David Smeed

National Oceanography Centre, Southampton | NOCS

The potential weakening of the Atlantic Meridional Overturning Circulation (AMOC) in response to anthropogenic forcing, suggested by climate models, is at the forefront of scientific debate. A key AMOC component, the Florida Current (FC), has been measured using submarine cables between Florida and the Bahamas at 27°N nearly continuously since 1982...

The Meridional Overturning Circulation (MOC) is key to the redistribution of heat and is projected to weaken due to climate change. The RAPID mooring array observes the strength of the MOC, showing an overall weakening of 1.4 Sv/decade from 2004–2022. However, the significance of this trend is controversial. Here we consider the RAPID observations...

The ocean biological carbon pump (BCP) plays a pivotal role in the global carbon cycle. The BCP magnitude is determined by the fraction of nutrients utilised in biological production and remineralised at depth, with the remainder being subducted into the interior unused as ‘preformed’ nutrients. This fraction is currently around 50% and subject to...

Continuous measurements of the Atlantic meridional overturning circulation (AMOC) and meridional ocean heat transport at 26.5° N began in April 2004 and are currently available through December 2020. Approximately 90% of the total meridional heat transport (MHT) at 26.5° N is carried by the zonally averaged overturning circulation, and an ev...

Patterns of variability in ocean properties are often closely related to large-scale climate pattern indices, and 2021 is no exception. The year 2021 started and ended with La Niña conditions, charmingly dubbed a “double-dip” La Niña. Hence, stronger-than-normal easterly trade winds in the tropical south Pacific drove westward surface current anoma...

The large-scale system of ocean currents that transport warm waters in the upper 1000 m northward and return deeper cooler waters southward is known as the Atlantic meridional overturning circulation (AMOC). Variations in the AMOC have significant repercussions for the climate system; hence, there is a need for long-term monitoring of AMOC fluctuat...

The zonally integrated component of surface and deep currents, known as the meridional overturning circulation (MOC), plays an important role in Earth’s climate because it provides a mechanism for ocean meridional heat transport (MHT). The observing system for the Atlantic MOC/MHT consists of several basin-wide moored arrays as well as the combinat...

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...

Labrador Slope Water (LSLW) is a relatively fresh and cool water mass that originates from the Labrador Current in the subarctic and is known to occur in the Eastern Slope Sea on the US-Canadian shelf-slope north of the Gulf Stream. It has potential densities of 27.4–27.65 kg m⁻³. Using ocean observations, we show here that the LSLW penetrates as a...

This chapter details 2020 global patterns in select observed oceanic physical, chemical, and biological variables relative to long-term climatologies, their differences between 2020 and 2019, and puts 2020 observations in the context of the historical record.

The OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the wo...

The large-scale system of ocean currents that transport warm surface (1000 m) waters northward and return cooler waters southward is known as the Atlantic meridional overturning circulation (AMOC). Variations in the AMOC have significant repercussions for the climate system, hence there is a need for long term monitoring of AMOC fluctuations. Curre...

A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2012 by the RAPID-MOCHA-WBTS (RAPID – Meridional Overturning Circulation and Heatflux Array – Western Boundary Time Series, hereafter RAPID array) with this weakened state of the AMOC persisting until 2017. Climate model and paleo-oceanograph...

A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2012 by the RAPID-MOCHA-WBTS (RAPID – Meridional Overturning Circulation and Heatflux Array – Western Boundary Time Series, hereafter RAPID array) with this weakened state of the AMOC persisting until 2017. Climate model and paleo-oceanograph...

The decadal to multidecadal temperature variability of the intermediate (700–2,000 m) North Atlantic Subpolar Gyre (SPG) significantly imprints the global pattern of ocean heat uptake. Here, the origins and dominant pathways of this variability are investigated with an ocean analysis product (EN4), an ocean state estimate (ECCOv4), and idealized mo...

A decline in Atlantic meridional overturning circulation (AMOC) strength has been observed between 2004 and 2012 by the RAPID array with this weakened state of the AMOC persisting until 2017. Climate model and paleo-oceanographic research suggests that the AMOC may have been declining for decades or even centuries before this, however direct observ...

