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Northern and southern hemispheric influences—particularly changes in Southern Hemisphere westerly winds (SSW) and Southern Ocean ventilation—triggered the stepwise atmospheric CO2 increase that accompanied the last deglaciation. One approach for gaining potential insights into past changes in SWW/CO2 upwelling is to reconstruct the positions of the northern oceanic fronts associated with the Antarctic Circumpolar Current. Using two deep-sea cores located ~600 km apart off the southern coast of Australia, we detail oceanic changes from ~23 to 6 ka using foraminifer faunal and biomarker alkenone records. Our results indicate a tight coupling between hydrographic and related frontal displacements offshore South Australia (and by analogy, possibly the entire Southern Ocean) and Northern Hemisphere (NH) climate that may help confirm previous hypotheses that the westerlies play a critical role in modulating CO2 uptake and release from the Southern Ocean on millennial and potentially even centennial timescales. The intensity and extent of the northward displacements of the Subtropical Front following well-known NH cold events seem to decrease with progressing NH ice sheet deglaciation and parallel a weakening NH temperature response and amplitude of Intertropical Convergence Zone shifts. In addition, an exceptional poleward shift of Southern Hemisphere fronts occurs during the NH Heinrich Stadial 1. This event was likely facilitated by the NH ice maximum and acted as a coup-de-grâce for glacial ocean stratification and its high CO2 capacitance. Thus, through its influence on the global atmosphere and on ocean mixing, “excessive” NH glaciation could have triggered its own demise by facilitating the destratification of the glacial ocean CO2 state.
Background: We reviewed our 12-year experience with staged reconstruction for hypoplasia of the left heart, examining the results of each surgical step and the impact of the year of the Norwood operation on survival. We compared survival of patients with hypoplasia of the left heart subsequent to completion of the Fontan circulation to survival of patients with a dominant left ventricle undergoing a Fontan procedure. Patients: Between 1989 and 2001, we performed a first stage procedure in 89 patients. Their median age was 9 days, with a range from 2 to 140 days, and the median weight was 3.4 kg, with a range from 2.4 to 5.4 kg. Results: Survival at 1, 4, and 10 years was 55%, 49%, and 49%, respectively. We experienced 23 early deaths (26%), and 12 deaths between the stages of the Norwood cascade. Of our patients, 42 underwent the second stage, and 30 the third stage. Prior to the first stage, symptoms of necrotising enterocolitis, and of obstructed pulmonary venous return, influenced survival significantly. The latter was eliminated as risk factor when surgery was performed within the first week of life. During the later part of our experience, survival at the first stage operation improved significantly, with survival at 3 years increasing from 42% to 75% for the patients at standard-risk (p = 0.017), and from 17% to 42% for those deemed to be at high-risk (p = 0.1). No deaths occurred in 23 patients older than 3 years of age, all of whom had proceeded through the third stage. After completion of the Fontan circulation, the survival of the patients with hypoplasia of the left heart at 4 years was comparable to the survival of patients undergoing the Fontan procedure with a dominant left ventricle (88% versus 90%, p = 0.8). Conclusions: Early and intermediate survival has improved significantly over the period of 12 years. Late death has been uncommon, and none of our patients are listed for cardiac transplantation.
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