Seasonal Production and Water Column Mixing
in the Gulf of Alaska
The OOI Global Station Papa Array is located in the eastern subtropical North Pacific in the Gulf of Alaska. The Array is co-located with the NOAA Pacific Marine Environmental Laboratory (PMEL) Surface Buoy and was the location of the historic ocean weather ship Station P from 1949 to 1981 and the current Line P program.
This nugget examines seasonal cycles of water column mixing and production at Station Papa. There is a clear annual cycle of stratification in the summer/fall (May-Oct) with mixing in the winter. Note that the mixed layer in the winter is shallow and does not reach down to the sensor at 130m. These data reveal a general relationship between stratification and production – when the water column is stratified and phytoplankton have sufficient light for growth, phytoplankton biomass increases. Although there are peaks in chlorophyll during late summer/fall (Aug/Sep), there is no large seasonal bloom. As the area is a high nitrate-low chlorophyll region, the lack of a large bloom is thought to be the result of iron limitation and/or grazing pressure by zooplankton.
The annual cycle of water column mixing and production in the Gulf of Alaska are often compared and contrasted with the North Atlantic, such as the OOI Global Irminger Sea Array, which has a very deep mixed layer and a large spring bloom. Check out the nuggets on Mixing and Seasonal Production in the Irminger Sea.
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.
Access from OOI Net:
Pull Data Using Python Code. Code demonstrates how to download data from multiple instruments on one OOI Global Flanking Mooring using the Machine-to-Machine (M2M) interface, remove outliers, calculate hourly averages, and export the data as a .csv file.
Seawater temperature data from the 5 shallowest CTDs on Global Station Papa Flanking Mooring B show the progression of the deepening of the mixed layer throughout the fall/winter and then re-stratification in the summer during 2013-14 (Deployment 1). The chlorophyll-a data from the fluorometer on the same mooring during 2013-14 shows a gradual decrease in chl-a as the mixed layer depth increases.
Global Station Papa Flanking Mooring B (GP03FLMB)
Location: Eastern subtropical North Pacific in the Gulf of Alaska
Lat/Lon: 50.3293°N, 144.398°W
Water Column Depth: 4,145 m
Platform: Mooring Riser
CTD (CTDMO-G) – fixed on inductive wire along the mooring riser at specific depths
3-Wavelength Fluorometer (FLORT-D) – 30m sensor cage
Graphics Credit: OOI Cabled Array program & the Center for Environmental Visualization, University of Washington
Essentials of Oceanography Textbook Sections
5.2 What important physical properties does water possess?
5.3 How salty is seawater?
5.6 How does seawater salinity vary at the surface and with depth?
5.7 How does seawater density vary with depth?
13.1 What is primary productivity?
13.3 How does regional primary productivity vary?
Next Gen Science Standard Connections
HS-PS3-4. Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics). This dataset illustrates a stratified water column where each layer has a different temperature, then as the water column mixes those water temperatures change to become uniform across multiple layers.
HS-LS1-5. Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy Discussion of light limitation of production provides a real world example of this concept.
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. Seasonal changes in conditions in the Gulf of Alaska produce dramatic changes in the ecosystem.
OOI Science Theme
Barth, J.A., et al. 2018. Warm blobs, low-oxygen events, and an eclipse: The Ocean Observatories Initiative Endurance Array captures them all. Oceanography 31(1):90–97. https://doi.org/10.5670/oceanog.2018.114.
Westberry, T.K., et al. 2016. Annual cycles of phytoplankton biomass in the subarctic Atlantic and Pacific Ocean. Global Biogeochemical Cycles 30:175–190. https://doi.org/10.1002/2015GB005276.
Whitney, F.A., et al. 2005. The uptake and export of silicon and nitrogen in HNLC waters of the NE Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 52(7-8):1055-1067. https://doi.org/10.1016/j.dsr2.2005.02.006.
Whitney, F.A. and H.J. Freeland. 1999. Variability in upper-ocean water properties in the NE Pacific Ocean. Deep Sea Research Part II: Topical Studies in Oceanography 46(11-12):2351-2370. https://doi.org/10.1016/S0967-0645(99)00067-3.