Despite evidence from a number of Earth systems that abrupt temporal changes known as regime shifts are important, their nature, scale and mechanisms remain poorly documented and understood. Applying principal component analysis, change‐point analysis and a sequential t‐test analysis of regime shifts to 72 time series, we confirm that the 1980s regime shift represented a major change in the Earth's biophysical systems from the upper atmosphere to the depths of the ocean and from the Arctic to the Antarctic, and occurred at slightly different times around the world. Using historical climate model simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) and statistical modelling of historical temperatures, we then demonstrate that this event was triggered by rapid global warming from anthropogenic plus natural forcing, the latter associated with the recovery from the El Chichón volcanic eruption. The shift in temperature that occurred at this time is hypothesized as the main forcing for a cascade of abrupt environmental changes. Within the context of the last century or more, the 1980s event was unique in terms of its global scope and scale; our observed consequences imply that if unavoidable natural events such as major volcanic eruptions interact with anthropogenic warming unforeseen multiplier effects may occur.

The alvarezsauroid theropod Linhenykus monodactylus from the Upper Cretaceous of Inner

Digital reduction is a striking evolutionary phenomenon that is clearly exemplified in theropod dinosaurs by the functionally didactyl manus of tyrannosaurids, the flight-adapted manus of birds (Aves), and the tridactyl but digit II-dominated manus of alvarezsauroids. The enlargement of manual digit II in alvarezsauroids and the concurrent reduction of the lateral digits have been interpreted as adaptations for digging, although no detailed biomechanical analysis of hand function has so far been carried out for this group. In the derived alvarezsauroid clade Parvicursorinae, the lateral digits are so small as to be presumably vestigial. Here we report a new alvarezsauroid, Linhenykus monodactylus gen. et sp. nov., based on a specimen from the Upper Cretaceous Wulansuhai Formation of Inner Mongolia, China. Cladistic analysis identifies Linhenykus as the most basal parvicursorine, and digit II of the manus retains a slender morphology and other primitive features. However, Linhenykus is also highly apomorphic in exhibiting the most extreme reduction of the lateral manual digits seen in any alvarezsauroid. Phalanges are retained only on the most medial digit (digit II), making Linhenykus the only known functionally monodactyl nonavian dinosaur. Other parvicursorines are more primitive in retaining a tridactyl manus but more derived in that digit II is highly robust and shows other apomorphic features in both of its phalanges. The unexpected combination of features seen in the hand of Linhenykus points to a complex mosaic pattern of manual evolution in alvarezsauroids, with loss of the presumably vestigial outer digits being decoupled from change in the form of digit II.

BackgroundThe Troodontidae represents one of the most bird-like theropod groups and plays an important role in our understanding of avian origins. Although troodontids have been known for over 150 years, few known derived troodontid specimens preserve significant portions of both the forelimb and the hindlimb.Methodology/Principal FindingsHere, we report a new troodontid taxon, Linhevenator tani gen. et sp. nov., based on a partial, semi-articulated skeleton recovered from the Upper Cretaceous Wulansuhai Formation of Wulatehouqi, Inner Mongolia, China. L. tani has an unusual combination of primitive and derived character states, though our phylogenetic analysis places it in a derived clade within the Troodontidae. As a derived taxon, L. tani has a dromaeosaurid-like pedal digit II, and this species also possesses a humerus that is proportionally much shorter and more robust than those of most other troodontids.Conclusion/SignificanceThe combination of features present in Linhevenator indicates a complex pattern of character evolution within the Troodontidae. In particular, the discovery of Linhevenator suggests that derived troodontids have independently evolved a highly specialized pedal digit II and have significantly shortened the forelimb over the course of their evolution.

We describe a new dromaeosaurid theropod from the Upper Cretaceous Wulansuhai Formation of Bayan Mandahu, Inner Mongolia. The new taxon, Linheraptor exquisitus gen. et sp. nov., is based on an exceptionally well-preserved, nearly complete skeleton. This specimen represents the fifth dromaeosaurid taxon recovered from the Upper Cretaceous Djadokhta Formation and its laterally equivalent strata, which include the Wulansuhai Formation, and adds to the known diversity of Late Cretaceous dromaeosaurids. Linheraptor exquisitus closely resembles the recently reported Tsaagan mangas. Uniquely among dromaeosaurids, the two taxa share a large, anteriorly located maxillary fenestra and a contact between the jugal and the squamosal that excludes the postorbital from the infratemporal fenestra. These features suggest a sister-taxon relationship between L. exquisitus and T. mangas, which indicates the presence of a unique dromaeosaurid lineage in the Late Cretaceous of Asia. A number of cranial and dental features seen in L. exquisitus and T. mangas, and particularly some postcranial features of L. exquisitus, suggest that these two taxa are probably intermediate in systematic position between known basal and derived dromaeosaurids. The discovery of Linheraptor exquisitus is thus important for understanding the evolution of some salient features seen in the derived dromaeosaurids.

