A TEST OF SIGNIFICANCE FOR PARTIAL LEAST SQUARES REGRESSION

Partial least squares (PLS) regression is a commonly used statistical technique for performingmultivariate calibration, especially in situations where there are more variables than samples. Choosingthe number of factors to include in a model is a decision that all users of PLS must make, but iscomplicated by the large number of empirical tests available. In most instances predictive ability is themost desired property of a PLS model and so interest has centred on making this choice based on aninternal validation process. A popular approach is the calculation of a cross-validated r~2 to gauge howmuch variance in the dependent variable can be explained from leave-one-out predictions. Using MonteCarlo simulations for different sizes of data set, the influence of chance effects on the cross-validationprocess is investigated. The results are presented as tables of critical values which are compared againstthe values of cross-validated r~2 obtained from the user's own data set. This gives a formal test forpredictive ability of a PLS model with a given number of dimensions.     

Gastric lavage as a non-lethal method for stingray (Myliobatiformes) diet sampling

Understanding the trophic interactions of ecologically important mesopredators such as Myliobatiformes (stingrays) is vital, but, given their susceptibility to overexploitation, the collection of stomach contents for dietary analysis necessitates the use of non-lethal methods. We provide a detailed method of using gastric lavage to collect stomach contents from the ‘Vulnerable’ porcupine ray Urogymnus asperrimus at the St Joseph Atoll of the Amirantes Group, Seychelles. Rays were captured by hand, inverted and restrained while a plastic hose, connected to a bilge pump, was inserted into the stomach to flush out the contents. A high percentage (94.5%) of gastric lavage attempts resulted in the collection of stomach contents. There was no visual evidence of stress or short-term, post-release mortality and, given the success and relative ease of this technique, we conclude that the described method of gastric lavage is an effective, non-lethal means of obtaining stomach contents from stingrays.     

Palynological analyses in the laminated sediment of Lake Holzmaar (Eifel, Germany): duration of Lateglacial and Preboreal biozones

The laminated sediment of Lake Holzmaar (Germany) has provided a continuous varve chronology for the last 3500 varve years (vy) and beyond that a floating varve chronology back to more than 22500 vy BP. This chronology in calendar years, in combination with palynology, enables us to determine the timing and the magnitude of Lateglacial and Early Holocene environmental changes on land (from 13838 to 10930 vy BP). The palynological diagram has a mean time resolution of 27 vy between samples. This paper establishes for the first time the biozonation for Lake Holzmaar below the Laacher See Tephra. Fifteen pollen subzones grouped in four biozones are defined by cluster analysis. After a period disturbed by microturbidites, only a part of the Bølling is present. Three cold periods have been evidenced by pollen analyses: the Older Dryas (96-vy-long), the Younger Dryas (654-vy-long) and the Rammelbeek phase (237-vy-long). The Allerød (883-vy-long) is bipartite with a first Betula -dominated period followed by a Pinus -dominated one. The Younger Dryas is also bipartite, with first a decrease of winter temperatures along with a change to a more continental climate. It is followed by a drier phase with a second decrease in temperatures, probably this time also affecting summer temperatures. The Preboreal is 702-yr-long. The duration of most phases corresponds to published records, except for that of the Younger Dryas. Cluster and rate-of-change analyses indicate a sharp change in the terrestrial vegetation assemblages that may be caused by a sedimentary hiatus of erosive origin during this cold and dry period. As a result, the chronology of Holzmaar has to be revised most likely below the middle of the Younger Dryas. Comparison with the varve record of Meerfelder Maar, a neighbour maar lake, suggests adding 320 vy below 12025 vy.     

Late Weichselian sea level changes at Sotra, Hordaland, western Norway

Sediments from twenty-eight basins were surveyed; ten of these basins with a representative lithostrati-gfaphy wee studied to determine their isolation from the sea during Late Weichselian. Diatom analysis was used to determine salinity changes, which were dated by pollen analysis and the radiocarbon method. The area was deglaciated in the early Boiling, and a regression of about 5 m followed. A transgression of more than 10 m started in late Boiling and terminated in middle Younger Dryas, with a transgression maximum between 38.2 and 40 m above present sea level. All the investigated basins were finally isolated in late Younger Dryas/early Preboreal, during a rapid regression. Repeated cycles of chinophilous/ chinophobous plant communities in the area reflect climatic changes in the period. No evidence of an Older Dryas ice readvance was found.     

