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Coral reef sessile organisms inhabiting cryptic spaces and cavities of the reef matrix perform vital and varied functional roles but are often understudied in comparison to those on exposed surfaces. Here, we assess the composition of cryptobenthic taxa from three remote tropical reef sites (Central Indian Ocean) alongside a suite of in situ environmental parameters to determine if, or how, significant patterns of diversity are shaped by local abiotic factors. To achieve this, we carried out a point-count analysis of autonomous reef monitoring structure (ARMS) plate images and employed in situ instrumentation to recover long-term (12 months) profiles of flow velocity, wave heights, temperature, dissolved oxygen, and salinity, and short-term (3 weeks) profiles of light and pH. We recovered distinct environmental profiles between sampling sites and observed that ocean-facing reefs experienced frequent but short-lived cooling internal wave events and that these were key in shaping in situ temperature variability. By comparing temperature and wave height profiles recovered using in situ loggers with ex situ models, we discovered that global satellite products either failed to recover site-specific profiles or both over- and underestimated actual in situ conditions. We found that site choice and recruitment plate face (top or bottom) significantly impacted the percentage cover of bryozoans, gastropods, soft and calcified tube worms, as well as crustose coralline algae (CCA) and fleshy red, brown, and green encrusting macroalgae on ARMS. We observed significant correlations between the abundance of bryozoans, CCA, and colonial tunicates with lower mean temperature and higher mean dissolved oxygen profiles observed across sites. Red and brown encrusting macroalgae abundance correlated significantly with medium-to-high flow velocities and wave height profiles, as well as higher pH and dissolved oxygen. This study provides the first insight into cryptobenthic communities in the Chagos Archipelago marine-protected area and adds to our limited understanding of tropical reef sessile communities and their associations with environmental parameters in this region. With climate change accelerating the decline of reef ecosystems, integrating analyses of cryptobenthic organisms and in situ physicochemical factors are needed to understand how reef communities, if any, may withstand the impacts of climate change.

Tierra del Fuego in Argentina is a unique location to examine past Holocene wind variability since it intersects the core of the Southern Hemisphere Westerly Winds (SHWW). The SHWW are the most powerful prevailing winds on Earth. Their variation plays a role in regulating atmospheric CO2 levels and rainfall amounts and distribution, both today and in the past. We obtained a piston core (LF06-PC8) from Bahia Grande, a protected sub-basin at the southern margin of Lago Fagnano, the largest lake in Tierra del Fuego. This article focuses on the uppermost 185 cm of this core, corresponding to laminated sediment from the last similar to 6.3 ka. Laminations consist of millimetre-scale paired dark and light layers. Previous studies and new geochemical analysis show that the dark and light layers are characterized by differing concentrations of Mn and Fe. We attribute the distribution of Mn and Fe to episodic hypolimnic oxic-anoxic variations. The age model suggests an approximately bidecadal timescale for the formation of each layer pair. We propose a new model of these redox changes with the SHWW variations. The most likely phenomenon to produce complete water-column mixing is thermobaric instability, which occurs in colder winters with low-intensity SHWW (El Nino-like conditions). In contrast, windier winters are characterized by higher temperatures and reduced mixing in the water column, facilitating a decline in oxygen concentration. Laminations, and the inferred presence of periodic hypolimnion redox changes, are common features of the past similar to 6.3 ka. Geochemical proxy variability is compatible with an intensification of El Nino/Southern Oscillation activity during the past similar to 2 ka., Beatriu de Pinos postdoctoral programme at Agencia de Gestio Academica i Universitaria at Generalitat de Catalunya, National Science Foundation (NSF) ATM-0408668 EAR-1103550, Spanish Government CTM2017-89711-C2-1-P, European Union through FEDER funds, Spanish Government RYC2015-18966

