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Antarctic Circumpolar Current

The Antarctic Circumpolar Current (ACC) is the dominant zonal circulation feature of the Southern Ocean, comprising the world's strongest and longest continuous ocean current system that flows eastward around Antarctica, unimpeded by continental barriers and linking the Atlantic, Pacific, and Indian Ocean basins over a circumnavigational path exceeding 24,000 kilometers.^[1]^[2] Primarily driven by persistent westerly winds, the ACC exhibits multiple fronts with meandering jets and eddy formation, achieving a mean full-depth volume transport of approximately 130–141 Sverdrups (1 Sv = 10⁶ m³ s⁻¹), far surpassing other global currents in mass flux.^[3]^[4]^[5] This formidable flow regulates inter-oceanic exchanges of heat, freshwater, and nutrients, modulates global thermohaline overturning, and enforces thermal isolation of the Antarctic continent, profoundly shaping Southern Hemisphere climate dynamics and carbon cycling.^[6]^[7] Recent observations and modeling indicate potential variability in ACC strength linked to wind stress changes and polar freshening, underscoring its sensitivity to high-latitude environmental shifts.^[8]^[9]

Physical Structure

Path and Extent

The Antarctic Circumpolar Current (ACC) flows eastward around Antarctica, forming the sole oceanic current to fully encircle a continental landmass and linking the Atlantic, Indian, and Pacific basins without continental barriers.^[10] Its continuous path spans approximately 24,000 km, constrained by the Antarctic continent to the south and subtropical gyres to the north.^[11] The current traverses critical passages, including the Drake Passage—a 850 km wide gap between South America and the Antarctic Peninsula—where it achieves its maximum constriction and transport focus.^[12] The ACC occupies a variable latitudinal band typically between 40°S and 60°S, with its mean position centered around 55°S; zonal shifts occur due to bottom topography, wind forcing, and eddy activity.^[7] Northern boundaries align with the Subantarctic Front (SAF), while southern limits trace the Polar Front (PF), enclosing distinct water masses within cores of intensified flow.^[13] In Drake Passage, the current's edges extend from roughly 55°S to 65°S, reflecting topographic steering by the passage's width and depth.^[14] Vertically, the ACC penetrates the full ocean depth, exceeding 4,000 m in places, with both baroclinic shear concentrated in upper layers and barotropic components extending to the seafloor.^[15] Horizontally, individual fronts within the system maintain widths of 40–60 km, though the broader zonal extent encompasses hundreds of kilometers modulated by meanders and eddies.^[16] Mean volume transport, predominantly through Drake Passage, averages 130 Sverdrups (1 Sv = 10^6 m³ s⁻¹), representing the world's largest oceanic flux.^[5]^[11]

Fronts and Associated Water Masses

The Antarctic Circumpolar Current (ACC) features multiple fronts defined by abrupt horizontal gradients in temperature, salinity, density, and other properties, which delineate boundaries between distinct water masses and align with deep-reaching eastward jets. These fronts, identified through historical hydrographic sections, exhibit circumpolar coherence despite meandering and topographic influences, with positions varying by longitude—typically spanning from about 40°S to 60°S. The primary fronts include the Subantarctic Front (SAF), Polar Front (PF), Southern ACC Front (SACCF), and Southern Boundary (SB), each associated with specific water mass transformations driven by air-sea interaction, mixing, and advection.^[17]^[18] The Subantarctic Front (SAF), the northernmost front, separates subtropical waters to the north from cooler subantarctic waters to the south, often splitting into multiple branches and marked by the 10°C surface isotherm or a salinity maximum core. It coincides with the formation and subduction of Subantarctic Mode Water (SAMW), a vertically homogeneous layer (potential temperature ~8–12°C, salinity ~34.6–35.0) produced by winter convection north of the ACC, which ventilates the thermocline and spreads equatorward as a precursor to Antarctic Intermediate Water (AAIW). AAIW, characterized by a salinity minimum (σ_θ ~27.2–27.4 kg/m³), forms from the densest SAMW near the SAF and flows northward, influencing intermediate depths globally.^[17]^[15]^[18] South of the SAF lies the Polar Front (PF), identifiable by the northernmost extent of the 2°C surface isotherm or steep isopycnal slopes, separating the Polar Frontal Zone from Antarctic Surface Waters; it supports strong geostrophic jets with surface speeds averaging ~40 cm/s. This front bounds winter water masses cooled to near-freezing temperatures (~1–2°C) in the mixed layer south of it, overlying Upper Circumpolar Deep Water (UCDW), an oxygen minimum layer (O₂ ~200–220 µmol/kg) that upwells from depths of 1000–2000 m, carrying heat and nutrients equatorward before transformation.^[15]^[17]^[18] The Southern ACC Front (SACCF) and Southern Boundary (SB) define the polar edge of the ACC, with the SACCF often at ~55–60°S tied to the winter sea ice edge and marked by salinity fronts or the -1°C isotherm, while the SB aligns with the continental slope. These southern features separate UCDW from shelf-influenced waters, including nascent Antarctic Bottom Water (AABW) precursors—dense, oxygen-rich bottom waters (θ <0°C, salinity ~34.6–34.8, σ_4 >46.0 kg/m³) formed by brine rejection on the Antarctic shelf and spilling northward. Deeper throughout the ACC, Lower Circumpolar Deep Water (LCDW), a salinity maximum (S ~34.7–34.8) derived from North Atlantic Deep Water, underlies these structures, facilitating meridional exchanges of ~30–50 Sv. Frontal positions shift with wind forcing and eddies, but water mass signatures remain robust tracers of ACC dynamics.^[17]^[18]^[19]

Dynamics and Driving Forces

Momentum Balance and Wind Forcing

The Antarctic Circumpolar Current (ACC) is primarily driven by persistent westerly winds in the Southern Hemisphere, which exert a surface zonal wind stress that inputs eastward momentum into the ocean. These winds, part of the mid-latitude Ferrel cell and modulated by the Southern Annular Mode, provide a year-round forcing that sustains the ACC's intense eastward flow without interruption by continental barriers. The wind stress acts directly on the surface Ekman layer, transferring momentum downward through turbulent mixing and ageostrophic flows, ultimately contributing to the barotropic component of the circulation.^[20] In the vertically integrated zonal momentum balance, the input from surface wind stress is predominantly counteracted by topographic form stress arising from interactions between the flow and the Southern Ocean's rough seafloor topography. Unlike subtropical gyres where Sverdrup balance involves wind stress curl and western boundary currents, the ACC's circumpolar nature lacks eastern closures for viscous dissipation, making form stress—manifest as correlations between sea surface height anomalies and bottom topography—the primary sink for zonal momentum.^[15] This balance holds in both idealized models and observations, where form stress accounts for the majority of the drag, with minor contributions from bottom friction and lateral eddy viscosity.^[21] Mesoscale eddies play a crucial role in facilitating this form stress by generating transient pressure perturbations that correlate with topographic slopes, effectively transferring momentum from the interior to the boundaries. Eddy activity, driven by baroclinic instability of the ACC fronts, enhances the meridional transport of zonal momentum and helps establish the standing meanders and waves necessary for the pressure-topography covariance.^[11] Without sufficient eddy vigor, models show that the ACC transport would accelerate under fixed wind forcing until topography alone cannot balance it, underscoring eddies' importance in maintaining equilibrium. Recent analyses from high-resolution simulations and satellite altimetry confirm that eddy form stress dominates over mean-flow contributions in the momentum closure.^[20]

