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The incidence of presyncopal events is high soon after a long-duration spaceflight;>60% of returning astronauts could not complete a 10-min 80° head-up tilt test on landing day (R+0) after ~6 months of spaceflight. The objective of this study was to demonstrate the ability of a lower body gradient compression garment (GCG) to protect against an excessive increase in heart rate and a decrease in blood pressure during standing after long-duration spaceflight. Methods: Eleven astronauts (9 M, 2 F) volunteered to participate. The stand test protocol consisted of 2 min of prone rest followed by 3.5 min of standing. Subjects completed one familiarization session, two preflight data collection sessions in standard clothing, and three tests on landing day while wearing GCG. Postflight tests were conducted 1–4 h (R+0A), ~12 h (R+0B), and ~28 h after landing (R+0C). Results: All astronauts completed the stand test preflight. Three astronauts were unable to attempt the stand test at R+0A, and one of these was unable to start the test at R+0B. One astronaut was unable to complete 3.5 min of standing at R+0B (test ended at 3.3 min). Review of the individual’s blood pressure data revealed no hypotension but the astronaut reported significant motion sickness. Of the astronauts who participated in testing on landing day, the heart rate and mean arterial pressure responses to standing (stand-prone) were not different than preflight at any of the postflight sessions. Conclusion: Wearing the GCG after spaceflight prevented the tachycardia that normally occurs while standing after spaceflight without compression garments and protected against a decrease in blood pressure during a short stand test.

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Because of operational constraints, no research studies are performed during return to Earth, when astronauts perform critical operational tasks such as piloting and egressing the vehicle. The objective of this study was to interview Space Shuttle crewmembers to collect a description of post-flight perception of self-motion and self-performance from the astronauts during reentry and immediately after landing. Thirty-four Space Shuttle crewmembers were interviewed immediately after they returned from space. Transcripts of the interviews recount the crewmembers' experiences associated with head movements during reentry, during egressing the vehicle, and shortly after landing. Head movements made during reentry and immediately after return to Earth caused an increase sensation of self-motion, which affected their balance and gait. Pitch and roll head movements provoked the largest effects. Crewmembers also reported a lag in motion perception after the movement had stopped. More than one-third of crewmembers thought they would be unable to egress the Space Shuttle cabin unaided during an emergency. A clinical otoneurological examination of the crewmembers immediately after landing is needed to better understand the extent of vestibular deficits and track recovery.

A compilation of foraminiferal stable isotope measurements from southern high latitude (SHL) deep-sea sites provides a novel perspective important for understanding Earth's paleotemperature and paleoceanographic changes across the rise and fall of the Cretaceous Hot Greenhouse climate and the subsequent Paleogene climatic optimum. Both new and previously published results are placed within an improved chronostratigraphic framework for southern South Atlantic and southern Indian Ocean sites. Sites studied were located between 58° and 65°S paleolatitude and were deposited at middle to upper bathyal paleodepths. Oxygen isotope records suggest similar trends in both bottom and surface water temperatures in the southern sectors of the South Atlantic and in the Indian Ocean basins. Warm conditions were present throughout the Albian, extreme warmth existed during the Cretaceous Thermal Maximum (early-mid-Turonian) through late Santonian, and long-term cooling began in the Campanian and culminated in Cretaceous temperature minima during the Maastrichtian. Gradients between surface and seafloor δ18O and δ13C values were unusually high throughout the 11.5 m.y. of extreme warmth during the Turonian-early Campanian, but these vertical gradients nearly disappeared by the early Maastrichtian. In absolute terms, paleotemperature estimates that use standard assumptions for pre-glacial seawater suggest sub-Antarctic bottom waters were ≥21 °C and sub-Antarctic surface waters were ≥27 °C during the Turonian, values warmer than published climate models support. Alternatively, estimated temperatures can be reduced to the upper limits of model results through freshening of high latitude waters but only if there were enhanced precipitation of water with quite low δ18O values. Regardless, Turonian planktonic δ18O values are ~1.5‰ lower than minimum values reported for the Paleocene-Eocene Thermal Maximum (PETM) from the same region, a difference which corresponds to Turonian surface temperatures ~6 °C warmer than peak PETM temperatures if Turonian and Paleocene temperatures are estimated using the same assumptions. It is likely that warm oceans surrounding and penetrating interior Antarctica (given higher relative sea level) prevented growth of Antarctic ice sheets at all but the highest elevations from the late Aptian through late Campanian; however, Maastrichtian temperatures may have been cool enough to allow growth of small, ephemeral ice sheets. The standard explanation for the sustained warmth during Cretaceous Hot Greenhouse climate invokes higher atmospheric CO2 levels from volcanic outgassing, but correlation among temperature estimates, proxy estimates of pCO2, and intervals of high fluxes of both mafic and silicic volcanism are mostly poor. This comparison demonstrates that the relative timing between events and their putative consequences need to be better constrained to test and more fully understand relationships among volcanism, pCO2, temperature ocean circulation, Earth's biota and the carbon cycle.

