Impacts of ocean wave‐dependent momentum flux on global ocean climate

Accurate knowledge of air‐sea fluxes of momentum, heat, and carbon are central to fully understanding the evolution of the climate system. The role of ocean surface waves has been largely overlooked in global climate models despite the growing body of work elucidating the influence of ocean wave state on air‐sea fluxes. Here we account for the impact of ocean surface waves on global ocean climate using a global ocean model through implementation of wave‐dependent momentum fluxes. Wave‐dependent momentum fluxes improve the simulation of observed ocean heat content (OHC) through increasing the trend in OHC over the last three decades. Specifically, the larger increase in OHC is attributable to increased net heat flux in the Southern Hemisphere (SH). These results highlight the important role of accounting for wave‐dependent momentum transfer in terms of both simulating future climate and understanding changes over the recent historical period

Natural hazards in Australia : sea level and coastal extremes

The Australian coastal zone encompasses tropical, sub- and extra-tropical climates and accommodates about 80 % of Australia’s population. Sea level extremes and their physical impacts in the coastal zone arise from a complex set of atmospheric, oceanic and terrestrial processes that interact on a range of spatial and temporal scales and will be modified by a changing climate, including sea level rise. This review details significant progress over recent years in understanding the causes of past and projections of future changes in sea level and coastal extremes, yet a number of research questions, knowledge gaps and challenges remain. These include efforts to improve knowledge on past sea level extremes, integrate a wider range of processes in projections of future changes to sea level extremes, and focus efforts on understanding long-term coastline response from the combination of contributing factors

Storm surges and extreme sea levels: Review, establishment of model intercomparison and coordination of surge climate projection efforts (SurgeMIP).

Coastal flood damage is primarily the result of extreme sea levels. Climate change is expected to drive an increase in these extremes. While proper estimation of changes in storm surges is essential to estimate changes in extreme sea levels, there remains low confidence in future trends of surge contribution to extreme sea levels. Alerting local populations of imminent extreme sea levels is also critical to protecting coastal populations. Both predicting and projecting extreme sea levels require reliable numerical prediction systems. The SurgeMIP (surge model intercomparison) community has been established to tackle such challenges. Efforts to intercompare storm surge prediction systems and coordinate the community's prediction and projection efforts are introduced. An overview of past and recent advances in storm surge science such as physical processes to consider and the recent development of global forecasting systems are briefly introduced. Selected historical events and drivers behind fast increasing service and knowledge requirements for emergency response to adaptation considerations are also discussed. The community's initial plans and recent progress are introduced. These include the establishment of an intercomparison project, the identification of research and development gaps, and the introduction of efforts to coordinate projections that span multiple climate scenarios

Dataset for concurrent echosounder and ADCP measurements at a tidal energy candidate site in Australia

Interaction uncertainties between tidal energy devices and marine animals have the potential to impede the tidal energy industry as it moves closer towards commercial-scale array installations. Developing standardised environmental impact assessment (EIA) practices would allow for potential impact concerns to the marine environment to be identified and mitigated early during project development. In an effort to help formulate a standardised EIA framework that addresses knowledge gaps in fish-current interactions at tidal energy candidate sites, Scherelis et\ua0al. [1] presented a case study for investigating changes in fish aggregations in response to changing environmental conditions including tidal currents at a tidal energy candidate site in Australia prior to turbine installation. Here, we present the dataset utilised for this study titled "Investigating biophysical linkages at tidal energy candidate sites: a case study for combining environmental assessment and resource characterisation" [1]. The dataset includes tidal current information from an Acoustic Doppler Current Profiler (ADCP), volume backscattering measurements from a four-frequency biological echosounder (Acoustic Zooplankton and Fish Profiler - AZFP) as an indicator for fish biomass, and fish aggregation metrics calculated from volume backscatter in post-processing. ADCP and AZFP were installed on a bottom-mounted mooring and engaged in a concurrent sampling plan for ∼2.5 months from December 2018 to February 2019. The mooring was deployed in the Banks Strait, a tidal energy candidate site located in the northeast of Tasmania, Australia, at a location favourable for tidal turbine installations considering current speed, depth, substrate, sediment type and proximity to shore. The ADCP dataset includes current velocity and direction measurements at 1 m vertical and 1-min time intervals. The raw AZFP dataset includes volume backscattering strength collected in 4-s time intervals with a vertical resolution of 0.072 m in raw, and 0.1 m in pre-processed form. Several post-processing steps were implemented to mitigate changes in background noise due to current speed and wind stress, and to isolate acoustic fish returns from remaining scattering sources. Once isolated, volume backscatter containing fish targets underwent post-processing to determine fish aggregation metrics including density, abundance, centre of mass, dispersion,% water column occupied, evenness, and index for aggregation. Each aggregation metric was then binned by minute matched with corresponding environmental conditions for current speed, shear, temperature, diel stage, and tidal stage. Raw and processed datasets for the AZFP and ADCP are provided. Post-processed data includes the derived fish aggregation metrics along with corresponding environmental conditions. The described datasets are freely available on the Australian Ocean Data Network (AODN)

