Geochemical Rate/RNA Integration Study (GRIST): A Pilot Field Experiment for Inter-Calibration of Biogeochemistry and Nucleic Acid Measurements Final Report

The Geochemical Rate/RNA Integration Study (GRIST) project sought to correlate biogeochemical flux rates with measurements of gene expression and mRNA abundance to demonstrate the application of molecular approaches to estimate the presence and magnitude of a suite of biogeochemical processes. The study was headed by Lee Kerkhoff of Rutgers University. In this component of the GRIST study, we characterized ambient nutrient concentrations and measured uptake rates for dissolved inorganic nitrogen (DIN, ammonium, nitrate and nitrite) and dissolved organic nitrogen (urea and dissolved free amino acids) during two diel studies at the Long-Term Ecosystem Observatory (LEO-15) on the New Jersey continental shelf

Symbiotic unicellular cyanobacteria fix nitrogen in the Arctic Ocean.

Biological dinitrogen (N2) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N2-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N2 uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N2 in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N2 fixation is not constrained to subtropical waters, challenging paradigms and models of global N2 fixation. The Arctic is particularly sensitive to climate change, and N2 fixation may increase in Arctic waters under future climate scenarios

A comparative study of iron and temperature interactive effects on diatoms and Phaeocystis antarctica from the Ross Sea, Antarctica

In the future, temperature and iron availability are predicted to change in the coastal polynyas of Antarctica, which are the most biologically productive regions of the Southern Ocean. We examined the individual and combined effects of iron addition (+500 nM) and temperature increase (4°C) on Phaeocystis antarctica and several dominant diatom species isolated from the McMurdo Sound sector of the Ross Sea. Iron addition increased growth, carbon fixation, iron uptake rates, cellular carbon quota, and cell size of almost all tested species, while temperature increase only affected certain species. Concurrent increases in temperature and iron synergistically stimulated the growth rates of some species, particularly Pseudo-nitzschia subcurvata. The diversified responses of these phytoplankton to iron and temperature may help explain the current spatial and temporal distributions of diatoms and prymnesiophytes in the Ross Sea. In the future, potential temperature and iron increases may promote the growth of the diatoms Chaetoceros sp., Fragilariopsis cylindrus, and especially P. subcurvata. In contrast, growth rates of P. antarctica did not increase at higher temperatures, suggesting that a shift in community composition toward diatoms may occur under warmer conditions in this biologically and biogeochemically important Southern Ocean polynya region

Nitrogen fixation rates from samples collected in the Chukchi Sea, Arctic Ocean near Barrow, Alaska in August of 2011 (ArcticNITRO project)

Dataset: Arctic Nitrogen Fixation RatesThis dataset provides rates of nitrogen fixation for the coastal Chukchi Sea near Barrow, Alaska. Nitrogen fixation supplies ‘new’ nitrogen to the global ocean and supports primary production and impacts global biogeochemical cycles. Historically, nitrogen fixation in marine waters was considered a predominantly warm water process but this and other recent studies have shown that nitrogen fixation is occurring at low rates in polar waters. This dataset reports rates of 3.5 – 17.2 nmol N L-1 d-1 in the ice-free coastal Alaskan Arctic. Additional investigations of high-latitude marine diazotrophic physiology are required to refine these N2 fixation estimates. For a complete list of measurements, refer to the supplemental document 'Field_names.pdf', and a full dataset description is included in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: http://www.bco-dmo.org/dataset/701789NSF Arctic Sciences (NSF ARC) PLR-090983

Nitrogen fixation and release of fixed nitrogen by Trichodesmium spp. in the Gulf of Mexico

