Greenland Melt and the Atlantic Meridional Overturning Circulation

Frajke-Williams, Eleanor; Bamber, Jonathan; Våge, Kjetil

doi:10.5670/oceanog.2016.96

Cited by 14 publications

(15 citation statements)

References 69 publications

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“…Starting in the early 1980s, several winters without deep convection would have gradually restratified the Greenland Sea. As the amount of heat that must be removed from the buoyant waters by air‐sea fluxes increases, it becomes more difficult for deep convection to reach a particular depth (Frajka‐Williams et al, ). Conversely, once the water column has been completely homogenized from the surface to the bottom, the stratification is not recovered immediately, and convective mixing can easily progress to great depths the following winter (Frajka‐Williams et al, ; Somavilla et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…As the amount of heat that must be removed from the buoyant waters by air-sea fluxes increases, it becomes more difficult for deep convection to reach a particular depth (Frajka-Williams et al, 2016). Conversely, once the water column has been completely homogenized from the surface to the bottom, the stratification is not recovered immediately, and convective mixing can easily progress to great depths the following winter (Frajka-Williams et al, 2016;Somavilla et al, 2011). This would have facilitated more frequent occurrences of deep convection before the 1980s.…”

Section: 1029/2018jc014249mentioning

confidence: 99%

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Draining and Upwelling of Greenland Sea Deep Waters

Somavilla

2019

JGR Oceans

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Since the beginning of the 1980s, deep convection has ceased in the Greenland Sea. The effects of this halt on the intense warming and salinification of Greenland Sea deep waters and on the “dome collapse” (sinking of the dome) have been intensively studied. However, their causes and the potential outflow of Greenland Sea deep and bottom waters toward southern adjacent basins have remained less investigated and are the focus of this work. Combining oceanic and atmospheric in situ data, together with satellite and reanalysis data, it is found that there is not a unique factor responsible for the halt of deep convection in the Greenland Sea. Changes in the Ekman pumping seem to only explain one tenth of the observed deepening of isopycnals of 1,300 m in the central Greenland Sea (dome collapse). Since the early 1980s, in addition, a decrease in the mean net heat loss from the ocean to the atmosphere and in the intensity and number of intense heat loss events would have contributed to the decrease in both the intensity of convective mixing and the generation of dense deep waters. The generation of waters not sufficiently dense to contribute to the reservoir of water below the Greenland Sea dome would have led to its emptying and sinking. More importantly, it is found that in situ evidence of a sustained bottom‐water upwelling driven by a secondary circulation cell whose major role in ventilating and draining the Greenland Sea deep and bottom waters has been largely underestimated.

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Section: Discussionmentioning

confidence: 99%

Section: 1029/2018jc014249mentioning

confidence: 99%

Draining and Upwelling of Greenland Sea Deep Waters

Somavilla

2019

JGR Oceans

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“…The AMV has been related to changes in Atlantic hurricane activity and tropospheric vertical shear, anomalous North American and European river flow and rainfall, and shifts in the Intertropical Convergence Zone and rainfall over northeastern Brazil and the African Sahel [ Sutton and Hodson , ; Knight et al ., ; Zhang and Delworth , ]. Decadal SPNA SST and OHC variations also show correlation with cryospheric changes, including Greenland ice sheet discharge, rates of Northern Hemisphere sea‐ice loss, and mass balance of glaciers in the Swiss Alps [ Huss et al ., ; Straneo and Heimbach , ; Zampieri et al ., ; Yeager et al ., ; Frajka‐Williams et al ., ]. Understanding SPNA SST and OHC changes and their predictability on decadal and longer time scales has thus been a major goal in climate research [ Keenlyside et al ., ; Dunstone et al .…”

