Papers by christian fritsen
The ecological role of heterotrophic bacteria in the microbial food web of the Southern Ocean is ... more The ecological role of heterotrophic bacteria in the microbial food web of the Southern Ocean is unresolved. A coupling between phytoplankton and bacterial production is well documented in mid-to low-latitude oceans (e.g., Cole, Findlay and Pace1988) and is thought to result from the heterotrophic uptake of dissolved organic carbon (DOC) released by the primary producers (i.e. the "microbial loop;" Pomeroy 1974; Bjørnsen 1988). In Antarctic waters, however, the extent to which bacteria rely on phytoplankton production, and consequently contribute to total ecosystem production, is disputed. A positive correlation between algal and bacterial biomass has been observed in regions of the Southern Ocean (e.g., . Conversely, variability in the strength of this correlation, and even an uncoupling of algae and bacteria, has also been documented (e.g. . Accurate characterization of the microbial loop in the Southern Ocean requires quantification of algal and bacterial biomass and activity over a seasonal time scale and in the diversity of marine habitats that surround Antarctica. This necessitates that bacteria-algae associations in the pelagic environment should not be studied apart from similar associations in the sea ice that is a prominent feature of most antarctic waters.
2015 AGU Fall Meeting, 2016
1-The brine of Lake Vida (Antarctica) contains oxychlorines complicating the study of volatiles 2... more 1-The brine of Lake Vida (Antarctica) contains oxychlorines complicating the study of volatiles 2-Carbon-limited experiments do not provide data on the effects of oxychlorine breakdown 3-High reduced-carbon/oxychlorine ratio is needed to detect organics on Mars via pyrolysis if these reactants co-occur
Metabolomics and the Legacy of Previous Ecosystems: a Case Study from the Brine of Lake Vida (Antarctica)
AGUFM, Dec 1, 2015
Organic Geochemistry, Aug 1, 2018
Lake Vida, located in an closed basin in the McMurdo Dry Valleys, East Antarctica, permanently en... more Lake Vida, located in an closed basin in the McMurdo Dry Valleys, East Antarctica, permanently encapsulates an interstitial anoxic, aphotic, cold (-13°C), brine ecosystem within 27+ m of ice. Metabolically active, but cold-limited, slow-growing bacteria were detected in the brine. Lake Vida brine is derived from the evaporation of a body of water that occupied the same basin prior to ~2800 years ago. The characteristics of this body of water changed over time and, at one point, likely resembled other modern well-studied perennial ice-covered lakes of the dry valleys. We characterized the dichloromethane-extractable fraction of the environmental metabolome of Lake Vida brine in order to constrain current and ancient biogeochemical processes. Analysis of the dichloromethane-extract of Lake Vida brine by gas chromatographymass spectrometry and comprehensive multidimensional gas chromatography-time of flightmass spectrometry reveals the presence of legacy compounds (i.e. diagenetic products of chlorophylls and carotenoids) deriving from photosynthetic algae and anaerobic, anoxygenic photosynthetic bacteria. This legacy component dilutes the environmental signal of metabolites deriving from the extant bacterial community. The persistence of legacy metabolites (paleometabolites), apparent in Lake Vida brine, is a result of the slow turnover rates of the extant bacterial population due to low metabolic activities caused by the cold limitation. Such paleometabolites may also be preserved in other cold-limited or nutrient-depleted slow-growing ecosystems. When analyzing ecosystems with low metabolic rates, the presence of legacy metabolites must first be addressed in order to confidently recognize and interpret the environmental metabolome of the extant ecosystem.
Proceedings of SPIE, Jul 29, 2004
There is growing evidence for ice and fluids near the surface of Mars with potential discharge of... more There is growing evidence for ice and fluids near the surface of Mars with potential discharge of brines, which may preserve a record of past life on the planet. Proven techniques to sample Mars subsurface will be critical for future NASA astrobiology missions that will search for such records. The required technology studies are underway in the McMurdo Dry valleys, Antarctica, which is serving as a Mars analog. The ice layer on Lake Vida in the dry valleys is estimated to be 20-meter thick where below 16-m depth there is a mix of ice and brine, which has never been sampled directly due to logistical constraints. A novel light weight, low power ultrasonic/sonic driller/corer (USDC) mechanism was developed that overcomes the need for high axial loads required by drilling via conventional techniques. The USDC was modified to produce an Ultrasonic/Sonic Gopher that is being developed to core down to the 20-m depth for in situ analysis and sample collection. Coring ice at-20 o C as in Lake Vida suggests that it is a greater challenge and current efforts are focused on the problems of ice core cutting, ice chip handling and potential ice melt (and refreezing) during drilling. An analytical model and a prototype are being developed with an effort to optimize the design while addressing the thermal issues, drilling rate, power, mass and the electromechanical behavior.
The Dynamic Coupling among Phytoplankton, Ice, Ice Algae and Krill (PIIAK)
Earth’s biosphere is cold, with 14% being polar and 90% (by volume) cold ocean <5 C. More than... more Earth’s biosphere is cold, with 14% being polar and 90% (by volume) cold ocean <5 C. More than 70% of Earth’s freshwater occurs as ice (Fig. 1) and a large portion of the soil ecosystem (~20%) exists as permafrost. Figure 1. Global locations of existing glacial ice sheets and caps (denoted by shading). Paleoclimate records for the past 500,000 years have shown that the surface temperature on Earth has fluctuated drastically, with strong evidence showing that the Earth was completely ice-covered during the Paleoproterozoic and Neoproterozoic periods [1, 2]. New discoveries of microbial life in cold (-5C) and saline lakes, permanent lake ice, cryoconite holes, polar snow, glacial ice, and subglacial environments are extending the known boundaries of the biosphere. Despite the mounting evidence for microbial life in frozen ecosystems, little is know about the psychrophilic or psychrotolerant microorganisms that inhabit them. Molecular-based ecological studies have revealed close phy...
