Antarctic Ocean and Resources Variability
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Sign up to take part. A Nature Research Journal. Understanding how the Antarctic ice sheet will respond to global warming relies on knowledge of how it has behaved in the past. As these processes do not observe disciplinary boundaries neither should our future research. Once this threshold is reached, global sea-level rise of several, possibly tens, of meters on timescales of centuries to millenia becomes inevitable 3 , 4. Currently, ice-sheet models disagree on the origin and magnitude of the main processes driving AIS retreat and on the proportion of its contribution to projected sea-level rise by and beyond 4 , 5 , 6 , as well as in the past 7 , 8.
It has been observed and modeled that in areas where the bed slopes toward the continental interior, ice shelf thinning can lead to a Marine Ice-Sheet Instability MISI 10 , Both numerical simulations and observations show that if the buttressing support of the floating ice shelves is removed from the grounded ice, ice-sheet flow to the ocean may be enhanced 12 , leading to accelerated and substantial mass loss in a few years to a few decades Direct measurements of physical processes and their feedbacks leading to MISI are difficult to aquire over the spatio-temporal scales of glaciological changes, however.
Alternatively, past evidence, testifying to repeated rapid retreats of both the East and West components of the AIS EAIS and WAIS over the past 5 million years 14 , provides a valuable basis for validation of the physics of numerical climate and ice-sheet models, allowing calibration between the past and future in our assessments of ice sheet evolution. Numerical studies have shown that kilometer to sub-kilometer spatial resolution is needed to simulate grounding zone migration of ice shelves and outlet glaciers 15 , and to calculate the intermittent and highly-localized incursions of oceanic warm waters across the continental shelf break, partly caused by short-term mesoscale eddy formation Fig.
Conceptual and simplified view of the Antarctic polar system. The depth and shape of the continental shelf edge and slope determine where the intrusions of CDW occur. The sub-cavity ocean processes and the glacio-isostatic adjustment will be discussed in upcoming reviews by Smith et al. Note that the oceanic processes represented in 2D view for the purpose of the illustration might not occur at the same locations on the continental shelf.
The resulting glacio-isostatic adjustment induces feedbacks that enhance or dampen ice retreat on various spatial and temporal scales to be discussed in an upcoming review by Whitehouse et al. These processes take place within the subsurface environment of both the ice sheet and the ocean, and at the physical interfaces between them, which necessitates cross-disciplinary research to observe, measure, and understand them. These three physiographic realms subglacial, continental shelf, and ocean are understudied, yet critical to forming knowledge of AIS evolution from the deep past to the future Fig.
Ice-sheet flow is controlled by processes acting at its bed. Although ice flow can occur slowly by the deformation of ice, it is sliding over an ice-rock interface or deformation of weak water-saturated basal sediments that mainly dictates the flux of ice to the ocean. Sliding of ice sheets is constrained by bed roughness at a variety of scales from the macro i. Basal water, where present, may lubricate the base of an ice sheet or a glacier, causing ice flow acceleration 19 and enhancing erosion of the bed Depending on bed morphology and conditions, subglacial water is now understood to exist in three ways Fig.
Key elements of suglacial hydrology. Sliding induces a reduction in basal drag and accelerates ice flow. Figure 2b has been adapted with permission from Springer Nature; Nature volume , pages —, Duncan J. Wingham, Martin J. Siegert, Andrew Shepherd, Alan S. Muir 20 April doi Figure 2ewas reproduced from Figure 4 of King, E. Thanks to radio-echo sounding RES campaigns, more than subglacial lakes, scattered across the continent, have been identified to date 20 , 21 Fig. Their bright, smooth specular radio-wave reflections are distinct from those over ice-rock Fig.
Although the heat for the meltwater that feeds subglacial lakes is not known well, geothermal heat and that developed from basal friction, as well as pressure melting point decrease from hydrostatic pressure, are the main factors Fig. How water flows beneath the ice sheet is critical to the dynamics of ice above. As a consequence, water melted beneath the center of an ice sheet is routed to its margins 24 , 25 , where drainage may occur 26 , 27 over a period of weeks and months. Hence, there is an association between the fast-flowing ice streams and sliding and the availability of water at their beds 28 , On longer timescales, groundwater could accumulate in subglacial aquifers during glaciations 30 and be released during interglacials, when the ice sheet thins and retreats, inducing further ice flow changes.