Mesoscale Eddies and Topographic Effects

Mesoscale eddies, with horizontal scales of 10 to 100 kilometers, play a pivotal role in the dynamics of the Antarctic Circumpolar Current (ACC) by facilitating the transfer of momentum from surface winds to the ocean bottom, thereby contributing to the zonal momentum balance.^[22] These eddies arise primarily from baroclinic and barotropic instabilities in the ACC's strong frontal zones and interact with the mean flow to produce eddy form stress, which counteracts wind-driven Ekman transport and prevents indefinite strengthening of the current under increased westerly winds—a phenomenon known as eddy saturation.^[23] Observations and models indicate that eddy kinetic energy is elevated along the ACC, particularly in regions of intensified shear, where eddies rectify standing meanders into time-mean zonal jets and modulate meridional heat and tracer fluxes.^[24] Topographic features, such as the rugged seafloor in the Drake Passage and around seamounts, significantly influence eddy generation and evolution by steering the ACC flow and inducing stationary waves or meanders.^[11] The interaction between the ACC's vigorous mesoscale eddy field and bottom topography generates form drag, which balances the wind stress input at depth, with eddies extending influence to the seabed and enhancing vertical momentum transfer.^[25] In areas of rough topography, such as the southern boundary of the ACC, eddies promote stirring and frontal sharpening, while suppressing large-scale meridional excursions of the current.^[26] High-resolution models reveal that topographic steering amplifies eddy activity at hotspots, where eddies drive enhanced upwelling of deep waters to the surface, particularly at major bathymetric features like the Kerguelen Plateau.^[27] The combined effects of mesoscale eddies and topography also influence submesoscale processes, including frontogenesis and instability, which further modulate the ACC's three-dimensional structure.^[28] For instance, baroclinic control near topographic obstacles leads to localized eddy upwelling, with eddy energy varying zonally along the ACC rather than uniformly, as evidenced by satellite altimetry and in-situ measurements.^[29] This topographic-eddy interplay ensures that the ACC maintains relative invariance in transport despite climatic wind variations, underscoring the causal importance of bottom friction and eddy dissipation over purely wind-forced acceleration.^[25]

Geological Formation and Evolution

Paleoceanographic Development

The paleoceanographic development of the Antarctic Circumpolar Current (ACC) commenced during the late Eocene to early Oligocene, driven by the progressive opening and deepening of key oceanic gateways separating Antarctica from South America and Australia. The Tasman Gateway between Antarctica and Australia deepened significantly between approximately 35.5 Ma and 30.2 Ma, allowing initial meridional flow restrictions, while the Drake Passage between Antarctica and South America experienced initial shallow connectivity as early as 62–59 Ma due to clockwise rotation of the Antarctic Peninsula, though substantive deepening occurred later.^[30] ^[31] These tectonic events, part of broader Cenozoic plate reconstructions, transitioned the Southern Ocean from a series of semi-enclosed basins to a latitudinally unobstructed circumpolar pathway.^[5] Proxy records from deep-sea sediments provide evidence for the emergence of a proto-ACC in the late Eocene, around 35 Ma, marked by the onset of marine diagenetic chert in drift deposits east of New Zealand, indicative of enhanced silica export and current-influenced deposition. Neodymium isotope signatures from ferromanganese crusts further corroborate circumpolar deep-water flow initiating near the Eocene-Oligocene boundary at ~34 Ma, aligning with the Oi-1 glaciation event and a global δ¹⁸O increase of 1.0–1.5‰ reflecting Antarctic cooling and ice volume growth. Siliceous microfossil assemblages and grain size distributions in Southern Ocean cores reveal strengthened bottom currents and erosion by ~30 Ma, signaling the ACC's role in isolating Antarctica thermally from subtropical heat sources.^[32] ^[33] ^[34] By the late Oligocene (31–26 Ma), sedimentologic and geochemical data indicate the establishment of a more vigorous ACC, with widespread deep-water circulation evidenced by hiatuses in benthic foraminifera records and increased terrigenous input from Antarctic margins. This phase coincided with further gateway deepening, enabling wind-forced momentum transfer across latitudes and reducing poleward heat flux by up to 50% in model reconstructions calibrated to proxy data. Paleomagnetic and stratigraphic analyses constrain the Drake Passage's full barrier removal to this interval, postdating initial rifting but predating Miocene intensifications linked to full Antarctic glaciation.^[35] ^[36] ^[37] Subsequent Miocene evolution saw ACC transport rates increase to near-modern levels around 10 Ma, inferred from enhanced aeolian dust fluxes and opal accumulation rates in Pacific Southern Ocean sediments, reflecting amplified westerly winds and ice-albedo feedbacks rather than solely tectonic reconfiguration. These records underscore the ACC's causal linkage to Southern Ocean restructuring, with multi-proxy syntheses emphasizing gateway tectonics as the primary initiator over atmospheric forcing alone in early phases.^[38] ^[39]

Mechanisms and Ongoing Debates

The Antarctic Circumpolar Current (ACC) originated primarily through tectonic reconfiguration of southern ocean gateways, enabling unimpeded zonal flow around Antarctica. The separation of South America from the Antarctic Peninsula initiated shallow openings in the Drake Passage as early as 62–59 million years ago (Ma), driven by clockwise rotation of the Antarctic Peninsula, but deeper connectivity sufficient for vigorous circumpolar circulation developed later, around 34–30 Ma during the Eocene-Oligocene transition.^[40]^[37] Concurrently, the Tasman Gateway between Australia and Antarctica widened, aligning with Southern Hemisphere westerly winds to facilitate wind-driven transport via Ekman processes and topographic form drag on the ocean floor.^[41] These changes isolated Antarctica thermally, promoting sea-ice formation and deep water production, which reinforced the current through enhanced density gradients and meridional overturning.^[42] Ongoing debates center on the precise timing and depth penetration of the ACC's initiation, with proxy records yielding conflicting estimates spanning from the late Eocene (~34 Ma) to the late Miocene (~8 Ma). Some neodymium isotope analyses from deep-sea sediments indicate a shallow, surface-restricted flow until the late Miocene, when gateway deepening and intensified westerly winds enabled modern-like deep-reaching circulation, challenging earlier links to Eocene-Oligocene glaciation (Oi-1 event at ~33.7 Ma).^[42]^[43] Others, drawing from upper Oligocene piston cores in the South Pacific, support an earlier onset around 26 Ma, evidenced by shifts in grain size and benthic foraminifera indicating stronger bottom currents.^[44] Paleogeographic models further complicate this, suggesting that Australasian continental barriers prevented coherent ACC flow even after initial Drake Passage openings, delaying full development until Oligocene reconfiguration.^[45] Causal linkages to global climate remain contentious, particularly whether the ACC drove Antarctic cooling or responded to it via pre-existing atmospheric shifts toward stronger westerlies. While gateway openings are causally tied to thermal isolation and carbon sequestration via upwelling, simulations indicate that without aligned wind forcing, circumpolar flow remained weak despite tectonic changes.^[46] Recent reconstructions using eccentricity-modulated proxies highlight periodic ACC strengthening over the past 5 Ma, but debates persist on the relative roles of deep convection versus wind stress in sustaining transport volumes exceeding 130 Sverdrups today.^[47] These uncertainties underscore the need for integrated proxy-model approaches, as sediment records may reflect local rather than basin-wide dynamics, and early ACC proxies risk conflating zonal jets with full circumpolar coherence.^[48]