Algal-Based Renewable Energy for Nevada
Polar Biology, 2011
Understanding the flow of solar energy into ecosystems is fundamental to understanding ecosystem ... more Understanding the flow of solar energy into ecosystems is fundamental to understanding ecosystem productivity and dynamics. To gain a better understanding of this fundamental process in the Antarctic winter sea ice, we produced a model that estimates the time-integrated exposure of seasonal Antarctic sea ice to PAR through the use of remotely sensed sea ice concentrations, sea ice movement and spatially distributed PAR calculations that account for cloud cover and have applied this model over the past three decades. The resulting spatially distributed estimates of sea ice exposure to PAR by midwinter are evaluated in context of changes in the timing of sea ice formation that have been documented along the Western Antarctic Peninsula (WAP) region and its potential effects on the variation (seasonal and inter-annual) in the accumulation of sea ice algae in this region. The analysis shows the ice pack is likely to have large inter-annual variations (10-100 fold) in productivity throughout the autumn to winter transition in the sea ice along the WAP. Moreover, the pack ice is likely to have spatial structure in regards to biological processes that cannot be determined from analysis of sea ice concentration information alone. The resulting inter-annual variations in winter processes are likely to affect the dynamics of Antarctic krill (Euphausia superba).
Altering Reservoir Withdrawal: a modeling approach to tail-water eutrophication on the South Fork Humboldt Reservoir, NV USA
ABSTRACT The South Fork Humboldt Reservoir (south of Elko, Nevada) represents an arid, hypolimnet... more ABSTRACT The South Fork Humboldt Reservoir (south of Elko, Nevada) represents an arid, hypolimnetic release dam with tail-water eutrophication exceeding 300mg Chla per m2. The USEPA model AQUATOX 3 has been used to simulate reservoir nutrient loadings on tail-water periphyton and to predict changes in stream response to top release conditions. From April to September of 2009, an investigation characterized reservoir stratified nutrient profiles and downstream riverine algal dynamics due to reservoir bottom withdrawal. The 2009 period represents calibration with exceptional downstream diel dissolved oxygen swings (3.76 to 19.75 mg/L) and gross primary productivity (30.7 g C m2 d¬-1) for model prediction. The observed period was additionally simulated with exclusively top release conditions to investigate potential best management practices. The results predict potential changes of attached algal communities and associated dissolved oxygen conditions based on varied release nutrient loadings.
Europa The Search for Life on Europa: Limiting Environmental Factors, Potential Habitats, and Earth Analogues
Astrobiology, 2003
Polar Biol, 2000
The organic carbon and nitrogen contents of sediments in the upper 2 cm of the soils surrounding ... more The organic carbon and nitrogen contents of sediments in the upper 2 cm of the soils surrounding several lakes in the McMurdo Dry Valleys were measured in a relatively high-density sampling grid, in order to better understand the present-day distribution of organic matter in the ecosystem that is most readily transportable via aeolean processes. Carbon and nitrogen contents of the bulk sediments and size-dierentiated sediments decreased in a series according to lake basins oriented along the Taylor Valley's main axis (Lake Fryxell > Hoare ³ west lobe Bonney ³ east lobe Bonney). Samples were also obtained around Lake Vida and showed this basin to contain less organic matter than those in the Taylor Valley. This regional spatial analysis supports the emerging view that each basin provides distinct environments for in situ microbial activity, lithogenic weathering, aeolian deposition and sorting that can be detected through synoptic sampling.
Macronutrients in the Summer Sea ice of the Ross Sea
Agu Fall Meeting Abstracts, Dec 1, 2004
The development and production of sea ice microbial communities is often linked to limitations im... more The development and production of sea ice microbial communities is often linked to limitations imposed by light, temperature and salinity. Nutrients also impose a limitation upon biomass development and production. Nutrient constraints on biomass development was readily evident in surface habitats of the pack ice of the Ross Sea during the summer of 1999. The spatial extent of nutrient depletions,
Identification and quantification of aquatic vegetation with hyperspectral remote sensing in western Nevada rivers, USA
Http Dx Doi Org 10 1080 01431161 2010 549850, Nov 7, 2011
... Lee a * , Kenneth C. McGwire a & Christian H. Fritsen a Available online: 13 Oct 2011. ..... more ... Lee a * , Kenneth C. McGwire a & Christian H. Fritsen a Available online: 13 Oct 2011. ... Rather than using NIR wavelengths, Hellweger et al. (200412. Hellweger, FL, Schlosser, P., Lall, U. andWeissel, JK 2004. Use of satellite imagery for water quality studies in New York harbor. ...
The formation of a 26m ice cover on Lake Vida, Antarctica
Spatial And Temporal Periphyton Distributions And Ecological Indices In An Anthropogenic-Influenced Montane-Desert Great Basin Stream
Big Soda Lake, Nevada, is a terminal, volcanic crater lake whose water level is maintained exclus... more Big Soda Lake, Nevada, is a terminal, volcanic crater lake whose water level is maintained exclusively by groundwater. The crater is Algae obtain from a depth of 10 m
Bacterial Distribution and Production Within Lake Ice and Glacial Ice Along the Fringe of the Antarctic Ice Cap
Third International Conference on Mars Polar Science and Exploration, Oct 1, 2003
Temporal and Spatial River Temperature Heterogeneity influences on Nutrient Cycling
Comment on �El Ni�o suppresses Antarctic warming� by N. Bertler et al
Geophys Res Lett, 2005
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Papers by christian fritsen