Johnson Gregory C.

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Johnson
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Gregory C.
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  • Article
    Correction to “Recent western South Atlantic bottom water warming”
    (American Geophysical Union, 2006-11-04) Johnson, Gregory C. ; Doney, Scott C.
  • Article
    The Argo Program : observing the global ocean with profiling floats
    (Oceanography Society, 2009-06) Roemmich, Dean ; Johnson, Gregory C. ; Riser, Stephen C. ; Davis, Russ E. ; Gilson, John ; Owens, W. Brechner ; Garzoli, Silvia L. ; Schmid, Claudia ; Ignaszewski, Mark
    The Argo Program has created the first global array for observing the subsurface ocean. Argo arose from a compelling scientific need for climate-relevant ocean data; it was made possible by technology development and implemented through international collaboration. The float program and its data management system began with regional arrays in 1999, scaled up to global deployments by 2004, and achieved its target of 3000 active instruments in 2007. US Argo, supported by the National Oceanic and Atmospheric Administration and the Navy through the National Oceanographic Partnership Program, provides half of the floats in the international array, plus leadership in float technology, data management, data quality control, international coordination, and outreach. All Argo data are freely available without restriction, in real time and in research-quality forms. Uses of Argo data range from oceanographic research, climate research, and education, to operational applications in ocean data assimilation and seasonal-to-decadal prediction. Argo’s value grows as its data accumulate and their applications are better understood. Continuing advances in profiling float and sensor technologies open many exciting possibilities for Argo’s future, including expanding sampling into high latitudes and the deep ocean, improving near-surface sampling, and adding biogeochemical parameters.
  • Article
    An equatorial ocean bottleneck in global climate models
    (American Meteorological Society, 2012-01-01) Karnauskas, Kristopher B. ; Johnson, Gregory C. ; Murtugudde, Raghu
    The Equatorial Undercurrent (EUC) is a major component of the tropical Pacific Ocean circulation. EUC velocity in most global climate models is sluggish relative to observations. Insufficient ocean resolution slows the EUC in the eastern Pacific where nonlinear terms should dominate the zonal momentum balance. A slow EUC in the east creates a bottleneck for the EUC to the west. However, this bottleneck does not impair other major components of the tropical circulation, including upwelling and poleward transport. In most models, upwelling velocity and poleward transport divergence fall within directly estimated uncertainties. Both of these transports play a critical role in a theory for how the tropical Pacific may change under increased radiative forcing, that is, the ocean dynamical thermostat mechanism. These findings suggest that, in the mean, global climate models may not underrepresent the role of equatorial ocean circulation, nor perhaps bias the balance between competing mechanisms for how the tropical Pacific might change in the future. Implications for model improvement under higher resolution are also discussed.
  • Preprint
    The WOCE–era 3–D Pacific Ocean circulation and heat budget
    ( 2009-08-17) Macdonald, Alison M. ; Mecking, Sabine ; Toole, John M. ; Robbins, Paul E. ; Johnson, Gregory C. ; Wijffels, Susan E. ; Talley, Lynne D. ; Cook, Margaret F.
    To address questions concerning the intensity and spatial structure of the 3–dimensional circulation within the Pacific Ocean and the associated advective and diffusive property flux divergences, data from approximately 3000 high–quality hydrographic stations collected on 40 zonal and meridional cruises have been merged into a physically consistent model. The majority of the stations were occupied as part of the World Ocean Circulation Experiment (WOCE), which took place in the 1990s. These data are supplemented by a few pre–WOCE surveys of similar quality, and time–averaged direct–velocity and historical hydrographic measurements about the equator. An inverse box model formalism is employed to estimate the absolute along–isopycnal velocity field, the magnitude and spatial distribution of the associated diapycnal flow and the corresponding diapycnal advective and diffusive property flux divergences. The resulting large–scale WOCE Pacific circulation can be described as two shallow overturning cells at mid– to low latitudes, one in each hemisphere, and a single deep cell which brings abyssal waters from the Southern Ocean into the Pacific where they upwell across isopycnals and are returned south as deep waters. Upwelling is seen to occur throughout most of the basin with generally larger dianeutral transport and greater mixing occurring at depth. The derived pattern of ocean heat transport divergence is compared to published results based on air–sea flux estimates. The synthesis suggests a strongly east/west oriented pattern of air–sea heat flux with heat loss to the atmosphere throughout most of the western basins, and a gain of heat throughout the tropics extending poleward through the eastern basins. The calculated meridional heat transport agrees well with previous hydrographic estimates. Consistent with many of the climatologies at a variety of latitudes as well, our meridional heat transport estimates tend toward lower values in both hemispheres.
