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

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.

Download Full-text

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

10.21203/rs.3.rs-637238/v1 ◽

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.

Download Full-text

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

10.5194/cp-2021-187 ◽

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.

Download Full-text

Implied ocean heat transport in CMIP6 models

10.5194/egusphere-egu21-9929 ◽

2021 ◽

Author(s):

Francesca Pearce ◽

Alejandro Bodas-Salcedo ◽

Christopher Thomas ◽

Thomas Allen

Keyword(s):

Heat Transport ◽

Energy Budget ◽

Climate Models ◽

Surface Fluxes ◽

Radiative Energy ◽

Ocean Heat Transport ◽

Energy Fluxes ◽

Data Set ◽

Ocean Heat Uptake ◽

Energy Convergence

The importance of heat transport in the ocean to maintain energy balance between different regions is well known, with heat typically being transported from the Equator to high latitudes. Ocean heat transport (OHT) can be separated into two different components; a divergent component which contributes directly to the Earths&#8217; energy budget as it is the energy that converges in an ocean basin to balance the release of heat into the atmosphere, and a rotational component which does not affect the energy budget. Climate models show significant uncertainty in projections of ocean heat uptake, both in terms of the magnitude and geographical pattern. Since the oceans&#8217; response under climate changes depends on the patterns of surface energy fluxes, it is important to assess the simulation of surface fluxes as a potential constraint of transient and long-term responses of the Earths&#8217; climate. Assuming that the ocean absorbs all of the excess energy within the Earth system, it is possible to directly relate the net surface flux (NSF) over the ocean to divergent OHT, potentially providing a metric to quantify how well climate models are able to reproduce observed patterns of NSF and OHT. In this work, we present a detailed comparison of different methods used to calculate divergent OHT from the NSF over the ocean using data from various CMIP6 models. The methods investigated include a least-squares solution to a matrix equation in which energy convergence is related to NSF via the Earths&#8217; energy imbalance, and solving a Poisson equation over the ocean surface (see Forget and Ferreira 2020). Comparison to observational estimates of OHT requires that the observational data set includes only sources of divergent heat transport, which is often not the case. Therefore, we intend to produce a data set of radiative energy fluxes that are consistent with both energy and water constraints (see Rodell et al. 2015, L&#8217;Ecuyer et al. 2015, Thomas et al. 2020) which can be subject to the same methods of determining OHT, and see how these estimates compare to the results from climate models.

Download Full-text

The Importance of Ocean Dynamical Feedback for Understanding the Impact of Mid–High-Latitude Warming on Tropical Precipitation Change

Journal of Climate ◽

10.1175/jcli-d-17-0402.1 ◽

2018 ◽

Vol 31 (6) ◽

pp. 2417-2434 ◽

Cited By ~ 6

Author(s):

Masakazu Yoshimori ◽

Ayako Abe-Ouchi ◽

Hiroaki Tatebe ◽

Toru Nozawa ◽

Akira Oka

Keyword(s):

Heat Transport ◽

General Circulation ◽

Circulation Model ◽

Hadley Circulation ◽

Precipitation Change ◽

Meridional Overturning Circulation ◽

Climate Projections ◽

Ocean Heat Transport ◽

Tropical Precipitation ◽

The Impact

It has been shown that asymmetric warming between the Northern and Southern Hemisphere extratropics induces a meridional displacement of tropical precipitation. This shift is believed to be due to the extra energy transported from the differentially heated hemisphere through changes in the Hadley circulation. Generally, the column-integrated energy flux in the mean meridional overturning circulation follows the direction of the upper, relatively dry branch, and tropical precipitation tends to be intensified in the hemisphere with greater warming. This framework was originally applied to simulations that did not include ocean dynamical feedback, but was recently extended to take the ocean heat transport change into account. In the current study, an atmosphere–ocean general circulation model applied with a regional nudging technique is used to investigate the impact of extratropical warming on tropical precipitation change under realistic future climate projections. It is shown that warming at latitudes poleward of 40° causes the northward displacement of tropical precipitation from October to January. Warming at latitudes poleward of 60° alone has a much smaller effect. This change in the tropical precipitation is largely explained by the atmospheric moisture transport caused by changes in the atmospheric circulation. The larger change in ocean heat transport near the equator, relative to the atmosphere, is consistent with the extended energy framework. The current study provides a complementary dynamical framework that highlights the importance of midlatitude atmospheric eddies and equatorial ocean upwelling, where the atmospheric eddy feedback modifies the Hadley circulation resulting in the northward migration of precipitation and the ocean dynamical feedback damps the northward migration from the equator.