This paper aims to review dysfunctions in spatial orientation, cognition, gaze stabilization, and posture and locomotor control recently documented in astronauts during and immediately after both short- and long-duration space flights. The spatial disorientation and cognitive deficits experienced by astronauts in microgravity are similar to those observed in individuals with vestibular disorders on Earth. After space flight, astronauts take more time to acquire visual targets while moving their head. Balance and locomotion control are impaired for approximately 15 days after long-duration space flight. Altered vestibular and proprioceptive inputs and changes in cortical sensory motor maps are presumed to be responsible for these deficits. Illusions of motion, underestimation of distance, delay in acquiring visual targets, and impairments in locomotion are potentially dangerous during operation of the spacecraft, especially during long-duration missions involving transitions between gravitational levels, and during landing when accurate manual and locomotor control is critical.

Background Ground-based studies have reported shifts of the vestibulo-ocular reflex (VOR) slow phase velocity (SPV) axis toward the resultant gravito-inertial force vector. The VOR was examined during eccentric roll rotation before, during and after an 8-day orbital mission. On orbit this vector is aligned with the head z-axis. Our hypothesis was that eccentric roll rotation on orbit would generate horizontal eye movements. Methods Two subjects were rotated in a semi-supine position with the head nasal-occipital axis parallel to the axis of rotation and 0.5 m off-center. The chair accelerated at 120 deg/s2 to 120 deg/s, rotated at constant velocity for one minute, and then decelerated to a stop in similar fashion. Results On Earth, the stimulation primarily generated torsional VOR. During spaceflight, in one subject torsional VOR became horizontal VOR, and then decayed very slowly. In the other subject, torsional VOR was reduced on orbit relative to pre- and post-flight, but the SPV axis did not rotate. Conclusion We attribute the shift from torsional to horizontal VOR on orbit to a spatial orientation of velocity storage toward alignment with the gravito-inertial force vector, and the inter-individual difference to cognitive factors related to the subjective straight-ahead.

A high-resolution multibeam echosounder (MBES) dataset covering over 279,000 km2 was acquired in the southeastern Indian Ocean to assist the search for Malaysia Airlines Flight 370 (MH370) that disappeared on 8 March 2014. The data provided an essential geospatial framework for the search and is the first large-scale coverage of MBES data in this region. Here we report on geomorphic analyses of the new MBES data, including a comparison with the Global Seafloor Geomorphic Features Map (GSFM) that is based on coarser resolution satellite altimetry data, and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area. Our comparison between the new MBES bathymetric model and the latest global topographic/bathymetric model (SRTM15_plus) reveals that 62% of the satellite-derived data points for the study area are comparable with MBES measurements within the estimated vertical uncertainty of the SRTM15_plus model (± 100 m). However, > 38% of the SRTM15_plus depth estimates disagree with the MBES data by > 100 m, in places by up to 1900 m. The new MBES data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the GSFM, with a 20% increase in the extent of hills and mountains. The new model also reveals four times more seamounts than presented in the GSFM, suggesting more of these features than previously estimated for the broader region. This is important considering the ecological significance of high-relief structures on the seabed, such as hosting high levels of biodiversity. Analyses of the new data also enabled sea knolls, fans, valleys, canyons, troughs, and holes to be identified, doubling the number of discrete features mapped. Importantly, mapping the study area using MBES data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes. For example, a large series of ridges extending over approximately 20% of the mapped area, in places capped by sea knolls, highlight the preserved seafloor spreading fabric and provide valuable insights into Southeast Indian Ridge seafloor spreading processes, especially volcanism. Rifting is also recorded along the Broken Ridge – Diamantina Escarpment, with rift blocks and well-bedded sedimentary bedrock outcrops discernible down to 2400 m water depth. Modern ocean floor sedimentary processes are documented by sediment mass transport features, especially along the northern margin of Broken Ridge, and in pockmarks (the finest-scale features mapped), which are numerous south of Diamantina Trench and appear to record gas and/or fluid discharge from underlying marine sediments. The new MBES data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with MBES. The availability of high-resolution and accurate maps of the ocean floor can clearly provide new insights into the Earth's geological evolution, modern ocean floor processes, and the location of sites that are likely to have relatively high biodiversity.

