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Holte, J, Talley LD, Gilson J, Roemmich D.  2017.  An Argo mixed layer climatology and database. Geophysical Research Letters. 44:5618-5626.   10.1002/2017gl073426   AbstractWebsite

A global climatology and database of mixed layer properties are computed from nearly 1,250,000 Argo profiles. The climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth (MLD) and a standard threshold method. The climatology provides accurate information about the depth, properties, extent, and seasonal patterns of global mixed layers. The individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest. The climatology and database are available online at . The MLDs calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method, particularly in regions of deep winter mixed layers; the new climatology differs the most from existing mixed layer climatologies in these regions. Examples are presented from the Labrador and Irminger Seas, the Southern Ocean, and the North Atlantic Ocean near the Gulf Stream. In these regions the threshold method tends to overestimate winter MLDs by approximately 10% compared to the algorithm.

Carter, BR, Feely RA, Mecking S, Cross JN, Macdonald AM, Siedlecki SA, Talley LD, Sabine CL, Millero FJ, Swift JH, Dickson AG, Rodgers KB.  2017.  Two decades of Pacific anthropogenic carbon storage and ocean acidification along Global Ocean Ship-lebased Hydrographic Investigations Program sections P16 and P02. Global Biogeochemical Cycles. 31:306-327.   10.1002/2016gb005485   AbstractWebsite

A modified version of the extended multiple linear regression (eMLR) method is used to estimate anthropogenic carbon concentration (C-anth) changes along the Pacific P02 and P16 hydrographic sections over the past two decades. P02 is a zonal section crossing the North Pacific at 30 degrees N, and P16 is a meridional section crossing the North and South Pacific at similar to 150 degrees W. The eMLR modifications allow the uncertainties associated with choices of regression parameters to be both resolved and reduced. Canth is found to have increased throughout the water column from the surface to similar to 1000 m depth along both lines in both decades. Mean column Canth inventory increased consistently during the earlier (1990s-2000s) and recent (2000s-2010s) decades along P02, at rates of 0.53 +/- 0.11 and 0.46 +/- 0.11 mol Cm-2 a(-1), respectively. By contrast, Canth storage accelerated from 0.29 +/- 0.10 to 0.45 +/- 0.11 mol Cm-2 a(-1) along P16. Shifts in water mass distributions are ruled out as a potential cause of this increase, which is instead attributed to recent increases in the ventilation of the South Pacific Subtropical Cell. Decadal changes along P16 are extrapolated across the gyre to estimate a Pacific Basin average storage between 60 degrees S and 60 degrees N of 6.1 +/- 1.5 PgC decade(-1) in the earlier decade and 8.8 +/- 2.2 PgC decade(-1) in the recent decade. This storage estimate is large despite the shallow Pacific Canth penetration due to the large volume of the Pacific Ocean. By 2014, Canth storage had changed Pacific surface seawater pH by -0.08 to -0.14 and aragonite saturation state by -0.57 to -0.82.

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.

Dong, S, Sprintall J, Gille ST, Talley L.  2008.  Southern Ocean mixed-layer depth from Argo float profiles. Journal of Geophysical Research-Oceans. 113   10.1029/2006jc004051   AbstractWebsite

Argo float profiles of temperature, salinity, and pressure are used to derive the mixed-layer depth (MLD) in the Southern Ocean. MLD is determined from individual profiles using both potential density and potential temperature criteria, and a monthly climatology is derived from individual MLDs using an objective mapping method. Quantitative data are available in the auxiliary material. The spatial structures of MLDs are similar in each month, with deep mixed layers within and just north of the Antarctic Circumpolar Current (ACC) in the Pacific and Indian oceans. The deepest mixed layers are found from June to October and are located just north of the ACC where Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water ( SAMW) are formed. Examination of individual MLDs indicates that deep mixed layers ( MLD >= 400 m) from both the density and temperature criteria are concentrated in a narrow surface density band which is within the density range of SAMW. The surface salinity for these deep mixed layers associated with the SAMW formation are slightly fresher compared to historical estimates. Differences in air-sea heat exchanges, wind stress, and wind stress curl in the Pacific and Indian oceans suggest that the mode water formation in each ocean basin may be preconditioned by different processes. Wind mixing and Ekman transport of cold water from the south may assist the SAMW formation in the Indian Ocean. In the eastern Pacific, the formation of mode water is potentially preconditioned by the relative strong cooling and weak stratification from upwelling.

