Thermohaline forcing and interannual variability of northwestern inflows into the northern North Sea

Sheehan, Peter M.; Berx, Barbara; Gallego, Alejandro; Hall, Rob; Heywood, Karen J.; Hughes, Sarah L.

doi:10.1016/j.csr.2017.01.016

Cited by 18 publications

(30 citation statements)

References 38 publications

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“…Discuss., https://doi.org/10.5194/os-2018-1 Manuscript under review for journal Ocean Sci. correlate with the NAO (Winther and Johannessen 2006;Marsh et al 2017;Sheehan et al 2017). This positive correlation means more (relatively) high salinity is advected onto the NWS under NAO positive condition, which would tend to increase the NWS salinity.…”

Section: Question 4: What Are the Prospects For Improving Nws Seasonamentioning

confidence: 77%

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What are the prospects for seasonal prediction of the marine environment of the Northwest European shelf?

Tinker¹,

Krijnen²,

Wood³

et al. 2018

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Abstract.Sustainable management and utilisation of the Northwest European Shelf Seas (NWS) could benefit from reliable forecasts 10 of the marine environment on monthly-to-seasonal timescales. Recent advances in global seasonal forecast systems, and regional marine reanalyses for the NWS, allow us to investigate the potential for seasonal forecasts of the state of the NWS.We identify three possible approaches to address this issue: A) basing NWS seasonal forecasts directly on output from the Met Office's GloSea5 global seasonal forecast system; B) developing empirical downscaling relationships between largescale climate drivers predicted by GloSea5, and the state of the NWS; and C) dynamically downscaling GloSea5 using a 15 regional model. We reject A) after showing that the GloSea5 system is inadequate for simulating the NWS directly. Turning to B), we explore empirical relationships between the winter North Atlantic Oscillation (NAO), and NWS variables estimated using a regional reanalysis. We find some statistically significant relationships, and present a skilful prototype seasonal forecast for English Channel sea surface temperature.We then consider the potential of C). We find large scale relationships between inter-annual variability in the boundary 20 conditions and inter-annual variability modelled on the shelf, suggesting that dynamic downscaling may be possible. We also show that for some variables there are opposing mechanisms correlated to the NAO, for which dynamic downscaling may improve on the skill possible with empirical forecasts. We conclude that there is potential for the development of reliable seasonal forecasts for the NWS, and consider the research priorities for their development. Copyright Statement 25The works published in this journal are distributed under the Creative Commons Attribution 4.0 License. This licence does not affect the Crown copyright work, which is re-usable under the Open Government Licence (OGL). The Creative Commons Attribution 4.0 License and the OGL are interoperable and do not conflict with, reduce or limit each other.

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Section: Question 4: What Are the Prospects For Improving Nws Seasonamentioning

confidence: 77%

“…Specific research priorities are: summer, but this is an active research area (e.g. Hall et al 2017). It may also be possible to demonstrate some degree of memory in the shelf seas themselves, which would add to forecast lead times.…”

Section: Conclusion and Prospects 25mentioning

confidence: 99%

What are the prospects for seasonal prediction of the marine environment of the Northwest European shelf?

Tinker¹,

Krijnen²,

Wood³

et al. 2018

Preprint

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“…1) is present in the north-western North Sea to the west of 1 • W (Turrell et al, 1996;Sheehan et al, 2017). The front is bottom-intensified and frequently has only a limited surface signature (Hughes, 2014;Sheehan et al, 2017).…”

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confidence: 99%

“…The high spatial resolution of glider observations permits a more accurate estimate of frontal location than is possible from shipbased observations (e.g. Schumacher et al, 1979;Hill et al, 1997;Sheehan et al, 2017). The method for calculating tidal velocities from DAC observations, outlined in Sect.…”

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confidence: 99%

“…The region, which is influenced by cool (< 9 • C), saline (> 35.4 g kg −1 ) water found to the east of the front (Sheehan et al, 2017;Hill et al, 2008), is characterised by features excluded from the heating-stirring theory: coastal and oceanic water masses flow south into the North Sea, introducing temperature and salinity gradients that are not a consequence of heating-stirring interactions (Turrell, 1992;Hill et al, 2008;Sheehan et al, 2017), and a generally southward residual current persists throughout the year (Dooley, 1974;Turrell, 1992;Winther and Johannessen, 2006). Nevertheless, it is thought that the location of the front is at least partially influenced by the local heating-stirring balance, with tidal stirring being responsible for maintaining fully mixed conditions west of the front (Svendsen et al, 1991).…”

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Shelf sea tidal currents and mixing fronts determined from ocean glider observations

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Abstract. Tides and tidal mixing fronts are of fundamental importance to understanding shelf sea dynamics and ecosystems. Ocean gliders enable the observation of fronts and tidedominated flows at high resolution. We use dive-average currents from a 2-month (12 October-2 December 2013) glider deployment along a zonal hydrographic section in the northwestern North Sea to accurately determine M 2 and S 2 tidal velocities. The results of the glider-based method agree well with tidal velocities measured by current meters and with velocities extracted from the TPXO tide model. The method enhances the utility of gliders as an ocean-observing platform, particularly in regions where tide models are known to be limited. We then use the glider-derived tidal velocities to investigate tidal controls on the location of a front repeatedly observed by the glider. The front moves offshore at a rate of 0.51 km day −1 . During the first part of the deployment (from mid-October until mid-November), results of a onedimensional model suggest that the balance between surface heat fluxes and tidal stirring is the primary control on frontal location: as heat is lost to the atmosphere, full-depth mixing is able to occur in progressively deeper water. In the latter half of the deployment (mid-November to early December), a front controlled solely by heat fluxes and tidal stirring is not predicted to exist, yet a front persists in the observations. We analyse hydrographic observations collected by the glider to attribute the persistence of the front to the boundary between different water masses, in particular to the presence of cold, saline, Atlantic-origin water in the deeper portion of the section. We combine these results to propose that the front is a hybrid front: one controlled in summer by the local balance between heat fluxes and mixing and which in winter exists as the boundary between water masses advected to the north-western North Sea from diverse source regions. The glider observations capture the period when the front makes the transition from its summertime to wintertime state. Fronts in other shelf sea regions with oceanic influence may exhibit similar behaviour, with controlling processes and locations changing over an annual cycle. These results have implications for the thermohaline circulation of shelf seas.Copyright statement. The works published in this journal are distributed under the Creative Commons Attribution 4.0 License. This license does not affect the Crown copyright work, which is re-usable under the Open Government Licence (OGL). The Creative Commons Attribution 4.0 License and the OGL are interoperable and do not conflict with, reduce or limit each other.

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Locally modified winds regulate North Sea circulation

Palmer

Inall

Berx

et al. 2021

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Thermohaline forcing and interannual variability of northwestern inflows into the northern North Sea

Cited by 18 publications

References 38 publications

What are the prospects for seasonal prediction of the marine environment of the Northwest European shelf?

What are the prospects for seasonal prediction of the marine environment of the Northwest European shelf?

Shelf sea tidal currents and mixing fronts determined from ocean glider observations

Locally modified winds regulate North Sea circulation

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