  • Article
    The technological, scientific, and sociological revolution of global subsurface ocean observing
    (Oceanography Society, 2022-01-07) Roemmich, Dean ; Talley, Lynne D. ; Zilberman, Nathalie ; Osborne, Emily ; Johnson, Kenneth S. ; Barbero, Leticia ; Bittig, Henry C. ; Briggs, Nathan ; Fassbender, Andrea J. ; Johnson, Gregory C. ; King, Brian A. ; McDonagh, Elaine L. ; Purkey, Sarah G. ; Riser, Stephen C. ; Suga, Toshio ; Takeshita, Yuichiro ; Thierry, Virginie ; Wijffels, Susan E.
    The complementary partnership of the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP; https://www.go-ship.org/) and the Argo Program (https://argo.ucsd.edu) has been instrumental in providing sustained subsurface observations of the global ocean for over two decades. Since the late twentieth century, new clues into the ocean’s role in Earth’s climate system have revealed a need for sustained global ocean observations (e.g., Gould et al., 2013; Schmitt, 2018) and stimulated revolutionary technology advances needed to address the societal mandate. Together, the international GO-SHIP and Argo Program responded to this need, providing insight into the mean state and variability of the physics, biology, and chemistry of the ocean that led to advancements in fundamental science and monitoring of the state of Earth's climate.
  • Book chapter
    Global Oceans [in “State of the Climate in 2020”]
    (American Meteorological Society, 2021-08-01) Johnson, Gregory C. ; Lumpkin, Rick ; Alin, Simone R. ; Amaya, Dillon J. ; Baringer, Molly O. ; Boyer, Tim ; Brandt, Peter ; Carter, Brendan ; Cetinić, Ivona ; Chambers, Don P. ; Cheng, Lijing ; Collins, Andrew U. ; Cosca, Cathy ; Domingues, Ricardo ; Dong, Shenfu ; Feely, Richard A. ; Frajka-Williams, Eleanor E. ; Franz, Bryan A. ; Gilson, John ; Goni, Gustavo J. ; Hamlington, Benjamin D. ; Herrford, Josefine ; Hu, Zeng-Zhen ; Huang, Boyin ; Ishii, Masayoshi ; Jevrejeva, Svetlana ; Kennedy, John J. ; Kersalé, Marion ; Killick, Rachel E. ; Landschützer, Peter ; Lankhorst, Matthias ; Leuliette, Eric ; Locarnini, Ricardo ; Lyman, John ; Marra, John F. ; Meinen, Christopher S. ; Merrifield, Mark ; Mitchum, Gary ; Moat, Bengamin I. ; Nerem, R. Steven ; Perez, Renellys ; Purkey, Sarah G. ; Reagan, James ; Sanchez-Franks, Alejandra ; Scannell, Hillary A. ; Schmid, Claudia ; Scott, Joel P. ; Siegel, David A. ; Smeed, David A. ; Stackhouse, Paul W. ; Sweet, William V. ; Thompson, Philip R. ; Trinanes, Joaquin ; Volkov, Denis L. ; Wanninkhof, Rik ; Weller, Robert A. ; Wen, Caihong ; Westberry, Toby K. ; Widlansky, Matthew J. ; Wilber, Anne C. ; Yu, Lisan ; Zhang, Huai-Min
    This chapter details 2020 global patterns in select observed oceanic physical, chemical, and biological variables relative to long-term climatologies, their differences between 2020 and 2019, and puts 2020 observations in the context of the historical record. In this overview we address a few of the highlights, first in haiku, then paragraph form: La Niña arrives, shifts winds, rain, heat, salt, carbon: Pacific—beyond. Global ocean conditions in 2020 reflected a transition from an El Niño in 2018–19 to a La Niña in late 2020. Pacific trade winds strengthened in 2020 relative to 2019, driving anomalously westward Pacific equatorial surface currents. Sea surface temperatures (SSTs), upper ocean heat content, and sea surface height all fell in the eastern tropical Pacific and rose in the western tropical Pacific. Efflux of carbon dioxide from ocean to atmosphere was larger than average across much of the equatorial Pacific, and both chlorophyll-a and phytoplankton carbon concentrations were elevated across the tropical Pacific. Less rain fell and more water evaporated in the western equatorial Pacific, consonant with increased sea surface salinity (SSS) there. SSS may also have increased as a result of anomalously westward surface currents advecting salty water from the east. El Niño–Southern Oscillation conditions have global ramifications that reverberate throughout the report.
