1,721,020 research outputs found
RRS Discovery Cruise 253, 04 May-20 Jun 2001. Faeroes, Iceland, Scotland Hydrographic and Environmental Survey (FISHES)
Full text linkThe FISHES 2001 cruise, RRS Discovery Cruise 253, was split into two legs. A large scale CTD survey of the Iceland Basin and Rockall Trough was carried out during the first and longer leg, 4 May – 21 May. The second leg, 1 June – 20 June, concentrated on repeated high resolution SeaSoar surveys of the Iceland Faeroes Front (IFF). A wide range of measurements were made alongside each scale of physical survey techniques used for the two legs of the cruise. These ranged from traditional biological sampling using net hauls to fast repetition fluorometric techniques for the underway determination of primary productivity parameters. Deck phytoplankton incubation experiments under controlled light environments involved both the usual measurements of N15 uptake and measurements of Si32 uptake. During the second leg of the cruise, a regional multi-disciplinary process model was used to forecast observations in near real-time
RRS Discovery Cruise 312, 11-31 Oct 2006. The extended Ellett Line 2006
Full text linkUK oceanographers have been making repeated measurements on a short section across the Rockall Trough, since 1975. The section consists of a series of stations from the Scottish continental shelf to Rockall. The time series was established by David Ellett and was thus called the "Ellett Line". The Ellett line is one of a relatively small number of high quality physical time series in the North Atlantic Ocean and is important for monitoring oceanic climate variability.Since 1996 NOCS and SAMS have been occupying an extended version of the Ellett Line that runs all the way to Iceland. The Extended Ellett line is important oceanographically because it completes the measurements of the warm saline water flowing into the Nordic Seas from the eastern North Atlantic. It also monitors around half of the returning deep and cold current, the overflow water (the rest returns to the Atlantic via the Denmark Strait to the west of Iceland).There is little added cost, either in time or financially, in making a number of biogeochemical measurements using water samples from the hydrographers' CTD stations. Thus, recently, the scientific interests in the Extended Ellett line have become more multidisciplinary; the 2006 occupation was no exception. Samples were filtered for POC, HPLC studies and trace aluminium concentration determination, in addition some extra time was found for a number of zooplankton net hauls.<br/
RRS Discovery Cruise 321, 24 Jul-23 Aug 2007. Biophysical interactions in the Iceland Basin 2007
Full text linkD321 was the first of three National Oceanography Centre ‘process study’ research cruises to be run by the Ocean Biogeochemistry and Ecosystems research group under the NERC Oceans 2025 research programme. The scientific work began by carrying out some of the extended Ellett Line stations on the way out to our study region; which centred around the historical JGOFS Ocean Weather Station India site (~ 59° N, ~ 19° W) and the northward turn of the extended Ellett line at 20° W. The Iceland Basin, like much of the N. Atlantic subpolar gyre, is characterised by a ‘bloom and bust’ seasonal cycle. Spring stratification triggers a major diatom dominated bloom event. This bloom is short lived, limited by silicate (orthosilicic acid) exhaustion (Brown et al., 2003). Two community succession pathways commonly follow the demise of the diatom bloom; typically through dinoflagellate and/or coccolithophore production. The spring bloom is dominated by eddy scale (several 10's of km) patchiness, driven by the upward and downward pumping effect of eddies on the newly forming spring stratification. However these eddy structures have another, more important, impact on phytoplankton production (Allen et al., 2005). In the release of potential energy, eddies effect a real three dimensional exchange of water across the thermocline bringing new dissolved nutrients from deeper waters up into the photic zone and transporting biogenic particles into the deep ocean. Thin ribbon like structures around the edges of eddies are clearly seen in ocean colour satellite images. The four repeated surveys carried out during D321 observed the evolution of an ‘eddy dipole’ in a background ocean full of eddies and other turbulent motions. Daily, near real-time, satellite images and in-situ vessel mounted acoustic current profiling were used to determine the movement of the eddy centres and the dipole