Coastal Antarctic Site Research Articles

Rapid DMSP production by an Antarctic phytoplankton community exposed to natural surface irradiances in late spring

Natural marine microbial communities sourced from under fast ice at an Antarctic coastal site were incubated in tanks under differently attenuated natural sunlight for 2 wk in late spring (Expt 1) and early summer (Expt 2). In the 18 d period between the 2 sampling episodes, the ice edge retreated from 10 to within 1.5 km of the sampling site, and the fast ice began to break up. Expt 1 rapidly produced significant quantities of total DMSP (DMSPt) with concentrations increasing from 16.6 nmol l �1 to 192.7�204.5 nmol l �1 in 2 d. We believe this is the largest observed increase in DMSPt in a semi-natural community over this time frame. Abundances of Phaeocystis antarctica increased significantly during this initial period, while other phytoplankton species/ groups remained stable. DMSPt concentrations then declined at rates averaging 39.2� 50.0 nmol l �1 d �1 between Days 2 and 4. No major DMSPt production event occurred during Expt 2 despite strong community similarities. Sea ice breakout exposes phytoplankton to significant light-related oxidative stress, and these results suggest the rapid production of DMSPt during Expt 1 was due to the initiation of anti-oxidant mechanisms by a low-light-acclimated community in response to solar radiation stress. DMS concentrations remained comparatively low throughout Expt 1, sug- gesting oxidation of DMSP to products other than DMS. Rapid sea ice breakout in coastal regions of Antarctica may result in similar fast DMSP production events during spring.

First investigations of IO, BrO, and NO2 summer atmospheric levels at a coastal East Antarctic site using mode‐locked cavity enhanced absorption spectroscopy

IO, BrO, and NO2 were measured for the first time at Dumont d'Urville (East Antarctic coast) during summer 2011/2012 by using a near‐UV‐Visible laser spectrometer based on mode‐locked cavity‐enhanced absorption spectroscopy. IO mixing ratios ranged from the 2σ detection limit (0.04 pptv) up to 0.15 pptv. BrO remained close or below the detection limit (2 pptv) of the instrument. Daily averaged NO2 values ranged between the detection limit (10 pptv) and 60 pptv being far higher than levels of a few pptv commonly observed in the remote marine boundary layer. Data are discussed and compared with those available for another coastal Antarctic station (Halley, West Antarctica). It is shown that the oxidative capacity of the atmospheric boundary layer at coastal Antarctic sites is quite different in nature from West to East Antarctica, with the halogen chemistry being promoted at West and the OH chemistry at East.

Measurements of OH and RO2 radicals at the coastal Antarctic site of Dumont d'Urville (East Antarctica) in summer 2010–2011

Measurements of OH and total peroxy RO2 (HO2 plus organic peroxy) radicals were conducted in December 2010/January 2011 at the coastal East Antarctic site of Dumont d'Urville (DDU, 66°40′S 140°01′E) as part of the Oxidant Production over Antarctic Land and its Export (OPALE) project. Compared to measurements carried out at the West Antarctic coast, relatively high concentrations of radicals were found with 24 h average values of 2.1 × 106 and 3.3 × 108 molecule cm−3 for OH and peroxy radicals, respectively. On the basis of the steady state calculations, the observed high concentration of peroxy radicals is in good agreement with the observed levels of O3 and HCHO representing via their photolysis the major primary radical sources. The observed OH levels at DDU could be explained only assuming some RO2 to OH conversion mechanism equivalent to the presence of NO in the range of 10 to 50 pptv. As neither NO nor halogen oxides were measured at DDU the mechanism of this recycling could not be explicitly identified. However, an examination of variability of radical levels as a function of the origin (oceanic versus continental) of sampled air masses suggests a more important OH production from RO2 recycling in continental air masses.

