Southern Ocean Marine Research Articles

Consensus or Not Consensus: That Is the CCAMLR Question

Recent commentary has highlighted inconsistencies between international legal concepts (norms and rules) and the capacity of States to adopt or implement them.1 In some cases, the State legal systems in place are readily able to accommodate the dynamic new norms that have evolved from rapid changes in contemporary international values or policies (e.g., in respect of torture, trade, greenhouse gas emissions, etc.). When this is not the case, the obvious conclusion is that legal operating systems need to adapt, or imbalances are likely to persist and new norms will not be given full effect.2 The Convention on the Conservation of Antarctic Marine Living Resources (CAMLR Convention)3 is a longstanding international agreement that celebrated its 25th annual meeting in 2006. In this article, we retrospectively analyze the Convention’s implementation by its administrative Commission (CCAMLR) to evaluate the regime’s adaptability. The article focuses on the key role that CCAMLR’s consensus-based decisionmaking has played in relation to a recent qualification to past practice arising from ‘‘consensus-minus-one’’ decisions. The overall effectiveness of the regime is accordingly assessed. Recognizing that consensus does not operate in a vacuum, we hypothesize that CCAMLR’s management of Southern Ocean marine living resources comprises at least four essential elements: cooperation, compromise, consensus, and compliance. To help explain how CCAMLR functions, a particular methodological template is applied to these elements to ascertain if it is possible to place them within either an operating or a normative system or sometimes both. As Figure 1 shows, the elements are essentially discrete, but linked; we emphasize this point by illustrating how they interact. Our study begins by exploring CCAMLR’s history and how cooperation has been achieved even though the overriding interests of the States involved encompass a commercially competitive activity (harvesting). Like many international legal instruments, the Convention’s negotiation invariably led to compromises. The Chairman’s Statement, appended to the Convention, is itself a built-in compromise on the application of CCAMLR’s jurisdiction. Finally, we examine what is meant by ‘‘consensus’’: how it operates to underpin compliance, and what the emerging notion of ‘‘consensus-minusone’’ implies. Our primary objective is to establish if the current CCAMLR decision-making process actually improves compliance—a reasonable expectation that indicates if the regime is working effectively.

Paradigm lost, or is top-down forcing no longer significant in the Antarctic marine ecosystem?

AbstractInvestigations in recent years of the ecological structure and processes of the Southern Ocean have almost exclusively taken a bottom-up, forcing-by-physical-processes approach relating various species' population trends to climate change. Just 20 years ago, however, researchers focused on a broader set of hypotheses, in part formed around a paradigm positing interspecific interactions as central to structuring the ecosystem (forcing by biotic processes, top-down), and particularly on a “krill surplus” caused by the removal from the system of more than a million baleen whales. Since then, this latter idea has disappeared from favour with little debate. Moreover, it recently has been shown that concurrent with whaling there was a massive depletion of finfish in the Southern Ocean, a finding also ignored in deference to climate-related explanations of ecosystem change. We present two examples from the literature, one involving gelatinous organisms and the other involving penguins, in which climate has been used to explain species' population trends but which could better be explained by including species interactions in the modelling. We conclude by questioning the almost complete shift in paradigms that has occurred and discuss whether it is leading Southern Ocean marine ecological science in an instructive direction.

Vegetation and climate of Auckland, New Zealand, since ca. 32 000 cal. yr ago: support for an extended LGM

