Using ocean bottom pressure from the gravity recovery and climate experiment (GRACE) to estimate transport variability in the southern Indian Ocean

Previous studies have suggested that ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE) can be used to measure the depth-averaged, or barotropic, transport variability of the Antarctic Circumpolar Current (ACC). Here, we use GRACE OBP observations to calculate transport variability in a region of the southern Indian Ocean encompassing the major fronts of the ACC. We use a statistical analysis of a simulated GRACE-like data set to determine the uncertainty of the estimated transport for the 2003.0–2013.0 time period. We find that when the transport is averaged over 60° of longitude, the uncertainty (one standard error) is close to 1 Sv (1 Sv = 106 m3 s−1) for low-pass filtered transport, which is significantly smaller than the signal and lower than previous studies have found. The interannual variability is correlated with the Southern Annual mode (SAM) (0.61), but more highly correlated with circumpolar zonally averaged winds between 45°S and 65°S (0.88). GRACE transport reflects significant changes in transport between 2007 and 2009 that is observed in the zonal wind variations but not in the SAM index. We also find a statistically significant trend in transport (−1.0 ± 0.4 Sv yr−1, 90% confidence) that is correlated with a local deceleration in zonal winds related to an asymmetry in the SAM on multidecadal periods.

[1]  S. Sokolov,et al.  Baroclinic transport variability of the Antarctic Circumpolar Current south of Australia (WOCE repeat section SR3) , 2001 .

[2]  M. Mazloff,et al.  Vertical structure and transport of the Antarctic Circumpolar Current in Drake Passage from direct velocity observations , 2011 .

[3]  S. Rintoul,et al.  The response of the Antarctic Circumpolar Current to recent climate change , 2008 .

[4]  M. Merrifield,et al.  A unique asymmetry in the pattern of recent sea level change , 2014 .

[5]  D. Chambers,et al.  Ocean bottom pressure seasonal cycles and decadal trends from GRACE Release-05: Ocean circulation implications , 2013 .

[6]  F. Landerer,et al.  The anatomy of recent large sea level fluctuations in the Mediterranean Sea , 2013 .

[7]  D. Chambers,et al.  Uncertainty estimates of a GRACE inversion modelling technique over Greenland using a simulation , 2013 .

[8]  A. Orsi,et al.  On the meridional extent and fronts of the Antarctic Circumpolar Current , 1995 .

[9]  N. Gillett,et al.  The role of eddies in the southern ocean temperature response to the southern annular mode. , 2009 .

[10]  R. Ponte,et al.  Estimating weights for the use of time-dependent gravity recovery and climate experiment data in constraining ocean models , 2008 .

[11]  S. Aoki.  Coherent sea level response to the Antarctic Oscillation , 2002 .

[12]  D. Chambers,et al.  Relative contributions of ocean mass and deep steric changes to sea level rise between 1993 and 2013 , 2014 .

[13]  J. Wallace,et al.  Annular Modes in the Extratropical Circulation. Part I: Month-to-Month Variability* , 2000 .

[14]  Don P. Chambers,et al.  Evaluation of Release-05 GRACE time-variable gravity coefficients over the ocean , 2012 .

[15]  Janet Sprintall,et al.  SUSTAINED MONITORING OF THE SOUTHERN OCEAN AT DRAKE PASSAGE: PAST ACHIEVEMENTS AND FUTURE PRIORITIES , 2011 .

[16]  Ichiro Fukumori,et al.  Mechanisms Controlling the Interannual Variation of Mixed Layer Temperature Averaged over the Niño-3 Region , 2007 .

[17]  S. Jayne,et al.  Observing ocean heat content using satellite gravity and altimetry , 2003 .

[18]  R. Hallberg,et al.  An Exploration of the Role of Transient Eddies in Determining the Transport of a Zonally Reentrant Current , 2001 .

[19]  T. Whitworth.  Monitoring the Transport of the Antarctic Circumpolar Current at Drake Passage , 1983 .

[20]  I. Fukumori,et al.  Vertical Structure of Ocean Pressure Variations with Application to Satellite-Gravimetric Observations , 2015 .

[21]  L. Perelman,et al.  A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers , 1997 .

[22]  H. Dobslaw,et al.  Short‐term transport variability of the Antarctic Circumpolar Current from satellite gravity observations , 2012 .

[23]  T. Lee,et al.  ECCO2: High Resolution Global Ocean and Sea Ice Data Synthesis , 2008 .

[24]  S. Gille.  Decadal-Scale Temperature Trends in the Southern Hemisphere Ocean , 2008 .

[25]  T. Chereskin,et al.  Strong bottom currents and cyclogenesis in Drake Passage , 2009 .

[26]  R. Steven Nerem,et al.  Ocean mass from GRACE and glacial isostatic adjustment , 2010 .

