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Standing meanders along the Antarctic Circumpolar Current (ACC) have been shown to be regions of elevated eddy variability, meridional heat transport, and vertical exchange. In this study, we investigate the influence of a standing meander south of Australia on air‐sea heat fluxes, upper ocean structure, and subduction in the 1/10° ACCESS‐OM2 ocean‐sea ice model forced by the JRA55 atmospheric reanalysis. We track the model's Subantarctic and Polar Fronts based on their jet and water mass structure, and produce composites of thermodynamical and dynamical properties of the meander in relaxed and flexed states. The standing meander induces trough‐to‐crest variations in surface heat flux, mixed layer depth (MLD), wind stress curl, vertical velocity, and subduction. At the crests, the ocean loses heat and the mixed layer is deeper; at the troughs, the ocean gains heat and the mixed layer is shallower. Wind stress curl, vertical velocity, and subduction change sign on entering and exiting crests and troughs. Vertical velocity due to the curvature of the meander is an order of magnitude larger than Ekman vertical velocity. The poleward excursion of Polar Front meander crests extends subduction to Antarctic Intermediate Water density classes. Finally, flexing of the meander enhances both air‐sea exchange and vertical velocity. The results show that standing meanders of the ACC influence the distribution and magnitude of air‐sea fluxes of heat and momentum and exchange between the surface and interior ocean. Plain Language Summary: Meanders along the Antarctic Circumpolar Current (ACC) funnel heat toward Antarctica. The research clarifies how meandering of ocean currents shapes air‐sea interaction and the transfer of surface ocean properties into the ocean interior in the ACC south of Australia. Meanders refer to curved patterns in the ACC's flow. We track specific ACC features and look at what is different inside and outside the meander in a computer model. We find that ocean meanders shape where the Southern Ocean gains and loses heat. These changes in heat exchange shape the mixed layer depth (MLD) in the ocean. The MLD is important for climate, biology productivity, and absorption of heat and carbon by the ocean. Meandering produces stronger vertical motion and increases sinking of water from the surface into the ocean interior, compared to regions where meanders are not present. When the meander flexes and becomes more curved, the vertical motion and atmosphere‐ocean exchange become even stronger. The results show that small‐scale patterns in ocean flow can have a strong influence on the atmosphere, with implications for climate and ocean circulation. These patterns are not well represented in climate models and our study is a step toward accounting for their absence. Key Points: Meanders in the Antarctic Circumpolar Current are locations of enhanced vertical velocity and air‐sea exchange of momentum and heatFlexing of the meander further enhances air‐sea exchange and vertical velocities due to increased curvaturePoleward excursion of meander crests extends subduction to Antarctic Intermediate Water densities along the Polar Front [ABSTRACT FROM AUTHOR]

Variations in the Atlantic Meridional Overturning Circulation (AMOC) redistribute heat and nutrients, causing pronounced anomalies of temperature and nutrient concentrations in the subsurface ocean. However, exactly how millennial‐scale deglacial AMOC variability influenced the subsurface is debated, and the role of other deglacial forcings of subsurface temperature change is unclear. Here, we present a new deglacial temperature reconstruction, which, with published records, helps assess competing hypotheses for deglacial warming in the upper tropical North Atlantic. Our record provides new evidence of regional subsurface warming in the western tropical North Atlantic within the core of modern Antarctic Intermediate Water (AAIW) during Heinrich Stadial 1 (HS1), an early deglacial interval of iceberg discharge into the North Atlantic. Our results are consistent with model simulations that suggest subsurface heat accumulates in the northern high‐latitude convection regions and along the upper AMOC return path when the AMOC weakens, and with warming due to rising greenhouse gases. Warming of AAIW may have also contributed to warming in the tropics at modern AAIW depths during late HS1. Nutrient and ΔCO32− ${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$ reconstructions from the same site suggest a link between AMOC intensity and the northward extent of AAIW in the northern tropics across the deglaciation and on millennial time scales. However, the timing of the initial deglacial increase in AAIW to the northern tropics is ambiguous. Deglacial trends and variability of ΔCO32− ${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$ in the upper North Atlantic have likely biased temperature reconstructions based on the elemental composition of calcitic benthic foraminifera. Plain Language Summary: The Atlantic Meridional Overturning Circulation (AMOC) is characterized by northward flow in the upper ocean and southward flow in the deep ocean. Understanding how the AMOC has changed in the past, and how such changes have affected surface climate and the distribution of ocean heat, carbon, and nutrients is important but challenging, as reconstructions of subsurface ocean properties are sometimes ambiguous. Here, we use the chemical composition of seafloor shells from a site in the western tropical Atlantic Ocean at ∼950 m water depth, within the northward‐flowing limb of the AMOC, to reconstruct temperature, nutrients, and carbon content during the end of the last Ice Age, an interval when AMOC strength is believed to have varied. Our results support a link between AMOC strength and tropical Atlantic nutrient content, and further suggest that both rising atmospheric CO2 and AMOC variations influenced temperatures and carbon in the subsurface tropical Atlantic Ocean. Key Points: Regional warming occurred in the tropical Atlantic at Antarctic Intermediate Water (AAIW) depths during Heinrich Stadial 1Deglacial nutrient and ΔCO32− ${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$ trends and variability suggest a strong link between Atlantic Meridional Overturning Circulation intensity and AAIW northward extentDeglacial ΔCO32− ${\Delta }\left[{\mathrm{C}\mathrm{O}}_{3}^{2-}\right]$ trends and variability likely affected upper Atlantic temperature estimates based on Mg/Ca of foraminifera [ABSTRACT FROM AUTHOR]

