Seasonal Phytoplankton Blooms at High Latitudes
Primary production in the ocean is driven by phytoplankton. Oceanographers often examine primary production by measuring chlorophyll-a concentration (a proxy for phytoplankton biomass) via fluorescence. In the ocean two main factors limit primary production – light and nutrients. In this nugget, the annual cycle of primary production (chlorophyll) from two OOI Global Array sites are examined – Irminger Sea Array and Argentine Basin Array.
Primary production in the Irminger Sea shows a strong signal of seasonal light limitation. During winter months, day length is shorter and there is deep mixing in the water column, so primary production is limited even with the plentiful nutrients in the area. As spring unfolds off the coast of Greenland, melting ice and solar heating produce fresh, warm surface water that stratifies the water column. The combination of a stratified water column and longer day length lead to a large bloom in May. Productivity continues through September, though much lower than the initial bloom. As fall arrives, the days shorten and the water column mixes again reducing primary production.
Similar to the Irminger Sea, productivity is focused in the summer and fall time periods in the Argentine Basin as mixed layer depths shoal (get shallower). As the Argentine Basin is in the Southern Hemisphere, however, its seasons are reversed with austral summer/fall occurring from January to April. The Argentine Basin Array is located in a convergence zone where nutrient-poor subtropical water flowing south in the Brazil Current meets nutrient rich water from the subarctic traveling north in the Malvinas Current. This area is collectively referred to as the Brazil-Malvinas Confluence Area.
Seasonal cycles of chlorophyll concentration at two high latitude locations – the Irminger Sea in the North Atlantic, and the Argentine Basin in the South Atlantic. Irminger Sea data (blue) depict one annual cycle from 2014-2015. Argentine Basin data (green) depict two annual cycles from 2015-2017.
Access the Data
Disclaimer: data used in this example and provided in the .csv file were downloaded from the OOI on Nov 5, 2019. The file format and/or contents could have changed if downloaded directly from OOI Net after this date.
Pull Data Using Python Code. Code demonstrates how to download chlorophyll-a data from the OOI system using the Machine-to-Machine (M2M) interface and export the data as a .csv file.
Global Irminger Sea Flanking Mooring A (GI03FLMA)
Location: SW of Greenland in the Irminger Sea
Lat/Lon: 59.8177°N, 39.8412°W
Water Column Depth: 2,800m
Platform: Mooring Riser
Instruments: 3-Wavelength Fluorometer (FLORT-D) – within a sensor cage
Global Argentine Basin Surface Mooring (GA01SUMO)
Location: Argentine Basin in the South Atlantic along the Brazil Current
Lat/Lon: 42.9204°S, 42.4409°W
Water Column Depth: 5,200m
Platform: Near Surface Instrument Frame
Instruments: 3-Wavelength Fluorometer (FLORT-D)
Graphics Credit: OOI Cabled Array program & the Center for Environmental Visualization, University of Washington
Essentials of Oceanography Textbook Sections:
13.1 What is primary productivity?
13.3 How does regional primary productivity vary?
Next Gen Science Standard Connections:
HS-LS1-5. Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy These datasets illustrate light limitation of production, providing a real world example of the need for light in primary production.
HS-ESS2-6. Develop a quantitative model to describe the cycling of carbon among the hydrosphere, atmosphere, geosphere, and biosphere. The cycling of carbon through the ocean varies by location and time of year. These data highlight examples of complexity needed in a model of the global ocean carbon cycle.
HS-LS2-6. Evaluate claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem. This nugget highlights how seasonal changes in environmental conditions in the Irminger Sea produce dramatic changes in the ecosystem, while these changes are more muted in the Argentine Basin.
OOI Science Theme:
Greengrove, C., et al. 2020. Using authentic data from NSF’s Ocean Observatories Initiative in undergraduate teaching: An invitation. Oceanography 33(1):62-73. https://doi.org/10.5670/oceanog.2020.103.
Glover, D. M., et al. 2018. Geostatistical analysis of mesoscale spatial variability and error in SeaWiFS and MODIS/Aqua global ocean color data. Journal of Geophysical Research: Oceans 123:22–39. https://doi.org/10.1002/2017JC013023.
Palevsky, H.I., and D.P. Nicholson. 2018. The North Atlantic biological pump: Insights from the Ocean Observatories Initiative Irminger Sea Array. Oceanography 31(1):42–49. https://doi.org/10.5670/oceanog.2018.108.
Garcia, C.A.E., et al. 2004. Chlorophyll variability and eddies in the Brazil-Malvinas Confluence region. Deep-Sea Research Part II 51:159-172. https://doi.org/10.1016/j.dsr2.2003.07.016.