The Antarctic Peninsula is a region that has experienced very rapid warming over the last 50 years, and this has been attributed with the collapse of a number of ice shelves and accelerating glacier mass loss [1][2][3][4][5][6][7] . In contrast, warming has been comparatively modest over West Antarctica and significant changes have not been observed over most of East Antarctica 8-9 , suggesting that the ice core palaeoclimate records available from these areas may not be representative of the climate history of the Antarctic Peninsula. Here we present an ice core record from James Ross Island that provides the first complete Holocene temperature history for the Antarctic Peninsula. The Antarctic Peninsula experienced an early Holocene temperature optimum followed by a long interval from ~9,200 -2,500 years before present (yrBP; 1950AD) of stable temperatures similar to modern day levels. We find that the late Holocene development of ice shelves on the northeastern Antarctic Peninsula was coincident with pronounced cooling from 2,500 to 550 yrBP, which was part of a millennial-scale climate excursion with opposing anomalies on the east and west Antarctic Peninsula. Whilst warming of the northeastern Antarctic Peninsula began around 600 years ago, the rapid rate of warming over the last century is unusual in the context of natural climate variability over the last two millennia. The connection shown here between past temperature and ice shelf stability suggests that warming for several centuries had left ice shelves on the northeastern Antarctic Peninsula poised for collapse, and that continued warming to temperatures that now exceed the stable conditions that persisted here for most of the Holocene is likely to see ice shelf instability encroach further southward along the Antarctic Peninsula.The Antarctic Peninsula is currently one of the most rapidly warming regions on Earth (Fig. 1a) 1 .Historical observations since 1958 at Esperanza Station (Fig. 1b) 2), which plays a role in driving present day variability of the Antarctic Dipole 21 . Antarctic Dipole-like cooling of the Weddell Sea in the late Holocene, and the propagation of these ocean temperature and sea ice anomalies along the eastern Antarctic Peninsula by the Weddell Gyre, may have also aided the rapid establishment of ice shelves in this region during the late Holocene.Sustained warming at James Ross Island began approximately 600 years ago (Fig. 4a). Lake sediments from Beak Island in Prince Gustav Channel also indicate warming beginning at ~1410 AD 18 ,and together these records demonstrate the absence of a widespread Little Ice Age signal on the Antarctic Peninsula that was comparable to northern hemisphere climate 22 (Fig. 4a). The overall rate of pre-anthropogenic temperature rise at JRI from 1400 AD to 1850 AD equates to 0.22 ± 0.06 °C per century. However, there are times in this interval when warming occurred at a much faster rate.Using annual-resolution data, trends were calculated for the JRI temperature record since 2,000 yrBP over moving ...

Over the past 50 years, warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves. A key driver of ice loss is summer melting; however, it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic. Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice. During the past millennium, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6 • C lower than that of 1981-2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%. The warming has occurred in progressive phases since about AD 1460, but intensification of melt is nonlinear, and has largely occurred since the mid-twentieth century. Summer melting is now at a level that is unprecedented over the past 1,000 years. We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature.

We present a novel instrument, the Sub-Ocean probe, allowing in situ and continuous measurements of dissolved methane in seawater. It relies on an optical feedback cavity enhanced absorption technique designed for trace gas measurements and coupled to a patent-pending sample extraction method. The considerable advantage of the instrument compared with existing ones lies in its fast response time of the order of 30 s, that makes this probe ideal for fast and continuous 3D-mapping of dissolved methane in water. It could work up to 40 MPa of external pressure, and it provides a large dynamic range, from subnmol of CH per liter of seawater to mmol L. In this work, we present laboratory calibration of the instrument, intercomparison with standard method and field results on methane detection. The good agreement with the headspace equilibration technique followed by gas-chromatography analysis supports the utility and accuracy of the instrument. A continuous 620-m depth vertical profile in the Mediterranean Sea was obtained within only 10 min, and it indicates background dissolved CH values between 1 and 2 nmol L below the pycnocline, similar to previous observations conducted in different ocean settings. It also reveals a methane maximum at around 6 m of depth, that may reflect local production from bacterial transformation of dissolved organic matter.