Publications

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2017
Verdy, A, Cornuelle B, Mazloff MR, Rudnick DL.  2017.  Estimation of the Tropical Pacific Ocean State 2010–13. Journal of Atmospheric and Oceanic Technology. 34(7):1501-1517.: American Meteorological Society AbstractWebsite

AbstractA data-assimilating ?° regional dynamical ocean model is evaluated on its ability to synthesize components of the Tropical Pacific Ocean Observing System. The four-dimensional variational data assimilation (4DVAR) method adjusts initial conditions and atmospheric forcing for overlapping 4-month model runs, or hindcasts, that are then combined to give an ocean state estimate for the period 2010?13. Consistency within uncertainty with satellite SSH and Argo profiles is achieved. Comparison to independent observations from Tropical Atmosphere Ocean (TAO) moorings shows that for time scales shorter than 100 days, the state estimate improves estimates of TAO temperature relative to an optimally interpolated Argo product. The improvement is greater at time scales shorter than 20 days, although unpredicted variability in the TAO temperatures implies that TAO observations provide significant information in that band. Larger discrepancies between the state estimate and independent observations from Spray gliders deployed near the Galápagos, Palau, and Solomon Islands are attributed to insufficient model resolution to capture the dynamics in strong current regions and near coasts. The sea surface height forecast skill of the model is assessed. Model forecasts using climatological forcing and boundary conditions are more skillful than climatology out to 50 days compared to persistence, which is a more skillful forecast than climatology out to approximately 20 days. Hindcasts using reanalysis products for atmospheric forcing and open boundary conditions are more skillful than climatology for approximately 120 days or longer, with the exact time scale depending on the accuracy of the state estimate used for initializing and on the reanalysis forcing. Estimating the model representational error is a goal of these experiments.AbstractA data-assimilating ?° regional dynamical ocean model is evaluated on its ability to synthesize components of the Tropical Pacific Ocean Observing System. The four-dimensional variational data assimilation (4DVAR) method adjusts initial conditions and atmospheric forcing for overlapping 4-month model runs, or hindcasts, that are then combined to give an ocean state estimate for the period 2010?13. Consistency within uncertainty with satellite SSH and Argo profiles is achieved. Comparison to independent observations from Tropical Atmosphere Ocean (TAO) moorings shows that for time scales shorter than 100 days, the state estimate improves estimates of TAO temperature relative to an optimally interpolated Argo product. The improvement is greater at time scales shorter than 20 days, although unpredicted variability in the TAO temperatures implies that TAO observations provide significant information in that band. Larger discrepancies between the state estimate and independent observations from Spray gliders deployed near the Galápagos, Palau, and Solomon Islands are attributed to insufficient model resolution to capture the dynamics in strong current regions and near coasts. The sea surface height forecast skill of the model is assessed. Model forecasts using climatological forcing and boundary conditions are more skillful than climatology out to 50 days compared to persistence, which is a more skillful forecast than climatology out to approximately 20 days. Hindcasts using reanalysis products for atmospheric forcing and open boundary conditions are more skillful than climatology for approximately 120 days or longer, with the exact time scale depending on the accuracy of the state estimate used for initializing and on the reanalysis forcing. Estimating the model representational error is a goal of these experiments.

Tamsitt, V, Drake HF, Morrison AK, Talley LD, Dufour CO, Gray AR, Griffies SM, Mazloff MR, Sarmiento JL, Wang J, Weijer W.  2017.  Spiraling pathways of global deep waters to the surface of the Southern Ocean. Nature Communications. 8(1):172.   0.1038/s41467-017-00197-0   AbstractWebsite

Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60–90 years.

