Western Antarctic Peninsula Region Research Articles

Fixed-Wing UAV Flight Operation under Harsh Weather Conditions: A Case Study in Livingston Island Glaciers, Antarctica

How do the weather conditions typical of the polar maritime glaciers in the western Antarctic Peninsula region affect flight operations of fixed-wing drones and how should these be adapted for a successful flight? We tried to answer this research question through a case study for Johnsons and Hurd glaciers, Livingston Island, using a fixed-wing RPAS, in particular, a Trimble UX5 UAV with electric pusher propeller by brushless 700 W motor, chosen for its ability to fly long distances and reach inaccessible areas. We also evaluated the accuracy of the point clouds and digital surface models (DSM) generated by aerial photogrammetry in our case study. The results were validated against ground control points taken by differential GNSS techniques, showing an accuracy of 0.16 ± 0.12 m in the vertical coordinate. Various hypotheses were proposed and flight-tested, based on variables affecting the flight operation and the data collection, namely, gusty winds, low temperatures, battery life, camera configuration, and snow reflectivity. We aim to provide some practical guidelines that can help other researchers using fixed-wing drones under climatic conditions similar to those of the South Shetland Islands. Performance of the drone under harsh weather conditions, the logistical considerations, and the amount of snow at the time of data collection are factors driving the necessary modifications from those of conventional flight operations. We make suggestions concerning wind speed and temperature limitations, and avoidance of sudden fog banks, aimed to improve the planning of flight operations. Finally, we make some suggestions for further research.

Spatiotemporal Overlap of Baleen Whales and Krill Fisheries in the Western Antarctic Peninsula Region

In Antarctica, abundant consumers rely on Antarctic krill for food, but krill are also the subject of a commercial fishery. The fishery overlaps in time and space with the foraging areas of these consumers, thus potential competition between krill fisheries and krill consumers is a major management concern. The fishery is managed by the Commission for the Conservation of Antarctic Marine Living Resources with an ecosystem approach, according to which fishing should not interfere with either the population growth of krill, or krill-dependent consumers. Krill catches have become increasingly spatially concentrated in a small number of hotspots, raising concerns about how local depletion of krill impacts consumers. Such concentrated fishing demonstrates that there is a mismatch between the spatial and temporal scale at which krill fisheries are currently managed, and that at which fisheries operate and consumers forage. Information on the seasonal dynamics of predator abundance and their foraging behaviour is fundamental to future precautionary management of the krill fishery. We analysed the spatiotemporal distribution of two major krill consumers – humpback and minke whales – and that of krill fishing, off the Western Antarctic Peninsula. We used whale tracking data (58 humpback whale tracks and 19 minke whale tracks) to develop spatial random forest models predicting the monthly distribution of whale foraging areas from January-July. Using these predictions, we calculated spatiotemporally-explicit geographic overlap between whales and fisheries, the latter represented by krill fishing effort and catch data. Over the krill fishing season, fishing effort and catch hotspots shifted to the southwest, into the Bransfield Strait where effort and catch was highest. Predicted humpback whale foraging areas increased in the Bransfield Strait over the same period, while predicted minke whale foraging areas showed an opposite trend. For both we predicted a whale-fishing interaction hotspot in the Bransfield Strait, strongest in April and May. Our results illustrate the fine spatial scale of likely interactions between baleen whales and the krill fishery, and their concentration over the season, underlining the need for fishery management more closely aligned to the spatiotemporal scale of likely predator-fishery interactions.

Warm acclimation alters antioxidant defences but not metabolic capacities in the Antarctic fish, Notothenia coriiceps.

