Artículos de revistas: "Thermohaline change"

1

Liu, Zhengyu. "Instability of Atlantic Meridional Overturning Circulation: Observations, Modelling and Relevance to Present and Future". Atmosphere 14, n.º 6 (12 de junio de 2023): 1011. http://dx.doi.org/10.3390/atmos14061011.

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The Atlantic Meridional Overturning Circulation (AMOC) has changed dramatically during the glacial–interglacial cycle. One leading hypothesis for these abrupt changes is thermohaline instability. Here, I review recent progress towards understanding thermohaline instability in both observations and modelling. Proxy records available seem to favor thermohaline instability as the cause of the abrupt climate changes during the glacial–deglacial period because the deep North Atlantic water mass and AMOC seemed to have changed before the North Atlantic climate. However, most fully Coupled General Circulation Models (CGCMs) so far seem to exhibit monostable AMOC, because (1) these models have failed to simulate abrupt AMOC changes unless they are forced by an abrupt change of external forcing and, (2) these models have shown opposite freshwater convergence from the current observations. This potential model bias in the AMOC stability leaves the model projection of the future AMOC change uncertain.

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2

Schatterer, Ulrich y Peter Anderman. "Thermohaline Circulation – Rapid Climate Change?" GAIA - Ecological Perspectives for Science and Society 8, n.º 3 (1 de septiembre de 1999): 193–96. http://dx.doi.org/10.14512/gaia.8.3.7.

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3

Anthoff, David, Francisco Estrada y Richard S. J. Tol. "Shutting Down the Thermohaline Circulation". American Economic Review 106, n.º 5 (1 de mayo de 2016): 602–6. http://dx.doi.org/10.1257/aer.p20161102.

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Past climatic changes were caused by a slowdown of the thermohaline circulation. We use results from experiments with three climate models to show that the expected cooling due to a slowdown of the thermohaline circulation is less in magnitude than the expected warming due to increasing greenhouse gas concentrations. The integrated assessment model FUND and a meta-analysis of climate impacts are used to evaluate the change in human welfare. We find modest but by and large positive effects on human welfare since a slowdown of the thermohaline circulation implies decelerated warming.

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4

Eldevik, Tor y Jan Even Ø. Nilsen. "The Arctic–Atlantic Thermohaline Circulation*". Journal of Climate 26, n.º 21 (16 de octubre de 2013): 8698–705. http://dx.doi.org/10.1175/jcli-d-13-00305.1.

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Abstract The Atlantic Ocean's thermohaline circulation is an important modulator of global climate. Its northern branch extends through the Nordic Seas to the cold Arctic, a region that appears to be particularly influenced by climate change. A thermohaline circulation is fundamentally concerned with two degrees of freedom. This is in particular the case for the inflow of warm and saline Atlantic Water through the Nordic Seas toward the Arctic that is balanced by two branches of outflow. The authors present an analytical model, rooted in observations, that constrains the strength and structure of this Arctic–Atlantic thermohaline circulation. It is found, maybe surprisingly, that the strength of Atlantic inflow is relatively insensitive to anomalous freshwater input; it mainly reflects changes in northern heat loss. Freshwater anomalies are predominantly balanced by the inflow's partition into estuarine and overturning circulation with southward polar outflow in the surface and dense overflow at depth, respectively. More quantitatively, the approach presented herein provides a relatively simple framework for making closed and consistent inference on the thermohaline circulation's response to observed or estimated past and future change in the northern seas.

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5

He, Zikang, Xiangyu Wu, Baogang Jin, Zhiqiang Chen, Juan Liu y Zhaoyi Wang. "Three-Dimensional Thermohaline Structure Reconstruction in the Northwest Pacific Ocean from HY-2 Satellite Data Based on a Variational Method". Journal of Physics: Conference Series 2486, n.º 1 (1 de mayo de 2023): 012035. http://dx.doi.org/10.1088/1742-6596/2486/1/012035.

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Abstract In this study, a variational method was used to reconstruct three-dimensional thermohaline fields in the Northwest Pacific Ocean. First, we evaluate the applicability of HY-2 satellite data in three-dimensional thermohaline fields reconstructions, and it confirms that the HY-2 data are reliable. A comparison with the forecast products of operational system shows the reconstructions can describe the structural characteristics of the ocean three-dimensional thermohaline fields and reflect the mesoscale change process of the ocean.

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6

Marotzke, J. "Abrupt climate change and thermohaline circulation: Mechanisms and predictability". Proceedings of the National Academy of Sciences 97, n.º 4 (15 de febrero de 2000): 1347–50. http://dx.doi.org/10.1073/pnas.97.4.1347.

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7

Tayar, Jamie y Meridith Joyce. "Is Thermohaline Mixing the Full Story? Evidence for Separate Mixing Events near the Red Giant Branch Bump". Astrophysical Journal Letters 935, n.º 2 (1 de agosto de 2022): L30. http://dx.doi.org/10.3847/2041-8213/ac85ab.

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Abstract The abundances of mixing-sensitive elements including lithium, [C/N], and 12C/13C are known to change near the red giant branch bump. The explanation most often offered for these alterations is double diffusive thermohaline mixing in the stellar interior. In this analysis, we investigate the ability of thermohaline mixing to explain the observed timing of these chemical depletion events. Recent observational measurements of lithium and [C/N] show that the abundance of lithium decreases before the abundance of [C/N], whereas numerical simulations of the propagation of the thermohaline-mixing region computed with MESA show that the synthetic abundances drop simultaneously. We therefore conclude that thermohaline mixing alone cannot explain the distinct events of lithium depletion and [C/N] depletion, as the simultaneity predicted by simulations is not consistent with the observation of separate drops. We thus invite more sophisticated theoretical explanations for the observed temporal separation of these chemical depletion episodes as well as more extensive observational explorations across a range of masses and metallicities.

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8

Bensi, Manuel, Vedrana Kovačević, Leonardo Langone, Stefano Aliani, Laura Ursella, Ilona Goszczko, Thomas Soltwedel et al. "Deep Flow Variability Offshore South-West Svalbard (Fram Strait)". Water 11, n.º 4 (2 de abril de 2019): 683. http://dx.doi.org/10.3390/w11040683.

