David Kevin Woolf

• Doctor of Philosophy
• Professor (Associate) at Heriot-Watt University

We evaluate global microplastics particle density distribution using field data from 1972 to 2022, made available by the NOAA (National Oceanic and Atmospheric Administration) NCEI (National Centers for Environmental Information) global marine microplastics database. We resampled the measured microplastics density data from NOAA NCEI into a regular...

Supplemement

The ocean annually absorbs about a quarter of all anthropogenic carbon dioxide (CO2) emissions. Global estimates of air–sea CO2 fluxes are typically based on bulk measurements of CO2 in air and seawater and neglect the effects of vertical temperature gradients near the ocean surface. Theoretical and laboratory observations indicate that these gradi...

Full-scale tidal turbines deployed in tidal channels are subjected to complex flow due to the effects of local bathymetry and coastline shape which modify the flow directionality, shear, twist and speed of the underlying tidally forced flow. In response to these effects, the wake of an operational tidal turbine will vary spatially and temporally. I...

Climate change and plastic pollution are two of the most pressing environmental challenges caused by human activity, and they are directly and indirectly linked. We focus on the relationship between marine plastic litter and the air-sea flux of greenhouse gases (GHGs). Marine plastic litter has the potential to both enhance and reduce oceanic GHG f...

The ocean plays a central role in modulating the Earth’s carbon cycle. Monitoring how the ocean carbon cycle is changing is fundamental to managing climate change. Satellite remote sensing is currently our best tool for viewing the ocean surface globally and systematically, at high spatial and temporal resolutions, and the past few decades have see...

Islands energy systems are often separated from mainland energy markets. Islands routinely rely on a single imported source of energy, which exposes islands to economic risks, and an increased likelihood of system failure. Integrating renewable energy into island energy systems can provide diversity of energy supply and improved system efficiency,...

The energy system of a small island is often separated from mainland energy markets. It may rely predominantly on a single imported source of energy, which increases the economic burden on the island communities. Integrating renewable energy generation into an existing island energy system can provide diversity of source, some degree of energy inde...

The ocean is a sink for~25% of the atmospheric CO 2 emitted by human activities, an amount in excess of 2 petagrams of carbon per year (PgC yr −1). Time-resolved estimates of global ocean-atmosphere CO 2 flux provide an important constraint on the global carbon budget. However, previous estimates of this flux, derived from surface ocean CO 2 concen...

The energy system of a small island is often separated from mainland energy markets. It may rely predominantly on a single imported source of energy, which increases the economic burden on the island communities. Integrating renewable energy generation into an existing island energy system can provide diversity of source, some degree of energy inde...

Staggered Sub-Array tidal farms provide an efficient energy extraction without any observable change in the environmental impact. Video presentation: https://youtu.be/-m5JE8Ay21k

The flow (flux) of climate-critical gases, such as carbon dioxide (CO2), between the ocean and the atmosphere is a fundamental component of our climate and an important driver of the biogeochemical systems within the oceans. Therefore, the accurate calculation of these air–sea gas fluxes is critical if we are to monitor the oceans and assess the im...

The contemporary air‐sea flux of CO2 is investigated by the use of an air‐sea flux equation, with particular attention to the uncertainties in global values and their origin with respect to that equation. In particular, uncertainties deriving from the transfer velocity and from sparse upper ocean sampling are investigated. Eight formulations of air...

Efficient tidal stream capture is affected by a number of factors, but the key elements are efficient device design and efficient array layout. This study focuses on array layout configuration. It proposes a new model of Staggered Sub-Array SSA layout which combines the benefit of packed sub-fences and the staggered grid. This improves the overall...

The ability to routinely quantify global carbon dioxide (CO2) absorption by the oceans has become crucial: it provides a powerful constraint for establishing global and regional carbon (C) budgets, and enables identification of the ecological impacts and risks of this uptake on the marine environment. Advances in understanding, technology, and inte...

Tidal stream energy technology has progressed to a point where commercial exploitation of this sustainable resource is practical, but tidal physics dictates interactions between tidal farms that raise political, legal and managerial challenges that are yet to be met. Fully optimising the design of a turbine array requires its developer to know abou...