The Southern Ocean surrounding the Western Antarctic Peninsula region is rapidly warming. Survival of members of the dominant suborder of Antarctic fishes, the Notothenioidei, will likely require thermal plasticity and adaptive capacity in key traits delimiting thermal tolerance. Herein, we have assessed the thermal plasticity of several cellular and biochemical pathways, many of which are known to be associated with thermal tolerance in notothenioids, including mitochondrial function, activities of aerobic and anaerobic enzymes, antioxidant defences, protein ubiquitination and degradation in cardiac, oxidative skeletal muscles and gill of Notothenia coriiceps warm acclimated to 4°C for 22 days or 5°C for 42 days. Levels of triacylglycerol (TAG) were measured in liver and oxidative and glycolytic skeletal muscles, and glycogen in liver and glycolytic muscle to assess changes in energy stores. Metabolic pathways displayed minimal thermal plasticity, yet antioxidant defences were lower in heart and oxidative skeletal muscles of warm-acclimated animals compared with animals held at ambient temperature. Despite higher metabolic rates at elevated temperature, energy storage depots of TAG and glycogen increase in liver and remain unchanged in muscle with warm acclimation. Overall, our studies reveal that N. coriiceps displays thermal plasticity in some key traits that may contribute to their survival as the Southern Ocean continues to warm.

Environmental drivers of phytoplankton taxonomic composition in an Antarctic fjord

The impact of ice-ocean interaction on the Southern Ocean is expected to intensify in the future. However, its influence on phytoplankton community composition remains an open question. The Antarctic Peninsula fjords offer an ideal system to understand the effect of ice-ocean forcing on phytoplankton community, providing an extreme in the spatial gradient from the glacio-marine boundary to the Western Antarctic Peninsula (WAP) continental shelf. During two cruises conducted in December 2015 and April 2016 in Andvord Bay, we found that glacial meltwater input altered surface salinity, promoting shallow mixed layers, and enriched surface waters in dissolved iron and nitrate. The three major groups of phytoplankton fueled by glacial input were: cryptophytes, diatoms, and a group of unidentified small flagellates. Prasinophytes and dinoflagellates were also present, in lower concentrations. In December, cryptophytes dominated the phytoplankton community and were correlated with relatively warmer temperatures in the surface layer; in addition, contrary to our hypothesis, no diatom bloom was observed in the fjord in spite of dissolved iron concentration >1 nM. By April, after the growth season, the overall phytoplankton abundance had decreased by an order of magnitude. Phytoplankton, in particular diatoms, were then limited by daytime length despite abundant macro-nutrient and iron concentrations. Mixed flagellates emerged as the dominant group during April due to the decline of other major taxa. Deep-learning algorithms for predicting the abundance of each major phytoplankton group captured the effects of these environmental factors on the phytoplankton community. Our results show that the fjord has relatively high phytoplankton biomass combined with high macro- and trace nutrient concentrations when compared to the broader WAP region. Based on this study, we confirm that flagellates can be the dominant taxon in Antarctic nearshore waters and we propose that iron concentration alone is insufficient to predict diatom growth. Furthermore, marine terminating glaciers in the WAP can enrich surface waters with nitrate even if the main fjord circulation is not driven by glacier meltwater discharge.

Modelling ground thermal regime in bordering (dis)continuous permafrost environments

Permafrost controls geomorphological dynamics in maritime Antarctic ecosystems. Here, we analyze and model ground thermal regime in bordering conditions between continuous and discontinuous permafrost to better understand its relationship with the timing of glacial retreat. In February 2017, a transect including 10 sites for monitoring ground temperatures was installed in the eastern fringe of Byers Peninsula (Livingston Island, northern Antarctic Peninsula), together with one station recording air temperatures and snow thickness. The sites were selected following the Mid-Late Holocene deglaciation of the area at a distance ranging from 0.30 to 3.15 km from the current Rotch Dome glacier front. The transect provided data on the effects of topography, snow cover and the timing of ice-free exposure, on the ground thermal regime. From February 2017 to February 2019, the mean annual air temperature was −2.0 °C, which was >0.5 °C higher than 1986–2015 average in the Western Antarctic Peninsula region. Mean annual ground temperature at 10 cm depth varied between 0.3 and −1.1 °C, similar to the modelled Temperatures on the Top of the Permafrost (TTOP) that ranged from 0.06 ± 0.08 °C to −1.33 ± 0.07 °C. The positive average temperatures at the warmest site were related to the long-lasting presence of snow which favoured warmer ground temperatures and may trigger permafrost degradation. The role of other factors (topography, and timing of the deglaciation) explained intersite differences, but the overall effect was not as strong as snow cover.