The Antarctic Intermediate Water (AAIW), one of the most important global intermediate water masses, spreads over the world ocean. Its propagation limit at the Northeast Subtropical Atlantic is characterized by its encounter with the Mediterranean Water (MW), which presents dissimilar thermohaline properties. Previous studies of the AAIW in this region have been based on traditional oceanographic cruise observations, which were later complemented by observations using autonomous systems such as ARGO floats. However, these observations present limitations for the study of processes occurring at mesoscale and smaller scales. In this study, we used high-resolution observations made by cutting edge platforms such as underwater gliders. Specifically, a meridional glider section realized in spring 2016 between the islands of Madeira and Gran Canaria has been used. The temperature, salinity and dissolved oxygen minima have allowed the detection of the AAIW signal north of the Canarian archipelago and significantly westward from its main northward propagation pathway in this region. The results of this work have shown that the encounter of AAIW and MW generates thermohaline intrusions or interleaving layers. It is suggested that double diffusion processes may play a role in the development of these structures, which may be important for water masses mixing and, therefore, in determining the northward spreading boundary of AAIW. The use of the high-resolution glider observations combined with other data products is essential for the study of water masses and dynamics when relevant processes have a wide range of scales. [ABSTRACT FROM AUTHOR]

Antarctic Intermediate Water (AAIW) is a water mass originating in the Southern Ocean characterised by its low salinity. The properties of the salinity minimum layer that characterise AAIW in the CMIP6 UKESM1 model and its response to different climate change scenarios are investigated. In UKESM1, the depth of the salinity minimum shoals by 116 m in the SSP5-8.5 run compared to the control run by 2080–2100. The salinity minimum also gets warmer (+ 1.9 °C) and lighter (− 0.4 kg/m3) and surface properties where the salinity minimum outcrops warm, freshen and lighten in all scenarios. In spite of these expected changes in properties, the location where the salinity minimum outcrops does not change in any of the future scenarios. The stability of the outcrop location of the salinity minimum is linked to the relative stability of the position of the Antarctic Circumpolar Current (ACC) in UKESM1. The position of the ACC does not follow the maximum wind stress trend, which intensifies and shifts poleward under radiative forcing. Changes in surface buoyancy fluxes in the region are consistent with the changes in hydrographic properties observed at depth on the salinity minimum mentioned above. However, transformation rates at the density corresponding to the salinity minimum outcrop remain constant in all scenarios. Stability in transformation rates at that density is due to the haline and thermal contributions counteracting one another. This analysis identifies two features (outcrop location, transformation rate) associated with the salinity minimum defining AAIW that show remarkable stability in an otherwise changing world. The effect of model resolution and other parameterisations on these findings have yet to be evaluated. [ABSTRACT FROM AUTHOR]

The Antarctic Intermediate Water (AAIW), one of the most important global intermediate water masses, spreads over the world ocean. Its propagation limit at the Northeast Subtropical Atlantic is characterized by its encounter with the Mediterranean Water (MW), which presents dissimilar thermohaline properties. Previous studies of the AAIW in this region have been based on traditional oceanographic cruise observations, which were later complemented by observations using autonomous systems such as ARGO floats. However, these observations present limitations for the study of processes occurring at mesoscale and smaller scales. In this study, we used high-resolution observations made by cutting edge platforms such as underwater gliders. Specifically, a meridional glider section realized in spring 2016 between the islands of Madeira and Gran Canaria has been used. The temperature, salinity and dissolved oxygen minima have allowed the detection of the AAIW signal north of the Canarian archipelago and significantly westward from its main northward propagation pathway in this region. The results of this work have shown that the encounter of AAIW and MW generates thermohaline intrusions or interleaving layers. It is suggested that double diffusion processes may play a role in the development of these structures, which may be important for water masses mixing and, therefore, in determining the northward spreading boundary of AAIW. The use of the high-resolution glider observations combined with other data products is essential for the study of water masses and dynamics when relevant processes have a wide range of scales.