Integration with Global Ocean and Climate Systems

Linkages to Thermohaline Circulation

The Antarctic Circumpolar Current (ACC) integrates with the global thermohaline circulation (THC) primarily through the Southern Ocean's residual meridional overturning, where wind-driven upwelling elevates deep waters to the surface, closing the upper limb of the THC. Westerly winds induce Ekman transport that tilts isopycnals, facilitating the ascent of North Atlantic Deep Water (NADW) along density surfaces such as 27.6 kg m⁻³, with eddy fluxes compensating to sustain a net overturning of approximately 10 Sverdrups (Sv).^[49] This process balances NADW formation in the North Atlantic, enabling the THC's pole-to-pole redistribution of heat and buoyancy without requiring extensive diapycnal mixing.^[49] In the lower overturning cell, the ACC influences Antarctic Bottom Water (AABW) dynamics by supplying deep branches that feed abyssal boundary currents, allowing dense shelf waters to ventilate the ocean interior northward. Deep waters diverging from the ACC fill bottom layers across basins, linking AABW export to global deep circulation pathways.^[50] Mesoscale eddies within the ACC further mediate cross-frontal exchanges, modulating water mass transformations essential for THC stability.^[51] Variability in ACC strength directly impacts THC components; enhanced ACC transport, as observed in interglacials with grain size proxies indicating up to 43% flow reduction during glacials, alters deep ventilation, salinity gradients, and nutrient cycling by connecting Pacific-Atlantic exchanges via the "cold water route."^[52] Modeling studies demonstrate that a strengthened ACC amplifies Southern Ocean overturning through intensified Ekman pumping, thereby reinforcing the Atlantic Meridional Overturning Circulation (AMOC) via augmented upwelling of THC return flows.^[53] The ACC's basin-spanning nature, enabled by Drake Passage, underscores its role in permitting the THC's inter-oceanic continuity, with theoretical frameworks tying ACC vigor to overall overturning closure.^[49]

Transport of Heat, Momentum, and Biogeochemical Tracers

The Antarctic Circumpolar Current (ACC) maintains a mean full-depth volume transport of approximately 140 Sverdrups (Sv; 1 Sv = 10^6 m^3 s^{-1}), derived from combined in situ measurements and satellite altimetry over multi-year periods, with values ranging from 134 Sv to 141 Sv depending on reference levels and observational methods.^[54]^[4] This zonal eastward flow, unconstrained by continental boundaries, primarily redistributes properties longitudinally but enables meridional exchanges through frontal variability, mesoscale eddies, and Ekman processes, influencing global climate and ocean biogeochemistry. Heat transport across the ACC occurs predominantly via mesoscale eddies and the residual overturning circulation, as the mean zonal flow yields negligible net meridional heat flux in a steady-state circumpolar system. Observations from current- and pressure-recording inverted echo sounders in Drake Passage over four years yield statistically stable estimates of eddy heat flux, highlighting eddies as the dominant mechanism for cross-frontal heat redistribution. Southward heat fluxes associated with deep overturning cells reach 0.033 petawatts (PW; 1 PW = 10^{15} W) at 56°S based on 1994 hydrographic data, though short-term variability amplifies this to higher values in five-day means. The Southern Ocean's heat budget south of 60°S reflects a net oceanic loss of 0.5–0.6 PW to the atmosphere, sustained by convergence of northward heat transport within the ACC envelope.^[55]^[56]^[7] Momentum transport in the ACC arises from westerly wind stress at the surface, which inputs zonal momentum and is balanced by form stress over abyssal topography and eddy Reynolds stresses, minimizing reliance on frictional dissipation. Wind stress curl generates Ekman divergence north of the current, driving upwelling and contributing to the Sverdrup balance, while enhanced winds accelerate the ACC through increased eddy activity that saturates further transport gains. Model simulations of spin-up in rotating channels demonstrate form stress establishment within months, analogous to ACC dynamics where topographic steering and eddy fluxes close the momentum budget.^[15]^[57]^[58] Biogeochemical tracers, including macronutrients (nitrate, phosphate, silicate), dissolved inorganic carbon (DIC), and oxygen, are transported zonally by the ACC's mean flow while experiencing meridional fluxes via eddies and Ekman divergence, which upwell deep reservoirs to the surface. Autonomous biogeochemical floats over six seasonal cycles reveal Ekman transport from subtropical gyres supporting net DIC outgassing in ACC zones, with annual means modulated by iron-limited productivity and seasonal upwelling. Eddy-induced DIC transport across ACC fronts compensates for weak mean-flow contributions, as inferred from heat and salt analogies, sustaining Southern Ocean carbon uptake variability. Nutrient distributions align with ACC fronts, where Circumpolar Deep Water intrusions elevate surface macronutrients, fueling phytoplankton blooms and global export of organic carbon.^[59]^[60]^[61]

Biological and Ecological Interactions

Phytoplankton Productivity and Blooms

The Antarctic Circumpolar Current (ACC) flows through High-Nutrient Low-Chlorophyll (HNLC) waters of the Southern Ocean, where phytoplankton productivity remains low despite elevated macronutrient concentrations, primarily due to iron (Fe) limitation.^[62] This limitation constrains primary production rates to approximately 50-120 g C m⁻² yr⁻¹ across much of the ACC domain, far below levels in iron-replete regions.^[63] Light availability further modulates growth, with deep mixing in winter suppressing division rates and delaying bloom initiation until austral summer.^[64] Phytoplankton blooms emerge in the ACC where episodic iron inputs overcome limitation, enabling rapid biomass accumulation. Sources include atmospheric dust, sub-Antarctic island sediments, continental shelf sediments transported via eddies, and deep-sea hydrothermal vents.^[65] For instance, a persistent massive bloom in the Pacific sector of the ACC, spanning ~160,000 km², is fueled by dissolved iron from the East Pacific Rise vents, reaching chlorophyll-a concentrations up to 1-2 mg m⁻³ and net primary production ~300% higher than surrounding HNLC waters.^[66] Similarly, blooms downstream of islands like South Georgia or the Crozet Plateau benefit from Fe-enriched runoff and upwelling, supporting diatom-dominated assemblages with enhanced carbon export fluxes exceeding 100 mg C m⁻² d⁻¹ during peak events.^[65]^[67] ACC dynamics, including frontal zones and mesoscale eddies, influence bloom spatial patterns and intensity by promoting nutrient upwelling and lateral Fe transport. The Antarctic Polar Front serves as a biogeochemical boundary, separating haptophyte-dominated communities northward from diatom-rich blooms southward, as evidenced by pigment analyses over 26 years showing circumpolar coherence in community structure.^[68] Seasonal blooms typically initiate post-sea ice retreat, peaking in December-February with satellite-observed chlorophyll-a anomalies >0.5 mg m⁻³ in productive hotspots.^[69] Wind-driven Ekman buoyancy fluxes can enhance Fe supply to surface waters, sustaining elevated productivity in specific ACC segments.^[63] Recent observations indicate variability in bloom phenology linked to ACC shifts and climate forcing, with poleward migration of fronts potentially expanding bloom habitats, though iron scarcity persists as the primary constraint.^[69] These blooms underpin the Southern Ocean biological pump, sequestering ~0.1-0.2 Pg C yr⁻¹ regionally, but their Fe dependence underscores sensitivity to changing dust fluxes or circulation patterns.^[69]