AbstractAuckland occupies a climatically sensitive position close to a major biogeographic boundary in the southern mid‐latitudes. A new pollen record from Kohuora maar crater, Auckland, displays vegetation and climatic changes for the past ca. 32 000 years. Of particular interest are the inferred climatic patterns for the first part of the interval, encompassing the Last Glacial Maximum (LGM). The Kohuora record corresponds closely with pollen records from other Auckland sites indicating that the patterns observed are at least regional in extent. It is also broadly consistent with a variety of palaeoenvironmental evidence from across New Zealand, including the glacial record from Westland, other palynological records from North Island, other palaeoecological records from the South Island, and aeolian quartz sequences from western North Island. These records show that glacial conditions prevailed across most, if not all, of New Zealand during the interval ca. 29–19 k cal. yr BP, longer and earlier than the LGM sensu stricto. We suggest that the term extended LGM (eLGM) may be more appropriate for the New Zealand region. Within this predominantly cold interval, the Auckland pollen records indicate a climatic amelioration for the interval ca. 26–24 k cal. yr BP, also consistent with other palaeocological data from Canterbury, that fall within a period of climate amelioration recognised between the first two eLGM glacial advances in Westland. We refer to this warming interval as the eLGM Interstadial. The ca. 27 k cal. yr BP Kawakawa/Oruanui tephra is instrumental in most of these inter‐site comparisons and occurs after the first peak of eLGM cooling in a short‐lived comparatively mild phase. A subsequent return to apparently colder climate in the Auckland records may indicate a volcanic cooling effect or, more likely, widespread landscape disturbance following this major eruption event. Strong correspondence between biotic responses, glacial fluctuations and aeolian quartz deposition linked to major shifts in strength and latitudinal extent of the southern westerlies suggest that both the eLGM and eLGM Interstadial may be more widely registered, at least across the Southern Ocean. Support for this assertion comes from parallel investigations in western and southernmost South America and isotopic and palaeoecological records from Southern Ocean marine cores. Recent reconstructions of the globally averaged ice‐equivalent sea‐level history are in line with this evidence from the Southern Hemisphere, suggesting that the eLGM may have a global registration. In light of these observations, we suggest a re‐examination of the defined timing of the LGM along with renewed effort to establish climatic patterns during this period and understand their causes. Copyright © 2007 John Wiley & Sons, Ltd.

Environmental forcing and Southern Ocean marine predator populations: effects of climate change and variability.

The Southern Ocean is a major component within the global ocean and climate system and potentially the location where the most rapid climate change is most likely to happen, particularly in the high-latitude polar regions. In these regions, even small temperature changes can potentially lead to major environmental perturbations. Climate change is likely to be regional and may be expressed in various ways, including alterations to climate and weather patterns across a variety of time-scales that include changes to the long interdecadal background signals such as the development of the El Niño-Southern Oscillation (ENSO). Oscillating climate signals such as ENSO potentially provide a unique opportunity to explore how biological communities respond to change. This approach is based on the premise that biological responses to shorter-term sub-decadal climate variability signals are potentially the best predictor of biological responses over longer time-scales. Around the Southern Ocean, marine predator populations show periodicity in breeding performance and productivity, with relationships with the environment driven by physical forcing from the ENSO region in the Pacific. Wherever examined, these relationships are congruent with mid-trophic-level processes that are also correlated with environmental variability. The short-term changes to ecosystem structure and function observed during ENSO events herald potential long-term changes that may ensue following regional climate change. For example, in the South Atlantic, failure of Antarctic krill recruitment will inevitably foreshadow recruitment failures in a range of higher trophic-level marine predators. Where predator species are not able to accommodate by switching to other prey species, population-level changes will follow. The Southern Ocean, though oceanographically interconnected, is not a single ecosystem and different areas are dominated by different food webs. Where species occupy different positions in different regional food webs, there is the potential to make predictions about future change scenarios.

Distribution and abundance of Wilson’s storm petrels Oceanites oceanicus at two locations in East Antarctica: testing habitat selection models

Over the last decades, Antarctic seabird populations have been studied as bioindicators of the variability in the Southern Ocean marine ecosystem. Little information is available on the distribution and abundance of Wilson’s storm petrel (Oceanites oceanicus) in East Antarctica although the bioindicator value of this species has been investigated. Regional surveys were conducted at two coastal locations, Casey (66°S, 110°E) and Mawson (67°S, 62°E), to locate Wilson’s storm petrel nests using systematic searches in sites selected with a balanced random sampling design. Conducted in ice-free areas of similar size, searches located 553 Wilson’s storm petrel nests at Mawson and 630 at Casey. Comparable densities were observed between locations but regional estimates suggest that Wilson’s storm petrels are more abundant at Casey. Habitat preferences of Wilson’s storm petrels were investigated using resource selection functions based on Generalized Additive and Linear Models (GAMs and GLMs), which allow their ecological niche to be graphically and quantitatively described. The orientation of nests in relation to the prevailing winds was identified as a determinant of nest distribution at both locations. However, selected rock substrate types differed between Mawson and Casey. Snow was confirmed to constrain the spatial distribution of nests, especially at Casey where snow precipitations and accumulation are more common in summer, confirming the results of previous temporal surveys focusing on breeding success. At the southern edge of its geographic distribution, the Wilson’s storm petrel may be subject to more obvious climate related habitat changes in East Antarctica. Such models may provide valuable information to detect the potential effect of climate variations on this species and others, in the context of a broad Antarctic ecosystem monitoring.

