Andrew J. Watson

University of Exeter | UoE · College of Life and Environmental Sciences

Increasing anthropogenic CO2 emissions to the atmosphere are partially sequestered into the global oceans through the air‐sea exchange of CO2 and its subsequent movement to depth, commonly referred to as the global ocean carbon sink. Quantifying this ocean carbon sink provides a key component for closing the global carbon budget, which is used to i...

The Atlantic Meridional Overturning Circulation (AMOC), vital for northward heat transport across the Atlantic Ocean, is projected to weaken due to global warming ¹ , with significant global climate impacts 2,3 . However, the extent of AMOC weakening is uncertain with wide variation across climate models 1,4,5 , while some statistical indicators su...

Increasing anthropogenic CO2 emissions to the atmosphere are partially sequestered into the global oceans through the air-sea exchange of CO2 and its subsequent movement to depth, and this collective large-scale absorption is commonly referred to as the global ocean carbon sink. Quantifying this ocean carbon sink provides a key component for closin...

Plain Language Summary The Atlantic Meridional Overturning Circulation (AMOC) is a system of ocean currents that move warm surface waters from the south to the north of the Atlantic Ocean where they cool, sink, and return southward at depth. Changes in the AMOC would have wide‐ranging impacts on our climate. It is predicted to weaken as the climate...

The Southern Ocean is a major sink of atmospheric CO2, but the nature and magnitude of its variability remains uncertain and debated. Estimates based on observations suggest substantial variability that is not reproduced by process-based ocean models, with increasingly divergent estimates over the past decade. We examine potential constraints on th...

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...

Future projections indicate the AMOC will weaken and shoal in response to global warming, but models disagree widely over the amount of weakening. We analyse projected AMOC weakening in 27 CMIP6 climate models, in terms of changes in three return pathways of the AMOC. The branch of the AMOC that returns through diffusive upwelling in the Indo-Pacif...

Throughout Earth’s history, the abundance of oxygen in our atmosphere has varied, but by how much remains debated. Previously, an upper limit for atmospheric oxygen has been bounded by assumptions made regarding the fire window: atmospheric oxygen concentrations higher than 30–40% would threaten the regeneration of forests in the present world. Her...

The North Atlantic Ocean is the most intense marine sink for anthropogenic carbon dioxide (CO 2) in the world's oceans, showing high variability and substantial changes over recent decades. However, the contribution of biology to the variability and trend of this sink is poorly understood. Here we use in situ plankton measurements, alongside observ...

The Southern Ocean is an important sink of anthropogenic CO2, but it is among the least well-observed ocean basins, and consequentially substantial uncertainties in the CO2 flux reconstruction exist. A recent attempt to address historically sparse wintertime sampling produced ‘pseudo’ wintertime observations of surface pCO2 using subsurface summert...

Rocket emissions and debris from spacecraft falling out of orbit are having increasingly detrimental effects on global atmospheric chemistry. Improved monitoring and regulation are urgently needed to create an environmentally sustainable space industry. https://rdcu.be/cTVAJ

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize datasets a...

We present new estimates of the regional North Atlantic (15–80∘ N) CO2 flux for the 2000–2017 period using atmospheric CO2 measurements from the NOAA long-term surface site network in combination with an atmospheric carbon cycle data assimilation system (GEOS-Chem–LETKF, Local Ensemble Transform Kalman Filter). We assess the sensitivity of flux est...

The ocean absorbs approximately a quarter of the carbon dioxide currently released to the atmosphere by human activities (Canth). A disproportionately large fraction accumulates in the North Atlantic due to the combined effects of transport by the Atlantic Meridional Overturning Circulation (AMOC) and air–sea exchange. However, discrepancies exist...

The response of the meridional overturning circulation (MOC) to changes in Southern Ocean (SO) zonal wind forcing and Pacific basin vertical diffusivity is investigated under varying buoyancy forcings, corresponding to ‘warm’, ‘present-day’ and ‘cold’ states, in a two-basin general circulation model connected by a southern circumpolar channel. We f...

The source of oxygen to Earth’s atmosphere is organic carbon burial, whilst the main sink is oxidative weathering of fossil carbon. However, this sink is to insensitive to counteract oxygen rising above its current level of about 21%. Biogeochemical models suggest that wildfires provide an additional regulatory feedback mechanism. However, none hav...

