Modelling the Overflows Across the Greenland–Scotland Ridge

Jungclaus, Johann; Macrander, Annecke; Käse, Rolf H.

doi:10.1007/978-1-4020-6774-7_23

Cited by 17 publications

(32 citation statements)

References 69 publications

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“…In IPSLCM4, anomalously shallow isopycnals in the central Nordic seas lead to an increase in the (baroclinic) pressure north of the ISR, causing a strengthened IcelandScotland overflow. The importance of the baroclinic pressure has been suggested by, e.g., Jungclaus et al (2008).…”

Section: Iceland-scotland Overflow Strength and Amo Index In The Simumentioning

confidence: 98%

“…According to the literature (e.g. Hansen and Østerhus, 2007;Jungclaus et al, 2008;Olsen et al, 2008;Sandø et al, 2012), the Iceland-Scotland overflow strength is affected by the pressure gradient across the ISR in the core depth of the overflow. Mechanism (ii) thus implies a similar variation of Iceland-Scotland overflow strength and AMO index due to the influence of the Nordic seas surface state and density structure on the pressure gradient across the ISR.…”

Section: Iceland-scotland Overflow Strength and Amo Index In The Simumentioning

confidence: 99%

“…Hansen et al, 2001) and modelling (e.g. Jungclaus et al, 2008) studies suggest that the overflow transport through the Faroe-Shetland channel (FSC), which carries the majority of the overflow between Iceland and Scotland, is controlled by internal hydraulics and affected by the baroclinic pressure gradient across the ISR in the core depth of the overflow. Further observational (e.g.…”

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confidence: 99%

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Using simulations of the last millennium to understand climate variability seen in palaeo-observations: similar variation of Iceland–Scotland overflow strength and Atlantic Multidecadal Oscillation

et al. 2015

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Abstract.A recent palaeo-reconstruction of the strength of the Iceland-Scotland overflow during the last 600 years suggests that its low-frequency variability exhibits strong similarity with palaeo-reconstructions of the Atlantic Multidecadal Oscillation (AMO). The underlying mechanism of the similar variation remains unclear, however, based on palaeo-reconstructions alone. In this study we use simulations of the last millennium driven by external forcing reconstructions with three coupled climate models in order to investigate possible mechanisms underlying the similar variation of Iceland-Scotland overflow strength and AMO index. Similar variation of the two time series is also largely found in the model simulations. Our analysis indicates that the basin-wide AMO index in the externally forced simulations is dominated by the low-latitude sea surface temperature (SST) variability and is not predominantly driven by variations in the strength of the Atlantic meridional overturning circulation (MOC). This result suggests that a large-scale link through the strength of the MOC is not sufficient to explain the (simulated) similar variation of Iceland-Scotland overflow strength and AMO index. Rather, a more local link through the influence of the Nordic seas surface state and density structure, which are positively correlated with the AMO index, on the pressure gradient across the IcelandScotland ridge is responsible for the (simulated) similar variation. In the model simulation showing a weaker correlation between the Iceland-Scotland overflow strength and the AMO index, the wind stress in the Nordic seas also influences the overflow strength. Our study demonstrates that palaeo-climate simulations provide a useful tool to understand mechanisms and large-scale connections associated with the relatively sparse palaeo-observations.

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Section: Iceland-scotland Overflow Strength and Amo Index In The Simumentioning

confidence: 98%

Section: Iceland-scotland Overflow Strength and Amo Index In The Simumentioning

confidence: 99%

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confidence: 99%

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Using simulations of the last millennium to understand climate variability seen in palaeo-observations: similar variation of Iceland–Scotland overflow strength and Atlantic Multidecadal Oscillation

et al. 2015

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“…It is noteworthy for our study that the GR1.5L40 grid possesses one grid pole over Antarctica and one grid pole over Greenland, which leads to considerably higher resolution in the regions of interest for this study, i.e. the northern North Atlantic (Jungclaus et al, 2008). In Fram Strait, for example, the grid size in cross-channel direction is about 30-40 km.…”

Section: The Model System and The Experimental Design Of The Last-milmentioning

confidence: 99%

Enhanced 20th-century heat transfer to the Arctic simulated in the context of climate variations over the last millennium

2014

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Abstract. Oceanic heat transport variations, carried by the northward-flowing Atlantic Water, strongly influence Arctic sea-ice distribution, ocean-atmosphere exchanges, and pan-Arctic temperatures. Palaeoceanographic reconstructions from marine sediments near Fram Strait have documented a dramatic increase in Atlantic Water temperatures over the 20th century, unprecedented in the last millennium. Here we present results from Earth system model simulations that reproduce and explain the reconstructed exceptional Atlantic Water warming in Fram Strait in the 20th century in the context of natural variability during the last millennium. The associated increase in ocean heat transfer to the Arctic can be traced back to changes in the ocean circulation in the subpolar North Atlantic. An interplay between a weakening overturning circulation and a strengthening subpolar gyre as a consequence of 20th-century global warming is identified as the driving mechanism for the pronounced warming along the Atlantic Water path toward the Arctic. Simulations covering the late Holocene provide a reference frame that allows us to conclude that the changes during the last century are unprecedented in the last 1150 years and that they cannot be explained by internal variability or natural forcing alone.

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“…In the current set-up, the ocean model's North Pole is shifted to Greenland and the South Pole to the center of the Antarctic continent. This approach not only removes the numerical singularity associated with the convergence of meridians at the geographical North Pole, but also produces higher resolution in the deep water formation regions in both hemispheres and gives a realistic representation of overflow water (Jungclaus et al 2008). Interactive runoff and glacier calving schemes are used.…”

Section: Model Description and Experimentsmentioning

confidence: 99%

Interdecadal variability of the meridional overturning circulation as an ocean internal mode

Zhu

Jungclaus

2008

Clim Dyn

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The meridional overturning circulation (MOC) in the coupled ECHAM5/MPIOM exhibits variability at periods of near 30 years and near 60 years. The 30-year variability, referred to as interdecadal variability (IDV), exist in an ocean model driven by climatological atmospheric forcing, suggesting that it is maintained by ocean dynamics; the 60-year variability, the multidecadal variability (MDV), is only observed in the fully coupled model and therefore is interpreted as an atmosphere-ocean coupled mode. The coexistence of the 30-year IDV and the 60-year MDV provides a possible explanation for the widespread time scales observed in climate variables. Further analyses of the climatologically forced ocean model shows that, the IDV is related to the interplay between the horizontal temperature-dominated density gradients and the ocean circulation: temperature anomalies move along the cyclonic subpolar gyre leading to fluctuations in horizontal density gradients and the subsequent weakening and strengthening of the MOC. This result is consistent with that from less complex models, indicating the robustness of the IDV. We further show that, along the North Atlantic Current path, the sea surface temperature anomalies are determined by the slow LSW advection at the intermediate depth.

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Modelling the Overflows Across the Greenland–Scotland Ridge

Cited by 17 publications

References 69 publications

Using simulations of the last millennium to understand climate variability seen in palaeo-observations: similar variation of Iceland–Scotland overflow strength and Atlantic Multidecadal Oscillation

Using simulations of the last millennium to understand climate variability seen in palaeo-observations: similar variation of Iceland–Scotland overflow strength and Atlantic Multidecadal Oscillation

Enhanced 20th-century heat transfer to the Arctic simulated in the context of climate variations over the last millennium

Interdecadal variability of the meridional overturning circulation as an ocean internal mode

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