Antarctic sea-ice extent, primary productivity and ocean circulation represent interconnected systems that form important components of the global carbon cycle. Subdecadal to centennial-scale variability can influence the characteristics and interactions of these systems, but observational records are too short to evaluate the impacts of this variability over longer timescales. Here, we use a 170-m-long sediment core collected from Integrated Ocean Drilling Program Site U1357B, offshore Adélie Land, East Antarctica to disentangle the impacts of sea ice and subdecadal climate variability on phytoplankton bloom frequency over the last ~11,400 years. We apply X-ray computed tomography, Ice Proxy for the Southern Ocean with 25 carbon atoms, diatom, physical property and geochemical analyses to the core, which contains an annually resolved, continuously laminated archive of phytoplankton bloom events. Bloom events occurred annually to biennially through most of the Holocene, but became less frequent (~2–7 years) at ~4.5 ka when coastal sea ice intensified. We propose that coastal sea-ice intensification subdued annual sea-ice break-out, causing an increased sensitivity of sea-ice dynamics to subdecadal climate modes, leading to a subdecadal frequency of bloom events. Our data suggest that projected loss of coastal sea ice will impact the influence of subdecadal variability on Antarctic margin primary productivity, altering food webs and carbon-cycling processes at seasonal timescales., This research used samples and data provided by IODP expedition 318, sponsored by the US National Science Foundation (NSF) and participating countries under the management of the Consortium for Ocean Leadership, including the Australian and New Zealand International Ocean Discovery Program Consortium. Funding was provided by Royal Society Te Apārangi Marsden Fund (18-VUW-089 to R.M.M. and 15-VUW-131 to N.A.N.B.) and the New Zealand Ministry of Business, Innovation and Employment through the Antarctic Science Platform (ANTA1801). Funding was also provided by the New Zealand Ministry of Business, Innovation and Employment Strategic Science Investment Fund (SSIF) through GNS Science (grant 540GCT32). We acknowledge funding from the Dumont d’Urville NZ-France Science and Technology Programme, MARICE project (Marine and Ice core reconstruction of East Antarctic sea ice variability over the past 2,000 years) (project nos. 45455NF and 19-VUW-047-DDU Catalyst Fund, RSNZ). J.E. and X.C. acknowledge funding by the ERC StG ICEPROXY (203441), the ANR CLIMICE and the FP7 Past4Future (243908) projects. F.J.J.-E. was funded by project 201830I092 (Spanish Research Council). C.E. and F.J.J.-E acknowledge funding by the Spanish Ministry of Science and Innovation (grant CTM2017-89711-C2-1-P), co-funded by the European Union through FEDER funds. C.R.R. was funded by a University of Otago research grant and a L’Oréal-UNESCO For Women in Science Australia and New Zealand Fellowship. The Natural Environment Research Council funded K.E.A. (CENTA PhD; NE/L002493/1) and J.B. (standard grant Ne/I00646X/1). Y.Y. was funded by the Japan Society for Promotion of Science (JSPS) grant no. JP20H00193. S.F.P. was supported by National Science Foundation grant OPP-0732796. R.B.D. was supported by National Science Foundation grants PLR-1644118 and OCE-1129101. The authors acknowledge the Norwegian Polar Institute’s Quantarctica package, and the use of imagery from the NASA Worldview application (https://worldview.earthdata.nasa.gov/), part of the NASA Earth Observing System Data and Information System.

A physical oceanographic, geophysical and marine geological survey of Edward VIII Gulf, Kemp Coast, collected data from conductivity–temperature–depth casts, multi-beam bathymetric swath mapping and 3.5 kHz sub-bottom surveying. Modified circumpolar deep water (mCDW) is observed in Edward VIII Gulf, as well as notable bathymetric features including mega-scale glacial lineations and a 1750 m-deep trough. Sedimentological, geochemical, rock-magnetic and micropalaeontological analysis of two kasten cores document regional palaeoclimate and palaeo-oceanographic conditions over the past 8000 years, with a warm period occurring fromc.8 to 4 ka and a shift to cooler conditions beginning atc.4 ka and persisting until at least 0.9 ka. Sediment packages > 40 m thick within deep troughs in Edward VIII Gulf present potential targets for higher-resolution Holocene and deglacial climate studies. Despite the presence of mCDW on the shelf, inland bed topography consisting of highland terrain suggests the likelihood of relative stability of this sector of the East Antarctic Ice Sheet.

Polar marine ecosystems are particularly vulnerable to the effects of climate change. Warming temperatures, freshening seawater, and disruption to sea-ice formation potentially all have cascading effects on food webs. New approaches are needed to better understand spatiotemporal interactions among biogeochemical processes at the base of Southern Ocean food webs. In marine systems, isoscapes (models of the spatial variation in the stable isotopic composition) of carbon and nitrogen have proven useful in identifying spatial variation in a range of biogeochemical processes, such as nutrient utilization by phytoplankton. Isoscapes provide a baseline for interpreting stable isotope compositions of higher trophic level animals in movement, migration, and diet research. Here, we produce carbon and nitrogen isoscapes across the entire Southern Ocean (>40°S) using surface particulate organic matter isotope data, collected over the past 50 years. We use Integrated Nested Laplace Approximation-based approaches to predict mean annual isoscapes and four seasonal isoscapes using a suite of environmental data as predictor variables. Clear spatial gradients in δ13C and δ15N values were predicted across the Southern Ocean, consistent with previous statistical and mechanistic views of isotopic variability in this region. We identify strong seasonal variability in both carbon and nitrogen isoscapes, with key implications for the use of static or annual average isoscape baselines in animal studies attempting to document seasonal migratory or foraging behaviors.