Basal motion is a key component of the total velocity solution for a modeled ice mass, and depends on both macro- and micro-scale roughness and basal resistance dragging stresses of the bed 18 Fig. Although model comparison studies show that this transition improves grounding-line tracking, the artificially imposed smoothing along the grounding line might not be valid everywhere.
Despite localized high-resolution bed observations for some areas, the current low spatial resolution of subglacial topography from BEDMAP2 34 precludes detailed knowledge of basal water pathways over most of Antarctica and impedes precise simulations of basal hydrology within ice-sheet models. Continent-wide models have achieved success with simulations using this and related techniques 5 , Inverting ice velocities does not provide explicit information on the basal hydrology nor on past or future changes in basal conditions.
Consequently, when climate conditions depart too much from present-day state and lead to substantial expansion or retreat of the AIS away from its present-day margins, this technique fails. Hence, there is an urgent need to refine the parameters for basal hydrologic processes in ice-sheet models. A hydrological scheme bridging the gap between relatively small-scale geophysically observed phenomena and their representation in continental-scale ice flow models has been implemented and tested within the Parallel Ice Sheet Model This mass-conservative scheme includes a subglacial deformable sediment layer combined with a distributed system of linked, water-filled cavities that open as a consequence of sliding and close due to the creep of ice over a range of spatial and timescales.
Some conceptual experiments have produced realistic simulations of ice flow over subglacial lakes using simplified geometry 38 or for a limited area domain At a continent scale, the best results will be achieved once high-resolution bed topography, geothermal heat flux distribution 40 , 41 , 42 , and the location and thickness of subglacial sediments are known well.
More direct observations of these are needed to account for hydrological processes and to improve ice-sheet models. A great utility of RES observations is in the identification and location of basal water, and mechanisms by which water may flow. This shortfall can be addressed by other methods such as sonar, gravity inversion, and seismic surveying that may reveal the thickness and extent of soft water-saturated basal sediments 43 , 44 Fig.
The need for high-resolution subglacial bed topography and seabed bathymetry is demonstrated by recent work that reveals a relict hydrological network dating back to the last glaciation and evidence for grounding line retreat across the Ross Sea shallow continental shelf Cross-cutting relationships between fluvial channels and grounding zone wedges also show that hydrological networks evolve through time 46 , 47 , as a consequence of glacial dynamics changes and of erosion of the subglacial bed itself.
Hence, there is much knowledge of modern hydrological processes to be gained from the study of paleo ice-sheet beds. Robust and accurate past subglacial bed and seabed morphology reconstructions e. Reconstructions of past subglacial and seabed morphology of the continental margins of Antarctica represent a challenge for the paleo-polar community. However, inherent inaccuracies arising from heterogeneous spatial data coverage Fig.
Paleo-ice-sheet simulations will be improved when robust reconstructed paleo-bed topography is provided to the modeling community. Present and past knowledge of continental margins morphology.
White or gray areas indicate little or no data coverage. The change from a prograding to aggrading continental shelf edge indicated by the arrows is observed after RSU2 from early to mid-Pliocene 4—3. For areas having dense seismic and deep drilling data coverage Fig. To reconstruct paleo-depths and continental shelf morphology between two maximum glacial advances, spatial sediment erosion has to be quantified.
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Sediment isopach maps 59 , 60 , 61 combined with seismic stratigraphy and drilling sites are used to trace back the eroded sediments to their source position Uncertainty in those reconstructions is large and depends on the spatial data coverage. In the case of the Ross Sea, backstripping and depth calculations for Miocene units robustly show a change in sedimentary deposition from shallow and seaward dipping to overdeepened and landward dipping continental shelves 52 Fig. The correct interpretation of backstripping reconstructions relies on the knowledge of past sedimentological and climatic history of the continental shelf environments.
The formation of trough-mouth fans at the continental shelf edge and a decreased sedimentation rate on the rise 69 both indicate extensive subglacial sediment erosion and glacial marine deposition on the outer shelf and upper slope. In several locations, progradational wedges imaged seismically show that an expansion of the continental shelves occurred before the mid-Pliocene Fig.