Mid-latitude Southern Indian Ocean response to Northern Hemisphere Heinrich events

The lack of temporal resolution and accurate chronology of Southern Ocean marine cores has hampered comparison of glacial millennial-scale oscillations between the Southern Ocean, Antarctic ice and other records from both hemispheres. In this study, glacial climate variability is investigated over the last 50 ka using a multi-proxy approach. A precise chrono-stratigraphy was developed on the high-sedimentation rate core MD94-103 (Indian Southern Ocean, 45°35′S 86°31′E, 3560 m water depth) by geomagnetic synchronization between the later core and NAPIS75, and 14C dates. High-resolution time-series of δ18O in planktonic foraminifera Globigerina bulloides and Neogloboquadrina pachyderma, and sea surface temperatures (SSTs) estimated from the alkenone UK′37 index and foraminifera assemblages have been generated. Temporal evolution of the two temperature proxy records is notably different during the last glacial period. While foraminifera data indicate a consistent cooling towards the last glacial maximum, anomalous warm glacial alkenone temperatures suggest a strong advection of 〈warm〉 “detrital” alkenones by surface waters of the Agulhas current. Superimposed to this general trend, during Heinrich events, foraminiferal SSTs point to warmer surface waters, while concurrent alkenone SSTs exhibit apparent coolings probably caused by enhanced local alkenone production. By analogy to modern observations, possible influence of ENSO-like conditions on the subantarctic Southern Ocean SSTs is discussed.

Management of Southern Ocean fisheries: global forces and future sustainability

The marine resources of the Antarctic region are of global significance. In managing Southern Ocean marine resources, especially fisheries, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has adopted principles that aim: to balance harvesting and conservation; to protect the needs of dependent species, and to avoid changes that are irreversible in 20–30 years. CCAMLR has pioneered ecosystem approaches to fishery and environmental management, through the incorporation of precaution and uncertainty into its management procedures and by establishing an ecosystem monitoring programme using indicator species and processes. This pioneering application of precautionary and ecosystem approaches in the management of harvesting has met with some success, notably in applying conservative yield models for toothfish and krill stocks and in establishing strict rules for undertaking new and exploratory fisheries. However, toothfish management has been recently compromised by Illegal, Unreported and Unregulated (IUU) fishing which is driven by forces outside the Southern Ocean. Southern Ocean harvestable resources are also subject to other global forces such as environmental changes, and their management systems remain very vulnerable to rapid shifts in worldwide fishery economics, and to inadequate management in adjacent areas, particularly high seas. CCAMLR needs quickly to develop the basis of more flexible and effective management to cater for rapid shifts in capacity and demand. The complementary task, however, is to raise the management standard of other Regional Fisheries Management Organisations (RFMOs) to those of CCAMLR if global high seas marine resources are to be sustainable for the rest of this century.