A reassessment of the budget of formic and acetic acids in the boundary layer at Dumont d'Urville (coastal Antarctica): The role of penguin emissions on the budget of several oxygenated volatile organic compounds

Initiated in 1997, the year‐round study of formic and acetic acids was maintained until 2011 at the coastal Antarctic site of Dumont d'Urville. The records show that formic and acetic acids are rather abundant in summer with typical mixing ratios of 200 pptv and 700 pptv, respectively. With the aim to constrain their budget, investigations of their potential marine precursors like short‐chain alkenes and acetaldehyde were initiated in 2011. Acetic acid levels in December 2010 were four times higher than those observed over summers back to 1997. These unusually high levels were accompanied by unusually high levels of ammonia, and by an enrichment of oxalate in aerosols. These observations suggest that the guano decomposition in the large penguin colonies present at the site was particularly strong under weather conditions encountered in spring 2010 (important snow storms followed by sunny days with mild temperatures). Although being dependent on environmental conditions, this process greatly impacts the local atmospheric budget of acetic acid, acetaldehyde, and acetone during the entire summer season. Present at levels as high as 500 pptv, acetaldehyde may represent the major precursor of acetic acid, alkene‐ozone reactions remaining insignificant sources. Far less influenced by penguin emissions, the budget of formic acid remains not fully understood even if alkene‐ozone reactions contribute significantly.

Short Note: Natural seasonal variability of aragonite saturation state within two Antarctic coastal ocean sites

. The observed threefold changes in &#937 ARAG shown here over a few months are of the same order of magnitude as those conditions used in artificial laboratory CO2 experiments. This makes the Antarctic coastal oceans a perfect natural mesocosm to investigate resilience of Southern Ocean marine ecosystems to ocean acidification.

Five-year analysis of background carbon dioxide and ozone variations during summer seasons at the Mario Zucchelli station (Antarctica)

Thework focuses on the analysis ofCO2 andO3 surface variations observed during five summer experimental campaigns carried out at the ‘Icaro Camp’ clean air facility (74.7◦S, 164.1◦E, 41 m a.s.l.) of the ‘Mario Zucchelli’ Italian coastal research station. This experimental activity allowed the definition of summer average background O3 values that ranged from 18.3 ± 4.7 ppbv (summer 2005–2006) to 21.3 ± 4.0 ppbv (summer 2003–2004). Background CO2 concentrations showed an average growth rate of 2.10 ppmv yr-1, with the highest CO2 increase between the summer campaigns 2002–2003 and 2001–2002 (+2.85 ppmv yr-1), probably reflecting the influence of the 2002/2003 ENSO event. A comparison with other Antarctic coastal sites suggested that the summer background CO2 and O3 at MZS-IC are well representative of the average conditions of the Ross Sea coastal regions. As shown by the analysis of local wind direction and by 3-D back-trajectory calculations, the highest CO2 and O3 values were recorded in correspondence to air masses flowing from the interior of the Antarctic continent. These results suggest that air mass transport from the interior of the continent exerts an important influence on air mass composition in Antarctic coastal areas.

Sulfate sources and oxidation chemistry over the past 230 years from sulfur and oxygen isotopes of sulfate in a West Antarctic ice core

The sulfur and oxygen isotopic composition of sulfate in polar ice cores provides information about atmospheric sulfate sources and formation pathways, which have been impacted regionally by human activity over the past several centuries. We present decadal scale mean ice core measurements of Δ17O, δ34S, Δ33S, and Δ36S of sulfate over the past 230 years from the West Antarctic Ice Sheet (WAIS) Divide deep ice core drill site (WDC05‐A). The low mean δ34S of non–sea‐salt sulfate at WAIS Divide (6.0 ± 0.2‰) relative to East Antarctic coastal and plateau sites may reflect a combination of stronger influence of volcanogenic and/or stratospheric sulfate with low δ34S and the influence of frost flowers on the sea‐salt sulfate‐to‐sodium ratio. Δ33S and Δ36S measurements are all within analytical uncertainty of zero but do not contradict a contribution of stratospheric sources to background sulfate deposition at WAIS Divide. Δ17O of non–sea‐salt sulfate shows a small but significant increase between the late 1700s (1.8‰ ± 0.2‰) and late 1800s (2.6‰ ± 0.2‰), but the influence of stratospheric scale volcanic events on Δ17O in the early 1800s remains uncertain. An isotope mass balance model shows that the lack of change in Δ17O of non–sea‐salt sulfate from the mid‐1800s to early 2000s (2.4‰–2.6‰ ± 0.2‰) is consistent with previous atmospheric chemistry model estimates indicating preindustrial to industrial increases in O3 as high as 50% and decreases in OH of 20% in the southern polar troposphere, as long as H2O2 concentrations also increase by over 50%.