Future wave-driven coastal sediment transport along the Catalan coast (NW Mediterranean)

The final publication is available at Springer via http://dx.doi.org/ 10.1007/s10113-015-0923-xIn the context of climate change, this study evaluates the impact on the long-shore and cross-shore sediment transport (LST and CST) along the Catalan coast (NW Mediterranean Sea) derived from climate projections obtained from five combinations of regional and global circulation models (RCMs and GCMs). Special emphasis is given to how inter-model variability translates from wave projections to wave-driven coastal impacts, which is still poorly known. Results show that the uncertainty is in general larger, especially for LST, for which the discrepancies among regional models are more relevant than those associated with the forcing wave parameters. Such increase in the uncertainty can be explained by the nonlinear processes involved, and the role of the forcing wave parameters having sometimes competing effects (e.g. wave height vs. wave direction). This illustrates that the performance of each RCM–GCM can vary from forcing to impact parameters; hence, the suitability of a particular RCM–GCM to evaluate a certain impact should be assessed based on its ability to properly simulate such impact. In this regard, LST and CST rates computed using empirical formulae that integrate several wave climate parameters, as in this study, can be used as a non-computationally expensive tool to assess the suitability of a given RCM–GCM to project changes in coastal dynamics.Peer ReviewedPostprint (author's final draft

Observation of wind-waves from a moored buoy in the Southern Ocean

The Southern Ocean is an important component in the global wave climate. However, owing to a lack of observations, our understanding of waves is poor compared to other regions. The Southern Ocean Flux Station (SOFS) has been deployed to fill this gap and represents the first successful moored air-sea flux station at these southern hemisphere latitudes. In this paper, we present for the first time the results from the analysis of the wave measurements, focused on statistics and extremes of the main wave parameters. Furthermore, a spectral characterization is performed regarding the number of wave systems and predominance of swell/wind-sea. Our results indicate a high consistency in terms of wave parameters for all deployments. The maximum significant wave height obtained in the 705 days of observation was 13.41 m. The main spectra found represent unimodal swell dominated cases; however, the dimensionless energy plotted against dimensionless peak frequency for these spectra follows a well-known relation for wind-sea conditions. In addition, the Centre for Australian Weather and Climate Research wave hindcast is validated with the SOFS data

Global wave hindcast with Australian and Pacific Island Focus: From past to present

Abstract Wind‐wave hindcast data have many applications including climatology assessments for renewable energy projects, maritime engineering design, event‐based impact assessments, generating boundary conditions for further downscaling, amongst others. Here, we present a global wave hindcast with nested high‐resolution grids for the Exclusive Economic Zones of Australia and south west Pacific Island Countries, that is extended in time monthly. The model employs strategic methods to incorporate the effects of subgrid sized features such as small islands and islets. Various bulk wave parameters are available hourly from January 1979 to present, along with the full wave spectra at a set of 3,683 predetermined points distributed globally

