Abstract
Quantifying the variability of North Sea inflows and understanding the temporal variability of their physical properties are essential for understanding, modelling and managing the ecosystems of the North Sea. The Joint North Sea Information System (JONSIS) line hydrographic section crosses the path of the main inflows of Atlantic water into the northwestern North Sea. We use observations from an autonomous underwater glider to observe the inflows at high spatial and temporal resolutions. The glider completed 10 partial sections of the JONSIS line in October and November of 2013. Key water masses of the inflow are identified; their spatial distribution varies greatly from section to section. This is not apparent from long-running ship surveys of the JONSIS line, which are generally several months apart. In particular, the distribution of water of most recent Atlantic origin varies as summer stratification decays throughout autumn: at the start of the deployment it is present as a thin layer beneath the thermocline; at the end of the deployment, it occupies the full depth of the water column. Thermohaline flow, i.e. that which is driven by horizontal density gradients, is focused into three or four jets (approximately 10 km wide). Jets as narrow as these have not previously been observed in the region. We also observe baroclinic eddies. The thermohaline transport of the inflows is compared with the absolute transport that is derived by referencing geostrophic shear to the glider's dive-average current. Thermohaline transport (approximately 0.2 Sv) is consistently smaller than absolute transport (approximately 0.5 Sv). The week-to-week variability in hydrography and flow structure identified in this study is relevant to on-going efforts to define a background state against which the nature of anthropogenic changes can be assessed, and future modelling efforts should represent the spatial and temporal variability that we have identified.
Original language | English |
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Article number | 103288 |
Journal | Journal of Marine Systems |
Volume | 204 |
Early online date | 26 Dec 2019 |
DOIs | |
Publication status | Published - Apr 2020 |
Keywords
- North Sea
- Fair Isle Current
- East Shetland Atlantic Inflow
- water masses
- transport
- ocean gliders
- Water masses
- CIRCULATION
- Ocean gliders
- HYPOTHESES
- FAIR ISLE CURRENT
- TIDES
- Transport
- WATER
Profiles
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Rob Hall
- School of Environmental Sciences - Associate Professor
- Centre for Ocean and Atmospheric Sciences - Member
- Collaborative Centre for Sustainable Use of the Seas - Member
Person: Research Group Member, Academic, Teaching & Research
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Karen Heywood
- School of Environmental Sciences - Professor of Physical Oceanography
- Centre for Ocean and Atmospheric Sciences - Member
- ClimateUEA - Member
Person: Research Group Member, Academic, Teaching & Research