The optical and biological properties of glacial meltwater in an Antarctic fjord.

As the Western Antarctic Peninsula (WAP) region responds to a warmer climate, the impacts of glacial meltwater on the Southern Ocean are expected to intensify. The Antarctic Peninsula fjord system offers an ideal system to understand meltwater’s properties, providing an extreme in the meltwater’s spatial gradient from the glacio-marine boundary to the WAP continental shelf. Glacial meltwater discharge in Arctic and Greenland fjords is typically characterized as relatively lower temperature, fresh and with high turbidity. During two cruises conducted in December 2015 and April 2016 in Andvord Bay, we found a water lens of low salinity and low temperature along the glacio-marine interface. Oxygen isotope ratios identified this water lens as a mixture of glacial ice and deep water in Gerlache Strait suggesting this is glacial meltwater. Conventional hydrographic measurements were combined with optical properties to effectively quantify its spatial extent. Fine suspended sediments associated with meltwater (nanoparticles of ~ 5nm) had a significant impact on the underwater light field and enabled the detection of meltwater characteristics and spatial distribution. In this study, we illustrate that glacial meltwater in Andvord Bay alters the inherent and apparent optical properties of the water column, and develop statistical models to predict the meltwater content from hydrographic and optical measurements. The predicted meltwater fraction is in good agreement with in-situ values. These models offer a potential for remote sensing and high-resolution detection of glacial meltwater in Antarctic waters. Furthermore, the possible influence of meltwater on phytoplankton abundance in the surface is highlighted; a significant correlation is found between meltwater fraction and chlorophyll concentration.

The Upper 1000-m Slope Currents North of the South Shetland Islands and Elephant Island Based on Ship Cruise Observations

While the Antarctic Slope Current (ASC) has been intensively studied for the East Antarctica slope area and the Weddell Sea, its fate in the western Antarctic Peninsula (WAP) region remains much less known. Data from two cruises conducted near the South Shetland Islands (SSIs) and the Elephant Island (EI), one in austral summer of 2004 and one in austral winter of 2006, were analyzed to provide a broad picture of the circulation pattern over the continental slope of the surveyed area, and an insight into the dynamical balance of the circulation. The results indicate that southwestward currents are present over the upper slope in the study area, indicating the ASC in the WAP region. Near the Shackleton Gap (SG) north of the EI, the southwestward slope currents near the shelf break are characterized by a water mass colder and fresher than the ambient water, which produces cross-slope density gradients and then vertical shear of the along-slope (or along-isobath) velocity. The vertical shear is associated with a reversal of the along-slope current from northeastward at surface to southwestward in deeper layers, or a depth-intensification of the southwestward slope currents. The water mass with temperature and salinity characteristics similar to the observed cold and fresh water is also revealed on the southern slope of the Scotia Sea, suggesting that this cold and fresh water is originated from the Scotia Sea slope and flows southwestward through the SG. Over the shelf north of the SSIs, the cold and fresh water mass is also observed and originates mainly from the Bransfield Strait. In this area, vertical structure of the southwestward slope currents is associated with the onshore intrusion of the upper Circumpolar Deep Water that creates cross-slope density gradients.

