scholarly journals The first 250 years of the Heinrich 11 iceberg discharge: Last Interglacial HadGEM3-GC3.1 simulations for CMIP6-PMIP4

2022 ◽  
Author(s):  
Maria Vittoria Guarino ◽  
Louise Sime ◽  
David Schroeder ◽  
Jeff Ridley
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Northern Hemisphere ◽  
Model Simulation ◽  
Meridional Overturning Circulation ◽  
Interglacial Period ◽  
Temperature Structure ◽  
Ocean Heat Transport ◽  
Last Interglacial ◽  
Antarctic Sea Ice

Abstract. The Heinrich 11 event is simulated using the HadGEM3 model during the Last Interglacial period. We apply 0.2 Sv of meltwater forcing across the North Atlantic during a 250 years long simulation. We find that the strength of the Atlantic Meridional Overturning Circulation is reduced by 60 % after 150 years of meltwater forcing, with an associated decrease of 0.2 to 0.4 PW in meridional ocean heat transport at all latitudes. The changes in ocean heat transport affect surface temperatures. The largest increase in the meridional surface temperature gradient occurs between 40–50 N. This increase is associated with a strengthening of 20 % in 850 hPa winds. The stream jet intensification in the Northern Hemisphere in return alters the temperature structure of the ocean heat through an increased gyre circulation, and associated heat transport (+0.1–0.2 PW), at the mid-latitudes, and a decreased gyre ocean heat transport (−0.2 PW) at high-latitudes. The changes in meridional temperature and pressure gradients cause the Intertropical Convergence Zone (ITCZ) to move southward, leading to stronger westerlies and a more positive Southern Annual Mode (SAM) in the Southern Hemisphere. The positive SAM influences sea ice formation leading to an increase in Antarctic sea ice. Our coupled-model simulation framework shows that the classical "thermal bipolar see-saw'' has previously undiscovered consequences in both Hemispheres: these include Northern Hemisphere gyre heat transport and wind changes; alongside an increase in Antarctic sea ice during the first 250 years of meltwater forcing.

scholarly journals Last interglacial temperature evolution – a model inter-comparison

2013 ◽  
Vol 9 (2) ◽  
pp. 605-619 ◽  
Author(s):  
P. Bakker ◽  
E. J. Stone ◽  
S. Charbit ◽  
M. Gröger ◽  
U. Krebs-Kanzow ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Meridional Overturning Circulation ◽  
Temperature Evolution ◽  
The Arctic ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Starting Point ◽  
Strong Control ◽  
July Temperature

Abstract. There is a growing number of proxy-based reconstructions detailing the climatic changes that occurred during the last interglacial period (LIG). This period is of special interest, because large parts of the globe were characterized by a warmer-than-present-day climate, making this period an interesting test bed for climate models in light of projected global warming. However, mainly because synchronizing the different palaeoclimatic records is difficult, there is no consensus on a global picture of LIG temperature changes. Here we present the first model inter-comparison of transient simulations covering the LIG period. By comparing the different simulations, we aim at investigating the common signal in the LIG temperature evolution, investigating the main driving forces behind it and at listing the climate feedbacks which cause the most apparent inter-model differences. The model inter-comparison shows a robust Northern Hemisphere July temperature evolution characterized by a maximum between 130–125 ka BP with temperatures 0.3 to 5.3 K above present day. A Southern Hemisphere July temperature maximum, −1.3 to 2.5 K at around 128 ka BP, is only found when changes in the greenhouse gas concentrations are included. The robustness of simulated January temperatures is large in the Southern Hemisphere and the mid-latitudes of the Northern Hemisphere. For these regions maximum January temperature anomalies of respectively −1 to 1.2 K and −0.8 to 2.1 K are simulated for the period after 121 ka BP. In both hemispheres these temperature maxima are in line with the maximum in local summer insolation. In a number of specific regions, a common temperature evolution is not found amongst the models. We show that this is related to feedbacks within the climate system which largely determine the simulated LIG temperature evolution in these regions. Firstly, in the Arctic region, changes in the summer sea-ice cover control the evolution of LIG winter temperatures. Secondly, for the Atlantic region, the Southern Ocean and the North Pacific, possible changes in the characteristics of the Atlantic meridional overturning circulation are crucial. Thirdly, the presence of remnant continental ice from the preceding glacial has shown to be important when determining the timing of maximum LIG warmth in the Northern Hemisphere. Finally, the results reveal that changes in the monsoon regime exert a strong control on the evolution of LIG temperatures over parts of Africa and India. By listing these inter-model differences, we provide a starting point for future proxy-data studies and the sensitivity experiments needed to constrain the climate simulations and to further enhance our understanding of the temperature evolution of the LIG period.