An aggradation of the shelf followed with deepening of the landward slope Fig. The dynamic geological history of the AIS margins clearly demonstrates how past continental shelf morphologies differed from the modern one. The time of the reconstruction is for the presumed onset of continental glaciation at the Eocene-Oligocene Transition EOT.
Sea ice drift in the Southern Ocean: Regional patterns, variability, and trends
To achieve pan-Antarctic paleobathymetric reconstructions of these key periods, and reduce uncertainties in basal morphology, precise age and environmental information e. Some regional maps of key Cenozoic horizons and sequences have recently been published 54 , 59 , 60 , 61 , 63 , 72 , however, the paucity of stratigraphic constraints hinders the comprehensive pan-Antarctic correlation of known horizons and pan-Antarctic bathymetric reconstructions.
Additional geophysical and drilling campaigns will be necessary to fill gaps in circum-Antarctic coverage and provide pan-Antarctic past boundary conditions to ice-sheet models. Recent numerical studies 17 , 57 , 73 highlight the large spread in simulated ice volumes and extents produced by the uncertainties, or the lack of definition, of past bed morphologies. For example, simulations of AIS dynamics across the EOT using a maximum, mostly emergent, topography lead to larger ice volume and extent than when using a minimum, more subdued topography.
Finally, the variations in bed over time likely had consequences for the AIS response to atmospheric and ocean forcing. When tested in ice-sheet simulations, AIS sensitivity to changes in ocean temperature increases along with a gradual deepening of the continental shelves. This is because the area of ice shelves that is exposed to ocean heat increases with a deepening of the bathymetry The role of ocean heat supply to AIS margins is a key aspect of ice-sheet vulnerability to global warming.
Nowadays, oceanic measurements show how subsurface water masses enter into floating ice-shelf cavities inducing melting from below 9 , Limited geological evidence for such processes exists, documenting grounded ice sheet retreat as ocean temperatures have risen However, the mechanisms, spatio-temporal scales, and magnitude of ocean heat and salt transport onto and across the shallow Antarctic continental margins, and into marine embayments, remain poorly understood.
As in the case of subglacial hydrology and ice-sheet dynamics, bed morphology exerts a fundamental control upon each of these factors 81 and must have done so in the geological past. In particular, bathymetry modulates Southern Ocean heat transport to the Antarctic continental slopes and shelves over the following three main spatial and temporal scales Fig. Schematics of bathymetric control on open-ocean circulation.
Impact of long-term continental shelf expansion on the Southern Ocean high-latitude circulation in the Weddell Sea during the mid-Miocene a , during the late-Pleistocene b , and under modern-like climate conditions. During mid-Miocene a , high-latitude ocean circulation is shifted southward due to the smaller continental shelf break 63 compared with the modern one b. Ice-sheet advance on the continental shelf inhibits oceanic circulation, which limits the incursions of CDW During ice-sheet retreat from the continental shelf edge, shallow-shelf ocean circulation is restored.
Model simulations of super interglacials suggest that Westerly and Easterly winds are strengthened and are shifted polewards compared to their modern position d. However, depending on the depth of the continental shelf break and the strength of the Easterly winds modulated by atmospheric teleconnections, CDW may or may not intrude on the continental shelf, despite warm conditions.
The Antarctic Circumpolar Current ACC position is, to a great extent, constrained by the bathymetry of the ocean basins and gateways, and by the topography of the continental landmasses that affects the position of the local maximum of the Westerly winds Climate simulations of the EOT have shown that the opening of the gateways did not substantially change the moisture supply to the AIS enough to explain its complete glaciation 84 , but the gateway opening did contribute to a large-scale cooling, leading to the gradual expansion of ice sheets Although the mean position of the ACC is controlled by long-term changes in ocean gateways, its strength and vigor depend upon the strength and relative position of the Westerly winds, in turn determined by the mean climate state.
In general, a warmer climate is associated with a southward shift and strengthening of the Westerly winds 86 , leading to a more vigorous ACC, enhanced advection and volume of Circumpolar Deep Water CDW , and strong-bottom Ekman transport and vice versa under cold climate conditions An intensification and poleward shift of near-surface ocean winds, attributed to positive Southern Annular Mode-like trends atmospheric teleconnection is projected for warmer climates by most climate models by This is of consequence, because heat transport to southern latitudes is in part regulated by the strength of the ACC.
