James Harle

Impacts of climate change on marine ecosystem production in societies dependent on fisheries

iesonmarinefisheries 3 .Predictedchanges in fish production indicate increased productivity at high latitudes and decreased productivity at low/mid latitudes, with considerable regional variations. With few exceptions, increases and decreases in fish production potential by 2050 are estimated to be<10% (meanC3.4%) from present yields. Among the nations showing a high dependency on fisheries 3 ,

Modelling the global coastal ocean

Shelf and coastal seas are regions of exceptionally high biological productivity, high rates of biogeochemical cycling and immense socio-economic importance. They are, however, poorly represented by the present generation of Earth system models, both in terms of resolution and process representation. Hence, these models cannot be used to elucidate the role of the coastal ocean in global biogeochemical cycles and the effects global change (both direct anthropogenic and climatic) are having on them. Here, we present a system for simulating all the coastal regions around the world (the Global Coastal Ocean Modelling System) in a systematic and practical fashion. It is based on automatically generating multiple nested model domains, using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System coupled to the European Regional Seas Ecosystem Model. Preliminary results from the system are presented. These demonstrate the viability of the concept, and we discuss the prospects for using the system to explore key areas of global change in shelf seas, such as their role in the carbon cycle and climate change effects on fisheries.

The effects of tides on the water mass mixing and sea ice in the Arctic Ocean

In this study, we use a novel pan-Arctic sea ice-ocean coupled model to examine the effects of tides on sea ice and the mixing of water masses. Two 30 year simulations were performed: one with explicitly resolved tides and the other without any tidal dynamics. We find that the tides are responsible for a ∼15% reduction in the volume of sea ice during the last decade and a redistribution of salinity, with surface salinity in the case with tides being on average ∼1.0–1.8 practical salinity units (PSU) higher than without tides. The ice volume trend in the two simulations also differs: −2.09 × 103 km3/decade without tides and −2.49 × 103 km3/decade with tides, the latter being closer to the trend of −2.58 × 103 km3/decade in the PIOMAS model, which assimilates SST and ice concentration. The three following mechanisms of tidal interaction appear to be significant: (a) strong shear stresses generated by the baroclinic clockwise rotating component of tidal currents in the interior waters; (b) thicker subsurface ice-ocean and bottom boundary layers; and (c) intensification of quasi-steady vertical motions of isopycnals (by ∼50%) through enhanced bottom Ekman pumping and stretching of relative vorticity over rough bottom topography. The combination of these effects leads to entrainment of warm Atlantic Waters into the colder and fresher surface waters, supporting the melting of the overlying ice.

Kilometric Scale Modeling of the North West European Shelf Seas: Exploring the Spatial and Temporal Variability of Internal Tides

The North West European shelf-break acts as a barrier to the transport and exchange between the open ocean and the shelf seas. The strong spatial variability of these exchange processes is hard to fully explore using observations, and simulations generally are too coarse to simulate the fine-scale processes over the whole region. In this context, under the FASTNEt programme, a new NEMO configuration of the North West European Shelf and Atlantic margin at 1/60° (∼1.8km) has been developed, with the objective to better understand and quantify the seasonal and interannual variability of shelf break processes. The capability of this configuration to reproduce the seasonal cycle in SST, the barotropic tide, and fine-resolution temperature profiles is assessed against a basin-scale (1/12°, ∼9km) configuration and a standard regional configuration (7 km resolution). The seasonal cycle is well reproduced in all configurations though the fine-resolution allows the simulation of smaller scale processes. Time-series of temperature at various locations on the shelf show the presence of internal waves with a strong spatio-temporal variability. Spectral analysis of the internal waves reveals peaks at the diurnal, semi-diurnal, inertial and quarter-diurnal bands, which are only realistically reproduced in the new configuration. Tidally induced pycnocline variability is diagnosed in the model and shown to vary with the spring neap cycle with mean displacement amplitudes in excess of 2m for 30% of the stratified domain. With sufficiently fine-resolution, internal tides are shown to be generated at numerous bathymetric features resulting in a complex pycnocline displacement superposition pattern.

Distributional Patterns of Polychaetes Across the West Antarctic Based on DNA Barcoding and Particle Tracking Analyses

Recent genetic investigations have uncovered a high proportion of cryptic species within Antarctic polychaetes. It is likely that these evolved in isolation during periods of glaciation, and it is possible that cryptic populations would have remained geographically restricted from one another occupying different regions of Antarctica. By analysing the distributions of nine morphospecies, (six of which contained potential cryptic species), we find evidence for widespread distributions within the Western Antarctic region. Around 60% of the cryptic species exhibited sympatric distributions, and at least one cryptic clade was found to be widespread. Additional DNA barcodes from GenBank and morphological records extended the observed range of three species studied here, and indicate potential circum-Antarctic traits. Particle tracking analyses was used to model theoretical dispersal ranges of pelagic larvae. Data from these models suggest that the observed species distributions inferred from genetic similarity could have been established and maintained through the regional oceanographic currents. West Antarctic continental shelf populations may be connected via the Antarctic Circumpolar Current or its coastal Counter Current, dependent on particle release location. Improved understanding of the distribution of Antarctic fauna is essential for predicting the impacts of environmental change and determining management strategies for the region.