scholarly journals Varying Biological Activity and Wind Stress Affect the DMS Response during the SAGE Iron Enrichment Experiment

2020 ◽  
Vol 8 (4) ◽  
pp. 268
Author(s):  
Graham Jones ◽  
Mike Harvey ◽  
Stacey King ◽  
Anke Schneider ◽  
Simon Wright ◽  
...  
Keyword(s):  
Surface Waters ◽  
Biological Response ◽  
Phytoplankton Production ◽  
Storm Activity ◽  
Chl A ◽  
Iron Enrichment ◽  
The Third ◽  
Enrichment Experiments ◽  
High Winds ◽  
Microzooplankton Grazing

Surface dissolved dimethylsulfide (DMS) and depth-integrated dimethylsulfoniopropionate (DMSP) measurements were made from March to April 2004 during the SOLAS Air–Sea Gas Exchange Experiment (SAGE), a multiple iron enrichment experiment in subantarctic waters SE of New Zealand. During the first two iron enrichments, chl a and DMS production were constrained, but during the third enrichment, large pulses of DMS occurred in the fertilised IN patch, compared with the unfertilised OUT patch. During the third and fourth iron infusions, total chl a concentrations doubled from 0.52 to 1.02 µg/L. Hapto8s and prasinophytes accounted for 50%, and 20%, respectively, of total chl a. The large pulses of DMS during the third iron enrichment occurred during high dissolved DMSP concentrations and wind strength; changes in dinoflagellate, haptophyte, and cyanobacteria biomass; and increased microzooplankton grazing that exerted a top down control on phytoplankton production. A further fourth iron enrichment did cause surface waters to increase in DMS, but the effect was not as great as that recorded in the third enrichment. Differences in the biological response between SAGE and several other iron enrichment experiments were concluded to reflect microzooplankton grazing activities and the microbial loop dominance, resulting from mixing of the MLD during storm activity and high winds during iron enrichment.

scholarly journals Oceanic response to the consecutive Hurricanes Dorian and Humberto (2019) in the Sargasso Sea

2020 ◽  
Author(s):  
Dailé Avila-Alonso ◽  
Jan M. Baetens ◽  
Rolando Cardenas ◽  
Bernard De Baets
Keyword(s):  
Heat Content ◽  
Biological Response ◽  
Euphotic Zone ◽  
Sea Surface ◽  
Sargasso Sea ◽  
Surface Cooling ◽  
Chl A ◽  
The Third ◽  
Oceanic Response ◽  
Sea Surface Cooling

Abstract. Understanding the oceanic response to tropical cyclones (TCs) is of importance for studies on climate change. Although the oceanic effects induced by individual TCs have been extensively investigated, studies on the oceanic response to the passage of consecutive TCs are rare. In this work, we assess the upper oceanic response to the passage of the Hurricanes Dorian and Humberto over the western Sargasso Sea in 2019 using satellite remote sensing and modelled data. We found that the combined effects of these slow-moving TCs led to an increased oceanic response during the third and fourth post-storm weeks of Dorian (accounting for both Dorian and Humberto effects) because of the induced mixing and upwelling at this time. Overall, anomalies of sea surface temperature, ocean heat content and mean temperature from the sea surface to a depth of 100 m were a 50, 63 and 57% smaller (more negative) in the third/fourth post-storm weeks than in the first/second poststorm weeks (accounting only for Dorian effects) of Dorian, respectively, while surface chlorophyll-a (chl-a) concentration anomalies, the mean ch-a concentration in the euphotic zone and the chl-a concentration in the deep chlorophyll maximum were 16, 4 and 16% higher in the third/fourth post-storm weeks than in the first/second post-storm weeks, respectively. The sea surface cooling and increased biological response induced by these TCs were significantly higher (Mann-Whitney test p < 0.05) as compared to climatological records. Our climatological analysis reveals that the strongest TC-induced oceanographic variability in the western Sargasso Sea can be associated with the occurrence of consecutive TCs and long-lasting TC forcing.

scholarly journals Oceanic response to the consecutive Hurricanes Dorian and Humberto (2019) in the Sargasso Sea