Broader Marine Ecosystem Dynamics

The Antarctic Circumpolar Current (ACC) structures the Southern Ocean into biogeographic provinces defined by its major fronts—the Subtropical, Subantarctic, Polar, and Southern ACC Fronts—which create gradients in temperature, salinity, nutrient availability, and mixing intensity, supporting distinct pelagic and benthic communities. North of the Polar Front, warmer waters harbor more diverse subantarctic assemblages including commercially important fish like Patagonian toothfish (Dissostichus eleginoides), while south of it, colder, nutrient-enriched conditions foster endemic Antarctic biota adapted to high-latitude conditions.^[70] This zonal differentiation arises from the ACC's role as a dynamic barrier, limiting meridional exchange and promoting evolutionary divergence, with over 90% endemism in Antarctic shelf species attributable to isolation by the current's flow.^[71] Eddy activity and frontal meandering within the ACC enhance vertical nutrient fluxes through Ekman divergence and diapycnal mixing, supplying macronutrients like nitrate and silicate from intermediate depths to the surface layer, which sustains primary production rates averaging 50–100 g C m⁻² yr⁻¹ across the circumpolar domain despite pervasive iron limitation. These nutrient dynamics underpin the region's short, intense food chains, where diatoms and other phytoplankton serve as the primary energy source for herbivores such as Antarctic krill (Euphausia superba), whose biomass acoustic surveys estimate at 60–155 million tonnes circumpolarly. Krill, in turn, channel energy to mid-trophic mesopelagic fishes (e.g., Electrona antarctica) and higher predators, comprising up to 70% of the diet for species like Adélie penguins (Pygoscelis adeliae) and crabeater seals (Lobodon carcinophaga), thereby stabilizing trophic transfers in a system characterized by low species diversity but high biomass.^[72]^[73]^[74] The ACC's transport of organic matter and larvae circum-Antarctica fosters connectivity among populations, enabling gene flow in broadcast-spawning invertebrates and fishes while eddies redistribute patches of prey, influencing foraging ranges of top predators tracked via satellite, which aggregate at productive frontal zones covering ~20% of the Southern Ocean surface. However, interannual variability in ACC strength, driven by wind forcing, modulates upwelling efficiency and sea-ice extent, indirectly affecting krill recruitment; for instance, reduced winter sea ice since the 1980s has correlated with southward krill displacements of up to 1° latitude in some sectors, altering predator-prey interactions and potentially destabilizing local food webs. Conservation measures under the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) cap krill harvest at precautionary levels below 1% of surveyed biomass to preserve these dynamics, recognizing the current's foundational role in sustaining ~50% of global seabird populations and key commercial fisheries.^[75]^[76]^[77]

Variability and Long-Term Changes

Observed Transport and Frontal Shifts

The Antarctic Circumpolar Current (ACC) total transport, often proxied by measurements through Drake Passage, has been quantified using moored arrays and ship-based observations. The DRAKE program (2006–2009) recorded a total transport of 141 ± 2.7 Sv, comprising 136 Sv baroclinic and 5 Sv barotropic components derived from current meters and satellite altimetry.^[78] The subsequent cDrake program (2007–2011) estimated 173.3 ± 10.7 Sv total transport, with 127.7 Sv baroclinic and 45.6 Sv barotropic, highlighting potential under-sampling of deep recirculations in earlier efforts but also underscoring methodological sensitivities in isolating barotropic contributions.^[78] Basin-wide estimates from ARGO floats and altimetry indicate interannual variability on the order of 10–20 Sv, yet observations over the satellite era (post-1990s) show no robust evidence of a sustained monotonic increase in total transport, despite regional enhancements in eddy kinetic energy.^[79] Satellite altimetry data from 1992–2011 reveal pronounced meridional variability in ACC frontal positions, with individual fronts exhibiting displacements of up to 2° latitude (~220 km) on interannual timescales, particularly in the Southeast Pacific where fluctuations correlate with ENSO (r up to -0.8) and SAM (r up to 0.55) indices.^[80] In the Southeast Indian sector (75°–150°E), a southward (poleward) drift is observed, amounting to 100–400 km over two decades for fronts like the Subantarctic Front, with maximum shifts of ~2° at 105°E potentially linked to subtropical gyre expansion.^[80] Seasonal cycles manifest as southward positions in summer and northward in winter, while overall altimetry assessments provide only weak support for a global southward migration of the ACC axis, emphasizing eddy-driven adjustments over uniform trends.^[79] These shifts occur amid meanders and ring formations, with lateral frontal movements reaching 100 km in as little as 10 days based on hydrographic surveys.^[15]

Drivers: Natural Variability vs. Anthropogenic Influences

The Antarctic Circumpolar Current (ACC) exhibits variability in transport and position driven primarily by fluctuations in Southern Hemisphere westerly winds, with the Southern Annular Mode (SAM) serving as the dominant atmospheric mode influencing these winds on intraseasonal to decadal timescales.^[81]^[82] Positive phases of the SAM, characterized by stronger and more poleward-shifted westerlies, correlate with increased ACC transport through Drake Passage, with observed interannual variations of up to 10-15 Sverdrups (Sv) linked to this mode.^[83] Natural internal variability, including eddy interactions and ocean-atmosphere coupling, further modulates ACC strength, as evidenced by paleoceanographic records spanning five million years that reveal no long-term linear trend in flow intensity despite orbital and tectonic forcings.^[47] Anthropogenic influences, particularly stratospheric ozone depletion and rising greenhouse gas concentrations, have contributed to a multidecadal positive trend in the SAM since the late 20th century, intensifying westerly winds by approximately 15-40% over the Southern Ocean and thereby enhancing ACC transport.^[84]^[79] Ozone depletion, peaking in the 1990s-2000s, shifted the westerly jet poleward and strengthened it, with modeling attributing up to 50% of the observed SAM trend to this factor before greenhouse gas effects dominated post-2000.^[85]^[86] Instrumental records from Drake Passage indicate a net ACC transport increase of about 10-20% since the 1990s, consistent with wind-driven acceleration, though eddy compensation in models limits the full wind-forcing response to roughly 10-20 Sv per unit wind stress doubling.^[87]^[88] Distinguishing natural from anthropogenic drivers remains challenging due to overlapping timescales and internal variability, with recent analyses suggesting that while ozone and greenhouse forcing explain the secular strengthening trend, short-term fluctuations (e.g., in sea ice or frontal positions) are predominantly natural, as internal atmospheric dynamics can produce similar anomalies without external forcing.^[89]^[90] Paleorecords indicate that pre-industrial ACC variability, driven by natural SAM-like modes and Southern Ocean eddies, encompassed ranges comparable to 20th-century changes, implying anthropogenic signals may amplify but not solely originate recent shifts.^[47]^[91] Peer-reviewed modeling underscores that ozone recovery projected for the 2060s could partially offset future wind intensification from greenhouse gases, potentially stabilizing or reversing ACC trends, though uncertainties in eddy parameterization and deep ocean response persist.^[85]^[92]