Full report available from https://unesdoc.unesco.org/ark:/48223/pf0000376708.locale=en doi:10.25607/h0gj-pq41

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate – the “global carbon budget” – is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we de...

We present new estimates of the regional North Atlantic (15° N–80° N) CO2 flux for the 2000–2017 period using atmospheric CO2 measurements from the NOAA long term surface site network in combination with an atmospheric data assimilation system (GEOSChem–LETKF). We also assess the sensitivity of flux estimates to the representation of the prior ocea...

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...

A dynamically passive inert tracer was released in the interior South Pacific Ocean at latitudes of the Antarctic Circumpolar Current. Observational cross sections of the tracer were taken over 4 consecutive years as it drifted through Drake Passage and into the Atlantic Ocean. The tracer was released within a region of high salinity relative to su...

The variation in the strength and structure of the overturning circulation under varying Southern Ocean buoyancy forcing, corresponding to present day, a cooler (glacial) state, and a possible future warmer state is analysed in an idealised two-basin general circulation model connected by a southern circumpolar channel. A connection between the Nor...

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...

The North Atlantic Ocean is a region of intense uptake of atmospheric CO2. To assess how this CO2 sink has evolved over recent decades, various approaches have been used to estimate basin‐wide uptake from the irregularly sampled in situ CO2 observations. Until now, the lack of robust uncertainties associated with observation‐based gap‐filling metho...

A dynamically passive inert tracer was released in the interior South Pacific Ocean at latitudes of the Antarctic Circumpolar Current. Observational cross sections of the tracer were taken over four consecutive years as it drifted through Drake Passage and into the Atlantic Ocean. The tracer was released within a region of high salinity relative to...

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The potential habitability of an exoplanet is traditionally assessed by determining if its orbit falls within the circumstellar `habitable zone' of its star, defined as the distance at which water could be liquid on the surface of a planet (Kopparapu et al., 2013). Traditionally, these limits are determined by radiative-convective climate models, w...

In this work, we use realistic isopycnal velocities with a 3-D eddy diffusivity to advect and diffuse a tracer in the Antarctic Circumpolar Current, beginning in the Southeast Pacific and progressing through Drake Passage. We prescribe a diapycnal diffusivity which takes one value in the SE Pacific west of 67°W and another value in Drake Passage ea...

Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere – the “global carbon budget” – is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and m...

The major biogeochemical cycles that keep the present-day Earth habitable are linked by a network of feedbacks, which has led to a broadly stable chemical composition of the oceans and atmosphere over hundreds of millions of years. This includes the processes that control both the atmospheric and oceanic concentrations of oxygen. However, one notab...

Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and tur...

This paper describes a Near Surface Ocean Profiler, which has been designed to precisely measure vertical gradients in the top 10 m of the ocean. Variations in the depth of seawater collection are minimised when using the profiler compared to conventional CTD/rosette deployments. The profiler consists of a remotely operated winch mounted on a tethe...

For the past several hundred million years, oxygen concentrations in Earth's atmosphere have been comparatively high ( 1 , 2 ). Yet, the oceans seem never to have been far from anoxia (oxygen depletion) and have occasionally suffered major oceanic anoxic events (OAEs), recognized in the rock record through accumulations of dark, organic-rich shales...

The Surface Ocean CO2 Atlas (SOCAT) is a synthesis of quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.7 million fCO2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.6 million fCO2 values rela...

The process of ocean acidification is now relatively well-documented at the global scale as a long-term trend in the open ocean. However, short-term and spatial variability can be high. New datasets made available since Charting Progress 2 make it possible to greatly improve the characterisation of CO2 and ocean acidification in UK waters.

The Surface Ocean CO2 Atlas (SOCAT) is a synthesis of quality-controlled fCO2 (fugacity of carbon dioxide) values for the global surface oceans and coastal seas with regular updates. Version 3 of SOCAT has 14.5 million fCO2 values from 3646 data sets covering the years 1957 to 2014. This latest version has an additional 4.4 million fCO2 values rela...

Ambitious response needed on climate front Letter to the Times – 16 th Dec 2015 Sir, The agreement reached in Paris shows there is now impressive global ambition to tackle climate change – with tough challenges ahead (Britain facing steeper emissions cuts; Dec 14). Further policy action is urgently required to transform ambition into reality. Unfor...