2021 ◽  
Vol 21 (2) ◽  
pp. 837-859
Author(s):  
Dailé Avila-Alonso ◽  
Jan M. Baetens ◽  
Rolando Cardenas ◽  
Bernard De Baets
Keyword(s):  
Heat Content ◽  
Biological Response ◽  
Euphotic Zone ◽  
Sea Surface ◽  
Sargasso Sea ◽  
Surface Cooling ◽  
Chl A ◽  
The Third ◽  
Oceanic Response ◽  
Sea Surface Cooling

Abstract. Understanding the oceanic response to tropical cyclones (TCs) is of importance for studies on climate change. Although the oceanic effects induced by individual TCs have been extensively investigated, studies on the oceanic response to the passage of consecutive TCs are rare. In this work, we assess the upper-oceanic response to the passage of Hurricanes Dorian and Humberto over the western Sargasso Sea in 2019 using satellite remote sensing and modelled data. We found that the combined effects of these slow-moving TCs led to an increased oceanic response during the third and fourth post-storm weeks of Dorian (accounting for both Dorian and Humberto effects) because of the induced mixing and upwelling at this time. Overall, anomalies of sea surface temperature, ocean heat content, and mean temperature from the sea surface to a depth of 100 m were 50 %, 63 %, and 57 % smaller (more negative) in the third–fourth post-storm weeks than in the first–second post-storm weeks of Dorian (accounting only for Dorian effects), respectively. For the biological response, we found that surface chlorophyll a (chl a) concentration anomalies, the mean chl a concentration in the euphotic zone, and the chl a concentration in the deep chlorophyll maximum were 16 %, 4 %, and 16 % higher in the third–fourth post-storm weeks than in the first–second post-storm weeks, respectively. The sea surface cooling and increased biological response induced by these TCs were significantly higher (Mann–Whitney test, p<0.05) compared to climatological records. Our climatological analysis reveals that the strongest TC-induced oceanographic variability in the western Sargasso Sea can be associated with the occurrence of consecutive TCs and long-lasting TC forcing.

scholarly journals Sea-surface CO<sub>2</sub> fugacity in the subpolar North Atlantic

2008 ◽  
Vol 5 (2) ◽  
pp. 535-547 ◽  
Author(s):  
A. Olsen ◽  
K. R. Brown ◽  
M. Chierici ◽  
T. Johannessen ◽  
C. Neill
Keyword(s):  
North Atlantic ◽  
Surface Waters ◽  
Mixed Layer Depth ◽  
Sea Surface ◽  
First Year ◽  
Layer Depth ◽  
High Resolution Data ◽  
Chl A ◽  
Wide Range ◽  
Summer Warming

Abstract. We present the first year-long subpolar trans-Atlantic set of surface seawater CO2 fugacity (fCO2sw) data. The data were obtained aboard the MV Nuka Arctica in 2005 and provide a quasi-continuous picture of the fCO2sw variability between Denmark and Greenland. Complementary real-time high-resolution data of surface chlorophyll-a (chl-a) concentrations and mixed layer depth (MLD) estimates have been collocated with the fCO2sw data. Off-shelf fCO2sw data exhibit a pronounced seasonal cycle. In winter, surface waters are saturated to slightly supersaturated over a wide range of temperatures. Through spring and summer, fCO2sw decreases by approximately 60 μatm, due to biological carbon consumption, which is not fully counteracted by the fCO2sw increase due to summer warming. The changes are synchronous with changes in chl-a concentrations and MLD, both of which are exponentially correlated with fCO2sw in off-shelf regions.

scholarly journals Thrombocytopenia in the Course of COVID-19 Infection

2020 ◽  
Author(s):  
Noel Lorenzo-Villalba ◽  
Abrar-Ahmad Zulfiqar ◽  
Marc Auburtin ◽  
Marie Helene Schuhmacher ◽  
Alain Meyer ◽  
...  
Keyword(s):  
Hospital Discharge ◽  
Biological Response ◽  
Intravenous Immunoglobulins ◽  
Severe Thrombocytopenia ◽  
The Third ◽  
Mucosal Bleeding

We report three cases of severe thrombocytopenia during COVID-19 infection associated with either cutaneous purpura or mucosal bleeding. The initial investigations ruled out other causes of thrombocytopenia. Two of the patients were treated with intravenous immunoglobulins and eltrombopag, while the third recovered spontaneously. A good clinical and biological response was achieved in all patients leading to hospital discharge.

