Impact Of Ocean Heat Transport Research Articles

Impact of Ocean Heat Transport on Arctic Sea Ice Variability in the GFDL CM2‐O Model Suite

AbstractThe impact of horizontal resolution on meridional Ocean Heat Transport (OHT) and sea ice in the Arctic is investigated using the GFDL CM2‐O climate model suite (1°, 1/4°, and 1/10°) in both preindustrial control and climate change simulations. Results show an increase in OHT associated to a decrease in sea ice extent (SIE) in the Arctic on interannual and decadal timescales. This link, however, is not monotonic with spatial resolution. While OHT increases and SIE decreases from the Low to the Medium resolution, the reverse is true from the Medium to the High resolution. Differences in OHT and SIE between the three model configurations mostly arise from the preindustrial state. As the spatial resolution increases, the Irminger Current is favored at the expense of the North Atlantic Drift. This rerouting of water to the Western side of Greenland results in less heat delivered to the Arctic in the High‐resolution configuration than in its Medium counterpart. As a result, the Medium‐resolution configuration is in best agreement with observed SIE and Atlantic OHT. Concurrent with the change in the partitioning in volume is a change in deep convection centers from the Greenland‐Irminger‐Norwegian Seas in the Low resolution to the Labrador Sea in the Medium and High resolutions. Results suggest a coupling between OHT into the Arctic and deep convection in the North Atlantic.

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

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 (sim {}100~text {W}~text {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.

Impact of ocean heat transport on the Arctic sea-ice decline: a model study with EC-Earth3

The recent increase in Atlantic and Pacific ocean heat transports has led to a decrease in Arctic sea-ice area and volume. As the respective contributions from both oceans in driving sea-ice loss is still uncertain, our study explores this. We use the EC-Earth3 coupled global climate model and perform different sensitivity experiments to gain insights into the relationships between ocean heat transport and Arctic sea ice. In these model experiments, the sea-surface temperature is artificially increased in different regions of the North Atlantic and North Pacific Oceans and with different levels of warming. All the experiments lead to enhanced ocean heat transport, and consequently to a decrease in Arctic sea-ice area and volume. We show that the wider the domain in which the sea-surface temperature is increased and the larger the level of warming, the larger the increase in ocean heat transport and the stronger the decrease in Arctic sea-ice area and volume. We also find that for a same amount of ocean heat transport increase, the reductions in Arctic sea-ice area and volume are stronger when the sea-surface temperature increase is imposed in the North Pacific, compared to the North Atlantic. This is explained by the lower-salinity water at the Bering Strait and atmospheric warming of the North Atlantic Ocean in the Pacific experiments. Finally, we find that the sea-ice loss is mainly driven by reduced basal growth along the sea-ice edge and enhanced basal melt in the Central Arctic. This confirms that the ocean heat transport is the primary driver of Arctic sea-ice loss in our experiments.

Oceanic heat transport into the Arctic under high and low hbox {CO}_2 forcing

Enhanced ocean heat transport into the Arctic is linked to stronger future Arctic warming and polar amplification. To quantify the impact of ocean heat transport on Arctic climate, it is imperative to understand how its magnitude and the associated mechanisms change in other climate states. This paper therefore assesses the ocean heat transport into the Arctic at 70^{circ }hbox {N} for climates forced with a broad range of carbon dioxide concentration levels, ranging from one-fourth to four times modern values. We focused on ocean heat transports through the Arctic entrances (Bering Strait, Canadian Archipelago, and Nordic Seas) and identified relative contributions of volume and temperature to these changes. The results show that ocean heat transport differences across the five climate states are dominated by heat transport changes in the Nordic Seas, although in the warmest climate state heat transport through the Bering Strait plays an almost equally important role. This is primarily caused by changes in horizontal currents owing to anomalous wind responses and to differential advection of thermal anomalies. Changes in sea ice cover play a prominent role by modulating the surface heat fluxes and the impact of wind stresses on ocean currents. The Atlantic meridional overturning circulation and its associated heat transport play a more modest role in the ocean heat transport into the Arctic. The net effect of these changes is that the poleward ocean heat transport at 70^{circ }hbox {N} strongly increases from the coldest climate to the warmest climate state.

Exploring the Climatic Response to Wide Variations in Ocean Heat Transport on an Aquaplanet

The climatic impact of ocean heat transport (OHT) is studied in a series of idealized aquaplanet climate model experiments. OHT is prescribed through a simple geometrical formula spanning a wide variety of amplitudes and meridional extents. Calculations with a comprehensive GCM are compared against a simple diffusive energy balance model (EBM). The GCM response differs from the EBM in several important ways that illustrate linkages between atmospheric dynamics and radiative processes. Increased OHT produces global mean warming at a rate of 2 K PW−1 OHT across 30° and a strong reduction in meridional temperature gradient. The tropics remain nearly isothermal despite locally large imposed ocean heat uptake. The warmer climate features reduced equatorial convection, moister subtropics, reduced cloudiness, and partial but incomplete compensation in atmospheric heat transport. Many of these effects are linked to a weakened Hadley circulation. Both the warming pattern and hydrological changes differ strongly from those driven by CO2. Similar results are found at 0° and 23.45° obliquity. It is argued that clouds, rather than clear-sky radiative processes, are principally responsible for the global warming and tropical thermostat effects. Cloud changes produce warming in all cases, but the degree of warming depends strongly on the meridional extent of OHT. The strongest warming occurs in response to mid- to high-latitude OHT convergence, which produces widespread loss of boundary layer clouds. Temperature responses to increased OHT are quantitatively reproduced in the EBM by imposing GCM-derived cloud radiative effects as additional forcing.

The impact of oceanic heat transport on the atmospheric circulation

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

Evaluation of the impact of oceanic heat transport in the North Atlantic and Barents sea on the Northern Hemispheric climate

In this work, we evaluate the impact of terminated oceanic heat flux in the North Atlantic and Barents Sea on the Northern Hemisphere climate in January by numerical experiments with a coupled model of atmospheric general circulation and a thermodynamic model of the upper mixed layer of the ocean. We analyze the variations in the atmospheric circulation and near-surface temperature. We found that the termination of the oceanic heat flux leads to a depression in atmospheric centers of action in the Northern Hemisphere (by 3-5 hPa) and a significant cooling over the continents with the strongest temperature decrease down to -10 degrees C in northwestern Eurasia.