  • Article
    Quantifying spread in spatiotemporal changes of upper-ocean heat content estimates: an internationally coordinated comparison
    (American Meteorological Society, 2022-01-15) Savita, Abhishek ; Domingues, Catia M. ; Boyer, Tim ; Gouretski, Viktor ; Ishii, Masayoshi ; Johnson, Gregory C. ; Lyman, John ; Willis, Joshua K. ; Marsland, Simon ; Hobbs, William ; Church, John A. ; Monselesan, Didier Paolo ; Dobrohotoff, Peter ; Cowley, Rebecca ; Wijffels, Susan E.
    The Earth system is accumulating energy due to human-induced activities. More than 90% of this energy has been stored in the ocean as heat since 1970, with ∼60% of that in the upper 700 m. Differences in upper-ocean heat content anomaly (OHCA) estimates, however, exist. Here, we use a dataset protocol for 1970–2008—with six instrumental bias adjustments applied to expendable bathythermograph (XBT) data, and mapped by six research groups—to evaluate the spatiotemporal spread in upper OHCA estimates arising from two choices: 1) those arising from instrumental bias adjustments and 2) those arising from mathematical (i.e., mapping) techniques to interpolate and extrapolate data in space and time. We also examined the effect of a common ocean mask, which reveals that exclusion of shallow seas can reduce global OHCA estimates up to 13%. Spread due to mapping method is largest in the Indian Ocean and in the eddy-rich and frontal regions of all basins. Spread due to XBT bias adjustment is largest in the Pacific Ocean within 30°N–30°S. In both mapping and XBT cases, spread is higher for 1990–2004. Statistically different trends among mapping methods are found not only in the poorly observed Southern Ocean but also in the well-observed northwest Atlantic. Our results cannot determine the best mapping or bias adjustment schemes, but they identify where important sensitivities exist, and thus where further understanding will help to refine OHCA estimates. These results highlight the need for further coordinated OHCA studies to evaluate the performance of existing mapping methods along with comprehensive assessment of uncertainty estimates.
  • Article
    On the future of Argo: A global, full-depth, multi-disciplinary array
    (Frontiers Media, 2019-08-02) Roemmich, Dean ; Alford, Matthew H. ; Claustre, Hervé ; Johnson, Kenneth S. ; King, Brian ; Moum, James N. ; Oke, Peter ; Owens, W. Brechner ; Pouliquen, Sylvie ; Purkey, Sarah G. ; Scanderbeg, Megan ; Suga, Koushirou ; Wijffels, Susan E. ; Zilberman, Nathalie ; Bakker, Dorothee ; Baringer, Molly O. ; Belbeoch, Mathieu ; Bittig, Henry C. ; Boss, Emmanuel S. ; Calil, Paulo H. R. ; Carse, Fiona ; Carval, Thierry ; Chai, Fei ; Conchubhair, Diarmuid Ó. ; d’Ortenzio, Fabrizio ; Dall'Olmo, Giorgio ; Desbruyeres, Damien ; Fennel, Katja ; Fer, Ilker ; Ferrari, Raffaele ; Forget, Gael ; Freeland, Howard ; Fujiki, Tetsuichi ; Gehlen, Marion ; Geenan, Blair ; Hallberg, Robert ; Hibiya, Toshiyuki ; Hosoda, Shigeki ; Jayne, Steven R. ; Jochum, Markus ; Johnson, Gregory C. ; Kang, KiRyong ; Kolodziejczyk, Nicolas ; Körtzinger, Arne ; Le Traon, Pierre-Yves ; Lenn, Yueng-Djern ; Maze, Guillaume ; Mork, Kjell Arne ; Morris, Tamaryn ; Nagai, Takeyoshi ; Nash, Jonathan D. ; Naveira Garabato, Alberto C. ; Olsen, Are ; Pattabhi Rama Rao, Eluri ; Prakash, Satya ; Riser, Stephen C. ; Schmechtig, Catherine ; Schmid, Claudia ; Shroyer, Emily L. ; Sterl, Andreas ; Sutton, Philip J. H. ; Talley, Lynne D. ; Tanhua, Toste ; Thierry, Virginie ; Thomalla, Sandy J. ; Toole, John M. ; Troisi, Ariel ; Trull, Thomas W. ; Turton, Jon ; Velez-Belchi, Pedro ; Walczowski, Waldemar ; Wang, Haili ; Wanninkhof, Rik ; Waterhouse, Amy F. ; Waterman, Stephanie N. ; Watson, Andrew J. ; Wilson, Cara ; Wong, Annie P. S. ; Xu, Jianping ; Yasuda, Ichiro
    The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo’s global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.