Examination of gene repertoires and physiological responses to iron and light limitation in Southern Ocean diatoms

Diatoms play a fundamental role at the base of the polar marine food web. In the Southern Ocean, low iron concentrations and light levels control diatom abundance and distribution. Diatoms must therefore employ strategies that allow them to cope when iron and/or light availability is growth limiting. Through a combination of physiological and molecular-based approaches, we have investigated the physiological response to variable iron concentrations and light levels along with the expressed gene repertoires of nine newly isolated diatoms from the Western Antarctic Peninsula (WAP) region of the Southern Ocean. The diatoms ranged across five orders of magnitude in biovolume and displayed various degrees of susceptibility to low iron and light availability. Under the performed laboratory culture conditions, the growth rates of most diatoms decreased more due to low light level rather than low iron concentrations. Additionally, most diatoms were not subject to further reductions in growth rates when grown under combined low-light and iron-limiting conditions, indicating they are less likely to be co-limited by an additive effect. By sequencing the transcriptomes of these diatoms, we identified genes that likely facilitate their growth under variable iron and light conditions commonly present in the Southern Ocean. Specifically, we investigated the presence of 20 key genes involved in iron acquisition and homeostasis, iron usage in photosynthesis and nitrogen assimilation, and protection from reactive oxygen species. When comparing gene repertoires of recently sequenced transcriptomes of diatoms isolated from around the globe, the prevalence of certain genes exhibited biogeographical patterns that clearly distinguish Southern Ocean diatoms from those isolated from other regions.

UAV-based detection and spatial analyses of periglacial landforms on Demay Point (King George Island, South Shetland Islands, Antarctica)

High-resolution aerial images allow detailed analyses of periglacial landforms, which is of particular importance in light of climate change and resulting changes in active layer thickness. The aim of this study is to show possibilities of using UAV-based photography to perform spatial analysis of periglacial landforms on the Demay Point peninsula, King George Island, and hence to supplement previous geomorphological studies of the South Shetland Islands.Photogrammetric flights were performed using a PW-ZOOM fixed-winged unmanned aircraft vehicle. Digital elevation models (DEM) and maps of slope and contour lines were prepared in ESRI ArcGIS 10.3 with the Spatial Analyst extension, and three-dimensional visualizations in ESRI ArcScene 10.3 software.Careful interpretation of orthophoto and DEM, allowed us to vectorize polygons of landforms, such as (i) solifluction landforms (solifluction sheets, tongues, and lobes); (ii) scarps, taluses, and a protalus rampart; (iii) patterned ground (hummocks, sorted circles, stripes, nets and labyrinths, and nonsorted nets and stripes); (iv) coastal landforms (cliffs and beaches); (v) landslides and mud flows; and (vi) stone fields and bedrock outcrops.We conclude that geomorphological studies based on commonly accessible aerial and satellite images can underestimate the spatial extent of periglacial landforms and result in incomplete inventories. The PW-ZOOM UAV is well suited to gather detailed geomorphological data and can be used in spatial analysis of periglacial landforms in the Western Antarctic Peninsula region.

Transcriptomic profiles of spring and summer populations of the Southern Ocean salp, Salpa thompsoni, in the Western Antarctic Peninsula region

The Southern Ocean salp, Salpa thompsoni (Tunicata, Thaliacea), is a pivotal species in the pelagic ecosystem of the Western Antarctic Peninsula (WAP), one of the fastest warming regions of the world oceans. This study produced a complete reference transcriptome for S. thompsoni containing 216,931 sequences; 41,210 (18%) were associated with predicted, hypothetical, or known proteins; 13,058 (6%) were mapped and annotated. Whole-transcriptome (RNA-seq) analysis of 39 samples collected during austral spring and summer 2011 in the WAP and in summer 2009 in the Indian Sector revealed clustering of samples by regions, seasons, and areas (Bray–Curtis similarity). The highest numbers of differentially expressed genes at the 4×, 20×, and 100× fold-change levels were found between salps collected during spring versus summer 2011 in the WAP (analysis of variance, ANOVA). Spring versus summer samples showed significant differential expression of 77 genes associated with environmental stress response and 51 genes associated with sexual reproduction (paired t tests, p < 0.05), with significant association between expression of these genes and temperature at the collection site shown by multidimensional scaling analysis. Gene Ontology (GO) term enrichment analysis identified 41 GO terms responsible for spring versus summer differences, including 156 genes associated with translation (i.e., protein synthesis). The reference transcriptome and characterization of time/space patterns of whole-transcriptome and target gene differential expression provide a foundation for functional analysis and identification of molecular markers of physiological condition, life history events, and responses to climate change in this key species in Antarctic pelagic ecosystems.

