Enrique Isla

The Southern Ocean ecosystem under multiple climate change stresses ‐ an integrated circumpolar assessment

A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem.

Shifts in Antarctic megabenthic structure after ice-shelf disintegration in the Larsen area east of the Antarctic Peninsula

The aim of this study was to contribute to a general understanding of the response of the Antarctic macrobenthos to environmental variability and climate-induced changes. The change in population size of selected macrobenthic organisms was investigated in the Larsen A area east of the Antarctic Peninsula in 2007 and 2011 using ROV-based imaging methods. The results were complemented by data from the Larsen B collected in 2007 to allow a conceptual reconstruction of the environment-driven changes before the period of investigation. Both Larsen areas are characterised by ice-shelf disintegration in 1995 and 2002, respectively, as well as high inter-annual variability in sea-ice cover and oceanographic conditions. In 2007 one ascidian species, Molgula pedunculata, was abundant north and south of the stripe of remaining ice shelf between Larsen A and B. Population densities decreased drastically in the Larsen A between 2007 and 2011, coincident with the decrease in Corella eumyota, another ascidian. Among the ophiuroids, the population of deposit feeders increased, while suspension feeders halved their abundance. Current measurements indicated a northward flow between the Larsen B and Larsen A, suggesting that a major physical forcing on benthic population development comes from the South. The results demonstrate that Antarctic macrobenthic populations can exhibit dramatic population dynamics. Analyses of sea-ice dynamics, salinity, temperature and surprisingly ice-shelf disintegration history, however, did not provide any clear evidence for environmental drivers underlying the apparent changes.The aim of this study was to contribute to a general understanding of the response of the Antarctic macrobenthos to environmental variability and climate-induced changes. The change in population size of selected macrobenthic organisms was investigated in the Larsen A area east of the Antarctic Peninsula in 2007 and 2011 using ROV-based imaging methods. The results were complemented by data from the Larsen B collected in 2007 to allow a conceptual reconstruction of the environment-driven changes before the period of investigation. Both Larsen areas are characterised by ice-shelf disintegration in 1995 and 2002, respectively, as well as high inter-annual variability in sea-ice cover and oceanographic conditions. In 2007 one ascidian species, Molgula pedunculata, was abundant north and south of the stripe of remaining ice shelf between Larsen A and B. Population densities decreased drastically in the Larsen A between 2007 and 2011, coincident with the decrease in Corella eumyota, another ascidian. Among the ophiuroids, the population of deposit feeders increased, while suspension feeders halved their abundance. Current measurements indicated a northward flow between the Larsen B and Larsen A, suggesting that a major physical forcing on benthic population development comes from the South. The results demonstrate that Antarctic macrobenthic populations can exhibit dramatic population dynamics. Analyses of sea-ice dynamics, salinity, temperature and surprisingly ice-shelf disintegration history, however, did not provide any clear evidence for environmental drivers underlying the apparent changes.

Downward particle fluxes and sediment accumulation rates in the western Bransfield Strait: Implications of lateral transport for carbon cycle studies in antarctic marginal seas

Downward particle and carbon fluxes were studied along with sediment and carbon accumulation fluxes in the western Bransfield Strait. Particle fluxes at 1000 m depth indicate that most of the carbon accumulated in the seabed at the study site is transported laterally. Biogenic components of the near-bottom particle fluxes included well-preserved organic matter with benthic diatoms, amphipoda and polychaetes that were resuspended and/or winnowed in shallow environments and transported basinward. High near-bottom particle and carbon fluxes were in agreement with high sediment and carbon accumulation fluxes. About 12% of the near-bottom OC downward flux is buried below the SML in the deeper part of the basin. Carbon recycling in the sediment column is lower near the mouth of the Orleans Canyon (about 10%) than at the deeper part of the basin (about 50%). The carbon preserved in the sediment near the mouth of the canyon and at the deeper part of the basin represents about 9% and 3%, respectively, of the carbon produced in the euphotic layer of the study area. However, because most of the organic carbon (OC) is transported laterally, the higher primary productivity from nearby shallower areas should be considered and the percentage of the OC preserved in the sediment would account only for 4.5% and 1.5% at each of the study sites. The results show that resuspension in shallow environments, lateral transport and near-bottom downward fluxes must be considered in addition to surface primary production, midwater downward fluxes and accumulation rates in order to better understand the carbon dynamics in Antarctic marginal seas. The accumulation rates at many sites of these seas appear to be more sensitive to variability in current-driven sediment redistribution than to changes in productivity, which must be taken into account when interpreting the paleoceanographic record.