OH and HO<sub>2</sub> chemistry in clean marine air during SOAPEX-2

Abstract. Model-measurement comparisons of HOx in extremely clean air ([NO]<3 ppt) are reported. Measurements were made during the second Southern Ocean Photochemistry Experiment (SOAPEX-2), held in austral summer 1999 at the Cape Grim Baseline Air Pollution Station in north-western Tasmania, Australia. The free-radical chemistry was studied using a zero-dimensional box-model based upon the Master Chemical Mechanism (MCM). Two versions of the model were used, with different levels of chemical complexity, to explore the role of hydrocarbons upon free-radical budgets under very clean conditions. The "detailed" model was constrained to measurements of CO, CH4 and 17 NMHCs, while the "simple" model contained only the CO and CH4 oxidation mechanisms, together with inorganic chemistry. The OH and HO2 (HOx) concentrations predicted by the two models agreed to within 5–10%. The model results were compared with the HOx concentrations measured by the FAGE (Fluorescence Assay by Gas Expansion) technique during four days of clean Southern Ocean marine boundary layer (MBL) air. The models overestimated OH concentrations by about 10% on two days and about 20% on the other two days. HO2 concentrations were measured during two of these days and the models overestimated the measured concentrations by about 40%. Better agreement with measured HO2 was observed by using data from several MBL aerosol measurements to estimate the aerosol surface area and by increasing the HO2 uptake coefficient to unity. This reduced the modelled HO2 overestimate by ~40%, with little effect on OH, because of the poor HO2 to OH conversion at the low ambient NOx concentrations. Local sensitivity analysis and Morris One-At-A-Time analysis were performed on the "simple" model, and showed the importance of reliable measurements of j(O1D) and [HCHO] and of the kinetic parameters that determine the efficiency of O(1D) to OH and HCHO to HO2 conversion. A 2σ standard deviation of 30–40% for OH and 25–30% for HO2 was estimated for the model calculations using a Monte Carlo technique coupled with Latin Hypercube Sampling (LHS).

Discovery of the first known benthic invasive species in the Southern Ocean: the North Atlantic spider crab Hyas araneus found in the Antarctic Peninsula

The Southern Ocean around Antarctica is no longer free from invasive marine species. The North Atlantic spider crab Hyas araneus (Linnaeus, 1758) (Crustacea: Decapoda: Majidae) has been recorded for the first time from the Antarctic Peninsula. Isolated for at least 25 million years, the endemic Antarctic Southern Ocean marine fauna is now being exposed to human-mediated influx of exotic species. Invasive species and polar warming combined can foster the probability of arrival and colonization by non-indigenous species, with unpredictable consequences for the Antarctic marine biota.

Winter distribution and behaviour of gentoo penguins Pygoscelis papua at South Georgia

Knowledge of the spatial and temporal dynamics of foraging penguins is important to our understanding of the Southern Ocean marine ecosystem. We use satellite tracking to provide the first data on the distribution and behaviour of gentoo penguins (Pygoscelis papua) during the winter at South Georgia. Five penguins tracked from Bird Island remained close inshore, and although they did not return to the initial tagging site, they did appear to return to land each evening. They made diurnal trips to sea of similar distance from land as those during the breeding season, even though the constraints of chick rearing were absent. Despite potential greater flexibility in their responses to variations in prey availability in winter, the penguins still returned to land each night. This may reflect benefits from conserving energy by resting on land, possibly facilitating information exchange and avoiding predation. The distribution and behaviour of gentoo penguins during the winter enables efficient exploitation of a dynamic, patchy prey resource and may ultimately determine the timing of return to the colony, and onset of breeding in the following season.

Measurements of OH and HO2 concentrations in the Southern Ocean marine boundary layer

Field measurements of hydroxyl (OH) and hydroperoxy (HO2) radicals have been made in the remote Southern Ocean marine boundary layer at the Cape Grim Baseline Air Pollution Station in northwestern Tasmania. Measurements were made with a time resolution of 30 s over a period of 4 weeks during austral summer 1999 in the second Southern Ocean Photochemistry Experiment. Laser‐induced fluorescence at reduced pressure was used to measure [OH] with an average detection limit at noon of (1.4 ± 0.5) × 105 molecule cm−3 (1σ), for a 2.5 min integration period, and HO2 was measured following its conversion to OH via the addition of NO, with an average detection limit of (5.4 ± 1.7) × 105 molecule cm−3 (1σ). Air masses arriving at Cape Grim originated from the Australian continent, Tasmania, and Southern Ocean/Antarctic regions, the latter (“Baseline” air) characterized by extremely low [NO] allowing a study of the chemistry of the unperturbed background atmosphere. In Baseline air, daytime average maxima for OH and HO2 of 3.5 × 106 molecule cm−3 (0.14 parts per trillion by volume (pptv)) and 2 × 108 molecule cm−3 (8 pptv) were observed, and a very high correlation coefficient (r = 0.95) was observed between the OH concentration and the rate of OH production from ozone photolysis. A steady state expression for OH, assuming production only from ozone photolysis and loss only by reaction with CO and CH4, overestimates the observed daytime maximum concentration in Baseline air by 20%. The HO2 concentration was found to depend upon the square root of the rate of O3 photolysis, as expected at very low concentrations of NO.

