Research

The Neuer team includes undergraduate, graduate students and PostDocs studying the link between plankton diversity, trophic dynamics and the biological carbon pump in the modern and ancient oceans.

Composition of the plankton community and its contribution to the particle flux in the Sargasso Sea

The ‘biological pump’, the photosynthetically mediated transformation of dissolved inorganic carbon into particulate and dissolved organic carbon in surface ocean waters and its subsequent export to deep water, is a significant driver of the atmospheric carbon uptake by the oceans. It is driven by the activity of planktonic organisms in the surface layer of the ocean, their growth as well as grazing. In an earlier NSF-Biological Oceanography project (“Composition of the Plankton Community and Its Contribution to Particle Flux in the Sargasso Sea”) we studied the phytoplankton communities in the water column and in sinking particles collected by shallow surface tethered traps from May 2008 till April 2010 at the Bermuda Atlantic Time-Series Station (BATS) in the Sargasso Sea. We used a combination of traditional (epifluorescence microscopy, flow cytometry, HPLC) and novel molecular approaches (rRNA gene based Clone Libraries and DGGE fingerprints) in this research The emergence of molecular methods in marine ecological research provides us with the unique opportunity to not only study the diversity of phytoplankton in the water column, but also the microscopically “invisible” plankton contained in the detritus or fecal pellets collected by the traps (see references below).

We are currently funded by NSF-Biological Oceanography for a project entitled “Plankton Community Composition and Trophic Interactions as Modifiers of Carbon Export in the Sargasso Sea”, in short “Trophic BATS” (in collaboration with Dr. Tammi Richardson from the University of South Carolina, USC, Dr. Mike Lomas from the Bermuda Institute of Ocean Sciences, BIOS, and Dr. Rob Condon from the Dauphin Island Sea Lab in Alabama). In this project we are studying the contribution of phytoplankton groups to the carbon export at the Bermuda Atlantic Time-Series Station in the context of the food web process in the upper ocean, with a particular focus on mesoscale cyclonic and anticyclonic eddies in the region. These are large circular oceanic features several 10’s of kilometers across that can either suppress or stimulate the activities of the plankton communities. In addition to studying the contribution of plankton organisms to particle flux, we are also measuring taxon specific growth and grazing rates using the dilution method to relate the importance of plankton organisms in the upper water column to their role in particle export. Read more about the first cruise in the trophic BATS project hereand this blog about the science and life onboard the ship written on the third cruise written by Doug Bell at BIOS (now at USC).


 

Astrobiology and cyanobacterial aggregation

In today’s ocean, animal grazers produce fecal pellets and aggregates that dominate carbon export, or the transport of organic matter from the surface ocean to the deep sea. During most of Earth’s history, however, marine life was limited to unicellular prokaryotes. These microorganisms are too small to sink as single cells, which presents a problem: how did carbon sink from the surface ocean to the deep if bacteria and their progenitors couldn’t sink on their own? The oxygenation of early Earth’s atmosphere could not have occurred without the sedimentation and burial of these single cells because carbon gobbled up in the surface ocean is simply released back into the atmosphere by respiration, interfering with oxygenation. The leading hypothesis states that these prokaryotic cells can form aggregates heavy enough to sink gravitationally to depth. Aggregate formation is driven by the production of sticky exopolymeric substances (EPS). Because of relation to carbon flux—which has implications for climate change—and to life on ancient Earth, this is a current topic of interest in ocean biogeochemistry and astrobiology.

As part of the Astrobiology Team at ASU, the Neuer lab is attempting to elucidate what drives and affects aggregate formation by using a strain of Synechococcus, a marine cyanobacterium, as a model organism for early photosynthetic marine bacteria. Graduate students Wei Deng and Amy Hansen and undergraduate students Kim Mohabir and Logan Monks have combined various techniques to tackle this issue. With epifluorescence microscopy and particle counter analysis, cell growth and the number and size of aggregates can be tracked over culture ages. Alcian Blue test is used to quantify the transparent exopolymer particles (TEP, the main component that holds aggregates together), together with other biochemical measurements of Chl-a, DOC and POC etc. to evaluate the aggregation of Synechococcus. Cultures are also transferred into roller tanks to enhance the aggregation like natural marine snow, with subsequent determination of different aggregate characteristics (number, size, sinking speed etc.). Current and future experiments involve testing the influence of clay minerals, nutrient limitation and acidification on Synechococcus aggregation, as well as making implications for the carbon export from experimental settings that mimic the early oceanic environment.