Tidal stream energy is an emerging sector of the energy generation industry. It has more potential than other renewable energy resources to provide base-load power due to the predictability of the speed and direction of tidal currents. However, the practical use of tidal stream energy requires efficient energy extraction-including an efficient devi...

High-resolution satellite images of ocean color and sea surface temperature reveal an abundance of ocean fronts, vortices and filaments at scales below 10 km but measurements of ocean surface dynamics at these scales are rare. There is increasing recognition of the role played by small scale ocean processes in ocean-atmosphere coupling, upper-ocean...

The flow (flux) of climate critical gases, such as carbon dioxide (CO2), between the ocean and the atmosphere is a fundamental component of our climate and the biogeochemical development of the oceans. Therefore, the accurate calculation of these air-sea gas fluxes is critical if we are to monitor the health of our oceans and changes to our climate...

Two-dimensional (2D) depth-averaged simulations are used to investigate the performance of tidal turbine arrays. However, those models are incapable of taking into account the effects of the vertical position of the turbine on its performance. Results suggest that optimising the vertical position of the turbines is as important as optimising the ho...

The practical use of tidal stream energy requires extraction that is both efficient and appropriate; in engineering design, social implication and economically viable. The study will design a tidal array for Orkney waters, testing it against a wide range of constraints from engineering efficiency to market suitability. Project description The devel...

Most estimates of the climatically-important transfer of atmospheric gases into, and out of, the ocean assume that the ocean surface is unbroken by breaking waves. However the trapping of bubbles of atmospheric gases in the ocean by breaking waves introduces an asymmetry in this flux. This asymmetry occurs as a bias towards injecting gas into the o...

As the marine renewable energy industry evolves, in parallel with an increase in the quantity of available data and improvements in validated numerical simulations, it is occasionally appropriate to reassess the wave and tidal resource of a region. This is particularly true for Scotland-a leading nation that the international community monitors for...

The Goto Islands in Nagasaki Prefecture, Japan, contain three parallel channels that are suitable for tidal energy development and are the planned location for a tidal energy test centre. Energy extraction is added to a 3D numerical hydrodynamic model of the region, using a sub-grid momentum sink approach, to predict the effects of tidal developmen...

Lashy Sound is a small channel in Orkney, Scotland, where a tidal stream energy development is planned. This study uses numerical modelling to investigate the energy resource of the Sound and the effects on the flow of removing this power. A new 3D regional-scale hydrodynamic model of the area was built using the MIKE software and was used to study...

Most estimates of the climatically-important transfer of atmospheric gases into, and out of, the ocean assume that the ocean surface is unbroken by breaking waves. However the trapping of bubbles of atmospheric gases in the ocean by breaking waves introduces an asymmetry in this flux. This asymmetry occurs as a bias towards injecting gas into the o...

The global oceans are considered a major sink of atmospheric carbon dioxide (CO2). Rain is known to alter the physical and chemical conditions at the sea surface, and thus influence the transfer of CO2 between the ocean and atmosphere. It can influence gas exchange through enhanced gas transfer velocity, the direct export of carbon from the atmosph...

Physical oceanography is the study of physical conditions, processes and variables within the ocean, including temperature–salinity distributions, mixing of the water column, waves, tides, currents and air–sea interaction processes. Here we provide a critical review of how satellite sensors are being used to study physical oceanography processes at...

The presence of vertical temperature and salinity gradients in the upper ocean and the occurrence of variations in temperature and salinity on time scales from hours to many years complicate the calculation of the flux of carbon dioxide (CO2) across the sea surface. Temperature and salinity affect the interfacial concentration of aqueous CO2 primar...

The air-sea flux of greenhouse gases [e.g., carbon dioxide (CO2)] is a critical part of the climate system and a major factor in the biogeochemical development of the oceans. More accurate and higher-resolution calculations of these gas fluxes are required if researchers are to fully understand and predict future climate. Satellite Earth observatio...

Models of the air-sea transfer velocity of gases may be either empirical or mechanistic. Extrapolations of empirical models to an unmeasured gas or to another water temperature can be erroneous if the basis of that extrapolation is flawed. This issue is readily demonstrated for the most well-known empirical gas transfer velocity models where the in...

Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. The Surface Ocean CO2 Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fugacity, fCO2 . As fCO2 ishighly...

Climatologies, or long-term averages, of essential climate variables are useful for evaluating models and providing a baseline for studying anomalies. The Surface Ocean Carbon Dioxide (CO2) Atlas (SOCAT) has made millions of global underway sea surface measurements of CO2 publicly available, all in a uniform format and presented as fugacity, fCO2....

Adaptation to climate change in coastal regions of northern and western Norway, Scotland and Ireland and the coasts of Iceland must respond to trends and variability in a number of physical parameters that affect the regional life and economy. Historical trends and variability are apparent in historical data over several decades in temperature, pre...

Increasing interest is apparent in marine energy resources, particularly tidal and wave. Some TeraWatts of energy propagate from the world’s oceans to its marginal seas in the form of surface waves (≈ 2 TW) and tides (≅ 2.6 TW) where that energy is naturally dissipated. The seas and coastlines around the UK and its neighbours are notable for dissip...

The efficiency of transfer of gases and particles across the air-sea interface is controlled by several physical, biological and chemical processes in the atmosphere and water which are described here (including waves, large- and small-scale turbulence, bubbles, sea spray, rain and surface films). For a deeper understanding of relevant transport me...

The Surface Ocean CO 2 Atlas (SOCAT) has made millions of global underway sea surface measurements of CO 2 publicly available, all in a uniform format and presented as fugacity, f CO2 . However, these f CO2 values are valid strictly only for the instantaneous temperature at measurement and are not ideal for climatology. We recomputed these f CO2 va...

Air-sea fluxes of gases, including carbon dioxide, are commonly calculated using an air-sea flux equation. Within this equation, fluxes are proportional to a transfer velocity, k. We can use Earth observation or in situ data for the calculation of the fluxes, only if we adopt a suitable algorithm that typically describes the dependence of k on wind...

The transfer of gases between the atmosphere and ocean is affected by a number of processes, of which wave action and rainfall are two of potential significance. Efforts have been made to quantify separately their contributions; however such assessments neglect the interaction of these phenomena. Here we look at the correlation statistics of waves...

A vast programme to exploit waves and tidal energy in Scottish waters is underway. The characterisation of nearshore waves in Scottish waters is complicated by the jagged coastline and archipelagos, and strong wave-current interactions in locations such as the Pentland Firth. In order to investigate the energy availability, the Environmental Resear...

Orkney is at the forefront of the development of marine renewable technologies and ocean energy exploitation. Since different technologies to harness energy from the tide would be located at different depths of the water column, 3-D simulations should be more appropriate than 2-D to predict effects on the environment. In 3-D simulations the vertica...

The roughness of the seas is rarely mentioned as a major factor in the economic or social welfare of a region. In this study, the relationship between the ocean wave climate and the economy of the Western Isles of Scotland is examined. A deterioration in wave and wind climate either in response to natural variability or as a regional response to an...

Numerous acoustic Doppler current profiler (ADCP) surveys were performed in the Inner Sound of the Pentland Firth, a channel between the Orkney Islands and the northern coast of Scotland connecting the Atlantic Ocean to the west and the North Sea to the east. The Pentland Firth has the highest tidal streams of the British Isles, and one of the high...

This study is the first to directly correlate gas transfer velocity, measured at sea using the eddy-correlation (EC) technique, and satellite altimeter backscattering. During eight research cruises in different parts of the world, gas transfer velocity of dimethyl sulfide (DMS) was measured. The sample times and locations were compared with overpas...

The presence of vertical temperature and salinity gradients in the upper ocean and the occurrence of variations in temperature and salinity on time scales from hours to many years complicate the calculation of the flux of carbon dioxide (CO2) across the sea surface. Temperature and salinity affect the interfacial concentration of aqueous CO2 primar...

Shelf tidal stream velocities are accelerated by nearshore geographic features, such as headlands and islands. In the search for sustainable forms of electrical energy generation, such locations may become attractive for tidal stream power developments. For some prospective tidal stream energy sites, however, little is known about the intricacies o...

