Robbins Paul E.
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PreprintThe WOCE–era 3–D Pacific Ocean circulation and heat budget( 2009-08-17) Macdonald, Alison M. ; Mecking, Sabine ; Toole, John M. ; Robbins, Paul E. ; Johnson, Gregory C. ; Wijffels, Susan E. ; Talley, Lynne D. ; Cook, Margaret F.To address questions concerning the intensity and spatial structure of the 3–dimensional circulation within the Pacific Ocean and the associated advective and diffusive property flux divergences, data from approximately 3000 high–quality hydrographic stations collected on 40 zonal and meridional cruises have been merged into a physically consistent model. The majority of the stations were occupied as part of the World Ocean Circulation Experiment (WOCE), which took place in the 1990s. These data are supplemented by a few pre–WOCE surveys of similar quality, and time–averaged direct–velocity and historical hydrographic measurements about the equator. An inverse box model formalism is employed to estimate the absolute along–isopycnal velocity field, the magnitude and spatial distribution of the associated diapycnal flow and the corresponding diapycnal advective and diffusive property flux divergences. The resulting large–scale WOCE Pacific circulation can be described as two shallow overturning cells at mid– to low latitudes, one in each hemisphere, and a single deep cell which brings abyssal waters from the Southern Ocean into the Pacific where they upwell across isopycnals and are returned south as deep waters. Upwelling is seen to occur throughout most of the basin with generally larger dianeutral transport and greater mixing occurring at depth. The derived pattern of ocean heat transport divergence is compared to published results based on air–sea flux estimates. The synthesis suggests a strongly east/west oriented pattern of air–sea heat flux with heat loss to the atmosphere throughout most of the western basins, and a gain of heat throughout the tropics extending poleward through the eastern basins. The calculated meridional heat transport agrees well with previous hydrographic estimates. Consistent with many of the climatologies at a variety of latitudes as well, our meridional heat transport estimates tend toward lower values in both hemispheres.
Technical ReportThe subduction experiment : cruise report R/V Knorr : cruise number 138 leg XV : subduction 3 mooring recovery cruise, 13-30 June 1993(Woods Hole Oceanographic Institution, 1993-12) Trask, Richard P. ; Galbraith, Nancy R. ; Robbins, Paul E. ; Ostrom, William M. ; Regier, Lloyd ; Pezzoli, Glenn ; McPhee, Neil M.Subduction is the mechanism by which water masses formed in the mixed layer and near the surface of the ocean find their way into the upper thermocline. The subduction process and its underlying mechanisms were studied though a combination of Eulerian and Langrangian measurements of velocity, measurements of tracer distributions and hydrographic properties and modeling. An array of five surface moorings carrying meteorological and oceanographic instrumentation were deployed for a period of two years beginning in June 1991 as part of an Office of Naval Research (ONR) funded Subduction experiment. Three eight month deployments were planned. The moorings were deployed at 18°N 34°W, 18°N 22°W, 25.5°N 29°W, 33°N 22°W and 33°N 34°W. A Vector Averaging Wind Recorder (VAWR) and an Improved Meteorological Recorder (IMET) collected wind speed and wind direction, sea surface temperature, air temperature, short wave radiation, barometric pressure and relative humidity. The IMET also measured precipitation. The moorings were heavily instrumented below the surface with Vector Measuring Current Meters (VMCM) and single point temperature recorders. Expendable bathythermograph (XBT) data were collected and meteorological observations were made while transmitting between mooring locations. This report describes the work that took place during R/V Knorr cruise number 138 leg XV which was the fourth scheduled Subduction mooring cruise. During this cruise the moorings previously deployed for a third and final eight month period were recovered. This report includes a description of the moorings and instrumentation that were recovered, has information about the underway measurements (XBT and meteorological observations) that were made including plots of the data, and presents a chronology of the cruise events.