scholarly journals Different mechanisms of Arctic and Antarctic sea ice response to ocean heat transport

2022 ◽  
Author(s):  
Jake Aylmer ◽  
David Ferreira ◽  
Daniel Feltham
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Climate Models ◽  
Heat Fluxes ◽  
Substantial Contribution ◽  
Climate Projections ◽  
Ocean Heat Transport ◽  
Antarctic Sea Ice ◽  
The Impact ◽  
Energy Convergence

AbstractUnderstanding drivers of Arctic and Antarctic sea ice on multidecadal timescales is key to reducing uncertainties in long-term climate projections. Here we investigate the impact of ocean heat transport (OHT) on sea ice, using pre-industrial control simulations of 20 models participating in the latest Coupled Model Intercomparison Project (CMIP6). In all models and in both hemispheres, sea ice extent is negatively correlated with poleward OHT. However, the similarity of the correlations in both hemispheres hides radically different underlying mechanisms. In the northern hemisphere, positive OHT anomalies primarily result in increased ocean heat convergence along the Atlantic sea ice edge, where most of the ice loss occurs. Such strong, localised heat fluxes ($$\sim {}100~\text {W}~\text {m}^{-2}$$ ∼ 100 W m - 2 ) also drive increased atmospheric moist-static energy convergence at higher latitudes, resulting in a pan-Arctic reduction in sea ice thickness. In the southern hemisphere, increased OHT is released relatively uniformly under the Antarctic ice pack, so that associated sea ice loss is driven by basal melt with no direct atmospheric role. These results are qualitatively robust across models and strengthen the case for a substantial contribution of ocean forcing to sea ice uncertainty, and biases relative to observations, in climate models.

scholarly journals Different Mechanisms of Arctic and Antarctic Sea Ice Response to Ocean Heat Transport

2021 ◽  
Author(s):  
Jake Robert Aylmer ◽  
David Ferreira ◽  
Daniel Feltham
Keyword(s):  
Sea Ice ◽  
Heat Transport ◽  
Climate Models ◽  
Heat Fluxes ◽  
Substantial Contribution ◽  
Climate Projections ◽  
Ocean Heat Transport ◽  
Antarctic Sea Ice ◽  
The Impact ◽  
Energy Convergence

Abstract Understanding drivers of Arctic and Antarctic sea ice on multidecadal timescales is key to reducing uncertainties in long-term climate projections. Here we investigate the impact of Ocean Heat Transport (OHT) on sea ice, using pre-industrial control simulations of 20 models participating in the latest Coupled Model Intercomparison Project (CMIP6). In all models and in both hemispheres, sea ice extent is negatively correlated with poleward OHT. However, the similarity of the correlations in both hemispheres hides radically different underlying mechanisms. In the northern hemisphere, positive OHT anomalies primarily result in increased ocean heat convergence along the Atlantic sea ice edge, where most of the ice loss occurs. Such strong, localised heat fluxes (~100 W m − 2 ) also drive increased atmospheric moist-static energy convergence at higher latitudes, resulting in a pan-Arctic reduction in sea ice thickness. In the southern hemisphere, increased OHT is released relatively uniformly under the Antarctic ice pack, so that associated sea ice loss is driven by basal melt with no direct atmospheric role. These results are qualitatively robust across models and strengthen the case for a substantial contribution of ocean forcing to sea ice uncertainty, and biases relative to observations, in climate models.

scholarly journals On Anomalous Ocean Heat Transport toward the Arctic and Associated Climate Predictability

2016 ◽  
Vol 29 (2) ◽  
pp. 689-704 ◽  
Author(s):  
Marius Årthun ◽  
Tor Eldevik
Keyword(s):  
Heat Transport ◽  
Air Temperature ◽  
Time Scale ◽  
Heat Content ◽  
Surface Air Temperature ◽  
Meridional Overturning Circulation ◽  
Ocean Heat Content ◽  
The Arctic ◽  
Ocean Heat Transport ◽  
Climate Predictability