  • Article
    Reduced Antarctic meridional overturning circulation reaches the North Atlantic Ocean
    (American Geophysical Union, 2008-11-19) Johnson, Gregory C. ; Purkey, Sarah G. ; Toole, John M.
    We analyze abyssal temperature data in the western North Atlantic Ocean from the 1980s–2000s, showing that reductions in Antarctic Bottom Water (AABW) signatures have reached even that basin. Trans-basin oceanographic sections occupied along 52°W from 1983–2003 and 66°W from 1985–2003 quantify abyssal warming resulting from deepening of the strong thermal boundary between AABW and North Atlantic Deep Water (NADW), hence a local AABW volume reduction. Repeat section data taken from 1981–2004 along 24°N also show a reduced zonal gradient in abyssal temperatures, consistent with decreased northward transport of AABW. The reduction in the Antarctic limb of the MOC within the North Atlantic highlights the global reach of climate variability originating around Antarctica.
  • Article
    Recent western South Atlantic bottom water warming
    (American Geophysical Union, 2006-07-28) Johnson, Gregory C. ; Doney, Scott C.
    Potential temperature differences are computed from hydrographic sections transiting the western basins of the South Atlantic Ocean from 60°S to the equator in 2005/2003 and 1989/1995. While warming is observed throughout much of the water column, the most statistically significant warming is about +0.04°C in the bottom 1500 dbar of the Brazil Basin, with similar (but less statistically significant) warming signals in the abyssal Argentine Basin and Scotia Sea. These abyssal waters of Antarctic origin spread northward in the South Atlantic. The observed abyssal Argentine Basin warming is of a similar magnitude to that previously reported between 1980 and 1989. The Brazil Basin abyssal warming is similar in size to and consistent in timing with previously reported changes in abyssal southern inflow and northern outflow. The temperature changes reported here, if they were to hold throughout the abyssal world ocean, would contribute substantially to global ocean heat budgets.
  • Article
    Measuring global ocean heat content to estimate the Earth energy Imbalance
    (Frontiers Media, 2019-08-20) Meyssignac, Benoit ; Boyer, Tim ; Zhao, Zhongxiang ; Hakuba, Maria Z. ; Landerer, Felix ; Stammer, Detlef ; Kohl, Armin ; Kato, Seiji ; L’Ecuyer, Tristan S. ; Ablain, Michaël ; Abraham, John Patrick ; Blazquez, Alejandro ; Cazenave, Anny ; Church, John A. ; Cowley, Rebecca ; Cheng, Lijing ; Domingues, Catia M. ; Giglio, Donata ; Gouretski, Viktor ; Ishii, Masayoshi ; Johnson, Gregory C. ; Killick, Rachel E. ; Legler, David ; Llovel, William ; Lyman, John ; Palmer, Matthew D. ; Piotrowicz, Stephen R. ; Purkey, Sarah G. ; Roemmich, Dean ; Roca, Rémy ; Savita, Abhishek ; von Schuckmann, Karina ; Speich, Sabrina ; Stephens, Graeme ; Wang, Gongjie ; Wijffels, Susan E. ; Zilberman, Nathalie
    The energy radiated by the Earth toward space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4–1 Wm–2). This imbalance is coined Earth’s Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gas emissions and is driving the current warming of the planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two orders of magnitude smaller than the radiation fluxes in and out of the Earth system. Over 93% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat. This accumulation of heat can be tracked with the ocean observing system such that today, the monitoring of Ocean Heat Content (OHC) and its long-term change provide the most efficient approach to estimate EEI. In this community paper we review the current four state-of-the-art methods to estimate global OHC changes and evaluate their relevance to derive EEI estimates on different time scales. These four methods make use of: (1) direct observations of in situ temperature; (2) satellite-based measurements of the ocean surface net heat fluxes; (3) satellite-based estimates of the thermal expansion of the ocean and (4) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. Achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System.