Villas Bôas, AB, Gille ST, Mazloff MR, Cornuelle BD.  2017.  Characterization of the Deep-Water Surface Wave Variability in the California Current Region. Journal of Geophysical Research: Oceans.   10.1002/2017JC013280   AbstractWebsite

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Verdy, A, Mazloff MR.  2017.  A data assimilating model for estimating Southern Ocean biogeochemistry. Journal of Geophysical Research - Oceans. 122   doi:10.1002/2016JC012650  
Mazloff, MR, Sallée J-B, Menezes VV, Macdonald AM, Meredith MP, Newman L, Pellichero V, Roquet F, Swart S, Wåhlin A.  2017.  Southern Ocean [in “State of the Climate in 2016”]. Bull. Amer. Meteor. Soc.. 98(8)
Rosso, I, Mazloff M, Verdy A, Talley L.  2017.  Space and Time Variability of the Southern Ocean Carbon Budget. Journal of Geophysical Research - Oceans. Accepted
2016
Musgrave, RC, Pinkel R, MacKinnon JA, Mazloff MR, Young WR.  2016.  Stratified tidal flow over a tall ridge above and below the turning latitude. Journal of Fluid Mechanics. 793:933–957.   10.1017/jfm.2016.150   AbstractWebsite
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Abernathey, RP, Cerovecki I, Holland PR, Newsom E, Mazloff M, Talley LD.  2016.  Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning. advance online publication:-.: Nature Publishing Group AbstractWebsite
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Wang, J, Mazloff MR, Gille ST.  2016.  The effect of the Kerguelen Plateau on the ocean circulation. Journal of Physical OceanographyJournal of Physical Oceanography. : American Meteorological Society AbstractWebsite

AbstractThe Kerguelen Plateau is a major topographic feature in the Southern Ocean. Located in the Indian sector and spanning nearly 2,000 kilometers in the meridional direction from the polar to the Subantarctic region, it deflects the eastward flowing Antarctic Circumpolar Current and influences the physical circulation and biogeochemistry of the Southern Ocean. The Kerguelen Plateau is known to govern the local dynamics, but its impact on the large-scale ocean circulation has not been explored. By comparing global ocean numerical simulations with and without the Kerguelen Plateau we identify two major Kerguelen Plateau effects: 1) The plateau supports a local pressure field that pushes the Antarctic Circumpolar Current northward. This process reduces the warm water transport from the Indian to the Atlantic Oceans. 2) The plateau-generated pressure field shields the Weddell Gyre from the influence of the warmer Subantarctic and Subtropical waters. The first effect influences the strength of the Antarctic Circumpolar Current and the Agulhas leakage, both of which are important elements in the global thermohaline circulation. The second effect results in a zonally asymmetric response of the subpolar gyres to Southern Hemisphere wind forcing.AbstractThe Kerguelen Plateau is a major topographic feature in the Southern Ocean. Located in the Indian sector and spanning nearly 2,000 kilometers in the meridional direction from the polar to the Subantarctic region, it deflects the eastward flowing Antarctic Circumpolar Current and influences the physical circulation and biogeochemistry of the Southern Ocean. The Kerguelen Plateau is known to govern the local dynamics, but its impact on the large-scale ocean circulation has not been explored. By comparing global ocean numerical simulations with and without the Kerguelen Plateau we identify two major Kerguelen Plateau effects: 1) The plateau supports a local pressure field that pushes the Antarctic Circumpolar Current northward. This process reduces the warm water transport from the Indian to the Atlantic Oceans. 2) The plateau-generated pressure field shields the Weddell Gyre from the influence of the warmer Subantarctic and Subtropical waters. The first effect influences the strength of the Antarctic Circumpolar Current and the Agulhas leakage, both of which are important elements in the global thermohaline circulation. The second effect results in a zonally asymmetric response of the subpolar gyres to Southern Hemisphere wind forcing.

Firing, YL, Chereskin TK, Watts RD, Mazloff MR.  2016.  Bottom pressure torque and the vorticity balance from observations in Drake Passage. Journal of Geophysical Research: Oceans. :n/a–n/a.   10.1002/2016JC011682   AbstractWebsite