scholarly journals Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO<sub>2</sub> levels

2008 ◽  
Vol 5 (1) ◽  
pp. 411-433 ◽  
Author(s):  
K. Suffrian ◽  
P. Simonelli ◽  
J. C. Nejstgaard ◽  
S. Putzeys ◽  
Y. Carotenuto ◽  
...  
Keyword(s):  
Growth Rates ◽  
Standing Stock ◽  
Measured Parameter ◽  
Growth Responses ◽  
Dilution Technique ◽  
Pigment Analysis ◽  
Chl A ◽  
Co2 Levels ◽  
Algae Growth ◽  
Microzooplankton Grazing

Abstract. Microzooplankton grazing and algae growth responses to increasing pCO2 levels (350, 700 and 1050 μatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Phytoplankton and microzooplankton composition were determined by light microscopy. Despite a range up to 3 times the present CO2 levels, there were no clear differences in any measured parameter between the different CO2 treatments. Thus, during the first 9 days of the experiment the algae community standing stock (SS), measured as chlorophyll a (Chl a), showed the highest instantaneous grow rates (0.02–0.99 d-1) and increased from ca 2–3 to 6–12 μg l−1, in all mesocosms. Afterwards the phytoplankton SS decreased in all mesocosms until the end of the experiment. The microzooplankton SS, that was mainly dinoflagellates and ciliates varied between 23 and 130 μg C l−1, peaking on day 13–15, apparently responding to the phytoplankton development. Instantaneous Chl a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (14–43% of the SS d-1) only in the pre-bloom phase when they were in low numbers and in the post-bloom phase when they were already limited by low nutrients and/or virus lysis. The cyanobacteria populations appeared more effected by microzooplankton grazing, generally removing 20–65% of the SS d−1.

scholarly journals Seasonal and spatial comparisons of phytoplankton growth and mortality rates due to microzooplankton grazing in the northern South China Sea

2012 ◽  
Vol 9 (11) ◽  
pp. 16005-16032
Author(s):  
B. Chen ◽  
L. Zheng ◽  
B. Huang ◽  
S. Song ◽  
H. Liu
Keyword(s):  
South China Sea ◽  
Mixed Layer ◽  
South China ◽  
Surface Waters ◽  
Northern South China Sea ◽  
Phytoplankton Growth ◽  
China Sea ◽  
Grazing Effect ◽  
Basin Surface ◽  
Microzooplankton Grazing

Abstract. We conducted a comprehensive investigation on the microzooplankton herbivory effect on phytoplankton in the northern South China Sea (SCS) using the seawater dilution technique at surface and deep chlorophyll maximum (DCM) layers in two cruises (July–August of 2009 and January of 2010). We compared vertical (surface vs. DCM), spatial (onshore vs. offshore), and seasonal (summer vs. winter) differences of phytoplankton growth (μ0) and microzooplankton grazing rates (m). During summer, both μ0 and m were significantly higher at the surface than at the layer of DCM, which was below the mixed layer. During winter, surface μ0 was significantly higher than at DCM, while m was not significantly different between the two layers, both of which were contained within the mixed layer. Surface μ0 was, on average, significantly higher in summer than in winter; while average surface m was not different between the two seasons. There were no significant cross-shelf trends of μ0 in summer or winter surface waters. In surface waters, μ0 was not correlated with ambient nitrate concentrations and the effect of nutrient enrichment on phytoplankton growth was not pronounced. There was a decreasing trend of m from shelf to basin surface waters in summer, but not in winter. Microzooplankton grazing effect on phytoplankton (m/μ0) did not increase with distance offshore, suggesting that the importance of microzooplankton as grazers of phytoplankton may not decrease in onshore waters. On average, microzooplankton grazed 73% and 65% of the daily primary production in summer and winter, respectively.

