1,721,053 research outputs found
RRS "Discovery" Cruise D279, 04 Apr - 10 May 2004. A Transatlantic hydrography section at 24.5N
Full text linkThe cruise report describes the acquisition and processing of transatlantic hydrographic, velocity, chemistry and other measurements made during three cruises in Spring 2004 at 24.5°N. Measurements were made from shallow water near Africa to shallow water just off Palm Springs beach on the eastern seaboard of the USA. During the principal cruise, RRS Discovery Cruise D279 (4 April to 10 May 2004), 125 full depth CTD and lowered acoustic Doppler current profiler (LADP) stations were completed between the USA and Africa and continuous underway observations were made of currents in the upper 1000m using a ship mounted 75kHz ADP and of surface salinity and temperature. At each station up to 24 water samples were captured for the analysis of oxygen, salinity, nitrate, silicate, phosphate, CFC11, 12, 113 and CCl4 (carbon tetrachloride), discrete total inorganic carbon (TCO2), discrete total alkalinity (TA) and, discrete partial pressure of CO2 (discrete pCO2). Direct, near real-time measurements were also made of the air-sea turbulent fluxes of momentum and sensible and latent heat in addition to various mean meteorological parameters including testing of a new Licor sensor to determine its suitability for making direct measurements of the air-sea CO2 flux. Atmospheric dust samples were gathered on a daily basis. Two prior cruisesD277 (26 February to 16 March) and D278 (19 to 30 March) completed 33 full depth CTD/LADP stations in the Florida and Deep Western Boundary Currents, including continuous underway observations of currents in the upper 1000m and of surface salinity and temperature. No LADP or chemistry measurements were made during these cruises. The three cruises provide one CTD and one CTD/LADP transect of the Florida Current, two Florida Current transects at 5knots with the shipboard ADP measuring to the bottom for high accuracy well resolved direct velocity measurements, one section of 16 CTD stations across the Deep Western Boundary Current and a 125 station transatlantic section with a full suite of physical and chemical measurements. The principal scientific objective is to estimate the circulation across 24.5°N, using for the first time, LADP profiles at each station as constraints in an inverse study. Using this circulation and the transatlantic distribution of temperature and other properties we will calculate Atlantic heat and property fluxes. We will also define the size and structure of the Atlantic Meridional Overturning Circulation (MOC) to compare to results from a recently deployed transatlantic mooring array designed to continuously measure the size and structure of the MOC. The 24.5°N section has now been occupied five times since 1957 (including the 2004 section reported here). Therefore, we will analyse temporal trends of temperature to see if the widely reported warming of the thermocline and intermediate waters and cooling of deep water is continuing. Carbon measurements were also obtained in 1992 and 1998 so this section provides a unique decadal view of anthropogenic carbon fluxes
RRS Discovery Cruise 242, 07 Sep-06 Oct 1999. Atlantic - Norwegian Exchanges
Full text linkThis report describes RRS Discovery cruise 242 from 07 September to 06 October 1999. The cruise title is Atlantic - Norwegian Exchanges. There are two distinct parts to this experiment with closely related objectives. The first is to measure the pathways and flux of warm, upper ocean water northward through the Iceland Basin and Rockall Trough to high latitudes. The second is to measure the returning flux of cold, deep water that flows through the Faroe Bank Channel into the North Atlantic. A full depth hydrographic section was occupied between Scotland and Iceland, repeating the frequently occupied Rockall Trough section (occupied 36 times between March 1975 and January 1996) and it's recent extension from Rockall to Iceland (occupied in 1997, 1998 and now in 1999). A second section was occupied from southeast Iceland to Lousy Bank (occupied in 1962,1990 and 1996). These two sections comprised CTD/LADCP stations with discrete vertical samples for salinity, oxygen, silicate, nitrate and phosphate. Horizontal station spacing was ~30 km in the Iceland