The vorticity balance of the Antarctic Circumpolar Current in Drake Passage is examined using 4 years of observations from current- and pressure-recording inverted echo sounders. The time-varying vorticity, planetary and relative vorticity advection, and bottom pressure torque are calculated in a two-dimensional array in the eddy-rich Polar Frontal Zone (PFZ). Bottom pressure torque is also estimated at sites across Drake Passage. Mean and eddy nonlinear relative vorticity advection terms dominate over linear advection in the local (50-km scale) vorticity budget in the PFZ, and are balanced to first order by the divergence of horizontal velocity. Most of this divergence comes from the ageostrophic gradient flow, which also provides a second-order adjustment to the geostrophic relative vorticity advection. Bottom pressure torque is approximately one-third the size of the local depth-integrated divergence. Although the cDrake velocity fields exhibit significant turning with depth throughout Drake Passage even in the mean, surface vorticity advection provides a reasonable representation of the depth-integrated vorticity balance. Observed near-bottom currents are strongly topographically steered, and bottom pressure torques grow large where strong near-bottom flows cross steep topography at small angles. Upslope flow over the northern continental slope dominates the bottom pressure torque in cDrake, and the mean across this Drake Passage transect, 3 to 4×10−9 m s−2, exceeds the mean wind stress curl by a factor of 15–20.

Sallée, J-B, Mazloff M, Meredith MP, Hughes CW, Rintoul S, Gomez R, Metzl N, Monaco LC, Schmidtko S, Mata MM, Wåhlin A, Swart S, Williams MJM, Naveria-Garabata AC, Monteiro P.  2016.  Southern Ocean [in “State of the Climate in 2015”]. Bull. Amer. Meteor. Soc.. 97(8):S166–S168. Abstract

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Erickson, ZK, Thompson AF, Cassar N, Sprintall J, Mazloff MR.  2016.  An advective mechanism for Deep Chlorophyll Maxima formation in southern Drake Passage. Geophysical Research Letters. :n/a–n/a.   10.1002/2016GL070565   AbstractWebsite

We observe surface and sub-surface fluorescence-derived chlorophyll maxima in southern Drake Passage during austral summer. Backscatter measurements indicate that the Deep Chlorophyll Maxima (DCMs) are also deep biomass maxima, and euphotic depth estimates show that they lie below the euphotic layer. Sub-surface, off-shore and near-surface, on-shore features lie along the same isopycnal, suggesting advective generation of DCMs. Temperature measurements indicate a warming of surface waters throughout austral summer, capping the Winter Water (WW) layer and increasing off-shelf stratification in this isopycnal layer. The outcrop position of the WW isopycnal layer shifts onshore, into a surface phytoplankton bloom. A lateral potential vorticity (PV) gradient develops, such that a down-gradient PV flux is consistent with offshore, along-isopycnal tracer transport. Model results are consistent with this mechanism. Subduction of chlorophyll and biomass along isopycnals represents a biological term not observed by surface satellite measurements which may contribute significantly to the strength of the biological pump in this region.

Jones, DC, Meijers AJS, Shuckburgh E, Sallée J-B, Haynes P, Karczewska E, Mazloff MR.  2016.  How does Subantarctic Mode Water ventilate the Southern Hemisphere subtropics? Journal of Geophysical Research: Oceans. :n/a–n/a.   10.1002/2016JC011680   AbstractWebsite

In several regions north of the Antarctic Circumpolar Current (ACC), deep wintertime convection refreshes pools of weakly stratified subsurface water collectively referred to as Subantarctic Mode Water (SAMW). SAMW ventilates the subtropical thermocline on decadal timescales, providing nutrients for low-latitude productivity and potentially trapping anthropogenic carbon in the deep ocean interior for centuries. In this work, we investigate the spatial structure and timescales of mode water export and associated thermocline ventilation. We use passive tracers in an eddy-permitting, observationally-informed Southern Ocean model to identify the pathways followed by mode waters between their formation regions and the areas where they first enter the subtropics. We find that the pathways followed by the mode water tracers are largely set by the mean geostrophic circulation. Export from the Indian and Central Pacific mode water pools is primarily driven by large-scale gyre circulation, whereas export from the Australian and Atlantic pools is heavily influenced by the ACC. Export from the Eastern Pacific mode water pool is driven by a combination of deep boundary currents and subtropical gyre circulation. More than 50% of each mode water tracer reaches the subtropical thermocline within 50 years, with significant variability between pools. The Eastern Pacific pathway is especially efficient, with roughly 80% entering the subtropical thermocline within 50 years. The time required for 50% of the mode water tracers to leave the Southern Ocean domain varies significantly between mode water pools, from 9 years for the Indian mode water pool to roughly 40 years for the Central Pacific mode water pool. This article is protected by copyright. All rights reserved.