Abstract Freshwater transports (Fov) by the Atlantic meridional overturning circulation (AMOC) are sensitive to salinity distributions and may determine AMOC stability. However, climate models show large salinity biases, distorting the relation between Fov and the AMOC. Using free‐running models and ocean reanalyses with realistic salinities but quite different AMOCs, we show that the fresh Antarctic Intermediate Water layer eliminates salinity differences across the AMOC branches at ~1,200 m, ∆S1200m, which decouples Fov from the AMOC south of ~10°N. As the Antarctic Intermediate Water disappears north of ~10°N, a large ∆S1200m allows the AMOC to drive substantial southward Fov in the North Atlantic. In the South Atlantic the 0–300 m zonal salinity contrasts control the gyre freshwater transports Fgyre, which also determine the total freshwater transports. This decoupling makes the southern Fov unlikely to play any role in AMOC stability, leaving indirect Fgyre feedbacks or Fov in the north, as more relevant factors.

Metal/calcium ratios in two long‐lived deep‐sea gorgonian corals (Lepidisis and Corallium spp.) in the Southwest Pacific evidence periodic decadal variability at depths that correspond to Antarctic Intermediate Water (AAIW) and shallow Upper Circumpolar Deep Water, and a shift in the mid‐1930s to late‐1930s in mean ambient temperatures, barium/silicate concentrations and possibly pH, the rate at which these properties change over time, and the relationship between temperatures at fixed depth and the Southern Annular Mode (SAM). The decadal periodicity, which is evident in other biological indices in the study area, can be accounted for by water mass heave on the order of 100–150 m, which is consistent with observed scales of variability in the AAIW. The proximate and ultimate causes of the midcentury shifts are unclear, but could be related to suggested mid‐20th century changes in climate parameters globally and, more specifically, in the subpolar SW Pacific. Plain Language Summary: The dynamics of the Southern Ocean play a critical role in global climate and oceanography, but sparse historical instrumental data make it difficult to assess the significance of recently observed changes. We help fill this information gap by analyzing apparent proxies for ambient temperature, barium/silicate concentrations, and possibly pH in the carbonate skeletons of a pair of very long‐lived deep‐sea corals. The data strongly suggest a previously unreported ∼23‐year periodicity in two Southern Ocean water masses (Antarctic Intermediate Water and Upper Circumpolar Deep Water), which is likely to be the result of vertical shifts in water mass distributions. The long‐term data also suggest the water masses cooled, became less acidic and had declining barium/silicate concentrations from at least the early 1700s until the early to mid‐1900s, after which the sign of the long‐term trends reversed. The causes of the long‐term trends and their reversal are not clear, but may be related to changes to climate parameters globally, but more specifically to those in the SE Pacific, where Antarctic Intermediate Water is formed. Key Points: Three environmental proxies were examined in skeletal composition of long‐lived deep‐water gorgonian corals in the SW PacificThe time series indicate coherent ca. 23‐year periodicity at depths corresponding to the AAIW and UCDWLong‐term trends in all three proxies reversed sign in the early to mid‐1900s, along with their relationship with the SAM [ABSTRACT FROM AUTHOR]

The evolution of intermediate circulation in the northern Indian Ocean since the last deglaciation has been reconstructed from two marine cores located at intermediate depths off the southern tip of India (MD77‐191) and in the northern Bay of Bengal (BoB) (MD77‐176). Benthic foraminiferal δ13C, seawater carbonate ion concentration ([CO32−]) estimated from the Sr/Ca, and paleotemperature reconstructed on the basis of the Mg/Li of aragonite benthic species Hoeglundina elegans were used to trace the evolution of past intermediate‐deepwater masses and to constrain ocean‐atmosphere exchanges during the two‐stage increase in atmospheric CO2 across the last deglaciation. The intermediate water [CO32−] was mainly affected by changes in the ocean alkalinity inventory, associated with the modulation of atmospheric CO2 on glacial‐interglacial timescales. Higher benthic foraminiferal δ13C, depleted [CO32−], and decreased benthic‐planktonic 14C age offsets at intermediate water depths suggest a release of deep‐sea CO2 to the atmosphere through the Antarctic Intermediate Water (AAIW) in the Southern Ocean during the 17–15.2 and 12.6–10.5 cal kyr BP time intervals. In addition, the decreased H. elegans Mg/Li record seems to reflect an increased contribution of cold water mass during the 17–15.2 and 12.6–11.9 cal kyr BP intervals and throughout the Holocene. In contrast, two warm events occurred in the 15–13.3 and 11–10.3 cal kyr BP time intervals. During the late Holocene, a decrease in the intermediate water [CO32−] indicates a contribution to atmospheric CO2 rise since 8 cal kyr BP, due to the depleted global ocean alkalinity and/or the variations in surface productivity (at least for MD77‐191). Key Points: We produced high‐resolution records of benthic foraminiferal elemental ratios, δ18O, and δ13C from two cores from the northern Indian OceanEvaluation of past IWT from the Mg/Li ratio and the δ18O since last deglaciation exhibit millennial‐scale changesVariations of the IW Δ[CO32−] calculated from H. elegans Sr/Ca are related to atmospheric CO2 changes on glacial‐interglacial timescales [ABSTRACT FROM AUTHOR]