central jet. Targeted nets and water collection within the various components of the eddy dipole enabled the assessment of its biological impacts.Since 1996 NOCS and SAMS have been occupying an extended version of the Ellett Line that runs all the way to Iceland. The Extended Ellett line is important oceanographically because it completes the measurements of the warm saline water flowing into the Nordic Seas from the eastern North Atlantic. It also monitors around half of the returning deep and cold current, the overflow water (the rest returns to the Atlantic via the Denmark Strait to the west of Iceland).There is little added cost, either in time or financially, in making a number of biogeochemical measurements using water samples from the hydrographers' CTD stations. Thus, recently, the scientific interests in the Extended Ellett line have become more multidisciplinary; the 2006 occupation was no exception. Samples were filtered for POC, HPLC studies and trace aluminium concentration determination, in addition some extra time was found for a number of zooplankton net hauls.<br/
Scheherezade - an interdisciplinary study of the Gulf of Oman, Strait of Hormuz and the southern Arabian Gulf, Charles Darwin Cruise 104, 12 Feb-30 Apr 1997. No. 13. Calibrated multifrequency target strength data from the EK500.. Leg 1, 12 Feb - 19 March
No full textRRS Discovery Cruise 224, Leg 1, 27 Nov-29 Dec 1996. OMEGA: Observations and Modelling of Eddy scale Geostrophic and Ageostrophic motion. Physical and biological observations in the eastern Alboran Sea (western Mediterranean)
Full text linkThe first leg of RRS Discovery Cruise 224, 27/11/96 - 29/12/96, was one of two cruise programs designed to provide the experimental field observations for the EU MAST 3 project, OMEGA (Observations and Modelling of Eddy scale Geostrophic and Ageostrophic motion). Towing the undulating CTD vehicle, SeaSoar, two large scale and three fine scale SeaSoar surveys were made of the Almeria-Oran front region of the western Mediterranean. In addition a brief SeaSoar survey was made of the head of the Algerian Current. These hydrographic measurements of the upper 370 metres of the water column were accompanied by VM-ADCP and ACCP derived ocean currents, underway physical, chemical and biological analysis of surface water samples, multi-frequency acoustic backscatter measurements, meteorological observations and sea surface radiation measurements. Between the surveys, CTD stations were accompanied by detailed measurements of ocean optical properties at strategic locations along and across the front. In addition 8 towed deployments of a Longhurst Hardy Plankton Recorder were made to look at the change in plankton species composition across frontal zones
Sub-mesoscale structure and the development of an eddy in the Subantarctic Front north of the Crozet Islands
No full textTwo stations only 20 km apart were observed to have quite different biological and biogeochemical characteristics. The first site had low concentrations of chlorophyll and sufficient nutrients to support phytoplankton growth. The second site had high concentrations of chlorophyll, depleted nutrient concentrations and significant export of phytodetrital material had taken place. The two sites were located in the Polar Frontal Zone of the Southern Ocean to the northwest of the Crozet Islands. The main physical difference between the two sites was in the depth of the mixed layer. At the first site, the mixed layer was deep and well mixed, whereas the second site had a shallow, stratified layer; otherwise the horizontal gradients of physical properties were weak. Survey data from the surrounding area showed that the productive site was located on the edge of a filament of water drawn into a developing meander of the Subantarctic Front. Remotely sensed data provided a history of the growth of the meander in the Subantarctic Front and its development into an eddy in the Polar Frontal Zone. The dynamics associated with the filament in the meander were clearly important in driving the primary productivity, as an intrusion of saline water into adjacent fresher water generated a shallow mixed layer and conditions suitable for phytoplankton growth. The dynamics promoting conditions favourable to phytoplankton growth continued to operate as chlorophyll was enhanced in the eddy after the main bloom had died away. Later measurements suggested that the surface layer had changed from diatom dominated to a coccolithophore or calcite-rich community
Eddy transport of Western Mediterranean Intermediate Water to the Alboran Sea
