艾德思：Nature海洋科学前沿扫描第29期

工业时代亚北极大西洋生产力下降 论文标题: Industrial-era decline in subarctic Atlantic productivity

论文作者: Matthew B. Osman, Sarah B. Das, Luke D. Trusel, Matthew J. Evans, Hubertus Fischer, Mackenzie M. Grieman, Sepp Kipfstuhl, Joseph R. McConnell & Eric S. Saltzman

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文章摘要: Marine phytoplankton have a crucial role in the modulation of marine-based food webs 1 , fishery yields 2  and the global drawdown of atmospheric carbon dioxide 3 . However, owing to sparse measurements before satellite monitoring in the twenty-first century, the long-term response of planktonic stocks to climate forcing is unknown. Here, using a continuous, multi-century record of subarctic Atlantic marine productivity, we show that a marked 10 ± 7% decline in net primary productivity has occurred across this highly productive ocean basin over the past two centuries. We support this conclusion by the application of a marine-productivity proxy, established using the signal of the planktonic-derived aerosol methanesulfonic acid, which is commonly identified across an array of Greenlandic ice cores. Using contemporaneous satellite-era observations, we demonstrate the use of this signal as a robust and high-resolution proxy for past variations in spatially integrated marine productivity. We show that the initiation of declining subarctic Atlantic productivity broadly coincides with the onset of Arctic surface warming 4 , and that productivity strongly covaries with regional sea-surface temperatures and basin-wide gyre circulation strength over recent decades. Taken together, our results suggest that the decline in industrial-era productivity may be evidence of the predicted 5  collapse of northern Atlantic planktonic stocks in response to a weakened Atlantic Meridional Overturning Circulation 6,7,8 . Continued weakening of this Atlantic Meridional Overturning Circulation, as projected for the twenty-first century 9,10 , may therefore result in further productivity declines across this globally relevant region.

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腔棘鱼的脑颅发育与肉鳍鱼头部的进化 论文标题: Neurocranial development of the coelacanth and the evolution of the sarcopterygian head

论文作者: Hugo Dutel, Manon Galland, Paul Tafforeau, John A. Long, Michael J. Fagan, Philippe Janvier, Anthony Herrel, Mathieu D. Santin, Gaël Clément & Marc Herbin

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文章摘要: The neurocranium of sarcopterygian fishes was originally divided into an anterior (ethmosphenoid) and posterior (otoccipital) portion by an intracranial joint, and underwent major changes in its overall geometry before fusing into a single unit in lungfishes and early tetrapods 1 . Although the pattern of these changes is well-documented, the developmental mechanisms that underpin variation in the form of the neurocranium and its associated soft tissues during the evolution of sarcopterygian fishes remain poorly understood. The coelacanth  Latimeria  is the only known living vertebrate that retains an intracranial joint 2,3 . Despite its importance for understanding neurocranial evolution, the development of the neurocranium of this ovoviviparous fish remains unknown. Here we investigate the ontogeny of the neurocranium and brain in  Latimeria chalumnae  using conventional and synchrotron X-ray micro-computed tomography as well as magnetic resonance imaging, performed on an extensive growth series for this species. We describe the neurocranium at the earliest developmental stage known for  Latimeria , as well as the major changes that the neurocranium undergoes during ontogeny. Changes in the neurocranium are associated with an extreme reduction in the relative size of the brain along with an enlargement of the notochord. The development of the notochord appears to have a major effect on the surrounding cranial components, and might underpin the formation of the intracranial joint. Our results shed light on the interplay between the neurocranium and its adjacent soft tissues during development in  Latimeria , and provide insights into the developmental mechanisms that are likely to have underpinned the evolution of neurocranial diversity in sarcopterygian fishes.

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