Abstract A potential for climate predictability is rooted in anomalous ocean heat transport and its consequent influence on the atmosphere above. Here the propagation, drivers, and atmospheric impact of heat anomalies within the northernmost limb of the Atlantic meridional overturning circulation are assessed using a multicentury climate model simulation. Consistent with observation-based inferences, simulated heat anomalies propagate from the eastern subpolar North Atlantic into and through the Nordic seas. The dominant time scale of associated climate variability in the northern seas is 14 years, including that of observed sea surface temperature and modeled ocean heat content, air–sea heat flux, and surface air temperature. A heat budget analysis reveals that simulated ocean heat content anomalies are driven by poleward ocean heat transport, primarily related to variable volume transport. The ocean’s influence on the atmosphere, and hence regional climate, is manifested in the model by anomalous ocean heat convergence driving subsequent changes in surface heat fluxes and surface air temperature. The documented northward propagation of thermohaline anomalies in the northern seas and their consequent imprint on the regional atmosphere—including the existence of a common decadal time scale of variability—detail a key aspect of eventual climate predictability.

scholarly journals Changes of Decadal SST Variations in the Subpolar North Atlantic under Strong CO2 Forcing as an Indicator for the Ocean Circulation’s Contribution to Atlantic Multidecadal Variability

2020 ◽  
Vol 33 (8) ◽  
pp. 3213-3228 ◽  
Author(s):  
Ralf Hand ◽  
Jürgen Bader ◽  
Daniela Matei ◽  
Rohit Ghosh ◽  
Johann H. Jungclaus
Keyword(s):  
Heat Transport ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Ocean Dynamics ◽  
Northwestern Part ◽  
Atlantic Multidecadal Variability ◽  
Ocean Heat Transport ◽  
Multidecadal Variability ◽  
Sst Variability ◽  
Basin Scale

AbstractThe question of whether ocean dynamics are relevant for basin-scale North Atlantic decadal temperature variability is the subject of ongoing discussions. Here, we analyze a set of simulations with a single climate model consisting of a 2000-yr preindustrial control experiment, a 100-member historical ensemble, and a 100-member ensemble forced with an incremental CO2 increase by 1% yr−1. Compared to previous approaches, our setup offers the following advantages: First, the large ensemble size allows us to robustly separate internally and externally forced variability and to robustly detect statistical links between different quantities. Second, the availability of different scenarios allows us to investigate the role of the background state for drivers of the variability. We find strong evidence that ocean dynamics, particularly ocean heat transport variations, form an important contribution to generate the Atlantic multidecadal variability (AMV) in the Max Planck Institute Earth System Model (MPI-ESM). Particularly the northwest North Atlantic is substantially affected by ocean circulation for the historical and preindustrial simulations. Anomalies of the Labrador Sea deep ocean density precede a change of the Atlantic meridional overturning circulation (AMOC) and heat advection to the region south of Greenland. Under strong CO2 forcing, the AMV–SST regression pattern shows crucial changes: SST variability in the northwestern part of the North Atlantic is strongly reduced, so that the AMV pattern in this scenario is dominated by the low-latitude branch. We found a connection to changes in the deep-water formation that cause a strong reduction of the mean AMOC and its variability. Consequently, ocean heat transport convergence becomes less important for the SST variability south of Greenland.

scholarly journals Antarctic Sea Ice Control on the Depth of North Atlantic Deep Water

2019 ◽  
Vol 32 (9) ◽  
pp. 2537-2551 ◽  
Author(s):  
Louis-Philippe Nadeau ◽  
Raffaele Ferrari ◽  
Malte F. Jansen
Keyword(s):  
Sea Ice ◽  
Deep Water ◽  
Formation Rate ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Ice Formation ◽  
Overturning Circulation ◽  
Antarctic Sea Ice ◽  
Meridional Overturning

Abstract Changes in deep-ocean circulation and stratification have been argued to contribute to climatic shifts between glacial and interglacial climates by affecting the atmospheric carbon dioxide concentrations. It has been recently proposed that such changes are associated with variations in Antarctic sea ice through two possible mechanisms: an increased latitudinal extent of Antarctic sea ice and an increased rate of Antarctic sea ice formation. Both mechanisms lead to an upward shift of the Atlantic meridional overturning circulation (AMOC) above depths where diapycnal mixing is strong (above 2000 m), thus decoupling the AMOC from the abyssal overturning circulation. Here, these two hypotheses are tested using a series of idealized two-basin ocean simulations. To investigate independently the effect of an increased latitudinal ice extent from the effect of an increased ice formation rate, sea ice is parameterized as a latitude strip over which the buoyancy flux is negative. The results suggest that both mechanisms can effectively decouple the two cells of the meridional overturning circulation (MOC), and that their effects are additive. To illustrate the role of Antarctic sea ice in decoupling the AMOC and the abyssal overturning cell, the age of deep-water masses is estimated. An increase in both the sea ice extent and its formation rate yields a dramatic “aging” of deep-water masses if the sea ice is thick and acts as a lid, suppressing air–sea fluxes. The key role of vertical mixing is highlighted by comparing results using different profiles of vertical diffusivity. The implications of an increase in water mass ages for storing carbon in the deep ocean are discussed.