[27]  C. Amante,et al.  ETOPO1 arc-minute global relief model : procedures, data sources and analysis , 2009 .

[28]  A. Hogg,et al.  An Analytical Model of the Response of the Meridional Overturning Circulation to Changes in Wind and Buoyancy Forcing , 2012 .

[29]  D. Chambers,et al.  GRACE, time-varying gravity, Earth system dynamics and climate change , 2014, Reports on progress in physics. Physical Society.

[30]  Robert Hallberg,et al.  The Role of Eddies in Determining the Structure and Response of the Wind-Driven Southern Hemisphere Overturning: Results from the Modeling Eddies in the Southern Ocean (MESO) Project , 2006 .

[31]  S. Sokolov,et al.  A 6 year record of baroclinic transport variability of the Antarctic Circumpolar Current at 140°E derived from expendable bathythermograph and altimeter measurements , 2002 .

[32]  S. Sokolov,et al.  Multiple Jets of the Antarctic Circumpolar Current South of Australia , 2007 .

[33]  J. Fyfe,et al.  On the response of the oceanic wind-driven circulation to atmospheric CO2 increase , 2005 .

[34]  F. Bryan,et al.  Time variability of the Earth's gravity field: Hydrological and oceanic effects and their possible detection using GRACE , 1998 .

[35]  M. Meredith,et al.  Changes in the ocean transport through Drake Passage during the 1980s and 1990s, forced by changes in the Southern Annular Mode , 2004 .

[36]  C. Hughes,et al.  Antarctic circumpolar transport and the southern mode: a model investigation of interannual to decadal timescales , 2013 .

[37]  Ichiro Fukumori,et al.  A Partitioned Kalman Filter and Smoother , 2002 .

[38]  D. Stammer,et al.  Impact of assimilating bottom pressure anomalies from GRACE on ocean circulation estimates , 2012 .

[39]  R. Peterson,et al.  Volume Transport of the Antarctic Circumpolar Current from Bottom Pressure Measurements , 1985 .

[40]  N. Gruber,et al.  Impact of the Southern Annular Mode on Southern Ocean circulation and biology , 2005 .

[41]  R. Ponte,et al.  Bottom pressure changes around Antarctica and wind‐driven meridional flows , 2009 .

[42]  Josh K. Willis,et al.  Balancing the Sea Level Budget , 2011 .

[43]  Jens Schröter,et al.  Measuring ocean mass variability from satellite gravimetry , 2011 .

[44]  M. Meredith,et al.  Coherence of Antarctic sea levels, Southern Hemisphere Annular Mode, and flow through Drake Passage , 2003 .

[45]  M. Brandon,et al.  Transport and variability of the Antarctic Circumpolar Current in Drake Passage , 2003 .

[46]  G. Marshall.  Trends in the Southern Annular Mode from Observations and Reanalyses , 2003 .

[47]  I. Fukumori,et al.  Antarctic Circumpolar Current Transport Variability during 2003–05 from GRACE , 2007 .

[48]  Mass‐induced sea level change in the northwestern North Pacific and its contribution to total sea level change , 2013 .

[49]  D. Chambers,et al.  Recent trends in the Southern Ocean eddy field , 2015 .

[50]  R. Ponte,et al.  Interannual Bottom Pressure Signals in the Australian–Antarctic and Bellingshausen Basins , 2014 .

[51]  ENSO-correlated fluctuations in ocean bottom pressure and wind-stress curl in the North Pacific , 2011 .

[52]  Dimitris Menemenlis,et al.  Using Green's Functions to Calibrate an Ocean General Circulation Model , 2005 .

[53]  J. Klinck,et al.  The physics of the Antarctic Circumpolar Current , 1986 .

[54]  J. Fyfe,et al.  Simulated changes in the extratropical Southern Hemisphere winds and currents , 2006 .

[55]  R. Steven Nerem,et al.  The 2011 La Niña: So strong, the oceans fell , 2012 .

[56]  John C. Ries,et al.  Effects of ice melting on GRACE observations of ocean mass trends , 2007 .

[57]  Michael P. Meredith,et al.  Wind-Driven Transport Fluctuations through Drake Passage: A Southern Mode , 1999 .

[58]  Robert Atlas,et al.  Application of satellite surface wind data to ocean wind analysis , 2008, Optical Engineering + Applications.

[59]  Jeffrey P. Walker,et al.  THE GLOBAL LAND DATA ASSIMILATION SYSTEM , 2004 .

[60]  A. Weaver,et al.  Southern Ocean Response to Strengthening Winds in an Eddy-Permitting Global Climate Model , 2010 .

[61]  S. Swenson,et al.  Post‐processing removal of correlated errors in GRACE data , 2006 .

[62]  Eric Rignot,et al.  Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise , 2011 .