Climate change is causing major changes to marine ecosystems globally, with ocean acidification of particular concern for coral reefs. Using a 200 d in situ carbon dioxide enrichment study on Heron Island, Australia, we simulated future ocean acidification conditions, and found reduced pH led to a drastic decline in net calcification of living corals to no net growth, and accelerated disintegration of dead corals. Net calcification declined more severely than in previous studies due to exposure to the natural community of bioeroding organisms in this in situ study and to a longer experimental duration. Our data suggest that reef flat corals reach net dissolution at an aragonite saturation state (ΩAR) of 2.3 (95% confidence interval: 1.8–2.8) with 100% living coral cover and at ΩAR > 3.5 with 30% living coral cover. This model suggests that areas of the reef with relatively low coral mortality, where living coral cover is high, are likely to be resistant to carbon dioxide-induced reef dissolution. A Free Ocean Carbon Enrichment study on the Great Barrier Reef finds that elevated carbon dioxide impairs net calcification of living corals and may accelerate dissolution of dead corals.

Bolbometopon muricatum are ecologically unique mega-consumers in coral reef ecosystems. They primarily divide their dietary intake between living scleractinian corals and coral rock, a substrate richly colonized by non-coral biota. Here we examine how the chemical, structural, and energetic content of these two main classes of forage material may influence B. muricatum feeding behavior and selectivity. We then also examine nutrient content, pH, and alkalinity of the carbonate-rich feces of B. muricatum as a step toward understanding how B. muricatum defecation could affect reef nutrient dynamics and localized seawater chemistry. Our results suggest that by most measures, coral rock constitutes a richer food source than living corals, exhibiting higher levels of eight biologically relevant elements, and containing approximately three times greater caloric value than living corals. Additionally, the two forage types also presented distinct mineralogy, with the coral rock resembling a Mg-enriched carbonate phase in contrast to the primarily aragonitic live corals. Despite the fact that individual B. muricatum excrete tons of macerated coral annually, the low measured concentrations of N and P in feces suggest that this excretion may have relatively minor effects of reef macronutrient budgets. We also observed negligible local-scale impacts of B. muricatum feces on seawater pH and alkalinity. The approaches applied here integrate perspectives from marine biogeochemistry, materials science, and ecology. Collectively, these results provide preliminary insight into how reef chemistry could shape foraging of this dominant and vulnerable coral reef consumer and how it, in turn, might affect the chemistry of these reefs.

Knowledge of how the Antarctic Ice Sheet (AIS) responded in the geologic past to warming climates will provide powerful insight into its poorly understood role in future global sea level change. Study of past natural climate changes allows us to determine the sensitivity of the AIS to higher-than-present atmospheric carbon dioxide (CO) concentrations and global temperatures, thereby providing the opportunity to improve the skill and performance of ice sheet models used for Intergovernmental Panel on Climate Change (IPCC) future projections. Antarctic and Southern Ocean (south of 60°S latitude) marine sediment records obtained over the last 50 years by seven scientific ocean drilling expeditions have revolutionized our understanding of Earth’s climate system and the evolution and dynamics of the Antarctic ice sheets through the Cenozoic (0–65 million years ago). These records document an ice-free subtropical Antarctica between ~52 and 40 million years ago when CO was ~1,000 ppm; the initiation of continental-scale Antarctic ice sheets ~34 million years ago as CO dropped below 800 ppm; evidence for a dynamic, largely terrestrial, ice sheet driving global sea level changes of up to 40 m amplitude between 34 and 15 million years ago; and colder periods of highly dynamic, marine-based ice sheets contributing up to 20 m of global sea level rise when CO levels were in the range of 500–300 ppm between ~14 and 3 million years ago. Notwithstanding these discoveries, paleoenvironmental records obtained around Antarctica are still limited in their geographical coverage and do not provide a basis for comprehensive understanding of how different sectors of Antarctica respond to climate perturbations. Transects of drill cores spanning ice-proximal to ice-distal environments across the continental margin and at sensitive locations that have been identified by models and recent observations are needed to fully understand temporal and spatial ice volume changes that result from complex ice sheet-ocean-atmosphere interactions. These records are also critical for reconstructing equator-to-pole temperature gradients through time to better understand global climate change, interhemispheric long-distance transmission of changes through the atmosphere and ocean (teleconnec-tions), and the amplification of climate signals in the polar regions. Future Antarctic scientific ocean drilling will remain key to obtaining records of past Antarctic Ice Sheet dynamics that can be integrated into coupled ice sheet-climate models for improved projections of sea level change. Thus, keeping an eye on ice sheet stability is critical for improving the accuracy and precision of predictions of future changes in global and regional temperatures and sea level rise., The authors are thankful for the opportunity to undertake this Antarctic scientific ocean drilling 50-year review and outlook into the future. We are especially thankful to two formal reviewers and to Anthony Koppers and Debbie Thomas for their useful comments on various aspects of the manuscript. Support for C. Escutia to conduct this activity comes from Grant CTM2017-89711-C2-1-P, CGL2016-75679P, co-funded by the European Union through FEDER funds.