Seasonal succession and UV sensitivity of marine bacterioplankton at an Antarctic coastal site

Despite extensive microbial biodiversity studies around the globe, studies focusing on diversity and community composition of Bacteria in Antarctic coastal regions are still scarce. Here, we studied the diversity and development of bacterioplankton communities from Prydz Bay (Eastern Antarctic) during spring and early summer 2002-2003. Additionally, we investigated the possible shaping effects of solar UV radiation (UV-R: 280-400 nm) on bacterioplankton communities incubated for 13-14 days in 650-L minicosm tanks. Ribosomal DNA sequence analysis of the natural bacterioplankton communities revealed an initial springtime community composed of three evenly abundant bacterial classes: Cytophaga-Flavobacteria-Bacteroidetes (CFB), Gammaproteobacteria and Alphaproteobacteria. At the end of spring, a shift occurred toward a CFB-dominated community, most likely a response to the onset of a springtime phytoplankton bloom. The tail end of Prydz Bay clone library diversity revealed sequences related to Deltaproteobacteria, Verrucomicrobiales, Planctomycetes, Gemmatimonadetes and an unclassified bacterium (ANT4E12). Minicosm experiments showed that incubation time was the principal determinant of bacterial community composition and that UV-R treatment significantly changed the composition in only two of the four experiments. Thus, the successional maturity of the microbial community in our minicosm studies appears to be a greater determinant of bacterial community composition rather than the nonprofound and subtle effects of UV-R.

In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities

Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O2 m−2 h−1 (~11.7 mg C m−2 h−1) while from the sediment it was 6.08 mmol O2 m−2 h−1 (~70.8 mg C m−2 h−1). When the ice was present O2 export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)−1 h−1 while those from the benthos were up to 1.53 mg C (mg Chl-a)−1 h−1. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55–65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.

Characterizing polar atmospheres and their effect on Rayleigh‐scattering optical depth

A large set of radiosoundings was analyzed to study the dependence of Rayleigh‐scattering optical depth (ROD) on pressure and temperature features of the polar clear‐sky atmosphere. This set consists of 1320 radiosoundings, launched throughout the year at six Arctic sites, and of 940 radiosoundings launched at five Antarctic sites. The vertical profiles of pressure, temperature, and relative humidity given by these radiosoundings were corrected for lag errors and dry biases and then completed up to 120 km altitude, using COSPAR International Reference Atmosphere (CIRA) monthly vertical profiles of pressure and temperature, water vapor mixing ratio data derived from various satellite observations, and standard CO2 vertical profile relative to 2007, when the ground‐level concentration was 380 ppmv. Calculations of the volume Rayleigh‐scattering coefficient were made for all the radiosoundings to study its seasonal variations with height due to pressure and temperature changes occurring in the troposphere and stratosphere. It was found that the surface‐level pressure and temperature conditions can account to a large extent for these seasonal effects. Therefore, average spectral evaluations of ROD were made at 88 selected wavelengths from 0.20 to 4.0 μm for all the radiosoundings, subdivided into eight latitude/altitude site classes, representing 70°N, 75°N, 80°N, 70°S, 75°S, 80°S, and 90°S latitudes, for which the average ground values of air pressure pa and air temperature Ta were defined. The dependence of ROD on the daily ground‐level values of air pressure po and air temperature To measured at each site can be accounted for by using an algorithm in which the pressure dependence is given with good approximation by ratio (po/pa), and the temperature linear dependence is expressed by the difference (Ta − To) multiplied by a spectral slope coefficient k(λ) which varies by site classification. This algorithm was estimated to provide values of ROD with accuracy within ±0.5% at the six sea‐level Arctic sites, ±0.5% at the three Antarctic coastal sites, and ±0.7% at the two Antarctic Plateau sites (Dome C and South Pole). When used to analyze the Sun photometer measurements, the present evaluations of ROD are estimated to provide aerosol optical depth values at visible wavelengths with relative errors of 1%–2% at the Arctic sites, 1%–4% at the coastal Antarctic sites, and 3%–13% at the Antarctic Plateau sites, for background aerosol extinction conditions.

