Palmer Station Research Articles

The Influence of Ultraviolet‐B Radiation on Growth, Hydroxycinnamic Acids and Flavonoids of Deschampsia antarctica during Springtime Ozone Depletion in Antarctica¶†

We examined the influence of solar ultraviolet-B radiation (UV-B; 280-320 nm) on the growth, biomass production and phenylpropanoid concentrations of Deschampsia antarctica during the springtime ozone depletion season at Palmer Station, along the Antarctic Peninsula. Treatments involved placing filters on frames over potted plants that reduced levels of biologically effective UV-B either by 83% (reduced UV-B) or by 12% (near-ambient UV-B) over the 63 day experiment (7 November 1998-8 January 1999) when ozone depletion averaged 17%. Plants growing under near-ambient UV-B had 41% and 40% lower relative growth rates and net assimilation rates, respectively, than those under reduced UV-B. The former plants produced 50% less total biomass as a result of having 47% less aboveground biomass. The reduction in aboveground biomass was a result of a 29% lower leaf elongation rate resulting in shorter leaves and 59% less total leaf area in plants grown under reduced UV-B. p-Coumaric, caffeic and ferulic acids were the major hydroxycinnamic acids, and luteolin derivatives were the major flavonoids in both insoluble and soluble leaf extracts. Concentrations of insoluble p-coumaric and caffeic acid and soluble ferulic acids were 38%, 48% and 60% higher, respectively, under near-ambient UV-B than under reduced UV-B. There were no UV-B effects on concentrations of insoluble or soluble flavonoids.

Photosynthetically Active Sunlight at High Southern Latitudes¶

ABSTRACTA network of scanning spectroradiometers has acquired a multiyear database of visible solar irradiance, covering wavelengths from 400 to 600 nm, at four sites in the high‐latitude Southern Hemisphere, from 55°S to 90°S. Monthly irradiations computed from the hourly measurements reveal the character of the seasonal cycle and illustrate the role of cloudiness as functions of latitude. Near summer solstice, the combined influences of solar elevation and the duration of daylight would produce a monthly irradiation with little latitude dependence under clear skies. However, the attenuation associated with local cloudiness varies geographically, with the greatest effect at the most morthern locations, Ushuaia, Argentina and Palmer Station on the Antartic Peninusula. Near summer solstice, the South Pole experiences the largest monthly irradiation of the sites studied, where relatively clear skies contribute to this result. Scaling factors derived from radiative‐transfer calculations combined with the measured 400–600 nm irradiances allow estiamting irradiances integrated over the wavelength band 400–700 nm. This produces a climatology of photosynthetically active radiation for each month of the year at each site.

The Ultraviolet Radiation Environment of High Southern Latitudes: Springtime Behavior over a Decadal Timescale¶

ABSTRACTFour spectroradiometers located at latitudes from 55° to 90°S conducted near‐continuous measurements of ground‐level solar ultraviolet irradiance from 1990 through 2001. The behavior during months from October through December is of special interest because this period includes the springtime loss in column ozone and the naturally large irradiances of early summer. Monthly integrated irradiances using biological weightings for erythema and damage to DNA show a distortion of the normal annual cycle in irradiance, with enhanced values occurring in October and November. In some cases, these irradiances exceed those near summer solstice in December. Changes in local cloudiness and column ozone both contribute significantly to interannual variability in erythemal irradiance. This is particularly the case at Palmer Station, near 65°S, where the monthly integrated erythemal irradiance in November 1997 was more than double that observed 5 years earlier. In general, at sites on the Antarctic continent, interannual variability in monthly integrated erythemal irradiance is greatest in November, when the observation for any given year can fall 40% above or below the multiyear mean. Near the tip of South America, interannual variability is approximately half that seen in Antarctica.

Evaluation and derivation of cloud-cover algorithms for calculation of surface irradiance in sub-Antarctic and Antarctic environments

To investigate approaches for parameterizing cloud cover effects in models of surface irradiance, the daily-averaged and hourly irradiances measured at Palmer Station (64°46′S, 64°3′W), McMurdo Station (77°5l′S, 166°40′E) and Ushuaia (54°49′S, 68°19′W) between 1993 and 1997 were compared to irradiance values computed with a clear sky radiative transfer model in which nine empirical cloud-cover correction relationships were included. The cloud cover correction algorithms improved the simulated irradiance by factors of 3 and 3.7 for Palmer Station and Ushuaia, respectively, over the non-corrected irradiances. No single cloud cover correction algorithm worked consistently at the three sites. Therefore, a power function cloud cover correction algorithm was derived from comparisons between the observed spectrally-integrated irradiances and the simulated irradiances at the three locations. New coefficient values for the power function cloud cover correction algorithm for the spectrally-resolved irradiances were also derived at the three sites, and were found to be spectrally-neutral and to differ in magnitude. The general trends in the values obtained for the three sites provide an approach for generalizing cloud cover correction algorithm coefficients to other parts of the Antarctic.