The Atlantic meridional overturning circulation (AMOC) is a key component of the ocean circulation system that is constantly moving water, heat, salt, carbon, nutrients, and other substances around the globe. The AMOC impacts the Atlantic Ocean in a unique way, making it the only ocean basin where heat is carried northward in both hemispheres. Reco...

The strength of the Atlantic meridional overturning circulation (AMOC) at 26∘ N has now been continuously measured by the RAPID array over the period April 2004–September 2018. This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transport from hy...

The physical mechanisms that remove energy from the Southern Ocean’s vigorous mesoscale eddy field are not well understood. One proposed mechanism is direct transfer of energy to the internal wave field in the ocean interior, via eddy-induced straining and shearing of pre-existing internal waves. The magnitude, vertical structure and temporal varia...

The RAPID-MOCHA-WBTS (RAPID-Meridional Overturning Circulation and Heatflux Array-Western Boundary Time Series) programme has produced a continuous time series of the Atlantic Meridional Overturning Circulation (AMOC) at 26N that started in April 2004. This release of the time series covers the period from April 2004 to Sept 2018, but differs from...

Abstract. The strength of the Atlantic meridional overturning circulation (AMOC) at 26° N has now been continuously measured by the RAPID array over the period Apr 2004–Sept 2018. This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transports fro...

The Atlantic Meridional Overturning Circulation (AMOC) is a key mechanism of heat, freshwater, and carbon redistribution in the climate system. The precept that the AMOC has changed abruptly in the past, notably during and at the end of the last ice age, and that it is “very likely” to weaken in the coming century due to anthropogenic climate chang...

Northward ocean heat transport at 26°N in the Atlantic has been measured since 2004. The ocean heat transport is large, about 1.25PW, and on interannual time scales it exhibits surprisingly large temporal variability. There has been a long-term reduction in ocean heat transport of 0.17 PW from 1.32 PW before 2009 to 1.15 PW after 2009 (2009-2016) o...

The OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the wo...

The OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the wo...

The OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the wo...

The purpose of RRS James Cook cruise JC174 was to refurbish the RAPID 26°N array of moorings that span the Atlantic from the Bahamas to the Canary Islands. Las Palmas on Saturday 20th October 2018 and ended in the evening of Tuesday 26th November at Freeport, Bahamas. There was a port call at Nassau, Bahamas on 16th November to take on board additi...

The RAPID-MOCHA-WBTS (RAPID-Meridional Overturning Circulation and Heatflux Array-Western Boundary Time Series) programme has produced a continuous time series of the Atlantic Meridional Overturning Circulation (AMOC) at 26N that started in April 2004. This release of the time series extends the data to September 2018. The 26N AMOC time series is d...

The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basi...

The Mediterranean Sea can be viewed as a “barometer” of the North Atlantic Ocean, because its sea level responds to oceanic-gyre-scale changes in atmospheric pressure and wind forcing, related to the North Atlantic Oscillation (NAO). The climate of the North Atlantic is influenced by the Atlantic Meridional Overturning Circulation (AMOC) as it tran...

The purpose of RRS James Cook cruise JC145 was to refurbish the RAPID 26°N array of moorings that span the Atlantic from the Bahamas to the Canary Islands. Cruise JC145 departed from Santa Cruz de Tenerife on Tuesday 28th February 2017 and ended on Saturday 8th April at Freeport, Bahamas. There was a port call at Nassau, Bahamas on 27th March to ex...

Major changes are occurring across the North Atlantic climate system, including in the atmosphere, ocean and cryosphere, and many observed changes are unprecedented in instrumental records. As the changes in the North Atlantic directly affect the climate and air quality of the surrounding continents, it is important to fully understand how and why...

Diabatic upwelling of abyssal waters is investigated in the Panama Basin employing the water mass transformation framework of Walin (). We find that, in large areas of the basin, the bottom boundary layer is very weakly stratified and extends hundreds of meters above the sea floor. Within the weakly stratified bottom boundary layer, neutral density...

The Panama Basin serves as a laboratory to investigate abyssal water upwelling. The basin has only a single abyssal water inflow pathway through the narrow Ecuador Trench. The estimated critical inflow through the Trench reaches 0.34 ± 0.07 m/s, resulting in an abyssal water volume inflow of 0.29 ± 0.07 Sv. The same trench carries the return flow o...

