National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2020

Seasonal patterns of near-bottom chlorophyll fluorescence in the eastern Chukchi Sea: 2010–2019

Stabeno, P.J., C.W. Mordy, and M.F. Sigler

Deep-Sea Res. II, 177, 104842, doi: 10.1016/j.dsr2.2020.104842, View online (2020)

The Chukchi Sea consists of a broad, shallow (<45 m) shelf that is seasonally (November–July) covered by sea ice. This study characterizes the seasonal patterns of near-bottom primary production using moored instruments measuring chlorophyll fluorescence, oxygen, nitrate, and photosynthetically active radiation. From 2010 to 2018, moorings were deployed at multiple sites each year. Instruments were restricted to within 10 m of the seafloor due to ice keels, which can reach 30 m below the surface in this region. Near-bottom blooms were common at all mooring sites. The bloom onset directly followed ice retreat whereas the end of the bloom followed loss of light in September. The intensity of light at the seafloor (~40 m deep) was similar to levels observed under 1–2 m thick ice floes in the spring/early summer, and was sufficient to support photosynthesis near the seafloor, utilizing nitrate and producing oxygen. We hypothesize that the near bottom bloom originated from aggregates of ice algae that sank during ice retreat. As a consequence of climate warming and earlier ice retreat, we predict that the near-bottom bloom onset will occur earlier, but the timing of the end of the near-bottom bloom will remain the same pending a sufficient nutrient supply. The Chukchi Sea is highly productive even though the growing season is short. This production is promoted by a shallow seafloor, which allows multiple production layers (surface open water, bottom of the mixed layer, under-ice algae, and disassociated ice algae which settles near the seafloor). We term this the Multiple Production Layers (MPL) hypothesis.

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