Section: Introductionmentioning

confidence: 99%

Mechanisms underlying recent decadal changes in subpolar North Atlantic Ocean heat content

et al. 2017

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The subpolar North Atlantic (SPNA) is subject to strong decadal variability, with implications for surface climate and its predictability. In 2004–2005, SPNA decadal upper ocean and sea‐surface temperature trends reversed from warming during 1994–2004 to cooling over 2005–2015. This recent decadal trend reversal in SPNA ocean heat content (OHC) is studied using a physically consistent, observationally constrained global ocean state estimate covering 1992–2015. The estimate's physical consistency facilitates quantitative causal attribution of ocean variations. Closed heat budget diagnostics reveal that the SPNA OHC trend reversal is the result of heat advection by midlatitude ocean circulation. Kinematic decompositions reveal that changes in the deep and intermediate vertical overturning circulation cannot account for the trend reversal, but rather ocean heat transports by horizontal gyre circulations render the primary contributions. The shift in horizontal gyre advection reflects anomalous circulation acting on the mean temperature gradients. Maximum covariance analysis (MCA) reveals strong covariation between the anomalous horizontal gyre circulation and variations in the local wind stress curl, suggestive of a Sverdrup response. Results have implications for decadal predictability.

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“…In particular, salinity responds to terrestrial runoff (river discharge), sea ice melt and growth, surface freshwater forcing (precipitation and evaporation), and exchanges with subarctic oceans via oceanic transports through Arctic gateways [24]. The Arctic freshwater changes that are associated with salinity alter the horizontal and vertical density structure of seawater, thereby influencing regional oceanic processes with global consequences [25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

The Potential and Challenges of Using Soil Moisture Active Passive (SMAP) Sea Surface Salinity to Monitor Arctic Ocean Freshwater Changes

et al. 2018

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Sea surface salinity (SSS) links various components of the Arctic freshwater system. SSS responds to freshwater inputs from river discharge, sea ice change, precipitation and evaporation, and oceanic transport through the open straits of the Pacific and Atlantic oceans. However, in situ SSS data in the Arctic Ocean are very sparse and insufficient to depict the large-scale variability to address the critical question of how climate variability and change affect the Arctic Ocean freshwater. The L-band microwave radiometer on board the NASA Soil Moisture Active Passive (SMAP) mission has been providing SSS measurements since April 2015, at approximately 60 km resolution with Arctic Ocean coverage in 1-2 days. With improved land/ice correction, the SMAP SSS algorithm that was developed at the Jet Propulsion Laboratory (JPL) is able to retrieve SSS in ice-free regions 35 km of the coast. SMAP observes a large-scale contrast in salinity between the Atlantic and Pacific sides of the Arctic Ocean, while retrievals within the Arctic Circle vary over time, depending on the sea ice coverage and river runoff. We assess the accuracy of SMAP SSS through comparative analysis with in situ salinity data collected by Argo floats, ships, gliders, and in field campaigns. Results derived from nearly 20,000 pairs of SMAP and in situ data North of 50 • N collocated within a 12.5-km radius and daily time window indicate a Root Mean Square Difference (RMSD) less thañ 1 psu with a correlation coefficient of 0.82 and a near unity regression slope over the entire range of salinity. In contrast, the Hybrid Coordinate Ocean Model (HYCOM) has a smaller RMSD with Argo. However, there are clear systematic biases in the HYCOM for salinity in the range of 25-30 psu, leading to a regression slope of about 0.5. In the region North of 65 • N, the number of collocated samples drops more than 70%, resulting in an RMSD of about 1.2 psu. SMAP SSS in the Kara Sea shows a consistent response to discharge anomalies from the Ob' and Yenisei rivers between 2015 and 2016, providing an assessment of runoff impact in a region where no in situ salinity data are available for validation. The Kara Sea SSS anomaly observed by SMAP is missing in the HYCOM SSS, which assimilates climatological runoffs without interannual changes. We explored the feasibility of using SMAP SSS to monitor the sea surface salinity variability at the major Arctic Ocean gateways. Results show that although the SMAP SSS is limited to about 1 psu accuracy, many large salinity changes are observable. This may lead to the potential application of satellite SSS in the Arctic monitoring system as a proxy of the upper ocean layer freshwater exchanges with subarctic oceans.

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Greenland Melt and the Atlantic Meridional Overturning Circulation

Cited by 14 publications

References 69 publications

Draining and Upwelling of Greenland Sea Deep Waters

Draining and Upwelling of Greenland Sea Deep Waters

Mechanisms underlying recent decadal changes in subpolar North Atlantic Ocean heat content

The Potential and Challenges of Using Soil Moisture Active Passive (SMAP) Sea Surface Salinity to Monitor Arctic Ocean Freshwater Changes

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