Oceanography and limnology projects often require the collection of water samples for chemical analysis. Manual water sample collection is labor-intensive and often difficult, especially in remote locations or during nighttime hours. Here we describe a compact and inexpensive autonomous submersible multiport water sampler (AutoSampler) that is largely fabricated with off-the-shelf parts making it easier to build and maintain. The system can collect up to 12 discrete samples at user controllable times or intervals and is operated using open source Arduino hardware and software that can be user modified to meet deployment requirements. While the underwater pressure housing presented here is custom built from readily available materials, there are many commercially available pressure case options that can be used as a substitute. The electronic mounting plates and battery pack are designed so that they can easily be adapted to fit into other pressure case housings. Samples can be collected into bags or syringes and sample volume is set by adjusting how long the peristaltic pump is actuated. This AutoSampler allows research that would otherwise be too labor-intensive or logistically difficult to conduct, especially in remote locations.

Polar marine ecosystems are particularly vulnerable to the effects of climate change. Warming temperatures, freshening seawater and disruption to sea ice formation potentially all have detrimental ...

Given the recent trend towards establishing very large marine protected areas (MPAs) and the high potential of these to contribute to global conservation targets, we review outcomes of the last decade of marine conservation research in the British Indian Ocean Territory (BIOT), one of the largest MPAs in the world. The BIOT MPA consists of the atolls of the Chagos Archipelago, interspersed with and surrounded by deep oceanic waters. Islands around the atoll rims serve as nesting grounds for sea birds. Extensive and diverse shallow and mesophotic reef habitats provide essential habitat and feeding grounds for all marine life, and the absence of local human impacts may improve recovery after coral bleaching events. Census data have shown recent increases in the abundance of sea turtles, high numbers of nesting seabirds and high fish abundance, at least some of which is linked to the lack of recent harvesting. For example, across the archipelago the annual number of green turtle clutches (Chelonia mydas) is ~ 20,500 and increasing and the number of seabirds is ~ 1 million. Animal tracking studies have shown that some taxa breed and/or forage consistently within the MPA (e.g. some reef fishes, elasmobranchs and seabirds), suggesting the MPA has the potential to provide long-term protection. In contrast, post-nesting green turtles travel up to 4000 km to distant foraging sites, so the protected beaches in the Chagos Archipelago provide a nesting sanctuary for individuals that forage across an ocean basin and several geopolitical borders. Surveys using divers and underwater video systems show high habitat diversity and abundant marine life on all trophic levels. For example, coral cover can be as high as 40–50%. Ecological studies are shedding light on how remote ecosystems function, connect to each other and respond to climate-driven stressors compared to other locations that are more locally impacted. However, important threats to this MPA have been identified, particularly global heating events, and Illegal, Unreported and Unregulated (IUU) fishing activity, which considerably impact both reef and pelagic fishes.

The export of particulate organic carbon (POC) from the sea surface is an essential part of the biological pump. Export fluxes are the result of what is produced in surface water and how much is consumed during particle sinking in the water column. In the Ross Sea, fluxes of POC and total mass are well correlated implying that particle fluxes are dominated by biogenic debris.Here, we report new and reference data of vertical particle fluxes to below the productive layer obtained on decadal time scales (1990-2017) by automatic sediment traps tethered to moorings in the western Ross Sea (Antarctica). Compilation of all data available in the Ross Sea (23 sites, >1000 samples) shows that annual POC fluxes to below 200 m average 4.4±3.3 g C m-2 y-1. Particle fluxes are relatively low when primary production is high (spring-summer) followed by enhanced sedimentation in late summer-fall. The high degree of decoupling between production and sedimentation is unusual compared to records of Antarctic Peninsula and may represent low grazing rates. Furthermore, data exhibit a large interannual variability and a decreasing trend over time, with a clear shift after 2000. Do the reduced export fluxes depend on lower biological production, enhanced OM consumption, or other processes (e.g., lateral transfer of biogenic particles outside the study area)?Satellite observations allow us to reconstruct the seasonal and interannual change of chlorophyll biomass, and sea ice extent and duration. Water temperature recorded at mid-depth is used to monitor the different intrusion over time of CDW, the main driver of temporal variability of Fe supply for the Ross Sea. Time series of particle fluxes, chlorophyll, sea ice cover and mid-depth temperature will be compared in order to test if the recent reduction of downward particle fluxes depend on primary production changes.

