Water Mass Transformation and Formation in the Labrador Sea

Myers, Paul G.; Donnelly, Chris

doi:10.1175/2007jcli1722.1

Cited by 27 publications

(23 citation statements)

References 48 publications

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“…While the temperature and salinity are dominated by a multi-decadal variability, the time series of dissolved oxygen and planetary potential vorticity show near-decadal occurrences of convective ventilation events in the Labrador Sea. This agrees with the analysis of Myers and Donnelly (2008) who also found a near-decadal occurrence of strong formation events of LSW, derived from the NCEP/NCAR surface fluxes. Talley and McCartney (1982) already noted in 1982 that potential vorticity is a powerful tracer for the study of LSW spreading.…”

Section: Discussionsupporting

confidence: 92%

“…In the following winter the surface water is cooled again, and convectively mixes into the existing LSW layer. Myers and Donnelly (2008) have estimated formation rates for different density classes LSW from surface buoyancy fluxes and sea surface hydrography over the years . They found a tremendous inter-annual variability of the formation rate.…”

Section: Introductionmentioning

confidence: 99%

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Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Aken

Jong

Yashayaev

2011

Deep Sea Research Part I: Oceanographic Research Papers

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a b s t r a c tTime series of profiles of potential temperature, salinity, dissolved oxygen, and planetary potential vorticity at intermediate depths in the Labrador Sea, the Irminger Sea, and the Iceland Basin have been constructed by combining the hydrographic sections crossing the sub-arctic gyre of the North Atlantic Ocean from the coast of Labrador to Europe, occupied nearly annually since 1990, and historic hydrographic data from the preceding years since 1950. The temperature data of the last 60 years mainly reflect a multi-decadal variability, with a characteristic time scale of about 50 years. With the use of a highly simplified heat budget model it was shown that this long-term temperature variability in the Labrador Sea mainly reflects the long-term variation of the net heat flux to the atmosphere. However, the analysis of the data on dissolved oxygen and planetary potential vorticity show that convective ventilation events, during which successive classes of Labrador Sea Water (LSW) are formed, occurring on decadal or shorter time scales. These convective ventilation events have performed the role of vertical mixing in the heat budget model, homogenising the properties of the intermediate layers (e.g. temperature) for significant periods of time. Both the long-term and the near-decadal temperature signals at a pressure of 1500 dbar are connected with successive deep LSW classes, emphasising the leading role of Labrador Sea convection in running the variability of the intermediate depth layers of the North Atlantic. These signals are advected to the neighbouring Irminger Sea and Iceland Basin. Advection time scales, estimated from the 60 year time series, are slightly shorter or of the same order as most earlier estimates, which were mainly based on the feature tracking of the spreading of the LSW 94 class formed in the period 1989

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Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Aken

Jong

Yashayaev

2011

Deep Sea Research Part I: Oceanographic Research Papers

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“…The surface buoyancy flux consists of a surface heat flux and a surface freshwater flux component. Although estimates of the freshwater flux contribution vary because of large uncertainties in the precipitation data (Sathiyamoorthy and Moore 2002;Straneo 2006a), Myers and Donnelly (2008) clearly show this term to be an order of magnitude smaller than the heat flux contribution. Moreover, the freshwater flux contribution is such that it adds buoyancy to the ocean surface and thereby inhibits convective mixing (Sathiyamoorthy and Moore 2002;Straneo 2006a;Myers and Donnelly 2008).…”

Section: Air-sea Fluxesmentioning

confidence: 97%

Mechanisms behind the Temporary Shutdown of Deep Convection in the Labrador Sea: Lessons from the Great Salinity Anomaly Years 1968–71

2012

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From 1969 to 1971 convection in the Labrador Sea shut down, thus interrupting the formation of the intermediate/dense water masses. The shutdown has been attributed to the surface freshening induced by the Great Salinity Anomaly (GSA), a freshwater anomaly in the subpolar North Atlantic. The abrupt resumption of convection in 1972, in contrast, is attributed to the extreme atmospheric forcing of that winter. Here oceanic and atmospheric data collected in the Labrador Sea at Ocean Weather Station Bravo and a one-dimensional mixed layer model are used to examine the causes of the shutdown and resumption of convection in detail. These results highlight the tight coupling of the ocean and atmosphere in convection regions and the need to resolve both components to correctly represent convective processes in the ocean. They are also relevant to present-day conditions given the increased ice melt in the Arctic Ocean and from the Greenland Ice Sheet. The analysis herein shows that the shutdown was initiated by the GSA-induced freshening as well as the mild 1968/69 winter. After the shutdown had begun, however, the continuing lateral freshwater flux as well as two positive feedbacks [both associated with the sea surface temperature (SST) decrease due to lack of convective mixing with warmer subsurface water] further inhibited convection. First, the SST decrease reduced the heat flux to the atmosphere by reducing the air-sea temperature gradient. Second, it further reduced the surface buoyancy loss by reducing the thermal expansion coefficient of the surface water. In 1972 convection resumed because of both the extreme atmospheric forcing and advection of saltier waters into the convection region.

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“…The density of this water mass varies from year to year depending on oceanic advection, stratification, air-sea fluxes, and preconditioning (Myers and Donnelly 2008). The density of this water mass varies from year to year depending on oceanic advection, stratification, air-sea fluxes, and preconditioning (Myers and Donnelly 2008).…”

Section: Introductionmentioning

confidence: 99%

The Influence of High-Frequency Atmospheric Forcing on the Circulation and Deep Convection of the Labrador Sea

Holdsworth

Myers

2015

Journal of Climate

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The influence of high-frequency atmospheric forcing on the circulation of the North Atlantic Ocean with emphasis on the deep convection of the Labrador Sea was investigated by comparing simulations of a coupled ocean-ice model with hourly atmospheric data to simulations in which the high-frequency phenomena were filtered from the air temperature and wind fields. In the absence of high-frequency atmospheric forcing, the strength of the Atlantic meridional overturning circulation and subpolar gyres was found to decrease by 25%. In the Labrador Sea, the eddy kinetic energy decreased by 75% and the average maximum mixed layer depth decreased by between 20% and 110% depending on the climatology. In particular, high-frequency forcing was found to have a greater impact on mixed layer deepening in moderate to warm years whereas in relatively cold years the temperatures alone were enough to facilitate deep convection. Additional simulations in which either the wind or temperature was filtered revealed that the wind, through its impact on the bulk formulas for latent and sensible heat, had a greater impact on deep convection than the temperature.

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Water Mass Transformation and Formation in the Labrador Sea

Cited by 27 publications

References 48 publications

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Decadal and multi-decadal variability of Labrador Sea Water in the north-western North Atlantic Ocean derived from tracer distributions: Heat budget, ventilation, and advection

Mechanisms behind the Temporary Shutdown of Deep Convection in the Labrador Sea: Lessons from the Great Salinity Anomaly Years 1968–71

The Influence of High-Frequency Atmospheric Forcing on the Circulation and Deep Convection of the Labrador Sea

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