Rodriguez, AR, Mazloff MR, Gille ST.  2016.  An oceanic heat transport pathway to the Amundsen Sea Embayment. Journal of Geophysical Research: Oceans. 121:3337–3349.   10.1002/2015JC011402   AbstractWebsite

The Amundsen Sea Embayment (ASE) on the West Antarctic coastline has been identified as a region of accelerated glacial melting. A Southern Ocean State Estimate (SOSE) is analyzed over the 2005–2010 time period in the Amundsen Sea region. The SOSE oceanic heat budget reveals that the contribution of parameterized small-scale mixing to the heat content of the ASE waters is small compared to advection and local air-sea heat flux, both of which contribute significantly to the heat content of the ASE waters. Above the permanent pycnocline, the local air-sea flux dominates the heat budget and is controlled by seasonal changes in sea ice coverage. Overall, between 2005 and 2010, the model shows a net heating in the surface above the pycnocline within the ASE. Sea water below the permanent pycnocline is isolated from the influence of air-sea heat fluxes, and thus, the divergence of heat advection is the major contributor to increased oceanic heat content of these waters. Oceanic transport of mass and heat into the ASE is dominated by the cross-shelf input and is primarily geostrophic below the permanent pycnocline. Diagnosis of the time-mean SOSE vorticity budget along the continental shelf slope indicates that the cross-shelf transport is sustained by vorticity input from the localized wind-stress curl over the shelf break.

Mazloff, MR, Boening C.  2016.  Rapid variability of Antarctic Bottom Water transport into the Pacific Ocean inferred from GRACE. Geophysical Research Letters. 43:3822–3829.   10.1002/2016GL068474   AbstractWebsite

Air-ice-ocean interactions in the Antarctic lead to formation of the densest waters on Earth. These waters convect and spread to fill the global abyssal oceans. The heat and carbon storage capacity of these water masses, combined with their abyssal residence times that often exceed centuries, makes this circulation pathway the most efficient sequestering mechanism on Earth. Yet monitoring this pathway has proven challenging due to the nature of the formation processes and the depth of the circulation. The Gravity Recovery and Climate Experiment (GRACE) gravity mission is providing a time series of ocean mass redistribution and offers a transformative view of the abyssal circulation. Here we use the GRACE measurements to infer, for the first time, a 2003–2014 time series of Antarctic Bottom Water export into the South Pacific. We find this export highly variable, with a standard deviation of 1.87 sverdrup (Sv) and a decorrelation timescale of less than 1 month. A significant trend is undetectable.

Tamsitt, V, Talley LD, Mazloff MR, Cerovečki I.  2016.  Zonal Variations in the Southern Ocean Heat Budget. Journal of Climate. 29:6563-6579.   10.1175/JCLI-D-15-0630.1   AbstractWebsite

AbstractThe spatial structure of the upper ocean heat budget in the Antarctic Circumpolar Current (ACC) is investigated using the ⅙°, data-assimilating Southern Ocean State Estimate (SOSE) for 2005–10. The ACC circumpolar integrated budget shows that 0.27 PW of ocean heat gain from the atmosphere and 0.38 PW heat gain from divergence of geostrophic heat transport are balanced by −0.58 PW cooling by divergence of Ekman heat transport and −0.09 PW divergence of vertical heat transport. However, this circumpolar integrated balance obscures important zonal variations in the heat budget. The air–sea heat flux shows a zonally asymmetric pattern of ocean heat gain in the Indian and Atlantic sectors and ocean heat loss in the Pacific sector of the ACC. In the Atlantic and Indian sectors of the ACC, the surface ocean heat gain is primarily balanced by divergence of equatorward Ekman heat transport that cools the upper ocean. In the Pacific sector, surface ocean heat loss and cooling due to divergence of Ekman heat transport are balanced by warming due to divergence of geostrophic heat advection, which is similar to the dominant heat balance in the subtropical Agulhas Return Current. The divergence of horizontal and vertical eddy advection of heat is important for warming the upper ocean close to major topographic features, while the divergence of mean vertical heat advection is a weak cooling term. The results herein show that topographic steering and zonal asymmetry in air–sea exchange lead to substantial zonal asymmetries in the heat budget, which is important for understanding the upper cell of the overturning circulation.

