The stability of modern ice shelves is threatened by atmospheric and oceanic warming. The geologic record of formerly glaciated continental shelves provides a window into the past of how ice shelves responded to a warming climate. Fields of deep (−560 m), linear iceberg furrows on the outer, western Ross Sea continental shelf record an early post-Last Glacial Maximum episode of ice-shelf collapse that was followed by continuous retreat of the grounding line for ∼200 km. Runaway grounding line conditions culminated once the ice became pinned on shallow banks in the western Ross Sea. This early episode of ice-shelf collapse is not observed in the eastern Ross Sea, where more episodic grounding line retreat took place. More widespread (∼280,000 km2) retreat of the ancestral Ross Ice Shelf occurred during the late Holocene. This event is recorded in sediment cores by a shift from terrigenous glacimarine mud to diatomaceous open-marine sediment as well as an increase in radiogenic beryllium (10Be) concentrations. The timing of ice-shelf breakup is constrained by compound specific radiocarbon ages, the first application of this technique systematically applied to Antarctic marine sediments. Breakup initiated around 5 ka, with the ice shelf reaching its current configuration ∼1.5 ka. In the eastern Ross Sea, the ice shelf retreated up to 100 km in about a thousand years. Three-dimensional thermodynamic ice-shelf/ocean modeling results and comparison with ice-core records indicate that ice-shelf breakup resulted from combined atmospheric warming and warm ocean currents impinging onto the continental shelf.

ABSTRACT. We have developed accelerator mass spectrometry (AMS) measurement techniques for ultra small-size samples ranging from 0.01 to 0.10 mg C with a new type of MC-SNICS ion source system. We can generate 4 times higher ion beam current intensity for ultra-small samples by optimization of graphite position in the target holder with the new ionizer geometry. CO 2 gas graphitized in the newly developed vacuum line is pressed to a depth of 1.5 mm from the front of the target holder. This is much deeper than the previous position at 0.35 mm depth. We measured 12 C 4 beam currents generated by small standards and ion beam currents (15-30 A) from the targets in optimized position, lasting 20 min for 0.01 mg C and 65 min for 0.10 mg C. We observed that the measured 14 C/ 12 C ratios are unaffected by the difference of ion beam currents ranging from 5 to 30 A, enabling measurement of ultra-small samples with high precision. Examination of the background samples revealed 1.1 g of modern and 1 g of dead carbon contaminations during target graphite preparation. We make corrections for the contamination from both the modern and background components. Reduction of the contamination is necessary for conducting more accurate measurement.

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Our new HL scale was demonstrated to be a reliable, valid instrument for measuring functional, communicative, and critical HL in patients with HF. Exploring a patient's HL level, including the ability to access, understand, and use health information as well as the ability to read and write, may provide better understanding of patients' potential barriers to self-care.