Brambilla, E, Talley LD.  2008.  Subpolar Mode Water in the northeastern Atlantic: 1. Averaged properties and mean circulation. Journal of Geophysical Research-Oceans. 113   10.1029/2006jc004062   AbstractWebsite

Subpolar Mode Waters (SPMW) in the eastern North Atlantic subpolar gyre are investigated with hydrographic and Lagrangian data (surface drifters and isopycnal floats). Historical hydrographic data show that SPMWs are surface water masses with nearly uniform properties, confined between the ocean surface and the permanent pycnocline. SPMWs represented by densities 27.3(sigma theta), 27.4(sigma theta), and 27.5(sigma theta) are present in the eastern subpolar gyre and are influenced by the topography and the regional circulation. Construction of an absolute surface stream function from surface drifters shows that SPMWs are found along the mean path of each of the several branches of the North Atlantic Current (NAC) and their density increases gradually downstream. The Rockall Trough branch of the NAC carries 27.3(sigma theta), 27.4(sigma theta), and 27.5(sigma theta) SPMW toward the Iceland-Faroe Front. In the Iceland Basin, the Subarctic Front along the western flank of the Rockall Plateau carries a similar sequence of SPMW. The western side of the Central Iceland Basin branch of the NAC, on the other hand, veers westward and joins the East Reykjanes Ridge Current, feeding the 27.5(sigma theta) SPMW on the Reykjanes Ridge. The separation among the various NAC branches most likely explains the different properties that characterize the 27.5(sigma theta) SPMW found on the Reykjanes Ridge and on the Iceland-Faroe Ridge. Since the branches of the NAC have a dominant northeastward direction, the newly observed distribution of SPMW combined with the new stream function calculation modify the original hypothesis of McCartney and Talley (1982) of a smooth cyclonic pathway for SPMW advection and density increase around the subpolar gyre.

Fiedler, PC, Talley LD.  2006.  Hydrography of the eastern tropical Pacific: A review. Progress in Oceanography. 69:143-180.   10.1016/j.pocean.2006.03.008   AbstractWebsite

Eastern tropical Pacific Ocean waters lie at the eastern end of a basin-wide equatorial current system, between two large subtropical gyres and at the terminus of two eastern boundary currents. Descriptions and interpretations of surface, pycnocline, intermediate and deep waters in the region are reviewed. Spatial and temporal patterns are discussed using (1) maps of surface temperature, salinity, and nutrients (phosphate, silicate, nitrate and nitrite), and thermocline and mixed layer parameters, and (2) meridional and zonal sections of temperature, salinity, potential density, oxygen, and nutrients. These patterns were derived from World Ocean Database observations by an ocean interpolation algorithm: loess-weighted observations were projected onto quadratic functions of spatial coordinates while simultaneously fitting annual and semiannual harmonics and the Southern Oscillation Index to account for interannual variability. Contrasts between the equatorial cold tongue and the eastern Pacific warm pool are evident in all the hydrographic parameters. Annual cycles and ENSO (El Nino-Southern Oscillation) variability are of similar amplitude in the eastern tropical Pacific, however, there are important regional differences in relative variability at these time scales. Unique characteristics of the eastern tropical Pacific are discussed: the strong and shallow pycnocline, the pronounced oxygen minimum layer, and the Costa Rica Dome. This paper is part of a comprehensive review of the oceanography of the eastern tropical Pacific. (c) 2006 Elsevier Ltd. All rights reserved.

Shcherbina, AY, Talley LD, Rudnick DL.  2003.  Direct observations of North Pacific ventilation: Brine rejection in the Okhotsk Sea. Science. 302:1952-1955.   10.1126/science.1088692   AbstractWebsite

Brine rejection that accompanies ice formation in coastal polynyas is responsible for ventilating several globally important water masses in the Arctic and Antarctic. However, most previous studies of this process have been indirect, based on heat budget analyses or on warm-season water column inventories. Here, we present direct measurements of brine rejection and formation of North Pacific Intermediate Water in the Okhotsk Sea from moored winter observations. A steady, nearly linear salinity increase unambiguously caused by local ice formation was observed for more than a month.

Speer, KG, Siedler G, Talley L.  1995.  The Namib Col Current. Deep-Sea Research Part I-Oceanographic Research Papers. 42:1933-1950.   10.1016/0967-0637(95)00088-7   AbstractWebsite

Recent measurements indicate the transatlantic extent of the Namib Col Current at depths of 1300-3000 m near Lat. 22 degrees S in the South Atlantic Ocean. This current forms a continuous circulation structure from the Namib Col on the Walvis Ridge to the western trough, though its characteristic change as deepwater with varying properties enters and leaves the current owing to a meridional flow component. Transport estimates from hydrographic sections on the Walvis Ridge and at 15 degrees W near the crest of the Mid-Atlantic Ridge indicate a strength of about 3 x 10(6) m(3) s(-1) The current is part of a larger-scale eastward Row at Lon. 25 degrees W; transport estimates across the salinity maximum core there show a similar strength. Associated with this high-salinity high-oxygen current is a basin-wide front in these properties of varying intensity (weaker in the east) marking the transition to deep water whose North Atlantic characteristics have been partly erased by mixing with Circumpolar Deep Water in the southwest South Atlantic. The water which finally crosses the Walvis Ridge is supplied both by the eastward flow of this (diluted) North Atlantic Deep Water and by a general southeastward interior flow from the northern Angola Basin. Evidence suggests that this deep water continues south in the eastern Cape Basin, leaving the South Atlantic near the African continent.