Continuous stable isotope records from marine sediment cores spanning the Pliocene have been used to assess the oceans' response to major perturbations in the climate system as the oceans play an integral role in regulating the global distribution of heat and gases. The Early to mid-Pliocene has previously been characterized as a time of relative warmth followed by Late Pliocene Southern Hemisphere cooling and bipolar glaciation at ~2.7 Ma. Previous studies have predominantly focused on the Atlantic and Equatorial Pacific Oceans. In this study, we extended the deep water benthic foraminifera stable isotope record from Ocean Drilling Program (ODP) Site 1123 in the southwest Pacific, back to the warm Early Pliocene. This is a high-latitude site at the gateway where the abyssal waters enter the Pacific Ocean and provides information about the connection between the Southern Ocean and the Pacific. We identify a dichotomy between the deep southwest Pacific and South Atlantic δC records spanning the mid-Pliocene and suggest that this is most likely the result of variations in the relative contributions of Northern versus Southern Hemisphere deep waters to the different basins. At 3.6 Ma, δC values start to decrease; this is interpreted to represent alteration in preformed values as a result of increased remineralization of carbon caused by a reduction in deep ocean ventilation in the Southern Ocean. This is likely the consequence of a greater extent and seasonal duration of sea ice in the Southern Ocean from Antarctic Ice Sheet expansion and cooling.

Coastal vegetated habitats can be important sinks of organic carbon (Corg) and mitigate global warming by sequestering significant quantities of atmospheric CO2 and storing sedimentary Corg for long periods, although their Corg burial and storage capacity may be affected by on-going sea level rise and human intervention. Geochemical data from published 210Pb-dated sediment cores, collected from low-energy microtidal coastal wetlands in El Salvador (Jiquilisco Bay) and in Mexico (Salada Lagoon; Estero de Urias Lagoon; Sian Ka'an Biosphere Reserve) were revisited to assess temporal changes (within the last 100years) of Corg concentrations, storage and burial rates in tropical salt marshes under the influence of sea level rise and contrasting anthropization degree. Grain size distribution was used to identify hydrodynamic changes, and δ13C to distinguish terrigenous sediments from those accumulated under the influence of marine transgression. Although the accretion rate ranges in all sediment records were comparable, Corg concentrations (0.2-30%), stocks (30-465Mgha-1, by extrapolation to 1m depth), and burial rates (3-378gm-2year-1) varied widely within and among the study areas. However, in most sites sea level rise decreased Corg concentrations and stocks in sediments, but increased Corg burial rates. Lower Corg concentrations were attributed to the input of reworked marine particles, which contribute with a lower amount of Corg than terrigenous sediments; whereas higher Corg burial rates were driven by higher mass accumulation rates, influenced by increased flooding and human interventions in the surroundings. Corg accumulation and long-term preservation in tropical salt marshes can be as high as in mangrove or temperate salt marsh areas and, besides the reduction of Corg stocks by ongoing sea level rise, the disturbance of the long-term buried Corg inventories might cause high CO2 releases, for which they must be protected as a part of climate change mitigation efforts.

A 24-meter jumbo piston core (NBP0101 JPC41) collected from an inner shelf basin in Iceberg Alley reveals an approximately 2000-year history of unusually high primary productivity. Iceberg Alley, an ~ 85 km long and 10–20 km wide cross-shelf trough on the Mac.Robertson Shelf, East Antarctica, reaches depths of 850 m and is bounded on either side by shallow banks that are lined with grounded icebergs. The sediments are laminated on a mm- to cm-scale throughout and are highly biosiliceous. Microscopic examination of smear slides, quantitative diatom slides, and sediment thin sections reveals that the sediments are visually dominated by the diatom Corethron pennatum, a large and lightly silicified species notable for its long and narrow shape; the valves, girdle bands and spines are all exceptionally well-preserved, suggesting rapid sedimentation. Other common species include sea ice-related Fragilariopsis, such as F. curta and F. cylindrus, with lesser contribution from other large diatoms, including Rhizosolenia spp. and Chaetoceros Ehrenberg subg. Chaetoceros. Chaetoceros Ehrenberg subg. Hyalochaete Gran resting spores, typically associated with large early-season blooms and common in many laminated sedimentary sections around the Antarctic margin, are surprisingly rare. Laminae with any significant terrigenous component are also very rare. Individual laminations appear to represent blooms, and in some cases sub-seasonal events are likely preserved. We suggest that this productive system is associated with the continuous presence of low-salinity meltwater derived from a combination of sea ice melt and grounded icebergs, which may be a source for a steady supply of micronutrients such as iron to the surface mixed layer.