Basin but much closer over steep bathymetry and in the Rockall Trough. Ancilliary measurements of transmittance and reversing temperature and salinity were also made. Shipbourne observations were made throughout the cruise and comprised ADCP, navigation, meteorology, waves, echosounding and surface temperature and salinity. These two sections were designed to measure the pathways of the northward flow through the Iceland Basin and Rockall Trough. Differences to earlier occupations will show the time variability of these flows. In the Faroe Bank Channel and on the Iceland Ridge eight sections were occupied (some repeats) to examine the cold outflow into the North Atlantic. These sections were made in the Faroe Bank Channel and downstream of the sill, at a horizontal separation of between 15 km and 40 km. Five of these were standard CTD/LADCP sections with chemistry observations. Three sections were also occupied using the BRIDGET deep tow vehicle. This vehicle carried a CTD and 12 bottle rosette for water samples as well as some auxiliary sensors. The key novelty was the mounting of self-contained downward and upward looking ADCP's. BRIDGET was towed at 100 m off bottom giving cross-stream measurements at high resolution of the velocity structure of the overflow. These sections were taken in and just downstream from the Faroe Bank Channel sill. We will examine the initial adjustment of the overflow and with contemporaneous observations made in the Faroe Shetland (Fisheries Research Services, Aberdeen) the role of hydraulic control at the Faroe Bank Channel sill. The two sections in the Iceland Basin cross the overflow 360 km and 660 km downstream from the source defining the far field location and properties of the overflow. A short section of XBT observations was made along the Wyville-Thomson Ridge to measure the temperature at two saddle points where it is occasionally observed that cold Faroe Bank Channel water passes into the Rockall Trough
Monitoring the Atlantic Meridional Overturning Circulation at 26.5°N: RAPID-WATCH
Full text linkThe Atlantic Meridional Overturning Circulation (AMOC) at 26.5°N carries a northward heat flux of 1.3 PW. Northward of 26.5°N over the Gulf Stream and its extension much of this heat is transferred to the atmosphere and subsequently is responsible for maintaining UK climate about 5°C warmer than the zonal average at this latitude. However, previous sparse observations did not resolve the temporal variability of the AMOC and so it is unknown whether it is slowing in response to global warming as suggested by recent model results. In 2004 NERC, NSF and NOAA funded a system of observations in the Atlantic at 26.5°N to observe on a daily basis the strength and structure of the AMOC. Two papers ([Cunningham, et al., 2007] & [Kanzow, et al., 2007]) demonstrated that not only does the system of observations achieve a mass balance for the AMOC, it reveals dramatic and unexpected richness of variability. In the first year the AMOC mean strength and variability is 18.7±5.6 Sv. From estimates of the degrees-of-freedom the year-long mean AMOC is defined with a resolution of around 1.5 Sv so abrupt changes would be readily identified and long-term changes will be measured relative to the 2004- 005 average. The NERC contribution to the first four years of continuous AMOC observations was funded under the directed programme RAPID Climate Change. Following an international review of the system NERC will continue funding to 2014 under the programme RAPID-WATCH. The NSF and NOAA have also continued funding and commitments so that the system can continue operating at the same level of activity as during the period 2004-2008. The objectives of RAPID-WATCH are: To deliver a decade-long time series of calibrated and quality-controlled measurements of the Atlantic MOC from the RAPID-WATCH arrays and; To exploit the data from the RAPID-WATCH arrays and elsewhere to determine and interpret recent changes in the Atlantic MOC, assess the risk of rapid climate change, and investigate the potential for predictions of the MOC and its impacts on climate
RRS James Clark Ross Cruise JR55, 21 Nov-14 Dec 2000. Drake Passage repeat hydrography: WOCE Southern Section 1b – Burdwood Bank to Elephant Island
