Access to the Sea Fund

Molecular Metabolic Fingerprinting to Identify Drivers of Phytoplankton Bloom Dynamics in the Southern Ocean

Harriet Alexander and Sonya T. Dyhrman

Marine phytoplankton are responsible for the net primary production of nearly 50 Pg (1015) of carbon per year, which is approximately 50% of the total primary production on earth. Marine primary production drives the global biogeochemical cycles of carbon as well as key nutrients (e.g. nitrogen (N) and phosphorus (P)). Overarching changes in the global climate stand to greatly alter both the biogeochemistry of the world’s oceans as well as the distribution and nature of primary production. The Southern Ocean is one of the largest High Nutrient-Low Chlorophyll (HNLC) regions in the ocean, representing the greatest reservoir of free macronutrients (e.g. N and P) in surface waters. Seasonal, massive phytoplankton blooms, dominated by Phaeocystis antarctica and pennate diatoms such as Fragilariopsis spp. and Pseudonitzschia spp. drive the production in the system. As the Southern Ocean is a crucial source of deep and intermediate water formation, it is a region of potentially great importance for carbon sequestration and the global carbon cycle. The forecasted large-scale climate alterations highlight the importance of a thorough comprehension of the global carbon cycle, which is tightly linked to biogeochemical cycling in the Southern Ocean. A more thorough understanding of the controls of phytoplankton bloom dynamics is crucial in the light of the changing ocean environment, yet there remain many fundamental questions surrounding phytoplankton growth dynamics in the Southern Ocean.

We have been offered berth space to participate in an upcoming series of cruises from the coast of Chile to Marguerite Bay on the west Antarctica peninsula currently scheduled for Fall (2012) and Spring (2013), providing us with a unique opportunity to apply molecular techniques that we have been developing in culture-based experiments to better understand the biogeochemical drivers of phytoplankton blooms in this critically important and difficult to access system. Using eukaryotic metatranscriptomic approaches, we will measure global gene expression in situ to derive metabolic fingerprints of the phytoplankton community along the cruise track. Coupling these samples with shipboard incubation experiments, we will quantitatively bound the differential gene expression signals observed in the field to address the following questions: 1) How do the blooming species P. antarctica, Fragilariopsis spp., and Pseudonitzschia spp. partition their biogeochemical niche space? and 2) What are the biogeochemical drivers of eukaryotic phytoplankton bloom formation in the Southern Ocean?

Our application of novel genome-enabled approaches, will identify biogeochemical drivers of bloom formation not discernable through traditional methods (e.g. incubation experiments and environmental chemical assays). Cutting-edge metatranscriptomic studies on eukaryotic phytoplankton have only been successfully done once before, and we anticipate that the access to the sea funding requested here will provide fundamental new insight, high-profile proof of concept papers, and lead to future federal funding. The high risk nature of this project combined with its short time-frame on these special cruises of opportunity make it difficult to fund the proposed work through traditional sources. Additionally, this funding will provide JP Student Harriet Alexander with her first at-sea experience, and the data gathered will form a significant portion of her graduate thesis work.

Last updated: June 21, 2012