The mid to late Pliocene (~4.2–2.8 Ma.) represents an experiment in climate sensitivity to orbital pacing in which nearly all continental ice was confined to the Southern Hemisphere. Most studies have emphasized the dominant role of obliquity in determining changes in ice volume and temperature at this time, although most records come from the Northern Hemisphere, instead of the hemisphere where the bulk of ice resided. We present the first orbitally‐resolved, mid to late Pliocene Southern Hemisphere paired records of surface and subsurface variability from two deep ocean archives from the Southwest Pacific Ocean (Sites 594 and 1125). These records indicate dominance of low frequencies centered at ~100 kyr for this time period. Because these signatures extend coherently and synchronously from middepth water properties (δ13C, δ18O of benthic foraminifera), which have their chemistry set in the subantarctic belt, to the surface (alkenone‐derived surface temperature estimates, color reflectance, and magnetic susceptibility), we infer that the fingerprint of the ~100‐kyr cycles must have extended over a large region of the Southern Hemisphere. We propose that nonlinearities in climate response to precessional forcing—most likely through ice sheet and/or carbon cycle behavior—generated the observed low frequency. A review of published mid to late Pliocene time series suggests that the ~100‐kyr pacing may be a widespread phenomenon and that major approximately 100‐kyr excursions in Pliocene climate were an important overlay to the underlying 41‐kyr glacial‐interglacial rhythm. These results caution against uncritical use of existing Pliocene isotopic templates to construct high‐resolution age models. Plain Language Summary: We recreated a detailed account of surface and subsurface ocean change at two locations within the Southern Hemisphere in the middle to late Pliocene Epoch (~4.2–2.8 Ma) using data obtained from deep‐ocean sediment cores. Our work showed that all variables measured (each representing a response from different parts of the climate system) fluctuated synchronously through time at specific rhythms and one of which, at approximately 100 kyr, was surprising to find. We found that the pervasive nature of this rhythm at ~100 kyr in our reconstructions is also found in other data sets connected to the Antarctic region. First, we propose that approximately 100‐kyr excursions in Pliocene climate are an important component in the overall pacing of glacial to interglacial times in the Pliocene. Such large excursions in climate would require powerful nonlinear feedbacks to forcing from the Earth's orbital precession cycle, likely involving ice sheet or carbon cycle dynamics. Second, we suggest that current global benthic isotope stacks (taken as an average representation of deep ocean temperature and ice volume changes on Earth) may not be fully representative of climate variability in some intervals of the Pliocene and therefore must be used carefully if used as a means to convert depth to time. Key Points: New, high‐resolution, paired surface‐subsurface paleoclimate reconstructions from the Southern Hemisphere, mid to late Pliocene EpochDominance of low frequencies centered at 100 kyr, extending coherently and synchronously from middepth water properties to the surfaceLow‐frequency dominance in power spectra likely related to underlying sensitivity to precessional forcing, requiring nonlinear amplifiers [ABSTRACT FROM AUTHOR]