Download Full-text

The Seasonality of submesoscale variability in the Antarctic Seasonal Ice Zone

10.5194/egusphere-egu2020-9934 ◽

2020 ◽

Author(s):

Isabelle Giddy ◽

Sarah Nicholson ◽

Marcel Du Plessis ◽

Andy Thompson ◽

Sebastiaan Swart

Keyword(s):

Sea Ice ◽

Mixed Layer ◽

Climate Models ◽

Critical Role ◽

Heat Fluxes ◽

Surface Boundary ◽

Surface Boundary Layer ◽

Antarctic Sea Ice ◽

The Antarctic ◽

Seasonal Ice Zone

The ocean surface boundary layer in the Southern Ocean plays a critical role in heat and carbon exchange with the atmosphere. Submesoscale flows have been found to be important in setting mixed layer variability in the Antarctic Circumpolar Current (ACC). However, sparsity in observations, particularly south of the ACC in the Antarctic Seasonal Ice Zone (SIZ) where the horizontal density structure of the mixed layer is influenced by sea ice melt/formation and mesoscale stirring, brings into question the ability of climate models to correctly resolve mixed layer variability. We present novel fine-scale observations of the activity of submesoscale variability in the ice-free Antarctic SIZ using three deployments of underwater gliders over an annual cycle. Salinity-dominated density fronts of O(1)km associated with strong horizontal buoyancy gradients are observed during all deployments. There is evidence that stratifying ageostrophic eddies, energised by salinity driven submesoscale fronts are active across seasons, with intermittent equivalent heat fluxes of the same order to, or greater than local atmospheric forcing. This study highlights the need to consider future changes of Antarctic sea-ice in respect to feedback mechanisms associated with salinity (sea-ice) driven submesoscale flows.

Download Full-text

Arctic and Antarctic Sea Ice Change: Contrasts, Commonalities, and Causes

Annual Review of Marine Science ◽

10.1146/annurev-marine-010816-060610 ◽

2019 ◽

Vol 11 (1) ◽

pp. 187-213 ◽

Cited By ~ 20

Author(s):

Ted Maksym

Keyword(s):

Sea Ice ◽

Climate Models ◽

Ice Cover ◽

Natural Variability ◽

Arctic Sea Ice ◽

Regional Variability ◽

Antarctic Sea Ice ◽

Induced Changes ◽

Natural Climate ◽

The Impact

Arctic sea ice has declined precipitously in both extent and thickness over the past four decades; by contrast, Antarctic sea ice has shown little overall change, but this masks large regional variability. Climate models have not captured these changes. But these differences do not represent a paradox. The processes governing, and impacts of, natural variability and human-induced changes differ markedly at the poles largely because of the ways in which differences in geography control the properties of and interactions among the atmosphere, ice, and ocean. The impact of natural variability on the ice cover is large at both poles, so modeled ice trends are not entirely inconsistent with contributions from both natural variability and anthropogenic forcing. Despite this concurrence, the coupling of natural climate variability, climate feedbacks, and sea ice is not well understood, and significant biases remain in model representations of the ice cover and the processes that drive it.