Introduction to the special issue on the Life in Antarctica: Boundaries and Gradients in a Changing Environment (XIth SCAR Biology Symposium)

Scientific research in Antarctica has reached maturity in recent decades. The interest in issues related to knowledge about the southern polar regions has increased significantly among researchers from all scientific and technological disciplines. Among the various fields, biology comprises perhaps the highest concentration of related activities and encompasses the most diverse research topics. This increase in the research activity has to be translated in a greater coordination research efforts. The Scientific Committee of Antarctic Research has positioned itself as the focal point of this activity, with the organized symposiums being the best forum to share and report progress in various fields. This was the philosophy of XIth Scientific Committee on Antarctic Research Symposium held in Barcelona in July 2013. The different contributions of the symposium developed around a main topic: “Life in Antarctica: Boundaries and Gradients in a Changing Environment”. The symposium had the objective of linking the functional importance of land and water ecosystems with their bio-complexity under an ecosystem perspective. Such an approach will lead to a better understanding of Antarctic food webs, effects of human impacts (e.g., ozone hole, climate change, tourism), flexible boundaries and dynamic gradients in Antarctic ecosystems, as well as Antarctic marine biodiversity through its patterns, processes and trends.

The instrumental period

The instrumental period began with the first voyages to the Southern Ocean during the Seventeenth and Eighteenth centuries when scientists such as Edmund Halley made observations of quantities such as geomagnetism. During the early voyages information was collected on the meteorological conditions across the Southern Ocean, ocean conditions, the sea ice extent and the terrestrial and marine biology. The continent itself was discovered in 1820, although the collection of data was sporadic through the remainder of the Nineteenth Century and it was not possible to venture into the inhospitable interior of Antarctica. At the start of the Twentieth Century stations were first operated year-round and this really began the period of organised scientific investigation in the Antarctic. Most of these stations were not operated for long periods, which is a handicap when trying to investigate climate change over the last century.

A shift in the biogenic silica of sediment in the Larsen B continental shelf, off the Eastern Antarctic Peninsula, resulting from climate change.

In 2002, section B of the Larsen ice shelf, off of the Eastern Antarctic Peninsula, collapsed and created the opportunity to study whether the changes at the sea surface left evidence in the sedimentary record. Biogenic silica is major constituent of Antarctic marine sediment, and its presence in the sediment column is associated with diatom production in the euphotic zone. The abundance of diatom valves and the number of sponge spicules in the biogenic silica was analyzed to determine how the origin of the biogenic silica in the upper layers of the sediment column responded to recent environmental changes. Diatom valves were present only in the upper 2 cm of sediment, which roughly corresponds to the period after the collapse of the ice shelf. In contrast, sponge spicules, a more robust form of biogenic silica, were also found below the upper 2 cm layer of the sediment column. Our results indicate that in this region most of the biogenic silica in the sedimentary record originated from sponge spicules rather than diatoms during the time when the sea surface was covered by the Larsen ice shelf. Since the collapse of the ice shelf, the development of phytoplankton blooms and the consequent influx of diatom debris to the seabed have shifted the biogenic silica record to one dominated by diatom debris, as occurs in most of the Antarctic marine sediment. This shift provides further evidence of the anthropogenic changes to the benthic habitats of the Antarctic and will improve the interpretation of the sedimentary record in Polar Regions where these events occur.

Fluxes and composition of settling particles during summer in an Antarctic shallow bay of Livingston Island, South Shetlands

A moored experiment using a sediment trap was conducted at Johnson’s Dock, Livingston Island from 11 December 1997 to 24 February 1998, as part of the EASIZ Programme activities carried out at the Juan Carlos I Spanish Antarctic base. Total mass vertical fluxes ranged from 23,235 mg m-2 day-1 to 89,073 mg m-2 day-1 during the experiment, with a mean value of 42,857 mg m-2 day-1. Lithogenic components were the major contributors to the settling particulate flux. Organic components accounted for a low fraction of the settling particulate matter, showing an inverse relation to total mass flux. Nevertheless, the fluxes of organic components at Johnson’s Dock are as high as in the open sea. The increases in chlorophyll a in water were related to increases in the organic carbon content, which dominated over inorganic carbon during the whole experiment. Calcium carbonate particles settle without being significantly altered in the water column and are dissolved in the upper centimetres of the bottom sediments, once they are buried. The settling material consisted of fine particles, with coarse clasts transported by icebergs. Antarctic shallow environments receive important sediment fluxes from the erosion and transport action of ice.

