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Talley, LD, Rosso I, Kamenkovich I, Mazloff MR, Wang J, Boss E, Gray AR, Johnson KS, Key RM, Riser SC, Williams NL, Sarmiento JL.  2019.  Southern Ocean biogeochemical float deployment strategy, with example from the Greenwich meridian line (GO-SHIP A12). Journal of Geophysical Research-Oceans. 124:403-431.   10.1029/2018jc014059   AbstractWebsite

Biogeochemical Argo floats, profiling to 2,000-m depth, are being deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling program (SOCCOM). The goal is 200 floats by 2020, to provide the first full set of annual cycles of carbon, oxygen, nitrate, and optical properties across multiple oceanographic regimes. Building from no prior coverage to a sparse array, deployments are based on prior knowledge of water mass properties, mean frontal locations, mean circulation and eddy variability, winds, air-sea heat/freshwater/carbon exchange, prior Argo trajectories, and float simulations in the Southern Ocean State Estimate and Hybrid Coordinate Ocean Model (HYCOM). Twelve floats deployed from the 2014-2015 Polarstern cruise from South Africa to Antarctica are used as a test case to evaluate the deployment strategy adopted for SOCCOM's 20 deployment cruises and 126 floats to date. After several years, these floats continue to represent the deployment zones targeted in advance: (1) Weddell Gyre sea ice zone, observing the Antarctic Slope Front, and a decadally-rare polynya over Maud Rise; (2) Antarctic Circumpolar Current (ACC) including the topographically steered Southern Zone chimney where upwelling carbon/nutrient-rich deep waters produce surprisingly large carbon dioxide outgassing; (3) Subantarctic and Subtropical zones between the ACC and Africa; and (4) Cape Basin. Argo floats and eddy-resolving HYCOM simulations were the best predictors of individual SOCCOM float pathways, with uncertainty after 2years of order 1,000km in the sea ice zone and more than double that in and north of the ACC.

Shi, JR, Xie SP, Talley LD.  2018.  Evolving relative importance of the Southern Ocean and North Atlantic in anthropogenic ocean heat uptake. Journal of Climate. 31:7459-7479.   10.1175/jcli-d-18-0170.1   AbstractWebsite

Ocean uptake of anthropogenic heat over the past 15 years has mostly occurred in the Southern Ocean, based on Argo float observations. This agrees with historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), where the Southern Ocean (south of 30 degrees S) accounts for 72% +/- 28% of global heat uptake, while the contribution from the North Atlantic north of 30 degrees N is only 6%. Aerosols preferentially cool the Northern Hemisphere, and the effect on surface heat flux over the subpolar North Atlantic opposes the greenhouse gas (GHG) effect in nearly equal magnitude. This heat uptake compensation is associated with weakening (strengthening) of the Atlantic meridional overturning circulation (AMOC) in response to GHG (aerosol) radiative forcing. Aerosols are projected to decline in the near future, reinforcing the greenhouse effect on the North Atlantic heat uptake. As a result, the Southern Ocean, which will continue to take up anthropogenic heat largely through the mean upwelling of water from depth, will be joined by increased relative contribution from the North Atlantic because of substantial AMOC slowdown in the twenty-first century. In the RCP8.5 scenario, the percentage contribution to global uptake is projected to decrease to 48% +/- 8% in the Southern Ocean and increase to 26% +/- 6% in the northern North Atlantic. Despite the large uncertainty in the magnitude of projected aerosol forcing, our results suggest that anthropogenic aerosols, given their geographic distributions and temporal trajectories, strongly influence the high-latitude ocean heat uptake and interhemispheric asymmetry through AMOC change.

Talley, LD.  2013.  Closure of the Global Overturning Circulation Through the Indian, Pacific, and Southern Oceans: Schematics and Transports. Oceanography. 26:80-97. AbstractWebsite

The overturning pathways for the surface-ventilated North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) and the diffusively formed Indian Deep Water (IDW) and Pacific Deep Water (PDW) are intertwined. The global overturning circulation (GOC) includes both large wind-driven upwelling in the Southern Ocean and important internal diapycnal transformation in the deep Indian and Pacific Oceans. All three northern-source Deep Waters (NADW, IDW, PDW) move southward and upwell in the Southern Ocean. AABW is produced from the denser, salty NADW and a portion of the lighter, low oxygen IDW/PDW that upwells above and north of NADW. The remaining upwelled IDW/PDW stays near the surface, moving into the subtropical thermoclines, and ultimately sources about one-third of the NADW. Another third of the NADW comes from AABW upwelling in the Atlantic. The remaining third comes from AABW upwelling to the thermocline in the Indian-Pacific. Atlantic cooling associated with NADW formation (0.3 PW north of 32 degrees S; 1 PW = 1015 W) and Southern Ocean cooling associated with AABW formation (0.4 PW south of 32 degrees S) are balanced mostly by 0.6 PW of deep diffusive heating in the Indian and Pacific Oceans; only 0.1 PW is gained at the surface in the Southern Ocean. Thus, while an adiabatic model of NADW global overturning driven by winds in the Southern Ocean, with buoyancy added only at the surface in the Southern Ocean, is a useful dynamical idealization, the associated heat changes require full participation of the diffusive Indian and Pacific Oceans, with a basin-averaged diffusivity on the order of the Munk value of 10(-4) m(2) s(-1).

Johnson, GC, Talley LD.  1997.  Deep tracer and dynamical plumes in the tropical Pacific Ocean. Journal of Geophysical Research-Oceans. 102:24953-24964.   10.1029/97jc01913   AbstractWebsite

Anomalous middepth plumes in potential temperature-salinity, theta-S, and buoyancy frequency squared, N-2, Originate east of the East Pacific Rise Crest and decay toward the west. Conductivity-temperature-depth (CTD) data from recent hydrographic sections at 15 degrees S and 10 degrees N are used together with meridional sections at 110 degrees, 135 degrees, and 151 degrees W to map these structures. Warm salty plumes west of the rise crest have maxima centered at 2700 m, 10 degrees S and 8 degrees N, and are interrupted by a cold, fresh tongue centered at 2900 m, 2 degrees S. The theta-S anomalies decay to half their peak strength 2800 km to the west of the rise crest, +/-300 km in the meridional, and +/-0.4 km in the vertical. Vertical N-2 minima occur within the plumes, regions of reduced vertical gradients in theta and S. These minima are underlain by maxima near the depth of the rise crest, about 3200 m. The N-2 plumes decay more rapidly to the west of the rise crest than do the theta-S plumes. The N-2 structure is consistent with a pair of stacked gyres in each hemisphere. There are at least three possible mechanisms consistent with some aspects of these features. First, a deep maximum in upwelling somewhere below 2700 m would result in equatorvard and westward interior flow at 2700 m. advecting these plumes along with it. Second, rapid upwelling of warm, salty, unstratified water in the eastern basins could result in westward overflows over the rise crest. Third, upwelling and associated entrainment processes owing to hydrothermal venting could result in stacked counter-rotating gyres west of the rise crest.