Yvonne L. Firing

National Oceanography Centre

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Alberto C. Naveira Garabato

University of Southampton

Kathleen Donohue

Duke University

T. K. Chereskin

Scripps Institution of Oceanography

Satoshi Kimura

Japan Agency for Marine-Earth Science and Technology

M. A. Merrifield

Scripps Institution of Oceanography

Xiaobiao Xu

Florida State University

Eric P. Chassignet

Florida State University

Brian King

National Oceanography Centre

Michael P. Meredith

British Antarctic Survey

Alexander Forryan

University of Southampton

Cooperative Institutions

National Oceanography Centre

University of Southampton

British Antarctic Survey

Natural Environment Research Council

Scripps Institution of Oceanography

University of East Anglia

University of Hawaiʻi at Mānoa

National Oceanic and Atmospheric Administration

University of Hawaii System

Oregon State University

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Increasing ocean model resolution reveals impact of tuning eddy permitting models

AGUFM (2019)

Maike Sonnewald A. J. George Nurser Yvonne L. Firing Joël Hirschi Andrew C. Coward

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RRS James Clark Ross Cruise JR18002, 3-22 Nov 2018. Repeat hydrographic measurements on GO-SHIP line SR1b.

Yvonne L. Firing

The 24th complete occupation of the Drake Passage section SR1b obtained full-depth temperature, salinity, dissolved oxygen, and lowered ADCP velocity profiles at 29 stations between Burdwood Bank and Elephant Island, along with water column samples of salinity, dissolved oxygen, nutrients, carbonate system parameters, oxygen and carbon isotopes, and CFCs and SF6, and underway surface ocean and meteorological data and vessel mounted current measurements. The aims of these decadal repeat hydrographic measurements are to monitor the Antarctic Circumpolar Current’s properties and transports and contribute to understanding the Southern Ocean’s role in heat and carbon storage and transports and the contribution of ocean circulation to regional patterns of warming and sea level rise. They contribute to the international Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) and were funded by NERC through the Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA) National Capability programme and Transient tracer-based Investigation of Circulation and Thermal Ocean Change (TICTOC) large grant. At approximately half the stations large-volume samples were taken to measure radium and actinium isotopes to constrain iron fluxes as part of the NERC-funded RaCE:TraX project. The cruise also included opportunistic measurements of water column microplastics (funded by the Collaborative Antarctic Science Scheme) and nutrient isotopes, and experiments on phytoplankton nutrient limitation.

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Macronutrient and carbon supply, uptake and cycling across the Antarctic Peninsula shelf during summer

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences (2018)

Sian F. Henley Elizabeth M. Jones Hugh J. Venables Michael P. Meredith Yvonne L. Firing

The West Antarctic Peninsula shelf is a region of high seasonal primary production which supports a large and productive food web, where macronutrients and inorganic carbon are sourced primarily from intrusions of warm saline Circumpolar Deep Water. We examined the cross-shelf modification of this water mass during mid-summer 2015 to understand the supply of nutrients and carbon to the productive surface ocean, and their subsequent uptake and cycling. We show that nitrate, phosphate, silicic acid and inorganic carbon are progressively enriched in subsurface waters across the shelf, contrary to cross-shelf reductions in heat, salinity and density. We use nutrient stoichiometric and isotopic approaches to invoke remineralization of organic matter, including nitrification below the euphotic surface layer, and dissolution of biogenic silica in deeper waters and potentially shelf sediment porewaters, as the primary drivers of cross-shelf enrichments. Regenerated nitrate and phosphate account for a significant proportion of the total pools of these nutrients in the upper ocean, with implications for the seasonal carbon sink. Understanding nutrient and carbon dynamics in this region now will inform predictions of future biogeochemical changes in the context of substantial variability and ongoing changes in the physical environment.This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'.

Biogeochemical Cycle

Ocean Acidification

Total inorganic carbon

10.1098/rsta.2017.0168

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Antarctic Circumpolar Current Transport Through Drake Passage: What Can We Learn From Comparing High‐Resolution Model Results to Observations?