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Water mass generation and mixing in the eastern Fram Strait are strongly influenced by the interaction between Atlantic and Arctic waters and by the local atmospheric forcing, which produce dense water that substantially contributes to maintaining the global thermohaline circulation. The West Spitsbergen margin is an ideal area to study such processes. Hence, in order to investigate the deep flow variability on short-term, seasonal, and multiannual timescales, two moorings were deployed at ~1040 m depth on the southwest Spitsbergen continental slope. We present and discuss time series data collected between June 2014 and June 2016. They reveal thermohaline and current fluctuations that were largest from October to April, when the deep layer, typically occupied by Norwegian Sea Deep Water, was perturbed by sporadic intrusions of warmer, saltier, and less dense water. Surprisingly, the observed anomalies occurred quasi-simultaneously at both sites, despite their distance (~170 km). We argue that these anomalies may arise mainly by the effect of topographically trapped waves excited and modulated by atmospheric forcing. Propagation of internal waves causes a change in the vertical distribution of the Atlantic water, which can reach deep layers. During such events, strong currents typically precede thermohaline variations without significant changes in turbidity. However, turbidity increases during April–June in concomitance with enhanced downslope currents. Since prolonged injections of warm water within the deep layer could lead to a progressive reduction of the density of the abyssal water moving toward the Arctic Ocean, understanding the interplay between shelf, slope, and deep waters along the west Spitsbergen margin could be crucial for making projections on future changes in the global thermohaline circulation.

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9

Lagarde, N., C. Reylé, A. C. Robin, G. Tautvaišienė, A. Drazdauskas, Š. Mikolaitis, R. Minkevičiūtė et al. "The Gaia-ESO Survey: impact of extra mixing on C and N abundances of giant stars". Astronomy & Astrophysics 621 (21 de diciembre de 2018): A24. http://dx.doi.org/10.1051/0004-6361/201732433.

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Context. The Gaia-ESO Public Spectroscopic Survey using FLAMES at the VLT has obtained high-resolution UVES spectra for a large number of giant stars, allowing a determination of the abundances of the key chemical elements carbon and nitrogen at their surface. The surface abundances of these chemical species are known to change in stars during their evolution on the red giant branch (RGB) after the first dredge-up episode, as a result of the extra mixing phenomena. Aims. We investigate the effects of thermohaline mixing on C and N abundances using the first comparison between the Gaia-ESO survey [C/N] determinations with simulations of the observed fields using a model of stellar population synthesis. Methods. We explore the effects of thermohaline mixing on the chemical properties of giants through stellar evolutionary models computed with the stellar evolution code STAREVOL. We include these stellar evolution models in the Besançon Galaxy model to simulate the [C/N] distributions determined from the UVES spectra of the Gaia-ESO survey and to compare them with the observations. Results. Theoretical predictions including the effect of thermohaline mixing are in good agreement with the observations. However, the field stars in the Gaia-ESO survey with C and N abundance measurements have a metallicity close to solar, where the efficiency of thermohaline mixing is not very large. The C and N abundances derived by the Gaia-ESO survey in open and globular clusters clearly show the impact of thermohaline mixing at low metallicity, which explains the [C/N] value observed in lower mass and older giant stars. Using independent observations of carbon isotopic ratio in clump field stars and open clusters, we also confirm that thermohaline mixing should be taken into account to explain the behaviour of 12C/13C as a function of stellar age. Conclusions. Overall, the current model including thermohaline mixing is able to reproduce very well the C and N abundances over the whole metallicity range investigated by the Gaia-ESO survey data.

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10

Clark, Peter U., Nicklas G. Pisias, Thomas F. Stocker y Andrew J. Weaver. "The role of the thermohaline circulation in abrupt climate change". Nature 415, n.º 6874 (febrero de 2002): 863–69. http://dx.doi.org/10.1038/415863a.

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11

Johnson, Helen L. y David P. Marshall. "Localization of abrupt change in the North Atlantic thermohaline circulation". Geophysical Research Letters 29, n.º 6 (marzo de 2002): 7–1. http://dx.doi.org/10.1029/2001gl014140.

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12

Ou, Hsien-Wang. "Thermohaline circulation: a missing equation and its climate-change implications". Climate Dynamics 50, n.º 1-2 (27 de marzo de 2017): 641–53. http://dx.doi.org/10.1007/s00382-017-3632-y.

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13

Nakanowatari, Takuya, Tomohiro Nakamura, Keisuke Uchimoto, Hiroki Uehara, Humio Mitsudera, Kay I. Ohshima, Hiroyasu Hasumi y Masaaki Wakatsuchi. "Causes of the Multidecadal-Scale Warming of the Intermediate Water in the Okhotsk Sea and Western Subarctic North Pacific". Journal of Climate 28, n.º 2 (15 de enero de 2015): 714–36. http://dx.doi.org/10.1175/jcli-d-14-00172.1.

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Abstract Causes of the multidecadal-scale warming of the intermediate water in the Okhotsk Sea and the western subarctic North Pacific during 1980–2008 are investigated using an ice–ocean coupled model with interannually varying atmospheric forcing. A hindcast experiment qualitatively reproduces the warming and decadal fluctuations of the intermediate water that are similar to those of observations: the warming is significant along the western part of the Okhotsk Sea and subarctic frontal region. The effects of the thermohaline- and wind-driven ocean circulation on the warming are evaluated from perturbation experiments on thermohaline (turbulent heat and freshwater fluxes) and wind causes, respectively. The thermohaline causes are shown to contribute positively to warming in the Okhotsk Sea Intermediate Water (OSIW). The heat budget analysis for the OSIW indicates that the warming is related to a decrease in cold and dense shelf water (DSW) flux, which is caused by a decrease in sea ice and surface water freshening. In contrast, the wind cause has a cooling effect in the OSIW through an increase in DSW. In the subarctic frontal region, the warming is mainly caused by the wind stress change. The heat budget analysis indicates that the warming is related to an increase in the northward advection of the subtropical warm water. These results imply that both thermohaline- and wind-driven ocean circulation changes are essential components of the warming in the intermediate water. The atmospheric conditions responsible for the warming are related to a weakened Aleutian low and Siberian high in early and late winter.

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14

Rahmstorf, Stefan y Kirsten Zickfeld. "Thermohaline Circulation Changes: A Question of Risk Assessment". Climatic Change 68, n.º 1-2 (enero de 2005): 241–47. http://dx.doi.org/10.1007/s10584-005-4038-0.

