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2018
Llanillo, PJ, Pelegri JL, Talley LD, Pena-Izquierdo J, Cordero RR.  2018.  Oxygen pathways and budget for the Eastern South Pacific Oxygen Minimum Zone. Journal of Geophysical Research-Oceans. 123:1722-1744.   10.1002/2017jc013509   AbstractWebsite

Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP-OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical-equatorial pathway, and (3) derive a refined annual-mean oxygen budget for the ESP-OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical-equatorial advection, with more than one-third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). Below the STC, at the OMZ's core, advection is weak and turbulent diffusion (isoneutral and dianeutral) accounts for 89% of the net oxygen supply, most of it coming from the oxygen-rich subtropical gyre. In the deep OMZ layer, net oxygen supply occurs only through turbulent diffusion and is dominated by the tropical-equatorial pathway. Considering the entire OMZ, net oxygen supply (3.8 +/- 0.42 mu mol kg(-1) yr(-1)) is dominated by isoneutral turbulent diffusion (56.5%, split into 32.3% of tropical-equatorial origin and 24.2% of subtropical origin), followed by isoneutral advection (32.0%, split into 27.6% of tropical-equatorial origin and 4.4% of subtropical origin) and dianeutral diffusion (11.5%). One-quarter (25.8%) of the net oxygen input escapes through dianeutral advection (most of it upwelling) and, assuming steady state, biological consumption is responsible for most of the oxygen loss (74.2%).

2016
Hernandez-Guerra, A, Talley LD.  2016.  Meridional overturning transports at 30 degrees S in the Indian and Pacific Oceans in 2002-2003 and 2009. Progress in Oceanography. 146:89-120.   10.1016/j.pocean.2016.06.005   AbstractWebsite

The meridional circulation and transports at 30 degrees S in the Pacific and Indian Oceans for the years 20022003 and 2009 are compared, using GO-SHIP hydrographic section data with an inverse box model and several choices of constraints. Southward heat transport across the combined Indian-Pacific sections, reflecting net heating north of these sections, doubled from -0.7 +/- 0.2 PW in 2002-2003 to -1.4 +/- 0.1 PW in 2009 (negative sign is southward), with the increase concentrated in the Indian Ocean (-0.6 PW compared with similar to 0.2 PW in the Pacific), and was insensitive to model choices for the Indonesian Throughflow. Diagnosed net evaporation also more than doubled in the Indian Ocean, from 0.21-0.27 Sv in 2002-2003 to 0.51-0.58 in 2009, with a smaller but significant increase in net evaporation in the Pacific, from 0.06-0.08 Sv to 0.16-0.32 Sv. These increased heat and freshwater exports coincided with Indian Ocean warming, a shift in the Indian's shallow gyre overturning transport to lower densities, and an increase in southward Agulhas Current transport from 75 Sv in 2002 to 92 Sv in 2009. The Indian's deep overturn weakened from about 11 Sv in 2002 to 7 Sv in 2009. In contrast, the Pacific Ocean overturning circulation was, nearly unchanged from 2003 to 2009, independent of model within the uncertainties. The East Australian Current transport decreased only slightly, from 52 Sv to 46 Sv. The southward Pacific Deep Water transport was at a higher density than the southward Indian Deep Water transport in both years and all models, similar to prior results. Estimated diapycnal diffusivity and velocity are strongly enhanced near the ocean bottom and are higher farther up in the water column in the Indian than in the Pacific, likely extending the reach of Indian Ocean overturning up to shallower depths than in the Pacific. The horizontal distribution of transports in the Pacific at all depths changed notably from 2003 to 2009, despite the stability of its meridional overturning structure. The 2009 horizontal structure resembles a "bowed gyre"; the hydrographic section data show that this disturbance extends to the abyss and disrupts the Deep Western Boundary Current structure in the Southwest Pacific Basin. Satellite altimetry suggests association with slow westward Rossby wave propagation generated in the eastern Pacific, with no apparent effect on the net overturning circulation. The Indian Ocean's upper ocean horizontal structure was stable between the two years even though its shallow gyre overturning transports changed significantly. On the other hand, northward abyssal transports concentrated' in the central Indian Ocean (Crozet Basin) in 2002 shifted westward to the Mozambique and Madagascar Basins in 2009, although the Crozet Basin's Deep Western Boundary Current existed in both years. (C) 2016 Elsevier Ltd. All rights reserved.

