Abstract
Abstract. The South Pole Ice Core (SPICEcore), which spans the past 54 300 years, was drilled far from an ice divide such that ice recovered at depth originated upstream of the core site. If the climate is different upstream, the climate history recovered from the core will be a combination of the upstream conditions advected to the core site and temporal changes. Here, we evaluate the impact of ice advection on two fundamental records from SPICEcore: accumulation rate and water isotopes. We determined past locations of ice deposition based on GPS measurements of the modern velocity field spanning 100 km upstream, where ice of ∼20 ka age would likely have originated. Beyond 100 km, there are no velocity measurements, but ice likely originates from Titan Dome, an additional 90 km distant. Shallow radar measurements extending 100 km upstream from the core site reveal large (∼20 %) variations in accumulation but no significant trend. Water isotope ratios, measured at 12.5 km intervals for the first 100 km of the flowline, show a decrease with elevation of −0.008 ‰ m−1 for δ18O. Advection adds approximately 1 ‰ for δ18O to the Last Glacial Maximum (LGM)-to-modern change. We also use an existing ensemble of continental ice-sheet model runs to assess the ice-sheet elevation change through time. The magnitude of elevation change is likely small and the sign uncertain. Assuming a lapse rate of 10 ∘C km−1 of elevation, the inference of LGM-to-modern temperature change is ∼1.4 ∘C smaller than if the flow from upstream is not considered.
Highlights
Ice cores provide unique and detailed records of past climate (e.g., Alley et al, 1993; Petit et al, 1999; NorthGRIP, 2004; Marcott et al, 2014)
We focus on the impact of ice flow on the South Pole Ice Core (SPICEcore)
The impact of horizontal advection can be observed as the older layers appear shifted to the left compared to the younger layers
Summary
Ice cores provide unique and detailed records of past climate (e.g., Alley et al, 1993; Petit et al, 1999; NorthGRIP, 2004; Marcott et al, 2014). Such records are most useful if they represent the change in climate at a fixed geographic location and elevation. Two important non-climatic influences on ice-core records are changes in ice-sheet elevation (Vinther et al, 2009; Steig et al, 2001; Stenni et al, 2011; Parennin et al, 2007; Cuffey and Clow, 1997) and changes in the location of ice origin due to flow (Whillans et al, 1984; Huybrechts et al, 2007; NEEM, 2013; Steig et al, 2013; Koutnik et al, 2016). We will use the term “advection impact” to refer to variations in the ice-core histories that are due to variations in the deposition location and paleo-elevation for different parcels of ice in the South
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