Ground temperature and permafrost distribution in Hurd Peninsula (Livingston Island, Maritime Antarctic): An assessment using freezing indexes and TTOP modelling

The Western Antarctic Peninsula region shows mean annual air temperatures ranging from −4 to −2°C. Due to its proximity to the climatic threshold of permafrost, and evidence of recent changes in regional air temperatures, this is a crucial area to analyse climate-ground interactions. Freezing indexes and n-factors from contrasting topographic locations in Hurd Peninsula (Livingston Island) are analysed to assess the influence of snow cover on soil's thermal regime. The snow pack duration, thickness and physical properties are key in determining the thermal characteristics and spatial distribution of permafrost. The Temperature at the Top Of the Permafrost (TTOP) model uses freezing and thawing indexes, n-factors and thermal conductivity of the ground, as factors representing ground-atmosphere interactions and provides a framework to understand permafrost conditions and distribution. Eight sites were used to calculate TTOP and evaluate its accuracy. They encompass different geological, morphological and climatic conditions selected to identify site-specific ground thermal regime controls. Data was collected in the freezing seasons of 2007 and 2009 for air, surface and ground temperatures, as well as snow thickness. TTOP model results from sites located between 140 and 275ma.s.l were very close to observational data, with differences varying from 0.05 to 0.4°C, which are smaller than instrumental error. TTOP results for 36ma.s.l confirm that permafrost is absent at low altitude and thermal offsets for rock areas show values between 0.01 and 0.48°C indicating a small effect of latent heat, as well as of advection.

Recent shallowing of the thaw depth at Crater Lake, Deception Island, Antarctica (2006–2014)

The Western Antarctic Peninsula region is one of the hot spots of climate change and one of the most ecologically sensitive regions of Antarctica, where permafrost is near its climatic limits. The research was conducted in Deception Island, an active stratovolcano in the South Shetlands archipelago off the northern tip of the Antarctic Peninsula. The climate is polar oceanic, with high precipitation and mean annual air temperatures (MAAT) close to −3°C. The soils are composed by ashes and pyroclasts with high porosity and high water content, with ice-rich permafrost at −0.8°C at the depth of zero annual amplitude, with an active layer of about 30cm. Results from thaw depth, ground temperature and snow cover monitoring at the Crater Lake CALM-S site over the period 2006 to 2014 are analyzed. Thaw depth (TD) was measured by mechanical probing once per year in the end of January or early February in a 100×100m with a 10m spacing grid. The results show a trend for decreasing thaw depth from ci. 36cm in 2006 to 23cm in 2014, while MAAT, as well as ground temperatures at the base of the active layer, remained stable. However, the duration of the snow cover at the CALM-S site, measured through the Snow Pack Factor (SF) showed an increase from 2006 to 2014, especially with longer lasting snow cover in the spring and early summer. The negative correlation between SF and the thaw depth supports the significance of the influence of the increasing snow cover in thaw depth, even with no trend in the MAAT. The lack of observed ground cooling in the base of the active layer is probably linked to the high ice/water content at the transient layer. The pyroclastic soils of Deception Island, with high porosity, are key to the shallow active layer depths, when compared to other sites in the Western Antarctic Peninsula (WAP). These findings support the lack of linearity between atmospheric warming and permafrost warming and induce an extra complexity to the understanding of the effects of climate change in the ice-free areas of the WAP, especially in scenarios with increased precipitation as snow fall.