[1] Using NOAA extended reconstruction SST (ERSST.v2) and NCEP/NCAR reanalysis, a moving t test technique is employed to detect the decadal abrupt change years (DACYs) in the time series of several atmosphere-ocean variables. The decadal abrupt changes (DACs) existed widely in the ocean-atmosphere system in 1973-1978. In the ocean, the decreased DACs (DDACs, the variable decreases after the DACY) occurred in the North and South Pacific and the increased DACs (IDACs, the variable increases after the DACY) mainly took place in the eastern Pacific, southern South Pacific and South Indian Ocean. In the atmosphere, the IDACs happened over the Eastern Hemispheric tropics and subtropics in the low troposphere and over the global tropics and subtropics in the middle and upper troposphere and stratosphere. The higher pressure levels, the larger the DAC regions and the later the DACYs generally. The initial oceanic DACs in the 1970s cannot be explained by the DACs of wind stress, which happened 2 years (a) later than the original oceanic DACs. In addition, the tropical influence through atmosphere and ocean cannot explain the initial DDACs of SST and atmosphere of the North Pacific, which occurred about 2 a in advance of tropical warming. The DDACs in the 1970s of the North Pacific cannot interpret that of other oceanic regions, because they were not the initial oceanic DACs in the 1970s. These findings suggest that the DACs in the 1970s may initially originate from the ocean and a coupled atmosphere-ocean decadal interaction mechanism existed in the winter of the North Pacific.Citation: Xiao, D., and J. Li (2007), Spatial and temporal characteristics of the decadal abrupt changes of global atmosphere-ocean system in the 1970s,

The possible influence of Atlantic sea surface temperature (SST) on winter haze days in China at interannual and decadal time scales is investigated using the observed haze-day data from 329 meteorological stations, National Centers for Environmental Prediction-National Centers for Atmospheric Research (NCEP-NCAR) reanalysis, and a SST dataset for 1978-2012. Wintertime haze days in China show robust interannual variations and significant increases over time. The SST anomalies over the North Atlantic from summer to the following winter exhibit a significant in-phase relationship with winter haze days on both decadal and interannual time scales, whereas the anomalous negative-positive SSTs from north to south over the South Atlantic from autumn to the following winter show a significant positive relationship with winter haze days on the interannual time scale. The anomalous warm SST over the North Atlantic, i.e., the positive phase of the Atlantic multidecadal oscillation (AMO), corresponds to the positive phase of the Arctic oscillation (AO). This result implies that a stable mean flow and strong westerly anomalies exist over north China. The anomalous dipole pattern in the South Atlantic results in the abnormal southerly airflow in the troposphere over eastern China. Neither the westerly anomalies over north China nor the southerly anomalies over eastern China, which are associated with the North Atlantic and South Atlantic SST anomalies, respectively, are conducive to occurrences of cold air. Consequently, the weakened cold airflow from north of eastern China suppresses the dispersion of pollutants over China and results in above-normal haze days.

ABSTRACT:The four-dimensional structures and possible physical process of the decadal abrupt changes (DACs) of the northern extratropical ocean-atmosphere system in 1983-1988 are investigated by using ERSST.v2 and NCEP/NCAR reanalysis data. The DACs of sea surface temperature (SST) appeared over the southern tropical Atlantic, middle Pacific, and northern midlatitude oceans in 1983-1988. The atmospheric DACs in 1983-1988 were characterized with lower and higher geopotential height and air temperature anomalies over the Arctic and northern midlatitude, respectively. The above atmospheric distributions are attributed by the mass removal between the Arctic and middle latitudes. The decadal anomalies of the Ferrel cells and meridional atmospheric mass exchanges between the northern midlatitude and Arctic were suggestive of the DAC of the Northern Hemisphere annular mode (NAM).Basing on the disclosed facts above, the possible physical process of the DACs in the 1980s is proposed as follows. The DACs of the northern midlatitude SST heated the lower tropospheric atmosphere and it made the meridional gradient of air temperature anomalies increase between the middle and high latitudes. Decadal anomalous Ferrel cell was triggered, which presented a meridional vertical current over the northern extratropics. The results of the meridional mass exchanges induced the lower geopotential height and air temperature over the Arctic, and higher ones over the northern midlatitude. In conclusion, the warming of the northern midlatitude SST may be responsible for the northern extratropical atmospheric DACs and associated climate change events in the 1980s.