International development country classifications are important for achieving development goals by directing differential support to a group of countries facing common development constraints. The small island developing States (SIDS) classification is a widely used country classification supporting developing island nations. Some nations are now self-identifying as “large ocean states” (LOS), citing the central role of the ocean for their development. Here we show the need for a new ocean-based LOS country classification by highlighting important limitations of current classifications. We analyze this further by enumerating 15 nations self-identifying as LOS since 2001 in official UN statements, most often citing ocean-based economy, size of ocean territory, and vulnerability to climate change as evidence. An ocean-based LOS classification, which requires further research to fully define, would complement existing classifications by targeting countries that disproportionately rely on the ocean to achieve sustainable development priorities, including the United Nations Sustainable Development Goals.

The anatomy of the Last Glacial Termination (T1) in the southern mid-latitudes, and its relationship with changes in the Southern Westerly Winds (SWW), offers empirical constraints for understanding the mechanisms involved in the transition from the Last Glacial Maximum into the current interglacial. Northwestern Patagonia (40°-44°S) is a sensitive region for monitoring past changes in the SWW, the Patagonian Ice Sheet, terrestrial ecosystems, and fire regimes through T1. Here we present results from Lago Fonk (∼40°S) to examine the structure of T1 based on the palynological, macroscopic charcoal, elemental, and isotopic composition of organic lake sediments. We observe an instantaneous establishment of Nothofagus-dominated forests at the onset of T1, followed by a diversification and densification trend that culminated with the establishment of thermophilous, Myrtaceae-dominated North Patagonian rainforests between ∼15.6–14.7 cal ka BP. The expansion of the conifer Podocarpus nubigena marks a shift to cool-temperate and hyperhumid conditions, coeval with high lake levels and enhanced algal productivity between ∼14.7–11.9 cal ka BP. Stand-replacing fires, driven by enhanced seasonality or high-frequency rainfall variability, started at ∼12.4 cal ka BP and catalyzed the rapid spread of Weinmannia trichosperma. Subsequent warming and a decline in precipitation at ∼11.4 cal ka BP led to intense fire activity, lake-level lowering, and establishment of the Valdivian rainforest trees Eucryphia/Caldcluvia. Our results suggest a coherent linkage between changes documented in the amphi south Pacific region and Antarctic ice cores during T1. This implies a zonal and hemispheric response to changes in the position/intensity of the SWW that emphasizes their central role as a key driver of the hemispheric and global climate evolution through T1.

The rail industry is being driven to reduce energy consumption and ensure value for money in order to remain competitive with emerging road transport technologies. Furthermore, rail networks are faced with the challenge of increasing capacity to meet a growing demand. The primary means of increasing capacity is to upgrade the signalling system. This paper therefore presents the development of a rapid railway simulation tool, designed to aid decision making at the conceptual stage of planning signalling upgrades. The railway simulation tool features a multi train simulator capable of evaluating the capacity and energy consumption of a section of track under two configurations of a new European signalling standard. The simulation tool also features an integrated Brute Force algorithm designed to optimise the train control strategy to reduce energy usage whilst not affecting the line capacity. Using the Cambrian line between Welshpool and Aberystwyth as a case study, the simulator found that up to 31 trains per hour is achievable. However, if the line should operate with a capacity of 10 trains per hour, the extra headway can be used to make an energy saving of 8% for a 1.2% increase in journey time.

Despite accounting for the majority of sedimentary methane, the physiology and relative abundance of subsurface methanogens remain poorly understood. We combined intact polar lipid and metagenome techniques to better constrain the presence and functions of methanogens within the highly reducing, organic-rich sediments of Antarctica’s Adélie Basin. The assembly of metagenomic sequence data identified phylogenic and functional marker genes of methanogens and generated the first Methanosaeta sp. genome from a deep subsurface sedimentary environment. Based on structural and isotopic measurements, glycerol dialkyl glycerol tetraethers with diglycosyl phosphatidylglycerol head groups were classified as biomarkers for active methanogens. The stable carbon isotope (δ13C) values of these biomarkers and the Methanosaeta partial genome suggest that these organisms are acetoclastic methanogens and represent a relatively small (0.2%) but active population. Metagenomic and lipid analyses suggest that Thaumarchaeota and heterotrophic bacteria co-exist with Methanosaeta and together contribute to increasing concentrations and δ13C values of dissolved inorganic carbon with depth. This study presents the first functional insights of deep subsurface Methanosaeta organisms and highlights their role in methane production and overall carbon cycling within sedimentary environments.