Journal of Geophysical Research Oceans (2020)

Xiaobiao Xu Eric P. Chassignet Yvonne L. Firing Kathleen Donohue

Abstract Uncertainty exists in the time‐mean total transport of the Antarctic Circumpolar Current (ACC), the world's strongest ocean current. The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively. In this paper, we use a realistic 1/12° global ocean simulation to interpret these observational estimates and reconcile their differences. We first show that the modeled ACC transport in the upper 1,000 m is in excellent agreement with repeat shipboard acoustic Doppler current profiler (SADCP) transects and that the exponentially decaying transport profile in the model is consistent with the profile derived from repeat hydrographic data. By further comparing the model results to the cDrake and DRAKE observations, we argue that the modeled 157.3 Sv transport, that is, approximately the average of the cDrake and DRAKE estimates, is actually representative of the time‐mean ACC transport through the Drake Passage. The cDrake experiment overestimated the barotropic contribution in part because the array undersampled the deep recirculation southwest of the Shackleton Fracture Zone, whereas the surface geostrophic currents used in the DRAKE estimate yielded a weaker near‐surface transport than implied by the SADCP data. We also find that the modeled baroclinic and barotropic transports are not correlated; thus, monitoring either baroclinic or barotropic transport alone may be insufficient to assess the temporal variability of the total ACC transport.

Barotropic fluid

Circumpolar star

10.1029/2020jc016365

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Finale: impact of the ORCHESTRA/ENCORE programmes on Southern Ocean heat and carbon understanding

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences (2023)

Andrew J. S. Meijers Michael P. Meredith Emily Shuckburgh Elizabeth C. Kent David Munday

The 5-year Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA) programme and its 1-year extension ENCORE (ENCORE is the National Capability ORCHESTRA Extension) was an approximately 11-million-pound programme involving seven UK research centres that finished in March 2022. The project sought to radically improve our ability to measure, understand and predict the exchange, storage and export of heat and carbon by the Southern Ocean. It achieved this through a series of milestone observational campaigns in combination with model development and analysis. Twelve cruises in the Weddell Sea and South Atlantic were undertaken, along with mooring, glider and profiler deployments and aircraft missions, all contributing to measurements of internal ocean and air–sea heat and carbon fluxes. Numerous forward and adjoint numerical experiments were developed and supported by the analysis of coupled climate models. The programme has resulted in over 100 peer-reviewed publications to date as well as significant impacts on climate assessments and policy and science coordination groups. Here, we summarize the research highlights of the programme and assess the progress achieved by ORCHESTRA/ENCORE and the questions it raises for the future. This article is part of a discussion meeting issue ‘Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities’.

Ocean observations

Mooring

Milestone

10.1098/rsta.2022.0070

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Wind-Driven Processes Controlling Oceanic Heat Delivery to the Amundsen Sea, Antarctica

Journal of Physical Oceanography (2019)

Tiago S. Dotto Alberto C. Naveira Garabato Sheldon Bacon Paul R. Holland Satoshi Kimura

Abstract Variability in the heat delivery by Circumpolar Deep Water (CDW) is responsible for modulating the basal melting of the Amundsen Sea ice shelves. However, the mechanisms controlling the CDW inflow to the region’s continental shelf remain little understood. Here, a high-resolution regional model is used to assess the processes governing heat delivery to the Amundsen Sea. The key mechanisms are identified by decomposing CDW temperature variability into two components associated with 1) changes in the depth of isopycnals [heave (HVE)], and 2) changes in the temperature of isopycnals [water mass property changes (WMP)]. In the Dotson–Getz trough, CDW temperature variability is primarily associated with WMP. The deeper thermocline and shallower shelf break hinder CDW access to that trough, and CDW inflow is regulated by the uplift of isopycnals at the shelf break—which is itself controlled by wind-driven variations in the speed of an undercurrent flowing eastward along the continental slope. In contrast, CDW temperature variability in the Pine Island–Thwaites trough is mainly linked to HVE. The shallower thermocline and deeper shelf break there permit CDW to persistently access the continental shelf. CDW temperature in the area responds to wind-driven modulation of the water mass on-shelf volume by changes in the rate of inflow across the shelf break and in Ekman pumping-induced vertical displacement of isopycnals within the shelf. The western and eastern Amundsen Sea thus represent distinct regimes, in which wind forcing governs CDW-mediated heat delivery via different dynamics.