2015
Cerovečki, I, Mazloff MR.  2015.  The spatiotemporal structure of diabatic processes governing the evolution of Subantarctic Mode Water in the Southern Ocean. Journal of Physical OceanographyJournal of Physical Oceanography. : American Meteorological Society   10.1175/JPO-D-14-0243.1   Abstract

A coupled ice-ocean eddy-permitting Southern Ocean State Estimate (SOSE) for 2008-2010 is used to describe and quantify the processes forming and destroying water in the Subantarctic Mode Water (SAMW) density range (σ?=26.7 ? 27.2 kg m-3). All the terms in the temperature and salinity equations have been diagnosed to obtain a three dimensional and time varying volume budget for individual isopycnal layers. We find that air-sea buoyancy fluxes, diapycnal mixing, advection, and storage are all important to the SAMW volume budget.The formation and destruction of water in the SAMW density range occurs over a large latitude range due to the seasonal migration of the outcrop window. The strongest formation is by wintertime surface ocean heat loss occurring equatorward of the Subantarctic Front. Spring and summertime formation occur in the polar gyres by freshening of water with σ? > 27.2 kg m-3, with an important contribution from sea ice melt. Further buoyancy gain by heating is accomplished only after these waters have already been transformed into the SAMW density range. The spatially integrated and time-averaged SAMW formation rate in the ocean surface layer is 7.9 Sv by air-sea buoyancy fluxes and 8.8 Sv by diapycnal mixing, and it is balanced by advective export into the interior ocean. These average rates are the result of highly variable processes with strong cancellation in both space and time. In this work we map the spatiotemporal structure of the formation and evolution processes that must be represented in climate models in order to properly represent the three-dimensional Southern Ocean overturning circulation.AbstractA coupled ice-ocean eddy-permitting Southern Ocean State Estimate (SOSE) for 2008-2010 is used to describe and quantify the processes forming and destroying water in the Subantarctic Mode Water (SAMW) density range (σ?=26.7 ? 27.2 kg m-3). All the terms in the temperature and salinity equations have been diagnosed to obtain a three dimensional and time varying volume budget for individual isopycnal layers. We find that air-sea buoyancy fluxes, diapycnal mixing, advection, and storage are all important to the SAMW volume budget.The formation and destruction of water in the SAMW density range occurs over a large latitude range due to the seasonal migration of the outcrop window. The strongest formation is by wintertime surface ocean heat loss occurring equatorward of the Subantarctic Front. Spring and summertime formation occur in the polar gyres by freshening of water with σ? > 27.2 kg m-3, with an important contribution from sea ice melt. Further buoyancy gain by heating is accomplished only after these waters have already been transformed into the SAMW density range. The spatially integrated and time-averaged SAMW formation rate in the ocean surface layer is 7.9 Sv by air-sea buoyancy fluxes and 8.8 Sv by diapycnal mixing, and it is balanced by advective export into the interior ocean. These average rates are the result of highly variable processes with strong cancellation in both space and time. In this work we map the spatiotemporal structure of the formation and evolution processes that must be represented in climate models in order to properly represent the three-dimensional Southern Ocean overturning circulation.

Meredith, MP, Mazloff M, Sallée J-B, Newman L, Wåhlin A, Williams MJM, Garabato NAC, Swart S, Monteiro P, and M. M. Mata SS, Schmidtko S.  2015.  Southern Ocean [in “State of the Climate in 2014”]. Bull. Amer. Meteor. Soc.. 96(7):S157–S160.
Masich, J, Chereskin TK, Mazloff MR.  2015.  Topographic form stress in the Southern Ocean State Estimate. Journal of Geophysical Research: Oceans. 120:7919–7933.   10.1002/2015JC011143   AbstractWebsite

We diagnose the Southern Ocean momentum balance in a 6 year, eddy-permitting state estimate of the Southern Ocean. We find that 95% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain. While the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, time-mean topographic form stress concentrates at shallow ridges and across the continents that lie within the Antarctic Circumpolar Current (ACC) latitudes; nearly 40% of topographic form stress occurs across South America, while the remaining 60% occurs across the major submerged ridges that underlie the ACC. Topographic form stress can be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88% of the variance in the 6 year form stress time series can be explained by the wind stress signal, suggesting that changes in the integrated wind stress signal are communicated via rapid barotropic response down to the level of bottom topography.