Cross-disciplinarity in the advance of Antarctic ecosystem research

The biodiversity, ecosystem services and climate variability of the Antarctic continent and the Southern Ocean are major components of the whole Earth system. Antarctic ecosystems are driven more strongly by the physical environment than many other marine and terrestrial ecosystems. As a consequence, to understand ecological functioning, cross-disciplinary studies are especially important in Antarctic research. The conceptual study presented here is based on a workshop initiated by the Research Programme Antarctic Thresholds - Ecosystem Resilience and Adaptation of the Scientific Committee on Antarctic Research, which focussed on challenges in identifying and applying cross-disciplinary approaches in the Antarctic. Novel ideas and first steps in their implementation were clustered into eight themes. These ranged from scale problems, through risk maps, and organism/ecosystem responses to multiple environmental changes and evolutionary processes. Scaling models and data across different spatial and temporal scales were identified as an overarching challenge. Approaches to bridge gaps in Antarctic research programmes included multi-disciplinary monitoring, linking biomolecular findings and simulated physical environments, as well as integrative ecological modelling. The results of advanced cross-disciplinary approaches can contribute significantly to our knowledge of Antarctic and global ecosystem functioning, the consequences of climate change, and to global assessments that ultimately benefit humankind.

Antarctic Marine Animal Forests: Three-Dimensional Communities in Southern Ocean Ecosystems

Both Southern Ocean and terrestrial systems contain three-dimensional biotic components that are key in shaping and defining their respective ecosystems and communities. Antarctic suspension-feeding communities, which inhabit the shelf of the Southern Ocean, resemble “Terrestrial Vegetation Forests” (TVF) or shrublands and support the concept of “Antarctic Marine Animal Forests” (AMAF). They comprise mostly sessile animals, provide microniches for an associated mobile fauna, and are fragmented and regionally mixed with other communities. On land, only high mountains and very dry regions are unsuitable for TVF, analogous to the virtual absence of AMAF from the deep sea (>1000 m). Besides fundamental differences between these systems in energy flow and other ecological drivers such as light requirements and dispersal opportunities, both “forests” experience similar disturbances, which impact ecosystem dynamics and diversity in similar ways. While land use affects and reduces terrestrial forests, climate change and fishing impacts are the most serious threats to the Southern Ocean ecosystem. Research priorities for a better understanding of “Antarctic Marine Animal Forests” demand (1) mapping biotic communities and their structural and functional diversity, especially in terms of hot and cold spots; (2) understanding ecological function, including ecosystem productivity and dynamics; (3) cross-system comparison to identify generality or uniqueness in ecosystem structure and dynamics; and (4) implication of existing and new research approaches and conservation strategies.

Temporal variation of seston biomarkers within the Humboldt Current System off northern Chile (21°S): first simultaneous records on fatty acids, n-alkanes and glycerol-dialkyl-glycerol-tetraethers (GDGT)

Proportions and concentrations of seston fatty acids, n-alkanes and glycerol dialkyl glycerol tetraethers (GDGTs) were used to assess potential differences in the phytoplankton composition and food quality in the Humboldt Current System (winter 2006, summer 2007 and winter 2007) in surface, oxycline, intermediate and bottom water layers. The zone below the intermediate depth was poorer in fatty acids (minimum 15 – maximum 117 µg fatty acids L−1) than the upper water layers (minimum 36 – maximum 210 µg fatty acids L−1), which were richer in saturated fatty acids (SAFA, up to 80%), but had a similar proportion of bacterial markers (13:0.15 iso/anteiso, 15:0, and 17:0 sum up to 67%). Isoprenoid GDGTs showed the presence of archaea in the different water layers. All the water layers also showed long chained fatty acids (22:0, 24:1 and 26:0), which can be considered to be of terrestrial origin. The n-alkanes were used to confirm this potential terrestrial origin through the Carbon Preference Index (CPI), which...