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Sample records for oceanic circulation

  1. Ocean circulation

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew F.; Rahmstorf, Stefan

    The ocean moderates the Earth's climate due to its vast capacity to store and transport heat; the influence of the large-scale ocean circulation on changes in climate is considered in this chapter. The ocean experiences both buoyancy forcing (through heating/cooling and evaporation/precipitation) and wind forcing. Almost all ocean forcing occurs at the surface, but these changes are communicated throughout the entire depth of the ocean through the meridional overturning circulation (MOC). In a few localized regions, water become sufficiently dense to penetrate thousands of meters deep, where it spreads, providing a continuous source of deep dense water to the entire ocean. Dense water returns to the surface and thus closes the MOC, either through density modification due to diapycnal mixing or by upwelling along sloping isopycnals across the Southern Ocean. Determination of the relative contributions of these two processes in the MOC remains an active area of research. Observations obtained primarily from isotopic compositions in ocean sediments provide substantial evidence that the structure of the MOC has changed significantly in the past. Indeed, large and abrupt changes to the Earth's climate during the past 120,000 years can be linked to either a reorganization or a complete collapse of the MOC. Two of the more dramatic instances of abrupt change include Dansgaard-Oeschger events, abrupt warmings that could exceed 10°C over a period as short as a few decades, and Heinrich events, which are associated with massive freshwater fluxes due to rapid iceberg discharges into the North Atlantic. Numerical models of varying complexity that have captured these abrupt transitions all underscore that the MOC is a highly nonlinear system with feedback loops, multiple equilibria, and hysteresis effects. Prediction of future abrupt shifts in the MOC or "tipping points" remains uncertain. However, the inferred behavior of the MOC during glacial climates suggests that

  2. Ocean circulation using altimetry

    NASA Technical Reports Server (NTRS)

    Minster, Jean-Francois; Brossier, C.; Gennero, M. C.; Mazzega, P.; Remy, F.; Letraon, P. Y.; Blanc, F.

    1991-01-01

    Our group has been very actively involved in promoting satellite altimetry as a unique tool for observing ocean circulation and its variability. TOPEX/POSEIDON is particularly interesting as it is optimized for this purpose. It will probably be the first instrument really capable of observing the seasonal and interannual variability of subtropical and polar gyres and the first to eventually document the corresponding variability of their heat flux transport. The studies of these phenomena require data of the best quality, unbiased extraction of the signal, mixing of these satellite data with in situ measurements, and assimilation of the whole set into a dynamic description of ocean circulation. Our group intends to develop responses to all these requirements. We will concentrate mostly on the circulation of the South Atlantic and Indian Oceans: This will be done in close connection with other groups involved in the study of circulation of the tropical Atlantic Ocean, in the altimetry measurements (in particular, those of the tidal issue), and in the techniques of data assimilation in ocean circulation models.

  3. World Ocean Circulation Experiment

    NASA Technical Reports Server (NTRS)

    Clarke, R. Allyn

    1992-01-01

    The oceans are an equal partner with the atmosphere in the global climate system. The World Ocean Circulation Experiment is presently being implemented to improve ocean models that are useful for climate prediction both by encouraging more model development but more importantly by providing quality data sets that can be used to force or to validate such models. WOCE is the first oceanographic experiment that plans to generate and to use multiparameter global ocean data sets. In order for WOCE to succeed, oceanographers must establish and learn to use more effective methods of assembling, quality controlling, manipulating and distributing oceanographic data.

  4. Ocean circulation studies

    NASA Technical Reports Server (NTRS)

    Koblinsky, C. J.

    1984-01-01

    Remotely sensed signatures of ocean surface characteristics from active and passive satellite-borne radiometers in conjunction with in situ data were utilized to examine the large scale, low frequency circulation of the world's oceans. Studies of the California Current, the Gulf of California, and the Kuroshio Extension Current in the western North Pacific were reviewed briefly. The importance of satellite oceanographic tools was emphasized.

  5. Modeling ocean circulation

    SciTech Connect

    Semtner, A.J.

    1995-09-08

    Ocean numerical models have become quite realistic over the past several years as a result of improved methods, faster computers, and global data sets. Models now treat basin-scale to global domains while retaining the fine spatial scales that are important for modeling the transport of heat, salt, and other properties over vast distances. Simulations are reproducing observed satellite results on the energetics of strong currents and are properly showing diverse aspects of thermodynamic and dynamic ocean responses ranging from deep-water production of El Nino. Now models can represent not only currents but also the consequences for climate, biology, and geo-chemistry over time spans for months to decades. However, much remains to be understood from models about ocean circulation on longer time scales, including the evolution of the dominant water masses, the predictability of climate, and the ocean`s influence on global change. 34 refs., 6 figs.

  6. Ocean General Circulation Models

    SciTech Connect

    Yoon, Jin-Ho; Ma, Po-Lun

    2012-09-30

    1. Definition of Subject The purpose of this text is to provide an introduction to aspects of oceanic general circulation models (OGCMs), an important component of Climate System or Earth System Model (ESM). The role of the ocean in ESMs is described in Chapter XX (EDITOR: PLEASE FIND THE COUPLED CLIMATE or EARTH SYSTEM MODELING CHAPTERS). The emerging need for understanding the Earth’s climate system and especially projecting its future evolution has encouraged scientists to explore the dynamical, physical, and biogeochemical processes in the ocean. Understanding the role of these processes in the climate system is an interesting and challenging scientific subject. For example, a research question how much extra heat or CO2 generated by anthropogenic activities can be stored in the deep ocean is not only scientifically interesting but also important in projecting future climate of the earth. Thus, OGCMs have been developed and applied to investigate the various oceanic processes and their role in the climate system.

  7. LLNL Ocean General Circulation Model

    Energy Science and Technology Software Center (ESTSC)

    2005-12-29

    The LLNL OGCM is a numerical ocean modeling tool for use in studying ocean circulation over a wide range of space and time scales, with primary applications to climate change and carbon cycle science.

  8. General circulation of the ocean

    SciTech Connect

    Abarbanel, H.D.I.; Young, W.R.

    1986-01-01

    This book is an analysis of the geophysics of ocean circulation and its interaction with the atmosphere. It reviews the new concepts and models which have emerged in the last five years, as well as classical theories and observations. The contributions cover topics such as: the observational basis for large-scale circulation, including surface and deep circulation and subtropical gyres; thermocline theories; inverse methods for ocean circulation; baroclinic theories of the wind-driven circulation; and single layer models. This volume sets the current research literature in context, and suggests promising avenues for future study.

  9. Global ocean circulation by altimetry

    NASA Technical Reports Server (NTRS)

    Wunsch, Carl; Haidvogel, D.

    1991-01-01

    The overall objectives of this project are to determine the general circulation of the oceans and many of its climate and biochemical consequences through the optimum use of altimetry data from TOPEX/POSEIDON and related missions. Emphasis is on the global-scale circulation, as opposed to the regional scale, but some more local studies will be carried out. Because of funding limitations, the primary initial focus will be on the time-dependent global-scale circulation rather than the mean; eventually, the mean circulation must be dealt with as well.

  10. Tracers of Past Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Lynch-Stieglitz, J.

    2003-12-01

    Information about how the ocean circulated during the past is useful in understanding changes in ocean and atmospheric chemistry, changes in the fluxes of heat and freshwater between the ocean and atmosphere, and changes in global wind patterns. The circulation of surface waters in the ocean leaves an imprint on sea surface temperature, and is also inextricably linked to the patterns of oceanic productivity. Much valuable information about past ocean circulation has been inferred from reconstructions of surface ocean temperature and productivity, which are covered in separate chapters. Here the focus is on the geochemical tracers that are used to infer the flow patterns and mixing of subsurface water masses.Several decades ago it was realized that chemistry of the shells of benthic foraminifera (carbon isotope and Cd/Ca ratios) carried an imprint of the nutrient content of deep-water masses (Shackleton, 1977; Broecker, 1982; Boyle, 1981). This led rapidly to the recognition that the water masses in the Atlantic Ocean were arrayed differently during the last glacial maximum than they are today, and the hypothesis that the glacial arrangement reflected a diminished contribution of low-nutrient North Atlantic deep water (NADW) ( Curry and Lohmann, 1982; Boyle and Keigwin, 1982). More detailed spatial reconstructions indicated a shallow nutrient-depleted water mass overlying a more nutrient-rich water mass in the glacial Atlantic. These findings spurred advances not only in geochemistry but in oceanography and climatology, as workers in these fields attempted to simulate the inferred glacial circulation patterns and assess the vulnerability of the modern ocean circulation to changes such as observed for the last ice age.While the nutrient distributions in the glacial Atlantic Ocean were consistent with a diminished flow of NADW, they also could have reflected an increase in inflow from the South Atlantic and/or a shallower yet undiminished deep-water mass. Clearly

  11. Spaceborne studies of ocean circulation

    NASA Technical Reports Server (NTRS)

    Patzert, W. C.

    1984-01-01

    The history and near-term future of ocean remote sensing to study ocean circulation are examined. Seasat provided the first-ever global data sets of sea surface topography (altimeter) and marine winds (scatterometer) and laid the foundation for the next generation of satellite missions planned for the late 1980s. The future missions are the next generation of altimeter and scatterometer to be flown aboard TOPEX (TOPography EXperiment) and NROSS (Navy Remote Sensing System), respectively. The data from these satellites will be coordinated with measurements made at sea to determine the driving forces of ocean circulation and to study the oceans' role in climate variability. The significance of such studies to such matters as climatic changes, fisheries, commerce, waste disposal, and national defense is noted.

  12. Ocean circulation and climate change

    NASA Astrophysics Data System (ADS)

    Hasselmann, Klaus

    1991-09-01

    Recent numerical simulations using global ocean circulation models are reviewed together with model experiments involving further important climate sub-systems with which the ocean interacts: the atmosphere, the air-sea interface and the global carbon cycle. A common feature of all ocean circulation experiments considered is the strong sensitivity of the circulation to relatively minor changes in surface forcing, particularly to the buoyancy fluxes in regions of deep water formation in high latitudes. This may explain some of the well-known deficiencies of past global ocean circulation simulations. The strong sensitivity may also have been the cause of rapid climate changes observed in paleoclimatic records and can lead further to significant natural climate variability on the time scales of a few hundred years through the stochastic forcing of the ocean by atmospheric weather variability. Gobal warming computations using two different coupled ocean-atmosphere models for the "business-as-usual" scenario of the Intergovernmental Panel on Climate Change yield a significantly stronger warming delay due to the heat uptake by the oceans in the Southern Ocean than estimated on the basis of box-diffusion models. Recent advances in surface wave modelling, illustrated by a comparison of wave height fields derived from the WAM model and the GEOSAT altimeter, hold promise for the development of an improved representation of ocean-atmosphere coupling based on an explicit description of the dynamical processes at the air-sea interface. Global carbon cycle simulations with a three dimensional carbon cycle model tuned to reproduce past variations of carbon cycle indices show a significant impact of variations in the ocean circulation on the CO2 concentration in the atmosphere and thereby on climate. The series of experiments suggest that for the study of climate in the time scale range from 10-Ocean circulation and climate change

    NASA Astrophysics Data System (ADS)

    Hasselmann, Klaus

    1991-08-01

    Recent numerical simulations using global ocean circulation models are reviewed together with model experiments involving further important climate sub-systems with which the ocean interacts: the atmosphere, the air-sea interface and the global carbon cycle. A common feature of all ocean circulation experiments considered is the strong sensitivity of the circulation to relatively minor changes in surface forcing, particularly to the buoyancy fluxes in regions of deep water formation in high latitudes. This may explain some of the well-known deficiencies of past global ocean circulation simulations. The strong sensitivity may also have been the cause of rapid climate changes observed in paleoclimatic records and can lead further to significant natural climate variability on the time scales of a few hundred years through the stochastic forcing of the ocean by atmospheric weather variability. Gobal warming computations using two different coupled ocean-atmosphere models for the "business-as-usual" scenario of the Intergovernmental Panel on Climate Change yield a significantly stronger warming delay due to the heat uptake by the oceans in the Southern Ocean than estimated on the basis of box-diffusion models. Recent advances in surface wave modelling, illustrated by a comparison of wave height fields derived from the WAM model and the GEOSAT altimeter, hold promise for the development of an improved representation of ocean-atmosphere coupling based on an explicit description of the dynamical processes at the air-sea interface. Global carbon cycle simulations with a three dimensional carbon cycle model tuned to reproduce past variations of carbon cycle indices show a significant impact of variations in the ocean circulation on the CO2 concentration in the atmosphere and thereby on climate. The series of experiments suggest that for the study of climate in the time scale range from 10-Numerical Modeling of Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Miller, Robert N.

    2007-01-01

    The modelling of ocean circulation is important not only for its own sake, but also in terms of the prediction of weather patterns and the effects of climate change. This book introduces the basic computational techniques necessary for all models of the ocean and atmosphere, and the conditions they must satisfy. It describes the workings of ocean models, the problems that must be solved in their construction, and how to evaluate computational results. Major emphasis is placed on examining ocean models critically, and determining what they do well and what they do poorly. Numerical analysis is introduced as needed, and exercises are included to illustrate major points. Developed from notes for a course taught in physical oceanography at the College of Oceanic and Atmospheric Sciences at Oregon State University, this book is ideal for graduate students of oceanography, geophysics, climatology and atmospheric science, and researchers in oceanography and atmospheric science. Features examples and critical examination of ocean modelling and results Demonstrates the strengths and weaknesses of different approaches Includes exercises to illustrate major points and supplement mathematical and physical details

  13. Global warming and changes in ocean circulation

    SciTech Connect

    Duffy, P.B.; Caldeira, K.C.

    1998-02-01

    This final report provides an overview of the goals and accomplishments of this project. Modeling and observational work has raised the possibility that global warming may cause changes in the circulation of the ocean. If such changes would occur they could have important climatic consequences. The first technical goal of this project was to investigate some of these possible changes in ocean circulation in a quantitative way, using a state-of -the-art numerical model of the ocean. Another goal was to develop our ocean model, a detailed three-dimensional numerical model of the ocean circulation and ocean carbon cycles. A major non-technical goal was to establish LLNL as a center of excellence in modelling the ocean circulation and carbon cycle.

  14. Heinrich events induced by oceanic circulation changes

    NASA Astrophysics Data System (ADS)

    Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa; Banderas, Rubén; Ritz, Catherine

    2014-05-01

    Proxy data reveal the existence of episodes of increased deposition of ice-rafted debris in the North Atlantic Ocean during the last glacial period. These are interpreted as massive iceberg discharges mainly from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence points to an active role of the oceanic circulation. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. The model generates a time series of iceberg calving that closely agrees with ice-rafted debris records over the past 80 ka. Our results indicate that oceanic circulation variations were responsible for the enigmatic ice purges of the last ice age through the control that ice shelves exert on the dynamics of the inland ice sheet

  15. Warm World Ocean Thermohaline Circulation Model

    NASA Astrophysics Data System (ADS)

    Zimov, N.; Zimov, S. A.

    2014-12-01

    Modern day ocean circulation is dominated by thermal convection with cold waters subsiding in the Northern Atlantic, filling the ocean interior with cold and heavy water. However, ocean circulation diminished during the last glaciation and consequently the downwelling of the cold. Therefore interior ocean water temperatures must have been affected by other mechanisms which are negligible in the current state. We propose that the submergence of highly saline water from warm seas with high rates of evaporation (like the Red or Mediterranean Sea) was a major factor controlling ocean circulation during the last glaciation. Even today, waters in these poorly connected seas are the heaviest waters in the World ocean (1.029 g/cm3). The second mechanism affecting ocean temperature is the geothermal heat flux. With no heat exchange between the atmosphere and the ocean, geothermal heat flux through the ocean floor is capable of increasing ocean temperature by tens of degrees C over a 100 thousand year glacial cycle. To support these hypotheses we present an ocean box model that describes thermohaline circulation in the World Ocean. According to the model parameters, all water circulation is driven by the water density gradient. Boxes include high-latitude seas, high salinity seas, surface ocean, glaciers, and rift and lateral zones of the ocean interior. External heat sources are radiative forcing, affected by Milankovich cycles, and geothermal heat flux. Additionally this model accounts for the heat produced by organic rain decay. Taking all input parameters close to currently observed values, the model manages to recreate the glacial-interglacial cycles. During the glacial periods only haline circulation takes place, the ocean is strongly stratified, and the interior ocean accumulates heat while high-latitudes accumulate ice. 112,000 years after glaciation starts, water density on the ocean bottom becomes equal to the density of water in high-latitude seas, strong thermal

  16. Sedimentary response to ocean gateway circulation changes

    NASA Astrophysics Data System (ADS)

    Heinze, Christoph; Crowley, Thomas J.

    1997-12-01

    Previous modeling studies suggested that changes in ocean gateways may have exerted a dramatic influence on the ocean circulation. In this pilot study we extend those results to examining the potential ramifications of circulation changes on the sedimentary record. A version of the Hamburg carbon cycle/sediment model is used in these sensitivity experiments. Results indicate that internal reorganization of the ocean circulation can potentially cause very large regional changes in lysocline depth (1500-3000 m) and opal deposition. These shifts are sometimes comparable in magnitude to those imposed by changes in external forcing (e.g., climate, sea level, and weathering). Comparisons of the model response with the geologic record indicate some significant levels of first-order agreement. This exercise suggests that opportunities now exist for physically based modeling of past sediment responses to circulation and climate changes.

  17. Sustaining observations of the unsteady ocean circulation.

    PubMed

    Frajka-Williams, E

    2014-09-28

    Sustained observations of ocean properties reveal a global warming trend and rising sea levels. These changes have been documented by traditional ship-based measurements of ocean properties, whereas more recent Argo profiling floats and satellite records permit estimates of ocean changes on a near real-time basis. Through these and newer methods of observing the oceans, scientists are moving from quantifying the 'state of the ocean' to monitoring its variability, and distinguishing the physical processes bringing signals of change. In this paper, I give a brief overview of the UK contributions to the physical oceanographic observations, and the role they have played in the wider global observing systems. While temperature and salinity are the primary measurements of physical oceanography, new transbasin mooring arrays also resolve changes in ocean circulation on daily timescales. Emerging technologies permit routine observations at higher-than-ever spatial resolutions. Following this, I then give a personal perspective on the future of sustained observations. New measurement techniques promise exciting discoveries concerning the role of smaller scales and boundary processes in setting the large-scale ocean circulation and the ocean's role in climate. The challenges now facing the scientific community include sustaining critical observations in the case of funding system changes or shifts in government priorities. These long records will enable a determination of the role and response of the ocean to climate change. PMID:25157191

  18. Satellite Altimetry, Ocean Circulation, and Data Assimilation

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    1999-01-01

    Ocean circulation is a critical factor in determining the Earth's climate. Satellite altimetry has been proven a powerful technique for measuring the height of the sea surface for the study of global ocean circulation dynamics. A major objective of my research is to investigate the utility of altimeter data for ocean circulation studies. The 6 years' data record of TOPEX/POSEIDON have been analyzed to study the spatial and temporal characteristics of large-scale ocean variability. A major result obtained in 1998 is the discovery of large-scale oscillations in sea level with a period of 25 days in the Argentine Basin of the South Atlantic Ocean (see diagram). They exhibit a dipole pattern with counterclockwise rotational propagation around the Zapiola Rise (centered at 45S and 317E), a small seamount in the abyssal plain of the basin. The peak-to-trough amplitude is about 10 cm over a distance of 500-1000 km. The amplitude of these oscillations has large seasonal-to-interannual variations. The period and rotational characteristics of these oscillations are remarkably similar to the observations made by two current meters deployed near the ocean bottom in the region. What TOPEX/POSEIDON has detected apparently are manifestations of the movement of the entire water column (barotropic motion). The resultant transport variation is estimated to be about 50 x 10(exp 6) cubic M/S, which is about 50% of the total water transport in the region. Preliminary calculations suggest that these oscillations are topographically trapped waves. A numerical model of the South Atlantic is used to investigate the nature of and causes for these waves. A very important property of sea surface height is that it is directly related to the surface geostrophic velocity, which is related to deep ocean circulation through the density field. Therefore altimetry observations are not only useful for determining the surface circulation but also for revealing information about the deep ocean. Another

  1. Variability in deep ocean circulation from GRACE

    NASA Astrophysics Data System (ADS)

    Boening, C.; Watkins, M. M.

    2015-12-01

    Although nearly impossible to observe on a global scale, total water mass transport and inter-basin exchange are central to understanding long-term changes in ocean circulation. Of particular interest are changes in the Meridional Overturning Circulation (MOC) as they pose potential impacts in continental climtae. However, in-situ observations are limited in space and time preventing a holistic view of current variability. The representation of long-term transports in ocean models is highly dependent on the atmospheric forcing fields, which may misrepresent real interannual variability. The bottom pressure observations from the Gravity Recovery And Climate Experiment (GRACE) provide for the first time the ability to observe this global water mass transport. Here, we present the first near-global maps of variability in the depth-independent ocean circulation derived from advanced analysis of GRACE data. We find that significant variability on annual to decadal time scales exists in the deep large-scale circulation, some of which are related to the Southern Annular Mode forcing dominating Southern Ocean variability.

  2. Ice sheet collapse affects ocean circulation

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-06-01

    As Earth's climate warms and ice melts, freshwater input to oceans could weaken the large-scale Atlantic meridional overturning circulation, which acts as an important conveyor of heat and has significant effects on climate. Green et al. used an intermediate complexity climate model to study how freshwater input to oceans can affect the meridional overturning circulation. They applied their model to the collapse of the Barents ice sheet about 140,000 years ago—the first study of this kind for the time period—which resulted in a huge influx of freshwater to the North Atlantic Ocean as large icebergs calved off of the ice sheet. (Paleoceanography, doi:10.1029/ 2010PA002088, 2011)

  3. Ocean circulation on the North Australian Shelf

    NASA Astrophysics Data System (ADS)

    Schiller, Andreas

    2011-07-01

    The ocean circulation on Australia's Northern Shelf is dominated by the Monsoon and influenced by large-scale interannual variability. These driving forces exert an ocean circulation that influences the deep Timor Sea Passage of the Indonesian Throughflow, the circulation on the Timor and Arafura Shelves and, further downstream, the Leeuwin Current. Seasonal maxima of northeastward (southwestward) volume transports on the shelf are almost symmetric and exceed 10 6 m 3/s in February (June). The associated seasonal cycle of vertical upwelling from June to August south of 8.5°S and between 124°E and 137.5°E exceeds 1.5×10 6 m 3/s across 40 m depth. During El Niño events, combined anomalies from the seasonal means of high regional wind stresses and low inter-ocean pressure gradients double the northeastward volume transport on the North Australian Shelf to 1.5×10 6 m 3/s which accounts for 20% of the total depth-integrated transport across 124°E and reduce the total transport of the Indonesian Throughflow. Variability of heat content on the shelf is largely determined by Pacific and Indian Ocean equatorial wind stress anomalies with some contribution from local wind stress forcing.

  4. Numerical simulation of the world ocean circulation

    NASA Technical Reports Server (NTRS)

    Takano, K.; Mintz, Y.; Han, Y. J.

    1973-01-01

    A multi-level model, based on the primitive equations, is developed for simulating the temperature and velocity fields produced in the world ocean by differential heating and surface wind stress. The model ocean has constant depth, free slip at the lower boundary, and neglects momentum advection; so that there is no energy exchange between the barotropic and baroclinic components of the motion, although the former influences the latter through temperature advection. The ocean model was designed to be coupled to the UCLA atmospheric general circulation model, for the study of the dynamics of climate and climate changes. But here, the model is tested by prescribing the observed seasonally varying surface wind stress and the incident solar radiation, the surface air temperature and humidity, cloudiness and the surface wind speed, which, together with the predicted ocean surface temperature, determine the surface flux of radiant energy, sensible heat and latent heat.

  5. Early concepts and charts of ocean circulation

    NASA Astrophysics Data System (ADS)

    Peterson, R. G.; Stramma, L.; Kortum, G.

    Charts of ocean currents from the late nineteenth century show that already by then the patterns of surface circulation in regions away from polar latitudes were well understood. This fundamental knowledge accumulated gradually through centuries of sea travel and had reached a state of near correctness by the time dedicated research cruises, full-depth measurements and the practical application of the dynamical method were being instituted. Perhaps because of the foregoing, many of the pioneering works, critical to establishing what the upper-level circulation is like, the majority of the charts accompanying them, and several of the groundbreaking theoretical treatments on the physics of currents, are only poorly known to present-day oceanographers. In this paper we trace Western developments in knowledge and understanding of ocean circulation from the earliest times to the late-1800s transition into the modern era. We also discuss certain peripheral advances that proved critical to the subject. The earliest known ideas, dating from the Bronze Age and described by Homer, necessarily reflect severe limitations to geographical knowledge, as well as basic human predilections toward conjecture and exaggeration in the face of inadequate information. People considered the earth to be flat and circular, with the ocean flowing like a river around it. They also believed in horrific whirlpools, a concept that persisted into the Renaissance and which would later provide subject material for modern literature. From the Greek Classical Age, we find hydrologic theories of Earth's interior being laced with subterranean channels (Socrates) and all motion deriving from a divine force forever propelling the heavens toward the west, the primum mobile (Aristotle). These ideas, particularly the latter, dominated opinions about ocean circulation into the late Renaissance. By late Antiquity mariners had very likely acquired intimate knowledge of coastal currents in the Mediterranean, but

  6. Early concepts and charts of ocean circulation

    NASA Astrophysics Data System (ADS)

    Peterson, R. G.; Stramma, L.; Kortum, G.

    Charts of ocean currents from the late nineteenth century show that already by then the patterns of surface circulation in regions away from polar latitudes were well understood. This fundamental knowledge accumulated gradually through centuries of sea travel and had reached a state of near correctness by the time dedicated research cruises, full-depth measurements and the practical application of the dynamical method were being instituted. Perhaps because of the foregoing, many of the pioneering works, critical to establishing what the upper-level circulation is like, the majority of the charts accompanying them, and several of the groundbreaking theoretical treatments on the physics of currents, are only poorly known to present-day oceanographers. In this paper we trace Western developments in knowledge and understanding of ocean circulation from the earliest times to the late-1800s transition into the modern era. We also discuss certain peripheral advances that proved critical to the subject. The earliest known ideas, dating from the Bronze Age and described by Homer, necessarily reflect severe limitations to geographical knowledge, as well as basic human predilections toward conjecture and exaggeration in the face of inadequate information. People considered the earth to be flat and circular, with the ocean flowing like a river around it. They also believed in horrific whirlpools, a concept that persisted into the Renaissance and which would later provide subject material for modern literature. From the Greek Classical Age, we find hydrologic theories of Earth's interior being laced with subterranean channels (Socrates) and all motion deriving from a divine force forever propelling the heavens toward the west, the primum mobile (Aristotle). These ideas, particularly the latter, dominated opinions about ocean circulation into the late Renaissance. By late Antiquity mariners had very likely acquired intimate knowledge of coastal currents in the Mediterranean, but

  7. Ocean general circulation models for parallel architectures

    SciTech Connect

    Smith, R.D.

    1993-05-01

    The authors report continuing work in developing ocean general circulation models for parallel architectures. In earlier work, they began with the widely-used Bryan-Cox ocean model, but reformulated the barotropic equations (which describe the vertically integrated flow) to solve for the surface-pressure field rather than the volume-transport streamfunction as in the original model. This had the advantage of being more easily parallelized and allowed for a more realistic representation of coastal and bottom topography. Both streamfunction and surface-pressure formulations use a rigid-lid approximation to eliminate fast surface waves. They have now replaced the rigid-lid with a free surface, and solve the barotropic equations implicitly to overcome the timestep restriction associated with the fast waves. This method has several advantages, including: (1) a better physical representation of the barotropic mode, and (2) a better-conditioned operator matrix, which leads to much faster convergence in the conjugate-gradient solver. They have also extended the model to allow use of arbitrary orthogonal curvilinear coordinates for the horizontal grid. The original model uses a standard polar grid that has a singularity at each pole, making it difficult to include the Arctic basin, which plays an important role in global ocean circulation. They can now include the Arctic (while still using an explicit time-integration scheme without high-latitude filtering) by using a distorted grid with a displaced pole for the North Atlantic - Arctic region of the ocean. The computer code, written in Fortran 90 and developed on the Connection Machine, has been substantially restructured so that all communication occurs in low-level stencil routines. The idea is that the stencil routines may be rewritten to optimize communication costs on a particular architecture, while the remainder of the code is for the most part machine-independent, involving only the simplest Fortran 90 constructs.

  8. Ocean circulation modeling by use of radar altimeter data

    NASA Technical Reports Server (NTRS)

    Olbers, Dirk; Alpers, W.; Hasselmann, K.; Maier-Reimer, E.; Kase, R.; Krauss, W.; Siedler, G.; Willebrand, J.; Zahel, W.

    1991-01-01

    The project will investigate the use of radar altimetry (RA) data in the determination of the ocean circulation models. RA data will be used to verify prognostic experiments of the steady state and seasonal cycle of large-scale circulation models and the statistical steady state of eddy-resolving models. The data will serve as initial and update conditions in data assimilation experiments and as constraints in inverse calculations. The aim of the project is a better understanding of ocean physics, the determination and mapping of ocean currents, and a contribution to the establishment of ocean circulation models for climate studies. The goal of the project is to use satellite radar altimetry data for improving our knowledge of ocean circulation both in a descriptive sense and through the physics that govern the circulation state. The basic tool is a series of ocean circulation models. Depending on the model, different techniques will be applied to incorporate the RA data.

  9. Topographic Effects On Wind Driven Oceanic Circulation

    NASA Astrophysics Data System (ADS)

    Bigorre, S.; Dewar, W. K.

    A large scale oceanic anticyclone has been recently observed above the Zapiola Drift in the Argentine Basin. Its transports are comparable to those of the Gulf Stream. Its proximity to the Malvinas-Brazil current confluence render it potentially important to several aspects of the South Atlantic oceanic climate. A conceptual multilayer turbu- lent quasigeostrophic model simulated a comparable anticyclonic circulation in the presence of an isolated topography. The model is able to generate an upslope eddy mass flux, in agreement with downgradient eddy potential vorticity diffusion. Maps of EKE are consistent with the eddy kinetic energy minimum observed by TOPEX above the Zapiola Drift. This paper investigates the time dependent dynamics of the flow, from a 150 years long simulation. Compared to the flat bottom case, the spectrum over the bump is redder, a multi-year (7 years) band is energized, and the mesoscale band is comparatively suppressed. The presence of the 7 years oscillation is variable and connected to an apparent tendency for the flow regime to switch between 'sta- ble' and 'unstable' states. During unstable periods, the phenomenology of the oscil- lation consists of the slow development of a large potential vorticity anomaly above the seamount driven by surface Ekman pumping. This is followed by a rapid ejection phase. In stable regimes, the potential vorticity anomaly can persist for longer peri- ods and is accompanied by a stronger eddy variability. Eddy potential vorticity fluxes show that relative vorticity flux, caused by vortex tube stretching along the slope of the seamount is dominant. A low order relaxation oscillator model has successfully reproduced the results of the turbulent numerical model.

  10. Slow and Steady: Ocean Circulation. The Influence of Sea Surface Height on Ocean Currents

    NASA Technical Reports Server (NTRS)

    Haekkinen, Sirpa

    2000-01-01

    The study of ocean circulation is vital to understanding how our climate works. The movement of the ocean is closely linked to the progression of atmospheric motion. Winds close to sea level add momentum to ocean surface currents. At the same time, heat that is stored and transported by the ocean warms the atmosphere above and alters air pressure distribution. Therefore, any attempt to model climate variation accurately must include reliable calculations of ocean circulation. Unlike movement of the atmosphere, movement of the ocean's waters takes place mostly near the surface. The major patterns of surface circulation form gigantic circular cells known as gyres. They are categorized according to their general location-equatorial, subtropical, subpolar, and polar-and may run across an entire ocean. The smaller-scale cell of ocean circulation is known' as an eddy. Eddies are much more common than gyres and much more difficult to track in computer simulations of ocean currents.

  11. The Atlantic Multidecadal Oscillation without a role for ocean circulation.

    PubMed

    Clement, Amy; Bellomo, Katinka; Murphy, Lisa N; Cane, Mark A; Mauritsen, Thorsten; Rädel, Gaby; Stevens, Bjorn

    2015-10-16

    The Atlantic Multidecadal Oscillation (AMO) is a major mode of climate variability with important societal impacts. Most previous explanations identify the driver of the AMO as the ocean circulation, specifically the Atlantic Meridional Overturning Circulation (AMOC). Here we show that the main features of the observed AMO are reproduced in models where the ocean heat transport is prescribed and thus cannot be the driver. Allowing the ocean circulation to interact with the atmosphere does not significantly alter the characteristics of the AMO in the current generation of climate models. These results suggest that the AMO is the response to stochastic forcing from the mid-latitude atmospheric circulation, with thermal coupling playing a role in the tropics. In this view, the AMOC and other ocean circulation changes would be largely a response to, not a cause of, the AMO. PMID:26472908

  12. The Ocean`s Thermohaline Circulation in a Fish Tank

    NASA Astrophysics Data System (ADS)

    Lavender, K.; Joyce, P.; Graziano, L.; Harris, S.; Jaroslow, G.; Lea, C.; Schell, J.; Witting, J.

    2005-12-01

    This demonstration develops intuition about density stratification, a concept critical to understanding the ocean`s thermohaline circulation. In addition, students learn how temperature and salinity affect density, how these characteristics may be density-compensating, and students gain practice in graphing and interpreting vertical profiles and temperature-salinity (T-S) diagrams. The demonstration requires a rectangular fish tank (5-10 gallons) with a plexiglass partition, preparation of three colored ''water masses'' representing surface water (warm and fresh), ''mystery'' Mediterranean Water (warm and salty), and North Atlantic Deep Water (NADW; cold and salty), a kitchen sponge, and a temperature and salinity probe. Density may be computed using an Equation of State calculator (e.g. online version at http://fermi.jhuapl.edu/denscalc.html). The larger side of the fish tank is filled halfway with NADW, then surface water is layered on top by carefully pouring it on a floating sponge. A student volunteer measures the temperature and salinity of the two water masses, while another computes the densities. Students draw vertical profiles and T-S diagrams representing the temperature, salinity, and density of the water column. The properties of the ''mystery'' water are measured and students predict what will happen when the water is poured on the opposite side of the partition and is allowed to overflow into the layered water. If the density gradients are sufficiently large, a beautiful internal wave develops as the mystery water overflows the sill and becomes intermediate Mediterranean Water. If time permits, having a student blow on the surface illustrates the limited influence of ''wind'' with depth; an internal wave may by forced by depressing the thermocline with a large, flat spoon; and pouring extra NADW on the sponge floating at the surface may illustrate deep convection.

  13. Acoustic Studies of the Large Scale Ocean Circulation

    NASA Technical Reports Server (NTRS)

    Menemenlis, Dimitris

    1999-01-01

    Detailed knowledge of ocean circulation and its transport properties is prerequisite to an understanding of the earth's climate and of important biological and chemical cycles. Results from two recent experiments, THETIS-2 in the Western Mediterranean and ATOC in the North Pacific, illustrate the use of ocean acoustic tomography for studies of the large scale circulation. The attraction of acoustic tomography is its ability to sample and average the large-scale oceanic thermal structure, synoptically, along several sections, and at regular intervals. In both studies, the acoustic data are compared to, and then combined with, general circulation models, meteorological analyses, satellite altimetry, and direct measurements from ships. Both studies provide complete regional descriptions of the time-evolving, three-dimensional, large scale circulation, albeit with large uncertainties. The studies raise serious issues about existing ocean observing capability and provide guidelines for future efforts.

  14. Strong coupling among Antarctic ice shelves, ocean circulation and sea ice in a global sea-ice - ocean circulation model

    NASA Astrophysics Data System (ADS)

    Sergienko, Olga

    2016-04-01

    The thermodynamic effects of Antarctic ice shelf interaction with ocean circulation are investigated using a global, high-resolution, isopycnal ocean-circulation model coupled to a sea-ice model. The model uses NASA MERRA Reanalysis from 1992 to 2011 as atmospheric forcing. The simulated long-period variability of ice-shelf melting/freezing rates differ across geographic locations. The ice shelves in Antarctic Peninsula, Amundsen and Bellingshausen sea embayments and the Amery Ice Shelf experience an increase in melting starting from 2005. This increase in melting is due to an increase in the subsurface (100-500 m) ocean heat content in the embayments of these ice shelves, which is caused by an increase in sea-ice concentration after 2005, and consequent reduction of the heat loss to the atmosphere. Our simulations provide a strong evidence for a coupling between ocean circulation, sea ice and ice shelves.

  15. Currents connecting communities: nearshore community similarity and ocean circulation.

    PubMed

    Watson, J R; Hays, C G; Raimondi, P T; Mitarai, S; Dong, C; McWilliams, J C; Blanchette, C A; Caselle, J E; Siegel, D A

    2011-06-01

    Understanding the mechanisms that create spatial heterogeneity in species distributions is fundamental to ecology. For nearshore marine systems, most species have a pelagic larval stage where dispersal is strongly influenced by patterns of ocean circulation. Concomitantly, nearshore habitats and the local environment are also influenced by ocean circulation. Because of the shared dependence on the seascape, distinguishing the relative importance of the local environment from regional patterns of dispersal for community structure remains a challenge. Here, we quantify the "oceanographic distance" and "oceanographic asymmetry" between nearshore sites using ocean circulation modeling results. These novel metrics quantify spatial separation based on realistic patterns of ocean circulation, and we explore their explanatory power for intertidal and subtidal community similarity in the Southern California Bight. We find that these metrics show significant correspondence with patterns of community similarity and that their combined explanatory power exceeds that of the thermal structure of the domain. Our approach identifies the unique influence of ocean circulation on community structure and provides evidence for oceanographically mediated dispersal limitation in nearshore marine communities. PMID:21797147

  16. EXPLORING THE FEEDBACKS BETWEEN CRETACEOUS OCEAN CIRCULATION, OCEANIC REDOX DYNAMICS AND SEDIMENT DIAGENESIS

    NASA Astrophysics Data System (ADS)

    Arndt, S.; Godderis, Y.; Donnadieu, Y.; Regnier, P.

    2009-12-01

    The Mid-Cretaceous oceanic anoxic events (OAEs) are witnesses of major perturbations of the Earth climate, which resulted from important changes in structure of the ocean-atmosphere system and its biogeochemical functioning. They are globally well documented by the ubiquitous presence of organic carbon-rich black shale layers. However, the exact nature and functioning of the palaeo-environment that fostered the massive and almost ubiquitous deposition of organic carbon-rich sediments is still a matter of debate. Numerous outstanding questions remain, not only concerning the dependence of black shale deposition on ocean circulation and redox zonation, but also its influence on the global ocean-atmosphere system. A new version of the coupled Earth system model GEOCLIM, which combines a climate model (FOAM 3-D GCM) with a vertically resolved diffusion-advection box model of the global ocean, a pelagic biogeochemical model and a fully formulated diagenetic model (BNRS) is used to examine the feedbacks between paleocirculation, ocean redox dynamics, sediment diagenesis and global climate. Different scenarios are designed to assess the influence of the global circulation on the biogeochemical functioning of the ocean during a mid-Cretaceous OAE. Simulation results illustrate the strong feedbacks between Cretaceous ocean circulation, oceanic geochemical dynamics, bioproductivity and sediment diagenesis. A weakening of the deep ocean ventilation increases the importance of diagenetic processes on the geochemical characteristics of the ocean. Ocean anoxia/euxinia can easily develop if the sedimentary nutrient recycling is high enough to sustain enhanced primary production. Thus, the earth system model provides a rational support for a detailed quantitative understanding of the ocean's biogeochemical response to potential circulation changes during a mid-Cretaceous OAE. It helps identify plausible scenarios for black shale deposition which are compared with simulation

  17. The buoyancy-driven ocean circulation with realistic bathymetry

    NASA Astrophysics Data System (ADS)

    Gjermundsen, Ada; LaCasce, Joseph H.; Denstad, Liv

    2015-04-01

    In contrast to the wind-driven ocean circulation, where the concept of a Sverdrup interior and western boundary currents is generally accepted, we lack a simple dynamical framework for rationalizing the buoyancy-driven circulation. Thus most of our intuition is based on numerical solutions, primarily in idealized basins (e.g. Huck et al., 1999; Park and Bryan, 2001). Here we examine numerical solutions of the global circulation with realistic bathymetry, driven solely by surface buoyancy forcing. Explicit wind forcing is excluded, although vertical mixing is retained. The model (the MITgcm) is run with a hybrid resolution scheme, to capture approximately the variation of the deformation radius. The character of the resulting flow is consistent in many ways with the observed ocean circulation. There is inflow to and sinking in the Nordic Seas, baroclinic western boundary currents and an overturning streamfunction which closely resembles those obtained in full GCMs and in observations. Furthermore, the solutions share many features with solutions obtained with a linear analytical model (Pedlosky, 1969; LaCasce, 2004), suggesting the latter may be conceptually useful, despite lacking bathymetry. We discuss these points, as well as implications for the climate system in general. References: Pedlosky, J. (1969). Linear theory of the circulation of a stratified ocean. Journal of Fluid Mechanics, 35, 185-205. Huck, T., A. J. Weaver and A. Colin de Verdière (1999). On the influence of the parameterization of lateral boundary layers on the thermohaline circulation in coarse-resolution ocean models. Journal of Marine Research, 57(3), 387-426. Park, Y. G. and K. Bryan (2001). Comparison of thermally driven circulations from a depth-coordinate model and an isopycnal-layer model. Part II: The difference and structure of the circulations. Journal of Physical Oceanography, 31(9), 2612-2624. LaCasce, J. H. (2004). Diffusivity and viscosity dependence in the linear thermocline

  18. A fully-implicit model of the global ocean circulation

    NASA Astrophysics Data System (ADS)

    Weijer, Wilbert; Dijkstra, Henk A.; Öksüzoğlu, Hakan; Wubs, Fred W.; de Niet, Arie C.

    2003-12-01

    With the recent developments in the solution methods for large-dimensional nonlinear algebraic systems, fully-implicit ocean circulation models are now becoming feasible. In this paper, the formulation of such a three-dimensional global ocean model is presented. With this implicit model, the sensitivity of steady states to parameters can be investigated efficiently using continuation methods. In addition, the implicit formulation allows for much larger time steps than can be used with explicit models. To demonstrate current capabilities of the implicit global ocean model, we use a relatively low-resolution (4° horizontally and 12 levels vertically) version. For this configuration, we present: (i) an explicit calculation of the bifurcation diagram associated with hysteresis behavior of the ocean circulation and (ii) the scaling behavior of the Atlantic meridional overturning versus the magnitude of the vertical mixing coefficient of heat and salt.

  19. Adaptation of a general circulation model to ocean dynamics

    NASA Technical Reports Server (NTRS)

    Turner, R. E.; Rees, T. H.; Woodbury, G. E.

    1976-01-01

    A primitive-variable general circulation model of the ocean was formulated in which fast external gravity waves are suppressed with rigid-lid surface constraint pressires which also provide a means for simulating the effects of large-scale free-surface topography. The surface pressure method is simpler to apply than the conventional stream function models, and the resulting model can be applied to both global ocean and limited region situations. Strengths and weaknesses of the model are also presented.

  20. Evaluating the deep-ocean circulation of a global ocean model using carbon isotopic ratios

    NASA Astrophysics Data System (ADS)

    Paul, André; Dutkiewicz, Stephanie; Gebbie, Jake; Losch, Martin; Marchal, Olivier

    2016-04-01

    We study the sensitivity of a global three-dimensional biotic ocean carbon-cycle model to the parameterizations of gas exchange and biological productivity as well as to deep-ocean circulation strength, and we employ the carbon isotopic ratios δ13C and Δ14C of dissolved inorganic carbon for a systematic evaluation against observations. Radiocarbon (Δ14C) in particular offers the means to assess the model skill on a time scale of 100 to 1000 years relevant to the deep-ocean circulation. The carbon isotope ratios are included as tracers in the MIT general circulation model (MITgcm). The implementation involves the fractionation processes during photosynthesis and air-sea gas exchange. We present the results of sixteen simulations combining two different parameterizations of the piston velocity, two different parameterizations of biological productivity (including the effect of iron fertilization) and four different overturning rates. These simulations were first spun up to equilibrium (more than 10,000 years of model simulation) and then continued from AD 1765 to AD 2002. For the model evaluation, we followed the OCMIP-2 (Ocean Carbon-Cycle Model Intercomparision Project phase two) protocol, comparing the results to GEOSECS (Geochemical Ocean Sections Survey) and WOCE (World Ocean Circulation Experiment) δ13C and natural Δ14C data in the world ocean. The range of deep natural Δ14C (below 1000 m) for our single model (MITgcm) was smaller than for the group of different OCMIP-2 models. Furthermore, differences between different model parameterizations were smaller than for different overturning rates. We conclude that carbon isotope ratios are a useful tool to evaluate the deep-ocean circulation. Since they are also available from deep-sea sediment records, we postulate that the simulation of carbon isotope ratios in a global ocean model will aid in estimating the deep-ocean circulation and climate during present and past.

  1. 14C-age tracers in global ocean circulation models

    NASA Astrophysics Data System (ADS)

    Koeve, W.; Wagner, H.; Kähler, P.; Oschlies, A.

    2015-07-01

    The natural abundance of 14C in total CO2 dissolved in seawater (DIC) is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, which is the time elapsed since a body of water has been in contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with ageing, i.e. the time component of circulation, and one associated with a "preformed 14C-age". The latter quantity exists because of the slow and incomplete atmosphere-ocean equilibration of 14C particularly in high latitudes where many water masses form. In the ocean's interior, preformed 14C-age behaves like a passive tracer. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. Here, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age. Between models, the variability of preformed 14C-age can also be considerable (factor of 2), related to the combination of physical model parameters, which influence circulation dynamics or gas exchange. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation, the choice of the gas-exchange constant from within the currently accepted range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age, it could easily impair the evaluation and tuning of a model's circulation on global and regional

  2. Exploring the feedbacks between Cretaceous ocean circulation, oceanic redox dynamics and sediment diagenesis

    NASA Astrophysics Data System (ADS)

    Arndt, Sandra; Regnier, Pierre; Donnadieu, Yannick; Godderis, Yves

    2010-05-01

    The Mid-Cretaceous oceanic anoxic events (OAEs) are witnesses of major perturbations of the Earth climate, which resulted from important changes in structure of the ocean-atmosphere system and its biogeochemical functioning. They are globally well documented by the ubiquitous presence of organic carbon-rich black shale layers. However, the exact nature and functioning of the palaeo-environment that fostered the massive and almost ubiquitous deposition of organic carbon-rich sediments is still a matter of debate. Numerous outstanding questions remain, not only concerning the dependence of black shale deposition on ocean circulation and redox zonation, but also its influence on the global ocean-atmosphere system. A new version of the coupled Earth system model GEOCLIM, which combines a climate model (FOAM 3-D GCM) with a vertically resolved diffusion-advection box model of the global ocean, a pelagic biogeochemical model and a fully formulated diagenetic model (BNRS) is used to examine the feedbacks between paleocirculation, ocean redox dynamics, sediment diagenesis and global climate. Different scenarios are designed to assess the influence of the global circulation on the biogeochemical functioning of the ocean during a mid-Cretaceous OAE. Simulation results illustrate the strong feedbacks between Cretaceous ocean circulation, oceanic geochemical dynamics, bioproductivity and sediment diagenesis. A weakening of the deep ocean ventilation increases the importance of diagenetic processes on the geochemical characteristics of the ocean. Ocean anoxia/euxinia can easily develop if the sedimentary nutrient recycling is high enough to sustain enhanced primary production. Thus, the earth system model provides a rational support for a detailed quantitative understanding of the ocean's biogeochemical response to potential circulation changes during a mid-Cretaceous OAE.

  3. Upper-level circulation in the South Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Peterson, Ray G.; Stramma, Lothar

    In this paper we present a literature survey of the South Atlantic's climate and its oceanic upper-layer circulation and meridional heat transport. The opening section deals with climate and is focused upon those elements having greatest oceanic relevance, i.e., distributions of atmospheric sea level pressure, the wind fields they produce, and the net surface energy fluxes. The various geostrophic currents comprising the upper-level general circulation are then reviewed in a manner organized around the subtropical gyre, beginning off southern Africa with the Agulhas Current Retroflection and then progressing to the Benguela Current, the equatorial current system and circulation in the Angola Basin, the large-scale variability adn interannual warmings at low latitudes, the Brazil Current, the South Atlantic Current, and finally to the Antarctic Circumpolar Current system in which the Falkland (Malvinas) Current is included. A summary of estimates of the meridional heat transport at various latitudes in the South Atlantic ends the survey.

  4. Atlantic Meridional Overturning Circulation slowdown cooled the subtropical ocean

    NASA Astrophysics Data System (ADS)

    Cunningham, Stuart A.; Roberts, Christopher D.; Frajka-Williams, Eleanor; Johns, William E.; Hobbs, Will; Palmer, Matthew D.; Rayner, Darren; Smeed, David A.; McCarthy, Gerard

    2013-12-01

    show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011. We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N. This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures. Here we connect, for the first time, variability in the northward heat transport carried by the Atlantic Meridional Overturning Circulation to widespread sustained cooling of the subtropical North Atlantic, challenging the prevailing view that the ocean plays a passive role in the coupled ocean-atmosphere system on monthly-to-seasonal timescales.

  5. Biogeochemical Proxies in Scleractinian Corals used to Reconstruct Ocean Circulation

    SciTech Connect

    Guilderson, T P; Kashgarian, M; Schrag, D P

    2001-02-23

    We utilize monthly {sup 14}C data derived from coral archives in conjunction with ocean circulation models to address two questions: (1) how does the shallow circulation of the tropical Pacific vary on seasonal to decadal time scales and (2) which dynamic processes determine the mean vertical structure of the equatorial Pacific thermocline. Our results directly impact the understanding of global climate events such as the El Nino-Southern Oscillation (ENSO). To study changes in ocean circulation and water mass distribution involved in the genesis and evolution of ENSO and decadal climate variability, it is necessary to have records of climate variables several decades in length. Continuous instrumental records are limited because technology for continuous monitoring of ocean currents has only recently been available, and ships of opportunity archives such as COADS contain large spatial and temporal biases. In addition, temperature and salinity in surface waters are not conservative and thus can not be independently relied upon to trace water masses, reducing the utility of historical observations. Radiocarbon ({sup 14}C) in sea water is a quasi-conservative water mass tracer and is incorporated into coral skeletal material, thus coral {sup 14}C records can be used to reconstruct changes in shallow circulation that would be difficult to characterize using instrumental data. High resolution {Delta}{sup 14}C timeseries such as these, provide a powerful constraint on the rate of surface ocean mixing and hold great promise to augment onetime surveys such as GEOSECS and WOCE. These data not only provide fundamental information about the shallow circulation of the Pacific, but can be used as a benchmark for the next generation of high resolution ocean models used in prognosticating climate change.

  6. Protactinium-thorium ratio as a proxy for ocean circulation

    NASA Astrophysics Data System (ADS)

    Balcerak, Ernie

    2011-12-01

    The Atlantic meridional overturning circulation (AMOC) transports water and heat over long distances in the Atlantic Ocean and is believed to have an important effect on Earth's climate. Knowing how strong the AMOC was in the past is essential to understanding past climate. One proxy researchers have used to assess the past strength of the AMOC is the sedimentary protactinium- thorium ratio (231Pa/230Th). Both 231Pa and 230Th are produced through decay of uranium at a constant rate in the ocean water column, but 230Th does not last long enough in the water to be transported away from the location where it was produced, while 231Pa has a longer residence time in the water. Therefore, sedimentary 231Pa/230Th ratios could provide information about the strength of past ocean circulation.

  7. The impact of oceanic heat transport on the atmospheric circulation

    NASA Astrophysics Data System (ADS)

    Knietzsch, M.-A.; Schröder, A.; Lucarini, V.; Lunkeit, F.

    2015-09-01

    A general circulation model of intermediate complexity with an idealized Earth-like aquaplanet setup is used to study the impact of changes in the oceanic heat transport on the global atmospheric circulation. Focus is on the atmospheric mean meridional circulation and global thermodynamic properties. The atmosphere counterbalances to a large extent the imposed changes in the oceanic heat transport, but, nonetheless, significant modifications to the atmospheric general circulation are found. Increasing the strength of the oceanic heat transport up to 2.5 PW leads to an increase in the global mean near-surface temperature and to a decrease in its equator-to-pole gradient. For stronger transports, the gradient is reduced further, but the global mean remains approximately constant. This is linked to a cooling and a reversal of the temperature gradient in the tropics. Additionally, a stronger oceanic heat transport leads to a decline in the intensity and a poleward shift of the maxima of both the Hadley and Ferrel cells. Changes in zonal mean diabatic heating and friction impact the properties of the Hadley cell, while the behavior of the Ferrel cell is mostly controlled by friction. The efficiency of the climate machine, the intensity of the Lorenz energy cycle and the material entropy production of the system decline with increased oceanic heat transport. This suggests that the climate system becomes less efficient and turns into a state of reduced entropy production as the enhanced oceanic transport performs a stronger large-scale mixing between geophysical fluids with different temperatures, thus reducing the available energy in the climate system and bringing it closer to a state of thermal equilibrium.

  8. 14C-age tracers in global ocean circulation models

    NASA Astrophysics Data System (ADS)

    Koeve, W.; Wagner, H.; Kähler, P.; Oschlies, A.

    2014-10-01

    The natural abundance of 14C in total CO2 dissolved in seawater is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, the time elapsed since a body of water had contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with aging, i.e. the time component of circulation and one associated with a "preformed 14C-age". This latter quantity exists because of the slow and incomplete atmosphere/ocean equilibration of 14C in particular in high latitudes where many water masses form. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability, e.g. in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. In the Atlantic, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age alone. Between models the variability of age can also be considerable (factor of 2), related to the combinations of physical model parameters, which influence circulation dynamics, and gas exchange in the models. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation exercise, the choice of the gas exchange constant from within the current range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age it could easily impair the evaluation and tuning of a models circulation on global and regional scales. Based on the results of this study, we propose that considering

  9. An integrated modeling study of ocean circulation, the ocean carbon cycle, marine ecosystems, and climate change

    NASA Astrophysics Data System (ADS)

    Cao, Long

    The unifying theme of this study is to conduct an extensive exploration of various interactions between ocean circulation, the carbon cycle, marine ecosystems, and climate change using an earth system model of intermediate complexity, ISAM-2.5D (Integrated Science Assessment Model). First, through the simulation of radiocarbon (in terms of Delta14C) it is demonstrated that the inclusion of isopycnal diffusion and a parameterization of eddy-induced circulation in the ISAM-2.5D model yields the most realistic representation of ocean mixing and circulation. Secondly, I demonstrate the value of the simulation of multiple tracers, combined with a variety of observational data, in constraining the ISAM-2.5D model that has been constrained by the simulation of Delta14C. Through the simulation of ocean biogeochemical cycles and CFC-11 and the use of the updated observational data of bomb radiocarbon, I improve the Delta14C-constrained ISAM-2.5D model's performance in simulating ocean circulation and air-sea gas exchange, as well as its credibility in predicting oceanic carbon uptake. Third, I use the ISAM-2.5D model to assess the efficiency of direct carbon injection into the deep ocean with the influence of climate change. It is shown that the consideration of climate change enhances the retention time of injected carbon into the Atlantic Ocean as a result of weakened North Atlantic overturning circulation in a warming climate. However, the climatic effect is insignificant on the efficiency of carbon injection into the Pacific and Indian Oceans. Finally, I quantify that increased atmospheric CO2 concentrations would be mainly responsible for future ocean acidification, including lowering in ocean pH and sea water saturation state with respect to carbonate minerals. The consideration of climate change produces a second-order modification to projected ocean acidification. Therefore, in addition to its radiative effects on climate change, increased atmospheric CO2

  10. Circulation of Antarctic intermediate water in the South Indian Ocean

    NASA Astrophysics Data System (ADS)

    Fine, Rana A.

    1993-10-01

    Chlorofluorocarbon (CFC) and hydrographic data collected on the R.R.S. Charles Darwin Cruise 29 along 32°S during November-December 1987, are used to examine the circulation in the South Indian Ocean. The emphasis is on Antarctic Intermediate Water (AAIW); bottom waters and mode waters are also examined. Bottom waters entering in the western boundary of the Crozet Basin (about 60°E) and in the Mozambique Basin (about 40°E) have low concentrations of anthropogenic CFCs. The rest of the bottom and deep waters up to about 2000 m have concentrations that are below blank levels. Above the intermediate waters there are injections of mode waters, which are progressively denser in the eastward direction. They form a broad subsurface CFC maximum between 200 and 400 m. The injections of recently ventilated (with respect to CFCs and oxygen) Subantarctic Mode Waters (SAMWs) at different densities indicate that there is considerable exchange between the subtropical and subantarctic regions. The tracer data presented show that the circulation of AAIW in the South Indian Ocean is different from that in the South Atlantic and South Pacific oceans in several ways. (1) The most recently ventilated AAIW is observed in a compact anticyclonic gyre west of 72°E. The shallow topography (e.g. that extending northeastward from the Kerguelen Plateau) may deflect and limit the eastward extent of the most recently ventilated AAIW. As a consequence, there is a zonal offset in the South Indian Ocean of the location of the most recently ventilated SAMW and AAIW, which does not occur in the other two oceans. The strongest component of SAMW is in the east, while the AAIW is strongest in the western-central South Indian Ocean. The offset results in a higher vertical gradient in CFCs in the east. (2) The Agulhas Current may impede input of AAIW along the western boundary. (3) Tracers are consistent with an inter-ocean flow from the South Pacific into the Eastern Indian Ocean, similar to the

  11. The Seasonal Variability of the South Indian Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Matano, R. P.; Beier, E. J.; Strub, P. T.

    2006-07-01

    This article compares the seasonal variability patterns of the South Indian Ocean circulation derived from a global, eddy-permitting, numerical model and altimeter observations. The seasonal variability of the Indian Ocean circulation is driven by the inflow from the Indonesian Passages and by the local wind forcing. Our analysis indicates that the influence of the Indonesian throughflow is confined to the easternmost portion of the basin, while the influence of the wind stress forcing is important everywhere. Model and observations indicates that, between ~105°E and 75°E, the seasonal variability is characterized by the southwestward propagation of an annual wave in a lapse of ~4 months. Preliminary calculations using Pathfinder data also indicates that, in the western region, there are seasonal perturbations that originates in the tropics and propagates poleward through the Mozambique Channel.

  12. Reconstructing Ocean Circulation using Coral (triangle)14C Time Series

    SciTech Connect

    Kashgarian, M; Guilderson, T P

    2001-02-23

    We utilize monthly {sup 14}C data derived from coral archives in conjunction with ocean circulation models to address two questions: (1) how does the shallow circulation of the tropical Pacific vary on seasonal to decadal time scales and (2) which dynamic processes determine the mean vertical structure of the equatorial Pacific thermocline. Our results directly impact the understanding of global climate events such as the El Nino-Southern Oscillation (ENSO). To study changes in ocean circulation and water mass distribution involved in the genesis and evolution of ENSO and decadal climate variability, it is necessary to have records of climate variables several decades in length. Continuous instrumental records are limited because technology for continuous monitoring of ocean currents (e.g. satellites and moored arrays) has only recently been available, and ships of opportunity archives such as COADS contain large spatial and temporal biases. In addition, temperature and salinity in surface waters are not conservative and thus can not be independently relied upon to trace water masses, reducing the utility of historical observations. Radiocarbon in sea water is a quasi-conservative water mass tracer and is incorporated into coral skeletal material, thus coral {sup 14}C records can be used to reconstruct changes in shallow circulation that would be difficult to characterize using instrumental data. High resolution {Delta}{sup 14}C timeseries such as ours, provide a powerful constraint on the rate of surface ocean mixing and hold great promise to augment one time oceanographic surveys. {Delta}{sup 14}C timeseries such as these, not only provide fundamental information about the shallow circulation of the Pacific, but can also be directly used as a benchmark for the next generation of high resolution ocean models used in prognosticating climate. The measurement of {Delta}{sup 14}C in biological archives such as tree rings and coral growth bands is a direct record of

  13. Barotropic-baroclinic time splitting for ocean circulation modeling

    SciTech Connect

    Higdon, R.L.; Szoeke, R.A. de

    1997-07-15

    This paper discusses the following topics on oceanic circulation modeling: time splitting in context of the nonlinear primitive equations; analysis of the stability of this splitting when applied to a linearized flow in two-layer fluid with one horizontal dimensions and a flat lower boundary; analysis of this splitting for horizontal dimensions in a rotating reference frame with constant coriolis parameters; and then numerical tests of the new splitting are discussed.

  14. Numerical simulation and prediction of coastal ocean circulation

    SciTech Connect

    Chen, P.

    1992-01-01

    Numerical simulation and prediction of coastal ocean circulation have been conducted in three cases. 1. A process-oriented modeling study is conducted to study the interaction of a western boundary current (WBC) with coastal water, and its responses to upstream topographic irregularities. It is hypothesized that the interaction of propagating WBC frontal waves and topographic Rossby waves are responsible for upstream variability. 2. A simulation of meanders and eddies in the Norwegian Coastal Current (NCC) for February and March of 1988 is conducted with a newly developed nested dynamic interactive model. The model employs a coarse-grid, large domain to account for non-local forcing and a fine-grid nested domain to resolve meanders and eddies. The model is forced by wind stresses, heat fluxes and atmospheric pressure corresponding Feb/March of 1988, and accounts for river/fjord discharges, open ocean inflow and outflow, and M[sub 2] tides. The simulation reproduced fairly well the observed circulation, tides, and salinity features in the North Sea, Norwegian Trench and NCC region in the large domain and fairly realistic meanders and eddies in the NCC in the nested region. 3. A methodology for practical coastal ocean hindcast/forecast is developed, taking advantage of the disparate time scales of various forcing and considering wind to be the dominant factor in affecting density fluctuation in the time scale of 1 to 10 days. The density field obtained from a prognostic simulation is analyzed by the empirical orthogonal function method (EOF), and correlated with the wind; these information are then used to drive a circulation model which excludes the density calculation. The method is applied to hindcast the circulation in the New York Bight for spring and summer season of 1988. The hindcast fields compare favorably with the results obtained from the prognostic circulation model.

  15. Ocean Surface Circulation with Implication for Marine Debris Distribution

    NASA Astrophysics Data System (ADS)

    Hafner, Jan; Maximenko, Nikolai; Niiler, Peter

    2010-05-01

    Modern, multi-instrumental Global Ocean Observing System (GOOS) includes satellites and in situ observations, monitoring the ocean state at the highest accuracy and resolution ever. By combining data of satellite altimetry, surface drifters, wind and gravity, ocean currents can be assessed globally and at research quality. The map of the mean surface currents shows a complex pattern of oceanic fronts and gyres. Distinct are the convergences of Ekman currents in subtropical gyres that, through the Sverdrup mechanism, are feeding anticyclonic circulation in the gyres. Drifter trajectories can also be utilized to simulate the evolution of the marine debris. Main problem is the inhomogeneous drifter data density, both due to convergence/divergence of the ocean currents and due to the drifter deployment scheme. A model constructed from statistics of the drifters exchange between small bins corrects this bias and was run from the uniform initial condition to study the fate of debris in the ocean. In addition to such actively studied debris accumulation areas as the Great Garbage Patch in the North Pacific, a new so far unrecognized, the world-strongest convergence is discovered in the South Pacific from the model solution. The same model reveals a complex pattern of convergence/divergence on the cold/warm flanks of major oceanic fronts. This pattern is studied in the framework of nonlinear interaction between Ekman drift and geostrophic baroclinic fronts outcropping at the sea surface. Results are generalized to assess the dynamics of internal Ekman layer distributed along the thermocline and controlling the secondary circulation at the fronts.

  16. Testing Components of New Community Isopycnal Ocean Circulation Model

    SciTech Connect

    Bryan, Kirk

    2008-05-09

    The ocean and atmosphere are both governed by the same physical laws and models of the two media have many similarities. However, there are critical differences that call for special methods to provide the best simulation. One of the most important difference is that the ocean is nearly opaque to radiation in the visible and infra-red part of the spectrum. For this reason water mass properties in the ocean are conserved along trajectories for long distances and for long periods of time. For this reason isopycnal coordinate models would seem to have a distinct advantage in simulating ocean circulation. In such a model the coordinate surfaces are aligned with the natural paths of near adiabatic, density conserving flow in the main thermocline. The difficulty with this approach is at the upper and lower boundaries of the ocean, which in general do not coincide with density surfaces. For this reason hybrid coordinate models were proposed by Bleck and Boudra (1981) in which Cartesian coordinates were used near the ocean surface and isopycnal coordinates were used in the main thermocline. This feature is now part of the HICOM model (Bleck, 2002).

  17. (CO sub 2 uptake in an Ocean Circulation Model)

    SciTech Connect

    Siegenthaler, U.C.

    1990-11-06

    The traveler collaborated with Drs. J. L. Sarmiento and J. C. Orr of the Program in Atmospheric Sciences at Princeton University to finish the article A Perturbation Simulation of CO{sub 2} Uptake in an Ocean Circulation Model,'' which has been submitted to the Journal of Geophysical Research for publication. With F. Joos, a graduate student from the University of Bern, the traveler started writing a journal article describing a box model of the global carbon cycle that is an extension of the one-dimensional box-diffusion model. The traveler further collaborated with F. Joos and Dr. J. L. Sarmiento on modeling the potential enhancement of oceanic CO{sub 2} uptake by fertilizing the southern ocean with iron. A letter describing the results is currently being written for the journal Nature.

  18. The World Ocean Circulation Experiment (WOCE): An ocean climatology for the 1990s

    SciTech Connect

    Chapman, P.; Nowlin, W.D. Jr.

    1997-11-01

    During the last ten years, scientists have made remarkable progress in predicting seasonal and interannual climate variability, based on interactions between the atmosphere and the tropical ocean. The goals of the World Ocean Circulation Experiment (WOCE) are to develop models useful for predicting climate variability on longer time scales and to collect the data from the global ocean necessary to test them. Using a variety of instrument platforms, researchers in the US and other nations have been sampling a suite of ocean variables which will be used to build up a climatology of the oceans in the 1990s and from the basis for developing both new models of ocean circulation and coupled models of the ocean and atmosphere. This paper presents some recent results from WOCE research. It includes examples of advances in the fields of sea surface temperature measurements, sea level monitoring, current velocities, upper ocean heat content, and air-sea flux measurements. In addition, we discuss some of the recent advances in modeling and the link between WOCE research and future programs such as CLIVAR, GOOS and GCOS. 27 refs., 2 tabs.

  19. Changes in North Atlantic nitrogen fixation controlled by ocean circulation.

    PubMed

    Straub, Marietta; Sigman, Daniel M; Ren, Haojia; Martínez-García, Alfredo; Meckler, A Nele; Hain, Mathis P; Haug, Gerald H

    2013-09-12

    In the ocean, the chemical forms of nitrogen that are readily available for biological use (known collectively as 'fixed' nitrogen) fuel the global phytoplankton productivity that exports carbon to the deep ocean. Accordingly, variation in the oceanic fixed nitrogen reservoir has been proposed as a cause of glacial-interglacial changes in atmospheric carbon dioxide concentration. Marine nitrogen fixation, which produces most of the ocean's fixed nitrogen, is thought to be affected by multiple factors, including ocean temperature and the availability of iron and phosphorus. Here we reconstruct changes in North Atlantic nitrogen fixation over the past 160,000 years from the shell-bound nitrogen isotope ratio ((15)N/(14)N) of planktonic foraminifera in Caribbean Sea sediments. The observed changes cannot be explained by reconstructed changes in temperature, the supply of (iron-bearing) dust or water column denitrification. We identify a strong, roughly 23,000-year cycle in nitrogen fixation and suggest that it is a response to orbitally driven changes in equatorial Atlantic upwelling, which imports 'excess' phosphorus (phosphorus in stoichiometric excess of fixed nitrogen) into the tropical North Atlantic surface. In addition, we find that nitrogen fixation was reduced during glacial stages 6 and 4, when North Atlantic Deep Water had shoaled to become glacial North Atlantic intermediate water, which isolated the Atlantic thermocline from excess phosphorus-rich mid-depth waters that today enter from the Southern Ocean. Although modern studies have yielded diverse views of the controls on nitrogen fixation, our palaeobiogeochemical data suggest that excess phosphorus is the master variable in the North Atlantic Ocean and indicate that the variations in its supply over the most recent glacial cycle were dominated by the response of regional ocean circulation to the orbital cycles. PMID:23965620

  20. OCEAN CIRCULATION. Observing the Atlantic Meridional Overturning Circulation yields a decade of inevitable surprises.

    PubMed

    Srokosz, M A; Bryden, H L

    2015-06-19

    The importance of the Atlantic Meridional Overturning Circulation (AMOC) heat transport for climate is well acknowledged. Climate models predict that the AMOC will slow down under global warming, with substantial impacts, but measurements of ocean circulation have been inadequate to evaluate these predictions. Observations over the past decade have changed that situation, providing a detailed picture of variations in the AMOC. These observations reveal a surprising degree of AMOC variability in terms of the intraannual range, the amplitude and phase of the seasonal cycle, the interannual changes in strength affecting the ocean heat content, and the decline of the AMOC over the decade, both of the latter two exceeding the variations seen in climate models. PMID:26089521

  1. Atlantic Meridional Overturning Circulation slowdown cooled the subtropical ocean

    PubMed Central

    Cunningham, Stuart A; Roberts, Christopher D; Frajka-Williams, Eleanor; Johns, William E; Hobbs, Will; Palmer, Matthew D; Rayner, Darren; Smeed, David A; McCarthy, Gerard

    2013-01-01

    [1] Observations show that the upper 2 km of the subtropical North Atlantic Ocean cooled throughout 2010 and remained cold until at least December 2011. We show that these cold anomalies are partly driven by anomalous air-sea exchange during the cold winters of 2009/2010 and 2010/2011 and, more surprisingly, by extreme interannual variability in the ocean's northward heat transport at 26.5°N. This cooling driven by the ocean's meridional heat transport affects deeper layers isolated from the atmosphere on annual timescales and water that is entrained into the winter mixed layer thus lowering winter sea surface temperatures. Here we connect, for the first time, variability in the northward heat transport carried by the Atlantic Meridional Overturning Circulation to widespread sustained cooling of the subtropical North Atlantic, challenging the prevailing view that the ocean plays a passive role in the coupled ocean-atmosphere system on monthly-to-seasonal timescales. PMID:26074634

  2. Stochastic Ocean Eddy Perturbations in a Coupled General Circulation Model.

    NASA Astrophysics Data System (ADS)

    Howe, N.; Williams, P. D.; Gregory, J. M.; Smith, R. S.

    2014-12-01

    High-resolution ocean models, which are eddy permitting and resolving, require large computing resources to produce centuries worth of data. Also, some previous studies have suggested that increasing resolution does not necessarily solve the problem of unresolved scales, because it simply introduces a new set of unresolved scales. Applying stochastic parameterisations to ocean models is one solution that is expected to improve the representation of small-scale (eddy) effects without increasing run-time. Stochastic parameterisation has been shown to have an impact in atmosphere-only models and idealised ocean models, but has not previously been studied in ocean general circulation models. Here we apply simple stochastic perturbations to the ocean temperature and salinity tendencies in the low-resolution coupled climate model, FAMOUS. The stochastic perturbations are implemented according to T(t) = T(t-1) + (∆T(t) + ξ(t)), where T is temperature or salinity, ΔT is the corresponding deterministic increment in one time step, and ξ(t) is Gaussian noise. We use high-resolution HiGEM data coarse-grained to the FAMOUS grid to provide information about the magnitude and spatio-temporal correlation structure of the noise to be added to the lower resolution model. Here we present results of adding white and red noise, showing the impacts of an additive stochastic perturbation on mean climate state and variability in an AOGCM.

  3. A Pacific Ocean general circulation model for satellite data assimilation

    NASA Technical Reports Server (NTRS)

    Chao, Y.; Halpern, D.; Mechoso, C. R.

    1991-01-01

    A tropical Pacific Ocean General Circulation Model (OGCM) to be used in satellite data assimilation studies is described. The transfer of the OGCM from a CYBER-205 at NOAA's Geophysical Fluid Dynamics Laboratory to a CRAY-2 at NASA's Ames Research Center is documented. Two 3-year model integrations from identical initial conditions but performed on those two computers are compared. The model simulations are very similar to each other, as expected, but the simulations performed with the higher-precision CRAY-2 is smoother than that with the lower-precision CYBER-205. The CYBER-205 and CRAY-2 use 32 and 64-bit mantissa arithmetic, respectively. The major features of the oceanic circulation in the tropical Pacific, namely the North Equatorial Current, the North Equatorial Countercurrent, the South Equatorial Current, and the Equatorial Undercurrent, are realistically produced and their seasonal cycles are described. The OGCM provides a powerful tool for study of tropical oceans and for the assimilation of satellite altimetry data.

  4. Anisotropic Mesoscale Eddy Transport in Ocean General Circulation Models

    NASA Astrophysics Data System (ADS)

    Reckinger, S. J.; Fox-Kemper, B.; Bachman, S.; Bryan, F.; Dennis, J.; Danabasoglu, G.