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15

Pitman, A. J. y R. J. Stouffer. "Abrupt change in climate and climate models". Hydrology and Earth System Sciences Discussions 3, n.º 4 (19 de julio de 2006): 1745–71. http://dx.doi.org/10.5194/hessd-3-1745-2006.

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Abstract. First, we review the evidence that abrupt climate changes have occurred in the past and then demonstrate that climate models have developing capacity to simulate many of these changes. In particular, the processes by which changes in the ocean circulation drive abrupt changes appear to be captured by climate models to a degree that is encouraging. The evidence that past changes in the ocean have driven abrupt change in terrestrial systems is also convincing, but these processes are only just beginning to be included in climate models. Second, we explore the likelihood that climate models can capture those abrupt changes in climate that may occur in the future due to the enhanced greenhouse effect. We note that existing evidence indicates that a major collapse of the thermohaline circulate seems unlikely in the 21st century, although very recent evidence suggests that a weakening may already be underway. We have confidence that current climate models can capture a weakening, but a collapse of the thermohaline circulation in the 21st century is not projected by climate models. Worrying evidence of instability in terrestrial carbon, from observations and modelling studies, is beginning to accumulate. Current climate models used by the Intergovernmental Panel on Climate Change for the 4th Assessment Report do not include these terrestrial carbon processes. We therefore can not make statements with any confidence regarding these changes. At present, the scale of the terrestrial carbon feedback is believed to be small enough that it does not significantly affect projections of warming during the first half of the 21st century. However, the uncertainties in how biological systems will respond to warming are sufficiently large to undermine confidence in this belief and point us to areas requiring significant additional work.

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16

Pitman, A. J. y R. J. Stouffer. "Abrupt change in climate and climate models". Hydrology and Earth System Sciences 10, n.º 6 (28 de noviembre de 2006): 903–12. http://dx.doi.org/10.5194/hess-10-903-2006.

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Abstract. First, we review the evidence that abrupt climate changes have occurred in the past and then demonstrate that climate models have developing capacity to simulate many of these changes. In particular, the processes by which changes in the ocean circulation drive abrupt changes appear to be captured by climate models to a degree that is encouraging. The evidence that past changes in the ocean have driven abrupt change in terrestrial systems is also convincing, but these processes are only just beginning to be included in climate models. Second, we explore the likelihood that climate models can capture those abrupt changes in climate that may occur in the future due to the enhanced greenhouse effect. We note that existing evidence indicates that a major collapse of the thermohaline circulation seems unlikely in the 21st century, although very recent evidence suggests that a weakening may already be underway. We have confidence that current climate models can capture a weakening, but a collapse in the 21st century of the thermohaline circulation is not projected by climate models. Worrying evidence of instability in terrestrial carbon, from observations and modelling studies, is beginning to accumulate. Current climate models used by the Intergovernmental Panel on Climate Change for the 4th Assessment Report do not include these terrestrial carbon processes. We therefore can not make statements with any confidence regarding these changes. At present, the scale of the terrestrial carbon feedback is believed to be small enough that it does not significantly affect projections of warming during the first half of the 21st century. However, the uncertainties in how biological systems will respond to warming are sufficiently large to undermine confidence in this belief and point us to areas requiring significant additional work.

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17

Higgins, Paul A. T. "Biogeochemical and Biophysical Responses of the Land Surface to a Sustained Thermohaline Circulation Weakening". Journal of Climate 17, n.º 21 (1 de noviembre de 2004): 4135–42. http://dx.doi.org/10.1175/jcli3207.1.

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Abstract Biotic responses to climate change may constitute significant feedbacks to the climate system by altering biogeochemistry (e.g., carbon storage) or biophysics (i.e., albedo, evapotranspiration, and roughness length) at the land surface. Accurate projection of future climate change depends on proper accounting of these biological feedbacks. Similarly, projections of future climate change must include the potential for nonlinear responses such as thermohaline circulation (THC) weakening, which is increasingly evident in paleoclimate reconstructions and model experiments. This article uses offline simulations with the Integrated Biosphere Simulator (IBIS) to determine long-term biophysical and biogeochemical responses to climate patterns generated by the third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3) under forced THC weakening. Total land surface carbon storage decreases by 0.5% in response to THC weakening, suggesting that the biogeochemical response would not constitute a significant climate feedback under this climate change scenario. In contrast, large regional and local changes in leaf area index (LAI) suggest that biophysical responses may constitute significant feedbacks to at least local and regional climate. Indeed, the LAI responses do lead to changes in midday direct and diffuse beam albedo over large regions of the land surface. As a result, there are large local and regional changes in the land surface's capacity to absorb solar radiation. Changes in energy partitioning between sensible and latent heat fluxes also occur. However, the change in latent heat flux from the land surface is primarily attributable to changes in precipitation that occur under forced THC weakening and not a result of the subsequent changes in vegetation.

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18

Vellinga, Michael y Richard A. Wood. "Impacts of thermohaline circulation shutdown in the twenty-first century". Climatic Change 91, n.º 1-2 (13 de enero de 2007): 43–63. http://dx.doi.org/10.1007/s10584-006-9146-y.

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19

Meijer, P. Th y H. A. Dijkstra. "The response of Mediterranean thermohaline circulation to climate change: a minimal model". Climate of the Past 5, n.º 4 (19 de noviembre de 2009): 713–20. http://dx.doi.org/10.5194/cp-5-713-2009.

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Abstract. Physics-based understanding of the effects of paleoclimate and paleogeography on the thermohaline circulation of the Mediterranean Sea requires an ocean model capable of long integrations and involving a minimum of assumptions about the atmospheric forcing. Here we examine the sensitivity of the deep circulation in the eastern Mediterranean basin to changes in atmospheric forcing, considered a key factor in the deposition of organic-rich sediments (sapropels). To this extent we explore the setup of an ocean general circulation model (MOMA) with realistic (present-day) bathymetry and highly idealized forcing. The model proves able to qualitatively capture some important features of the large-scale overturning circulation, in particular for the eastern basin. The response to (i) a reduction in the imposed meridional temperature gradient, or (ii) a reduction in net evaporation, proves to be non-linear and, under certain conditions, of transient nature. Consistent with previous model studies, but now based on a minimum of assumptions, we find that a reduction in net evaporation (such as due to an increase in freshwater input) may halt the deep overturning circulation. The ability to perform long model integrations allows us to add the insight that, in order to have the conditions favourable for sapropel formation persist, we must also assume that the vertical mixing of water properties was reduced. The "minimal" model here presented opens the way to experiments in which one truly follows the basin circulation into, or out of, the period of sapropel formation and where forcing conditions are continously adjusted to the precession cycle.