2014
Wang, J, Mazloff MR, Gille ST.  2014.  Pathways of the Agulhas waters poleward of 29S. Journal of Geophysical Research: Oceans. 119:4234–4250.   10.1002/2014JC010049   Abstract

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Peña-Molino, B, Rintoul SR, Mazloff MR.  2014.  Barotropic and baroclinic contributions to along-stream and across-stream transport in the Antarctic Circumpolar Current. Journal of Geophysical Research: Oceans. 119:8011–8028.   10.1002/2014JC010020   AbstractWebsite

The Southern Ocean's ability to store and transport heat and tracers as well as to dissipate momentum and energy are intimately related to the vertical structure of the Antarctic Circumpolar Current (ACC). Here the partition between barotropic and baroclinic flow in the time-mean ACC is investigated in a Southern Ocean state estimate. The zonal geostrophic transport is predominantly baroclinic, with at most 25% of the transport at any longitude carried by the barotropic component. Following surface streamlines, changes in vertical shear and near-bottom velocity are large, and result in changes in the local partition of barotropic/baroclinic vertically integrated transport from 10/90% in the center of the basins, to 50/50% near complex topography. The velocity at depth is not aligned with the surface velocity. This nonequivalent barotropic flow supports significant cross-stream transports. Barotropic and baroclinic mass transport across the ACC is, on average, in opposite directions, with the net barotropic cross-stream transport being poleward and the net baroclinic equatorward. The sum partially cancels out, leaving a net geostrophic poleward transport across the different fronts between −5 and −20 Sv. Temperature is also transported across the fronts by the nonequivalent barotropic part of the ACC, with maximum values across the northern ACC fronts equivalent to −0.2 PW. The sign and magnitude of these transports are not sensitive to the choice of stream-coordinate. These cross-stream volume and temperature transports are variable in space, and dependent on the interactions between deep flow and bathymetry, thus difficult to infer from surface and hydrographic observations alone.

Mazloff, MR, Gille ST, Cornuelle B.  2014.  Improving the geoid: Combining altimetry and mean dynamic topography in the California coastal ocean. Geophysical Research Letters. 41:8944–8952.   10.1002/2014GL062402   AbstractWebsite

Satellite gravity mapping missions, altimeters, and other platforms have allowed the Earth's geoid to be mapped over the ocean to a horizontal resolution of approximately 100 km with an uncertainty of less than 10 cm. At finer resolution this uncertainty increases to greater than 10 cm. Achieving greater accuracy requires accurate estimates of the dynamic ocean topography (DOT). In this study two DOT estimates for the California Current System with uncertainties less than 10 cm are used to solve for a geoid correction field. The derived field increases the consistency between the DOTs and along-track altimetric observations, suggesting it is a useful correction to the gravitational field. The correction is large compared to the dynamic ocean topography, with a magnitude of 15 cm and significant structure, especially near the coast. The results are evidence that modern high-resolution dynamic ocean topography products can be used to improve estimates of the geoid.

Verdy, A, Mazloff MR, Cornuelle BD, Kim SY.  2014.  Wind-Driven Sea Level Variability on the California Coast: An Adjoint Sensitivity Analysis. Journal of Physical Oceanography. 44:297-318.   10.1175/JPO-D-13-018.1   AbstractWebsite
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2013
van Sebille, E, Spence P, Mazloff MR, England MH, Rintoul SR, Saenko OA.  2013.  Abyssal connections of Antarctic Bottom Water in a Southern Ocean State Estimate. Geophysical Research Letters. 40:2177–2182.   10.1002/grl.50483   AbstractWebsite

Antarctic Bottom Water (AABW) is formed in a few locations around the Antarctic continent, each source with distinct temperature and salinity. After formation, the different AABW varieties cross the Southern Ocean and flow into the subtropical abyssal basins. It is shown here, using the analysis of Lagrangian trajectories within the Southern Ocean State Estimate (SOSE) model, that the pathways of the different sources of AABW have to a large extent amalgamated into one pathway by the time it reaches 31°S in the deep subtropical basins. The Antarctic Circumpolar Current appears to play an important role in the amalgamation, as 70% of the AABW completes at least one circumpolar loop before reaching the subtropical basins. This amalgamation of AABW pathways suggests that on decadal to centennial time scales, changes to properties and formation rates in any of the AABW source regions will be conveyed to all three subtropical abyssal basins.