No full textDuring the second cruise of the EU funded OMEGA project the towed undulating vehicle SeaSoar, was deployed to survey the upper 350 m of the water column in the eastern Alboran Sea and extreme western Algerian basin. With an effective along-track resolution of 4 km, the data sets enabled a detailed description of the different upper ocean water types and the fronts that separate them. The Almeria Oran front forms at the eastern boundary of the Alboran Sea gyre system, in the upper 150–200 m of the water column, and separates waters of predominantly Atlantic origin from those formed in the Western Mediterranean Sea. Below these surface waters, but above the Levantine Intermediate Water, Western Mediterranean Intermediate Waters, believed to be formed to the north of the Balearic Sea, are normally observed in this region. However, to our knowledge, this is the first time a discrete eddy of Western Mediterranean Intermediate Water, a “weddy,” has been described in the extreme western Algerian basin. Repeated surveys of the region allowed us to observe the evolution of the eddy over a period of 40 d. A climatological analysis of historical data in the MEDAR/MEDATLAS database provides evidence for the repeatability of this observation and the significance of the estimated transport
Diagnosis of vertical velocities with the QG omega equation: an examination of the errors due to sampling strategy
No full textVertical motion at the mesoscale plays a key role in ocean circulation, ocean-atmosphere interaction, and hence climate. It is not yet possible to make direct Eulerian measurements of vertical velocities less than 1000 m day?1. However, by assuming quasi-geostrophic (QG) balance, vertical velocities O (10 m day?1) can be diagnosed from the geostrophic velocity field and suitable boundary conditions. Significant errors in the accuracy of this diagnosis arise from the necessary compromise between spatial resolution and synopticity of a hydrographic survey. This problem has been addressed by sampling the output of a numerical ocean model to simulate typical oceanographic surveys of mesoscale fronts. The balance between the number of observations and the synopticity of observations affects the apparent flow and in particular the diagnosed vertical motion. A combination of effects can typically lead to errors of 85% in the estimation of net vertical heat flux. An analytical two-layer model is used to understand components of this error and indicate the key parameters for the design of mesoscale sampling
SeaSoar and CTD sections across the Iceland-Faeroes Front and Faeroe Shetland Channel, August 1990
Full text linkDiurnal variations of dinoflagellate bioluminescence within the open-ocean north-east Atlantic
No full textIn regions where dinoflagellates dominate bioluminescent emissions, diurnal variations in bioluminescence potential (BPOT) can be influenced by both exogenous and endogenous factors. In summer 2009, measurements were made in the north-east Atlantic to examine the diurnal variations in BPOT in natural dinoflagellate communities and determine the influence of circadian regulation and light exposure. The maximum night BPOT was >23 times greater than the daytime levels for the same populations. Photosynthetic species were responsible for 55–75% of measured BPOT based on calculated light budgets. Under continual darkness, diurnal variability of BPOT was retained over a 48-h period, demonstrating a degree of circadian control. Results suggest that both photosynthetic and heterotrophic dinoflagellates exhibit circadian regulation of their bioluminescent capacity and light strongly influences the diurnal variation of BPOT. Circadian rhythms were photo-entrained to the phase of the natural photoperiod and light further inhibited daytime bioluminescence. Maximum night BPOT was significantly correlated with the previous day integrated photosynthetically active radiation (PAR) suggesting photo-enhancement within natural populations. A 21% decrease in integrated PAR was associated with a 26–29% decrease in maximum night BPOT for constant populations. Maximum night BPOT was damped by up to 73% when organisms were kept in constant darkness. Findings further quantify diurnal variations in BPOT in natural dinoflagellate populations and their relation to a number of taxonomic, cellular and environmental factors. Results emphasize the importance of considering the recent light history of bioluminescent communities when analysing or predicting in situ BPOT
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