Then, as the continental margin prograded northward close to its modern position, the model simulations show that AABW formation weakened. Impact of extent and location of the continental shelf break on ocean circulation for different mean climate states. Comparison between a and b gives the impact of the continental shelf extent and location, whereas comparison between a and c shows the impact of AIS extent and CO 2 concentration, which is of minor importance.
Changes in ocean circulation on shorter timescales thereafter resulted from orbital effects, atmospheric CO 2 forcing and sea-ice cover change.
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The degree of local bathymetric control upon ocean circulation is strongly dependent on the mean climate state. Furthermore, during the last deglaciation and the Pliocene warm periods, paleoceanographic data point to increased upwelling of CDW and incursion onto the continental shelf on suborbital timescales 80 , 92 , 93 Fig. If sea-ice cover is absent or reduced over the Antarctic continental shelves, freshening of the sea surface, along with strong Easterlies, facilitates upwelling of relatively warm CDW by increasing southward Ekman transport 94 , consistent with simulated mid-Pliocene ocean dynamics Fig.
During glacials, the subsurface ocean circulation cannot reach the continental shelf break Fig. Due to strong winds and enhanced sea-ice formation during glacials relative to pre-industrial conditions Fig. On the one hand, incursions of CDW are controlled by the depth and the curvature of the continental shelf break 97 , as well as by the concavity or convexity of the isobaths along the slope, as, e. Episodically, when Easterly winds weaken and bottom water accumulates on the continental shelf, overflow occurs and allows for the inflow of CDW.
The main circulation path is also modulated at regional scale by mesoscale eddy activity. Those slope processes are essential to the AABW formation; however, according to model grid resolution, the steepness and morphology of the continental slope can be misrepresented. As a consequence, models might not capture adequately the overflow of AABW from the shelf across the shelf break and downslope, and the subsequent strongly baroclinic inflow of CDW. The lack of resolved bathymetry in models creates an incorrect heat transport across the continental shelf and incorrect sub-shelf melting, which in turn might induce an incorrect grounding line responses.
However, this is a challenge, because high-resolution simulations cannot be integrated over the millennial timescales that are needed to account for long-term heat transport at global and regional scale. In the absence of pan-Antarctic high-resolution coupled ice-sheet-ocean models, we must learn about the AIS response to ocean warming from stand-alone circum-Antarctic 99 or regional ocean implementations such as the Weddell Sea or the Ross Sea , or from physically based sub-shelf melting parameterizations in stand-alone ice-sheet models Those implementations are nevertheless useful to investigate how, under warmer than present mean climate states, ice sheets display threshold behavior in landward-deepening subglacial basins in response to relatively short-lived high-intensity ocean heat supply , This review provides insights into processes operating at the interfaces between the ice sheet, its bed, the ocean and the continental margins around Antarctica Fig.
It highlights the processes least understood, poorly investigated or not implemented in models, that are understood to operate in a connected manner Fig. Atmospheric and solid Earth processes may also come into play. For example, an interplay between long-term faulting and shorter term differential erosion 49 , may influence the ice flow and lead to formation of pinning areas that have a stabilizing effect on the ice shelves, and therefore on the ice sheet, during both advance and retreat across the continental shelf.
These interactions potentially induce MISI. Main gaps identified for the three realms discussed in the review colored circles. The largest unknowns are the processes and interactions at the interfaces between each realm arrows , which urgently require cross-disciplinary research. The impact of sub-shelf ocean circulation on ice-sheet dynamics across the grounding zone dashed arrow is one of the least understood feedbacks and could contribute to processes leading to MISI. The knowledge gap has consequences for climate and ice-sheet model development, and experimental design strategies, because observations are needed to validate those recently developed or to develop new parameterizations of ocean—ice-sheet interactions Timescales of grounding line response to ice-sheet advance, MISI, or ice-sheet retreat may span several thousands of years to a few years or centuries.
Conversely, ice-sheet response to atmospheric or oceanic warming and circulation changes can span centuries or millennia e. The spatial framework for MISI and for grounding line advance or retreat is regional to local, whereas atmospheric or ocean circulation and heat transport changes are affected by processes that act both at the local scale and regional to global scales.