Coral bleaching caused by heat stress (warm water) will arguably be the greatest driver of coral reef loss in the coming decades. Understanding how corals have adapted to distinct oceanographic regimes on multiple scales can provide insight into future tolerance and persistence, information critical to directed intervention or targeted protections. The northern Line Islands span a gradient in oceanographic regimes across latitudes, with seawater becoming warmer, fresher, more oligotrophic, and more saturated with aragonite away from the equator. The combination of this regional gradient and island-scale (local) conditions was used as a natural experiment against which to test how massive Porites corals respond to these background conditions and episodic heat stress. We found that coral condition, represented by a metric combining tissue thickness, lipids, and calcification, was similar at almost all islands, though there were differences in how corals allocate resources among these biological parameters. Corals at Teraina, the most densely inhabited island, showed evidence for reduced calcification, potentially associated with human impacts and/or outflow of freshwater from the island. In contrast, Porites corals at Palmyra, a wildlife reserve, exhibited unexpectedly high tissue-condition metrics for its latitude, suggesting an additional food source, possibly plankton-rich lagoonal outflow. We did not find a strong relationship between human habitation and the response of Porites corals to recent heat stress. However, differences in coral calcification rates and energy stores between observed values and those expected based solely on the regional oceanographic gradient, suggests local effects have indirect impacts on these corals.

Although the Ross Sea is one of the most productive regions in Antarctica, it is not clear to what extent this region is an atmospheric CO2 sink. We calculate instantaneous CO2 flux rates with in situ pCO2 and wind speed data from 20 cruises in the Ross Sea. In addition, we estimate annual CO2 fluxes into the Ross Sea with nutrient budgets from a late summer cruise. We find that the Ross Sea is a lesser atmospheric CO2 sink (-7.5±0.5 Tg C yr−1, -1.3±0.1 mol C m−2 yr−1) than previously reported (-13 Tg C yr−1, -1.7 to -4.2 mol C m−2 yr−1). One exception is Terra Nova Bay (TNB) in the western Ross Sea, with CO2 flux rates (-4.8±0.3 mol C m−2, January-March) that are 3-4 times greater than the Ross Sea mean. The majority of the CO2 flux into TNB occurs during the late summer with instantaneous CO2 flux rates up to -246 mmol C m−2 d−1. These extraordinary CO2 flux rates are caused by the unique coupling of strong katabatic winds and low surface pCO2 values. Although strong katabatic winds deepen the mixed layer and entrain CO2 rich water from below, late season net community productivity maintains low surface water pCO2 levels. While TNB only covers ∼1% (3600 km2) of the Ross Sea continental shelf, extraordinary air-to-sea CO2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas (148,000 km2 combined), including Antarctic Bottom Water formation regions.

Trace elemental ratios preserved in the calcitic skeleton of bamboo corals have been shown to serve as archives of past ocean conditions. The concentration of dissolved barium (BaSW), a bioactive nutrientlike element, is linked to biogeochemical processes such as the cycling and export of nutrients. Recent work has calibrated bamboo coral Ba/Ca, a new BaSW proxy, using corals spanning the oxygen minimum zone beneath the California Current System. However, it was previously unclear whether Ba/Cacoral records were internally reproducible. Here we investigate the accuracy of using laser ablation inductively coupled plasma mass spectrometry for Ba/Cacoral analyses and test the internal reproducibility of Ba/Ca among replicate radial transects in the calcite of nine bamboo corals collected from the Gulf of Alaska (643–720 m) and the California margin (870–2054 m). Data from replicate Ba/Ca transects were aligned using visible growth bands to account for nonconcentric growth; smoothed data were reproducible within ~4% for eight corals (n = 3 radii/coral). This intracoral reproducibility further validates using bamboo coral Ba/Ca for BaSW reconstructions. Sections of the Ba/Ca records that were potentially influenced by noncarbonate bound Ba phases occurred in regions where elevated Mg/Ca or Pb/Ca and coincided with anomalous regions on photomicrographs. After removing these regions of the records, increased Ba/Cacoral variability was evident in corals between ~800 and 1500 m. These findings support additional proxy validation to understand BaSW variability on interannual timescales, which could lead to new insights into deep sea biogeochemistry over the past several centuries.

Antarctica's continental shelves generate the densest waters in the world and are responsible for the formation of Antarctic Bottom Water (AABW), a water mass with the potential to sequester carbon in the deep ocean for millennia. One such form of marine carbon is dissolved organic carbon (DOC), the ocean's largest standing stock of reduced carbon. In this study, we quantify DOC enrichment in dense shelf waters (DSW) in the Ross Sea and assess the potential for DOC to be sequestered from Antarctic shelves into AABW. We find that Ross Sea DSW is enriched in DOC by ∼7 μmol kg−1 relative to the incoming source waters (initial conditions), which is primarily caused by vertical mixing. The total DOC excess in DSW suggests that 4.0 ± 0.6 Tg DOC yr−1 is exported off the shelf. However, this exported fraction does not appear to persist in newly formed AABW and is likely remineralized, sequestering this carbon as TCO2 in the deep ocean.