Research Approaches and Key Findings

Historical and Observational Methods

Early observations of the Antarctic Circumpolar Current (ACC) relied on ship-based hydrographic measurements, primarily through expendable bathythermographs (XBTs) and conductivity-temperature-depth (CTD) profiles, which provided initial estimates of volume transport by integrating velocity profiles across sections like Drake Passage, the current's narrowest constriction.^[4] These methods, initiated in the mid-20th century, faced challenges from sparse sampling and assumptions about geostrophic balance, yielding variable transport estimates ranging from 100 to 200 Sverdrups (Sv).^[15] A pivotal advancement came during the 1979 Drake Passage experiment (DRAKE79), which deployed moored current meters and hydrographic lines for a full year, establishing a canonical baroclinic transport of approximately 134 Sv, though total transport including barotropic components required additional corrections.^[93] Subsequent historical efforts incorporated bottom pressure recorders (BPRs) to capture barotropic fluctuations, extending the 1979 time series and revealing transport variability linked to wind forcing and eddies.^[94] The World Ocean Circulation Experiment (WOCE) in the 1990s marked a systematic shift, employing repeat full-depth hydrographic sections across Southern Ocean choke points, combined with moored arrays, to resolve meridional overturning and ACC structure with improved accuracy.^[10] These shipborne methods, often supplemented by lowered acoustic Doppler current profilers (LADCPs) for absolute velocities, provided baseline data but were limited by logistical constraints in the harsh Southern Ocean environment.^[95] Modern observational techniques build on these foundations with sustained in-situ networks, including long-term moored arrays in Drake Passage equipped with upward-looking acoustic Doppler current profilers (ADCPs) and pressure sensors, which from 2007 to 2011 achieved unprecedented horizontal resolution and confirmed mean transports around 150-160 Sv with reduced uncertainty.^[95] ^[96] Satellite altimetry, operational since the TOPEX/Poseidon mission in 1992, derives surface geostrophic currents from sea surface height anomalies, enabling basin-wide mapping of ACC fronts and mesoscale variability, though it underestimates deep transport without in-situ calibration.^[10] The Argo float array, deployed since 2000, contributes temperature and salinity profiles to 2,000 meters, aiding eddy kinetic energy estimates and frontal positioning, but its sparse coverage in the ACC limits full-depth transport quantification.^[97] Complementary ship-of-opportunity programs, such as XBT lines, provide ongoing transects for monitoring upper-ocean thermal structure and validating remote sensing.^[4] These integrated approaches underscore the ACC's dynamic nature, with ongoing refinements addressing gaps in deep circulation via initiatives like Deep Argo extensions.^[98]

Numerical Modeling and Future Projections

Numerical models of the Antarctic Circumpolar Current (ACC) primarily employ ocean general circulation models (OGCMs) and coupled climate models to simulate its dynamics, incorporating wind forcing, eddy processes, and topographic interactions.^[15] High-resolution eddy-resolving models, such as FRAM and POP, reveal the ACC's filamentary jet structure and eddy kinetic energies reaching 15–27 cm/s, highlighting eddies' role in momentum transfer and meridional overturning.^[99] These models demonstrate that eddy fluxes compensate for wind-driven momentum, maintaining the ACC's balance in idealized channel configurations.^[100] Coupled Model Intercomparison Project Phase 6 (CMIP6) ensembles have improved ACC transport simulations, converging toward observed strengths of approximately 130–150 Sverdrups, with better representation of wind stress and density gradients compared to CMIP3 and CMIP5.^[101] ^[102] However, persistent biases include overestimated Southern Ocean surface temperatures and underestimated freshening trends, which affect projections of circulation changes.^[103] Quasigeostrophic and stereographic projection models further elucidate basin-scale influences and submesoscale processes, such as Rossby waves, that modulate ACC variability.^[104] ^[105] Future projections from CMIP6 and regional models indicate potential ACC weakening rather than strengthening under high-emissions scenarios (SSP5-8.5), with transport declining up to 20% by 2050 due to ice-shelf meltwater-induced freshening that stratifies surface waters and reduces sinking.^[9] This freshening overrides historical wind-driven intensification from positive Southern Annular Mode trends, potentially disrupting global heat and carbon uptake by altering Southern Ocean overturning.^[106] ^[107] Some simulations project poleward shifts of ACC fronts by up to 5°, enhancing Circumpolar Deep Water intrusion onto shelves and accelerating ice loss, though natural orbital forcings may induce northward migrations counteracting anthropogenic signals.^[108] ^[109] Uncertainties persist in eddy parameterization and meltwater feedbacks, as CMIP6 underestimates observed freshening and surface cooling, implying models may overestimate ACC resilience to polar amplification.^[107] High-resolution projections suggest increased eddy activity in high latitudes under warming, potentially amplifying nutrient upwelling but complicating biogeochemical cycles.^[110] These dynamics underscore the ACC's sensitivity to Southern Ocean stratification, with implications for global meridional overturning circulation stability.^[53]