The Ultraviolet Radiation Environment of High Southern Latitudes: Springtime Behavior over a Decadal Timescale

Four spectroradiometers located at latitudes from 55 degrees to 90 degrees S conducted near-continuous measurements of ground-level solar ultraviolet irradiance from 1990 through 2001. The behavior during months from October through December is of special interest because this period includes the springtime loss in column ozone and the naturally large irradiances of early summer. Monthly integrated irradiances using biological weightings for erythema and damage to DNA show a distortion of the normal annual cycle in irradiance, with enhanced values occurring in October and November. In some cases, these irradiances exceed those near summer solstice in December. Changes in local cloudiness and column ozone both contribute significantly to interannual variability in erythemal irradiance. This is particularly the case at Palmer Station, near 65 degrees S, where the monthly integrated erythemal irradiance in November 1997 was more than double that observed 5 years earlier. In general, at sites on the Antarctic continent, interannual variability in monthly integrated erythemal irradiance is greatest in November, when the observation for any given year can fall 40% above or below the multiyear mean. Near the tip of South America, interannual variability is approximately half that seen in Antarctica.

Photosynthetically active sunlight at high southern latitudes

A network of scanning spectroradiometers has acquired a multiyear database of visible solar irradiance, covering wavelengths from 400 to 600 nm, at four sites in the high-latitude Southern Hemisphere, from 55 degrees S to 90 degrees S. Monthly irradiations computed from the hourly measurements reveal the character of the seasonal cycle and illustrate the role of cloudiness as functions of latitude. Near summer solstice, the combined influences of solar elevation and the duration of daylight would produce a monthly irradiation with little latitude dependence under clear skies. However, the attenuation associated with local cloudiness varies geographically, with the greatest effect at the most northern locations, Ushuaia, Argentina and Palmer Station on the Antarctic Peninsula. Near summer solstice, the South Pole experiences the largest monthly irradiation of the sites studied, where relatively clear skies contribute to this result. Scaling factors derived from radiative-transfer calculations combined with the measured 400-600 nm irradiances allow estimating irradiances integrated over the wavelength band 400-700 nm. This produces a climatology of photosynthetically active radiation for each month of the year at each site.

Photosynthetically Active Sunlight at High Southern Latitudes¶

Abstract A network of scanning spectroradiometers has acquired a multiyear database of visible solar irradiance, covering wavelengths from 400 to 600 nm, at four sites in the high-latitude Southern Hemisphere, from 55°S to 90°S. Monthly irradiations computed from the hourly measurements reveal the character of the seasonal cycle and illustrate the role of cloudiness as functions of latitude. Near summer solstice, the combined influences of solar elevation and the duration of daylight would produce a monthly irradiation with little latitude dependence under clear skies. However, the attenuation associated with local cloudiness varies geographically, with the greatest effect at the most northern locations, Ushuaia, Argentina and Palmer Station on the Antarctic Peninsula. Near summer solstice, the South Pole experiences the largest monthly irradiation of the sites studied, where relatively clear skies contribute to this result. Scaling factors derived from radiative-transfer calculations combined with the me...

The Ultraviolet Radiation Environment of High Southern Latitudes: Springtime Behavior over a Decadal Timescale¶

Four spectroradiometers located at latitudes from 55° to 90°S conducted near-continuous measurements of ground-level solar ultraviolet irradiance from 1990 through 2001. The behavior during months from October through December is of special interest because this period includes the springtime loss in column ozone and the naturally large irradiances of early summer. Monthly integrated irradiances using biological weightings for erythema and damage to DNA show a distortion of the normal annual cycle in irradiance, with enhanced values occurring in October and November. In some cases, these irradiances exceed those near summer solstice in December. Changes in local cloudiness and column ozone both contribute significantly to interannual variability in erythemal irradiance. This is particularly the case at Palmer Station, near 65°S, where the monthly integrated erythemal irradiance in November 1997 was more than double that observed 5 years earlier. In general, at sites on the Antarctic continent, interannual variability in monthly integrated erythemal irradiance is greatest in November, when the observation for any given year can fall 40% above or below the multiyear mean. Near the tip of South America, interannual variability is approximately half that seen in Antarctica.

