Our track is now heading south to the MK line (see map below) where a series of CTD rosette casts are being done along the Beaufort Shelf moving from deep water to relatively shallow water. Seas are quite rough today with swells in the 2-3 meter range (and maybe bigger?). Made for an interesting dinner – first time I had to hold my plate with one hand while I shoveled food with the other in an attempt to keep the plate from sliding across the table. Lots of weaving and dodging as one walks around the hallways.
In today's science meeting, Arthi Ramachandran a PhD student at Concordia University, and on her second JOIS cruise, discussed some of her research she is working on in collaboration with Connie Lovejoy (Laval University). Arthi says she has found a new subclass of bacteria that belong to a larger group called the methylotrophic bacteria. Thus far her research has found them only in surface waters of the Western Arctic Ocean, but she has lots of questions about their origins still to answer.
As part of today's post Connie Lovejoy (Laval University) offered the following on microbial research in the Arctic:
Biogeography, taxonomic diversity and metabolic functions of microbial communities in the Western Arctic
On board: Connie Lovejoy (P. I., University of Laval) and Arthi Ramachandran (PhD Candidate, Concordia).
Principle investigators: Connie Lovejoy (Université Laval, Québec QC Canada), David Walsh (Concordia University, Montreal, QC, Canada).
Most of the diversity on the planet is microbial and includes all three domains of life: Bacteria, Archaea, and single celled Eukaryota, referred to as microbial eukaryotes. These three domains work together in the ocean to support oceanographic food chains all the way up to fish, seals, marine birds and, in the Arctic, polar bears. They also and mediate many of the steps in global biogeochemical cycle especially the Carbon Cycle.
The microbial eukaryotes, which include photosynthetic phytoplankton, protists that eat bacteria (called phagotrophy) and groups that do both, along with Bacteria and Archaea in the Arctic Ocean are distinct from other oceans and could be vulnerable to rapid changes in the climate. Phytoplankton require inorganic nutrients and light to photosynthesize and fix atmospheric carbon to organic carbon, which is the stored energy for zooplankton (and ultimately the polar bears). The increasing freshwater in the upper Arctic ocean is affecting the depth of stratification, where fresher water mixed with Arctic Ocean water stays above more saline water entering from the Pacific and Atlantic Ocean. Because of density stratification this fresher upper layer near the surface is cut off from the nutrient supply from deeper waters. As this layer becomes thicker, phytoplankton are forced to grow in deeper and deeper waters to find the nutrients they need.
In the Canada Basin, smaller phytoplankton species are becoming more prevalent as this fresher layer thickens, which has implications for the overall carbon transfer and cycling in the region. Such changes signal the development of a more complex microbial food web where unicellular phagotrophic eukaryotes and bacteria become relatively more central in the transfer of energy and carbon to higher food webs compared to classical diatom (a particular type of phytoplankton), copepod based food chains. The net effect could be to favor jellyfish, which are lower quality food for the higher trophic levels.
Despite the ecological importance, apparent abundance, and wide distribution of microorganisms, most aspects of their ecology, diversity and oceanography are poorly understood. As change continues, knowledge of the species distribution and functional diversity of microbial life will become critical for predicting consequences of a warmer, more stratified Arctic Ocean.
We have been working across much of the North American Arctic over the last 15 years using mostly gene targeted molecular techniques and taking advantage of the revolution in DNA sequencing technology to process many samples at a time to identify the microbes in the waters. Past JOIS and other Arctic expeditions have enabled us to test spatial and temporal variability of these microorganisms. Our current project will continue this targeted gene search but also move more into metagenomics, where we sequence all of the DNA in the samples and use bioinformatics to reconstruct (in a computer) the genome of the most abundant organisms. We will combine metagenomics and metaproteomics; identifying the most abundant proteins in the samples to study the metabolic diversity and activity the marine microbial communities.
New this year is collaboration with the dissolved organic matter group led by Prof. Celine Gueguen at Trent. We will combine our multiple meta-omics approaches, used to functionally and taxonomically identify microbial communities, with molecular-level characterization of dissolved organic matter. The aim is to characterize Arctic microbes, including phytoplankton that produce and degrade marine DOM and compare these with the rare set of microbes capable of metabolizing different types of carbon compounds in the Arctic. Knowledge of these steps is key to predicting aspects of carbon and energy balances in the Arctic needed for the other JOIS collaborators.
Beaufort Gyre Observing system: Mackenzie Line
The Mackenzie line crosses a very interesting region from the oceanographic, biologic and ecosystem view point, where the fresh waters of the Mackenzie River (annual discharge is around 300 cubic kilometers) interact with saline waters of the Beaufort Gyre (BG) region. It is speculated with some observational evidence that in 2003-2009, the Mackenzie fresh water was one of the major sources supplying Beaufort Gyre freshwater reservoir. Our model outputs and results of geochemical analysis (Michiyo Yamamoto-Kawai) show that since 2003 more than 1300 cubic kilometers of fresh water from Mackenzie River were accumulated in the BG region.
Another importance of the MK Line region study is related to the needs of better understanding of mechanisms of interaction between fresh and saline waters. In these interaction zones, internal waves, eddies, and turbulence play important roles in the mixing processes.
Satellite images have long revealed the surface expression of large amplitude internal waves that propagate along density interfaces under the sea surface. Internal waves are typically the most energetic high-frequency events in the coastal ocean, displacing water parcels by up to 100m and generating strong currents and turbulence that mix nutrients into near-surface waters for biological utilization.
While internal waves, known to be generated by tidal currents over ocean-bottom topography, they have also been observed frequently in the absence of any apparent tide–topography interactions. Figure 6 shows an example of manifestations of internal waves observed from satellites in 2002 in the region of Columbia River. Figure 7 shows manifestation of internal waves at the sea surface in the vicinity of MK-Line. Underwater parameters of this wave are available from Figure 8. Investigation of these waves improves our understanding of ocean mixing.
Reproduction, and parameterization of these waves in the ocean models helps us to simulate and predict ocean changes more realistically and accurately.
Our location. Also Mackenzie Line (ML) and Mackenzie River delta are shown. Read text explaining major goals for this region study.
Arthi Ramachandran. Photo by David Jones.
Arthi Ramachandran and Cassie DeFrancesco on ice in the Beaufort Sea. Photo by David Jones.
Arthi Ramachandran works on an ice core temperature measurement. Photo by David Jones.
Overview of the Microbial work being done by Connie Lovejoy and Arthi Ramachandran. Courtesy of Connie Lovejoy.
Figure 6: We expected to observe similar images in the region of MK Line. Shown is a synthetic aperture radar (SAR) image of the Columbia River plume on 9 August 2002. Image indicates regions of enhanced surface roughness associated with plume-front and internal wave velocity convergences. SAR image courtesy of P. Orton, T. Sanders and D. Jay; image was processed at the Alaska Satellite Facility, and is copyright Canadian Space Agency. This image was published by Jonathan D. Nash & James N. Moum (River plumes as a source of large-amplitude internal waves in the coastal ocean) in 2005 in Nature Letters: Vol 437|15 September 2005|doi:10.1038/nature03936.
Figure 7: Manifestations of internal waves at the sea surface in the vicinity of MK-Line. Courtesy of Bill Williams.
Figure 8: Internal wave observed by fishing radar in summer 2006 in the vicinity of MK-Line. The radar shows arctic code in different water layers and at the same time there is an excellent reflection of sound from lower boundary of surface fresh water layer where plankton has high concentration. Wave-like structure of this layer indicates internal wave propagation. Prepared by A. Proshutinsky and Bill Williams.