Freshwater transports (Fov) by the Atlantic meridional overturning circulation (AMOC) are sensitive to salinity distributions and may determine AMOC stability. However, climate models show large salinity biases, distorting the relation between Fov and the AMOC. Using free‐running models and ocean reanalyses with realistic salinities but quite different AMOCs, we show that the fresh Antarctic Intermediate Water layer eliminates salinity differences across the AMOC branches at ~1,200 m, ∆S1200m, which decouples Fov from the AMOC south of ~10°N. As the Antarctic Intermediate Water disappears north of ~10°N, a large ∆S1200m allows the AMOC to drive substantial southward Fov in the North Atlantic. In the South Atlantic the 0–300 m zonal salinity contrasts control the gyre freshwater transports Fgyre, which also determine the total freshwater transports. This decoupling makes the southern Fov unlikely to play any role in AMOC stability, leaving indirect Fgyre feedbacks or Fov in the north, as more relevant factors. Plain language summary: The Atlantic Ocean has an upper circulation branch transporting warm waters toward the Arctic. These waters sink due to changes in both salinity and temperature, leading to a cold and deep southward circulation branch throughout the Atlantic. This "overturning circulation" moves heat and freshwater over large distances, contributing to regulate Earth's climate, but the circulation strength may also be affected by these transports via feedback effects. It has been proposed that South Atlantic freshwater transports are a sensitive indicator of circulation feedback, which could lead to instability in the climate system. However, models of the ocean and atmospheric circulations used to study climate often show large errors in salinity distributions and freshwater transports and therefore may misrepresent climate stability. We show that with realistic salinities, the overturning circulation produces virtually no freshwater transports throughout the South Atlantic and is unlikely to have any role in feedbacks causing climate instability. Horizontal gyre circulations dominate South Atlantic freshwater transports, which could still have some indirect influence on climate stability. In contrast, the overturning circulation does drive a strong freshwater transport in the North Atlantic, and therefore, salinity feedbacks on the climate stability are much more likely to be important in the north. Key Points: Atlantic overturning freshwater transport is explained by spatial variation in the vertical salinity contrasts between the AMOC branchesNegligible South Atlantic vertical salinity contrasts produce weak freshwater transports, decoupled from the AMOC strengthGyre‐driven freshwater transports depend on 0–300 m zonal salinity contrasts and determine the total South Atlantic freshwater transports [ABSTRACT FROM AUTHOR]

Abstract The two-stage increase in atmospheric carbon dioxide (CO 2), and the associated decrease in radiocarbon (14C) during the last deglaciation, are thought to have been linked to enhanced Southern Ocean upwelling and the rapid release of sequestered 14C-depleted CO 2. Antarctic Intermediate Water (AAIW), originating from the Southern Ocean, reflects variations in the Southern Ocean and, crucially, mirrors the chemical signature of upwelling deep water. However, the penetration of AAIW into the Northern Indian Ocean and its relationship with deglacial climate changes have not been thoroughly elucidated to date. Here, we present the neodymium isotopic composition (ε Nd) of mixed planktonic foraminifera from core MD77-176 from an intermediate depth in the Northern Indian Ocean to reconstruct the past evolution of intermediate water during deglaciation. The ε Nd record in the Northern Indian Ocean displays two pulse-like shifts towards more radiogenic Southern Ocean values during the deglaciation, and these shifts coincide with excursions in Δ 14 C and ε Nd records in the Pacific and Atlantic Oceans. These results suggest invasion of AAIW into the Northern Hemisphere oceans associated with enhanced Southern Ocean ventilation during deglaciation. Our new ε Nd record strongly supports the close linkage of AAIW propagation and atmospheric CO 2 rise through Southern Ocean ventilation during deglaciation. Highlights • Deglacial radiogenic ε Nd indicates AAIW penetration into the norther Indian Ocean. • AAIW could occupy the northern intermediate Indian Ocean during deglaciation. • Intermediate thermohaline reorganization was linked to deglacial atmospheric CO 2 rise. [ABSTRACT FROM AUTHOR]

Abstract: This study evaluates the capability of eddy‐permitting regional ocean models to reproduce the interocean exchange south of Africa. In this highly turbulent region, we show that the vertical structure of the horizontal flows need to be appropriately resolved to realistically advect thermocline water masses into the South Atlantic. Our results point out that a grid‐spacing of 1/24° on the horizontal and 50 m on the vertical homogeneously distributed are required to account for a correct transport of surface and subsurface water masses properties and their in‐route transformation by mixing. Preliminary Lagrangian analyses highlight the primary role of the upper‐ocean mesoscale eddies on water masses transport and fate, with a particular emphasis on Antarctic Intermediate Waters (AAIWs) dynamics and characteristics. We evaluate the numerical results against observations (AVISO data and Argo floats profiles). Modeled and observed eddies were examined in number, polarity, size, trajectory, and for their contribution to AAIW properties. A clear asymmetry, in number and radius, emerges between cyclones and anticyclones. The high‐resolution simulation was the most energetic, with more abundant and smaller structures than those detected in AVISO. However, eddy statistics compare reasonably well in terms of mean pathways when restricted to Agulhas Rings, which are on average quasi‐Gaussian in shape. Regionally, the Ertel potential vorticity anomaly is marked at the surface by a temporal variability with winter intensification, directly reflected in the seasonal cycle of the eddies number. Noting the growth of the baroclinic Rossby radius in winter, this suggests baroclinic processes as essential for these eddies generation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Bayesian method to estimate a transit-time distribution (TTD) is presented. [•] All known significant sources of uncertainty are taken into account. [•] IG TTD is inadequate for representing the full TTD in the ocean. [•] Mean ages are in significant error in POP where there is SAMW. [•] Errors in mean ages cannot explain errors in POP in other IG parameter. [Copyright &y& Elsevier]