In 2017, the dominant greenhouse gases released into Earth's atmosphere-carbon dioxide, methane, and nitrous oxide-reached new record highs. The annual global average carbon dioxide concentration at Earth's surface for 2017 was 405.0 ± 0.1 ppm, 2.2 ppm greater than for 2016 and the highest in the modern atmospheric measurement record and in ice cor...

The weakly stratified bottom boundary layer (wsBBL) of the global ocean is currently unmapped; even the definition of the wsBBL layer is yet lacking. However, recent studies point to the wsBBL as a region where most of the abyssal water transformation takes place. In this study, historical high-resolution density profiles are used to map the proper...

The RAPID-MOCHA-WBTS time-series of overturning at 26N has been extended to cover the time period up to February 2017, 12.9 years in total. New results will be presented for the overturning stream function and its component parts. Previous results, from the start of measurements in 2004 till 2011, showed a decline of the AMOC in the subtropical gyr...

The Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004-2008. This change of AMOC state is concur...

Previous modeling and observational studies have established that it is possible to accurately monitor the Atlantic Meridional Overturning Circulation (AMOC) at 26.5°N using a coast-to-coast array of instrumented moorings supplemented by direct transport measurements in key boundary regions (the RAPID/MOCHA/WBTS Array). The main sources of observat...

The RAPID-MOCHA-WBTS (RAPID-Meridional Overturning Circulation and Heatflux Array-Western Boundary Time Series) programme has produced a continuous time series of the Atlantic Meridional Overturning Circulation (AMOC) at 26N that started in April 2004. This release of the time series extends the data to February 2017. The 26N AMOC time series is de...

Numerous gliders have been deployed in the Gulf of Lions (Northwestern Mediterranean Sea) and in particular during episodes of open-ocean deep convection in the winter 2012–2013. The data collected represents an unprecedented density of in-situ observations providing a first in-situ statistical and 3D characterization of the important mixing agents...

Ch 7. Regional Climates: f. Europe and the Middle East

• The AMOC is key to maintaining the mild climate of the UK. • The AMOC is predicted to decline in the 21st century in response to a changing climate. • Past abrupt changes in the AMOC have had dramatic climate consequences. • There is growing evidence that the AMOC has been declining for at least a decade, pushing the Atlantic Multidecadal Variabi...

Lee waves are thought to play a prominent role in Southern Ocean dynamics, facilitating a transfer of energy from the jets of the Antarctic Circumpolar Current to microscale, turbulent motions important in water mass transformations. Two EM-APEX profiling floats deployed in the Drake Passage during the Diapycnal and Isopycnal Mixing Experiment (DIM...

Numerical studies of the flow over an underwater glider was simulated to investigate; 1) the extent to which the measurements of sensors (including turbulence sensors) on an AUV are affected by the distortion of the flow around the vehicle body, 2) the occurrence of bioluminescence in the wakes of autonomous vehicles, and 3) the quantification of t...

The suitability of computational fluid dynamics (CFD) to numerically simulate the flow of water over autonomous underwater vehicles (AUVs) was investigated. The aim was to examine the feasibility of using large-eddy simulation to investigate; 1) the extent to which the measurements of sensors (including turbulence sensors) on an AUV are affected by...

Using underwater gliders we have identified canyon driven upwelling across the Celtic Sea shelf-break, in the vicinity of Whittard Canyon. The presence of this upwelling appears to be tied to the direction and strength of the local slope current, which is in itself highly variable. During typical summer time equatorward flow, an unbalanced pressure...

The supply of nitrate to surface waters plays a crucial role in maintaining marine life. Physical processes at the mesoscale (~10-100?km) and smaller have been advocated to provide a major fraction of the global supply. Whilst observational studies have focussed on well-defined features, such as isolated eddies, the vertical circulation and nutrien...

Variability in the North Atlantic ocean heat transport at 26.5°N on short (5-day) timescales is identified and contrasted with different behaviour at monthly intervals using a combination of RAPID/MOCHA/WBTS measurements and the NEMO-LIM2 1/12° ocean circulation/sea ice model. Wind forcing plays the leading role in establishing the heat transport v...