During a 3‐yr study in the Gulf of Mexico, we measured dinitrogen (N2) fixation and nitrogen (N) release by Trichodesmium and compared these rates with water column N demand and the estimated N necessary to support blooms of Karenia brevis, a toxic dinoflagellate that severely affects the West Florida shelf. Net and gross N2 fixation rates were compared in simultaneous incubations using δ15N2 uptake and acetylene reduction, respectively. The difference between net and gross N2 fixation is assumed to be an approximation of the rate of N release. Results demonstrate that Trichodesmium in the Gulf of Mexico are fixing N2 at high rates and that an average of 52% of this recently fixed N2 is rapidly released. Calculations suggest that observed densities of Trichodesmium can provide enough N to support moderately sized K. brevis blooms. Based on other studies where δ15N2 and acetylene reduction were compared directly, it appears that N release from Trichodesmium is common but varies in magnitude among environments. In addition, carbon (C) and N‐based doubling times for Trichodesmium vary among studies and environments. Comparing gross N2 fixation and C fixation directly, C‐based doubling times exceeded N‐based doubling times, which suggests an imbalance in elemental turnover or a failure to fully quantify Trichodesmium N use

Marine plankton food webs and climate change

VIMS climate change white papers: Marine plankton food webs and climate chang

Microbial Community Response to Terrestrially Derived Dissolved Organic Matter in the Coastal Arctic

Warming at nearly twice the global rate, higher than average air temperatures are the new \u27normal\u27 for Arctic ecosystems. This rise in temperature has triggered hydrological and geochemical changes that increasingly release carbon-rich water into the coastal ocean via increased riverine discharge, coastal erosion, and the thawing of the semipermanent permafrost ubiquitous in the region. To determine the biogeochemical impacts of terrestrially derived dissolved organic matter (tDOM) on marine ecosystems we compared the nutrient stocks and bacterial communities present under ice-covered and ice-free conditions, assessed the lability of Arctic tDOM to coastal microbial communities from the Chukchi Sea, and identified bacterial taxa that respond to rapid increases in tDOM. Once thought to be predominantly refractory, we found that similar to 7% of dissolved organic carbon and similar to 38% of dissolved organic nitrogen from tDOM was bioavailable to receiving marine microbial communities on short 4 - 6 day time scales. The addition of tDOM shifted bacterial community structure toward more copiotrophic taxa and away from more oligotrophic taxa. Although no single order was found to respond universally (positively or negatively) to the tDOM addition, this study identified 20 indicator species as possible sentinels for increased tDOM. These data suggest the true ecological impact of tDOM will be widespread across many bacterial taxa and that shifts in coastal microbial community composition should be anticipated

Longitudinal variability of size-fractionated N-2 fixation and DON release rates along 24.5 degrees N in the subtropical North Atlantic

Dinitrogen (N-2) fixation and dissolved organic nitrogen (DON) release rates were measured on fractionated samples (\u3e10 mu m and m) along 24.5 degrees N in the subtropical North Atlantic. Net N-2 fixation rates (N-2 assimilation into biomass) ranged from 0.01 to 0.4 nmol N L-1 h(-1), and DON release rates ranged from 0.001 to 0.09 nmol N L-1 h(-1). DON release represented approximate to 14% and approximate to 23% of \u3e10 mu m and (assimilation into biomass plus DON release), respectively. This implies that by overlooking DON release, N-2 fixation rates are underestimated. Net N-2 fixation rates were higher in the east and decreased significantly toward the west (r(s)=-0.487, p=0.002, and r(s)=-0.496, p=0.001, for the \u3e10 mu m and fractions, respectively). The sum of both fractions correlated with aerosol optical depth at 550 nm (AOD 550 nm) (r(s)=0.382, p=0.017) and phosphate (PO43-) concentrations (r(s)=0.453, p=0.018), suggesting an enhancement of diazotrophy as a response to aerosol inputs and phosphorus availability. In contrast, DON release was constant among size fractions and did not correlate with any of these variables. We also compared N-2 fixation rates obtained using the N-15(2) dissolved and bubble methods. The first gave average rates 50% (49% 39) higher than the latter, which supports the finding that previously published N-2 fixation rates are likely underestimated. We suggest that by combining N-2 fixation and DON release measurements using dissolved N-15(2), global N-2 fixation rates could increase enough to balance oceanic fixed nitrogen budget disequilibria