Mazloff, MR, Ferrari R, Schneider T.  2013.  The Force Balance of the Southern Ocean Meridional Overturning Circulation. Journal of Physical Oceanography. 43:1193-1208.   10.1175/JPO-D-12-069.1   AbstractWebsite
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Cerovečki, I, Talley LD, Mazloff MR, Maze G.  2013.  Subantarctic Mode Water Formation, Destruction, and Export in the Eddy-Permitting Southern Ocean State Estimate. Journal of Physical Oceanography. 43:1485-1511.   10.1175/JPO-D-12-0121.1   AbstractWebsite
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2012
Mazloff, MR.  2012.  On the Sensitivity of the Drake Passage Transport to Air–Sea Momentum Flux. Journal of Climate. 25:2279–2290.: American Meteorological Society   10.1175/JCLI-D-11-00030.1   Abstract

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Griesel, A, Mazloff MR, Gille ST.  2012.  Mean dynamic topography in the Southern Ocean: Evaluating Antarctic Circumpolar Current transport. J. Geophys. Res.. 117:2156-2202.: AGU   10.1029/2011JC007573   Abstract

Mean Dynamic Ocean Topography (MDT) is the difference between the time-averaged sea surface height and the geoid. Combining sea level and geoid measurements, which are both attained primarily by satellite, is complicated by ocean variability and differences in resolved spatial scales. Accurate knowledge of the MDT is particularly difficult in the Southern Ocean as this region is characterized by high temporal variability, relatively short spatial scales, and a lack of in situ gravity observations. In this study, four recent Southern Ocean MDT products are evaluated along with an MDT diagnosed from a Southern Ocean state estimate. MDT products differ in some locations by more than the nominal error bars. Attempts to decrease this discrepancy by accounting for temporal differences in the time period each product represents were unsuccessful, likely due to issues regarding resolved spatial scales. The mean mass transport of the Antarctic Circumpolar Current (ACC) system can be determined by combining the MDT products with climatological ocean density fields. On average, MDT products predict higher ACC transports than inferred from observations. More importantly, the MDT products imply an unrealistic lack of mass conservation that cannot be explained by the a priori uncertainties. MDT estimates can possibly be improved by accounting for an ocean mass balance constraint.

Todd, RE, Rudnick DL, Mazloff MR, Cornuelle BD, Davis RE.  2012.  Thermohaline structure in the California Current System: Observations and modeling of spice variance. J. Geophys. Res.. 117: AGU   10.1029/2011JC007589   Abstract

Upper ocean thermohaline structure in the California Current System is investigated using sustained observations from autonomous underwater gliders and a numerical state estimate. Both observations and the state estimate show layers distinguished by the temperature and salinity variability along isopycnals (i.e., spice variance). Mesoscale and submesoscale spice variance is largest in the remnant mixed layer, decreases to a minimum below the pycnocline near 26.3†kg m8722;3, and then increases again near 26.6†kg m8722;3. Layers of high (low) meso- and submesoscale spice variance are found on isopycnals where large-scale spice gradients are large (small), consistent with stirring of large-scale gradients to produce smaller scale thermohaline structure. Passive tracer adjoint calculations in the state estimate are used to investigate possible mechanisms for the formation of the layers of spice variance. Layers of high spice variance are found to have distinct origins and to be associated with named water masses; high spice variance water in the remnant mixed layer has northerly origin and is identified as Pacific Subarctic water, while the water in the deeper high spice variance layer has southerly origin and is identified as Equatorial Pacific water. The layer of low spice variance near 26.3†kg m8722;3 lies between the named water masses and does not have a clear origin. Both effective horizontal diffusivity, 954;h, and effective diapycnal diffusivity, 954;v, are elevated relative to the diffusion coefficients set in the numerical simulation, but changes in 954;h and 954;v with depth are not sufficient to explain the observed layering of thermohaline structure.

