Holocene stability of the Amundsen-Weddell ice divide, West Antarctica

Abstract

We analyze Holocene ice fl ow using global positioning system and radio-echo sounding data acquired near the Amundsen-Weddell ice divide, between Pine Island Glacier and the Institute Ice Stream, West Antarctica. The data show that this part of the West Antarctic Ice Sheet (WAIS) has maintained a stable ice fl ow regime and ice divide position for ~7000 yr. Independent glacial geological data, in support of this assertion, suggest that the interior of the WAIS west of the Ellsworth Mountains has thinned by only a few hundred meters since the Last Glacial Maximum (LGM) and that the position of the ice divide may be recurrent over longer (more than 20 k.y., perhaps pre-Quaternary) time scales. We suggest that basal topography constrains ice fl ow in this sector of the WAIS, making the ice divide relatively insensitive to perturbations around the margins of the ice sheet compared with other ice divides. Large-scale forcing measured elsewhere in the WAIS as major reorganizations of the ice sheet surface and fl owline pattern may be manifested only in simple vertical changes of the Amundsen-Weddell interior.

Holocene accumulation and ice flow near the West Antarctic Ice Sheet Divide ice core site

“…While the Holocene history of ice‐divide position cannot be resolved in detail, we find that the average position of the ice divide was likely within a few kilometers of the modern position throughout the Holocene. This is broadly consistent with Holocene stability inferred for the Amundsen‐Weddell ice divide [ Ross et al , ] and could imply that centennial‐scale fast‐flow events from major WAIS outlet glaciers [e.g., Johnson et al , ] and/or the Ross ice streams [e.g., Catania et al , ] did not significantly alter interior ice geometry during the Holocene. This means that the driver of the large‐scale pattern of accumulation across Central West Antarctica (high accumulation at the Amundsen Sea coast transitioning to lower accumulation across the Ross Ice Streams) should be investigated using our new understanding that the Holocene accumulation pattern has likely remained similar to the modern pattern near the Central West Antarctic divide.…”

Ice flow velocities over Vostok Subglacial Lake, East Antarctica, determined by 10 years of GNSS observations

“…The structures originate at bedrock topographic features at the upstream (western) lake shore and result from the motion of the ice sheet over these features. Generally, they reflect the cumulative evolution of the ice flow pattern since their formation (Ross and others, 2011). In cases where the flow regime did not change throughout the transit time of the ice from the upper to the lower lake shore, these structures represent flowlines.…”

“…Internal structures were tracked, which reflect the ice flow and are related to bedrock topographic features at the upstream lake shore. They can be interpreted as flowlines only under the condition that the ice flow pattern remains unchanged throughout the transit time between the upstream and downstream lake shore (Ross and others, 2011). This approach is limited to the immediate lake area and is not able to provide estimates of the velocity magnitudes.…”

Origin and dynamic significance of longitudinal structures ("flow stripes") in the Antarctic Ice Sheet

“…If this is the case, the basic elements of the flow configuration have been stable since the end of the last glacial cycle and through the entire Holocene. In support of this conclusion we note that (1) continental-shelf landforms deposited by an expanded Antarctic Ice Sheet indicate prolonged periods of sediment delivery focused at the mouths of glacial troughs, creating trough-mouth fans with several hundred metres of sediment, implying that these areas have been occupied by fast-flowing glaciers and ice streams for tens of millennia (Dowdeswell et al, 2003(Dowdeswell et al, , 2008, or even tens of millions of years, as in the case of the Lambert Glacier-Amery Ice Shelf system Hambrey et al, 1991;Taylor et al, 2004); (2) numerical ice-sheet modelling studies (Pollard and DeConto, 2009) and evidence from blue-ice areas indicate that the central dome and overall patterns of ice flow in the West Antarctic Ice Sheet have remained intact for > 200 000 years (Fogwill et al, 2012); and (3) radarstratigraphic studies indicate near-stationary flow conditions over millennia near major ice divides (Ross et al, 2011) and locally at ice rises (Martín et al, 2014).…”

“…4). After mapping and describing the pattern of surface features on the Antarctic Ice Sheet, we discuss their possible origin in relation to these three hypotheses and consider their relationship with internal ice-sheet features, such as buckled layers and folds inferred from radar studies (Conway et al, 2002;Campbell et al, 2008;Ross et al, 2011;Martín et al, 2014).…”