Abstract: The Australia/New Zealand region of the Southern Ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the Pacific basin. During the last glacial there was increased sea-ice extent around Antarctica (as far north as 55°S), as well as increased iceberg presence inferred from ice-rafted debris. Evidence from microfossil assemblages suggests that sea surface temperatures (SST) were up to 7 °C cooler, consistent with recent estimates of cooling for New Zealand derived from glacier modelling and other terrestrial proxies. The Subtropical Front (STF), Subantarctic Front (SAF) and Polar Front (PF) had migrated north, except where the position of the fronts were controlled bathymetrically. Despite the potential for iron fertilisation by increased dust input into the ocean during the glacial, there is limited evidence for higher total biological productivity in the Pacific sector of the Southern Ocean. The altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of CO2. This contributed to an increased storage of CO2 in the deep waters and lowering of the carbonate lysocline. During the deglaciation, sea-ice retreat and SST increased rapidly at ∼18 ka, roughly synchronous with the reinvigoration of deep water circulation in the Southern Ocean and the release of CO2 stored in the deep waters. The gradient in carbon isotopes (δ13Cbenthic) between Antarctic Intermediate Water (AAIW) and lower Circumpolar Deep Water (LCDW) was greatest at the start of the deglaciation, suggesting that the AAIW ventilation preceded LCDW ventilation, or there was a significant change in air-sea fractionation of δ13C. There was a slight enrichment in δ18Oplanktic, decrease in SSTs and a reduction in intermediate and deep water circulation between ∼14 and 12.5 ka BP during the Antarctic Cold Reversal (ACR), coincident with glacier advances in the New Zealand Southern Alps and other terrestrial records of cooling. Following the ACR, there was a second, more minor, release of deep water CO2, most likely related to reinvigoration of North Atlantic Deep Water (NADW). From 10 ka onwards the modern intermediate and deep water circulation was established. Air temperatures and SSTs reached a maximum in the early Holocene, with the STF located at its most southerly position, and there was a widespread retreat of Antarctic ice sheets to their modern position. A decline to modern SST and air temperatures in the mid to late Holocene followed. While millennial cycles overprinted on the SST and δ18Oplanktic records, may be the result of subtle changes in the position and strength of the westerly winds during the Holocene. [Copyright &y& Elsevier]

Abstract: The importance of southern hemisphere driven climate change is increasingly recognized in paleoclimate research. This is in particular relevant with regard to the rate of climate change initiated in the southern hemisphere and the phasing thereof compared to climate variability elsewhere. Here, we use previously published benthic oxygen isotope data from two deep sea sediment cores from the deep N-Atlantic and the intermediate depth Indian Ocean to quantify rates of oceanic change at the millennial-scale. The oxygen isotope data represent an integrated signal of temperature and global sea level changes. At both locations the sea surface ocean records strongly resemble Greenland climate change. When used to synchronize these surface ocean records with the GISP2 ice core chronology we show that the highest rates of change in the benthic oxygen isotope records, occur during late marine isotope stage 5 (MIS 5), MIS 3 and the last deglaciation, whilst generally modest rates of change prevail during the full glacial conditions of MIS 2. The synchronous variation of oceanic rates of change and Antarctic climate history suggests that the benthic oxygen isotope records from the glacial deep N-Atlantic and the intermediate Indian Ocean reflect variations in southern sourced Antarctic Bottom Water (AABW) and Glacial Antarctic Intermediate Water (GAAIW) respectively. Millennial-scale temperature variations in GAAIW are larger than in AABW. The repeated rapid heat storage in GAAIW during northern hemisphere cold phases points to an important role of GAAIW, potentially acting as an energy buffer, maintaining the pole-to-pole climate imbalance as part of the bi-polar seesaw. Combining the benthic oxygen isotope records with independent sea level records shows a pulsed sea level rise history during the deglaciation with conservative estimates of peak rates change of about ~2m/100yr. Similar rates of sea level change occurred during most Heinrich Events. [Copyright &y& Elsevier]

