Microbial oceanography and the Hawaii Ocean Time-series programme

Journal name:
Nature Reviews Microbiology
Year published:
Published online


The Hawaii Ocean Time-series (HOT) programme has been tracking microbial and biogeochemical processes in the North Pacific Subtropical Gyre since October 1988. The near-monthly time series observations have revealed previously undocumented phenomena within a temporally dynamic ecosystem that is vulnerable to climate change. Novel microorganisms, genes and unexpected metabolic pathways have been discovered and are being integrated into our evolving ecological paradigms. Continued research, including higher-frequency observations and at-sea experimentation, will help to provide a comprehensive scientific understanding of microbial processes in the largest biome on Earth.

At a glance


  1. Station ALOHA habitat characteristics.
    Figure 1: Station ALOHA habitat characteristics.

    a | Location of Station ALOHA (A Long-term Oligotrophic Habitat Assessment) in the North Pacific Subtropical Gyre (NPSG) depicted on a Sea-viewing Wide Field-of-view Sensor (SeaWiFS) map of ocean colour (see Further information) showing the low concentrations of chlorophyll a (dark blue) that surround the site. b | The schematic shows the general habitat characteristics at Station ALOHA based on the 25 year climatology. This is an extremely oligotrophic environment that is characterized by low-standing stocks of chlorophyll (the subsurface chlorophyll peaks at ~105 m) and nitrate concentrations (note that primary production peaks where light is high but nutrients (such as nitrate) are nearly absent). Light that is sufficient for photosynthesis penetrates to at least 175 m. Temperature and the amount of turbulent mixing are also shown.

  2. Selected examples of temporal variability in the NPSG.
    Figure 2: Selected examples of temporal variability in the NPSG.

    a | Euphotic-zone depth (0–200 m)-integrated chlorophyll a concentrations from 1968 to 2013, showing a >twofold step increase mid-record just before the start of the Hawaii Ocean Time-series (HOT) era, based on observations presented by Venrick et al.24 (blue) combined with HOT programme data (red). b | Anomalous subsurface water masses at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) have been observed only twice during the 25 year observation period — in January 2000 and in June 2013. The left-hand panel shows a temperature versus salinity plot, which depicts the climatology (in red) and the two anomalies. The right-hand panel shows a satellite-based chlorophyll a (mg per m3) image of the region north of Hawaii, which shows a major phytoplankton bloom near Station ALOHA (white symbol at 22°45′N, 158°W) in July 2005. c | Secular increase in the pCO2 of the atmosphere (red) and upper ocean (blue) during the HOT era. Left-hand side of part a of the figure from Venrick, E.L., McGowan, J.A., Cayan, D.R. & Hayward, T.L. Climate and chlorophyll a: long-term trends in the central North Pacific Ocean. Science 238, 70-72 (1987). Modified with permission from AAAS. The satellite-based chlorophyll a image in part b is provided by J. Nahorniak, Oregon State University, USA, using AQUA MODIS L2 ocean colour data that is publicly available from the NASA Ocean Biology Processing Group website (see Further information).

  3. Prochlorococcus spp. distributions and dynamics.
    Figure 3: Prochlorococcus spp. distributions and dynamics.

    a | Vertical profile of mean (±SE; n = 63) Prochlorococcus spp. cells, mean (±SE, n = 63) divinyl chlorophyll a concentrations (red) and divinyl chlorophyll a per cell (green) at Station ALOHA (A Long-term Oligotrophic Habitat Assessment) for the period October 2005–December 2011, which shows a light-dependent change in chlorophyll (known as photoadaptation). b | Representative flow cytometric signature of red autofluoresence versus forward scatter for Prochlorococcus spp. collected at 143 m at Station ALOHA. c | Depth profiles of Prochlorococcus spp. ecotypes at Station ALOHA for August 2007. The ecotypes that were tracked were: MIT9312 (black), MED4 (red), NATL (green), SS120 (light blue) and MIT9313 (dark blue). Part c of the figure adapted from Ref. 44, Nature Publishing Group.

  4. Temporal and depth variability in primary production at Station ALOHA.
    Figure 4: Temporal and depth variability in primary production at Station ALOHA.

    a | Contour plot of upper water column (0–100 m) primary production (14C-based; mg C per m3 per day) based on approximately monthly observations throughout a 23 year period. b | Annual production climatology (mg carbon per m3 per day). c | Individual euphotic zone depth-integrated (0–200 m) primary production estimates shown with annual climatology (red line) to show both seasonal and interannual variations. d | The diagram shows the free-drifting primary production and sediment trap arrays that were used to collect the data shown. Particulate carbon (PC) export (sediment traps at 150 m reference depth) versus depth-integrated (0–150 m) primary production with export ratio (e = flux/production) contours of 0.01 and 0.20.


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  1. Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawaii, 1950 East-West Road, Honolulu, Hawaii 96822, USA.

    • David M. Karl &
    • Matthew J. Church

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  • David M. Karl

    David M. Karl is the Victor and Peggy Brandstrom Pavel Professor of Ocean and Earth Science and founding Director of the Daniel K. Inouye Center for Microbial Oceanography: Research and Education (C-MORE) at the University of Hawaii at Manoa, Hawaii, USA. He received his Ph.D. from the Scripps Institution of Oceanography in 1978, and an honorary D.Sc. degree from the University of Chicago, Illinois, USA, in 2010. He is Co-founder (with Roger Lukas) of the Hawaii Ocean Time-series programme and Codirector (with Edward DeLong) of the Simons Collaboration on Ocean Processes and Ecology (SCOPE). His research interests focus on microbially mediated biogeochemical cycles and energy flow in marine ecosystems.

  • Matthew J. Church

    Matthew J. Church is Associate Professor in the Department of Oceanography in the School of Ocean and Earth Science and Technology at the University of Hawaii at Manoa, USA. He received his B.Sc. degree from The Evergreen State College, Washington, USA, in 1994 and his Ph.D. from the School of Marine Science at The College of William and Mary, Williamsburg, Virginia, USA, in 2004. He actively leads the Hawaii Ocean Time-series (HOT) programme and is a scientific investigator in the Center for Microbial Oceanography: Research and Education (C-MORE) and Simons Collaboration on Ocean Processes and Ecology (SCOPE), USA, where his research focuses on the ecology of nitrogen-cycling microorganisms in the open sea.

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