This is the author accepted manuscript. The final version is available from Royal Society Publishing via http://dx.doi.org/10.1098/rsta.2014.0428

Atmospheric CO2 concentrations over glacial-interglacial cycles closely correspond to Antarctic temperature patterns. These are distinct from temperature variations in the mid to northern latitudes, so this suggests that the Southern Ocean is pivotal in controlling natural CO2 concentrations. Here we assess the sensitivity of atmospheric CO2 concen...

We test the use of a measure to diagnose a sub-mesoscale isopycnal diffusivity by determining the best match between observations of a tracer and simulations with varying small-scale diffusivities. Specifically, the robustness of a ‘roughness’ measure to discriminate between tracer fields experiencing different sub-mesoscale isopycnal diffusivities...

The accumulation of carbon within the Weddell Gyre, and its exchanges across the gyre boundaries are investigated with three recent full-depth oceanographic sections enclosing this climatically-important region. The combination of carbon measurements with ocean circulation transport estimates from a box inverse analysis reveal that deep water trans...

The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The meridional eddy diffusivity,...

The Southern Ocean plays a pivotal role in the global ocean circulation and climate1–3. There, the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths, forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere4,5. The sensitivity of the u...

The Southern Ocean fascinates us. It retains an aura of mystery from the time of the early European explorers, when to sail through the Straits of Magellan or around Cape Horn was to leave the known world behind. Then, as now, the waters of the Southern Ocean earned a reputation as the roughest and

Significance We investigate the balance between two mechanisms that remove carbon from the atmosphere and oceans over long timescales—weathering of terrestrial silicates and alteration of the ocean floor. We show that this balance should strongly influence atmospheric oxygen concentration, since it dictates the delivery rate of the ultimate limitin...

Water column dissolved inorganic carbon and total alkalinity were measured during five hydrographic sections in the Atlantic Ocean and Drake Passage. The work was funded through the Strategic Funding Initiative of the UK's Oceans2025 programme, which ran from 2007 to 2012. The aims of this programme were to establish the regional budgets of natural...

The Surface Ocean CO2 Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO2 (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version 1) with more data (increased from 6.3 million to 10.1 million surface wat...

The Surface Ocean CO2 Atlas (SOCAT), an activity of the international marine carbon research community, provides access to synthesis and gridded fCO2 (fugacity of carbon dioxide) products for the surface oceans. Version 2 of SOCAT is an update of the previous release (version 1) with more data (increased from 6.3 million to 10.1 million surface wat...

Water column dissolved inorganic carbon and total alkalinity were measured during five hydrographic sections in the Atlantic Ocean and Drake Passage. The work was funded through the Strategic Funding Initiative of the UK's Oceans2025 programme, which ran from 2007 to 2012. The aims of this programme were to establish the regional budgets of natural...

Diapycnal mixing (across density surfaces) is an important process in the global ocean overturning circulation. Mixing in the interior of most of the ocean, however, is thought to have a magnitude just one-tenth of that required to close the global circulation by the downward mixing of less dense waters. Some of this deficit is made up by intense n...

Abstract The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star un...

The Surface Ocean CO2 Atlas (SOCAT) is an effort by the international marine carbon research community. It aims to improve access to carbon dioxide measurements in the surface oceans by regular releases of quality controlled and fully documented synthesis and gridded fCO2 (fugacity of carbon dioxide) products. SOCAT version 2 presented here extends...

As a response to public demand for a welldocumented, quality controlled, publically available, global surface ocean carbon dioxide (CO2) data set, the international marine carbon science community developed the Surface Ocean CO2 Atlas (SOCAT). The first SOCAT product is a collection of 6.3 million quality controlled surface CO2 data from the global...

A well-documented, publicly available, global data set of surface ocean carbon dioxide (CO2) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO2 Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly availab...

[1] The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent di...

This chapter describes investigations into how in test fires the rate of spread and probability of ignition varied with the concentration of atmospheric oxygen. It discusses two sets of experiments in more detail to present the results and compare them briefly with subsequent investigations of similar intent, and to draw attention to the implicatio...

Modelling diapycnal diffusivity in Drake Passage with MITgcm and the DIMES tracer