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20

Meijer, P. Th y H. A. Dijkstra. "The response of Mediterranean thermohaline circulation to climate change: a minimal model". Climate of the Past Discussions 5, n.º 3 (30 de junio de 2009): 1731–49. http://dx.doi.org/10.5194/cpd-5-1731-2009.

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Abstract. Physics-based understanding of the effects of paleoclimate and paleogeography on the thermohaline circulation of the Mediterranean Sea requires an ocean model capable of long integrations and involving a minimum of assumptions about the atmospheric forcing. Here we examine the sensitivity of the deep circulation in the eastern Mediterranean basin to changes in atmospheric forcing, considered a key factor in the deposition of organic-rich sediments (sapropels). To this extent we explore the setup of an ocean general circulation model (MOMA) with realistic (present-day) bathymetry and highly idealized forcing. The model proves able to qualitatively capture some important features of the large-scale overturning circulation, in particular for the eastern basin. The response to (i) a reduction in the imposed meridional temperature gradient, or (ii) a reduction in net evaporation, proves to be non-linear and, under certain conditions, of transient nature. Consistent with previous model studies, but now based on a minimum of assumptions, we find that a reduction in net evaporation (such as due to an increase in freshwater input) may halt the deep overturning circulation. The ability to perform long model integrations allows us to add the insight that, in order to have the conditions favourable for sapropel formation persist, we must also assume that the vertical mixing of water properties was reduced. The "minimal" model here presented opens the way to experiments in which one truly follows the basin circulation into, or out of, the period of sapropel formation and where forcing conditions are continuously adjusted to the precession cycle.

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21

Longworth, Hannah, Jochem Marotzke y Thomas F. Stocker. "Ocean Gyres and Abrupt Change in the Thermohaline Circulation: A Conceptual Analysis". Journal of Climate 18, n.º 13 (1 de julio de 2005): 2403–16. http://dx.doi.org/10.1175/jcli3397.1.

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Abstract The implications are investigated of representing ocean gyre circulations by a diffusion term in the Stommel and Rooth box models of the thermohaline circulation (THC) in one and two hemispheres, respectively. The approach includes mostly analytical solution and study of the bifurcation structure, but also numerical integration and feedback analysis. Sufficient diffusion (gyre strength) eliminates multiple equilibria from either model, highlighting the need for accurate gyre circulation strength in general circulation models (GCMs) when considering the potential for abrupt climate change associated with THC shutdown. With diffusion, steady-state flow strength in the Rooth model depends on freshwater forcing (i.e., implied atmospheric water vapor transport) in both hemispheres, not only on that in the upwelling hemisphere, as in the nondiffusive case. With asymmetric freshwater forcing, two solutions (strong stable and weak unstable) are found with sinking in the hemisphere with stronger forcing and one solution with sinking in the other hemisphere. Under increased freshwater forcing the two solutions in the hemisphere with stronger forcing meet in a saddle-node bifurcation (if diffusion is sufficiently strong to prevent a subcritical Hopf bifurcation first), followed by flow reversal. Thus, the bifurcation structure with respect to freshwater forcing of the diffusive Rooth model of two-hemisphere THC is similar to that of the Stommel model of single-hemisphere THC, albeit with a very different dynamical interpretation. Gyre circulations stabilize high-latitude sinking in the Stommel model. In the Rooth model, gyre circulations only stabilize high-latitude sinking if the freshwater forcing is weaker in the sinking hemisphere than in the upwelling hemisphere, by an amount that increases with diffusion. The values of diffusion and freshwater forcing at which qualitative change in behavior occurs correspond to the range of the values used in and obtained with GCMs, suggesting that this analysis can provide a conceptual foundation for analyzing the stability of the interhemispheric THC, and also for the potential of the Atlantic THC to undergo abrupt change.

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22

Wang, Huaxiao y G. Edward Birchfield. "Atmospheric water vapor flux, bifurcation of the thermohaline circulation, and climate change". Climate Dynamics 8, n.º 1 (octubre de 1992): 49–53. http://dx.doi.org/10.1007/bf00209343.

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23

Broecker, W. S. "Was a change in thermohaline circulation responsible for the Little Ice Age?" Proceedings of the National Academy of Sciences 97, n.º 4 (15 de febrero de 2000): 1339–42. http://dx.doi.org/10.1073/pnas.97.4.1339.

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24

Lee, Sang-Ki y Chunzai Wang. "Delayed Advective Oscillation of the Atlantic Thermohaline Circulation". Journal of Climate 23, n.º 5 (1 de marzo de 2010): 1254–61. http://dx.doi.org/10.1175/2009jcli3339.1.

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Abstract A simple dynamic model is proposed to illustrate the multidecadal oscillation of the Atlantic Ocean thermohaline circulation. The proposed oscillation relies on alternating actions of positive and negative feedbacks, which are operated by a slow adjustment of the ocean circulation and the associated time delay in the advective flux response to a change in meridional density gradient. The key element of the oscillation is the time delay, which is conceptually related to the basin-crossing time of long Rossby waves in the high-latitude North Atlantic. For a sufficiently long time delay, the solution becomes unstable in some regions of model parameter space and oscillates with a period of approximately 2 times the delay time.

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25

Dyakonov, Gleb S. y Rashit A. Ibrayev. "Long-term evolution of Caspian Sea thermohaline properties reconstructed in an eddy-resolving ocean general circulation model". Ocean Science 15, n.º 3 (16 de mayo de 2019): 527–41. http://dx.doi.org/10.5194/os-15-527-2019.