  • Article
    Sensor corrections for Sea-Bird SBE-41CP and SBE-41 CTDs
    (American Meteorological Society, 2007-06) Johnson, Gregory C. ; Toole, John M. ; Larson, Nordeen G.
    Sensor response corrections for two models of Sea-Bird Electronics, Inc., conductivity–temperature–depth (CTD) instruments (the SBE-41CP and SBE-41) designed for low-energy profiling applications were estimated and applied to oceanographic data. Three SBE-41CP CTDs mounted on prototype ice-tethered profilers deployed in the Arctic Ocean sampled diffusive thermohaline staircases and telemetered data to shore at their full 1-Hz resolution. Estimations of and corrections for finite thermistor time response, time shifts between when a parcel of water was sampled by the thermistor and when it was sampled by the conductivity cell, and the errors in salinity induced by the thermal inertia of the conductivity cell are developed with these data. In addition, thousands of profiles from Argo profiling floats equipped with SBE-41 CTDs were screened to select examples where thermally well-mixed surface layers overlaid strong thermoclines for which standard processing often yields spuriously fresh salinity estimates. Hundreds of profiles so identified are used to estimate and correct for the conductivity cell thermal mass error in SBE-41 CTDs.
  • Article
    Argo data 1999-2019: two million temperature-salinity profiles and subsurface velocity observations from a global array of profiling floats.
    (Frontiers Media, 2020-09-15) Wong, Annie P. S. ; Wijffels, Susan E. ; Riser, Stephen C. ; Pouliquen, Sylvie ; Hosoda, Shigeki ; Roemmich, Dean ; Gilson, John ; Johnson, Gregory C. ; Martini, Kim I. ; Murphy, David J. ; Scanderbeg, Megan ; Udaya Bhaskar, T. V. S. ; Buck, Justin J. H. ; Merceur, Frederic ; Carval, Thierry ; Maze, Guillaume ; Cabanes, Cécile ; André, Xavier ; Poffa, Noé ; Yashayaev, Igor ; Barker, Paul M. ; Guinehut, Stéphanie ; Belbeoch, Mathieu ; Ignaszewski, Mark ; Baringer, Molly O. ; Schmid, Claudia ; Lyman, John ; McTaggart, Kristene E. ; Purkey, Sarah G. ; Zilberman, Nathalie ; Alkire, Matthew ; Swift, Dana ; Owens, W. Brechner ; Jayne, Steven R. ; Hersh, Cora ; Robbins, Pelle E. ; West-Mack, Deb ; Bahr, Frank B. ; Yoshida, Sachiko ; Sutton, Philip J. H. ; Cancouët, Romain ; Coatanoan, Christine ; Dobbler, Delphine ; Garcia Juan, Andrea ; Gourrion, Jérôme ; Kolodziejczyk, Nicolas ; Bernard, Vincent ; Bourlès, Bernard ; Claustre, Hervé ; d’Ortenzio, Fabrizio ; Le Reste, Serge ; Le Traon, Pierre-Yves ; Rannou, Jean-Philippe ; Saout-Grit, Carole ; Speich, Sabrina ; Thierry, Virginie ; Verbrugge, Nathalie ; Angel-Benavides, Ingrid M. ; Klein, Birgit ; Notarstefano, Giulio ; Poulain, Pierre Marie ; Vélez-Belchí, Pedro ; Suga, Toshio ; Ando, Kentaro ; Iwasaska, Naoto ; Kobayashi, Taiyo ; Masuda, Shuhei ; Oka, Eitarou ; Sato, Kanako ; Nakamura, Tomoaki ; Sato, Katsunari ; Takatsuki, Yasushi ; Yoshida, Takashi ; Cowley, Rebecca ; Lovell, Jenny L. ; Oke, Peter ; van Wijk, Esmee ; Carse, Fiona ; Donnelly, Matthew ; Gould, W. John ; Gowers, Katie ; King, Brian A. ; Loch, Stephen G. ; Mowat, Mary ; Turton, Jon ; Pattabhi Rama Rao, Eluri ; Ravichandran, M. ; Freeland, Howard ; Gaboury, Isabelle ; Gilbert, Denis ; Greenan, Blair J. W. ; Ouellet, Mathieu ; Ross, Tetjana ; Tran, Anh ; Dong, Mingmei ; Liu, Zenghong ; Xu, Jianping ; Kang, KiRyong ; Jo, HyeongJun ; Kim, Sung-Dae ; Park, Hyuk-Min