scholarly journals A Model Simulation of 20 Years of Northern Hemisphere Sea-Ice Fluctuations

1984 ◽  
Vol 5 ◽  
pp. 170-176 ◽  
Author(s):  
John E. Walsh ◽  
William D. Hibler ◽  
Becky Ross
Keyword(s):  
Sea Ice ◽  
Northern Hemisphere ◽  
Model Simulation ◽  
Thickness Distribution ◽  
Arctic Basin ◽  
The Arctic ◽  
Data Set ◽  
Ice Dynamics ◽  
Thermodynamic Computations ◽  
Covered Area

A dynamic-thermodynamic sea-ice model (Hibler 1979) is used to simulate northern hemisphere sea ice for a 20-year period, 1961 to 1980. The model is driven by daily atmospheric grids of sea-level pressure (geo-strophic wind) and by temperatures derived from the Russian surface temperature data set. Among the modifications to earlier formulations are the inclusion of snow cover and a multilevel ice-thickness distribution in the thermodynamic computations.The time series of the simulated anomalies show relatively large amounts of ice during the early 1960s and middle 1970s, and relatively small amounts during the late 1960s and early 1970s. The fluctuations of ice mass, both in the entire domain and in individual regions, are more persistent than are the fluctuations of ice-covered area. The ice dynamics tend to introduce more high-frequency variability into the regional (and total) amounts of ice mass. The simulated annual ice export from the Arctic Basin into the East Greenland Sea varies interannually by factors of 3 to 4.

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

2016 ◽  
Vol 12 (2) ◽  
pp. 543-552 ◽  
Author(s):  
Willem P. Sijp ◽  
Matthew H. England
Keyword(s):  
Heat Transport ◽  
Northern Hemisphere ◽  
Substantial Reduction ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Temperature Gradients ◽  
Overturning Circulation ◽  
Radiative Balance ◽  
Greenhouse Climate ◽  
Reduced Temperature

Abstract. 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.

scholarly journals Impacts of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in the Goddard Earth Observing System, Version 5 (GEOS-5)

2016 ◽  
Vol 29 (9) ◽  
pp. 3199-3218 ◽  
Author(s):  
Feng Li ◽  
Yury V. Vikhliaev ◽  
Paul A. Newman ◽  
Steven Pawson ◽  
Judith Perlwitz ◽  
...  
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Sea Ice ◽  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Meridional Overturning Circulation ◽  
Stratospheric Chemistry ◽  
Earth Observing System ◽  
Antarctic Sea Ice ◽  
The Antarctic

Abstract Stratospheric ozone depletion plays a major role in driving climate change in the Southern Hemisphere. To date, many climate models prescribe the stratospheric ozone layer’s evolution using monthly and zonally averaged ozone fields. However, the prescribed ozone underestimates Antarctic ozone depletion and lacks zonal asymmetries. This study investigates the impact of using interactive stratospheric chemistry instead of prescribed ozone on climate change simulations of the Antarctic and Southern Ocean. Two sets of 1960–2010 ensemble transient simulations are conducted with the coupled ocean version of the Goddard Earth Observing System Model, version 5: one with interactive stratospheric chemistry and the other with prescribed ozone derived from the same interactive simulations. The model’s climatology is evaluated using observations and reanalysis. Comparison of the 1979–2010 climate trends between these two simulations reveals that interactive chemistry has important effects on climate change not only in the Antarctic stratosphere, troposphere, and surface, but also in the Southern Ocean and Antarctic sea ice. Interactive chemistry causes stronger Antarctic lower stratosphere cooling and circumpolar westerly acceleration during November–January. It enhances stratosphere–troposphere coupling and leads to significantly larger tropospheric and surface westerly changes. The significantly stronger surface wind stress trends cause larger increases of the Southern Ocean meridional overturning circulation, leading to year-round stronger ocean warming near the surface and enhanced Antarctic sea ice decrease.

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