Abstract: In 2007, we demonstrated that radiolarians are proxies for a wide range of oceanic physico-chemical properties from the surface to depths of up to 500 m below sea level. In this study, our results are refined and Correspondence Analysis (CA) scores derived from census counts of radiolarian subfossils from southern Indian Ocean core-tops are correlated with the physico-chemical properties of the region obtained from the 2005 World Ocean Database. Calibration and regression techniques are employed to reconstruct palaeoenvironmental conditions spanning the last 40 ka for four Indian Ocean cores MD88-769 [46°04′S 90°06′E], MD88-770 [46°01′S 96°27′E], MD94-102 [43°30′S 79°50′E], and MD94-103 [45°35′S 86°31′E], all from close to the Southeast Indian Ridge. For the first time, reconstructions of temperature, salinity, dissolved oxygen, and the silicate, nitrate, and phosphate concentrations for a range of water depths are proved possible. Changes of the oceanic environment and the movement of water masses over the last 40 ka, as suggested by these reconstructions, are discussed. During Marine Isotope Stages 2 and 3 (MIS-2 and MIS-3), the water column at some of the core sites has similar characteristics to the waters south of the Polar Front today. At the MIS-1/MIS-2 transition, the development of the Subantarctic Mode Water is apparent. Temperature reconstructions include evidence of the Antarctic Cold Reversal and the Holocene Optimum. [Copyright &y& Elsevier]

Abstract: During the last deglaciation the concentration of CO2 in the atmosphere increased and the radiocarbon activity (Δ14C) of the atmosphere declined in two steps corresponding in timing to Heinrich Stadial 1 and the Younger Dryas. These changes have been attributed to the redistribution of 14C-depleted carbon from the deep ocean into the upper ocean and atmosphere. Recently, reconstructions of Δ14C in intermediate waters of the eastern tropical Pacific have revealed pulses of very old water during the deglaciation, consistent with the release of 14C-depleted carbon from the deep ocean at this time. Here, we present reconstructions of intermediate water Δ14C from the northern Arabian Sea near the coast of Oman. These reconstructions record significant aging of intermediate waters in the Arabian Sea during Heinrich Stadial 1 and, to a lesser extent, during the Younger Dryas. The timing and magnitude of 14C depletion in the Arabian Sea during Heinrich Stadial 1 is very similar to that previously observed in the eastern North Pacific near Baja California, indicating that similar mechanisms were involved in controlling Δ14C at these two sites. The most parsimonious explanation of the Δ14C records from the Arabian Sea and Baja California remains the release of 14C-depleted carbon from the deep ocean by renewal of upwelling and mixing in the Southern Ocean. These 14C-depleted waters would have been incorporated into thermocline and intermediate water masses formed in the Southern Ocean and spread northward into the Pacific, Indian and Atlantic Ocean basins. [ABSTRACT FROM AUTHOR]

Abstract: Evidence from geochemical tracers (salinity, oxygen, silicate, nutrients, alkalinity, dissolved inorganic carbon (DIC), carbon isotopes (δ13CDIC) and radiocarbon (Δ14C)) collected during the Pacific Ocean World Ocean Circulation Experiment (WOCE) voyages (P10, P15, P17 and P19) indicate there are three main water types at intermediate depths in the Pacific Ocean; North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW) and Equatorial Pacific Intermediate Waters (EqPIW). We support previous suggestions of EqPIW as a separate equatorial intermediate depth water as it displays a distinct geochemical signature characterised by low salinity, low oxygen, high nutrients and low Δ14C (older radiocarbon). Using the geochemical properties of the different intermediate depth waters, we have mapped out their distribution in the main Pacific Basin. From the calculated pre-formed δ13Cair–sea conservative tracer, it is evident that EqPIW is a combination of AAIW parental waters, while quasi-conservative geochemical tracers, such as radiocarbon, also indicate mixing with old upwelling Pacific Deep Waters (PDW). The EqPIW also displays a latitudinal asymmetry in non-conservative geochemical tracers and can be further split into North (NEqPIW) and South (SEqPIW) separated at ∼2°N. The reason for this asymmetry is caused by higher surface diatom production in the north driven by higher silicate concentrations. The δ13C signature measured in benthic foraminifera, Cibicidoides spp. (δ13CCib), from four core tops bathed in AAIW, SEqPIW and NPIW, reflects that of the overlying intermediate depth waters. The δ13CCib from these cores show similarities and variations down-core that highlight changes in mixing over the last 30,000yr BP. The reduced offset between the δ13CCib of AAIW and SEqPIW during the last glacial indicates that AAIW might have had an increased influence in the eastern equatorial Pacific (EEP) region at this time. Additional intermediate depth cores and other paleo-geochemical proxies such as Cd/Ca and radiocarbon are required from the broader Pacific Ocean to further understand changes in intermediate depth water formation, circulation and mixing over glacial/interglacial cycles. [Copyright &y& Elsevier]

