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Strait to the north and west, and source phase of Pacific multi-decadal oscillation, the foehn conditions contributes to strong
waters circulate between them, potentially underscoring the importance of tropical– snow ablation, so that relatively little sur-
allowing the influx of diatom valves. The polar teleconnections (Goodwin et al., face melting is needed to consume the
Larsen B, on the other hand, is an embay- 2016). The ice core–derived accumulation winter snowpack and initiate surface-melt
ment connected only to the continental record also correlates with Bellingshausen ponding. This relationship is perhaps best
shelf of the Weddell Sea, where gyre circu- Sea sea-ice extent, and both records exhibit illustrated by the foehn-induced prolifera-
lation brings water from the south, which a common response to short-term varia- tion of melt ponds prior to the 2002 disinte-
has heavy perennial sea-ice cover and low tions in the SAM and El Niño Southern gration event. Similar melt seasons and
productivity. The limited ocean circulation Oscillation (Porter et al., 2016). Interest‐ melt ponding occurred in 1995 (the year of
to the Larsen B cavity, now embayment, is ingly, mean air-temperature trends derived the Larsen A disintegration) and 2006, but
also apparent from benthic foraminiferal from an inversion of borehole temperature surface-melt ponding was moderated dur-
faunal and stable isotope data (Domack et profiles (Zagorodnov et al., 2012) show ing the period of the LARISSA project due
al., 2005a), indicating an absence of upper differences from those estimated from the to cooler climate conditions (Turner et al.,
Circumpolar Deep Water or other warm, ice core–derived δ O record. Core sample 2016). Moreover, the downslope wind
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deep-water masses in the area. δ O enrichment, which indicates warm- regime creates an extreme precipitation
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Large increases in sediment flux ing, is modest during the twentieth cen- shadow effect on the eastern Peninsula
occurred in all the ice-shelf–covered areas tury. This suggests that in addition to glaciers and shelf areas. Measurements
after shelf breakup. These included organic increased local near-surface temperatures, from automated multi-sensor stations
particulates and ice rafted and hemipelagic which are well documented from station (automated meteorology-ice-geophysics
siliciclastic materials. Some sites received data, other processes may have influenced observing systems, or AMIGOS) show that
>3 m of sediment per year following ice- the isotopic signature of the water vapor during 2010–2012, accumulation ranged
shelf breakup in the immediate vicinity of arriving over the Bruce Plateau (Goodwin from ~3 m water equivalent per year at the
the glacier fronts (Rebesco et al., 2014), in et al., 2016). Moreover, in addition to con- LARISSA Site Beta site, to ~0.5 m per year
contrast to <1 mm per year in the shelf- ditions in the moisture source area such on lower Flask Glacier, and near zero on
covered cavities during the Holocene as reduced sea-ice extent in the Bellings‐ the Scar Inlet Ice Shelf surface (Fig. 3).
(Domack et al., 2005a). hausen Sea, the increased annual net accu- A series of bedrock-sited continuous
Similar to the Larsen A embayment, mulation likely reflects other processes GPS (cGPS) recording stations were
reduced glacier-ice extent and seasonally that affect the rate at which precipitation is installed to determine current uplift rates,
open water during the early to mid- delivered to the site. arranged to surround the inferred Bruce
Holocene is observed on the western Deployment of weather stations along Plateau ice dome and augment the longer-
Antarctic Peninsula in Barilari Bay, the margins of the Larsen B, in conjunction term record from Palmer Station. The
followed by late Holocene expansion of with the analysis of a long-term weather cGPS records show exceptionally high
sea-ice cover that reached a maximum time series recorded at the Argentine base uplift rates, up to 14.9 ± 2.7 mm yr
−1
during the Little Ice Age (Christ et al., Matienzo (situated between the Larsen A (Nield et al., 2014). The present-day rates of
2015). Outer bay glaciers in their advanced and Larsen B embayments; Fig. 3), pro- rapid uplift represent acceleration from the
late Holocene positions were also sensitive vided further insight into the evolution of longer-term rates of uplift in the Antarctic
to conditions akin to positive mean the regional climate since the 1960s. The Peninsula, which is tied to the accelerated
Southern Annular Mode (SAM) states observational record indicates a strong loss of ice from the region (Nield et al.,
(Reilly et al., 2016). Late Holocene cooling surface-warming trend over the Larsen 2014). Further, the cGPS data were used
is also recorded in sediments from the tip embayments between 1962 and the early to estimate a local mantle viscosity of
of the Antarctic Peninsula, where the twenty-first century. This is linked to a (2 × 10 Pa s) and infer the local crustal
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western and eastern Antarctic Peninsula higher frequency of foehn winds, warm, thickness. The very low upper mantle vis-
systems meet (Kyrmanidou et al., 2018). dry winds that flow down the lee side of a cosity results in a lithosphere system that
mountain range. In the Antarctic Peninsula, responds very rapidly to changes in mass
CLIMATE AND CRYOSPHERE foehn winds result from the vertical deflec- loading. Almost none of the current uplift
EVOLUTION tion of the polar westerlies by the Antarctic can be attributed to residual rebound from
At the ridge summit above the southern- Peninsula orography and dry adiabatic the LGM ice retreat (Nield et al., 2014).
most Larsen B, a 448.12 m ice core was heating of the air mass as it descends the
collected to bedrock (LARISSA Site Beta lee side (Cape et al., 2015). While their sea- ONGOING ECOSYSTEM CHANGES
ice core; Fig. 3). The time period from AD sonal occurrence is tied to climatological A profound transformation in ecosystem
1900 to 2009 is recorded in approximately storm tracks, their frequency is also tightly structure and function has occurred in the
the top 195 m of the ice core (Goodwin et correlated to the SAM and the ongoing region as a result of the ice-shelf collapse.
al., 2016). The core records an increase in strengthening of the polar westerlies The previously dark, oligotrophic waters
annual net accumulation over the twentieth (Turner et al., 2014). Foehn events are beneath the Larsen B ice shelf now support
century, with the greatest increase begin- responsible for almost all temperature a thriving light-based phytoplankton com-
ning in the 1970s contemporaneously with excursions above the freezing point in the munity, with productivity rates and phyto-
the increasing positive trend in the SAM. Larsen B region, linking melt intensity to plankton composition similar to other
However, the relationship between SAM seasonal foehn frequency. The combination productive areas of the Weddell Sea and
and accumulation greatly depends on the of strong winds and low humidity during Antarctic continental shelf (Cape et al.,

8 GSA Today | August 2019