The ocean is responsible for the sequestration of more than 25% of the carbon released by anthropogenic activities every year. A combination of different biological processes (biological carbon pump) play an essential role in the sequestration of the atmospheric carbon to the ocean interior. Briefly, the phytoplankton convert atmospheric CO2 through photosynthesis to particulate and dissolved organic matter. Most of this organic carbon is recycled through utilization by planktonic grazers and respired back into the atmosphere, but a small fraction is exported to deeper depths and removed from contact with the atmosphere for decades or centuries. The objective of this research was to investigate how different taxa of pico- and nano-phytoplankton and their trophic dynamics are linked to the carbon flux in Sargasso Sea near the open ocean times series station BATS (Bermuda Atlantic Time-series Station). This site was chosen because of its more than 25 yr record of ongoing investigations, but also because it is considered representative of subtropical gyre regions that are expected to expand in response to the continuing warming of the oceans. This research was a collaborative effort by researchers from four different US universities and institutes. We used a combination of experiments coupled with microscopy and DNA-based tools to determine composition and taxon specific growth and grazing rates of the resident phytoplankton communities in the water column, as well as the composition of the sinking particulate matter. We also investigated prey utilization and fecal pellet production by the resident zooplankton community. We collected seawater samples in the upper 100m of the water column and sinking particles using particle traps at 150m during the spring and the summer of 2011 and 2012 at the Bermuda Atlantic Time-series Study station and in the surrounding mesoscale eddies. Mesoscale eddies are large circular features several 10s of km in diameter that influence nutrient availability to the phytoplankton community. Our results show that primary productivity in the Sargasso Sea is linked to the close relationship between phytoplankton and its micro grazers, and there were no specific patterns in productivity and grazing related to the interaction between mesoscale features and seasonality. We also found that micro grazers tightly control the growth of the pico and nano phytoplankton community, impacting the export of carbon in different ways. In some cases this coupled relationship favors efficient recycling of carbon within the euphotic zone (depth where sufficient light is available for photosynthesis, usually around 100m in the open ocean). In other cases, despite the coupled relationship, we found specific taxa of pico and nano-phytoplankton in the trap material, suggesting that the export of pico and nano-phytoplankton to the deeper ocean involves other pathways that still need further clarification. In addition, we found that larger zooplankton help mediate the transport of specific taxa of pico- and nanoplankton out of the epipelagic via the consumption of cells and detrital aggregates and subsequent production of fecal pellets. The results of this study will establish a baseline that will enable us to better predict the consequences of a changing community on the biological carbon pump in a future ocean. The data have been submitted to the Biological and Chemical Oceanography Data Management Office. The research also supported the educational and scientific development of one PostDoc, two undergraduate students who completed theses, one Master of Science and one PhD student and one high school student. We participated in several international conferences and are in the process of preparing several publications for the peer-reviewed literature. We publicized this research and its importance in outreach material for the public and K-12 on ASUÆs award winning Ask-a-Biologist web site. Last Modified: 03/11/2...
©2020 Biological and Chemical Oceanography Data Management Office.