Seasonal and interannual variation of dissolved iodine speciation at a coastal Antarctic site

Dissolved iodine speciation in surface seawater at a coastal Antarctic site has been studied over a period spanning three austral summers. The sampling site is biologically productive, with a summertime algal bloom accompanying strong seasonal variations in physical and chemical parameters. The results suggest a seasonal cycle in which iodide concentrations increase and iodate concentrations decrease during the summer, though the magnitude of these changes appears to be subject to considerable interannual variability. Iodide concentrations were typically very low, with minimum values of 10 to 20 nM at the beginning and end of the ice-free summer periods and summertime maxima of about 35 nM in 2005/06, 150 nM in 2006/07 and 82 nM in 2007/08. More detailed observations of iodide and iodate concentrations made during summer 2005/06 demonstrated that the accumulation of iodide was strongly correlated with integrated biological primary productivity, with an implied I/C assimilation ratio of 1.6 × 10 −4.

Observations on the relationship between the Antarctic coastal diatoms Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen and sea ice concentrations during the late Quaternary

The available ecological and palaeoecological information for two sea ice-related marine diatoms (Bacillariophyceae), Thalassiosira antarctica Comber and Porosira glacialis (Grunow) Jørgensen, suggests that these two species have similar sea surface temperature (SST), sea surface salinity (SSS) and sea ice proximity preferences. From phytoplankton observations, both are described as summer or autumn bloom species, commonly found in low SST waters associated with sea ice, although rarely within the ice. Both species form resting spores (RS) as irradiance decreases, SST falls and SSS increases in response to freezing ice in autumn. Recent work analysing late Quaternary seasonally laminated diatom ooze from coastal Antarctic sites has revealed that sub-laminae dominated either by T. antarctica RS, or by P. glacialis RS, are nearly always deposited as the last sediment increment of the year, interpreted as representing autumn flux. In this study, we focus on sites from the East Antarctic margin and show that there is a spatial and temporal separation in whether T. antarctica RS or P. glacialis RS form the autumnal sub-laminae. For instance, in deglacial sediments from the Mertz Ninnis Trough (George V Coast) P. glacialis RS form the sub-laminae whereas in similar age sediments from Iceberg Alley (Mac.Robertson Shelf) T. antarctica RS dominate the autumn sub-lamina. In the Dumont d'Urville Trough (Adélie Land), mid-Holocene (Hypsithermal warm period) autumnal sub-laminae are dominated by T. antarctica RS whereas late Holocene (Neoglacial cool period) sub-laminae are dominated by P. glacialis RS. These observations from late Quaternary seasonally laminated sediments would appear to indicate that P. glacialis prefers slightly cooler ocean–climate conditions than T. antarctica. We test this relationship against two down-core Holocene quantitative diatom abundance records from Dumont d'Urville Trough and Svenner Channel (Princess Elizabeth Land) and compare the results with SST and sea ice concentration results of an Antarctic and Southern Ocean Holocene climate simulation that used a coupled atmosphere–sea ice–vegation model forced with orbital parameters and greenhouse gas concentrations. We find that abundance of P. glacialis RS is favoured by higher winter and spring sea ice concentrations and that a climatically-sensitive threshold exists between the abundance of P. glacialis RS and T. antarctica RS in the sediments. An increase to > 0.1 for the ratio of P. glacialis RS: T. antarctica RS indicates a change to increased winter sea ice concentration (to >80% concentration), cooler spring seasons with increased sea ice, slightly warmer autumn seasons with less sea ice and a change from ~ 7.5 months annual sea ice cover at a site to much greater than 7.5 months. In the East Antarctic sediment record, an increase in the ratio from <0.1 to above 0.1 occurs at the transition from the warmer Hypsithermal climate into the cooler Neoglacial climate (~ 4 cal kyr) indicating that the ratio between these two diatoms has the potential to be used as a semi-quantitative climate proxy.