    2014-12-01

    Modern climate models are limited to coarse-resolution representations of large-scale ocean circulation that rely on parameterizations for mesoscale eddies. The effects of eddies are typically introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically in general circulation models. Thus, only a single parameter, namely the eddy diffusivity, is used at each spatial and temporal location to impart the influence of mesoscale eddies on the resolved flow. However, the diffusive processes that the parameterization approximates, such as shear dispersion, potential vorticity barriers, oceanic turbulence, and instabilities, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters to three: a major diffusivity, a minor diffusivity, and the principal axis of alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the newly introduced parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces global temperature and salinity biases. These effects can be improved even further by parameterizing the anisotropic transport mechanisms in the ocean.

  5. The Southwest Pacific Ocean circulation and climate experiment (SPICE)

    NASA Astrophysics Data System (ADS)

    Ganachaud, A.; Cravatte, S.; Melet, A.; Schiller, A.; Holbrook, N. J.; Sloyan, B. M.; Widlansky, M. J.; Bowen, M.; Verron, J.; Wiles, P.; Ridgway, K.; Sutton, P.; Sprintall, J.; Steinberg, C.; Brassington, G.; Cai, W.; Davis, R.; Gasparin, F.; Gourdeau, L.; Hasegawa, T.; Kessler, W.; Maes, C.; Takahashi, K.; Richards, K. J.; Send, U.

    2014-11-01

    The Southwest Pacific Ocean Circulation and Climate Experiment (SPICE) is an international research program under the auspices of CLIVAR. The key objectives are to understand the Southwest Pacific Ocean circulation and the South Pacific Convergence Zone (SPCZ) dynamics, as well as their influence on regional and basin-scale climate patterns. South Pacific thermocline waters are transported in the westward flowing South Equatorial Current (SEC) toward Australia and Papua-New Guinea. On its way, the SEC encounters the numerous islands and straits of the Southwest Pacific and forms boundary currents and jets that eventually redistribute water to the equator and high latitudes. The transit in the Coral, Solomon, and Tasman Seas is of great importance to the climate system because changes in either the temperature or the amount of water arriving at the equator have the capability to modulate the El Niño-Southern Oscillation, while the southward transports influence the climate and biodiversity in the Tasman Sea. After 7 years of substantial in situ oceanic observational and modeling efforts, our understanding of the region has much improved. We have a refined description of the SPCZ behavior, boundary currents, pathways, and water mass transformation, including the previously undocumented Solomon Sea. The transports are large and vary substantially in a counter-intuitive way, with asymmetries and gating effects that depend on time scales. This paper provides a review of recent advancements and discusses our current knowledge gaps and important emerging research directions.

  6. A parallel coupled oceanic-atmospheric general circulation model

    SciTech Connect

    Wehner, M.F.; Bourgeois, A.J.; Eltgroth, P.G.; Duffy, P.B.; Dannevik, W.P.

    1994-12-01

    The Climate Systems Modeling group at LLNL has developed a portable coupled oceanic-atmospheric general circulation model suitable for use on a variety of massively parallel (MPP) computers of the multiple instruction, multiple data (MIMD) class. The model is composed of parallel versions of the UCLA atmospheric general circulation model, the GFDL modular ocean model (MOM) and a dynamic sea ice model based on the Hiber formulation extracted from the OPYC ocean model. The strategy to achieve parallelism is twofold. One level of parallelism is accomplished by applying two dimensional domain decomposition techniques to each of the three constituent submodels. A second level of parallelism is attained by a concurrent execution of AGCM and OGCM/sea ice components on separate sets of processors. For this functional decomposition scheme, a flux coupling module has been written to calculate the heat, moisture and momentum fluxes independent of either the AGCM or the OGCM modules. The flux coupler`s other roles are to facilitate the transfer of data between subsystem components and processors via message passing techniques and to interpolate and aggregate between the possibly incommensurate meshes.

  7. Studies of Current Circulation at Ocean Waste Disposal Sites

    NASA Technical Reports Server (NTRS)

    Klemas, V. (Principal Investigator); Davis, G.; Henry, R.

    1976-01-01

    The author has identified the following significant results. Acid waste plume was observed in LANDSAT imagery fourteen times ranging from during dump up to 54 hours after dump. Circulation processes at the waste disposal site are highly storm-dominated, with the majority of the water transport occurring during strong northeasterlies. There is a mean flow to the south along shore. This appears to be due to the fact that northeasterly winds produce stronger currents than those driven by southeasterly winds and by the thermohaline circulation. During the warm months (May through October), the ocean at the dump site stratifies with a distinct thermocline observed during all summer cruising at depths ranging from 10 to 21 m. During stratified conditions, the near-bottom currents were small. Surface currents responded to wind conditions resulting in rapid movement of surface drogues on windy days. Mid-depth drogues showed an intermediate behavior, moving more rapidly as wind velocities increased.

  8. Studies of Current Circulation at Ocean Waste Disposal Sites. [Delaware

    NASA Technical Reports Server (NTRS)

    Klemas, V. (Principal Investigator); Davis, G.; Henry, R.

    1975-01-01

    The author has identified the following significant results. Circulation processes at the acid waste disposal site are highly event-dominated, with the majority of the water transport occurring during strong northeasters. There is a mean flow to the south alongshore. This appears to be due to the fact that northeasterly winds produce stronger currents than those driven by southeasterly winds and by the thermohaline circulation. During the warm months, the ocean stratifies with warm water over cold water. A distinct thermocline was observed with expendable bathythermographs during all summer cruises at depths ranging from 10 to 21 meters. During stratified conditions, the near-bottom drogues showed very little movements. The duPont waste plume was observed in LANDSAT satellite imagery during dump up to 54 hours after dump.

  9. Volume, heat, and freshwater transports of the global ocean circulation 1993-2000, estimated from a general circulation model constrained by World Ocean Circulation Experiment (WOCE) data

    NASA Astrophysics Data System (ADS)

    Stammer, D.; Wunsch, C.; Giering, R.; Eckert, C.; Heimbach, P.; Marotzke, J.; Adcroft, A.; Hill, C. N.; Marshall, J.

    2003-01-01

    An analysis of ocean volume, heat, and freshwater transports from a fully constrained general circulation model (GCM) is described. Output from a data synthesis, or state estimation, method is used by which the model was forced to large-scale, time-varying global ocean data sets over 1993 through 2000. Time-mean horizontal transports, estimated from this fully time-dependent circulation, have converged with independent time-independent estimates from box inversions over most parts of the world ocean but especially in the southern hemisphere. However, heat transport estimates differ substantially in the North Atlantic where our estimates result in only 1/2 previous results. The models drift over the estimation period is consistent with observations from TOPEX/Poseidon in their spatial pattern, but smaller in their amplitudes by about a factor of 2. Associated temperature and salinity changes are complex, and both point toward air-sea interaction over water mass formation regions as the primary source for changes in the deep ocean. The estimated mean circulation around Australia involves a net volume transport of 11 Sv through the Indonesian Throughflow and the Mozambique Channel. In addition, we show that this flow regime exists on all timescales above 1 month, rendering the variability in the South Pacific strongly coupled to the Indian Ocean. Moreover, the dynamically consistent variations in the model show temporal variability of oceanic heat transports, heat storage, and atmospheric exchanges that are complex and with a strong dependence upon location, depth, and timescale. Our results demonstrate the great potential of an ocean state estimation system to provide a dynamical description of the time-dependent observed heat transport and heat content changes and their relation to air-sea interactions.

  10. World Ocean Circulation Experiment (WOCE) Young Investigator Workshops

    NASA Technical Reports Server (NTRS)

    Austin, Meg

    2004-01-01

    The World Ocean Circulation Experiment (WOCE) Young Investigator Workshops goals and objectives are: a) to familiarize Young Investigators with WOCE models, datasets and estimation procedures; b) to offer intensive hands-on exposure to these models ard methods; c) to build collaborations among junior scientists and more senior WOCE investigators; and finally, d) to generate ideas and projects leading to fundable WOCE synthesis projects. To achieve these goals and objectives, the Workshop will offer a mixture of tutorial lectures on numerical models and estimation procedures, advanced seminars on current WOCE synthesis activities and related projects, and the opportunity to conduct small projects which put into practice the techniques advanced in the lectures.

  11. Large-scale ocean circulation-cloud interactions reduce the pace of transient climate change

    NASA Astrophysics Data System (ADS)

    Trossman, D. S.; Palter, J. B.; Merlis, T. M.; Huang, Y.; Xia, Y.

    2016-04-01

    Changes to the large-scale oceanic circulation are thought to slow the pace of transient climate change due, in part, to their influence on radiative feedbacks. Here we evaluate the interactions between CO2-forced perturbations to the large-scale ocean circulation and the radiative cloud feedback in a climate model. Both the change of the ocean circulation and the radiative cloud feedback strongly influence the magnitude and spatial pattern of surface and ocean warming. Changes in the ocean circulation reduce the amount of transient global warming caused by the radiative cloud feedback by helping to maintain low cloud coverage in the face of global warming. The radiative cloud feedback is key in affecting atmospheric meridional heat transport changes and is the dominant radiative feedback mechanism that responds to ocean circulation change. Uncertainty in the simulated ocean circulation changes due to CO2 forcing may contribute a large share of the spread in the radiative cloud feedback among climate models.

  12. circulation of the upper layer of the south Indian Ocean

    NASA Astrophysics Data System (ADS)

    de Ruijter, Will; Lambert, Erwin; Aguiar Gonzalez, Borja

    2016-04-01

    The south IO is characterized by high variability and mesoscale eddies. After separation the East Madagascar Current forms dipoles that continue to the south-west and connect remote (eco)systems. The Mozambique Current breaks up in eddies that move southward. They connect upstream to the Indonesian Through Flow and downstream to the Agulhas system. East of Madagascar the 'South Indian Ocean Counter Current' (SICC) flows to the east into the Leeuwin Current system while submerged eddies form a return flow to the west. Hypotheses on the coherence of these flows range from local scale frontal systems to large scale connection via the subtropical super gyre. We aim to present a coherent large-scale picture of the upper south Indian Ocean circulation, the role of the eddies as connectors and drivers of vertical exchanges that may control observed large-scale phenomena like the plankton blooms east of Madagascar.

  13. Modeling the impact of polar mesocyclones on ocean circulation

    NASA Astrophysics Data System (ADS)

    Condron, Alan; Bigg, Grant R.; Renfrew, Ian A.

    2008-10-01

    Subsynoptic polar mesoscale cyclones (or mesocyclones) are underrepresented in atmospheric reanalysis data sets and are subgrid scale processes in most models used for seasonal or climate forecasting. This lack of representation, particularly over the Nordic Seas, has a significant impact on modeled ocean circulation due to a consequent underestimation of atmospheric forcing at the air-sea boundary. Using Rankine vortices and a statistically significant linear relationship between mesocyclone diameter and maximum wind speed, a novel parameterization is developed that allows the bogusing in of missing or underrepresented vortices by exploiting a satellite-derived mesocyclone database. From October 1993 to September 1995, more than 2500 cyclones known to be missing from reanalysis data over the northeast Atlantic are parameterized into the forcing fields for a global ocean-only numerical modeling experiment. A comparison of this perturbed forcing simulation to a control simulation shows enhanced surface latent and sensible heat fluxes and a dramatic increase in the cyclonic rotation of the Nordic Seas gyre by four times the average interannual variability. In response to these changes, Greenland Sea Deep Water (GSDW) formation generally increases by up to 20% in 1 month, indicating more active open ocean convection. However such enhancements are smaller than the considerable monthly variability in GSDW production. An accompanying increase in the volume transport of intermediate and deep water overflowing the Denmark Strait highlights an important coupling between short-lived, intense atmospheric activity and deep ocean circulation. The parameterization scheme has the potential to be adapted for use in coupled climate models.

  14. Global thermohaline circulation and ocean-atmosphere coupling

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoli

    1997-09-01

    A global ocean general circulation model (GCM) with idealized geometry (two basins of equal size, Marotzke and Willebrand, 1991) is coupled to an energy balance atmospheric model with nonlinear parameterizations of meridional atmospheric transports of heat and moisture. With the coupled model that prescribes the atmospheric heat and moisture transports, the North Atlantic meridional mass overturning rates at equilibrium increases as the global hydrological cycle strength increases. Furthermore, the equilibrium overturning rate is primarily controlled by the hydrological cycle of the Southern Hemisphere, whereas the Northern Hemispheric hydrological cycle has little impact. The transition of the thermohaline circulation from the conveyor belt to the southern sinking state is controlled by two factors, the hydrological cycle in Northern Hemisphere, and the ratio of hydrological cycle strengths between the Northern Hemisphere and the Southern Hemisphere. Increasing either of them destabilizes the thermohaline circulation. The large-scale dynamics of the North Atlantic overturning is mainly interhemispheric, with the bulk of the overturning rising in the Southern Hemisphere. Multiple intermediate states exist that are only quantitatively different, under very small salinity perturbations. The coupled feedbacks between the thermohaline circulation and the atmospheric heat and moisture transports are demonstrated to exist in the coupled model, and all of them are positive. In addition, it is identified that the coupled feedbacks associated with the atmospheric transports in the Southern Hemisphere are also positive. Two different flux adjustments are used in the coupled model, with one adjusting the atmospheric transports efficiencies, the other adjusting the surface fluxes. Different flux adjustments influence the coupled feedback intensities, and hence the stability of the thermohaline circulation. (Copies available exclusively from MIT Libraries, Rm. 14

  15. A new geometrical approach to Eulerian transport: an application to the ocean circulation; final report

    NASA Technical Reports Server (NTRS)

    McWilliams, J. C.; Chao, Y.

    2003-01-01

    The main objective of this work is to investigate the transport processes in the large-scale ocean circulations using the new transport theory. We focus on the mid-latitude ocean circulation, especially the Gulf Stream, because it is recognized as a most energetic ocean current and plays a crucial role in maintaining the earth's climate system.

  16. Seasonal Characteristics of Circulation in the Southeastern Tropical Indian Ocean

    NASA Astrophysics Data System (ADS)

    Qu, T.; Meyers, G.

    2004-12-01

    The circulation in the southeastern tropical Indian Ocean is studied using historical temperature and salinity data. A southward shift of the subtropical gyre at increasing depth dominates the structure of the annual mean circulation. Near the southern Indonesian coast, the westward South Equatorial Current (SEC) is at the sea surface and strongest near 10°-11°S, reflecting strong influence of the Indonesian Throughflow (ITF). In latitudes 13°-25°S the SEC is a subsurface flow and its velocity core deepens toward the south, falling below 500 m at 25°S. The Eastern Gyral Current (EGC) is a surface flow overlying the SEC, associated with the meridional gradients of near-surface temperature and salinity. The ITF supplies water to the SEC mainly in the upper 400 m, and below that depth the flow is reversed along the coast of Sumatra and Java. Monsoon-winds strongly force the annual variation in circulation. Dynamic height at the sea surface has a maximum amplitude at 10°-13°S, and the maximum at deeper levels is located further south. Annual variation is also strong in the coastal wave guides, but is mainly confined to the near-surface layer. Although the South Java Current at the sea surface is not well resolved in the present dataset, semiannual variation is markedly evident at depth and tends to extend much deeper than annual variation along the coast of Sumatra and Java.

  17. Glacial greenhouse-gas fluctuations controlled by ocean circulation changes.

    PubMed

    Schmittner, Andreas; Galbraith, Eric D

    2008-11-20

    Earth's climate and the concentrations of the atmospheric greenhouse gases carbon dioxide (CO(2)) and nitrous oxide (N(2)O) varied strongly on millennial timescales during past glacial periods. Large and rapid warming events in Greenland and the North Atlantic were followed by more gradual cooling, and are highly correlated with fluctuations of N(2)O as recorded in ice cores. Antarctic temperature variations, on the other hand, were smaller and more gradual, showed warming during the Greenland cold phase and cooling while the North Atlantic was warm, and were highly correlated with fluctuations in CO(2). Abrupt changes in the Atlantic meridional overturning circulation (AMOC) have often been invoked to explain the physical characteristics of these Dansgaard-Oeschger climate oscillations, but the mechanisms for the greenhouse-gas variations and their linkage to the AMOC have remained unclear. Here we present simulations with a coupled model of glacial climate and biogeochemical cycles, forced only with changes in the AMOC. The model simultaneously reproduces characteristic features of the Dansgaard-Oeschger temperature, as well as CO(2) and N(2)O fluctuations. Despite significant changes in the land carbon inventory, CO(2) variations on millennial timescales are dominated by slow changes in the deep ocean inventory of biologically sequestered carbon and are correlated with Antarctic temperature and Southern Ocean stratification. In contrast, N(2)O co-varies more rapidly with Greenland temperatures owing to fast adjustments of the thermocline oxygen budget. These results suggest that ocean circulation changes were the primary mechanism that drove glacial CO(2) and N(2)O fluctuations on millennial timescales. PMID:19020618

  18. Ocean water cycle: its recent amplification and impact on ocean circulation

    NASA Astrophysics Data System (ADS)

    Vinogradova, Nadya

    2016-04-01

    Oceans are the largest reservoir of the world's water supply, accounting for 97% of the Earth's water and supplying more than 75% of the evaporated and precipitated water in the global water cycle. Therefore, in order to predict the future of the global hydrological cycle, it is essential to understand the changes in its largest component, which is the flux of freshwater over the oceans. Here we examine the change in the ocean water cycle and the ocean's response to such changes that were happening during the last two decades. The analysis is based on a data-constrained ocean state estimate that synthesizes all of the information available in the surface fluxes, winds, observations of sea level, temperature, salinity, geoid, etc., as well as in the physical constraints, dynamics, and conservation statements that are embedded in the equations of the MIT general circulation model. Closeness to observations and dynamical consistency of the solution ensures a physically realistic correspondence between the atmospheric forcing and oceanic fluxes, including the ocean's response to freshwater input. The results show a robust pattern of change in the ocean water cycle in the last twenty years. The pattern of changes indicates a general tendency of drying of the subtropics, and wetting in the tropics and mid-to-high latitudes, following the "rich get richer and the poor get poorer" paradigm in many ocean regions. Using a closed property budget analysis, we then investigate the changes in the oceanic state (salinity, temperature, sea level) during the same twenty-year period. The results are discussed in terms of the origin of surface signatures, and differentiated between those that are attributed to short-term natural variability and those that result from an intensified hydrological cycle due to warming climate.

  19. Interpreting 231Pa/230Th observations and changes in ocean circulation

    NASA Astrophysics Data System (ADS)

    Tretkoff, Ernie

    2011-05-01

    Understanding past changes in ocean circulation is important, because the ocean transports heat and changes in ocean circulation can affect climate. To better understand past ocean circulation changes, some researchers have used the ratio of two isotopes, protactinium-231 (231Pa) and thorium-230 (230Th), in sediments as a proxy to infer changes in the Atlantic meridional overturning circulation (AMOC). Some studies have suggested that AMOC during the climate fluctuations of the Last Glacial Maximum (LGM; ˜21,000-18,000 years ago) and Heinrich Event 1 (H1; ˜17,000-15,000 years ago) was different from modern AMOC.

  20. Arctic Ocean circulation during the anoxic Eocene Azolla event

    NASA Astrophysics Data System (ADS)

    Speelman, Eveline; Sinninghe Damsté, Jaap; März, Christian; Brumsack, Hans; Reichart, Gert-Jan

    2010-05-01

    The Azolla interval, as encountered in Eocene sediments from the Arctic Ocean, is characterized by organic rich sediments ( 4wt% Corg). In general, high levels of organic matter may be caused by increased productivity, i.e. extensive growth of Azolla, and/or enhanced preservation of organic matter, or a combination of both. Anoxic (bottom) water conditions, expanded oxygen minimum zones, or increased sedimentation rates all potentially increase organic matter preservation. According to plate tectonic, bathymetric, and paleogeographic reconstructions, the Arctic Ocean was a virtually isolated shallow basin, with one possible deeper connection to the Nordic Seas represented by a still shallow Fram Strait (Jakobsson et al., 2007), hampering ventilation of the Arctic Basin. During the Azolla interval surface waters freshened, while at the same time bottom waters appear to have remained saline, indicating that the Arctic was highly stratified. The restricted ventilation and stratification in concert with ongoing export of organic matter most likely resulted in the development of anoxic conditions in the lower part of the water column. Whereas the excess precipitation over evaporation maintained the freshwater lid, sustained input of Nordic Sea water is needed to keep the deeper waters saline. To which degree the Arctic Ocean exchanged with the Nordic Seas is, however, still largely unknown. Here we present a high-resolution trace metal record (ICP-MS and ICP-OES) for the expanded Early/Middle Eocene section capturing the Azolla interval from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. Euxinic conditions throughout the interval resulted in the efficient removal of redox sensitive trace metals from the water column. Using the sedimentary trace metal record we also constrained circulation in the Arctic Ocean by assessing the relative importance of trace metal input sources (i.e. fluvial, eolian, and

  1. Changes in ocean circulation in the South-east Atlantic Ocean during the Pliocene

    NASA Astrophysics Data System (ADS)

    Petrick, B. F.; McClymont, E.; Felder, S.; Leng, M. J.

    2013-12-01

    The Southeast Atlantic Ocean is an important ocean gateway because major oceanic systems interact with each other in a relatively small geographic area. These include the Benguela Current, Antarctic Circumpolar Current, and the input of warm and saline waters from the Indian Ocean via the Agulhas leakage. However, there remain questions about circulation change in this region during the Pliocene, including whether there was more or less Agulhas Leakage, which may have implications for the strength of the global thermohaline circulation. ODP Site 1087 (31°28'S, 15°19'E, 1374m water depth) is located outside the Benguela upwelling region and is affected by Agulhas leakage in the modern ocean. Sea-surface temperatures (SSTs) are thus sensitive to the influence of Agulhas Leakage at this site. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the Pliocene history of ODP 1087, including the UK37' index (SSTs), pigments (primary productivity) and planktonic foraminifera (water mass changes). SSTs during the Pliocene range from 17 to 22.5 °C (mean SSTs at 21 °C), and show variability on orbital and suborbital time scales. Our results indicate that the Benguela upwelling system had intensified and/or shifted south during the Pliocene. We find no evidence of Agulhas leakage, meaning that either Agulhas Leakage was severely reduced or displaced during the mid-Pliocene. Potential causes of the observed signals include changes to the local wind field and/or changes in the temperature of intermediate waters which upwell in the Benguela system. Pronounced cooling is observed during cold stages in the Pliocene, aligned with the M2 and KM2 events. These results may indicate that changes to the extent of the Antarctic ice sheet had impact on circulation in the south east Atlantic during the Pliocene via displacement of the Antarctic Circumpolar Currents.

  2. Horizontal density compensation in ocean general circulation models

    NASA Astrophysics Data System (ADS)

    Koch, Andrey O.; Helber, Robert W.; Richman, James G.; Barron, Charlie N.

    2013-04-01

    Density compensation is the condition where temperature (T) and salinity (S) gradients counteract in their effect on density. Open ocean observations with SeaSoar tows and recent glider observations in the Gulf of Mexico reported in the scientific literature suggest that horizontal gradients in the surface mixed layer tend to be strongly density compensated over a range of spatial scales while in seasonal thermocline and deeper layers T,S-fronts are only partially compensated or uncompensated. We assess the capability of ocean general circulation models (OGCM) to develop horizontal density compensation as observed in the upper ocean. The physics required to evolve the initial density compensated mixed layer toward the partially compensated conditions of the thermocline is tested. Idealistic scenarios with horizontal, partially compensated density fronts in the mixed layer are examined in submesoscale-resolved run-down simulations on Hybrid Coordinate Ocean Model (HYCOM). Simulations with no atmospheric forcing show that initial Density compensation does not change substantially experiencing only minor decrease with time simultaneously with the restratification of the mixed layer by submesoscale eddies. Submesoscale fronts tend to be more compensated than mesoscale fronts. A sensitivity analysis shows that the density compensation of submesoscale fronts is particularly sensitive to the horizontal diffusion rate. Simulations with wind forcing exhibit destruction of initial density compensation due to ageostrophic frontogenesis which is confirmed by recent glider observations in the Gulf of Mexico. The lack of the model skill to develop and maintain compensated thermohaline variability is attributed to the T, S horizontal diffusion parameterization used in HYCOM and generally in modern OGCMs: it is decoupled from vertical diffusion and T and S diffusion is horizontally identical. Our findings suggest that OGCM's skill to develop compensated thermohaline variability

  3. Ocean Bottom Pressure Seasonal Cycles and Decadal Trends from GRACE Release-05: Ocean Circulation Implications

    NASA Astrophysics Data System (ADS)

    Johnson, G. C.; Chambers, D. P.

    2013-12-01

    Ocean mass variations are important for diagnosing sea level budgets, the hydrological cycle and global energy budget, as well as ocean circulation variability. Here seasonal cycles and decadal trends of ocean mass from January 2003 to December 2012, both global and regional, are analyzed using GRACE Release 05 data. The trend of global flux of mass into the ocean approaches 2 cm decade-1 in equivalent sea level rise. Regional trends are of similar magnitude, with the North Pacific, South Atlantic, and South Indian oceans generally gaining mass and other regions losing mass. These trends suggest a spin-down of the North Pacific western boundary current extension and the Antarctic Circumpolar Current in the South Atlantic and South Indian oceans. The global average seasonal cycle of ocean mass is about 1 cm in amplitude, with a maximum in early October and volume fluxes in and out of the ocean reaching 0.5 Sv (1 Sv = 1 × 106 m3 s-1) when integrated over the area analyzed here. Regional patterns of seasonal ocean mass change have typical amplitudes of 1-4 cm, and include maxima in the subtropics and minima in the subpolar regions in hemispheric winters. The subtropical mass gains and subpolar mass losses in the winter spin up both subtropical and subpolar gyres, hence the western boundary current extensions. Seasonal variations in these currents are order 10 Sv, but since the associated depth-averaged current variations are only order 0.1 cm s-1, they would be difficult to detect using in situ oceanographic instruments. a) Amplitude (colors, in cm) and b) phase (colors, in months of the year) of an annual harmonic fit to monthly GRACE Release 05 CSR 500 km smoothed maps (concurrently with a trend and the semiannual harmonic). The 97.5% confidence interval for difference from zero is also indicated (solid black line). Data within 300 km of coastlines are not considered.

  4. Mean Upper-Ocean Circulation of the Southern Hemisphere Oceans Based on Goce Data

    NASA Astrophysics Data System (ADS)

    Menezes, V. V.; Bingham, R. J.; Vianna, M. L.; Phillips, H. E.

    2012-12-01

    One of the main goals of the Gravity and steady-state Ocean Circulation Explorer (GOCE) satellite mission launched in 2009 is to improve the previous estimates of the global ocean circulation structures determined from Mean Dynamic Topographies (MDTs). Recently published studies suggest that the GOCE-based MDTs and their respective mean geostrophic circulation fields (MGCs) are superior to those obtained from GRACE (Gravity Recovery and Climate Experiment)-only data. These studies focus mostly on the circulation of the North Atlantic and North Pacific oceans with emphasis on the strong western boundary current systems. In contrast, no detailed assessment has yet been made to determine the impact of the GOCE models in the southern hemisphere (SH) upper-ocean circulation especially in the subtropical region. It is generally recognized that the SH circulation is still not well established even at large scales, and the new GOCE and GRACE products can contribute to increase our understanding of the dominant currents in these regions, which may have even greater impact on the global climate than the NH counterparts. In the present work, we compute five global GOCE-derived MDTs with a 0.25 x 0.25 degree spatial grid based on three GOCE geoid models (TIM3, GOCO02S, GOCO3S) and three mean sea surfaces (CLS01, CLS11, DTU10) using the standard spectral approach (MSS minus Geoid). These MDTs do not have the well-known large-amplitude striation-type noise that plagued all of the GRACE-only MDTs with he same resolution, but still present commission errors which are filptered out with Singular Spectrum Analysis methods. Additionally, the MGCs were calculated by use of a Anderssen-Hegland averaging scheme for estimation of derivatives, which is able to filter out the well-known high amplitude noise caused by standard finite-difference methods. Comparisons with previous GRACE-only MGCs show that GOCE permits retrieval of currents with much higher intensities (e.g. the Agulhas

  5. Assimilation of GRACE-derived oceanic mass distributions with a global ocean circulation model

    NASA Astrophysics Data System (ADS)

    Saynisch, J.; Bergmann-Wolf, I.; Thomas, M.

    2015-02-01

    To study the sub-seasonal distribution and generation of ocean mass anomalies, Gravity Recovery and Climate Experiment (GRACE) observations of daily and monthly resolution are assimilated into a global ocean circulation model with an ensemble-based Kalman-Filter technique. The satellite gravimetry observations are processed to become time-variable fields of ocean mass distribution. Error budgets for the observations and the ocean model's initial state are estimated which contain the full covariance information. The consistency of the presented approach is demonstrated by increased agreement between GRACE observations and the ocean model. Furthermore, the simulations are compared with independent observations from 54 bottom pressure recorders. The assimilation improves the agreement to high-latitude recorders by up to 2 hPa. The improvements are caused by assimilation-induced changes in the atmospheric wind forcing, i.e., quantities not directly observed by GRACE. Finally, the use of the developed Kalman-Filter approach as a destriping filter to remove artificial noise contaminating the GRACE observations is presented.

  6. Ocean circulation and climate during the past 120,000 years.

    PubMed

    Rahmstorf, Stefan

    2002-09-12

    Oceans cover more than two-thirds of our blue planet. The waters move in a global circulation system, driven by subtle density differences and transporting huge amounts of heat. Ocean circulation is thus an active and highly nonlinear player in the global climate game. Increasingly clear evidence implicates ocean circulation in abrupt and dramatic climate shifts, such as sudden temperature changes in Greenland on the order of 5-10 degrees C and massive surges of icebergs into the North Atlantic Ocean --events that have occurred repeatedly during the last glacial cycle. PMID:12226675

  7. A Coupled Ocean General Circulation, Biogeochemical, and Radiative Model of the Global Oceans: Seasonal Distributions of Ocean Chlorophyll and Nutrients

    NASA Technical Reports Server (NTRS)

    Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

    2000-01-01

    A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability. and the interactions among three functional phytoplankton groups (diatoms. chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (greater than 1000 km) model chlorophyll results are in overall agreement with CZCS pigments in many global regions. Seasonal variability observed in the CZCS is also represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are generally in conformance although occasional departures are apparent. Model nitrate distributions agree with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicates that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent many aspects of the great diversity of physical, biological, chemical, and radiative environments encountered in the global oceans.

  8. Circulation in Vilkitsky Canyon in the eastern Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Janout, Markus; Hölemann, Jens

    2016-04-01

    The eastern Arctic Ocean is characterized by steep continental slopes and vast shallow shelf seas that receive a large amount of riverine freshwater from some of the largest rivers on earth. The northwestern Laptev Sea is of particular interest, as it is a freshwater transport pathway for a swift surface-intensified current from the Kara Sea toward the Arctic Basin, as was recently highlighted by high-resolution model studies. The region features complex bathymetry including a narrow strait and a large submarine canyon, strong tides, polynyas and severe sea ice conditions throughout much of the year. A year-long mooring record as well as detailed hydrographic shipboard measurements resulted from summer expeditions to the area in 2013 and 2014, and now provide a detailed picture of the region's water properties and circulation. The hydrography is characterized by riverine Kara Sea freshwater near the surface in the southern part of the canyon, while warmer (~0°C) saline Atlantic-derived waters dominate throughout the canyon at depths >150m. Cold shelf-modified waters near the freezing point are found along the canyon edges. The mean flow at the 300 m-deep mooring location near the southern edge of the canyon is swift (30 cm/s) and oriented eastward near the surface as suggested by numerical models, while the deeper flow follows the canyon topography towards the north-east. Wind-driven deviations from the mean flow coincide with sudden changes in temperature and salinity. This study characterizes the general circulation in Vilkitsky Canyon and investigates its potential as a conduit for upwelling of Atlantic-derived waters from the Arctic Basin to the Laptev Sea shelf.

  9. Consequences of future increased Arctic runoff on Arctic Ocean stratification, circulation, and sea ice cover

    NASA Astrophysics Data System (ADS)

    Nummelin, Aleksi; Ilicak, Mehmet; Li, Camille; Smedsrud, Lars H.

    2016-01-01

    The Arctic Ocean has important freshwater sources including river runoff, low evaporation, and exchange with the Pacific Ocean. In the future, we expect even larger freshwater input as the global hydrological cycle accelerates, increasing high-latitude precipitation, and river runoff. Previous modeling studies show some robust responses to high-latitude freshwater perturbations, including a strengthening of Arctic stratification and a weakening of the large-scale ocean circulation; some idealized modeling studies also document a stronger cyclonic circulation within the Arctic Ocean itself. With the broad range of scales and processes involved, the overall effect of increasing runoff requires an understanding of both the local processes and the broader linkages between the Arctic and surrounding oceans. Here we adopt a more comprehensive modeling approach by increasing river runoff to the Arctic Ocean in a coupled ice-ocean general circulation model, and show contrasting responses in the polar and subpolar regions. Within the Arctic, the stratification strengthens, the halocline and Atlantic Water layer warm, and the cyclonic circulation spins up, in agreement with previous work. In the subpolar North Atlantic, the model simulates a colder and fresher water column with weaker barotropic circulation. In contrast to the estuarine circulation theory, the volume exchange between the Arctic Ocean and the surrounding oceans does not increase with increasing runoff. While these results are robust in our model, we require experiments with other model systems and more complete observational syntheses to better constrain the sensitivity of the climate system to high-latitude freshwater perturbations.

  10. Comment on "The Atlantic Multidecadal Oscillation without a role for ocean circulation".

    PubMed

    Zhang, Rong; Sutton, Rowan; Danabasoglu, Gokhan; Delworth, Thomas L; Kim, Who M; Robson, Jon; Yeager, Stephen G

    2016-06-24

    Clement et al (Reports, 16 October 2015, p. 320) claim that the Atlantic Multidecadal Oscillation (AMO) is a thermodynamic response of the ocean mixed layer to stochastic atmospheric forcing and that ocean circulation changes have no role in causing the AMO. These claims are not justified. We show that ocean dynamics play a central role in the AMO. PMID:27339976

  11. Determination of the ocean circulation using Geosat altimetry

    SciTech Connect

    Nerem, R.S.; Tapley, B.D.; Shum, C.K. )

    1990-03-15

    A spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the Earth's geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using Geosat altimeter data and tracking data from 14 different satellites. The sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data. Currently, errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower, corresponding to a minimum wavelength of 4,000 km. Error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0.2, indicating good separation of the geoid and the sea surface topography at wavelengths of 4,000 km or longer. Estimates of the scale factor for the significant wave height (H{sub 1/3}), which is used to compute the electromagnetic bias correction and the bias for the Geosat altimeter, are obtained. The estimate of the H{sub 1/3} correction is 3.6 {plus minus} 1.5%, and the height bias estimate is zero.

  12. Assimilation impacts on Arctic Ocean circulation, heat and freshwater budgets

    NASA Astrophysics Data System (ADS)

    Zuo, Hao; Mugford, Ruth I.; Haines, Keith; Smith, Gregory C.

    We investigate the Arctic basin circulation, freshwater content (FWC) and heat budget by using a high-resolution global coupled ice-ocean model implemented with a state-of-the-art data assimilation scheme. We demonstrate that, despite a very sparse dataset, by assimilating hydrographic data in and near the Arctic basin, the initial warm bias and drift in the control run is successfully corrected, reproducing a much more realistic vertical and horizontal structure to the cyclonic boundary current carrying the Atlantic Water (AW) along the Siberian shelves in the reanalysis run. The Beaufort Gyre structure and FWC and variability are also more accurately reproduced. Small but important changes in the strait exchange flows are found which lead to more balanced budgets in the reanalysis run. Assimilation fluxes dominate the basin budgets over the first 10 years (P1: 1987-1996) of the reanalysis for both heat and FWC, after which the drifting Arctic upper water properties have been restored to realistic values. For the later period (P2: 1997-2004), the Arctic heat budget is almost balanced without assimilation contributions, while the freshwater budget shows reduced assimilation contributions compensating largely for surface salinity damping, which was extremely strong in this run. A downward trend in freshwater export at the Canadian Straits and Fram Strait is found in period P2, associated with Beaufort Gyre recharge. A detailed comparison with observations and previous model studies at the individual Arctic straits is also included.

  13. Correlated signals and causal transport in ocean circulation

    NASA Astrophysics Data System (ADS)

    Jeffress, Stephen

    2014-05-01

    This paper presents a framework for interpreting the time-lagged correlation of oceanographic data in terms of physical transport mechanisms. Previous studies have inferred aspects of ocean circulation by correlating fluctuations in temperature and salinity measurements at distant stations. Typically, the time-lag of greatest correlation is interpreted as an advective transit time and hence the advective speed of the current. In this paper we relate correlation functions directly to the underlying equations of fluid transport. This is accomplished by expressing the correlation functions in terms of the Green's function of the transport equation. Two types of correlation functions are distinguished: field-forcing correlation and field-field correlation. Their unique relationships to the Green's function are illustrated in two idealized models of geophysical transport: a leaky pipe model and an advective-diffusive model. Both models show that the field-forcing correlation function converges to the Green's function as the characteristic (time or length) scale of forcing autocorrelation decreases. The leaky pipe model provides an explanation for why advective speeds inferred from time-lagged correlations are often less than the speed of the main current. The advective-diffusive model reveals a structural bias in the field-field correlation function when used to estimate transit times.

  14. Uncertainty quantification for large-scale ocean circulation predictions.

    SciTech Connect

    Safta, Cosmin; Debusschere, Bert J.; Najm, Habib N.; Sargsyan, Khachik

    2010-09-01

    Uncertainty quantificatio in climate models is challenged by the sparsity of the available climate data due to the high computational cost of the model runs. Another feature that prevents classical uncertainty analyses from being easily applicable is the bifurcative behavior in the climate data with respect to certain parameters. A typical example is the Meridional Overturning Circulation in the Atlantic Ocean. The maximum overturning stream function exhibits discontinuity across a curve in the space of two uncertain parameters, namely climate sensitivity and CO{sub 2} forcing. We develop a methodology that performs uncertainty quantificatio in the presence of limited data that have discontinuous character. Our approach is two-fold. First we detect the discontinuity location with a Bayesian inference, thus obtaining a probabilistic representation of the discontinuity curve location in presence of arbitrarily distributed input parameter values. Furthermore, we developed a spectral approach that relies on Polynomial Chaos (PC) expansions on each sides of the discontinuity curve leading to an averaged-PC representation of the forward model that allows efficient uncertainty quantification and propagation. The methodology is tested on synthetic examples of discontinuous data with adjustable sharpness and structure.

  15. Determination of the ocean circulation using Geosat altimetry

    NASA Technical Reports Server (NTRS)

    Nerem, R. S.; Tapley, B. D.; Shum, C. K.

    1990-01-01

    A spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the earth's geopotential field complete to degree and order 50 have been obtained in a simultaneous solution using Geosat altimeter data and tracking data from 14 different satellites. The sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data. Currently, errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower, corresponding to a minimum wavelength of 4000 km. Error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0.2, indicating good separation of the geoid and the sea surface topography at wavelengths of 4000 km or longer. Estimates of the scale factor for the significant wave height (H1/3), which is used to compute the electromagnetic bias correction and the bias for the Geosat altimeter, are obtained. The estimate of the H1/3 correction is 3.6 + or - 1.5 percent, and the height bias estimate is zero.

  16. Interannual variability in the stratospheric-tropospheric circulation in a coupled ocean-atmosphere GCM

    SciTech Connect

    Kitoh, Akio; Koide, Hiroshi; Kodera, Kunihiko

    1996-03-01

    The authors look for interannual variations in circulation patterns in the stratosphere/troposphere circulation and sea surface temperatures within the Meteorological Research Institute coupled ocean-atmosphere general circulation model. They are able to identify two modes in this model which exhibit this type of variability. One involves the stratospheric polar vortex, coupled via tropospheric circulation to SST variations. The second mode involves El Nino type phenomena coupled into the tropospheric subtropical jet.

  17. Global Observations and Understanding of the General Circulation of the Oceans

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The workshop was organized to: (1) assess the ability to obtain ocean data on a global scale that could profoundly change our understanding of the circulation; (2) identify the primary and secondary elements needed to conduct a World Ocean Circulation Experiment (WOCE); (3) if the ability is achievable, to determine what the U.S. role in such an experiment should be; and (4) outline the steps necessary to assure that an appropriate program is conducted. The consensus of the workshop was that a World Ocean Circulation Experiment appears feasible, worthwhile, and timely. Participants did agree that such a program should have the overall goal of understanding the general circulation of the global ocean well enough to be able to predict ocean response and feedback to long-term changes in the atmosphere. The overall goal, specific objectives, and recommendations for next steps in planning such an experiment are included.

  18. Antarctic glaciation caused ocean circulation changes at the Eocene-Oligocene transition.

    PubMed

    Goldner, A; Herold, N; Huber, M

    2014-07-31

    Two main hypotheses compete to explain global cooling and the abrupt growth of the Antarctic ice sheet across the Eocene-Oligocene transition about 34 million years ago: thermal isolation of Antarctica due to southern ocean gateway opening, and declining atmospheric CO2 (refs 5, 6). Increases in ocean thermal stratification and circulation in proxies across the Eocene-Oligocene transition have been interpreted as a unique signature of gateway opening, but at present both mechanisms remain possible. Here, using a coupled ocean-atmosphere model, we show that the rise of Antarctic glaciation, rather than altered palaeogeography, is best able to explain the observed oceanographic changes. We find that growth of the Antarctic ice sheet caused enhanced northward transport of Antarctic intermediate water and invigorated the formation of Antarctic bottom water, fundamentally reorganizing ocean circulation. Conversely, gateway openings had much less impact on ocean thermal stratification and circulation. Our results support available evidence that CO2 drawdown--not gateway opening--caused Antarctic ice sheet growth, and further show that these feedbacks in turn altered ocean circulation. The precise timing and rate of glaciation, and thus its impacts on ocean circulation, reflect the balance between potentially positive feedbacks (increases in sea ice extent and enhanced primary productivity) and negative feedbacks (stronger southward heat transport and localized high-latitude warming). The Antarctic ice sheet had a complex, dynamic role in ocean circulation and heat fluxes during its initiation, and these processes are likely to operate in the future. PMID:25079555

  19. Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation.

    PubMed

    Knorr, Gregor; Lohmann, Gerrit

    2003-07-31

    During the two most recent deglaciations, the Southern Hemisphere warmed before Greenland. At the same time, the northern Atlantic Ocean was exposed to meltwater discharge, which is generally assumed to reduce the formation of North Atlantic Deep Water. Yet during deglaciation, the Atlantic thermohaline circulation became more vigorous, in the transition from a weak glacial to a strong interglacial mode. Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation. We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation, triggered by increased mass transport into the Atlantic Ocean via the warm (Indian Ocean) and cold (Pacific Ocean) water route. This effect prevails over the influence of meltwater discharge, which would oppose a strengthening of the thermohaline circulation. A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation, in agreement with the available proxy records. PMID:12891352

  20. Temporal relationships of carbon cycling and ocean circulation at glacial boundaries.

    PubMed

    Piotrowski, Alexander M; Goldstein, Steven L; Hemming, Sidney R; Fairbanks, Richard G

    2005-03-25

    Evidence from high-sedimentation-rate South Atlantic deep-sea cores indicates that global and Southern Ocean carbon budget shifts preceded thermohaline circulation changes during the last ice age initiation and termination and that these were preceded by ice-sheet growth and retreat, respectively. No consistent lead-lag relationships are observed during abrupt millennial warming events during the last ice age, allowing for the possibility that ocean circulation triggered some millenial climate changes. At the major glacial-interglacial transitions, the global carbon budget and thermohaline ocean circulation responded sequentially to the climate changes that forced the growth and decline of continental ice sheets. PMID:15790848

  1. Oceanic variability around Madagascar : connections to the large-scale Indian Ocean circulation and its forcing

    NASA Astrophysics Data System (ADS)

    Palastanga, V.

    2007-06-01

    The connection between the mesoscale eddy activity around Madagascar and the large-scale interannual variability in the Indian Ocean is investigated. We use the combined TOPEX/Poseidon-ERS sea surface height (SSH) data for the period 1993-2003. The SSH-fields in the Mozambique Channel and east of Madagascar exhibit a significant interannual oscillation. This is related to the arrival of large-scale anomalies that propagate westward in the band 10-15S in response to the Indian Ocean dipole (IOD) events. Positive (negative) SSH anomalies associated to a positive (negative) IOD phase induce a shift in the intensity and position of the tropical and subtropical gyres in the Indian Ocean. A weakening (strengthening) results in the intensity of the South Equatorial Current and its branches along east Madagascar. In addition, the flow through the narrows of the Mozambique Channel around 17S increases (decreases) during periods of a stronger and northward (southward) extension of the subtropical (tropical) gyre. Interaction between the currents in the narrows and southward propagating eddies from the northern Channel leads to interannual variability in the eddy kinetic energy of the central Channel in phase with the one in the SSH-field. The origin of the eddy variability along the 25S band in the Indian Ocean is also investigated. We have found that the surface circulation east of Madagascar shows an anticyclonic subgyre bounded to the south by eastward flow from southwest Madagascar and to the north by the westward flowing South Equatorial Current (SEC) between 15-20S. The shallow, eastward flow, named the South Indian Ocean Countercurrent (SICC), extends above the deep reaching, westward flowing SEC up to 95E, with its core over the latitude of the high variability band. Applying a 2-layer model reveals that regions of large vertical shear along the SICC-SEC system are baroclinically unstable. Estimates of the frequencies (3.5-6 times/year) and wavelengths (290-470 km

  2. A numerical method for the study of the circulation of the world ocean

    SciTech Connect

    Bryan, K.

    1997-08-01

    This paper describes a detail computational procedure involving a finite difference numerical schemes to study the circulation models of the world oceans. To obtain an efficient numerical method for low-frequency, large-scale current systems, surfaces gravity-inertial waves are filtered out by the rigid-lid approximation. Special features of the ocean circulation are resolved in the numerical model by allowing for a variable spacing in either the zonal or meridional direction. 20 refs., 5 figs., 1 tab.

  3. Tectonically restricted deep-ocean circulation at the end of the Cretaceous greenhouse

    NASA Astrophysics Data System (ADS)

    Voigt, Silke; Jung, Claudia; Friedrich, Oliver; Frank, Martin; Teschner, Claudia; Hoffmann, Julia

    2013-05-01

    The evolution of global ocean circulation toward deep-water production in the high southern latitudes is thought to have been closely linked to the transition from extreme mid-Cretaceous warmth to the cooler Cenozoic climate. The relative influences of climate cooling and the opening and closure of oceanic gateways on the mode of deep-ocean circulation are, however, still unresolved. Here we reconstruct intermediate- to deep-water circulation for the latest Cretaceous based on new high-resolution radiogenic neodymium (Nd) isotope data from several sites and for different water depths in the South Atlantic, Southern Ocean, and proto-Indian Ocean. Our data document the presence of markedly different intermediate water Nd-isotopic compositions in the South Atlantic and Southern Ocean. In particular, a water mass with a highly radiogenic Nd isotope signature most likely originating from intense hotspot-related volcanic activity bathed the crest of Walvis Ridge between 71 and 69 Ma, which formed a barrier that prevented deep-water exchange between the Southern Ocean and the North Atlantic basins. We suggest that the Cenozoic mode of global deep-ocean circulation was still suppressed by tectonic barriers in the latest Cretaceous, and that numerous, mostly regionally-formed and sourced intermediate to deep waters supplied the deep ocean prior to 68 million yr ago.

  4. Tectonically restricted deep-ocean circulation at the end of the Cretaceous greenhouse

    NASA Astrophysics Data System (ADS)

    Voigt, Silke; Jung, Claudia; Friedrich, Oliver; Frank, Martin; Teschner, Claudia; Hoffman, Julia

    2013-04-01

    The evolution of global ocean circulation towards deep-water production in the high southern latitudes is thought to have been closely linked to the transition from extreme mid-Cretaceous warmth to the cooler Cenozoic climate. The relative influences of climate cooling and the opening and closure of oceanic gateways on the mode of deep-ocean circulation are, however, still unresolved. Here we reconstruct intermediate- to deep-water circulation for the latest Cretaceous based on new high-resolution radiogenic neodymium (Nd) isotope data from several sites and for different water depths in the South Atlantic, Southern Ocean, and proto-Indian Ocean. Our new late Campanian to Maastrichtian data documents the presence of markedly different intermediate water Nd-isotopic compositions in the South Atlantic and Southern Ocean suggesting the presence of multiple, local water sources at nearly every site and a circulation system that was fundamentally different from the modern. In particular, a water mass with a highly radiogenic Nd isotope signature most likely originating from intense hotspot-related volcanic activity bathed the crest of Walvis Ridge between 71 and 69 Ma, which formed a barrier that prevented deep-water exchange between the Southern Ocean and the North Atlantic basins. The narrow geometry of the Atlantic Ocean together with tight to closed connections towards the Tethys and the Pacific Ocean limited volumetrically substantial deep-water exchange and promoted a local mode of deep oceanic convection in the Atlantic. Available Nd isotope data from the North Atlantic indicate the prevalence of different water masses in the abyssal plains and support a mode of ocean circulation that was maintained by down- and upwelling in various meso-scale eddies as proposed by Hay (2011, Sedim. Geol. 235, 5-26). Climatic cooling and the opening of gateways between 83-78 Ma may have initiated SCW formation in the southern hemisphere oceans. However, SCW formation did not

  5. Ocean topography mapping, improvement of the marine geoid, and global permanent ocean circulation studies from TOPEX/Poseidon altimeter data

    NASA Technical Reports Server (NTRS)

    Marsh, James G.; Lerch, F. J.; Koblinsky, C. J.; Nerem, R. S.; Klosko, S. M.; Williamson, R. G.

    1991-01-01

    The TOPEX/POSEIDON altimeter measurements will be the first global observations of the sea surface with accuracy sufficient to make quantitative determinations of the ocean's general circulation and its variations. These measurements are an important step to understanding global change in the ocean and its impact on the climate. Our investigation will focus on the examination of features in the sea surface elevation at the largest spatial and temporal scales. TOPEX/POSEIDON altimeter measurements will be used in conjunction with observations from past satellite-altimeter missions, such as NASA's GEOS-3 and Seasat, the U.S. Navy's Geosat and SALT, and the European Remote Sensing satellite in order to address the following issues: (1) Improve models of the marine geoid, especially at wavelengths needed to understand the basin-scale ocean dynamic topograpy. (2) Measure directly from the altimeter data the expression of the mean global ocean circulation in the sea surface at the largest scales through a simultaneous solution for gravity, orbital, and oceanographic parameters. (3) Examine the sea surface measurements for changes in global ocean mass or volume, interannual variations in the basin-scale ocean circulation, and annual changes in the heating and cooling of the upper ocean.

  6. Remote sensing of surface ocean circulation with satellite altimetry.

    PubMed

    Mather, R S; Rizos, C; Coleman, R

    1979-07-01

    The Geodynamics Experimental Ocean Satellite (GEOS-3) radar altimeter has provided some information on the dynamic sea-surface topography of the global oceans. Regional studies of the densely surveyed Sargasso Sea indicate that the average nontidal variability of the oceans is +/- 28 centimeters. Sea-surface highs and lows determined from GEOS-3 altimetry correlate favorably with eddy structures inferred from Nimbus-6 infrared imagery. PMID:17778877

  7. Application of Satellite Altimetry to Ocean Circulation Studies: 1987-1994

    NASA Technical Reports Server (NTRS)

    Fu, L. -L.; Cheney, R. E.

    1994-01-01

    Altimetric measurement of the height of the sea surface from space provides global observation of the world's oceans. The last eight years have witnessed a rapid growth in the use of altimetry data from the study of the ocean circulations, thanks to the multiyear data from the Geosat Mission.

  8. Iceberg discharges of the last glacial period driven by oceanic circulation changes.

    PubMed

    Alvarez-Solas, Jorge; Robinson, Alexander; Montoya, Marisa; Ritz, Catherine

    2013-10-01

    Proxy data reveal the existence of episodes of increased deposition of ice-rafted detritus in the North Atlantic Ocean during the last glacial period interpreted as massive iceberg discharges from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence of the crucial role that the ocean plays both for past and future behavior of the cryosphere suggests a climatic control of these ice surges. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. The model generates a time series of iceberg discharge that closely agrees with ice-rafted debris records over the past 80 ka, indicating that oceanic circulation variations were responsible for the enigmatic ice purges of the last ice age. PMID:24062437

  9. Dynamical response of the oceanic circulation and temperature to interdecadal variability in the surface winds over the Indian Ocean

    SciTech Connect

    Reason, C.J.C.; Allan, R.J.; Lindesay, J.A.

    1996-01-01

    A global ocean general circulation model (OGCM) is used to investigate the sensitivity of the circulation and temperature fields to observed interdecadal variability in Indian Ocean winds for the austral summer. Focus is placed on the dynamical response of the model to the imposed winds. These comprise the observed winds from COADS for the region 46{degrees}S-30{degrees}N, 17{degrees}-152{degrees}E organized into four 21-yr epochs. During the first two epochs, the southern Indian anticyclone, African monsoonal flow, and associated trades were anomalously weak, whereas during the 1963-1983 period the reverse was true. The 1942-1962 epoch appears to be a transition. The model indicates an overall decrease (increase) in the transports of the southern Indian and tropical Indian gyres for the 1900-1920, 1921-1941 cases in dynamical response to the variability in the surface winds over the Indian Ocean. Sea surface temperature (SST) perturbations in the southern Indian Ocean have the same sign as the observed anomalies but are smaller in magnitude. The model SST patterns are restricted to the southern Indian Ocean midlatitudes, whereas observations indicate anomalies throughout the Indian Ocean basin. Analysis of the streamfunction anomalies induced by the epoch winds in the model indicates that the JEBAR term is important in modulating Indian gyre transports. While it is noted that thermodynamic effects not explicitly included in the model may contribute toward the observed SST variability in certain regions and that previous model studies have shown that SST in the southern Indian Ocean is sensitive to variations in the Indonesian throughflow and the Pacific trade winds, the results lend support to the hypothesis that changes in the basin-scale ocean circulation driven by the Indian Ocean epoch winds may contribute significantly toward the observed interdecadal variability in SST in the southern regions of this ocean. 29 refs., 17 figs.

  10. The influence of wind-driven ocean circulation on earth rotation

    SciTech Connect

    Steinberg, D.J.

    1992-01-01

    In this work, the authors have studied the role of barotropic, wind driven ocean circulation in exciting polar motion and the length of day at weekly to seasonal frequencies. The rotation of the earth is variable in length of day and in position of the rotation pole. The sources of these variations are not fully known. They have used the Cox and Bryan (1984) general circulation ocean model driven by daily NMC global winds to compute first the ocean currents and sea level variations, and then the rotational excitation functions, between 1980 and 1986. It is found that the wind driven ocean circulation can explain much of the residual power in the length of day which is not accounted for by atmospheric angular momentum. It also appears that there is significant power, as much as 50% of that needed, in polar motion excitation at the Chandler and seasonal frequencies.

  11. Adaptive Error Estimation in Linearized Ocean General Circulation Models

    NASA Technical Reports Server (NTRS)

    Chechelnitsky, Michael Y.

    1999-01-01

    Data assimilation methods are routinely used in oceanography. The statistics of the model and measurement errors need to be specified a priori. This study addresses the problem of estimating model and measurement error statistics from observations. We start by testing innovation based methods of adaptive error estimation with low-dimensional models in the North Pacific (5-60 deg N, 132-252 deg E) to TOPEX/POSEIDON (TIP) sea level anomaly data, acoustic tomography data from the ATOC project, and the MIT General Circulation Model (GCM). A reduced state linear model that describes large scale internal (baroclinic) error dynamics is used. The methods are shown to be sensitive to the initial guess for the error statistics and the type of observations. A new off-line approach is developed, the covariance matching approach (CMA), where covariance matrices of model-data residuals are "matched" to their theoretical expectations using familiar least squares methods. This method uses observations directly instead of the innovations sequence and is shown to be related to the MT method and the method of Fu et al. (1993). Twin experiments using the same linearized MIT GCM suggest that altimetric data are ill-suited to the estimation of internal GCM errors, but that such estimates can in theory be obtained using acoustic data. The CMA is then applied to T/P sea level anomaly data and a linearization of a global GFDL GCM which uses two vertical modes. We show that the CMA method can be used with a global model and a global data set, and that the estimates of the error statistics are robust. We show that the fraction of the GCM-T/P residual variance explained by the model error is larger than that derived in Fukumori et al.(1999) with the method of Fu et al.(1993). Most of the model error is explained by the barotropic mode. However, we find that impact of the change in the error statistics on the data assimilation estimates is very small. This is explained by the large

  12. Benchmarking ocean circulation models on massively parallel computers

    SciTech Connect

    Poling, D.A.

    1997-08-01

    General circulation models are becoming the premier theoretical tools for studying the complex structure of the global climate. GEONET was envisioned as exercising the resources developed for the nuclear weapons program to address environmental problems. The similarity of circulation models to weapons codes made them an attractive field for them to develop expertise. The author hoped to become an active player in mainline climate research through computer simulation. This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The intention of this research was to establish the Laboratory in mainstream climate research in conjunction with the GEONET project.

  13. Miocene ocean circulation inferred from marine carbon cycle modeling combined with benthic isotope records

    NASA Astrophysics Data System (ADS)

    Butzin, Martin; Lohmann, Gerrit; Bickert, Torsten

    2011-02-01

    In a modeling sensitivity study we investigate the evolution of the ocean circulation and of marine carbon isotope (δ13C) records during the Miocene (about 23-5 million years ago). For this purpose we ran an ocean-circulation carbon cycle model of intermediate complexity (Large Scale Geostrophic- Hamburg Ocean Carbon Cycle Model, version 2s) exploring various seaway configurations. Our investigations confirm that the Central American Seaway played a decisive role in the history of the Miocene ocean circulation. In simulations with a deep Central American Seaway (depth range 1-3 km), typical for the early to middle Miocene, deep water production in the North Atlantic is absent or weak, while the meridional overturning circulation is dominated by water mass formation in the Southern Ocean. Deep water formation in the North Atlantic begins when the Central American Seaway shoals to a few hundreds of meters, which is typical for the late Miocene. Our results do not support ideas that the mid-Miocene closing of the Eastern Tethys contributed to Antarctic glaciation. On the other hand, we find some water exchange between the Indian Ocean and the Atlantic via the Eastern Tethys during the early Miocene. Our model results for the Atlantic meridional overturning circulation and for Atlantic δ13C during the late Miocene are largely independent from depth variations of the Greenland-Scotland Ridge. To a large extent, the evolution of Miocene deep-sea δ13C records can be explained with large-scale ocean circulation changes. Our model-data comparison for the middle and early Miocene suggests that during the early Neogene the seaway effect on benthic δ13C may have been superimposed by further factors such as climate regime shifts and/or terrestrial carbon cycle changes.

  14. The effect of low ancient greenhouse climate temperature gradients on the ocean's overturning circulation

    NASA Astrophysics Data System (ADS)

    Sijp, W. P.; England, M. H.

    2015-10-01

    We examine whether the reduced meridional temperature gradients of past greenhouse climates might have reduced oceanic overturning, leading to a more quiescent subsurface ocean. A substantial reduction of the pole to equator temperature difference is achieved in a coupled climate model via an altered radiative balance in the atmosphere. Contrary to expectations, we find that the meridional overturning circulation and deep ocean kinetic energy remain relatively unaffected. Reducing the wind strength also has remarkably little effect on the overturning. Instead, overturning strength depends on deep ocean density gradients, which remain relatively unaffected by the surface changes, despite an overall decrease in ocean density. Ocean poleward heat transport is significantly reduced only in the Northern Hemisphere, as now the circulation operates across a reduced temperature gradient, suggesting the overturning circulation dominates heat transport in greenhouse climates. These results indicate that climate models of the greenhouse climate during the Cretaceous and early Paleogene may yield a reasonable overturning circulation, despite failing to fully reproduce the extremely reduced temperature gradients of those time periods.

  15. The effect of low ancient greenhouse climate temperature gradients on the ocean's overturning circulation

    NASA Astrophysics Data System (ADS)

    Sijp, Willem P.; England, Matthew H.

    2016-02-01

    We examine whether the reduced meridional temperature gradients of past greenhouse climates might have reduced oceanic overturning, leading to a more quiescent subsurface ocean. A substantial reduction of the pole-to-Equator temperature difference is achieved in a coupled climate model via an altered radiative balance in the atmosphere. Contrary to expectations, we find that the meridional overturning circulation and deep ocean kinetic energy remain relatively unaffected. Reducing the wind strength also has remarkably little effect on the overturning. Instead, overturning strength depends on deep ocean density gradients, which remain relatively unaffected by the surface changes, despite an overall decrease in ocean density. Ocean poleward heat transport is significantly reduced only in the Northern Hemisphere, as now the circulation operates across a reduced temperature gradient, suggesting a sensitivity of Northern Hemisphere heat transport in greenhouse climates to the overturning circulation. These results indicate that climate models of the greenhouse climate during the Cretaceous and early Paleogene may yield a reasonable overturning circulation, despite failing to fully reproduce the extremely reduced temperature gradients of those time periods.

  16. Calibrating the ECCO ocean general circulation model using Green's functions

    NASA Technical Reports Server (NTRS)

    Menemenlis, D.; Fu, L. L.; Lee, T.; Fukumori, I.

    2002-01-01

    Green's functions provide a simple, yet effective, method to test and calibrate General-Circulation-Model(GCM) parameterizations, to study and quantify model and data errors, to correct model biases and trends, and to blend estimates from different solutions and data products.

  17. Cloud-radiative effects on implied oceanic energy transports as simulated by atmospheric general circulation models

    SciTech Connect

    Gleckler, P.J.; Randall, D.A.; Boer, G.

    1994-03-01

    This paper reports on energy fluxes across the surface of the ocean as simulated by fifteen atmospheric general circulation models in which ocean surface temperatures and sea-ice boundaries are prescribed. The oceanic meridional energy transport that would be required to balance these surface fluxes is computed, and is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean energy transport can be affected by the errors in simulated cloud-radiation interactions.

  18. Arctic Ocean circulation and variability - advection and external forcing encounter constraints and local processes

    NASA Astrophysics Data System (ADS)

    Rudels, B.

    2011-12-01

    The first hydrographic data from the Arctic Ocean, the section from the Laptev Sea to the passage between Greenland and Svalbard obtained by Nansen on the drift by Fram 1893-1896, aptly illustrate the main features of Arctic Ocean oceanography and indicate possible processes active in transforming the water masses in the Arctic Ocean. Many, perhaps most, of these processes were identified already by Nansen, who put his mark on almost all subsequent research in the Arctic Ocean. Here we shall revisit some key questions and follow how our understanding has evolved from the early 20th century to present. What questions, if any, can now be regarded as solved and which remain still open? Five different but connected topics will be discussed: (1) The low salinity surface layer and the storage and export of freshwater. (2) The vertical heat transfer from the Atlantic water to sea ice and to the atmosphere. (3) The circulation and mixing of the two Atlantic inflow branches. (4) The formation and circulation of deep and bottom waters in the Arctic Ocean. (5) The exchanges through Fram Strait. Foci will be on the potential effects of increased freshwater input and reduced sea ice export on the freshwater storage and residence time in the Arctic Ocean, on the deep waters of the Makarov Basin and on the circulation and relative importance of the two inflows, over the Barents Sea and through Fram Strait, for the distribution of heat in the intermediate layers of the Arctic Ocean.

  19. The early Miocene onset of a ventilated circulation regime in the Arctic Ocean.

    PubMed

    Jakobsson, Martin; Backman, Jan; Rudels, Bert; Nycander, Jonas; Frank, Martin; Mayer, Larry; Jokat, Wilfried; Sangiorgi, Francesca; O'Regan, Matthew; Brinkhuis, Henk; King, John; Moran, Kathryn

    2007-06-21

    Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events. PMID:17581581

  20. Zonal momentum budget along the equator in the Indian Ocean from a high-resolution ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Nagura, Motoki; McPhaden, Michael J.

    2014-07-01

    This study examines the zonal momentum budget along the equator in the Indian Ocean in a high-resolution ocean general circulation model. Wyrtki Jets, wind-driven eastward flows in the upper 100 m that appear typically twice per year in boreal spring and fall, are a prominent feature of the ocean circulation in this region. Our results indicate that nonlinearity associated with these jets is an important element of the zonal momentum budget, with wind driven eastward momentum advected downward into the thermocline. This advection results in annually averaged zonal currents that flow against the zonal pressure gradient in the upper 200 m, such that there is no mean subsurface undercurrent in the Indian Ocean as there is in the Pacific and Atlantic Oceans. Zonal momentum is further distributed along the equator by zonal advection, with eastward flow substantially enhanced in the eastern basin relative to the western basin. Meridional advection, though generally weak, tends to decelerate surface eastward flow along the equator. These results contrast with those from previous idealized wind-forced model experiments that primarily emphasized the importance of vertical momentum advection. Also, beyond semiannual period fluctuations, significant momentum advection results from a broad range of interacting processes, spanning intraseasonal to interannual time scales. We conclude that proper simulation of zonal flows along the equator in the Indian Ocean, including their climatically relevant impacts on the mass and heat balance, requires accurate representation of nonlinearities that derive from a broad range of time and space scales.

  1. Assimilation of TOPEX/POSEIDON Altimeter Data into a Global Ocean Circulation Model: Are the Results Any Good?

    NASA Technical Reports Server (NTRS)

    Fukumori, I.; Fu, L. L.; Chao, Y.

    1998-01-01

    The feasibility of assimilating satellite altimetry data into a global ocean general ocean general circulation model is studied. Three years of TOPEX/POSEIDON data is analyzed using a global, three-dimensional, nonlinear primitive equation model.

  2. Variability of the thermohaline circulation in a simple coupled atmosphere-ocean model

    NASA Astrophysics Data System (ADS)

    Taboada, J. J.; Lorenzo, M. N.

    2003-04-01

    The behavior of the Atlantic thermohaline circulation (THC) is essential to a better understanding of climate change. Paleoclimatic studies suggest that this circulation has experimented repeated changes throughout the history of the Earth associated to climate changes [1]. The coupled 3-dimensional climate models are useful in quantitatively assessing the details of the thermohaline circulation and for comparison with observations. However, the currently available computing capacity reduces the possibility of carry out exhaustive parametric studies of the THC. Models of reduced complexity can help overcome this difficulty and make valuable contributions to a better understanding of parameter space. Moreover, these models are most useful as exploratory tools for hypothesis building. Here we study a low-order coupled atmosphere-ocean general circulation model in order to understand the behavior of the thermohaline circulation through different changes on the interaction between atmosphere-ocean [1,2]. The atmosphere is represented by a low-order atmospheric "general circulation" model introduced by Lorenz in 1984 [3] and the ocean model considered here is a 3-box model which simulates the North Atlantic thermohaline circulation [2]. [1] Broecker W.S. (1997) Thermohaline circulation, the Achilles Heel of our climate system: will man-made CO_2 upset the current balance?. Science, 278, 1582-1588. [2] Roebber, P.J. (1995) Climate variability in a low-order coupled atmosphere-ocean model. Tellus, 47A, 473-494. [3] Lorenz, E.N. (1984) Irregularity. A fundamental property of the atmosphere. Tellus, 36A, 98-110.

  3. Observed impact of mesoscale circulation on oceanic response to Typhoon Man-Yi (2007)

    NASA Astrophysics Data System (ADS)

    Nam, Sunghyun; Kim, Duk-Jin; Moon, Wooil M.

    2012-01-01

    The oceanic response to a typhoon, where mesoscale ocean circulations co-exist, was investigated by analyzing the independent observations of profiling floats data at three different locations, satellite altimetry data near the eye of Typhoon Man-Yi (2007) before and after its passage, and synthetic aperture radar data taken during the typhoon's passage. In spite of the nearly symmetric wind pattern around the eye, the distribution of mesoscale eddies had a major impact on the surface currents and mixed layer (ML) depths. As a result, the entrainment of the water below the ML into the ML was affected by the mesoscale circulation and became asymmetric, which accounted for most of the changes observed in the temperature profiles. Changes in the isotherms were driven primarily by the westward propagation of the mesoscale pattern rather than by the typhoon-induced shoaling. The typhoon-induced shoaling could have played a significant role in the generation of high-frequency (e.g., near-inertial) oscillations and/or sub-mesoscale structures. Although a similar or even greater energy flux was observed at the surface, the entrainment within the anticyclonic circulation was weaker than that within the cyclonic circulation and at the edge of the anticyclonic circulation because of the thick pre-existing ML. A strong ocean response to Typhoon Man-Yi (2007) within a cyclonic circulation or at the edge of an anticyclonic circulation, rather than within an anticyclonic eddy, has implications for the role of mesoscale ocean circulations in better understanding and forecasting the typhoon intensity.

  4. Idealised modelling of ocean circulation driven by geothermal and hydrothermal fluxes at the seabed

    NASA Astrophysics Data System (ADS)

    Barnes, Jowan; Morales Maqueda, Miguel; Polton, Jeff

    2016-04-01

    There are two distinct processes by which heat is transferred from the solid Earth into the abyssal ocean. The first is conductive geothermal heating and the second is hydrothermal heating, involving advection of heated water from within the Earth's crust. Here, the noticeably different impacts of these two physical systems on ocean circulation are investigated. Previous modelling studies have applied geothermal heat fluxes at the seabed and shown discrepancies in circulation compared to cases which neglected heat from the Earth in their boundary conditions. The true heat flux in the ocean, however, is not entirely geothermal. From areas where the crust is younger a significant proportion of the heat input from the Earth could be in the form of fluid flow from hydrothermal vents, introducing forcing to the circulation which has previously been unaccounted for. In this study a set of idealised modelling experiments are run in order to investigate the effects of changing the balance of the total heat flux from purely geothermal to purely hydrothermal, via intermediate states in which the two boundary conditions are combined in different ratios. By performing such experiments it will be shown which of the two processes is dominant in its effects on circulation driven by heating at the seabed, and whether neglecting the hydrothermal advection in favour of a fully conductive geothermal boundary condition is justifiable. The results will inform the construction of boundary conditions for future circulation models involving ocean floor heat fluxes, specifically a regional study of geothermal and hydrothermal contributions within the Panama Basin.

  5. Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings

    NASA Astrophysics Data System (ADS)

    Borrelli, Chiara; Cramer, Benjamin S.; Katz, Miriam E.

    2014-04-01

    We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning ~38.5 Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene, ~1-4 Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (~34 Ma) and the consequent development of a circumpolar proto-ACC.

  6. Characterizing the circulation off the Kenyan-Tanzanian coast using an ocean model

    NASA Astrophysics Data System (ADS)

    Gabriela Mayorga-Adame, C.; Ted Strub, P.; Batchelder, Harold P.; Spitz, Yvette H.

    2016-02-01

    The Kenyan-Tanzanian coastal region in the western Indian Ocean faces several environmental challenges including coral reef conservation, fisheries management, coastal erosion, and nearshore pollution. The region lacks hydrodynamic records and oceanographic studies at adequate spatial and temporal scales to provide information relevant to the local environmental issues. We have developed a 4 km horizontal resolution ocean circulation model of the region: the Kenyan-Tanzanian Coastal Model (KTCM) that provides coastal circulation and hydrography with higher resolution than previous models and observational studies of this region. Comparisons to temperature profiles, satellite-derived sea surface temperature and sea surface height anomaly fields, indicate that the model reproduces the main features of the regional circulation, while greatly increasing the details of the nearshore circulation. We describe the seasonal ocean circulation and hydrography of the Kenyan-Tanzanian coastal region based on a climatology of 8 years (2000-2007) of the KTCM simulations. The regional monsoon seasonality produces two distinct coastal circulation regimes: (1) during December-March, there are relatively sluggish shelf flows and (2) during April-November, there are strong northward transports. Simulations from the model will be useful for examining dispersal of pollutants and spatial connectivity of coral reef species.

  7. Estimation and Validation of Oceanic Mass Circulation from the GRACE Mission

    NASA Technical Reports Server (NTRS)

    Boy, J.-P.; Rowlands, D. D.; Sabaka, T. J.; Luthcke, S. B.; Lemoine, F. G.

    2011-01-01

    Since the launch of the Gravity Recovery And Climate Experiment (GRACE) in March 2002, the Earth's surface mass variations have been monitored with unprecedented accuracy and resolution. Compared to the classical spherical harmonic solutions, global high-resolution mascon solutions allows the retrieval of mass variations with higher spatial and temporal sampling (2 degrees and 10 days). We present here the validation of the GRACE global mascon solutions by comparing mass estimates to a set of about 100 ocean bottom pressure (OSP) records, and show that the forward modelling of continental hydrology prior to the inversion of the K-band range rate data allows better estimates of ocean mass variations. We also validate our GRACE results to OSP variations modelled by different state-of-the-art ocean general circulation models, including ECCO (Estimating the Circulation and Climate of the Ocean) and operational and reanalysis from the MERCATOR project.

  8. Cloud-radiative effects on implied oceanic energy transport as simulated by atmospheric general circulation models

    NASA Technical Reports Server (NTRS)

    Gleckler, P. J.; Randall, D. A.; Boer, G.; Colman, R.; Dix, M.; Galin, V.; Helfand, M.; Kiehl, J.; Kitoh, A.; Lau, W.

    1995-01-01

    This paper summarizes the ocean surface net energy flux simulated by fifteen atmospheric general circulation models constrained by realistically-varying sea surface temperatures and sea ice as part of the Atmospheric Model Intercomparison Project. In general, the simulated energy fluxes are within the very large observational uncertainties. However, the annual mean oceanic meridional heat transport that would be required to balance the simulated surface fluxes is shown to be critically sensitive to the radiative effects of clouds, to the extent that even the sign of the Southern Hemisphere ocean heat transport can be affected by the errors in simulated cloud-radiation interactions. It is suggested that improved treatment of cloud radiative effects should help in the development of coupled atmosphere-ocean general circulation models.