Volcanism associated with the Kerguelen Large Igneous Province is found scattered in southwestern Australia (the ca 136 to ca 130 Ma Bunbury Basalts, and ca 124 Ma Wallaby Plateau), India (ca 118 Ma Rajmahal Traps and Cona Basalts), and Tibet (the ca 132 Ma Comei Basalts), but apart from the ∼70 000 km2 Wallaby Plateau, these examples are spatially and volumetrically minor. Here, we report dredge, geochronological and geochemical results from the ∼90 000 km2 Naturaliste Plateau, located ∼170 to ∼500 km southwest of Australia. Dredged lavas and intrusive rocks range from mafic to felsic compositions, and prior geophysical analyses indicate these units comprise much of the plateau substrate. 40Ar/39Ar plagioclase ages from mafic units and U–Pb zircon ages from silicic rocks indicate magmatic emplacement from 130.6 ± 1.2 to 129.4 ± 1.3 Ma for mafic rocks and 131.8 ± 3.9 to 128.2 ± 2.3 Ma for silicic rocks (2σ). These Cretaceous Naturaliste magmas incorporated a significant component of continental crust, with relatively high 87Sr/86Sr (up to 0.78), high 207Pb/204 Pb ratios (15.5–15.6), low 143Nd/144Nd (0.511–0.512) and primitive-mantle normalised Th/Nb of 11.3 and La/Nb of 3.97. These geochemical results are consistent with the plateau being underlain by continental basement, as indicated by prior interpretations of seismic and gravity data, corroborated by dredging of Mesoproterozoic granites and gneisses on the southern plateau flank. The Cretaceous Naturaliste Plateau igneous rocks have signatures indicative of extraction from a depleted mantle, with trace-element and isotopic values that overlap with Kerguelen Plateau lavas reflect crustal contamination. Our chemical and geochronological results therefore show the Naturaliste Plateau contains evidence of an extensive igneous event representing some of the earliest voluminous Kerguelen hotspot magmas. Prior work reports that contemporaneous correlative volcanic sequences underlie the nearby Mentelle Basin, and the Enderby Basin and Princess Elizabeth Trough in the Antarctic. When combined, the igneous rocks in the Naturaliste, Mentelle, Wallaby, Enderby, Princess Elizabeth, Bunbury and Comei-Cona areas form a 136–124 Ma Large Igneous Province covering >244 000 km2.

Intermittent artificial gravity (AG) treatments may reduce bone, muscle, and cardiovascular deconditioning during prolonged space flight; however, the effects of repeated centrifugation on central processing of vestibular information remain unknown. This study investigated the effects of one intermittent AG prescription on balance control and neuromotor reflex function in a ground-based study of subjects exposed to bed rest. Fifteen male volunteers were exposed to 21 days of 6° head-down-tilt (HDT) bed rest (BR) to simulate some of the effects of space flight. Eight were treated with daily 1 h AG exposures aboard a short radius centrifuge that provided 1-g footward loading at heart level. The other seven served as control subjects. Balance control was assessed using a computerized dynamic posturography (CDP) protocol modified by adding low frequency pitch-plane head movements. Neuromotor reflex function was assessed using tendon (MSR) and functional stretch reflex (FSR) data collected from the triceps surae muscle group. CDP performance was degraded by BR in both groups, but was unaffected by AG. BR also degraded MSR and FSR functions in both groups, but AG blunted the decrement in MSR. This AG prescription had little functionally relevant effect on balance control, but may have had some salutary effect on neuromotor reflexes.

We present highlights of the first multibeam and bottom sampling survey surrounding the UNESCO World Heritage listed Heard and McDonald Islands (HIMI), conducted in the HIMI Marine Reserve InnerMarine Zone. These insular shelf data reveal that persistent eastward flowing currents and retreating glaciers drive patterns of sediment distribution. Sedimentary bedform directionality, corroborated by drifter data, suggest that the prevailing energy in this region dominates from west to east, and is deflected in an anticlockwise direction around Heard Island, causing sediment deposition to be concentrated on the eastern (downcurrent) side of the islands. Sediment bedform morphology likely mirrors the eastward flowing Antarctic Circumpolar Current and oscillating east!west tidal currents. Thick sediment accumulations north of Heard Island may be related to deglaciation since the Last Glacial Maximum. Sample sites on the northern down-current side of Heard Islands and on the western up-current side of the McDonald Islands contain a diverse range of taxonomic groups compared to all other sample sites. Benthic specimens obtained in rock dredges and sediment grabs show a range of invertebrate species that are likely endemic to the HIMI region.

Bubble emission mechanisms from submerged Large Igneous Provinces (LIPs) remains enigmatic. The Kerguelen Plateau, a LIP in the southern Indian Ocean, has a long‐sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the under‐explored volcanically‐active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multi‐frequency decibel differencing. Deep‐tow camera footage, water properties, water‐column δ3He, sub‐bottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with sub‐bottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest Heard seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems (Procesi et al., 2019). These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands. Science Foundation Ireland Australian Antarctic Science Program Australian Research Council Australian Government