Comprehensive evaluation of the palatability and chemical defenses of subtidal macroalgae from the Antarctic Peninsula

The palatability of 35 non-encrusting, subtidal macroalgal species collected from the vicinity of Palmer Station, Antarctica (64° 46' S, 64° 03' W), was determined in laboratory bioassays utilizing sympatric sea stars and fish known to consume macroalgae in nature. Overall, 63% of the macroalgal species offered to sea stars and 83% of the macroalgal species offered to fish in thallus bioassays were significantly unpalatable. This included all of the ecologically dominant, overstory brown macroalgae in the region. When organic extracts of unpalatable macroalgal species were incorporated into artificial foods, 76% of the species unpalatable as thallus to sea stars were also unpalatable to them as extract, and 53% of the species unpalatable as thallus to fish were also unpalatable to them as extract. If either sea stars or fish rejected thallus of a macroalgal species, palatability of organic extracts of that species to herbivorous amphipods was determined: 63% of such algal species were unpalatable as extract to the amphipods. It was concluded that antarctic macroalgae are commonly unpalatable to sympatric consumers and that much of this unpalatability is the result of chemical defenses. As a whole, neither thallus toughness nor a variety of nutritional quality parameters appeared to be related to macroalgal palatability. We also tested the hypothesis that nitrogen-containing metabolites should be common in macroalgae from nitrogen-replete, carbon-limited environments such as the coastal waters of Antarctica. Macroalgal acid extracts targeting nitrogenous secondary metabolites were subjected to thin-layer chromatography analysis; no such compounds were detected.

Localization of individual lightning discharges via directional and temporal triangulation of sferic measurements at two distant sites

Lightning discharges generate electromagnetic pulses, known as sferics, that propagate through the waveguide formed by the Earth and the ionosphere. The energy in the VLF band can propagate over great distances (∼10,000 km) with low loss (3 dB/Mm) and can therefore be detected far from the source lightning location. Using sferic measurements from VLF receivers at Palmer Station, Antarctica, and Vieques Island, Puerto Rico, the locations of lightning discharges from regions such as South America, North America, and Africa are triangulated. Both sferic arrival azimuth at the two receivers and the time of arrival difference between the receivers are used to find the best estimate of the lightning discharge location. Owing to the extremely wide separation of the two receivers, ambiguities sometimes result in pairing sferics detected at one site to their matching sferics detected at the other site. In these cases a best‐best estimate scheme is used. Simulation results indicate that for the two receivers considered here the most accurate location performance is in South America with an expected median location error of ∼75 km. The system has the worst performance due north of the Vieques Island site, with an expected median location error of ∼2000 km. Triangulation results for South America are shown for the period 7–10 September 2001. Results for 8 September 2001 are compared to cloud‐to‐ground lightning flashes detected by the National Lightning Detection Network. For this day, 49% of flashes were detected with a median error of about 200 km. Results are also compared to lightning discharges detected by the Lightning Imaging Sensor (LIS) aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. For a particular TRMM pass over South America, 20% of flashes detected by LIS were correctly located using the described technique, with a median error of 187 km. The event rate for a localized South American storm is also monitored and documented for the same 4‐day period.

Effect of Sex and Age on the Supercooling Point of the Winter-Active Diamesa mendotae Muttkowski (Diptera: Chironomidae)

Supercooling points (SCP) of adult Diamesa mendotae Muttkowski, 1915 (Diptera: Chironomidae) were determined at 3, 5, 9, 12 and 17 days post-collection. Supercooling points were recorded using surface contact thermometry and a cooling rate of ca. 1°C min−1. Female SCPs averaged −22.81, −23.76, −23.85, −23.65, and −20.87°C on each date post-collection and did not differ significantly. Male SCPs were statistically similar and averaged −21.75, −23.53, −23.68, −23.66, and −22.92°C on each date post-collection. Paired comparisons of female/male SCPs on each date post-collection did not show significant differences over time. The overall mean SCP of D. mendotae (−23.05°C) is substantially lower than values of −5.3°C and −5.7°C published for adults and larvae of Belgica antarctica Jacobs 1900 collected at Palmer Station (Antarctica) and −14.2°C for larvae of Paraclunio alaskensis Coquillett 1900 collected at Vancouver Island, British Columbia. In addition, the SCP of this species appears to be lower than that of other winter-active insect species reported in the literature. Although no adults survived after the SCP was recorded, further studies are necessary to determine if D. mendotae is a freeze-intolerant insect. Nevertheless, our results suggest that a low SCP could be used as a mechanism to facilitate emergence and adult activity of this species during winter conditions.

