Ice front retreat reconfigures meltwater-driven gyres modulating ocean heat delivery to an Antarctic ice shelf

Abstract

Pine Island Ice Shelf (PIIS) buttresses the Pine Island Glacier, the key contributor to sea-level rise. PIIS has thinned owing to ocean-driven melting, and its calving front has retreated, leading to buttressing loss. PIIS melting depends primarily on the thermocline variability in its front. Furthermore, local ocean circulation shifts adjust heat transport within Pine Island Bay (PIB), yet oceanic processes underlying the ice front retreat remain unclear. Here, we report a PIB double-gyre that moves with the PIIS calving front and hypothesise that it controls ocean heat input towards PIIS. Glacial melt generates cyclonic and anticyclonic gyres near and off PIIS, and meltwater outflows converge into the anticyclonic gyre with a deep-convex-downward thermocline. The double-gyre migrated eastward as the calving front retreated, placing the anticyclonic gyre over a shallow seafloor ridge, reducing the ocean heat input towards PIIS. Reconfigurations of meltwater-driven gyres associated with moving ice boundaries might be crucial in modulating ocean heat delivery to glacial ice.

Unprecedented differences in phytoplankton community structures in the Amundsen Sea Polynyas, West Antarctica

“…These are among the previously reported dominant species in this area, and our results are consistent with those of previous studies that noted the effects of environmental factors, such as sea ice, iron, light, and mixed layer depth, on phytoplankton community distribution in this area (Alderkamp et al 2015, 2022. However, phytoplankton in the PIP exhibited an unprecedented community structure.…”

“…D. tenuijunctus that are entrapped in ice during the autumn are released into the water column in spring (Saggiomo et al 2017) and may have grown and accumulated near the ice shelves by currently unknown physical processes. Meltwater-driven gyres in the PIB (Yoon et al 2022) could be a physical phenomenon that explains the distribution of this species in the PIP. The waters dominated by D. tenuijunctus could have different sinking rates, Fv/Fm ratios, net community productions, and carbon uptake rates than those in P. antarctica-dominated waters.…”

“…antarctica and D. tenuijunctus could have different sinking rates. Previous studies have shown that large diatoms and P. antarctica colonies have higher sinking rates than small diatoms and P. antarctica single cells (Lee et al 2016, 2022, Smith et al 2017. D. tenuijunctus is a lightly silicified diatom with a diameter of less than 15 µm and floats longer in the water column due to its higher buoyancy.…”

Reversal of ocean gyres near ice shelves in the Amundsen Sea caused by the interaction of sea ice and wind

“…Below warm-cavity ice shelves, the water is stratified with a fresh meltwater-rich upper layer and a warm yet salty mCDW lower layer. This isopycnal displacement may allow warmer mCDW to enter the ice cavity and melt ice shelves (Yoon et al, 2022). The intrusion of warm water into the base of warm-cavity ice shelves is via the dense lower layer, the so-called "salt wedge" (Robel et al, 2022).…”

“…Zheng et al (2021), Mankoff et al (2012) and Tortell et al (2012) also suggest that the PIB gyre entrains water as it exits the ice cavity, contributing to the spreading of glacial meltwater and its associated heat, nutrients and freshwater. Yoon et al (2022) further mention that the PIB gyre can modulate heat delivery to the Pine Island Ice Shelf.…”