Light and dissolved iron (dFe) availability control net primary production (NPP) in much of the Southern Ocean, but the primary controller during spring in the western Antarctic Peninsula has never been assessed. Underwater light and dFe availability are sensitive to climate‐induced changes in upper ocean circulation, stratification, and sea ice cover, which can affect NPP and phytoplankton community composition, both of which can alter carbon drawdown and food web structure. We estimated in situ NPP, net community production, and heterotrophic respiration and contextualized our field measurements with satellite‐based historical NPP estimates. Average light exposure mainly controlled NPP, while low dFe was associated with greatest NPP, indicating that spring phytoplankton growth is light‐limited and not dFe‐limited. Using experiments that simulated varying mixed layer depths by exposing phytoplankton to a short period of in situ surface light (up to 150× the mean light in the mixed layer, comparable to the difference in light experienced by phytoplankton mixed from 50 m to the surface), we assessed the effect of phytoplankton photoacclimation on NPP and relative success of individual taxa. At moderate light exposure (<30×), phytoplankton experienced little photodamage or changes in NPP, and
As the physical environment of the Arctic Ocean shifts seasonally from ice‐covered to open water, the limiting resource for phytoplankton growth shifts from light to nutrients. To understand the phytoplankton photophysiological responses to these environmental changes, we evaluated photoacclimation strategies of phytoplankton during the low‐light, high‐nutrient, ice‐covered spring and the high‐light, low‐nutrient, ice‐free summer. Field results show that phytoplankton effectively acclimated to reduced irradiance beneath the sea ice by maximizing light absorption and photosynthetic capacity. In fact, exceptionally high maximum photosynthetic rates and efficiency observed during the spring demonstrate that abundant nutrients enable prebloom phytoplankton to become “primed” for increases in irradiance. This ability to quickly exploit increasing irradiance can help explain the ability of phytoplankton to generate massive blooms beneath sea ice. In comparison, phytoplankton growth and photosynthetic rates are reduced postbloom due to severe nutrient limitation. These results advance our knowledge of photoacclimation by polar phytoplankton in extreme environmental conditions and indicate how phytoplankton may acclimate to future changes in light and nutrient resources under continued climate change.
more » « less- NSF-PAR ID:
- 10075898
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 64
- Issue:
- 1
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 284-301
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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