The Palmer LTER: A Long-Term Ecological Research Program at Palmer Station, Antarctica

THE ANTARCTIC marine ecosystem-the assemblage of plants, animals, ocean, sea ice, and island components south of the Antarctic Convergence is among the largest readily defined ecosystems on Earth (36 X 106 km2 ) (Hedgpeth, 1977; Petit et al., 1991). This ecosystem is composed of an interconnected system of functionally distinct hydrographic and biogeochemical subdivisions (Treguer and Jacques, 1992) and includes open ocean, frontal regions, shelf-slope waters, sea ice, and marginal ice zones. Oceanic, atmospheric, and biogeochemical processes within this system are thought to be globally significant, have been infrequently studied, and are poorly understood relative to more accessible marine ecosystems (Harris and Stonehouse, 1991; Johannessen et al., 1994). The Palmer Long-Term Ecological Research (Palmer LTER) area west of the Antarctic Peninsula (Fig. la) is a complex combination of a coastal/continental shelf zone and a seasonal sea ice zone, because this area is swept by the yearly advance and retreat of sea ice. The Palmer LTER program is a multidisciplinary program established to study this polar marine ecosystem

BMC Nephrol

Background Early kidney transplantation (KT) is the best option for patients with end-stage kidney disease, but little is known about dialysis access strategy in this context. We studied practice patterns of dialysis access and how they relate with outcomes in adults wait-listed early for KT according to the intended donor source. Methods This study from the REIN registry (2002–2014) included 9331 incident dialysis patients (age 18–69) wait-listed for KT before or by 6 months after starting dialysis: 8342 candidates for deceased-donor KT and 989 for living-donor KT. Subdistribution hazard ratios (SHR) of KT and death associated with hemodialysis by catheter or peritoneal dialysis compared with arteriovenous (AV) access were estimated with Fine and Gray models. Results Living-donor candidates used pretransplant peritoneal dialysis at rates similar to deceased-donor KT candidates, but had significantly more frequent catheter than AV access for hemodialysis (adjusted OR 1.25; 95%CI 1.09–1.43). Over a median follow-up of 43 (IQR: 23–67) months, 6063 patients received transplants and 305 died before KT. Median duration of pretransplant dialysis was 15 (7–27) months for deceased-donor recipients and 9 (5–15) for living-donor recipients. Catheter use in deceased-donor candidates was associated with a lower SHR for KT (0.88, 95%CI 0.82–0.94) and a higher SHR for death (1.53, 95%CI 1.14–2.04). Only five deaths occurred in living-donor candidates, three of them with catheter use. Conclusions Pretransplant dialysis duration may be quite long even when planned with a living donor. Advantages from protecting these patients from AV fistula creation must be carefully evaluated against catheter-related risks

High-Resolution Time-Series Data for 1991/1992 Primary Production and Related Parameters at a Palmer LTER Coastal Site: Implications for Modeling Carbon Fixation in the Southern Ocean

Our goal was to provide a high-resolution temporal data base for modeling primary production in shelf waters adjacent to Palmer Station, Antarctica. Here, the resulting 1991/1992 data base is used to: (1) determine in situ productivity over a range of seasonal to subseasonal time scales; (2) identify time scales of significant variability in marine productivity during the peak growing season; (3) identify environmental, experimental and analytical factors that can significantly impact the accuracy of daily, weekly and seasonal productivity estimates; and (4) integrate our findings with previous studies of Antarctic coastal primary pro- duction. Data were gathered every 2–3 days during a 3-month period in the austral spring/summer of 1991/1992. Photosynthesis-irradiance (P-I) relationships were determined throughout the euphotic zone and P-I parameters, combined with knowledge of the in-water light field, were used to derive instantaneous rates of in situ primary production. Additionally, weekly samples were collected from surface and chlorophyll a maxima for characterization of the patterns of diel periodicity in P-I parameters. Seven diel patterns were discerned over the season and used to time-correct instantaneous measurements and derive noontime, daily, monthly and seasonally integrated estimates of production. During the season, a large bloom was responsible for some of the highest daily produc- tivity rates reported for the Southern Ocean (0.8 g C m-3 d-1, 6.3 g C m-2 d-1). Significant variation in daily integrated rates occurred generally on time scales less than a week. Peak timing and magnitude of daytime periodicities in photosynthesis varied widely over the season, closely coupled to changes in phytoplankton community composition. Instantaneous measurements of primary production, if uncorrected or improperly corrected for daytime periodicities in carbon fixation, were unreliable predictors of production on longer time scales even if the water column was sampled every few days. High frequency sampling and consideration of diel periodicity may be requirements when attempting to discern differences between short time-scale variability and long-term trends in Antarctic primary production

Long-term Monitoring and Analyses of Physical Factors Regulating Variability in Coastal Antarctic Phytoplankton Biomass, in situ Productivity and Taxonomic Composition Over Subseasonal, Seasonal and Interannual Time Scales

A 3 yr high-resolution temporal data base related to phytoplankton dynamics was collected during the austral spring/summer periods of 1991 to 1994 in shelf waters adjacent to Palmer Station, Antarctica. Here, the data base is used (1) to quantify the variability in phytoplankton biomass, in situ productivity and taxonomic composition over subseasonal, seasonal and interannual time scales; (2) to elucidate environmental mechanisms controlling these temporal patterns; and (3) to ascertain which phytoplankton markers are most suitable for detecting longer-term (i.e. decadal) trends in phytoplankton dynamics in coastal waters of the Southern Ocean. The Long-Term Ecological Research (LTER) coastal study sites showed high interannual variability in peak phytoplankton biomass (75 to 494 mg chl a m-2) and integrated primary production (1.08 to 6.58 g C m-2 d-1). Seasonal and annual patterns in biomass and productivity were shown to be driven by shorter-time-scale physical forcing by local wind stress. Low daily wind speeds (s-1) were associated with water-column stabilization. However, extended periods (\u3e1 wk) of low wind stress were required for increased phytoplankton growth and biomass accumulation. Temperature data supports the view that water masses can be replaced on time scales of a less than a day to a few days in these coastal waters. Such disruptions are associated with abrupt changes in local primary production and may lead to sudden shifts in local phytoplankton community structure. Despite the high seasonal and interannual variability in biomass and associated in situ productivity in this coastal environment, the replacement sequence of one dominant phytoplankton group by another was very similar on subseasonal time scales for all 3 years. We suggest that changes in phytoplankton successional patterns may be a more sensitive marker for detecting long-term trends in Southern Ocean ecosystems than either biomass or productivity indices, where short-term variability of the latter is as great or greater than interannual variations documented to date