Technical ReportImpact of Irminger Rings on Deep Convection in the Labrador Sea : mooring instrument, cruise CTD, and APEX data report September 2007 – September 2009(Woods Hole Oceanographic Institution, 2013-05) Furey, Heather H. ; McKee, Theresa K. ; de Jong, Marieke F. ; Robbins, Paul E. ; Bower, Amy S.This is the final data report of all hydrographic station, mooring, and subsurface float data collected by the Woods Hole Oceanographic Institution in 2007-2009 during the Impact of Irminger Rings on Deep Convection in the Labrador Sea experiment (IRINGS). The objectives of IRINGS were to (1) to determine the full water column hydrographic and velocity structure of newlyformed Irminger Rings that have entered the interior Labrador Sea; (2) to observe how Irminger Ring core properties are modified by atmospheric forcing over their lifetime; and (3) to improve the interpretation of sea surface height (SSH) anomalies in terms of newly formed coherent heat containing Irminger Rings. The mooring deployment and recovery cruises were both on the R/V Knorr: KN192-01 in September 2007 and KN196-01 in September 2009, respectively. The single mooring held eight Aanderaa current meters (RCM-11), two Submerged Autonomous Launch Platforms (SALPs), and nine Seabird microcats (SBE37), deployed from 26 September 2007 through 27 September 2009, yeilding full water column (100-3000 meters) records of temperature, salinity, pressure, and velocity data for the two year period. The two SALP cages contained eleven APEX floats, and released some of these floats according to local oceanographic conditions, so as to seed the floats in passing Irminger Rings, and the remainder of floats as timed releases. Thirteen conductivity-temperature-depth (CTD) stations were taken on the mooring recovery cruise, creating a boundary current cross-section from the mooring site to Nuuk, Greenland.
ThesisTemporal evolution of tritium-³He age in the North Atlantic : implications for thermocline ventilation(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1997-09) Robbins, Paul E.This thesis is a study of the physical mechanisms that ventilate the subtropical thermocline of the eastern North Atlantic. The starting point is an analysis of the existent historical database of natural and anthropogenic tracers, with special emphasis on 3He and tritium, that can be used to infer rates of ventilation. If the flow is predominantly advective, the temporal evolution of coupled transient tracers can be used to define a tracer age which measures the elapsed time since a water parcel was resident in the surface mixed layer. A principle finding is that the observed tracer age shows a large and systematic change over time. Tritium-3He age in the eastern Atlantic thermocline is seen to increase over time; the magnitude of the change is greatest for the deeper, more slowly ventilated layers of the thermocline. The first hypothesis examined is that the observed shift in the tracer age field is the manifestation of a slackening of the physical ventilation. A time series of the meridional geostrophic velocity shear in the eastern Atlantic shows no indication of a change in the strength of the large-scale circulation. Uncertainty of the geostrophic calculation due to data sparsity and mesoscale eddy contamination prevents conclusive rejection of the hypothesis of a changing circulation. There are other tracers which offer useful clues: comparison of the tritium-3He age field with dissolved oxygen reveals a temporal trend in the property-property correlation. The spatial structure of the oxygen field, however, shows no long-term evolution over time. From this line of evidence it is concluded that the physical ventilation of the thermocline has not altered over time and, therefore, the temporal change in the tritium-3He age field must be the signal of the tritium invasion itself. A second hypothesis, which analysis shows is more consistent with the observations, is that the changing tracer age is a consequence of mixing effects in the ventilation of 3He and tritium. Numerical simulations of the thermocline ventilation of 3H and 3He are performed to examine the steadiness of the tracer age field under different advective-diffusive regimes. A one-dimensional model is constructed based on the assumption that the totality of the fluid in the thermocline derives from subduction out of the surface mixed layer. The temporal behavior of the tracer age field is found to be dependent on the radiotracer Peclet number, which measures the ratio of the diffusive and advective time scales. In a model with steady circulation, the observed temporal behavior of the tracer age field can be reproduced only when the effects of lateral mixing play a significant role in the process of ventilation. The vertical structure and magnitude of the implied lateral diffusivity are, however, inconsistent with other observations. The numerical simulations are next extended to two-dimensions to allow for the presence of a pool of unventilated, re-circulated water within the anti-cyclonic, subtropical gyre. Comparison of the model with the observed transient tracer field in the lower thermocline shows consistency with conventional estimates of lateral mixing rates only when the diffusively ventilated "pool" region extends across the entire zonal domain of the gyre. In contrast, the transient tracer fields in the upper portion of the thermocline are best reproduced when the isopycnal surfaces are ventilated by advection directly from the surface mixed layer. The results obtained here are consistent with numerical simulations which reveal a prominent role for mesoscale eddies in the ventilation of the thermocline.