Interannual variability in net community production at the Western Antarctic Peninsula region (1997–2014)

AbstractIn this study, we examined the interannual variability of net community production (NCP) in the Western Antarctic Peninsula (WAP) using in situ O2/Ar‐NCP estimates (2008–2014) and satellite data (SeaWiFS and MODIS‐Aqua) from 1997 to 2014. We found that NCP generally first peaks offshore and follows sea‐ice retreat from offshore to inshore. Annually integrated NCP (ANCP) displays an onshore‐to‐offshore gradient, with coastal and shelf regions up to 8 times more productive than offshore regions. We examined potential drivers of interannual variability in the ANCP using an Empirical Orthogonal Function (EOF) analysis. The EOF's first mode explains ∼50% of the variance, with high interannual variability observed seaward of the shelf break. The first principal component is significantly correlated with the day of sea‐ice retreat (R = −0.58, p &lt; 0.05), as well as the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO) climate indices in austral spring. Although the most obvious pathway by which the day of sea‐ice retreat influences NCP is by controlling light availability early in the growing season, we found that the effect of day of sea‐ice retreat on NCP persists throughout the growing season, suggesting that additional controls, such as iron availability, are preconditioned or correlated to the day of sea‐ice retreat.

The imbalance of new and export production in the western Antarctic Peninsula, a potentially “leaky” ecosystem

AbstractTo quantify the balance between new production and vertical nitrogen export of sinking particles, we measured nitrate uptake, net nitrate drawdown, ΔO2/Ar‐based net community production, sediment trap flux, and 234Th export at a coastal site near Palmer Station, Antarctica, during the phytoplankton growing season from October 2012 to March 2013. We also measured nitrate uptake and 234Th export throughout the northern western Antarctic Peninsula (WAP) region on a cruise in January 2013. We used a nonsteady state 234Th equation with temporally varying upwelling rates and an irradiance‐based phytoplankton production model to correct our export and new production estimates in the complex coastal site near Palmer Station. Results unequivocally showed that nitrate uptake and net community production were significantly greater than the sinking particle export on region‐wide spatial scales and season‐long temporal scales. At our coastal site, new production (105 ± 17.4 mg N m−2 d−1, mean ± standard error) was 5.3 times greater than vertical nitrogen export (20.4 ± 2.4 mg N m−2 d−1). On the January cruise in the northern WAP, new production (47.9 ± 14.4 mg N m−2 d−1) was 2.4 times greater than export (19.9 ± 1.4 mg N m−2 d−1). Much of this imbalance can be attributed to diffusive losses of particulate nitrogen from the surface ocean due to diapycnal mixing, indicative of a “leaky” WAP ecosystem. If these diffusive losses are common in other systems where new production exceeds export, it may be necessary to revise current estimates of the ocean's biological pump.

Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics.

Rapid warming in the highly productive western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels, yet viral influences on microbial processes and ecosystem function remain understudied in the Southern Ocean. Here we use cultivation-independent quantitative ecological and metagenomic assays, combined with new comparative bioinformatic techniques, to investigate double-stranded DNA viruses during the WAP spring–summer transition. This study demonstrates that (i) temperate viruses dominate this region, switching from lysogeny to lytic replication as bacterial production increases, and (ii) Southern Ocean viral assemblages are genetically distinct from lower-latitude assemblages, primarily driven by this temperate viral dominance. This new information suggests fundamentally different virus–host interactions in polar environments, where intense seasonal changes in bacterial production select for temperate viruses because of increased fitness imparted by the ability to switch replication strategies in response to resource availability. Further, temperate viral dominance may provide mechanisms (for example, bacterial mortality resulting from prophage induction) that help explain observed temporal delays between, and lower ratios of, bacterial and primary production in polar versus lower-latitude marine ecosystems. Together these results suggest that temperate virus–host interactions are critical to predicting changes in microbial dynamics brought on by warming in polar marine systems.

