Air–Sea Interaction: Heat and Fresh-Water Fluxes in the Aegean Sea

Abstract. Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean-atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air--sea buoyancy fluxes is less clear. We use a global, eddy permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around 10° latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy flux forced anomalies are in phase with variations driven by wind stress changes but their effect on the prevailing anomalies and the importance of heat and fresh water fluxes vary locally. In the eastern tropical basin interannual sea level variability is amplified by anomalous heat fluxes, while the importance of fresh water fluxes is small and neither has any impact on decadal timescales. In the western tropical Pacific the variability on interannual and decadal timescales is dampened by both, heat and freshwater fluxes. The mechanism involves westward propagating Rossby waves that are triggered during ENSO events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.

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Systematic study of the impact of fresh water fluxes on the glacial carbon cycle

Climate of the Past ◽

10.5194/cp-8-589-2012 ◽

2012 ◽

Vol 8 (2) ◽

pp. 589-607 ◽

Cited By ~ 19

Author(s):

N. Bouttes ◽

D. M. Roche ◽

D. Paillard

Keyword(s):

Carbon Cycle ◽

Fresh Water ◽

Climate Changes ◽

Water Flux ◽

Ice Cores ◽

Atmospheric Co2 ◽

Water Fluxes ◽

Oceanic Circulation ◽

Fresh Water Flux ◽

The Impact

Abstract. During glacial periods, atmospheric CO2 concentration increases and decreases by around 15 ppm. At the same time, the climate changes gradually in Antarctica. Such climate changes can be simulated in models when the AMOC (Atlantic Meridional Oceanic Circulation) is weakened by adding fresh water to the North Atlantic. The impact on the carbon cycle is less straightforward, and previous studies give opposite results. Because the models and the fresh water fluxes were different in these studies, it prevents any direct comparison and hinders finding whether the discrepancies arise from using different models or different fresh water fluxes. In this study we use the CLIMBER-2 coupled climate carbon model to explore the impact of different fresh water fluxes. In both preindustrial and glacial states, the addition of fresh water and the resulting slow-down of the AMOC lead to an uptake of carbon by the ocean and a release by the terrestrial biosphere. The duration, shape and amplitude of the fresh water flux all have an impact on the change of atmospheric CO2 because they modulate the change of the AMOC. The maximum CO2 change linearly depends on the time integral of the AMOC change. The different duration, amplitude, and shape of the fresh water flux cannot explain the opposite evolution of ocean and vegetation carbon inventory in different models. The different CO2 evolution thus depends on the AMOC response to the addition of fresh water and the resulting climatic change, which are both model dependent. In CLIMBER-2, the rise of CO2 recorded in ice cores during abrupt events can be simulated under glacial conditions, especially when the sinking of brines in the Southern Ocean is taken into account. The addition of fresh water in the Southern Hemisphere leads to a decline of CO2, contrary to the addition of fresh water in the Northern Hemisphere.

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How much Arctic fresh water participates in the subpolar overturning circulation?

10.5194/egusphere-egu21-2824 ◽

2021 ◽

Author(s):

Isabela Le Bras ◽

Fiamma Straneo ◽

Morven Muilwijk ◽

Lars Henrik Smedsrud ◽

Feili Li ◽

...

Keyword(s):

Fresh Water ◽

Climate Models ◽

Deep Ocean ◽

The Arctic ◽

Water Fluxes ◽

Overturning Circulation ◽

Ice Melt ◽

Flow Through ◽

Heat Budgets ◽

Water Outflow

<p><span>Fresh Arctic waters flowing into the Atlantic are thought to have two primary fates. They may be mixed into the deep ocean as part of the overturning circulation, or flow alongside regions of deep water formation without impacting overturning. Climate models suggest that as increasing amounts of fresh water enter the Atlantic, the overturning circulation will be disrupted, yet we lack an understanding of how much fresh water is mixed into the overturning circulation's deep limb in the present day. To constrain these fresh water pathways, we build steady-state volume, salt, and heat budgets east of Greenland that are initialized with observations and closed using inverse methods. Fresh water sources are split into oceanic Polar Waters from the Arctic and surface fresh water fluxes, which include net precipitation, runoff, and ice melt, to examine how they imprint the circulation differently. We find that 65 mSv of the total 110 mSv of surface fresh water fluxes that enter our domain participate in the overturning circulation, as do 0.6 Sv of the total 1.2 Sv of Polar Waters that flow through Fram Strait. Based on these results, we hypothesize that the overturning circulation is more sensitive to future changes in Arctic fresh water outflow and precipitation, while Greenland runoff and iceberg melt are more likely to stay along the coast of Greenland.</span></p>