During 2008 and 2009 we applied coincident Earth observation data collected from multiple sensors (RA2, AATSR and MERIS, mounted on the European Space Agency satellite Envisat) to characterise environmental conditions and net sea-air fluxes of CO2 in three Arctic seas (Greenland, Barents, Kara) to assess net CO2 sink sensitivity due to changes in t...

A number of geochemical processes are dependent on bubbles primarily produced by "whitecapping" breaking waves, notably primary marine aerosol production, bubble-mediated gas exchange and the renewal of the organically rich surface marine microlayer. It is convenient to predict the magnitude of these processes through a "whitecap method" that then...

Shipboard measurements of fractional whitecap coverage W and wind speed at 10-m height, obtained during the 2006 Marine Aerosol Production (MAP) campaign, have been combined with ECMWF wave model and Quick Scatterometer (QuikSCAT) satellite wind speed data for assessment of existing W parameterizations. The wind history trend found in an earlier st...

Many countries now recognise the need for mitigation of climate change induced by human activities and have incorporated renewable energy resources within their energy policy. There are extensive resources of renewable energy within the marine environment and increasing interest in extracting energy from locations with either large tidal range, rap...

For the purpose of identifying potential sources of predictability of Scottish mean air temperature (SMAT), a redundancy analysis (RA) was accomplished to quantitatively assess the predictability of SMAT from North Atlantic SSTs as well as the temporal consistency of this predictability. The RA was performed between the main principal components of...

The Pentland Firth, located between the north coast of mainland Scotland (UK) and the Orkney Islands, is recognised as an excellent location for the utilisation of tidal stream technology. Potential ecological impacts associated with tidal stream technology may ultimately depend on device design, array size and deployment location. Available ecolog...

As part of the U. K. contribution to the international Surface Ocean-Lower Atmosphere Study, a series of three related projects-DOGEE, SEASAW, and HiWASE-undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of u...

The primary instrumentation that deals with the problems of parameterizing the physical exchange of gases and aerosol at the air-sea interface has been described while some additional details of measurement systems and techniques have been provided. The measurement systems being discussed include the autoflux, wave measurements, aerosol measurement...

This document is a supplement to “Physical Exchanges at the Air–Sea Interface: UK–SOLAS Field Measurements,” by Ian M. Brooks, Margaret J. Yelland, Robert C. Upstill-Goddard, Philip D. Nightingale, Steve Archer, Eric d’Asaro, Rachael Beale, Cory Beatty, Byron Blomquist, A. Anthony Bloom, Barbara J. Brooks, John Cluderay, David Coles, John Dacey, Mi...

We present the results of a 1D modelling study using a two equation k–ϵ turbulence closure model to generate realistic upper-ocean temperatures. The model is forced hourly with a variety of idealized diurnal wind and cloud profiles to investigate the sensitivity of the diurnal response and its effect on air–sea CO2 transfer at low to moderate wind...

Gas transfer velocities are estimated for one year using a 1-d upper-ocean model and a modified NOAA- COARE transfer velocity parameterization. Tuning parameters are evaluated with the aim of bringing the parameterization in line with current estimates based on simple wind-speed dependent models, derived from bomb-radiocarbon inventories and delibe...

Global air-sea flux of carbon dioxide (CO2) is calculated from wind data acquired by the satellite scatterometer QuikSCAT, the passive microwave radiometer AMSR-E, and the model reanalysis ERA-40 using four of the most commonly used wind speed dependent parameterizations of gas transfer velocity. Assuming QuikSCAT as reference, the results are comp...

Monitoring from ships of opportunity allows a wide range of parameters to be measured, thereby extending the coverage of operational oceanographic studies. Observation of dissolved oxygen using new sensors offers an effective way of monitoring changes in biological production. The limits of the application were tested following the transition from...

Radar altimeters are among the more common satellite-borne Earth Observation instruments with a long history including continuous data since 1991. They are also exceptionally versatile providing information on sea level, ocean dynamics, wind speed and a number of wave parameters. Radar altimetry is a "point" rather than a "swath" instrument so that...

Present estimates of air-sea carbon dioxide (CO2) transfer during low wind speeds and strong solar heating underestimate the net amount of gas exchanged, as they fail to consider the response of the near surface ocean to diurnal temperature variability and subsequent buoyancy-driven convective overturning. We present results that aim to assess the...

