scholarly journals Sea-ice retreat suggests re-organization of water mass transformation in the Nordic and Barents Seas

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
G. W. K. Moore ◽  
K. Våge ◽  
I. A. Renfrew ◽  
R. S. Pickart
Keyword(s):  
Sea Ice ◽  
Water Mass ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Spatiotemporal Variability ◽  
Warming Climate ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Sea Ice Retreat ◽  
Water Mass Transformation

AbstractWater mass transformation in the Nordic and Barents Seas, triggered by air-sea heat fluxes, is an integral component of the Atlantic Meridional Overturning Circulation (AMOC). These regions are undergoing rapid warming, associated with a retreat in ice cover. Here we present an analysis covering 1950−2020 of the spatiotemporal variability of the air-sea heat fluxes along the region’s boundary currents, where water mass transformation impacts are large. We find there is an increase in the air-sea heat fluxes along these currents that is a function of the currents’ orientation relative to the axis of sea-ice change suggesting enhanced water mass transformation is occurring. Previous work has shown a reduction in heat fluxes in the interior of the Nordic Seas. As a result, a reorganization seems to be underway in where water mass transformation occurs, that needs to be considered when ascertaining how the AMOC will respond to a warming climate.

Evolving air-sea interaction due to sea-ice retreat points to a re-organisation of water mass transformation in the Nordic and Barents Seas

2021 ◽  
Author(s):  
Kent Moore ◽  
Kjetil Våge ◽  
Ian Renfrew ◽  
Bob Pickart
Keyword(s):  
Sea Ice ◽  
Water Mass ◽  
Critical Role ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Spatiotemporal Variability ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Sea Ice Retreat ◽  
Water Mass Transformation

<p>The Nordic and Barents Seas play a critical role in the climate system resulting from water mass transformation, triggered by intense air-sea heat fluxes, that is an integral component of the Atlantic Meridional Overturning Circulation (AMOC). These seas are undergoing rapid warming, associated with a retreat in ice cover. Here we present a novel analysis, covering the period 1950-2020, of the spatiotemporal variability of the air-sea heat fluxes along the region’s boundary currents, where the impacts on the water mass transformation are large.  We find that the variability is a function of the relative orientation of the current and the axis of sea-ice change that can result in up to a doubling of the heat fluxes over the period of interest. This implies enhanced water mass transformation is occurring along these currents. In contrast, previous work has shown a reduction in fluxes in the interior sites of the Nordic Seas, where ocean convection is also observed, suggesting that a reorganization may be underway in the nature of the water mass transformation, that needs to be considered when ascertaining how the AMOC will respond to a warming climate.</p>

Deep-water formation and Arctic circulation under sea-ice retreat: a comparison between CMIP6 models

2021 ◽  
Author(s):  
Anais Bretones ◽  
Kerim Hestnes Nisancioglu ◽  
Mari Fjalstad Jensen
Keyword(s):  
Sea Ice ◽  
Climate Models ◽  
Mixed Layer Depth ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Overturning Circulation ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Sea Ice Edge ◽  
Sea Ice Retreat

<div> <div> <div> <div> <p>While a rapid sea-ice retreat in the Arctic has become ubiquitous, the potential weakening of the Atlantic Meridional Overturning circulation (AMOC), in response to rising greenhouse gases, is still under debate. Although climate models predict a weakening of the AMOC, observations are so far inconclusive. It has been suggested that the strength and vertical extent of the AMOC responds to sea-ice retreat, as deep mixing occurs in open-ocean areas close to the sea-ice edge. Here, we investigate this hypothesis by looking at the Arctic tidional Overturning Circulation (ArMOC) and mixed-layer depth in several CMIP6 models forced with the SSP5- 8.5 scenario. For every models we find a decoupling of the ArMOC with the AMOC: while the AMOC weakens during the 21st century, the ArMOC is enhanced.</p> </div> </div> </div> </div>

scholarly journals Transient increase in Arctic deep-water formation and ocean circulation under sea-ice retreat

2021 ◽  
pp. 1
Author(s):  
Anaïs Bretones ◽  
Kerim H. Nisancioglu ◽  
Mari F. Jensen ◽  
Ailin Brakstad ◽  
Shuting Yang
Keyword(s):  
Sea Ice ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Deep Water Formation ◽  
Water Formation ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Ice Edge ◽  
Sea Ice Edge ◽  
Sea Ice Retreat