  9. Constraints on ocean circulation at the Paleocene-Eocene Thermal Maximum from neodymium isotopes

    NASA Astrophysics Data System (ADS)

    Abbott, April N.; Haley, Brian A.; Tripati, Aradhna K.; Frank, Martin

    2016-04-01

    Global warming during the Paleocene-Eocene Thermal Maximum (PETM) ˜ 55 million years ago (Ma) coincided with a massive release of carbon to the ocean-atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role of changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites to reconstruct past deep-ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth Nd isotopes and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for initiation and recovery of the ocean-atmosphere system associated with the PETM.

  10. Constraints on ocean circulation at the Paleocene-Eocene Thermal Maximum from neodymium isotopes

    NASA Astrophysics Data System (ADS)

    Abbott, A. N.; Haley, B. A.; Tripati, A. K.; Frank, M.

    2015-06-01

    Global warming during the Paleocene Eocene Thermal Maximum (PETM) ~55 million years ago (Ma) coincided with a massive release of carbon to the ocean-atmosphere system, as indicated by carbon isotopic data. Previous studies have argued for a role for changing ocean circulation, possibly as a trigger or response to climatic changes. We use neodymium (Nd) isotopic data to reconstruct short high-resolution records of deep-water circulation across the PETM. These records are derived by reductively leaching sediments from seven globally distributed sites and comparing data with published data from fossil fish debris to reconstruct past deep ocean circulation across the PETM. The Nd data for the leachates are interpreted to be consistent with previous studies that have used fish teeth and benthic foraminiferal δ13C to constrain regions of convection. There is some evidence from combining Nd isotope and δ13C records that the three major ocean basins may not have had substantial exchanges of deep waters. If the isotopic data are interpreted within this framework, then the observed pattern may be explained if the strength of overturning in each basin varied distinctly over the PETM, resulting in differences in deep-water aging gradients between basins. Results are consistent with published interpretations from proxy data and model simulations that suggest modulation of overturning circulation had an important role for global recovery of the ocean-atmosphere system after the PETM.

  11. Effects of Southern Hemisphere Wind Changes on the Meridional Overturning Circulation in Ocean Models.

    PubMed

    Gent, Peter R

    2016-01-01

    Observations show that the Southern Hemisphere zonal wind stress maximum has increased significantly over the past 30 years. Eddy-resolving ocean models show that the resulting increase in the Southern Ocean mean flow meridional overturning circulation (MOC) is partially compensated by an increase in the eddy MOC. This effect can be reproduced in the non-eddy-resolving ocean component of a climate model, providing the eddy parameterization coefficient is variable and not a constant. If the coefficient is a constant, then the Southern Ocean mean MOC change is balanced by an unrealistically large change in the Atlantic Ocean MOC. Southern Ocean eddy compensation means that Southern Hemisphere winds cannot be the dominant mechanism driving midlatitude North Atlantic MOC variability. PMID:26163010

  12. The response of an ocean general circulation model to surface wind stress produced by an atmospheric general circulation model

    SciTech Connect

    Huang, B.; Schneider, E.K.

    1995-10-01

    Two surface wind stress datasets for 1979-91, one based on observations and the other from an investigation of the COLA atmospheric general circulation model (AGCM) with prescribed SST, are used to drive the GFDL ocean general circulation model. These two runs are referred to as the control and COLA experiments, respectively. Simulated SST and upper-ocean heat contents (HC) in the tropical Pacific Ocean are compared with observations and between experiments. Both simulation reproduced the observed mean SST and HC fields as well as their annual cycles realistically. Major errors common to both runs are colder than observed SST in the eastern equatorial ocean and HC in the western Pacific south of the equator, with errors generally larger in the COLA experiment. New errors arising from the AGCM wind forcing include higher SST near the South American coast throughout the year and weaker HC gradients along the equator in boreal spring. The former is associated with suppressed coastal upwelling by weak along shore AGCM winds, and the latter is caused by weaker equatorial easterlies in boreal spring. The low-frequency ENSO fluctuations are also realistic for both runs. Correlations between the observed and simulated SST anomalies from the COLA simulation are as high as those from the control run in the central equatorial Pacific. A major problem in the COLA simulation is the appearance of unrealistic tropical cold anomalies during the boreal spring of mature El Nino years. These anomalies propagate along the equator from the western Pacific to the eastern coast in about three months, and temporarily eliminate the warm SST and HC anomalies in the eastern Pacific. This erroneous oceanic response in the COLA simulation is caused by a reversal of the westerly wind anomalies on the equator, associated with an unrealistic southward shift of the ITCZ in boreal spring during El Nino events. 66 refs., 16 figs.

  13. Arctic Ocean circulation and variability - advection and external forcing encounter constraints and local processes

    NASA Astrophysics Data System (ADS)

    Rudels, B.

    2012-04-01

    The first hydrographic data from the Arctic Ocean, the section from the Laptev Sea to the passage between Greenland and Svalbard obtained by Nansen on his drift with Fram 1893-1896, aptly illustrate the main features of Arctic Ocean oceanography and indicate possible processes active in transforming the water masses in the Arctic Ocean. Many, perhaps most, processes were identified already by Nansen, who put his mark on almost all subsequent research in the Arctic. Here we shall revisit some key questions and follow how our understanding has evolved from the early 20th century to present. What questions, if any, can now be regarded as solved and which remain still open? Five different but connected topics will be discussed: (1) The low salinity surface layer and the storage and export of freshwater. (2) The vertical heat transfer from the Atlantic water to sea ice and to the atmosphere. (3) The circulation and mixing of the two Atlantic inflow branches. (4) The formation and circulation of deep and bottom waters in the Arctic Ocean. (5) The exchanges through Fram Strait. Foci will be on the potential effects of increased freshwater input and reduced sea ice export on the freshwater storage and residence time in the Arctic Ocean, on the deep waters of the Makarov Basin, and on the circulation and relative importance of the two inflows, over the Barents Sea and through Fram Strait, for the distribution of heat in the intermediate layers of the Arctic Ocean.

  14. A Nd Isotopic Composition Modeling Approach of the Oceanic Thermohaline Circulation Change During LGM

    NASA Astrophysics Data System (ADS)

    Arsouze, T.; Dutay, J.; Lacan, F.; Jeandel, C.; Alkama, R.; Kageyama, M.; Piotrowski, A.

    2006-12-01

    The role of thermohaline circulation in climate change has been a matter of debate for a long time. Proxies of past ocean circulation such as δ13C or 231Pa/230Th suggest a relationship between North Atlantic Deep Water (NADW) strength and rapid climate change. Neodymium isotopic composition (Nd IC) is a quasi conservative geochemical tracer of water masses in the ocean interior and thus can be used as a proxy for NADW. Seawater Nd IC being recorded in marine sediments, this proxy is used to infer paleo-circulations on various time scales. Recent studies of Nd IC records, in the ferromanganese oxide components of a South Atlantic core, confirm the close relation between thermohaline circulation and North Atlantic climate changes through the last deglaciation (Piotrowski et al., 2004). Our purpose here is to model the Nd IC during the LGM and the Holocene with the Ocean Global Circulation Model NEMO, in the ORCA2 (2°) configuration. The explicit simulation of this proxy in the model allows to investigate and quantify the circulation change that corresponds to the Nd isotopic composition variation recorded in the sediments. We consider that the main source of Nd into the ocean is the interaction between water masses and continental margins (Boundary Exchange process; (Lacan and Jeandel, 2005). Boundary exchange is parameterized using a relaxing term (Arsouze et al., 2006). Simulated Nd IC distributions are evaluated by comparison with available records for the LGM and Holocene. References: Arsouze, T., Dutay, J.-C., Lacan, F. and Jeandel, C., 2006. Modeling the neodymium isotopic composition with a global ocean circulation model Chemical Geology, in press. Lacan, F. and Jeandel, C., 2005. Neodymium isotopes as a new tool for quantifying exchange fluxes at the continent - ocean interface. Earth and Planetary Science Letters, 232(3-4): 245-257. Piotrowski, A.M., Goldstein, S.L., Hemming, S.R. and Fairbanks, R.G., 2004. Intensification and variability of ocean

  15. A Preliminary Study on the Circulation of an ocean covering a Synchronously Rotating Planet

    NASA Astrophysics Data System (ADS)

    Matsuo, H.; Ishiwatari, M.; Takehiro, S.; Hayashi, Y.; Nakajima, K.

    2012-12-01

    Recently, nearly 800 extrasolar planets have been detected. It seems that some of them present into habitable zone, in which planets can have ocean, and such planets rotate synchronously with their central stars. Ocean is necessary for life, and the circulation makes climate mild by heat transport on the earth. The earth is the only planet that has ocean in the solar system so that it has not been understood what oceanic circulation is like in another planets. The purpose of this study is prediction of oceanic circulation on extrasolar planets by using numerical simulation. As a first step, elementary consideration is made. The planet is almost entirely covered with ocean and whose rotation period corresponds with its orbital period. On synchronously rotating planets, the thermal contrast between day-hemisphere and night-hemisphere would be extreme. However, it may be lessend if there is significant zonal heat transport. The circulation in such conditions has not been known well. We performed a numerical experiment based on the linear shallow water equation, assuming that both the evaporation and the precipitation occur only on day-hemisphere (Noda et al., 2011). With these distributions of the evaporation and the precipitation, one may anticipate the circulation occurs in only day-hemisphere. However, the resulting calculation is characterized with zonally uniform zonal flow, which also covers night hemisphere. In addition, the intensity of the flow increases with time. That behavior can be understood by constructing asymptotic solution which is first degree in time. The importance of Coriolis force, which bends meridional flow to zonal flow, is identified. It is implied that, even when only day-hemisphere has the evaporation and precipitation, there may be significant amount of heat can be transported from the day-hemisphere to the night-hemisphere by the strong zonal flow. The growth of zonal flow would be stopped when the evaporation and the precipitation are

  16. Southern Ocean circulation changes across the last deglaciation: contribution from Marion-Dufresne cruises

    NASA Astrophysics Data System (ADS)

    Michel, Elisabeth; Siani, Giuseppe; Mazaud, Alain; Paterne, Martine; deVries, Tim; Jaccard, Samuel; Waelbroeck, Claire; Crosta, Xavier; Isguder, Gulay; Dewilde, Fabien; De Pol-Holz, Ricardo; Skinner, Luke; Kissel, Catherine

    2015-04-01

    The last deglaciation is marked by rapid climatic events linked to large reorganizations of the deep ocean circulation. To decipher the role of the Southern Ocean in these deep circulation changes requires reconstructing the evolution of its stratification and its zonal behavior during the last deglaciation from high resolution, well dated records. Furthermore, nowadays the connection between atmosphere and the deep ocean occurs through the Southern Ocean, and it might had a leading role in the evolution of atmospheric CO2 concentrations across the deglaciation. However, establishing a precise chronology for marine sediment records in high latitudes is a difficult task, as it requires the determination of radiocarbon surface water age changes. It has been possible to retrieve high sedimentation rate cores during Indian and Pacific oceanographic cruises, particularly PACHIDERME and INDIEN SUD expeditions. We pre. We aim at tying these marine records to terrestrial records, using tephra deposited in marine and terrestrial region in the different sector of the Southern Ocean when it is possible. This work is in progress within a French-Swedish project. We will present results at different depth from South West Pacific sector of the Southern Ocean and from the Indian sector. A precise chronology in the Indian sector requires to first establish the tephrochronology of Kerguelen Islands that is under progress. We compare these new records with previously published records of the Atlantic and Pacific sectors. It indicates that upwelling events drive radiocarbon changes in waters above 2500 m depth and increases in atmospheric CO2. Oceanic circulation changes are not synchroneous at deeper depth between 2500 and 4000 m depth. Southern Ocean temperature and vertical mixing increases occurs synchroneously with temperature increase above the Antarctic and atmospheric CO2 increases within error of marine and Ice chronologies, while the ACC current intensity decrease (or

  17. Mid-latitude wind forced ocean circulation studies

    NASA Technical Reports Server (NTRS)

    Harrison, D. E.

    1981-01-01

    A simple barotropic vorticity equation model was developed to study some of the various modeling factors that affect the characteristics of strong western boundary currents like the Gulf Stream and Kuroshio. Successful prediction of sea surface temperature, both in the climatological mean and over periods as short as 1 month requires that the heating tendency, due to horizontal advection of heat by these currents, be accurately modeled. Conventional, coarse resolution ocean models do not satisfactorily reproduce the dominant features of these currents. It is concluded that it is important to understand why they do not and what must be done to do so in the future.

  18. Biogeochemical, Isotopic and Bacterial Distributions Trace Oceanic Abyssal Circulation.

    PubMed

    Rubino, Angelo; Bensi, Manuel; Hainbucher, Dagmar; Zanchettin, Davide; Mapelli, Francesca; Ogrinc, Nives; Marchetto, Davide; Borin, Sara; Cardin, Vanessa; Fajon, Vesna; Horvat, Milena; Taricco, Carla; Baldi, Franco

    2016-01-01

    We explore the possibility of tracing routes of dense waters toward and within the ocean abyss by the use of an extended set of observed physical and biochemical parameters. To this purpose, we employ mercury, isotopic oxygen, biopolymeric carbon and its constituents, together with indicators of microbial activity and bacterial diversity found in bottom waters of the Eastern Mediterranean. In this basin, which has been considered as a miniature global ocean, two competing sources of bottom water (one in the Adriatic and one in the Aegean seas) contribute to the ventilation of the local abyss. However, due to a recent substantial reduction of the differences in the physical characteristics of these two water masses it has become increasingly complex a water classification using the traditional approach with temperature, salinity and dissolved oxygen alone. Here, we show that an extended set of observed physical and biochemical parameters allows recognizing the existence of two different abyssal routes from the Adriatic source and one abyssal route from the Aegean source despite temperature and salinity of such two competing sources of abyssal water being virtually indistinguishable. Moreover, as the near-bottom development of exogenous bacterial communities transported by convectively-generated water masses in the abyss can provide a persistent trace of episodic events, intermittent flows like those generating abyssal waters in the Eastern Mediterranean basin may become detectable beyond the availability of concomitant measurements. PMID:26761666

  19. Biogeochemical, Isotopic and Bacterial Distributions Trace Oceanic Abyssal Circulation

    PubMed Central

    Rubino, Angelo; Bensi, Manuel; Hainbucher, Dagmar; Zanchettin, Davide; Mapelli, Francesca; Ogrinc, Nives; Marchetto, Davide; Borin, Sara; Cardin, Vanessa; Fajon, Vesna; Horvat, Milena; Taricco, Carla; Baldi, Franco

    2016-01-01

    We explore the possibility of tracing routes of dense waters toward and within the ocean abyss by the use of an extended set of observed physical and biochemical parameters. To this purpose, we employ mercury, isotopic oxygen, biopolymeric carbon and its constituents, together with indicators of microbial activity and bacterial diversity found in bottom waters of the Eastern Mediterranean. In this basin, which has been considered as a miniature global ocean, two competing sources of bottom water (one in the Adriatic and one in the Aegean seas) contribute to the ventilation of the local abyss. However, due to a recent substantial reduction of the differences in the physical characteristics of these two water masses it has become increasingly complex a water classification using the traditional approach with temperature, salinity and dissolved oxygen alone. Here, we show that an extended set of observed physical and biochemical parameters allows recognizing the existence of two different abyssal routes from the Adriatic source and one abyssal route from the Aegean source despite temperature and salinity of such two competing sources of abyssal water being virtually indistinguishable. Moreover, as the near-bottom development of exogenous bacterial communities transported by convectively-generated water masses in the abyss can provide a persistent trace of episodic events, intermittent flows like those generating abyssal waters in the Eastern Mediterranean basin may become detectable beyond the availability of concomitant measurements. PMID:26761666

  20. Anisotropic mesoscale eddy transport in ocean general circulation models

    NASA Astrophysics Data System (ADS)

    Reckinger, Scott; Fox-Kemper, Baylor; Bachman, Scott; Bryan, Frank; Dennis, John; Danabasoglu, Gokhan

    2014-11-01

    In modern climate models, the effects of oceanic mesoscale eddies are introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically. However, the diffusive processes that the parameterization approximates, such as shear dispersion and potential vorticity barriers, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters from one to three: major diffusivity, minor diffusivity, and alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces temperature and salinity biases. These effects can be improved by parameterizing the oceanic anisotropic transport mechanisms.

  1. Relaxation oscillations in an idealized ocean circulation model

    NASA Astrophysics Data System (ADS)

    Roberts, Andrew; Saha, Raj

    2016-06-01

    This work is motivated by a desire to understand transitions between stable equilibria observed in Stommel's 1961 thermohaline circulation model. We adapt the model, including a forcing parameter as a dynamic slow variable. The resulting model is a piecewise-smooth, three time-scale system. The model is analyzed using geometric singular perturbation theory to demonstrate the existence of attracting periodic orbits. The system is capable of producing classical relaxation oscillations as expected, but there is also a parameter regime in which the model exhibits small amplitude oscillations known as canard cycles. Forcing the model with obliquity variations from the last 100,000 years produces oscillations that are modulated in amplitude and frequency. The output shows similarities with important features of the climate proxy data of the same period.

  2. Impacts of Interannual Ocean Circulation Variability on Japanese Eel Larval Migration in the Western North Pacific Ocean

    PubMed Central

    Chang, Yu-Lin; Sheng, Jinyu; Ohashi, Kyoko; Béguer-Pon, Mélanie; Miyazawa, Yasumasa

    2015-01-01

    The Japanese eel larvae hatch near the West Mariana Ridge seamount chain and travel through the North Equatorial Current (NEC), the Kuroshio, and the Subtropical Countercurrent (STCC) region during their shoreward migration toward East Asia. The interannual variability of circulation over the subtropical and tropical regions of the western North Pacific Ocean is affected by the Philippines–Taiwan Oscillation (PTO). This study examines the effect of the PTO on the Japanese eel larval migration routes using a three-dimensional (3D) particle tracking method, including vertical and horizontal swimming behavior. The 3D circulation and hydrography used for particle tracking are from the ocean circulation reanalysis produced by the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2). Our results demonstrate that bifurcation of the NEC and the strength and spatial variation of the Kuroshio affect the distribution and migration of eel larvae. During the positive phase of PTO, more virtual eels (“v-eels”) can enter the Kuroshio to reach the south coast of Japan and more v-eels reach the South China Sea through the Luzon Strait; the stronger and more offshore swing of the Kuroshio in the East China Sea leads to fewer eels entering the East China Sea and the onshore movement of the Kuroshio to the south of Japan brings the eels closer to the Japanese coast. Significant differences in eel migration routes and distributions regulated by ocean circulation in different PTO phases can also affect the otolith increment. The estimated otolith increment suggests that eel age tends to be underestimated after six months of simulation due to the cooler lower layer temperature. Underestimation is more significant in the positive PTO years due to the wide distribution in higher latitudes than in the negative PTO years. PMID:26642318

  3. Impacts of Interannual Ocean Circulation Variability on Japanese Eel Larval Migration in the Western North Pacific Ocean.

    PubMed

    Chang, Yu-Lin; Sheng, Jinyu; Ohashi, Kyoko; Béguer-Pon, Mélanie; Miyazawa, Yasumasa

    2015-01-01

    The Japanese eel larvae hatch near the West Mariana Ridge seamount chain and travel through the North Equatorial Current (NEC), the Kuroshio, and the Subtropical Countercurrent (STCC) region during their shoreward migration toward East Asia. The interannual variability of circulation over the subtropical and tropical regions of the western North Pacific Ocean is affected by the Philippines-Taiwan Oscillation (PTO). This study examines the effect of the PTO on the Japanese eel larval migration routes using a three-dimensional (3D) particle tracking method, including vertical and horizontal swimming behavior. The 3D circulation and hydrography used for particle tracking are from the ocean circulation reanalysis produced by the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2). Our results demonstrate that bifurcation of the NEC and the strength and spatial variation of the Kuroshio affect the distribution and migration of eel larvae. During the positive phase of PTO, more virtual eels ("v-eels") can enter the Kuroshio to reach the south coast of Japan and more v-eels reach the South China Sea through the Luzon Strait; the stronger and more offshore swing of the Kuroshio in the East China Sea leads to fewer eels entering the East China Sea and the onshore movement of the Kuroshio to the south of Japan brings the eels closer to the Japanese coast. Significant differences in eel migration routes and distributions regulated by ocean circulation in different PTO phases can also affect the otolith increment. The estimated otolith increment suggests that eel age tends to be underestimated after six months of simulation due to the cooler lower layer temperature. Underestimation is more significant in the positive PTO years due to the wide distribution in higher latitudes than in the negative PTO years. PMID:26642318

  4. Numerics-Characteristics-Asymptotics: A Case Study from Large Scale Ocean Circulation

    ERIC Educational Resources Information Center

    Hodnett, P. F.; Courtney, C.

    2007-01-01

    This paper uses a partial differential equation which occurs in a reduced model of large scale circulation in an ocean basin as an educational vehicle through which to demonstrate the usefulness of a set of mathematical techniques in analysing the equation. A parameter occurring in the equation does in reality vary from very small through…

  5. Barbi: a simplified general circulation model for a baroclinic ocean with topography

    NASA Astrophysics Data System (ADS)

    Eden, C.; Olbers, D.

    2003-04-01

    A new type of ocean general circulation model with simplified physics is described and tested for various simple wind--driven circulation problems.The model consists of the vorticity balance of the depth-averaged flow and a hierarchy of equations for ``vertical moments'' of density and baroclinic velocity. The first vertical density moment is the (vertically integrated) potential energy, which is used to describe the predominant link between the barotropic and the baroclinic oceanic flow in the presence of sloping topography. Tendency equations for the vertical moments of density and baroclinic velocity and an appropriate truncation of the coupled hierarchy of moments are derived which, together with the barotropic vorticity balance, yield a closed set of equations describing the BARotropic-Baroclinic-Interaction (BARBI) model of the oceanic circulation. Idealized companion experiments with a numerical implementation of the BARBI model and a primitive equation model indicate that wave propagation properties and baroclinic adjustments are correctly represented in BARBI in mid latitudes as well as in equatorial latitudes. Furthermore, a set of experiments with a realistic application to the Atlantic/Southern Ocean system reproduces important aspects which have been previously reported by studies of gyre circulations and circumpolar currents using full primitive equation models.

  6. Simulation of seasonal anomalies of atmospheric circulation using coupled atmosphere-ocean model

    NASA Astrophysics Data System (ADS)

    Tolstykh, M. A.; Diansky, N. A.; Gusev, A. V.; Kiktev, D. B.

    2014-03-01

    A coupled atmosphere-ocean model intended for the simulation of coupled circulation at time scales up to a season is developed. The semi-Lagrangian atmospheric general circulation model of the Hydrometeorological Centre of Russia, SLAV, is coupled with the sigma model of ocean general circulation developed at the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), INMOM. Using this coupled model, numerical experiments on ensemble modeling of the atmosphere and ocean circulation for up to 4 months are carried out using real initial data for all seasons of an annual cycle in 1989-2010. Results of these experiments are compared to the results of the SLAV model with the simple evolution of the sea surface temperature. A comparative analysis of seasonally averaged anomalies of atmospheric circulation shows prospects in applying the coupled model for forecasts. It is shown with the example of the El Niño phenomenon of 1997-1998 that the coupled model forecasts the seasonally averaged anomalies for the period of the nonstationary El Niño phase significantly better.

  7. Oceanic circulation models help to predict global biogeography of pelagic yellow-bellied sea snake.

    PubMed

    Brischoux, François; Cotté, Cédric; Lillywhite, Harvey B; Bailleul, Frédéric; Lalire, Maxime; Gaspar, Philippe

    2016-08-01

    It is well recognized that most marine vertebrates, and especially tetrapods, precisely orient and actively move in apparently homogeneous oceanic environments. Here, we investigate the presumptive role of oceanic currents in biogeographic patterns observed in a secondarily marine tetrapod, the yellow-bellied sea snake (Hydrophis [Pelamis] platurus). State-of-the-art world ocean circulation models show how H. platurus, the only pelagic species of sea snake, can potentially exploit oceanic currents to disperse and maintain population mixing between localities that spread over two-thirds of the Earth's circumference. The very close association of these snakes with surface currents seems to provide a highly efficient dispersal mechanism that allowed this species to range extensively and relatively quickly well beyond the central Indo-Pacific area, the centre of origin, abundance and diversity of sea snakes. Our results further suggest that the pan-oceanic population of this species must be extraordinarily large. PMID:27555651

  8. Improvement in Geoid Models for Ocean Circulation Studies

    NASA Technical Reports Server (NTRS)

    Tapley, Byron D.; Chambers, Don P.; Poole, Steve; Ries, John c.

    2003-01-01

    At wavelengths of 500 km and longer, the GRACE GGM01 Model produces a significantly better marine geoid than any previous model. This conclusion follows from evaluating the geostrophic currents determined by combining the model with a mean sea surface from altimetry. The agreement with currents computed from a traditional hydrographic map is very close, which suggests that one of the primary missions of the TOPEX/POSEIDON mission, to determine the absolute dynamic ocean topography, may soon be met. This solution has been made available to the public at http://www.csr.utexs.edu/grace/gravity. The results reported in this paper have been presented at the 2003 EGS-AGU-EUG Joint Assembly. Two articles are currently being prepared for Geophysical Research Letters to summarize these results.

  9. The shallow meridional overturning circulation in the northern Indian Ocean and its interannual variability

    NASA Astrophysics Data System (ADS)

    Hu, Ruijin; Liu, Qinyu; Wang, Qi; Godfrey, J. Stuart; Meng, Xiangfeng

    2005-03-01

    The shallow meridional overturning circulation (upper 1000 m) in the northern Indian Ocean and its interannual variability are studied, based on a global ocean circulation model (MOM2) with an integration of 10 years (1987 1996). It is shown that the shallow meridional overturning circulation has a prominent seasonal reversal characteristic. In winter, the flow is northward in the upper layer and returns southward at great depth. In summer, the deep northward inflow upwells north of the equator and returns southward in the Ekman layer. In the annual mean, the northward inflow returns through two branches: one is a southward flow in the Ekman layer, the other is a flow that sinks near 10°N and returns southward between 500 m and 1000 m. There is significant interannual variability in the shallow meridional overturning circulation, with a stronger (weaker) one in 1989 (1991) and with a period of about four years. The interannual variability of the shallow meridional overturning circulation is intimately related to that of the surface wind stress. Several indices are proposed to describe the anomaly of this circulation associated with the cross-equatorial part.

  10. Impact of ocean heat transport variations on the zonal mean circulation in an idealized moist GCM

    NASA Astrophysics Data System (ADS)

    Bischoff, T.; Schneider, T.

    2012-12-01

    We study how equatorial surface heat sources affect the strength and width of the Hadley circulation to elucidate the dynamics of tropical-extratropical interactions. The well-known atmospheric response to El Niño-like forcings includes an equatorward shift in the Hadley circulation terminus and the subtropical jets. One proposed mechanisms for this response involves changes in subtropical baroclinicity and associated equatorward shifts in critical latitudes. Here we use an idealized aquaplanet general circulation model with a hydrological cycle and a time-independent, zonally symmetric background ocean heat transport to investigate systematically how the zonal mean climate responds to imposed equatorial ocean heating anomalies. This approach allows for dynamically adjusted surface temperatures and closed surface energy budgets. We study the sensitivity to the equatorial heating anomalies for different imposed longwave optical thickness profiles representing cold, Earth-like and warm climates. Consistent with previous studies, we find a shift of the Hadley circulation terminus towards the equator and a concomitant increase in subtropical baroclinicity for equatorial warming, and vice versa for an equatorial cooling. Together with the Hadley circulation terminus, the subtropical jets, regions of poleward eddy momentum and heat fluxes as well as storm tracks, shift towards (away from) the equator for simulations with imposed equatorial warming (cooling). We account for the circulation response with theoretical arguments for the structure of baroclinic eddies.

  11. Interhemispheric controls on deep ocean circulation and carbon chemistry during the last two glacial cycles

    NASA Astrophysics Data System (ADS)

    Wilson, David J.; Piotrowski, Alexander M.; Galy, Albert; Banakar, Virupaxa K.

    2015-06-01

    Changes in ocean circulation structure, together with biological cycling, have been proposed for trapping carbon in the deep ocean during glacial periods of the Late Pleistocene, but uncertainty remains in the nature and timing of deep ocean circulation changes through glacial cycles. In this study, we use neodymium (Nd) and carbon isotopes from a deep Indian Ocean sediment core to reconstruct water mass mixing and carbon cycling in Circumpolar Deep Water over the past 250 thousand years, a period encompassing two full glacial cycles and including a range of orbital forcing. Building on recent studies, we use reductive sediment leaching supported by measurements on isolated phases (foraminifera and fish teeth) in order to obtain a robust seawater Nd isotope reconstruction. Neodymium isotopes record a changing North Atlantic Deep Water (NADW) component in the deep Indian Ocean that bears a striking resemblance to Northern Hemisphere climate records. In particular, we identify both an approximately in-phase link to Northern Hemisphere summer insolation in the precession band and a longer-term reduction of NADW contributions over the course of glacial cycles. The orbital timescale changes may record the influence of insolation forcing, for example via NADW temperature and/or Antarctic sea ice extent, on deep stratification and mixing in the Southern Ocean, leading to isolation of the global deep oceans from an NADW source during times of low Northern Hemisphere summer insolation. That evidence could support an active role for changing deep ocean circulation in carbon storage during glacial inceptions. However, mid-depth water mass mixing and deep ocean carbon storage were largely decoupled within glacial periods, and a return to an interglacial-like circulation state during marine isotope stage (MIS) 6.5 was accompanied by only minor changes in atmospheric CO2. Although a gradual reduction of NADW export through glacial periods may have produced slow climate feedbacks

  12. North Atlantic ocean circulation and abrupt climate change during the last glaciation.

    PubMed

    Henry, L G; McManus, J F; Curry, W B; Roberts, N L; Piotrowski, A M; Keigwin, L D

    2016-07-29

    The most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations, whose origin remains unresolved. Variations in oceanic meridional heat transport may contribute to these repeated climate changes, which were most pronounced during marine isotope stage 3, the glacial interval 25 thousand to 60 thousand years ago. We examined climate and ocean circulation proxies throughout this interval at high resolution in a deep North Atlantic sediment core, combining the kinematic tracer protactinium/thorium (Pa/Th) with the deep water-mass tracer, epibenthic δ(13)C. These indicators suggest reduced Atlantic overturning circulation during every cool northern stadial, with the greatest reductions during episodic Hudson Strait iceberg discharges, while sharp northern warming followed reinvigorated overturning. These results provide direct evidence for the ocean's persistent, central role in abrupt glacial climate change. PMID:27365315

  13. Chemical Clues of a Changing Upper Arctic Ocean Circulation: A tribute to John M. Edmond

    NASA Astrophysics Data System (ADS)

    Falkner, K. K.

    2001-12-01

    Chemical Clues of a Changing Upper Arctic Ocean Circulation: A tribute to John M. Edmond In April 2000, an international research team, supported by the National Science Foundation (NSF), embarked on a five-year program to undertake atmosphere-ice-ocean observations at distributed locations in the high Arctic Ocean. The first temporary camp at the North Pole that year laid the groundwork for taking the pulse of the Arctic Ocean and learning how the world's northernmost sea helps regulate global climate. The Arctic Ocean has been affected in recent years by dramatic thinning of sea ice and shifts in ocean circulation which seem to be related to a pattern of change in the atmospheric circulation of the Northern Hemisphere. The objective of the "North Pole Environmental Observatory" or NPEO is to document further change and to understand what is controlling the Arctic system. Among other things, the NPEO includes a hydrographic component in which Twin Otter aircraft are landed on the ice at targeted stations in order to record ocean properties and take water samples through holes drilled in the ice. I am responsible for contributing chemical measurements to deciphering upper ocean circulation patterns under the ice. Properties analyzed thus far include salinity, nutrients, oxygen, oxygen isotopic composition of water and barium. Results are posted at http://chemoc.oce.orst.edu/users/kfalkner/index.html this web-site by year. This site is linked to the main project web-site where additional information about NPEO can be found. In my AGU presentation, I will describe the challenging field program and summarize implications of the chemical data to date. The news of John Edmond's untimely death reached me while I was en route to the North Pole camp this past April. Seemingly endless hours on a Canadian Hercules allowed me to reflect on the many influences John had on me as his graduate student and beyond. One thing is certain; there was no way in hell I'd have been

  14. Iceberg discharges and oceanic circulation changes during glacial abrupt climate changes

    NASA Astrophysics Data System (ADS)

    Alvarez-Solas, Jorge; Robinson, Alexander; Banderas, Rubén; Montoya, Marisa

    2015-04-01

    Proxy data reveal the existence of episodes of increased deposition of ice-rafted debris in the North Atlantic Ocean during the last glacial period. These are interpreted as massive iceberg discharges mainly from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence points to an active role of the oceanic circulation. Here we will present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model. Two mechanisms producing iceberg discharges are compared. First, we reproduce the classic binge-purge by which the iceberg surges are produced thanks to the existence of an internal thermo-mechanical feedback that allows the ice sheet to behave under an oscillatory regime. Second, our ice-sheet model is forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. In this case, the model generates a time series of iceberg calving that agrees with ice-rafted debris records over the past 80 ka. We compare the two theories and discuss their advantages and weaknesses in terms of both the robustness of the physics on which they are based and their comparison with proxies. This comparison highlights the importance of considering past oceanic circulation changes in order to understand the ice-sheet dynamics. However, the ultimate processes determining abrupt changes in the Atlantic Meridional Overturning Circulation (AMOC) remain elusive. Therefore we will also analyze several proposed mechanisms that aims to explain such AMOC reorganizations, focusing on those that do not require freshwater flux forcing.

  15. Dynamics of the Atlantic meridional overturning circulation and Southern Ocean in an ocean model of intermediate complexity

    NASA Astrophysics Data System (ADS)

    McCreary, Julian P.; Furue, Ryo; Schloesser, Fabian; Burkhardt, Theodore W.; Nonaka, Masami

    2016-04-01

    A steady-state, variable-density, 2-layer, ocean model (VLOM) is used to investigate basic dynamics of the Atlantic meridional overturning circulation and Southern Ocean. The domain consists of idealized (rectangular) representations of the Atlantic, Southern, and Pacific Oceans. The model equations represent the depth-averaged, layer-1 response (except for one solution in which they represent the depth-integrated flow over both layers). To allow for overturning, water can cross the bottom of layer 1 at the velocity we =wd +wm +wn , the three parts representing: interior diffusion wd that increases the layer-1 thickness h throughout the basin, mixed-layer entrainment wm that ensures h is never less than a minimum value hm , and diapycnal (cooling) processes external to the basin wn that adjust h to hn . For most solutions, horizontal mixing has the form of Rayleigh damping with coefficient ν , which we interpret to result from baroclinic instability through the closure, V∗ = - (ν /f2) ∇P , where ∇P = ∇(1/2 g‧h2) is the depth-integrated pressure gradient, g‧ is the reduced-gravity coefficient, and ν is a mixing coefficient; with this interpretation, the layer-1 flow corresponds to the sum of the Eulerian-mean and eddy-mean (V∗) transport/widths, that is, the "residual" circulation. Finally, layer-1 temperature cools polewards in response to a surface heat flux Q, and the cooling can be strong enough in the Southern Ocean for g‧ = 0 south of a latitude y0 , in which case layer 1 vanishes and the model reduces to a single layer 2. Solutions are obtained both numerically and analytically. The analytic approach splits fields into interior and boundary-layer parts, from which a coupled set of integral constraints can be derived. The set allows properties of the circulation (upwelling-driven transport out of the Southern Ocean M , downwelling transport in the North Atlantic, transport of the Antarctic Circumpolar Current) and stratification (Atlantic

  16. Simulating the three-dimensional circulation and hydrography of Halifax Harbour using a multi-nested coastal ocean circulation model

    NASA Astrophysics Data System (ADS)

    Shan, Shiliang; Sheng, Jinyu; Thompson, Keith Richard; Greenberg, David Alexander

    2011-07-01

    Halifax Harbour is located on the Atlantic coast of Nova Scotia, Canada. It is one of the world's largest, ice-free natural harbours and of great economic importance to the region. A good understanding of the physical processes controlling tides, flooding, transport and dispersion, and hydrographic variability is required for pollution control and sustainable development of the Harbour. For the first time, a multi-nested, finite difference coastal ocean circulation model is used to reconstruct the three-dimensional circulation and hydrography of the Harbour and its variability on timescales of hours to months for 2006. The model is driven by tides, wind and sea level pressure, air-sea fluxes of heat, and terrestrial buoyancy fluxes associated with river and sewage discharge. The predictive skill of the model is assessed by comparing the model simulations with independent observations of sea level from coastal tide gauges and currents from moored instruments. The simulated hydrography is also compared against a new monthly climatology created from all available temperature and salinity observations made in the Harbour over the last century. It is shown that the model can reproduce accurately the main features of the observed tides and storm surge, seasonal mean circulation and hydrography, and wind driven variations. The model is next used to examine the main physical processes controlling the circulation and hydrography of the Harbour. It is shown that non-linear interaction between tidal currents and complex topography occurs over the Narrows. The overall circulation can be characterized as a two-layer estuarine circulation with seaward flow in the thin upper layer and landward flow in the broad lower layer. An important component of this estuarine circulation is a relatively strong, vertically sheared jet situated over a narrow sill connecting the inner Harbour to the deep and relatively quiescent Bedford Basin. Local wind driven variability is strongest in

  17. Evaporites and the Salinity of the Ocean During the Phanerozoic: Implications for Climate, Ocean Circulation and Life

    NASA Astrophysics Data System (ADS)

    Floegel, S.; Hay, W. W.; Migdisov, A.; Balukhovsky, A. N.; Wold, C. N.; Soeding, E.

    2005-12-01

    A compilation of data on volumes and masses of evaporite deposits is used as the basis for reconstruction of the salinity of the ocean in the past. Chloride is tracked as the only ion essentially restricted to the ocean, and past salinities are calculated from reconstructed chlorine content of the ocean. Models for ocean salinity through the Phanerozoic are developed using maximal and minimal estimates of the volumes of existing evaporite deposits, and constant and declining volumes of ocean water through the Phanerozoic. We conclude that there have been significant changes in the mean salinity of the ocean accompanying a general decline throughout the Phanerozoic. The greatest changes are related to major extractions of salt into the ocean basins which developed during the Mesozoic as Pangaea broke apart. Unfortunately, the sizes of these salt deposits are also the least well known. The last major extractions of salt from the ocean occurred during the Miocene, shortly after the large scale extraction of water from the ocean to form the ice cap of Antarctica. However, these two modifications of the masses of H2O and salt in the ocean followed in sequence and did not cancel each other out. Accordingly, salinities during the Early Miocene were reconstructed to be between 37‰ and 39‰. The Mesozoic was a time of generally declining salinity associated with the deep sea salt extractions of the North Atlantic and Gulf of Mexico (Middle to Late Jurassic) and South Atlantic (Early Cretaceous). The earliest of the major extractions of the Phanerozoic occurred during the Permian. There were few large extractions of salt during the earlier Paleozoic. The models suggest that this was a time of relatively stable but slowly increasing salinities ranging through the upper 40‰'s into the lower 50‰'s. Higher salinities for the world ocean had profound consequences for the thermohaline circulation of the ocean in the past. In the modern ocean, with an average salinity of

  18. Abrupt pre-Bølling-Allerød warming and circulation changes in the deep ocean

    NASA Astrophysics Data System (ADS)

    Thiagarajan, Nivedita; Subhas, Adam V.; Southon, John R.; Eiler, John M.; Adkins, Jess F.

    2014-07-01

    Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling-Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean's usual thermal stratification pre-dates the Bølling-Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the

  19. Two regimes of the Arctic's circulation from ocean models with ice and contaminants.

    PubMed

    Proshutinsky, A Y; Johnson, M

    2001-01-01

    A two-dimensional barotropic, coupled, ocean-ice model with a space resolution of 55.5 km and driven by atmospheric forces, river run-off, and sea-level slope between the Pacific and the Arctic Oceans, has been used to simulate the vertically averaged currents and ice drift in the Arctic Ocean. Results from 43 years of numerical simulations of water and ice motions demonstrate that two wind-driven circulation regimes are possible in the Arctic, a cyclonic and an anti-cyclonic circulation. These two regimes appear to alternate at 5-7 year intervals with the 10-15 year period. It is important to pollution studies to understand which circulation regime prevails at any time. It is anticipated that 1995 is a year with a cyclonic regime, and during this cyclonic phase and possibly during past cyclonic regimes as well, pollutants may reach the Alaskan shelf. The regime shifts demonstrated in this paper are fundamentally important to understanding the Arctic's general circulation and particularly important for estimating pollution transport. PMID:11601534

  20. Carbon dioxide induced ocean climatic change and tracer experiment with an atmosphere-ocean general circulation model

    SciTech Connect

    Jiang, Xingjian.

    1991-01-01

    The principal objective of this study is to determine whether or not the penetration of a passive tracer is analogous to the penetration of a greenhouse-gas-induced heating. The Atmosphere Ocean General Circulation Model (A-O GCM) has been used to study CO2-induced climate change and the penetration of passive tracers into the world ocean. The present climate and a 2 x CO2 climate have been simulated. The passive tracers tritium, CFC-11, CFC-12 and a 'passive CO2- induced heating' are simulated. The CO2-induced active and passive warmings are larger in the subtropics and high latitudes than in the tropics. The largest difference between the active and passive CO2-induced heatings occur in the North Atlantic deep ocean, with maximum cooling about -1.5C for the active case in layer four of the ocean (1150m). There is no hemispherically asymmetric warming as that found by Manabe et al. (1990) and Stouffer et al. (1990). The convective overturning and large-scale sinking motion are responsible for the large penetration of CO2-induced warming in high latitudes. The CO2-induced circulation changes show that the North Atlantic thermohaline circulation is significantly weakened due to the penetration of CO2-induced heating. Associated with this change, the strength of North Atlantic conveyor belt is reduced, which results in a large warming in the upper ocean and cooling in the deep layers. The characteristic response time ranges from 40-50 years for the active CO2-induced climate change, and 70-160 years for passive CO2-induced climate change. The physical processes controlling the geochemical tracer penetration are very similar to those for the CO2-induced heating. There is not a single tracer which penetrates into the ocean exactly like the active CO2-induced heating in terms of distribution, transport or physical process. CFC's may be the best candidate as a surrogate for the CO2-induced oceanic climate study.

  1. Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

    NASA Astrophysics Data System (ADS)

    Chen, K.; He, R.

    2015-07-01

    A regional-scale ocean model was used to hindcast the coastal circulation over the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM) from 2004 to 2013. The model was nested inside a data assimilative global ocean model that provided initial and open boundary conditions. Realistic atmospheric forcing, tides and observed river runoff were also used to drive the model. Hindcast solutions were compared against observations, which included coastal sea levels, satellite altimetry sea surface height, in situ temperature and salinity measurements in the GOM, and observed mean depth-averaged velocities. Good agreements with observations suggest that the hindcast model is capable of capturing the major circulation variability in the MAB and GOM. Time- and space-continuous hindcast fields were used to depict the mean circulation, along- and cross-shelf transport and the associated momentum balances. The hindcast confirms the presence of the equatorward mean shelf circulation, which varies from 2.33 Sv over the Scotian Shelf to 0.22 Sv near Cape Hatteras. Using the 200 m isobath as the shelf/slope boundary, the mean cross-shelf transport calculations indicate that the shelfbreak segments off the Gulf of Maine (including the southern flank of Georges Bank and the Northeast Channel) and Cape Hatteras are the major sites for shelf water export. The momentum analysis reveals that the along-shelf sea level difference from Nova Scotia to Cape Hatteras is about 0.36 m. The nonlinear advection, stress, and horizontal viscosity terms all contribute to the ageostrophic circulation in the along-isobath direction, whereas the nonlinear advection plays a dominant role in determining the ageostrophic current in the cross-isobath direction.

  2. Mean circulation in the coastal ocean off northeastern North America from a regional-scale ocean model

    NASA Astrophysics Data System (ADS)

    Chen, K.; He, R.

    2014-12-01

    A regional-scale ocean model was used to hindcast the coastal circulation over the Middle Atlantic Bight (MAB) and Gulf of Maine (GOM) from 2004 to 2013. The model was nested inside a data assimilative global ocean model that provided initial and open boundary conditions. Realistic atmospheric forcing, tides and observed river runoff were also used to drive the model. Hindcast solutions were compared against observations, which included coastal sea levels, satellite altimetry sea surface height, temperature and salinity time series in the GOM, glider transects in the MAB, and observed mean depth-averaged velocities by Lentz (2008a). Good agreements with observations suggest that the hindcast model is capable of capturing the major circulation variability in the MAB and GOM. Time- and space-continuous hindcast fields were used to depict the mean circulation, along- and cross-shelf transport and the associated momentum balances. The hindcast confirms the presence of the equatorward mean shelf circulation, which varies from 2.33 Sv at Scotian Shelf to 0.22 Sv near Cape Hatteras. Using the 200 m isobath as the shelf/slope boundary, the mean cross-shelf transport calculations indicate that the shelfbreak segments off the Gulf of Maine (including the southern flank of Georges Bank and the Northeast Channel) and Cape Hatteras are the major sites for shelf water export. The momentum analysis reveals that the along-shelf sea level difference from Nova Scotia to Cape Hatteras is about 0.36 m. The nonlinear advection, stress, and horizontal viscosity terms all contribute to the ageostrophic circulation in the along-isobath direction, whereas the nonlinear advection plays a dominant role in determining the ageostrophic current in the cross-isobath direction.

  3. Impact of variable seawater conductivity on motional induction simulated with an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Irrgang, C.; Saynisch, J.; Thomas, M.

    2016-01-01

    Carrying high concentrations of dissolved salt, ocean water is a good electrical conductor. As seawater flows through the Earth's ambient geomagnetic field, electric fields are generated, which in turn induce secondary magnetic fields. In current models for ocean-induced magnetic fields, a realistic consideration of seawater conductivity is often neglected and the effect on the variability of the ocean-induced magnetic field unknown. To model magnetic fields that are induced by non-tidal global ocean currents, an electromagnetic induction model is implemented into the Ocean Model for Circulation and Tides (OMCT). This provides the opportunity to not only model ocean-induced magnetic signals but also to assess the impact of oceanographic phenomena on the induction process. In this paper, the sensitivity of the induction process due to spatial and temporal variations in seawater conductivity is investigated. It is shown that assuming an ocean-wide uniform conductivity is insufficient to accurately capture the temporal variability of the magnetic signal. Using instead a realistic global seawater conductivity distribution increases the temporal variability of the magnetic field up to 45 %. Especially vertical gradients in seawater conductivity prove to be a key factor for the variability of the ocean-induced magnetic field. However, temporal variations of seawater conductivity only marginally affect the magnetic signal.

  4. Century-scale variability in a randomly forced, two-dimensional thermohaline ocean circulation model

    SciTech Connect

    Mysak, L.A.; Stocker, T.F.; Huang, F.

    1993-01-01

    The response of a two-dimensional thermohaline ocean circulation model to a random freshwater flux superimposed on the usual mixed boundary conditions for temperature and salinity is considered. It is shown that for a wide range of vertical and horizontal diffusivities and a box geometry that approximates the Atlantic Ocean, 200-300 yr period oscillations exist in the basic-state, interhemispheric meridional overturning circulation with deep convection in the north. These fluctuations can also be described in terms of propagating salinity anomalies which travel in the direction of the thermohaline flow. For large horizontal (K{sub h} = 15 x 10{sup 3} m{sup 2}/s) and small vertical (K{sub v}=0.5 x 10{sup -4}m{sup 2}/s) diffusivities, the random forcing also excites deca-millennial oscillations in the basic structure of the thermohaline circulation. In this case, the meridional circulation pattern slowly oscillates between three different stages: a large positive cell, with deep convection in the North Atlantic and upwelling in the south; a symmetric two-cell circulation, with deep convection in both polar regions and upwelling near the equator; and a large negative cell, with deep convection in the South Atlantic and upwelling in the north. Each state can persist for 0 (10 kyr).

  5. A parallel Atmosphere-Ocean Global Circulation Model of intermediate complexity for Earth system climate research

    NASA Astrophysics Data System (ADS)

    Silva, T. A.; Schmittner, A.

    2007-12-01

    We present the evolution of an Earth System model of intermediate complexity featuring an ocean global circulation model to include a fully coupled 3D primitive equations atmospheric model. The original Earth System climate model, UVic ESCM (Weaver et al. 2001), uses an ocean global circulation model coupled to a one layer atmospheric energy-moisture balance model. It also comprises a viscous-plastic rheology sea ice model, a mechanical land ice model, land surface, oceanic and terrestrial carbon models and a simple 3D marine ecosystem model (Schmittner et al. 2005). A spectral atmospheric, model, PUMA (Fraedrich et al. 2005), was coupled to the UVic ESCM to provide an atmosphere with nonlinear dynamics in target resolutions of T21, T31 and T42, as required. The coupling with the atmosphere, which involves data transfer, preprocessing and interpolation, is done through the OASIS3 coupler. During a run there are 2 + 2N parallel processes: the UVic ESCM, the Oasis3 coupler and the PUMA model with its domain split across 2N processes. The choice of N allows to balance more or less complex configurations of UVic model (e.g. higher level marine ecosystem model or number of biogeochemical tracers) with the atmospheric model at different resolutions, in order to maintain computational efficiency. The relatively simple parameterizations make this new atmosphere-ocean global circulation model much faster than a state-of-the-art Atmosphere-Ocean Global Circulation Model, and so optimally geared for decadal to millennial scale integrations. The latter require special care with the conservation of fluxes during coupling. A second order conservative interpolation method was applied (Jones 1999) and this is compared with the use of typical non-conservative methods.

  6. Zoogeography of Intertidal Communities in the West Indian Ocean as Determined by Ocean Circulation Systems: Patterns from the Tetraclita Barnacles

    PubMed Central

    Tsang, Ling Ming; Achituv, Yair; Chu, Ka Hou; Chan, Benny Kwok Kan

    2012-01-01

    The Indian Ocean is the least known ocean in the world with the biogeography of marine species in the West Indian Ocean (WIO) understudied. The hydrography of WIO is characterized by four distinct oceanographic systems and there were few glacial refugia formations in the WIO during the Pleistocene. We used the widely distributed intertidal barnacle Tetraclita to test the hypothesis that the distribution and connectivity of intertidal animals in the WIO are determined by the major oceanographic regime but less influenced by historical events such as Pleistocene glaciations. Tetraclita were studied from 32 locations in the WIO. The diversity and distribution of Tetraclita species in the Indian Ocean were examined based on morphological examination and sequence divergence of two mitochondrial genes (12S rDNA and COI) and one nuclear gene (histone 3, H3). Divergence in DNA sequences revealed the presence of seven evolutionarily significant units (ESUs) of Tetraclita in WIO, with most of them recognized as valid species. The distribution of these ESUs is closely tied to the major oceanographic circulation systems. T. rufotincta is distributed in the Monsoonal Gyre. T. ehsani is present in the Gulf of Oman and NW India. Tetraclita sp. nov. is associated with the Hydrochemical Front at 10°S latitude. T. reni is confined to southern Madagascan and Mauritian waters, influenced by the West Wind Drift. The endemic T. achituvi is restricted to the Red Sea. Tetraclita serrata consists of two ESUs (based on mtDNA analysis) along the east to west coast of South Africa. The two ESUs could not be distinguished from morphological analysis and nuclear H3 sequences. Our results support that intertidal species in the West Indian Ocean are associated with each of the major oceanographic circulation systems which determine gene flow. Geographical distribution is, however, less influenced by the geological history of the region. PMID:23024801

  7. Modeling of submarine melting of Greenland tidewater glaciers using an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Rignot, E. J.; Menemenlis, D.; Koppes, M.

    2010-12-01

    The acceleration of Greenland tidewater glaciers has increased the mass loss from the Greenland Ice Sheet. Submarine melting is one of the possible drivers for glacier acceleration. Enhanced submarine melting could result from ocean warming, changes in ocean current, and increase in sub-glacial runoff. We use a combination of numerical modeling and field data to understand the mechanism of submarine melting in Greenland. Specifically, oceanographic data (temperature, salinity, and current velocity) were collected in August 2008 and 2010 near the calving fronts of the Lille Gletscher, Store Gletscher, Eqip Sermia, Kangilerngata Sermia, Sermeq Kujatdleq and Sermeq Avangnardleq glaciers in central West Greenland. These data are compared to high-resolution regional ocean simulations carried out using the Massachusetts Institute of Technology general circulation model (MITgcm). MITgcm includes submarine melting at the base of an ice shelf and we have added a new module to simulate the melting process along the vertical calving face of Greenland tidewater glaciers. We integrate the MITgcm with JRA25 atmospheric and ECCO2 oceanic boundary conditions and compare the simulation results with the West Greenland data. We also conduct model sensitivity studies for ocean temperature, sub-glacial runoff, and fjord. The preliminary results show a quadratic increase in submarine melting with warmer ocean temperature and a role of sub-glacial runoff in changing ocean circulation. This study could help us evaluate the impact of ocean warming and enhanced runoff on submarine melting and in turn on glacier mass balance. This work is performed at UCI under a contact with NASA Cryosphere Science Program.

  8. On the water masses and mean circulation of the South Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Stramma, Lothar; England, Matthew

    1999-09-01

    We examine recent observations of water mass distribution and circulation schemes at different depths of the South Atlantic Ocean to propose a layered, qualitative representation of the mean distribution of flow in this region. This furthers the simple upper layer geostrophic flow estimates of Peterson and Stramma [1991]. In addition, we assess how well ocean general circulation models (GCMs) capture the overall structure of flow in the South Atlantic in this regard. The South Atlantic Central Water (SACW) is of South Atlantic origin in the subtropical gyre, while the SACW in the tropical region in part originates from the South Indian Ocean. The Antarctic Intermediate Water in the South Atlantic originates from a surface region of the circumpolar layer, especially in the northern Drake Passage and the Falkland Current loop, but also receives some water from the Indian Ocean. The subtropical South Atlantic above the North Atlantic Deep Water and north of the Antarctic Circumpolar Current (ACC) is dominated by the anticyclonic subtropical gyre. In the eastern tropical South Atlantic the cyclonic Angola Gyre exists, embedded in a large tropical cyclonic gyre. The equatorial part of the South Atlantic shows several depth-dependent zonal current bands besides the Angola Gyre. Ocean GCMs have difficulty capturing this detailed zonal circulation structure, even at eddy-permitting resolution. The northward extent of the subtropical gyre reduces with increasing depth, located near Brazil at 16°S in the near-surface layer and at 26°S in the Antarctic Intermediate Water layer, while the tropical cyclonic gyre progresses southward. The southward shift of the northern part of the subtropical gyre is well resolved in global ocean GCMs. However, high horizontal resolution is required to capture the South Atlantic Current north of the ACC. The North Atlantic Deep Water in the South Atlantic progresses mainly southward in the Deep Western Boundary Current, but some water also

  9. Influence of changing deep ocean circulation on the Phanerozoic oxygen isotopic record

    SciTech Connect

    Railsback, L.B. )

    1990-05-01

    Isotopic segregation in seawater caused by changing ocean circulation may in part explain the enigmatic oxygen isotopic record of Phanerozoic marine carbonates. Paleoceanographic evidence suggests that circulation of warm saline deep waters has occurred during at least two periods of warm global climate; those saline deep waters should have preferentially stored {sup 18}O in the deep oceans. Corresponding depletion of {sup 18}O in surface waters would have resulted in lower {delta}{sup 18}O of marine carbonates deposited on continental shelves. Modeling of paleoceanographic isotopic data suggests that this storage effect is similar in magnitude (but opposite in sign) to that of modern enrichment of {sup 18}O in the oceans by glacial storage. Modeling of carbonate compositions through time that takes into account such storage effects (as predicted by changing global climate) suggests that large changes in the mean oceanic isotopic composition, but neither extreme temperatures nor sudden changes in mean ocean compositions are needed to explain the isotopic record.

  10. Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation.

    PubMed

    Knutti, R; Flückiger, J; Stocker, T F; Timmermann, A

    2004-08-19

    The climate of the last glacial period was extremely variable, characterized by abrupt warming events in the Northern Hemisphere, accompanied by slower temperature changes in Antarctica and variations of global sea level. It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation. Here we use a coupled ocean-atmosphere-sea ice model to show that freshwater discharge into the North Atlantic Ocean, in addition to a reduction of the thermohaline circulation, has a direct effect on Southern Ocean temperature. The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process. We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes, the slow changes in Antarctic temperature and its similarity to sea level, as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3. PMID:15318212

  11. Geochemical constraints on ocean general circulation models. Final report, May 1, 1995--April 30, 1997

    SciTech Connect

    Broecker, W.S.

    1998-05-17

    A better understanding of the manner in which the ocean operates is essential to the preparation for the consequences of the generation of CO{sub 2} by fossil fuel burning. Examples are as follows: (1) the ocean will ultimately take up a major fraction of the CO{sub 2} produced, but this uptake is retarded by the slow mixing rates, in order to predict the uptake, researchers must develop and validate general circulation models for the ocean; (2) during glacial time large global climate changes occurred. The changes were abrupt happening in a few decades. The trigger for these changes appears to have been reorganizations of the large-scale thermohaline circulation of the ocean. Models suggest that if the CO{sub 2} content of the atmosphere rises to more than 700 ppm, then a possibility exists that another such reorganization might occur. Hence, researchers must learn more about the factors influencing deep-water formation both in the northern Atlantic and in the Souther Ocean. The thrust of this research was to develop constraints based on the distributions of chemicals and tracers in the sea. The accomplishments are outlined in this report.

  12. A review of the Southern Oscillation - Oceanic-atmospheric circulation changes and related rainfall anomalies

    NASA Technical Reports Server (NTRS)

    Kousky, V. E.; Kagano, M. T.; Cavalcanti, I. F. A.

    1984-01-01

    The region of South America is emphasized in the present consideration of the Southern Oscillation (SO) oceanic and atmospheric circulation changes. The persistence of climate anomalies associated with El Nino-SO events is due to strong atmosphere-ocean coupling. Once initiated, the SO follows a certain sequence of events with clearly defined effects on tropical and subtropical rainfall. Excessive rainfall related to the SO in the central and eastern Pacific, Peru, Ecuador, and southern Brazil, are complemented by drought in Australia, Indonesia, India, West Africa, and northeast Brazil. El Nino-SO events are also associated with dramatic changes in the tropospheric flow pattern over a broad area of both hemispheres.

  13. Effects of tropical cyclones on large-scale circulation and ocean heat transport in the South China Sea

    NASA Astrophysics Data System (ADS)

    Wang, Xidong; Wang, Chunzai; Han, Guijun; Li, Wei; Wu, Xinrong

    2014-12-01

    In this study, we investigate the influence of tropical cyclones (TCs) on large-scale circulation and ocean heat transport in the South China Sea (SCS) by using an ocean general circulation model at a 1/8° resolution during 2000-2008. The model uses a data assimilation system to assimilate observations in order to improve the representation of SCS circulation. The results reveal an unexpected deep SCS circulation anomaly induced by TCs, which suggests that effects of TC can penetrate deeper into the ocean. This deep effect may result from the near inertial oscillations excited by TCs. The inertial oscillations can propagate downward to the oceanic interior. The analyses confirm that TCs have two effects on ocean heat transport of the SCS. Firstly, the wind stress curl induced by TCs affects the structure of SCS circulation, and then changes heat transport. Secondly, TCs pump surface heat downward to the thermocline, increasing the heat injection from the atmosphere to the ocean. Two effects together amplify the outflow of the surface heat southward away the SCS through the Mindoro and Karimata Straits. The TC-induced heat transports through the Mindoro, Balabac and Karimata Straits account for 20 % of the total heat transport through three straits. An implication of this study is that ocean models need to simulate the TC effect on heat transport in order to correctly evaluate the role of the SCS through flow in regulating upper ocean circulation and climate in the Indonesian maritime continent and its adjacent regions.

  14. Development of a high-resolution coastal circulation model for the ocean observatory in lunenburg bay

    NASA Astrophysics Data System (ADS)

    Wang, Liang; Sheng, Jinyu

    2005-10-01

    An advanced ocean observatory has been established in Lunenburg Bay of Nova Scotia, Canada as part of an interdisciplinary research project of marine environmental prediction. The development of a high-resolution coastal circulation model is one of important components of the observatory. The model horizontal resolution is 60 m and the vertical resolution is about lm. The coastal circulation model is used to simulate the semi-diurnal tidal circulation and associated nonlinear dynamics with the M2 forcing specified at the model open boundaries. The model is also used to simulate the storm-induced circulation in the bay during Hurricane Juan in September 2003, with the model forcing to be the combination of tides and remotely generated waves specified at the model open boundaries and wind stress applied at the sea surface. The model results demonstrate strong interactions between the local wind stress, tidal forcing, and remotely generated waves during this period. Comparison of model results with the surface elevation and current observations demonstrates that the coastal circulation model has reasonable skills in simulating the tidal and storm-induced circulation in the bay.

  15. Sensitivity of Southern Ocean circulation to wind stress changes: Role of relative wind stress

    NASA Astrophysics Data System (ADS)

    Munday, D. R.; Zhai, X.

    2015-11-01

    The influence of different wind stress bulk formulae on the response of the Southern Ocean circulation to wind stress changes is investigated using an idealised channel model. Surface/mixed layer properties are found to be sensitive to the use of the relative wind stress formulation, where the wind stress depends on the difference between the ocean and atmosphere velocities. Previous work has highlighted the surface eddy damping effect of this formulation, which we find leads to increased circumpolar transport. Nevertheless the transport due to thermal wind shear does lose sensitivity to wind stress changes at sufficiently high wind stress. In contrast, the sensitivity of the meridional overturning circulation is broadly the same regardless of the bulk formula used due to the adiabatic nature of the relative wind stress damping. This is a consequence of the steepening of isopycnals offsetting the reduction in eddy diffusivity in their contribution to the eddy bolus overturning, as predicted using a residual mean framework.

  16. Interdecadal variations of the thermohaline circulation in a coupled ocean-atmosphere model

    SciTech Connect

    Delworth, T.; Manabe, S.; Stouffer, R.J. )

    1993-11-01

    A fully coupled ocean-atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the NOrth Atlantic Ocean with a time scale of approximately 50 years. The irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation (approximately 52[degrees]N to 72[degrees]N) combined with much smaller density anomalies of opposite sign in the broad, rising region. The spatial pattern of sea surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the North Atlantic. The anomalies of sea surface temperature induce model surface air temperature anomalies over the northern North Atlantic, Arctic, and northwestern Europe. 21 refs., 28 figs.

  17. Recurring Cold Winters over the Gulf Stream and Implications for Northern Hemisphere Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Strey, S. T.

    2015-12-01

    As polar amplification of climate warming continues, the potential for increased blocking patterns in the Northern Hemisphere jet stream in conjunction with Arctic climate change exists. During such blocking events the Gulf Stream may be exposed to repeated Cold Air Outbreak (CAO) events, especially during winter. Hypothesizing, based upon basic physical and thermodynamic properties of seawater, one would expect increased CAO events to lead alteration of key characteristics of the Gulf Stream. As the Gulf Stream is a well-known participant in the Atlantic meridional overturning circulation (AMOC), and the Gulf Stream feeds the North Atlantic Current into the Arctic Ocean, interesting consequences to alterations of this local system into the large-scale general climate circulation are expected. This study uses CESM's POP to examine 30 years of CAO intensive winters alongside 30 years of repeated winter warm events to quantify potential subsequent changes in the AMOC and North Atlantic Arctic Ocean inflow.

  18. The seasonal variability of the circulation in the South Indian Ocean: Model and observations

    NASA Astrophysics Data System (ADS)

    Matano, R. P.; Beier, E. J.; Strub, P. T.

    2008-11-01

    This article compares the seasonal variability patterns of the South Indian Ocean circulation derived from a global, eddy-permitting, numerical model and altimeter observations. The seasonal variability of the Indian Ocean circulation is driven by the inflow from the Indonesian Passages and by the local wind forcing. Our analysis indicates that the influence of the Indonesian throughflow is confined to the easternmost portion of the basin, while the influence of the wind stress forcing is important everywhere. Model and observations indicate that, between ~ 105°E and 75°E, the seasonal variability is characterized by the southwestward propagation of an annual wave over a period of ~ 4 months. Preliminary calculations using Pathfinder data also indicate that, in the western region, there are seasonal perturbations that originate in the tropics and propagate poleward through the Mozambique Channel. Our calculations, however, did not find the connections between the tropical and the Agulhas Current variability suggested by earlier modeling studies.

  19. North Atlantic ocean circulation and abrupt climate change during the last glaciation

    NASA Astrophysics Data System (ADS)

    Henry, L. G.; McManus, J. F.; Curry, W. B.; Roberts, N. L.; Piotrowski, A. M.; Keigwin, L. D.

    2016-07-01

    The most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations, whose origin remains unresolved. Variations in oceanic meridional heat transport may contribute to these repeated climate changes, which were most pronounced during marine isotope stage 3, the glacial interval 25 thousand to 60 thousand years ago. We examined climate and ocean circulation proxies throughout this interval at high resolution in a deep North Atlantic sediment core, combining the kinematic tracer protactinium/thorium (Pa/Th) with the deep water-mass tracer, epibenthic δ13C. These indicators suggest reduced Atlantic overturning circulation during every cool northern stadial, with the greatest reductions during episodic Hudson Strait iceberg discharges, while sharp northern warming followed reinvigorated overturning. These results provide direct evidence for the ocean’s persistent, central role in abrupt glacial climate change.

  20. The Influence of Indian Ocean Atmospheric Circulation on Warm Pool Hydroclimate During the Holocene Epoch

    NASA Technical Reports Server (NTRS)

    Tierney, J.E.; Oppo, D. W.; LeGrande, A. N.; Huang, Y.; Rosenthal, Y.; Linsley, B. K.

    2012-01-01

    Existing paleoclimate data suggest a complex evolution of hydroclimate within the Indo-Pacific Warm Pool (IPWP) during the Holocene epoch. Here we introduce a new leaf wax isotope record from Sulawesi, Indonesia and compare proxy water isotope data with ocean-atmosphere general circulation model (OAGCM) simulations to identify mechanisms influencing Holocene IPWP hydroclimate. Modeling simulations suggest that orbital forcing causes heterogenous changes in precipitation across the IPWP on a seasonal basis that may account for the differences in time-evolution of the proxy data at respective sites. Both the proxies and simulations suggest that precipitation variability during the September-November (SON) season is important for hydroclimate in Borneo. The preeminence of the SON season suggests that a seasonally lagged relationship between the Indian monsoon and Indian Ocean Walker circulation influences IPWP hydroclimatic variability during the Holocene.

  1. Global coupled ocean-atmosphere general circulation models in LASG/IAP

    NASA Astrophysics Data System (ADS)

    Yongqiang, Yu; Xuehong, Zhang; Yufu, Guo

    2004-06-01

    Coupled ocean-atmospheric general circulation models are the only tools to quantitatively simulate the climate system. Since the end of the 1980s, a group of scientists in the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), have been working to develop a global OGCM and a global coupled ocean-atmosphere general circulation model (CGCM). From the original flux anomaly-coupling model developed in the beginning of the 1990s to the latest directly-coupling model, LASG scientists have developed four global coupled GCMs. This study summarizes the development history of these models and describes the third and fourth coupled GCMs and selected applications. Strengths and weaknesses of these models are highlighted.

  2. A multi-level adaptation model of circulation for the western Indian Ocean

    NASA Astrophysics Data System (ADS)

    Shaji, C.; Bahulayan, N.; Dube, S. K.; Rao, A. D.

    1999-12-01

    A three-dimensional, fully non-linear semi-diagnostic (adaptation) model is described. This model is used to compute the climatological mean circulation and to understand the role of local, steady forcing of the wind and thermohaline forcing on the observed circulation in the western tropical Indian Ocean. The model consists of equations of motion and continuity, sea surface topography, equations of state and temperature, and salinity diffusion equations. While the sea surface topography equation is solved by a successive overrelaxation technique, the other model equations are solved by a leap-frog numerical scheme. Two versions of the model, having 18 and 33 levels in the vertical direction, were prepared to study climatological mean circulation in the western tropical Indian Ocean. The first numerical experiment is carried out with the 18-level adaptation model to study the sensitivity of the solution to different values of eddy coefficients. The main scientific rationale behind these numerical experiments was to obtain the most appropriate values of the eddy coefficients for the realistic computation of climatological circulation in the western tropical Indian Ocean. Three numerical experiments were conducted for the month of February to understand the sensitivity of the model solution to different eddy coefficients. The model reproduced the circulation features during February, even with low values of horizontal and vertical eddy coefficients. In the second experiment, the adaptation model, with 33 levels in the vertical direction, is applied to study the seasonal mean climatological circulation at selected depths during Spring in the western tropical Indian Ocean. Adapted (steady state) results of currents, sea surface topography, temperature and salinity anomaly fields are presented. Reasonable agreement is obtained between the model results on currents and the observational data. The computed anomaly fields for temperature and salinity at selected depths

  3. Impact of oceanic circulation changes on the CO2 concentration during past interglacials

    NASA Astrophysics Data System (ADS)

    Bouttes, Nathaelle; Swingedouw, Didier; Crosta, Xavier; Fernanda Sanchez Goñi, Maria; Roche, Didier

    2016-04-01

    Interglacials before the Mid-Bruhnes Event (around 430 kyrs BP) were characterized by colder temperature in Antarctica, lower sea level and lower atmospheric CO2 compared to the more recent interglacials. Recent climate simulations have shown that the climate of the interglacials before and after the MBE can only be reproduced when taking into account changes in orbital parameters and atmospheric CO2 concentrations (Yin and Berger, 2010; Yin and Berger, 2012). Indeed, interglacial atmospheric CO2 concentrations were ~250 ppm and ~280 ppm prior and after the MBE, respectively. Yet, the cause for this change in atmospheric CO2 remains mainly unknown. climate simulations suggest that oceanic circulation was different during the interglacials due to the different climate states (Yin, 2013). The changes of oceanic circulation could have modified the carbon cycle: a more sluggish circulation would lead to greater carbon sequestration in the deep ocean and, subsequently, a decrease of atmospheric CO2. However, the impact of oceanic circulation changes on the carbon cycle during the interglacials of the last 800 kyrs has never been tested in coupled carbon-climate models. Here, we evaluate the role of ocean circulation changes on the carbon cycle during interglacials by using the intermediate complexity model iLOVECLIM (Goosse et al., 2010 ; Bouttes et al., 2015). This model includes a carbon cycle module on land and in the ocean and simulates carbon isotopes. The interglacial simulations are forced with orbital parameters, ice sheets and CO2 concentrations from data reconstructions. The model computes carbon fluxes between the reservoirs and an atmospheric CO2 that is distinct from the one used as a forcing. We will present simulations from this climate model for different interglacial periods of the last 800 000 years and use model-data comparison to analyse and evaluate the changes in the carbon cycle, including CO2. References Bouttes, N. et al. (2015), Geosci. Model

  4. Vertical heat flux in the ocean: Estimates from observations and from a coupled general circulation model

    NASA Astrophysics Data System (ADS)

    Cummins, Patrick F.; Masson, Diane; Saenko, Oleg A.

    2016-06-01

    The net heat uptake by the ocean in a changing climate involves small imbalances between the advective and diffusive processes that transport heat vertically. Generally, it is necessary to rely on global climate models to study these processes in detail. In the present study, it is shown that a key component of the vertical heat flux, namely that associated with the large-scale mean vertical circulation, can be diagnosed over extra-tropical regions from global observational data sets. This component is estimated based on the vertical velocity obtained from the geostrophic vorticity balance, combined with estimates of absolute geostrophic flow. Results are compared with the output of a non-eddy resolving, coupled atmosphere-ocean general circulation model. Reasonable agreement is found in the latitudinal distribution of the vertical heat flux, as well as in the area-integrated flux below about 250 m depth. The correspondence with the coupled model deteriorates sharply at depths shallower than 250 m due to the omission of equatorial regions from the calculation. The vertical heat flux due to the mean circulation is found to be dominated globally by the downward contribution from the Southern Hemisphere, in particular the Southern Ocean. This is driven by the Ekman vertical velocity which induces an upward transport of seawater that is cold relative to the horizontal average at a given depth. The results indicate that the dominant characteristics of the vertical transport of heat due to the mean circulation can be inferred from simple linear vorticity dynamics over much of the ocean.

  5. Use of Ocean Remote Sensing Data to Enhance Predictions with a Coupled General Circulation Model

    NASA Technical Reports Server (NTRS)

    Rienecker, Michele M.

    1999-01-01

    Surface height, sea surface temperature and surface wind observations from satellites have given a detailed time sequence of the initiation and evolution of the 1997/98 El Nino. The data have beet complementary to the subsurface TAO moored data in their spatial resolution and extent. The impact of satellite observations on seasonal prediction in the tropical Pacific using a coupled ocean-atmosphere general circulation model will be presented.

  6. An implementation of a barotropic quasigeostrophic model of ocean circulation on the MPP

    NASA Technical Reports Server (NTRS)

    Grosch, C. E.; Fatoohi, R.

    1987-01-01

    The implementation on the Massively Parallel Processor (MPP) of a barotropic quasigeostrophic model of ocean circulation is discussed. The mathematical model, including scalings and boundary conditions is discussed. The numerical scheme, which uses compact differencing is also discussed. The implementation of this model on the MPP is then presented. Finally, some performance results are given and compared to results obtained using the VPS-32 and one processor of a CRAY-2.