Seasonality of sulfur species (dimethyl sulfide, sulfate, and methanesulfonate) in Antarctica: Inland versus coastal regions

To gain a better understanding of sulfate and methanesulfonate (MS−) signals recorded in central Antarctic ice cores in terms of past atmospheric changes, an atmospheric year‐round study of these aerosols was performed in 2006 at the Concordia station (75°S, 123°E) located on the high Antarctic plateau. In addition, a year‐round study of dimethyl sulfide (DMS), the gaseous precursor of sulfur aerosol, was conducted in 2007. The DMS mixing ratio remains below 1 pptv from October to January and exhibits a maximum of 10 pptv during the first half of winter (from April to July). Surprisingly, the well‐marked maximum of sulfur aerosol recorded in January at coastal Antarctic sites is observed at Concordia for sulfate but not for MS− which peaks before and after sulfate in November and March, respectively. This first study of DMS and of its by‐oxidation aerosol species conducted at inland Antarctica points out the complex coupling between transport and photochemistry of sulfur species over Antarctica. The findings highlight the complexity of the link between MS− ice core records extracted at high Antarctic plateau sites and DMS emissions from the Southern ocean.

Seasonal changes in phytoplankton growth and microzooplankton grazing at an Antarctic coastal site

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 50:157-167 (2008) - DOI: https://doi.org/10.3354/ame01149 Seasonal changes in phytoplankton growth and microzooplankton grazing at an Antarctic coastal site Imojen Pearce, Andrew T. Davidson*, Simon Wright, Rick van den Enden Australian Government Antarctic Division and Antarctic Climate and Ecosystems Cooperative Research Centre, Channel Highway, Kingston, 7050 Tasmania, Australia *Corresponding author. Email: andrew.davidson@aad.gov.au ABSTRACT: Despite being a major pathway for carbon flow in aquatic systems, little is known about annual changes in microzooplankton grazing in Antarctic waters and its top-down control of phytoplankton. We determined changes in the growth and mortality of phytoplankton in near-shore waters off East Antarctica between February and November 2004 using the grazing dilution technique. Results showed large seasonal variation in the microzooplankton grazing rate and top-down control of phytoplankton. In late summer (February to March), microzooplankton consumed around 34% of primary production and 33% of the phytoplankton standing stock d–1. As sea ice formed in early April, grazing mortality increased to 762% of primary production and 72% of the phytoplankton standing stock d–1, coinciding with a rapid decline in phytoplankton biomass, cell volume and chlorophyll a concentration. In winter (late April to September), phytoplankton abundance and productivity were insufficient to sustain extensive herbivory; only 5 of the 12 winter experiments yielded microzooplankton grazing rates that were significantly different from zero. The few significant experiments showed that microheterotrophs occasionally consumed ca. 54% of the phytoplankton standing stock and >100% primary production d–1. In spring (October to November), rates of microzooplankton grazing and phytoplankton growth were highly significant but negative. Our study showed that microzooplankton contributed substantially to the termination of the summer phytoplankton bloom. Thereafter, microzooplankton grazing, though occasionally substantial, was commonly low or insignificant. Furthermore, during the aphotic Antarctic winter, negative rates of phytoplankton growth commonly exceeded those of microzooplankton grazing, suggesting that herbivory was not the principal cause of phytoplankton mortality. KEY WORDS:Antarctic · Microzooplankton · Grazing · Phytoplankton growth Full text in pdf format PreviousNextCite this article as: Pearce I, Davidson AT, Wright S, van den Enden R (2008) Seasonal changes in phytoplankton growth and microzooplankton grazing at an Antarctic coastal site. Aquat Microb Ecol 50:157-167. https://doi.org/10.3354/ame01149 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 50, No. 2. Online publication date: January 31, 2008 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2008 Inter-Research.