What is already happening High Confidence - A greater incidence of severe winds and larger mean wave heights in western and northern UK waters are being observed. What could happen Low Confidence - Models predict overall fewer Atlantic depressions crossing to UK waters but there will be a greater number of deep depressions (intense storms) and ass...

Monomolecular surface films (“sea slicks”) and mineral oil spills are both well known to dampen small-scale waves at the water surface, and thereby to influence transport processes at the air-sea interface. Because of their strong wave-damping capabilities they can often be delineated on synthetic aperture radar (SAR) imagery, but also on satellite...

Diurnal changes in seawater temperature affect the amount of air–sea gas exchange taking place through changes in solubility and buoyancy-driven nocturnal convection, which enhances the gas transfer velocity. We use a combination of in situ and satellite derived radiometric measurements and a modified version of the General Ocean Turbulence Model (...

One of the dominant sources of uncertainty in the calculation of air–sea flux of carbon dioxide on a global scale originates from the various parameterizations of the gas transfer velocity, k, that are in use. Whilst it is undisputed that most of these parameterizations have shortcomings and neglect processes which influence air–sea gas exchange an...

The air–water exchange of gases can be substantially enhanced by wave breaking and specifically by bubble-mediated transfer. A feature of bubble-mediated transfer is the additional pressure on bubbles resulting from the hydrostatic forces on a submerged bubble and from surface tension and curvature. This peculiarity results in asymmetry of bubble-m...

Air–water gas exchange experiments were carried out in a large wind wave tunnel in Marseille, France, to investigate gas transfer processes under energetic wind and wave fields, where macroscale breaking waves create bubble plumes (white caps) and turbulence on the water surface. We measured the gas transfer velocities of N2O, DMS, He, SF6, CH3Br,...

Air-water gas exchange experiments were carried out in a large wind wave tunnel in Marseille, France, to investigate gas transfer processes under energetic wind and wave fields, where macroscale breaking waves create bubble plumes (white caps) and turbulence on the water surface. We measured the gas transfer velocities of N2O, DMS, He, SF6, CH3Br,...

Monomolecular surface films (“sea slicks”) are well known to dampen small-scale waves at the water sur-face, and thereby to influence transport processes at the air-sea interface. Because of their strong wave-damping capabilities they can often be delineated on synthetic aperture radar (SAR) imagery, but also on satellite im-agery acquired in the v...

Within the framework of a 1-dimensional model, processes occurring near the air-sea interface can be examined in detail. Diurnal changes in seawater temperature will affect the amount of gas exchange taking place through changes in solubility and subsequent buoyancy driven nocturnal convection will enhance the gas transfer velocity. We propose the...

Seasonal new production (g C m−2) estimates obtained from dissolved oxygen and nitrate concentrations in surface waters (5 m depth) along a track between the UK (Portsmouth) and northern Spain (Bilbao) are compared. An oxygen flux method, in combination with a ship of opportunity (SOO), was tested on the northwest European shelf for its value in di...

Before the advent of radar altimeters our understanding of the world's climate was based on a few instruments moored off the coats of Europe, Japan and North America and visual observations taken from merchant ships. This information was patchy and in many cases of poor quality. It was difficult to relate what was happening at one location with ano...

Wave height in the North Atlantic has been observed to increase over the last quarter-century, based on monthly-mean data derived from observations. Empirical models have linked a large part of this increase in wave height with the North Atlantic Oscillation. Wave models provide a tool to study impacts of various climate change scenarios and invest...

The thermosteric contribution of the North Atlantic Oscillation (NAO) to the North Sea sea-level for the winter period is investigated. Satellite sea surface temperature as well as in situ measurements are used to define the sensitivity of winter water temperature to the NAO as well as to determine the trends in temperature. The sea surface tempera...

Processes within the sea surface microlayer have been relatively little studied considering their major role in air-sea interaction, especially gas exchange. This state of affairs can be explained by the inaccessibility of this very thin layer to most methods. One of the few suitable tools is radiometry which can probe a surface layer of ∼1-1000 mi...