2003
Talley, LD, Reid JL, Robbins PE.  2003.  Data-based meridional overturning streamfunctions for the global ocean. Journal of Climate. 16:3213-3226.   10.1175/1520-0442(2003)016<3213:dmosft>2.0.co;2   AbstractWebsite

The meridional overturning circulation for the Atlantic, Pacific, and Indian Oceans is computed from absolute geostrophic velocity estimates based on hydrographic data and from climatological Ekman transports. The Atlantic overturn includes the expected North Atlantic Deep Water formation ( including Labrador Sea Water and Nordic Sea Overflow Water), with an amplitude of about 18 Sv through most of the Atlantic and an error of the order of 3 - 5 Sv (1 Sv = 10(6) m(3) s(-1)). The Lower Circumpolar Deep Water ( Antarctic Bottom Water) flows north with about 8 Sv of upwelling and a southward return in the South Atlantic, and 6 Sv extending to and upwelling in the North Atlantic. The northward flow of 8 Sv in the upper layer in the Atlantic ( sea surface through the Antarctic Intermediate Water) is transformed to lower density in the Tropics before losing buoyancy in the Gulf Stream and North Atlantic Current. The Pacific overturning streamfunction includes 10 Sv of Lower Circumpolar Deep Water flowing north into the South Pacific to upwell and return southward as Pacific Deep Water, and a North Pacific Intermediate Water cell of 2 Sv. The northern North Pacific has no active deep water formation at the sea surface, but in this analysis there is downwelling from the Antarctic Intermediate Water into the Pacific Deep Water, with upwelling in the Tropics. For global Southern Hemisphere overturn across 30degreesS, the overturning is separated into a deep and a shallow overturning cell. In the deep cell, 22 - 27 Sv of deep water flows southward and returns northward as bottom water. In the shallow cell, 9 Sv flows southward at low density and returns northward just above the intermediate water density. In all three oceans, the Tropics appear to dominate upwelling across isopycnals, including the migration of the deepest waters upward to the thermocline in the Indian and Pacific. Estimated diffusivities associated with this tropical upwelling are the same order of magnitude in all three oceans. It is shown that vertically varying diffusivity associated with topography can produce deep downwelling in the absence of external buoyancy loss. The rate of such downwelling for the northern North Pacific is estimated as 2 Sv at most, which is smaller than the questionable downwelling derived from the velocity analysis.

1999
McCarthy, MC, Talley LD.  1999.  Three-dimensional isoneutral potential vorticity structure in the Indian Ocean. Journal of Geophysical Research-Oceans. 104:13251-13267.   10.1029/1999jc900028   AbstractWebsite

The three-dimensional isoneutral potential vorticity structure of the Indian Ocean is examined using World Ocean Circulation Experiment and National Oceanic and Atmospheric Administration conductivity-temperature-depth data and historical bottle data. The distribution of the potential vorticity is set by the Indian Ocean's source waters and their circulation inside the basin. The lower thermocline has a high potential vorticity signal extending westward from northwest of Australia and a low signal from the Subantarctic Mode Water in the south. The Antarctic Intermediate Water inflow creates patches of high potential vorticity at intermediate depths in the southern Indian Ocean, below which the field becomes dominated by planetary vorticity, indicating a weaker meridional circulation and weaker potential vorticity sources. Wind-driven gyre depths have lower potential vorticity gradients primarily due to same-source waters. Homogenization and western shadow zones are not observed. The P-effect dominates the effect of the Somali Current and the Red Sea Water on the potential vorticity distribution. Isopleths tilt strongly away from latitude lines in the deep and abyssal waters as the Circumpolar Deep Water fills the basins in deep western boundary currents, indicating a strong meridional circulation north of the Antarctic Circumpolar Current. The lower-gradient intermediate layer surrounded vertically by layers with higher meridional potential vorticity gradients in the subtropical Indian Ocean suggests that Rossby waves will travel similar to 1.3 times faster than standard theory predicts. To the south, several pools of homogenized potential vorticity appear in the upper 2000 m of the Southern Ocean where gyres previously have been identified. South of Australia the abyssal potential vorticity structure is set by a combination of the Antarctic Circumpolar Current and the bathymetry.

1997
McCarthy, MC, Talley LD, Baringer MO.  1997.  Deep upwelling and diffusivity in the southern Central Indian Basin. Geophysical Research Letters. 24:2801-2804.   10.1029/97gl02112   AbstractWebsite

Transport of the deepest water westward through a gap at 28 degrees S in the Ninetyeast Ridge between the Central Indian Basin and the West Australia Basin is calculated from hydrographic data collected as part of WOCE Hydrographic Program section I8N. Zero reference velocity levels at mid-depth were chosen through consideration of water masses. The small transport of 1.0 Sv westward of water denser than sigma(4) = 45.92 kg m(-3) through the gap must all upwell in the southern Central Indian Basin. Of this, 0.7 Sv upwells between the central and western sill sections, that is, close to the sill itself. Using the areas covered by the isopycnal, we calculate an average vertical velocity of 3.3 . 10(-3) cm s(-1) close to the sill and of 4.2 . 10(-4) cm s(-1) west of the sill. Associated average vertical diffusivities are 105 cm(2) s(-1) close to the sill and 13 cm(2) s(-1) west of the sill, in this bottom layer.