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The Arctic Ocean has experienced significant sea ice loss over recent decades, shifting towards a thinner and more mobile seasonal ice regime. However, the impacts of these transformations on the upper ocean dynamics of the biologically productive Pacific Arctic continental shelves remain underexplored. Here, we quantified the summer upper mixed layer depth and analyzed its interannual to decadal evolution with sea ice and atmospheric forcing, using hydrographic observations and model reanalysis from 1996 to 2021. Before 2006, a shoaling summer mixed layer was associated with sea ice loss and surface warming. After 2007, however, the upper mixed layer reversed to a generally deepening trend due to markedly lengthened open water duration, enhanced wind-induced mixing, and reduced ice meltwater input. Our findings reveal a shift in the primary drivers of upper ocean dynamics, with surface buoyancy flux dominant initially, followed by a shift to wind forcing despite continued sea ice decline. These changes in upper ocean structure and forcing mechanisms may have substantial implications for the marine ecosystem, potentially contributing to unusual fall phytoplankton blooms and intensified ocean acidification observed in the past decade
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This content will become publicly available on April 1, 2027
Modeling Upper Ocean Ecosystem Dynamics in Response to Interannual Sea‐Ice Variability in the Western Antarctic Peninsula
In the Western Antarctic Peninsula (WAP), marine plankton dynamics are tightly linked to the interannual variability in environmental conditions, including phenological shifts in sea‐ice seasonality. To explore these linkages, we use a 1‐dimensional vertical ocean‐ice‐ecosystem model (KPP‐Eco‐Ice, or KEI) that simulates physical and ecosystem conditions at a continental shelf mooring location in the Palmer Long Term Ecological Research program sampling grid. KEI allows for year‐round examination of the ecosystem in a region where in situ observations on the shelf are limited to January. Comparisons are made between seasonal sea‐ice retreat, mixed layer depth, primary productivity, and phytoplankton relative abundance, grazing, and loss rates. KEI successfully captures seasonal patterns in the WAP, demonstrating that total seasonal primary production was highest following a winter with late sea‐ice retreat. Stability in the surface mixed layer enables high photosynthetic rates by alleviating light limitation, while wind‐induced surface mixing results in lower phytoplankton production and biomass in years with early sea‐ice retreat. However, mixing reduces iron limitation in surface waters, which may influence phytoplankton species composition. Small, non‐diatom phytoplankton are better‐adapted to high light and low iron conditions, thriving longer in a year with late sea‐ice retreat and higher seasonal primary production, while larger diatoms are more abundant in the years with early sea‐ice retreat and lower seasonal production. These findings have implications for grazer populations and subsequent carbon export from the surface to depth in the WAP region. This study validates the role that sea ice plays in shaping Antarctic ecosystem dynamics.
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- PAR ID:
- 10677343
- Publisher / Repository:
- Journal of Geophysical Research: Biogeosciences
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 131
- Issue:
- 4
- ISSN:
- 2169-8953
- Subject(s) / Keyword(s):
- Antarctica Phytoplankton Primary productivity Ocean–ice–ecosystem modeling Light limitation Iron limitation Ocean carbon
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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