2011
Cerovecki, I, Talley LD, Mazloff MR.  2011.  A Comparison of Southern Ocean Air–Sea Buoyancy Flux from an Ocean State Estimate with Five Other Products. Journal of Climate. 24:6283–6306.: American Meteorological Society   10.1175/2011JCLI3858.1   Abstract

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Todd, RE, Rudnick DL, Mazloff MR, Davis RE, Cornuelle BD.  2011.  Poleward flows in the southern California Current System: Glider observations and numerical simulation. J. Geophys. Res.. 116:2156-2202.: AGU   10.1029/2010JC006536   Abstract

Three years of continuous Spray glider observations in the southern California Current System (CCS) are combined with a numerical simulation to describe the mean and variability of poleward flows in the southern CCS. Gliders provide upper ocean observations with good across-shore and temporal resolution along two across-shore survey lines while the numerical simulation provides a dynamically consistent estimate of the ocean state. Persistent poleward flows are observed in three areas: within 100 km of the coast at Point Conception, within the Southern California Bight (SCB), and offshore of the SCB and the Santa Rosa Ridge (SRR). Poleward transport by the flows within the SCB and offshore of the SRR exceeds the poleward transport off Point Conception, suggesting that the poleward flows are not continuous over the 225 km between observation lines. The numerical simulation shows offshore transport between the survey lines that is consistent with some of the poleward flow turning offshore before reaching Point Conception. The poleward current offshore of the SRR is unique in that it is strongest at depths greater than 350 m and it is observed to migrate westward away from the coast. This westward propagation is tied to westward propagating density anomalies originating in the SCB during the spring-summer upwelling season when wind stress curl is most strongly positive. The across-shore wave number, frequency, and phase speed of the westward propagation and the lack of across-shore transport of salinity along isopycnals are consistent with first-mode baroclinic Rossby dynamics.

Woloszyn, M, Mazloff M, Ito T.  2011.  Testing an eddy-permitting model of the Southern Ocean carbon cycle against observations. Ocean Modelling. 39:170-182. Abstract
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Firing, YL, Chereskin TK, Mazloff MR.  2011.  Vertical structure and transport of the Antarctic Circumpolar Current in Drake Passage from direct velocity observations. Journal of Geophysical Research: Oceans. 116:n/a–n/a.   10.1029/2011JC006999   AbstractWebsite

The structure of the Antarctic Circumpolar Current (ACC) in Drake Passage is examined using 4.5 years of shipboard acoustic Doppler current profiler (ADCP) velocity data. The extended 1000 m depth range available from the 38 kHz ADCP allows us to investigate the vertical structure of the current. The mean observed current varies slowly with depth, while eddy kinetic energy and shear variance exhibit strong depth dependence. Objectively mapped streamlines are self-similar with depth, consistent with an equivalent barotropic structure. Vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m. The mean observed transport of the ACC in the upper 1000 m is estimated at 95 ± 2 Sv or 71% of the canonical total transport of 134 Sv. Mean current speeds in the ACC jets remain quite strong at 1000 m, 10–20 cm s−1. Vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full-depth profiles from lowered ADCP and a 3 year mean from the Southern Ocean State Estimate (SOSE). A number of functions, including an exponential, are nearly equally good fits to the observations, explaining >75% of the variance. Fits to an exponentially decaying function can be extrapolated to give an estimate of 154 ± 38 Sv for the full-depth transport.

2010
Ito, T, Woloszyn M, Mazloff MR.  2010.  Anthropogenic carbon dioxide transport in the Southern Ocean driven by Ekman flow. Nature. 463:80-83. Abstract

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Mazloff, MR, Heimbach P, Wunsch C.  2010.  An Eddy-Permitting Southern Ocean State Estimate. Journal of Physical Oceanography. 40:880-899.   10.1175/2009JPO4236.1   Abstract

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Abernathey, R, Marshall J, Mazloff MR, Shuckburgh E.  2010.  Enhancement of Mesoscale Eddy Stirring at Steering Levels in the Southern Ocean. Journal of Physical Oceanography. 40:170-184.   10.1175/2009JPO4201.1   Abstract

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