  7. Use of variational methods in the determination of wind-driven ocean circulation

    NASA Technical Reports Server (NTRS)

    Gelos, R.; Laura, P. A. A.

    1976-01-01

    Simple polynomial approximations and a variational approach were used to predict wind-induced circulation in rectangular ocean basins. Stommel's and Munk's models were solved in a unified fashion by means of the proposed method. Very good agreement with exact solutions available in the literature was shown to exist. The method was then applied to more complex situations where an exact solution seems out of the question.

  8. Observation of the Global Ocean Circulation From the TOPEX/POSEIDON Mission

    NASA Technical Reports Server (NTRS)

    Fu, L. -L.

    1995-01-01

    Since 1992, the TOPEX/POSEIDON satellite has been making altimetric sea surface observations with a sea level accuracy of 4.4 cm. This data can be used for studying regional and seasonal differences in sea level and for evaluating oceanic circulation models and tidal models. Longer term changes can also be studied, such as El Nino and overall sea level rising (although the latter is still within the margin of error).

  9. Pliocene pre-glacial North Atlantic: A coupled sea surface-deep ocean circulation climate response

    SciTech Connect

    Ishman, S.E.; Dowsett, H.J. . National Center)

    1992-01-01

    A latitudinal transect of North Atlantic Deep Sea Drilling Project Holes from the equatorial region to 56 N in the 2,300- to 3,000-meter depth range was designed for a high-resolution study of coupled sea surface and deep ocean response to climate change. Precise age control was provided using magnetostratigraphic and biostratigraphic data from the cores to identify the 4.0 to 2.2 Ma interval, a period of warm-to-cool climatic transitions in the North Atlantic. The objective is to evaluate incremental (10 kyr) changes in sea surface temperatures (SST) and deep North Atlantic circulation patterns between 4.0 and 2.2 Ma to develop a coupled sea surface-deep ocean circulation response model. Sea surface temperature (SST) estimates are based on planktic foraminifer-based factor-analytic transfer functions. Oxygen isotopic data from paired samples provide tests of the estimated temperature gradients between localities. Benthic foraminifer assemblage data and [partial derivative]O-18 and [partial derivative]C-13 Isotopic data are used to quantitatively determine changes in deep North Atlantic circulation. These data are used to determine changes in source area (North Atlantic Deep Water (NADW) or Antarctic Bottom Water) and (or) in the components of NADW that were present (Upper or Lower NADW). These paired paleoceanographic sea surface and deep circulation interpretations over a 1.8 my interval form the basis for a coupled sea surface-deep circulation response model for the Pliocene North Atlantic Ocean.

  10. Stochastic Forcing of the North Atlantic Wind-Driven Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Chhak, K. C.; Moore, A. M.; Milliff, R. F.; Branstator, G.; Holland, W. R.; Fisher, M.

    2004-12-01

    At midlatitudes, the magnitude of stochastic wind stress forcing due to atmospheric weather is comparable to that associated with the seasonal cycle. Stochastic forcing is therefore likely to have a significant influence on the ocean circulation. In this work, we examine the influence of the stochastic component of the wind stress forcing on the large-scale, wind-driven circulation of the North Atlantic Ocean. To this end a quasi-geostrophic model of the North Atlantic was forced with estimates of the stochastic component of wind stress curl obtained from the NCAR Community Climate Model. Analysis reveals that much of the stochastically-induced variability in the ocean circulation occurs in the vicinity of the western boundary and some major bathymetric features. Using the ideas of generalized stability theory (GST), we find that the patterns of wind stress curl that are most effective for inducing variability in the model have their largest projection on the most nonnormal eigenmodes of the system. These eigenmodes are confined primarily to the western boundary region and are composed of long Rossby wave packets that are Doppler shifted by the Gulf Stream to have eastward group velocity. Linear interference of these eigenmodes yields transient growth of stochastically-induced perturbations, and it is this process that maintains the variance of the stochastically-induced circulations. By examining the model pseudospectra, we find that the nonnormal nature of the system enhances the transient growth of perturbation enstrophy and therefore elevates and also maintains the variance of the stochastically-induced circulations in the aforementioned regions.

  11. Ocean circulation during the Middle Jurassic in the presence/absence of a circumglobal current system

    NASA Astrophysics Data System (ADS)

    Brunetti, Maura; Baumgartner, Peter O.; Vérard, Christian; Hochard, Cyril

    2013-04-01

    Pangea breakup started in the Early Jurassic by the formation of the Central Atlantic and its connection with the Neotethys. By the Middle Jurassic, rifting between North and South America may have opened a first marine proto-Caribbean passage. However, the oldest known proto-Caribbean ocean crust is only of early Late Jurassic age. Based on earlier plate tectonic reconstructions featuring a wide open proto-Caribbean seaway, the existence of a circumglobal equatorial current system has been suggested by many authors as a possible physical mechanism for increasing the poleward ocean heat transport, and hence, producing the reduced meridional temperature gradient documented for the Middle Jurassic. Models with increased atmospheric pCO2, estimated to be between 1 and 7 times pre-industrial values in the Jurassic, generate elevated temperatures both in the tropics and in polar regions, but do not reduce the meridional gradient. A different mechanism needs to be considered in order to reproduce such reduced meridional temperature gradient. A possibility is enhanced poleward heat transport through the ocean. However, this hypothesis has been questioned by Late Jurassic simulations with a specified, reduced meridional gradient, which showed that the required ocean heat transport is much smaller than in present-day simulations. We investigate the critical role of a Tethyan-Atlantic-proto-Caribbean passage with respect to the Middle Jurassic ocean circulation by means of coupled ocean/sea-ice numerical models based on detailed plate reconstructions of the oceanic realms. We perform numerical experiments with an open/closed western boundary of the proto-Caribbean basin and we discuss the water properties, the gyre transport and the overturning meridional circulation for these different bathymetric configurations. For an open western boundary, we find a trans-Pangean circumglobal current of the order of 1 Sv, that flows in the upper 300 m along the northern margin of the

  12. Ensemble simulations of the magnetic field induced by global ocean circulation: Estimating the uncertainty

    NASA Astrophysics Data System (ADS)

    Irrgang, Christopher; Saynisch, Jan; Thomas, Maik

    2016-03-01

    The modeling of the ocean global circulation induced magnetic field is affected by various uncertainties that originate from errors in the input data and from the model itself. The amount of aggregated uncertainties and their effect on the modeling of electromagnetic induction in the ocean is unknown. For many applications, however, the knowledge of uncertainties in the modeling is essential. To investigate the uncertainty in the modeling of motional induction at the sea surface, simulation experiments are performed on the basis of different error scenarios and error covariance matrices. For these error scenarios, ensembles of an ocean general circulation model and an electromagnetic induction model are generated. This ensemble-based approach allows to estimate both the spatial distribution and temporal variation of the uncertainty in the ocean-induced magnetic field. The largest uncertainty in the ocean-induced magnetic field occurs in the area of the Antarctic Circumpolar Current. Local maxima reach values of up to 0.7 nT. The estimated global annual mean uncertainty in the ocean-induced magnetic field ranges from 0.1 to 0.4 nT. The relative amount of uncertainty reaches up to 30% of the signal strength with largest values in regions in the northern hemisphere. The major source of uncertainty is found to be introduced by wind stress from the atmospheric forcing of the ocean model. In addition, the temporal evolution of the uncertainty in the induced magnetic field shows distinct seasonal variations. Specific regions are identified which are robust with respect to the introduced uncertainties.

  13. Ross ice shelf cavity circulation, residence time, and melting: Results from a model of oceanic chlorofluorocarbons

    NASA Astrophysics Data System (ADS)

    Reddy, Tasha E.; Holland, David M.; Arrigo, Kevin R.

    2010-04-01

    Despite their harmful effects in the upper atmosphere, anthropogenic chlorofluorocarbons dissolved in seawater are extremely useful for studying ocean circulation and ventilation, particularly in remote locations. Because they behave as a passive tracer in seawater, and their atmospheric concentrations are well-mixed, well-known, and have changed over time, they are ideal for gaining insight into the oceanographic characteristics of the isolated cavities found under Antarctic ice shelves, where direct observations are difficult to obtain. Here we present results from a modeling study of air-sea chlorofluorocarbon exchange and ocean circulation in the Ross Sea, Antarctica. We compare our model estimates of oceanic CFC-12 concentrations along an ice shelf edge transect to field data collected during three cruises spanning 16 yr. Our model produces chlorofluorocarbon concentrations that are quite similar to those measured in the field, both in magnitude and distribution, showing high values near the surface, decreasing with depth, and increasing over time. After validating modeled circulation and air-sea gas exchange through comparison of modeled temperature, salinity, and chlorofluorocarbons with field data, we estimate that the residence time of water in the Ross Ice Shelf cavity is approximately 2.2 yr and that basal melt rates for the ice shelf average 10 cm yr -1. The model predicts a seasonal signature to basal melting, with highest melt rates in the spring and also the fall.

  14. Seasonal dynamics of circulation in Hooghly Estuary and its adjacent coastal oceans

    NASA Astrophysics Data System (ADS)

    Mishra, Shashank Kr.; Nayak, Gourav; Nayak, R. K.; Dadhwal, V. K.

    2016-05-01

    Hooghly is one of the major estuaries in Ganges, the largest and longest river in the Indian subcontinent. The Hooghly estuary is a coastal plain estuary lying approximately between 21°-23° N and 87°-89° E. We used a terrain following ocean model to study tide driven residual circulations, seasonal mean flow patterns and its energetics in the Hooghly estuary and adjacent coastal oceans on the north eastern continental shelf of India. The model is driven by tidal levels at open ocean end and winds at the air-sea interface. The sources of forcing fields for tides were from FES2012, winds from ECMWF. Harmonic analysis is carried out to compute the tidal and non-tidal components of currents and sea level from the model solutions. The de-tidal components were averaged for the entire period of simulation to describe residual and mean-seasonal circulations in the regions. We used tide-gauge, SARAL-ALTIKA along track sea level measurements to evaluate model solutions. Satellite measure Chla were used along with simulated currents to describe important features of the circulations in the region.

  15. Efficient removal of recalcitrant deep-ocean dissolved organic matter during hydrothermal circulation

    NASA Astrophysics Data System (ADS)

    Hawkes, Jeffrey A.; Rossel, Pamela E.; Stubbins, Aron; Butterfield, David; Connelly, Douglas P.; Achterberg, Eric P.; Koschinsky, Andrea; Chavagnac, Valérie; Hansen, Christian T.; Bach, Wolfgang; Dittmar, Thorsten

    2015-11-01

    Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood. Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The oldest, most recalcitrant forms of DOC, which make up most of oceanic DOC, can be recovered by solid-phase extraction. Here we present measurements of solid-phase extractable DOC from samples collected between 2009 and 2013 at seven vent sites in the Atlantic, Pacific and Southern oceans, along with magnesium concentrations, a conservative tracer of water circulation through hydrothermal systems. We find that magnesium and solid-phase extractable DOC concentrations are correlated, suggesting that solid-phase extractable DOC is almost entirely lost from solution through mineralization or deposition during circulation through hydrothermal vents with fluid temperatures of 212-401 °C. In laboratory experiments, where we heated samples to 380 °C for four days, we found a similar removal efficiency. We conclude that thermal degradation alone can account for the loss of solid-phase extractable DOC in natural hydrothermal systems, and that its maximum lifetime is constrained by the timescale of hydrothermal cycling, at about 40 million years.

  16. Contribution of ocean overturning circulation to tropical rainfall peak in the Northern Hemisphere

    NASA Astrophysics Data System (ADS)

    Frierson, Dargan M. W.; Hwang, Yen-Ting; Fučkar, Neven S.; Seager, Richard; Kang, Sarah M.; Donohoe, Aaron; Maroon, Elizabeth A.; Liu, Xiaojuan; Battisti, David S.

    2013-11-01

    Rainfall in the tropics is largely focused in a narrow zonal band near the Equator, known as the intertropical convergence zone. On average, substantially more rain falls just north of the Equator. This hemispheric asymmetry in tropical rainfall has been attributed to hemispheric asymmetries in ocean temperature induced by tropical landmasses. However, the ocean meridional overturning circulation also redistributes energy, by carrying heat northwards across the Equator. Here, we use satellite observations of the Earth's energy budget, atmospheric reanalyses and global climate model simulations to study tropical rainfall using a global energetic framework. We show that the meridional overturning circulation contributes significantly to the hemispheric asymmetry in tropical rainfall by transporting heat from the Southern Hemisphere to the Northern Hemisphere, and thereby pushing the tropical rain band north. This northward shift in tropical precipitation is seen in global climate model simulations when ocean heat transport is included, regardless of whether continents are present or not. If the strength of the meridional overturning circulation is reduced in the future as a result of global warming, as has been suggested, precipitation patterns in the tropics could change, with potential societal consequences.

  17. Mechanisms of Interannual Variations of the Meridional Overturning Circulation of the North Atlantic Ocean

    NASA Technical Reports Server (NTRS)

    Cabanes, Cecile; Lee, Tong; Fu, Lee-Lueng

    2008-01-01

    The authors investigate the nature of the interannual variability of the meridional overturning circulation (MOC) of the North Atlantic Ocean using an Estimating the Circulation and Climate of the Ocean (ECCO) assimilation product for the period of 1993-2003. The time series of the first empirical orthogonal function of the MOC is found to be correlated with the North Atlantic Oscillation (NAO) index, while the associated circulation anomalies correspond to cells extending over the full ocean depth. Model sensitivity experiments suggest that the wind is responsible for most of this interannual variability, at least south of 40(deg)N. A dynamical decomposition of the meridional streamfunction allows a further look into the mechanisms. In particular, the contributions associated with 1) the Ekman flow and its depth-independent compensation, 2) the vertical shear flow, and 3) the barotropic gyre flowing over zonally varying topography are examined. Ekman processes are found to dominate the shorter time scales (1.5-3 yr), while for longer time scales (3-10 yr) the MOC variations associated with vertical shear flow are of greater importance. The latter is primarily caused by heaving of the pycnocline in the western subtropics associated with the stronger wind forcing. Finally, how these changes in the MOC affect the meridional heat transport (MHT) is examined. It is found that overall, Ekman processes explain a larger part of interannual variability (3-10 yr) for MHT (57%) than for the MOC (33%).

  18. Seasonal Distributions of Global Ocean Chlorophyll and Nutrients: Analysis with a Coupled Ocean General Circulation Biogeochemical, and Radiative Model

    NASA Technical Reports Server (NTRS)

    Gregg, Watson W.

    1999-01-01

    A coupled general ocean circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. The model is driven by climatological meteorological conditions, cloud cover, and sea surface temperature. Biogeochemical processes in the model are determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chorophytes, and picoplankton) and three nutrient groups (nitrate, ammonium, and silicate). Phytoplankton groups are initialized as homogeneous fields horizontally and vertically, and allowed to distribute themselves according to the prevailing conditions. Basin-scale model chlorophyll results are in very good agreement with CZCS pigments in virtually every global region. Seasonal variability observed in the CZCS is also well represented in the model. Synoptic scale (100-1000 km) comparisons of imagery are also in good conformance, although occasional departures are apparent. Agreement of nitrate distributions with in situ data is even better, including seasonal dynamics, except for the equatorial Atlantic. The good agreement of the model with satellite and in situ data sources indicates that the model dynamics realistically simulate phytoplankton and nutrient dynamics on synoptic scales. This is especially true given that initial conditions are homogenous chlorophyll fields. The success of the model in producing a reasonable representation of chlorophyll and nutrient distributions and seasonal variability in the global oceans is attributed to the application of a generalized, processes-driven approach as opposed to regional parameterization, and the existence of multiple phytoplankton groups with different physiological and physical properties. These factors enable the model to simultaneously represent the great diversity of physical, biological

  19. Summer mean full depth circulation in North Atlantic Ocean along 59.5 N

    NASA Astrophysics Data System (ADS)

    Gladyshev, Vsevolod; Sokov, Alexey; Gladyshev, Sergey

    2016-04-01

    The large scale oceanic circulation in the North Atlantic is an important part of the climate system. Warm saline upper-ocean waters derived in subtropics release heat into the atmosphere while moving northward as North Atlantic Current and by mixing with colder fresher Arctic waters sink in the subpolar basins therefore originating reverse equatorward flow of cold fresh water. This mechanism, known as Atlantic Meridional Overturning Circulation (MOC) is of fundamental importance in the meridional heat transport. Using data from yearly direct hydrographic measurements at 59.5 N with satellite altimetry data in the period 2009-2015 a mean state of the full-depth summer circulation in the region is estimated. Zonal distribution of the 2009-2015 mean summer velocities across the 59.5 N is obtained using four different data sets from (1) pair of WS 300 kHz LADCPs measurements, (2) ship mounted TRDI OS 38 kHz ADCP measurements, (3) AVISO altimetry data (surface absolute geostrophic velocities), and (4) geostrophic velocities data calculated using CTD measurements. By combining those data mean absolute transport is estimated. Results are compared and analyzed confirming and elaborating previous research. Also assessment of the errors associated with full-depth ADCP profiles is settled. This evaluation allows arguing about certainty of collected data and can be used to improve accuracy of circulation rating.

  20. Transport of 137Cs to the Southern Hemisphere in an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Tsumune, Daisuke; Aoyama, Michio; Hirose, Katsumi; Bryan, Frank O.; Lindsay, Keith; Danabasoglu, Gokhan

    2011-04-01

    137Cs originating from global fallout is transported into the ocean interior by advection and diffusion, and the 137Cs concentration is reduced by radioactive decay. 137Cs concentrations in the global ocean can be simulated by global integration of the coarse-resolution Parallel Ocean Program to understand the mechanism of material transport in the ocean. We investigated the transport mechanism of 137Cs to the Southern Hemisphere using an ocean general circulation model (OGCM) and compared the simulated results with observations of 137Cs concentrations in the Southern Hemisphere. 137Cs was deposited on the ocean surface mainly as global fallout originating from atmospheric nuclear weapons testing since 1945, and the global distribution of cumulative 137Cs deposition has been reconstructed from global measurements of 137Cs in rain, seawater, and soil. We estimated the global distribution of 137Cs deposition from 1945 to 2003 using these distribution data, 137Cs deposition data observed at the Meteorological Research Institute, Tsukuba, Japan, from 1958 to 2003, and 137Cs deposition data for 1945-1957 estimated from ice-core data. We compared the simulated results with 137Cs sections from the South Pacific, Indian, and South Atlantic Oceans obtained during the BEAGLE2003 cruise in 2003. The simulated 137Cs sections were in good agreement with the observations, except for the effects of mesoscale eddies, which not be simulated by the model because of its coarse resolution. OGCMs can simulate the general pattern of 137Cs distribution in the world’s oceans and improve our understanding of the transport mechanism leading to those 137Cs distributions on a time scale of several decades. The model simulation results suggest that the 137Cs deposited in the North Pacific advected to the South Pacific and Indian Ocean, and then to the South Atlantic over about four decades. The North Pacific is thus an important source area of 137Cs to the Southern Hemisphere.

  1. Dynamic Proxies of Ocean Circulation in the North Atlantic During the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Praetorius, S.; McManus, J.

    2007-05-01

    The North Atlantic Deep Water (NADW) is a major component of the Atlantic's meridional overturning circulation, which is strongly linked to climate through the sea-to-air heat transfer by water transported from low to high latitudes. Changes in this circulation system have been implicated in the abrupt climate reversal of the Younger Dryas. Previous studies using nutrient proxies such as δ13C and Cd/Ca show a nutrient enrichment in the North Atlantic during the Younger Dryas, reflecting a reduction in the volume of nutrient-depleted NADW. Although valuable, water mass tracers cannot constrain the rate of overturning; a crucial factor in the overall heat flux of deep water formation. Dynamic proxies such as 231Pa/230Th disequilibria and the grain size of deep sea sediments provide tools to measure changes in the vigor of ocean circulation. 231Pa/230Th ratios act as a proxy for the export rate of subsurface waters from the North Atlantic. Changes in the non-cohesive sortable silt (SS) size fraction (10-63μm) of terrigenous sediments reflect variations in the current strength as a result of the relative entrainment capacity of flow velocity. Here we compare the grain size record from site 984, along the Rekjanes Ridge, with 231Pa/230Th data from core GGC5 on the Bermuda Rise. Site 984 is well situated to monitor both the modern deep water overflows and the intermediate depth waters of the glacial period, whereas core GGC5 offers a more basin-wide measure of circulation export. These records indicate similarly robust overturning circulation during the last glacial maximum and Holocene. In contrast, the deglacial period reveals significant reductions in the circulation. The Younger Dryas exhibits the most dramatic decrease in grain size throughout the 20,000 year record, and the 231Pa/230Th data indicate a reduction in export rate that is rivaled only by the first Heinrich iceberg discharge event. The reduction in current strength during the Younger Dryas is

  2. Predictive Understanding of the Oceans' Wind-Driven Circulation on Interdecadal Time Scales

    SciTech Connect

    Michael Ghil; Temam, Roger; Y. Feliks; Simonnet, E.; Tachim-Medjo, T.

    2008-09-30

    The goal of this project was to obtain a predictive understanding of a major component of the climate system's interdecadal variability: the oceans' wind-driven circulation. To do so, we developed and applied advanced computational and statistical methods to the problem of climate variability and climate change. The methodology was developed first for models of intermediate complexity, such as the quasi-geostrophic and the primitive equations, which describe the wind-driven, near-surface flow in mid-latitude ocean basins. Our computational work consisted in developing efficient multi-level methods to simulate this flow and study its dependence on physically relevant parameters. Our oceanographic and climate work consisted in applying these methods to study the bifurcations in the wind-driven circulation and their relevance to the flows observed at present and those that might occur in a warmer climate. Both aspects of the work are crucial for the efficient treatment of large-scale, eddy-resolving numerical simulations of the oceans and an increased understanding and better prediction of climate change. Considerable progress has been achieved in understanding ocean-atmosphere interaction in the mid-latitudes. An important by-product of this research is a novel approach to explaining the North Atlantic Oscillation.

  3. The sensitivity of latent heat flux to the air humidity approximations used in ocean circulation models

    NASA Technical Reports Server (NTRS)

    Liu, W. Timothy; Niiler, Pearn P.

    1990-01-01

    In deriving the surface latent heat flux with the bulk formula for the thermal forcing of some ocean circulation models, two approximations are commonly made to bypass the use of atmospheric humidity in the formula. The first assumes a constant relative humidity, and the second supposes that the sea-air humidity difference varies linearly with the saturation humidity at sea surface temperature. Using climatological fields derived from the Marine Deck and long time series from ocean weather stations, the errors introduced by these two assumptions are examined. It is shown that the errors reach above 100 W/sq m over western boundary currents and 50 W/sq m over the tropical ocean. The two approximations also introduce erroneous seasonal and spatial variabilities with magnitudes over 50 percent of the observed variabilities.

  4. Investigation of Deep Ocean Circulation and Mixing Using Ar-39 (Invited)

    NASA Astrophysics Data System (ADS)

    Smethie, W. M.; Schlosser, P.

    2013-12-01

    Ar-39 is a radioactive noble gas that forms in the atmosphere by cosmic ray interaction with Ar-40. It has a half-life of 269 years and its production rate in the atmosphere has varied no more than 7% during the past 1000 years. It enters the surface ocean with an average equilibration time of about one month and thus the entire surface ocean, except for ice covered regions at high latitudes, is in quasi-equilibrium with the atmospheric Ar-39:Ar ratio. The well known input to the ocean, radioactive decay constant and chemical inertness make Ar-39 an ideal tracer of circulation and mixing in the deep ocean, where anthropogenic transient tracers such as CFCs and tritium have not yet penetrated. However, due to the difficult measurement, only about 125 oceanic Ar-39 samples have been measured to date. This was done by counting the decays of Ar-39 atoms and required a half liter of argon gas per sample, extracted from about 1500 liters of water. The 125 samples that have been measured provide a glimpse of the information that can be gained from Ar-39 observations. In the Pacific Ocean three vertical profiles show a decrease in Ar-39 from the surface mixed layer through the thermocline to a minimum at intermediate depths and an increase from there to the bottom. This reflects formation of bottom water around the Antarctic continent, spreading of this water northward and upwelling and mixing into intermediate depths. The lowest concentration was 6×4% modern which is equivalent to a 900-1600 year isolation time from the surface. In the Atlantic Ocean newly formed North Atlantic Deep Water has an Ar-39 concentration of about 85% modern compared to 55% modern for newly formed Antarctic Bottom Water and reach values as low as about 40% modern in the interior reflecting the more rapid ventilation of the deep Atlantic Ocean relative to the deep Pacific Ocean. In the Arctic Ocean the mean residence time of deep water in the Nansen, Amundsen and Makarov Basins based on Ar-39

  5. Linkages between ocean circulation, heat uptake and transient warming: a sensitivity study

    NASA Astrophysics Data System (ADS)

    Pfister, Patrik; Stocker, Thomas

    2016-04-01

    Transient global warming due to greenhouse gas radiative forcing is substantially reduced by ocean heat uptake (OHU). However, the fraction of equilibrium warming that is realized in transient climate model simulations differs strongly between models (Frölicher and Paynter 2015). It has been shown that this difference is not only related to the magnitude of OHU, but also to the radiative response the OHU causes, measured by the OHU efficacy (Winton et al., 2010). This efficacy is strongly influenced by the spatial pattern of the OHU and its changes (Rose et al. 2014, Winton et al. 2013), predominantly caused by changes in the Atlantic meridional overturning circulation (AMOC). Even in absence of external greenhouse gas forcing, an AMOC weakening causes a radiative imbalance at the top of the atmosphere (Peltier and Vettoretti, 2014), inducing in a net warming of the Earth System. We investigate linkages between those findings by performing both freshwater and greenhouse gas experiments in an Earth System Model of Intermediate Complexity. To assess the sensitivity of the results to ocean and atmospheric transport as well as climate sensitivity, we use an ensemble of model versions, systematically varying key parameters. We analyze circulation changes and radiative adjustments in conjunction with traditional warming metrics such as the transient climate response and the equilibrium climate sensitivity. This aims to improve the understanding of the influence of ocean circulation and OHU on transient climate change, and of the relevance of different metrics for describing this influence. References: Frölicher, T. L. and D.J. Paynter (2015), Extending the relationship between global warming and cumulative carbon emissions to multi-millennial timescales, Environ. Res. Lett., 10, 075022 Peltier, W. R., and G. Vettoretti (2014), Dansgaard-Oeschger oscillations predicted in a comprehensive model of glacial climate: A "kicked" salt oscillator in the Atlantic, Geophys. Res

  6. Global ocean circulation and equator-pole heat transport as a function of ocean GCM resolution

    SciTech Connect

    Covey, C.

    1994-06-01

    To determine whether resolution of smaller scales is necessary to simulate large-scale ocean climate correctly, I examine results from a global ocean GCM run with horizontal grid spacings spanning a range from coarse resolutions traditionally used in climate modeling to nearly the highest resolution attained with today`s computers. The experiments include four cases employing 4{degrees}, 2{degrees}, 1{degrees} and 1/2{degrees} spacing in latitude and longitude, which were run with minimal differences among them, i.e., in a controlled experiment. Two additional cases-1/2{degrees} spacing with a more scale-selective sub-gridscale mixing of heat and momentum, and approximate 1/4{degrees} spacing-are also included. The 1/4{degrees} run resolves most of the observed mesoscale eddy energy in the ocean. Several artificial constraints on the model tend to minimize differences among the different resolution cases. Nevertheless, for quantities of interest to global climate studies,the simulations show significant changes as resolution increases.

  7. Assessing reconstruction techniques of the Atlantic Ocean circulation variability during the last millennium

    NASA Astrophysics Data System (ADS)

    Moreno-Chamarro, Eduardo; Ortega, Pablo; González-Rouco, Fidel; Montoya, Marisa

    2016-04-01

    We assess the use of the meridional thermal-wind transport estimated from zonal density gradients to reconstruct the oceanic circulation variability during the last millennium in a forced simulation with the ECHO-G coupled climate model. Following a perfect-model approach, model-based pseudo-reconstructions of the Atlantic meridional overturning circulation (AMOC) and the Florida Current volume transport (FCT) are evaluated against their true simulated variability. The pseudo-FCT is additionally verified as proxy for AMOC strength and compared with the available proxy-based reconstruction. The thermal-wind component reproduces most of the simulated AMOC variability, which is mostly driven by internal climate dynamics during the preindustrial period and by increasing greenhouse gases afterwards. The pseudo-reconstructed FCT reproduces well the simulated FCT and reasonably well the variability of the AMOC strength, including the response to external forcing. The pseudo-reconstructed FCT, however, underestimates/overestimates the simulated variability at deep/shallow levels. Density changes responsible for the pseudo-reconstructed FCT are mainly driven by zonal temperature differences; salinity differences oppose but play a minor role. These results thus support the use of the thermal-wind relationship to reconstruct the oceanic circulation past variability, in particular at multidecadal timescales. Yet model-data comparison highlights important differences between the simulated and the proxy-based FCT variability. ECHO-G simulates a prominent weakening in the North Atlantic circulation that contrasts with the reconstructed enhancement. Our model results thus do not support the reconstructed FC minimum during the Little Ice Age. This points to a failure in the reconstruction, misrepresented processes in the model, or an important role of internal ocean dynamics.

  8. Changes in the strength of Atlantic Ocean overturning circulation across repeated Eocene warming events

    NASA Astrophysics Data System (ADS)

    Kirtland Turner, S.; Sexton, P. F.; Norris, R. D.; Wilson, P. A.; Charles, C. D.; Ridgwell, A.

    2015-12-01

    The Paleogene Period (~65 to 34 Ma) was a time of acute climatic warmth, with deep ocean temperatures exceeding 12°C at the height of the Early Eocene Climatic Optimum (~53 to 50 Ma). Multiple rapid warming events, associated with transient deep sea temperature increases of 2 to 4°C (termed 'hyperthermals'), potentially related to orbital forcing of the carbon cycle and climate, occurred from the late Paleocene through at least the early middle Eocene and onset of long-term Cenozoic cooling (~47 Ma). While deep ocean circulation patterns associated with the great glaciations of the Plio-Pleistocene have been studied extensively, the behavior of the ocean's overturning circulation on orbital-timescales in the extreme warmth of the early Cenozoic is largely unknown. Here we present new evidence for changing patterns of ocean overturning in the southern hemisphere associated with four orbitally paced hyperthermal events in the early-middle Eocene (~50 to 48 Ma) based on a combination of multi-site bulk carbonate and benthic foraminiferal stable isotope measurements and Earth system modeling. Our results suggest that southern-sourced overturning weakens and shoals in response to modest atmospheric carbon injections and consequent warming, and is replaced by invasion of nutrient-rich North Atlantic-sourced deep water, leading to predictable spatial patterns in deep-sea carbon isotope records. The changes in abyssal carbon isotope 'aging' gradients associated with these hyperthermals are, in fact, two to three times larger than the change in aging gradient associated with the switch in Atlantic overturning between the Last Glacial Maximum and today. Our results suggest that the Atlantic overturning circulation was sensitive to orbital-scale climate variability during Eocene extreme warmth, not just to interglacial-glacial climatic variability of the Plio-Pleistocene.

  9. Primary reasoning behind the double ITCZ phenomenon in a coupled ocean-atmosphere general circulation model

    NASA Astrophysics Data System (ADS)

    Li, Jianglong; Zhang, Xuehong; Yu, Yongqiang; Dai, Fushan

    2004-12-01

    This paper investigates the processes behind the double ITCZ phenomenon, a common problem in Coupled ocean-atmosphere General Circulation Models (CGCMs), using a CGCM—FGCM-0 (Flexible General Circulation Model, version 0). The double ITCZ mode develops rapidly during the first two years of the integration and becomes a perennial phenomenon afterwards in the model. By way of Singular Value Decomposition (SVD) for SST, sea surface pressure, and sea surface wind, some air-sea interactions are analyzed. These interactions prompt the anomalous signals that appear at the beginning of the coupling to develop rapidly. There are two possible reasons, proved by sensitivity experiments: (1) the overestimated east-west gradient of SST in the equatorial Pacific in the ocean spin-up process, and (2) the underestimated amount of low-level stratus over the Peruvian coast in CCM3 (the Community Climate Model, Version Three). The overestimated east-west gradient of SST brings the anomalous equatorial easterly. The anomalous easterly, affected by the Coriolis force in the Southern Hemisphere, turns into an anomalous westerly in a broad area south of the equator and is enhanced by atmospheric anomalous circulation due to the underestimated amount of low-level stratus over the Peruvian coast simulated by CCM3. The anomalous westerly leads to anomalous warm advection that makes the SST warm in the southeast Pacific. The double ITCZ phenomenon in the CGCM is a result of a series of nonlocal and nonlinear adjustment processes in the coupled system, which can be traced to the uncoupled models, oceanic component, and atmospheric component. The zonal gradient of the equatorial SST is too large in the ocean component and the amount of low-level stratus over the Peruvian coast is too low in the atmosphere component.

  10. Abrupt pre-Bølling-Allerød warming and circulation changes in the deep ocean.

    PubMed

    Thiagarajan, Nivedita; Subhas, Adam V; Southon, John R; Eiler, John M; Adkins, Jess F

    2014-07-01

    Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere--probably linked to changes in deep ocean circulation--occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling-Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling-Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling-Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean's usual thermal stratification pre-dates the Bølling-Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique feature of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the

  11. Atlantic Ocean Circulation during the Latest Cretaceous and Early Paleogene: Progressive Deep Water Exchange

    NASA Astrophysics Data System (ADS)

    Batenburg, Sietske J.; Voigt, Silke; Friedrich, Oliver; Osborne, Ann; Frank, Martin

    2015-04-01

    The Atlantic deep ocean circulation in the Latest Cretaceous (75-66 Ma) was dominated by regional processes, as indicated by the presence of distinct deep water masses. Due to the opening of the Atlantic Ocean, its different sub-basins became progressively connected and a global mode of ocean circulation commenced in the early Paleogene, ~60 Ma. To understand the evolution of deep water formation and exchange, Nd-isotope data and δ13C stratigraphies are generated for a range of sites in the North and South Atlantic. These permit to identify different intermediate and deep-water masses, to recognize their potential source regions and to determine the exact timing of deep water connection. The carbonate-rich pelagic sediments of Site U1403 near Newfoundland can be astronomically tuned and correlated to the global δ13C framework. Relatively negative seawater ɛNd(t) signatures in the 67-62 Ma interval at Site U1403 of ~-10 are distinct from those recorded further south in the North Atlantic. Possible explanations could include elevated non-radiogenic weathering inputs from the North American craton. In the latest Maastrichtian, the Site U1403 ɛNd(t) record displays a short-term positive excursion before the K/Pg boundary (67-66 Ma) followed by a sudden drop to unradiogenic values at the boundary. Changes in ocean circulation might be related to climatic changes in the pre-extinction interval and the impact itself. The ɛNd(t) records at Sites 1267 and 525 at Walvis Ridge show that an early Maastrichtian excursion to highly radiogenic values reflects a brief interval at 72-70 Ma, related to a period of increased hot-spot volcanism. Concomitant measurements of ɛNd(t) values in three different archives, fish teeth, ferromanganese coatings of bulk sediments and of foraminifera, provide a test for the partial influence of detrital particles on the isotopic composition of coatings. The first data of Sites U1403, 1267 and 525 indicate the occurrence of a common deep

  12. Ocean circulation model predicts high genetic structure observed in a long-lived pelagic developer.

    PubMed

    Sunday, J M; Popovic, I; Palen, W J; Foreman, M G G; Hart, M W

    2014-10-01

    Understanding the movement of genes and individuals across marine seascapes is a long-standing challenge in marine ecology and can inform our understanding of local adaptation, the persistence and movement of populations, and the spatial scale of effective management. Patterns of gene flow in the ocean are often inferred based on population genetic analyses coupled with knowledge of species' dispersive life histories. However, genetic structure is the result of time-integrated processes and may not capture present-day connectivity between populations. Here, we use a high-resolution oceanographic circulation model to predict larval dispersal along the complex coastline of western Canada that includes the transition between two well-studied zoogeographic provinces. We simulate dispersal in a benthic sea star with a 6-10 week pelagic larval phase and test predictions of this model against previously observed genetic structure including a strong phylogeographic break within the zoogeographical transition zone. We also test predictions with new genetic sampling in a site within the phylogeographic break. We find that the coupled genetic and circulation model predicts the high degree of genetic structure observed in this species, despite its long pelagic duration. High genetic structure on this complex coastline can thus be explained through ocean circulation patterns, which tend to retain passive larvae within 20-50 km of their parents, suggesting a necessity for close-knit design of Marine Protected Area networks. PMID:25231198

  13. Oceanic mesoscale variability and general circulation from satellite altimetry: A status report

    NASA Technical Reports Server (NTRS)

    Fu, L. L.

    1983-01-01

    Progress on the applications of satellite altimetry from SEASAT and Geos-3 to the study of oceanic mesoscale variability and general circulation is reviewed. The major conclusion for the applications to mesoscale variability is that an optimally designed altimetric mission with a lifetime of several years will improve our knowledge of the global mesoscale variability to an extent unattainable by any other practical means. The proposed Topex mission will allow one to view the global oceanic variability in such a wide range of periods and wavelengths: from 20 days to 3 to 5 years; from 50 to 10,000 km. However, the goal of determining the general circulation cannot be achieved by a single altimetric mission, because a highly accurate geoid needs to be determined independently. The scenario of the combination of Topex with Gravsat, a gravity mission that will give accurate geoid information, will allow the global general circulation to be determined at scales as small as 100 km. Areas of research needing to be performed with existing altimeter data are also discussed.

  14. Towards Improved Forecasts of Atmospheric and Oceanic Circulations over the Complex Terrain of the Eastern Mediterranean

    NASA Technical Reports Server (NTRS)

    Chronis, Themis; Case, Jonathan L.; Papadopoulos, Anastasios; Anagnostou, Emmanouil N.; Mecikalski, John R.; Haines, Stephanie L.

    2008-01-01

    Forecasting atmospheric and oceanic circulations accurately over the Eastern Mediterranean has proved to be an exceptional challenge. The existence of fine-scale topographic variability (land/sea coverage) and seasonal dynamics variations can create strong spatial gradients in temperature, wind and other state variables, which numerical models may have difficulty capturing. The Hellenic Center for Marine Research (HCMR) is one of the main operational centers for wave forecasting in the eastern Mediterranean. Currently, HCMR's operational numerical weather/ocean prediction model is based on the coupled Eta/Princeton Ocean Model (POM). Since 1999, HCMR has also operated the POSEIDON floating buoys as a means of state-of-the-art, real-time observations of several oceanic and surface atmospheric variables. This study attempts a first assessment at improving both atmospheric and oceanic prediction by initializing a regional Numerical Weather Prediction (NWP) model with high-resolution sea surface temperatures (SST) from remotely sensed platforms in order to capture the small-scale characteristics.

  15. Longitudinal biases in the Seychelles Dome simulated by 35 ocean-atmosphere coupled general circulation models

    NASA Astrophysics Data System (ADS)

    Nagura, Motoki; Sasaki, Wataru; Tozuka, Tomoki; Luo, Jing-Jia; Behera, Swadhin K.; Yamagata, Toshio

    2013-02-01

    Seychelles Dome refers to the shallow climatological thermocline in the southwestern Indian Ocean, where ocean wave dynamics efficiently affect sea surface temperature, allowing sea surface temperature anomalies to be predicted up to 1-2 years in advance. Accurate reproduction of the dome by ocean-atmosphere coupled general circulation models (CGCMs) is essential for successful seasonal predictions in the Indian Ocean. This study examines the Seychelles Dome as simulated by 35 CGCMs, including models used in phase five of the Coupled Model Intercomparison Project (CMIP5). Among the 35 CGCMs, 14 models erroneously produce an upwelling dome in the eastern half of the basin whereas the observed Seychelles Dome is located in the southwestern tropical Indian Ocean. The annual mean Ekman pumping velocity in these models is found to be almost zero in the southern off-equatorial region. This result is inconsistent with observations, in which Ekman upwelling acts as the main cause of the Seychelles Dome. In the models reproducing an eastward-displaced dome, easterly biases are prominent along the equator in boreal summer and fall, which result in shallow thermocline biases along the Java and Sumatra coasts via Kelvin wave dynamics and a spurious upwelling dome in the region. Compared to the CMIP3 models, the CMIP5 models are even worse in simulating the dome longitudes.

  16. The impact of polar mesoscale storms on northeast Atlantic ocean circulation (Invited)

    NASA Astrophysics Data System (ADS)

    Condron, A.; Renfrew, I.

    2013-12-01

    Every year thousands of mesoscale (<1000 km) storms cross the climatically sensitive sub-polar regions of the world's oceans. These storms are frequently too small, or short-lived, to be captured in meteorological reanalyses or numerical climate prediction models. As a result, the magnitude of the near-surface wind speeds and heat fluxes are considerably under-represented over the world's oceans where the atmosphere influences mixing, deep convection, upwelling, and deep water mass formation. Numerical models must, however, realistically simulate these processes in order to accurately predict future changes in the strength of the Atlantic Meridional Overturning Circulation (MOC) and the climate system. Implementing a parameterization to simulate mesoscale cyclones in the atmospheric fields driving an ocean model produced air-sea fluxes in remarkable agreement with observations. Over the Nordic Seas we found that mesoscale cyclones increased the depth, frequency and area of open ocean deep convection. At Denmark Strait we found a significant increase in the southward transport of Denmark Strait Overflow Water (DSOW); the deep water mass that plays a major role in driving the Atlantic MOC. Further south there was an increase in the cyclonic rotation of the sub-polar gyres and an increase in the northward transport of heat into the region. We conclude that polar mesoscale cyclones play an important role in driving the large-scale ocean circulation and so must be simulated globally in order to make accurate short-term climate predictions. An illustration of the effectiveness of our polar mesoscale parameterization. Panels show a 6-hourly snapshot of 10-m wind speed for (left) ECMWF ERA-40, (middle) ERA-40 with a polar mesoscale cyclone parameterized (right) satellite derived wind speed. The satellite data reveal a polar mesoscale cyclone over the Norwegian Sea with a diameter of ~400 km. The standard ERA-40 reanalysis (~1 deg.) does not capture this vortex

  17. Impact of oceanic circulation changes on atmospheric δ13CO2

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Mouchet, A.; Meissner, K. J.; Joos, F.; England, M. H.

    2015-11-01

    δ13CO2 measured in Antarctic ice cores provides constraints on oceanic and terrestrial carbon cycle processes linked with millennial-scale changes in atmospheric CO2. However, the interpretation of δ13CO2 is not straightforward. Using carbon isotope-enabled versions of the LOVECLIM and Bern3D models, we perform a set of sensitivity experiments in which the formation rates of North Atlantic Deep Water (NADW), North Pacific Deep Water (NPDW), Antarctic Bottom Water (AABW), and Antarctic Intermediate Water (AAIW) are varied. We study the impact of these circulation changes on atmospheric δ13CO2 as well as on the oceanic δ13C distribution. In general, we find that the formation rates of AABW, NADW, NPDW, and AAIW are negatively correlated with changes in δ13CO2: namely, strong oceanic ventilation decreases atmospheric δ13CO2. However, since large-scale oceanic circulation reorganizations also impact nutrient utilization and the Earth's climate, the relationship between atmospheric δ13CO2 levels and ocean ventilation rate is not unequivocal. In both models atmospheric δ13CO2 is very sensitive to changes in AABW formation rates: increased AABW formation enhances the transport of low δ13C waters to the surface and decreases atmospheric δ13CO2. By contrast, the impact of NADW changes on atmospheric δ13CO2 is less robust and might be model dependent. This results from complex interplay between global climate, carbon cycle, and the formation rate of NADW, a water body characterized by relatively high δ13C.

  18. Changing currents: a strategy for understanding and predicting the changing ocean circulation.

    PubMed

    Bryden, Harry L; Robinson, Carol; Griffiths, Gwyn

    2012-12-13

    Within the context of UK marine science, we project a strategy for ocean circulation research over the next 20 years. We recommend a focus on three types of research: (i) sustained observations of the varying and evolving ocean circulation, (ii) careful analysis and interpretation of the observed climate changes for comparison with climate model projections, and (iii) the design and execution of focused field experiments to understand ocean processes that are not resolved in coupled climate models so as to be able to embed these processes realistically in the models. Within UK-sustained observations, we emphasize smart, cost-effective design of the observational network to extract maximum information from limited field resources. We encourage the incorporation of new sensors and new energy sources within the operational environment of UK-sustained observational programmes to bridge the gap that normally separates laboratory prototype from operational instrument. For interpreting the climate-change records obtained through a variety of national and international sustained observational programmes, creative and dedicated UK scientists should lead efforts to extract the meaningful signals and patterns of climate change and to interpret them so as to project future changes. For the process studies, individual scientists will need to work together in team environments to combine observational and process modelling results into effective improvements in the coupled climate models that will lead to more accurate climate predictions. PMID:23129709

  19. M2 baroclinic tide variability modulated by the ocean circulation south of Japan

    NASA Astrophysics Data System (ADS)

    Varlamov, Sergey M.; Guo, Xinyu; Miyama, Toru; Ichikawa, Kaoru; Waseda, Takuji; Miyazawa, Yasumasa

    2015-05-01

    We analyze a concurrent simulation result of the ocean circulation and tidal currents using a data-assimilative ocean general circulation model covering the Western North Pacific with horizontal resolution of 1/36° to investigate possible interactions between them. Four sites of active M2 internal tide variability in open ocean (hot spots), such as Tokara Strait, Izu Ridge, Luzon Strait, and Ogasawara Ridge, are detected from both the satellite observation and the simulation. Energy cycle analysis of the simulated M2 baroclinic tide indicates two types of the hot spots: dissipation (Tokara Strait and Izu Ridge) and radiation (Luzon Strait and Ogasawara Ridge) dominant sites. Energy conversion from barotropic to baroclinic M2 tides at the hot spots is modulated considerably by the lower-frequency changes in the density field. Modulation at the two spots (Tokara Strait and Izu Ridge) is affected by the Kuroshio path variation together with the seasonal variation of the shallow thermocline. At the other two sites, influence from changes in the relatively deep stratification through the Kuroshio intrusion into South China Sea (Luzon Strat) and mesoscale eddy activity (Ogasawara Ridge) is dominant in the modulation.

  20. Revisiting annual mean and seasonal cycle of deep meridional overturning circulation of the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Wang, Weiqiang; Xie, Qiang; Li, Sha; Zhu, Xiuhua

    2014-05-01

    The annual mean and seasonal cycle of the deep meridional overturning circulation (MOC) of the Indian Ocean is being revisited here using GECCO synthesis. Resulting from ocean general circulation models, the annual mean deep MOC of the Indian Ocean are generally weak with inflow in the bottom layer and outflow in the intermediate and upper layer mixing with strong Indonesian Throughflow. For seasonal cycle of deep MOC, two significant and seasonal reversed counter-rotating deep cells over full depth of water column, roughly separated by 20S, are revealed during boreal summer and winter. The coincidences of the latitude 20S with where the maximum climatological wind curl for most of seasons reveals intimate relations between the deep meridional overturning and surface winds. Dynamical decompositions on annual mean and complete seasonal cycle of the meridional overturning show varying relative contribution of each dynamical component at different time scale. For annual mean deep MOC, Ekman dynamics is found to be dominant in the region of north of 25S, particularly in upper 3000m, whereas south of 25S external and vertical shear components show remarkable "seamount" features and are compensated with much larger strengths because of topo-modulated strong western boundary topography. At seasonal time scale, dominant role of Ekman dynamics and secondary role of external mode are found in the deep cell north of 20S in January and July. However in transition seasons, vertical shear is responsible for major part of meridional overturning and Ekman dynamics has comparable contribution north of Equator.

  1. Simulated strengthening of the Atlantic Meridional Overturning Circulation in response to abyssal ocean warming around Antarctica

    NASA Astrophysics Data System (ADS)

    Patara, L.; Boning, C. W.

    2013-12-01

    Studies of repeat hydrographic observations have revealed a conspicuous multi-decadal warming, and partly, freshening, of the frigid abyssal ocean waters originating from the fringes of the Antarctic continent. The warming and contraction of Antarctic Bottom Water (AABW) represents one of the most prominent signals of change in Earth's climate and accounts for a substantial fraction of the present global energy and sea level budgets. Here we present a set of ocean model experiments demonstrating that the ongoing loss of AABW also has important dynamical consequences for the large-scale meridional overturning circulation in the Atlantic Ocean. In conjunction with a slowdown of the bottom cell, we find that the upper cell of the Atlantic Meridional Overturning Circulation (AMOC) progressively strengthens in response to changes in density gradients in the deep South Atlantic. Changes in the AMOC are tightly connected to increased meridional heat transport and therefore have a strong influence on global and regional climate patterns in the North Atlantic. The simulations suggest that the AABW-induced strengthening of the AMOC is already extending into the North Atlantic, progressing at a rate of about 0.2 Sv per decade, implying that the process may need to be taken into account in projections of future North Atlantic climate.

  2. Ocean circulation off east Antarctica affects ecosystem structure and sea-ice extent.

    PubMed

    Nicol, S; Pauly, T; Bindoff, N L; Wright, S; Thiele, D; Hosie, G W; Strutton, P G; Woehler, E

    2000-08-01

    Sea ice and oceanic boundaries have a dominant effect in structuring Antarctic marine ecosystems. Satellite imagery and historical data have identified the southern boundary of the Antarctic Circumpolar Current as a site of enhanced biological productivity. Meso-scale surveys off the Antarctic peninsula have related the abundances of Antarctic krill (Euphausia superba) and salps (Salpa thompsoni) to inter-annual variations in sea-ice extent. Here we have examined the ecosystem structure and oceanography spanning 3,500 km of the east Antarctic coastline, linking the scales of local surveys and global observations. Between 80 degrees and 150 degrees E there is a threefold variation in the extent of annual sea-ice cover, enabling us to examine the regional effects of sea ice and ocean circulation on biological productivity. Phytoplankton, primary productivity, Antarctic krill, whales and seabirds were concentrated where winter sea-ice extent is maximal, whereas salps were located where the sea-ice extent is minimal. We found enhanced biological activity south of the southern boundary of the Antarctic Circumpolar Current rather than in association with it. We propose that along this coastline ocean circulation determines both the sea-ice conditions and the level of biological productivity at all trophic levels. PMID:10952309

  3. Upper-Ocean Heat Balance Processes and the Walker Circulation in CMIP5 Model Projections

    NASA Technical Reports Server (NTRS)

    Robertson, F. R.; Roberts, J. B.; Funk, C.; Lyon, B.; Ricciardulli, L.

    2012-01-01

    Considerable uncertainty remains as to the importance of mechanisms governing decadal and longer variability of the Walker Circulation, its connection to the tropical climate system, and prospects for tropical climate change in the face of anthropogenic forcing. Most contemporary climate models suggest that in response to elevated CO2 and a warmer but more stratified atmosphere, the required upward mass flux in tropical convection will diminish along with the Walker component of the tropical mean circulation as well. Alternatively, there is also evidence to suggest that the shoaling and increased vertical stratification of the thermocline in the eastern Pacific will enable a muted SST increase there-- preserving or even enhancing some of the dynamical forcing for the Walker cell flow. Over the past decade there have been observational indications of an acceleration in near-surface easterlies, a strengthened Pacific zonal SST gradient, and globally-teleconnected dislocations in precipitation. But is this evidence in support of an ocean dynamical thermostat process posited to accompany anthropogenic forcing, or just residual decadal fluctuations associated with variations in warm and cold ENSO events and other stochastic forcing? From a modeling perspective we try to make headway on this question by examining zonal variations in surface energy fluxes and dynamics governing tropical upper ocean heat content evolution in the WCRP CMIP5 model projections. There is some diversity among model simulations; for example, the CCSM4 indicates net ocean warming over the IndoPacific region while the CSIRO model concentrates separate warming responses over the central Pacific and Indian Ocean regions. The models, as with observations, demonstrate strong local coupling between variations in column water vapor, downward surface longwave radiation and SST; but the spatial patterns of changes in the sign of this relationship differ among models and, for models as a whole, with

  4. Lowering of glacial atmospheric CO2 in response to changes in oceanic circulation and marine biogeochemistry

    NASA Astrophysics Data System (ADS)

    Brovkin, Victor; Ganopolski, Andrey; Archer, David; Rahmstorf, Stefan

    2007-12-01

    We use an Earth system model of intermediate complexity, CLIMBER-2, to investigate what recent improvements in the representation of the physics and biology of the glacial ocean imply for the atmospheric concentration. The coupled atmosphere-ocean model under the glacial boundary conditions is able to reproduce the deep, salty, stagnant water mass inferred from Antarctic deep pore water data and the changing temperature of the entire deep ocean. When carbonate compensation is included in the model, we find a CO2 drawdown of 43 ppmv associated mainly with the shoaling of the Atlantic thermohaline circulation and an increased fraction of water masses of southern origin in the deep Atlantic. Fertilizing the Atlantic and Indian sectors of the Southern Ocean north of the polar front leads to a further drawdown of 37 ppmv. Other changes to the glacial carbon cycle include a decrease in the amount of carbon stored in the terrestrial biosphere (540 Pg C), which increases atmospheric CO2 by 15 ppmv, and a change in ocean salinity resulting from a drop in sea level, which elevates CO2 by another 12 ppmv. A decrease in shallow water CaCO3 deposition draws down CO2 by 12 ppmv. In total, the model is able to explain more than two thirds (65 ppmv) of the glacial to interglacial CO2 change, based only on mechanisms that are clearly documented in the proxy data. A good match between simulated and reconstructed distribution of δ13C changes in the deep Atlantic suggests that the model captures the mechanisms of reorganization of biogeochemistry in the Atlantic Ocean reasonably well. Additional, poorly constrained mechanisms to explain the rest of the observed drawdown include changes in the organic carbon:CaCO3 ratio of sediment rain reaching the seafloor, iron fertilization in the subantarctic Pacific Ocean, and changes in terrestrial weathering.

  5. Modelling of the circulation in the Northwestern Mediterranean Sea with the Princeton Ocean Model

    NASA Astrophysics Data System (ADS)

    Ahumada, M. A.; Cruzado, A.

    2006-08-01

    The Princeton Ocean Model - POM (Blumberg and Mellor, 1987) has been implemented in the Northwestern Mediterranean nested (in one-way off-line mode) to a general circulation model of the Mediterranean Sea - OGCM (Pinardi and Masetti, 2000; Demirov and Pinardi, 2002) in order to investigate if this model configuration is capable of reproducing the major features of the circulation as known from observations and to improve what has been made by previous numerical modeling works. According to the model results, the large-scale cyclonic circulation in the northern part of the Northwestern Mediterranean is, at least in the upper layers, less coherent in winter and spring than in summer and autumn. Furthermore, there is evidence that the mesoscale structure (eddies and meanders) is, during all year, a significant dynamic characteristic in this region of the Mediterranean Sea. Finally, concerning the circulation in the lower layers has been confirmed that the Levantine Intermediate Water and the Western Mediterranean Deep Water follow essentially a cyclonic path during all year.

  6. Modeling of the circulation in the Northwestern Mediterranean Sea with the Princeton Ocean Model

    NASA Astrophysics Data System (ADS)

    Ahumada, M. A.; Cruzado, A.

    2007-02-01

    The Princeton Ocean Model - POM (Blumberg and Mellor, 1987) has been implemented in the Northwestern Mediterranean nested (in one-way off-line mode) to a general circulation model of the Mediterranean Sea - OGCM (Pinardi and Masetti, 2000; Demirov and Pinardi, 2002) in order to investigate if this model configuration is capable of reproducing the major features of the circulation as known from observations and to improve what has been made by previous numerical modeling works. According to the model results, the large-scale cyclonic circulation in the northern part of the Northwestern Mediterranean is, at least in the upper layers, less coherent in winter and spring than in summer and autumn. Furthermore, there is evidence that the mesoscale structure (eddies and meanders) is, during all year, a significant dynamic characteristic in this region of the Mediterranean Sea. Finally, concerning the circulation in the lower layers, the model results have confirmed that Levantine Intermediate Water (LIW) and Western Mediterranean Deep Water (WMDW) follow essentially a cyclonic path during all year.

  7. Regional eddy vorticity transport and the equilibrium vorticity budgets of a numerical model ocean circulation

    NASA Technical Reports Server (NTRS)

    Harrison, D. E.; Holland, W. R.

    1981-01-01

    A mean vorticity budget analysis is presented of Holland's (1978) numerical ocean general circulation experiment. The stable budgets are compared with classical circulation theory to emphasize the ways in which the mesoscale motions of the model alter (or leave unaltered) classical vorticity balances. The basinwide meridional transports of vorticity by the mean flow and by the mesoscale flow in the mean are evaluated to establish the role(s) of the mesoscale in the larger scale equilibrium vorticity transports. The vorticity equation for this model fluid system is presented and the budget analysis method is described. Vorticity budgets over the selected regions and on a larger scale are given, and a summary of budget results is provided along with remarks about the utility of this type of analysis.

  8. An eddy-permitting oceanic general circulation model and its preliminary evaluation

    NASA Astrophysics Data System (ADS)

    Liu, Hailong; Zhang, Xuehong; Li, Wei; Yu, Yongqiang; Yu, Rucong

    2004-10-01

    An eddy-permitting, quasi-global oceanic general circulation model, LICOM (LASG/IAP (State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics) Climate System Ocean Model), with a uniform grid of 0.5° × 0.5° is established. Forced by wind stresses from Hellerman and Rosenstain (1983), a 40-yr integration is conducted with sea surface temperature and salinity being restored to the Levitus 94 datasets. The evaluation of the annual mean climatology of the LICOM control run shows that the large-scale circulation can be well reproduced. A comparison between the LICOM control run and a parallel integration of L30T63, which has the same framework but a coarse resolution, is also made to confirm the impact of resolution on the model performance. On account of the reduction of horizontal viscosity with the enhancement of the horizontal resolution, LICOM improves the simulation with respect to not only the intensity of the large scale circulations, but also the magnitude and structure of the Equatorial Undercurrent and South Equatorial Current. Taking advantage of the fine grid size, the pathway of the Indonesian Throughflow (ITF) is better represented in LICOM than in L30T63. The transport of ITF in LICOM is more convergent in the upper layer. As a consequence, the Indian Ocean tends to get warmer in LICOM. The poleward heat transports for both the global and individual basins are also significantly improved in LICOM. A decomposed analysis indicates that the transport due to the barotropic gyre, which primarily stands for the barotropic effect of the western boundary currents, plays a crucial role in making the difference.

  9. Monitoring estuarine circulation and ocean waste dispersion using an integrated satellite-aircraft-drogue approach

    NASA Technical Reports Server (NTRS)

    Klemas, V.; Davis, G.; Wang, H.; Whelan, W.; Tornatore, G.

    1976-01-01

    The mounting economic pressure to extract oil and other resources from the Continental Shelf and to continue using the Shelf for waste disposal is creating a need for cost-effective synoptic means of determining currents in this area. An integrated satellite-aircraft-drogue approach has been developed which employs remotely tracked expendable drogues together with satellite and aircraft observations of waste plumes and tracers, such as dyes or suspended sediment. Tests conducted on the Continental Shelf and in Delaware Bay indicate that the system provides a cost-effective means of studying current circulation, oil slick movement, and ocean waste dispersion even under severe environmental conditions.

  10. On determining the large-scale ocean circulation from satellite altimetry

    NASA Technical Reports Server (NTRS)

    Tai, C.-K.

    1983-01-01

    It is contended that a spherical harmonic expansion of the difference between the altimeter-derived mean sea surface and the geoid estimate should reveal the large-scale circulation of the ocean surface layer when the low-degree terms are examined. Methods based on this principle are proposed and partially demonstrated over the Pacific Ocean with the aid of the mean sea surface derived from the Seasat altimeter and the Goddard Earth Model 9 earth gravity model. The preliminary results reveal a well-defined clockwise gyre in the North Pacific and a much less well defined counterclockwise gyre in the South Pacific. When the dynamic topography thus obtained is compared with Wyrtki's (1975) dynamic topography derived from hydrographic data, the agreement is found to be within the limit of geoid uncertainties and satellite orbital errors.

  11. Observing Global Ocean Circulation From Space: The First Year's Results From the TOPEX/POSEIDON Mission

    NASA Technical Reports Server (NTRS)

    Fu, L. -L.

    1993-01-01

    The joint U.S./France TOPEX/Poseidon satellite was launched on August 10, 1992, and became operational 43 days later. The major goal of the mission is to use a radar altimeter system for making precise measurements of the height of the sea surface for the study of the dynamics of large-scale ocean circulation, which is a key to understanding global climate change. Additionally, the data are used for studying ocean tides and marine geophysics. The radar altimeter also measures wave height and wind speed. The mission is being conducted to optimize the sea surface height measurements for a minimum of three years. The primary objective of the first six months of the mission was to calibrate and validate the mission's measurements...

  12. On the choice of orbits for an altimetric satellite to study ocean circulation and tides

    NASA Technical Reports Server (NTRS)

    Parke, Michael E.; Stewart, Robert H.; Farless, David L.; Cartwright, David E.

    1987-01-01

    The choice of an orbit for satellite altimetric studies of the ocean's circulation and tides requires an understanding of the orbital characteristics that influence the accuracy of the satellite's measurements of sea level and the temporal and spatial distribution of the measurements. The orbital characteristics that influence accurate calculations of the satellite's position as a function of time are examined, and the pattern of ground tracks laid down on the ocean's surface as a function of the satellite's altitude and inclination is studied. The results are used to examine the aliases in the measurements of surface geostrophic currents and tides. Finally, these considerations are used to specify possible orbits that may be useful for the upcoming Topex/Poseidon mission.

  13. Observing Global Ocean Circulation From Space: The First Year's Results From the TOPEX/POSEIDON Mission

    NASA Technical Reports Server (NTRS)

    Fu, L. -L.

    1993-01-01

    The joint U.S./France TOPEX/Poseidon satellite was launched on August 10, 1992, and became operational 42 days later. The major goal of the mission is to use a radar altimeter system for making precise measurements of the height of the sea surface for the study of the dynamics of large-scale ocean circulation, which is a key to understanding global climate change. Additionally, the data are used for studying ocean tides and marine geophysics. The radar altimeter also measures wave height and wind speed. The mission is being conducted to optimize the sea surface height measurements for a minimum of three years. The primary objective of the first six months of the mission was to calibrate and validate the mission's measurements. The verification results indicate that all the measurement objectives have been met...

  14. Millennial-scale interaction between ice sheets and ocean circulation during marine isotope stage 100

    NASA Astrophysics Data System (ADS)

    Ohno, Masao; Hayashi, Tatsuya; Sato, Masahiko; Kuwahara, Yoshihiro; Mizuta, Asami; Kita, Itsuro; Sato, Tokiyuki; Kano, Akihiro

    2016-05-01

    Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remain largely unclear. Here we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.

  15. Ocean Circulation and Gateway Closures During the Late Miocene (~13-5 Ma)

    NASA Astrophysics Data System (ADS)

    Nathan, S. A.; Leckie, R. M.

    2004-12-01

    Long-term climate change is driven by tectonic influences, including changes in ocean circulation that are the result of ocean gateway closure. During the middle to late Miocene (~13-5 Ma), both tropical ocean circulation and deep water production were reorganized due to the increasing constriction of the Indonesian and Central American seaways. For example, the waters of the modern Pacific equatorial current system do not move freely into the Indian Ocean (i.e., via the Indonesian Throughflow, ITF) but instead pile up to form the Western Pacific Warm Pool (a thermal anomaly that greatly influences tropical Pacific climate and ocean circulation). Here we use a continuous record of multispecies stable isotope stratigraphy and foraminiferal assemblage counts from Ontong Java Plateau to demonstrate that during middle to late Miocene time, progressive restriction of the ITF, modulated by sea level fluctuations, resulted in the waxing and waning of a proto-warm pool in the western equatorial Pacific (WEP). The proto-warm pool profoundly affected the early late Miocene "carbonate crash" (an anomalous decrease of carbonate in deep sea sediments) and the late Miocene "biogenic bloom" (sharp increase in carbonate accumulation rates across the tropical Indo-Pacific). We hypothesize that El Niño/La Niña-like alternations of tropical carbonate preservation and productivity between the western and eastern equatorial Pacific during the late Miocene were the consequence of early warm pool development and decay. A proto-warm pool was formed ~12.1-10.6 Ma, which initiated a nutrient-rich Equatorial Undercurrent and/or increased Trade Wind strength. These La Niña-like conditions sustained carbonate productivity in the eastern equatorial Pacific (EEP) at a time when carbonate preservation sharply declined in the Caribbean. Proto-warm pool weakening and El Niño-like conditions ~10.6-8.8 Ma intensified a "carbonate crash" in the EEP, while resurgence of the warm pool and La Ni

  16. Reconstruction of ocean circulation from sparse data using the adjoint method: LGM and the present

    NASA Astrophysics Data System (ADS)

    Kurahashi-Nakamura, T.; Losch, M. J.; Paul, A.; Mulitza, S.; Schulz, M.

    2010-12-01

    Understanding the behavior of the Earth's climate system under different conditions in the past is the basis for more robust projections of future climate. It is thought that the ocean circulation plays a very important role in the climate system, because it can greatly affect climate by dynamic-thermodynamic (as a medium of heat transport) and biogeochemical processes (by affecting the global carbon cycle). In this context, studying the period of the Last Glacial Maximum (LGM) is particularly promising, as it represents a climate state that is very different from today. Furthermore the LGM, compared to other paleoperiods, is characterized by a relatively good paleo-data coverage. Unfortunately, the ocean circulation during the LGM is still uncertain, with a range of climate models estimating both a stronger and a weaker formation rate of North Atlantic Deep Water (NADW) as compared to the present rate. Here, we present a project aiming at reducing this uncertainty by combining proxy data with a numerical ocean model using variational techniques. Our approach, the so-called adjoint method, employs a quadratic cost function of model-data differences weighted by their prior error estimates. We seek an optimal state estimate at the global minimum of the cost function by varying the independent control variables such as initial conditions (e.g. temperature), boundary conditions (e.g. surface winds, heat flux), or internal parameters (e.g. vertical diffusivity). The adjoint or dual model computes the gradient of the cost function with respect to these control variables and thus provides the information required by gradient descent algorithms. The gradients themselves provide valuable information about the sensitivity of the system to perturbations in the control variables. We use the Massachusetts Institute of Technology ocean general circulation model (MITgcm) with a cubed-sphere grid system that avoids converging grid lines and pole singularities. This model code is

  17. Carbon dioxide, climate and the deep ocean circulation: Carbon chemistry model. Final report

    SciTech Connect

    Menawat, A.S.

    1992-09-21

    The objective of this study was to investigate the role of oceanic carbon chemistry in modulating the atmospheric levels of CO{sub 2}. It is well known that the oceans are the primary sink of the excess carbon pumped into the atmosphere since the beginning of the industrial period. The suspended particulate and the dissolved organic matters in the deep ocean play important roles as carriers of carbon and other elements critical to the fate of CO{sub 2}. In addition, the suspended particulate matter provides sites for oxidation-reduction reactions and microbial activities. The problem is of an intricate system with complex chemical, physical and biological processes. This report describes a methodology to describe the interconversions of different forms of the organic and inorganic nutrients, that may be incorporated in the ocean circulation models. Our approach includes the driving force behind the transfers in addition to balancing the elements. Such thermodynamic considerations of describing the imbalance in the chemical potentials is a new and unique feature of our approach.

  18. Carbon dioxide, climate and the deep ocean circulation: Carbon chemistry model

    SciTech Connect

    Menawat, A.S.

    1992-09-21

    The objective of this study was to investigate the role of oceanic carbon chemistry in modulating the atmospheric levels of CO[sub 2]. It is well known that the oceans are the primary sink of the excess carbon pumped into the atmosphere since the beginning of the industrial period. The suspended particulate and the dissolved organic matters in the deep ocean play important roles as carriers of carbon and other elements critical to the fate of CO[sub 2]. In addition, the suspended particulate matter provides sites for oxidation-reduction reactions and microbial activities. The problem is of an intricate system with complex chemical, physical and biological processes. This report describes a methodology to describe the interconversions of different forms of the organic and inorganic nutrients, that may be incorporated in the ocean circulation models. Our approach includes the driving force behind the transfers in addition to balancing the elements. Such thermodynamic considerations of describing the imbalance in the chemical potentials is a new and unique feature of our approach.

  19. Mechanical power input from buoyancy and wind to the circulation in an ocean model

    NASA Astrophysics Data System (ADS)

    Saenz, J. A.; Hogg, A. M.; Hughes, G. O.; Griffiths, R. W.

    2012-07-01

    We make a systematic quantitative comparison of the effects that surface buoyancy forcing and wind stress have on the energy balance of an idealized, rotating, pole-to-pole ocean model with a zonally re-entrant channel in the south, forced by realistic heat (buoyancy) fluxes and wind stresses representative of global climatology. Surface buoyancy fluxes and wind stress forcing are varied independently; both have significant effects on the reservoirs of various forms of energy and the rates of transfer between them. Importantly, we show for the first time that in the ocean, each power input has a positive feedback on the other. Changes in the rate of generation of available potential energy by buoyancy fluxes at the surface lead to similar changes in the rate of conversion of potential energy to kinetic energy by buoyancy forces (sinking) in the interior, and to changes in the rate of generation of kinetic energy by wind stress. Conversely, changes in the rate of generation of kinetic energy by wind stress lead to changes in the rate of generation of available potential energy by buoyancy forcing. We discuss how this feedback is mediated by the circumpolar current, and processes involving buoyancy, mixing and geostrophic balances. Our results support the notion that surface buoyancy forcing, along with wind and tidal forcing, plays an active role in the energy balance of the oceans. The overturning circulation in the oceans is not the result of a single driving force. Rather, it is a manifestation of a complex and subtle balance.

  20. El Nino-southern oscillation simulated in an MRI atmosphere-ocean coupled general circulation model

    SciTech Connect

    Nagai, T.; Tokioka, T.; Endoh, M.; Kitamura, Y. )

    1992-11-01

    A coupled atmosphere-ocean general circulation model (GCM) was time integrated for 30 years to study interannual variability in the tropics. The atmospheric component is a global GCM with 5 levels in the vertical and 4[degrees]latitude X 5[degrees] longitude grids in the horizontal including standard physical processes (e.g., interactive clouds). The oceanic component is a GCM for the Pacific with 19 levels in the vertical and 1[degrees]x 2.5[degrees] grids in the horizontal including seasonal varying solar radiation as forcing. The model succeeded in reproducing interannual variations that resemble the El Nino-Southern Oscillation (ENSO) with realistic seasonal variations in the atmospheric and oceanic fields. The model ENSO cycle has a time scale of approximately 5 years and the model El Nino (warm) events are locked roughly in phase to the seasonal cycle. The cold events, however, are less evident in comparison with the El Nino events. The time scale of the model ENSO cycle is determined by propagation time of signals from the central-eastern Pacific to the western Pacific and back to the eastern Pacific. Seasonal timing is also important in the ENSO time scale: wind anomalies in the central-eastern Pacific occur in summer and the atmosphere ocean coupling in the western Pacific operates efficiently in the first half of the year.

  1. Behavior of 137Cs concentrations in the North Pacific in an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Tsumune, Daisuke; Aoyama, Michio; Hirose, Katsumi

    2003-08-01

    We have carried out a first simulation of the spatial distributions and the temporal variations of 137Cs concentrations in the North Pacific in off line calculations by using archived output of an ocean general circulation model (OGCM) developed by the National Center of Atmospheric Research (NCAR). Artificial radionuclides including 137Cs are introduced into ocean surface due to global fallout originating from the large-scale atmospheric nuclear weapons tests in 1961-1962. The distribution of radioactive deposition used as forcing for this simulation is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute (MRI) in Japan. 137Cs originating from global fallout have been transported into the ocean interior by advection and diffusion, and the 137Cs concentrations reduced by radioactive decay. We assess the skill of the model calculations by comparing simulated values of 137Cs in seawater with the observed values included in the database compiled by MRI because 137Cs is one of the most useful tracers regarding water motion in the ocean. The vertical and horizontal distributions of the calculated 137Cs concentrations were in good agreement with those of the observed 137Cs concentrations, except in the deep layer.

  2. Interactions between the Indonesian Throughflow and circulations in the Indian and Pacific Oceans

    NASA Astrophysics Data System (ADS)

    McCreary, Julian P.; Miyama, Toru; Furue, Ryo; Jensen, Tommy; Kang, Hyoun-Woo; Bang, Bohyun; Qu, Tangdong

    2007-10-01

    Circulations associated with the Indonesian Throughflow (IT), particularly concerning subsurface currents in the Pacific Ocean, are studied using three types of models: a linear, continuously stratified (LCS) model and a nonlinear, 4{1}/{2}-layer model (LOM), both confined to the Indo-Pacific basin; and a global, ocean general circulation model (COCO). Solutions are wind forced, and obtained with both open and closed Indonesian passages. Layers 1-4 of LOM correspond to near-surface, thermocline, subthermocline (thermostad), and upper-intermediate (AAIW) water, respectively, and analogous layers are defined for COCO. The three models share a common dynamics. When the Indonesian passages are abruptly opened, barotropic and baroclinic waves radiate into the interiors of both oceans. The steady-state, barotropic flow field from the difference (open - closed) solution is an anticlockwise circulation around the perimeter of the southern Indian Ocean, with its meridional branches confined to the western boundaries of both oceans. In contrast, steady-state, baroclinic flows extend into the interiors of both basins, a consequence of damping of baroclinic waves by diapycnal processes (internal diffusion, upwelling and subduction, and convective overturning). Deep IT-associated currents are the subsurface parts of these baroclinic flows. In the Pacific, they tend to be directed eastward and poleward, extend throughout the basin, and are closed by upwelling in the eastern ocean and Subpolar Gyre. Smaller-scale aspects of their structure vary significantly among the models, depending on the nature of their diapycnal mixing. At the exit to the Indonesian Seas, the IT is highly surface trapped in all the models, with a prominent, deep core in the LCS model and in LOM. The separation into two cores is due to near-equatorial, eastward-flowing, subsurface currents in the Pacific Ocean, which drain layer 2 and layer 3 waters from the western ocean to supply water for the upwelling

  3. Using Green's Functions to initialize and adjust a global, eddying ocean biogeochemistry general circulation model

    NASA Astrophysics Data System (ADS)

    Brix, H.; Menemenlis, D.; Hill, C.; Dutkiewicz, S.; Jahn, O.; Wang, D.; Bowman, K.; Zhang, H.