Fatty acid composition of lipid-rich myctophids and mackerel icefish (Champsocephalus gunnari) – Southern Ocean food-web implications

The lipid content, fatty acid composition and calorific value of seven species of mesopelagic deep-sea fish of the family Myctophidae and the mackerel icefish, Champsocephalus gunnari, important in the diet of Southern Ocean marine predators, are presented. Fish were sampled at the Kerguelen Plateau (KP) and Mac- quarie Ridge (MR) in the Indian and Pacific sectors of the Southern Ocean respectively, to examine geographic variation in lipid compositon. All species of myctophid from KP and Electrona antarctica from MR were high in lipid content (6-18% wet mass), particularly Gymnoscopelus nicholsi (18%) and E. antarctica (15%). The mackerel icefish, and G. fraseri and Protomyctop- hum tenisoni from MR were generally lower in lipid content (3-5%) and varied significantly in fatty acid composition from KP species. KP myctophids were high in calorific content (9.3 kJ g -1 wet mass) when compared with icefish (5.4 kJ g -1 wet mass) and other published values for prey items of marine predators such as squid (1.7-4.5 kJ g -1 ). KP myctophids were distinguished from each other and from C. gunnari and MR specimens by cluster and discriminant function analysis using six fatty acids (16:0, 18:1x9, 20:1x9, 22:1x11, 20:5x3, 22:6x3). Findings presented here highlight trophic links between high-latitude fish and their prey and emphasise the im- portance of myctophids as a significant energy source for marine predators foraging in the Polar Frontal Zone.

Ecology of Southern Ocean pack ice

Around Antarctica the annual five-fold growth and decay of sea ice is the most prominent physical process and has a profound impact on marine life there. In winter the pack ice canopy extends to cover almost 20 million square kilometres--some 8% of the southern hemisphere and an area larger than the Antarctic continent itself (13.2 million square kilometres)--and is one of the largest, most dynamic ecosystems on earth. Biological activity is associated with all physical components of the sea-ice system: the sea-ice surface; the internal sea-ice matrix and brine channel system; the underside of sea ice and the waters in the vicinity of sea ice that are modified by the presence of sea ice. Microbial and microalgal communities proliferate on and within sea ice and are grazed by a wide range of proto- and macrozooplankton that inhabit the sea ice in large concentrations. Grazing organisms also exploit biogenic material released from the sea ice at ice break-up or melt. Although rates of primary production in the underlying water column are often low because of shading by sea-ice cover, sea ice itself forms a substratum that provides standing stocks of bacteria, algae and grazers significantly higher than those in ice-free areas. Decay of sea ice in summer releases particulate and dissolved organic matter to the water column, playing a major role in biogeochemical cycling as well as seeding water column phytoplankton blooms. Numerous zooplankton species graze sea-ice algae, benefiting additionally because the overlying sea-ice ceiling provides a refuge from surface predators. Sea ice is an important nursery habitat for Antarctic krill, the pivotal species in the Southern Ocean marine ecosystem. Some deep-water fish migrate to shallow depths beneath sea ice to exploit the elevated concentrations of some zooplankton there. The increased secondary production associated with pack ice and the sea-ice edge is exploited by many higher predators, with seals, seabirds and whales aggregating there. As a result, much of the Southern Ocean pelagic whaling was concentrated at the edge of the marginal ice zone. The extent and duration of sea ice fluctuate periodically under the influence of global climatic phenomena including the El Niño Southern Oscillation. Life cycles of some associated species may reflect this periodicity. With evidence for climatic warming in some regions of Antarctica, there is concern that ecosystem change may be induced by changes in sea-ice extent. The relative abundance of krill and salps appears to change interannually with sea-ice extent, and in warm years, when salps proliferate, krill are scarce and dependent predators suffer severely. Further research on the Southern Ocean sea-ice system is required, not only to further our basic understanding of the ecology, but also to provide ecosystem managers with the information necessary for the development of strategies in response to short- and medium-term environmental changes in Antarctica. Technological advances are delivering new sampling platforms such as autonomous underwater vehicles that are improving vastly our ability to sample the Antarctic under sea-ice environment. Data from such platforms will enhance greatly our understanding of the globally important Southern Ocean sea-ice ecosystem.