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Abstract. Decadal variability in Caspian Sea thermohaline properties is investigated using a high-resolution ocean general circulation model including sea ice thermodynamics and air–sea interaction forced by prescribed realistic atmospheric conditions and riverine runoff. The model describes synoptic, seasonal and climatic variations of sea thermohaline structure, water balance, and sea level. A reconstruction experiment was conducted for the period of 1961–2001, covering a major regime shift in the global climate during 1976–1978, which allowed for an investigation of the Caspian Sea response to such significant episodes of climate variability. The model reproduced sea level evolution reasonably well despite the fact that many factors (such as possible seabed changes and insufficiently explored underground water infiltration) were not taken into account in the numerical reconstruction. This supports the hypothesis relating rapid Caspian Sea level rise in 1978–1995 with global climate change, which caused variation in local atmospheric conditions and riverine discharge reflected in the external forcing data used, as is shown in the paper. Other effects of the climatic shift are investigated, including a decrease in salinity in the active layer, strengthening of its stratification and corresponding diminishing of convection. It is also demonstrated that water exchange between the three Caspian basins (northern, middle and southern) plays a crucial role in the formation of their thermohaline regime. The reconstructed long-term trends in seawater salinity (general downtrend after 1978), temperature (overall increase) and density (general downtrend) are studied, including an assessment of the influence of main surface circulation patterns and model error accumulation.

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26

Latif, M., M. Collins, H. Pohlmann y N. Keenlyside. "A Review of Predictability Studies of Atlantic Sector Climate on Decadal Time Scales". Journal of Climate 19, n.º 23 (1 de diciembre de 2006): 5971–87. http://dx.doi.org/10.1175/jcli3945.1.

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Abstract This review paper discusses the physical basis and the potential for decadal climate predictability over the Atlantic and its adjacent land areas. Many observational and modeling studies describe pronounced decadal and multidecadal variability in the Atlantic Ocean. However, it still needs to be quantified to which extent the variations in the ocean drive variations in the atmosphere and over land. In particular, although a clear impact of the Tropics on the midlatitudes has been demonstrated, it is unclear if and how the extratropical atmosphere responds to midlatitudinal sea surface temperature anomalies. Although the mechanisms behind the decadal to multidecadal variability in the Atlantic sector are still controversial, there is some consensus that some of the longer-term multidecadal variability is driven by variations in the thermohaline circulation. The variations in the North Atlantic thermohaline circulation appear to be predictable one to two decades ahead, as shown by a number of perfect model predictability experiments. The next few decades will be dominated by these multidecadal variations, although the effects of anthropogenic climate change are likely to introduce trends. Some impact of the variations of the thermohaline circulation on the atmosphere has been demonstrated in some studies so that useful decadal predictions with economic benefit may be possible.

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27

Bleck, Rainer y Shan Sun. "Diagnostics of the oceanic thermohaline circulation in a coupled climate model". Global and Planetary Change 40, n.º 3-4 (febrero de 2004): 233–48. http://dx.doi.org/10.1016/j.gloplacha.2003.04.002.

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28

Yang, Haijun y Lu Wang. "Tropical Oceanic Response to Extratropical Thermal Forcing in a Coupled Climate Model: A Comparison between the Atlantic and Pacific Oceans*". Journal of Climate 24, n.º 15 (1 de agosto de 2011): 3850–66. http://dx.doi.org/10.1175/2011jcli3927.1.

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Abstract The tropical oceanic response to the extratropical thermal forcing is quantitatively estimated in a coupled climate model. This work focuses on comparison of the responses between the tropical Atlantic and Pacific. Under the same extratropical forcing, the tropical sea surface temperature responses are comparable. However, the responses in the tropical subsurface in the two oceans are distinct. The tropical subsurface response in the Atlantic can be twice of that in the Pacific. The maximum subsurface temperature change in the tropical Pacific occurs in the eastern lower thermocline, while that in the tropical Atlantic occurs in the west and well below the lower thermocline. The different responses in the tropical Atlantic and Pacific are closely related to the different changes in the meridional overturning circulations. The Pacific shallow overturning circulation, or the subtropical cell, tends to slow down (speed up) in response to the extratropical warming (cooling) forcing. The changes in the upwelling in the eastern equatorial Pacific as well as the shallow subduction from the extratropical southern Pacific along the eastern boundary are accountable for the eastern Pacific temperature change. The Atlantic overturning circulation consists of the shallow subtropical cell and the deep thermohaline circulation. A weakened thermohaline circulation will result in a strengthened northern subtropical cell, in which the change in the lower branch, or the low-latitude North Brazil Current, can cause strong response below the western tropical thermocline. Here the coastal Kelvin wave along the western boundary on the intermediate isopycnal level also plays an important role in the equatorward conveying of the climate anomalies in the mid-to-high-latitude Atlantic, particularly during the initial stage of the extratropical forcing.

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29

Timmermann, A., S.-I. An, U. Krebs y H. Goosse. "ENSO Suppression due to Weakening of the North Atlantic Thermohaline Circulation*". Journal of Climate 18, n.º 16 (15 de agosto de 2005): 3122–39. http://dx.doi.org/10.1175/jcli3495.1.

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Abstract Changes of the North Atlantic thermohaline circulation (THC) excite wave patterns that readjust the thermocline globally. This paper examines the impact of a freshwater-induced THC shutdown on the depth of the Pacific thermocline and its subsequent modification of the El Niño–Southern Oscillation (ENSO) variability using an intermediate-complexity global coupled atmosphere–ocean–sea ice model and an intermediate ENSO model, respectively. It is shown by performing a numerical eigenanalysis and transient simulations that a THC shutdown in the North Atlantic goes along with reduced ENSO variability because of a deepening of the zonal mean tropical Pacific thermocline. A transient simulation also exhibits abrupt changes of ENSO behavior, depending on the rate of THC change. The global oceanic wave adjustment mechanism is shown to play a key role also on multidecadal time scales. Simulated multidecadal global sea surface temperature (SST) patterns show a large degree of similarity with previous climate reconstructions, suggesting that the observed pan-oceanic variability on these time scales is brought about by oceanic waves and by atmospheric teleconnections.

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30

Silva, Brenno J., Felipe L. Gaspar, Pedro Tyaquiçã, Nathalie Lefèvre y Manuel J. Flores Montes. "Carbon chemistry variability around a tropical archipelago". Marine and Freshwater Research 70, n.º 6 (2019): 767. http://dx.doi.org/10.1071/mf18011.