References

[1]
Antarctic Circumpolar Current (ACC)
The only current that flows completely around the globe is the Antarctic Circumpolar Current (ACC), the dominant circulation feature of the Southern Ocean.
[2]
Dynamics of the Pacific Antarctic Circumpolar Current (Full Book)
Jul 18, 2021 · The Antarctic Circumpolar Current (ACC), the world's strongest zonal current system, connects all three major ocean basins of the global ocean.
[3]
[PDF] Observations of Upwelling and Downwelling Around Antarctica ...
Jun 10, 2022 · The Antarctic Circumpolar Current (ACC) is driven by the prevailing zonal westerlies. The effect of these winds is not only to impart zonal ...
[4]
Volume transport of the Antarctic Circumpolar Current: Production ...
Jul 14, 2014 · The full-depth volume transport has a mean of 141 Sv (standard error of the mean 2.7 Sv), a standard deviation (std) of 13 Sv, and a range of ...
[5]
[PDF] and Development of the Antarctic circumpolar current
The largest ocean current in the world, it averages about 130 Sv (106 m3s-1) volume transport through Drake Passage. It is mainly or entirely wind-driven, but ...Missing: facts | Show results with:facts
[6]
XBT Analysis - Antarctic Circumpolar Current variability at ~0°E
The Antarctic Circumpolar Current (ACC) is a major conduit for interoceanic exchange of heat and salt. The variability of this current is largely determined by ...
[7]
[PDF] Heat flux carried by the Antarctic Circumpolar Current mean flow
heat flux problem in the Antarctic Circumpolar Current (ACC). The ACC is defined as a circumpolar band consisting of mean streamlines passing through Drake ...
[8]
Optimal Precursors Triggering Sudden Shifts in the Antarctic ...
Nov 16, 2021 · As the strongest ocean current in the world, the Antarctic Circumpolar Current (ACC) flows powerfully eastward around Antarctica in the ...
[9]
Decline of Antarctic Circumpolar Current due to polar ocean ...
Abstract. The Antarctic Circumpolar Current (ACC) is the world's strongest ocean current and plays a disproportionate role in the climate system due to its role ...
[10]
[PDF] The Antarctic Circumpolar Current System - EPIC
The Antarctic Circumpolar Current (ACC) is a strong eastward flow connecting ocean basins, with two major cores: the Subantarctic and Polar Front.
[11]
[PDF] eddies and jets in the Antarctic Circumpolar Current
The ACC is both the longest and strongest current in the ocean carrying a volume transport of 130 Sv (1 Sverdrup. =1Sv=1×106 m3 s−1) along a 24 000 km path ...
[12]
Antarctic Circumpolar Current Dynamics at the Pacific Entrance to ...
Jun 11, 2020 · The DP is located between South America and Antarctica; it is 850 km wide and represents the major geographical constriction for the transport ...Missing: longitude | Show results with:longitude<|separator|>
[13]
Fronts of the Antarctic Circumpolar Current - GIS data - CMR Search
This line shapefile represents the following features of the Antarctic Circumpolar Current: Subtropical Front (STF); Subantarctic Front (SAF); Southern ...
[14]
[PDF] Note on the Dynamics of the Antarctic Circumpolar Current
At the narrowest sec- tion, Drake Passage, the boundaries are at 65' S and 55' S latitudes, and T = 101s g sec-1. The observed transport is 1014 g sec-1. The ...
[15]
[PDF] The Physics of the Antarctic Circumpolar Current
These fronts meander, and current rings form from them; lateral frontal shifts of as much as 100 km in 10 days have been observed. The volume transport of the ...Missing: facts | Show results with:facts
[16]
The effect of Antarctic Circumpolar Current transport on the frontal ...
The mean width of the PF and the SAF are approximately between 40 km and 60 km Nowlin and Clifford, 1982, Gille, 1994, Moore et al., 1997. The width of SACCF is ...
[17]
[PDF] The Antarctic Circumpolar Current System - EPIC
The ACC consists of a number of circumpo- lar fronts, which correspond to water mass bound- aries as well as deep-reaching jets of eastward flow (Orsi et al., ...
[18]
On the meridional extent and fronts of the Antarctic Circumpolar ...
Large-scale features of the Antarctic Circumpolar Current (ACC) are described using all historical hydrographic data available from the Southern Ocean.
[19]
Observations of the Antarctic Circumpolar Current Over the Udintsev ...
May 22, 2019 · The five Antarctic Circumpolar Current fronts (NB, SAF, PF, SACCF, and SB) from Figure 3 are superposed on prominent topographic features.
[20]
Maintenance of the Zonal Momentum Balance of the Antarctic ...
The vertically integrated zonal momentum balance of the Antarctic Circumpolar Current (ACC) is dominated by wind stress at the surface and topographic form ...
[21]
The Southern Ocean Momentum Balance - AMS Journals
Oct 1, 1997 · In the momentum budget a strong zonal wind stress drives the eastward flowing Antarctic Circumpolar Current (ACC). No substantial continental ...
[22]
The Role of Mesoscale Eddies in the Rectification of the Southern ...
Eddies are thus believed to act as a buffer against wind changes and, when this effect is properly represented in models, the isopycnal slope, ACC strength, and ...
[23]
[PDF] The Role of Eddies in Determining the Structure and Response of ...
It demonstrates that me- soscale eddies play a critical role in determining the connection between the Southern Ocean momentum and buoyancy budgets. JPO2980 ...
[24]
“Eddy” Saturation of the Antarctic Circumpolar Current by Standing ...
Abstract It is now well established that changes in the zonal wind stress over the Antarctic Circumpolar Current ... mesoscale eddies, rather than time-mean flows ...
[25]
[PDF] Minimal change in Antarctic Circumpolar Current flow speeds
surface is balanced at depth by topographic form drag, relative invariance of the bottom ... Mesoscale eddies associated with the ACC. 54 extend to the seabed16, ...
[26]
Stirring across the Antarctic Circumpolar Current's southern ... - OS
Oct 18, 2023 · In this study, the southern boundary in the Weddell Sea sector at the prime meridian is surveyed for the first time in high resolution over 2 months.Missing: longitude | Show results with:longitude
[27]
Spiraling pathways of global deep waters to the surface of ... - Nature
Aug 2, 2017 · Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ...
[28]
Three-Dimensional Structure of Mesoscale Eddies and Their Impact ...
May 23, 2024 · Mesoscale eddies are prevalent in the Antarctic Circumpolar Current (ACC), especially in the hot spots with rough topography [4]. The topography ...
[29]
Baroclinic Control of Southern Ocean Eddy Upwelling Near ...
Mar 26, 2022 · In the Southern Ocean, mesoscale eddies ... Eddy energy (EE) is not uniformly distributed along the Antarctic Circumpolar Current (ACC).
[30]
Evidence for late Oligocene establishment of the Antarctic ...
Timing of TG deepening beginning around 35.5 Ma and completed by ∼30.2 Ma is well constrained [2] and it has been argued that the widespread Marshall ...
[31]
The Initial Opening of the Drake Passage Occurred During ca. 62 ...
Apr 6, 2025 · Our new findings reveal that the continents separated between ca. 62 and 59 Ma, as a result of the clockwise rotation of the Antarctic Peninsula ...
[32]
Late Eocene onset of the Proto-Antarctic Circumpolar Current - Nature
Jul 12, 2019 · We present new seismic evidence of widespread Late Eocene to Oligocene marine diagenetic chert in sedimentary drift deposits east of New Zealand.
[33]
Pacific Ocean and Cenozoic evolution of climate - Lyle - AGU Journals
Apr 19, 2008 · There are three main age groupings of geologic evidence related to the ACC. First, Scher and Martin [2006] investigated Nd isotopes in the ...
[34]
Onset and role of the Antarctic Circumpolar Current - ScienceDirect
It was commonly considered that the ACC started at the Eocene–Oligocene boundary and caused the full development of Antarctic continental glaciation by ...
[35]
Drake Passage gateway opening and Antarctic Circumpolar Current ...
Jun 5, 2021 · Antarctic Circumpolar Current likely started during this 31 to 26 Ma time interval. The Antarctic Circumpolar Current onset did not trigger the ...
[36]
[PDF] Drake Passage Gateway opening and Antarctic Circumpolar Current
The Drake Passage gateway opened and deepened between 31-26 Ma, which is the timing of the Antarctic Circumpolar Current (ACC) onset.
[37]
Drake Passage and the Scotia arc: A tortuous space-time gateway ...
Apr 1, 2014 · The opening of Drake Passage between South America and the Antarctic Peninsula may have removed the last barrier for the wind-driven Antarctic Circumpolar ...<|separator|>
[38]