Longshore wind, waves and currents: climate and climate projections at Ninety Mile Beach, south-eastern Australia

It is shown that Lakes Entrance, a township located at the northern end of Ninety Mile Beach in southeastern Australia, is situated in a region that may experience noticeable changes in longshore wind, wave and ocean currents compared to present day climate variability as a consequence of the southward shifting subtropical ridge (STR) predicted in global climate change models. These changes could modify sediment transport in the littoral zone and impact the coastline position. Thirty-year hindcasts of winds, coastal currents and waves are shown to agree well with available observations and provide a long-term dataset of the climate variability. Hindcasts of coastal ocean currents and waves indicate that while the annual net mean wave and current transport are in opposing directions, their seasonal adjusted monthly anomalies are positively correlated. Furthermore they are also correlated with the position of the STR location index. On seasonal to annual time scales a weak connection between the transport variables and Southern Oscillation Index (SOI) is found. It appears that during multiple years of positive (negative) SOI conditions the STR is located north (south) of its mean monthly position, resulting in anomalous eastward (westward) transport. The four climate models used in this study indicate a southward shift in the STR for most months under a high emission future. In summer months the shift in the STR results in both increased summer westward wind-driven currents and westward wave forcing. Changes in winter months are less related to the STR location and it is discussed that the contraction and increased intensity of the westerly storm belt linked to Southern Annular Mode could possibly influence the transport. The analysis is presented at the coastal scale to provide insights into how these changes may affect net transport across the littoral zone in more detailed numerical nearshore sediment transport modelling

Future wave-driven coastal sediment transport along the Catalan coast (NW Mediterranean)

The final publication is available at Springer via http://dx.doi.org/ 10.1007/s10113-015-0923-xIn the context of climate change, this study evaluates the impact on the long-shore and cross-shore sediment transport (LST and CST) along the Catalan coast (NW Mediterranean Sea) derived from climate projections obtained from five combinations of regional and global circulation models (RCMs and GCMs). Special emphasis is given to how inter-model variability translates from wave projections to wave-driven coastal impacts, which is still poorly known. Results show that the uncertainty is in general larger, especially for LST, for which the discrepancies among regional models are more relevant than those associated with the forcing wave parameters. Such increase in the uncertainty can be explained by the nonlinear processes involved, and the role of the forcing wave parameters having sometimes competing effects (e.g. wave height vs. wave direction). This illustrates that the performance of each RCM–GCM can vary from forcing to impact parameters; hence, the suitability of a particular RCM–GCM to evaluate a certain impact should be assessed based on its ability to properly simulate such impact. In this regard, LST and CST rates computed using empirical formulae that integrate several wave climate parameters, as in this study, can be used as a non-computationally expensive tool to assess the suitability of a given RCM–GCM to project changes in coastal dynamics.Peer Reviewe

Investigating biophysical linkages at tidal energy candidate sites; a case study for combining environmental assessment and resource characterisation

As the tidal energy industry looks to expand into commercial-scale array installations, uncertainty in methodology and outcome for environmental impact assessments can encumber tidal energy developments. Incorporating environmental monitoring measures into site characterisation campaigns can provide baseline information about biophysical relationships and help recognise potential impacts to the marine environment early in the development process. Concurrent measurements of fish and tidal currents were taken at a tidal energy candidate site in Australia over ∼2.5 months during its tidal resource assessment. Fish aggregation metrics (density, abundance, centre-of-mass (CM), dispersion, %-water column occupied, evenness, and relative aggregation) were investigated for their relation to environmental conditions (current speed, shear, temperature, diel stage, and tidal stage). Diel stage was the most significant indicator for fish density, abundance, and %-water column occupied. Fish density and abundance were elevated during strong currents, with vertical fish distribution (CM and dispersion) also influenced by current speed. Environmental conditions were able to explain up to 25% of variation in fish aggregation metrics using linear models. This study shows that early-stage environmental monitoring can successfully provide baseline information about fish aggregation responses to prevailing environmental conditions, thus reducing uncertainty risks for stakeholders of tidal energy developments