Full text linkThis report describes the sixth repeat hydrography section across Drake Passage, first established during the International World Ocean Circulation Experiment. Through continuation of this time series the nature of the interannual variability in the location and properties of the ACC at this choke point between South America and the Antarctic Peninsula can be determined. Across the 644km section from Burdwood Bank to Elephant Island, thirty-one CTD/LADCP stations (including one test station) were made on the southbound journey with a maximum station spacing of 33km. Water samples were drawn for salinity analysis and CTD conductivity calibration. The underway measurements included: Vessel Mounted Acoustic Doppler Current Profiler, measuring currents to depths of 300m beneath the ship, navigation, sea surface temperatures recorded by thermosalinograph, meteorology logged via the oceanlogger system and Simrad echo sounder determining water depths. CTD station 32 was at the Rothera time series (RaTs) site just off Rothera Pier, carried out primarily for collected water samples for nutrient analysis back at SOC.On the northbound crossing of Drake Passage, to the west of the southbound section, an extra two full depth CTD/LADCP stations were made to test CTD DEEP03. XBTs were deployed at two hourly intervals and underway data logged. This report was compiled by Louise M. Duncan
RRS Discovery Cruise D334, 27 Oct-24 Nov 2008. RAPID Mooring Cruise Report
Full text linkThis report describes the mooring and underway operations conducted during RRS Discovery cruise D334 between 27 October and 24 November 2008. These mooring operations were completed as a part of the United Kingdom Natural Environment Research Council (NERC) funded RAPID Programme to monitor the Atlantic Meridional Overturning Circulation at 26.5°N. The primary purpose of this cruise was to service the Eastern Boundary and Mid-Atlantic Ridge sections of the 26.5°N mooring array first deployed during RRS Discovery cruises D277 and D278 (SOC cruise report number 53), and serviced in 2005 during RRS Charles Darwin cruise CD177 (NOCS cruise report number 5), in 2006 on RRS Discovery cruise D304 (NOCS cruise report number 16) and FS Poseidon cruises P343 and P345 (NOCS cruise report number 28) and in 2007 on RRS Discovery cruise D324 (NOCS cruise report number 34). Cruise D334 started and finished in Tenerife, Spain and covered the Eastern Boundary and Mid-Atlantic Ridge moorings deployed on D324 and P343. This cruise was the fourth annual refurbishment of the Eastern Boundary and Mid-Atlantic Ridge sections of the mooring array. The array will be further refined and refurbished during subsequent years. The instruments deployed consist of a variety of current meters, bottom pressure recorders, CTD loggers and Inverted Echosounders, which, combined with time series measurements of the Florida Straits current and wind stress estimates, will be used to determine the strength and structure of the MOC at 26.5°N. (http://www.noc.soton.ac.uk/rapidmoc
RRS Charles Darwin Cruise CD177, 12-29 Nov 2005. RAPID Mooring Cruise Report
Full text linkThis report describes mooring operations and underway measurements conducted during RRS Charles Darwin Cruise CD177. Cruise CD177 was conducted between 12 November 2005 and 29 November 2005. The first part of the cruise consisted of a transit from Falmouth, UK to Santa Cruz de Tenerife, Tenerife with mooring preparation conducted on this leg. Further scientific staff joined in Santa Cruz de Tenerife for the second leg that started on the 19 November. The cruise finished in Tenerife on the 29 November.This cruise was completed as part of the United Kingdom Natural Environment Research Council (NERC) funded RAPID Programme to monitor the Atlantic Meridional Overturning Circulation at 26.5ºN. The primary purposes of this cruise were to service the two key moorings (EB1 and EB2) on the eastern boundary of the 26.5ºN mooring array and to deploy two Pressure Inverted Echosounders (PIES). The array was first deployed in 2004 during RRS Discovery cruises D277 and D278 (Southampton Oceanography Centre Cruise Report No. 53) in order to set up a pre-operational prototype system to continuously observe the Atlantic Meridional Overturning Circulation (MOC). It was subsequently serviced on RRS Charles Darwin cruise CD170 and RV Knorr cruise KN182-2 (both covered in National