    In the past two decades, the Argo Program has collected, processed, and distributed over two million vertical profiles of temperature and salinity from the upper two kilometers of the global ocean. A similar number of subsurface velocity observations near 1,000 dbar have also been collected. This paper recounts the history of the global Argo Program, from its aspiration arising out of the World Ocean Circulation Experiment, to the development and implementation of its instrumentation and telecommunication systems, and the various technical problems encountered. We describe the Argo data system and its quality control procedures, and the gradual changes in the vertical resolution and spatial coverage of Argo data from 1999 to 2019. The accuracies of the float data have been assessed by comparison with high-quality shipboard measurements, and are concluded to be 0.002°C for temperature, 2.4 dbar for pressure, and 0.01 PSS-78 for salinity, after delayed-mode adjustments. Finally, the challenges faced by the vision of an expanding Argo Program beyond 2020 are discussed.
  • Article
    Pacific anthropogenic carbon between 1991 and 2017
    (American Geophysical Union, 2019-04-29) Carter, Brendan ; Feely, Richard A. ; Wanninkhof, Rik ; Kouketsu, Shinya ; Sonnerup, Rolf E. ; Pardo, Paula Conde ; Sabine, Christopher L. ; Johnson, Gregory C. ; Sloyan, Bernadette M. ; Murata, Akihiko ; Mecking, Sabine ; Tilbrook, Bronte ; Speer, Kevin G. ; Talley, Lynne D. ; Millero, Frank J. ; Wijffels, Susan E. ; Macdonald, Alison M. ; Gruber, Nicolas ; Bullister, John L.
    We estimate anthropogenic carbon (Canth) accumulation rates in the Pacific Ocean between 1991 and 2017 from 14 hydrographic sections that have been occupied two to four times over the past few decades, with most sections having been recently measured as part of the Global Ocean Ship‐based Hydrographic Investigations Program. The rate of change of Canth is estimated using a new method that combines the extended multiple linear regression method with improvements to address the challenges of analyzing multiple occupations of sections spaced irregularly in time. The Canth accumulation rate over the top 1,500 m of the Pacific increased from 8.8 (±1.1, 1σ) Pg of carbon per decade between 1995 and 2005 to 11.7 (±1.1) PgC per decade between 2005 and 2015. For the entire Pacific, about half of this decadal increase in the accumulation rate is attributable to the increase in atmospheric CO2, while in the South Pacific subtropical gyre this fraction is closer to one fifth. This suggests a substantial enhancement of the accumulation of Canth in the South Pacific by circulation variability and implies that a meaningful portion of the reinvigoration of the global CO2 sink that occurred between ~2000 and ~2010 could be driven by enhanced ocean Canth uptake and advection into this gyre. Our assessment suggests that the accuracy of Canth accumulation rate reconstructions along survey lines is limited by the accuracy of the full suite of hydrographic data and that a continuation of repeated surveys is a critical component of future carbon cycle monitoring.
  • Thesis
    Near-equatorial deep circulation in the Indian and Pacific oceans
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1990-09) Johnson, Gregory C.