Iron plays a role in nitrate drawdown by phytoplankton in Lake Erie surface waters as observed in lake-wide assessments

2012 ◽  
Vol 69 (2) ◽  
pp. 369-381 ◽  
Author(s):  
Sonya M. Havens ◽  
Christel S. Hassler ◽  
Rebecca L. North ◽  
Stephanie J. Guildford ◽  
Greg Silsbe ◽  
...  
Keyword(s):  
Surface Waters ◽  
Thermal Stratification ◽  
Lake Erie ◽  
Phytoplankton Community ◽  
Sampling Depth ◽  
Phytoplankton Pigment ◽  
Chl A ◽  
Dissolved Iron ◽  
Continuous Surface

Phytoplankton interactions with iron (Fe) were examined in surface waters of Lake Erie during summer thermal stratification. Lake-wide sampling in June and September 2005 was conducted using a continuous surface water sampler (1 m sampling depth) and in July at 18 hydrographic stations (5 m sampling depth). In situ measurements of photosynthetic efficiency (maximum quantum yield of photosystem II) and phytoplankton community composition were measured using fast repetition rate fluorometry and a phytoplankton pigment-specific fluorometer, respectively, during June and September. High ratios (73%–85%) of intracellular Fe to particulate Fe coincident with increases in chlorophyll a (Chl a) concentrations in the western and central basins in June and July imply that the majority of Fe in these regions was associated with intracellular pools. Correlations between intracellular Fe and Chl a were frequently observed when Heterokontophyta and Pyrrophyta dominated the phytoplankton community. Assimilation of Fe by the phytoplankton strongly influenced its partitioning between the dissolved and particulate phase. Dissolved iron (<0.45 µm) concentrations were proportional to Chl a concentrations and both dissolved iron and Chl a were inversely proportional to nitrate concentrations in July and September, suggesting that dissolved iron influenced both nitrate drawdown and Chl a concentrations in Lake Erie surface waters in summer.

scholarly journals Evidence of high N<sub>2</sub> fixation rates in the temperate northeast Atlantic

2019 ◽  
Vol 16 (5) ◽  
pp. 999-1017 ◽  
Author(s):  
Debany Fonseca-Batista ◽  
Xuefeng Li ◽  
Virginie Riou ◽  
Valérie Michotey ◽  
Florian Deman ◽  
...  
Keyword(s):  
Primary Production ◽  
North Atlantic ◽  
Surface Waters ◽  
N2 Fixation ◽  
Active Sites ◽  
Chl A ◽  
Future Assessment ◽  
Fixation Activity ◽  
Carbon Concentrations ◽  
Iberian Margin

Abstract. Diazotrophic activity and primary production (PP) were investigated along two transects (Belgica BG2014/14 and GEOVIDE cruises) off the western Iberian Margin and the Bay of Biscay in May 2014. Substantial N2 fixation activity was observed at 8 of the 10 stations sampled, ranging overall from 81 to 384 µmol N m−2 d−1 (0.7 to 8.2 nmol N L−1 d−1), with two sites close to the Iberian Margin situated between 38.8 and 40.7∘ N yielding rates reaching up to 1355 and 1533 µmol N m−2 d−1. Primary production was relatively lower along the Iberian Margin, with rates ranging from 33 to 59 mmol C m−2 d−1, while it increased towards the northwest away from the peninsula, reaching as high as 135 mmol C m−2 d−1. In agreement with the area-averaged Chl a satellite data contemporaneous with our study period, our results revealed that post-bloom conditions prevailed at most sites, while at the northwesternmost station the bloom was still ongoing. When converted to carbon uptake using Redfield stoichiometry, N2 fixation could support 1 % to 3 % of daily PP in the euphotic layer at most sites, except at the two most active sites where this contribution to daily PP could reach up to 25 %. At the two sites where N2 fixation activity was the highest, the prymnesiophyte–symbiont Candidatus Atelocyanobacterium thalassa (UCYN-A) dominated the nifH sequence pool, while the remaining recovered sequences belonged to non-cyanobacterial phylotypes. At all the other sites, however, the recovered nifH sequences were exclusively assigned phylogenetically to non-cyanobacterial phylotypes. The intense N2 fixation activities recorded at the time of our study were likely promoted by the availability of phytoplankton-derived organic matter produced during the spring bloom, as evidenced by the significant surface particulate organic carbon concentrations. Also, the presence of excess phosphorus signature in surface waters seemed to contribute to sustaining N2 fixation, particularly at the sites with extreme activities. These results provide a mechanistic understanding of the unexpectedly high N2 fixation in productive waters of the temperate North Atlantic and highlight the importance of N2 fixation for future assessment of the global N inventory.