Modeling the spatial and temporal dynamics of foraging movements of humpback whales (Megaptera novaeangliae) in the Western Antarctic Peninsula.

BackgroundA population of humpback whales (Megaptera novaeangliae) spends the austral summer feeding on Antarctic krill (Euphausia superba) along the Western Antarctic Peninsula (WAP). These whales acquire their annual energetic needs during an episodic feeding season in high latitude waters that must sustain long-distance migration and fasting on low-latitude breeding grounds. Antarctic krill are broadly distributed along the continental shelf and nearshore waters during the spring and early summer, and move closer to land during late summer and fall, where they overwinter under the protective and nutritional cover of sea ice. We apply a novel space-time utilization distribution method to test the hypothesis that humpback whale distribution reflects that of krill: spread broadly during summer with increasing proximity to shore and associated embayments during fall.ResultsHumpback whales instrumented with satellite-linked positional telemetry tags (n = 5), show decreased home range size, amount of area used, and increased proximity to shore over the foraging season.ConclusionsThis study applies a new method to model the movements of humpback whales in the WAP region throughout the feeding season, and presents a baseline for future observations of the seasonal changes in the movement patterns and foraging behavior of humpback whales (one of several krill-predators affected by climate-driven changes) in the WAP marine ecosystem. As the WAP continues to warm, it is prudent to understand the ecological relationships between sea-ice dependent krill and krill predators, as well as the interactions among recovering populations of krill predators that may be forced into competition for a shared food resource.

When shape matters: Strategies of different Antarctic ascidians morphotypes to deal with sedimentation

Climate change leads to increased melting of tidewater glaciers in the Western Antarctic Peninsula region and sediment bearing glacial melt waters negatively affects filter feeding species as solitary ascidians. In previous work the erect-forms Molgula pedunculata and Cnemidocarpa verrucosa (Order Stolidobranchiata) appeared more sensitive than the flat form Ascidia challengeri (Order Phlebobranchiata). Sedimentation exposure is expected to induce up-regulation of anaerobic metabolism by obstructing the organs of gas exchange (environmental hypoxia) or causes enhanced squirting activity (functional hypoxia). In this study we evaluated the possible relationship between ascidian morphotype and their physiological response to sedimentation. Together with some behavioural observations, we analysed the response of anaerobic metabolic parameters (lactate formation and glycogen consumption) in different tissues of three Antarctic ascidians, exposed to high sediment concentrations (200 mgL−1). The results were compared to experimental hypoxia (10% pO2) and exercise (induced muscular contraction) effects, in order to discriminate the effect of sediment on each species and morpho-type (erect vs. flat forms). Our results suggest that the styled (erect) C. verrucosa increases muscular squirting activity in order to expulse excessive material, while the flat-form A. challengeri reacts more passively by down-regulating its aerobic metabolism under sediment exposure. Contrary, the erect ascidian M. pedunculata did not show any measurable response to the treatments, indicating that filtration and ingestion activities were not reduced or altered even under high sedimentation (low energetic material) which could be disadvantageous on the long-term and could explain why M. pedunculata densities decline in the study area.

Estimates of potential new production (PNP) for the waters off the western Antarctic Peninsula (WAP) region