    Theory and observations of deep circulation in the near-equatorial Atlantic, Indian and Pacific Oceans are reviewed. Flow of deep and bottom water in the near-equatorial Indian and Pacific oceans, the two oceans with only a southern source of bottom water, is described through analysis of recent CTD data. Zero-velocity surfaces are chosen through use of water-mass properties and transports are estimated. Effects of basin geometry, bottom bathymetry and vertical diffusivity as well as a model meridional inertial current on a sloping bottom near the equator are all discussed in conjunction with the flow patterns inferred from observations. In the western equatorial Indian Ocean, repeat CTD surveys in the Somali Basin at the height of subsequent northeast and southwest monsoons show only small differences in the strength of the circulation of the bottom water (potential temperature θ ≤1.2°C). A deep western boundary current (DWBC) carrying about 4x106 m3 s-1 of this water is observed moving north along the continental rise of Africa at 3°S. The cross-equatorial sections suggest that the current turns eastward at the equator. The northern sections show a large mass of the coldest water in the interior east of the Chain Ridge, augmenting the evidence that the DWBC observed south of the equator turns east at the equator rather than remaining on the boundary, and feeds the interior circulation in the northern part of the basin from the equator. The circulation of deep water (1.2°C< θ ≤ 1.7°C) in the Somali and Arabian Basins is also analyzed. A DWBC flowing southward along the Carlsberg ridge in the Arabian Basin is described. In the central equatorial Pacific Ocean a recent zonal CTD section at 10°N, allows estimation that 5.0x106 m3 s-1 of Lower Circumpolar Water (LCPW, θ ≤ 1.2°C) moves northward as a DWBC along the Caroline Seamounts in the East Mariana Basin. In the Central Pacific Basin, 8.1x106 m3 s-1 of LCPW is estimated to move northward along the Marshal Seamounts as a DWBC at this latitude. An estimated 4.7x106 m3 s-1 of the LCPW moves back southward across 10°N in the Northeast Pacific Basin along the western flank of the East Pacific Rise and an equatorial jet is observed to flow westward from 138°W to 148°W shifting south of the Line Islands at 2.5°S, 159°W. The net northward flow of LCPW across 10°N in the Pacific Ocean is estimated at 8.4x106 m3 s-I. The net southward flow of the silica-rich North Pacific Deep Water (NPDW, 1.2 < θ ≤ 2.0°C) in the central Pacific Ocean estimated at 2.7x106 m3 s-1 is also discussed. In the Indian Ocean, the eastward equatorial flow in the the bottom water of the Somali Basin differs from the prediction of a flat-bottom uniform-upwelling Stommel-Arons calculation with realistic basin geometry and source location. The behavior of a uniform potential vorticity meridional jet on a sloping bottom is examined in an attempt to explain the observed behavior at the equator. The inertial jet does not cross the equator in a physically plausible fashion owing to the constraint of conservation of potential vorticity. Mass and heat budgets for the bottom water of the Somali Basin are of interest with respect to the equatorial feature. Upwelling through the θ = 1.2°C surface is estimated at 12±4x10-5 cm s-1 and a rough heat budget for the deep Somali Basin results in an estimate of vertical diffusivity of 9±5 cm2 s-1 at 3800 m. Numerical model results indicate that large vertical diffusivities result in eastward jets in the bottom water at the equator. In the Pacific Ocean the DWBC observed flowing northward south of the equator crosses the equator with transport nearly intact, albeit split into two at 10°N by the tortuous bathymetry. However the southward flow along the East Pacific Rise in the Northeast Pacific Basin and the westward equatorial jet this flow feeds are puzzling. The basin depth decreases equatorward and eastward, which may allow some southeastward flow in the Stommel-Arons framework. However, the equatorial jet is still unexplained. The estimated vertical velocity and diffusivity at 3600 db of 2±2x10-5 cm s-1 and 4±3 cm2 s-1 for the area between 12°8 and 10°N are much smaller than estimates in the Somali Basin. Thus the two oceans, similar in their single southern source of bottom water, have DWBC's which behave remarkably differently near the equator. In the Somali Basin of the Indian Ocean the DWBC appears to turn eastward at the equator, with large vertical upwelling velocity and large vertical diffusivity estimates for the bottom water of the basin. In the Pacific Ocean the DWBC appears to cross the equator, but there is a puzzling westward flowing equatorial jet in the bottom water of the Northeast Pacific Basin.
  • Article
    Heat stored in the Earth system: where does the energy go?