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Oceanic islands affect the surrounding oceanic circulation by producing upwelling or vortices, resulting in the rising of a richer and colder subsurface water mass. This process increases primary production and can change some biogeochemical processes, such as carbon chemistry and the biological pump. The aim of this study was to describe the vertical variability of carbon chemistry around Fernando de Noronha Archipelago (FNA) and to verify how the island mass effect (IME) can affect carbon distribution. Two transects on opposite sides of the FNA were established according to the direction of the central South Equatorial Current, and samples were collected in July 2010, September 2012 and July 2014 from the surface down to a depth of 500m. The results showed strong stratification, with an uplift of the thermohaline structure, which resulted in an increase of chlorophyll-a concentration downstream of the island during the 2010 and 2014 cruises. Carbon chemistry parameters were strongly correlated with temperature, salinity and dissolved oxygen along the water column and did not change between sides of the island in the periods studied. We conclude that the IME did not significantly affect carbon chemistry, which was more correlated with thermohaline gradient.

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31

Zhang, Rong y Thomas L. Delworth. "Simulated Tropical Response to a Substantial Weakening of the Atlantic Thermohaline Circulation". Journal of Climate 18, n.º 12 (15 de junio de 2005): 1853–60. http://dx.doi.org/10.1175/jcli3460.1.

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Abstract In this study, a mechanism is demonstrated whereby a large reduction in the Atlantic thermohaline circulation (THC) can induce global-scale changes in the Tropics that are consistent with paleoevidence of the global synchronization of millennial-scale abrupt climate change. Using GFDL’s newly developed global coupled ocean–atmosphere model (CM2.0), the global response to a sustained addition of freshwater to the model’s North Atlantic is simulated. This freshwater forcing substantially weakens the Atlantic THC, resulting in a southward shift of the intertropical convergence zone over the Atlantic and Pacific, an El Niño–like pattern in the southeastern tropical Pacific, and weakened Indian and Asian summer monsoons through air–sea interactions.

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32

Taboada, J. J. y M. N. Lorenzo. "Effects of the synoptic scale variability on the thermohaline circulation". Nonlinear Processes in Geophysics 12, n.º 4 (24 de marzo de 2005): 435–39. http://dx.doi.org/10.5194/npg-12-435-2005.

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Abstract. In this paper the effect of the synoptic scale variability is analyzed using a simple atmosphere-ocean coupled model. This high frequency variability has been taken into account in the model adding white gaussian noise in variables related to zonal and meridional temperature differences. Results show that synoptic scale frequency variability on longitudinal heating contrast between land and sea can produce a collapse of thermohaline circulation when a threshold of noise is overcome. This result is significant because if synoptic scale variability in the next century increases due to the climatic change an increment of the probability of this collapse could be produced.

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33

JACOBS, STANLEY S. "Bottom water production and its links with the thermohaline circulation". Antarctic Science 16, n.º 4 (30 de noviembre de 2004): 427–37. http://dx.doi.org/10.1017/s095410200400224x.

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For more than a century it has been known that the abyssal basins of the world ocean are primarily occupied by relatively cold and fresh waters that originate in the Southern Ocean. Their distinguishing characteristics are acquired by exposure of surface and shelf waters to ‘ventilation’ by the polar atmosphere and to the melting and freezing of ice over and near the Antarctic continental shelf. Subsequent mixing with deep water over the continental slope results in ‘Bottom Water’ that forms the southern sinking limb of the global ‘Thermohaline Circulation.’ Over recent decades, oceanographers have wrestled with a variety of bottom water and thermohaline circulation problems, ranging from basic definitions to forcing and formation sites, source components and properties, generation processes and rates, mixing and sinking, pathways and transports. A brief review of these efforts indicates both advances and anomalies in our understanding of Antarctic Bottom Water production and circulation. Examples from ongoing work illustrate increasing interest in the temporal variability of bottom water in relation to climate change.

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34

Budillon, G. y G. Spezie. "Thermohaline structure and variability in the Terra Nova Bay polynya, Ross Sea". Antarctic Science 12, n.º 4 (diciembre de 2000): 493–508. http://dx.doi.org/10.1017/s0954102000000572.

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Hydrological measurements from three cruises during the summers 1994/95, 1995/96 and 1997/98 in the western sector of the Ross Sea allow summer and year to year changes in heat and salt content in the Terra Nova Bay polynya to be analysed. Changes in the surface layer (upper pycnocline) followed the expected seasonal pattern of warming and freshening from the beginning to the end of the summer. These near-surface changes, expressed as net heating and salting rate, were about 11 W m−2 and -6 mg salt m−2 s−1. The heating changes were substantially lower than the estimated heat supplied by the atmosphere during the summer, which underlines the importance for this season of the advective component carried by the currents in the total heat budget. The year to year differences were about one or two orders of magnitude smaller than the seasonal changes in the surface layer. In the intermediate and deep layers, the summer heat and salt variability were of the same order as or one order higher than from one summer to the next. The differences in sign and magnitude for the heat change in the upper and in the lower pycnocline indicate a weak connection in the summer period between the surface heat fluxes and the deep waters. A local source of very cold water (with temperatures below the surface freezing point) of about 0.3 Sv has been detected close to the Terra Nova Bay coast. It arose out of the interaction of the shallow–intermediate layers of High Salinity Shelf Water with the coastal glaciers. The presence and the variability of this cold water point to the significant role of the thermohaline properties of Terra Nova Bay waters in controlling the floating glacier by governing the basal melting processes.

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35

Barrera, Enriqueta, Samuel M. Savin, Ellen Thomas y Charles E. Jones. "Evidence for thermohaline-circulation reversals controlled by sea-level change in the latest Cretaceous". Geology 25, n.º 8 (1997): 715. http://dx.doi.org/10.1130/0091-7613(1997)025<0715:eftcrc>2.3.co;2.

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36

Zickfeld, K. y T. Bruckner. "Reducing the Risk of Abrupt Climate Change: Emissions Corridors Preserving the Atlantic Thermohaline Circulation". Integrated Assessment 4, n.º 2 (junio de 2003): 106–15. http://dx.doi.org/10.1076/iaij.4.2.106.16702.

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37

Lohmann, G., M. Butzin, A. Micheels, T. Bickert y V. Mosbrugger. "Effect of vegetation on the Late Miocene ocean circulation". Climate of the Past Discussions 2, n.º 4 (23 de agosto de 2006): 605–31. http://dx.doi.org/10.5194/cpd-2-605-2006.