Oceanography Centre Southampton Cruise Report No. 2). The array will be further refined and refurbished during subsequent years.This cruise was planned in response to mooring losses suffered in the first year of the 26.5ºN array deployment. The two key eastern boundary moorings were subjected to damage through suspected fishing activity causing the loss of data above 1200m at the eastern boundary. To reduce the risk of data loss we plan to service the two key moorings on a six-monthly cycle.Instruments deployed on the array consists of a variety of current meters, bottom pressure recorders and CTD loggers which, combined with time series measurements of the Florida Channel Current and wind stress estimates, will be used to determine the strength and structure of the MOC at 26.5ºN. (http://www.noc.soton.ac.uk/rapidmoc
RRS Discovery Cruise D324, 06 Oct-09 Nov 2007. RAPID Mooring Cruise Report
Full text linkThis report describes the mooring operations and underway measurements conducted during RRS Discovery Cruise D324 conducted between 6th October 2007 and 9th November 2007. This cruise was completed as part of the United Kingdom Natural Environment Research Council (NERC) funded RAPID Programme to monitor the Atlantic Meridional Overturning Circulation at 26.5ºN. The primary purpose of this cruise was to service the Eastern Boundary and Mid-Atlantic ridge sections of the 26.5ºN mooring array. The array was first deployed in 2004 during RRS Discovery cruises D277 and D278 (SOC cruise report number 53), and serviced in 2005 during RRS Charles Darwin Cruise CD170 and RV Knorr Cruise KN182-2 (NOCS cruise report number 2), RRS Charles Darwin Cruise CD177 (NOCS cruise report number 5), in 2006 on RV Ronald H. Brown Cruise RB0602, RRS Discovery Cruise D304 (NOCS cruise report number 16) and FS Poseidon Cruises P343 and P345 (NOCS cruise report number 28), and in 2007 on RV Ronald H. Brown Cruise RB0701 (NOCS cruise report number 29). Cruise D324 had two legs with the first a transit from Falmouth, UK to Santa Cruz de Tenerife, Tenerife and the second sailing from, and returning to, Santa Cruz de Tenerife, Tenerife. The moorings serviced on this cruise were deployed on D304, P343 and P345, along with two landers deployed on CD170. The Rapid-MOC array of moorings was deployed across the Atlantic to set up a pre- operational prototype system to continuously observe the Atlantic Meridional Overturning Circulation (MOC). This array will be further refined and refurbished during subsequent years as part of the Rapid-WATCH programme. The instrumentation deployed on the array consists of a variety of CTD loggers, current meters, bottom pressure recorders, and Inverted Echo-sounders, which, combined with time series measurements of the Florida Current and wind stress estimates, can be used to determine the strength and structure of the MOC at 26.5ºN
Southern ocean circulation
Full text linkThe Discovery Investigations of the 1930s provided a compelling description of the main elements of the Southern Ocean circulation. Over the intervening years, this has been extended to include ideas on ocean dynamics based on physical principles. In the modern description, the Southern Ocean has two main circulations that are intimately linked: a zonal (west-east) circumpolar circulation and a meridional (north-south) overturning circulation. The Antarctic Circumpolar Current transports around 140 million cubic metres per second west to east around Antarctica. This zonal circulation connects the Atlantic, Indian and Pacific Oceans, transferring and blending water masses and properties from one ocean basin to another. For the meridional circulation, a key feature is the ascent of waters from depths of around 2,000 metres north of the Antarctic Circumpolar Current to the surface south of the Current. In so doing, this circulation connects deep ocean layers directly to the atmosphere. The circumpolar zonal currents are not stable: meanders grow and separate, creating eddies and these eddies are critical to the
dynamics of the Southern Ocean, linking the zonal circumpolar and meridional circulations. As a result of this connection, a global three-dimensional ocean circulation exists in which the Southern Ocean plays a central role in regulating the Earth’s climate
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