    2015-11-01

    The NASA Carbon Monitoring System (CMS) Flux Project aims to attribute changes in the atmospheric accumulation of carbon dioxide to spatially resolved fluxes by utilizing the full suite of NASA data, models, and assimilation capabilities. For the oceanic part of this project, we introduce ECCO2-Darwin, a new ocean biogeochemistry general circulation model based on combining the following pre-existing components: (i) a full-depth, eddying, global-ocean configuration of the Massachusetts Institute of Technology general circulation model (MITgcm), (ii) an adjoint-method-based estimate of ocean circulation from the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project, (iii) the MIT ecosystem model "Darwin", and (iv) a marine carbon chemistry model. Air-sea gas exchange coefficients and initial conditions of dissolved inorganic carbon, alkalinity, and oxygen are adjusted using a Green's Functions approach in order to optimize modeled air-sea CO2 fluxes. Data constraints include observations of carbon dioxide partial pressure (pCO2) for 2009-2010, global air-sea CO2 flux estimates, and the seasonal cycle of the Takahashi et al. (2009) Atlas. The model sensitivity experiments (or Green's Functions) include simulations that start from different initial conditions as well as experiments that perturb air-sea gas exchange parameters and the ratio of particulate inorganic to organic carbon. The Green's Functions approach yields a linear combination of these sensitivity experiments that minimizes model-data differences. The resulting initial conditions and gas exchange coefficients are then used to integrate the ECCO2-Darwin model forward. Despite the small number (six) of control parameters, the adjusted simulation is significantly closer to the data constraints (37% cost function reduction, i.e., reduction in the model-data difference, relative to the baseline simulation) and to independent observations (e.g., alkalinity). The adjusted air-sea gas

  4. Higher Laurentide and Greenland ice sheets strengthen the North Atlantic ocean circulation

    NASA Astrophysics Data System (ADS)

    Gong, Xun; Zhang, Xiangdong; Lohmann, Gerrit; Wei, Wei; Zhang, Xu; Pfeiffer, Madlene

    2015-07-01

    During the last glacial-interglacial cycle, changes in the large-scale North Atlantic ocean circulation occurred, and at the same time topography of the Laurentide and Greenland ice sheets also varied. In this study, we focus on detecting the changes of the North Atlantic gyres, western boundary current, and the Atlantic meridional overturning circulation (AMOC) corresponding to different Laurentide and Greenland ice sheet topographies. Using an Earth System Model, we conducted simulations for five climate states with different ice sheet topographies: Pre-industrial, Mid Holocene, Last Glacial Maximum, 32 kilo years before present and Eemian interglacial. Our simulation results indicate that higher topographies of the Laurentide and Greenland ice sheets strengthen surface wind stress curl over the North Atlantic ocean, intensifying the subtropical and subpolar gyres and the western boundary currents. The corresponding decrease in sea surface height from subtropical to subpolar favors a stronger AMOC. An offshore shift of the Gulf Stream is also identified during the glacial periods relative to that during the Pre-industrial due to lower sea levels, explaining a weaker glacial Gulf Stream detected in proxy data. Meanwhile, the North Atlantic gyres and AMOC demonstrate a positively correlated relation under each of the climate conditions with higher ice sheets.

  5. Modeling of the World Ocean circulation with the four-dimensional assimilation of temperature and salinity fields

    NASA Astrophysics Data System (ADS)

    Marchuk, G. I.; Zalesny, V. B.

    2012-02-01

    The problem of modeling the World Ocean circulation with the four-dimensional assimilation of temperature and salinity fields is considered. A mathematical model of the ocean general circulation and a numerical algorithm for its solution are formulated. The model equations are written in a σ coordinate system on the sphere with the North Pole shifted to the point of the continent (60° E, 60.5° N). The model has a flexible numerical structure and consists of two parts: the forward prognostic model and its adjoint analog. The numerical algorithm for solving the forward and adjoint problems is based on the method of multicomponent splitting. This method includes splitting with respect to physical processes and geometric coordinates. Three series of numerical experiments are performed: (1) a test solution to the problem of the four-dimensional variational assimilation, (2) modeling of the World Ocean circulation with the variational assimilation of climatic temperature and salinity fields, and (3) modeling of the World Ocean circulation with the variational assimilation of climatic temperature and salinity fields and the data of Argo buoys. The results of calculations demonstrate the expediency of using the model of World Ocean circulation with the procedure of assimilating observational data for a description of the general structure of thermohaline fields.

  6. Subaqueous melting in Zachariae Isstrom, Northeast Greenland combining observations and an ocean general circulation model

    NASA Astrophysics Data System (ADS)

    Cai, C.; Rignot, E. J.; Menemenlis, D.

    2015-12-01

    Zachariae Isstrom, a major ice stream in northeast Greenland, has lost its entire ice shelf in the past decade. Here, we study the evolution of subaqueous melting of its floating section during the transition. Observations show that the rate of ice shelf melting has doubled during 1999-2010 and is twice higher than that maintaining the ice shelf in a state of mass equilibrium. The ice shelf melt rate depends on the thermal forcing from warm, salty, subsurface ocean water of Atlantic origin (AW), and - in contrast with Antarctic ice shelves - on the mixing of AW with fresh buoyant subglacial discharge. Subglacial discharge has increased as result of enhanced ice sheet runoff driven by warmer air temperature; ocean thermal forcing has increased due enhanced advection of AW. Here, we employ the Massassuchetts Institute of Technology general circulation model (MITgcm) at a high spatial resolution (1 m horizontal and 1 m vertical spacing near the grounding line) to simulate the melting process in 3-D. The model is constrained by ice thickness from mass conservation, oceanic bathymetry from NASA Operation IceBridge gravity data, in-situ ocean temperature/salinity data, ocean tide height and current from the Arctic Ocean Tidal Inverse Model (AOTIM-5) and subglacial discharge from output products of the Regional Atmospheric Climate Model (RACMO). We compare the results in winter (no runoff) with summer (maximum runoff) at two different stages with (prior to 2012) and without the ice shelf (after 2012) to subaqueous melt rates deduced from remote sensing observations. We show that ice melting by the ocean has increased by one order of magnitude as a result of the transition from ice shelf terminating to near-vertical calving front terminating. We also find that subglacial discharge has a significant impact on the ice shelf melt rates in Greenland. We conclude on the impact of ocean warming and air temperature warming on the melting regime of the ice margin of Zachariae

  7. An Improved Heat Budget Estimation Including Bottom Effects for General Ocean Circulation Models

    NASA Technical Reports Server (NTRS)

    Carder, Kendall; Warrior, Hari; Otis, Daniel; Chen, R. F.

    2001-01-01

    This paper studies the effects of the underwater light field on heat-budget calculations of general ocean circulation models for shallow waters. The presence of a bottom significantly alters the estimated heat budget in shallow waters, which affects the corresponding thermal stratification and hence modifies the circulation. Based on the data collected during the COBOP field experiment near the Bahamas, we have used a one-dimensional turbulence closure model to show the influence of the bottom reflection and absorption on the sea surface temperature field. The water depth has an almost one-to-one correlation with the temperature rise. Effects of varying the bottom albedo by replacing the sea grass bed with a coral sand bottom, also has an appreciable effect on the heat budget of the shallow regions. We believe that the differences in the heat budget for the shallow areas will have an influence on the local circulation processes and especially on the evaporative and long-wave heat losses for these areas. The ultimate effects on humidity and cloudiness of the region are expected to be significant as well.

  8. Drastic changes in the Nordic Seas oceanic circulation and deepwater formation in a Pliocene context

    NASA Astrophysics Data System (ADS)

    Contoux, Camille; Zhang, Zhongshi; De Schepper, Stijn; Li, Camille; Nisancioglu, Kerim; Risebrobakken, Bjorg

    2016-04-01

    The Nordic Seas are a major area of deepwater formation, thus playing a crucial role in the global oceanic circulation. In the recent years a cooling and freshening of the Norwegian Sea has been observed (Blindheim et al., 2000), highlighting potential changes in this area linked to climate change. Here, we use climate simulations of the mid-Pliocene warm period with the NorESM-L model. This period is considered to be the last interval when Earth experienced temperatures higher than today for a sustained period of time, in equilibrium with CO2 concentrations similar to present-day and a reduced Greenland Ice Sheet. We find that oceanic circulation in the Nordic Seas is drastically modified. The strength of the East Greenland Current is reduced, which implies less Arctic water going to the North Atlantic from the west of the Fram strait, which creates a compensating outflow current from the east of the Fram Strait to the North Atlantic along the Voring plateau (coast of Norway). The Norwegian Atlantic current is shifted westward, meaning that there is increased Atlantic water influence in the Greenland Sea, which becomes much warmer, and increased Arctic influence along Norway, which becomes colder than present. Circulation becomes anticyclonic instead of cyclonic. Circulation in the subpolar gyre is strongly reduced, together with deepwater formation on average both in the Irminger Sea and the Nordic Seas. Convection sites in the Nordic Seas shift from the eastern part to the western part. Sensitivity experiments show that these changes are not reproduced in other Pliocene contexts, such as when CO2 is low (280 ppm) or when Barents Sea is turned to land, suggesting that the ultimate driver of these changes is higher CO2. When Barents Sea is land, which was the reality of the Pliocene, circulation and sea-surface temperature show a good agreement with reconstructions from marine proxies (De Schepper et al., 2015). This means that NorESM-L is able to properly

  9. Deglacial Ocean Circulation Scheme at Intermediate Depths in the Tropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Xie, R. C.; Marcantonio, F.; Schmidt, M. W.

    2014-12-01

    In the modern Atlantic Ocean, intermediate water circulation is largely governed by the southward flowing upper North Atlantic Deep Water (NADW) and the northward return flow Antarctic Intermediate Water (AAIW). During the last deglaciation, it is commonly accepted that the southward flow Glacial North Atlantic Intermediate Water, the glacial analogue of NADW, contributed significantly to past variations in intermediate water circulation. However, to date, there is no common consensus of the role AAIW played during the last deglaciation, especially across abrupt climate events such as the Heinrich 1 and the Younger Dryas. This study aims to reconstruct intermediate northern- and southern-sourced water circulation in the tropical North Atlantic during the past 22 kyr and attempts to confine the boundary between AAIW and northern-sourced intermediate waters in the past. High-resolution Nd isotopic compositions (ɛNd thereafter) of fish debris and bulk sediment acid-reductive leachate from the Southern Caribbean (VM12-107; 1079 m) are inconsistent, again casting concerns, as already raised by recent studies, on the reliability of the leachate method in extracting seawater ɛNd signature. This urges the need to carefully verify the seawater ɛNd integrity in sediment acid-reductive leachate in various oceanic settings. Fish debris Nd isotope record in our study displays a two-step decreasing trend from the early deglaciation to early Holocene. We interpret this as recording a two-step deglacial recovery of the upper NADW, given the assumption on a more radiogenic glacial northern-sourced water is valid. Comparing with authigenic ɛNd records in the Florida Straits [1] and the Demarara Rise [2], our new fish debris ɛNd results suggest that, in the tropical western North Atlantic, glacial and deglacial AAIW never penetrated beyond the lower depth limit of modern AAIW. [1] Xie et al., GCA (140) 2014; [2] Huang et al., EPSL (389) 2014

  10. A zonally averaged, three-basin ocean circulation model for climate studies

    SciTech Connect

    Hovine, S.; Fichefet, T.

    1994-09-01

    A two-dimensional, three-basin ocean model suitable for long-term climate studies is developed. The model is based on the zonally averaged form of the primitive equations written in spherical coordinates. The east-west density difference which arises upon averaging the momentum equations is taken to be proportional to the meridional density gradient. Lateral exchanges of heat and salt between the basins are explicitly resolved. Moreover, the model includes bottom topography and has representations of the Arctic Ocean and of the Weddell and Ross seas. Under realistic restoring boundary conditions, the model reproduces the global conveyor belt: deep water is formed in the Atlantic between 60 and 70{degree}N at a rate of about 17 Sv (1 Sv=10{sup 6} m{sup 3}S{sup {minus}1}) and in the vicinity of the Antarctic continent, while the Indian and Pacific basins show broad upwelling. Superimposed on this thermohaline circulation are vigorous wind-driven cells in the upper thermocline. The simulated temperature and salinity fields and the computed meridional heat transport compare reasonably well with the observational estimates. When mixed boundary conditions i.e., a restoring condition no sea-surface temperature and flux condition on sea-surface salinity are applied, the model exhibits an irregular behavior before reaching a steady state characterized by self-sustained oscillations of 8.5-y period. The conveyor-belt circulation always results at this stage. A series of perturbation experiments illustrates the ability of the model to reproduce different steady-state circulations under mixed boundary conditions. Finally, the model sensitivity to various factors is examined. This sensitivity study reveals that the bottom topography and the presence of a submarine meridional ridge in the zone of the Drake passage play a crucial role in determining the properties of the model bottom-water masses. The importance of the seasonality of the surface forcing is also stressed.

  11. Ocean Circulation Modeling for Aquatic Dispersion of Liquid Radioactive Effluents from Nuclear Power Plants

    SciTech Connect

    Chung, Y.G.; Lee, G.B.; Bang, S.Y.; Choi, S.B.; Lee, S.U.; Yoon, J.H.; Nam, S.Y.; Lee, H.R.

    2006-07-01

    Recently, three-dimensional models have been used for aquatic dispersion of radioactive effluents in relation to nuclear power plant siting based on the Notice No. 2003-12 'Guideline for investigating and assessing hydrological and aquatic characteristics of nuclear facility site' of the Ministry of Science and Technology (MOST) in Korea. Several nuclear power plants have been under construction or planed, which are Shin-Kori Unit 1 and 2, Shin-Wolsong Unit 1 and 2, and Shin-Ulchin Unit 1 and 2. For assessing the aquatic dispersion of radionuclides released from the above nuclear power plants, it is necessary to know the coastal currents around sites which are affected by circulation of East Sea. In this study, a three dimensional hydrodynamic model for the circulation of the East Sea of Korea has been developed as the first phase, which is based on the RIAMOM (Research Institute of Applied Mechanics' Ocean Model, Kyushu University, Japan). The model uses the primitive equation with hydrostatic approximation, and uses Arakawa-B grid system horizontally and Z coordinate vertically. Model domain is 126.5 deg. E to 142.5 deg. E of east longitude and 33 deg. N and 52 deg. N of the north latitude. The space of the horizontal grid was 1/12 deg. to longitude and latitude direction and vertical level was divided to 20. This model uses Generalized Arakawa Scheme, Slant Advection, and Mode-Splitting Method. The input data were from JODC (Japan Oceanographic Data Center), KNFRDI (Korea National Fisheries Research and Development Institute), and ECMWF (European Center for Medium-Range Weather Forecasts). The modeling results are in fairly good agreement with schematic patterns of the surface circulation in the East Sea/Japan Sea. The local current model and aquatic dispersion model of the coastal region will be developed as the second phase. The oceanic dispersion experiments will be also carried out by using ARGO Drifter around a nuclear power plant site. (authors)

  12. A Tailored Computation of the Mean Dynamic Topography for a Consistent Integration into Ocean Circulation Models

    NASA Astrophysics Data System (ADS)

    Becker, S.; Losch, M.; Brockmann, J. M.; Freiwald, G.; Schuh, W.-D.

    2014-11-01

    Geostrophic surface velocities can be derived from the gradients of the mean dynamic topography—the difference between the mean sea surface and the geoid. Therefore, independently observed mean dynamic topography data are valuable input parameters and constraints for ocean circulation models. For a successful fit to observational dynamic topography data, not only the mean dynamic topography on the particular ocean model grid is required, but also information about its inverse covariance matrix. The calculation of the mean dynamic topography from satellite-based gravity field models and altimetric sea surface height measurements, however, is not straightforward. For this purpose, we previously developed an integrated approach to combining these two different observation groups in a consistent way without using the common filter approaches (Becker et al. in J Geodyn 59(60):99-110, 2012; Becker in Konsistente Kombination von Schwerefeld, Altimetrie und hydrographischen Daten zur Modellierung der dynamischen Ozeantopographie 2012). Within this combination method, the full spectral range of the observations is considered. Further, it allows the direct determination of the normal equations (i.e., the inverse of the error covariance matrix) of the mean dynamic topography on arbitrary grids, which is one of the requirements for ocean data assimilation. In this paper, we report progress through selection and improved processing of altimetric data sets. We focus on the preprocessing steps of along-track altimetry data from Jason-1 and Envisat to obtain a mean sea surface profile. During this procedure, a rigorous variance propagation is accomplished, so that, for the first time, the full covariance matrix of the mean sea surface is available. The combination of the mean profile and a combined GRACE/GOCE gravity field model yields a mean dynamic topography model for the North Atlantic Ocean that is characterized by a defined set of assumptions. We show that including the

  13. How stationary are the internal tides in a high-resolution global ocean circulation model?

    NASA Astrophysics Data System (ADS)

    Shriver, Jay F.; Richman, James G.; Arbic, Brian K.

    2014-05-01

    The stationarity of the internal tides generated in a global eddy-resolving ocean circulation model forced by realistic atmospheric fluxes and the luni-solar gravitational potential is explored. The root mean square (RMS) variability in the M2 internal tidal amplitude is approximately 2 mm or less over most of the ocean and exceeds 2 mm in regions with larger internal tidal amplitude. The M2 RMS variability approaches the mean amplitude in weaker tidal areas such as the tropical Pacific and eastern Indian Ocean, but is smaller than the mean amplitude near generation regions. Approximately 60% of the variance in the complex M2 tidal amplitude is due to amplitude-weighted phase variations. Using the RMS tidal amplitude variations normalized by the mean tidal amplitude (normalized RMS variability (NRMS)) as a metric for stationarity, low-mode M2 internal tides with NRMS < 0.5 are stationary over 25% of the deep ocean, particularly near the generation regions. The M2 RMS variability tends to increase with increasing mean amplitude. However, the M2 NRMS variability tends to decrease with increasing mean amplitude, and regions with strong low-mode internal tides are more stationary. The internal tide beams radiating away from generation regions become less stationary with distance. Similar results are obtained for other tidal constituents with the overall stationarity of the constituent decreasing as the energy in the constituent decreases. Seasonal variations dominate the RMS variability in the Arabian Sea and near-equatorial oceans. Regions of high eddy kinetic energy are regions of higher internal tide nonstationarity.

  14. Local and Global Views of Systematic Errors of Atmosphere-Ocean General Circulation Models

    NASA Astrophysics Data System (ADS)

    Mechoso, C. Roberto; Wang, Chunzai; Lee, Sang-Ki; Zhang, Liping; Wu, Lixin

    2014-05-01

    Coupled Atmosphere-Ocean General Circulation Models (CGCMs) have serious systematic errors that challenge the reliability of climate predictions. One major reason for such biases is the misrepresentations of physical processes, which can be amplified by feedbacks among climate components especially in the tropics. Much effort, therefore, is dedicated to the better representation of physical processes in coordination with intense process studies. The present paper starts with a presentation of these systematic CGCM errors with an emphasis on the sea surface temperature (SST) in simulations by 22 participants in the Coupled Model Intercomparison Project phase 5 (CMIP5). Different regions are considered for discussion of model errors, including the one around the equator, the one covered by the stratocumulus decks off Peru and Namibia, and the confluence between the Angola and Benguela currents. Hypotheses on the reasons for the errors are reviewed, with particular attention on the parameterization of low-level marine clouds, model difficulties in the simulation of the ocean heat budget under the stratocumulus decks, and location of strong SST gradients. Next the presentation turns to a global perspective of the errors and their causes. It is shown that a simulated weak Atlantic Meridional Overturning Circulation (AMOC) tends to be associated with cold biases in the entire Northern Hemisphere with an atmospheric pattern that resembles the Northern Hemisphere annular mode. The AMOC weakening is also associated with a strengthening of Antarctic bottom water formation and warm SST biases in the Southern Ocean. It is also shown that cold biases in the tropical North Atlantic and West African/Indian monsoon regions during the warm season in the Northern Hemisphere have interhemispheric links with warm SST biases in the tropical southeastern Pacific and Atlantic, respectively. The results suggest that improving the simulation of regional processes may not suffice for a more

  15. Circulation constrains the evolution of larval development modes and life histories in the coastal ocean.

    PubMed

    Pringle, James M; Byers, James E; Pappalardo, Paula; Wares, John P; Marshall, Dustin

    2014-04-01

    The evolutionary pressures that drive long larval planktonic durations in some coastal marine organisms, while allowing direct development in others, have been vigorously debated. We introduce into the argument the asymmetric dispersal of larvae by coastal currents and find that the strength of the currents helps determine which dispersal strategies are evolutionarily stable. In a spatially and temporally uniform coastal ocean of finite extent, direct development is always evolutionarily stable. For passively drifting larvae, long planktonic durations are stable when the ratio of mean to fluctuating currents is small and the rate at which larvae increase in size in the plankton is greater than the mortality rate (both in units of per time). However, larval behavior that reduces downstream larval dispersal for a given time in plankton will be selected for, consistent with widespread observations of behaviors that reduce dispersal of marine larvae. Larvae with long planktonic durations are shown to be favored not for the additional dispersal they allow, but for the additional fecundity that larval feeding in the plankton enables. We analyzed the spatial distribution of larval life histories in a large database of coastal marine benthic invertebrates and documented a link between ocean circulation and the frequency of planktotrophy in the coastal ocean. The spatial variation in the frequency of species with planktotrophic larvae is largely consistent with our theory; increases in mean currents lead to a decrease in the fraction of species with planktotrophic larvae over a broad range of temperatures. PMID:24933820

  16. Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf

    NASA Astrophysics Data System (ADS)

    Jacobs, Stanley S.; Jenkins, Adrian; Giulivi, Claudia F.; Dutrieux, Pierre

    2011-08-01

    In 1994, ocean measurements near Antarctica's Pine Island Glacier showed that the ice shelf buttressing the glacier was melting rapidly. This melting was attributed to the presence of relatively warm, deep water on the Amundsen Sea continental shelf. Heat, salt and ice budgets along with ocean modelling provided steady-state calving and melting rates. Subsequent satellite observations and modelling have indicated large system imbalances, including ice-shelf thinning and more intense melting, glacier acceleration and drainage basin drawdown. Here we combine our earlier data with measurements taken in 2009 to show that the temperature and volume of deep water in Pine Island Bay have increased. Ocean transport and tracer calculations near the ice shelf reveal a rise in meltwater production by about 50% since 1994. The faster melting seems to result mainly from stronger sub-ice-shelf circulation, as thinning ice has increased the gap above an underlying submarine bank on which the glacier was formerly grounded. We conclude that the basal melting has exceeded the increase in ice inflow, leading to the formation and enlargement of an inner cavity under the ice shelf within which sea water nearly 4°C above freezing can now more readily access the grounding zone.

  17. Isotopic evaluation of ocean circulation in the Late Cretaceous North American seaway

    NASA Astrophysics Data System (ADS)

    Coulson, Alan B.; Kohn, Matthew J.; Barrick, Reese E.

    2011-12-01

    During the mid- and Late Cretaceous period, North America was split by the north-south oriented Western Interior Seaway. Its role in creating and maintaining Late Cretaceous global greenhouse conditions remains unclear. Different palaeoceanographic reconstructions portray diverse circulation patterns. The southward extent of relatively cool, low-salinity, low-δ18O surface waters critically distinguishes among these models, but past studies of invertebrates could not independently assess water temperature and isotopic compositions. Here we present oxygen isotopes in biophosphate from coeval marine turtle and fish fossils from western Kansas, representing the east central seaway, and from the Mississippi embayment, representing the marginal Tethys Ocean. Our analyses yield precise seawater isotopic values and geographic temperature differences during the main transition from the Coniacian to the early Campanian age (87-82 Myr), and indicate that the seaway oxygen isotope value and salinity were 2‰ and 3‰ lower, respectively, than in the marginal Tethys Ocean. We infer that the influence of northern freshwater probably reached as far south as Kansas. Our revised values imply relatively large temperature differences between the Mississippi embayment and central seaway, explain the documented regional latitudinal palaeobiogeographic zonation and support models with relatively little inflow of surface waters from the Tethys Ocean to the Western Interior Seaway.

  18. Finding the 'lost years' in green turtles: insights from ocean circulation models and genetic analysis.

    PubMed

    Putman, Nathan F; Naro-Maciel, Eugenia

    2013-10-01

    Organismal movement is an essential component of ecological processes and connectivity among ecosystems. However, estimating connectivity and identifying corridors of movement are challenging in oceanic organisms such as young turtles that disperse into the open sea and remain largely unobserved during a period known as 'the lost years'. Using predictions of transport within an ocean circulation model and data from published genetic analysis, we present to our knowledge, the first basin-scale hypothesis of distribution and connectivity among major rookeries and foraging grounds (FGs) of green turtles (Chelonia mydas) during their 'lost years'. Simulations indicate that transatlantic dispersal is likely to be common and that recurrent connectivity between the southwestern Indian Ocean and the South Atlantic is possible. The predicted distribution of pelagic juvenile turtles suggests that many 'lost years hotspots' are presently unstudied and located outside protected areas. These models, therefore, provide new information on possible dispersal pathways that link nesting beaches with FGs. These pathways may be of exceptional conservation concern owing to their importance for sea turtles during a critical developmental period. PMID:23945687

  19. Assimilation of temperature into an isopycnal ocean general circulation model using a parallel ensemble Kalman filter

    NASA Astrophysics Data System (ADS)

    Keppenne, Christian L.; Rienecker, Michele M.

    2003-04-01

    Temperature data from the Tropical Atmosphere and Ocean (TAO) array are assimilated into the Pacific basin configuration of the Poseidon quasi-isopycnal ocean general circulation model (OGCM) using a multivariate ensemble Kalman filter (EnKF) implemented on a massively parallel computer architecture. An assimilation algorithm whereby each processing element (PE) solves a localized analysis problem is used. The algorithm relies on a locally supported error-covariance model to avoid the introduction of spurious long-range covariances associated with small ensemble sizes and to facilitate its efficient parallel implementation on a computing platform with distributed memory. Each time data are assimilated, multivariate background-error statistics estimated from the phase-space distribution of an ensemble of model states are used to calculate the Kalman gain matrix and the analysis increments. The resulting cross-field covariances are used to compute temperature, salinity and current increments. The layer thicknesses are left unchanged by the analysis. Instead, they are dynamically adjusted by the model between successive analyses. Independent acoustic Doppler current profiler data are used to assess the performance of the temperature data assimilation. The temperature analyses are also compared to analyses obtained with a univariate optimal interpolation (UOI) algorithm and to a control run without temperature assimilation. The results demonstrate that the multivariate EnKF is both practical and effective for assimilating in situ and remotely sensed observations into a high resolution ocean model in a quasi-operational framework.

  20. Numerical study of sea ice and ocean circulation in the Arctic

    SciTech Connect

    Semtner, A.J. Jr.

    1987-08-01

    A sea-ice model based on bulk-viscous plastic dynamics and 3-layer thermodynamics is coupled to a multilevel primitive equation model of the Arctic Ocean and Greenland Sea. The combined model is forced by inflow through the Faeroe--Shetland Channel and Bering Strait and by observed monthly atmospheric forcing and river runoff. A long-term integration produces a realistic seasonal cycle of ice cover, whose extent is strongly influenced by ocean heat transport. The wintertime maximum is controlled by northward heat transport of 0.4 petawatts in the Greenland Sea and by southward transport of ice and water through the Fram Strait. The summertime minimum extent of sea ice is influenced by subsurface flow through the Fram Strait of warm Atlantic water, which rises in winter and thins the ice lying over the Eurasian continental shelf and along the Alaskan and Siberian coasts. The oceanic circulation in the Canadian Basin is anticyclonic at all depths, but changes to cyclonic in the Eurasian Basin below 200 meters. Offshore ice transport in the Barents Sea promotes oceanic convection on the continental shelf through enhanced brine rejection, whereas surface heat loss in the ice-free Greenland Sea produces intermediate water sources similar in T--S characteristics to observed water masses of the region. Two short additional integrations of the coupled model show that the Arctic sea ice is vulnerable to the environmental effects of atmospheric CO/sub 2/ increase, but relatively insensitive to the maximum proposed amount of Soviet river diversions.

  1. Interaction between surface wind and ocean circulation in the Carolina Capes in a coupled low-order model

    SciTech Connect

    Xie, L.; Pietrafesa, L.J.; Raman, S.

    1997-03-18

    Interactions between surface winds and ocean currents over an east-coast continental shelf are studied using a simple mathematical model. The model physics include cross-shelf advection of sea surface temperature (SST) by Ekman drift, upwelling due to Ekman transport divergence, differential heating of the low-level atmosphere by a cross-shelf SST gradient, and the Coriolis effect. Additionally, the effects of diabatic cooling of surface waters due to air-sea heat exchange and of the vertical density stratification on the thickness of the upper ocean Ekman layer are considered. The model results are qualitatively consistent with observed wind-driven coastal ocean circulation and surface wind signatures induced by SST. This simple model also demonstrates that two-way air-sea interaction plays a significant role in the subtidal frequency variability of coastal ocean circulation and mesoscale variability of surface wind fields over coastal waters.

  2. Changes in atmospheric circulation and ocean ice cover over the North Atlantic during the last 41,000 years

    SciTech Connect

    Mayewski, P.A.; Meeker, L.D.; Whitlow, S.; Twickler, M.S.; Morrison, M.C. ); Bloomfield, P. ); Alley, R.B. ); Gow, A.J.; Meese, D.A. ); Grootes, P.M. )

    1994-03-25

    High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PC)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansion of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.

  3. The Effects of Eddy-Induced Ekman Pumping on Mesoscale and Large-Scale Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Chelton, D. B., Jr.; Matano, R. P.; Combes, V.; Schlax, M.

    2014-12-01

    The simultaneous availability of scatterometer measurements of surface winds, microwave measurements of sea surface temperature (SST) and altimeter measurements of sea surface height (SSH) allows a quantitative assessment of the two mechanisms for self-induced Ekman pumping by oceanic mesoscale eddies. Analysis of these combined satellite datasets reveals that the effects of eddy-induced surface currents on the surface stress usually dominate the effects of air-sea interaction from the influence of eddy-induced SST anomalies on the surface wind field (see figure). The former arises from the surface current effect on the relative wind that determines the surface stress. The latter arises from the effects of SST on vertical mixing in the atmospheric boundary layer. Although this SST influence is generally weaker than the surface current effect, it is not negligible. While the effects of mesoscale eddies on Ekman pumping are clearly documented from the satellite data, it is not yet known how the feedback of this Ekman pumping on the ocean affect the kinematic properties and evolution of oceanic mesoscale eddies. This is being investigated from empirically coupled numerical model simulations in which the SST and surface current effects on eddy-induced Ekman pumping are imposed individually and together, and the resulting ocean circulation is compared with a Control run in which the eddy-induced Ekman pumping is turned off. Preliminary results have found that both SST and surface currents attenuate the mesoscale eddy field. Consistent with the analysis of QuikSCAT and other satellite data, surface current effects attenuate the eddy field more than SST effects. The SST effects are not negligible, however. They alter the eddy fields in the numerical simulations in more subtle but significant ways. The effects of eddy-induced Ekman pumping on the large-scale circulation will also be investigated from the various numerical simulations. Figure Caption: Maps of Ekman pumping

  4. The Effect of Changes in the Hadley Circulation on Oceanic Oxygen Minimum Zones

    NASA Astrophysics Data System (ADS)

    De La Cruz Tello, G.; Ummenhofer, C.; Karnauskas, K. B.

    2014-12-01

    Recent research argued that the Hadley circulation (HC) is composed of three regional cells located at the eastern edges of the ocean basins, rather than a single, globe-encircling cell as the classic textbook view suggests. The HC is expected to expand in concert with global warming, which means that the dry regions beneath the descending branches of the HC are projected to become even drier. Changes in the HC are thus likely to impact freshwater resources on land, as well as the underlying ocean in the subtropics. The eastern edges of ocean basins are characterized by oxygen minimum zones (OMZs), which are regions of very low oxygen concentrations. They affect marine life, as many animals cannot handle the stress caused by such conditions. OMZs have expanded and shoaled in the last 50 years, and they are expected to continue to do so as global climate changes. The purpose of this research is to find links between the projected changes in OMZs and the HC. The National Center for Atmospheric Research (NCAR) Community Earth System Model 1.0 (CESM), Representative Concentration Pathways 8.5 (RCP8.5) experiment with a resolution of 0.9 by 1.25 degrees, which formed part of the Coupled Model Intercomparison Project phase 5 (CMIP5), was used for this analysis. Meridional winds and oceanic oxygen concentrations were the primarily analyzed variables. Latitudinal ocean oxygen slices demonstrate the OMZs' location along the eastern edges of ocean basins. Meridional winds overlayed with oxygen concentration are consistent with the idea that surface meridional 'Hadleywise flow' (i.e., towards the equator at the surface and towards the poles aloft) and OMZs are linked through changes in upwelling. Area-averaged time series spanning the historical period through to the end of the 21st century with RCP8.5 confirm that future changes in OMZs and the HC may be connected. Further research could lead to improved understanding of the factors that drive changes in both, which could

  5. Sensitivity of an oceanic general circulation model forced by satellite wind stress fields

    NASA Astrophysics Data System (ADS)

    Grima, Nicolas; Bentamy, Abderrahim; Katsaros, Kristina; Quilfen, Yves; Delecluse, Pascale; Levy, Claire

    1999-04-01

    Satellite wind and wind stress fields at the sea surface, derived from the scatterometers on European Remote Sensing satellites 1 and 2 (ERS-1 and ERS-2) are used to drive the ocean general circulation model (OGCM) "OPA" in the tropical oceans. The results of the impact of ERS winds are discussed in terms of the resulting thermocline, current structures, and sea level anomalies. Their adequacy is evaluated on the one hand by comparison with simulations forced by the Arpege-Climat model and on the other hand by comparison with measurements of the Tropical Atmosphere-Ocean (TAO) buoy network and of the TOPEX/Poseidon altimeter. Regarding annual mean values, the thermal and current responses of the OGCM forced by ERS winds are in good agreement with the TAO buoy observations, especially in the central and eastern Pacific Ocean. In these regions the South Equatorial Current, the Equatorial Undercurrent, and the thermocline features simulated by the OGCM forced by scatterometer wind fields are described. The impact of the ERS-1 winds is particularly significant to the description of the main oceanic variability. Compared to the TAO buoy observations, the high-frequency (a few weeks) and the low-frequency of the thermocline and zonal current variations are described. The correlation coefficients between the time series of the thermocline simulated by ERS winds and that observed by the TAO buoy network are highly significant; their mean value is 0.73, over the whole basin width, while it is 0.58 between Arpege model simulation and buoy observations. At the equator the time series of the zonal current simulated by the ERS winds, at three locations (110°W, 140°W, and 165°E) and at two depths, are compared to the TAO current meter and acoustic Doppler current profiler (ADCP) measurements. The mean value of the significant correlation coefficients computed with the in situ measurements is 0.72 for ERS, while it is 0.51 for the Arpege-Climat model. Thus ERS wind fields

  6. Comparison of TOPEX/Poseidon Sea Level Observations to Simulations by the Los Alamos Ocean General Circulation Mode

    NASA Technical Reports Server (NTRS)

    Fu, L.; Smith, R.

    1995-01-01

    The sea level observations from the TOPEX/Poseidon radar altimeter from October, 1992 to October, 1994 were used to study the circulation of the global oceans and their temporal changes. To provide a framework for interpreting the observations, the Parallel Ocean Program model of the Los Alamos National Laboratory was run for the same period of time for comparison. A report of that data is given.

  7. Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing

    NASA Astrophysics Data System (ADS)

    Morrison, Adele K.; Hogg, Andrew M.; Ward, Marshall L.

    2011-07-01

    The sensitivity of the Southern Ocean overturning to altered surface buoyancy forcing is investigated in a series of eddy-permitting, idealised simulations. The modelled response indicates that heat and freshwater fluxes in the Southern Hemisphere mid-latitudes may play a significant role in setting the strength of the overturning circulation. Enhanced buoyancy fluxes act to increase the meridional overturning up to a limit approaching the wind-driven Ekman transport. The sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile, buoyancy forcing and upwelling region. The numerical simulations provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes, instead of, or in addition to, changes in wind stress.

  8. Variational data assimilation system with nesting model for high resolution ocean circulation

    NASA Astrophysics Data System (ADS)

    Ishikawa, Yoichi; In, Teiji; Nakada, Satoshi; Nishina, Kei; Igarashi, Hiromichi; Hiyoshi, Yoshimasa; Sasaki, Yuji; Wakamatsu, Tsuyoshi; Awaji, Toshiyuki

    2015-10-01

    To obtain the high-resolution analysis fields for ocean circulation, a new incremental approach is developed using a four-dimensional variational data assimilation system with nesting models. The results show that there are substantial biases when using a classical method combined with data assimilation and downscaling, caused by different dynamics resulting from the different resolutions of the models used within the nesting models. However, a remarkable reduction in biases of the low-resolution model relative to the high-resolution model was observed using our new approach in narrow strait regions, such as the Tsushima and Tsugaru straits, where the difference in the dynamics represented by the high- and low-resolution models is substantial. In addition, error reductions are demonstrated in the downstream region of these narrow channels associated with the propagation of information through the model dynamics.

  9. Influence of Sea Ice on the Thermohaline Circulation in the Arctic-North Atlantic Ocean

    NASA Technical Reports Server (NTRS)

    Mauritzen, Cecilie; Haekkinen, Sirpa

    1997-01-01

    A fully prognostic coupled ocean-ice model is used to study the sensitivity of the overturning cell of the Arctic-North-Atlantic system to sea ice forcing. The strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the Arctic to the Greenland Sea and further to the subpolar gyre. The model produces a 2-3 Sv increase of the meridional circulation cell at 25N (at the simulation year 15) corresponding to a decrease of 800 cu km in the sea ice export from the Arctic. Previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic, implying that sea ice induced variability in the overturning cell can reach 5-6 Sv from peak to peak.

  10. Validation of a Three-Dimensional Model of the Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Monier, L.; Brossier, F.; Razafimahery, F.

    2008-10-01

    This paper is devoted to a numerical model of the oceanic circulation. In order to obtain the variability of the currents with respect to time and depth, we have to use 3D Navier-Stokes equations. The horizontal gradient of pressure appears as an unknown term in these equations. It is directly related to the gradient of the sea surface topography and obtained by solving a 2D model governed by shallow water equations. Numerical experiments are carried out in a parallelepiped canal located in the south hemisphere. First experiment proves coherence between the 2D and 3D models. Then, we test the influence of the Coriolis stress on a southward flow. Finally, we compute different vertical profiles of velocity depending on virtual viscosity used in order to model turbulence.

  11. Changes in benthic ecosystems and ocean circulation in the Southeast Atlantic across Eocene Thermal Maximum 2

    NASA Astrophysics Data System (ADS)

    Jennions, S. M.; Thomas, E.; Schmidt, D. N.; Lunt, D.; Ridgwell, A.

    2015-08-01

    Eocene Thermal Maximum 2 (ETM2) occurred ~1.8 Myr after the Paleocene-Eocene Thermal Maximum (PETM) and, like the PETM, was characterized by a negative carbon isotope excursion and warming. We combined benthic foraminiferal and sedimentological records for Southeast Atlantic Sites 1263 (1500 m paleodepth) and 1262 (3600 m paleodepth) to show that benthic foraminiferal diversity and accumulation rates declined more precipitously and severely at the shallower site during peak ETM2. As the sites are in close proximity, differences in surface productivity cannot have caused this differential effect. Instead, we infer that changes in ocean circulation across ETM2 may have produced more pronounced warming at intermediate depths (Site 1263). The effects of warming include increased metabolic rates, a decrease in effective food supply and increased deoxygenation, thus potentially explaining the more severe benthic impacts at Site 1263. In response, bioturbation may have decreased more at Site 1263 than at Site 1262, differentially affecting bulk carbonate records. We use a sediment-enabled Earth system model to test whether a reduction in bioturbation and/or the likely reduced carbonate saturation of more poorly ventilated waters can explain the more extreme excursion in bulk δ13C and sharper transition in wt % CaCO3 at Site 1263. We find that both enhanced acidification and reduced bioturbation during the ETM2 peak are needed to account for the observed features. Our combined ecological and modeling analysis illustrates the potential role of ocean circulation changes in amplifying local environmental changes and driving temporary, but drastic, loss of benthic biodiversity and abundance.

  12. North Atlantic meridional overturning circulation variations from GRACE ocean bottom pressure anomalies

    NASA Astrophysics Data System (ADS)

    Landerer, Felix W.; Wiese, David N.; Bentel, Katrin; Boening, Carmen; Watkins, Michael M.

    2015-10-01

    Concerns about North Atlantic Meridional Overturning Circulation (NAMOC) changes imply the need for a continuous, large-scale observation capability to detect changes on interannual to decadal time scales. Here we present the first measurements of Lower North Atlantic Deep Water (LNADW) transport changes using only time-variable gravity observations from Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 until now. Improved monthly gravity field retrievals allow the detection of North Atlantic interannual bottom pressure anomalies and LNADW transport estimates that are in good agreement with those from the Rapid Climate Change-Meridional Overturning Circulation and Heatflux Array (RAPID/MOCHA). Concurrent with the observed AMOC transport anomalies from late 2009 through early 2010, GRACE measured ocean bottom pressures changes in the 3000-5000 m deep western North Atlantic on the order of 20 mm-H2O (200 Pa), implying a southward volume transport anomaly in that layer of approximately -5.5 sverdrup. Our results highlight the efficacy of space gravimetry for observing AMOC variations to evaluate latitudinal coherency and long-term variability.

  13. Transport of very short-lived halocarbons from the Indian Ocean to the stratosphere through the Asian monsoon circulation

    NASA Astrophysics Data System (ADS)

    Fiehn, Alina; Hepach, Helmke; Atlas, Elliot; Quack, Birgit; Tegtmeier, Susann; Krüger, Kirstin

    2016-04-01

    Halogenated organic compounds are naturally produced in the ocean and emitted to the atmosphere. The halogenated very short-lived substances (VSLS), such as bromoform, have atmospheric lifetimes of less than half a year. When VSLS reach the stratosphere, they enhance ozone depletion and thus impact the climate. During boreal summer, the Asian monsoon circulation transfers air masses from the Asian troposphere to the global stratosphere. Still, the extent to which VSLS from the Indian Ocean contribute to the stratospheric halogen burden and their exact origin is unclear. Here we show that the monsoon circulation transports VSLS from the Indian Ocean to the stratosphere. During the research cruises SO234-2 and SO235 in July-August 2014 onboard RV SONNE, we measured oceanic and atmospheric concentrations of bromoform (tropical lifetime at 10 km = 17 days), dibromomethane (150 days) and methyl iodide (3.5 days) in the subtropical and tropical West Indian Ocean and calculated their emission strengths. We use the Langrangian transport model FLEXPART driven by ERA-Interim meteorological fields to investigate the transport of oceanic emissions in the atmosphere. We analyze the direct contribution of observed bromoform emissions to the stratospheric halogen budget with forward trajectories. Furthermore, we investigate the connection between the Asian monsoon anticyclone and the oceanic source regions using backward trajectories. The West Indian Ocean is a strong source region of VSLS to the atmosphere and the monsoon transport is fast enough for bromoform to reach the stratosphere. However, the main source regions for the entrainment of oceanic air masses through the Asian monsoon anticyclone are the West Pacific and Bay of Bengal as well as the Arabian Sea. Our findings indicate that changes in emission or circulation in this area due to climate change can directly affect the stratospheric halogen burden and thus the ozone layer.

  14. Emulation of a couple atmosphere-ocean general circulation model with a simple climate model

    NASA Astrophysics Data System (ADS)

    Ishizaki, Y.; Emori, S.; Oki, T.; Shiogama, H.; Yokohata, T.; Yoshimori, M.

    2013-12-01

    Simple climate models have been used to investigate uncertainty of future projections under a very wide range of emission scenarios because the use of Atmosphere-ocean general circulation models (AOGCMs) requires very huge computer resources to project future climate changes under many different socio-economic scenarios. We developed a simple climate model, and investigated the ability of the simple climate model to emulate global mean surface air temperature (SAT) changes of an AOGCM (MIROC5) in a representative concentration pathway (RCP8.5). Some previous research indicated that climate sensitivity, ocean vertical diffusion and anthropogenic aerosol forcing (direct and indirect effects of sulfate aerosol, black carbon and organic carbon) are essentially important factors to emulate of global mean SAT changes of AOGCMs. We, therefore, estimate these important factors in the simple climate model using a Metropolis-Hastings Markov chain Monte Carlo (MCMC) approach, and compared the results of the emulation of the simple climate model with those of AIM/impact[policy] simple climate model. Although root mean square error (RMSE) in decadal means of global mean SAT changes during the period of 2001-2100 in the AIM/impact[policy] simple climate model are large (0.6), the RMSE in our new simple climate model are dramatically improved (0.02). Thus, the estimation of these important factors by a MCMC is very useful for emulation of AOGCMs by the use of simple climate models.

  15. On the circulation of the upper waters in the western equatorial Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Toole, J. M.; Zou, E.; Millard, R. C.

    1988-09-01

    Historical hydrographic data and CTD/O 2 observations obtained on two recent cruises are used to investigate the circulation of the upper waters of the western equatorial Pacific Ocean. The study area lies between 20°N and the land boundary of the Papua New Guinea-Solomon Island coasts, 170°E and the Philippine coast. Seasonal mean and annual averaged sections are constructed from the historical data set to address the strength of the major equatorial currents and the water mass budget of the far western region of the study area. We find indication of significant contribution of southern hemisphere waters to the North Equatorial Countercurrent with an inferred Pacific to Indian Ocean throughflow of Mindanao Current waters of order 1 Sv. The recent observations, acquired under the auspices of a cooperative program between the United States and People's Republic of China, were collected in January-February and November-December 1986. The thermohaline structure of the various currents and net transports estimated for the 1986 data sets are examined and compared with the historical mean data. Large differences are seen between the two modern sections obtained along 165°E. These reflect high frequency variability (as demonstrated by comparison with a third section obtained 2 weeks prior to the January-February cruise) and interannual variability (the second of the cruises occurred during the onset of the 1986-1987 El Niño event).

  16. Secular Trends and Climate Drift in Coupled Ocean-Atmosphere General Circulation Models

    SciTech Connect

    Covey, C C; Gleckler, P J; Phillips, T J; Bader, D C

    2004-11-23

    Coupled ocean-atmosphere general circulation models (coupled GCMs) with interactive sea ice are the primary tool for investigating possible future global warming and numerous other issues in climate science. A long-standing problem with such models is that when different components of the physical climate system are linked together, the simulated climate can drift away from observations unless constrained by ad hoc adjustments to interface fluxes. However, eleven modern coupled GCMs--including three that do not employ flux adjustments--behave much better in this respect than the older generation of models. Surface temperature trends in control run simulations (with external climate forcing such as solar brightness and atmospheric carbon dioxide held constant) are small compared with observed trends, which include 20th century climate change due to both anthropogenic and natural factors. Sea ice changes in the models are dominated by interannual variations. Deep ocean temperature and salinity trends are small enough for model control runs to extend over 1000 simulated years or more, but trends in some regions, most notably the Arctic, are inconsistent among the models and may be problematic.

  17. Seasonal mixed-layer dynamics in an eddy-resolving ocean circulation model

    NASA Astrophysics Data System (ADS)

    Schiller, Andreas; Ridgway, Ken R.

    2013-07-01

    Mean and seasonal mixed-layer depths (MLDs) derived from an eddy-resolving ocean general circulation model with a horizontal resolution of (1/10)° are validated with climatological observations. Associated heat budgets on seasonal timescales are analyzed for six boundary current regions with high eddy kinetic energy (Somali Current, Agulhas Current region, Kuroshio, East Australian Current, Gulf Stream, and Brazil-Malvinas/Falkland Confluence). In all of these regions and on seasonal timescales, (a) horizontal advection significantly contributes to the mixed-layer heat budget (MLHB) on eddy scales and locally exceeds ±5°C/month; (b) lateral mixing (calculated as a residual term) is similar in size to surface net heat flux, horizontal advection, and vertical entrainment in defining the mixed-layer temperature; (c) seasonal vertical entrainment has a cooling effect on mixed-layer temperature throughout the year in the regions investigated; and (d) a phase lag between MLD and changes in mixed-layer heat content exists such that local cooling (warming) in the mixed layer precedes maxima (minima) in MLD by 1-3 months. A rather complex picture emerges where the MLHB in ocean boundary currents on larger spatial scales is determined by net surface heat fluxes and entrainment, whereas local, eddy-related advection and stirring modulate the large-scale signals.

  18. Paleocene/Eocene boundary changes in atmospheric and oceanic circulation: A Southern Hemisphere record

    SciTech Connect

    Hovan, S.A.; Rea, D.K. )

    1992-01-01

    Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocene boundary, the most complete mid-latitude sequence from a Southern Hemisphere location in the Indo-Pacific area. The events of this transition occurred during a span of about 1.2 m.y. Oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1.0{per thousand}, a decrease most likely related to warming of deep ocean waters. Turnovers of benthic foraminifera accompany {delta}{sup 18}O changes and culminate in the predominant extinction event at the end of the Paleocene Epoch. Carbon isotope ratios also shift dramatically toward lighter values near the end of the Paleocene, beginning about 0.45 m.y. after oxygen isotope values start to change. The intensity of Southern Hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0.45 m.y. later. A significant reduction of zonal wind strength at the Paleocene/Eocene boundary, until now observed only at Northern Hemisphere locations, appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean.

  19. Serological evidence for the circulation of flaviviruses in seabird populations of the western Indian Ocean.

    PubMed

    Jaeger, A; Lecollinet, S; Beck, C; Bastien, M; Le Corre, M; Dellagi, K; Pascalis, H; Boulinier, T; Lebarbenchon, C

    2016-02-01

    Birds play a central role in the epidemiology of several flaviviruses of concern for public and veterinary health. Seabirds represent the most abundant and widespread avifauna in the western Indian Ocean and may play an important role as host reservoirs and spreaders of arthropod-borne pathogens such as flaviviruses. We report the results of a serological investigation based on blood samples collected from nine seabird species from seven islands in the Indian Ocean. Using a commercial competitive enzyme-linked immunosorbent assay directed against the prototypic West Nile flavivirus, antibodies against flaviviruses were detected in the serum of 47 of the 855 seabirds tested. They were detected in bird samples from three islands and from four bird species. Seroneutralization tests on adults and chicks suggested that great frigatebirds (Fregata minor) from Europa were infected by West Nile virus during their non-breeding period, and that Usutu virus probably circulated within bird colonies on Tromelin and on Juan de Nova. Real-time polymerase chain reactions performed on bird blood samples did not yield positive results precluding the genetic characterization of flavivirus using RNA sequencing. Our findings stress the need to further investigate flavivirus infections in arthropod vectors present in seabird colonies. PMID:26194365

  20. The Development of a Degree 360 Expansion of the Dynamic Ocean Topography of the POCM_4B Global Circulation Model

    NASA Technical Reports Server (NTRS)

    Rapp, Richard H.

    1998-01-01

    This paper documents the development of a degree 360 expansion of the dynamic ocean topography (DOT) of the POCM_4B ocean circulation model. The principles and software used that led to the final model are described. A key principle was the development of interpolated DOT values into land areas to avoid discontinuities at or near the land/ocean interface. The power spectrum of the POCM_4B is also presented with comparisons made between orthonormal (ON) and spherical harmonic magnitudes to degree 24. A merged file of ON and SH computed degree variances is proposed for applications where the DOT power spectrum from low to high (360) degrees is needed.

  1. "What Controls the Structure and Stability of the Ocean Meridional Overturning Circulation: Implications for Abrupt Climate Change?"

    SciTech Connect

    Fedorov, Alexey

    2013-11-23

    The central goal of this research project is to understand the properties of the ocean meridional overturning circulation (MOC) – a topic critical for understanding climate variability and stability on a variety of timescales (from decadal to centennial and longer). Specifically, we have explored various factors that control the MOC stability and decadal variability in the Atlantic and the ocean thermal structure in general, including the possibility abrupt climate change. We have also continued efforts on improving the performance of coupled ocean-atmosphere GCMs.

  2. The impact of multidecadal Atlantic meridional overturning circulation variations on the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; Delworth, Thomas L.; Zeng, Fanrong

    2016-05-01

    The impact of multidecadal variations of the Atlantic meridional overturning circulation (AMOC) on the Southern Ocean (SO) is investigated in the current paper using a coupled ocean-atmosphere model. We find that the AMOC can influence the SO via fast atmosphere teleconnections and subsequent ocean adjustments. A stronger than normal AMOC induces an anomalous warm SST over the North Atlantic, which leads to a warming of the Northern Hemisphere troposphere extending into the tropics. This induces an increased equator-to-pole temperature gradient in the Southern Hemisphere (SH) upper troposphere and lower stratosphere due to an amplified tropical upper tropospheric warming as a result of increased latent heat release. This altered gradients leads to a poleward displacement of the SH westerly jet. The wind change over the SO then cools the SST at high latitudes by anomalous northward Ekman transports. The wind change also weakens the Antarctic bottom water (AABW) cell through changes in surface heat flux forcing. The poleward shifted westerly wind decreases the long term mean easterly winds over the Weddell Sea, thereby reducing the turbulent heat flux loss, decreasing surface density and therefore leading to a weakening of the AABW cell. The weakened AABW cell produces a temperature dipole in the SO, with a warm anomaly in the subsurface and a cold anomaly in the surface that corresponds to an increase of Antarctic sea ice. Opposite conditions occur for a weaker than normal AMOC. Our study here suggests that efforts to attribute the recent observed SO variability to various factors should take into consideration not only local process but also remote forcing from the North Atlantic.

  3. Circulation, eddies, oxygen, and nutrient changes in the eastern tropical South Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Czeschel, R.; Stramma, L.; Weller, R. A.; Fischer, T.

    2015-06-01

    A large subsurface oxygen deficiency zone is located in the eastern tropical South Pacific Ocean (ETSP). The large-scale circulation in the eastern equatorial Pacific and off the coast of Peru in November/December 2012 shows the influence of the equatorial current system, the eastern boundary currents, and the northern reaches of the subtropical gyre. In November 2012 the equatorial undercurrent (EUC) is centered at 250 m depth, deeper than in earlier observations. In December 2012, the equatorial water is transported southeastward near the shelf in the Peru-Chile undercurrent (PCUC) with a mean transport of 1.4 Sv. In the oxygen minimum zone (OMZ), the flow is overlaid with strong eddy activity on the poleward side of the OMZ. Floats with parking depth at 400 m show fast westward flow in the mid-depth equatorial channel and sluggish flow in the OMZ. Floats with oxygen sensors clearly show the passage of eddies with oxygen anomalies. The long-term float observations in the upper ocean lead to a net community production estimate at about 18° S of up to 16.7 mmol C m-3 yr-1 extrapolated to an annual rate and 7.7 mmol C m-3 yr-1 for the time period below the mixed layer. Oxygen differences between repeated ship sections are influenced by the Interdecadal Pacific Oscillation (IPO), by the phase of El Niño, by seasonal changes, and by eddies, and hence have to be interpreted with care. At and south of the Equator the decrease in oxygen in the upper ocean since 1976 is related to an increase in nitrate, phosphate, and in part silicate.

  4. Eddy properties in the Mozambique Channel: A comparison between observations and two numerical ocean circulation models

    NASA Astrophysics Data System (ADS)

    Halo, I.; Backeberg, B.; Penven, P.; Ansorge, I.; Reason, C.; Ullgren, J. E.

    2014-02-01

    Analysis of satellite altimetry observations, transports estimates from a mooring array, as well as output from two different numerical ocean circulation models (ROMS and HYCOM), have been used to investigate the mesoscale eddy properties and transport variability in the Mozambique Channel. The power spectral density of model transports at 17°S indicates the models ability to represent the transport variability at mesoscale frequencies (range between 3 yr-1 and 10 yr-1). The models have shown an exaggerated representation of the lower frequencies (~ <3 yr-1), while underestimating the higher frequency signals (~ >10 yr-1). The overestimation of the seasonal cycle appears in our case not to be related to a misrepresentation of the mesoscale variability. The eddies were identified using an automatic eddy tracking scheme. Both anticyclonic and cyclonic eddies appeared to have a preferred site of formation within the channel. The density distribution showed that the anticyclones exhibited a bi-modal distribution: the first mode was associated with the typical scale for the oceanic mesoscale turbulence, while the second mode was related to the passage of large rings at a frequency of about 4-7 per year. On the other hand, cyclonic eddies had a single mode distribution that follows the first baroclinic Rossby radius of deformation, which is a typical scale for the oceanic mesoscale surface eddy variability, suggesting that their formation is associated with baroclinic instability. Eddy mean amplitudes per class of radius (<100 km), increase linearly with increasing radius, while no linear relationship exists for the rings. Different from the rings, the increase in the amplitude of the eddies was consistent with the increase of their life expectancy and travelling distances.

  5. High resolution modeling of the monsoon circulation in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Diansky, N. A.; Zalesny, V. B.; Moshonkin, S. N.; Rusakov, A. S.

    2006-10-01

    The goal of this paper is to present some results on the monsoon circulation in the Indian Ocean simulated with a σ-coordinate ocean model developed at the Institute of Numerical Mathematics, RAS. The model has a horizontal resolution of (1/8)° × (1/12)° and contains 21 σ-layers of uneven thickness. Realistic bottom topography and land geometry are used. The numerical experiments were carried out for 15 years starting from the Levitus climatology for January and monthly mean climatic atmospheric forcing from the NCEP reanalysis data. The annual cycle of the surface and subsurface currents and temperature and salinity fields were analyzed. The model reproduces well the Summer Monsoon and the Winter Monsoon currents and their time evolution and spatial structures. The Somali Current is adequately modeled. During the Summer Monsoon, the velocities of the current exceed 2 m/s, while the total mass transport is approximately 70 Sv. The model results show that a reversal of the Somali Current from the northern direction in the summer to the southern direction in the winter is accompanied by the generation of anticyclonic eddies, which drift westward owing to the β-effect and dissipate either near the Somali shore or in the Gulf of Aden. The monsoon variability of the equatorial surface current and equatorial subsurface countercurrent system are analyzed. It is shown that these currents are generated predominantly by the zonal component of wind stress, in which the half-year harmonic dominates. This leads to the fact that the equatorial surface current also changes its direction with a half-year periodicity almost in phase with the wind. The oppositely directed subsurface compensational countercurrent changes its direction with a time lag of approximately one month. Gradient currents, which appear in the Bay of Bengal due to the riverine runoff, make an important contribution to the circulation. This effect manifests itself especially strongly in the summer during

  6. 3D movies for teaching seafloor bathymetry, plate tectonics, and ocean circulation in large undergraduate classes

    NASA Astrophysics Data System (ADS)

    Peterson, C. D.; Lisiecki, L. E.; Gebbie, G.; Hamann, B.; Kellogg, L. H.; Kreylos, O.; Kronenberger, M.; Spero, H. J.; Streletz, G. J.; Weber, C.

    2015-12-01

    Geologic problems and datasets are often 3D or 4D in nature, yet projected onto a 2D surface such as a piece of paper or a projection screen. Reducing the dimensionality of data forces the reader to "fill in" that collapsed dimension in their minds, creating a cognitive challenge for the reader, especially new learners. Scientists and students can visualize and manipulate 3D datasets using the virtual reality software developed for the immersive, real-time interactive 3D environment at the KeckCAVES at UC Davis. The 3DVisualizer software (Billen et al., 2008) can also operate on a desktop machine to produce interactive 3D maps of earthquake epicenter locations and 3D bathymetric maps of the seafloor. With 3D projections of seafloor bathymetry and ocean circulation proxy datasets in a virtual reality environment, we can create visualizations of carbon isotope (δ13C) records for academic research and to aid in demonstrating thermohaline circulation in the classroom. Additionally, 3D visualization of seafloor bathymetry allows students to see features of seafloor most people cannot observe first-hand. To enhance lessons on mid-ocean ridges and ocean basin genesis, we have created movies of seafloor bathymetry for a large-enrollment undergraduate-level class, Introduction to Oceanography. In the past four quarters, students have enjoyed watching 3D movies, and in the fall quarter (2015), we will assess how well 3D movies enhance learning. The class will be split into two groups, one who learns about the Mid-Atlantic Ridge from diagrams and lecture, and the other who learns with a supplemental 3D visualization. Both groups will be asked "what does the seafloor look like?" before and after the Mid-Atlantic Ridge lesson. Then the whole class will watch the 3D movie and respond to an additional question, "did the 3D visualization enhance your understanding of the Mid-Atlantic Ridge?" with the opportunity to further elaborate on the effectiveness of the visualization.

  7. Toward Improved Estimation of the Dynamic Topography and Ocean Circulation in the High Latitude and Arctic Ocean: The Importance of GOCE

    NASA Astrophysics Data System (ADS)

    Johannessen, J. A.; Raj, R. P.; Nilsen, J. E. Ø.; Pripp, T.; Knudsen, P.; Counillon, F.; Stammer, D.; Bertino, L.; Andersen, O. B.; Serra, N.; Koldunov, N.

    2014-05-01

    The Arctic plays a fundamental role in the climate system and shows significant sensitivity to anthropogenic climate forcing and the ongoing climate change. Accelerated changes in the Arctic are already observed, including elevated air and ocean temperatures, declines of the summer sea ice extent and sea ice thickness influencing the albedo and CO2 exchange, melting of the Greenland Ice Sheet and increased thawing of surrounding permafrost regions. In turn, the hydrological cycle in the high latitude and Arctic is expected to undergo changes although to date it is challenging to accurately quantify this. Moreover, changes in the temperature and salinity of surface waters in the Arctic Ocean and Nordic Seas may also influence the flow of dense water through the Denmark Strait, which are found to be a precursor for changes in the Atlantic meridional overturning circulation with a lead time of around 10 years (Hawkins and Sutton in Geophys Res Lett 35:L11603, 2008). Evidently changes in the Arctic and surrounding seas have far reaching influences on regional and global environment and climate variability, thus emphasizing the need for advanced quantitative understanding of the ocean circulation and transport variability in the high latitude and Arctic Ocean. In this respect, this study combines in situ hydrographical data, surface drifter data and direct current meter measurements, with coupled sea ice-ocean models, radar altimeter data and the latest GOCE-based geoid in order to estimate and assess the quality, usefulness and validity of the new GOCE-derived mean dynamic topography for studies of the ocean circulation and transport estimates in the Nordic Seas and Arctic Ocean.

  8. Indications for a North Atlantic ocean circulation regime shift at the onset of the Little Ice Age

    NASA Astrophysics Data System (ADS)

    Schleussner, C.-F.; Divine, D. V.; Donges, J. F.; Miettinen, A.; Donner, R. V.

    2015-12-01

    A prominent characteristic of the reconstructed Northern Hemisphere temperature signal over the last millennium is the transition from the Medieval Climate Anomaly to the Little Ice Age (LIA). Here we report indications for a non-linear regime shift in the North Atlantic ocean circulation at the onset of the LIA. Specifically, we apply a novel statistical test based on horizontal visibility graphs to two ocean sediment August sea-surface temperature records from the Norwegian Sea and the central subpolar basin and find robust indications of time-irreversibility in both records during the LIA onset. Despite a basin-wide cooling trend, we report an anomalous warming in the central subpolar basin during the LIA that is reproduced in ensemble simulations with the climate model of intermediate complexity CLIMBER-3α as a result of a non-linear regime shift in the subpolar North Atlantic ocean circulation. The identified volcanically triggered non-linear transition in the model simulations provides a plausible explanation for the signatures of time-irreversibility found in the ocean sediment records. Our findings indicate a potential multi-stability of the North Atlantic ocean circulation and its importance for regional climate change on centennial time scales.

  9. Eocene to Miocene Southern Ocean Deep Water Circulation Revealed From Fossil Fish Teeth Nd Isotopes

    NASA Astrophysics Data System (ADS)

    Scher, H.; Martin, E. E.

    2001-12-01

    We have evaluated Nd and Sr isotopic compositions of cleaned fossil fish teeth for the late Eocene to early Miocene from ODP site 1090 (43° S, 9° E, 3599 m) in the Atlantic sector of the Southern Ocean. Using an age model based on biostratigraphy and paleomagnetics, Sr isotopic values from the fossil fish teeth tend to plot slightly below the seawater curve. This offset may be due to early diagenetic reactions, but overall the seawater trace metal chemistry appears to be well preserved in these samples. At site 1090, \\epsilonNd values increase from ~-7.5 at 39 Ma to ~-6 at 35 Ma and stay at this value until ~28.5 Ma. A high resolution Nd isotope record demonstrates steadily decreasing \\epsilonNd values from -6 to -8 between 28.5 and 23 Ma. Sampling during this interval reveals two rapid oscillations (<.5 Myr) in \\epsilonNd values superimposed on this decreasing trend; a one \\epsilonNd unit decrease at ~26 Ma and a one \\epsilonNd unit increase at ~23 Ma. Bottom water Nd composition is controlled by deep-water circulation, dissolved and particulate riverine inputs, and eolian inputs. In the late Eocene, bottom waters at site 1090 became increasingly radiogenic as benthic \\delta18O values began to reflect cooler deep-sea temperatures and the growth of ice sheets on Antarctica. It has been speculated that deep water in the Southern Ocean during the Eocene may have had a Tethyan origin. The shift toward radiogenic values at Site 1090 may reflect decreasing flow of nonradiogenic seawater from this low latitude deepwater source (modern Mediterranean \\epsilonNd ~-9). It may also be a result of the emergence of ice sheets on Antarctica, which reduced chemical weathering of nonradiogenic material into Southern Ocean. Although we anticipated that the opening of Drake Passage would introduce radiogenic Pacific waters into the Southern Atlantic, decreasing \\epsilonNd values coincide with age estimates for the opening based on geophysical data. Ocean circulation models

  10. Carbon and Neodymium Isotopic Fingerprints of Atlantic Deep Ocean Circulation During the Warm Pliocene

    NASA Astrophysics Data System (ADS)

    Riesselman, C. R.; Scher, H.; Robinson, M. M.; Dowsett, H. J.; Bell, D. B.

    2012-12-01

    Earth's future climate may resemble the mid-Piacenzian Age of the Pliocene, a time when global temperatures were sustained within the range predicted for the coming century. Surface and deep water temperature reconstructions and coupled ocean-atmosphere general circulation model simulations by the USGS PRISM (Pliocene Research Interpretation and Synoptic Mapping) Group identify a dramatic North Atlantic warm surface temperature anomaly in the mid-Piacenzian (3.264 - 3.025 Ma), accompanied by increased evaporation. The anomaly is detected in deep waters at 46°S, suggesting enhanced meridional overturning circulation and more southerly penetration of North Atlantic Deep Water (NADW) during the PRISM interval. However deep water temperature proxies are not diagnostic of water mass and some coupled model simulations predict transient decreases in NADW production in the 21st century, presenting a contrasting picture of future climate. We present a new multi-proxy investigation of Atlantic deep ocean circulation during the warm mid-Piacenzian, using δ13C of benthic foraminifera as a proxy for water mass age and the neodymium isotopic composition of fossil fish teeth (ɛNd) as a proxy for water mass source and mixing. This reconstruction utilizes both new and previously published data from DSDP and ODP cores along equatorial (Ceara Rise), southern mid-latitude (Walvis Ridge), and south Atlantic (Meteor Rise/Agulhas Ridge) depth transects. Additional end-member sites in the regions of modern north Atlantic and Southern Ocean deep water formation provide a Pliocene baseline for comparison. δ13C throughout the Atlantic basin is remarkably homogenous during the PRISM interval. δ13C values of Cibicidoides spp. and C. wuellerstorfi largely range between 0‰ and 1‰ at North Atlantic, shallow equatorial, southern mid-latitude, and south Atlantic sites with water depths from 2000-4700 m; both depth and latitudinal gradients are generally small (~0.3‰). However, equatorial

  11. The significance of the centripetal acceleration due to the earth's rotation on the generation of oceanic circulation

    SciTech Connect

    Wichner, R.P.

    1991-11-01

    This report proposes that the tangential component of the centrifugal body force due to the earth's rotation plays a significant role as a motive force for the major oceanic circulations. A comparison of its magnitude relative to the Coriolis force and wind shear, on which current circulation models are based, indicates its potential effect is significant if an appropriate mechanism can be constructed that generates a circulation force. Such a mechanism is proposed, based on the coupled effect of water-density variations with the tangential component of the centrifugal force. An order-of-magnitude model, which equates the generated circulation force with a rough estimate of the flow resistance, indicates a favorable comparison between predicted and observed current velocity. 13 refs., 4 figs.

  12. Modeling tidal circulation and stratification in Skagit River estuary using an unstructured grid ocean model

    NASA Astrophysics Data System (ADS)

    Yang, Zhaoqing; Khangaonkar, Tarang

    Tidal circulation and river plume dynamics in shallow-water estuarine systems with large intertidal zones are complex. Strong asymmetries in tidal currents and stratification often occur in the intertidal zones and subtidal channels over a tidal cycle. The Skagit River is the largest estuary with respect to the discharge of a significant amount of freshwater and sediment into Puget Sound, Washington. It consists of a large intertidal zone with multiple tidal channels near the mouth of the estuary. To simulate the tidal circulation and salinity stratification accurately in the intertidal region, an unstructured grid numerical model with wetting-drying capability and the capability to accurately represent the bathymetry of tidal flats and the geometry of shallow distributary channels is necessary. In this paper, a modeling study for the Skagit River estuary using a three-dimensional unstructured grid, finite-volume coastal ocean model (FVCOM) supported by high-resolution LIDAR data is presented. The hydrodynamic model was validated with observed water surface elevation, velocity, and salinity data over spring and neap tidal cycles under low-river-flow and high-river-flow conditions. Wetting and drying processes in the intertidal zone and strong stratification in the estuary were simulated successfully by the model. Model results indicate that the Skagit River estuary is a highly stratified estuary, but destratification can occur during flood tide. Tides and baroclinic motion are the dominant forcing in the Skagit River estuary, but strong wind events can affect the currents in the intertidal zone significantly. Preliminary analysis also indicated that the salinity intrusion length scale is proportional to the river flow to the -¼ power.

  13. The Closure History of the Central American Seaway and its Relationship to Ocean Circulation and Climate

    NASA Astrophysics Data System (ADS)

    Waite, A. J.; Martin, E. E.; Lawrence, K. T.; Ladlow, C. G.; Newkirk, D.

    2014-12-01

    Paleoceanographic and ecologic studies suggest that gradual shoaling of the Central American Seaway (CAS) as the Isthmus of Panama rose between ~13 to 2 Ma caused a stepwise shutdown of deep, intermediate, and shallow Pacific water flow through the seaway into the Caribbean. This diminishing communication is thought to have significantly influenced surface currents, ocean circulation at depth, and ultimately regional and global climate. However, new studies of Panama's volcanic/tectonic history suggest the isthmus rose much earlier than previous estimates, calling into question many of our accepted implications for this gateway event under the 'Panama Hypothesis,' including strengthened thermohaline circulation, North Atlantic Deep Water production, increased North Atlantic temperature, and ties to Northern Hemisphere glaciation. Despite considerable research, few paleoceanographic studies have directly examined the possibility of earlier events in the closure history of the CAS and thus the precise linkages and timing are not well defined. To investigate early restricted CAS flow related to sill formation or pulsed exhumation events, we examine two sets of independent paleoceanographic reconstructions from Ocean Drilling Program sediment cores from the region. We assess the presence of Pacific waters within the Caribbean over the last 30 Ma via the Nd-isotopic composition of fish teeth from several Caribbean sites; these records point to sustained transport of Pacific waters into the Caribbean from at least 30 to 10 Ma. Further, alkenone-derived sea surface temperature (SST) reconstructions from the Eastern Equatorial Pacific (EEP) indicate the presence of consistently warm (>27 °C) waters in the EEP from ~12 to ~5 Ma, after which time SSTs at sites within the modern cold tongue begin to cool appreciably. The SST data imply that the EEP cold tongue, which some studies suggest is linked in part to the rise of the Panamanian isthmus, did not develop until after 5

  14. Ocean circulation and biogeochemistry moderate interannual and decadal surface water pH changes in the Sargasso Sea

    USGS Publications Warehouse

    Nathalie F. Goodkin; Bo-Shian Wang; Chen-Feng You; Konrad Hughen; Prouty, Nancy G.; Nicholas Bates; Scott Doney

    2015-01-01

    The oceans absorb anthropogenic CO2 from the atmosphere, lowering surface ocean pH, a concern for calcifying marine organisms. The impact of ocean acidification is challenging to predict as each species appears to respond differently and because our knowledge of natural changes to ocean pH is limited in both time and space. Here we reconstruct 222 years of biennial seawater pH variability in the Sargasso Sea from a brain coral, Diploria labyrinthiformis. Using hydrographic data from the Bermuda Atlantic Time-series Study and the coral-derived pH record, we are able to differentiate pH changes due to surface temperature versus those from ocean circulation and biogeochemical changes. We find that ocean pH does not simply reflect atmospheric CO2 trends but rather that circulation/biogeochemical changes account for >90% of pH variability in the Sargasso Sea and more variability in the last century than would be predicted from anthropogenic uptake of CO2 alone.

