In “Frontiers in Polar Biology in the Genomic Era,” the National Academy of Science’s Polar Research Board reported that key questions on polar ecosystem biology could be addressed by genomics and other new technologies. Two of these questions are: 1) what types of microorganisms are present in polar aquatic ecosystems and what roles do they play in ecosystem processes? and 2) what is the relationship between the composition and biogeochemical function of polar microbial communities? Creative use of new molecular approaches, such as we propose in this research study, is expected to help make progress on these fronts. In this project, we aim to emphasize understanding the adaptation of organisms to the unique aspects of the Arctic environment and to better understand ocean science projects that advance knowledge of the processes of the Arctic Ocean and adjacent seas and their interactions with their boundaries by using a hypothesis-driven fundamental research approach at a time in history when improved mechanistic understanding is critical to projections of future change.
The objective of this project is to investigate the microbial controls on the productivity of a coastal Arctic ecosystem by focusing on the competition between autotrophs and heterotrophs for nitrogen. In the winter and summer waters near Barrow, Alaska, supplemented with complementary international research opportunities, we propose to measurein situ concentrations of key microbial and biogeochemical constituents, relevant uptake activities, and expression of key nitrogen cycling genes to address the following hypotheses:
H1: The balance of autotrophy and heterotrophy in the Arctic is regulated both temporally and spatially by nitrate (NO3) and light.
1.1: Phytoplankton outcompete heterotrophic bacteria for nitrate during the well-lit spring and summer conditions.
1.2: Heterotrophic bacterial uptake of nitrate will be greater during the dark winter and under sea ice than in open water or well-lit summer conditions when bacteria are replete with phytoplankton-derived dissolved organic nitrogen.
1.3: Nitrate combined with terrestrial dissolved organic carbon derived from riverine and groundwater flow, may provide the means for bacterial growth and respiration during the dark winter.
H2: Microbial community structure will vary according to the seasonal light cycle and the sources of available nitrogen. The observed lag in bacterial response to phytoplankton growth is due to a community shift.
2.1: Bacterial community composition will vary significantly between winter and summer.
2.2: The composition and dynamics of bacterial communities will correspond to concentrations and sources of nitrogen.
2.3: The expression of key nitrogen-cycling genes, nitrogen-uptake and regeneration, and dissolved organic nitrogen uptake kinetics will vary with season and community composition.
Although nitrate assimilation by bacteria is observed in other marine environments, its impact on present and future Arctic productivity is potentially unique for several reasons. First, the high-latitudes experience long periods of darkness that shut down photosynthesis relative to respiration. Thus, the microbial heterotrophs have a significant opportunity to impact nitrate levels without competition from autotrophs during a large part of the year. Second, unlike the Antarctic, the Arctic receives more than twice as much riverine input than any other ocean (~10% of the global discharge to ~5% of the global area and ~1.5% of global ocean volume), which delivers large amounts of terrestrial dissolved organic matter derived from the tundra that is rich in carbon but relatively low in nitrogen. Thus, unlike the Antarctic, the coastal microbes in the Arctic are replete with dissolved organic carbon, but require other sources of nitrogen for their metabolic needs. Third, the Arctic Ocean is dominated by continental shelves (25% of the world’s shelf area in 5% of the world’s oceans). Tight benthic-pelagic coupling is common, denitrification rates are high, and nitrogen fixation appears to be insignificant. Thus, relative to other coastal oceans, nitrogen is particularly limiting during the summer. Finally, climate change in the Arctic is expected to increase the flow of rivers and the amount of terrestrial dissolved organic carbon contributed to the Arctic Ocean, but the seasonal dark-light cycle will not change. Future projections of increased Arctic productivity depend on a supply of nitrogen to the autotrophs. The coastal Arctic is where the battle for nitrogen will likely be most intense in the future.
NSF Report: Solving the Puzzle: Researching the Impacts of Climate Change Around the World
A NSF report for the non-specialist summarizing the current state of knowledge about climate change. The succinct format is enhanced with slideshows and videos.
Yager presentation to Schoolyard Saturday
A powerpoint presentation of the talk given by Dr. Yager to the BASC Schoolyard Saturday on February 27, 2010. The background, hypotheses, and objectives of the Arctic Nitro project are discussed.
Pumping Carbon - a kinesthetic learning activity
Lollie Gary and Tish Yager put this activity together for a presentation to teachers about ways to introduce middle-school students to the idea of the marine carbon cycle. Thanks to PolarTrec for support!