The warmer the ocean surface, the shallower the mixed layer. <scp>H</scp>ow much of this is true?

Somavilla, R.; González‐Pola, C.; Fernández‐Díaz, J. M.

doi:10.1002/2017jc013125

Cited by 87 publications

(90 citation statements)

References 65 publications

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“…There is a transition from a broad range of T-S properties during low index years and narrower range (toward cold/less salty) during high index years probably due to the increase of water formed through deep convection in the Labrador Sea. As reported previously by Somavilla et al (2017) salinity changes can compensate for the expected surface density decrease due to surface warming.…”

Section: 1029/2018jc014822supporting

confidence: 78%

North Atlantic Sub‐Polar Gyre Climate Index: A New Approach

Biri

Klein

2019

JGR Oceans

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As decadal predictions become operational, the need to use, understand, and extract information from them becomes essential. A climate index is a simple diagnostic quantity that can be used to characterize integral aspects of a geophysical system such as circulation patterns, and thus can be used to evaluate decadal forecasts. One of the most studied and well documented regions of the World Ocean is the North Atlantic. The North Atlantic subpolar gyre is an important region for the modulation of European climate and where skillful predictions of up to a decade can be obtained. Ocean re‐analysis (ORA‐S4) data from 1959 to 2017 are used to introduce a new methodology to compute a climate index of the North Atlantic subpolar gyre that captures both the variability in its strength and shape, the latter was to our knowledge never investigated previously as part of the variability of the gyre on interannual to decadal time scales. The methodology reveals two states of the gyre (before and after 2000), the former is mainly driven by temperature and the latter by a combination of mechanisms that interact to sustain a relatively stable subpolar gyre in terms of strength.

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Section: 1029/2018jc014822supporting

confidence: 78%

North Atlantic Sub‐Polar Gyre Climate Index: A New Approach

Biri

Klein

2019

JGR Oceans

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“…The w EK Ekman is related to the wind stress curl through the expression:

w_{EK} = curl ((), \frac{τ}{ρ f}) w_{EK} = - \frac{1}{ρ} \cdot ([], \frac{δ τ_{y}}{δ x \cdot f} - \cdot \frac{δ τ_{x}}{δ y \cdot f})

where ρ is the sea water density and f the Coriolis parameter. Following this expression and using the zonal ( τ x ) and meridional ( τ y ) components of the wind stress obtained from the NCEP/NCAR Reanalysis data set, for each grid point in the central Greenland Sea (74°–76 ° N, 0–6°W), its corresponding w Ek (m/s) and resulting vertical displacement Δ h Ek (m) time series (Δ h Ek = w EK Δ t ; see Figure 8 in Somavilla et al, , for additional information) have been calculated.…”

Section: Methodsmentioning

confidence: 99%

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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“…We performed lake model simulations with different scenarios of seasonal extinction, which in these lakes is primarily determined by phytoplankton chlorophyll . Here the thermodynamic model was modified to account for seasonally variable extinction, following a typical bimodal pattern according to the Plankton Ecology Group (PEG) model (Sommer et al, 1986(Sommer et al, , 2012, as described in detail in Shatwell et al (2016). A base seasonal extinction pattern was derived from long-term observations of extinction and/or Secchi depth in each study lake, preserving important seasonal characteristics including long-term annual mean extinction (see Table 1), minimum extinction, and timing and magnitude of the spring and summer blooms (Fig.…”

Section: Extinction Scenariosmentioning

confidence: 99%

Future projections of temperature and mixing regime of European temperate lakes

Shatwell

Thiery

Kirillin

2019

Hydrol. Earth Syst. Sci.

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The physical response of lakes to climate warming is regionally variable and highly dependent on individual lake characteristics, making generalizations about their development difficult. To qualify the role of individual lake characteristics in their response to regionally homogeneous warming, we simulated temperature, ice cover, and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model. We forced the model with an ensemble of 12 climate projections (RCP4.5) up to 2100. The lakes were projected to warm at 0.10-0.11 • C decade −1 , which is 75 %-90 % of the projected air temperature trend. In simulations, surface temperatures increased strongly in winter and spring, but little or not at all in summer and autumn. Mean bottom temperatures were projected to increase in all lakes, with steeper trends in winter and in shallower lakes. Modelled ice thaw and summer stratification advanced by 1.5-2.2 and 1.4-1.8 days decade −1 respectively, whereas autumn turnover and winter freeze timing was less sensitive. The projected summer mixed-layer depth was unaffected by warming but sensitive to changes in water transparency. By midcentury, the frequency of ice and stratification-free winters was projected to increase by about 20 %, making ice cover rare and shifting the two deeper dimictic lakes to a predominantly monomictic regime. The polymictic lake was unlikely to become dimictic by the end of the century. A sensi-tivity analysis predicted that decreasing transparency would dampen the effect of warming on mean temperature but amplify its effect on stratification. However, this interaction was only predicted to occur in clear lakes, and not in the study lakes at their historical transparency. Not only lake morphology, but also mixing regime determines how heat is stored and ultimately how lakes respond to climate warming. Seasonal differences in climate warming rates are thus important and require more attention. Recent studies highlighted that lakes respond quite individually to climate change. Although surface water temperature (T s ) is perhaps the most predictable indicator of warming , trends in T s remain highly variable at a global scale (O'Reilly et al., 2015). Deep water temperatures respond less predictably to warming and have been Published by Copernicus Publications on behalf of the European Geosciences Union.

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The warmer the ocean surface, the shallower the mixed layer. How much of this is true?

Cited by 87 publications

References 65 publications

North Atlantic Sub‐Polar Gyre Climate Index: A New Approach

North Atlantic Sub‐Polar Gyre Climate Index: A New Approach

Draining and Upwelling of Greenland Sea Deep Waters

Future projections of temperature and mixing regime of European temperate lakes

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