One of the major challenges for the polar community to surmount is the representation of the interplay of long-term, large-scale processes, and small-scale, short-term processes from both observational and modeling points of view Fig. Processes occurring within the ice-shelf cavities are emblematic of this interplay, insofar as they span short timescales of hours e. Knowledge of the cavity environment is imprecise because of the scarce spatial and temporal data coverage for the present-day circum-Antarctic ocean and sub-shelf circulation, and for geological proxies that inform about past cavity conditions.
However, processes within the cavity may impact on the overall AIS dynamics and may have long-term consequences on AIS volume, potentially inducing large-scale changes in the global climate system and vice versa Fig. Therefor, it is paramount to acquire geological proxies for paleo-oceanic conditions at sufficient temporal and spatial resolution for direct comparison with present-day observations Spatio-temporal scales of the processes discussed in the present review. Short-term processes occurring at local to regional scales are the ones potentially triggering MISI.
Heat transport from open ocean to the continental shelf also depends on the long-term meridional overturning circulation dashed orange line.
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The difficulty for the modeling community resides in capturing the long-term essence of those processes, occurring at continental to global scale and short-term response occurring at local to regional scales within the same simulation. A trade-off between numerical model horizontal resolution and integration time is so far still necessary. Note that vertical resolution of numerical models is not mentioned but is essential to capture the continental slope and shelf oceanic processes heat, salt and nutrient transport. Note that glacio-isostatic adjustment GIA and sub-shelf melting are to be discussed in upcoming reviews by Smith et al.
The use of unstructured grids in climate and ice-sheet models is a good example of optimization and is under development. To support high-resolution modeling, improved continental shelf and sub-shelf bathymetry among other quantities is a priority. This publication summarizes the presentations and discussions from the workshop. View the Workshop Agenda with links to the presentations.
Workshop Proceeding. Get the Workshop Proceeding. Related Resources. This will open avenues for large-scale monitoring operations at the circumpolar level in the coming decades. The development of new sensors and on-board data-processing systems augurs for future studies to determine in situ , and store, in enhanced memories, information about the environment at fine scales so as to provide a true dynamic vision of the state of the Southern Ocean.
Linking the foraging behavior, trophic interactions and population dynamics of top predators, will also contribute significantly to the development of more efficient food-web models, which are crucial for the assessments of the life in the changing Southern Ocean. Universal food-web models e. Finally, the continuous improvements for realizing cost-effective high-throughput molecular sequencing will also impact various disciplines, including biogeochemistry, following previous work Bohmann et al.
Modeling forecasting tools have been developed and available to allow predictions, although there is a need for improvement Xavier et al. From a marine food webs forecasting perspective, in order to improve worldwide biological forecasting i. Moreover, assessing how these tipping points may affect Southern Ocean functioning is a relevant issue for the coming 20 years.
To this end, in addition to traditional monitoring, we need to conduct experimental manipulations over long timescales e. It remains a challenge to incorporate life-history parameters e. Furthermore, it is difficult to consider all ecologically relevant species, or the entire community, under multiple—instead of single—stressors in ecological risk models Gutt et al.
Special attention should be paid to invasive marine species or indigenous species that extend their biogeographic range and may cause a diversity shift that will disturb an existing dynamic equilibrium between trophic guilds. One of the questions of interest to Antarctic marine resource managers and policy makers concerns with our ability to differentiate ecosystem changes and climate-driven change from the effects of fisheries exploitation Figure 3. With respect to management of Southern Ocean living resources, in the face of near-future environmental change, CCAMLR endorsed the development of a feedback management strategy.
This system will use information on the status of the ecosystem to alter the levels of harvesting and spatial management of the Antarctic krill fishery. Such an approach offers the opportunity to make the initial attempts to forecast, and respond accordingly to, the potential impacts of climate change CCAMLR, through signals from components of the ecosystem such as meso- and top predators.
Similar initiatives must be carried out for other currently commercially exploited species, such as toothfish and icefish, whilst knowledge gaps in the ecology of species that have the potential to be exploited in the future should urgently be identified. The possibility to use Antarctic top predators as oceanographic samplers has already been demonstrated. For example, Southern elephant seals Mirounga leonina habitat cover huge areas of the Southern Ocean and are therefore useful to examine physical and biological changes occurring in the vast, remote, Southern Ocean throughout the year Roquet et al.