Growth in the limpet Nacella concinna from contrasting sites in Antarctica

Annual shell growth was determined by mark and recapture in the limpet Nacella concinna (Strebel 1908) at two contrasting sites in Antarctica. At Signy Island, 60°S, growth was moderately fast, comparable with some limpets in more temperate areas. The fluorescent calcium marker calcein was used to validate the results from the mark/recapture study, and fine-scale growth increments showed that shell growth was seasonal. Further south at Rothera Point, 67°S, mean annual growth over a 3-year period was significantly slower than at Signy, and in 1 year was the slowest yet reported for a limpet. Comparison with an earlier mark/recapture study at Arthur Harbour, Palmer Station (64°S) revealed a cline of decreasing growth performance with increasing latitude along the Antarctic Peninsula. It is not clear whether the slower annual growth rate at higher latitude was caused by physiological constraints, a reduced length of growing season, or a combination of both. Limpets show a global cline in growth performance, which decreases towards higher latitudes.

Further membranolide diterpenes from the antarctic sponge dendrilla membranosa.

Chemical investigation of the Antarctic sponge Dendrilla membranosa collected from the vicinity of Palmer Station on Anvers Island, Antarctica, yielded three new diterpenes, membranolides B-D (2-4), as well as three previously reported sponge metabolites. Membranolides C and D (3, 4), bearing carboxylic acid functional groups, display Gram-negative antibiotic and antifungal activities.

Thermodynamic phase of maritime Antarctic clouds from FTIR and supplementary radiometric data

A Fourier Transform Infrared (FTIR) spectroradiometer was deployed at Palmer Station, Antarctica, from 1 September to 17 November 1991. This instrument is similar to the Atmospheric Emitted Radiance Interferometer (AERI) deployed with the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program. The instrument measured downwelling zenith radiance in the spectral interval 400–2000 cm−1, at a resolution of 1 cm−1. The spectral radiance measurements, which can be expressed as spectral brightness temperature Tb(ν), contain information about cloud optical properties in the middle infrared window (800–1200 cm−1, 8.3–12.5 μm). In this study, this information is exploited to (1) provide additional characterization of Antarctic cloud radiative properties, and (2) demonstrate how multisensor analysis of ARM data can potentially retrieve cloud thermodynamic phase. Radiative transfer simulations demonstrate how Tb(ν) is a function of cloud optical depth τ, effective particle radius re, and thermodynamic phase. For typical values of τ and re, the effect of increasing the ice fraction of the total optical depth is to flatten the slope of Tb(ν) between 800–1000 cm−1. For optically thin clouds (τ ∼ 3) and larger ice particles (re (ice) > 50 μm) the behavior of Tb(ν) in this interval switches from a decrease with increasing wavenumber ν to an increase with ν, once the ice fraction of the total optical depth exceeds ∼0.7. The FTIR spectra alone cannot be interpreted to obtain thermodynamic phase, because a relatively small slope in Tb(ν) between 800–1000 cm−1 could represent either an optically thin cloud in the ice or mixed phase, or an optically thick cloud radiating as a blackbody. Sky observations and ancillary radiometric data are needed to sort the FTIR spectra into categories of small cloud optical depth, where the mid‐IR window data can be interpreted; and larger cloud optical depth, where the FTIR data contain information only about cloud base temperature. Spectral solar ultraviolet (UV) irradiance measurements from the U.S. National Science Foundation's UV Monitor at Palmer Station are used to estimate area‐averaged effective cloud optical depth τsw, and these estimates are used to sort the FTIR data. FTIR measurements with colocated τsw < 16 are interpreted to estimate cloud thermodynamic phase. Precipitating cloud decks generally show flatter slopes in Tb(ν), consistent with the ice or mixed phase. Altostratus decks show a larger range in Tb(ν) slope than low cloud decks, including increasing slopes with ν, suggesting a more likely occurrence of the ice phase. This study illustrates how cloud thermodynamic phase can be defensibly retrieved from FTIR data if high quality shortwave radiometric data are also available to sort the FTIR measurements by cloud opacity, and both data types are available at the ARM sites.