Nonmethane hydrocarbons in Southern Ocean boundary layer air

Measurements at the remote marine boundary layer station of Cape Grim, Northwest Tasmania, allow study of the unperturbed background atmosphere. Here we present a continuous data series of nonmethane hydrocarbons (NMHCs), measured in situ and with high sensitivity during the Second Southern Ocean Photochemistry Experiment (SOAPEX 2) during austral summer 1999. Air masses arriving at Cape Grim originate from the Australian continent, Tasmania, and Southern Ocean and Antarctic regions. In Southern Ocean marine boundary layer (MBL) air, C2 and C3 alkanes show a highly uniform abundance (ethane 142±11.9 parts per trillion by volume (pptv), propane 8.9±1.7 pptv) at around 4 times lower concentrations than encountered in unpolluted Northern Hemisphere MBL air. The presence of shorter‐lived NMHCs in marine air indicates sources of both C4–C6 alkanes and several alkenes in the Southern Ocean. The alkane isomer distributions and abundances are in broad agreement with literature sea‐air flux rates. In dynamically stable maritime air, midday maxima in ethene, propene, and isoprene concentrations of a few pptv indicate photochemically driven sources very near to the sea surface. Despite their high reactivity, the impact of these oceanic alkenes on local OH concentrations in remote MBL air is not significant. However, the abundance of isoprene in marine air may significantly elevate formaldehyde above that generated by methane oxidation.

Long-term population trends in seven Antarctic seabirds at Pointe Géologie (Terre Adélie)

Antarctic seabird populations have been much studied over the last decades as bioindicators of the nature of variability in the Southern Ocean marine ecosystem, and most attention has been focused on the role of food supply and the extent of sea ice. In addition, the rapid spread of tourism and the activities of researchers since the early 1960s have raised questions related to their real and potential impact on bird populations. Our data sets start in 1952 for several species of Antarctic seabirds and this study documents the trends over a 14-year period (1985–1999) in seven species breeding on Pointe Geologie archipelago (Terre Adelie, Antarctica). This is the first study where the direct impact of destruction of breeding sites (for building of an airstrip) is examined and where such long-term populations trends have been assessed in such a number of Antarctic species at one site. Trends from 1985 show that for the whole archipelago and when excluding islands destroyed, Adelie penguins and south polar skuas were the only species to show a significant increase (>3.5% annual change). The others species showed opposite trends, three increasing slightly (southern fulmars +0.4%, cape petrels +2.3%, snow petrels +0.9%) and two decreasing (emperor penguin −0.9%, southern giant petrel −3.9%). Three species particularly affected by the destruction of their breeding habitat (Adelie penguin, cape petrel, snow petrel) showed the capability to restore their populations. The availability of food and nesting sites is discussed in relation to environmental change. Species feeding on krill (Adelie penguins and cape petrels) increased more than other species; however, decrease of ice cover can increase availability of nesting sites. The importance of long-term studies is shown when assessing the role of human activities in Antarctica compared to larger-scale changes.