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Abstract. A weak and shallow thermohaline circulation in the North Atlantic Ocean is related to an open Central American gateway and exchange with fresh Pacific waters. We estimate the effect of vegetation on the ocean general circulation using the atmospheric circulation model simulations for the Late Miocene climate. Caused by an increase in net evaporation in the Miocene North Atlantic, the North Atlantic water becomes more saline which enhances the overturning circulation and thus the northward heat transport. This effect reveals a potentially important feedback between the ocean circulation, the hydrological cycle and the land surface cover for Cenozoic climate evolution.

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38

Bennett, Andrew F. "The Geometry of Neutral Paths". Journal of Physical Oceanography 49, n.º 12 (diciembre de 2019): 3037–44. http://dx.doi.org/10.1175/jpo-d-19-0047.1.

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AbstractCarathéodory’s axiomatic development of thermodynamics is applied here to the thermohaline circulation of the ocean. The helicity of the differential form for the density change in an isentropic and isohaline ascent, relative to the change in the water column, does not vanish since the ratio of the thermal and haline compressibilities is a function of pressure. The form for relative density consequently lacks an integrating denominator and so there are no surfaces of constant relative density, or so-called neutral surfaces (McDougall and Jackett). As a consequence of a remarkable theorem (Carathéodory), any two points in the thermohaline state space or equivalently in the real space of the ocean are mutually accessible, in the sense that they can be joined by a neutral path. Many of the paths between any two points and possibly all may only be piecewise smooth. The theorem is supported here with analytical examples of neutral paths in state space, and a numerical example of an idealized ocean in real space, for all of which the seawater obeys a relatively simple equation of state. The existence of multiple neutral paths for pairs of close points is explicitly demonstrated. Some such neutral paths take large excursions throughout state space and throughout the ocean basin. The implications for hydrography and for ocean modeling are discussed.

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39

Zickfeld, Kirsten y Thomas Bruckner. "Reducing the risk of Atlantic thermohaline circulation collapse: sensitivity analysis of emissions corridors". Climatic Change 91, n.º 3-4 (9 de septiembre de 2008): 291–315. http://dx.doi.org/10.1007/s10584-008-9467-0.

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40

Bruckner, T. y K. Zickfeld. "Emissions corridors for reducing the risk of a collapse of the Atlantic thermohaline circulation". Mitigation and Adaptation Strategies for Global Change 14, n.º 1 (24 de julio de 2008): 61–83. http://dx.doi.org/10.1007/s11027-008-9150-9.

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41

Lorenzo, María N., Juan J. Taboada y Isabel Iglesias. "Sensitivity of thermohaline circulation to decadal and multidecadal variability". ICES Journal of Marine Science 66, n.º 7 (28 de marzo de 2009): 1439–47. http://dx.doi.org/10.1093/icesjms/fsp061.

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Abstract Lorenzo, M. N., Taboada, J. J., and Iglesias, I. 2009. Sensitivity of thermohaline circulation to decadal and multidecadal variability. – ICES Journal of Marine Science, 66: 1439–1447. In this paper, stochastic freshwater inputs with different variabilities are introduced into an Earth Model of Intermediate Complexity to study their effect on the behaviour of the thermohaline circulation (THC). The variability in the stochastic signal was set to be either decadal or multidecadal (70 years), based on intensity modulation of the El Niño-Southern Oscillation (ENSO) phenomenon. The results demonstrate a weakening of the THC in both the decadal and the multidecadal cases. This weakening results in a reduction in air surface temperature, mainly in the North Atlantic. Moreover, the 500-mb stream function also weakens. This causes lower rainfall in Western Europe, except in the areas most influenced by the Gulf Stream. Sea surface temperature is reduced significantly in the area around Greenland, whereas sea surface salinity is reduced around Greenland and in the Gulf Stream, but increased in the Labrador Sea and in Hudson Strait. The latter effects are more marked in the case where the variability of the inputs is multidecadal. The main implication of these results is that the natural decadal or multidecadal variability in freshwater inputs could have noticeable effects on the fate of the THC, which may be superimposed on the effects of climate change.

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42

Boyle, Edward A. "Is ocean thermohaline circulation linked to abrupt stadial/interstadial transitions?" Quaternary Science Reviews 19, n.º 1-5 (enero de 2000): 255–72. http://dx.doi.org/10.1016/s0277-3791(99)00065-7.

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43

Dalan, Fabio, Peter H. Stone, Igor V. Kamenkovich y Jeffery R. Scott. "Sensitivity of the Ocean’s Climate to Diapycnal Diffusivity in an EMIC. Part I: Equilibrium State". Journal of Climate 18, n.º 13 (1 de julio de 2005): 2460–81. http://dx.doi.org/10.1175/jcli3411.1.

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Abstract The diapycnal diffusivity in the ocean is one of the least known parameters in current climate models. Measurements of this diffusivity are sparse and insufficient for compiling a global map. Inferences from inverse methods and energy budget calculations suggest as much as a factor of 5 difference in the global mean value of the diapycnal diffusivity. Yet, the climate is extremely sensitive to the diapycnal diffusivity. In this paper the sensitivity of the current climate to the diapycnal diffusivity is studied, focusing on the changes occurring in the ocean circulation. To this end, a coupled model with a three-dimensional ocean with idealized geometry is used. The results show that, at equilibrium, the strength of the thermohaline circulation in the North Atlantic scales with the 0.44 power of the diapycnal diffusivity, in contrast to the theoretical value based on scaling arguments for uncoupled models of 2/3. On the other hand, the strength of the circulation in the South Pacific scales with the 0.63 power of the diapycnal diffusivity in closer accordance with the theoretical value. The vertical heat balance in the global ocean is controlled by, in the downward direction, (i) advection and (ii) diapycnal diffusion; in the upward direction, (iii) isopycnal diffusion and (iv) parameterized mesoscale eddy [Gent–McWilliams (GM)] advection. The size of the latter three fluxes increases with diapycnal diffusivity, because the thickness of the thermocline also increases with diapycnal diffusivity leading to greater isopycnal slopes at high latitudes, and hence, enhanced isopycnal diffusion and GM advection. Thus larger diapycnal diffusion is compensated for by changes in isopycnal diffusion and GM advection. Little change is found for the advective flux because of compensation between downward and upward advection. Sensitivity results are presented for the hysteresis curve of the thermohaline circulation. The stability of the climate system to slow freshwater perturbations is reduced as a consequence of a smaller diapycnal diffusivity. This result is consistent with the findings of two-dimensional climate models. However, contrary to the results of these studies, a common threshold for the shutdown of the thermohaline circulation is not found in this model.