AbstractWhile a rapid sea-ice retreat in the Arctic has become ubiquitous, the potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to global warming is still under debate. As deep mixing occurs in the open-ocean close to the sea-ice edge, the strength and vertical extent of the AMOC is likely to respond to ongoing and future sea-ice retreat. Here, we investigate the link between changes in Arctic sea-ice cover and AMOC strength in a long simulation with the EC-Earth-PISM climate model under the emission scenario RCP8.5. The extended duration of the experiment (years 1850-2300) captures the disappearance of summer sea ice in 2060 and the removal of winter sea ice in 2165. By introducing a new metric, the Arctic Meridional Overturning Circulation (ArMOC), we document changes beyond the Greenland-Scotland Ridge and into the central Arctic. We find an ArMOC strengthening as the areas of deep mixing move north, following the retreating winter sea-ice edge into the Nansen Basin. At the same time, mixing in the Labrador and Greenland Seas reduces and the AMOC weakens. As the winter sea-ice edge retreats further into the regions with high surface freshwater content in the central Arctic Basin, the mixing becomes shallower and the ArMOC weakens. Our results suggest that the location of deep-water formation plays a decisive role in the structure and strength of the ArMOC; however, the intermittent strengthening of the ArMOC and convection north of the Greenland-Scotland Ridge cannot compensate for the progressive weakening of the AMOC.

scholarly journals Southern Ocean Deep Circulation and Heat Uptake in a High-Resolution Climate Model

2016 ◽  
Vol 29 (7) ◽  
pp. 2597-2619 ◽  
Author(s):  
Emily R. Newsom ◽  
Cecilia M. Bitz ◽  
Frank O. Bryan ◽  
Ryan Abernathey ◽  
Peter R. Gent
Keyword(s):  
High Resolution ◽  
Southern Ocean ◽  
Sea Ice ◽  
Climate Model ◽  
Water Mass ◽  
Global Climate Model ◽  
Substantial Reduction ◽  
Meridional Overturning Circulation ◽  
Heat Uptake ◽  
Water Mass Transformation

Abstract The dynamics of the lower cell of the meridional overturning circulation (MOC) in the Southern Ocean are compared in two versions of a global climate model: one with high-resolution (0.1°) ocean and sea ice and the other a lower-resolution (1.0°) counterpart. In the high-resolution version, the lower cell circulation is stronger and extends farther northward into the abyssal ocean. Using the water-mass-transformation framework, it is shown that the differences in the lower cell circulation between resolutions are explained by greater rates of surface water-mass transformation within the higher-resolution Antarctic sea ice pack and by differences in diapycnal-mixing-induced transformation in the abyssal ocean. While both surface and interior transformation processes work in tandem to sustain the lower cell in the control climate, the circulation is far more sensitive to changes in surface transformation in response to atmospheric warming from raising carbon dioxide levels. The substantial reduction in overturning is primarily attributed to reduced surface heat loss. At high resolution, the circulation slows more dramatically, with an anomaly that reaches deeper into the abyssal ocean and alters the distribution of Southern Ocean warming. The resolution dependence of associated heat uptake is particularly pronounced in the abyssal ocean (below 4000 m), where the higher-resolution version of the model warms 4.5 times more than its lower-resolution counterpart.

Water mass transformation and overturning circulation in the Arabian Gulf

2021 ◽  
Author(s):  
Maryam R. Al-Shehhi ◽  
Hajoon Song ◽  
Jeffery Scott ◽  
John Marshall
Keyword(s):  
Water Mass ◽  
Arabian Gulf ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Transformation Rate ◽  
Overturning Circulation ◽  
Resolution Model ◽  
Meridional Overturning ◽  
High Resolution Model ◽  
Water Mass Transformation

