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T. K. Chereskin and D. Roemmich


A comparison of measured and wind-derived ageostrophic transport is presented from a zonal transect spanning the Atlantic Ocean along 11°N. The transport per unit depth shows a striking surface maximum that decays to nearly zero at a depth of approximately 100 m. We identify this flow in the upper 100 m as the Ekman transport. The sustained values of wind stress and the penetration depth of the Ekman transport reported here are considerably greater than in previous observations, which were made in conditions of light winds. The transport of 12.0 ± 5.5 × 106 m3 s−1, calculated from the difference of geostrophic shear and shear measured by an acoustic Doppler current profiler, is in good agreement with that estimated from the shipboard winds, 8.8 ± 1.9 × 106 m3 s−1, and from climatology, 13.5 ± 0.3 × 106 m3 s−1. Qualitatively, the horizontal distribution of the wind-driven flow was best predicted by the shipboard winds. The cumulative transport increased linearly over the western three-fourths of the basin, where the winds were large and spatially uniform, and remained constant over the eastern fourth where the easterly stress was uncharacteristically low. The mean depth of the Ekman transport extended below the mixed layer depth, which varied from 25 to 90 m. The profile of ageostrophic transport does not appear consonant with slablike behavior in the mixed layer, even when spatial variations in mixed layer depth are taken into account.

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N. V. Zilberman, D. H. Roemmich, and S. T. Gille


The meridional transport in the Pacific Ocean subtropical cell is studied for the period from 2004 to 2011 using gridded Argo temperature and salinity profiles and atmospheric reanalysis surface winds. The poleward Ekman and equatorward geostrophic branches of the subtropical cell exhibit an El Niño–Southern Oscillation signature with strong meridional transport occurring during La Niña and weak meridional transport during El Niño. At 7.5°S, mean basinwide geostrophic transport above 1000 dbar is 48.5 ± 2.5 Sv (Sv ≡ 106 m3 s−1) of which 30.3–38.4 Sv return to the subtropics in the surface Ekman layer, whereas 10.2–18.3 Sv flow northward, feeding the Indonesian Throughflow. Geostrophic transport within the subtropical cell is stronger in the ocean interior and weaker in the western boundary during La Niña, with changes in the interior dominating basinwide transport. Using atmospheric reanalyses, only half of the mean heat gain by the Pacific north of 7.5°S is compensated by oceanic heat transport out of the region. The National Oceanography Centre at Southampton air–sea flux climatology is more consistent for closing the oceanic heat budget. In summary, the use of Argo data for studying the Pacific subtropical cell provides an improved estimate of basinwide mean geostrophic transport, includes both interior and western boundary contributions, quantifies El Niño/La Niña transport variability, and illustrates how the meridional overturning cell dominates ocean heat transport at 7.5°S.

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N. V. Zilberman, D. H. Roemmich, S. T. Gille, and J. Gilson


Western boundary currents (WBCs) are highly variable narrow meandering jets, making assessment of their volume transports a complex task. The required high-resolution temporal and spatial measurements are available only at a limited number of sites. In this study a method is developed for improving estimates of the East Australian Current (EAC) mean transport and its low-frequency variability, using complementary modern datasets. The present calculation is a case study that will be extended to other subtropical WBCs. The method developed in this work will reduce uncertainties in estimates of the WBC volume transport and in the interannual mass and heat budgets of the meridional overturning circulations, improving our understanding of the response of WBCs to local and remote forcing on long time scales. High-resolution expendable bathythermograph (HR-XBT) profiles collected along a transect crossing the EAC system near Brisbane, Australia, are merged with coexisting profiles and parking-depth trajectories from Argo floats, and with altimetric sea surface height data. Using HR-XBT/Argo/altimetry data combined with Argo trajectory-based velocities at 1000 m, the 2004–15 mean poleward alongshore transport of the EAC is 19.5 ± 2.0 Sv (1 Sv ≡ 106 m3 s−1) of which 2.5 ± 0.5 Sv recirculate equatorward just offshore of the EAC. These transport estimates are consistent in their mean and variability with concurrent and nearly collocated moored observations at 27°S, and with earlier moored observations along 30°S. Geostrophic transport anomalies in the EAC system, including the EAC recirculation, show a standard deviation of ±3.1 Sv at interannual time scales between 2004 and 2015.

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Worth D. Nowlin Jr., Melbourne Briscoe, Neville Smith, Michael J. McPhaden, Dean Roemmich, Piers Chapman, and J. Frederick Grassle

The Global Ocean Observing System (GOOS) was initiated in the early 1990s with sponsorship by the Intergovernmental Oceanographic Commission, the International Council for Science, the United Nations Environment Programme, and the World Meteorological Organization. Its objective is to design and assist with the implementation of a sustained, integrated, multidisciplinary ocean observing system focused on the production and delivery of data and products to a wide variety of users. The initial design for the GOOS is nearing completion, and implementation has begun.

The initial task in developing a sustained observing system is to identify the requirements of users for sustained data and products. Once such needs are known, the next task is to examine observing system elements that already exist; many necessary elements will be found to exist. The next tasks are to identify and integrate the useful elements into an efficient and effective system, while removing the unneeded elements, and to develop and implement effective data management activities. Moreover, the system must be augmented with new elements because some requirements cannot be met with existing elements and because of technological advances.

Our key objective is to discuss the mechanism whereby new candidate observing system elements are transformed from development status into elements of the sustained system. Candidate systems normally will pass through many different phases on the path from idea and concept to a mature, robust technique. These stages are discussed and examples are given:

  1. Development of an observational/analysis technique within the ocean community.

  2. Community acceptance of the methodology gained through experience within pilot projects to demonstrate the utility of the methods and data.

  3. Pre-operational use of the methods and data by researchers, application groups, and other end users, to ensure proper integration within the global system and to ensure that the intended augmentation (and perhaps phased withdrawal of an old technique) does not have any negative impact on the integrity of the GOOS data set and its dependent products.

  4. Incorporation of the methods and data into an operational framework with sustained support and sustained use to meet societal objectives.

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