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Briggs, EM, Martz TR, Talley LD, Mazloff MR, Johnson KS.  2018.  Physical and biological drivers of biogeochemical tracers within the seasonal sea ice zone of the Southern Ocean from profiling floats. Journal of Geophysical Research-Oceans. 123:746-758.   10.1002/2017jc012846   AbstractWebsite

Here we present initial findings from nine profiling floats equipped with pH, O-2, , and other biogeochemical sensors that were deployed in the seasonal ice zone (SIZ) of the Southern Ocean in 2014 and 2015 through the Southern Ocean Carbon and Climate Observations and Modelling (SOCCOM) project. A large springtime phytoplankton bloom was observed that coincided with sea ice melt for all nine floats. We argue this bloom results from a shoaling of the mixed layer depth, increased vertical stability, and enhanced nutrient and light availability as the sea ice melts. This interpretation is supported by the absence of a springtime bloom when one of the floats left the SIZ in the second year of observations. During the sea ice covered period, net heterotrophic conditions were observed. The rate of uptake of O-2 and release of dissolved inorganic carbon (derived from pH and estimated total alkalinity) and is reminiscent of biological respiration and is nearly Redfieldian for the nine floats. A simple model of mixed layer physics was developed to separate the physical and biological components of the signal in pH and O-2 over one annual cycle for a float in the Ross Sea SIZ. The resulting annual net community production suggests that seasonal respiration during the ice covered period of the year nearly balances the production in the euphotic layer of up to 5 molCm(-2) during the ice free period leading to a net of near zero carbon exported to depth for this one float.

Rosso, I, Mazloff MR, Verdy A, Talley LD.  2017.  Space and time variability of the Southern Ocean carbon budget. Journal of Geophysical Research-Oceans. 122:7407-7432.   10.1002/2016jc012646   AbstractWebsite

The upper ocean dissolved inorganic carbon (DIC) concentration is regulated by advective and diffusive transport divergence, biological processes, freshwater, and air-sea CO2 fluxes. The relative importance of these mechanisms in the Southern Ocean is uncertain, as year-round observations in this area have been limited. We use a novel physical-biogeochemical state estimate of the Southern Ocean to construct a closed DIC budget of the top 650 m and investigate the spatial and temporal variability of the different components of the carbon system. The dominant mechanisms of variability in upper ocean DIC depend on location and time and space scales considered. Advective transport is the most influential mechanism and governs the local DIC budget across the 10 day-5 year timescales analyzed. Diffusive effects are nearly negligible. The large-scale transport structure is primarily set by upwelling and downwelling, though both the lateral ageostrophic and geostrophic transports are significant. In the Antarctic Circumpolar Current, the carbon budget components are also influenced by the presence of topography and biological hot spots. In the subtropics, evaporation and air-sea CO2 flux primarily balances the sink due to biological production and advective transport. Finally, in the subpolar region sea ice processes, which change the seawater volume and thus the DIC concentration, compensate the large impact of the advective transport and modulate the timing of biological activity and air-sea CO2 flux.

Marshall, J, Andersson A, Bates N, Dewar W, Doney S, Edson J, Ferrari R, Forget G, Fratantoni D, Gregg M, Joyce T, Kelly K, Lozier S, Lumpkin R, Maze G, Palter J, Samelson R, Silverthorne K, Skyllingstad E, Straneo F, Talley L, Thomas L, Toole J, Weller R, Climode G.  2009.  The CLIMODE FIELD CAMPAIGN Observing the Cycle of Convection and Restratification over the Gulf Stream. Bulletin of the American Meteorological Society. 90:1337-1350.   10.1175/2009bams2706.1   AbstractWebsite
Holte, J, Talley L.  2009.  A New Algorithm for Finding Mixed Layer Depths with Applications to Argo Data and Subantarctic Mode Water Formation. Journal of Atmospheric and Oceanic Technology. 26:1920-1939.   10.1175/2009jtecho543.1   AbstractWebsite

A new hybrid method for finding the mixed layer depth (MLD) of individual ocean profiles models the general shape of each profile, searches for physical features in the profile, and calculates threshold and gradient MLDs to assemble a suite of possible MLD values. It then analyzes the patterns in the suite to select a final MLD estimate. The new algorithm is provided in online supplemental materials. Developed using profiles from all oceans, the algorithm is compared to threshold methods that use the C. de Boyer Monte gut et al. criteria and to gradient methods using 13 601 Argo profiles from the southeast Pacific and southwest Atlantic Oceans. In general, the threshold methods find deeper MLDs than the new algorithm and the gradient methods produce more anomalous MLDs than the new algorithm. When constrained to using only temperature profiles, the algorithm offers a clear improvement over the temperature threshold and gradient methods; the new temperature algorithm MLDs more closely approximate the density algorithm MLDs than the temperature threshold and gradient MLDs. The algorithm is applied to profiles from a formation region of Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). The density algorithm finds that the deepest MLDs in this region routinely reach 500 dbar and occur north of the A. H. Orsi et al. mean Subantarctic Front in the southeastern Pacific Ocean. The deepest MLDs typically occur in August and September and are congruent with the subsurface salinity minimum, a signature of AAIW.