Download Full-text

Biased thermohaline exchanges with the Arctic across the Iceland–Faroe Ridge in ocean climate models

Ocean Science ◽

10.5194/os-12-545-2016 ◽

2016 ◽

Vol 12 (2) ◽

pp. 545-560 ◽

Cited By ~ 6

Author(s):

S. M. Olsen ◽

B. Hansen ◽

S. Østerhus ◽

D. Quadfasel ◽

H. Valdimarsson

Keyword(s):

Heat Transport ◽

Climate Models ◽

Thermohaline Circulation ◽

Salt Transport ◽

The Arctic ◽

Global Ocean ◽

Climate Projections ◽

Ocean Heat Transport ◽

Ice Melt ◽

Predictive Skill

Abstract. The northern limb of the Atlantic thermohaline circulation and its transport of heat and salt towards the Arctic strongly modulate the climate of the Northern Hemisphere. The presence of warm surface waters prevents ice formation in parts of the Arctic Mediterranean, and ocean heat is directly available for sea-ice melt, while salt transport may be critical for the stability of the exchanges. Through these mechanisms, ocean heat and salt transports play a disproportionally strong role in the climate system, and realistic simulation is a requisite for reliable climate projections. Across the Greenland–Scotland Ridge (GSR) this occurs in three well-defined branches where anomalies in the warm and saline Atlantic inflow across the shallow Iceland–Faroe Ridge (IFR) have been shown to be particularly difficult to simulate in global ocean models. This branch (IF-inflow) carries about 40 % of the total ocean heat transport into the Arctic Mediterranean and is well constrained by observation during the last 2 decades but associated with significant inter-annual fluctuations. The inconsistency between model results and observational data is here explained by the inability of coarse-resolution models to simulate the overflow across the IFR (IF-overflow), which feeds back onto the simulated IF-inflow. In effect, this is reduced in the model to reflect only the net exchange across the IFR. Observational evidence is presented for a substantial and persistent IF-overflow and mechanisms that qualitatively control its intensity. Through this, we explain the main discrepancies between observed and simulated exchange. Our findings rebuild confidence in modelled net exchange across the IFR, but reveal that compensation of model deficiencies here through other exchange branches is not effective. This implies that simulated ocean heat transport to the Arctic is biased low by more than 10 % and associated with a reduced level of variability, while the quality of the simulated salt transport becomes critically dependent on the link between IF-inflow and IF-overflow. These features likely affect sensitivity and stability of climate models to climate change and limit the predictive skill.

Download Full-text

Biased thermohaline exchanges with the arctic across the Iceland-Faroe Ridge in ocean climate models

Ocean Science Discussions ◽

10.5194/osd-12-1471-2015 ◽

2015 ◽

Vol 12 (4) ◽

pp. 1471-1510 ◽

Cited By ~ 2

Author(s):

S. M. Olsen ◽

B. Hansen ◽

S. Østerhus ◽

D. Quadfasel ◽

H. Valdimarsson

Keyword(s):

Heat Transport ◽

Climate Models ◽

Thermohaline Circulation ◽

Salt Transport ◽

The Arctic ◽

Global Ocean ◽

Climate Projections ◽

Ocean Heat Transport ◽

Ice Melt ◽

Predictive Skill

Abstract. The northern limb of the Atlantic thermohaline circulation and its transport of heat and salt towards the Arctic strongly modulates the climate of the Northern Hemisphere. Presence of warm surface waters prevents ice formation in parts of the Arctic Mediterranean and ocean heat is in critical regions directly available for sea-ice melt, while salt transport may be critical for the stability of the exchanges. Hereby, ocean heat and salt transports play a disproportionally strong role in the climate system and realistic simulation is a requisite for reliable climate projections. Across the Greenland-Scotland Ridge (GSR) this occurs in three well defined branches where anomalies in the warm and saline Atlantic inflow across the shallow Iceland-Faroe Ridge (IFR) have shown particularly difficult to simulate in global ocean models. This branch (IF-inflow) carries about 40 % of the total ocean heat transport into the Arctic Mediterranean and is well constrained by observation during the last two decades but is associated with significant inter-annual fluctuations. The inconsistency between model results and observational data is here explained by the inability of coarse resolution models to simulate the overflow across the IFR (IF-overflow), which feeds back on the simulated IF-inflow. In effect, this is reduced in the model to reflect only the net exchange across the IFR. Observational evidence is presented for a substantial and persistent IF-overflow and mechanisms that qualitatively control its intensity. Through this, we explain the main discrepancies between observed and simulated exchange. Our findings rebuild confidence in modeled net exchange across the IFR, but reveal that compensation of model deficiencies here through other exchange branches is not effective. This implies that simulated ocean heat transport to the Arctic is biased low by more than 10 % and associated with a reduced level of variability while the quality of the simulated salt transport becomes critically dependent on the link between IF-inflow and IF-overflow. These features likely affect sensitivity and stability of climate models to climate change and limit the predictive skill.