Potential new production (PNP) can be used as a proxy for new primary production (nPP) and sets the upper bound limit of nitrate-derived primary production (PP). For this study, we estimate PNP by employing a one-dimensional analytical model using in situ and model data for the waters off the western Antarctica Peninsula (WAP) for midsummer, centered around January. Field observations were made during the Palmer Long Term Ecological Research (Palmer LTER) program. A decade long time-series of NO3 vertical profile data (1998–2007, N=516) was used for PNP computations.PNP was calculated for the WAP region by subdividing it into three sub-regions i.e. Coastal, Shelf and Slope based on bathymetry and water mass properties. The Coastal sub-region includes waters with bathymetric depths of 450m or less with Slope water accounting for the oceanic region greater than 750m water depth, while the extensive Shelf region occupies the area between these depth limits. Mean PNP estimates were computed to be 2482.6±197.5, 384.5±61.7, and 891.1±81.8mgCm−2d−1 for the Coastal, Shelf and Slope sub-regions, respectively. The estimated overall mean PNP rate for the entire Palmer LTER WAP region during midsummer (January) was 1257.5±113.6mgCm−2d−1. The mean potential f-ratio (PNP:PP) for the WAP region was closer to unity (potential f-ratio=1.2) indicating that nPP (as opposed to recycled production) plays a major role in sustaining this sporadic but highly productive Antarctic ecosystem during mid-summer. We have also analyzed a longer time series from oceanic sampling stations off Palmer Station, Anvers Island, Antarctica spanning yeardays 310–45 (late November–mid February, 1994–2007). Harmonic regression fit of PNP data from all stations within this nearshore sampling grid of the Palmer LTER Program during the growth season provides maximum and minimum PNP rates of 2181.78 and 14.69mgCm−2d−1 on yeardays 335 (late November) and 43 (mid February), respectively. The overall mean PNP for this region was estimated to be 1040.93±764.58mgCm−2d−1 by employing a constant Kz value of 10−5ms−2. The maximum and minimum PNP values coincide approximately with the onset and demise of annual algal bloom.Analysis of the terms used in the PNP equation indicate that both NO3 drawdown rates (mean=13.25±9.57mmolm−2d−1, N=156) and NO3 flux into the euphotic layer (mean=1.36±1.79mmolm−2d−1, N=156) have high temporal and spatial variability. NO3 drawdown rates were higher than NO3 flux into the control volume by approximately an order of magnitude. Sensitivity analyses of the model using two extreme values of Kz, (10−4 and 10−5ms−2) that are widely reported in the literature for the WAP region, yielded a PNP range of 97.13mgCm−2d−1. The latter accounted for approximately 10% of the overall computed PNP. PNP estimates for the coastal sub-region which includes Marguerite Bay agreed well with estimates of nPP from north Marguerite Bay in a recent study which employed different datasets and research approach.

Chemical mediation of mutualistic interactions between macroalgae and mesograzers structure unique coastal communities along the western Antarctic Peninsula.

Hard bottom communities along the western Antarctic Peninsula region are dominated by thick macroalgal forests, which support high densities of mesograzers, particularly amphipods, and also numerous gastropods. The macroalgae are chemically defended from consumption by the mesograzers and other herbivores and they provide the mesograzers a chemically defended refuge from predation by omnivorous fish. The macroalgae benefit in return because the mesograzers remove epiphytic algae from them. Since these two assemblages are major components of the community, this can be viewed as a community-wide mutualism. Most subcomponents of these interactions have also been documented in lower latitude communities and the similarities and differences between the communities in Antarctica and in other regions are discussed.

West Antarctic Peninsula: An Ice-Dependent Coastal Marine Ecosystem in Transition

The extent, duration, and seasonality of sea ice and glacial discharge strongly influence Antarctic marine ecosystems. Most organisms' life cycles in this region are attuned to ice seasonality. The annual retreat and melting of sea ice in the austral spring stratifies the upper ocean, triggering large phytoplankton blooms. The magnitude of the blooms is proportional to the winter extent of ice cover, which can act as a barrier to wind mixing. Antarctic krill, one of the most abundant metazoan populations on Earth, consume phytoplankton blooms dominated by large diatoms. Krill, in turn, support a large biomass of predators, including penguins, seals, and whales. Human activity has altered even these remote ecosystems. The western Antarctic Peninsula region has warmed by 7°C over the past 50 years, and sea ice duration has declined by almost 100 days since 1978, causing a decrease in phytoplankton productivity in the northern peninsula region. Besides climate change, Antarctic marine systems have been greatly altered by harvesting of the great whales and now krill. It is unclear to what extent the ecosystems we observe today differ from the pristine state.