Chemotaxonomic investigation of phytoplankton in the shelf ecosystem of the KwaZulu-Natal Bight,South Africa

Phytoplankton community structure was elucidated during summer and winter in the KwaZulu-Natal Bight using pigment and CHEMTAX analyses. The surface pattern in January 2010 indicated that diatoms, haptophytes and prasinophytes tended to be the most prominent groups inshore and in the southern sector of the bight, whereas Prochlorococcus and Synechococcus were more dominant in the north and towards the offshore region. At the deep chlorophyll maximum (DCM), diatoms were dominant in the inner bight and in the south, with prasinophytes being the prominent flagellates, but this changed to Prochlorococcus and pelagophytes being the important groups in the northern sector and outer part of the bight. A different pattern was observed at the surface in July 2010, where diatoms, haptophytes, prasinophytes and cryptophytes in varying proportions comprised most of the community in the inner half of the bight, whereas Synechococcus and haptophytes were the main groups in the outer sector. A similar pattern occurred at the DCM, except that Synechococcus was less prominent and pelagophytes were distributed across the bight in both the inshore and offshore zones. Observations and relationships between phytoplankton groups and environmental parameters indicated that the groups were most closely related to temperature, accounting for 24–64% of the deviance. The influence of nutrients on phytoplankton was less clear but nitrate and silicate seemed to account for some of the patchy distribution patterns.     

Deglacial and Holocene conditions in northernmost Baffin Bay: sediments, foraminifera, diatoms and stable isotopes

A multiproxy study of palaeoceanographic and climatic changes in northernmost Baffin Bay shows that major environmental changes have occurred since the deglaciation of the area at about 12 500 cal. yr BP. The interpretation is based on sedimentology, benthic and planktonic foraminifera and their isotopic composition, as well as diatom assemblages in the sedimentary records at two core sites, one located in the deeper central part of northernmost Baffin Bay and one in a separate trough closer to the Greenland coast. A revised chronology for the two records is established on the basis of 15 previously published AMS ¹⁴C age determinations. A basal diamicton is overlain by laminated, fossil-free sediments. Our data from the early part of the fossiliferous record (12 300–11 300 cal. yr BP), which is also initially laminated, indicate extensive seasonal sea-ice cover and brine release. There is indication of a cooling event between 11 300 and 10 900 cal. yr BP, and maximum Atlantic Water influence occurred between 10 900 and 8200 cal. yr BP (no sediment recovery between 8200 and 7300 cal. yr BP). A gradual, but fluctuating, increase in sea-ice cover is seen after 7300 cal. yr BP. Sea-ice diatoms were particularly abundant in the central part of northernmost Baffin Bay, presumably due to the inflow of Polar waters from the Arctic Ocean, and less sea ice occurred at the near-coastal site, which was under continuous influence of the West Greenland Current. Our data from the deep, central part show a fluctuating degree of upwelling after c . 7300 cal. yr BP, culminating between 4000 and 3050 cal. yr BP. There was a gradual increase in the influence of cold bottom waters from the Arctic Ocean after about 3050 cal. yr BP, when agglutinated foraminifera became abundant. A superimposed short-term change in the sea-surface proxies is correlated with the Little Ice Age cooling.     

Lateglacial varve chronology and biostratigraphy of lakes Holzmaar and Meerfelder Maar, Germany

In this paper we briefly compare previously published data on four lateglacial sediment profiles from lakes Holzmaar and Meerfelder Maar in the Eifel region. Two of these profiles (one from each lake) are varvedated, whereas the other two pollen profiles are on depth scales. In general, the palynological signal in all profiles compares well, proving the regional validity of the individual data sets. There are some discrepancies between Holzmaar and Meerfelder Maar, however, mainly concerning varve dating of major lateglacial features, and these are explained after detailed correlation using a combination of varve dating and palynological signals. The result is a consistent varve-dated biostratigraphy for the Lateglacial in the Eifel region. Moreover, it is demonstrated that a combination of varve chronology and high resolution palynostratigraphy in several lake profiles enables even gaps of a few decades up to a few centuries to be detected, thus providing a valuable tool for precise regional palaeoenvironmental study. This multi-core study on two lakes from the same region demonstrates the likelihood of undetected errors in single-core studies on non-varved sediments.