 

Sea Ice Communities

Microorganisms living in sea ice affect carbon and nutrient cycling in polar seas, but their susceptibility to the changing environmental conditions of polar regions is not well understood. The Neuer lab has been studying the adaptation of sea ice organisms living immured in the brine channels of sea ice, using a model organism that was isolated from sea ice brine. In addition, we have been studying the microbial community structure of land-fast Arctic Sea Ice and how environmental variables, such as light and temperature, influence these sea ice communities (see references below). In the ongoing NSF project “Sinking rates and nutritional quality of organic mater exported from sea ice; the importance of exopolymeric substances” in collaboration with Dr. Andrew Juhl from Columbia University, the Neuer lab studies sea ice algae with a particular focus on the flux of the organisms and organic matter from the sea ice to the water column as the ice melts. The work is done by coring and melting coastal ice sampled in the frozen coastal ocean of the Chuckchi Sea and utilizing the UMIAQ field station in Barrow, Alaska as a logistical base.


Carbon Flux in the Subtropical North Atlantic

The subtropical gyres are the largest coherent biomes of the global oceans, circular water masses located in the subtropical latitudes of each major ocean basin, and bounded by several ocean currents. These anticyclonic gyres are known as open ocean deserts because of the paucity of nutrients and phytoplankton biomass and can be recognized in satellite images of ocean color (see image above) as blue regions.

Because of their vast area (about 50% of the global ocean), subtropical gyres are important in the global carbon cycle. We are investigating carbon export from the subtropical North Atlantic gyre in a comparative fashion at two time series stations, one located in the eastern subtropical gyre north of the Canary Islands (ESTOC, European Station for Time-Series in the Ocean, Canary Islands) and in the western subtropical Atlantic south of Bermuda (BATS, Bermuda Atlantic Time-Series station), a US JGOFS station. Despite their similar look at the surface, we have found that there are differences in the supply of new nutrients to the surface which ultimately determine the removal efficiency of primary production to the deep sea. In this former NASA funded research project we combined the analysis of water column and particle trap measurements at the time series stations ESTOC and BATS with satellite remote sensing to link open ocean productivity with the export of carbon and associated elements to the deep ocean. See references below for results stemming from this project.


Algal blooms in the Salt River Reservoirs

The Salt River reservoirs are a major water supply system for the Phoenix Metro area. In addition to water storage and hydropower, the lakes also have a great recreational value, including boating and fishing. In recent years (2003 onwards) however, fish mortality has been a recurrent problem in the Salt River Lakes. Recurrent blooms of algae known to release toxins, such as the chrysophytePrymnesium parvum (Golden Alga), as well as cyanobacteria (Anabaena, Anabaenopsis, and Cylindrospermopsis) have been linked to these fish kills. In a project funded by the NSF Water Quality Center at ASU as well as by the Salt River Project, the Neuer lab investigated the succession of plankton populations in the Salt River Reservoirs, specifically Saguaro and Roosevelt Lake, with the goal to develop an early warning system of noxious algal blooms using satellite remote sensing.


Early Warning Systems for Algae-induced Tastes and Odors

The reservoirs in central Arizona are a major water supply system for the Phoenix metropolitan area. These reservoirs are fed by a combination of the Salt River water shed, the Verde River water shed, and Central Arizona Project water transported by a canal system from the Colorado River.  In addition to water storage and hydropower, the lakes also have a great recreational value, including boating and fishing. But fish mortality has been a recurrent problem in the Salt River Lakes and blooms of algae known to release toxins, such as the chrysophyte Prymnesium parvum (Golden Alga), as well as cyanobacteria (e.g., Cylindrospermopsis) that have been linked to these fish kills are found at high abundances in the AZ reservoirs.  Some of these nuisance algal species, particularly the cyanobacteria, are also known to be responsible for taste and odor issues, which can significantly impact customer satisfaction and reduce customer confidence in the quality of the water supply. Additionally, algal biomass makes a significant contribution to the particle loading of the water column, increasing the total suspended matter (total organic matter + sediments) loading.  These increased particle loadings can prove problematic for city water treatment plants.  Therefore the ability to remotely monitor the reservoirs for the presence of algal biomass, in particular those species known to be responsible for taste and odor problems, has the potential for providing advance warning of both environmental and water processing issues.

This AWWA (American Water Works Association) sponsored project is intended to test the ability of some of the new technology that is now available to identify the presence of taste and odor causing organisms.  We are using a FlowCAM® digital analyzer to process samples collected from the Salt River in order to monitor which species are present during taste and odor events.  We hope to correlate these species types with high levels of measured MIB (Methyl Isoborneol) and Geosmin.