Further developments in the use of top predators as oceanographic samplers, bearing ethical concerns in mind, would not only address key issues on the ecology of the species, but also be an important step toward a more complete sampling and monitoring of the Southern Ocean. Figure 3. Conceptual diagram illustrating gaps of knowledge in Southern Ocean life and ecology research, examples of the main needs for technological developments, and how these must be linked to monitoring and modeling efforts to forecast future changes in the Southern Ocean.
The Arctic and the Antarctic differ in age, stability and heterogeneity, human presence, and ecosystem services Meltofte et al. How polar ecosystems are responding and will respond to change is paramount to our understanding of worldwide processes, and therefore much insight can be gained from comparative studies Smetacek and Nicol, ; Convey et al. Comparing these Polar Regions at species- and ecosystem-functioning levels will be very important in the coming years, under climate change scenarios, through collaboration across the international scientific community e.
Southern Ocean ecosystems are remote, sometimes isolated and may, consequently, be more easily affected by changes. Signals of natural dispersal, colonization, and diversification for Antarctica and the Southern Ocean are now at risk of being overwhelmed by impacts associated with changing climates and rapidly increasing human movement both into the region and between its distinct regions Chown et al. These characteristics imply that scientists must exert special care when conducting their experiments and, in this context, the international nature of Antarctic Science calls for a greater coordination among countries in defining ethical guidelines that will address the challenges of the coming decades.
Based on the Protocol on Environmental Protection to the Antarctic Treaty Madrid Protocol national Antarctic programs should continue to submit their science proposals to the impartial, national environmental agencies, but procedures may differ for each country. This diversity in the evaluation processes means that the same survey or experiment submitted to two different countries may not experience the same level of restriction. In addition, ethics committees could be aware of specific scientific approaches e. Absence of data could indeed be extremely prejudicial to producing effective conservation measures.
Due to the huge public interest in Antarctic animals e.
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As such, Antarctic marine ecologists should be encouraged to engage in science communication to the general public, address societal concerns about Antarctic environmental issues Pace et al. If Antarctica-is to be protected, remote ecosystems like the Southern Ocean deep-sea, under-ice shelves and those under permanent sea-ice, will have to be studied and monitored more intensively than in the past and principles of modern conservation science must be applied Kennicutt et al.
Based on the questions originally sent by the scientific community we consider the major gaps in the present ecological knowledge that are essential to shed light on tomorrow's Southern Ocean life and ecology. We concluded that basic biological information on the taxonomy and the physiology of organisms, ranging from viruses to top predators particularly the former , is still lacking, as well as in areas such as the deep-ocean floor or the under-ice environments. At an ecosystem level, the response and resilience to change is largely unknown, rendering accurate forecasting virtually impossible in the near future.
However, a future thorough understanding of these responses will be crucial for quantifying the importance of the various components of Antarctic ecosystem services e. Filling in these gaps will require the continuation of a long-term commitment and the development and use of innovative technology to adequately research and monitor the Southern Ocean ecosystems, to detect changes at an early stage, and to evaluate multi-stressor effects in marine ecosystems in order to improve modeling efforts focused on interactive effects.
Importantly, disciplines like taxonomy and long-term monitoring should receive strong logistical and financial support if we are to predict likely consequences of climate change and other threats. Finally, informing stakeholders, policy makers and the general public on the results of these studies will draw attention to the importance of this unique ecosystem, emphasize its global pivotal role, and most importantly, its increasing vulnerability to human-induced changes. JX, AB, and YR coordinated the manuscript and all the authors contributed writing and reviewing the manuscript.
All authors were highly active at the Horizon Scan, coordinating sessions with the Horizon Scan. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Finally, we also thank members of the SCAR expert groups e.
WS is funded by Arcadia. Agnew, D. Antarctic Sci. Arrigo, K. Marine microorganisms and global nutrient cycles. Nature , — Phytoplankton community structure and the drawdown of nutrients and CO 2 in the southern ocean. Science , — Baeseman, J. Krupnik, I. Allison, R. Bell, P. Culer, D. Hik, J. Lopez-Martinez, V. Rachold, E. Sarukhanian, and C. Barnosky, A. Approaching a state shift in Earth's biosphere. Nature , 52— Bennett, J. Polar lessons learned: long-term management based on shared threats in Arctic and Antarctic environments. Bohmann, K. Environmental DNA for wildlife biology and biodiversity monitoring.
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