Symbiotic unicellular cyanobacteria fix nitrogen in the Arctic Ocean

Biological dinitrogen (N2) fixation is an important source of nitrogen (N) in low-latitude open oceans. The unusual N2-fixing unicellular cyanobacteria (UCYN-A)/haptophyte symbiosis has been found in an increasing number of unexpected environments, including northern waters of the Danish Straight and Bering and Chukchi Seas. We used nanoscale secondary ion mass spectrometry (nanoSIMS) to measure 15N2 uptake into UCYN-A/haptophyte symbiosis and found that UCYN-A strains identical to low-latitude strains are fixing N2 in the Bering and Chukchi Seas, at rates comparable to subtropical waters. These results show definitively that cyanobacterial N2 fixation is not constrained to subtropical waters, challenging paradigms and models of global N2 fixation. The Arctic is particularly sensitive to climate change, and N2 fixation may increase in Arctic waters under future climate scenarios

MOLECULAR APPROACHES FOR IN SITU IDENTIFCIATION OF NITRATE UTILIZATION BY MARINE BACTERIA AND PHYTOPLANKTON

Traditionally, the importance of inorganic nitrogen (N) for the nutrition and growth of marine phytoplankton has been recognized, while inorganic N utilization by bacteria has received less attention. Likewise, organic N has been thought to be important for heterotrophic organisms but not for phytoplankton. However, accumulating evidence suggests that bacteria compete with phytoplankton for nitrate (NO3-) and other N species. The consequences of this competition may have a profound effect on the flux of N, and therefore carbon (C), in ocean margins. Because it has been difficult to differentiate between N uptake by heterotrophic bacterioplankton versus autotrophic phytoplankton, the processes that control N utilization, and the consequences of these competitive interactions, have traditionally been difficult to study. Significant bacterial utilization of DIN may have a profound effect on the flux of N and C in the water column because sinks for dissolved N that do not incorporate inorganic C represent mechanisms that reduce the atmospheric CO2 drawdown via the ?biological pump? and limit the flux of POC from the euphotic zone. This project was active over the period of 1998-2007 with support from the DOE Biotechnology Investigations ? Ocean Margins Program (BI-OMP). Over this period we developed a tool kit of molecular methods (PCR, RT-PCR, Q-PCR, QRT-PCR, and TRFLP) and combined isotope mass spectrometry and flow-cytometric approaches that allow selective isolation, characterization, and study of the diversity and genetic expression (mRNA) of the structural gene responsible for the assimilation of NO3- by heterotrophic bacteria (nasA). As a result of these studies we discovered that bacteria capable of assimilating NO3- are ubiquitous in marine waters, that the nasA gene is expressed in these environments, that heterotrophic bacteria can account for a significant fraction of total DIN uptake in different ocean margin systems, that the expression of nasA is differentially regulated in genetically distinct NO3- assimilating bacteria, and that the best predictors of nasA gene expression are either NO3- concentration or NO3- uptake rates. These studies provide convincing evidence of the importance of bacterial utilization of NO3-, insight into controlling processes, and provide a rich dataset that are being used to develop linked C and N modeling components necessary to evaluate the significance of bacterial DIN utilization to global C cycling. Furthermore, as a result of BI-OMP funding we made exciting strides towards institutionalizing a research and education based collaboration between the Skidaway Institute of Oceanography (SkIO) and Savannah State University (SSU), an historically black university within the University System of Georgia with undergraduate and now graduate programs in marine science. The BI-OMP program, in addition to supporting undergraduate (24) graduate (10) and postdoctoral (2) students, contributed to the development of a new graduate program in Marine Sciences at SSU that remains an important legacy of this project. The long-term goals of these collaborations are to increase the capacity for marine biotechnology research and to increase representation of minorities in marine, environmental and biotechnological sciences