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Impact of sea-ice formation on the properties of Antarctic bottom water

Annals of Glaciology ◽

10.3189/s0260305500014154 ◽

1997 ◽

Vol 25 ◽

pp. 276-281 ◽

Cited By ~ 7

Author(s):

H. Goosse ◽

J. M. Campin ◽

T. Fichefet ◽

E. Deleersnijder

Keyword(s):

Fresh Water ◽

Deep Water ◽

Bottom Water ◽

Formation Rate ◽

Water Flux ◽

Three Dimensional ◽

Deep Ocean ◽

Ocean Model ◽

Antarctic Bottom Water ◽

Water Fluxes

It is generally accepted that fresh-water fluxes due to ice accretion or melting profoundly influence the formation of Antarctic bottom water (AABW). This is investigated by means of a global, three-dimensional ice–ocean model. Two model runs were conducted. At the high southern latitudes, the control experiment exhibits positive (i.e. towards the ocean) fresh-water fluxes over the deep ocean, and large negative fluxes over the Antarctic continental shelf, because of the intense ice-production taking place in this region. The salinity of shelf water can increase in such a way that deep-water formation is facilitated. The simulated net fresh-water flux over the shelf has an annual mean value of −1 m a−1. This flux induces a transport of salt to bottom waters, which corresponds to an increase of their salinity estimated to be around 0.05 psu. In the second model run, the fresh-water fluxes due to ice melting or freezing are neglected, leading to a rearrangement of the water masses. In particular, the AABW-formation rate decreases, which allows the influence of North Atlantic deep water (NADW) to increase. As NADW is warmer and saltier than AABW, the bottom-water salinity and temperature become higher.

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East Antarctic seasonal sea-ice and ocean stability: a model study

Annals of Glaciology ◽

10.3189/1998aog27-1-477-482 ◽

1998 ◽

Vol 27 ◽

pp. 477-482 ◽

Cited By ~ 9

Author(s):

Simon Marsland ◽

Jörg-Olaf Wolff

Keyword(s):

Sea Ice ◽

Fresh Water ◽

Water Flux ◽

Coupled System ◽

Threshold Value ◽

Ocean Model ◽

Spatial And Temporal Variability ◽

Thermal Mode ◽

Water Fluxes ◽

Model Study

A high-resolution primitive equation ocean model has been coupled to a dynamic/thermodynamic sea-ice model and applied to a region of the Southern Ocean south of Australia. The model is found to be very sensitive to the surface fresh-water flux! A stable seasonal cycle of sea-ice advance and retreat is simulated only for sufficient surface fresh-water fluxes. For fresh-water fluxes below a threshold value of around 40 cm a−1 the coupled system enters a thermal mode characterised by vertical homogeneity of the oceanic temperature and salinity fields. Such an ocean has a surface temperature that is too warm for a sea-ice cover to develop. Spatial and temporal variability of the oceanic heat llux into the upper model layer iS examined for the stable simulations. High values of this oceanic heat flux (~40Wm−2) occur during the sea-ice formation period (March-June), with values as low as 5 wM−2 occurring in November. The source of this heat is primarily convective, a process induced by brine rejection during ice growth.

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Modelling the water mass circulation in the Aegean Sea. Part I: wind stresses, thermal and haline fluxes

Annales Geophysicae ◽

10.1007/s00585-994-0794-9 ◽

1994 ◽

Vol 12 (8) ◽

pp. 794-807 ◽

Cited By ~ 4

Author(s):

I. A. Valioulis ◽

Y. N. Krestenitis

Keyword(s):