  15. Ocean circulation and biogeochemistry moderate interannual and decadal surface water pH changes in the Sargasso Sea

    NASA Astrophysics Data System (ADS)

    Goodkin, Nathalie F.; Wang, Bo-Shian; You, Chen-Feng; Hughen, Konrad A.; Grumet-Prouty, Nancy; Bates, Nicholas R.; Doney, Scott C.

    2015-06-01

    The oceans absorb anthropogenic CO2 from the atmosphere, lowering surface ocean pH, a concern for calcifying marine organisms. The impact of ocean acidification is challenging to predict as each species appears to respond differently and because our knowledge of natural changes to ocean pH is limited in both time and space. Here we reconstruct 222 years of biennial seawater pH variability in the Sargasso Sea from a brain coral, Diploria labyrinthiformis. Using hydrographic data from the Bermuda Atlantic Time-series Study and the coral-derived pH record, we are able to differentiate pH changes due to surface temperature versus those from ocean circulation and biogeochemical changes. We find that ocean pH does not simply reflect atmospheric CO2 trends but rather that circulation/biogeochemical changes account for >90% of pH variability in the Sargasso Sea and more variability in the last century than would be predicted from anthropogenic uptake of CO2 alone.

  16. Lessons from Multi-Millenium Runs of Coupled Atmospheric-Ocean General Circulation Models

    NASA Astrophysics Data System (ADS)

    Liang, M.; Lin, L.; Tung, K.; Yung, Y. L.; Sun, S.

    2012-12-01

    Coupled atmosphere-ocean general circulation models (AOGCM) are used for climate prediction on the degree of warming due to increases in greenhouse gases, and for policy recommendations on emission curbs. We first demonstrate that the currently adopted protocol for obtaining such a prediction does not yield a robust solution and therefore cannot be relied upon for policy recommendations. The range of uncertainty in such predictions may have been underreported when models participating in Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) were run with their oceans at various stages of flux adjustment with their atmosphere, and could change significantly simply by running them longer. This is shown by comparing multi-millennium long runs of the Goddard Institute for Space Studies coupled model (GISS-EH) and the Community Climate System Model (CCSM4) with what were reported to AR4. For common predictions from preindustrial condition to 2030-2100, the previously predicted warming and spatial patterns vary even in ensemble average. The commonly adopted remedy of subtracting the "climate drift" is ineffective and often leads to a wrong solution. The long model runs here also reveal the range of variability (~30%) in the Transient Climate Response (TCR) within the same model with the same Equilibrium Climate Sensitivity (ECS). Fortunately, for simulations with multi-decadal to century long time horizon, robust solutions can be obtained off thousand-year-long control runs that reach "quasi-equilibrium" using a new protocol. The problem of different quasi-equilibrium states in long runs and the memory of the solution on these states are also addressed.

  17. An Empirical Model of Global Climate: Reduced Impact of Volcanoes upon Consideration of Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Canty, T. P.; Mascioli, N. R.; Smarte, M.; Salawitch, R. J.

    2012-12-01

    Observed reductions in Earth's surface temperature following explosive volcanic eruptions are often used as a proxy for geo-engineering of climate by enhancement of stratospheric sulfate. We use a multiple linear regression model applied to the global surface temperature record to suggest that exchange of heat between the atmosphere and ocean, driven by variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC), has been an important factor in the decline of temperature following the four major volcanic eruptions since 1900. The veracity of this suggestion depends on whether the Atlantic Multidecadal Oscillation (AMO) truly represents a proxy for the strength of the AMOC and quantification of volcanic cooling depends on how the AMO is detrended. If the AMO is detrended using anthropogenic radiative forcing of climate, surface cooling attributed to Mount Pinatubo, using the Hadley surface temperature record, maximizes at 0.15°C globally and 0.35°C over land. These values are about a factor of 2 lower than found when the AMO is neglected. We show that the satellite record of atmospheric temperature is also consistent with our suggestion that volcanic cooling may have been over estimated by about a factor of 2. The AMO had begun to decrease prior to the four major eruptions, suggesting that exchange of heat between the atmosphere and ocean due to variations in the strength of the AMOC drives the climate system, rather than responds to volcanic perturbations. We will discuss implications of our study for the Geoengineering Model Intercomparison Project (GeoMIP).

  18. Heat-flow and hydrothermal circulation at the ocean-continent transition of the eastern gulf of Aden

    NASA Astrophysics Data System (ADS)

    Lucazeau, Francis; Leroy, Sylvie; Rolandone, Frédérique; d'Acremont, Elia; Watremez, Louise; Bonneville, Alain; Goutorbe, Bruno; Düsünur, Doga

    2010-07-01

    In order to investigate the importance of fluid circulation associated with the formation of ocean-continent transitions (OCT), we examine 162 new heat-flow (HF) measurements in the eastern Gulf of Aden, obtained at close locations along eight seismic profiles and with multi-beam bathymetry. The average HF values in the OCT and in the oceanic domain (~ 18 m.y.) are very close to the predictions of cooling models, showing that the overall importance of fluids remains small at the present time compared to oceanic ridge flanks of the same age. However, local HF anomalies are observed, although not systematically, in the vicinity of the unsedimented basement and are interpreted by the thermal effect of meteoric fluids flowing laterally. We propose a possible interpretation of hydrothermal paths based on the shape of HF anomalies and on the surface morphology: fluids can circulate either along-dip or along-strike, but are apparently focussed in narrow "pipes". In several locations in the OCT, there is no detectable HF anomaly while the seismic velocity structure suggests serpentinization and therefore past circulation. We relate the existence of the present day fluid circulation in the eastern Gulf of Aden to the presence of unsedimented basement and to the local extensional stress in the vicinity of the Socotra-Hadbeen fault zone. At the scale of rifted-margins, fluid circulation is probably not as important as in the oceanic domain because it can be inhibited rapidly with high sedimentation rates, serpentinization and stress release after the break-up.

  19. Examination of Physical Processes Influencing Coastal Circulation over the Inner Scotian Shelf using a Five-Level Nested-Grid Ocean Circulation Model

    NASA Astrophysics Data System (ADS)

    Sheng, J.

    2008-12-01

    A multiply nested-grid ocean circulation modeling system was developed for coastal waters of the Inner Scotian Shelf (ISS) by coupling a limited-area coastal circulation model to an operational shelf circulation model known as Dalcoast. The nested-grid system has five relocatable, dynamically-downscaling five sub- components. The outermost sub-component of the system has a coarse horizontal resolution of (1/12)o for simulating storm surges and two-dimensional barotropic shelf waves over the eastern Canadian shelf (ECS) from Labrador Shelf to the Gulf of Maine, and the innermost sub-component has a fine horizontal resolution of about ~180 m for simulating three-dimensional circulation and hydrographic distributions over Lunenburg Bay of Nova Scotia in the default setup. The nested-grid system is driven by meteorological and astronomical forcing. The meteorological forcing includes sea level air pressures, wind stress and surface heat/freshwater fluxes converted from the 3 hourly weather forecasts produced by the Meteorological Service of Canada. The astronomical forcing is the tidal sea levels and depth-mean currents produced by WebTide based on pre-calculated harmonic constants of five major tidal constitutes over the ECS. In this study, the nested-grid system is used to investigate main physical processes affecting the three-dimensional (3D) circulation and hydrographic distributions over the ISS in June and July 2006. Model results demonstrate that the coastal circulation and hydrographic distributions over the study region are affected significantly by tides, local wind forcing, remotely generated coastal waves during the study period.

  20. Deep Ocean Circulation at the Bermuda Rise during the Last 150ka: A New Centennial-Resolution Nd Isotope Record

    NASA Astrophysics Data System (ADS)

    Roberts, N. L.; Piotrowski, A. M.; Curry, W. B.; Keigwin, L. D.

    2014-12-01

    Today the Deep Western Boundary Current in the NW Atlantic basin transports an average of 28.7 Sv (Toole et al., 2011), making it a crucial part of the Atlantic Meridional Overturning Circulation, and linking ocean heat transport and carbon storage with northern hemisphere climate. Greenland ice cores have provided high resolution archives for northern hemisphere climate change over the past glacial cycle. However, accurate comparison between changes in climate and ocean dynamics is hampered by generally low marine sedimentation rates relative to ice accumulation. Here we present an ultra-high resolution Nd isotope record, with an average of 164 years between samples, reconstructing past changes in ocean circulation from MIS 6 to the present. The Nd isotope measurements were made on uncleaned planktonic foraminifera, recording bottom water composition changes (Roberts et al., 2010; Roberts et al., 2012), on a high sedimentation rate core (average 24 cm/kyr) taken from the Bermuda Rise (33°N, 57°W, 4500m) to the west of the Deep Western Boundary Current. Such high resolution allows for detailed reconstruction of millennial and centennial-scale deep ocean circulation events and statistical comparison with Greenland and Antarctic ice core records as well as other terrestrial climate records.

  1. Atmospheric Torques on the Solid Earth and Oceans Based on the GEOS-1 General Circulation Model

    NASA Technical Reports Server (NTRS)

    Sanchez, Braulio V.; Au, Andrew Y.

    1998-01-01

    The GEOS-1 general circulation model has been used to compute atmospheric torques on the oceans and solid Earth for the period 1980-1995. The time series for the various torque components have been analyzed by means of Fourier transform techniques. It was determined that the wind stress torque over land is more powerful than the wind stress torque over water by 55%, 42%, and 80% for the x, y, and z components respectively. This is mainly the result of power in the high frequency range. The pressure torques due to polar flattening, equatorial ellipticity, marine geoid, and continental orography were computed. The orographic or "mountain torque" components are more powerful than their wind stress counterparts (land plus ocean) by 231% (x), 191% (y), and 77% (z). The marine pressure torques due to geoidal undulations are much smaller than the orographic ones, as expected. They are only 3% (x), 4% (y), and 5% (z) of the corresponding mountain torques. The geoidal pressure torques are approximately equal in magnitude to those produced by the equatorial ellipticity of the Earth. The pressure torque due to polar flattening makes the largest contributions to the atmospheric torque budget. It has no zonal component, only equatorial ones. Most of the power of the latter, between 68% and 69%, is found in modes with periods under 15 days. The single most powerful mode has a period of 361 days. The gravitational torque ranks second in power only to the polar flattening pressure torque. Unlike the former, it does produce a zonal component, albeit much smaller (1%) than the equatorial ones. The gravitational and pressure torques have opposite signs, therefore, the gravitational torque nullifies 42% of the total pressure torque. Zonally, however, the gravitational torque amounts to only 6% of the total pressure torque. The power budget for the total atmospheric torque yields 7595 and 7120 Hadleys for the equatorial components and 966 Hadleys for the zonal. The x-component exhibits

  2. Atmospheric Torques on the Solid Earth and Oceans Based on the GEOS-1 General Circulation Model

    NASA Technical Reports Server (NTRS)

    Sanchez, Braulio

    1999-01-01

    The GEOS-1 general circulation model has been used to compute atmospheric torques on the oceans and solid Earth for the period 1980-1995. The time series for the various torque components have been analyzed by means of Fourier transform techniques. It was determined that the wind stress torque over land is more powerful than the wind stress torque over water by 55\\%, 42\\%, and 80\\t for the x, y, and z components respectively. This is mainly the result of power in the high frequency range. The pressure torques due to polar flattening, equatorial ellipticity, marine geoid, and continental orography were computed. The orographic or "mountain torque" components are more powerful than their wind stress counterparts (land plus ocean) by 231\\% (x), 191\\% (y), and 77\\% (z). The marine pressure torques due to geoidal undulations are much smaller than the orographic ones, as expected. They are only 3\\% (x), 4\\% (y), and 5\\% (z) of the corresponding mountain torques. The geoidal pressure torques are approximately equal in magnitude to those produced by the equatorial ellipticity of the Earth. The pressure torque due to polar flattening makes the largest contributions to the atmospheric'torque budget. It has no zonal component, only equatorial ones. Most of the power of the latter, between 68\\% and 69 %, is found in modes with periods under 15 days. The single most powerful mode has a period of 361 days. The gravitational torque ranks second in power only to the polar flattening pressure torque. Unlike the former, it does produce a zonal component, albeit much smaller (1\\ ) than the equatorial ones. The gravitational and pressure torques have opposite signs, therefore, the gravitational torque nullifies 42\\% of the total pressure torque. Zonally, however, the gravitational torque amounts to only 6\\% of the total pressure torque. The power budget for the total atmospheric torque yields 7595 and 7120 Hadleys for the equatorial components and 966 Hadleys for the

  3. A semi-implicit ocean circulation model using a generalized topography-following coordinate system

    SciTech Connect

    Song, Yuhe; Haidvogel, D.

    1994-11-01

    We introduce a new ocean circulation model featuring an improved vertical coordinate representation. This new coordinate is a generalized {sigma}coordinate; however, it is capable of simultaneously maintaining high resolution in the surface layer as well as dealing with steep and/or tall topography. The model equations are the tree-dimensional, free surface, primitive equations with orthogonal curvilinear coordinates in the horizontal and the new general coordinate in the vertical. Vertical mixing is treated implicitly by the generalized Crank-Nicolson method based on a Galerkin finite element formulation. Two alternate parameterizations of surface mixing are incorporated, based respectively on the approaches of Price, Weller, and Pinkel and Mellor and Yamada. Finally, a quadrature formula of Lagrange interpolation is employed to produce a more accurate calculation of pressure and vertical velocity. Three tests are used to demonstrate the accuracy, stability, and applicability of the model: the diurnal cycling of the surface mixed layer, flow around a tall seamount, and a regional simulation of the California current system.

  4. Scaling laws for parametrizations of subgrid interactions in simulations of oceanic circulations.

    PubMed

    Kitsios, V; Frederiksen, J S; Zidikheri, M J

    2014-06-28

    Parametrizations of the subgrid eddy-eddy and eddy-meanfield interactions are developed for the simulation of baroclinic ocean circulations representative of an idealized Antarctic Circumpolar Current. Benchmark simulations are generated using a spectral spherical harmonic quasi-geostrophic model with maximum truncation wavenumber of T=504, which is equivalent to a resolution of 0.24° globally. A stochastic parametrization is used for the eddy-eddy interactions, and a linear deterministic parametrization for the eddy-meanfield interactions. The parametrization coefficients are determined from the statistics of benchmark simulations truncated back to the large eddy simulation (LES) truncation wavenumber, TR

  5. Scaling laws for parametrizations of subgrid interactions in simulations of oceanic circulations

    PubMed Central

    Kitsios, V.; Frederiksen, J. S.; Zidikheri, M. J.

    2014-01-01

    Parametrizations of the subgrid eddy–eddy and eddy–meanfield interactions are developed for the simulation of baroclinic ocean circulations representative of an idealized Antarctic Circumpolar Current. Benchmark simulations are generated using a spectral spherical harmonic quasi-geostrophic model with maximum truncation wavenumber of T=504, which is equivalent to a resolution of 0.24° globally. A stochastic parametrization is used for the eddy–eddy interactions, and a linear deterministic parametrization for the eddy–meanfield interactions. The parametrization coefficients are determined from the statistics of benchmark simulations truncated back to the large eddy simulation (LES) truncation wavenumber, TR

  6. Ocean Surface Geostrophic Circulation Climatology and Annual Variations Inferred from Satellite Altimetry and GOCE Gravity Data

    NASA Astrophysics Data System (ADS)

    Sánchez-Reales, J. M.; Vigo, M. I.; Trottini, M.

    2016-03-01

    We have studied, for the first time, variations in absolute surface geostrophic currents (SGC) using satellite data only. The proposed approach combines 18 years' altimetry data, which provide reliable measurements of absolute sea level (ASL), with a gravity field and steady-state ocean circulation explorer geoid model to obtain dynamic topography, and achieves unprecedented precision and accuracy. Our proposal overcomes the main limitations of existing approaches based solely on altimetry data (which suffer from lack of an independent reference for derivation of ASL maps), and approximations based on in-situ data (which are characterized by a sparse and inhomogeneous coverage in time and space). Features of annual variations of SGC are also addressed. As a result of our study we provide new absolute SGC climatology in the form of a 52-week data set of surface current fields, gridded at quarter degree longitude and latitude resolution and resolving spatial scales as short as 140 km. For presentation, this data set is averaged monthly and the results, presented as monthly climatology, are compared with climatology based on in-situ observations from drifter data.

  7. The North Atlantic subpolar circulation in an eddy-resolving global ocean model

    NASA Astrophysics Data System (ADS)

    Marzocchi, Alice; Hirschi, Joël J.-M.; Holliday, N. Penny; Cunningham, Stuart A.; Blaker, Adam T.; Coward, Andrew C.

    2015-02-01

    The subpolar North Atlantic represents a key region for global climate, but most numerical models still have well-described limitations in correctly simulating the local circulation patterns. Here, we present the analysis of a 30-year run with a global eddy-resolving (1/12°) version of the NEMO ocean model. Compared to the 1° and 1/4° equivalent versions, this simulation more realistically represents the shape of the Subpolar Gyre, the position of the North Atlantic Current, and the Gulf Stream separation. Other key improvements are found in the representation of boundary currents, multi-year variability of temperature and depth of winter mixing in the Labrador Sea, and the transport of overflows at the Greenland-Scotland Ridge. However, the salinity, stratification and mean depth of winter mixing in the Labrador Sea, and the density and depth of overflow water south of the sill, still present challenges to the model. This simulation also provides further insight into the spatio-temporal development of the warming event observed in the Subpolar Gyre in the mid 1990s, which appears to coincide with a phase of increased eddy activity in the southernmost part of the gyre. This may have provided a gateway through which heat would have propagated into the gyre's interior.

  8. ESA's Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) Mission

    NASA Astrophysics Data System (ADS)

    Drinkwater, M. R.; Haagmans, R.

    2004-12-01

    The Earth's gravity field is the fundamental physical force for every dynamic process on its surface. With the Gravity Field and steady-state Ocean Circulation Explorer (GOCE) Mission as its first Earth Explorer core mission, the European Space Agency (ESA) is playing an important role in this `geopotential decade' by preparing for acquisition of a high quality, high spatial resolution gravity field and geoid for future scientific applications. GOCE combines an innovative new three-axis gravity gradiometer (EGG) instrument (comprising three x, y, z pairs of accelerometers with a baseline separation of 0.5 m) with a drag-compensating ion-propulsion system to measure for the first time the full gravity gradient tensor along its orbit at 250 km altitude. GOCE will carry a GPS satellite-to-satellite tracking navigation system for 3-dimensional positioning, star trackers for precise pointing knowledge, and a laser retroreflector for ground laser tracking. GOCE is specifically designed to make accurate and precise measurements of the stationary gravity field and gravity anomalies (to 1 mGal) at high spatial resolution (100 km). The data will facilitate the computation of a high spatial resolution (100 km) global geoid model to 1-2 cm accuracy. Applications of these products will be illustrated using examples in oceanography, solid-earth physics and geodesy. After a successful completion of the design consolidation phase, the construction phase for the GOCE satellite is presently underway, with an anticipated a launch in late 2006.

  9. Numerical simulation of the seasonal and interannual variability of the tropical Atlantic Ocean circulation during the 1980s

    SciTech Connect

    Huang, Bohua.

    1992-01-01

    A nine-year (1980-88) surface wind stress data set over the tropical Atlantic ocean is constructed based on the European Centre for Medium Range Weather Forecasts (ECMWF) twice-daily wind analysis. Its quality is checked against an independent data set by Servain et al. (1985) based on ship observations. A comprehensive analysis of these two data sets shows a strong seasonal cycle of the wind stress over the equatorial Atlantic ocean. Interannually, the stress field is dominated by a seesaw between the northeast and southeast trade winds, with anomalously strong (weak) southeast (northeast) trade winds during 1980-83 and a reversed pattern during 1984-88. Two nine-year simulations of the tropical Atlantic ocean circulation are performed with a general circulation model, one forced by the twice-daily, and the second by monthly averaged ECMWF surface wind stresses. Comparisons with available observations show that the seasonal ocean circulation and interannual signals of the sea surface temperature (SST), i.e., the dipole oscillation and abnormal warmings, are that the seasonal cycle of the subtropical and tropical Atlantic has an in-phase relationship with the seasonal change of the surface wind stress and the interannual SST dipole oscillation is generally in balance with the seesaw pattern of the trade wind systems although wave processes are important during the transition of phase. In 1984, the transition of the SST dipole from north-warm/south-cold to its opposite occurred during an equatorial warming event. This warming event was initiated by the relaxation of equatorial easterly wind, which stimulated heat transfer first eastward along the equator, then to the southern ocean and caused a deepening of the thermocline in the Gulf of Guinea and the southern ocean. Another warming event occurred in 1987-88, which restored the disappearing north cold/warm dipole.

  10. Effect of improved subgrid scale transport of tracers on uptake of bomb radiocarbon in ghe GFDL ocean general circulation model

    SciTech Connect

    Duffy, P.B.; Elgroth, P.; Caldeira, K.

    1995-05-01

    The authors show that the Gent-McWilliams tracer transport parameterization greatly improves the ability of the GFDL ocean general circulation model to simulate vertical profiles of both temperature and bomb radiocarbon with a single set of model parameter values. This parameterization, which includes new advection terms as well as isopycnal mixing, has previously been shown to greatly improve simulated temperature fields. Here, the authors show that it does not markedly affect the already good simulation of oceanic absorption of bomb radiocarbon, and discuss the reasons for this result. 19 refs., 3 figs., 2 tabs.

  11. Surface water and atmospheric underway carbon data obtained during the World Ocean Circulation Experiment Indian Ocean survey cruises (R/V Knorr, December 1998--January 1996)

    SciTech Connect

    Kozyr, A.; Allison, L.

    1997-11-01

    This data documentation presents the results of the surface water and atmospheric underway measurements of mole fraction of carbon dioxide (xCO{sub 2}), sea surface salinity, and sea surface temperature, obtained during the World Ocean Circulation Experiment (WOCE) Indian Ocean survey cruises (December 1994--January 1996). Discrete and underway carbon measurements were made by members of the CO{sub 2} survey team. The survey team is a part of the Joint Global Ocean Flux Study supported by the US Department of Energy to make carbon-related measurements on the WOCE global survey cruises. Approximately 200,000 surface seawater and 50,000 marine air xCO{sub 2} measurements were recorded.

  12. The influence of ocean surface temperature gradient and continentality on the Walker circulation. II - Prescribed global changes

    NASA Technical Reports Server (NTRS)

    Stone, P. H.; Chervin, R. M.

    1984-01-01

    The series of experiments presently used to investigate the mechanisms responsible for forcing the global Walker circulation features worldwide changes in ocean surface temperatures (OSTs), topography, and/or continents. The primary factor affecting circulation is noted to be the global distribution of continents and oceans; while OST gradients are also important, topography emerges as comparatively unimportant. Continentality and OST gradients force the model atmosphere through the introduction of zonal variations in surface heating. The vertical motions to which they give rise yield moisture convergence and condensation variations which reinforce vertical motions. The forcing by OST gradients is partly nonlocal, and the atmospheric response is effected by continentality. In all cases, vertical motion zonal variations correlate with precipitation.

  13. Can large scale surface circulation changes modulate the sea surface warming pattern in the Tropical Indian Ocean?

    NASA Astrophysics Data System (ADS)

    Rahul, S.; Gnanaseelan, C.

    2016-06-01

    The increased rate of Tropical Indian Ocean (TIO) surface warming has gained a lot of attention in the recent years mainly due to its regional climatic impacts. The processes associated with this increased surface warming is highly complex and none of the mechanisms in the past studies could comprehend the important features associated with this warming such as the negative trends in surface net heat fluxes and the decreasing temperature trends at thermocline level. In this work we studied a previously unexplored aspect, the changes in large scale surface circulation pattern modulating the surface warming pattern over TIO. We use ocean reanalysis datasets and a suit of Ocean General Circulation Model (OGCM) experiments to address this problem. Both reanalysis and OGCM reveal strengthening large scale surface circulation pattern in the recent years. The most striking feature is the intensification of cyclonic gyre circulation around the thermocline ridge in the southwestern TIO. The surface circulation change in TIO is mainly associated with the surface wind changes and the geostrophic response to sea surface height decrease in the western/southwestern TIO. The surface wind trends closely correspond to SST warming pattern. The strengthening mean westerlies over the equatorial region are conducive to convergence in the central and divergence in the western equatorial Indian Ocean (IO) resulting central warming and western cooling. The resulting east west SST gradient further enhances the equatorial westerlies. This positive feedback mechanism supports strengthening of the observed SST trends in the equatorial Indian Ocean. The cooling induced by the enhanced upwelling in the west is compensated to a large extent by warming due to reduction in mixed layer depth, thereby keeping the surface temperature trends in the west to weak positive values. The OGCM experiments showed that the wind induced circulation changes redistribute the excess heat received in the western

  14. The role of the hydrological cycle and the ocean`s thermohaline circulation in climate change: A multicomponent climate model study. Ph.D. Thesis

    SciTech Connect

    Wang, Huaxiao

    1993-12-31

    Global ocean-atmosphere and ocean-atmosphere-continental ice sheet models are developed to address the question of feedbacks between the hydrological cycle and the global thermohaline circulation capable of explaining the climate changes seen in paleoclimate records of the late Pleistocene and the last deglaciation. The ocean-atmosphere model climate system displays two distinct stable equilibria controlled by latitudinal water vapor transport and the net flux of water vapor from the Atlantic to the Pacific Ocean. If the inter-basin transport is sufficiently large, small changes in water vapor transport over the North Atlantic can effect bifurcation; maximum difference between the modes occurs in the North Atlantic. If the inter-basin transport is from the Pacific to the Atlantic and sufficiently large, latitudinal vapor transport in the North Pacific controls the bifurcations, with maximum changes occurring in the North Pacific. For intermediate values of inter-basin transport, no rapid transitions occur in either basin. In the regime with vapor flux from the Atlantic to the Pacific, one mode has strong production of deep water in the North Atlantic and a large flux of heat to the atmosphere from the high latitude North Atlantic. The other has strong deep water production in the Southern Ocean and weak production in the North Pacific and small heat transport to high-latitude North Atlantic. The ocean-atmosphere-ice sheet system displays feedbacks which produce century/millennium time scale oscillations. The thermohaline circulation plays a central role in these feedbacks because of its transport of both heat and salt. The feedbacks could potentially play a causal role in the century/milliennium climate change seen in the paleoclimate record.

  15. Monitoring estuarine circulation and ocean waste dispersion using an integrated satellite-aircraft-drogue approach. [Continental Shelf and Delaware Bay

    NASA Technical Reports Server (NTRS)

    Klemas, V. (Principal Investigator); Davis, G. R.; Wang, H.

    1975-01-01

    The author has identified the following significant results. An integrated satellite-aircraft-drogue approach was developed which employs remotely tracked expendable drogues together with satellite and aircraft observations of oil slicks, waste plumes, and natural tracers, such as suspended sediment. Tests conducted on the Continental Shelf and in Delaware Bay indicate that the system provides a cost effective means of monitoring current circulation and verifying oil slick and ocean waste dispersion models even under severe environmental conditions.

  16. Large variations in the Holocene marine radiocarbon reservoir effect reflect ocean circulation and climatic changes

    NASA Astrophysics Data System (ADS)

    Hua, Quan; Webb, Gregory E.; Zhao, Jian-xin; Nothdurft, Luke D.; Lybolt, Matthew; Price, Gilbert J.; Opdyke, Bradley N.

    2015-07-01

    Accurate radiocarbon dating of marine samples requires knowledge of the marine radiocarbon reservoir effect. This effect for a particular site/region is generally assumed constant through time when calibrating marine 14C ages. However, recent studies have shown large temporal variations of several hundred to a couple of thousand years in this effect for a number of regions during the late Quaternary and Holocene. Here we report marine radiocarbon reservoir correction (ΔR) for Heron Reef and Moreton Bay in southwestern (SW) Pacific for the last 8 ka derived from 14C analysis of 230Th-dated corals. Most of our ΔR for the last ∼5.4 ka agree well with their modern value, but large ΔR variability of ∼410 yr (from trough to peak) with possible decadal/centennial fluctuations is evident for the period ∼5.4-8 ka. The latter time interval also has significant variations with similar features in previously published ΔR values for other sites in the Pacific, including southern Peru-northern Chile in southeastern (SE) Pacific, the South China Sea, Vanuatu and Papua New Guinea, with the largest magnitude of ∼920 yr from SE Pacific. The mechanisms for these large ΔR variations across the Pacific during the mid-Holocene are complex processes involving (1) changes in the quantity and 14C content of upwelled waters in tropical east Pacific (TEP) (frequency and intensity of ocean upwelling in the TEP, and contribution of Subantarctic Mode Water to the upwelled waters, which is influenced by the intensity and position of southern westerly winds), and (2) variations in ocean circulation associated with climate change (La Niña/El Niño conditions, intensity of easterly trade winds, positions of the Intertropical Convergence Zone and the South Pacific Convergence Zone), which control the spreading of the older upwelled surface waters in the TEP to the western sites. Our results imply the need for employing temporal changes in ΔR values, instead of constant (modern) values

  17. Barium-isotopic fractionation in seawater mediated by barite cycling and oceanic circulation

    NASA Astrophysics Data System (ADS)

    Horner, Tristan J.; Kinsley, Christopher W.; Nielsen, Sune G.

    2015-11-01

    The marine biogeochemical cycle of Ba is thought to be controlled by particulate BaSO4 (barite) precipitation associated with the microbial oxidation of organic carbon and its subsequent dissolution in the BaSO4-undersaturated water column. Despite many of these processes being largely unique to Ba cycling, concentrations of Ba and Si in seawater exhibit a strong linear correlation. The reasons for this correlation are ambiguous, as are the depth ranges corresponding to the most active BaSO4 cycling and the intermediate sources of Ba to particulate BaSO4. Stable isotopic analyses of dissolved Ba in seawater should help address these issues, as Ba-isotopic compositions are predicted to be sensitive to the physical and biogeochemical process that cycle Ba. We report a new methodology for the determination of dissolved Ba-isotopic compositions in seawater and results from a 4500 m depth profile in the South Atlantic at 39.99° S, 0.92° E that exhibit oceanographically-consistent variation with depth. These data reveal that water masses obtain their [Ba] and Ba-isotopic signatures when at or near the surface, which relates to the cycling of marine BaSO4. The shallow origin of these signatures requires that the substantial Ba-isotopic variations in the bathypelagic zone were inherited from when those deep waters were last ventilated. Indeed, the water column below 600 m is well explained by conservative mixing of water masses with distinct [Ba] and Ba-isotopic compositions. This leads us to conclude that large scale oceanic circulation is important for sustaining the similar oceanographic distributions of Ba and Si in the South Atlantic, and possibly elsewhere. These data demonstrate that the processes of organic carbon oxidation, BaSO4 cycling, and Ba-isotopic fractionation in seawater are closely coupled, such that Ba-isotopic analyses harbor great potential as a tracer of the carbon cycle in the modern and paleo-oceans.

  18. North and equatorial Pacific Ocean circulation in the CORE-II hindcast simulations

    NASA Astrophysics Data System (ADS)

    Tseng, Yu-heng; Lin, Hongyang; Chen, Han-ching; Thompson, Keith; Bentsen, Mats; Böning, Claus W.; Bozec, Alexandra; Cassou, Christophe; Chassignet, Eric; Chow, Chun Hoe; Danabasoglu, Gokhan; Danilov, Sergey; Farneti, Riccardo; Fogli, Pier Giuseppe; Fujii, Yosuke; Griffies, Stephen M.; Ilicak, Mehmet; Jung, Thomas; Masina, Simona; Navarra, Antonio; Patara, Lavinia; Samuels, Bonita L.; Scheinert, Markus; Sidorenko, Dmitry; Sui, Chung-Hsiung; Tsujino, Hiroyuki; Valcke, Sophie; Voldoire, Aurore; Wang, Qiang; Yeager, Steve G.

    2016-08-01

    We evaluate the mean circulation patterns, water mass distributions, and tropical dynamics of the North and Equatorial Pacific Ocean based on a suite of global ocean-sea ice simulations driven by the CORE-II atmospheric forcing from 1963-2007. The first three moments (mean, standard deviation and skewness) of sea surface height and surface temperature variability are assessed against observations. Large discrepancies are found in the variance and skewness of sea surface height and in the skewness of sea surface temperature. Comparing with the observation, most models underestimate the Kuroshio transport in the Asian Marginal seas due to the missing influence of the unresolved western boundary current and meso-scale eddies. In terms of the Mixed Layer Depths (MLDs) in the North Pacific, the two observed maxima associated with Subtropical Mode Water and Central Mode Water formation coalesce into a large pool of deep MLDs in all participating models, but another local maximum associated with the formation of Eastern Subtropical Mode Water can be found in all models with different magnitudes. The main model bias of deep MLDs results from excessive Subtropical Mode Water formation due to inaccurate representation of the Kuroshio separation and of the associated excessively warm and salty Kuroshio water. Further water mass analysis shows that the North Pacific Intermediate Water can penetrate southward in most models, but its distribution greatly varies among models depending not only on grid resolution and vertical coordinate but also on the model dynamics. All simulations show overall similar large scale tropical current system, but with differences in the structures of the Equatorial Undercurrent. We also confirm the key role of the meridional gradient of the wind stress curl in driving the equatorial transport, leading to a generally weak North Equatorial Counter Current in all models due to inaccurate CORE-II equatorial wind fields. Most models show a larger

  19. Coupling of wave and circulation models in coastal-ocean predicting systems: a case study for the German Bight

    NASA Astrophysics Data System (ADS)

    Staneva, J.; Wahle, K.; Günther, H.; Stanev, E.

    2015-12-01

    This study addresses the impact of coupling between wind wave and circulation models on the quality of coastal ocean predicting systems. This is exemplified for the German Bight and its coastal area known as the Wadden Sea. The latter is the area between the barrier islands and the coast. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales, which in many cases are due to unresolved nonlinear feedback between strong tidal currents and wind-waves. In this study we present analysis of wave and hydrographic observations, as well as results of numerical simulations. A nested-grid modelling system is used to producing reliable nowcasts and short-term forecasts of ocean state variables, including wind waves and hydrodynamics. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecast system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and sea level are investigated by considering the wave-dependent stress and wave breaking parameterization. Also the effects which the circulation exerts on the wind waves are tested for the coastal areas using different parameterizations. The improved skill of the coupled forecasts compared to the non-coupled ones, in particular during extreme events, justifies the further enhancements of coastal operational systems by including wind wave models.

  20. Impact of anthropogenic Pb and ocean circulation on the recent distribution of Pb isotopes in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Mi; Boyle, Edward A.; Gamo, Toshitaka; Obata, Hajime; Norisuye, Kazuhiro; Echegoyen, Yolanda

    2015-12-01

    Pb and Pb isotope ratios in the modern ocean have been altered significantly by anthropogenic Pb inputs over the past century. Most studies of anthropogenic Pb in the ocean have focused on the North Atlantic and North Pacific Oceans, and the impact of anthropogenic Pb inputs to the Indian Ocean and processes controlling the distribution of Pb in the Indian Ocean are poorly known. This study presents the Pb and Pb isotopic composition (206Pb/207Pb, 208Pb/207Pb) of 11 deep stations from the Indian Ocean Japanese GEOTRACES cruise (KH-09-5), from the Bay of Bengal and Arabian Sea to the Southern Ocean (62°S). The Pb isotope ratios of the Indian Ocean range 1.140-1.190 for 206Pb/207Pb and 2.417-2.468 for 208Pb/207Pb, with lower ratios appearing in the shallow waters of the northern Indian Ocean and higher ratios appearing in the deep layers of the Southern Ocean. This result agrees with a previous study on Pb concentrations (Echegoyen et al., 2014) showing that the Indian Ocean, particularly its northern part, is largely perturbed by anthropogenic Pb inputs. 206Pb/207Pb and 208Pb/207Pb of the Indian sector Southern Ocean are still lower than natural Pb, showing this region was also affected by anthropogenic Pb. Anomalously low or high 206Pb/207Pb and 208Pb/207Pb were observed in the thermocline and shallow waters of the southern Indian Ocean and the Arabian Sea, which are ascribed to water mass distribution (e.g., Subantarctic Mode Water) and evolving Pb isotope ratios of this region as dominant anthropogenic Pb sources change. 206Pb/207Pb and 208Pb/207Pb in the Bay of Bengal are higher than those in the Arabian Sea, which might be the result of the anthropogenic Pb inputs from different provenance or seawater exchanging Pb isotopes with natural particles derived from rivers and/or sediments at the basin boundaries.

  1. Impacts of Sea Surface Salinity Bias Correction on North Atlantic Ocean Circulation and Climate Variability in the Kiel Climate Model

    NASA Astrophysics Data System (ADS)

    Park, Taewook; Park, Wonsun; Latif, Mojib

    2016-04-01

    We investigated impacts of correcting North Atlantic sea surface salinity (SSS) biases on the ocean circulation of the North Atlantic and on North Atlantic sector mean climate and climate variability in the Kiel Climate Model (KCM). Bias reduction was achieved by applying a freshwater flux correction over the North Atlantic to the model. The quality of simulating the mean circulation of the North Atlantic Ocean, North Atlantic sector mean climate and decadal variability is greatly enhanced in the freshwater flux-corrected integration which, by definition, depicts relatively small North Atlantic SSS biases. In particular, a large reduction in the North Atlantic cold sea surface temperature (SST) bias is observed and a more realistic Atlantic Multidecadal Variability (AMV) simulated. Improvements relative to the non-flux corrected integration also comprise a more realistic representation of deep convection sites, sea ice, gyre circulation and Atlantic Meridional Overturning Circulation (AMOC). The results suggest that simulations of North Atlantic sector mean climate and decadal variability could strongly benefit from alleviating sea surface salinity biases in the North Atlantic, which may enhance the skill of decadal predictions in that region.

  2. Coupling of wave and circulation models in coastal-ocean predicting systems: a case study for the German Bight

    NASA Astrophysics Data System (ADS)

    Staneva, Joanna; Wahle, Kathrin; Günther, Heinz; Stanev, Emil

    2016-06-01

    This study addresses the impact of coupling between wave and circulation models on the quality of coastal ocean predicting systems. This is exemplified for the German Bight and its coastal area known as the Wadden Sea. The latter is the area between the barrier islands and the coast. This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales, which in many cases are due to unresolved non-linear feedback between strong currents and wind waves. In this study we present analysis of wave and hydrographic observations, as well as results of numerical simulations. A nested-grid modelling system is used to produce reliable nowcasts and short-term forecasts of ocean state variables, including waves and hydrodynamics. The database includes ADCP observations and continuous measurements from data stations. The individual and combined effects of wind, waves and tidal forcing are quantified. The performance of the forecast system is illustrated for the cases of several extreme events. The combined role of wave effects on coastal circulation and sea level are investigated by considering the wave-dependent stress and wave breaking parameterization. Also the response, which the circulation exerts on the waves, is tested for the coastal areas. The improved skill of the coupled forecasts compared to the non-coupled ones, in particular during extreme events, justifies the further enhancements of coastal operational systems by including wave effects in circulation models.

  3. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates*

    NASA Astrophysics Data System (ADS)

    Sarnthein, M.; Prange, M.; Schmittner, A.; Schneider, B.; Weinelt, M.

    2009-01-01

    A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern Hemisphere Glaciation (NHG) and pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic, that and continue until today. The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3) and 2.7 Ma (glacial MIS G6/4). Various models and paleoceanographic records (intercalibrated using orbital age control) suggest clear linkages between the onset of NHG and three steps in the final closure of the Central American Seaways (CAS), deduced from rising salinity differences between Caribbean and East Pacific. Each closing event led to enhanced North Atlantic meridional overturning circulation and strengthened the poleward transport of salt and heat (warmings of +2-3°C). Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia, which led to enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS), and increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, the closing of CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC). Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~1 psu from 3.16-3.00 Ma, right after the first but still reversible attempt of closing the CAS.

  4. Mid-Pliocene shifts in ocean overturning circulation and the onset of Quaternary-style climates

    NASA Astrophysics Data System (ADS)

    Sarnthein, M.; Bartoli, G.; Prange, M.; Schmittner, A.; Schneider, B.; Weinelt, M.; Andersen, N.; Garbe-Schönberg, D.

    2009-06-01

    A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern-Hemisphere Glaciation (NHG) and of pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic and continue until today (Zachos et al., 2001). The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3) and 2.7 Ma (glacial MIS G6/4) (Lisiecki and Raymo, 2005). Various models (sensu Driscoll and Haug, 1998) and paleoceanographic records (intercalibrated using orbital age control) suggest clear linkages between the onset of NHG and the three steps in the final closure of the Central American Seaways (CAS), deduced from rising salinity differences between Caribbean and the East Pacific. Each closing event led to an enhanced North Atlantic meridional overturning circulation and this strengthened the poleward transport of salt and heat (warmings of +2-3°C) (Bartoli et al., 2005). Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia (Lunt et al., 2007), which probably led to an enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS), and an increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, new evidence shows that the closing of the CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC). Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~2 psu from 3.25/3.16-3.00 Ma, right after the first but still reversible attempt of closing the CAS.

  5. ENSO Bred Vectors in Coupled Ocean-Atmosphere General Circulation Models

    NASA Technical Reports Server (NTRS)

    Yang, S. C.; Cai, Ming; Kalnay, E.; Rienecker, M.; Yuan, G.; Toth, ZA.

    2004-01-01

    The breeding method has been implemented in the NASA Seasonal-to-Interannual Prediction Project (NSIPP) Coupled General Circulation Model (CGCM) with the goal of improving operational seasonal to interannual climate predictions through ensemble forecasting and data assimilation. The coupled instability as cap'tured by the breeding method is the first attempt to isolate the evolving ENSO instability and its corresponding global atmospheric response in a fully coupled ocean-atmosphere GCM. Our results show that the growth rate of the coupled bred vectors (BV) peaks at about 3 months before a background ENSO event. The dominant growing BV modes are reminiscent of the background ENSO anomalies and show a strong tropical response with wind/SST/thermocline interrelated in a manner similar to the background ENSO mode. They exhibit larger amplitudes in the eastern tropical Pacific, reflecting the natural dynamical sensitivity associated with the presence of the shallow thermocline. Moreover, the extratropical perturbations associated with these coupled BV modes reveal the variations related to the atmospheric teleconnection patterns associated with background ENSO variability, e.g. over the North Pacific and North America. A similar experiment was carried out with the NCEP/CFS03 CGCM. Comparisons between bred vectors from the NSIPP CGCM and NCEP/CFS03 CGCM demonstrate the robustness of the results. Our results strongly suggest that the breeding method can serve as a natural filter to identify the slowly varying, coupled instabilities in a coupled GCM, which can be used to construct ensemble perturbations for ensemble forecasts and to estimate the coupled background error covariance for coupled data assimilation.

  6. Construction of the adjoint MIT ocean general circulation model and application to Atlantic heat transport sensitivity

    NASA Astrophysics Data System (ADS)

    Marotzke, Jochem; Giering, Ralf; Zhang, Kate Q.; Stammer, Detlef; Hill, Chris; Lee, Tong

    1999-12-01

    We first describe the principles and practical considerations behind the computer generation of the adjoint to the Massachusetts Institute of Technology ocean general circulation model (GCM) using R. Giering's software tool Tangent-Linear and Adjoint Model Compiler (TAMC). The TAMC's recipe for (FORTRAN-) line-by-line generation of adjoint code is explained by interpreting an adjoint model strictly as the operator that gives the sensitivity of the output of a model to its input. Then, the sensitivity of 1993 annual mean heat transport across 29°N in the Atlantic, to the hydrography on January 1, 1993, is calculated from a global solution of the GCM. The "kinematic sensitivity" to initial temperature variations is isolated, showing how the latter would influence heat transport if they did not affect the density and hence the flow. Over 1 year the heat transport at 29°N is influenced kinematically from regions up to 20° upstream in the western boundary current and up to 5° upstream in the interior. In contrast, the dynamical influences of initial temperature (and salinity) perturbations spread from as far as the rim of the Labrador Sea to the 29°N section along the western boundary. The sensitivities calculated with the adjoint compare excellently to those from a perturbation calculation with the dynamical model. Perturbations in initial interior salinity influence meridional overturning and heat transport when they have propagated to the western boundary and can thus influence the integrated east-west density difference. Our results support the notion that boundary monitoring of meridional mass and heat transports is feasible.

  7. "Going with the flow" or not: evidence of positive rheotaxis in oceanic juvenile loggerhead turtles (Caretta caretta) in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data.

    PubMed

    Kobayashi, Donald R; Farman, Richard; Polovina, Jeffrey J; Parker, Denise M; Rice, Marc; Balazs, George H

    2014-01-01

    The movement of juvenile loggerhead turtles (n = 42) out-fitted with satellite tags and released in oceanic waters off New Caledonia was examined and compared with ocean circulation data. Merging of the daily turtle movement data with drifter buoy movements, OSCAR (Ocean Surface Current Analyses--Real time) circulation data, and three different vertical strata (0-5 m, 0-40 m, 0-100 m) of HYCOM (HYbrid Coordinate Ocean Model) circulation data indicated the turtles were swimming against the prevailing current in a statistically significant pattern. This was not an artifact of prevailing directions of current and swimming, nor was it an artifact of frictional slippage. Generalized additive modeling was used to decompose the pattern of swimming into spatial and temporal components. The findings are indicative of a positive rheotaxis whereby an organism is able to detect the current flow and orient itself to swim into the current flow direction or otherwise slow down its movement. Potential mechanisms for the means and adaptive significance of rheotaxis in oceanic juvenile loggerhead turtles are discussed. PMID:25098694

  8. “Going with the Flow” or Not: Evidence of Positive Rheotaxis in Oceanic Juvenile Loggerhead Turtles (Caretta caretta) in the South Pacific Ocean Using Satellite Tags and Ocean Circulation Data

    PubMed Central

    Kobayashi, Donald R.; Farman, Richard; Polovina, Jeffrey J.; Parker, Denise M.; Rice, Marc; Balazs, George H.

    2014-01-01

    The movement of juvenile loggerhead turtles (n = 42) out-fitted with satellite tags and released in oceanic waters off New Caledonia was examined and compared with ocean circulation data. Merging of the daily turtle movement data with drifter buoy movements, OSCAR (Ocean Surface Current Analyses - Real time) circulation data, and three different vertical strata (0–5 m, 0–40 m, 0–100 m) of HYCOM (HYbrid Coordinate Ocean Model) circulation data indicated the turtles were swimming against the prevailing current in a statistically significant pattern. This was not an artifact of prevailing directions of current and swimming, nor was it an artifact of frictional slippage. Generalized additive modeling was used to decompose the pattern of swimming into spatial and temporal components. The findings are indicative of a positive rheotaxis whereby an organism is able to detect the current flow and orient itself to swim into the current flow direction or otherwise slow down its movement. Potential mechanisms for the means and adaptive significance of rheotaxis in oceanic juvenile loggerhead turtles are discussed. PMID:25098694

  9. Millennial-scale tropical atmospheric and Atlantic Ocean circulation change from the Last Glacial Maximum and Marine Isotope Stage 3

    NASA Astrophysics Data System (ADS)

    Them, T. R.; Schmidt, M. W.; Lynch-Stieglitz, J.

    2015-10-01

    Abrupt, millennial-scale climate oscillations, known as Dansgaard-Oeschger (D-O) cycles, characterized the climate system of the last glacial period. Although proxy evidence shows that D-O cycles resulted in large-scale changes in atmospheric circulation patterns around the planet, an understanding of how Atlantic Meridional Overturning Circulation (AMOC) varied across these events remains unclear. Here, we take advantage of the fact that both tropical atmospheric circulation changes corresponding to north-south shifts in the Intertropical Convergence Zone (ITCZ) and large-scale changes in ocean circulation associated with AMOC variability can be reconstructed in the same sediment core from the Florida Straits to examine the relationship between atmospheric and ocean circulation changes across D-O events. To reconstruct surface water conditions, Mg/Ca-paleothermometry and stable isotope measurements were combined on the planktonic foraminifera Globigerinoides ruber (white variety) from sediment core KNR166-2 JPC26 (24°19.61‧N, 83°15.14‧W; 546 m depth) to reconstruct a high-resolution record of sea surface temperature and δO18seawater (a proxy for upper mixed layer salinity) during Marine Isotope Stages (MIS) 2 and 3 from 20-35 ka BP. As an additional proxy for upper water column salinity change, we also generate a faunal abundance record of the salinity-sensitive planktonic foraminifera Neogloboquadrina dutertrei. Our results suggest that rapid reductions in sea surface salinity occurred at the onset of D-O interstadials, while stadials are characterized by increased surface salinities. The most likely cause of these salinity changes was variation in the strength and position of the ITCZ across D-O events. Finally, we examine the relationship between millennial-scale atmospheric circulation changes recorded in the planktonic records and ocean circulation changes inferred from the benthic δ18O record from our core. Our results provide some of the first

  10. Significant Findings: Seasonal Distributions of Global Ocean Chlorophyll and Nutrients With a Coupled Ocean General Circulation, Biogeochemical, and Radiative Model. 2; Comparisons With Satellite and In Situ Data

    NASA Technical Reports Server (NTRS)

    Gregg, Watson W.; Busalacchi, Antonio (Technical Monitor)

    2000-01-01

    A coupled ocean general circulation, biogeochemical, and radiative model was constructed to evaluate and understand the nature of seasonal variability of chlorophyll and nutrients in the global oceans. Biogeochemical processes in the model were determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among three functional phytoplankton groups (diatoms, chlorophytes, and picoplankton) and three nutrients (nitrate, ammonium, and silicate). Basin scale (>1000 km) model chlorophyll seasonal distributions were statistically positively correlated with CZCS chlorophyll in 10 of 12 major oceanographic regions, and with SeaWiFS in all 12. Notable disparities in magnitudes occurred, however, in the tropical Pacific, the spring/summer bloom in the Antarctic, autumn in the northern high latitudes, and during the southwest monsoon in the North Indian Ocean. Synoptic scale (100-1000 km) comparisons of satellite and in situ data exhibited broad agreement, although occasional departures were apparent. Model nitrate distributions agreed with in situ data, including seasonal dynamics, except for the equatorial Atlantic. The overall agreement of the model with satellite and in situ data sources indicated that the model dynamics offer a reasonably realistic simulation of phytoplankton and nutrient dynamics on basin and synoptic scales.

  11. High-precision measurements of {sup 14}C as a circulation tracer in the Pacific, Indian, and Southern Oceans with Accelerator Mass Spectrometry (AMS)

    SciTech Connect

    Reden, Karl F. von; Peden, John C.; Schneider, Robert J.; Bellino, Mary; Donoghue, Joanne; Elder, Kathryn L.; Gagnon, Alan R.; Long, Patricia; McNichol, Ann P.; Morin, Tracey; Stuart, Dana; Hayes, John M.; Key, Robert M.

    1999-04-26

    The National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) has completed the carbon isotope analysis of a major fraction of the 13,500 sea water samples collected in the framework of the World Ocean Circulation Experiment (WOCE) from three of the major world oceans between 1991 and 1996. We will describe the AMS technique employed at NOSAMS and, using 3-D data visualization techniques we will demonstrate the present status of the data set and offer some preliminary conclusions about the distribution of natural and anthropogenic {sup 14}C in the oceans. In particular, we will be able to compare some of the data with results from the Geochemical Ocean Sections Study (GEOSECS, 1972-1978) to obtain information about the time dependence of oceanic circulation processes, tracing the {sup 14}C signal introduced into the oceans during the atmospheric nuclear bomb tests in the 1950's and 1960's.

  12. On improving the accuracy of the M2 barotropic tides embedded in a high-resolution global ocean circulation model

    NASA Astrophysics Data System (ADS)

    Ngodock, Hans; Wallcraft, Alan; Souopgui, Innocent; Richman, James; Shriver, Jay; Arbic, Brian

    2016-04-01

    The ocean tidal velocity and elevation can be estimated concurrently with the ocean circulation by adding the astronomical tidal forcing, parameterized topographic internal wave drag, and self-attraction and loading to the general circulation physics. However, the accuracy of these tidal estimates does not yet match accuracies in the best data-assimilative barotropic tidal models. This paper investigates the application of an Augmented State Ensemble Kalman Filter (ASEnKF) to improve the accuracy of M2 barotropic tides embedded in a 1/12.5° three-dimensional ocean general circulation model. The ASEnKF is an alternative to the techniques typically used with linearized tide-only models; such techniques cannot be applied to the embedded tides in a nonlinear eddying circulation. An extra term, meant to correct for errors in the tide model due to imperfectly known topography and damping terms, is introduced into the tidal forcing. Ensembles of the model are created with stochastically generated forcing correction terms. The discrepancies for each ensemble member with TPXO, an existing data-assimilative tide model, are computed. The ASEnKF method yields an optimal estimate of the model forcing correction terms, that minimizes resultant root mean square (RMS) tidal sea surface elevation error with respect to TPXO, as well as an estimate of the tidal elevation. The deep-water, global area-averaged RMS sea surface elevation error of the principal lunar semidiurnal tide M2 is reduced from 4.4 cm in a best-case non-assimilative solution to 2.6 cm. The largest elevation errors in both the non-assimilative and ASEnKF solutions are in the North Atlantic, a highly resonant basin. Possible pathways for achieving further reductions in the RMS error are discussed.

  13. On improving the accuracy of the M2 barotropic tides embedded in a high-resolution global ocean circulation model

    NASA Astrophysics Data System (ADS)

    Ngodock, Hans E.; Souopgui, Innocent; Wallcraft, Alan J.; Richman, James G.; Shriver, Jay F.; Arbic, Brian K.

    2016-01-01

    The ocean tidal velocity and elevation can be estimated concurrently with the ocean circulation by adding the astronomical tidal forcing, parameterized topographic internal wave drag, and self-attraction and loading to the general circulation physics. However, the accuracy of these tidal estimates does not yet match accuracies in the best data-assimilative barotropic tidal models. This paper investigates the application of an augmented state ensemble Kalman Filter (ASEnKF) to improve the accuracy of M2 barotropic tides embedded in a 1/12.5° three-dimensional ocean general circulation model. The ASEnKF is an alternative to the techniques typically used with linearized tide-only models; such techniques cannot be applied to the embedded tides in a nonlinear eddying circulation. An extra term, meant to correct for errors in the tide model due to imperfectly known topography and damping terms, is introduced into the tidal forcing. Ensembles of the model are created with stochastically generated forcing correction terms. The discrepancies for each ensemble member with TPXO, an existing data-assimilative tide model, are computed. The ASEnKF method yields an optimal estimate of the model forcing correction terms, that minimizes resultant root mean square (RMS) tidal sea surface elevation error with respect to TPXO, as well as an estimate of the tidal elevation. The deep-water, global area-averaged RMS sea surface elevation error of the principal lunar semidiurnal tide M2 is reduced from 4.4 cm in a best-case non-assimilative solution to 2.6 cm. The largest elevation errors in both the non-assimilative and ASEnKF solutions are in the North Atlantic, a highly resonant basin. Possible pathways for achieving further reductions in the RMS error are discussed.

  14. Distribution of He-3 in the intermediate waters of the Indian Ocean: implications for mid-depth circulation and mixing

    NASA Astrophysics Data System (ADS)

    Schlosser, P.; Hohmann, R.; Winckler, G.; Newton, R.; Srinivasan, A.; Top, Z.; Lupton, J.; Jenkins, W.; Jean-Baptiste, P.

    2003-04-01

    Since the discovery of mantle He-3 in the ocean by Clarke et al. (1969) this isotope has been used in numerous studies of the mid-depth circulation of the ocean. Data from GEOSECS and a number of cruises dedicated to the mapping of He-3 in the Pacific Ocean provided a solid foundation for oceanographic applications even before the WOCE survey. In the Indian Ocean the data set was sparser and the WOCE Hydrographic Program for the first time provided coverage that was sufficiently dense to map out the major features of the 3He plumes. We present and discuss d3He distributions constructed from WOCE data, the GEOSECS survey, as well as from smaller cruises that aimed at defining sources on the Mid Ocean Ridges. The delta He-3 distributions are plotted on isopycnal surfaces corresponding to depths of major He-3 sources. The major plume can be found close to the depth of the Mid-Ocean Ridge crests. This main plume spreads from the western basin to the eastern Indian Ocean. It seems to be emanated from a limited stretch of the MOR near to, but distinctly off, the Triple Junction. It is slightly elongated in a southwestern direction and can easily be distinguished from the plumes originating in the Indonesian Throughflow regime and in the Gulf of Aden. The d3He values in the mid-depth plume emanating from the MOR decrease towards the south (ACC). This feature indicates ventilation in the Southern Ocean. It is concentrated at depths between 1500 and 3500 meters with maximum delta He-3 concentrations (about 18%) found around 2500 meters depth. The plume can easily be traced over distances of 2500 km or more. Implications of the delta He-3 field for mixing and spreading of the intermediate waters are discussed.

  15. Southwest Pacific Ocean surface reservoir ages since the last glaciation: Circulation insights from multiple-core studies

    NASA Astrophysics Data System (ADS)

    Sikes, Elisabeth L.; Guilderson, Thomas P.

    2016-02-01

    Radiocarbon (14C) in dissolved inorganic carbon in the ocean can trace the age of ocean water relative to the atmosphere and provide insight into climate-driven changes in ocean circulation since the last glaciation. Here we estimate surface radiocarbon ages from the last glaciation through the deglaciation into the Holocene in the southwestern Pacific by using tephras, both as stratigraphic tie points and for the availability of existing radiocarbon dates from terrestrial- based analyses of the organic carbon associated with them, as markers of past atmospheric Δ14C. The glacial surface reservoir age of subtropical waters was ~700 14C years older than the coeval atmosphere at ~25,000 cal yr B.P. This was significantly older (more 14C depleted) by ~ 300 14C years, than modern reservoir ages. At the same time, subantarctic surface water reservoir age was ~3200 14C years, almost 5 times the modern reservoir age, making the difference in age between subtropical and subantarctic surface water masses treble the modern difference. This pattern is attributed to the upwelling and exchange of very old deep waters from the glacial abyss in the Southern Ocean. In the early deglaciation, surface reservoir ages were ~600 to 700 14C years. Recent atmospheric Δ14C calibrations project that these surface reservoir ages were older than modern by 1.2-fold to 2-fold. This increased reservoir effect can be attributed to shallow circulation that differed from modern, delivering waters with lower 14C content to the region. Early Holocene surface reservoir ages of ~300 to 500 14C years, similar to recent, suggest modern circulation patterns were in place by that time.

  16. Cenozoic Circulation History of the North Atlantic Ocean From Seismic Stratigraphy of the Newfoundland Ridge Drift Complex

    NASA Astrophysics Data System (ADS)

    Boyle, P. R.; Romans, B.; Norris, R. D.; Tucholke, B. E.; Swift, S. A.; Sexton, P. F.

    2014-12-01

    In the North Atlantic Ocean, contour-following bottom currents have eroded regional unconformities and deposited contourite drifts that exceed two km in thickness and extend for 100s of km. The character of deep-water masses that are conveyed through ocean basins by such currents influence global heat transfer and ocean-atmosphere partitioning of CO2. The Newfoundland Ridge Drift Complex lies directly under the modern Deep Western Boundary Current southeast of Newfoundland, close to the site of overturning in the northwest Atlantic Ocean and at the intersection of the warm Gulf Stream and cool Labrador surface currents. To the south are regions of the western North Atlantic basin that are influenced by southern- as well as northern-sourced bottom waters. Here, we document the evolution of North Atlantic deep-water circulation by seismic-stratigraphic analysis of the long-lived and areally extensive Newfoundland Ridge Drift Complex. IODP Expedition 342 boreholes provide age control on seismic units, allowing sedimentation patterns to be placed in a temporal framework. We find three major phases of sedimentation: pre-contourite drift (~115-50 Ma), active contourite drift (~50-2.6 Ma), and late-contourite drift (~2.6-0 Ma). Bottom-current-controlled deposition of terrigenous-rich sediment began at ~50 Ma, which correlates to the onset of a long-term global cooling trend. A further change in deep circulation near the Eocene-Oligocene transition (~30 Ma) is indicated by more focused drift sedimentation with greatly increased accumulation rates and stratal architecture dominated by mud waves. At ~2.6 Ma to present the axis of drift accumulation shifted markedly towards shallower water depths, corresponding with the onset of Northern Hemisphere ice sheets. We discuss how these reorganizations of deep circulation correlate with results of other North Atlantic seismic stratigraphic studies to the north and south.

  17. Inferring surface water equilibrium calcite δ18O during the last deglacial period from benthic foraminiferal records: Implications for ocean circulation

    NASA Astrophysics Data System (ADS)

    Amrhein, Daniel E.; Gebbie, Geoffrey; Marchal, Olivier; Wunsch, Carl

    2015-11-01

    The ocean circulation modifies mixed layer (ML) tracer signals as they are communicated to the deep ocean by advection and mixing. We develop and apply a procedure for using tracer signals observed "upstream" (by planktonic foraminifera) and "downstream" (by benthic foraminifera) to constrain how tracer signals are modified by the intervening circulation and, by extension, to constrain properties of that circulation. A history of ML equilibrium calcite δ18O (δ18Oc) spanning the last deglaciation is inferred from a least-squares fit of eight benthic foraminiferal δ18Oc records to Green's function estimated for the modern ocean circulation. Disagreements between this history and the ML history implied by planktonic records would indicate deviations from the modern circulation. No deviations are diagnosed because the two estimates of ML δ18Oc agree within their uncertainties, but we suggest data collection and modeling procedures useful for inferring circulation changes in future studies. Uncertainties of benthic-derived ML δ18Oc are lowest in the high-latitude regions chiefly responsible for ventilating the deep ocean; additional high-resolution planktonic records constraining these regions are of particular utility. Benthic records from the Southern Ocean, where data are sparse, appear to have the most power to reduce uncertainties in benthic-derived ML δ18Oc. Understanding the spatiotemporal covariance of deglacial ML δ18Oc will also improve abilities of δ18Oc records to constrain deglacial circulation.

  18. Seawater-derived neodymium isotope records in the Chukchi Sea, western Arctic Ocean during Holocene: implications for oceanographic circulation

    NASA Astrophysics Data System (ADS)

    Lee, Borom; Nam, Seung-Il; Huh, Youngsook; Lee, Mi Jung

    2015-04-01

    Changes in oceanographic circulation in the Artic have a large influence on the global oceanic and climate system of the Earth through the geological times. In particular, freshwater input from the North Pacific to the western Arctic Ocean affects the Atlantic meridional overturning circulation (AMOC) after the opening of the Bering Strait. Seawater-derived neodymium isotope in marine sediments has been used as a proxy to trace the origin of water masses and oceanic circulation system. The global average residence time of Nd is shorter than the global ocean mixing time and dissolved Nd in seawater behaves quasi-conservatively. In the modern Arctic Ocean, the Nd isotope distribution is dominated by Atlantic source water, although the circum-Arctic riverine discharge and Pacific-derived waters also have noticeable impacts. In this study, we investigated seawater-derived neodymium isotope records from a sediment core recovered from the Chukchi Sea to understand the changes in hydrograhic circulation of the western Arctic during the Holocene. A gravity core, ARA02B 01A, was collected on the northern shelf of the Chukchi Sea (73°37.8939'N, 166°30.9838'W, ca. 111 m in water depth) during the RV Araon expedition in 2011. To obtain seawater-derived Nd records, we extracted Fe-Mn oxide coatings as an authigenic fraction from bulk sediments by leaching with acid-reducing solution after removing carbonate by leaching with acetic acid. Our preliminary results might show a general pattern of increasing radiogenic ɛNd values through Holocene intervals. Therefore, it implies that ɛNd results may be related with variations in the intensity of Bering Strait inflow during the last ~9.31 ka BP. The radiogenic trend was strongly pronounced from the late Holocene (ɛNd -7.23; ca. 8.84 ka BP) to the middle Holocene (ɛNd -4.78; ca. 6.18 ka BP) and vaguely during the middle Holocene. After 4.13 ka BP, ɛNd values were increased again from -4.86 to -4.03 at 0.57 ka BP. But 87Sr/86Sr

  19. A Comparison between the TOPEX/POSEIDON Data and a Global Ocean General Circulation Model during 1992-1993

    NASA Technical Reports Server (NTRS)

    Chao, Yi; Fu, Lee-Lueng

    1995-01-01

    The TOPEX/POSEIDON altimetric sea level observation during 1992-1993 was used to validate the simulation made by a global ocean general circulation model (OGCM) forced by the daily wind stress and heat flux derived from the National Meteorological Center operational analysis. The OGCM is a version of the modular ocean model with a horizontal resolution of 2 deg longitude and 1 deg latitude and 22 levels in the vertical. The model simulation is compared to the observation at spatial scales of the order of 500 km and larger. Only the temporal variations are examined. The variability is composed primarily of the annual cycle and intraseasonal fluctuations (periods shorter than 100 days). The basic features of the annual cycle are simulated well by the model. Major discrepancies are found in the eastern tropical Pacific, as well as the eastern North Pacific and most of the interior of the North Atlantic. The culprit is suspected to be the inadequate heat forcing and mixing parameterizations of the model. Significant intraseasonal variability is found in the central North Pacific and the Southern Ocean. The simulation is highly correlated with the observation at periods from 20 to 100 days. The spatial scales are larger than 1000 km in many places. These variabilities are apparently the barotropic response of the ocean to wind forcing. The results of the study provide a basis for future assimilation of the data into the OGCM for improved description of the large-scale ocean variabilities.

  20. Comparison of ocean surface solar irradiance in the GLA General Circulation Model and satellite-based calculations

    NASA Technical Reports Server (NTRS)

    Chertock, Beth; Sud, Y. C.

    1993-01-01

    A global, 7-year satellite-based record of ocean surface solar irradiance (SSI) is used to assess the realism of ocean SSI simulated by the nine-layer Goddard Laboratory for Atmospheres (GLA) General Circulation Model (GCM). January and July climatologies of net SSI produced by the model are compared with corresponding satellite climatologies for the world oceans between 54 deg N and 54 deg S. This comparison of climatologies indicates areas of strengths and weaknesses in the GCM treatment of cloud-radiation interactions, the major source of model uncertainty. Realism of ocean SSI is also important for applications such as incorporating the GLA GCM into a coupled ocean-atmosphere GCM. The results show that the GLA GCM simulates too much SSI in the extratropics and too little in the tropics, especially in the summer hemisphere. These discrepancies reach magnitudes of 60 W/sq m and more. The discrepancies are particularly large in the July case off the western coast of North America. Positive and negative discrepancies in SSI are shown to be consistent with discrepancies in planetary albedo.

  1. Comparison of ocean surface solar irradiance in the GLA General Circulation Model and satellite-based calculations

    SciTech Connect

    Chertock, B. ); Sud, Y.C. )

    1993-03-01

    A global, 7-year satellite-based record of ocean surface solar irradiance (SSI) is used to assess the realism of ocean SSI simulated by the nine-layer Goddard Laboratory for Atmospheres (GLA) General Circulation Model (GCM). January and July climatologies of net SSI produced by the model are compared with corresponding satellite climatologies for the world oceans between 54[degrees]N and 54[degrees]S. This comparison of climatologies indicates areas of strengths and weaknesses in the GCM treatment of cloud-radiation interactions, the major source of model uncertainty. Realism of ocean SSI is also important for applications such as incorporating the GLA GCM into a coupled ocean-atmosphere GCM. The results show that the GLA GCM simulates too much SSI in the extratropics and too little in the tropics, especially in the summer hemisphere. These discrepancies reach magnitudes of 60 W m[sup [minus]2] and more. The discrepancies are particularly large in the July case off the western coast of North America. In this region of persistent marine stratus, the GCM climatological values exceed the satellite climatological values by as much as 131 W m[sup [minus]2]. Positive and negative discrepancies in SSI are shown to be consistent with discrepancies in planetary albedo.

  2. Prognostic residual mean flow in an ocean general circulation model and its relation to prognostic Eulerian mean flow

    SciTech Connect

    Saenz, Juan A.; Chen, Qingshan; Ringler, Todd

    2015-05-19

    Recent work has shown that taking the thickness-weighted average (TWA) of the Boussinesq equations in buoyancy coordinates results in exact equations governing the prognostic residual mean flow where eddy–mean flow interactions appear in the horizontal momentum equations as the divergence of the Eliassen–Palm flux tensor (EPFT). It has been proposed that, given the mathematical tractability of the TWA equations, the physical interpretation of the EPFT, and its relation to potential vorticity fluxes, the TWA is an appropriate framework for modeling ocean circulation with parameterized eddies. The authors test the feasibility of this proposition and investigate the connections between the TWA framework and the conventional framework used in models, where Eulerian mean flow prognostic variables are solved for. Using the TWA framework as a starting point, this study explores the well-known connections between vertical transfer of horizontal momentum by eddy form drag and eddy overturning by the bolus velocity, used by Greatbatch and Lamb and Gent and McWilliams to parameterize eddies. After implementing the TWA framework in an ocean general circulation model, we verify our analysis by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.

  3. Prognostic residual mean flow in an ocean general circulation model and its relation to prognostic Eulerian mean flow

    DOE PAGESBeta

    Saenz, Juan A.; Chen, Qingshan; Ringler, Todd

    2015-05-19

    Recent work has shown that taking the thickness-weighted average (TWA) of the Boussinesq equations in buoyancy coordinates results in exact equations governing the prognostic residual mean flow where eddy–mean flow interactions appear in the horizontal momentum equations as the divergence of the Eliassen–Palm flux tensor (EPFT). It has been proposed that, given the mathematical tractability of the TWA equations, the physical interpretation of the EPFT, and its relation to potential vorticity fluxes, the TWA is an appropriate framework for modeling ocean circulation with parameterized eddies. The authors test the feasibility of this proposition and investigate the connections between the TWAmore » framework and the conventional framework used in models, where Eulerian mean flow prognostic variables are solved for. Using the TWA framework as a starting point, this study explores the well-known connections between vertical transfer of horizontal momentum by eddy form drag and eddy overturning by the bolus velocity, used by Greatbatch and Lamb and Gent and McWilliams to parameterize eddies. After implementing the TWA framework in an ocean general circulation model, we verify our analysis by comparing the flows in an idealized Southern Ocean configuration simulated using the TWA and conventional frameworks with the same mesoscale eddy parameterization.« less

  4. The effect of sudden ice sheet melt on ocean circulation and surface climate 14-16 ka

    NASA Astrophysics Data System (ADS)

    Ivanovic, Ruza; Gregoire, Lauren; Wickert, Andrew; Valdes, Paul

    2016-04-01

    Collapse of ice sheets can cause significant sea-level rise and widespread climate change. Around 14.6 thousand years ago, global sea level rose by ˜15 m in less than 350 years[1] during an event known as Meltwater Pulse 1a. Modelling work[2,3] has suggested that approximately half of this ˜50 mm yr‑1 sea level rise came from a North American ice Saddle Collapse that drained into the Arctic and Atlantic Oceans. However, dating uncertainties make it difficult to determine the sequence of events and their drivers, leaving many fundamental questions. For example, did the abrupt ice melting and subsequent ocean freshening have any detectable climatic impact? Was melting from the Northern American ice sheets responsible for the Older-Dryas[4] or other cooling events? And how were all these signals linked to changes in Atlantic Ocean overturning circulation[e.g.5]? To address these questions, we examined the effect of the North American ice Saddle Collapse using a newly developed high resolution network drainage model coupled to an atmosphere-ocean-vegetation General Circulation Model. Here, we present the first quantitative routing estimates of the consequent meltwater discharge and its impact on climate. The results show that approximately 50% of the Saddle Collapse meltwater pulse was routed down the Mackenzie River into the Arctic Ocean, and around half was discharged directly into the Atlantic via the St. Lawrence River. This meltwater flux, equivalent to a total of 7 m of sea-level rise, caused a strong weakening of Atlantic Meridional Overturning Circulation (AMOC) and widespread Northern Hemisphere cooling. The greatest cooling is in the Arctic, but there is also significant warming over North America. We find that AMOC (and climate) is most sensitive to meltwater discharged to the Arctic Ocean. [1] Deschamps et al. (2012) Nature 483, 559-564. [2] Gregoire et al. (2012) Nature 487, 219-222. [3] Gomez et al. (2015) GRL 42(10), 3954-3962. [4] Menviel et al

  5. Response to Comment on "The Atlantic Multidecadal Oscillation without a role for ocean circulation".

    PubMed

    Clement, Amy; Cane, Mark A; Murphy, Lisa N; Bellomo, Katinka; Mauritsen, Thorsten; Stevens, Bjorn

    2016-06-24

    Zhang et al interpret the mixed-layer energy budget in models as showing that "ocean dynamics play a central role in the AMO." Here, we show that their diagnostics cannot reveal the causes of the Atlantic Multidecadal Oscillation (AMO) and that their results can be explained with minimal ocean influence. Hence, we reaffirm our findings that the AMO in models can be understood primarily as the upper-ocean thermal response to stochastic atmospheric forcing. PMID:27339977

  6. Correcting North Atlantic sea surface salinity biases in the Kiel Climate Model: influences on ocean circulation and Atlantic Multidecadal Variability

    NASA Astrophysics Data System (ADS)

    Park, T.; Park, W.; Latif, M.