EPIPELAGIC EUPHAUSIDS (EUPHAUSIACEA) AND SPRING MESOSCALE FEATURES IN THE GULF OF MEXICO

Crustaceana ◽  
1999 ◽  
Vol 72 (4) ◽  
pp. 391-404 ◽  
Author(s):  
◽  
Keyword(s):  
Gulf Of Mexico ◽  
Surface Waters ◽  
Abundant Species ◽  
Time Of Day ◽  
Migratory Behaviour ◽  
The Third ◽  
Density Values ◽  
Hydrographic Features ◽  
Anticyclonic Eddies ◽  
Abundance And Distribution

AbstractThe abundance and distribution of 21 species of euphausids collected in surface waters (0-200 m) at 69 stations of the Gulf of Mexico and the Yucatan Shelf was analyzed. Zooplankton samples were taken during the JS8601 cruise on board the R/V "Justo Sierra" of the UNAM, in April-May, 1986. During this survey mesoscale hydrographic features such as anticyclonic and cyclonic gyres, and upwelling, were detected in the area. The most abundant species was Stylocheiron carinatum (29.86%), followed by Euphausia tenera (19.97%) and S. suhmi (15.18%). Species richness increased at night: densities were 3.07 times higher then. Apparently, the migratory behaviour, of euphausids buffered the expected effect of the mesoscale features in the local euphausid community. The Bray-Curtis Index revealed three clusters of stations. The first one represented the influence of coastal and shelf waters on the euphausid community. The second group is a mixed oceanic-shelf community, and the third one was related to the Gulf oligotrophic oceanic waters. A fourth group included shallow areas in which no euphausids occurred. The relatively poor anticyclonic eddies did not influence the local euphausid community although low euphausid densities were expected. The relatively richer features, the cyclones, showed higher average densities. Euphausid densities related to the influence of upwelling areas showed density values similar to those recorded in the anticyclones. Two species (S. suhmi and S. carinatum) occurred in all the Gulf of Mexico regardless of the mesoscale environments or the time of day. L'abondance et la repartition de 21 especes d'Euphausiaces recoltes dans les eaux de surface (0-200 m) sur 69 stations du Golfe du Mexique et du plateau du Yucatan ont ete analysees. Les echantillons de zooplancton ont ete preleves au cours de la campagne JS8601 a bord du R/V "Justo Sierra" de l'UNAM, en avril-mai 1986. Au cours de cette mission, de variations hydrographiques d'amplitude moyenne comme les phenomenes cycloniques et anticycloniques, ainsi que l'upwelling, ont ete detectees dans la region. Les especes les plus abondantes etaient Stylocheiron carinatum (29,86%) suivie de Euphausia tenera (19,97%) et S. suhmi (15,18%). La richesse specifique augmentait dans les echantillons nocturnes; les densites etaient 3,07 fois plus elevees la nuit. Apparemment le comportement migratoire des Euphausiaces compensait l'effet attendu des particularites hydrographiques dans la communaute locale d'Euphausiaces. L'indice de Bray-Curtis a revele trois groupes de stations. Le premier representait l'influence des eaux cotieres et de la plate-forme continentale sur la communaute des Euphausiaces. Le second groupe etait une communaute mixte oceanique-plate-forme et le troisieme se rapportait aux eaux oceaniques oligotrophes du Golfe. Un quatrieme groupe incluait les zones peu profondes sans Euphausiaces. Les phenomenes anticycloniques relativement faibles n'avaient pas d'influence sur la communaute locale des Euphausiaces, bien que l'on se soit attendu a des densites d'Euphausiaces basses. Les phenomenes relativement plus marques, les cyclones, ont montre des densites moyennes plus elevees. Les densites d'Euphausiaces liees a l'influence des zones d'upwelling ont indique des valeurs similaires a celles relevees pour les anticyclones. Deux especes (S. suhmi and S. carinatum) sont presentes dans tout le Golfe du Mexique independamment des environnements consideres et du moment de la journee.

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