Abstract
Antarctic sea-ice extent, primary productivity and ocean circulation represent interconnected systems that form important components of the global carbon cycle. Subdecadal to centennial-scale variability can influence the characteristics and interactions of these systems, but observational records are too short to evaluate the impacts of this variability over longer timescales. Here, we use a 170-m-long sediment core collected from Integrated Ocean Drilling Program Site U1357B, offshore Adélie Land, East Antarctica to disentangle the impacts of sea ice and subdecadal climate variability on phytoplankton bloom frequency over the last ~11,400 years. We apply X-ray computed tomography, Ice Proxy for the Southern Ocean with 25 carbon atoms, diatom, physical property and geochemical analyses to the core, which contains an annually resolved, continuously laminated archive of phytoplankton bloom events. Bloom events occurred annually to biennially through most of the Holocene, but became less frequent (~2–7 years) at ~4.5 ka when coastal sea ice intensified. We propose that coastal sea-ice intensification subdued annual sea-ice break-out, causing an increased sensitivity of sea-ice dynamics to subdecadal climate modes, leading to a subdecadal frequency of bloom events. Our data suggest that projected loss of coastal sea ice will impact the influence of subdecadal variability on Antarctic margin primary productivity, altering food webs and carbon-cycling processes at seasonal timescales.
Highlights
Antarctica’s marine margin is a complex biological and oceanographic system in which sea-ice growth, Antarctic Bottom
High primary productivity occurs where nutrients are brought to the surface, including oceanographic fronts[3], polynyas[4], upwelling near the continental shelf break[5] and the marginal ice zone (MIZ)[6], all of which are influenced by Antarctic wind fields
We investigate a 170 m sediment core recovered from the Adélie Basin (Integrated Ocean Drilling Program (IODP) Site U1357B)[17] along the Wilkes Land margin of East Antarctica (Fig. 1)
Summary
Antarctica’s marine margin is a complex biological and oceanographic system in which sea-ice growth, Antarctic Bottom. Diatom analysis from MD03-2597 in the Adélie Drift and nearby MD03-2601 interprets light laminae as biogenic bloom events, occurring during spring sea-ice retreat, which are rapidly exported to the seafloor[24,25]. From 4.5 ka, a baseline shift occurs in coastal sea-ice proxies and sand percent, which correspond with less-frequent bloom events relative to the overall record (Fig. 3 and Extended Data Fig. 6).
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