Seasonal changes in the concentration and metabolic activity of bacteria and viruses at an Antarctic coastal site

Bacteria play a key role in the world's oceans, supporting nutrient remineralisation and mediating carbon transfer. Little is known about annual changes in bacterial concentration, produc- tion and metabolism during the extreme seasonal changes in biological productivity in Antarctic waters. We measured rates of bacterial production, concentrations of viruses and bacteria and envi- ronmental parameters between February 2004 and January 2005 at an Antarctic coastal site. Concen- trations of total bacteria and viruses were obtained using 4',6-diamidino-2-phenylindole (DAPI) and SYBR Green I (Molecular Probes), respectively. Populations of bacteria in different metabolic states were estimated using vital stains. Concentrations of bacteria with intact or compromised plasma membranes were estimated using BacLight (Molecular Probes) and active cells estimated using 6- carboxyfluorescein diacetate (6CFDA). Our study showed 6CFDA and BacLight gave rapid and eco- logically valuable insights into bacterial physiology, production and growth in natural Antarctic com- munities that were poorly represented by changes in total cell concentrations. Concentrations of total, active and intact bacteria declined rapidly at the end of summer probably owing to viral infection and microheterotrophic grazing. The decline continued over winter, likely owing to substrate limitation, and concentrations only increased after the phytoplankton bloom in spring and summer. Bacterial abundance was positively correlated with particulate organic carbon (POC) and nitrogen (PON), but not dissolved organic carbon (DOC), reflecting the refractory nature of the DOC pool. Only active and intact bacteria were significantly correlated with concentrations of chl a and rates of bacterial production. Furthermore, the obtained rates of ( 3 H)thymidine uptake suggest that bacterial growth rates can be sustained by the populations identified as intact or by active cells alone.

Mesozooplankton assemblages in two bays in the Beagle Channel (Argentina) during January, 2001

This paper describes the composition and abundance of mesozooplankton of Bahia Ushuaia and Bahia Golondrina. These small bays are located in the northern Beagle Channel. Sampling was carried out from January 20 to 23, 2001 and samples were collected from the upper layer at nine stations. This study is the first research on mesozooplankton in this part of the Beagle Channel. Due to their dominance in the mesozooplankton community, we compared our Copepoda data with those reported by other authors from Antarctic coastal environments. By applying cluster analysis, we found two station groups in both bays: one in slightly polluted zones and the other in undisturbed external zones. Four assemblages in Bahia Ushuaia and two in Bahia Golondrina were determined by using non-metric multidimensional scaling (MDS) and cluster analysis. Mesozooplanktonic assemblages showed a certain resemblance in zones with and without anthropogenic influence. Most of the copepod species in our samples are typical of the sub-Antarctic region. Oithona similis (=O. helgolandica sensu Ramirez, 1966), Oncaea curvata , and Ctenocalanus citer show either similar or higher abundances at Antarctic coastal sites, including the upper layer in oceanic areas, in comparison with sub-Antarctic coastal localities. This suggests that, in agreement with other findings, the Polar Front is probably not a major geographic boundary for the distribution of these species.

Firn-air δ15N in modern polar sites and glacial–interglacial ice: a model-data mismatch during glacial periods in Antarctica?

The phase lag between atmospheric composition (air bubbles) and temperature (water isotopes) can be quantified from ice cores provided that the age difference between entrapped air and the surrounding air can be correctly estimated. This difference depends on the lock-in depth (LID), when air no longer mixes with the atmosphere. The LID can be estimated from firnification models or from the air isotopic composition ( δ 15N and δ 40Ar). Both methods give consistent results for Greenland and one coastal site in Antarctica (Byrd). New firn measurements in Greenland (NorthGRIP) and Antarctica (Berkner Island, BAS depot, Dome C) confirm that firnification models correctly reproduce the present LID over a large range of surface conditions. However, a systematic mismatch is observed for the Last Glacial Maximum (LGM) in East Antarctic sites (Vostok, Dome C, Dome F) questioning the model's validity. Here we use new δ 15N measurements from two coastal Antarctic sites (Kohnen Station and Law Dome) providing depth estimates again distinct from firnification model calculations. We show that this discrepancy can be resolved by revising the estimate of past accumulation rates. δ 15N measurements can therefore help to constrain past accumulation rate and improve ice core dating.

