The Paleogene to Neogene climate evolution and driving factors on the Qinghai-Tibetan Plateau

Science China Earth Sciences - The growth of the Qinghai-Tibetan Plateau (QTP) during the Cenozoic drove dramatic climate and environmental change in this region. However, there has been limited...     

High Arctic sea ice conditions influence marine birds wintering in Low Arctic regions

Ocean climate change is having profound biological effects in polar regions. Such change can also have far-reaching downstream effects in sub-polar regions. This study documents an environmental relationship between High Arctic sea ice changes and mortality events of marine birds in Low Arctic coastal regions. During April 2007 and March 2009, hundreds of beached seabird carcasses and moribund seabirds were found along the east and northeast coasts of Newfoundland, Canada. These seabird “wrecks” (i.e. dead birds on beaches) coincided with a period of strong, persistent onshore winds and heavily-accumulated sea ice that blocked bays and trapped seabirds near beaches. Ninety-two percent of wreck seabirds were Thick-billed Murres (Uria lomvia). Body condition and demographic patterns of wreck murres were compared to Thick-billed Murres shot in the Newfoundland murre hunt. Average body and pectoral masses of wreck carcasses were 34% and 40% lighter (respectively) than shot murres, indicating that wreck birds had starved. The acute nature of each wreck suggested that starvation and associated hypothermia occurred within 2–3 days. In 2007, first-winter murres (77%) dominated the wreck. In 2009, there were more adults (78%), mostly females (66%). These results suggest that spatial and temporal segregation in ages and sexes can play a role in differential survival when stochastic weather conditions affect discrete areas where these groups aggregate. In wreck years, southward movement of Arctic sea ice to Low Arctic latitudes was later and blocked bays longer than in most other years. These inshore conditions corresponded with recent climate-driven changes in High Arctic ice break-up and ice extent; coupled with local weather conditions, these ice conditions appeared to be the key environmental features that precipitated the ice-associated seabird wrecks in the Low Arctic region.     

On the role of bottom roughness in overflows

Overflows play an important role in the downwelling limb of the oceanic thermohaline circulation. In light of the recognition that some overflows are not homogenous but exhibit a vertical density structure, and details of topography influence the pathways of some overflows, the impact of topographic roughness on the product property distribution is explored using the 3D non-hydrostatic spectral element model Nek5000. Numerical experiments are carried out by varying bottom roughness amplitude and ambient stratification parameters, in a regime where equilibrated product water masses are formed in a non-rotating environment.Our main finding is that bottom roughness can influence the overflow product distribution such that the highest salinity classes are removed and neutral buoyancy level is attained higher up in the stratified ambient water column. It is also shown that the form drag coefficients in overflows over rough bottom can be much larger than the skin drag coefficient over smooth bottom. To our knowledge, form drag has never been measured in oceanic overflows. As such, these numerical experiments imply that such measurements would be useful for a better understanding of overflow dynamics. It is also found that the ratio of source and product overflow mass transports is robust to changes in bottom roughness. This appears to happen because the distribution of entrainment is totally different in the case of rough bottom. Entrainment tends to initiate earlier (due to vertical motion induced by topography) and terminate earlier (due to development of form drag) than that over smooth topography.     

Influence of wavelength on the parameterization of drag coefficient and surface roughness

Surface waves are the roughness element of the ocean surface, the air-sea interaction processes are influenced by the wave conditions. The dynamic influence of surface waves decays exponentially with distance from the air-water interface. The relevant length scale characterizing the decay rate is the wavelength. The parameterization of drag coefficient and surface roughness can be significantly improved by using wavelength as the reference length scale of atmospheric measurements. The wavelength scaling of drag coefficient and dynamic roughness also receives support from theoretical studies of wind and wave coupling.     

Micropaleontological,mineralogical, and geochemical record in late quaternary cores from abyssal Grenada Basin

Clay mineralogy and trace-element geochemistry of two abyssal cores indicate that the primary source of surface-current-transported detrital material in the southern Grenada Basin changed from a continental, South American terrane to a volcanic, Lesser Antillean terrane at the end of the Pleistocene. The record of benthic foraminiferal assemblages demonstrates that the Caribbean Bottom Water (CBW) was relatively oxygen poor and less corrosive in late Pleistocene glacial times than in interglacial times. The change in the properties of CBW in the Holocene was related to a renewed influx of North Atlantic Deep Water in the Caribbean.     

Mass movement of fine-grained sediment to the basin floor,bering sea,Alaska

Large volumes of fine-grained sediment have been transported to the deepbasin floor in the Bering Sea, especially during glacial low stands of sea level. Turbidity currents and several types of mass movement have been the chief transporting agents.     

Organic geochemical study of the Upper Kimmeridge Clay of the Dorset type area

Results are presented from an organic geochemical investigation of a suite of rock samples taken from the Upper Kimmeridge Clay near Kimmeridge, Dorset. All samples contain immature organic matter of marine origin, although one horizon, the Whitestone Band, contains an additional secondary input of partially biodegraded mature hydrocarbons, due to an oil seepage of unknown origin. With the exception of increased relative abundances of 4-methylsteroidal hydrocarbons in the more organic-rich samples, the immature molecular distributions are very similar, suggesting a consistent source of organic matter. The results are in agreement with the palaeoenvironmental model proposed by Tyson et al. (1979) for the deposition of the Kimmeridge Clay, where the different lithologies are controlled by a fluctuating oxic/anoxic boundary, with only the organic-poor mudstones being deposited in relatively oxygenated waters.     

A chemical investigation of the transport and fate of petroleum hydrocarbons in littoral and benthic environments: The TSESIS oil spill

The fate of saturated and aromatic hydrocarbons discharged into the coastal Baltic Sea environment from the TSESIS oil spill has been studied in the acute and postacute (one year) phases of the spill. Periodic samples of Mytilus edulis (mussels) from eight littoral zone stations and Macoma balthica from nine soft bottom stations were obtained as well as sediment trap samples and surface sediment samples. Glass capillary gas chromatography and gas chromatographic mass spectrometry were used as the analytical tools to determine saturated and aromatic hydrocarbon composition and concentrations in these samples.Sediment trap samples indicated that sizable quantities of chemically and microbially weathered oil were sedimented, and available for benthic uptake shortly after the spill. After initial uptake of sedimented oil (500 to 1000 μ/g dry weight), Macoma populations appear to have begun slow depuration through the first winter after the spill, but TSESIS oil was again introduced to the benthic stations studied during the following summer. Mytilus populations in the region were severely impacted by the oil. Initial depuration of spilled oil during the first month was rapid and nearly complete at all but the most heavily impacted stations one year after the spill. The post-spill depuration of assimilated hydrocarbons was characterised by a relative retention of alkylated dibenzothiophenes and alkylated phenanthrenes compared to their unsubstituted parent compounds and compared with the entire homologous naphthalene series.These data suggest that petroleum hydrocarbons from the TSESIS spill have become a chronic source of degraded saturated and aromatic hydrocarbons to the soft bottom benthic communities. Petroleum hydrocarbons in the benthic environment from this spill appear to reside in the difficulty sampled and mobile flucculent layer at the sediment/water interface and may affect epifaunal communities for an extended period of time.