AbstractWe diagnose the ocean’s residual overturning circulation of the Arabian Gulf in a high-resolution model and interpret it in terms ofwater-mass transformation processes mediated by air-sea buoyancy fluxes and interior mixing. We attempt to rationalise the complex three-dimensional flow in terms of the superposition of a zonal (roughly along-axis) and meridional (transverse) overturning pattern. Rates of overturning and the seasonal cycle of air-sea fluxes sustaining them are quantified and ranked in order of importance. Air-sea fluxes dominate the budget so that, at zero order, the magnitude and sense of the overturning circulation can be inferred from air-sea fluxes, with interior mixing playing a lesser role. We find that wintertime latent heat fluxes dominate the water-mass transformation rate in the interior waters of the Gulf leading to a diapycnal volume flux directed toward higher densities. In the zonal overturning cell, fluid is drawn in from the Sea of Oman through the Strait of Hormuz, transformed and exits the Strait near the southern and bottom boundaries. Along the southern margin of the Gulf, evaporation plays an important role in the meridional overturning pattern inducing sinking there.

scholarly journals Influences of Precipitation on Water Mass Transformation and Deep Convection

2012 ◽  
Vol 42 (10) ◽  
pp. 1684-1700 ◽  
Author(s):  
Michael A. Spall
Keyword(s):  
Numerical Model ◽  
Water Mass ◽  
Numerical Models ◽  
Deep Convection ◽  
Meridional Overturning Circulation ◽  
Critical Threshold ◽  
Overturning Circulation ◽  
Model Calculations ◽  
Meridional Overturning ◽  
Water Mass Transformation

Abstract The influences of precipitation on water mass transformation and the strength of the meridional overturning circulation in marginal seas are studied using theoretical and idealized numerical models. Nondimensional equations are developed for the temperature and salinity anomalies of deep convective water masses, making explicit their dependence on both geometric parameters such as basin area, sill depth, and latitude, as well as on the strength of atmospheric forcing. In addition to the properties of the convective water, the theory also predicts the magnitude of precipitation required to shut down deep convection and switch the circulation into the haline mode. High-resolution numerical model calculations compare well with the theory for the properties of the convective water mass, the strength of the meridional overturning circulation, and also the shutdown of deep convection. However, the numerical model also shows that, for precipitation levels that exceed this critical threshold, the circulation retains downwelling and northward heat transport, even in the absence of deep convection.

scholarly journals Climate control of sea-ice edge phytoplankton blooms in the Hudson Bay system

Elem Sci Anth ◽  
2020 ◽  
Vol 8 (1) ◽  
Author(s):  
Lucas Barbedo ◽  
Simon Bélanger ◽  
Jean-Éric Tremblay
Keyword(s):  
Sea Ice ◽  
Primary Productivity ◽  
Marine Ecosystem ◽  
Spatiotemporal Variability ◽  
Climate Indices ◽  
Hudson Bay ◽  
The North ◽  
Ice Retreat ◽  
Ice Edge ◽  
Sea Ice Retreat

The Hudson Bay System (HBS), the world’s largest inland sea, has experienced disproportionate atmospheric warming and sea-ice decline relative to the whole Arctic Ocean during the last few decades. The establishment of almost continuous positive atmospheric air temperature anomalies since the late 1990s impacted its primary productivity and, consequently, the marine ecosystem. Here, four decades of archived satellite ocean color were analyzed together with sea-ice and climatic conditions to better understand the response of the HBS to climate forcing concerning phytoplankton dynamics. Using satellite-derived chlorophyll-a concentration [Chla], we examined the spatiotemporal variability of phytoplankton concentration with a focus on its phenology throughout the marginal ice zone. In recent years, phytoplankton phenology was dominated by two peaks of [Chla] during the ice-free period. The first peak occurs during the spring-to-summer transition and the second one happens in the fall, contrasting with the single bloom observed earlier (1978–1983). The ice-edge bloom, that is, the peak in [Chla] immediately found after the sea-ice retreat, showed substantial spatial and interannual variability. During the spring-to-summer transition, early sea-ice retreat resulted in ice-edge bloom intensification. In the northwest polynya, a marine wildlife hot spot, the correlation between climate indices, that is, the North Atlantic Oscillation and Arctic Oscillation (NAO/AO), and [Chla] indicated that the bloom responds to large-scale atmospheric circulation patterns in the North Hemisphere. The intensification of westerly winds caused by the strong polar vortex during positive NAO/AO phases favors the formation of the polynya, where ice production and export, brine rejection, and nutrient replenishment are more efficient. As a result, the winter climate preconditions the upper layer of the HBS for the subsequent development of ice-edge blooms. In the context of a decline in the NAO/AO strength related to Arctic warming, primary productivity is likely to decrease in the HBS and the northwest polynya in particular.