Diatoms are one of the predominant contributors to global carbon fixation by accounting for over 40% of total oceanic primary production and dominate export production. They play a significant role in marine biogeochemistry cycle. The diatom mat deposits are results of vast diatoms bloom. By analysis of diatom mats in 136°00′-140°00'E,15°00'?21°00'N, Eastern Philippines Sea, we identified the species of the diatoms as giant Ethmodiscus rex (Wallich) Hendey. AMS 14C dating shows that the sediments rich in diatom mats occurred during 16000-28600 a B.P., which means the bloom mainly occurred during the last glacial period, while there are no diatom mat deposits in other layers. Preliminary analysis indicates that Antarctic Intermediate Water (AAIW) expanded northward and brought silicate-rich water into the area, namely, silicon leakage processes caused the bloom of diatoms. In addition, the increase of iron input is one of the main reasons for the diatom bloom. [ABSTRACT FROM AUTHOR]

Abstract: The spatial distribution of Antarctic intermediate water (AAIW) formation and ventilation remains a matter of debate. Some studies suggest that AAIW forms nearly homogeneously in a circumpolar pattern, whereas others favor more localized formation particularly in the southeast Pacific Ocean. We show here that the patterns and magnitude of AAIW formation and ventilation are substantially affected by mesoscale eddies. To diagnose the role of eddies, we made global CFC-11 simulations in two versions of the ocean general circulation model OPA9, a “non-eddying”, coarse-resolution version (, ORCA2) and an “eddying” or eddy-permitting version (, ORCA05). In the non-eddying simulation, AAIW subducts in a near homogeneous, circumpolar pattern; in the eddying simulation, the distribution of AAIW ventilation is patchier. Increasing resolution causes the AAIW layer to thin by 32% on average in the Indian sector, but only by 11% in the Pacific sector. This patchiness appears due to the zonal wind stress, which is weak over much of the Pacific and southwest Atlantic sectors but is strong over the Indian sector. Consequently, the effect of eddies is largest in the Indian Ocean, moderate in the Atlantic, and smallest in the Pacific basin. Although the Gent and McWilliams (GM) eddy parameterization improves the overall vertical structure of density in the Southern Ocean, applying it in our non-eddying model still results in the nearly uniform circumpolar distribution of AAIW ventilation, in contrast to the observations. [Copyright &y& Elsevier]

Abstract: During the last glacial period, polar ice cores indicate climate asynchrony between the poles at the millennial time-scale. Yet, surface ocean circulation in large parts of the globe varied in tune with Greenland temperature fluctuations suggesting that any anti-phase behavior to a substantial degree must lie in the deeper global ocean circulation which is poorly understood outside the Atlantic Ocean. Here we present data from the north-western Indian Ocean which indicate that the timing of maxima in northward extensions of glacial Antarctic Intermediate Water (GAAIW) coincides with dramatically reduced thermohaline overturn in the North Atlantic associated with the Heinrich-ice surge events (HE). The repeated expansion of the GAAIW during HEs, recorded far north of the equator in the Arabian Sea, suggests that southern hemisphere driven intermediate water mass variability forms an integral part of the inter-hemisphere asynchronous climate change behavior at the millennial time-scale. [Copyright &y& Elsevier]

Over the last 5 million years, the global climate system has evolved toward a colder mean state, marked by large-amplitude oscillations in continental ice volume. Equatorward expansion of polar waters and strengthening temperature gradients have been detected. However, the response of the mid latitudes and high latitudes of the Southern Hemisphere is not well documented, despite the potential importance for climate feedbacks including sea ice distribution and low-high latitude heat transport. Here we reconstruct the Pliocene-Pleistocene history of both sea surface and Antarctic Intermediate Water (AAIW) temperatures on orbital time scales from Deep Sea Drilling Project Site 593 in the Tasman Sea, southwest Pacific. We confirm overall Pliocene-Pleistocene cooling trends in both the surface ocean and AAIW, although the patterns are complex. The Pliocene is warmer than modern, but our data suggest an equatorward displacement of the subtropical front relative to present and a poleward displacement of the subantarctic front of the Antarctic Circumpolar Current (ACC). Two main intervals of cooling, from ~3 Ma and ~1.5 Ma, are coeval with cooling and ice sheet expansion noted elsewhere and suggest that equatorward expansion of polar water masses also characterized the southwest Pacific through the Pliocene-Pleistocene. However, the observed trends in sea surface temperature and AAIW temperature are not identical despite an underlying link to the ACC, and intervals of unusual surface ocean warmth (~2 Ma) and large-amplitude variability in AAIW temperatures (from ~1 Ma) highlight complex interactions between equatorward displacements of fronts associated with the ACC and/or varying poleward heat transport from the subtropics.