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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
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