ALBERT

Description: The Arctic cryosphere is changing and making significant contributions to 21st century sea level rise. The Pliocene epoch had similar CO2 levels to present and a warming comparable to model predictions for the end of this century, providing an opportunity to investigate the operation of Arctic climate in a warm world. The Late Pliocene has well documented climatic conditions. However, the state of the Arctic cryosphere remains partially constrained. Here, for the first time, we couple outputs from a Pliocene climate model with a thermodynamic iceberg model to simulate likely source regions for Ice Rafted Debris (IRD) found in the Nordic Seas from Marine Isotope Stage M2 to the mid Pliocene Warm Period (mPWP). We compare the fraction of melt given by the model scenarios with IRD data from four Ocean Drilling Program (ODP) sites within the Nordic Seas region. Marine sites 911A, 909C and 907A show a persistent occurrence of IRD that modeling results suggest is consistent with permanent ice on Svalbard. Our model results indicate that icebergs sourced from the east coast of Greenland do not reach the Nordic Seas sites during the warm late Pliocene, but instead travel south into the North Atlantic. Small amounts of IRD are found at Hole 642B in the Late Pliocene. Model results identify coastal Norway as the potential source, however this is inconsistent with current understanding of the Late Pliocene Scandinavian climate.

Description: Planktonic foraminifera are widely used in biostratigraphic, palaeoceanographic and evolutionary studies, but the strength of many study conclusions could be weakened if taxonomic identifications are not reproducible by different workers. In this study, to assess the relative importance of a range of possible reasons for among-worker disagreement in identification, 100 specimens of 26 species of macroperforate planktonic foraminifera were selected from a core-top site in the subtropical Pacific Ocean. Twenty-three scientists at different career stages – including some with only a few days experience of planktonic foraminifera – were asked to identify each specimen to species level, and to indicate their confidence in each identification. The participants were provided with a species list and had access to additional reference materials. We use generalised linear mixed-effects models to test the relevance of three sets of factors in identification accuracy: participant-level characteristics (including experience), species-level characteristics (including a participant's knowledge of the species) and specimen-level characteristics (size, confidence in identification). The 19 less experienced scientists achieve a median accuracy of 57 %, which rises to 75 % for specimens they are confident in. For the 4 most experienced participants, overall accuracy is 79 %, rising to 93 % when they are confident. To obtain maximum comparability and ease of analysis, everyone used a standard microscope with only 35× magnification, and each specimen was studied in isolation. Consequently, these data provide a lower limit for an estimate of consistency. Importantly, participants could largely predict whether their identifications were correct or incorrect: their own assessments of specimen-level confidence and of their previous knowledge of species concepts were the strongest predictors of accuracy.