Experimental Evidence ◽

Black Sea ◽

Computer Model ◽

Seasonal Variations ◽

Water Mass ◽

Eastern Mediterranean ◽

Aegean Sea ◽

Water Fluxes ◽

Physical Processes ◽

Mass Circulation

Abstract. The aim of this work is to develop a computer model capable of simulating the water mass circulation in the Aegean Sea. There is historical, phenomenological and recent experimental evidence of important hydrographical features whose causes have been variably identified as the highly complex bathymetry, the extreme seasonal variations in temperature, the considerable fresh water fluxes, and the large gradients in salinity or temperature across neighbouring water masses (Black Sea and Eastern Mediterranean). In the approach taken here, physical processes are introduced into the model one by one. This method reveals the parameters responsible for permanent and seasonal features of the Aegean Sea circulation. In the first part of the work reported herein, wind-induced circulation appears to be seasonally invariant. This yearly pattern is overcome by the inclusion of baroclinicity in the model in the form of surface thermohaline fluxes. The model shows an intricate pattern of sub-basin gyres and locally strong currents, permanent or seasonal, in accord with the experimental evidence.

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Impact of sea-ice formation on the properties of Antarctic bottom water

Annals of Glaciology ◽

10.1017/s0260305500014154 ◽

1997 ◽

Vol 25 ◽

pp. 276-281 ◽

Cited By ~ 7

Author(s):

H. Goosse ◽

J. M. Campin ◽

T. Fichefet ◽

E. Deleersnijder

Keyword(s):

Fresh Water ◽

Deep Water ◽

Bottom Water ◽

Formation Rate ◽

Water Flux ◽

Three Dimensional ◽

Deep Ocean ◽

Ocean Model ◽

Antarctic Bottom Water ◽

Water Fluxes

It is generally accepted that fresh-water fluxes due to ice accretion or melting profoundly influence the formation of Antarctic bottom water (AABW). This is investigated by means of a global, three-dimensional ice-ocean model. Two model runs were conducted. At the high southern latitudes, the control experiment exhibits positive (i.e. towards the ocean) fresh-water fluxes over the deep ocean, and large negative fluxes over the Antarctic continental shelf, because of the intense ice-production taking place in this region. The salinity of shelf water can increase in such a way that deep-water formation is facilitated. The simulated net fresh-water flux over the shelf has an annual mean value of −1 m a−1. This flux induces a transport of salt to bottom waters, which corresponds to an increase of their salinity estimated to be around 0.05 psu. In the second model run, the fresh-water fluxes due to ice melting or freezing are neglected, leading to a rearrangement of the water masses. In particular, the AABW-formation rate decreases, which allows the influence of North Atlantic deep water (NADW) to increase. As NADW is warmer and saltier than AABW. the bottom-water salinity and temperature become higher.

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How much Arctic fresh water participates in the subpolar overturning circulation?

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0240.1 ◽

2021 ◽

Author(s):

Isabela Le Bras ◽

Fiamma Straneo ◽

Morven Muilwijk ◽

Lars H. Smedsrud ◽

Feili Li ◽

...

Keyword(s):

Fresh Water ◽

Climate Models ◽

Deep Ocean ◽

The Arctic ◽

Water Fluxes ◽

Overturning Circulation ◽

Ice Melt ◽

Flow Through ◽

Heat Budgets ◽

Water Outflow

AbstractFresh Arctic waters flowing into the Atlantic are thought to have two primary fates. They may be mixed into the deep ocean as part of the overturning circulation, or flow alongside regions of deep water formation without impacting overturning. Climate models suggest that as increasing amounts of fresh water enter the Atlantic, the overturning circulation will be disrupted, yet we lack an understanding of how much fresh water is mixed into the overturning circulation’s deep limb in the present day. To constrain these fresh water pathways, we build steady-state volume, salt, and heat budgets east of Greenland that are initialized with observations and closed using inverse methods. Fresh water sources are split into oceanic Polar Waters from the Arctic and surface fresh water fluxes, which include net precipitation, runoff, and ice melt, to examine how they imprint the circulation differently. We find that 65 mSv of the total 110 mSv of surface fresh water fluxes that enter our domain participate in the overturning circulation, as do 0.6 Sv of the total 1.2 Sv of Polar Waters that flow through Fram Strait. Based on these results, we hypothesize that the overturning circulation is more sensitive to future changes in Arctic fresh water outflow and precipitation, while Greenland runoff and iceberg melt are more likely to stay along the coast of Greenland.

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