Download Full-text

Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

Climate of the Past ◽

10.5194/cp-8-2079-2012 ◽

2012 ◽

Vol 8 (6) ◽

pp. 2079-2092 ◽

Cited By ~ 31

Author(s):

A. Voigt ◽

D. S. Abbot

Keyword(s):

Sea Ice ◽

Heat Transport ◽

General Circulation ◽

Climate Models ◽

Ice Cover ◽

The State ◽

Snowball Earth ◽

Ocean Heat Transport ◽

Ice Dynamics ◽

Sea Ice Dynamics

Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we study the effect of bare sea-ice albedo, sea-ice dynamics and ocean heat transport on (CO2, SI)* in the atmosphere–ocean general circulation model ECHAM5/MPI-OM with Marinoan (~ 635 Ma) continents and solar insolation (94% of modern). In its standard setup, ECHAM5/MPI-OM initiates a~Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Replacing the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). This is consistent with previous work and results from net evaporation and local melting near the sea-ice margin. When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a hundred times lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, the simulation of sea-ice dynamics in ECHAM5/MPI-OM is a dominant determinant of its high critical CO2 for Snowball initiation relative to other models. Ocean heat transport has no effect on the critical sea-ice cover and only slightly decreases the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no indication of the Jormungand bifurcation and hysteresis in ECHAM5/MPI-OM. The state with 85% sea-ice cover therefore is a soft Snowball state rather than a true Jormungand state. Overall, our results demonstrate that differences in sea-ice dynamics schemes can be at least as important as differences in sea-ice albedo for causing the spread in climate models' estimates of the Snowball Earth bifurcation. A detailed understanding of Snowball Earth initiation therefore requires future research on sea-ice dynamics to determine which model's simulation is most realistic.

Download Full-text

Ocean heat transport as a driver of sea ice extent in CMIP6 models

10.5194/egusphere-egu21-2170 ◽

2021 ◽

Author(s):

Jake Aylmer ◽

David Ferreira ◽

Daniel Feltham

Keyword(s):

Sea Ice ◽

Heat Transport ◽

Surface Fluxes ◽

The Arctic ◽

Balance Model ◽

Climate Projections ◽

Ocean Heat Transport ◽

Sea Ice Extent ◽

Atlantic Sector ◽

The Mean

Estimating long-term projections of sea ice extent is a key part of understanding the possible future climate state. This is hampered by uncertainties within and across comprehensive climate models, and the relative importance and nature of contributing factors are not fully understood. Here, we investigate the role of ocean and atmospheric forcing on sea ice on multidecadal time scales.Pre-industrial control simulations of 19 CMIP6 models are analysed. Sea ice extent is negatively correlated with ocean heat transport (OHT), and positively correlated with atmospheric heat (moist-static energy) transport (AHT), in both hemispheres. In most models, increased OHT into the Arctic enhances surface fluxes in the Atlantic sector just south of the sea ice edge, which in turn increases the AHT convergence at higher latitudes. In the southern ocean, increased OHT directly increases the mean ocean&#8211;ice heat flux while AHT plays no direct role. Sensitivities of the sea ice cover to OHT are consistent with predictions from an idealised energy balance model (EBM), which is fitted to each model in turn. This shows that the sensitivities are constrained by atmospheric radiation parameters and the mean surface temperature response, with no explicit dependence on ocean parameters. These results are a step towards quantifying the effect of ocean biases on sea ice uncertainty in climate projections.

Download Full-text