CLIMATOLOGIES OF OZONE AND UV-B IRRADIANCES OVER ANTARCTICA IN THE LAST DECADES

Antarctica is the continent that has suffered the strongest variations in total column and UV-B radiation, during the last decades, as consequence of the ozone hole. Systematic measurements of total column are being performed since the late 1950s at ground stations, and global coverage is available since the late 1970s, with measurements provided by instruments installed at different satellites (Nimbus-7, Meteor-3, Adeos, Earth-Probe, Gome). In 1988, the National Science Foundation (US) initiated the activities of the NSF UV Radiation Monitoring Network, installing three spectro-radiometers SUV-100/BSI in South Pole, Mc Murdo and Palmer Stations, and one in Ushuaia. Now, a time series of more than ten years is available for all stations. Nevertheless, there are no records of background spectral irradiances, prior to the ozone hole. Then, we completed the databases, for South Pole, dating back to the late 1970´s, with narrow-band and biologically weighted irradiances inferred, applying a multi-regressive model, from total column and pyranometer data from the NOAA/CMDL surface radiation budget database. Combining the above-mentioned databases, we will present a discussion on the climatologies of and irradiances over Antarctica, in the last decades

Observed trends for CF 3-containing compounds in background air at Cape Meares, Oregon, Point Barrow, Alaska, and Palmer Station, Antarctica

The concentrations of CF 3-containing compounds in archived air samples collected at Cape Meares, Oregon, from 1978 to 1997, at Point Barrow, Alaska, from 1995 to 1998, and at Palmer Station, Antarctica, from 1991 to 1997, were determined by high resolution gas chromatography and high resolution mass spectrometry. The CF 3-containing compounds measured by this method and discussed here are: the perfluorinated compound, C 3F 8 (FC 218); four perhalogenated compounds, CF 3Cl (CFC 13), CF 3CF 2Cl (CFC 115), CF 3CFCl 2 (CFC 114a), and CF 3Br (Halon 1301); and three hydrofluorocompounds, CF 3H (HFC 23), CF 3CH 3 (HFC 143a), and CF 3CH 2F (HFC 134a). For four of these compounds, very few measurements have been previously reported. The atmospheric concentrations of all of the CF 3-containing compounds continuously increased in time over the sample collection periods. From these data, the annual rates of emission into the atmosphere have been estimated. The emission rates fall into one of three distinct categories. The annual emission rates of C 3F 8, CF 3H, CF 3CH 3, and CF 3CH 2F have continuously increased over the last two decades. That of CF 3CFCl 2 has decreased continuously. Emission rates for CF 3Cl, CF 3CF 2Cl, and CF 3Br reached maximum levels in the late 1980s, and have been decreasing in the 1990s. The emission rates of C 3F 8, CF 3CH 3 and CF 3CH 2F were nearly zero 20 years ago but have increased rapidly during the last decade.

A predator's perspective on causal links between climate change, physical forcing and ecosystem response

The mechanisms by which variability in sea ice cover and its effects on the demography of the Antarctic krill Euphausia superba cascade to other ecosystem components such as apex preda- tors remain poorly understood at all spatial and temporal scales, yet these interactions are essential for understanding causal links between climate change, ecosystem response and resource monitor- ing and management in the Southern Ocean. To address some of these issues, we examined the long- term foraging responses of Adelie penguins Pygoscelis adeliae near Palmer Station, western Antarc- tic Peninsula, in relation to ice-induced changes in krill recruitment and availability. Our results suggest that (1) there is a direct, causal relationship between variability in ice cover, krill recruitment, prey availability and predator foraging ecology, (2) regional patterns and trends detected in this study are consistent with similar observations in areas as far north as South Georgia, and (3) large- scale forcing associated with the Antarctic Circumpolar Wave may be governing ecological inter- actions between ice, krill and their predators in the western Antarctic Peninsula and Scotia Sea regions. Another implication of our analyses is that during the last 2 decades in particular, krill pop- ulations have been sustained by strong age classes that emerge episodically every 4 to 5 yr. This raises the possibility that cohort senescence has become an additional ecosystem stressor in an envi- ronment where ice conditions conducive to good krill recruitment are deteriorating due to climate warming. In exploring these interactions, our results suggest that at least 1 'senescence event' has already occurred in the western Antarctic Peninsula region, and it accounts for significant coherent decreases in krill abundance, predator populations and predator foraging and breeding perfor- mance. We propose that krill longevity should be incorporated into models that seek to identify and understand causal links between climate change, physical forcing and ecosystem response in the western Antarctic Peninsula region.

