RRS James Clark Ross Cruise JR15003, 17 Dec 2015 - 13 Jan 2016. Hydrographic measurements on GO-SHIP line SR1b and investigations of circulation and isotope cycles in coastal West Antarctica.

This cruise comprised work contributing to five projects. The twenty-first complete occupationof the Drake Passage GO-SHIP section SR1b obtained full-depth temperature, salinity, and lowered ADCP velocity profiles at 28 stations, along with underway measurements, with the objectives of investigating and monitoring interannual variability and trends in Antarctic Circumpolar Current structure and property transports and Southern Ocean water mass properties. Turnarounds of bottom pressure recorder (BPR) moorings contributed to the long time series of bottom pressure in Drake Passage. Biogeochemically-equipped Argo floats were deployed as part of the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) project to increase climate-quality observations in the Southern Ocean. Gliders were deployed over the Western Antarctic Peninsula continental shelf to measure properties and circulation with the aim of understanding flow and mixing of warm waters onto the shelf. Hydrographic profiles and water column and sediment samples taken over the continental shelf will be used to investigate stable isotope nutrient cycling processes

RRS James Clark Ross Cruise JR16002, 10 Nov - 03 Dec 2016. Hydrographic measurements on GO-SHIP line SR1b.

RRS James Clark Ross cruise JR16002 included work contributing to two National Capability projects. Bottom pressure recorder (BPR) landers previously deployed on the northern and southern continental slopes of Drake Passage to monitor ACC transport as part of Antarctic Circumpolar Current Levels from Altimetry and Island Measurement (ACCLAIM) were recovered, wrapping up a 28-year time series. The twenty-second complete occupation of the Drake Passage GO-SHIP section SR1b obtained full-depth temperature, salinity, and lowered ADCP velocity profiles at 30 stations, along with water column samples for oxygen isotope analysis and with underway measurements, with the objectives of investigating and monitoring interannual variability and trends in Antarctic Circumpolar Current structure and property transports and Southern Ocean water mass properties as part of Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA). Deployment of three Deep Apex autonomous profiling floats was also intended to contribute to ORCHESTRA as well as the global Deep Argo programme

RRS James Clark Ross Cruise JR15003, 17 Dec 2015 - 13 Jan 2016. Hydrographic measurements on GO-SHIP line SR1b and investigations of circulation and isotope cycles in coastal West Antarctica.

This cruise comprised work contributing to five projects. The twenty-first complete occupation of the Drake Passage GO-SHIP section SR1b obtained full-depth temperature, salinity, and lowered ADCP velocity profiles at 28 stations, along with underway measurements, with the objectives of investigating and monitoring interannual variability and trends in Antarctic Circumpolar Current structure and property transports and Southern Ocean water mass properties. Turnarounds of bottom pressure recorder (BPR) moorings contributed to the long time series of bottom pressure in Drake Passage. Biogeochemically-equipped Argo floats were deployed as part of the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) project to increase climate-quality observations in the Southern Ocean. Gliders were deployed over the Western Antarctic Peninsula continental shelf to measure properties and circulation with the aim of understanding flow and mixing of warm waters onto the shelf. Hydrographic profiles and water column and sediment samples taken over the continental shelf will be used to investigate stable isotope nutrient cycling processes

Variation of the Western Equatorial Pacific ocean, 1986-1988

Twenty one oceanographic sections made along 165°E during 1984-1988 provide a unique picture of the 1986-1987 El Nino and the subsequent La Nina in the Western Equatorial Pacific. The mean of six cruises from January 1984 throught June 1986, a relatively normal period, provides a reference with which the later sections are compared... Changes in the stratification along 165°E were corresponddingly large, reflecting both the geostrophic balance of the strong zonal currents and the changes in the volume of warm water in the Western Equatorial Pacific. The anomaly of warm water volume corresponded closely to the time integral of the warm water transport across 165°E. Local wind forcing and remotely forced waves were both important causes of the transport fluctuations. Winds, precipitation, and currents were all important factors determining the depth of the surface mixed layer and the thickness of the underlying barrier layer. The way in which these factors interact is a strong function of latitude. (D'après résumé d'auteur