From ten years of observations of the Atlantic meridional overturning circulation (MOC) at 26° N (2004-2014), we revisit the question of flow compensation between components of the circulation. Contrasting with early results from the observations, transport variations of the Florida Current (FC) and upper mid-ocean (UMO) transports (top 1000 m east...

Abstract The Atlantic meridional overturning circulation (AMOC) plays a critical role in the climate system and is responsible for much of the meridional heat transported by the ocean. In this paper, the potential of using AMOC observations from the 26∘N RAPID array to predict North Atlantic sea surface temperatures is investigated for the first ti...

From ten years of observations of the Atlantic meridional overturning circulation at 26° N (MOC, 2004–2014), we revisit the question of flow compensation between components of the circulation. Contrasting with early results from the observations, transport variations of the Florida Current (FC) and upper mid-ocean transports (UMO, top 1000 m east o...

This study examines the seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) and its eastern boundary contributions. The cycle has a magnitude of 6 Sv, as measured by the RAPID/MOCHA/WBTS project array at 26°N, which is driven largely by the eastern boundary. The eastern boundary variations are explored in the context of the reg...

This cruise report covers scientific operations conducted during RRS James Cook Cruise 103. The purpose of the cruise was the refurbishment of an array of moorings spanning the latitude of 26.5°N from the Bahamas to the Canary Islands. Cruise JC103 departed from Port of Spain on Wednesday 23rd April 2014, calling twice at Nassau, Bahamas before fin...

The RAPID-MOCHA-WBTS (RAPID-Meridional Overturning Circulation and Heatflux Array-Western Boundary Time Series) programme has produced a continuous time series of the Atlantic Meridional Overturning Circulation (AMOC) at 26°N that started in April 2004. This release of the time series extends the data to March 2014. The 26°N AMOC time series is der...

The Earth releases heat through its crust into the overlaying ocean and atmosphere and, ultimately, into outer space. This heat flux amounts to only about 0.1 W m-2 on average, which is more than 10,000 times smaller than the solar power at the top of the atmosphere, and about 30 times smaller than the current radiative forcing of anthropogenic gre...

Decadal variability is a notable feature of the Atlantic Ocean and the climate of the regions it influences. Prominently, this is manifested in the Atlantic Multidecadal Oscillation (AMO) in sea surface temperatures. Positive (negative) phases of the AMO coincide with warmer (colder) North Atlantic sea surface temperatures. The AMO is linked with d...

The impact of a mesoscale eddy on the magnitude and spatial distribution of diapycnal ocean mixing is investigated using a set of hydrographic and microstructure measurements collected in the Southern Ocean. These data sampled a baroclinic, middepth eddy formed during the disintegration of a deep boundary current. Turbulent dissipation is suppresse...

The Atlantic meridional overturning circulation (AMOC) has received considerable attention, motivated by its major role in the global climate system.Observations ofAMOCstrength at 268Nmade by the RapidClimateChange (RAPID) array provide the best current estimate of the state of the AMOC. The period 2004–11 when RAPID AMOC is available is too short...

The last decade has seen the eagerly anticipated introduction of marine autonomous systems as a pragmatic tool for ocean observation. However, outstanding reliability problems means that these vehicles are not yet fulfilling their true potential. Of the classes of problems, loss of communication with a marine autonomous system is both fundamental a...

Seasonal variations of sea surface height (SSH) and mass within the Red Sea are caused mostly by exchange of heat with the atmosphere and by flow through the strait opening into the Gulf of Aden to the south. That flow involves a net mass transfer into the Red Sea during fall and out during spring, though in summer there is an influx of cool water...

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...

A combination of scientific, economic, technological and policy drivers is behind a recent upsurge in the use of marine autonomous systems (and accompanying miniaturized sensors) for environmental mapping and monitoring. Increased spatial–temporal resolution and coverage of data, at reduced cost, is particularly vital for effective spatial manageme...

It has been 20 years since the concept of the Autonomous Ocean Sampling Network (AOSN) was first introduced. This vision has been brought closer to reality with the introduction of underwater gliders. While in terms of functionality the underwater glider has shown to be capable of meeting the AOSN vision, in terms of reliability there is no communi...