Late Quaternary volcanic activity in Marie Byrd Land: Potential 40Ar/39Ar-dated time horizons in West Antarctic ice and marine cores

Research Article| October 01, 1999 Late Quaternary volcanic activity in Marie Byrd Land: Potential 40Ar/39Ar-dated time horizons in West Antarctic ice and marine cores T. I. Wilch; T. I. Wilch 1Department of Geological Sciences, Albion College, Albion, Michigan 49224 Search for other works by this author on: GSW Google Scholar W. C. McIntosh; W. C. McIntosh 2Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology3New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar N. W. Dunbar N. W. Dunbar 3New Mexico Bureau of Mines and Mineral Resources, Socorro, New Mexico 87801 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1999) 111 (10): 1563–1580. https://doi.org/10.1130/0016-7606(1999)111<1563:LQVAIM>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation T. I. Wilch, W. C. McIntosh, N. W. Dunbar; Late Quaternary volcanic activity in Marie Byrd Land: Potential 40Ar/39Ar-dated time horizons in West Antarctic ice and marine cores. GSA Bulletin 1999;; 111 (10): 1563–1580. doi: https://doi.org/10.1130/0016-7606(1999)111<1563:LQVAIM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Late Quaternary volcanic activity at three major alkaline composite volcanoes in Marie Byrd Land, West Antarctica, is dominated by explosive eruptions, many capable of depositing ash layers as regional time-stratigraphic horizons in the West Antarctic Ice Sheet and in Southern Ocean marine sediments. A total of 20 eruptions at Mount Berlin, Mount Takahe, and Mount Siple are recorded in lava and welded and nonwelded pyroclastic fall deposits, mostly peralkaline trachyte in composition. The eruptions, dated by the 40Ar/39Ar laser-fusion and furnace step-heating methods, range in age from 571 to 8.2 ka.Tephra from these 40Ar/39Ar-dated Marie Byrd Land eruptions are identified by geochemical fingerprinting in the 1968 Byrd Station ice core. The 74 ka ice-core record contained abundant coarse ash layers, with model ice-flow ages ranging from 7.5 to 40 ka, all of which were previously geochemically correlated to the Mount Takahe volcano. We identify a one-to-one geochemical and age correlation of the youngest (ca. 7.5 ka) tephra layer in the Byrd ice core to an 8.2 ± 5.4 ka (2sigma uncertainty) pyroclastic deposit at Mount Takahe. We infer that the 20–30 ka tephra layers in the Byrd ice core actually were erupted from Mount Berlin, on the basis of age and geochemical similarities. If products of these youngest, as well as the older 40Ar/39Ar-dated eruptions are identified by geochemical fingerprinting in future ice and marine cores, they will provide the cores with independently dated time horizons.More than 12 40Ar/39Ar-dated tephra layers, exposed in bare ice on the summit ice cap of Mount Moulton, 30 km from their inferred source at Mount Berlin, range in age from 492 to 15 ka. These englacial tephra layers provide a minimum age of 492 ka for the oldest isotopically dated ice in West Antarctica. This well-dated section of locally derived glacial ice contains a potential “horizontal ice core” record of paleoclimate that extends back through several glacial-interglacial cycles. The coarse grain size and density of the englacial tephra (mean diameters 17–18 mm, densities 540–780 kg/m3), combined with their distance from source, indicate derivation from highly explosive Plinian eruptions of Mount Berlin. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The sequence of events surrounding Termination II and their implications for the cause of glacial‐interglacial CO2 changes

Events surrounding Termination II, as preserved in the Vostok ice core, provide a number of clues about the mechanisms controlling glacial to interglacial climate change. Antarctic temperature and the atmosphere's CO2 content increased together over a period of ∼8000 years. This increase is bounded by a drop in dust flux at its onset and by a drop in the δ18O of trapped air at its finish. A similar lag between dust flux and foraminiferal δ18O is seen in a Southern Ocean marine record, suggesting that the δ18O in air trapped in Vostok ice is a valid proxy for ice volume. The synchronous change of atmospheric CO2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets. This observation, coupled with the fact that nutrient reorganization in the North Atlantic occurs with or after the sea level rise, eliminates many scenarios proposed to explain the CO2 rise, including those which rely on sea level change, conveyor‐related nutrient redistribution, or North Atlantic cooling. Southern Ocean scenarios become the front runners, but the most popular mechanism, iron fertilization, has two problems in explaining the CO2 rise before Termination II. First, much of the dust demise occurs prior to the change in CO2, so if iron is the villain, a threshold value of its supply must be called upon above which productivity does not continue to increase. Second, the CO2 rise continues for some 4–5 kyr after the dust flux has fallen to close to zero. These problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods. In this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric CO2.