The deep equatorial ocean circulation in wind-forced numerical solutions

We perform eddy-resolving and high-vertical-resolution numerical simulations of the circulation in an idealized equatorial Atlantic Ocean in order to explore the formation of the deep equatorial circulation (DEC) in this basin. Unlike in previous studies, the deep equatorial intraseasonal variability (DEIV) that is believed to be the source of the DEC is generated internally by instabilities of the upper ocean currents. Two main simulations are discussed: Solution 1, configured with a rectangular basin and with wind forcing that is zonally and temporally uniform; and Solution 2, with realistic coastlines and with an annual cycle of wind forcing varying zonally. Somewhat surprisingly, Solution 1 produces the more realistic DEC: The large-vertical-scale currents (Equatorial Intermediate Currents or EICs) are found over a large zonal portion of the basin, and the small-vertical-scale equatorial currents (Equatorial Deep Jets or EDJs) form low-frequency, quasi-resonant, baroclinic equatorial basin modes with phase propagating mostly downward, consistent with observations. We demonstrate that both types of currents arise from the rectification of DEIV, consistent with previous theories. We also find that the EDJs contribute to maintaining the EICs, suggesting that the nonlinear energy transfer is more complex than previously thought. In Solution 2, the DEC is unrealistically weak and less spatially coherent than in the first simulation probably because of its weaker DEIV. Using intermediate solutions, we find that the main reason for this weaker DEIV is the use of realistic coastlines in Solution 2. It remains to be determined, what needs to be modified or included to obtain a realistic DEC in the more realistic configuration

Ocean mixing beneath Pine Island Glacier ice shelf, West Antarctica

Ice shelves around Antarctica are vulnerable to an increase in ocean-driven melting, with the melt rate depending on ocean temperature and the strength of flow inside the ice-shelf cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier ice shelf, West Antarctica. These measurements were obtained by CTD, ADCP, and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The highest turbulent kinetic energy dissipation rate is found near the grounding line. The thermal variance dissipation rate increases closer to the ice-shelf base, with a maximum value found ∼0.5 m away from the ice. The measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf. The dissipation-rate-based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the Monin-Obukhov similarity theory for stratified boundary layers. We argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting

Deep temperature variability in Drake Passage

Observations made on 21 occupations between 1993 and 2016 of GO-SHIP line SR1b in eastern Drake Passage show an average temperature of 0.53°C deeper than 2000 dbar, with no significant trend, but substantial year-to-year variability (standard deviation 0.08°C). Using a neutral density framework to decompose the temperature variability into isopycnal displacement (heave) and isopycnal property change components shows that approximately 95% of the year-to-year variance in deep temperature is due to heave. Changes on isopycnals make a small contribution to year-to-year variability but contribute a significant trend of -1.4±0.6 m°C per year, largest for density (?n)?>?28.1, south of the Polar Front (PF). The heave component is depth-coherent and results from either vertical or horizontal motions of neutral density surfaces, which trend upward and northward around the PF, downward for the densest levels in the southern section, and downward and southward in the Subantarctic Front and Southern Antarctic Circumpolar Current Front (SACCF). A proxy for the locations of the Antarctic Circumpolar Current (ACC) fronts is constructed from the repeat hydrographic data and has a strong relationship with deep ocean heat content, explaining 76% of deep temperature variance. The same frontal position proxy based on satellite altimeter-derived surface velocities explains 73% of deep temperature variance. The position of the PF plays the strongest role in this relationship between ACC fronts and deep temperature variability in Drake Passage, although much of the temperature variability in the southern half of the section can be explained by the position of the SACCF. This article is protected by copyright. All rights reserved

The response of the Western Equatorial Pacific ocean to Westerly wind bursts during november 1989 to january 1990

Several 5 to 10 m s-1 westerly wind bursts of 10-15 days' duration occurred in the Western Equatorial Pacific during november 1989 to January 1990. The response to these wind bursts was characterized by a 400- to 600 km wide eastward jet in the upper 100-150 m along the equator between 135°E and the date line. Flow in this jet accelarated to speeds of over 100 cm s-1 within 1 week after the onset of westerly winds in november 1989 in association with super thyphoon Irma. In addition, a 20 to 40 cm s-1 westward counterflow developed between 2°N and 2°S below the surface jet separating it from the eastward flow of the Equatorial undercurrent in the thermocline. Changes in surface layer zonal volume transport in the Western Pacific due to westerly wind bursts were 25-56 Sv based on comparison of three shipboard velocity transects in november and december 1989. Although fluctuations in current speeds in the thermocline were generally smaller and less directly related to local wind forcing than those in the surface layer, the Equatorial undercurrent decelerated to less than 20 cm s-1 (i.e., less than half its speed before the onset of westerlies) by early december 1989. (D'après résumé d'auteur

Deep zonal currents in the central equatorial Pacific

A complex system of deep zonal currents in the central equatorial Pacific persisted during 16 months of current measurements spanning the 1982–1983 EI Niño episode. At least three extra equatorialcurrents appear to be permanent: the north and south intermediate countercurrents, with eastward velocity cores at 600 m depth, located 1.5–2.0° from the equator; and the south equatorial intermediate current, with a westward core at 900 m depth three or more degrees south of the equator. On the equator, the deep jets were nearly stationary during the period of these measurements. Comparison with earlier measurements shows that over longer periods the jets neither propagate uniformly nor stay in place