Patterns of Pacific decadal variability recorded by Indian Ocean corals

We investigate Pacific Decadal Oscillation (PDO) signals recorded by two bimonthly resolved coral δ18O series from La Réunion and Ifaty (West Madagascar), Indian Ocean from 1882 to 1993. To isolate the main PDO frequencies, we apply a band pass filter to the time series passing only periodicities from 16 to 28 years. We investigate the covariance patterns of the coral time series with sea surface temperature (SST) and sea level pressure (SLP) of the Indian and Pacific Oceans. In addition, the empirical orthogonal functions of the filtered SST and SLP fields (single and coupled) are related to the filtered coral times series. The covariance maps show the typical PDO pattern for SST and SLP, confirming the coupling between the Indian and Pacific Oceans. Both corals show the strongest signal in boreal summer. The La Réunion (Ifaty) coral better records SST (SLP) than SLP (SST) pattern variability. We suggest that the filtered La Réunion coral δ18O represents δ18O of seawater that varies with the South Equatorial Current, which, in turn, is linked with the SST PDO. The filtered Ifaty coral δ18O represents SST and is remotely linked with the SLP PDO variability. A combined coral record of the Ifaty and La Réunion boreal summer δ18O series explains about 64% of the variance of the coupled SST/SLP PDO time series

Effect of trace metal availability on coccolithophorid calcification

The deposition of atmospheric dust into the ocean has varied considerably over geological time. Because some of the trace metals contained in dust are essential plant nutrients which can limit phytoplankton growth in parts of the ocean, it has been suggested that variations in dust supply to the surface ocean might influence primary production. Whereas the role of trace metal availability in photosynthetic carbon fixation has received considerable attention, its effect on biogenic calcification is virtually unknown. The production of both particulate organic carbon and calcium carbonate (CaCO3) drives the ocean\u27s biological carbon pump. The ratio of particulate organic carbon to CaCO3 export, the so-called rain ratio, is one of the factors determining CO2 sequestration in the deep ocean. Here we investigate the influence of the essential trace metals iron and zinc on the prominent CaCO3-producing microalga Emiliania huxleyi. We show that whereas at low iron concentrations growth and calcification are equally reduced, low zinc concentrations result in a de-coupling of the two processes. Despite the reduced growth rate of zinc-limited cells, CaCO3 production rates per cell remain unaffected, thus leading to highly calcified cells. These results suggest that changes in dust deposition can affect biogenic calcification in oceanic regions characterized by trace metal limitation, with possible consequences for CO2 partitioning between the atmosphere and the ocean

A 40-million-year history of atmospheric CO2

The alkenone–pCO2 methodology has been used to reconstruct the partial pressure of ancient atmospheric carbon dioxide (pCO2) for the past 45 million years of Earth's history (Middle Eocene to Pleistocene epochs). The present long-term CO2 record is a composite of data from multiple ocean localities that express a wide range of oceanographic and algal growth conditions that potentially bias CO2 results. In this study, we present a pCO2 record spanning the past 40 million years from a single marine locality, Ocean Drilling Program Site 925 located in the western equatorial Atlantic Ocean. The trends and absolute values of our new CO2 record site are broadly consistent with previously published multi-site alkenone–CO2 results. However, new pCO2 estimates for the Middle Miocene are notably higher than published records, with average pCO2 concentrations in the range of 400–500?ppm. Our results are generally consistent with recent pCO2 estimates based on boron isotope-pH data and stomatal index records, and suggest that CO2 levels were highest during a period of global warmth associated with the Middle Miocene Climatic Optimum (17–14 million years ago, Ma), followed by a decline in CO2 during the Middle Miocene Climate Transition (approx. 14 Ma). Several relationships remain contrary to expectations. For example, benthic foraminiferal ?18O records suggest a period of deglaciation and/or high-latitude warming during the latest Oligocene (27–23?Ma) that, based on our results, occurred concurrently with a long-term decrease in CO2 levels. Additionally, a large positive ?18O excursion near the Oligocene–Miocene boundary (the Mi-1 event, approx. 23?Ma), assumed to represent a period of glacial advance and retreat on Antarctica, is difficult to explain by our CO2 record alone given what is known of Antarctic ice sheet history and the strong hysteresis of the East Antarctic Ice Sheet once it has grown to continental dimensions. We also demonstrate that in the Neogene with low CO2 levels, algal carbon concentrating mechanisms and spontaneous biocarbonate–CO2 conversions are likely to play a more important role in algal carbon fixation, which provides a potential bias to the alkenone–pCO2 method

An extended approach to adjust inconsistent minority peer- and self-assessment scores of teamwork using assessor’s reliability

Teamwork is generally assessed either solely by academic staff or by both academic staff andstudents themselves confidentially as well as collaboratively. Peer- and self-assessments have beenused primarily to assess teamwork process and teacher assessment to assess teamwork product.Peer- and self-assessments are useful to elicit team members’ contribution towards teamwork and toconvert team mark into individual marks, provided the scores are reliable (the extent to which thescores are consistent). However, not all peer- and self-assessment scores are reliable. Anecdotal andliterature evidence suggest that there are several cases of inconsistencies in these scores. Individualcontribution scores given by teammates to an assessee (including himself/herself) can sometimesvary significantly due to both intentional and unintentional reasons. Simply using total individual ratingscores without considering an assessor’s reliability to estimate individual contribution factors cansometime results unfair grades and becomes hindrance to learning through teamwork.PURPOSEThis study proposes an extended approach to adjust inconsistent and/or distorted minority peer andself-assessment scores of teamwork using standard normal probability concept.APPROACHIn order to adjust inconsistent and/or distorted minority peer-and self-assessment scores of teamwork,an extended approach has been proposed. The approach uses the reliability of assessor’s scores ofan assessee using standard normal probability curve. The evaluation of the extended approach isconducted by comparing with the existing approaches using two case examples of peer- and selfassessmentof teamwork where minority team members’ scores are inconsistent.RESULTSThe evaluation of the extended approach shows that the proposed method is superior to the availableapproaches in order to adjust inconsistent peer- and self-assessment scores for special cases wherescores of minority team members are inconsistent. The extended approach helps both to automaticallydetect such scoring anomalies and to adjust the scores so that the fairer contributions to the teamworkwould be obtained and utilised.CONCLUSIONSThe extended approach is useful in that it helps both to automatically detect scoring anomalies and todevise the methods to adjust them. However, the approach does not address the issue of scoringinconsistencies by majority of team members as it uses average score as a basis for identifyinginconsistencies. Moreover, the approach needs to be implemented in the real teamwork environmentin order to identify the impacts of these scoring adjustments in teamwork process and teamworkproduct