Aircraft and satellite derived arctic BrO profiles of the tropospheric column

We derive tropospheric column BrO during the ARCTAS and ARCPAC field campaigns in spring 2008 using retrievals of total column BrO from the satellite UV nadir sensors OMI and GOME-2 using a radiative transfer model and stratospheric column BrO from a photochemical simulation. We conduct a comprehensive comparison of satellite-derived tropospheric BrO column to aircraft in-situ observations of BrO and related species. The aircraft profiles reveal that tropospheric BrO, when present during April 2008, was distributed over a broad range of altitudes rather than being confined to the planetary boundary layer (PBL). Perturbations to the total column resulting from tropospheric BrO are the same magnitude as perturbations due to longitudinal variations in the stratospheric component, so proper accounting of the stratospheric signal is essential for accurate determination of satellite-derived tropospheric BrO. We find reasonably good agreement between satellite-derived tropospheric BrO and columns found using aircraft in-situ BrO profiles, particularly when satellite radiances were obtained over bright surfaces (albedo >0.7), for solar zenith angle <80° and clear sky conditions. The rapid activation of BrO due to surface processes (the bromine explosion) is apparent in both the OMI and GOME-2 based tropospheric columns. The wide orbital swath of OMI allows examination of the evolution of tropospheric BrO on about hourly time intervals near the pole. Low surface pressure, strong wind, and high PBL height are associated with an observed BrO activation event, supporting the notion of bromine activation by high winds over snow.

(Table 3) Growth rates of the juvenile polychaete Scolelepis squamata obtained from ice cores under varying conditions

In spring, Arctic coastal fast ice is inhabited by high densities of sea ice algae and, among other fauna, juveniles of benthic polychaetes. This paper investigates the hypothesis that growth rates of juveniles of the common sympagic polychaete, Scolelepis squamata (Polychaeta: Spionidae), are significantly faster at sea ice algal bloom concentrations compared to concurrent phytoplankton concentrations. Juvenile S. squamata from fast ice off Barrow, Alaska, were fed with different algal concentrations at 0 and 5 °C, simulating ambient high sea ice algal concentrations, concurrent low phytoplankton concentrations, and an intermediate concentration. Growth rates, calculated using a simple linear regression equation, were significantly higher (up to 115 times) at the highest algal concentration compared to the lowest. At the highest algal concentration, juveniles grew faster at 5 °C compared to those feeding at 0 °C with a Q10 of 2.0. We conclude that highly concentrated sea ice algae can sustain faster growth rates of polychaete juveniles compared to the less dense spring phytoplankton concentrations. The earlier melt of Arctic sea ice predicted with climate change might cause a mismatch between occurrence of polychaete juveniles and food availability in the near future. Our data indicate that this reduction in food availability might counteract any faster growth of a pelagic juvenile stage based on forecasted increased water temperatures.

(Table 1) Climate characteristics of the four North American Tundra Experiment (ITEX) sites

Climate warming is expected to differentially affect CO2 exchange of the diverse ecosystems in the Arctic. Quantifying responses of CO2 exchange to warming in these ecosystems will require coordinated experimentation using standard temperature manipulations and measurements. Here, we used the International Tundra Experiment (ITEX) standard warming treatment to determine CO2 flux responses to growing-season warming for ecosystems spanning natural temperature and moisture ranges across the Arctic biome. We used the four North American Arctic ITEX sites (Toolik Lake, Atqasuk, and Barrow [USA] and Alexandra Fiord [Canada]) that span 10° of latitude. At each site, we investigated the CO2 responses to warming in both dry and wet or moist ecosystems. Net ecosystem CO2 exchange (NEE), ecosystem respiration (ER), and gross ecosystem photosynthesis (GEP) were assessed using chamber techniques conducted over 24-h periods sampled regularly throughout the summers of two years at all sites. At Toolik Lake, warming increased net CO2 losses in both moist and dry ecosystems. In contrast, at Atqasuk and Barrow, warming increased net CO2 uptake in wet ecosystems but increased losses from dry ecosystems. At Alexandra Fiord, warming improved net carbon uptake in the moist ecosystem in both years, but in the wet and dry ecosystems uptake increased in one year and decreased the other. Warming generally increased ER, with the largest increases in dry ecosystems. In wet ecosystems, high soil moisture limited increases in respiration relative to increases in photosynthesis. Warming generally increased GEP, with the notable exception of the Toolik Lake moist ecosystem, where warming unexpectedly decreased GEP >25%. Overall, the respiration response determined the effect of warming on ecosystem CO2 balance. Our results provide the first multiple-site comparison of arctic tundra CO2 flux responses to standard warming treatments across a large climate gradient. These results indicate that (1) dry tundra may be initially the most responsive ecosystems to climate warming by virtue of strong increases in ER, (2) moist and wet tundra responses are dampened by higher water tables and soil water contents, and (3) both GEP and ER are responsive to climate warming, but the magnitudes and directions are ecosystem-dependent.

Radiocarbon dates of peatland initiation across the northern high latitudes

A compilation of basal dates of peatland initiation across the northern high latitudes, associated metadata including location, age, raw and calibrated radiocarbon ages, and associated references. Includes previously published datasets from sources below as well as 365 new data points.