the formation of those MnOx–OM-rich particles may alter the composition and vertical flux of POM, potentially contributing to a higher transfer efficiency of POC in GB. This idea is consistent with observations of fresher and less degraded organic matter in deep waters of GB than LD.

Long-term changes in the North Sea ecosystem

2001 ◽  
Vol 9 (3) ◽  
pp. 131-187 ◽  
Author(s):  
R A Clark ◽  
C LJ Frid
Keyword(s):  
North Sea ◽  
Primary Productivity ◽  
Trophic Levels ◽  
Benthic Fish ◽  
Nutrient Inputs ◽  
Climatic Fluctuations ◽  
The North ◽  
Long Term Changes ◽  
The North Sea

Long-term data on the North Sea ecosystem are available for phytoplanktonic, zooplanktonic, benthic, fish, and seabird communities. Temporal changes in these have been examined by numerous researchers over the course of the 20th century, their main objective being to determine how the interannual dynamics of these communities are controlled. Ultimately, long-term changes in the North Sea ecosystem appear to be driven by two wide-ranging, but separate processes. In the northern, western and central areas of the North Sea, long-term changes are predominantly influenced by climatic fluctuations. Here, primary productivity during a particular year is related to the effect of weather on the timing of stratification and the resulting spring bloom. In the southern and eastern areas of the North Sea, the lack of stratification and the large inputs of nutrients mean that primary productivity is more strongly influenced by variations in anthropogenic nutrient inputs, and is only weakly related to climatic variation. Long-term changes at higher trophic levels (zooplankton, benthic, fish, and seabirds) are generally affected by fluctuations in their food source (i.e., the lower trophic levels), although because of the high complexity of the North Sea ecosystem there are many exceptions to these general patterns. However, the weight of evidence shows that long-term changes in the ecosystem may ultimately be related to long-term changes in either climate or nutrients, although the long-term dynamics of certain taxa and communities do show evidence of being influenced by both anthropogenic factors and (or) internal factors such as competition and predation. Key words: long-term changes, North Sea, time series, climate change, ecosystem functioning, anthropogenic impacts.

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