Trough (economics)

Inflow

Circumpolar deep water

10.1175/jpo-d-19-0064.1

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Citations (60)

Ocean mixing beneath Pine Island Glacier ice shelf, West Antarctica

Journal of Geophysical Research Oceans (2016)

Satoshi Kimura Adrian Jenkins Pierre Dutrieux Alexander Forryan Alberto C. Naveira Garabato

Ice shelves around Antarctica are vulnerable to an increase in ocean-driven melting, with the melt rate depending on ocean temperature and the strength of flow inside the ice-shelf cavities. We present measurements of velocity, temperature, salinity, turbulent kinetic energy dissipation rate, and thermal variance dissipation rate beneath Pine Island Glacier ice shelf, West Antarctica. These measurements were obtained by CTD, ADCP, and turbulence sensors mounted on an Autonomous Underwater Vehicle (AUV). The highest turbulent kinetic energy dissipation rate is found near the grounding line. The thermal variance dissipation rate increases closer to the ice-shelf base, with a maximum value found ∼0.5 m away from the ice. The measurements of turbulent kinetic energy dissipation rate near the ice are used to estimate basal melting of the ice shelf. The dissipation-rate-based melt rate estimates is sensitive to the stability correction parameter in the linear approximation of universal function of the Monin-Obukhov similarity theory for stratified boundary layers. We argue that our estimates of basal melting from dissipation rates are within a range of previous estimates of basal melting.

10.1002/2016jc012149

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Citations (29)

Internal Waves Across the Antarctic Circumpolar Current

AGU Fall Meeting Abstracts (2018)

A. M. Thurnherr Yvonne L. Firing T. K. Chereskin Stephanie Waterman

Circumpolar star

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Stabilization of dense Antarctic water supply to the Atlantic Ocean overturning circulation

Nature Climate Change (2019)

E. Povl Abrahamsen Andrew J. S. Meijers Kurt L. Polzin Alberto C. Naveira Garabato Brian King

Antarctic Bottom Water

Abyssal zone

Throughflow

Tropical Atlantic

10.1038/s41558-019-0561-2

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Citations (55)

Vertical structure and transport of the Antarctic Circumpolar Current in Drake Passage from direct velocity observations

Journal of Geophysical Research Atmospheres (2011)

Yvonne L. Firing T. K. Chereskin Matthew R. Mazloff

[1] The structure of the Antarctic Circumpolar Current (ACC) in Drake Passage is examined using 4.5 years of shipboard acoustic Doppler current profiler (ADCP) velocity data. The extended 1000 m depth range available from the 38 kHz ADCP allows us to investigate the vertical structure of the current. The mean observed current varies slowly with depth, while eddy kinetic energy and shear variance exhibit strong depth dependence. Objectively mapped streamlines are self-similar with depth, consistent with an equivalent barotropic structure. Vertical wavenumber spectra of observed currents and current shear reveal intermediate wavenumber anisotropy and rotation indicative of downward energy propagation above 500 m and upward propagation below 500 m. The mean observed transport of the ACC in the upper 1000 m is estimated at 95 ± 2 Sv or 71% of the canonical total transport of 134 Sv. Mean current speeds in the ACC jets remain quite strong at 1000 m, 10–20 cm s−1. Vertical structure functions to describe the current and extrapolate below 1000 m are explored with the aid of full-depth profiles from lowered ADCP and a 3 year mean from the Southern Ocean State Estimate (SOSE). A number of functions, including an exponential, are nearly equally good fits to the observations, explaining >75% of the variance. Fits to an exponentially decaying function can be extrapolated to give an estimate of 154 ± 38 Sv for the full-depth transport.

Current meter

Wavenumber

Barotropic fluid

Circumpolar star

Boundary current

10.1029/2011jc006999

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Citations (103)