Variability and Dynamics of the Coastal Circulation along the West Antarctic Peninsula (WAP)
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Abstract
TheWest Antarctic Peninsula (WAP) hosts a rich biological community and has
undergone significant changes in both oceanic and climatic environments since the later
half of the twentieth century. The complexity of the WAP environment is highlighted
by its sensitivity to the dynamics of coastal circulation, which is pivotal in distributing
and modulating key oceanographic properties such as salinity, temperature, and biogeochemical
constituents, crucial for the vitality of local and surrounding ecosystems.
The intricate interplay between various dynamics and the coastal circulation makes
understanding the structure of the circulating pattern in the WAP critical, thereby
forming the focal point of this thesis. High-resolution numerical model outputs, available
observational data sets, and reanalysis products are used in this study. Results
first reveal a strong along-shore water exchange between the warm and cold shelves
along the WAP in Chapter 3. Seasonal and interannual variabilities are observed in
the along-shore water exchange processes. Summer is characterized by the intrusion
of warm Circumpolar Deep Water (CDW) into the Bransfield Strait, contrasted by
winter’s influx of colder Weddell-sourced water into central WAP. Under downwelling-favorable
wind conditions, cold water intrusion intensifies, cooling the warm shelf by
approximately 0.5◦C. Additionally, the along-shore coastal current circulation system
and the freshwater transport have been analyzed in Chapters 4 and 5. The coastal
current along the WAP is semi-continuous, the first Coastal Current extends from the
Weddell Sea to Anvers Island, where the Antarctic Coastal Current (AACC) emerges
and flows southwestward. Glacier meltwater dominates the AACC meltwater input
north of Marguerite Bay. South of Marguerite Bay, ice shelf meltwater becomes comparable
to, and eventually exceeds, glacier input. Approximately 46 Gt/year of glacier
meltwater and 57 Gt/year of ice shelf meltwater carried by AACC at Charcot Island, respectively. Strong buoyancy input is the primary mechanism generating the AACC,
with significant wind impact that strengthens the coastal current under favorable downwelling
conditions. Moreover, export of freshwater offshore from the buoyant plume
persists, predominantly driven by mesoscale, anticyclonic eddies—which comprise 77%
to 80% of the total—resulted from baroclinic and barotropic instabilities. Eddies vary
in size from 5 to 40 km in radius and transport water offshore especially south of Marguerite
Bay where exists massive melting. The offshore freshwater export, driven by
eddies, can exceed the onshore wind-driven Ekman transport, reaching up to approximately
0.11 Sv. The exported freshwater strongly modulate the freshwater content
variability in the outer shelf. Overall, this dissertation reveals the importance of investigating
coastal circulation over the WAP continental shelf and its diverse dynamics for
a deeper understanding of local property distributions and the oceanic environment.