Brambilla, E, Talley LD.  2006.  Surface drifter exchange between the North Atlantic subtropical and subpolar gyres. Journal of Geophysical Research-Oceans. 111   10.1029/2005jc003146   AbstractWebsite

[ 1] Surface drifters deployed in the subtropical and subpolar North Atlantic from 1990 to 2002 show almost no connection between the subtropical and subpolar gyres; only one drifter crosses the intergyre boundary even though other data types ( e. g., dynamic topography and tracers) suggest a major connection. Two of several possible causes for the lack of intergyre connectivity in this two-dimensional data set are examined: ( 1) undersampling and short drifter lifetime leading to underestimation of the northward flow, and ( 2) the southward mean Ekman velocity. Advection of a large number of long-lived synthetic drifters through the observed mean velocity results in a 5% increase in cross-gyre flux compared with that for synthetic drifters with realistic lifetimes. By further advecting synthetic drifters through the observed mean velocity field with and without the Ekman component, estimated from the wind field associated with the actual drifters, it is shown that removal of the Ekman component further increases the intergyre flux by up to 6%. With a turbulent component added to the mean velocity field to simulate the eddy field, there is a further increase in connection by 5%. Thus the Ekman and eddy contributions to the drifter trajectories nearly cancel each other. Consideration of three-dimensional processes ( subduction and obduction) is reserved for complete modeling studies.

Tsuchiya, M, Talley LD, McCartney MS.  1992.  An Eastern Atlantic Section from Iceland Southward across the Equator. Deep-Sea Research Part a-Oceanographic Research Papers. 39:1885-1917.   10.1016/0198-0149(92)90004-d   AbstractWebsite

A long CTD/hydrographic section with closely-spaced stations was occupied in July-August 1988 from Iceland southward to 3-degrees-S along a nominal longitude of 20-degrees-W. The section extends from the surface down to the bottom, and spans the entire mid-ocean circulation regime of the North Atlantic from the subpolar gyre through the subtropical gyre and the equatorial currents. Vertical sections of potential temperature, salinity and potential density from CTD measurements and of oxygen, silica, phosphate and nitrate, based on discrete water-sample measurements are presented and discussed in the context of the large-scale circulation of the North Atlantic Ocean. The close spacing of high-quality stations reveals some features not described previously. The more important findings include: (1) possible recirculation of the lightest Subpolar Mode Water into the tropics; (2) a thermostad at temperatures of 8-9-degrees-C, lying below that of the Equatorial 13-degrees-C Water; (3) the nutrient distribution in the low-salinity water above the Mediterranean Outflow Water that supports the previous conjecture of northern influence of the Antarctic Intermediate Water; (4) a great deal of lateral structure of the Mediterranean Outflow Water, with a number of lobes of high salinity; (5) an abrupt southern boundary of the Labrador Sea Water at the Azores-Biscay Rise and a vertically well-mixed region to its south; (6) a sharp demarcation in the central Iceland Basin between the newest Iceland-Scotland Overflow Water and older bottom water, which has a significant component of southern water; (7) evidence that the Northeast Atlantic Deep Water is a mixture of the Mediterranean Outflow Water and the Northwest Atlantic Bottom Water with very little input from the Iceland-Scotland Overflow Water; (8) an isolated core of the high-salinity, low-silica Upper North Atlantic Deep Water at the equator; (9) a core of the high-oxygen, low-nutrient Lower North Atlantic Deep Water pressed against the southern flank of the Mid-Atlantic Ridge just south of the equator; (10) a weak minimum of salinity, and well-defined maxima of nutrients associated with the oxygen minimum that separates the Middle and Lower North Atlantic Deep Waters south of the equator; (11) a large body of nearly homogeneous water beneath the Middle North Atlantic Deep Water between 20-degrees-N and the Azores-Biscay Rise; and (12) a deep westward boundary undercurrent on the southern slope of the Rockall Plateau.