On trend detection

A main obstacle to trend detection in time series occurs when they are autocorrelated. By reducing the effective sample size of a series, autocorrelation leads to decreased trend significance. Numerous recipes attempt to mitigate the effect of autocorrelation, either by adjusting for the reduced effective sample size or by removing the autocorrelated components of a series. This short note deals with the latter, also called prewhitening (PW). It is known that removal of autocorrelation also removes part of the trend, which may affect the signal‐to‐noise ratio. Two popular methods have dealt with this problem, the trend‐free prewhitening (TFPW) and the iterative prewhitening. Although it is generally accepted that both methods reduce the adverse effects of PW on the trend magnitude, corresponding effects on statistical significance have not been clearly stated for TFPW. Using a Monte Carlo approach, it is demonstrated that both methods entail quite different Type‐I error rates. The iterative prewhitening produces rates that are generally close to the nominal significance level. The TFPW, however, shows very high Type‐I error rates with increasing autocorrelation. The corresponding rate of false trend detections is unacceptable for applications, so that published trends based on TFPW need to be reassessed.     

Interpretation of SOFIE PMC measurements: Cloud identification and derivation of mass density,particle shape,and particle size

The Solar Occultation For Ice Experiment (SOFIE) was launched onboard the Aeronomy of Ice in the Mesosphere (AIM) spacecraft to measure polar mesospheric clouds (PMCs) and their environment. This work describes methods for identifying PMCs in SOFIE observations and determining mass density, particle shape, particle effective radius, and the parameters of a Gaussian size distribution. Results using SOFIE measurements from the northern summer of 2007 are compared with concurrent observations by the ALOMAR lidar in northern Norway. Ice particle properties determined from SOFIE are in good agreement with the lidar results, considering the differences in instrument characteristics.     

Reconstruction of the Late Holocene climate and environmental history from North Bolgoda Lake,Sri Lanka,using lipid biomarkers and pollen records

The catastrophic impact and unpredictability of the Indian Ocean Monsoon (IOM) over South Asia are evident from devastating floods, mudslides and droughts in one of the most densely populated regions of the globe. However, our understanding as to how the IOM has varied in the past, as well as its impact on local environments, remains limited. This is particularly the case for Sri Lanka, where erosional landscapes have limited the availability of well-stratified, high-resolution terrestrial archives. Here, we present novel data from an undisturbed sediment core retrieved from the coastal Bolgoda Lake. This includes the presentation of a revised Late Holocene age model as well as an innovative combination of pollen, source-specific biomarkers, and compound-specific stable carbon isotopes of n-alkanes to reconstruct the shifts in precipitation, salinity and vegetation cover. Our record documents variable climate between 3000 years and the present, with arid conditions c. 2334 and 2067 cal a bp. This extreme dry period was preceded and followed by more wet conditions. The high-resolution palaeoenvironmental reconstruction fills a major gap in our knowledge on the ramifications of IOM shifts across South Asia and provides insights during a time of major redistribution of dense human settlements across Sri Lanka.     

Implications of the principle of effective stress

Acta Geotechnica - While Terzaghi justified his principle of effective stress for water-saturated soil empirically, it can be derived by means of the neutrality of the mineral with respect to...     

Polymetallic Nodule Mining, Waste Disposal, and Species Extinction at the Abyssal Seafloor

The size of individual mining blocks for polymetallic nodule extraction seems to be rather small, not more than 100 km² in the French mining claim. Even when adding an additional resedimentation zone to the directly impacted area, the size of the affected seabed would remain below 200 km². We assume that even rare species in the abyss inhabit larger areas and propose discussions of the International Seabed Authority and other stakeholders for the different subregions on mining strategies from the perspective of exploitation versus species extinction and conservation. Although impacts of waste disposal at the abyssal seafloor are different from those of nodule mining, the 200 km² concept may also be applied.     

Decadal-scale variations of water mass properties in the deep Weddell Sea

Data from cruises between 1989 and 2003 with FS Polarstern were used to construct section-wide potential temperature and salinity time series of the main water masses in the Weddell Gyre. In tandem with these CTD data, two time series between 1989 and 1995 are presented from moored instruments in the central Weddell Sea. The regional and methodological consistency of the dataset allows us to quantify variations which are not visible in less homogeneous datasets. The data reveal significant temperature and salinity variations of the Warm Deep Water and the Weddell Sea Bottom Water on a decadal time scale. The longest time series were obtained at the prime meridian. Here warming is observed in the Warm Deep Water from 1992 to 1998 followed by cooling. In the Weddell Sea proper, measurements of instruments moored in the Weddell Sea Bottom Water layer recorded a temperature increase over 6 years at a rate of 0.01 °C a^–1. After the mooring period, CTD casts in 1998 point to a weakening of the trend. The warming trend in the bottom water occurs over most of the Weddell Sea, as detected in the additional CTD surveys. The variations are close to the detection level in the voluminous Weddell Sea Deep Water. The initial warming trend of the Warm Deep Water is consistent with warming trends reported in literature of subsurface waters of the Antarctic Circumpolar Current. The reversal of the trend in the Weddell Sea seems to be related to variations of the atmospheric conditions which can affect both the intrusion of Circumpolar Deep Water from the north and the circulation of the Weddell Gyre. Because the Warm Deep Water is the major source water for the formation of deep and bottom water in the Weddell Sea, it is suggested that its increase in temperature and salinity is likely to at least partly cause the variations which were observed in the bottom water.Responsible Editor: Jörg-Olaf Wolff