Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Publications
• Parameters
• Deployments
• Project Information
• Funding

Prochlorococcus in situ growth rates from cell cycle analysis.

These data were published in:

Hynes et al., 2015 

Rhodes, 2019.

Other relevant files and publications:

Braunwarth & Sommer, 1985

Liu et al., 1997

McDuff & Chrisholm, 1982

Prochlorococcus growth rates were calculated from diel time courses of the cell cycle phase fractions in data set ProCellCyclePhase from this project, as described in McDuff & Chisholm (1982) and modified by Liu et al. (1997). These calculations require an estimate of Td, the duration of the terminal cell cycle phase (in this case the combined duration of S and G2). Td is derived here using the areal median of the S and G2 time series (Braunwarth and Sommer 1985) as recommended by Hynes et al. (2015).

BCO-DMO Data Processing Notes:

- separated dateTime columns from Time.Start.UTC and Time.End.UTC to date_start_UTC and time_start_UTC and date_end_UTC and time_end_UTC (created 2 new columns)
- replaced all decimal points in column names with underscores
- reformatted date from mm/dd/yy to yyyy/mm/dd and time from AM/PM to 24hr time
- added ISO_DateTime_UTC column

The intellectual merit of the research is to extend our understanding of the biology and ecology of marine picophytoplankton, a group of microbes that are responsible for a large proportion of the total photosynthetic carbon fixation that occurs in the world's oceans. The importance of picophytoplankton as the dominant primary producers in open-ocean ecosystems is well-established. However, the factors that regulate the distribution and abundance of these populations remain poorly understood. The investigators will explore the dynamics of top-down (grazer-mediated) regulation of picophytoplankton populations in a specific context: the maintenance of summertime subsurface maxima in the pico-cyanobacterium Prochlorococcus (but not Synechococcus) in the Sargasso Sea. This phenomenon represents a relatively simple and predictable model system within which to test hypotheses about the regulation of oceanic picophytoplankton in general.
Recent results suggest that despite their abundance, Prochlorococcus in the subsurface maxi-mum are growing (and being grazed) rather slowly, as compared to the smaller population at the surface. In order to understand the factors responsible for this apparent paradox, this project will use a combination of field and laboratory studies to characterize and compare the interactions between Prochorococcus and its protozoan grazers at these two contrasting depths, and in relation to Synechococcus, which forms no such sub-surface maximum.
The broader impacts include training for graduate and undergraduate students. In addition, given the significance of picophytoplankton as primary producers at the base of oceanic microbial food webs, the results of this project should inform efforts to describe and model the broader oceanic ecosystem, and ultimately to understand its role in the global carbon cycle.