Investigation of evaporation and biodegradation of fuel spills in Antarctica: II—Extent of natural attenuation at Casey Station

In many temperate regions, fuel and oil spills are sometimes managed simply by allowing natural degradation to occur, while monitoring soils and groundwater to ensure that there is no off-site migration or on-site impact. To critically assess whether this approach is suitable for coastal Antarctic sites, we investigated the extent of evaporation and biodegradation at three old fuel spills at Casey Station. Where the contaminants migrated across frozen ground, probably beneath snow, approximately half the fuel evaporated in the first few months prior to infiltration at the beginning of summer. Once in the ground, however, evaporation rates were negligible. In contrast, minor spills from fuel drums buried in an abandoned waste disposal site did not evaporate to the same extent. Biodegradation within all three spill sites is generally very minor. We conclude that natural attenuation is not a suitable management strategy for fuel-contaminated soils in Antarctic coastal regions.

A one dimensional model study of the mechanism of halogen liberation and vertical transport in the polar troposphere

Abstract. Sudden depletions of tropospheric ozone during spring were reported from the Arctic and also from Antarctic coastal sites. Field studies showed that those depletion events are caused by reactive halogen species, especially bromine compounds. However the source and seasonal variation of reactive halogen species is still not completely understood. There are several indications that the halogen mobilisation from the sea ice surface of the polar oceans may be the most important source for the necessary halogens. Here we present a one dimensional model study aimed at determining the primary source of reactive halogens. The model includes gas phase and heterogeneous bromine and chlorine chemistry as well as vertical transport between the surface and the top of the boundary layer. The autocatalytic Br release by photochemical processes (bromine explosion) and subsequent rapid bromine catalysed ozone depletion is well reproduced in the model and the major source of reactive bromine appears to be the sea ice surface. The sea salt aerosol alone is not sufficient to yield the high levels of reactive bromine in the gas phase necessary for fast ozone depletion. However, the aerosol efficiently "recycles" less reactive bromine species (e.g. HBr) and feeds them back into the ozone destruction cycle. Isolation of the boundary layer air from the free troposphere by a strong temperature inversion was found to be critical for boundary layer ozone depletion to happen. The combination of strong surface inversions and presence of sunlight occurs only during polar spring.

Year‐round records of gas and particulate formic and acetic acids in the boundary layer at Dumont d'Urville, coastal Antarctica

Multiple year‐round levels of acetate and formate in gas and aerosol phases were investigated at Dumont d'Urville (DDU, a coastal Antarctic site) by using mist chamber and aerosol filter sampling. Formate and acetate aerosol levels range from &lt;0.5 ppt in winter to 3 ppt in summer. With corresponding gas phase levels of more than a hundred of pptv, formic and acetic acids are mainly (99%) present in the gas phase, representing the 2 major acidic gases before inorganic species (HCl, HNO3 and SO2) there. Mixing ratios of formic acid are minimal from May to August (70 pptv) and increase regularly toward November–February months when levels reach ∼200 pptv. Mixing ratios of acetic acid exhibit a more well‐marked seasonal cycle with values remaining close to 70 pptv from April to October and strongly increase during November–February months (mean value of 400 pptv). These seasonal changes suggest that the 2 carboxylic acids mainly originate from biogenic emissions of the Antarctic ocean whose variations follow the annual cycle of sea ice extent and solar radiation via photochemical production of alkenes from dissolved organic carbon released by phytoplankton. In summer, acetic acid levels show daily variations with maxima at noon and minima at night whereas formic acid levels peaks later in the afternoon. These dial variations in summer suggest that carboxylic acids are rapidly produced during the day and lost at night due to dry deposition on wet surface. It is suggested that the reactions of peroxy acetyl radical produced from propene with HO2 and CH3O2 in these poor NOx environments represent in summer the dominant chemical mechanisms producing acetic acid whereas ozone‐alkene reactions remain of minor importance at that season. Neither ozone‐alkene reactions nor aqueous phase HCHO oxidation can explain the summer levels of formic acid. In winter the long range transport of alkenes emitted at more temperate oceanic regions and reactions with ozone could account for the observed level of formic acid and possibly of acetic acid.