A test of three‐dimensional radiative transfer simulation using the radiance signatures and contrasts at a high latitude coastal site

A three‐dimensional Monte Carlo radiation code is used to analyze surface observations of sky radiance at a high latitude coastal site. Observations were made at Palmer Station, Antarctica, under uniform marine stratus clouds during both ice‐free and iced‐in ocean conditions. The model results using actual snow/ocean area coverage show good qualitative agreement with all‐sky images and high spectral resolution radiometer scans. When viewing over the island, toward the northeast, observations and modeling indicate that sky radiance in the visible bands is up to a factor of two greater than for directions toward the southwest, viewing out over open ocean. Owing to a decrease in snow reflectance at longer wavelengths, modeled and observed radiance distributions in the near infrared tend to be much more symmetric. Results of the modeling study indicate that details of the snow BRDF, or island topography, have a very small effect on model predictions. In addition, the model indicates that the angular distribution of sky radiance is fairly insensitive to cloud optical depth (assumed homogeneous) and is independent of cloud height as long as cloud layer thickness is not much larger than the cloud base height.

Long‐range tracking of thunderstorms using sferic measurements

Each lightning stroke launches an electromagnetic pulse, known as a radio atmospheric or sferic that propagates in the waveguide between the Earth and the ionosphere. Sferics, with most of their energy contained in the frequency band from 3 Hz to 30 kHz, can propagate with low loss to distances of tens of megameters. Using very low frequency (VLF) magnetic field measurements at Palmer Station, Antarctica, the azimuths of sferics originating in North America (∼10,000 km range) are found to be measurable to less than 1 degree accuracy. Analysis of the arrival azimuths at Palmer Station allows the assessment of lightning flash rates of storms occurring in diverse regions of the globe including North America and Africa. Arrival azimuths are compared with flash level data from the National Lightning Detection Network (NLDN) and 83.6% of the sferics that could be matched to NLDN flashes were within 2 degrees of the predicted azimuths for those flashes. Results are also compared with data from the satellite‐based Optical Transient Detector (OTD), and the arrival azimuths of sferics detected at Palmer Station are consistent with the location of lightning occurring elsewhere around the world. The relative distribution of and the relationship between ground flashes and cloud flashes are discussed for a specific localized thunderstorm. Evidence that sferics generated by intracloud discharges were detected at Palmer Station is also presented.

RESPONSE OF ANTARCTIC TERRESTRIAL MICROARTHROPODS TO LONG-TERM CLIMATE MANIPULATIONS

The terrestrial biota of the Antarctic Peninsula region are experiencing marked changes in climate, especially rising temperatures, precipitation, and UV-B radiation—a combination unique worldwide. These changes, combined with the inherent simplicity of terrestrial communities, have led to their use as “model systems” to predict the future climate change responses of biota at lower latitudes. However, studies integrating responses at different levels of the community trophic structure are lacking. We report here the consequences on the soil microarthropod community of a four-year, multivariate, climate-manipulation experiment carried out over vegetation near Palmer Station, Anvers Island, western Antarctic Peninsula. The experiment used a multifactorial randomized-block design, deploying filters to raise temperatures and reduce ultraviolet (UV)-B (280–320 nm) or both UV-B and UV-A (320–400 nm) radiation of existing vegetation, with further water and fertilizer amendment treatments. Seven microarthropod species recovered in sufficient numbers for statistical analyses showed considerable spatial aggregation independent of treatment, a feature typical of many soil invertebrates. Analyses using negative binomial generalized linear modeling identified further significant and consistent treatment impacts on both individual species and species groups. Relative to controls, manipulations increasing temperature decreased numbers of microarthropods (particularly Collembola), as did exposure to near-ambient levels of UV radiation (separate significant effects for both UV-A and UV-B), while water amendment increased numbers. The impacts of temperature and water are consistent with our understanding of the importance of these two environmental variables and their interaction in Antarctic terrestrial ecosystems. The negative impact of UV (-A or -B) on arthropod heterotroph and detritivore populations in the Antarctic terrestrial food web is likely to be a secondary consequence of UV impact on vegetation characteristics. This is, again, consistent with general predictions of the impact of changing UV climate on ecosystem function.