Drivers of the water mass transformations that set the overturning circulation in the subpolar North Atlantic

2021 ◽  
Author(s):  
D. Gwyn Evans ◽  
N. Penny Holliday ◽  
Marilena Oltmanns
Keyword(s):  
North Atlantic ◽  
Water Mass ◽  
Meridional Overturning Circulation ◽  
Mass Analysis ◽  
Overturning Circulation ◽  
Water Mass Analysis ◽  
Meridional Overturning ◽  
The Mean ◽  
Water Mass Transformation ◽  
Water Mass Transformations

<p>The OSNAP (Overturning in the Subpolar North Atlantic Program) array at ~60°N has provided new and unprecedented insight into the strength and variability of the meridional overturning circulation in the subpolar North Atlantic. OSNAP has identified the region of the subpolar North Atlantic east of Greenland as a key region for the water mass transformation and densification that sets the strength and variability of the overturning circulation. Here, we will investigate the drivers of this water mass transformation and their roles in driving the overturning circulation at OSNAP. Using a water mass analysis on both model-based and observational-based datasets, we isolate diathermal (across surfaces of constant temperature) and diahaline (across surfaces of constant salinity) transformations due to air-sea buoyancy fluxes, and mixing. We show that the time-mean overturning strength is set by both the air-sea buoyancy fluxes and the strength of subsurface mixing. This balance is apparent on a seasonal timescale, where we resolve large seasonal fluctuations in the both the air-sea buoyancy fluxes and mixing. The residual of this seasonal cycle then corresponds to the mean overturning strength. On interannual timescales, mixing becomes the dominant driver of variability in the overturning circulation. To determine the location of these water mass transformations and the dynamical processes responsible for the mixing-driven variability, our water mass analysis is projected onto geographical coordinates.</p>

scholarly journals Impacts of Ice-Shelf Melting on Water-Mass Transformation in the Southern Ocean from E3SM Simulations

2020 ◽  
Vol 33 (13) ◽  
pp. 5787-5807
Author(s):  
Hyein Jeong ◽  
Xylar S. Asay-Davis ◽  
Adrian K. Turner ◽  
Darin S. Comeau ◽  
Stephen F. Price ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Water Mass ◽  
Dominant Role ◽  
Heat Fluxes ◽  
Ice Formation ◽  
Ice Shelf ◽  
Overturning Circulation ◽  
Antarctic Sea Ice ◽  
Water Mass Transformation

AbstractThe Southern Ocean overturning circulation is driven by winds, heat fluxes, and freshwater sources. Among these sources of freshwater, Antarctic sea ice formation and melting play the dominant role. Even though ice-shelf melt is relatively small in magnitude, it is located close to regions of convection, where it may influence dense water formation. Here, we explore the impacts of ice-shelf melting on Southern Ocean water-mass transformation (WMT) using simulations from the Energy Exascale Earth System Model (E3SM) both with and without the explicit representation of melt fluxes from beneath Antarctic ice shelves. We find that ice-shelf melting enhances transformation of Upper Circumpolar Deep Water, converting it to lower density values. While the overall differences in Southern Ocean WMT between the two simulations are moderate, freshwater fluxes produced by ice-shelf melting have a further, indirect impact on the Southern Ocean overturning circulation through their interaction with sea ice formation and melting, which also cause considerable upwelling. We further find that surface freshening and cooling by ice-shelf melting cause increased Antarctic sea ice production and stronger density stratification near the Antarctic coast. In addition, ice-shelf melting causes decreasing air temperature, which may be directly related to sea ice expansion. The increased stratification reduces vertical heat transport from the deeper ocean. Although the addition of ice-shelf melting processes leads to no significant changes in Southern Ocean WMT, the simulations and analysis conducted here point to a relationship between increased Antarctic ice-shelf melting and the increased role of sea ice in Southern Ocean overturning.

Sign in / Sign up

Export Citation Format

Share Document