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Ogle, SE, Tamsitt V, Josey SA, Gille ST, Cerovecki I, Talley LD, Weller RA.  2018.  Episodic Southern Ocean heat loss and its mixed layer impacts revealed by the farthest south multiyear surface flux mooring. Geophysical Research Letters. 45:5002-5010.   10.1029/2017gl076909   AbstractWebsite

The Ocean Observatories Initiative air-sea flux mooring deployed at 54.08 degrees S, 89.67 degrees W, in the southeast Pacific sector of the Southern Ocean, is the farthest south long-term open ocean flux mooring ever deployed. Mooring observations (February 2015 to August 2017) provide the first in situ quantification of annual net air-sea heat exchange from one of the prime Subantarctic Mode Water formation regions. Episodic turbulent heat loss events (reaching a daily mean net flux of -294W/m(2)) generally occur when northeastward winds bring relatively cold, dry air to the mooring location, leading to large air-sea temperature and humidity differences. Wintertime heat loss events promote deep mixed layer formation that lead to Subantarctic Mode Water formation. However, these processes have strong interannual variability; a higher frequency of 2 sigma and 3 sigma turbulent heat loss events in winter 2015 led to deep mixed layers (>300m), which were nonexistent in winter 2016.

Russell, JL, Kamenkovich I, Bitz C, Ferrari R, Gille ST, Goodman PJ, Hallberg R, Johnson K, Khazmutdinova K, Marinov I, Mazloff M, Riser S, Sarmiento JL, Speer K, Talley LD, Wanninkhof R.  2018.  Metrics for the evaluation of the Southern Ocean in coupled climate models and earth system models. Journal of Geophysical Research-Oceans. 123:3120-3143.   10.1002/2017jc013461   AbstractWebsite

The Southern Ocean is central to the global climate and the global carbon cycle, and to the climate's response to increasing levels of atmospheric greenhouse gases, as it ventilates a large fraction of the global ocean volume. Global coupled climate models and earth system models, however, vary widely in their simulations of the Southern Ocean and its role in, and response to, the ongoing anthropogenic trend. Due to the region's complex water-mass structure and dynamics, Southern Ocean carbon and heat uptake depend on a combination of winds, eddies, mixing, buoyancy fluxes, and topography. Observationally based metrics are critical for discerning processes and mechanisms, and for validating and comparing climate and earth system models. New observations and understanding have allowed for progress in the creation of observationally based data/model metrics for the Southern Ocean. Metrics presented here provide a means to assess multiple simulations relative to the best available observations and observational products. Climate models that perform better according to these metrics also better simulate the uptake of heat and carbon by the Southern Ocean. This report is not strictly an intercomparison, but rather a distillation of key metrics that can reliably quantify the "accuracy" of a simulation against observed, or at least observable, quantities. One overall goal is to recommend standardization of observationally based benchmarks that the modeling community should aspire to meet in order to reduce uncertainties in climate projections, and especially uncertainties related to oceanic heat and carbon uptake. Plain Language Summary Observationally based metrics are essential for the standardized evaluation of climate and earth system models, and for reducing the uncertainty associated with future projections by those models.

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.

Johnson, KS, Plant JN, Coletti LJ, Jannasch HW, Sakamoto CM, Riser SC, Swift DD, Williams NL, Boss E, Haentjens N, Talley LD, Sarmiento JL.  2017.  Biogeochemical sensor performance in the SOCCOM profiling float array. Journal of Geophysical Research-Oceans. 122:6416-6436.   10.1002/2017jc012838   AbstractWebsite

The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program has begun deploying a large array of biogeochemical sensors on profiling floats in the Southern Ocean. As of February 2016, 86 floats have been deployed. Here the focus is on 56 floats with quality-controlled and adjusted data that have been in the water at least 6 months. The floats carry oxygen, nitrate, pH, chlorophyll fluorescence, and optical backscatter sensors. The raw data generated by these sensors can suffer from inaccurate initial calibrations and from sensor drift over time. Procedures to correct the data are defined. The initial accuracy of the adjusted concentrations is assessed by comparing the corrected data to laboratory measurements made on samples collected by a hydrographic cast with a rosette sampler at the float deployment station. The long-term accuracy of the corrected data is compared to the GLODAPv2 data set whenever a float made a profile within 20 km of a GLODAPv2 station. Based on these assessments, the fleet average oxygen data are accurate to 1 +/- 1%, nitrate to within 0.5 +/- 0.5 mu mol kg(-1), and pH to 0.005 +/- 0.007, where the error limit is 1 standard deviation of the fleet data. The bio-optical measurements of chlorophyll fluorescence and optical backscatter are used to estimate chlorophyll a and particulate organic carbon concentration. The particulate organic carbon concentrations inferred from optical backscatter appear accurate to with 35 mg C m(-3) or 20%, whichever is larger. Factors affecting the accuracy of the estimated chlorophyll a concentrations are evaluated.

Williams, NL, Feely RA, Sabine CL, Dickson AG, Swift JH, Talley LD, Russell JL.  2015.  Quantifying anthropogenic carbon inventory changes in the Pacific sector of the Southern Ocean. Marine Chemistry. 174:147-160.   10.1016/j.marchem.2015.06.015   AbstractWebsite

The Southern Ocean plays a major role in mediating the uptake, transport, and long-term storage of anthropogenic carbon dioxide (CO2) into the deep ocean. Examining the magnitude and spatial distribution of this oceanic carbon uptake is critical to understanding how the earth's carbon system will react to continued increases in this greenhouse gas. Here, we use the extended multiple linear regression technique to quantify the total and anthropogenic change in dissolved inorganic carbon (DIC) along the S04P and P16S CLIVAR/U.S. Global Ocean Carbon and Repeat Hydrography Program lines south of 67 degrees S in the Pacific sector of the Southern Ocean between 1992 and 2011 using discrete bottle measurements from repeat occupations. Along the S04P section, which is located in the seasonal sea ice zone south of the Antarctic Circumpolar Current in the Pacific, the anthropogenic component of the DIC increase from 1992 to 2011 is mostly found in the Antarctic Surface Water (AASW, upper 100 m), while the increase in DIC below the mixed layer in the Circumpolar Deep Water can be primarily attributed to either a slowdown in circulation or decreased ventilation of deeper, high CO2 waters. In the AASW we calculate an anthropogenic increase in DIC of 12-18 mu mol kg(-1) and an average storage rate of anthropogenic CO2 of 0.10 +/- 0.02 mol m(-2) yr(-1) for this region compared to a global average of 0.5 +/- 0.2 mol m(-2) yr(-1). In surface waters this anthropogenic CO2 uptake results in an average pH decrease of 0.0022 +/- 0.0004 pH units yr(-1), a 0.47 +/- 0.10% yr(-1) decrease in the saturation state of aragonite (Omega(Aragonite)) and a 2.0 +/- 0.7 m yr(-1) shoaling of the aragonite saturation horizons (calculated for the Omega(Aragonite) = 1.3 contour). (C) 2015 Published by Elsevier B.V.