Influence of sea-salt on aerosol radiative properties in the Southern Ocean marine boundary layer

There has been considerable debate about the relative importance of sea-salt and sulphate from non-sea-salt sources in determining aerosol radiative effects in the marine boundary layer. In the marine boundary layer, the most numerous aerosols are volatile sulphate particles smaller than about 0.08 µm (ref. 1) and most of the aerosol mass is in a few sea-salt particles larger than 1 µm. Yet intermediate-size aerosols between about 0.08 and 1 µm diameter are the most relevant to the radiative forcing of climate because they efficiently scatter solar radiation and also serve as cloud nuclei2. Indeed, Charlson et al.3 hypothesized that oceanic production of sulphate aerosols from the oxidation of dimethyl sulphide could be a powerful feedback in the climate system. It is generally assumed that marine aerosols smaller than about 1 µm are non-sea-salt sulphate, but a recent review cites indirect evidence that many aerosols in the sub-micrometre range contain at least some sea-salt4,5. Here we present direct observational evidence from a remote Southern Ocean region that almost all aerosols larger than 0.13 µm in the marine boundary layer contained sea-salt. These sea-salt aerosols had important radiative effects: they were responsible for the majority of aerosol-scattered light, and comprised a significant fraction of the inferred cloud nuclei.

Trends in entanglement of Antarctic fur seals ( Arctocephalus gazella) in man-made debris at South Georgia

A study conducted at South Georgia in 1988/1989 indicated that several thousand Antarctic fur seals were entangled mainly in man-made material originating from fishing vessels. Consequently, the authority responsible for the management of Southern Ocean marine resources (CCAMLR) actively campaigned for compliance with the MARPOL provisions relating to waste disposal at sea, and for cutting of any material unavoidably jettisoned which could form collars to entangle seals. Five subsequent years of recording entangled fur seals confirms that entanglement is a persistent problem, although its incidence has been halved in recent years. However, the South Georgia fur seal population has approximately doubled in the same period, so that the overall total of animals entangled may even have increased. Nevertheless, because most seals entangled are juvenile males, the current rate of entanglement will have negligible effects on the reproductive rate of the South Georgia population, especially in relation to its current rate of population increase. The reduction in observed entanglement incidence cannot be attributed mainly to improved waste disposal practices because it has coincided with substantial reductions in fishing activity around South Georgia. However, the particular reduction in entanglement due to packing bands and the fact that all such bands washed ashore over the last 2 years have been cut, does suggest a general improvement in standards of waste disposal on Southern Ocean fishing vessels.

POTENTIAL EFFECTS OF UV‐B RADIATION ON MARINE ORGANISMS OF THE SOUTHERN OCEAN: DISTRIBUTIONS OF PHYTOPLANKTON AND KRILL DURING AUSTRAL SPRING

AbstractIncreases in UV‐B radiation resulting from ozone depletion during austral spring could potentially alter the balance of the Southern Ocean marine ecosystem. A quantitative assessment ol the effects of UV‐B enhancement requires knowledge of (1) the wavelength‐dependent fluxes of UV‐B in the upper ocean, (2) action spectra for UV‐B damage to Antarctic phytoplankton and zooplankton, and (3) depth‐dependent distributions and residence times of Southern Ocean phytoplankton and zooplankton during austral spring. Unfortunately, only limited data arc currently available to address this impact directly. To provide some of the information required for such an assessment, available data regarding plankton distributions and their photophysiological characteristics have been summarized. A preliminary assessment of the available literature suggests that Antarctic phytoplankton and krill receive very low doses of UV‐B during austral spring. The high spectral attenuation coefficients associated with the environments in which most plankton arc found during springtime precludes the possibility of UV damage. Future research directions are described which should provide a better understanding of the ecological consequences of the “ozone hole” which resides over the Antarctic continent during austral spring.