    2016-01-01

    A long-standing problem in climate models is the large sea surface salinity (SSS) biases in the North Atlantic. In this study, we describe the influences of correcting these SSS biases on the circulation of the North Atlantic as well as on North Atlantic sector mean climate and decadal to multidecadal variability. We performed integrations of the Kiel Climate Model (KCM) with and without applying a freshwater flux correction over the North Atlantic. The quality of simulating the mean circulation of the North Atlantic Ocean, North Atlantic sector mean climate and decadal variability is greatly enhanced in the freshwater flux-corrected integration which, by definition, depicts relatively small North Atlantic SSS biases. In particular, a large reduction in the North Atlantic cold sea surface temperature bias is observed and a more realistic Atlantic Multidecadal Variability simulated. Improvements relative to the non-flux corrected integration also comprise a more realistic representation of deep convection sites, sea ice, gyre circulation and Atlantic Meridional Overturning Circulation. The results suggest that simulations of North Atlantic sector mean climate and decadal variability could strongly benefit from alleviating sea surface salinity biases in the North Atlantic, which may enhance the skill of decadal predictions in that region.

  7. Structure and predictability of the El Nino/Southern Oscillation phenomenon in a coupled ocean-atmosphere general circulation model

    SciTech Connect

    Latif, M.; Sterl, A.; Maier-Reimer, E.; Junge, M.M. )

    1993-04-01

    The space-time structure and predictability of the El Nino/Southern Oscillation (ENSO) phenomenon was investigated. Two comprehensive datasets were analyzed by means of an advanced statistical method, one based on observational data and other on data derived from an extended-range integration performed with a coupled ocean atmosphere general circulation model. It is shown that a considerable portion of the ENSO related low-frequency climate variability in both datasets is associated with a cycle implies the possibility of climate predictions in the tropics up to lead times of about one year. This is shown by conducting an ensemble of predictions with our coupled general circulation model. For the first time a coupled model of this type was successfully applied to ENSO predictions. 34 refs., 6 figs.

  8. Rapid seawater circulation through animal burrows in mangrove forests - A significant source of saline groundwater to the tropical coastal ocean

    NASA Astrophysics Data System (ADS)

    Clark, J. F.; Stieglitz, T. C.; Hancock, G. J.

    2010-12-01

    A common approach for quantifying rates of submarine groundwater discharge (SGD) to the coastal ocean is to use geochemical tracers that are part of the U- and Th-decay chains such as Rn-222 and short lived radium isotopes. These radionuclides are naturally enriched in groundwater relative to seawater and have well understood chemistries within the marine environment. They occur in both fresh (continental) and saline (marine) groundwaters and thus the water source is often ambiguous. Stieglitz (2005, Marine Pollution Bulletin 51, 51-59) has shown that some coastal areas within the Great Barrier Reef (GBR) lagoon (Australia) are enriched in the SGD tracer, Rn-222; he attributed this to four possible processes including the tidal flushing of mangrove forest floors. Here, we present a detailed investigation into the tidal circulation of seawater through animal burrows using Rn-222 and isotopes of radium in the Coral Creek mangrove forest, Hinchinbrook Island, Queensland, Australia. The study was conducted at the end of the dry season in a creek with no freshwater inputs. Significant export of radionuclides and salt from the forest into the creek indicates continuous tidally driven circulation through the burrows. Results demonstrate that the forest sediment is efficiently flushed, with a water flux of about 30 L/m2/ day of forest floor, which is equivalent to flushing about 10% of the total burrow volume per tidal cycle. Annual average circulation flux through mangrove forest floors are of the same order as annual river discharge in the central GBR. However, unlike the river discharge, the tidal circulation should be relatively stable throughout the year. This work documents the importance of animal burrows in maintaining productive sediments in these systems, and illustrates the physical process that supports large exports of organic and inorganic matter from mangrove forests to the coastal zone. It also illustrates the importance of considering saline groundwater

  9. Adaptation of an unstructured-mesh, finite-element ocean model to the simulation of ocean circulation beneath ice shelves

    NASA Astrophysics Data System (ADS)

    Kimura, Satoshi; Candy, Adam S.; Holland, Paul R.; Piggott, Matthew D.; Jenkins, Adrian

    2013-07-01

    Several different classes of ocean model are capable of representing floating glacial ice shelves. We describe the incorporation of ice shelves into Fluidity-ICOM, a nonhydrostatic finite-element ocean model with the capacity to utilize meshes that are unstructured and adaptive in three dimensions. This geometric flexibility offers several advantages over previous approaches. The model represents melting and freezing on all ice-shelf surfaces including vertical faces, treats the ice shelf topography as continuous rather than stepped, and does not require any smoothing of the ice topography or any of the additional parameterisations of the ocean mixed layer used in isopycnal or z-coordinate models. The model can also represent a water column that decreases to zero thickness at the 'grounding line', where the floating ice shelf is joined to its tributary ice streams. The model is applied to idealised ice-shelf geometries in order to demonstrate these capabilities. In these simple experiments, arbitrarily coarsening the mesh outside the ice-shelf cavity has little effect on the ice-shelf melt rate, while the mesh resolution within the cavity is found to be highly influential. Smoothing the vertical ice front results in faster flow along the smoothed ice front, allowing greater exchange with the ocean than in simulations with a realistic ice front. A vanishing water-column thickness at the grounding line has little effect in the simulations studied. We also investigate the response of ice shelf basal melting to variations in deep water temperature in the presence of salt stratification.

  10. Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

    PubMed

    Hogg, Andrew McC; Munday, David R

    2014-07-13

    The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change. PMID:24891390

  11. Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability.

    PubMed

    Hu, Aixue; Meehl, Gerald A; Han, Weiqing; Timmermann, Axel; Otto-Bliesner, Bette; Liu, Zhengyu; Washington, Warren M; Large, William; Abe-Ouchi, Ayako; Kimoto, Masahide; Lambeck, Kurt; Wu, Bingyi

    2012-04-24

    Abrupt climate transitions, known as Dansgaard-Oeschger and Heinrich events, occurred frequently during the last glacial period, specifically from 80-11 thousand years before present, but were nearly absent during interglacial periods and the early stages of glacial periods, when major ice-sheets were still forming. Here we show, with a fully coupled state-of-the-art climate model, that closing the Bering Strait and preventing its throughflow between the Pacific and Arctic Oceans during the glacial period can lead to the emergence of stronger hysteresis behavior of the ocean conveyor belt circulation to create conditions that are conducive to triggering abrupt climate transitions. Hence, it is argued that even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as the Bering Strait remains open. PMID:22493225

  12. What is the skill of ocean tracers in reducing uncertainties about ocean diapycnal mixing and projections of the Atlantic Meridional Overturning Circulation?

    NASA Astrophysics Data System (ADS)

    Goes, Marlos; Urban, Nathan M.; Tonkonojenkov, Roman; Haran, Murali; Schmittner, Andreas; Keller, Klaus

    2010-12-01

    Current projections of the oceanic response to anthropogenic climate forcings are uncertain. Two key sources of these uncertainties are (1) structural errors in current Earth system models and (2) imperfect knowledge of model parameters. Ocean tracer observations have the potential to reduce these uncertainties. Previous studies typically consider each tracer separately, neglect potentially important statistical properties of the system, or use methods that impose rather daunting computational demands. Here we extend and improve upon a recently developed approach using horizontally averaged vertical profiles of chlorofluorocarbon (CFC-11), radiocarbon (Δ14C), and temperature (T) observations to reduce model parametric and structural uncertainties. Our method estimates a joint probability density function, which considers cross-tracer correlations and spatial autocorrelations of the errors. We illustrate this method by estimating two model parameters related to the vertical diffusivity, the background vertical diffusivity, and the upper Southern Ocean mixing. We show that enhancing the upper Southern Ocean mixing in the model improves the representations of ocean tracers and improves the hindcasts of the Atlantic Meridional Overturning Circulation (AMOC). The most probable value of the background vertical diffusivity in the pelagic pycnocline is between 0.1 and 0.2 cm2 s-1. According to the statistical method, observations of Δ14C reduce the uncertainty about the background vertical diffusivity mostly followed by CFC-11 and T. Using all three tracers jointly reduces the model uncertainty by 40%, more than each tracer individually. Given several important caveats, we illustrate how the reduced model parametric uncertainty improves probabilistic projections of the AMOC.

  13. Ocean circulation in the southern Benguela region from the Pliocene to the Pleistocene: tracking Agulhas leakage into the SE Atlantic

    NASA Astrophysics Data System (ADS)

    Petrick, Benjamin; McClymont, Erin; Felder, Sojna; Leng, Melanie

    2013-04-01

    The transition from the warmth of the middle Pliocene to the large amplitude, 100 kyr glacial-interglacial cycles of the late Pleistocene provides a way to understand the forcings and impacts of regional and global climate change. Here, we investigate changes in ocean circulation over the period from 3.5 Ma to present using a marine sediment core, ODP Site 1087 (31o28'S, 15o19'E, 1374m water depth). ODP 1087 is located in the South-east Atlantic Ocean, outside the Benguela upwelling region. Its location allows investigation of the history of the heat and salt transfer to the Atlantic Ocean from the Indian Ocean ("Agulhas leakage"), which plays an important part in the global thermohaline circulation. It is not known how this transfer reacted to generally warmer global temperatures during the mid-Pliocene, nor to the transition to a globally cooler climate in the early Pleistocene. Our approach is to apply several organic geochemistry proxies and foraminiferal analyses to reconstruct the history of ODP 1087. These include the U37K' index to reconstruct sea surface temperatures, pigment analysis for understanding productivity changes, and foraminifera assemblage analysis to detect the presence of different water masses at the site. We have identified changes in SSTs and biological productivity that we argue to reflect shifts in the position of the Benguela upwelling cells, and a changing influence of Agulhas leakage. Our new data reveal a different organization in the Southeast Atlantic. It shows that during the Pliocene ODP 1087 was dominated by Benguela upwelling which had shifted south. We find no evidence for Agulhas leakage during the mid Pliocene, which could mean that Agulhas Leakage was severely reduced during the mid Pliocene. The implications of these results for understanding Plio-Pleistocene climate changes will be explored here.

  14. Hydrothermal circulation in fast spread ocean crust - where and how much? Insight from ODP Hole 1256D

    NASA Astrophysics Data System (ADS)

    Harris, M.; Coggon, R. M.; Smith-Duque, C. E.; Teagle, D. A. H.

    2014-12-01

    Understanding and quantifying hydrothermal circulation is critical to testing models of the accretion of lower ocean crust and quantifying global geochemical cycles. However, our understanding is principally limited by a lack of direct observations from intact ocean crust. Key questions remain about the magnitude of hydrothermal fluid fluxes, the nature and distribution of fluid pathways and their global variability. ODP Hole 1256D in the eastern equatorial Pacific samples a complete section of 15 Myr old upper ocean crust down to the dike/gabbro transition zone. A high spatial resolution Sr isotope profile is integrated with wireline studies, volcanostratigraphy, petrography and mineral geochemistry to document fluid pathways and develop a model for the evolving hydrothermal system during volcanic construction of the crust. Major off-axis fluid conduits in the volcanic sequence are restricted to the flow margins of two anomalously thick (>25 m) massive flows, indicating that massive flows act as a permeability barrier for fluid flow. Dike margins are pathways for both recharge and discharge hydrothermal fluids. Sub-horizontal channeling of high temperature fluids at the dike/gabbro boundary is a common attribute of most cartoons of mid ocean ridge hydrothermal systems. Hole 1256D provides the first in situ observations of the dike/gabbro transition zone and records lateral fluid transport along intrusive boundaries. The time-integrated fluid flux in the sheeted dikes of Hole 1256D calculated using Sr isotope mass balance is ~1.8 x 106 kg/m2. This is similar to fluid fluxes from other studies (Hole 504B, Pito Deep, Hess Deep) despite large variations in the thickness and Sr isotope profiles of the sheeted dike complexes, suggesting that hydrothermal fluid fluxes are remarkably uniform and independent of the local structure of the crust. This fluid flux is not large enough to completely remove the heat flux from crystallizing and cooling the lower crust and requires

  15. Detection of the Earth rotation response to a rapid fluctuation of Southern Ocean circulation in November 2009

    NASA Astrophysics Data System (ADS)

    Marcus, S. L.; Dickey, J. O.; Fukumori, I.; de Viron, O.

    2012-02-01

    At seasonal and shorter periods the solid Earth and its overlying geophysical fluids form a closed dynamical system, which (except for tidal forcing) conserves its total angular momentum. While atmospheric effects dominate changes in the Earth's rate of rotation and hence length-of-day (LOD) on these time scales, the addition of oceanic angular momentum (OAM) estimates has been shown to improve closure of the LOD budget in a statistical sense. Here we demonstrate, for the first time, the signature of a specific, sub-monthly ocean current fluctuation on the Earth's rotation rate, coinciding with recently-reported anomalies which developed in southeast Pacific surface temperature and bottom pressure fields during late 2009. Our results show that concurrent variations in the Antarctic Circumpolar Current (ACC), which saw a sharp drop and recovery in zonal transport during a two-week period in November, were strong enough to cause a detectable change in LOD following the removal of atmospheric angular momentum (AAM) computed from the Modern Era Retrospective Analysis for Research and Applications (MERRA) database. The strong OAM variations driving the LOD-AAM changes were diagnosed from ocean state estimates of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO) and involved roughly equal contributions from the current and pressure terms, with in situ confirmation for the latter provided by tide-corrected bottom pressure recorder data from the South Drake Passage site of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements (ACCLAIM) network.

  16. Modeling evidences for global warming, Arctic seawater freshening, and sluggish oceanic circulation during the Early Toarcian anoxic event

    NASA Astrophysics Data System (ADS)

    Dera, Guillaume; Donnadieu, Yannick

    2012-06-01

    The paleoecological disturbances recorded during the Early Toarcian warming event (183 Myr ago), including marine anoxia, sea level rise, seawater acidification, carbonate production crisis, and species extinctions, are often regarded as past examples of Earth's possible responses to the rapid emergence of super greenhouse conditions. However, physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated. Here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pCO2 levels at a multiscale resolution using a fully coupled ocean-atmosphere model (FOAM). We show that, in association with stronger high-latitude precipitation rates and enhanced continental runoff, the demise of polar sea ice due to the global warming event involved a regional freshening of Arctic surface seawaters. These disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins. In agreement with very negative oxygen isotope values measured on fossil shells from the NW Tethys, our simulations also show that recurrent discharges of brackish and nutrient-rich Arctic surface waters through the Viking Corridor could have led to both vertical and geographical gradients in salinity and seawater δ18O in the NW Tethyan seas. Locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted Euro-boreal domains, as it has been previously suggested and modeled regionally.

  17. Marine 187Os/188Os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during Oceanic Anoxic Event 2

    NASA Astrophysics Data System (ADS)

    Du Vivier, Alice D. C.; Selby, David; Sageman, Bradley B.; Jarvis, Ian; Gröcke, Darren R.; Voigt, Silke

    2014-03-01

    High-resolution osmium (Os) isotope stratigraphy across the Cenomanian-Turonian Boundary Interval from 6 sections for four transcontinental settings has produced a record of seawater chemistry that demonstrates regional variability as a function of terrestrial and hydrothermal inputs, revealing the impact of palaeoenvironmental processes. In every section the 187Os/188Os profiles show a comparable trend; radiogenic values in the lead up to Oceanic Anoxic Event 2 (OAE 2); an abrupt unradiogenic trend at the onset of OAE 2; an unradiogenic interval during the first part of OAE 2; and a return to radiogenic values towards the end of the event, above the Cenomanian-Turonian boundary. The unradiogenic trend in 187Os/188Os is synchronous in all sections. Previous work suggests that activity of the Caribbean LIP (Large Igneous Province) was the source of unradiogenic Os across the OAE 2 and possibly an instigator of anoxia in the oceans. Here we assess this hypothesis and consider the influence of activity from other LIPs; such as the High Arctic LIP. A brief shift to high radiogenic 187Os/188Os values occurred in the Western Interior Seaway before the onset of OAE 2. We evaluate this trend and suggest that a combination of factors collectively played critical roles in the initiation of OAE 2; differential input of nutrients from continental and volcanogenic sources, coupled with efficient palaeocirculation of the global ocean and epeiric seas, enhanced productivity due to higher nutrient availability, which permitted penecontemporaneous transport of continental and LIP-derived nutrients to trans-equatorial basins.

  18. Anthropogenic CO2 uptake, transport, storage, and dynamical controls in the ocean imposed by the meridional overturning circulation: A modeling study

    NASA Astrophysics Data System (ADS)

    Nakano, H.; Ishii, M.; Rodgers, K. B.; Tsujino, H.; Yamanaka, G.

    2015-10-01

    Using an ocean carbon cycle model embedded in an ocean general circulation model, we examine how the budget of anthropogenic CO2 (Cant) is controlled by ocean dynamics. To complement recent studies showing only vertically integrated budgets, we provide a step-by-step description by making use of three different coarse grainings of the full vertical resolution of the ocean model in our budget analysis. For the 11 subdomains of the global ocean, these coarse grainings are (1) a one-layer (vertically integrated) budget, (2) a three-layer budget, and (3) an 11-layer budget. We largely focus on the Pacific circulation. We identify and quantify substantial carbon transport associated with the subtropical cells (STCs), which are dominant contributors to the meridional overturning circulation in the upper ocean in the tropics and subtropics, as playing a fundamental role in governing the ocean interior distribution of Cant. The upper branch of the STCs transports Cant-rich water from the tropics to the subtropics, contributing to the precondition for the high Cant inventory in mode waters. The lower branch of the STCs carries about two thirds of the transported Cant back to the tropics, while it largely excludes Subtropical Mode Waters. This work implies that the reemergence of Cant through recirculation within the STCs may lead to a reduced capacity for further Cant uptake via gas exchange into the surface ocean, potentially contributing to a positive carbon-climate feedback.

  19. Changes in erosion and ocean circulation recorded in the Hf isotopic compositions of North Atlantic and Indian Ocean ferromanganese crusts

    USGS Publications Warehouse

    Piotrowski, Alexander M.; Lee, Der-Chuen; Christensen, John N.; Burton, Kevin W.; Halliday, Alex N.; Hein, James R.; Günther, Detlef

    2000-01-01

    High-resolution Hf isotopic records are presented for hydrogenetic Fe–Mn crusts from the North Atlantic and Indian Oceans. BM1969 from the western North Atlantic has previously been shown to record systematically decreasing Nd isotopic compositions from about 60 to ∼4 Ma, at which time both show a rapid decrease to unradiogenic Nd composition, thought to be related to the increasing influence of NADW or glaciation in the northern hemisphere. During the Oligocene, North Atlantic Hf became progressively less radiogenic until in the mid-Miocene (∼15 Ma) it reached +1. It then shifted gradually back to an ϵHf value of +3 at 4 Ma, since when it has decreased rapidly to about −1 at the present day. The observed shifts in the Hf isotopic composition were probably caused by variation in intensity of erosion as glaciation progressed in the northern hemisphere. Ferromanganese crusts SS663 and 109D are from about 5500 m depth in the Indian Ocean and are now separated by ∼2300 km across the Mid-Indian Ridge. They display similar trends in Hf isotopic composition from 20 to 5 Ma, with the more northern crust having a composition that is consistently more radiogenic (by ∼2 ϵHf units). Paradoxically, during the last 20 Ma the Hf isotopic compositions of the two crusts have converged despite increased separation and subsidence relative to the ridge. A correlatable negative excursion at ∼5 Ma in the two records may reflect a short-term increase in erosion caused by the activation of the Himalayan main central thrust. Changes to unradiogenic Hf in the central Indian Ocean after 5 Ma may alternatively have been caused by the expanding influence of NADW into the Mid-Indian Basin via circum-Antarctic deep water or a reduction of Pacific flow through the Indonesian gateway. In either case, these results illustrate the utility of the Hf isotope system as a tracer of paleoceanographic changes, capable of responding to subtle changes in erosional regime not readily resolved

  20. Combination of TOPEX/POSEIDON Data with a Hydrographic Inversion for Determination of the Oceanic General Circulation and its Relation to Geoid Accuracy

    NASA Technical Reports Server (NTRS)

    Ganachaud, Alexandre; Wunsch, Carl; Kim, Myung-Chan; Tapley, Byron

    1997-01-01

    A global estimate of the absolute oceanic general circulation from a geostrophic inversion of in situ hydrographic data is tested against and then combined with an estimate obtained from TOPEX/POSEIDON altimetric data and a geoid model computed using the JGM-3 gravity-field solution. Within the quantitative uncertainties of both the hydrographic inversion and the geoid estimate, the two estimates derived by very different methods are consistent. When the in situ inversion is combined with the altimetry/geoid scheme using a recursive inverse procedure, a new solution, fully consistent with both hydrography and altimetry, is found. There is, however, little reduction in the uncertainties of the calculated ocean circulation and its mass and heat fluxes because the best available geoid estimate remains noisy relative to the purely oceanographic inferences. The conclusion drawn from this is that the comparatively large errors present in the existing geoid models now limit the ability of satellite altimeter data to improve directly the general ocean circulation models derived from in situ measurements. Because improvements in the geoid could be realized through a dedicated spaceborne gravity recovery mission, the impact of hypothetical much better, future geoid estimates on the circulation uncertainty is also quantified, showing significant hypothetical reductions in the uncertainties of oceanic transport calculations. Full ocean general circulation models could better exploit both existing oceanographic data and future gravity-mission data, but their present use is severely limited by the inability to quantify their error budgets.

  1. Observations of subtidal circulation variability in Sermilik Fjord, Greenland, and its impact on ice-ocean interactions

    NASA Astrophysics Data System (ADS)

    Sutherland, D. A.; Stearns, L. A.; Hamilton, G. S.; Straneo, F.

    2010-12-01

    Helheim Glacier, located in southeast Greenland, is a large outlet glacier that drains approximately 10% of the Greenland Ice Sheet (GIS), emptying into Sermilik Fjord. The glacier speed and terminus location have both shown large variability over the past decade, with significant impacts on the freshwater and heat transport within the fjord, as well as on the mass balance of the GIS. Yet the cause for these changes is still debated. Here we present full year time series of velocity and hydrographic observations collected in Sermilik Fjord over 2009-2010, focusing on linking ice-ocean processes directly. The velocity data show that tidal circulation is small inside Sermilik Fjord, with the dominant variability at subtidal timescales. This allows for a more complete description of the fjord circulation than has been possible from inferring the flow from hydrography alone. We then relate the circulation in the fjord to processes directly related to the glacier, including the timing of calving events and iceberg drift. Map of Sermilik Fjord showing the location of field observations made in 2009-2010.

  2. Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y

    PubMed Central

    Lachniet, Matthew S.; Asmerom, Yemane; Bernal, Juan Pablo; Polyak, Victor J.; Vazquez-Selem, Lorenzo

    2013-01-01

    The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18–24 cal ka B.P.) monsoon with similar δ18O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9–11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka. PMID:23690596

  3. Coupling of wave and circulation models in coastal-ocean predicting systems: A case study for the German Bight

    NASA Astrophysics Data System (ADS)

    Staneva, Joanna; Wahle, Kathrin

    2015-04-01

    This study addresses the coupling between wind wave and circulation models on the example of the German Bight and its coastal area called the Wadden Sea (the area between the barrier islands and the coast). This topic reflects the increased interest in operational oceanography to reduce prediction errors of state estimates at coastal scales. The uncertainties in most of the presently used models result from the nonlinear feedback between strong tidal currents and wind-waves, which can no longer be ignored, in particular in the coastal zone where its role seems to be dominant. A nested modelling system is used in the Helmholtz-Zentrum Geesthacht to producing reliable now- and short-term forecasts of ocean state variables, including wind waves and hydrodynamics. In this study we present analysis of wave and hydrographic observations, as well as the results of numerical simulations. The data base includes ADCP observations and continuous measurements from data stations. The individual and collective role of wind, waves and tidal forcing are quantified. The performance of the forecasting system is illustrated for the cases of several extreme events. Effects of ocean waves on coastal circulation and SST simulations are investigated considering wave-dependent stress and wave breaking parameterization during extreme events, e.g. hurricane Xavier in December, 2013. Also the effect which the circulation exerts on the wind waves is tested for the coastal areas using different parameterizations. The improved skill resulting from the new developments in the forecasting system, in particular during extreme events, justifies further enhancements of the coastal pre-operational system for the North Sea and German Bight.

  4. Orbital pacing and ocean circulation-induced collapses of the Mesoamerican monsoon over the past 22,000 y.

    PubMed

    Lachniet, Matthew S; Asmerom, Yemane; Bernal, Juan Pablo; Polyak, Victor J; Vazquez-Selem, Lorenzo

    2013-06-01

    The dominant controls on global paleomonsoon strength include summer insolation driven by precession cycles, ocean circulation through its influence on atmospheric circulation, and sea-surface temperatures. However, few records from the summer North American Monsoon system are available to test for a synchronous response with other global monsoons to shared forcings. In particular, the monsoon response to widespread atmospheric reorganizations associated with disruptions of the Atlantic Meridional Overturning Circulation (AMOC) during the deglacial period remains unconstrained. Here, we present a high-resolution and radiometrically dated monsoon rainfall reconstruction over the past 22,000 y from speleothems of tropical southwestern Mexico. The data document an active Last Glacial Maximum (18-24 cal ka B.P.) monsoon with similar δ(18)O values to the modern, and that the monsoon collapsed during periods of weakened AMOC during Heinrich stadial 1 (ca. 17 ka) and the Younger Dryas (12.9-11.5 ka). The Holocene was marked by a trend to a weaker monsoon that was paced by orbital insolation. We conclude that the Mesoamerican monsoon responded in concert with other global monsoon regions, and that monsoon strength was driven by variations in the strength and latitudinal position of the Intertropical Convergence Zone, which was forced by AMOC variations in the North Atlantic Ocean. The surprising observation of an active Last Glacial Maximum monsoon is attributed to an active but shallow AMOC and proximity to the Intertropical Convergence Zone. The emergence of agriculture in southwestern Mexico was likely only possible after monsoon strengthening in the Early Holocene at ca. 11 ka. PMID:23690596

  5. Carbon-nitrogen interactions regulate climate-carbon cycle feedbacks: results from an atmosphere-ocean general circulation model

    SciTech Connect

    Thornton, Peter E; Doney, Scott C.; Lindsay, Keith; Moore, Jefferson Keith; Mahowald, Natalie; Randerson, James T; Fung, Inez; Lamarque, Jean-Francois H; Feddema, Johan J.

    2009-01-01

    Inclusion of fundamental ecological interactions between carbon and nitrogen cycles in the land component of an atmosphere-ocean general circulation model (AOGCM) leads to decreased carbon uptake associated with CO{sub 2} fertilization, and increased carbon uptake associated with warming of the climate system. The balance of these two opposing effects is to reduce the fraction of anthropogenic CO{sub 2} predicted to be sequestered in land ecosystems. The primary mechanism responsible for increased land carbon storage under radiatively forced climate change is shown to be fertilization of plant growth by increased mineralization of nitrogen directly associated with increased decomposition of soil organic matter under a warming climate, which in this particular model results in a negative gain for the climate-carbon feedback. Estimates for the land and ocean sink fractions of recent anthropogenic emissions are individually within the range of observational estimates, but the combined land plus ocean sink fractions produce an airborne fraction which is too high compared to observations. This bias is likely due in part to an underestimation of the ocean sink fraction. Our results show a significant growth in the airborne fraction of anthropogenic CO{sub 2} emissions over the coming century, attributable in part to a steady decline in the ocean sink fraction. Comparison to experimental studies on the fate of radio-labeled nitrogen tracers in temperate forests indicates that the model representation of competition between plants and microbes for new mineral nitrogen resources is reasonable. Our results suggest a weaker dependence of net land carbon flux on soil moisture changes in tropical regions, and a stronger positive growth response to warming in those regions, than predicted by a similar AOGCM implemented without land carbon-nitrogen interactions. We expect that the between-model uncertainty in predictions of future atmospheric CO{sub 2} concentration and

  6. Eddy-resolving simulations of the Fimbul Ice Shelf cavity circulation: Basal melting and exchange with open ocean

    NASA Astrophysics Data System (ADS)

    Hattermann, T.; Smedsrud, L. H.; Nøst, O. A.; Lilly, J. M.; Galton-Fenzi, B. K.

    2014-10-01

    Melting at the base of floating ice shelves is a dominant term in the overall Antarctic mass budget. This study applies a high-resolution regional ice shelf/ocean model, constrained by observations, to (i) quantify present basal mass loss at the Fimbul Ice Shelf (FIS); and (ii) investigate the oceanic mechanisms that govern the heat supply to ice shelves in the Eastern Weddell Sea. The simulations confirm the low melt rates suggested by observations and show that melting is primarily determined by the depth of the coastal thermocline, regulating deep ocean heat fluxes towards the ice. Furthermore, the uneven distribution of ice shelf area at different depths modulates the melting response to oceanic forcing, causing the existence of two distinct states of melting at the FIS. In the simulated present-day state, only small amounts of Modified Warm Deep Water enter the continental shelf, and ocean temperatures beneath the ice are close to the surface freezing point. The basal mass loss in this so-called state of “shallow melting” is mainly controlled by the seasonal inflow of solar-heated surface water affecting large areas of shallow ice in the upper part of the cavity. This is in contrast to a state of “deep melting”, in which the thermocline rises above the shelf break depth, establishing a continuous inflow of Warm Deep Water towards the deep ice. The transition between the two states is found to be determined by a complex response of the Antarctic Slope Front overturning circulation to varying climate forcings. A proper representation of these frontal dynamics in climate models will therefore be crucial when assessing the evolution of ice shelf basal melting along this sector of Antarctica.

  7. Modelling twentieth century global ocean circulation and iceberg flux at 48°N: implications for west Greenland iceberg discharge

    NASA Astrophysics Data System (ADS)

    Wilton, David J.; Bigg, Grant R.; Hanna, Edward

    2015-11-01

    We have used a coupled ocean-iceberg model to study the variation in global ocean circulation and North Atlantic iceberg flux from 1900 to 2008. The latter component of the study focused particularly on Greenland icebergs feeding into the Labrador Current and past Newfoundland. The model was forced with daily heat, freshwater and wind fluxes from the Twentieth Century Reanalysis. The reanalysis heat fluxes were shown to be offset from the, shorter, NCEP reanalysis and a grid-point correction was applied to this component of the forcing. The model produces a generally realistic ocean circulation, although with an enhanced Atlantic Meridional Overturning largely due to the forcing. The modelled iceberg flux at 48°N is well correlated with the long-term observed flux when using a modelled iceberg discharge that varies in a similar fashion to the highly variable observed flux at 48°N. From this model we infer changes in the spatial and temporal variability of iceberg calving from western Greenland. During the first third of the twentieth century the majority of modelled icebergs reaching 48°N derive from southern Greenland, while only after 1930 is the traditional perspective of a majority of such icebergs originating from Baffin Bay consistent with model results. Decadal-scale changes in the dominant regional sources are found, with oscillations between western Greenland and northern Baffin Bay. The latter origin was modelled to be most important in the last third of the twentieth century, although west Greenland sources have increased in importance in recent years. The model correctly reproduces the pronounced late spring peak in flux at 48°N for southern Greenland icebergs, but has an approximately six month offset for icebergs from Baffin Bay, most likely due to resolution issues leading to model icebergs not being delayed in shallow coastal waters, whereas in reality they may be grounded for some time or trapped in coastal sea-ice.

  8. Impact of assimilating surface salinity from SMOS on ocean circulation estimates

    NASA Astrophysics Data System (ADS)

    Köhl, A.; Sena Martins, M.; Stammer, D.

    2014-08-01

    In a pilot attempt, the GECCO2 synthesis system is being used to investigate the impact of SMOS sea surface salinity (SSS) observations on estimates of SSS and freshwater fluxes. The paper focuses on the period 2010-2011, during which, in addition to traditional in situ and satellite observations, SMOS SSS is assimilated. A prior SMOS SSS error field is inferred through a comparison of the satellite data with in situ salinity data and reveals large biases (>1 g/kg) in the SMOS product near continents and in the Southern Ocean. Employing this error estimate in the assimilation procedure leads only to an insignificant impact of SMOS SSS on the estimated ocean state. However, when reducing the error artificially by a factor of 10, the SMOS data can be reproduced well in the interior ocean. In this case, the previously remaining positive model bias with respect to in situ salinity is changed to a negative bias while the misfit slightly increased. The clear freshening can be attributed to the SMOS bias with respect to in situ data. The associated increase in freshwater input in the tropical oceans enhances slightly the correspondence of the estimated fluxes to the independent satellite-based estimate from HOAPS except for the South Pacific and South Atlantic. On short-timescales, changes in the estimated surface salinity result primarily from changes in surface freshwater fluxes, while over longer periods ocean dynamics become increasingly more important for changing the near-surface salinity.

  9. Sensitivity of near-inertial internal waves to spatial interpolations of wind stress in ocean generation circulation models

    NASA Astrophysics Data System (ADS)

    Jing, Zhao; Wu, Lixin; Ma, Xiaohui

    2016-03-01

    The oceanic near-inertial internal waves (NIWs) have been extensively studied using ocean general circulation models (OGCMs). Currently most OGCMs use the bilinear or bicubic interpolation to interpolate wind stress onto models' surface grids. In this study, we examine the influences of bilinear and bicubic interpolations on the wavenumber and frequency spectra of wind stress and on the simulated NIWs in the ocean. It is demonstrated that both the bilinear and bicubic interpolations are equivalent to spatial low-pass filters with the former leading to more significant loss of wind stress variance at high wavenumbers. When coarse (e.g., 2°) wind stress is used to force OGCMs, the bilinear and bicubic interpolations significantly damp the wavenumber spectrum of wind stress at mesoscales, leading to decreased near-inertial wind stress variance. Using the bilinear (bicubic) interpolation could weaken the near-inertial wind work by ∼43% (22%) in the subtropical region (10°N-30°N) and by ∼16% (4%) at the midlatitudes (30°N-50°N). We propose a new interpolation method, i.e., the bi-sinc-function interpolation, which is able to retain all the wind stress variance within the Nyquist wavenumber. Compared to the bilinear and bicubic interpolations, the bi-sinc-function interpolation improves the simulations of NIWs and should be incorporated into OGCMs especially when coarse wind stress is used.

  10. Influence of the Central American Seaway and Drake Passage on ocean circulation and neodymium isotopes: A model study

    NASA Astrophysics Data System (ADS)

    Pfister, Patrik L.; Stocker, Thomas F.; Rempfer, Johannes; Ritz, Stefan P.

    2014-12-01

    The sensitivity of the neodymium isotopic composition (ɛNd) to tectonic rearrangements of seaways is investigated using an Earth System Model of Intermediate Complexity. The shoaling and closure of the Central American Seaway (CAS) is simulated, as well as the opening and deepening of Drake Passage (DP). Multiple series of equilibrium simulations with various intermediate depths are performed for both seaways, providing insight into ɛNd and circulation responses to progressive throughflow evolutions. Furthermore, the sensitivity of these responses to the Atlantic Meridional Overturning Circulation (AMOC) and the neodymium boundary source is examined. Modeled ɛNd changes are compared to sediment core and ferromanganese (Fe-Mn) crust data. The model results indicate that the North Atlantic ɛNd response to the CAS shoaling is highly dependent on the AMOC state, i.e., on the AMOC strength before the shoaling to shallow depths (preclosure). Three scenarios based on different AMOC forcings are discussed, of which the model-data agreement favors a shallow preclosure (Miocene) AMOC (˜6 Sv). The DP opening causes a rather complex circulation response, resulting in an initial South Atlantic ɛNd decrease preceding a larger increase. This feature may be specific to our model setup, which induces a vigorous CAS throughflow that is strongly anticorrelated to the DP throughflow. In freshwater experiments following the DP deepening, ODP Site 1090 is mainly influenced by AMOC and DP throughflow changes, while ODP Site 689 is more strongly influenced by Southern Ocean Meridional Overturning Circulation and CAS throughflow changes. The boundary source uncertainty is largest for shallow seaways and at shallow sites.

  11. Pliocene (3.2-2.4 Ma) ostracode faunal cycles and deep ocean circulation, North Atlantic Ocean

    USGS Publications Warehouse

    Cronin, T. M.; Raymo, M.E.; Kyle, K.P.

    1996-01-01

    Ostracode assemblages from Deep Sea Drilling Project Sites 607 (western Mid-Atlantic Ridge) and 610 (southeast Rockall Plateau) show rapid, systematic shifts during late Pliocene glacial-interglacial cycles that reflect deep-sea environmental change. Progressive decreases in North Atlantic deep-water taxa and increases in Southern Ocean taxa occur from 3.4 to 2.4 Ma, and high-amplitude faunal cycles begin near 2.8 Ma. Four ostracode assemblages, each with a characteristic phase relative to 41 k.y. obliquity glacial-interglacial ??18O cycles, characterize the benthic faunal record at Site 607. Cross-spectral analysis shows that the Site 607 glacial assemblage has a 41 k.y. periodicity significant at the 95% level; other assemblages show a less significant, but still obvious, concentration of variance at 41 k.y. Faunal patterns suggest climatically controlled reorganization of deep-sea benthic communities during glacial-interglacial cycles due to oscillating deep-sea environments.

  12. Equator-to-Pole and Ocean-Land Temperature Gradients in CMIP5 models and their Relation to Midlatitude Atmospheric Circulation

    NASA Astrophysics Data System (ADS)

    Karamperidou, C.; Booth, J. F.; Lall, U.

    2013-12-01

    Zonal and meridional surface temperature gradients are associated with mean zonal circulation and storm-track variability. We investigate the projected changes in the equator-to-pole gradient and the ocean-land contrast in the suite of models participating in the Coupled Model Intercomparison Project 5 (CMIP5). The projected decrease in the gradients is in accordance with the poleward amplification of temperature increases and the faster warming of land compared to the ocean. However, we note differences in the projections between the Northern and the Southern Hemisphere, and among ocean basins in the Northern Hemisphere, that are indicative of competing mechanisms that underlie the projected shifts in the mean zonal circulation and storm tracks. As an additional indicator of the position and strength of midlatitude mean and transient atmospheric circulation, as well as the expansion of the tropics, we study the projected changes in the latitude of maximum meridional surface temperature gradient.

  13. Natural variability of the climate as predicted by a simple ocean model with parameterized thermohaline circulation

    SciTech Connect

    Watts, R.G.; Li, S.

    1995-12-31

    Variability of the Earth`s climate can take place on many time scales as a result of internal features. This natural variability is important to humans since it affects such important human enterprises as agriculture, floods, droughts, etc. The authors investigate natural variability within a simple ocean model.

  14. Derivation of revised formulae for eddy viscous forces used in the ocean general circulation model

    NASA Technical Reports Server (NTRS)

    Chou, Ru Ling

    1988-01-01

    Presented is a re-derivation of the eddy viscous dissipation tensor commonly used in present oceanographic general circulation models. When isotropy is imposed, the currently-used form of the tensor fails to return to the laplacian operator. In this paper, the source of this error is identified in a consistent derivation of the tensor in both rectangular and earth spherical coordinates, and the correct form of the eddy viscous tensor is presented.

  15. Inter-comparison of the mean circulation in the Coral and Solomon Sea simulated by high resolution ocean models

    NASA Astrophysics Data System (ADS)

    Maes, C.; Durand, F.; Gasparin, F.; Melet, A.; Ganachaud, A.

    2010-12-01

    Of primary importance to the properties of water masses transported by the northern limb of the South Pacific subtropical gyre toward the equatorial band, the transfer within the Coral and, ultimately, the Solomon Sea is perturbed by the labyrinthine topography of the region. It results in highly energetic currents and complex pathways through the Vanuatu Archipelago and New Caledonia, at the entrance of the Coral Sea, and through the Solomon Sea once the flow has bifurcated northward along the coasts of Australia and of the Louisiade Archipelago of Papua New Guinea. In the Coral Sea, the existence of the North Vanuatu Jet and North Caledonian Jet is now well established but their variations as well as their detailed characteristics, including for instance their vertical extension, remain largely unknown. In this study, recourse to ocean simulations is made in order to highlight the representation of such complex circulation of the south western Pacific Ocean and to analyze the long term variability and physical mechanism implied in the jet dynamics. A brief overview of recent observations collected through the comprehensive observational SPICE program (CLIVAR/WCRP) will first be presented in order to set the context. Then, 6 different state-of-the-art numerical experiments with high horizontal resolution, ranging from 1/10 to 1/12 degree, and realistic topography regionally focused on the Coral and Solomon Sea or extracted from global experiments, are analyzed. Here, we will consider OGCMs forced by realistic and observed atmospheric fields but each model has its own strategy in terms of diffusion, topography representation and boundaries condition when appropriate. The focus is set primarily on the annual mean circulation of the upper ocean layers (above the 1000-m depth) and on the water mass transports simulated in the vicinity of the various topographic obstacles. The results will underline that most of high resolution numerical models have reached a high

  16. Open oceanic productivity changes at mid-latitudes during interglacials and its relation to the Atlantic Meridional Overturning Circulation

    NASA Astrophysics Data System (ADS)

    Nave, Silvia; Lebreiro, S.; Kissel, C.; Guihou, A.; Figueiredo, M. O.; Silva, T. P.; Michel, E.; Cortijo, E.; Labeyrie, L.; Voelker, A.

    2010-05-01

    Variations in the interactions between marine ecosystems, thermohaline circulation, external forcing and atmospheric greenhouse gases concentrations are not yet fully represented in detailed models of the glacial-interglacial transitions. Most of the research on past productivity changes has been focused so far on high-productivity areas such as upwelling areas (i.e. equatorial or coastal upwelling areas) even though those regions appraise only a little part of the ocean. Accordingly, the importance of oceanic productivity changes over glacial/interglacial cycles should be better known, as it may also play an important role on the loss of photosynthetically generated carbon as a central mechanism in the global carbon cycle. Its understanding will help quantifying the parameters needed to run comprehensive climate models, and subsequently help to better predict climate change for the near future. A high-resolution study of oceanic productivity, bottom water flow speed, surface and deep-water mass, bottom water ventilation, and terrestrial input changes during two interglacials (Holocene and Marine Isotope Stage [MIS] 5), at an open ocean site approximately 300 km west off Portugal [IMAGES core MD01-2446: 39°03'N, 12°37'W, 3547 m water depth] was conducted within the AMOCINT project (ESF-EUROCORES programme, 06-EuroMARC-FP-008). Even though siliceous productivity is expectedly low for oceanic regions, it shows a robust and consistent pattern with increased values during cold phases of MIS 5, and during the glacial stages 4 and 6 suggesting higher nutrient availability, during these periods. The same pattern is observed for MIS2 and the last deglaciation. The opal record is fully supported by the organic carbon content and to the estimated productivity using foraminifera based FA20 and SIMMAX.28 transfer functions for a near location. The benthic δ13C record suggests less North Atlantic Deep Water (NADW) coincident with periods of higher productivity. The grain

  17. Numerical simulation of 137Cs and (239,240)Pu concentrations by an ocean general circulation model.

    PubMed

    Tsumune, Daisuke; Aoyama, Michio; Hirose, Katsumi

    2003-01-01

    We simulated the spatial distributions and the temporal variations of 137Cs and (239,240)Pu concentrations in the ocean by using the ocean general circulation model which was developed by National Center of Atmospheric Research. These nuclides are introduced into seawaters from global fallout due to atmospheric nuclear weapons tests. The distribution of radioactive deposition on the world ocean is estimated from global precipitation data and observed values of annual deposition of radionuclides at the Meteorological Research Institute in Japan and several observed points in New Zealand. Radionuclides from global fallout have been transported by advection, diffusion and scavenging, and this concentration reduces by radioactive decay in the ocean. We verified the results of the model calculations by comparing simulated values of 137Cs and (239,240)Pu in seawater with the observed values included in the Historical Artificial Radionuclides in the HAM database, which has been constructed by the Meteorological Research Institute. The vertical distributions of the calculated 137Cs concentrations were in good agreement and are in good agreement with the observed profiles in the 1960s up to 250 m, in the 1970s up to 500 m, in the 1980s up to 750 m and in the 1990s up to 750 m. However, the calculated 137Cs concentrations were underestimated compared with the observed 137Cs at the deeper layer. This may suggest other transport processes of 137Cs to deep waters. The horizontal distributions of 137Cs concentrations in surface water could be simulated. A numerical tracer release experiment was performed to explain the horizontal distribution pattern. A maximum (239,240)Pu concentration layer occurs at an intermediate depth for both observed and calculated values, which is formed by particle scavenging. The horizontal distributions of the calculated (239,240)Pu concentrations in surface water could be simulated by considering the scavenging effect. PMID:12860090

  18. The impact of ozone depleting substances on the circulation, temperature, and salinity of the Southern Ocean: An attribution study with CESM1(WACCM)

    NASA Astrophysics Data System (ADS)

    Solomon, A.; Polvani, L. M.; Smith, K. L.; Abernathey, R. P.

    2015-07-01

    Observations show robust changes in the circulation, temperature, and salinity of the Southern Ocean in recent decades. To what extent these changes are related to the formation of the ozone hole in the late twentieth century is an open question. Using a comprehensive chemistry-climate Earth system model, we contrast model runs with varying and with fixed surface concentrations of ozone depleting substances (ODS) from 1955 to 2005. In our model, ODS cause the majority of the summertime changes in surface wind stress which, in turn, induce a clear poleward shift of the ocean's meridional overturning circulation. In addition, more than 30% of the model changes in the temperature and salinity of the Southern Ocean are caused by ODS. These findings offer unambiguous evidence that increased concentrations of ODS in the late twentieth century are likely to have been been an important driver of changes in the Southern Ocean.

  19. Data Organization and I/O in a Parallel Ocean Circulation Model

    SciTech Connect

    Ding, Chris H.Q.; He, Yun

    1999-05-01

    We describe an efficient and scalable parallel I/0 strategy for writing out gigabytes of data generated hourly in the ocean model simulations on massively parallel distributed-memory architectures. Working with Modular Ocean Model, using net CIF file system? and implemented on Cray T3E, the strategy speedup I/0 by a factor of 50 in the sequential case. In parallel case, on 8 PEs up to 256 PEs, our implementation writes out most model dynamic fields of about 1GB to a single netCDF file in 65 seconds, independent of the number of processors. The remap-and-write parallel strategy resolves the memory limitation problem and requires minimal collective I/0 capability of the file system. Several critical optimization on memory management and file access are carried out which ensure this scalability and also speedup the numerical simulation due to improved memory management.

  20. Circumpolar Circulation Patterns Over the Northern Hemisphere Oceans in Late Winter, 1949-2002.

    NASA Technical Reports Server (NTRS)

    Otterman, J.; Starr, D. OC.; Atlas, R.; Jusem, J. C.; Saaroni, H.

    2003-01-01

    To assess interannual changes in ocean-to-land advection, we extract zonal winds for February and March, 1949-2002, from NCEP/NCAR Reanalysis. Winds are analyzed at pairs of locations (55 deg N and 35 deg N) in the N. Pacific (15 deg W), N. Atlantic (30 deg W) and Baltic/Mediterranean (30 deg E). The monthly means at the northern and southern sites are negatively correlated. For N. Pacific, winds at 55 deg N show negative trends at all levels (magnitude increasing with altitude), versus positive at 35 deg N. An opposite scenario is observed over N. Atlantic, positive (negative) trends at 55 deg N (35 deg N) and similarly, but weaker, over the Baltic/Mediterranean. The geographic variability of trends is attributed to displacement of the polar vortex wave pattern. Increasing storm strength/frequency over N. Hemisphere oceans is inherently related to the strong positive trends in wind speed and vertical shear.

  1. The role of mesoscale tracer transports in the global ocean circulation

    SciTech Connect

    Danabasoglu, G.; McWilliams, J.C.; Gent, P.R.

    1994-05-20

    Ocean models routinely used in simulations of the Earth`s climate do not resolve mesoscale eddies because of the immense computational cost. A new parameterization of the effects of these eddies has been implemented in a widely used model. A comparison of its solution with that of the conventional parameterization shows significant improvements in the global temperature distribution, the poleward and surface heat fluxes, and the locations of deep-water formation.

  2. Deep ocean circulation by acoustic-gravity waves: from snowball to greenhouse earth

    NASA Astrophysics Data System (ADS)

    Kadri, Usama

    2015-04-01

    Acoustic-gravity waves are compression-type waves propagating with amplitudes governed by the restoring force of gravity. They are generated, among others, by wind-wave interactions, surface waves interactions, submarine earthquakes, and movements of ice-blocks. We show that acoustic-gravity waves contribute to deep ocean water transport through different climate timelines: from snowball to greenhouse earth; they cause chaotic flow trajectories of individual water parcels, which can be transported up to a few centimetres per second.

  3. A consistent formulation of the anisotropic stress tensor for use in models of the large-scale ocean circulation

    SciTech Connect

    Wajsowicz, R.C. )

    1993-04-01

    Subgrid-scale dissipation of momentum in numerical models of the large-scale ocean circulation is commonly parameterized as a viscous diffusion resulting from the divergence of a stress tensor of the form [omega] = Au. The form of the fourth-order coefficient tensor A is derived for anisotropic dissipation with an axis of rotational symmetry. Sufficient conditions for A to be positive definite for incompressible flows, so guaranteeing a net positive dissipation of kinetic energy, are found. The divergence of the stress tensor, in Cartesian and spherical polar coordinates, is given for A with constant and spatially varying elements. A consistent form of A and [omega] for use in models based on the Arakawa B- and C-grids is also derived. 16 refs.

  4. Reactive transport modeling of hydrothermal circulation in oceanic crust: effect of anhydrite precipitation on the dynamics of submarine hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Yang, J.

    2009-12-01

    Hydrothermal fluid circulation represents an extremely efficient mechanism for the exchange of heat and matter between seawater and oceanic crust. Precipitation and dissolution of minerals associated with hydrothermal flow at ridge axes can alter the crustal porosity and permeability and hence influence the dynamics of hydrothermal systems. In this study, a fully coupled fluid flow, heat transfer and reactive mass transport model was developed using TOUGHREACT to evaluate the role of mineral precipitation and dissolution on the evolution of hydrothermal flow systems, with a particular attention focused on anhydrite precipitation upon heating of seawater in recharge zones and the resultant change in the crustal porosity and permeability. A series of numerical case studies were carried out to assess the effect of temperature and aqueous phase inflow concentrations on the reactive geochemical system. The impact of chemically induced porosity and permeability changes on the dynamics of hydrothermal systems was also addressed.

  5. Antarctic sea ice control on ocean circulation in present and glacial climates.

    PubMed

    Ferrari, Raffaele; Jansen, Malte F; Adkins, Jess F; Burke, Andrea; Stewart, Andrew L; Thompson, Andrew F

    2014-06-17

    In the modern climate, the ocean below 2 km is mainly filled by waters sinking into the abyss around Antarctica and in the North Atlantic. Paleoproxies indicate that waters of North Atlantic origin were instead absent below 2 km at the Last Glacial Maximum, resulting in an expansion of the volume occupied by Antarctic origin waters. In this study we show that this rearrangement of deep water masses is dynamically linked to the expansion of summer sea ice around Antarctica. A simple theory further suggests that these deep waters only came to the surface under sea ice, which insulated them from atmospheric forcing, and were weakly mixed with overlying waters, thus being able to store carbon for long times. This unappreciated link between the expansion of sea ice and the appearance of a voluminous and insulated water mass may help quantify the ocean's role in regulating atmospheric carbon dioxide on glacial-interglacial timescales. Previous studies pointed to many independent changes in ocean physics to account for the observed swings in atmospheric carbon dioxide. Here it is shown that many of these changes are dynamically linked and therefore must co-occur. PMID:24889624

  6. Data Assimilation on HBM Circulation Model within MyOcean2 project

    NASA Astrophysics Data System (ADS)

    Siiriä, Simo-Matti; Axell, Lars

    2014-05-01

    To ensure good quality of the operational marine forecasts, it is very important to keep the state of the operational ocean model as close to the real physical state of the ocean as possible. However, applying observations into a model is far from trivial. In the MyOcean project, the Baltic Monitoring and Forecasting Centre (BALMFC) aims to combine the modelling efforts around Baltic Sea. As a part of this, a data assimilation system, based on optimal interpolation, originally developed in SMHI for HIROMB model has been added in hydrodynamic HIROMB-BOOS Model (HBM). BALMFC aims to create a common framework for operational data assimilation around Baltic Sea. This is done by combining and further developing the existing implementations. As a collaborative work between FMI (Finnish Meteorological Institute), SMHI (Swedish Meteorological and Hydrological Institute), DMI (Danish Meteorological Institute) and BSH (Bundesamt für Seeschifffahrt und Hydrographie), the long term aim is to have one unified data assimilation platform for the Baltic Sea models. As initial phase, the satellite Sea Surface Temperature (SST) has been assimilated. Improvements on the forecast quality will be discussed. To further develop the assimilation system, salinity and temperature measurements from ferryboxes are discussed, as well as the possibilities of assimilating ice observations in the model. We also discuss the possibilities to use ARGO floats as a data source for data assimilation schemes.

  7. A study of the circulation and salinity budget of the Arabian Sea with an isopycnic coordinate ocean model

    NASA Astrophysics Data System (ADS)

    Esenkov, Oleg E.; Olson, Donald B.; Bleck, Rainer

    2003-07-01

    The evolution of surface circulation and salinity budget are studied with the open-boundary version of the Miami Isopycnic Coordinate Ocean Model (MICOM) that uses a global MICOM simulation as a boundary condition. Under climatological wind and thermodynamic forcing, the model develops solutions that are in good agreement with the climatologically forced global MICOM results and with observations. When the observed winds force the model, interannual variability of the surface fields increases significantly. However, coalescence of the two large eddies off Somalia in the end of the summer monsoon suggested in earlier observations does not occur in the model. To identify what processes facilitate or restrict the merger, a series of experiments was performed with modified model parameters and forcing fields. The eddies coalesced when half-slip, rather than no-slip, boundary conditions were used. In this case, less positive vorticity was produced at the coast, resulting in reduced blocking effect on the propagation of the southern eddy. The Socotra Island, which is submerged in the standard model, hinders a northward movement of the Great Whirl, leading to a stronger interaction between the eddies, which results in their subsequent merging. A more realistic coalescence occurs in an experiment where winds are held constant after reaching the peak summer value. Freshwater fluxes from the east and south are important for the salinity budget in the Arabian Sea, where evaporation exceeds precipitation. The only significant cross-equatorial transport of low-salinity water occurs in the upper 400 m in the model. Most of this water is advected below the surface mixed layer at the western boundary. The strongest interaction between the mixed layer and the oceanic interior occurs during the summer in the coastal upwelling regions off Somalia. Almost half of all upwelled water comes from depths between 100 and 200 m, thus signifying the importance of mid-depth circulation and

  8. Cold-air outbreaks over the ocean at high latitudes and associated mesoscale atmospheric circulations: Problems of numerical modelling

    NASA Astrophysics Data System (ADS)

    Chechin, D. G.; Pichugin, M. K.

    2015-12-01

    A review of the current state of research in the field of numerical modelling and forecasting of cold-air outbreaks over the ocean at high latitudes and associated mesoscale circulations is presented. It is shown that the most relevant tasks are as follows: (1) the improvement of predictability and the adequacy of reproduction of polar mesocyclones, (2) a more adequate representation of the marginal sea-ice zone in the numerical models, and (3) solving problems of the parametrization and explicit reproduction of organized convection and orographic jets in numerical atmosphere models. It is demonstrated that these tasks only can be accomplished as a result of a comprehensive development of different components of the climatic system models and technology of the numerical weather prediction (NWP). One of the most promising approaches to overcome the identified problems is to develop and use methods of satellite remote sensing of the atmosphere and underlying surface in NWP technology. The high potential of analyzing the satellite multisensor data for quantifying parameters of different-scale atmospheric circulations is demonstrated using the example of cold-air outbreaks over the seas of the Far East.

  9. An overlooked problem in model simulations of the thermohaline circulation and heat transport in the Atlantic Ocean

    SciTech Connect

    Boening, C.W.; Holland, W.R.; Bryan, F.O.; Danabasoglu, G.; Mcwilliams, J.C. |

    1995-03-01

    Many models of the large-scale thermohaline circulation in the ocean exhibit strong zonally integrated upwelling in the midlatitude North Atlantic that significantly decreases the amount of deep water that is carried from the formation regions in the subpolar North Atlantic toward low latitudes and across the equator. In an analysis of results from the Community Modeling Effort using a suite of models with different horizontal resolution, wind and thermohaline forcing, and mixing parameters, it is shown that the upwelling is always concentrated in the western boundary layer between roughly 30 deg and 40 deg N. The vertical transport across 1000 m appears to be controlled by local dynamics and strongly depends on the horizontal resolution and mixing parameters of the model. It is suggested that in models with a realistic deep-water formation rate in the subpolar North Atlantic, the excessive upwelling can be considered as the prime reason for the typically too low meridional overturning rates and northward heat transports in the subtropical North Atlantic. A new isopycnal advection and mixing parameterization of tracer transports by mesoscale eddies yield substantial improvements in these integral measures of the circulation.

  10. The Determination of the Large-Scale Circulation of the Pacific Ocean from Satellite Altimetry using Model Green's Functions

    NASA Technical Reports Server (NTRS)

    Stammer, Detlef; Wunsch, Carl

    1996-01-01

    A Green's function method for obtaining an estimate of the ocean circulation using both a general circulation model and altimetric data is demonstrated. The fundamental assumption is that the model is so accurate that the differences between the observations and the model-estimated fields obey a linear dynamics. In the present case, the calculations are demonstrated for model/data differences occurring on very a large scale, where the linearization hypothesis appears to be a good one. A semi-automatic linearization of the Bryan/Cox general circulation model is effected by calculating the model response to a series of isolated (in both space and time) geostrophically balanced vortices. These resulting impulse responses or 'Green's functions' then provide the kernels for a linear inverse problem. The method is first demonstrated with a set of 'twin experiments' and then with real data spanning the entire model domain and a year of TOPEX/POSEIDON observations. Our present focus is on the estimate of the time-mean and annual cycle of the model. Residuals of the inversion/assimilation are largest in the western tropical Pacific, and are believed to reflect primarily geoid error. Vertical resolution diminishes with depth with 1 year of data. The model mean is modified such that the subtropical gyre is weakened by about 1 cm/s and the center of the gyre shifted southward by about 10 deg. Corrections to the flow field at the annual cycle suggest that the dynamical response is weak except in the tropics, where the estimated seasonal cycle of the low-latitude current system is of the order of 2 cm/s. The underestimation of observed fluctuations can be related to the inversion on the coarse spatial grid, which does not permit full resolution of the tropical physics. The methodology is easily extended to higher resolution, to use of spatially correlated errors, and to other data types.

  11. Dynamical budgets of the Antarctic Circumpolar Current using ocean general-circulation models

    NASA Astrophysics Data System (ADS)

    Grezio, A.; Wells, N. C.; Ivchenko, V. O.; de Cuevas, B. A.

    2005-04-01

    Three general-circulation models (FRAM, OCCAM and POP) are used to investigate the dynamics of the Antarctic Circumpolar Current (ACC) at the latitudes of the Drake Passage where the ACC is unbounded. In these general circulation models, bottom form stress balances the wind stress in the momentum budgets. In the vorticity budgets, the main balance is between wind curl and bottom pressure torque in FRAM, OCCAM and POP. Moreover, in the ACC belt all topographic features are regions of nonlinearity and bottom pressure torque variations, with the Drake Passage playing the largest role. Transient eddy Reynolds stresses (TERSs) play a different role in the three models. In the upper levels, TERSs accelerate the flow in the POP and FRAM models, but decelerate the flow in OCCAM. The behaviour of TERSs change throughout the whole water column in the ACC belt and Reynolds stresses have a dragging effect on the flow below the levels where the topography starts to obstruct the flow. The total volume transport in three models is very different. Additionally, the different spatial resolution, which results in a different level of eddy kinetic energy, has a significant influence on the transport.

  12. Early Pliocene onset of modern Nordic Seas circulation related to ocean gateway changes

    PubMed Central

    De Schepper, Stijn; Schreck, Michael; Beck, Kristina Marie; Matthiessen, Jens; Fahl, Kirsten; Mangerud, Gunn

    2015-01-01

    The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene. PMID:26507275

  13. Early Pliocene onset of modern Nordic Seas circulation related to ocean gateway changes

    NASA Astrophysics Data System (ADS)

    de Schepper, Stijn; Schreck, Michael; Beck, Kristina Marie; Matthiessen, Jens; Fahl, Kirsten; Mangerud, Gunn

    2015-10-01

    The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene.

  14. Early Pliocene onset of modern Nordic Seas circulation related to ocean gateway changes.

    PubMed

    De Schepper, Stijn; Schreck, Michael; Beck, Kristina Marie; Matthiessen, Jens; Fahl, Kirsten; Mangerud, Gunn

    2015-01-01

    The globally warm climate of the early Pliocene gradually cooled from 4 million years ago, synchronous with decreasing atmospheric CO2 concentrations. In contrast, palaeoceanographic records indicate that the Nordic Seas cooled during the earliest Pliocene, before global cooling. However, a lack of knowledge regarding the precise timing of Nordic Seas cooling has limited our understanding of the governing mechanisms. Here, using marine palynology, we show that cooling in the Nordic Seas was coincident with the first trans-Arctic migration of cool-water Pacific mollusks around 4.5 million years ago, and followed by the development of a modern-like Nordic Seas surface circulation. Nordic Seas cooling precedes global cooling by 500,000 years; as such, we propose that reconfiguration of the Bering Strait and Central American Seaway triggered the development of a modern circulation in the Nordic Seas, which is essential for North Atlantic Deep Water formation and a precursor for more widespread Greenland glaciation in the late Pliocene. PMID:26507275

  15. The northern North Atlantic Ocean mean circulation in the early 21st century

    NASA Astrophysics Data System (ADS)

    Daniault, Nathalie; Mercier, Herlé; Lherminier, Pascale; Sarafanov, Artem; Falina, Anastasia; Zunino, Patricia; Pérez, Fiz F.; Ríos, Aida F.; Ferron, Bruno; Huck, Thierry; Thierry, Virginie; Gladyshev, Sergey

    2016-08-01

    The decadal mean circulation in the northern North Atlantic was assessed for the early 21st century from repeated ship-based measurements along the Greenland-Portugal OVIDE line, from satellite altimetry and from earlier reported transports across 59.5°N and at the Greenland-Scotland sills. The remarkable quantitative agreement between all data sets allowed us to draw circulation pathways with a high level of confidence. The North Atlantic Current (NAC) system is composed of three main branches, referred to as the northern, central and southern branches, which were traced from the Mid-Atlantic Ridge (MAR), to the Irminger Sea, the Greenland-Scotland Ridge and the subtropical gyre. At OVIDE, the northern and central branches of the NAC fill the whole water column and their top-to-bottom integrated transports were estimated at 11.0 ± 3 Sv and 14.2 ± 6.4 Sv (1 Sv = 106 m3 s-1), respectively. Those two branches feed the cyclonic circulation in the Iceland Basin and the flow over the Reykjanes Ridge into the Irminger Sea. This cross-ridge flow was estimated at 11.3 ± 4.2 Sv westward, north of 58.5°N. The southern NAC branch is strongly surface-intensified and most of its top-to-bottom integrated transport, estimated at 16.6 ± 2 Sv, is found in the upper layer. It is composed of two parts: the northern part contributes to the flow over the Rockall Plateau and through the Rockall Trough toward the Iceland-Scotland Ridge; the southern part feeds the anticyclonic circulation toward the subtropical gyre. Summing over the three NAC branches, the top-to-bottom transport of the NAC across OVIDE was estimated at 41.8 ± 3.7 Sv. Because of the surface-intensification of the southern NAC branch, the intermediate water is transported to the northeast Atlantic mostly by the northern and central branches of the NAC (11.9 ± 1.8 Sv eastward). This water circulates cyclonically in the Iceland Basin and anticyclonically in the West European Basin, with similar transport

  16. A Curvilinear Version of the Bryan-Cox-Semtner Ocean Model and Its Representation of the Arctic Circulation

    NASA Astrophysics Data System (ADS)

    Murray, Ross J.; Reason, C. J. C.

    2001-07-01

    Continuous and finite difference forms of the governing equations are derived for a version of the Bryan-Cox-Semtner ocean general circulation model which has been recast in orthogonal, transversely curvilinear coordinates. The coding closely follows the style of the Geophysical Fluid Dynamics Laboratory modular ocean model No. 1. Curvilinear forms are given for the tracer, internal momentum, and stream function calculations, with the options of horizontal and isopycnal diffusion, eddy-induced transport, nonlinear viscosity, and semiimplicit treatment of the Coriolis force. The model is designed to operate on a rectangular three-dimensional array of points and can accommodate reentrant boundary conditions at both 'northern' and 'east-west' boundaries. Horizontal grid locations are taken as input and need to be supplied by a separate grid generation program. The advantages of using a better behaved and more economical grid in the north polar region are investigated by comparing simulations performed on two curvilinear grids with one performed on a latitude-longitude grid and by comparing filtered and unfiltered latitude-longitude simulations. Resolution of horizontally separated currents in Fram Strait emerges as a key challenge for representing exchanges with the Arctic in global models.

  17. On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model

    NASA Astrophysics Data System (ADS)

    Berg, Peter; Döscher, Ralf; Koenigk, Torben

    2015-08-01

    Impacts of spectral nudging on simulations of Arctic climate in coupled simulations have been investigated in a set of simulations with a regional climate model (RCM). The dominantly circumpolar circulation in the Arctic lead to weak constraints on the lateral boundary conditions (LBCs) for the RCM, which causes large internal variability with strong deviations from the driving model. When coupled to an ocean and sea ice model, this results in sea ice concentrations that deviate from the observed spatial distribution. Here, a method of spectral nudging is applied to the atmospheric model RCA4 in order to assess the potentials for improving results for the sea ice concentrations when coupled to the RCO ocean-sea ice model. The spectral nudging applied to reanalysis driven simulations significantly improves the generated sea ice regarding its temporal evolution, extent and inter-annual trends, compared to simulations with standard LBC nesting. The method is furthermore evaluated with driving data from two CMIP5 GCM simulations for current and future conditions. The GCM biases are similar to the RCA4 biases with ERA-Interim, however, the spectral nudging still improves the surface winds enough to show improvements in the simulated sea ice. For both GCM downscalings, the spectrally nudged version retains a larger sea ice extent in September further into the future. Depending on the sea ice formulation in the GCM, the temporal evolution of the regional sea ice model can deviate strongly.

  18. The impacts of Meltwater Pulse-1A in the South Atlantic Ocean deep circulation since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Marson, J. M.; Wainer, I.; Liu, Z.; Mata, M. M.

    2013-11-01

    Since 21 000 yr ago, the oceans have received large amounts of freshwater in pulses coming from the melting ice sheets. A specific event, known as meltwater pulse 1A (MWP-1A), has been identified in sea-level and temperature proxy records as responsible for the increase of ~20 m in sea level in less than 500 yr. Although its origin and timing are still under discussion, MWP-1A seems to have had a significant impact on several components of the climatic system. The present work aims to elucidate these impacts on the water mass distribution of the South Atlantic Ocean through the analysis of a transient simulation of the climate evolution from the Last Glacial Maximum to Present Day using a state-of-art CGCM, the National Center for Atmospheric Research Community Climate System Model version 3 (NCAR CCSM3). Results show that the freshwater discharge associated with the timing of MWP-1A was crucial to establish the present thermohaline structure associated with the North Atlantic Deep Water, marking the transition between a shallower and a deeper Atlantic Meridional Overturning Circulation.

  19. On the effects of constraining atmospheric circulation in a coupled atmosphere-ocean Arctic regional climate model

    NASA Astrophysics Data System (ADS)

    Berg, Peter; Döscher, Ralf; Koenigk, Torben

    2016-06-01

    Impacts of spectral nudging on simulations of Arctic climate in coupled simulations have been investigated in a set of simulations with a regional climate model (RCM). The dominantly circumpolar circulation in the Arctic lead to weak constraints on the lateral boundary conditions (LBCs) for the RCM, which causes large internal variability with strong deviations from the driving model. When coupled to an ocean and sea ice model, this results in sea ice concentrations that deviate from the observed spatial distribution. Here, a method of spectral nudging is applied to the atmospheric model RCA4 in order to assess the potentials for improving results for the sea ice concentrations when coupled to the RCO ocean-sea ice model. The spectral nudging applied to reanalysis driven simulations significantly improves the generated sea ice regarding its temporal evolution, extent and inter-annual trends, compared to simulations with standard LBC nesting. The method is furthermore evaluated with driving data from two CMIP5 GCM simulations for current and future conditions. The GCM biases are similar to the RCA4 biases with ERA-Interim, however, the spectral nudging still improves the surface winds enough to show improvements in the simulated sea ice. For both GCM downscalings, the spectrally nudged version retains a larger sea ice extent in September further into the future. Depending on the sea ice formulation in the GCM, the temporal evolution of the regional sea ice model can deviate strongly.

  20. The joint impact of ocean circulation and plate tectonics on the glacial South Pacific carbon pool

    NASA Astrophysics Data System (ADS)

    Ronge, T.; Tiedemann, R.; Lamy, F.; Köhler, P.; Alloway, B.; De Pol-Holz, R.; Pahnke, K.; Southon, J. R.

    2015-12-01

    To understand the whereabouts of CO2 during glacials and its pathways during deglacial transitions is one of the main priorities in paleoclimate research. The opposing patterns of atmospheric CO2 and Δ14C suggest that the bulk of CO2 was released from an old and therefore 14C-depleted carbon reservoir. As the modern deep ocean, below ~2000 m, stores up to 60-times more carbon than the entire atmosphere, it is considered to be a major driver of the atmospheric CO2 pattern, storing CO2 during glacials, releasing it during deglacial transitions. We use a South Pacific transect of sediment cores, covering the Antarctic Intermediate Water (AAIW), the Upper Circumpolar Deep Water (UCDW) and the Lower Circumpolar Deep Water (LCDW), to reconstruct the spatio-temporal evolution of oceanic Δ14C over the last 30,000 years. During the last glacial, we find significantly 14C-depleted waters between 2000 and 4300 m water depth, indicating a strong stratification and the storage of carbon in these water masses. However, two sediment cores from 2500 m and 3600 m water depth reveal an extreme glacial atmosphere-to-deep-water Δ14C offset of up to -1000‰ and ventilation ages (deep-water to atmosphere 14C-age difference) of ~8000 years. Such old water masses are expected to be anoxic, yet there is no evidence of anoxia in the glacial S-Pacific. Recent studies showed an increase of Mid Ocean Ridge (MOR) volcanism during glacials due to the low stand of global sea level. For this reason, we hypothesize that the admixture of 14C-dead carbon via tectonic activity along MORs might have contributed to these extremely low radiocarbon values. With a simple 1-box model, we calculated if the admixture of hydrothermal CO2 has the potential to lower the deep Pacific Δ14C signal. We show that if the oceanic turnover time is at least 2700 years, an increased hydrothermal flux of 1.2 μmol kg-1 yr-1 has the potential to reproduce the extreme radiocarbon values observed in our records.

  1. Coupling of the distribution of silicon isotopes to the meridional overturning circulation of the North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Brzezinski, Mark A.; Jones, Janice L.

    2015-06-01

    The distribution of silicon isotopes within silicic acid, δ30Si(OH)4, was examined along a section in the North Atlantic from the Cape Verde Islands off Africa to Cape Cod, Massachusetts in North America. Surface water displayed elevated δ30Si(OH)4 associated with biological fractionation of Si during silica production. Below 300 m variations in δ30Si(OH)4 were closely tied to the distribution of water masses as diagnosed through optimum multiparameter analysis, confirming a tight relationship between δ30Si(OH)4 and the meridional overturning circulation in the Atlantic. A linear relationship between δ30Si(OH)4 and the inverse of silicic acid concentration supported control of Si isotope distribution by conservative mixing of end member water masses of different isotopic composition in the Atlantic. There was a suggestion of a weak local minimum in δ30Si(OH)4 in deep waters above the Trans-Atlantic Geotraverse hydrothermal zone on the mid-Atlantic Ridge consistent with the light δ30Si(OH)4 of hydrothermal waters. The lightest δ30Si(OH)4 values were observed in the deep western and deep eastern basins where Antarctic Bottom Water (AABW) dominated. The heaviest values in subsurface waters occurred in North Atlantic Deep Water due to strong ventilation and the contribution of heavy northern source waters that are influenced by the Arctic Ocean. The concept of a silicon isotope bipole is introduced to explain how the isotopic differences between the northern and southern end-member water masses arise, and how they influence Si isotope distributions. Northern end-member water masses are heavy due to the influence of the Arctic Ocean. Bottom topography prevents light deep waters from entering the Arctic and the further removal of light isotopes through local biological productivity results in extremely heavy δ30Si(OH)4 within the Arctic. Light AABW dominates the southern end member. The Southern Ocean silicic acid trap distills heavier isotopes of Si out of the

  2. The Sensitivity of Ocean Circulation and Carbon Uptake to the Rate of CO2 Increase and the Resultant Changes in Climate and Hydrological Cycle

    NASA Astrophysics Data System (ADS)

    Cao, L.; Jain, A. K.

