Tropical forcing of increased Southern Ocean climate variability revealed by a 140-year subantarctic temperate reconstruction

Occupying 14% of the world’s surface, the Southern Ocean plays a fundamental role in global climate, ocean circulation, carbon cycling and Antarctic ice-sheet stability. Unfortunately, high interannual variability and a dearth of instrumental observations before the 1950s limits our understanding of how marine-atmosphere-ice domains interact on multi-decadal timescales and the impact of anthropogenic forcing. Here we integrate climate-sensitive tree growth with ocean and atmospheric observations on southwest Pacific subantarctic islands that lie at the boundary of polar and subtropical climates (52–54˚S). Our annually-resolved temperature reconstruction captures regional change since the 1870s and demonstrates a significant increase in variability from the mid-twentieth century, a phenomenon predating the observational record. Climate reanalysis and modelling shows a parallel change in tropical Pacific sea surface temperatures that generate an atmospheric Rossby wave train which propagates across a large part of the Southern Hemisphere during the austral spring and summer

Multi-decadal variations in Southern Hemisphere atmospheric ¹⁴C: Evidence against a Southern Ocean sink at the end of the Little Ice Age CO₂ anomaly.

Northern Hemisphere-wide cooling during the Little Ice Age (LIA; CE 1650-1775) is associated with a ~5 ppmv decrease in atmospheric carbon dioxide. Changes in terrestrial and ocean carbon reservoirs have been postulated as possible drivers of this relatively large shift in atmospheric CO₂, potentially providing insights into the mechanisms and sensitivity of the global carbon cycle. Here we report decadally-resolved radiocarbon (¹⁴C) levels in a network of tree rings series spanning CE 1700-1950 located along the northern boundary of, and within, the Southern Ocean. We observe regional dilutions in atmospheric radiocarbon (relative to the Northern Hemisphere) associated with upwelling of ¹⁴CO₂–depleted abyssal waters. We find the inter-hemispheric ¹⁴C offset approaches zero during increasing global atmospheric CO₂ at the end of the LIA, with reduced ventilation in the Southern Ocean and a Northern Hemisphere source of old carbon (most probably originating from deep Arctic peat layers). The coincidence of the atmospheric CO₂ increase and reduction in the inter-hemispheric ¹⁴C offset imply a common climate control. Possible mechanisms of synchronous change in the high latitudes of both hemispheres are discussed

Smart Sketch System for 3D Reconstruction Based Modeling

Current user interfaces of CAD systems are still not suited to the initial stages of product development, where freehand drawings are used by engineers and designers to express their visual thinking. In order to exploit these sketching skills, we present a sketch based modeling system, which provides a reduced instruction set calligraphic interface to create orthogonal polyhedra, and an extension of them we named quasi-normalons. Our system allows users to draw lines on free-hand axonometric-like drawings, which are automatically tidied and beautified. These line drawings are then converted into a threedimensional model in real time because we implemented a fast reconstruction process, suited for quasi-normalon objects and so-called axonometric inflation method, providing in this way an innovative integrated 2D sketching and 3D view visualization work environment

Growth response of an invasive alien species to climate variations on subantarctic Campbell Island

Invasive alien species (IAS) are a recognised threat to biodiversity and ecosystem services. With increasing tourism and projected 21st century climate changes across the mid-to high-latitudes of the southern hemisphere, subantarctic islands are potentially highly vulnerable to IAS, but suffer from a dearth of baseline monitoring. Here we report tree-ring measurements from a lone exotic Sitka spruce (Picea sitchensis (Bong.) Carr) on subantarctic Campbell Island to determine past growth rates and likely future response to climate changes. Though the samples were unable to resolve exactly when the tree was planted, the fast growth rate indicates it is likely to have been later than the reported date of 1901. Since at least 1941, the tree appears to have responded favourably to the relatively warm summers experienced on Campbell Island, resulting in growth more rapid than that observed in natural stands (North American Pacific Coast). Although trees of similar age are normally mature and produce cones, none have so far been observed on Campbell Island -possibly the result of the fast growth causing an extended ‘juvenile’ or pre-reproductive phase -preventing seeding across the island. Importantly, relatively dry periods are needed for cones to open and disperse seeds, conditions not recorded in the instrumental record. Examination of the Coupled Model Intercomparison Project 5 (CMIP5) outputs show increasing rainfall across the region during the 21st century under a range of emission scenarios, suggesting that even when mature, the Sitka spruce poses a limited threat to the long-term ecology of Campbell Island

Pleistocene Glacial History of the New Zealand Subantarctic Islands

The New Zealand subantarctic islands of Auckland and Campbell, situated between the subtropical front and the Antarctic Convergence in the Pacific sector of the Southern Ocean, provide valuable terrestrial records from a globally important climatic region. Whilst the islands show clear evidence of past glaciation, the timing and mechanisms behind Pleistocene environmental and climate changes remain uncertain. Here we present a multidisciplinary study of the islands-including marine and terrestrial geomorphological surveys, extensive analyses of sedimentary sequences, a comprehensive dating programme, and glacier flow line modelling-to investigate multiple phases of glaciation across the islands. We find evidence that the Auckland Islands hosted a small ice cap 384 000±26 000 years ago (384±26 ka), most likely during Marine Isotope Stage 10, a period when the subtropical front was reportedly north of its present-day latitude by several degrees, and consistent with hemispheric-wide glacial expansion. Flow line modelling constrained by field evidence suggests a more restricted glacial period prior to the LGM that formed substantial valley glaciers on the Campbell and Auckland Islands around 72-62 ka. Despite previous interpretations that suggest the maximum glacial extent occurred in the form of valley glaciation at the Last Glacial Maximum (LGM; ∼ 21 ka), our combined approach suggests minimal LGM glaciation across the New Zealand subantarctic islands and that no glaciers were present during the Antarctic Cold Reversal (ACR; ∼ 15-13 ka). Instead, modelling implies that despite a regional mean annual air temperature depression of ∼ 5 °C during the LGM, a combination of high seasonality and low precipitation left the islands incapable of sustaining significant glaciation. We suggest that northwards expansion of winter sea ice during the LGM and subsequent ACR led to precipitation starvation across the middle to high latitudes of the Southern Ocean, resulting in restricted glaciation of the subantarctic islands