Changing Atlantic influences on northwest European shelf seas

Marine ecosystems in the shelf seas around the UK have undergone major changes over the last 30 years, most notably in the North Sea, where warm water species have largely replaced cold water species. These changes appear to be physically driven, by a combination of local warming and shifting ocean currents. Following the UK shelf edge, between the shallow European shelf seas and the deep Atlantic Ocean, the Slope Current provides an Atlantic inflow to the North Sea. In time series extracted from Continuous Plankton Recorder (CPR) data, counts of two key zooplankton species in the North Sea vary with Atlantic inflow events, superimposed on the multi-decadal transition from cold to warm species as the inflow brings waters from a more southerly source (Reid et al., 2003). The changing provenance of Slope Current water, and hence Atlantic inflow, is further related to changes across the subpolar gyre of the North Atlantic (Marsh et al., 2017). The student will combine latest observations and models to investigate how past and future environmental conditions in UK shelf seas are driven by basin-scale Atlantic change, testing the hypothesis that selected marine ecosystems are more susceptible to remote physical forcing than to local climate change.

The initial objective is to update time series of temperature, salinity and plankton species, for selected locations and regions, to establish the variability in ocean and shelf sea conditions on timescales from seasonal to decadal. The student will examine observations that include various hydrographic datasets and CPR data, spanning the historical era from around 1950 to the present. Complementing these observations are ocean/shelf physics-ecosystem model hindcasts that provide further information on regional ocean currents and biogeochemistry. These models are also used in predictive mode, under transient anthropogenic forcing through the 21st century. The models are configured at the very high horizontal resolution necessary to accurately simulate interplay between the Atlantic and adjacent shelf seas. To explore mechanisms driving observed variability and trends in shelf seas, the student will analyse these hindcasts to distinguish between the influences on shelf sea ecosystems of local air-sea interaction and remotely-forced ocean currents, in both the past and the future. Further insights will be gained through: particle tracking, to trace Atlantic inflow water back upstream to the range of sources; idealized model experiments, to test the influence of variability in local and remote influences, holding each influence constant while the other is allowed to vary.

The SPITFIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered and hosted at the University of Southampton. Specific training will include:

· Analysis of historical hydrographic and CPR datasets

· Analysis of three model simulations (NEMO-ERSEM at ~10-km resolution; AMM7-ERSEM at 7-km resolution; AMM60-ERSEM at ~1 km resolution), with experiments spanning 1960 to 2060 or 2100

· Use of particle trajectory software to investigate the provenance of Atlantic Water

· Experiments with the NEMO shelf model

The student will also become familiar with: key physical processes that determine environmental conditions in shelf seas, including advection, mixing and planetary waves; drivers of flows and exchanges, including winds, buoyancy exchange, unsteadiness and frictional effects; biological responses to variable environmental conditions, in particular temperatures and currents.