    2003-12-01

    We investigate an important feedback loop in the climate-carbon cycle system that involves increase in atmospheric CO2 and the resulting changes in temperature, the hydrological cycle, ocean circulation, and oceanic carbon uptake. This study is conducted using the coupled atmosphere-ocean-carbon cycle component of the Integrated Science Assessment Model (ISAM). The coupled model includes an energy-moisture balance atmosphere module, a thermodynamic sea-ice module, and a zonal mean ocean module. The ocean component resolves major ocean basins and is based on the balance equations of momentum, temperature, salinity and carbon and its isotopes. The coupled model has the ability to successfully simulate historical and current climates, the ocean thermohaline circulation (THC), oceanic carbon uptake, and bomb 14C. Global warming may cause a weakening or even a collapse of the THC through the increased sea surface temperature and an enhanced hydrological cycle, which can reduce oceanic carbon uptake, thus accelerate the global warming. Recent studies find that the change in the THC is dependent not only on the concentration of atmospheric CO2, but also on the rate of CO2 increase. Using a variety of CO2 increase scenarios (e.g., 0.5%, 1%, 2%/yr CO2 increase from present concentration to the level of doubling or quadrupling of CO2), we extend previous studies by assessing the effect of the rate of CO2 increase, temperature, and hydrological cycle not only on the THC but also on the oceanic carbon uptake. We also explore the threshold values of the rate of CO2 increase and the absolute amount of atmospheric CO2 that are likely to induce the collapse of the North Atlantic Deep Water (NADW) formation, which can have dramatic effects on oceanic uptake of CO2.

  3. Mean full-depth summer circulation and transports at the northern periphery of the Atlantic Ocean in the 2000s

    NASA Astrophysics Data System (ADS)

    Sarafanov, Artem; Falina, Anastasia; Mercier, Herlé; Sokov, Alexey; Lherminier, Pascale; Gourcuff, Claire; Gladyshev, Sergey; Gaillard, Fabienne; Daniault, Nathalie

    2012-01-01

    A mean state of the full-depth summer circulation in the Atlantic Ocean in the region in between Cape Farewell (Greenland), Scotland and the Greenland-Scotland Ridge (GSR) is assessed by combining 2002-2008 yearly hydrographic measurements at 59.5°N, mean dynamic topography, satellite altimetry data and available estimates of the Atlantic-Nordic Seas exchange. The mean absolute transports by the upper-ocean, mid-depth and deep currents and the Meridional Overturning Circulation (MOCσ = 16.5 ± 2.2 Sv, at σ0= 27.55) at 59.5°N are quantified in the density space. Inter-basin and diapycnal volume fluxes in between the 59.5°N section and the GSR are then estimated from a box model. The dominant components of the meridional exchange across 59.5°N are the North Atlantic Current (NAC, 15.5 ± 0.8 Sv,σ0 < 27.55) east of the Reykjanes Ridge, the northward Irminger Current (IC, 12.0 ± 3.0 Sv) and southward Western Boundary Current (WBC, 32.1 ± 5.9 Sv) in the Irminger Sea and the deep water export from the northern Iceland Basin (3.7 ± 0.8 Sv, σ0 > 27.80). About 60% (12.7 ± 1.4 Sv) of waters carried in the MOCσ upper limb (σ0< 27.55) by the NAC/IC across 59.5°N (21.1 ± 1.0 Sv) recirculates westward south of the GSR and feeds the WBC. 80% (10.2 ± 1.7 Sv) of the recirculating NAC/IC-derived upper-ocean waters gains density ofσ0 > 27.55 and contributes to the MOCσlower limb. Accordingly, the contribution of light-to-dense water conversion south of the GSR (˜10 Sv) to the MOCσ lower limb at 59.5°N is one and a half times larger than the contribution of dense water production in the Nordic Seas (˜6 Sv).

  4. Reorganization of North Pacific Ocean Circulation at ~1300 AD during the Terminal American SW Drought of the Medieval Climate Anomaly

    NASA Astrophysics Data System (ADS)

    Hendy, I. L.; Pak, D. K.; Schimmelmann, A.

    2012-12-01

    Southern California has a Mediterranean-type climate characterized by warm, dry summers associated with the seasonal position of the North Pacific High and cool, wet winters primarily associated with cyclonic storms originating in the high latitude North Pacific. Extreme precipitation events in the region are associated, however, with strong zonal flow that brings warm, moist tropical air across the Pacific (atmospheric rivers). Here we present an ultra-high resolution reconstruction of riverine input (via scanning XRF elemental composition of bulk sediments) into Santa Barbara Basin during the Medieval Climate Anomaly (MCA) and transition into the Little Ice Age (LIA) from a series of kasten cores collected in 2009 by the RV Sproul. We compare precipitation shifts in the region with the response of marine biota to ocean circulation change during the same interval to demonstrate that not all droughts in the America Southwest are associated with the same atmospheric and ocean circulation conditions. Droughts are expressed in Santa Barbara Basin sediments by low concentrations of elements associated with lithogenic sediment (Ti, K, Al and Fe) and were centered at 890, 980, 1140 and 1450 AD. The SBB droughts of the MCA were interrupted by flood events at ˜1270 AD and ˜1380 AD ± 15 which were associated with a dramatic increase in the abundance of the subpolar planktonic foraminiferal sp. Neoglobogerina pachyderma (sinistral). Although variable, this interval dominated by a foraminiferal species preferring water <10°C lasted from ˜1275 to 1340 AD with a brief return to dominantly subtropical planktonic foraminferal species between 1340 and 1400 AD before the foraminiferal assemblage shifted toward cooler subpolar species again until >1500 AD. Of the major Native American population declines during the MCA coincident with drought conditions (990-1060 AD, 1135-1170 AD and 1276-1297 AD) in the Western US (Benson et al., 2007), only the last decline associated with

  5. An empirical model of global climate - Part 1: Reduced impact of volcanoes upon consideration of ocean circulation

    NASA Astrophysics Data System (ADS)

    Canty, T.; Mascioli, N. R.; Smarte, M.; Salawitch, R. J.

    2012-09-01

    Observed reductions in Earth's surface temperature following explosive volcanic eruptions have been used as a proxy for geo-engineering of climate by the artificial enhancement of stratospheric sulfate. Earth cools following major eruptions due to an increase in the reflection of sunlight caused by a dramatic enhancement of the stratospheric sulfate aerosol burden. Significant global cooling has been observed following the four major eruptions since 1900: Santa María, Mount Agung, El Chichón, and Mount Pinatubo, leading IPCC (2007) to state "major volcanic eruptions can thus cause a drop in global mean surface temperature of about half a degree Celsius that can last for months and even years". We use a multiple linear regression model applied to the global surface temperature anomaly to suggest that exchange of heat between the atmosphere and ocean, driven by variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC), has been a factor in the decline of global temperature following these eruptions. The veracity of this suggestion depends on whether the Atlantic Multidecadal Oscillation (AMO) truly represents a proxy for the strength of the AMOC and the precise quantification of global cooling due to volcanoes depends on how the AMO is detrended. If the AMO is detrended using anthropogenic radiative forcing of climate, we find that surface cooling attributed to Mount Pinatubo, using the Hadley Centre/University of East Anglia surface temperature record, maximizes at 0.15 °C globally and 0.35 °C over land. These values are about a factor of 2 less than found when the AMO is neglected in the model and quite a bit lower than the canonical 0.5 °C cooling usually attributed to Pinatubo. The AMO had begun to decrease prior to the four major eruptions, suggesting that exchange of heat between the atmosphere and ocean due to variations in the strength of the AMOC drives the climate system, rather than responds to volcanic perturbations. The

  6. Ensemble climate simulations using a fully coupled ocean-troposphere-stratosphere general circulation model.

    PubMed

    Huebener, H; Cubasch, U; Langematz, U; Spangehl, T; Niehörster, F; Fast, I; Kunze, M

    2007-08-15

    Long-term transient simulations are carried out in an initial condition ensemble mode using a global coupled climate model which includes comprehensive ocean and stratosphere components. This model, which is run for the years 1860-2100, allows the investigation of the troposphere-stratosphere interactions and the importance of representing the middle atmosphere in climate-change simulations. The model simulates the present-day climate (1961-2000) realistically in the troposphere, stratosphere and ocean. The enhanced stratospheric resolution leads to the simulation of sudden stratospheric warmings; however, their frequency is underestimated by a factor of 2 with respect to observations.In projections of the future climate using the Intergovernmental Panel on Climate Change special report on emissions scenarios A2, an increased tropospheric wave forcing counteracts the radiative cooling in the middle atmosphere caused by the enhanced greenhouse gas concentration. This leads to a more dynamically active, warmer stratosphere compared with present-day simulations, and to the doubling of the number of stratospheric warmings. The associated changes in the mean zonal wind patterns lead to a southward displacement of the Northern Hemisphere storm track in the climate-change signal. PMID:17569652

  7. Circulation and water properties of the southwest Indian Ocean, Spring 1987

    NASA Astrophysics Data System (ADS)

    Gründlingh, M. L.; Carter, R. A.; Stanton, R. C.

    The results obtrained during a cruise in the south-western Indian Ocean, from South Africa to Mauritius in September 1987, are presented. Temperature, salinity, oxygen and nutrients were measured at 70 CTD station, 20 nautical miles apart. The data perspective is enhanced by NOAA satellite infrared imagery and Geosat altimetry. The major features encountered on the cruise were two intense cyclonic eddies in the vicinity of the Mozambique Ridge and the Mozambique Basin and which seemed to form part of the broader western boundary region of the southern Indian Ocean. Evidence was found of a significant equatoward flux at the Madagascar Ridge, which provided input of water from higher latitudes. The passage of North Atlantic Deep Water was constrained by the bottom topography south of the Madagascar Ridge, and this led to a reduction of its salinity and oxygen concentration. The positive correlation between the CTD results and the altimetry enabled the identification, tracking and description of a number of eddies in the region. The transition zone of these eddies from east of Madagascar to the African continent was identified, and so was the apparent closure of the southern entrance of the Mozambique Channel to migrating eddies.

  8. Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions.

    PubMed

    Swingedouw, Didier; Ortega, Pablo; Mignot, Juliette; Guilyardi, Eric; Masson-Delmotte, Valérie; Butler, Paul G; Khodri, Myriam; Séférian, Roland

    2015-01-01

    While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Here we show that the subset of CMIP5 historical climate simulations that produce such bidecadal variability exhibits a robust synchronization, with a maximum in Atlantic Meridional Overturning Circulation (AMOC) 15 years after the 1963 Agung eruption. The mechanisms at play involve salinity advection from the Arctic and explain the timing of Great Salinity Anomalies observed in the 1970s and the 1990s. Simulations, as well as Greenland and Iceland paleoclimate records, indicate that coherent bidecadal cycles were excited following five Agung-like volcanic eruptions of the last millennium. Climate simulations and a conceptual model reveal that destructive interference caused by the Pinatubo 1991 eruption may have damped the observed decreasing trend of the AMOC in the 2000s. Our results imply a long-lasting climatic impact and predictability following the next Agung-like eruption. PMID:25818017

  9. Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS).

    PubMed

    Nyamweya, Chrispine; Desjardins, Christopher; Sigurdsson, Sven; Tomasson, Tumi; Taabu-Munyaho, Anthony; Sitoki, Lewis; Stefansson, Gunnar

    2016-01-01

    Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September-May) and mixing (June-August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore-offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria. PMID:27030983

  10. Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS)

    PubMed Central

    Sigurdsson, Sven; Tomasson, Tumi; Taabu-Munyaho, Anthony; Sitoki, Lewis; Stefansson, Gunnar

    2016-01-01

    Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1st January 2000 to 31st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September–May) and mixing (June–August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore—offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria. PMID:27030983

  11. Diagnosing southeast tropical Atlantic SST and ocean circulation biases in the CMIP5 ensemble

    NASA Astrophysics Data System (ADS)

    Xu, Zhao; Chang, Ping; Richter, Ingo; Kim, Who; Tang, Guanglin

    2014-12-01

    Warm sea-surface temperature (SST) biases in the southeastern tropical Atlantic (SETA), which is defined by a region from 5°E to the west coast of southern Africa and from 10°S to 30°S, are a common problem in many current and previous generation climate models. The Coupled Model Intercomparison Project Phase 5 (CMIP5) ensemble provides a useful framework to tackle the complex issues concerning causes of the SST bias. In this study, we tested a number of previously proposed mechanisms responsible for the SETA SST bias and found the following results. First, the multi-model ensemble mean shows a positive shortwave radiation bias of ~20 W m-2, consistent with models' deficiency in simulating low-level clouds. This shortwave radiation error, however, is overwhelmed by larger errors in the simulated surface turbulent heat and longwave radiation fluxes, resulting in excessive heat loss from the ocean. The result holds for atmosphere-only model simulations from the same multi-model ensemble, where the effect of SST biases on surface heat fluxes is removed, and is not sensitive to whether the analysis region is chosen to coincide with the maximum warm SST bias along the coast or with the main SETA stratocumulus deck away from the coast. This combined with the fact that there is no statistically significant relationship between simulated SST biases and surface heat flux biases among CMIP5 models suggests that the shortwave radiation bias caused by poorly simulated low-level clouds is not the leading cause of the warm SST bias. Second, the majority of CMIP5 models underestimate upwelling strength along the Benguela coast, which is linked to the unrealistically weak alongshore wind stress simulated by the models. However, a correlation analysis between the model simulated vertical velocities and SST biases does not reveal a statistically significant relationship between the two, suggesting that the deficient coastal upwelling in the models is not simply related to the

  12. Arctic Ocean circulation, processes and water masses: A description of observations and ideas with focus on the period prior to the International Polar Year 2007-2009

    NASA Astrophysics Data System (ADS)

    Rudels, Bert

    2015-03-01

    The evolving knowledge of the Arctic Ocean, its hydrography and its water masses and their transformations and circulation is reviewed starting with the observations made on Fram 1893-1896 and extending to the International Polar Year (IPY) 2007-2009. The expeditions and observations after Fram to the mid 20th century as well as the more extensive and systematic studies of water masses and circulation made from ice stations and airborne expeditions from the late 1940s to the late 1970s are briefly described. The early concepts of the connections and exchanges between the Arctic Ocean and the world ocean are also discussed. In the 1980s scientific icebreakers were beginning to enter the inner parts of the Arctic Ocean and large international programmes were launched, culminating in the IPY. The changes in the Arctic Ocean, first noted in the Atlantic layer in 1990 and shortly after in the upper layers, are described. The exchanges between the Arctic Ocean and the surrounding seas through the four main openings, Fram Strait, Barents Sea, Bering Strait and the Canadian Arctic Archipelago as well the volume and freshwater balances of the Arctic Ocean are examined.

  13. Changes in Mediterranean circulation and water characteristics due to restriction of the Atlantic connection: a high-resolution ocean model

    NASA Astrophysics Data System (ADS)

    Topper, R. P. M.; Meijer, P. Th.

    2015-02-01

    A high-resolution parallel ocean model is set up to examine how the sill depth of the Atlantic connection affects circulation and water characteristics in the Mediterranean Basin. An analysis of the model performance, comparing model results with observations of the present-day Mediterranean, demonstrates its ability to reproduce observed water characteristics and circulation (including deep water formation). A series of experiments with different sill depths in the Atlantic-Mediterranean connection is used to assess the sensitivity of Mediterranean circulation and water characteristics to sill depth. Basin-averaged water salinity and, to a lesser degree, temperature rise when the sill depth is shallower and exchange with the Atlantic is lower. Lateral and interbasinal differences in the Mediterranean are, however, largely unchanged. The strength of the upper overturning cell in the western basin is proportional to the magnitude of the exchange with the Atlantic, and hence to sill depth. Overturning in the eastern basin and deep water formation in both basins, on the contrary, are little affected by the sill depth. The model results are used to interpret the sedimentary record of the Late Miocene preceding and during the Messinian Salinity Crisis. In the western basin, a correlation exists between sill depth and rate of refreshment of deep water. On the other hand, because sill depth has little effect on the overturning and deep water formation in the eastern basin, the model results do not support the notion that restriction of the Atlantic-Mediterranean connection may cause lower oxygenation of deep water in the eastern basin. However, this discrepancy may be due to simplifications in the surface forcing and the use of a bathymetry different from that in the Late Miocene. We also tentatively conclude that blocked outflow, as found in experiments with a sill depth ≤10 m, is a plausible scenario for the second stage of the Messinian Salinity Crisis during which

  14. Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation

    PubMed Central

    Hall, Brenda L.; Denton, George H.; Fountain, Andrew G.; Hendy, Chris H.; Henderson, Gideon M.

    2010-01-01

    The phasing of millennial-scale oscillations in Antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change, particularly those involving the Southern Ocean. However, records of millennial-scale variability from Antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores, some of which show little variability through that time. Here, we present new data from closed-basin lakes in the Dry Valleys region of East Antarctica that show high-magnitude, high-frequency oscillations in surface level during the late Pleistocene synchronous with climate fluctuations elsewhere in the Southern Hemisphere. These data suggest a coherent Southern Hemisphere pattern of climate change on millennial time scales, at least in the Pacific sector, and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes. PMID:21115838

  15. Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation.

    PubMed

    Hall, Brenda L; Denton, George H; Fountain, Andrew G; Hendy, Chris H; Henderson, Gideon M

    2010-12-14

    The phasing of millennial-scale oscillations in Antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change, particularly those involving the Southern Ocean. However, records of millennial-scale variability from Antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores, some of which show little variability through that time. Here, we present new data from closed-basin lakes in the Dry Valleys region of East Antarctica that show high-magnitude, high-frequency oscillations in surface level during the late Pleistocene synchronous with climate fluctuations elsewhere in the Southern Hemisphere. These data suggest a coherent Southern Hemisphere pattern of climate change on millennial time scales, at least in the Pacific sector, and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes. PMID:21115838

  16. Discovery of hantavirus circulating among Rattus rattus in French Mayotte island, Indian Ocean.

    PubMed

    Filippone, Claudia; Castel, Guillaume; Murri, Séverine; Beaulieux, Frédérik; Ermonval, Myriam; Jallet, Corinne; Wise, Emma L; Ellis, Richard J; Marston, Denise A; McElhinney, Lorraine M; Fooks, Anthony R; Desvars, Amélie; Halos, Lénaı G; Vourc'h, Gwenaël; Marianneau, Philippe; Tordo, Noël

    2016-05-01

    Hantaviruses are emerging zoonotic viruses that cause human diseases. In this study, sera from 642 mammals from La Réunion and Mayotte islands (Indian Ocean) were screened for the presence of hantaviruses by molecular analysis. None of the mammals from La Réunion island was positive, but hantavirus genomic RNA was discovered in 29/160 (18 %) Rattus rattus from Mayotte island. The nucleoprotein coding region was sequenced from the liver and spleen of all positive individuals allowing epidemiological and intra-strain variability analyses. Phylogenetic analysis based on complete coding genomic sequences showed that this Murinae-associated hantavirus is a new variant of Thailand virus. Further studies are needed to investigate hantaviruses in rodent hosts and in Haemorrhagic Fever with Renal Syndrome (HFRS) human cases. PMID:26932442

  17. Development of an AMS method to study oceanic circulation characteristics using cosmogenic 39Ar

    USGS Publications Warehouse

    Collon, P.H.; Bichler, M.; Caggiano, J.; Cecil, L.D.; El, Masri Y.; Golser, R.; Jiang, C.L.; Heinz, A.; Henderson, D.; Kutschera, W.; Lehmann, B.E.; Leleux, P.; Loosli, H.H.; Pardo, R.C.; Paul, M.; Rehm, K.E.; Schlosser, P.; Scott, R.H.; Smethie, W.M., Jr.; Vondrasek, R.

    2004-01-01

    Initial experiments at the ATLAS facility [Nucl. Instr. and Meth. B 92 (1994) 241] resulted in a clear detection of cosmogenic 39Ar signal at the natural level. The present paper summarizes the recent developments of 39Ar AMS measurements at ATLAS: the use of an electron cyclotron resonance (ECR) positive ion source equipped with a special quartz liner to reduce 39K background, the development of a gas handling system for small volume argon samples, the acceleration of 39Ar8+ ions to 232 MeV, and the final separation of 39Ar from 39K in a gas-filled spectrograph. The first successful AMS measurements of 39Ar in ocean water samples from the Southern Atlantic ventilation experiment (SAVE) are reported. Published by Elsevier B.V.

  18. Pathways of marine debris in statistical and diagnostic ocean circulation models

    NASA Astrophysics Data System (ADS)

    Maximenko, N.; Hafner, J.; Lumpkin, R.

    2012-04-01

    Statistical and diagnostic models are used in this study to describe long-term dynamics of objects floating at the sea surface. The statistical model is based of the particle displacement probability density function, derived from trajectories of drifting buoys, and is supplemented by the probability of running aground. This model reveals five main areas of debris accumulation in the subtropical ocean, all confirmed with direct observations. It also reveals the global pattern of shores impacted by marine debris, correlated with dominant winds. The diagnostic model (SCUD - Surface CUrrents from Diagnostic) utilizes satellite data of altimetry and QuikSCAT/ASCAT winds to assess near-real time surface velocities and its parameters are optimized using drifter trajectories. Numerical experiments with various sources and life times of the model debris help to understand main pathways of the tracer and distributions of its properties within and across individual oceans. Applications of statistical and diagnostic models help to assess probable motion of the debris, generated in Japan by tsunami of March 11, 2011. The timeline, derived from the statistical model, and maps, computed with SCUD, are used to coordinate operational at-sea and on-coast observations and preparations for the debris impact. Most of debris is drifting from Japan towards east, while dispersing over increasing area. After passing Hawaii in the north it is expected to recirculate into the so-called North Pacific Garbage Patch - the area, located between Hawaii and California, where convergent surface currents collect all floating waste. Only a small fraction of tsunami debris, on the edge of the debris field, will "touch" Hawaii and US/Canada west coast. Yet the amount and composition may be anomalous. Mixed with the older waste, tsunami debris will slowly leak from the patch, polluting Hawaiian Islands.

  19. Evaluation of a dynamically downscaled atmospheric reanalyse in the prospect of forcing long term simulations of the ocean circulation in the Gulf of Lions

    NASA Astrophysics Data System (ADS)

    Langlais, C.; Barnier, B.; Molines, J. M.; Fraunié, P.; Jacob, D.; Kotlarski, S.

    The paper evaluates atmospheric reanalysis as possible forcing of model simulations of the ocean circulation inter-annual variability in the Gulf of Lions in the Western Mediterranean Sea between 1990 and 2000. The sensitivity of the coastal atmospheric patterns to the model resolution is investigated using the REMO regional climate model (18 km, 1 h), and the recent global atmospheric reanalysis ERA40 (125 km, 6 h). At scales from a few years to a few days, both atmospheric data sets exhibit a very similar weather, and agreement between REMO and ERA40 is especially good on the seasonal cycle and at the daily variability scale. At smaller scales, REMO reproduces more realistic spatio-temporal patterns in the ocean forcing: specific wind systems, particular atmospheric behaviour on the shelf, diurnal cycle, sea-breeze. Ocean twin experiments (1990-1993) clearly underline REMO skills to drive dominant oceanic processes in this microtidal area. Finer wind patterns induce a more realistic circulation and hydrology of the shelf water: unique shelf circulation, upwelling, temperature and salinity exchanges at the shelf break. The hourly sampling of REMO introduces a diurnal forcing which enhances the behaviour of the ocean mixed layer. In addition, the more numerous wind extremes modify the exchanges at the shelf break: favouring the export of dense shelf water, enhancing the mesoscale variability and the interactions of the along slope current with the bathymetry.

  20. The influence of an Antarctic glacier tongue on near-field ocean circulation and mixing

    NASA Astrophysics Data System (ADS)

    Stevens, C. L.; McPhee, M. G.; Forrest, A. L.; Leonard, G. H.; Stanton, T.; Haskell, T. G.

    2014-04-01

    In situ measurements of flow and stratification in the vicinity of the Erebus Glacier Tongue, a 12 km long floating Antarctic glacier, show the significant influence of the glacier. Three ADCPs (75, 300, and 600 kHz) were deployed close (<50 m) to the sidewall of the glacier in order to capture near-field flow distortion. Scalar (temperature and conductivity) and shear microstructure profiling captured small-scale vertical variability. Flow magnitudes exceeded 0.3 m s-1 through a combination of tidal flow (˜8 cm s-1) and a background/residual flow (˜4-10 cm s-1) flowing to the NW. Turbulence was dominated by deeper mixing during spring tide, likely indicative of the role of bathymetric variation which locally forms an obstacle as great as the glacier. During the neap tide, near-surface mixing was as energetic as that seen in the spring tide, suggesting the presence of buoyancy-driven near-surface flows. Estimates of integrated dissipation rate suggest that these floating extensions of the Antarctic ice sheet alter energy budgets through enhanced dissipation, and thus influence coastal near-surface circulation.

  1. 3D modelling of the ocean circulation in the gulf of Fos

    NASA Astrophysics Data System (ADS)

    Ulses, C.; Grenz, C.; Marsaleix, P.; Schaaff, E.; Estournel, C.; Pinazo, C.

    2003-04-01

    The Gulf of Fos, near Marseille (France), is a semi-enclosed bay covering 42 km2 for a mean depth of 8 m. Freshwater inputs come mainly from the Rhone river, main river of the NW Mediterranean sea which mouth is located on the southwestern part of the gulf. This coastal zone is also influenced by the entrance of water originating from three channels in the northwestern part and from the Berre lagoon which is connected to the gulf through the Caronte channel, in the eastern part. The gulf of Fos is studied with a high horizontal resolution (200 m) three dimensional hydrodynamic model. Academic simulations under typical wind forcing conditions are described. They reveal several features of the exchange of water masses in the Gulf of Fos, in particularly the intrusion of the Rhone river plume generated by south winds. Residence times in the different areas of the Gulf are also investigated. Then a realistic simulation, where Rhone river discharge, meteorological forcing and the surrounding general circulation are taken into account, is presented. This simulation is computed by a chain of three models : a 3-km regional scale model, a 1-km continental shelf model and the coastal model. To assess the quality of the numerical procedure, the model outputs, mainly salinity fields, are compared to MODELFOS2 surveys, that took place in May 2001, as part of the OAERRE program (Oceanographic Application of Eutrophisation in Regions of Restricted Exchanges). The sensitivity of the model results to the wind direction is discussed.

  2. Biologically induced initiation of snowball-Earth events, and the circulations of ice and ocean in a globally glaciated scenario

    NASA Astrophysics Data System (ADS)

    McPhaden, M. J.; Finn, C.; McEntee, C.; Krause, F.; Harden, J. W.; Rosenbloom, N. A.; Pendall, E.; Alves Jesus Rydin, C.; Krasa, D.; Shrestha, G.; Cavallaro, N.; Kuperberg, J.; Løvholt, F.; Horspool, N.; Cavanaugh, M. A.; Hankin, E. R.; Davis, J. L.; Evans, J. E.; Gurwick, N. P.; Richardson, R. M.; Landau, E. A.; Uhlenbrock, K. M.; Albert, M. R.; Rack, F. R.; Van Wyk de Vries, B.; Giardino, M.; Wiggins, H. V.; Habib, M. A.; Horan, P.; Stover, D. B.; Kuperberg, J.; Koch, D. M.; Jacob, D. J.; Isern, A. R.; Borg, S. G.; Ryabinin, V.; Hik, D.; Winther, J.; McConnell, W. J.; Baerwald, T. J.; Liu, J.; Winter, J. M.; Ruane, A. C.; Rosenzweig, C.; Jacobs, C. A.; Zanzerkia, E. E.; Cummins, P. R.; Harjadi, P.; Widiyantoro, S.; Natawidjaja, D. H.; Netting, R.; Grunsfeld, J. M.; Freilich, M. H.; Green, J. L.; Giles, B. L.; Stammer, D.; Wefer, G.; Lefebvre, A.; Lucarini, V.; Kanzow, T.; Goddard, L.; McCreary, J. P.; Sprintall, J.; Patterson, M.; Manduca, C. A.; Bralower, T. J.; Egger, A. E.; Klimchuk, J. A.; Nave, L. E.; Harden, J. W.; Horan, P.; Koch, D. M.; Laviolette, R.; Frost, G. J.; Middleton, P.; Uhle, M. E.; Gurney, R. J.; Impey, A.; Carroll, M.; Brown, M. E.; Escobar, V. M.; Murphy, F.; Callaghan, S.; Graber, J. R.; Lawford, R. G.; Koike, T.; Cripe, D.; Gundersen, L. C.; Valette-Silver, N. J.; Bohan, M.; Kaye, J. A.; Freilich, M. H.; Volz, S. M.; Friedl, L.; Komar, G.; Jacobberger-Jellison, P. A.; Luce, P.; Torn, M. S.; Baldocchi, D. D.; Agarwal, D.; Biraud, S. C.; Billesbach, D. P.; Humphrey, M.; Law, B. E.; Papale, D.; Wofsy, S. C.; Quadrelli, R.; Wilson, S.; Liverman, D. M.; Liss, P. S.; Killeen, T.; Watson, R.; Zebiak, S. E.; Tang, Q.; Hong, Y.; Chen, D.; Yang, D.; Rumburg, J.; Newmark, J. S.; Giles, B. L.; DeLuca, E.; Hagan, M. E.; Studinger, M.; Jezek, K. C.; Richter-Menge, J.; Lea, P.; Passalacqua, P.; Oskin, M. E.; Crosby, C.; Glennie, C. L.; Lechner, H. N.; Bowman, L. J.; Barton, T.; Uhle, M. E.; Anderson, G. J.; Fountain, D. M.; Hess, J. W.; Harper, H. E.; Gingerich, P. D.; Groffman, P. M.; Weathers, K. C.; Bernhardt, E. S.; SanClements, M.; Loescher, H. W.; Pitelka, L.; Sandgathe, S. A.; Eleuterio, D. P.; Cortinas, J. V.; McElroy, B. J.; Hsu, L.; Kim, W.; Martin, R. L.; Arrowsmith, R.; Hill, M. C.; Freymueller, J. T.; Marks, D. G.; Sztein, E.; Eichelberger, J. C.; Ismail-Zadeh, A.; Gordeev, E.; Myers, M.; Scholl, D. W.; Ackley, S. F.; Schofield, O.; Costa, D. P.; Marin, J. A.; Pilpipenko, V. A.; Vega, P.; Zesta, E.; Stepanova, M. V.; Uozumi, T.; Nolin, A. W.; Sturm, M.; Tziperman, E.; Abbot, D. S.; Ashkenazy, Y.; Gildor, H.; Halevy, I.; Johnston, D. T.; Knoll, A.; Losch, M. J.; Pollard, D.; Schoof, C.; Schrag, D. P.

    2012-12-01

    Three different aspects of Neoproterozoic snowball events will be presented. First, the glaciations of the Neoproterozoic Era (1,000 to 542 Myr BP) were preceded by dramatically light 13C isotopic excursions preserved in pre-glacial deposits. Standard explanations of these excursions involve remineralization of isotopically light organic matter and imply strong enhancement of atmospheric CO2 greenhouse gas concentration, apparently inconsistent with the glaciations that followed. We propose a scenario in which the isotopic signal, as well as the global glaciation, result from changes to the ocean biology, possibly due to the evolution of microorganisms, specifically eukaryotes. These changes may have lead to enhanced export of organic matter from the upper ocean into anoxic sub-surface waters and sediments. The organic matter undergoes anoxic remineralization at depth via either sulfate- or iron-reducing bacteria. In both cases this can lead to changes in carbonate alkalinity and dissolved inorganic pool that efficiently lower the atmospheric CO2 concentration, possibly plunging Earth into an ice age. (With Itay Halevy, Andrew Knoll, David Johnston, Dan Schrag). Second, the problem of ice flow in two horizontal dimensions over a snowball ocean will be briefly discussed. The formulation of ice flow problem in two dimensions, following the well-known ice-shelf equations in glaciology, will be derived in spherical coordinates, and numerical solutions and scaling arguments developed. It will be shown how the existence of semi-enclosed seas or narrow passages between continents may lead to strong sea-ice thickness gradients, consistent with previous studies that demonstrated this in simpler geometry. (With Dorian Abbot, Yossi Ashkenazy, Hezi Gildor, David Pollard, Christian Schoof, Dan Schrag). Finally, the ocean circulation under a thick snowball cover based on GCM simulations and dynamical analysis will be described and its dynamics analyzed. (With Yossi Ashkenazy

  3. Assessment of the numerical efficiency of ocean circulation model : Hycom contribution to the COMODO project

    NASA Astrophysics Data System (ADS)

    Lathuilière, Cyril; Baraille, Rémy; Le Boyer, Arnaud

    2015-04-01

    The French navy hydrographic service uses a modified version of the Hybrid coordinate ocean model (HYCOM) for operational oceanographic applications. In the framework of the COMODO project, a series of test cases has been carried out to measure the numerical efficiency of the model. It addresses a wide panel of oceanic processes (baroclinic eddy, baroclinic jet, coastal upwelling, internal tides) and is useful to examine most of numerical schemes (advection schemes, time stepping, pressure gradient, …). The objectives of this study are first to assess the numerical performance of the present model to guide the modelers to make the suitable choices, and second to examine how the performances may be improved in the next years. We examine the sensitivity of the main choices for Hycom (2th or 4th order advection schemes, and viscosity values) in baroclinic eddy and baroclinic jet test cases. Both test cases are run using increasing resolution. The highest resolution provides a reference for studying the coarser resolutions. In the baroclinic vortex test case, the second order vector form scheme is well performing whereas the 4th order scheme appears to be more accurate in the baroclinic jet test case. This is probably due to the lack of fine scale energy in the baroclinic vortex test case allowing simulations with very tiny dissipation rates. We focus then on the sensitivity of the performance to vertical coordinate choices. The ability of Hycom to switch between isopycnal coordinate and quasi geopotential coordinate provides useful insights for example on the sensitivity of numerical diapycnal mixing to remapping scheme. This is particularly visible on the internal tide test case. The type of vertical coordinate is also important for potential vorticity structures. The shape of the baroclinic vortex is found to be different in geopotential and isopycnal coordinates. At coarse resolution, the potential vorticity structures seem to be better resolved in isopycnal

  4. A Reduced Grid Method for a Parallel Global Ocean General Circulation Model

    SciTech Connect

    Wickett, M.E.

    1999-12-01

    A limitation of many explicit finite-difference global climate models is the timestep restriction caused by the decrease in cell size associated with the convergence of meridians near the poles. A computational grid in which the number of cells in the longitudinal direction is reduced toward high-latitudes, keeping the longitudinal width of the resulting cells as uniform as possible and increasing the allowable timestep, is applied to a three-dimensional primitive equation ocean-climate model. This ''reduced'' grid consists of subgrids which interact at interfaces along their northern and southern boundaries, where the resolution changes by a factor of three. Algorithms are developed to extend the finite difference techniques to this interface, focusing on the conservation required to perform long time integrations, while preserving the staggered spatial arrangement of variables and the numerics used on subgrids. The reduced grid eliminates the common alternative of filtering high-frequency modes from the solution at high-latitudes to allow a larger timestep and reduces execution time per model step by roughly 20 percent. The reduced grid model is implemented for parallel computer architectures with two-dimensional domain decomposition and message passing, with speedup results comparable to those of the original model. Both idealized and realistic model runs are presented to show the effect of the interface numerics on the model solution. First, a rectangular, mid-latitude, at-bottomed basin with vertical walls at the boundaries is driven only by surface wind stress to compare three resolutions of the standard grid to reduced grid cases which use various interface conditions. Next, a similar basin with wind stress, heat, and fresh water forcing is used to compare the results of a reduced grid with those of a standard grid result while exercising the full set of model equations. Finally, global model runs, with topography, forcing, and physical parameters similar to

  5. Mixed boundary conditions in ocean general circulation models and their influence on the stability of the model`s conveyor belt

    SciTech Connect

    Mikolajewicz, U.; Maier-reimer, E.

    1994-11-01

    When driven under `mixed boundary conditions` coarse resolution ocean general circulation models (OGCMs) generally show a high sensitivity of the present-day thermohaline circulation against perturbations. We will show that an alternative formulation of the boundary condition for temperature, a mixture of prescribed heat fluxes and additional restoring of the sea surface temperature to a climatological boundary temperature with a longer time constant, drastically alters the stability of the modes of the thermohaline circulation. The results from simulations with the Hamburg large-scale geostrophic OGCM indicate that the stability of the mode of the thermohaline circulation with formation of North Atlantic deepwater increases, if the damping of sea surface temperature anomalies is reduced, whereas the opposite is true for the mode without North Atlantic deep water formation. It turns out that the formulation of the temperature boundary condition also affects the variability of the model.

  6. Dynamic intermediate ocean circulation in the North Atlantic during Heinrich Stadial 1: A radiocarbon and neodymium isotope perspective

    NASA Astrophysics Data System (ADS)

    Wilson, David J.; Crocket, Kirsty C.; Flierdt, Tina; Robinson, Laura F.; Adkins, Jess F.

    2014-11-01

    The last deglaciation was characterized by a series of millennial-scale climate events that have been linked to deep ocean variability. While often implied in interpretations, few direct constraints exist on circulation changes at mid-depths. Here we provide new constraints on the variability of deglacial mid-depth circulation using combined radiocarbon and neodymium isotopes in 24 North Atlantic deep-sea corals. Their aragonite skeletons have been dated by uranium-series, providing absolute ages and the resolution to record centennial-scale changes, while transects spanning the lifetime of a single coral allow subcentennial tracer reconstruction. Our results reveal that rapid fluctuations of water mass sourcing and radiocarbon affected the mid-depth water column (1.7-2.5 km) on timescales of less than 100 years during the latter half of Heinrich Stadial 1. The neodymium isotopic variability (-14.5 to -11.0) ranges from the composition of the modern northern-sourced waters towards more radiogenic compositions, suggesting the presence of a greater southern-sourced component at some times. However, in detail, simple two-component mixing between well-ventilated northern-sourced and radiocarbon-depleted southern-sourced water masses cannot explain all our data. Instead, corals from ~15.0 ka and ~15.8 ka may record variability between southern-sourced intermediate waters and radiocarbon-depleted northern-sourced waters, unless there was a major shift in the neodymium isotopic composition of the northern end-member. In order to explain the rapid shift towards the most depleted radiocarbon values at ~15.4 ka, we suggest a different mixing scenario involving either radiocarbon-depleted deep water from the Greenland-Iceland-Norwegian Seas or a southern-sourced deep water mass. Since these mid-depth changes preceded the Bolling-Allerod warming and were apparently unaccompanied by changes in the deep Atlantic, they may indicate an important role for the intermediate ocean in

  7. Simulation of anthropogenic CO2 uptake in the CCSM3.1 ocean circulation-biogeochemical model: comparison with data-based estimates

    NASA Astrophysics Data System (ADS)

    Wang, S.; Moore, J. K.; Primeau, F. W.; Khatiwala, S.

    2011-11-01

    The global ocean has taken up a large fraction of the CO2 released by human activities since the industrial revolution. Quantifying the oceanic anthropogenic carbon (Cant) inventory and its variability is important for predicting the future global carbon cycle. The detailed comparison of data-based and model-based estimates is essential for the validation and continued improvement of our prediction capabilities. So far, three global estimates of oceanic Cant inventory that are "data-based" and independent of global ocean circulation models have been produced: one based on the ΔC* method, and two are based on reconstructions of the Green function for the surface-to-interior transport, the TTD method and the maximum entropy inversion method (KPH). The KPH method, in particular, is capable of reconstructing the history of Cant inventory through the industrial era. In the present study we use forward model simulations of the Community Climate System Model (CCSM3.1) to estimate the Cant inventory and compare the results with the data-based estimates. We also use the simulations to test several assumptions of the KPH method, including the assumption of constant climate and circulation, which is common to all the data-based estimates. Though the integrated estimates of global Cant inventories are consistent with each other, the regional estimates show discrepancies up to 50 %. The CCSM3 model underestimates the total Cant inventory, in part due to weak mixing and ventilation in the North Atlantic and Southern Ocean. Analyses of different simulation results suggest that key assumptions about ocean circulation and air-sea disequilibrium in the KPH method are generally valid on the global scale, but may introduce significant errors in Cant estimates on regional scales. The KPH method should also be used with caution when predicting future oceanic anthropogenic carbon uptake.

  8. Overturn of the Oceasn Flow in the North Atlantic as a Trigger of Inertia Motion to Form a Meridional Ocean Circulation

    NASA Astrophysics Data System (ADS)

    Nakamura, Shigehisa

    2010-05-01

    This work is an introduction of a meridional ocean circulation. As for the zonal motions,there have been many contributions. Recent oceanographic works noticed an overturn of the ocean current in the North Atlantic. The author notices this overturn is a trigger to generate a meridional ocean circulation to have a track through the deep Atlantic, the deep circum-polar current, the deep branch flow to the Pacific between the Australian and the South America. The east part of the branch flow relates to the upwelling off Peru, and the west part relates to form a deep water in the Northwest Pacific. THe overturn of the North Atlantic suggests an outflow of the deep water and a storage of the old aged deep water in the Northwest Pacific. The storage water increase in the Northwest Pacific shoould be a trigger of the swelling up of the sea level mid Pacific to affect to the ocean front variations between the coastal waters and the ocean water. In order to keep a hydrodynamic balance on the earth, an increase of the deep water in the Pacific should flow through the Bering Sea and the Arctic Sea to get to the North Atlantic. It should be noted that a budget of the ocean water flow must be hold the condition of the water masses concservation on the earth surface. This inertia motion is maintained once induced after any natural effect or some man-made influences. At this stage, the author has to notice that there has been developed a meridional inertia path of the air particle as well as the ocean water parcel, nevertheless nobody has had pointed out this inertiamotion with a meridional path in the ocean. Air-sea interaction must be one of the main factors for driving the ocean water though the inertia motion in the global scale is more energetic. To the details, the scientists should pursue what geophysical dynamics must be developed in the future.

  9. Simulating transoceanic migrations of young loggerhead sea turtles: merging magnetic navigation behavior with an ocean circulation model.

    PubMed

    Putman, Nathan F; Verley, Philippe; Shay, Thomas J; Lohmann, Kenneth J

    2012-06-01

    Young loggerhead sea turtles (Caretta caretta) from eastern Florida, USA, undertake a transoceanic migration in which they gradually circle the Sargasso Sea before returning to the North American coast. Loggerheads possess a 'magnetic map' in which regional magnetic fields elicit changes in swimming direction along the migratory pathway. In some geographic areas, however, ocean currents move more rapidly than young turtles can swim. Thus, the degree to which turtles can control their migratory movements has remained unclear. In this study, the movements of young turtles were simulated within a high-resolution ocean circulation model using several different behavioral scenarios, including one in which turtles drifted passively and others in which turtles swam briefly in accordance with experimentally derived data on magnetic navigation. Results revealed that small amounts of oriented swimming in response to regional magnetic fields profoundly affected migratory routes and endpoints. Turtles that engaged in directed swimming for as little as 1-3 h per day were 43-187% more likely than passive drifters to reach the Azores, a productive foraging area frequented by Florida loggerheads. They were also more likely to remain within warm-water currents favorable for growth and survival, avoid areas on the perimeter of the migratory route where predation risk and thermal conditions pose threats, and successfully return to the open-sea migratory route if carried into coastal areas. These findings imply that even weakly swimming marine animals may be able to exert strong effects on their migratory trajectories and open-sea distributions through simple navigation responses and minimal swimming. PMID:22573765

  10. Response of Northern Hemisphere storm tracks to Indian-western Pacific Ocean warming in atmospheric general circulation models

    NASA Astrophysics Data System (ADS)

    Chu, Cuijiao; Yang, Xiuqun; Ren, Xuejuan; Zhou, Tianjun

    2013-04-01

    With 40 yr integration output of two atmospheric general circulation models (GAMIL/IAP and HadAM3/UKMO) forced with identical prescribed seasonally-varying sea surface temperature, this study examines the effect of the observed Indian-western Pacific Ocean (IWP) warming on the Northern Hemisphere storm tracks (NHSTs). Both models indicate that the observed IWP warming tends to cause both the North Pacific storm track (NPST) and the North Atlantic storm track (NAST) to move northward. Such a consistent effect on the two storm tracks is closely associated with the changes in the low-level atmospheric baroclinicity, high-level jet stream and upper-level geopotential height. The IWP warming can excite a wavelike circum-global teleconnection in the geopotential height that gives rise to an anticyclonic anomaly over the midlatitude North Pacific and a positive-phase NAO anomaly over the North Atlantic. These geopotential height anomalies tend to enhance upper-level zonal westerly winds north of the climatological jet axes and increase low-level baroclinicity and eddy growth rates, thus favoring transient eddy more active north of the climatological storm track axes, responsible for the northward shift of the both storm tracks. The IWP warming-induced northward shift of the NAST is quite similar to the observed, suggesting that the IWP warming can be one of key factors to cause decadal northward shift of the NAST since the 1980s. However, the IWP warming-induced northward shift of the NPST is completely opposite to the observed, implying that the observed southward shift of the NPST since the 1980s would be primarily attributed to other reasons, although the IWP warming can have a cancelling effect against those reasons. Keywords: Northern Hemisphere storm tracks, Indian-western Pacific Ocean warming, baroclinicity, eddy growth rate

  11. Effects of the Eastern Mediterranean Sea circulation on the thermohaline properties as recorded by fixed deep-ocean observatories

    NASA Astrophysics Data System (ADS)

    Bensi, Manuel; Velaoras, Dimitris; Meccia, Virna L.; Cardin, Vanessa

    2016-06-01

    Temperature and salinity time-series from three fixed observatories in the Eastern Mediterranean Sea (EMed) are investigated using multi-annual (2006-2014), high-frequency (up to 3 h sampling rate) data. Two observatories are deployed in the two dense water formation (DWF) areas of the EMed (Southern Adriatic Sea, E2-M3A; Cretan Sea, E1-M3A) and the third one (Southeast Ionian Sea, PYLOS) lays directly on the intermediate water masses pathway that connects the DWF sources. The long-term variations of the hydrological characteristics at the observatories reflect the oscillating large-scale circulation modes of the basin (i.e. BiOS-Bimodal Oscillating System and internal thermohaline pump theories). In particular, between 2006 and 2014 an anti-correlated behaviour of the intermediate layer (200-600 m) salinity between the Adriatic and Cretan Sea observatories is verified. This behaviour is directly linked to reversals of the North Ionian Gyre, which appeared cyclonic during 2006-2011 and turned anticyclonic after 2011. Statistical analysis suggests that the travel time of the intermediate salinity maximum signal between the Cretan and Adriatic Sea is roughly 1.5 years, in good agreement with the analysis of additionally presented ARGO data as well as previous literature references. We argue that the understanding of such oscillations provides important foresight on future DWF events, as increased salinity may act as a crucial preconditioning factor for DWF processes. Additionally, energy spectrum analysis of the time-series revealed interesting short-term variability connected to mesoscale activity at the observatories. Hence, the sustain of permanent observatories able to monitor oceanic parameters at high sampling rates may play a key role in understanding both climatic and oceanic processes and trends.

  12. Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node

    NASA Astrophysics Data System (ADS)

    Thomsen, Laurenz; Barnes, Christopher; Best, Mairi; Chapman, Ross; Pirenne, Benoît; Thomson, Richard; Vogt, Joachim

    2012-08-01

    The NEPTUNE Canada cabled observatory network enables non-destructive, controlled experiments and time-series observations with mobile robots on gas hydrates and benthic community structure on a small plateau of about 1 km2 at a water depth of 870 m in Barkley Canyon, about 100 km offshore Vancouver Island, British Columbia. A mobile Internet operated vehicle was used as an instrument platform to monitor and study up to 2000 m2 of sediment surface in real-time. In 2010 the first mission of the robot was to investigate the importance of oscillatory deep ocean currents on methane release at continental margins. Previously, other experimental studies have indicated that methane release from gas hydrate outcrops is diffusion-controlled and should be much higher than seepage from buried hydrate in semipermeable sediments. Our results show that periods of enhanced bottom currents associated with diurnal shelf waves, internal semidiurnal tides, and also wind-generated near-inertial motions can modulate methane seepage. Flow dependent destruction of gas hydrates within the hydrate stability field is possible from enhanced bottom currents when hydrates are not covered by either seafloor biota or sediments. The calculated seepage varied between 40-400 μmol CH4 m-2 s-1. This is 1-3 orders of magnitude higher than dissolution rates of buried hydrates through permeable sediments and well within the experimentally derived range for exposed gas hydrates under different hydrodynamic boundary conditions. We conclude that submarine canyons which display high hydrodynamic activity can become key areas of enhanced seepage as a result of emerging weather patterns due to climate change.

  13. Experiences modeling ocean circulation problems on a 30 node commodity cluster with 3840 GPU processor cores.

    NASA Astrophysics Data System (ADS)

    Hill, C.

    2008-12-01

    for which this technology is currently most useful. However, many interesting problems fit within this envelope. Looking forward, we extrapolate our experience to estimate full-scale ocean model performance and applicability. Finally we describe preliminary hybrid mixed 32-bit and 64-bit experiments with graphics cards that support 64-bit arithmetic, albeit at a lower performance.

  14. Deep Circulation in the Lau Basin of the South Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Speer, K.; Thurnherr, A.

    2006-12-01

    The Lau Basin is a semi-enclosed basin in the tropical South Pacific, located approximately 1500 km north of New Zealand. Below 1000m it is largely closed to the east, south and west by the Lau and the Tonga Ridges, respectively. The Zephyr Shoal at 15S blocks the northern edge of the Lau Basin below 2000m almost completely. The East Lau Spreading Center (ELSC), which form the "bull's eye" of the Lau Basin Integrated Study Sites (ISS), runs approximately parallel to the Tonga Ridge in the Lau Basin between 19S and 23S. Its depth is shallowest (2000m) near its southern end and deepens northward to about 2800m. There are currently 11 neutrally buoyant floats drifting in the Lau Basin at 1700m, near the depth of the hydrothermal plumes known at the time of deployment. The floats, which were deployed during three R2K cruises in 2004/05, return to the surface every 3 4 weeks in order to transmit their positions and temperature data back to shore via a network of satellites. The data are made available in near real-time on the web. In contrast to current-meter data, which become available only after mooring recovery and which, because of their Eulerian nature, are not very well suited for studying dispersal near topography, the float data yield timely, cost-effective and directly usable information about dispersal in the deep ocean. The available float data currently span 261 drift cycles and cover a good portion of the Lau Basin. Between April 2004 and June 2006, the mean meridional velocity at 1700m was 3.2 ± 1.1 mm/s to the north, while the zonal flow was indistinguishable from zero. Individual float-cycle-averaged velocities, on the other hand, are randomly distributed and associated with speeds up to 9 cm/s. These observations imply that on timescales of months to years horizontal dispersal in the deep interior of the Lau Basin is primarily eddy diffusive, while the observed northward mean flow becomes important on longer timescales. As a consequence, larval

  15. The Southern Oscillation in Surface Circulation and Climate over the Tropical Atlantic, Eastern Pacific, and Indian Oceans as Captured by Cluster Analysis.

    NASA Astrophysics Data System (ADS)

    Wolter, Klaus

    1987-04-01

    Clusters of sea level pressure (SLP), surface wind, cloudiness, and sea surface temperature (SST) in the domain of the tropical Atlantic, eastern Pacific, and Indian Oceans are introduced and discussed in terms of general circulation and climate. They appear to capture well the large-scale degrees of freedom of the seasonal fields. In the Atlantic and, to a lesser extent, in the eastern Pacific, most analyzed fields group into zonally oriented `trade wind' clusters. These are separated distinctly by the near-equatorial trough axis. By contrast the Indian Ocean features strong interhemispheric connections associated with the monsoon systems of boreal summer and, to a lesser degree, of boreal winter.The usefulness of clusters thus established is elucidated with respect to the Southern Oscilation (SO). General circulation changes associated with this planetary pressure seesaw are deduced from correlation maps of surface field clusters for January/February and July/August. During the positive SO phase (i.e., anomalously high pressure over the eastern Pacific and anomalously low pressure over Indonesia), both the Atlantic and eastern Pacific near-equatorial troughs are inferred to be shifted towards the north from July/August SLP, wind, and cloudiness fields. While eastern Pacific trade winds are weakened in both seasons in the positive SO phase, the Atlantic trades appear strengthened at the same time in the winter hemisphere only. Over the Indian Ocean, the monsoon circulation seems to be strengthened during the positive SO phase, with the summer monsoon displaying a more complex picture. Its SLP, cloudiness and SST fields support an enhanced southwest monsoon, while its surface winds appear largely inconclusive. SST is lowered during the positive SO phase in all three tropical oceans.Since all major tropical circulation components over the Atlantic, eastern Pacific, and Indian Ocean participate in the Southern Oscillation, as is evidenced by field significance tests

  16. Coastal ocean variability in the US Pacific Northwest region: seasonal patterns, winter circulation, and the influence of the 2009-2010 El Niño

    NASA Astrophysics Data System (ADS)

    Durski, Scott M.; Kurapov, Alexander L.; Allen, John S.; Kosro, P. Michael; Egbert, Gary D.; Shearman, R. Kipp; Barth, John A.

    2015-12-01

    A 2-km horizontal resolution ocean circulation model is developed for a large coastal region along the US Pacific Northwest (34-50N) to study how continental shelf, slope, and interior ocean variability influence each other. The model has been run for the time period September 2008-May 2011, driven by realistic surface momentum and heat fluxes obtained from an atmospheric model and lateral boundary conditions obtained from nesting in a global ocean model. The solution compares favorably to satellite measurements of sea surface temperature and sea surface height, observations of surface currents by high-frequency radars, mooring temperature time series, and glider temperature and salinity sections. The analysis is focused on the seasonal response of the coastal ocean with particular emphasis on the winter circulation patterns which have previously garnered relatively little attention. Interannual variability is examined through a comparison of the 2009-2010 winter influenced by El Niño and the winters in the preceding and following years. Strong northward winds combined with reduced surface cooling along the coast north of Cape Mendocino (40.4N) in winter 2009-2010, resulting in a vigorous downwelling season, characterized by relatively energetic northward currents and warmer ocean temperatures over the continental shelf and upper slope. An analysis of the time variability of the volume-averaged temperature and salinity in a coastal control volume (CV), that extends from 41 to 47N and offshore from the coast to the 200-m isobath, clearly shows relevant integrated characteristics of the annual cycle and the transitions between winter shelf circulation forced by northward winds and the summer circulation driven primarily by southward, upwelling-favorable winds. The analysis also reveals interesting interannual differences in these characteristics. In particular, the CV volume-average temperature remains notably warmer during January-March 2010 of the El Niño winter.

  17. Coherency of European speleothem δ18O records linked to North Atlantic ocean circulation

    NASA Astrophysics Data System (ADS)

    Deininger, Michael; McDermott, Frank

    2016-04-01

    demonstrate that a common signal (expressed by the 1st PCs) is shared by the investigated speleothem δ18O records for each individual time window and that the 1st PCs agree in the overlapping periods. This allowed us to construct a common speleothem record (CSR) for the last 4.5 ka. The CSR shows a strong millennial cyclicity in the investigated period. We demonstrate that the large-scale changes in the European CSR, reflected by its millennial cyclicity, are in phase with the well-known Bond cycles during the last 4.5 ka that reflect changes of drift ice in the North Atlantic (Bond et al., 2001). Evidence for this link was also shown by Mangini et al. (2007) using a stalagmite from the Central Alps. Furthermore, the CSR shows a very good agreement with a recent, independently dated reconstruction for the strength of the sub-polar gyre (Thornalley et al., 2009) and we argue that these changes during the last 4.5 ka are likely caused by the variability of the atmospheric circulation affecting the interplay between the subpolar gyre and the subtropical gyre in the North Atlantic, as well as European speleothem δ18O records. BOND, G., KROMER, B., BEER, J., MUSCHELER, R., EVANS, M. N., SHOWERS, W., HOFFMANN, S., LOTTI-BOND, R., HAJDAS, I. & BONANI, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science, 294, 2130-6. MANGINI, A., VERDES, P., SPÖTL, C., SCHOLZ, D., VOLLWEILER, N. & KROMER, B. 2007. Persistent influence of the North Atlantic hydrography on central European winter temperature during the last 9000 years. Geophysical Research Letters, 34. THORNALLEY, D. J. R., ELDERFIELD, H. & MCCAVE, I. N. 2009. Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic. Nature, 457, 711-714.

  18. Design and Implementation of a Parallel Multivariate Ensemble Kalman Filter for the Poseidon Ocean General Circulation Model

    NASA Technical Reports Server (NTRS)

    Keppenne, Christian L.; Rienecker, Michele M.; Koblinsky, Chester (Technical Monitor)

    2001-01-01

    A multivariate ensemble Kalman filter (MvEnKF) implemented on a massively parallel computer architecture has been implemented for the Poseidon ocean circulation model and tested with a Pacific Basin model configuration. There are about two million prognostic state-vector variables. Parallelism for the data assimilation step is achieved by regionalization of the background-error covariances that are calculated from the phase-space distribution of the ensemble. Each processing element (PE) collects elements of a matrix measurement functional from nearby PEs. To avoid the introduction of spurious long-range covariances associated with finite ensemble sizes, the background-error covariances are given compact support by means of a Hadamard (element by element) product with a three-dimensional canonical correlation function. The methodology and the MvEnKF configuration are discussed. It is shown that the regionalization of the background covariances; has a negligible impact on the quality of the analyses. The parallel algorithm is very efficient for large numbers of observations but does not scale well beyond 100 PEs at the current model resolution. On a platform with distributed memory, memory rather than speed is the limiting factor.

  19. On estimating the basin-scale ocean circulation from satellite altimetry. Part 1: Straightforward spherical harmonic expansion

    NASA Technical Reports Server (NTRS)

    Tai, Chang-Kou

    1988-01-01

    Direct estimation of the absolute dynamic topography from satellite altimetry has been confined to the largest scales (basically the basin-scale) owing to the fact that the signal-to-noise ratio is more unfavorable everywhere else. But even for the largest scales, the results are contaminated by the orbit error and geoid uncertainties. Recently a more accurate Earth gravity model (GEM-T1) became available, providing the opportunity to examine the whole question of direct estimation under a more critical limelight. It is found that our knowledge of the Earth's gravity field has indeed improved a great deal. However, it is not yet possible to claim definitively that our knowledge of the ocean circulation has improved through direct estimation. Yet, the improvement in the gravity model has come to the point that it is no longer possible to attribute the discrepancy at the basin scales between altimetric and hydrographic results as mostly due to geoid uncertainties. A substantial part of the difference must be due to other factors; i.e., the orbit error, or the uncertainty of the hydrographically derived dynamic topography.

  20. A Spectral Element Ocean Model on the Cray T3D: the interannual variability of the Mediterranean Sea general circulation

    NASA Astrophysics Data System (ADS)

    Molcard, A. J.; Pinardi, N.; Ansaloni, R.

    A new numerical model, SEOM (Spectral Element Ocean Model, (Iskandarani et al, 1994)), has been implemented in the Mediterranean Sea. Spectral element methods combine the geometric flexibility of finite element techniques with the rapid convergence rate of spectral schemes. The current version solves the shallow water equations with a fifth (or sixth) order accuracy spectral scheme and about 50.000 nodes. The domain decomposition philosophy makes it possible to exploit the power of parallel machines. The original MIMD master/slave version of SEOM, written in F90 and PVM, has been ported to the Cray T3D. When critical for performance, Cray specific high-performance one-sided communication routines (SHMEM) have been adopted to fully exploit the Cray T3D interprocessor network. Tests performed with highly unstructured and irregular grid, on up to 128 processors, show an almost linear scalability even with unoptimized domain decomposition techniques. Results from various case studies on the Mediterranean Sea are shown, involving realistic coastline geometry, and monthly mean 1000mb winds from the ECMWF's atmospheric model operational analysis from the period January 1987 to December 1994. The simulation results show that variability in the wind forcing considerably affect the circulation dynamics of the Mediterranean Sea.

  1. Constraints On Fluid Evolution During Mid-Ocean Ridge Hydrothermal Circulation From Anhydrite Sampled by ODP Hole 1256D

    NASA Astrophysics Data System (ADS)

    Smith-Duque, C.; Teagle, D. A.; Alt, J. C.; Cooper, M. J.

    2008-12-01

    Anhydrite is potentially a useful mineral for recording the evolution of seawater-derived fluids during mid- ocean ridge hydrothermal circulation because it exhibits retrograde solubility, and hence may precipitate due to the heating of seawater or the sub-surface mixing of seawater with black smoker-like fluids. Here we provide new insights into the chemical and thermal evolution of seawater during hydrothermal circulation through analyses of anhydrite recovered from ODP Hole 1256D, the first complete penetration of intact upper oceanic crust down to gabbros. Previously, crustal anhydrite has been recovered only from Hole 504B. Measurements of 87Sr/86Sr, major element ratios, Rare Earth Elements and δ18O in anhydrite constrain the changing composition of fluids as they chemically interact with basalt. Anhydrite fills veins and pore-space in the lower lava sequences from ~530 to ~1000 meters sub- basement (msb), but is concentrated in the lava-dike transition (754 to 811 msb) and uppermost sheeted dikes. Although present in greater quantities than in Hole 504B, the amount of anhydrite recovered from the Site 1256 crust is low compared to that predicted by models of hydrothermal circulation (e.g., Sleep, 1991). Two distinct populations of anhydrite are indicated by measurements of 87Sr/86Sr suggesting different fluid evolution paths within Site 1256. One group of anhydrites have 87Sr/86Sr of 0.7070 to 0.7085, close to that of 15 Ma seawater (0.70878), suggesting that some fluids penetrate through the lavas and into the sheeted dikes with only minimal Sr-exchange with the host basalts. A second group, with low 87Sr/86Sr between 0.7048 and 0.7052, indicates precipitation from a fluid that has undergone far greater interaction with basalt. This range is close to that estimated from Sr-isotopic analyses of epidote for the Hole 1256D hydrothermal fluids (87Sr/86Sr ~0.705). Sr/Ca and 87Sr/86Sr indicate a similar relationship to that seen at ODP Hole 504B suggesting that

  2. Northern versus southern gateways control on ocean overturning circulation at the Eocene-Oligocene transition and possible implications to global cooling

    NASA Astrophysics Data System (ADS)

    Abelson, M.; Erez, J.

    2013-12-01

    There is a growing body of evidence indicating reorganization in the ocean overturning circulation during the transition from the Eocene to the Oligocene, in particular, the initiation of the northern-sourced overturning circulation that comprises the northern component water (NCW) and northward flowing intermediate water. This evidence includes Nd isotopes from the Southern Hemisphere, δ13C from intermediate water in the subtropical North Atlantic, and increasing difference in the benthic δ18O between the Northern and Southern Hemispheres. We compare all these sets of proxies and show that the increasing trends have been conjugated throughout most of the Oligocene indicating enhancement of the northern-sourced overturning circulation that began around the Eocene-Oligocene transition (EOT). This reorganization was attributed mainly to the development of the wind-driven Antarctic circumpolar current (ACC). Based on variety of geological inferences, we suggest that the shift to interhemispheric bipolar overturning circulation was initiated by buoyancy fluxes formed by the development of anti-estuarine circulation between the Nordic Seas and the North Atlantic around the EOT, which significantly intensified the NCW. The Nordic anti-estuarine circulation began at a critical threshold during rapid tectonic subsidence of the Greenland-Scotland Ridge (GSR) triggered by the suppression of the Iceland mantle plume. We show that the development of northern-sourced circulation cell during the Oligocene correlates compellingly with the histories of the GSR subsidence and the activity of the Iceland mantle plume, and to a lesser degree with the ACC history. Accordingly, this circulation was enhanced as long as the GSR subsided rapidly. The onset of the northern-sourced overturning circulation, which is the biologically productive circulation domain, has probably triggered the marked increase in the ocean productivity during the EOT. The relationship between the EOT climatic

  3. Sensitivity of the North Atlantic Ocean Circulation to an abrupt change in the Nordic Sea overflow in a high resolution global coupled climate model

    NASA Astrophysics Data System (ADS)

    Zhang, Rong; Delworth, Thomas L.; Rosati, Anthony; Anderson, Whit G.; Dixon, Keith W.; Lee, Hyun-Chul; Zeng, Fanrong

    2011-12-01

    The sensitivity of the North Atlantic Ocean Circulation to an abrupt change in the Nordic Sea overflow is investigated for the first time using a high resolution eddy-permitting global coupled ocean-atmosphere model (GFDL CM2.5). The Nordic Sea overflow is perturbed through the change of the bathymetry in GFDL CM2.5. We analyze the Atlantic Meridional Overturning Circulation (AMOC) adjustment process and the downstream oceanic response to the perturbation. The results suggest that north of 34°N, AMOC changes induced by changes in the Nordic Sea overflow propagate on the slow tracer advection timescale, instead of the fast Kelvin wave timescale, resulting in a time lead of several years between subpolar and subtropical AMOC changes. The results also show that a stronger and deeper-penetrating Nordic Sea overflow leads to stronger and deeper AMOC, stronger northward ocean heat transport, reduced Labrador Sea deep convection, stronger cyclonic Northern Recirculation Gyre (NRG), westward shift of the North Atlantic Current (NAC) and southward shift of the Gulf Stream, warmer sea surface temperature (SST) east of Newfoundland and colder SST south of the Grand Banks, stronger and deeper NAC and Gulf Stream, and stronger oceanic eddy activities along the NAC and the Gulf Stream paths. A stronger/weaker Nordic Sea overflow also leads to a contracted/expanded subpolar gyre (SPG). This sensitivity study points to the important role of the Nordic Sea overflow in the large scale North Atlantic ocean circulation, and it is crucial for climate models to have a correct representation of the Nordic Sea overflow.

  4. (abstract) Ekman Pumping/Suction and Wind-Driven Ocean Circulation from ERS-1 Scatterometer Measurements Over the Arabian Sea During October 1994-October 1995

    NASA Technical Reports Server (NTRS)

    Halpern, D.; Freilich, M. H.; Weller, R. A.

    1996-01-01

    Spatial variations of the east-west and north-south components of surface wind stress are critical in studies of ocean circulation and biological-physical interactions because surface wind stress curl produces a vertical velocity in the upper ocean at the bottom of the Ekman Layer.The ERS-1 scatterometer provides reasonable coverage and direct measurements of vector of winds. Three schemes are evaluated relative to high-quality moored-bouy wind observations recorded in the central Arabian Sea, where high surface waves and high atmospheric water content during the southeast monsoon adversely affect the estimation of satellite-derived winds.

  5. Using Advanced Data Assimilation For Assessing The Capabilities And Limits Of Using The GOCE Geoid To Improve The Shelf And Coastal Ocean Low-Frequency Circulations

    NASA Astrophysics Data System (ADS)

    Julien, L.; Pierre J., D.; Guilhem, M.; Georges, B.; Matthieu, L.; Muriel, L.; Roger, H.; Catherine, B.

    2008-12-01

    Realistic ocean modelling is part of the new challenges that has arisen in the past decade in order to access precise and accurate knowledge of the ocean circulation, especially at regional and coastal scales. An efficient ocean modelling system is now built both on both a hydrodynamic model and a data assimilation technique. Altimetric data plays a central role because of their relative abundance, coverage and repetitive sampling. At the large scales, using a geostrophic balance equation, the upper-layer ocean circulation could be approximately retrieved from the ocean surface topography, assuming that the ocean surface reference level, given by the geoid, is known with sufficient accuracy. However the geoid solutions do not contain the smaller scales characterizing coastal dynamics. More generally, the lack of control over the permanent circulations is a serious limitation for the regional ocean modelling and forecasting. The need for better ocean geoids has then been identified for a long time, and the recent gravimetric satellite missions are a first step to solve the problem. The GOCE satellite, developed at ESA and scheduled for lift- off in September 2008, will operate between two and two and a half years. Its main objective is to further improve our knowledge of the geopotential in providing a higher resolution static model for a variety of applications, especially in oceanography. The scientific community expects that the improved geoid model from GOCE will significantly advance our skill at modelling the mean ocean circulation, by using (1) precise geocentric sea surface elevations obtained from global altimetric measurements, (2) a mean geoid model with an accuracy of the order of one centimeter on spatial scales down to the width of boundary currents, (3) additional oceanographic data sets required to constrain ocean circulation models with data assimilation. The study presented here aims to assess the capabilities and the limits of the use of the GOCE

  6. Validating and assessing the sensitivity of the climate model with an ocean general circulation model developed at the Institute of Atmospheric Physics, Russian Academy of Sciences

    NASA Astrophysics Data System (ADS)

    Muryshev, K. E.; Eliseev, A. V.; Mokhov, I. I.; Diansky, N. A.

    2009-08-01

    A new version of the Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS), climate model (CM) has been developed using an ocean general circulation model instead of the statistical-dynamical ocean model applied in the previous version. The spatial resolution of the new ocean model is 3° in latitude and 5° in longitude, with 25 unevenly spaced vertical levels. In the previous version of the oceanic model, as in the atmospheric model, the horizontal resolution was 4.5° in latitude and 6° in longitude, with four vertical levels (the upper quasi-homogeneous layer, seasonal thermocline, abyssal ocean, and bottom friction layer). There is no correction for the heat and momentum fluxes between the atmosphere and ocean in the new version of the IAP RAS CM. Numerical experiments with the IAP RAS CM have been performed under current initial and boundary conditions, as well as with an increasing concentration of atmospheric carbon dioxide. The main simulated atmospheric and oceanic fields agree quite well with observational data. The new version’s equilibrium temperature sensitivity to atmospheric CO2 doubling was found to be 2.9 K. This value lies in the mid-range of estimates (2-4.5 K) obtained from simulations with state-of-the-art models of different complexities.

  7. The scale of hydrothermal circulation of the Iheya-North field inferred from intensive heat flow measurements and ocean drilling

    NASA Astrophysics Data System (ADS)

    Masaki, Y.; Kinoshita, M.; Yamamoto, H.; Nakajima, R.; Kumagai, H.; Takai, K.

    2014-12-01

    Iheya-North hydrothermal field situated in the middle Okinawa trough backarc basin is one of the largest ongoing Kuroko deposits in the world. Active chimneys as well as diffuse ventings (maximum fluid temperature 311 °C) have been located and studied in detail through various geological and geophysical surveys. To clarify the spatial scale of the hydrothermal circulation system, intensive heat flow measurements were carried out and ~100 heat flow data in and around the field from 2002 to 2014. In 2010, Integrated Ocean Drilling Program (IODP) Expedition 331 was carried out, and subbottom temperature data were obtained around the hydrothermal sites. During the JAMSTEC R/V Kaiyo cruise, KY14-01 in 2014, Iheya-North "Natsu" and "Aki" hydrothermal fields were newly found. The Iheya-Noth "Natsu" and "Aki" sites are located 1.2 km and 2.6 km south from the Iheya-North original site, respectively, and the maximum venting fluid temperature was 317 °C. We obtained one heat flow data at the "Aki" site. The value was 17 W/m2. Currently, the relationship between these hydrothermal sites are not well known. Three distinct zones are identified by heat flow values within 3 km from the active hydrothermal field. They are high-heat flow zone (>1 W/m2; HHZ), moderate-heat-flow zone (1-0.1 W/m2; MHZ); and low-heat-flow zone (<0.1 W/m2; LHZ). With increasing distance east of the HHZ, heat flow gradually decreases towards MHZ and LHZ. In the LHZ, temperature at 37m below the seafloor (mbsf) was 6 °C, that is consistent with the surface low heat flow suggesting the recharge of seawater. However, between 70 and 90 mbsf, the coarser sediments were cored, and temperature increased from 25 °C to 40°C. The temperature was 905°C at 151 mbsf, which was measured with thermoseal strips. The low thermal gradient in the upper 40 m suggests downward fluid flow. We infer that a hydrothermal circulation in the scale of ~1.5 km horizontal vs. ~a few hundred meters vertical.

  8. Deep Ocean Circulation and Nutrient Contents from Atlantic-Pacific Gradients of Neodymium and Carbon Isotopes During the Last 1 Ma

    NASA Astrophysics Data System (ADS)

    Piotrowski, A. M.; Elderfield, H.; Howe, J. N. W.

    2014-12-01

    The last few million years saw changing boundary conditions to the Earth system which set the stage for bi-polar glaciation and Milankovich-forced glacial-interglacial cycles which dominate Quaternary climate variability. Recent studies have highlighted the relative importance of temperature, ice volume and ocean circulation changes during the Mid-Pleistocene Transition at ~900 ka (Elderfield et al., 2012, Pena and Goldstein, 2014). Reconstructing the history of global deep water mass propagation and its carbon content is important for fully understanding the ocean's role in amplifying Milankovich changes to cause glacial-interglacial transitions. A new foraminiferal-coating Nd isotope record from ODP Site 1123 on the deep Chatham Rise is interpreted as showing glacial-interglacial changes in the bottom water propagation of Atlantic-sourced waters into the Pacific via the Southern Ocean during the last 1 million years. This is compared to globally-distributed bottom water Nd isotope records; including a new deep western equatorial Atlantic Ocean record from ODP Site 929, as well as published records from ODP 1088 and Site 1090 in the South Atlantic (Pena and Goldstein, 2014), and ODP 758 in the deep Indian Ocean (Gourlan et al., 2010). Atlantic-to-Pacific gradients in deep ocean neodymium isotopes are constructed for key time intervals to elucidate changes in deep water sourcing and circulation pathways through the global ocean. Benthic carbon isotopes are used to estimate deep water nutrient contents of deep water masses and constrain locations and modes of deep water formation. References: Elderfield et al. Science 337, 704 (2012) Pena and Goldstein, Science 345, 318 (2014) Gourlan et al., Quaternary Science Reviews 29, 2484-2498 (2010)