    (Copernicus Publications, 2020-09-07) von Schuckmann, Karina ; Cheng, Lijing ; Palmer, Matthew D. ; Hansen, James ; Tassone, Caterina ; Aicher, Valentin ; Adusumilli, Susheel ; Beltrami, Hugo ; Boyer, Tim ; Cuesta-Valero, Francisco José ; Desbruyeres, Damien ; Domingues, Catia M. ; García-García, Almudena ; Gentine, Pierre ; Gilson, John ; Gorfer, Maximilian ; Haimberger, Leopold ; Ishii, Masayoshi ; Johnson, Gregory C. ; Killick, Rachel E. ; King, Brian A. ; Kirchengast, Gottfried ; Kolodziejczyk, Nicolas ; Lyman, John ; Marzeion, Ben ; Mayer, Michael ; Monier, Maeva ; Monselesan, Didier Paolo ; Purkey, Sarah G. ; Roemmich, Dean ; Schweiger, Axel ; Seneviratne, Sonia I. ; Shepherd, Andrew ; Slater, Donald A. ; Steiner, Andrea K. ; Straneo, Fiammetta ; Timmermans, Mary-Louise ; Wijffels, Susan E.
    Human-induced atmospheric composition changes cause a radiative imbalance at the top of the atmosphere which is driving global warming. This Earth energy imbalance (EEI) is the most critical number defining the prospects for continued global warming and climate change. Understanding the heat gain of the Earth system – and particularly how much and where the heat is distributed – is fundamental to understanding how this affects warming ocean, atmosphere and land; rising surface temperature; sea level; and loss of grounded and floating ice, which are fundamental concerns for society. This study is a Global Climate Observing System (GCOS) concerted international effort to update the Earth heat inventory and presents an updated assessment of ocean warming estimates as well as new and updated estimates of heat gain in the atmosphere, cryosphere and land over the period 1960–2018. The study obtains a consistent long-term Earth system heat gain over the period 1971–2018, with a total heat gain of 358±37 ZJ, which is equivalent to a global heating rate of 0.47±0.1 W m−2. Over the period 1971–2018 (2010–2018), the majority of heat gain is reported for the global ocean with 89 % (90 %), with 52 % for both periods in the upper 700 m depth, 28 % (30 %) for the 700–2000 m depth layer and 9 % (8 %) below 2000 m depth. Heat gain over land amounts to 6 % (5 %) over these periods, 4 % (3 %) is available for the melting of grounded and floating ice, and 1 % (2 %) is available for atmospheric warming. Our results also show that EEI is not only continuing, but also increasing: the EEI amounts to 0.87±0.12 W m−2 during 2010–2018. Stabilization of climate, the goal of the universally agreed United Nations Framework Convention on Climate Change (UNFCCC) in 1992 and the Paris Agreement in 2015, requires that EEI be reduced to approximately zero to achieve Earth's system quasi-equilibrium. The amount of CO2 in the atmosphere would need to be reduced from 410 to 353 ppm to increase heat radiation to space by 0.87 W m−2, bringing Earth back towards energy balance. This simple number, EEI, is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control, and we call for an implementation of the EEI into the global stocktake based on best available science. Continued quantification and reduced uncertainties in the Earth heat inventory can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling, and the establishment of an international framework for concerted multidisciplinary research of the Earth heat inventory as presented in this study. This Earth heat inventory is published at the German Climate Computing Centre (DKRZ, https://www.dkrz.de/, last access: 7 August 2020) under the DOI https://doi.org/10.26050/WDCC/GCOS_EHI_EXP_v2 (von Schuckmann et al., 2020).
  • Article
    The Argo Program : present and future
    (Oceanography Society, 2017-06) Jayne, Steven R. ; Roemmich, Dean ; Zilberman, Nathalie ; Riser, Stephen C. ; Johnson, Kenneth S. ; Johnson, Gregory C. ; Piotrowicz, Stephen R.
    The Argo Program has revolutionized large-scale physical oceanography through its contributions to basic research, national and international climate assessment, education, and ocean state estimation and forecasting. This article discusses the present status of Argo and enhancements that are underway. Extensions of the array into seasonally ice-covered regions and marginal seas as well as increased numbers of floats along the equator and around western boundary current extensions have been proposed. In addition, conventional Argo floats, with their 2,000 m sampling limit, currently observe only the upper half of the open ocean volume. Recent advances in profiling float technology and in the accuracy and stability of float-mounted conductivity-temperature-depth sensors make it practical to obtain measurements to 6,000 m. The Deep Argo array will help observe and constrain the global budgets of heat content, freshwater, and steric sea level, as well as the full-depth ocean circulation. Finally, another extension to the Argo Program is the addition of a diverse set of chemical sensors to profiling floats in order to build a Biogeochemical-Argo array to understand the carbon cycle, the biological pump, and ocean acidification.