34 research outputs found
Chlorophyll-a in Antarctic landfast sea ice: a first synthesis of historical ice-core data
Historical sea ice core chlorophyll-a (Chla) data are used to describe the seasonal, regional, and vertical distribution of ice algal biomass in Antarctic landfast sea ice. The analyses are based on the Antarctic Fast Ice Algae Chlorophyll-a data set, a compilation of currently available sea ice Chla data from landfast sea ice cores collected at circum-Antarctic nearshore locations between 1970 and 2015. Ice cores were typically sampled from thermodynamically grown first-year ice and have thin snow depths (mean\ua0=\ua00.052\ua0\ub1\ua00.097\ua0m). The data set comprises 888 ice cores, including 404 full vertical profile cores. Integrated ice algal Chla biomass (range: <0.1\u2013219.9\ua0mg/m2, median\ua0=\ua04.4\ua0mg/m2, interquartile range\ua0=\ua09.9\ua0mg/m2) peaks in late spring and shows elevated levels in autumn. The seasonal Chla development is consistent with the current understanding of physical drivers of ice algal biomass, including the seasonal cycle of irradiance and surface temperatures driving landfast sea ice growth and melt. Landfast ice regions with reported platelet ice formation show maximum ice algal biomass. Ice algal communities in the lowermost third of the ice cores dominate integrated Chla concentrations during most of the year, but internal and surface communities are important, particularly in winter. Through comparison of biomass estimates based on different sea ice sampling strategies, that is, analysis of full cores versus bottom-ice section sampling, we identify biases in common sampling approaches and provide recommendations for future survey programs: for example, the need to sample fast ice over its entire thickness and to measure auxiliary physicochemical parameters
Characterizing Spatial Variability of Ice Algal Chlorophyll a and Net Primary Production between Sea Ice Habitats Using Horizontal Profiling Platforms
Assessing the role of sea ice algal biomass and primary production for polar ecosystems
remains challenging due to the strong spatio-temporal variability of sea ice algae.
Therefore, the spatial representativeness of sea ice algal biomass and primary production
sampling remains a key issue in large-scale models and climate change predictions
of polar ecosystems. To address this issue, we presented two novel approaches to
up-scale ice algal chl a biomass and net primary production (NPP) estimates based
on profiles covering distances of 100 to 1,000 s of meters. This was accomplished
by combining ice core-based methods with horizontal under-ice spectral radiation
profiling conducted in the central Arctic Ocean during summer 2012. We conducted
a multi-scale comparison of ice-core based ice algal chl a biomass with two profiling
platforms: a remotely operated vehicle and surface and under ice trawl (SUIT). NPP
estimates were compared between ice cores and remotely operated vehicle surveys.
Our results showed that ice core-based estimates of ice algal chl a biomass and NPP
do not representatively capture the spatial variability compared to the remotely operated
vehicle-based estimates, implying considerable uncertainties for pan-Arctic estimates
based on ice core observations alone. Grouping sea ice cores based on region or ice
type improved the representativeness. With only a small sample size, however, a high
risk of obtaining non-representative estimates remains. Sea ice algal chl a biomass
estimates based on the dominant ice class alone showed a better agreement between
ice core and remotely operated vehicle estimates. Grouping ice core measurements
yielded no improvement in NPP estimates, highlighting the importance of accounting
for the spatial variability of both the chl a biomass and bottom-ice light in order to
get representative estimates. Profile-based measurements of ice algae chl a biomass
identified sea ice ridges as an underappreciated component of the Arctic ecosystem because chl a biomass was significantly greater in this unique habitat. Sea ice ridges
are not easily captured with ice coring methods and thus require more attention in future
studies. Based on our results, we provide recommendations for designing an efficient
and effective sea ice algal sampling program for the summer season
Multiple Trophic Markers Trace Dietary Carbon Sources in Barents Sea Zooplankton During Late Summer
We investigated diets of 24 Barents Sea zooplankton taxa to understand pelagic food-web processes during late summer, including the importance of sea ice algae-produced carbon. This was achieved by combining insights derived from multiple and complementary trophic marker approaches to construct individual aspects of feeding. Specifically, we determined proportions of algal-produced fatty acids (FAs) to reflect the reliance on diatom- versus dinoflagellate-derived carbon, highly branched isoprenoid (HBI) lipids that distinguish between ice-associated and pelagic carbon sources, and sterols to indicate the degree of carnivory. Copepods had the strongest diatom signal based on FAs, while a lack of sea ice algae-associated HBIs (IP25, IPSO25) suggested that they fed on pelagic rather than ice-associated diatoms. The amphipod Themisto libellula and the ctenophores Beroë cucumis and Mertensia ovum had a higher contribution of dinoflagellate-produced FAs. There was a high degree of carnivory in this food web, as indicated by the FA carnivory index 18:1(n−9)/18:1(n−7) (mean value &lt; 1 only in the pteropod Clione limacina), the presence of copepod-associated FAs in most of the taxa, and the absence of algal-produced HBIs in small copepod taxa, such as Oithona similis and Pseudocalanus spp. The coherence between concentrations of HBIs and phytosterols within individuals suggested that phytosterols provide a good additional indication for algal ingestion. Sea ice algae-associated HBIs were detected in six zooplankton species (occurring in krill, amphipods, pteropods, and appendicularians), indicating an overall low to moderate contribution of ice-associated carbon from late-summer sea ice to pelagic consumption. The unexpected occurrence of ice-derived HBIs in pteropods and appendicularians, however, suggests an importance of sedimenting ice-derived material at least for filter feeders within the water column at this time of year.</jats:p