The development of the modern Antarctic Circumpolar Current ...
The onset of the Antarctic Circumpolar Current (ACC) was solely triggered by the opening and deepening of Southern Ocean Gateways.
[39]
Paleoceanography and ice sheet variability offshore Wilkes Land ...
Jul 11, 2018 · The timing and impact of onset of Antarctic Circumpolar Current (ACC) on climate and Antarctic ice are unclear. We reconstruct late Eocene ...<|control11|><|separator|>
[40]
The Initial Opening of the Drake Passage Occurred During ca. 62 ...
Apr 6, 2025 · 62 and 59 Ma, caused by the clockwise rotation of the Antarctic Peninsula. The separation induced the initial opening of the Drake Passage and ...
[41]
Onset of Antarctic Circumpolar Current 30 million years ago as ...
Aug 9, 2025 · ... ... In contrast, recent research by Scher et al. (2015) concluded an onset date of 30 Ma for the ACC after an initial westward flow through ...
[42]
Late Miocene onset of the modern Antarctic Circumpolar Current
Jan 18, 2024 · One precondition for the inception of the ACC is the deep tectonic opening of two gateways that blocked circumpolar flow in the geological past ...
[43]
reconciling the Cenozoic history of the Antarctic Circumpolar Current
Abstract. The timing of the onset of the Antarctic Circumpolar Current (ACC) is a crucial event of the Cenozoic because of its cooling and isolating effect ...
[44]
(PDF) Late Oligocene initiation of the Antarctic Circumpolar Current
Aug 6, 2025 · However, estimates for ACC initiation range over 20 m.y., from the middle Eocene to early Miocene. A new piston core of upper Oligocene to ...
[45]
Paleogeographic controls on the onset of the Antarctic circumpolar ...
Sep 10, 2013 · Here we present climate model results that show that a coherent ACC was not possible during the Oligocene due to Australasian paleogeography.
[46]
The Drake Passage opening from an experimental fluid dynamics ...
The opening of the southern seaways enabled the development of the Antarctic Circumpolar Current (ACC) which inhibits warm surface currents to transport ...
[47]
Five million years of Antarctic Circumpolar Current strength variability
Mar 27, 2024 · The largest decrease in glacial ACC flow occurred in the SAZ, the zone of strongest current transport under modern conditions. Within the SAZ, ...Missing: facts | Show results with:facts
[48]
Absence of a strong, deep-reaching Antarctic Circumpolar Current ...
Despite the critical role of today's strong deep-reaching ACC flow in the global ocean circulation and Earth's climate, there is still an ongoing debate ...
[49]
[PDF] Closure of the meridional overturning circulation through Southern ...
Feb 26, 2012 · strength of the ACC, and how the Southern Ocean operated in past ... Effect of Drake Passage on the global thermohaline circulation. Deep ...
[50]
Circulation, mixing, and production of Antarctic Bottom Water
It is clear that deep waters branching off the Antarctic Circumpolar Current supply all of the observed Abyssal Boundary Currents, filling the bottom layers ...
[51]
Observing the Local Emergence of the Southern Ocean Residual ...
Mar 7, 2019 · The role of mesoscale turbulence in maintaining the mean buoyancy structure and overturning circulation of the Southern Ocean is investigated
[52]
Orbital- and millennial-scale Antarctic Circumpolar Current ... - Nature
Jun 24, 2021 · It connects wind-driven surface circulation and thermohaline deep and bottom water circulation with impacts on global salinity, nutrients ...<|separator|>
[53]
Impacts of Strengthened Antarctic Circumpolar Current on the ...
Mar 13, 2025 · Owing to the strengthened ACC, the Southern Ocean Meridional Overturning ... Effect of Drake Passage on the global thermohaline circulation.
[54]
Transport and variability of the Antarctic Circumpolar Current in ...
The average yearlong absolute transport is 134 Sv, and the standard deviation of the average is 11.2 Sv; the error of the average transport is 15 to 27 Sv. We ...
[55]
Estimates of Eddy Heat Flux Crossing the Antarctic Circumpolar ...
The 4-yr measurements by current- and pressure-recording inverted echo sounders in Drake Passage produced statistically stable eddy heat flux estimates.
[56]
Meridional heat transport across the Antarctic Circumpolar Current ...
The heat fluxed southward by the deep overturning cell using the annual mean field for 1994 at 56S is 0.033 PW, but the 5-day mean fields give a larger heat ...<|separator|>
[57]
Establishment of momentum balance by form stress in a wind-driven ...
... Antarctic Circumpolar Current. Initially, the force balance resembles Ekman ... wind stress curl and are defined by the background planetary PV field ...
[58]
Acceleration of the Antarctic Circumpolar Current by Wind Stress ...
Dec 1, 2013 · We have demonstrated that the Antarctic Circumpolar Current transport can be influenced by changes in the surface stress both along the ACC, ...Missing: facts | Show results with:facts<|separator|>
[59]
Carbon Outgassing in the Antarctic Circumpolar Current Is ...
Nov 1, 2023 · We investigate the processes that determine the annual mean and seasonal cycle of DIC fluxes in two different zones of the Southern Ocean.
[60]
(PDF) Eddy‐induced carbon transport across the Antarctic ...
Eddies play a critical role in the meridional transport of heat and salt across the Antarctic Circumpolar Current. However, observations of the heat and salt ...
[61]
The Southern Ocean Hub for Nutrients, Micronutrients, and Their ...
May 8, 2024 · The distribution of biogeochemical properties in the surface Southern Ocean is strongly guided by the Antarctic Circumpolar Current (ACC), ...
[62]
Southern Ocean Iron Limitation of Primary Production between Past ...
Primary production in the Southern Ocean highly depends on phytoplankton and has been reported to be limited by the availability of the micronutrient iron.
[63]
Wind‐Driven Iron Supply by Ekman Buoyancy Flux Enhances ...
Aug 3, 2025 · Controls of primary production in two phytoplankton blooms in the Antarctic circumpolar current. Deep Sea Research Part II: Topical Studies ...
[64]
Seasonal modulation of phytoplankton biomass in the Southern Ocean
Our analysis reveals seasonal phytoplankton accumulation ('blooming') events occurring during periods of declining modeled division rates.
[65]
Interaction of the Antarctic Circumpolar Current With Seamounts ...
In the Antarctic Circumpolar Current region of the Southern Ocean, the massive phytoplankton blooms stemming from islands support large trophic chains.
[66]
Massive Southern Ocean phytoplankton bloom fed by iron of ...
Feb 22, 2021 · Here the authors show that iron from hydrothermal vents fuels massive phytoplankton blooms in the Southern Ocean that have recurred in the same location for ...
[67]
(PDF) Controls of primary production in two phytoplankton blooms in ...
Aug 6, 2025 · The Antarctic Circumpolar Current has a high potential for primary production and carbon sequestration through the biological pump. In the ...<|control11|><|separator|>
[68]
Twenty-six years of phytoplankton pigments reveal a circumpolar ...
Feb 20, 2024 · The analysis confirms that the Antarctic Polar Front (APF) is a circumpolar phytoplankton class boundary, separating haptophyte dominated communities to the ...
[69]
Widespread changes in Southern Ocean phytoplankton blooms ...
Aug 28, 2023 · Climate change is expected to elicit widespread alterations to nutrient and light supply, which interact to influence phytoplankton growth ...
[70]
Biogeography of the Southern Ocean: environmental factors driving ...
May 10, 2021 · Using our current knowledge of the fine structure of the Antarctic Circumpolar Current, we compared effects of four hydrological fronts, i.e., ...Missing: peer- | Show results with:peer-
[71]
The Antarctic Circumpolar Current isolates and connects
The Antarctic Circumpolar Current (ACC) is an unusually strong barrier to the north‐south exchange of organisms owing to its thermal and density‐driven ...1. Introduction · 2. Materials & Methods · 3. Results
[72]
Identification of Southern Ocean Upwelling From Biogeochemical ...
May 31, 2025 · Our analysis reveals that upwelling is strongest at the southern latitudes of the Antarctic Circumpolar Current. We also partially endorse ...
[73]
[PDF] CCAMLR and Antarctic Krill: Ecosystem Management Around the ...
Acoustic surveys have estimated the circumpolar biomass of Antarctic krill to be from 60 to 155 million tonnes.3 The dis- tribution of Antarctic krill ...
[74]
Two scales of distribution and biomass of Antarctic krill (Euphausia ...