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44

Marsz, Andrzej y Anna Styszyńska. "Proces ocieplenia w Polsce – przebieg i przyczyny (1951–2018). Przejaw wewnętrznej dynamiki systemu klimatycznego czy proces antropogeniczny?" Prace i Studia Geograficzne 67, n.º 2 (18 de octubre de 2022): 51–82. http://dx.doi.org/10.48128/pisg/2022-67.2-04.

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The work discusses the course of the annual air temperature over Poland in the years 1951–2018, stating in it a sudden change of the regime that took place in 1987–1989. In the period 1951–1988 and 1931–1988 the annual temperature trend was zero, and the warming did not start until 1988, with the change of the temperature regime. The reason for the change in the thermal regime was an equally radical change in the macrocirculation conditions that took place as a result of the change in the phase of the thermohaline circulation in the North Atlantic. Explanation of the sequence of processes, which led to the increase in temperature, indicates that they are the result of the internal dynamics of the climate system and not a consequence of the increase in the concentration of greenhouse gases in the atmosphere.

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45

Zhai, Xiaoming, Helen L. Johnson y David P. Marshall. "A Model of Atlantic Heat Content and Sea Level Change in Response to Thermohaline Forcing". Journal of Climate 24, n.º 21 (1 de noviembre de 2011): 5619–32. http://dx.doi.org/10.1175/jcli-d-10-05007.1.

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Abstract The response of ocean heat content in the Atlantic to variability in the meridional overturning circulation (MOC) at high latitudes is investigated using a reduced-gravity model and the Massachusetts Institute of Technology (MIT) general circulation model (MITgcm). Consistent with theoretical predictions, the zonal-mean heat content anomalies are confined to low latitudes when the high-latitude MOC changes rapidly, but extends to mid- and high latitudes when the high-latitude MOC varies on decadal or multidecadal time scales. This low-pass-filtering effect of the mid- and high latitudes on zonal-mean heat content anomalies, termed here the “Rossby buffer,” is shown to be associated with the ratio of Rossby wave basin-crossing time to the forcing period at high northern latitudes. Experiments using the MITgcm also reveal the importance of advective spreading of cold water in the deep ocean, which is absent in the reduced-gravity model. Implications for monitoring ocean heat content and sea level changes are discussed in the context of both models. It is found that observing global sea level variability and sea level rise using tide gauges can substantially overestimate the global-mean values.

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46

Dong, B. W. y R. T. Sutton. "Adjustment of the coupled ocean-atmosphere system to a sudden change in the Thermohaline Circulation". Geophysical Research Letters 29, n.º 15 (agosto de 2002): 18–1. http://dx.doi.org/10.1029/2002gl015229.

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47

Zickfeld, Kirsten, Thomas Slawig y Stefan Rahmstorf. "A low-order model for the response of the Atlantic thermohaline circulation to climate change". Ocean Dynamics 54, n.º 1 (1 de febrero de 2004): 8–26. http://dx.doi.org/10.1007/s10236-003-0054-7.

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48

Ballarotta, M., S. Falahat, L. Brodeau y K. Döös. "On the glacial and inter-glacial thermohaline circulation and the associated transports of heat and freshwater". Ocean Science Discussions 11, n.º 2 (20 de marzo de 2014): 979–1022. http://dx.doi.org/10.5194/osd-11-979-2014.

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Abstract. The change of the thermohaline circulation (THC) between the Last Glacial Maximum (LGM, &approx; 21 kyr ago) and the present day climate are explored using an Ocean General Circulation Model and stream functions projected in various coordinates. Compared to the present day period, the LGM circulation is reorganised in the Atlantic Ocean, in the Southern Ocean and particularly in the abyssal ocean, mainly due to the different haline stratification. Due to stronger wind stress, the LGM tropical circulation is more vigorous than under modern conditions. Consequently, the maximum tropical transport of heat is slightly larger during the LGM. In the North Atlantic basin, the large sea-ice extent during the LGM constrains the Gulf Stream to propagate in a more zonal direction, reducing the transport of heat towards high latitudes and reorganising the freshwater transport. The LGM circulation is represented as a large intrusion of saline Antarctic Bottom Water into the Northern Hemisphere basins. As a result, the North Atlantic Deep Water is shallower in the LGM simulation. The stream functions in latitude-salinity coordinates and thermohaline coordinates point out the different haline regimes between the glacial and interglacial period, as well as a LGM Conveyor Belt circulation largely driven by enhanced salinity contrast between the Atlantic and the Pacific basin. The thermohaline structure in the LGM simulation is the result of an abyssal circulation that lifts and deviates the Conveyor Belt cell from the area of maximum volumetric distribution, resulting in a ventilated upper layer above a deep stagnant layer, and an Atlantic circulation more isolated from the Pacific. An estimation of the turnover times reveal a deep circulation almost sluggish during the LGM, and a Conveyor Belt cell more vigorous due to the combination of stronger wind stress and shortened circulation route.

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49

Gawarkiewicz, Glen. "Shelfbreak processes affecting acoustic propagation in a changing ocean". Journal of the Acoustical Society of America 152, n.º 4 (octubre de 2022): A25. http://dx.doi.org/10.1121/10.0015419.

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Fundamental physical oceanographic processes affecting sound speed fields and acoustic propagation have been studied in shelfbreak regions for some time. Integrated observations extending back to the 1990s have related acoustic propagation variability to basic thermohaline structure as well as physical oceanographic processes causing significant variability in sound speed fields. Key shelfbreak processes such as frontal wave propagation, eddy-Shelfbreak Jet interactions, and wind-driven motions will be described. The influence of ocean warming and climate change impacts on these processes will be outlined with emphasis on the Middle Atlantic Bight in the northeastern United States. The impacts of changes in both the atmospheric Jet Stream as well as the Gulf Stream on the Shelfbreak Front and Jet and implications for acoustic propagation will be presented.

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50

Higgins, Paul A. T. y Stephen H. Schneider. "Long-term potential ecosystem responses to greenhouse gas-induced thermohaline circulation collapse". Global Change Biology 11, n.º 5 (mayo de 2005): 699–709. http://dx.doi.org/10.1111/j.1365-2486.2005.00952.x.

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