Panama's extreme hydroclimate seasonality is driven by Intertropical Convergence Zone rainfall and resulting runoff. River discharge (Q) carries terrestrially-derived barium to coastal waters that can be recorded in coral. We present a Ba/Ca record (1996–1917) generated from a Porites coral colony in the Gulf of Chiriqui near Coiba Island (Panama) to understand regional hydroclimate. Here coral Ba/Ca is correlated to instrumental Q (R = 0.67, p

The phytoplankton bloom in the Ross Sea is the largest in spatial extent and one of the most productive in Antarctica, yet the fate of the summer bloom remains poorly understood. Here we present carbon system data from the first biogeochemical process cruise to be conducted in both the western and central Ross Sea during late summer (February–March 2013). Using one-dimensional carbon budgets, we found evidence for substantial positive net community production (425 ± 204 mmol C m−2 d−1) during the late summer in Terra Nova Bay (TNB) of the western Ross Sea, which was rapidly exported to below 200 m. In addition, seasonally integrated carbon export was higher in diatom-dominated TNB (7.3 ± 0.9 mol C m−2) compared to the Phaeocystis antarctica-dominated central Ross Sea (3.4 ± 0.8 mol C m−2). Substantial late summer productivity and export may be a widespread phenomenon in Antarctic coastal regions that is not accounted for in regional carbon models.

We present a hydrodynamic analysis of an atoll system from modeling simulations using a coupled wave and three-dimensional hydrodynamic model (COAWST) applied to Palmyra Atoll in the Central Pacific. This is the first time the vortex force formalism has been applied in a highly frictional reef environment. The model results agree well with field observations considering the model complexity in terms of bathymetry, bottom roughness, and forcing (waves, wind, metrological, tides, regional boundary conditions), and open boundary conditions. At the atoll scale, strong regional flows create flow separation and a well-defined wake, similar to 2D flow past a cylinder. Circulation within the atoll is typically forced by waves and tides, with strong waves from the north driving flow from north to south across the atoll, and from east to west through the lagoon system. Bottom stress is significant for depths less than about 60 m, and in addition to the model bathymetry, is important for correct representation of flow in the model. Connectivity within the atoll system shows that the general trends follow the mean flow paths. However, some connectivity exists between all regions of the atoll system due to nonlinear processes such as eddies and tidal phasing. Moderate wave stress, short travel time (days since entering the reef system), and low temperature appear to be the most ideal conditions for high coral cover at this site.

Kelp forests are among the world's most productive marine ecosystems, yet little is known about their biogeochemistry. This study presents a 14-month time series (July 2013–August 2014) of surface and benthic dissolved inorganic carbon and total alkalinity measurements, along with accompanying hydrographic measurements, from six locations within a central California kelp forest. We present ranges and patterns of variability in carbonate chemistry, including pH (7.70–8.33), pCO2 (172–952 µatm), and the aragonite saturation state, ΩAr (0.94–3.91). Surface-to-bottom gradients in CO2 system chemistry were as large as the spatial gradients throughout the bottom of the kelp forest. Dissolved inorganic carbon variability was the main driver of the observed CO2 system variability. The majority of spatial variability in the kelp forest can be explained by advection of cold, dense high-CO2 waters into the bottom of the kelp forest, with deeper sites experiencing high-CO2 conditions more frequently. Despite the strong imprint of advection on the biogeochemical variability of the kelp forest, surface waters were undersaturated with CO2 in the spring through fall, indicative of the strong role of photosynthesis on biogeochemical variability. We emphasize the importance of spatially distributed measurements for developing a process-based understanding of kelp forest ecosystem function in a changing climate.

Although reef coral skeletal carbon isotopes (δ13C) are routinely measured, interpretation remains controversial. Here we show results of a consistent inverse relationship between coral δ13C and skeletal extension rate over the last several centuries in Porites corals at Fiji, Tonga, Rarotonga and American Samoa in the southwest Pacific. Beginning in the 1950s, this relationship breaks down as the atmospheric 13C Suess effect shifts skeletal δ13C > 1.0‰ lower. We also compiled coral δ13C from a global array of sites and find that mean coral δ13C decreases by −1.4‰ for every 5 m increase in water depth (R = 0.68, p, Rising anthropogenic CO2 levels in the atmosphere are resulting in ocean acidification which may impact coral growth rates. Here, the authors quantify the relationship between water depth and δ13C compositions of South Pacific corals from the pre-industrial era, and their results should lead to improvements in the precision of sea level reconstructions using fossil corals.