Aug 24, 2022 · Krill biomass for the eastern sector of CCAMLR Division 58.4.2 is estimated at 4.2 million tonnes with areal biomass densities of 6.4 gm-2.
[75]
Massive circumpolar biomass of Southern Ocean zooplankton ...
Sep 9, 2022 · The purpose of this paper is to provide a wider appraisal of the base of the food web, by conducting a circumpolar-scale, comparative biomass ...
[76]
Antarctic krill head south – Australian Antarctic Program (News 2023)
Dec 19, 2023 · Some populations of Antarctic krill are shifting south, closer to Antarctica, as ocean warming and sea-ice changes alter their habitat.
[77]
Commission for the Conservation of Antarctic Marine Living Resources
Results indicate that the estimated krill biomass in the Scotia Sea may be as high as 192.4 Mt (CV=11.7%), or as low as 109.4 Mt (CV=10.4%), depending solely on ...
[78]
Antarctic Circumpolar Current Transport Through Drake Passage ...
Jun 17, 2020 · The two most recent observational programs in Drake Passage, DRAKE and cDrake, yielded transports of 141 and 173.3 Sv, respectively.Abstract · Introduction · Numerical Simulation and... · Model-Data Comparison
[79]
Temporal Changes in the Antarctic Circumpolar Current
Dec 11, 2016 · In addition, submarine canyons and winds are hypothesized to be critical for transporting CDW across the continental shelves. The specific ...Missing: width | Show results with:width<|separator|>
[80]
On the Variability of Antarctic Circumpolar Current Fronts Inferred ...
Antarctic Circumpolar Current (ACC) fronts, defined as water mass boundaries, have been known to respond to large-scale atmospheric variabilities ...
[81]
Variability of Antarctic circumpolar transport and the Southern ...
Dec 31, 2004 · The variability of oceanic Antarctic circumpolar transport and the atmospheric Southern Annular Mode (SAM) on intraseasonal (30–70-day) ...
[82]
Interannual Variability and Multidecadal Trend in - AMS Journals
The main mode of variability of the Southern Hemisphere winds is a zonally symmetric mode called the southern annular mode (SAM) or Antarctic Oscillation. This ...
[83]
[PDF] Changes in the ocean transport through Drake Passage during the ...
Nov 6, 2004 · changes in ocean transport through Drake Passage are forced by variability in the Southern Annular Mode (SAM). This evidence is derived from ...
[84]
Antarctica and climate change - British Antarctic Survey - Publication
Jun 30, 2022 · The ozone hole and global warming have changed Antarctic weather patterns such that strengthened westerly winds force warm air eastward over the ...
[85]
Twenty-first-century Southern Hemisphere impacts of ozone ... - WCD
Feb 1, 2022 · We systematically investigate the impacts of ozone recovery and increasing GHGs on the atmospheric and oceanic circulation in the Southern Hemisphere during ...
[86]
[PDF] greenhouse gas and ozone forcing asymmetric Arctic and Antarctic ...
Jun 2, 2014 · By mid-century, however, ozone-hole effects may instead be adding to GHG warming around. Antarctica but with diminished amplitude as the ozone ...
[87]
On the Relationship between Southern Ocean Overturning and ACC ...
Jan 1, 2013 · Most eddy-permitting models show a weak, nonzero ACC transport sensitivity (~10%–20% ACC increase for doubled wind stress). A similar phenomenon ...
[88]
Human-Induced Change in the Antarctic Circumpolar Current in
The poleward shift, along with a significant increase in the transport of water around Antarctica, is predicted to continue into the future.
[89]
Role of anthropogenic forcing in Antarctic sea ice variability ...
Dec 20, 2024 · While the precise impact of anthropogenic forcing remains uncertain, natural fluctuations have been shown to be important for this variability.
[90]
Global Drivers on Southern Ocean Ecosystems: Changing Physical ...
Elsewhere in Antarctica, teasing out anthropogenic change from natural variability has proven challenging for many variables, suggesting that the observed ...
[91]
Shifting Antarctic Circumpolar Current south of Africa over the past ...
Jan 1, 2025 · The Antarctic Circumpolar Current (ACC) dominates the transfer of heat, salt, and tracers around the Southern Ocean (SO), driving the upwelling of carbon-rich ...
[92]
Role of the Antarctic Circumpolar Circulation in Current Asymmetric ...
Jul 7, 2024 · On the other hand, the strengthened ACC in response to doubled CO2 reduces the warming in the Southern Ocean. Therefore, the oceanic circulation ...
[93]
Revisiting Antarctic Circumpolar Current Transport Estimates - ADS
The canonical transport of 134 Sv through Drake Passage, the narrowest choke point of the ACC, derives from a year-long experiment conducted in 1979 (DRAKE79).
[94]
Volume Transport of the Antarctic Circumpolar Current from Bottom ...
Meausrements from bottom pressure gauges located at the north and south sides of Drake Passage are used to extend the one-year time series of volume transport ...
[95]
Mean Antarctic Circumpolar Current transport measured in Drake ...
Nov 1, 2016 · These combine to give a total of 90 ± 5 Sv, which is in agreement with the estimate from direct velocity measurements. Recently, through a ...
[96]
Baroclinic Transport Time Series of the Antarctic Circumpolar ...
The first multiyear continuous time series of Antarctic Circumpolar Current (ACC) baroclinic transport through Drake Passage measured by moored observations is ...
[97]
Argo Program - Global Ocean Monitoring and Observing
Argo provides scientists with measurements of the evolving state of the upper ocean by collecting temperature and salinity profiles from the surface to 2,000 ...
[98]
Observing the full ocean volume using Deep Argo floats - Frontiers
Nov 28, 2023 · These instruments supplement satellite, Core Argo float, and ship-based observations to measure heat and freshwater content in the full ocean volume.
[99]
Eddies in Numerical Models of the Antarctic Circumpolar Current ...
The POP results are found to be in reasonable agreement. For example, the highest value is 15 cm s−1 in FRAM, about 27 cm s−1 in the Semtner–Chervin model, and ...
[100]
Modelling the Antarctic Circumpolar Current: eddy-dynamics and ...
The Antarctic Circumpolar Current ... wind stress, a mechanism that is mainly responsible for the momentum balance of the currents in the northern hemisphere ...
[101]
Representation of Southern Ocean Properties across Coupled ...
Aug 1, 2020 · 1) The simulation of the strength of the ACC has improved from CMIP3 to CMIP6, with modeled. ACC strength converging toward the magnitude of ...
[102]
Biogeochemical and Physical Assessment of CMIP5 and CMIP6 ...
Apr 26, 2023 · Indeed, Beadling et al. (2020) found CMIP6 improvements for the simulated ACC strength, all surface wind stress metrics, and density differences ...
[103]
Origins of Southern Ocean warm sea surface temperature bias in ...
Aug 24, 2023 · Using the latest CMIP6 models, here we find that the warm SST bias in the SO features a zonally oriented non-uniform pattern mainly located ...
[104]
Thesis | Dynamics of a quasigeostrophic antarctic circumpolar current
The idea that basin-like dynamics may influence or control the Antarctic Circumpolar Current (ACC) is investigated with idealized analytic and numerical models.
[105]
Submesoscale Rossby waves on the Antarctic circumpolar current
Although our observations were limited in time and space, high-resolution numerical models could help to quantify the influence of submesoscales on water mass ...<|separator|>
[106]
Earth's strongest ocean current could slow down by 20% by 2050 in ...
Mar 3, 2025 · In a high emissions future, the world's strongest ocean current could slow down by 20% by 2050, further accelerating Antarctic ice sheet melting ...
[107]
The Impact of Underestimated Southern Ocean Freshening on ...
Mar 27, 2025 · Climate model simulations underestimate the Southern Ocean freshening trend and fail to simulate the observed surface cooling. Here, we quantify ...
[108]
Extremely poleward shift of Antarctic Circumpolar Current by ...
Oct 6, 2025 · The Antarctic Circumpolar Current (ACC), the largest current system on Earth, flows eastward between ~45°S and ~70°S, encircling the Antarctic ...
[109]
Is the Circumpolar Current Shifting Back North? - Universität Bonn
Oct 7, 2025 · Modeling indicates that natural conditions could push the Antarctic Circumpolar Current northward in the future, counteracting a southward shift ...Missing: total 2020-2025
[110]
High-latitude Southern Ocean eddy activity projected to evolve with ...
Mar 26, 2025 · Using a high-resolution ocean model and cost-reducing simulation design, eddy activity in the high southern latitudes is revealed in detail, ...<|control11|><|separator|>