Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the Last Glacial Termination.

Reconstructing the dynamic response of the Antarctic ice sheets to warming during the Last Glacial Termination (LGT; 18,000-11,650 yrs ago) allows us to disentangle ice-climate feedbacks that are key to improving future projections. Whilst the sequence of events during this period is reasonably well-known, relatively poor chronological control has precluded precise alignment of ice, atmospheric and marine records, making it difficult to assess relationships between Antarctic ice-sheet (AIS) dynamics, climate change and sea level. Here we present results from a highly-resolved 'horizontal ice core' from the Weddell Sea Embayment, which records millennial-scale AIS dynamics across this extensive region. Counterintuitively, we find AIS mass-loss across the full duration of the Antarctic Cold Reversal (ACR; 14,600-12,700 yrs ago), with stabilisation during the subsequent millennia of atmospheric warming. Earth-system and ice-sheet modelling suggests these contrasting trends were likely Antarctic-wide, sustained by feedbacks amplified by the delivery of Circumpolar Deep Water onto the continental shelf. Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections. With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise

Identifying drivers of leaf water and cellulose stable isotope enrichment in Eucalyptus in northern Australia

Several previous studies have investigated the use of the stable hydrogen and oxygen isotope composi- tions in plant materials as indicators of palaeoclimate. However, accurate interpretation relies on a detailed understanding of both physiological and environmental drivers of the variations in isotopic enrichments that occur in leaf water and associated organic compounds. To pro- gress this aim we measured δ18O and δ2H values in euca- lypt leaf and stem water and δ18O values in leaf cellulose, along with the isotopic compositions of water vapour, across a north-eastern Australian aridity gradient. Here we compare observed leaf water enrichment, along with pre- viously published enrichment data from a similar north Australian transect, to Craig–Gordon-modelled predic- tions of leaf water isotopic enrichment. Our investigation of model parameters shows that observed 18O enrichment across the aridity gradients is dominated by the relation- ship between atmospheric and internal leaf water vapour pressure while 2H enrichment is driven mainly by variation in the water vapour—source water isotopic disequilibrium. During exceptionally dry and hot conditions (RH 37 °C) we observed strong deviations from Craig– Gordon predicted isotope enrichments caused by partial stomatal closure. The atmospheric–leaf vapour pressure relationship is also a strong predictor of the observed leaf cellulose δ18O values across one aridity gradient. Our find- ing supports a wider applicability of leaf cellulose δ18O composition as a climate proxy for atmospheric humidity conditions during the leaf growing season than previously documented

First continuous shipboard δ18O and δD measurements in sea water by diffusion sampling: cavity ring-down spectrometry

Combined measurements of salinity and the oxygen/hydrogen stable isotope composition of marine waters can characterise processes such as freshwater mixing, evaporation, precipitation and sea-ice formation. However, stable isotope data with high spatial and temporal resolution are necessary for a detailed understanding of mixed water bodies with multiple inputs. So far analysis of δ18O and δD values in water has been a relatively expensive, laboratory-based technique requiring collection of discrete samples. This has greatly limited the scope and scale of field research that can be undertaken using stable isotope analysis. Here, we report the first continuous shipboard measurements of δ18O and δD values in water by diffusion sampling-cavity ring-down spectrometry. Combined with continuous salinity recordings, a data set of nearly 6,000 measurements was made at 30-s intervals during a 3-day voyage through the Great Barrier Reef Lagoon. Our results show that continuous shipboard measurement of δ18O/δD values provides additional discriminatory power for assessing water mass formation processes and histories. Precise identification of river plumes within the Great Barrier Reef Lagoon was only possible because unique δ18O/δD–salinity relationships of individual plumes were measured at high spatial and temporal resolution. The main advantage of this new technique is the ability to collect continuous, real-time isotope data at a small fraction of the cost of traditional isotope analysis of discrete samples. Water δ18O and δD values measured by diffusion sampling-cavity ring-down spectrometry and laboratory-based isotope ratio mass spectrometry have similar accuracy and precision