Spectacular blooms of Phaeocystis antarctica in the Ross Sea, Antarctica are the source of some of the world's highest concentrations of dimethylsulfoniopropionate (DMSP) and its volatile degradation product, dimethylsulfide (DMS). The flux of DMS from the oceans to the atmosphere in this region and its subsequent gas phase oxidation generates aerosols that have a strong influence on cloud properties and possibly climate. In the oceans, DMS and DMSP are quantitatively significant components of the carbon, sulfur, and energy flows in marine food webs, especially in the Ross Sea. Despite its central role in carbon and sulfur biogeochemistry in the Ross Sea, surprisingly little is known about the physiological functions of DMSP in P. Antarctica. The research will isolate and characterize DMSP lyases from P. antarctica, with the goal of obtaining amino acid and gene sequence information on these important enzymes. The physiological studies will focus on the effects of varying intensities of photosynthetically active radiation, with and without ultraviolet radiation as these are factors that we have found to be important controls on DMSP and DMS dynamics. The research also will examine the effects of prolonged darkness on the dynamics of DMSP and related compounds in P. antarctica, as survival of this species during the dark Antarctic winter and at sub-euphotic depths appears to be an important part of the Phaeocystis? ecology. A unique aspect of this work is the focus on measurements of intracellular MSA, which if detected, would provide strong evidence for in vivo radical scavenging functions for methyl sulfur compounds. The study will advance understanding of what controls DMSP cycling and ultimately DMS emissions from the Ross Sea and also provide information on what makes P. antarctica so successful in this extreme environment. The research will directly benefit and build on several interrelated ocean-atmosphere programs including the International Surface Ocean Lower Atmosphere Study (SOLAS) program. The PIs will participate in several activities involving K-12 education, High School teacher training, public education and podcasting through the auspices of the Dauphin Island Sea Lab Discovery Hall program and SUNY ESF. Two graduate students will be employed full time, and six undergraduates (2 each summer) will be trained as part of this project.
The marine algal species Phaeocystis antarctica is responsible for massive blooms that occur in the Austral spring covering large swaths of the Ross Sea, hundreds of square km in extent, and accounting for approximately 23% of the total annual production of algal biomass in the Southern Ocean. Two important determinants for the growth of this algal species in Antarctic waters are (1) concentrations of the nutrient iron and (2) the intensity and spectral qualities, and ultraviolet radiation (UV) coming from the sun that enter into the oceans. Therefore, we conducted experiments with cultures of P. antarctica that were grown in the lab to determine the effect of the intensity of light and its spectral qualities on the growth of P. antarctica with and without added iron that is needed for growth. We determined that two compounds, dimethylsulphoniopropionate (DMSP) and acrylate, are present in P. antarctica cells at very high concentrations, and these high concentrations persisted irrespective of growth conditions, light levels or iron content. Acrylate and DMSP comprise approximately 2 and 10% of the total amount of cellular carbon. At these high concentrations, these two compounds are de facto antioxidants, and it is unlikely that P. antarctica regulates concentrations of DMSP or acrylate for this antioxidant function. Reduction in stratospheric ozone and changes in the depth of the surface mixed layer in Antarctic waters due to climate change are projected to increase cellular concentrations of these compounds in P. antarctica and increase their fluxes into the dissolved phase in the photic zone. The high concentrations of acrylate and DMSP in P. antarctica may partly explain why it grows so well under nutrient-limited conditions or during periods of very high or low light levels or UV exposures. It is a very curious finding that P. antarctica contains so much acrylate because this compound is thought to be toxic to living organisms. This finding is not a sampling artifact as we conducted numerous tests to assure the accuracy of our measurements. Even though there is a lot of acrylate associated with P. antarctica cells, there is still 40-70% of acrylate present in the dissolved phase, and we predict that dissolved acrylate will be an important compound fueling the growth of the microbial community in the Ross Sea, since microorganisms will use acrylate for energy and growth. One of the main indicators of physiological stress in P. antarctica due to iron limitation or light stress is the very large increase in dimethylsulfoxide (DMSO). Given that there are no known biochemical sources of DMSO in marine algae, this compound may serve as an indicator of stress and free radical activity in DMSP-containing marine algae. Nearly all of the DMSO that is produced in P. antarctica diffuses into the dissolved phase, and there is a lot of carbon that flows through this molecule. This observation has been seen not only for P. antarctica but for all high-DMSP containing algal species that we have examined. A lot of organic carbon produced by P. antarctica in the form of DMSO and acrylate is released into the dissolved phase. This needs to be explored in further detail to try and understand why an algal species would "let go" of so much carbon that it has produced through photosynthesis. One hypothesis is that these compounds are produced and released during times of photosynthetic imbalance.
